CA2197693C - Interference mitigation method and apparatus for multiple collocated transceivers - Google Patents
Interference mitigation method and apparatus for multiple collocated transceivers Download PDFInfo
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- CA2197693C CA2197693C CA002197693A CA2197693A CA2197693C CA 2197693 C CA2197693 C CA 2197693C CA 002197693 A CA002197693 A CA 002197693A CA 2197693 A CA2197693 A CA 2197693A CA 2197693 C CA2197693 C CA 2197693C
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
- H04B1/38—Transceivers, i.e. devices in which transmitter and receiver form a structural unit and in which at least one part is used for functions of transmitting and receiving
- H04B1/40—Circuits
- H04B1/50—Circuits using different frequencies for the two directions of communication
- H04B1/52—Hybrid arrangements, i.e. arrangements for transition from single-path two-direction transmission to single-direction transmission on each of two paths or vice versa
- H04B1/525—Hybrid arrangements, i.e. arrangements for transition from single-path two-direction transmission to single-direction transmission on each of two paths or vice versa with means for reducing leakage of transmitter signal into the receiver
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B7/00—Radio transmission systems, i.e. using radiation field
- H04B7/005—Control of transmission; Equalising
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
- H04B1/02—Transmitters
- H04B1/04—Circuits
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
- H04B1/06—Receivers
- H04B1/10—Means associated with receiver for limiting or suppressing noise or interference
- H04B1/12—Neutralising, balancing, or compensation arrangements
- H04B1/123—Neutralising, balancing, or compensation arrangements using adaptive balancing or compensation means
- H04B1/126—Neutralising, balancing, or compensation arrangements using adaptive balancing or compensation means having multiple inputs, e.g. auxiliary antenna for receiving interfering signal
Abstract
An apparatus and method for mitigating interference between multiple collocated radio transceivers operating through a common antenna. In a preferredform, the apparatus includes a filter bank containing bandpass filters corresponding to a number of desired operating frequency bands. Each transceiver can be selectively electrically interconnected with the common antenna through an appropriate filter.
The filters attenuate out-of-band interference. An adaptive cancellation device is also provided to compare samples of the transmitted and received signals and produce an interference cancellation signal that is substantially equal in amplitude and 180° out of phase with the coherent portions of the compared and received signals.
The filters attenuate out-of-band interference. An adaptive cancellation device is also provided to compare samples of the transmitted and received signals and produce an interference cancellation signal that is substantially equal in amplitude and 180° out of phase with the coherent portions of the compared and received signals.
Description
~ 2197693 ~I~TFRhF.RF.l~CF. MrlI(.Al~ON MFl~On ~ T) APPAl~ATUS
FOR MULTIPI ~. CO~,~ OCATFn TRANSCF.IVF.12.
RACKGROUND OF l~F. ~VF.l~TION
FiPld of the InvPntion The present imention relates to radio communications, and more particularly - relates to mitigation of ulle.rcrellce between collocated radio lr~nsceivers.
Descnption of thP. Prior Art In order to minirnize the overall size of cornmunications systems employing multiple radio l~nscG;~ers, it is desirable to coUocate the transceivers on a common platform. However, this can lead to the problem of cosite interference, that is,inte.~nce caused by radiative and conductive interactions ofthe coUocated transceivers.
Interfering signals, which can hamper reception of in-bound communications by ll~lsceivers operating in receive mode, may result from a number of causes. These may include the carrier waves or wideband noise generated by collocated ll ~nsceivers operating in transmit mode; co-channel operation in ~equency-hopping systems; and ~ntPnn~ paKern distonion (in multiple ~ntetm~ systems). Collocated t~anscei~ers may also generate spurio~s ullel rel ing signals at odd harmonics of their fundamental ~equency as well as pseudo-white-noise over a wide band of frequencies on either side oftheir operating frequency. Several techniques have been proposed to ,-,;ni...;~e undesirable illtelrer-,nce between collocated transceivers, inchl~ing agile filtering, agile filtering with multicoupling and interference cancellation. Agile filtering involves coupling a frequency-adjustable filter, typically a bandpass filter, to the input of a transceiver ope~ ~ling in receive mode. While the filter atten~l~tes out-of-band noise, no protection is provided against interfering signals in the filter's passband. Further, 2~9769~
agile filtering requires a priori~ mana~ement scheme wherein a priority rank is ~csigred to each transceiver, if collocated L~A~ erS and receivers are acsi~ned close or identic~l operating frequencies, the lower-priority one must be shut down until the frequencies are re~csi~nPd This may result in loss of data associated with the S ll~ -s.. ~;on or receipt of signals by the subordil1ate transceiver.
In agile f~tering with multicoupling, similar techniques are employed, but a single ~ntenn~ is used to ~ e ~ntenn~ pattern distortion. The in-band illlc~re.~"~ce and priority-Tn~n~em~nt problems clisc~lssed above are still encountered.
L-le-r, ~-~ce G~nC~ tion techniques may involve sampling the output of l~ s~ g llansceivers to Pl;"~;ni~le, from the desired received signal, any ul~elre~ulg signal with a frequency close to the transmitter carrier frequency. This method is not practical where the ultel~lei~ce is strong or where substantial wide band noise is produced by the l-;~n~ ;nf~ l-dnscei~er. Alternatively, one can instead implement an illte.r~ ce c~nc~ tion scheme which involves c~nc~ tion of sul~s~ ;ally all ~.le.r~ l;ng signals outside the receiver's operating frequency band. However, this latter technique does not protect against interfering signals with frequencies close to, or the same as, the desired received signal.
A more advanced approach to interference elimin:-1ion has recently been set forth in co-assigned C~n~ n Patent Application No. 2,165,456; filed December 5, 1995 and entitled "Adaptive Method and Apparatus for Flimin~ting Interference Between Radio Transceivers". In the '456 application, a plurality of transceivers are coupled to a common antenna through a power combiner. A filter circuit is provided for each transceiver. The filtered signal from each transmitting transceiver is sampled and compared to the received signal in a plurality of cancelers; the cancelers then produce a plurality of cancellation signals that are combined and injected into the received signal. The cancellation signals consist of the coherent portions of the tr~n~mitted and received signals, shi~ed 180~. The combined cancellation signals are injected into the received signal before it is sampled, thereby providing adaptive interference ~ ;on.
The t~hnoloQy of the '456-application, ~lthol~h an irnprovement over the prior art, still has several disadv~nt~gçs The use of a power colllbil1er to couple the S h~ulsce;vers to a ~ - -. ~ nt~nn~ entails power loss. Further, the filter circuits require bulky, eAy~ e dual hopping filters.
In view ofthe disad~ ges ofthe prior art, there is a need for an u~l~"r~ e mitig~tion method and app~lus for multiple collocated transceivers which provides prol~;Lion against both inband and out-of-band intelrerence, even where the u~tel~n.1ce is strong; which .. ~ es power loss; which çl;.. ~ les data loss; and which can be easily ull~l~m~nted at relatively low cost with available, compact hardware.
OBJF.CI S AND SUMl~A~Y OF T~E INVFNTION
It is an object ofthe present invention to provide an interference mitig~tion method and a~p~allls for multiple collocated transceivers which permit operationthrough a col,ullon ~nt~nn~ while .~ ;ilg power loss.
It is another object of the present invention to provide an intel rel ence mitigation method and appardllls for multiple collocated transceivers which afford protection against both in-band and out-of-band interference.
It is yet another object of the present invention to provide an interference mitigation method and appal aLIlS for multiple collocated transceivers which prevent the loss of critical data.
~ ' 2l97693 It is a further object of the present invention to provide an interference mitigation method and app~al,ls for multiple collocated Llansceivers which afford protection even against strong interference.
It is still a further object of the present invention to provide an i-~telr~l ~ nce S .~ ig~l;ol1 app~allls for multiple coUocated tlallsceivers which co.llb;.les the use of bAn~p~cs filters with i.-le.r~r~,.lce c?ncell~tiQn te~ ;y~les using relatively compact and e~ e h~d~a e, and to also provide an int~r~nce mitig~tion nlethod using such an apparal~s.
Ln accG. lance with one forrn of the present invention, an "ILe. L. re.-ce 0 mitig~tion app~alus for multiple collocated transceivers il~cllldes a filter bank having a filter for each of a plurality of desired operating frequency bands. The filter bank is electrically coupled to a conh-,on ~ntenn~ A switch matrix has a series of first ports which are electrically interconne.;led with the filter bank (one first port for each filter).
The switch matrix also has a series of second ports (one for each transceiver), each of which can be selectively electrically i,-lerco~-l-e~led with any ofthe first ports. Each scei~er may in turn be selectively electrically intercom)ected to the co, l ~)onding switch matrix second port through either of a pair of tr~ncmicsion paths, in~llldin~ a ~r..l.~ led signal tr~ncnnicsiQn line and a received signal path. A c~nc~ tion device is electrically interconnected with the tr~ncmiccion lines to obtain a sample of each ll~ ed signal, and is also electrically interco~me~led with the received signal paths for sarnpling of received signals and injection of an interference c~ncell~tion signal.
The filter bank may be subdivided into odd and even filter banks. The odd and even filter banks may then be electrically intercoMe~,led to the ~ntenn~ through a circulator or a two way power splitter.
In accofdallce with another form of the present invention, the switch matrix may be dispensed with and each transceiver may be coupled to the common ~nt.onn~
219769~
through its own individual tunable bAndpAes filter. The tunable b~ndpAss filters are each individually tuned to the opelatu~g frequency of their transceiver.
In a method according to the present invention, a main output signal of each llA'~ ;n8 l-~an.3Ce;Ver ;S sarnpled to provide sampled output signals; each of the main 5 output signats is then filtered through a bAndpA~s filter (part of a filter bank) cG.- .,..~,on l-ng to the given l-ansc~iver's acsi~ed frequency band; and the filtered main output signals are l-A~ e~l A main received signal is passed through the filter bank which has a filter set to receive in each frequency band co..esponding to areceiving ll~sce;ver, re~lllting in filtering of subst~nt~ y all out-of-band u~lel~r~nce.
The main received signal is sampled to provide a sampled received signal, which is co...pared to the sampled output signals and used to gel~e~aLe an intG.re.el1ce cAneell~tion signal. The inle~ r~n,l1ce cAncçll~tion signal is co...bined ~,vith the main received signal and divided for distribution to the receiving ~l~nsceivers.
These and other objects, fealures and advantages of the present invention will become apparenL from the following dePile~ description of illustrative embo~
thereof, which is to be read in conneclion with the accoulpa~ ing drawings.
BI2~FF DESCRIPI ION OF THE DRAWINGS
Figure 1 is a sch~mAtic of an inte. rerence mitigation âpp&l ~ s in accordallce with the present invention;
Figure 2 is a schemAtic similar to Figure 1 showing an alternative arrangement of the filter bank;
Figure 3 is a schematic similar to Figures 1 and 2 showing yet another alternative ~.A.lg"."~ ofthe filter bank;
- ~ 2197693 Figure 4 is a schematic depicting the interconnection of canceler loops with theappar~ s of the present invention; and Figure 5 is a sch~m~tic of an interference mitig~tion appa,~us in accordance with an alternative embodiment of the present invention.
nF.TAl~ Fn nF.. ~CR~l ION OF TEIF P~F.~FRR~D Fl~IROD~ TS
Re~li"g to Figure 1, an inte~Çerence mitigation apparallls, dçsi~ted generally as 10, conne~tC a plurality offrequency-agile radio transceivers 12 with a co,.unon ~ n~ 14. In general, the number oftransceivers is d~cign~ted as N and the individual ~ sceivers are labeled as TR(1) through TR(N). At least some, and 10 preferably each ofthe l~&1sceivers may operate in either l.~ ..lit or receive mode.
Those of the N ~. ~njceivers operating in ~l ~1s.,li~ mode are referred to interchangeably as tl~ s or l-~nC...;l~ transceivers, while those ofthe N ~ldnsceivers opela~ing in receive mode are r~rell~d to inter~hangeably as receivers or receiving transceivers.
At any given time, a t,~nsceiver may be ~ lc.~ receiving, or open-circuited.
Apparatus 10 incl~ldes a filter bank 16 with a plurality of filters 18 electrically .Jllercol-~-ected with CGllullOl1 ~ntenn~ 14. In general, the number of filters is des~ ted as M and the individual filters are labeled as Fl(1) through FI(M).
Preferably, the filters are b~ndp~ss filters with contiguous p~CCb~n~C each filter's pAS~ljAnd co"esponding to one of M desired ope-dL;ng frequency bands for the N
collocated L. ~sceivers. The number of filters M should be greater than or equal to the number of Lrdnsceivers N so that each of the M desired operating frequency bands will only be used by one transceiver at a time.
The band pass filters ideally present, within their p~ssban~ an impedance subst~nti~lly the same as the characteristic impedance ofthe tr~ncmiecion metlillm (e.g., 50 ohms for a coaxial line). Outside the passband the impedance is ve~y high, effectively an open circuit. Accordingly, when a plurality of contiguous b~ndp~cs filters are conne~,Led to a common antenna, as in the present invention, only one of the filters pr~,se."s the characteristic impedance at any given frequency. The r~rn~inder of the filters ideally present an open circuit and draw no power from the ~nt.o~n~
Accordingly, the present invention permits interconnection of a plurality of filters to the co~ --on ~ntenna, effectively in parallel with one another, without the necç$~ for a power co.l~ lcr with its conco"uL~It combiner power loss. It is to be understood that the lowest frequency filter may be a low pass filter instead of a b~ld~cs filter, if signals or inl~.r~...nce below the lowest desired frequency band are not ~nticiF~e l, while still ol~t~ling the ror~goii~ benefits. Similarly, if signals or i"te,r~,rence above 10 the highest desired frequency band are not anticipated, the highest frequency filter may be a high pass filter.
Still referring to Figure 1, the appar~ s 10 also includes a switch matrix 20, which has M first ports 22 which are electrically interconnected with the M filters of the filter matrix, and N second ports 24. Preferably, the filters are coMected in a 15 st~ P~I (i.e., electrically parallel) arrangement between the common ~ntenn~ 14 and the M first ports 22 of switch matrix 20. Switch matrix 20 provides selective electrical il-tercoMection between any of the M first ports and N second ports, through any of a number of techniques well-known in the art. Accordingly, at least one, and preferably each of, the N second ports 24 which correspond to the N transceivers 12, may be20 selectively electrically in~er~,ol-nected with the common antenn~ through at least one, and preferably any desired one, of the M filters of the filter bank for ~ s.~;on or reception in the desired frequency band to which the filter col I ~sponds. Out-of-band signals are thus att~n~l~te~ It will be apprec;ated that switch matrix 20 can have any suitable constmction. Typically, a plurality of diodes are provided for illLer~iolule-;Lion 25- purposes. They can be individually biased on or offby control signals, thereby present;.-p a short or open circuit and e~iLing a selected interconnection between any one of the M first ports and any one of the N second ports. A suitable switch matrix which may be used is described in U.S. Patent No. 5,446,424, entitled "MicrowaveCrosspoint Blocking Switch Matrix and Assembly Employing Multilayer Stripline and 21!~7693 Pin Diode Switching Elements".
The N second ports 24 of s~vitch matrix 20 may in turn be selectively S elect~ically illter~ol~n~led with the N transceivers 12 through N L,Anc~.~;cc:on path pairs. At least one of, and pr.,~er_bly each, trAncmisciQrl path pair i~rlud~s aL,n~ ed signal l,A~ -.;on line 26 and a received signal Llnllc~ cc:on path (a pr~ ,d cG~ gv~ion of which will be described in greater detail below). When a given l~ sce;ver 12 is in ~ lUl mode, it is co.lilected to its corresponding switch 10 matrLx second port through the associated l,n~ ed signal ~IA~s~ c~;on line 26.
When in receiw mode, a t~anscei~er 12 is connecte~l to its corresponding switch matriY second port through the associated received signal trAncmicsion path.
Apparatus 10 also preferably includes cArlc~ tion device 28. The cAnc~llA~ion device is electrically coupled to each of the L~ A ~lc~ l led signal trAncmission lines 26, preferably with directional couplers 30, in order to receive a sample ofthe l,A~.c.,l;lled signal from each ofthe N l~lsceivers that is opel~ lg in ~ sl~u~ mode. The cancellation device 28 is also electrically interconnected with each of the received signal ~rArs..l~icsion paths ofthe N tr~ncmis.sion path pairs forboth receipt of a received signal sample and injection of an interference cancellation signal. A pi~;Çe~, ed method of i~ler~;onllection of c~nce~lation device 28 with the received signal trAn~mi~sion paths will be diccllssed below.
The received signal sarnple includes both an interference portion and a non-interference portion. The cAncell~tion device 28 is electrically configured to co~ -e the transrnitted signal samples with the received signal sample and to produce an interference cancellation signal that has substAntiAlly the same frequency and arnplitude characteristics as the interference portion of the received signal sarnple but is substantially 180~ out of phase with it, so as to result in destructive interference, effectively canceling the interference portion of the received signal.
Still referring to Figure 1, a prefel -ed form of received signal trancmission path hldes N first tr~ncmicr;on line se~ynentc 32 having first and second ends. The first ends are selectively electrically interconnected with the N second ports 24 of switch matrix 20 through switches 36. The second ends are selectively electrically S inLe~w~ne~led to a main power combiner 38 having N input ports, through switches 40. Preferably, the input ports of main power col"biner 38 can also be ~on~e~ledthrough a~ilches 40 to il.lpedance matched t~,l...inalions, in order to prevent rPfle~honc Main power combiner 38 comb;ncs the received signals from all Op~lalillg 10 frequency bands. An error correction tr~nsmission line 42 is coupled to the output of co~,l)iner 38 to calTy the colllbu~ed slgnals. The prere.. ed form of received signal ;c~;on path also incl~ldes main power splitter 44 having N output ports and an input port. The coll-bined signals enter the input port of splitter 44. N secondC...:c.cion line s~.~e~s 46 have first ends which are selectively electrically 15 intercGn-le~ with the N output ports of spliKer 44 via switches 48, and also have second ends which are selectively electrically i"lerco~ ecled with transceivers 12 via switches 50. Pl~,f~-~bly, the output ports of spliKer 44 can also be connected to imred~nce~ hed te,lll-na~ions through switches 48 to prevent reflections. Switches 50 are electrically configured to perrnit selective electrical i.lLerco~ ection of 20 l-~nscei~ers 12 with either tr~nsmiScion lines 26 or the received signal ~ .C;c.i;on paths just described, i.e., the first and second tr~ncmicsion line segments 32 and 46, error correction tr~ncmiscion line 42, main power colllbincr 38, and main power spliKer 44.
Contin-lin~ to refer to Figure 1, the ~ fel,ed i~,~ere~m~ection between inte.ft:rence rqnc~ tion device 28 and the received signal tr~nsmiSsion paths incl~des error correction signal injection directional coupler 52 coupled to error correction hi~ ;csion line 42 for injection ofthe inte-rerence ç~nc~ tion signal, and also includes error sampling directional coupler 54, also coupled to error correctiontr~ncmicsion line 42. Preferably, error sampling directional coupler 54 is interconnected with error correction transmission line 42 at a point where it samples the received signals after the error correction signal injection directional coupler 52 has injected the interference c~llcell~tion (error correction) signal. In this way, adaptive il.le.rclence cAncellAtion is achieved, i.e., the corrected signal is sampled for the portions that are coherent with the tr~nsmitted signals. In order to make up for at least a portion of power losses incurred in the received signals between the çGm.llon A.~tellnA
14 and the main power splitter 44, low noise amplifier 56 îs pl~ef~;lably provided in error correction h ~ .. s~;on line 42, to amplify the col .~ ,d received signal.
In opelal;on, the ll~lc-";ll;n~ transceiver(s) (TR(l) and TR(N) in Figure 1) are10 electricaUy ~le~onne~led with corresponding second ports 24 of switch matrix 20 through ~vvil~ Les 50, 1l ;..,cn,;l le~ signal trAncmicsiQn lines 26 and switches 36. Second ports 24 are then in turn ele~,ll;cally inlercon~le.,led with co.lll..on ~ntenn~ 14 through switch matrix 20 and app~opliale filters 18 of filter bank 16. Each port 24 is coi-l-e~,led to ~nt~nn~ 14 through only one filter 18, co-,~ onding to the desired tr~n.cmithnp frequency band of its coll.,sponding tr~nsmitting ~nsceiver. Accordingly, each "n~,..;lled signal is filtered to att~nl.~te out-of-band noise.
The receiving transceiver(s) (TR(2) in Figure 1) are electrically interconnectedto collt~onding second ports 24 of switch matrix 20 through the previously-described received signal ~ ,e...is~;on path inclllding switches 36, first tr~ncmicsion line se~g" - .~s 32, main power co.llbiner 38, error correction ll~ s~;on line 42, low noise amplifier 56, main power splitter 44, switches 48, second h~,.c...;c~;on line se~n~ntS
46 and switches 50. Second ports 24 of switch matrix 20 are in turn electrical~yinterconnected with cormnon ~ntçnna 14 through switch matrix 20 and appropriate filters 18 of filter bank 16. Each port 24 is connected to ~ntenn~ 14 through only one filter 18, co-l~,~ponding to the desired receive frequency band of its corresponding receiving llansceiver. Accor-lingly, each receive signal is filtered to attçnn~te out-of-band noise. The filtering of the transmitted and received signals to P~ ;n~te out-of-band noise reduces the power required for the interference cancellation signal.
C~ncellAtion device 28 samples each trAnsmitted signal through directional couplers 30 and col-lpares the ~lA~ ed signals to a received signal sample from directional coupler 54. Those portions of the IlAns...;~ed and received signals that are coherent ~pr~nl inte~r~re.lce. Based on the ~letection of the coherent signals, the 5 ~,Ail~P1lA1;~n device 28 effectively modifies a portion ofthe sampled t~An~ (ed signals and gc~c~atcs an error c~ ,lion signal (also ~er~ ,d to as an u~l~,.r~ ce c~ncPllA~ion signal) which is c~ie l;Ally equal in ATnrlit~e and 180~ out-of-phase with the ull~r~i-u~g signals on the received signal path. This cAnC~ll-Ation signat is injected via error co"~,~lion signal ~"e~ioll directional coupler 52 (also rere,~d to as a sl~mmi~
coupler) into error correction line 42 where it cancels or at least .. ,in;~ 5 the ulLelr~rulg signat portion ofthe received signat to form a cGl~ d signal. Low noise amplifier 56 -Amrlifi~s the coll~led signal to make up for losses. As mentioned above, because both reception and l A~ s~;on are filtered, the amount of intelre~j1ce to be c~ncPled by c~An~ Ation device 28 is redl-ce-l thereby cutting its power requir~.nellLs.
A pler~ -~td form of ~ncellAtion device 28 wilt be ~lisa~sse~ in greater detail below.
Rert;llu~g now to Figure 2, wherein like elements have been given the same r~Ç~r~l1ce numbers as in Figure 1 incremented by 100, there is shown an embodiment of the invention employing a modified electrical i.~Lercon.~ection between the filter bank 116 and tolll.u~n antenna 114. In this embodiment, filter bank 116 is divided into two sep~te filter banks, odd filter bank 166 and even filter bank 168. The odd filter bank 166 Colllaills those of the M fitters that are odd-numbered and the even filter bank COIllaills those of the M filters that are even numbered. The odd and even numbering ofthe filters 118 refers to the frequenGy position ofthe individuat filters in the operating band of filter banks 166, 168 in relati'on to all other filters.
The odd filter bank 166 and even filter bank 168 are electrically interconnectedwith comrnon antenna 114 via circulator 170. The book Microwave Receivers and Related Components. by Jarnes B. Tsui, Peninsula Publishing, 1985, desclibes (atpages 296-97) the interco~ e~;iion of a circulator with odd and even filter banks, Circulator 170 includes an input port 172 and first f 2197693 and second output ports 174 and 176 respectively. First output port 174 is electrically interco~u~ected with one of the odd and even filter banks, for example, the even filter bank 168 as shown in Figure 2, while second output port 176 is electrically inte. conne~ led with the other of the odd and even filter banks, for example, the odd filter bank 166 as shown in Figure 2. The input signal from common ~ntenn~ 114 is fed into input port 172 of circulator 170. It first reaches first output port 174, where it will pass through the even fi ter bank 168 if it ,~ f 5 any of the characteristic freql~enl ies ofthe filters 118 in even filter bank 168. If it does not match any ofthose frequencies, it will reflect and reach second output port 176 where it will pass through an app,oytiate filter 118 in odd filter bank 166.
The purpose of using circulator 170 with odd and even filter banks 166 and 168 is to achieve a better voltage st~n~ing wave ratio (VSWR) than is possible with the confi~ration shown in Figure 1. In Figure 1, there is potential for signals at the edge of a given desired frequency band to be partially passed by an adjac~nt filter, due to overlap in the pA~b~n~ls of neighboring filters. This is ~ n~ted in the configuration of Figure 2, wherein the adjacent filters are separated into odd and even banks. It is to be understood that the filters are numbered consecutively (from lowest frequency to highest) in accordance with their desired frequency band. Losses incirculator 170 are generally on the order of 0.2-0.3 dB. The r~m~ind~r of the apy~l~s of Figure 2 is identical to that of Figure 1.
At low frequencie~ on the order of 50-100 MHz, circulators are either unavailable, or otherwise bulky and expensive. For operation at these frequencies, another alternative configuration, shown in Figure 3, is possible. In Figure 3, like clP ..c..l~ have received the same numbers as in Figure 2, il1crellle.,led by 100. In the configuration shown in Figure 3, circulator 170 of Figure 2 is replaced by filter bank power splitter 286. Operation is similar to the configuration of Figure 2, except that a 3 dB power loss is encountered in the filter bank power splitter 286. Thus, at frequencies where a circulator is available, the configuration of Figure 2 is prefelled.
. . ~ 2197693 Figure S depicts an altemative embodiment of the present invention which does not employ a switch matrix. Like parts have the same ~;çc;r(~nce numbers as in Figure 1, incrPrnented by 300. Instead of the switch matrix, tunable b~ndp~s filters 390 are interposed between switches 336 and comrnon ~nt~nn~ 314~ Rather than colu~e~,l each hansceiver 312 to ~ntçnn~ 314 via a fixed filter co-.~,sponding to the l.~1sceiver's Ope~alin~3 frequency band (by use of a switch matrix), in the embodiment of Figure 5, each ~1sce;ver is provided with its own tunable ~ndp~c~ filter which is adjusted by control signals to the desired OpC~al;ng frequency of the L~sc~ er. In all other~spe~,ls, the embodiment of Figure 5 is similar to that of Figures 1-3.
Referring now to Figure 4, a prèrellèd embodiment ofthe c~ncell~tion device 28 will be described. Preferably, c~ncell~tion device 28 inrludes N c-~nc~ tion loops co,. e;~ponding to each of the l. ~nc~ ed signal tr~mmi~sion lines of the N tr~n.cmiC~ion path pairs and the number of l.a,~scei~ers. Each loop incl~ldes a t.i...c,.,;l~ed signal sample input port S8 electrically interconnected by one ofthe directional couplers 30 (shown in Figure 1) to its co--~s~ondil1g ll~nclil;~led signal tl~ncl~l;ssion line 26 (shown in Figure 1). Each loop also in~ des a received signal sarnple input port 59 and an interference c~ncçll~tion signal output port 60.
Each loop also includes a phase detector 61 (also referred to as a synchronous detector) and a vector modulator 62 (also refe.led to as a signal controller). Phase detector 61 has a first input port electrically interconnected ~.vith l~ s~.. ;l led signal sarnple input port 58 via directional coupler 63 for input of a sarnple of the l, ~n~...;Lled signal from the co.~e~pondil-g lr~r,smilling transceiver. Phase detector 61 also has a second input port which is the same as received signal sarnple input port 59. Phase detector 61 also has I and Q output ports respectively connected to the inputs of I and Q loop integrators and/or amplifiers 6i and 65 respectively. Phase detector 61 cG".pares the received and ll;~ns~ ed signal samples in order to detect in-phase(coherent) portions of the received and transrnitted signal samples and then supplies I
(in-phase) and Q (quadrature phase) DC signals to the I and Q output ports respectively. The I and Q signals are then amplified and/or integrated by components 64 and 65 to create control signals provided to the vector modulator.
Vector modulator 62 has a first input port (which is the same as l~ s~;Lled signal sarnple input port 58), and also has I and Q control signal input ports conne~e~
S to the outputs of I and Q loop ;nleg~alo~J~lpl;~e~ 64 and 65 res~Je~ ely. Vector modulator 62 also has an output port (which is the same as illlel r~nce c~nc~ tion signal output port 60). Based on the I and Q control signals provided to it, vector modulator 62 effectively modifies a portion ofthe sample signal ofthe Ll~n~ èd signal to produce an i~llelre.~nce c~ncell~tion signal that is essenti~lly equal in ~mrlitude and 180~ out of phase with the L~llelr~;lu~g signal in the received signal path (on lt~n~ ;on line 42).
The operation of the c~nc~ tion loop ~iscussed above is described in greater detail in U.S. Patent No. 5,117,50S, entitled ~Inte~,rerei1ce C~ncell~l;on System Having Noise Reduction Features and Method". It is to be understood that, although Figure 4 shows only a single cancellation loop, one is provided for each of the N
transceivers.
Still refe~ g to Figure 4, cancellation device 28 also includes error s~mrlin~
power splitter 78 having an input port electrically i.llel~;olule~iled with error sarnpling directional coupler 54, and having N output ports, each electrically illlercounected with the received signal samp!e input port 59 of one of the N cancellation loops.
C~ncPll~tion device 28 also includes an u-le.r~ ce cancellation signal power combiner 79 having N input ports each electrically interconnected with the interference cancellation system output port 60 of one of the N canceler loops. Interference cancellation system power co"~binef 79 combines the interference cancellation signals ~om all the loops to produce a colubined interference cancellation signal at its output port, which is electrically interconnected with the error correction signal injection directional coupler 52 for injection of the combined interference cancellation signal into error correction transrnission line 42.
It is to be understood that the embodiments of the invention shown in Figures 1, 2, 3 and 5 may be provided with control circuits (not shown) for adjusting the ope~dLing frequency bands of the tl~sceivers; controlling the various switches and switch l..al~;ces to conn~ct the lr~lsceivers to corresponding filters (Figures 1, 2 and 3) or tuning the ~o~tPd tunable filter (Figure 5); and C1~A~ the l A~ s~:on pathbetween Ant~nn~ and ll~nâeeiver depending on whether the ha~sceiver is op~"dlillg in the ll An~ or receiving mode. Suitable control signals for the control circuits can be g~n~aled by a control computer or microprocessor such as described in United States Patent No. 5,140,699.
The present invention provides a method for miti~ tin~ inlelre,cnce b~lweell N
collocated radio t~lsceivers opeldL,ng through a common ~nt~nn~, where each l- -dnsce;ver has a ll ~alnll and a receive mode and an associated frequency band. In this method, a main output signal of each ofthe N l-~nscei~rers operating in ~ slllil mode is s~mpled to provide a sarnpled ~ n~ ed output signal. Each of the main output signals is filtered through a filter CGI res~,onding to the associated frequency band of the Ll~lsceiver that has produced the signal in order to substantially prevent subsequent ~ ... cC;on of out-of-band interference. Subsequent to the scullpli~lg step, after the signals have been filtered, they are tr~n~mitted through the common ~ntenn~
The number ofthe N lld~lsceivers opel dlillg in receive mode can be. design~ted as X.
A main received signal is filtered through a filter bank having a filter set to receive in each of the asso.,;dled frequency bands of the X receiving transceivers. The main received signa~ will have an ulterference component (caused by the tr~nS~
tl~lâcei~ers and any other interference) and a non-interference component (i.e., the desired signal received by the ~nt~nn~) The filtering step removes substantially all out-of-band interference from the main received signal. The method further includes sampling the main received signal to provide a sampled received signal and comparing the sampled ll~la.~ ed output signals and the sampled receive signals in a cancellat;on device. The r~ncPll~tion device generates an error correction signal which is subst~nti~lly identical to but is 180~ out of phase with the interference component of ~ ~ 2197693 the main received signal f~ ini~lg in the received signal path. The final steps include co"lb;ning the main received signal (in the received signal path) and the error correction signal to produce an error-co- re~iLed received signal that is subst~lti~lly free of interference, and dividing the received signal X-ways for distribution to the X
5 Llai~sceivers op~alihg in receive mode.
As a result ofthe present invention, it is possible to provide an ,.lle~ref~.lcamitig~tion method and app~allls for multiple collocated ll ~ sce;vas which permit operation through a co.. on ~ntPnn~ while .. ;.-;.. ;,;~g power loss. The present invendon provides protection against both in-band and out-of-band inte, e~fence. The ~ ;on of potential priority conflicts on a given band prevents the loss of critical data. The use of filters in conjunction with a cancPll~tion device results in an"llel~renca mitig~tion method and app~al.ls which afford protection even againststrong illL~Ir~fence. The col"bu~aLion of interference cancellation with band pass filters is achieved, in the present invention, using relatively compact and ine~ens;~e hardware.
Although illustrative embodil"el,Ls ofthe present invention have been desclil)cdherein with ,efefence to the acco,.~pan~ing drawings, it is to be understood that the invention is not limited to those precise embo~ c and that various other r.l~ ges and morlific~tions may be effected therein by one skilled in the art without departing from the scope or spirit of the invention.
FOR MULTIPI ~. CO~,~ OCATFn TRANSCF.IVF.12.
RACKGROUND OF l~F. ~VF.l~TION
FiPld of the InvPntion The present imention relates to radio communications, and more particularly - relates to mitigation of ulle.rcrellce between collocated radio lr~nsceivers.
Descnption of thP. Prior Art In order to minirnize the overall size of cornmunications systems employing multiple radio l~nscG;~ers, it is desirable to coUocate the transceivers on a common platform. However, this can lead to the problem of cosite interference, that is,inte.~nce caused by radiative and conductive interactions ofthe coUocated transceivers.
Interfering signals, which can hamper reception of in-bound communications by ll~lsceivers operating in receive mode, may result from a number of causes. These may include the carrier waves or wideband noise generated by collocated ll ~nsceivers operating in transmit mode; co-channel operation in ~equency-hopping systems; and ~ntPnn~ paKern distonion (in multiple ~ntetm~ systems). Collocated t~anscei~ers may also generate spurio~s ullel rel ing signals at odd harmonics of their fundamental ~equency as well as pseudo-white-noise over a wide band of frequencies on either side oftheir operating frequency. Several techniques have been proposed to ,-,;ni...;~e undesirable illtelrer-,nce between collocated transceivers, inchl~ing agile filtering, agile filtering with multicoupling and interference cancellation. Agile filtering involves coupling a frequency-adjustable filter, typically a bandpass filter, to the input of a transceiver ope~ ~ling in receive mode. While the filter atten~l~tes out-of-band noise, no protection is provided against interfering signals in the filter's passband. Further, 2~9769~
agile filtering requires a priori~ mana~ement scheme wherein a priority rank is ~csigred to each transceiver, if collocated L~A~ erS and receivers are acsi~ned close or identic~l operating frequencies, the lower-priority one must be shut down until the frequencies are re~csi~nPd This may result in loss of data associated with the S ll~ -s.. ~;on or receipt of signals by the subordil1ate transceiver.
In agile f~tering with multicoupling, similar techniques are employed, but a single ~ntenn~ is used to ~ e ~ntenn~ pattern distortion. The in-band illlc~re.~"~ce and priority-Tn~n~em~nt problems clisc~lssed above are still encountered.
L-le-r, ~-~ce G~nC~ tion techniques may involve sampling the output of l~ s~ g llansceivers to Pl;"~;ni~le, from the desired received signal, any ul~elre~ulg signal with a frequency close to the transmitter carrier frequency. This method is not practical where the ultel~lei~ce is strong or where substantial wide band noise is produced by the l-;~n~ ;nf~ l-dnscei~er. Alternatively, one can instead implement an illte.r~ ce c~nc~ tion scheme which involves c~nc~ tion of sul~s~ ;ally all ~.le.r~ l;ng signals outside the receiver's operating frequency band. However, this latter technique does not protect against interfering signals with frequencies close to, or the same as, the desired received signal.
A more advanced approach to interference elimin:-1ion has recently been set forth in co-assigned C~n~ n Patent Application No. 2,165,456; filed December 5, 1995 and entitled "Adaptive Method and Apparatus for Flimin~ting Interference Between Radio Transceivers". In the '456 application, a plurality of transceivers are coupled to a common antenna through a power combiner. A filter circuit is provided for each transceiver. The filtered signal from each transmitting transceiver is sampled and compared to the received signal in a plurality of cancelers; the cancelers then produce a plurality of cancellation signals that are combined and injected into the received signal. The cancellation signals consist of the coherent portions of the tr~n~mitted and received signals, shi~ed 180~. The combined cancellation signals are injected into the received signal before it is sampled, thereby providing adaptive interference ~ ;on.
The t~hnoloQy of the '456-application, ~lthol~h an irnprovement over the prior art, still has several disadv~nt~gçs The use of a power colllbil1er to couple the S h~ulsce;vers to a ~ - -. ~ nt~nn~ entails power loss. Further, the filter circuits require bulky, eAy~ e dual hopping filters.
In view ofthe disad~ ges ofthe prior art, there is a need for an u~l~"r~ e mitig~tion method and app~lus for multiple collocated transceivers which provides prol~;Lion against both inband and out-of-band intelrerence, even where the u~tel~n.1ce is strong; which .. ~ es power loss; which çl;.. ~ les data loss; and which can be easily ull~l~m~nted at relatively low cost with available, compact hardware.
OBJF.CI S AND SUMl~A~Y OF T~E INVFNTION
It is an object ofthe present invention to provide an interference mitig~tion method and a~p~allls for multiple collocated transceivers which permit operationthrough a col,ullon ~nt~nn~ while .~ ;ilg power loss.
It is another object of the present invention to provide an intel rel ence mitigation method and appardllls for multiple collocated transceivers which afford protection against both in-band and out-of-band interference.
It is yet another object of the present invention to provide an interference mitigation method and appal aLIlS for multiple collocated transceivers which prevent the loss of critical data.
~ ' 2l97693 It is a further object of the present invention to provide an interference mitigation method and app~al,ls for multiple collocated Llansceivers which afford protection even against strong interference.
It is still a further object of the present invention to provide an i-~telr~l ~ nce S .~ ig~l;ol1 app~allls for multiple coUocated tlallsceivers which co.llb;.les the use of bAn~p~cs filters with i.-le.r~r~,.lce c?ncell~tiQn te~ ;y~les using relatively compact and e~ e h~d~a e, and to also provide an int~r~nce mitig~tion nlethod using such an apparal~s.
Ln accG. lance with one forrn of the present invention, an "ILe. L. re.-ce 0 mitig~tion app~alus for multiple collocated transceivers il~cllldes a filter bank having a filter for each of a plurality of desired operating frequency bands. The filter bank is electrically coupled to a conh-,on ~ntenn~ A switch matrix has a series of first ports which are electrically interconne.;led with the filter bank (one first port for each filter).
The switch matrix also has a series of second ports (one for each transceiver), each of which can be selectively electrically i,-lerco~-l-e~led with any ofthe first ports. Each scei~er may in turn be selectively electrically intercom)ected to the co, l ~)onding switch matrix second port through either of a pair of tr~ncmicsion paths, in~llldin~ a ~r..l.~ led signal tr~ncnnicsiQn line and a received signal path. A c~nc~ tion device is electrically interconnected with the tr~ncmiccion lines to obtain a sample of each ll~ ed signal, and is also electrically interco~me~led with the received signal paths for sarnpling of received signals and injection of an interference c~ncell~tion signal.
The filter bank may be subdivided into odd and even filter banks. The odd and even filter banks may then be electrically intercoMe~,led to the ~ntenn~ through a circulator or a two way power splitter.
In accofdallce with another form of the present invention, the switch matrix may be dispensed with and each transceiver may be coupled to the common ~nt.onn~
219769~
through its own individual tunable bAndpAes filter. The tunable b~ndpAss filters are each individually tuned to the opelatu~g frequency of their transceiver.
In a method according to the present invention, a main output signal of each llA'~ ;n8 l-~an.3Ce;Ver ;S sarnpled to provide sampled output signals; each of the main 5 output signats is then filtered through a bAndpA~s filter (part of a filter bank) cG.- .,..~,on l-ng to the given l-ansc~iver's acsi~ed frequency band; and the filtered main output signals are l-A~ e~l A main received signal is passed through the filter bank which has a filter set to receive in each frequency band co..esponding to areceiving ll~sce;ver, re~lllting in filtering of subst~nt~ y all out-of-band u~lel~r~nce.
The main received signal is sampled to provide a sampled received signal, which is co...pared to the sampled output signals and used to gel~e~aLe an intG.re.el1ce cAneell~tion signal. The inle~ r~n,l1ce cAncçll~tion signal is co...bined ~,vith the main received signal and divided for distribution to the receiving ~l~nsceivers.
These and other objects, fealures and advantages of the present invention will become apparenL from the following dePile~ description of illustrative embo~
thereof, which is to be read in conneclion with the accoulpa~ ing drawings.
BI2~FF DESCRIPI ION OF THE DRAWINGS
Figure 1 is a sch~mAtic of an inte. rerence mitigation âpp&l ~ s in accordallce with the present invention;
Figure 2 is a schemAtic similar to Figure 1 showing an alternative arrangement of the filter bank;
Figure 3 is a schematic similar to Figures 1 and 2 showing yet another alternative ~.A.lg"."~ ofthe filter bank;
- ~ 2197693 Figure 4 is a schematic depicting the interconnection of canceler loops with theappar~ s of the present invention; and Figure 5 is a sch~m~tic of an interference mitig~tion appa,~us in accordance with an alternative embodiment of the present invention.
nF.TAl~ Fn nF.. ~CR~l ION OF TEIF P~F.~FRR~D Fl~IROD~ TS
Re~li"g to Figure 1, an inte~Çerence mitigation apparallls, dçsi~ted generally as 10, conne~tC a plurality offrequency-agile radio transceivers 12 with a co,.unon ~ n~ 14. In general, the number oftransceivers is d~cign~ted as N and the individual ~ sceivers are labeled as TR(1) through TR(N). At least some, and 10 preferably each ofthe l~&1sceivers may operate in either l.~ ..lit or receive mode.
Those of the N ~. ~njceivers operating in ~l ~1s.,li~ mode are referred to interchangeably as tl~ s or l-~nC...;l~ transceivers, while those ofthe N ~ldnsceivers opela~ing in receive mode are r~rell~d to inter~hangeably as receivers or receiving transceivers.
At any given time, a t,~nsceiver may be ~ lc.~ receiving, or open-circuited.
Apparatus 10 incl~ldes a filter bank 16 with a plurality of filters 18 electrically .Jllercol-~-ected with CGllullOl1 ~ntenn~ 14. In general, the number of filters is des~ ted as M and the individual filters are labeled as Fl(1) through FI(M).
Preferably, the filters are b~ndp~ss filters with contiguous p~CCb~n~C each filter's pAS~ljAnd co"esponding to one of M desired ope-dL;ng frequency bands for the N
collocated L. ~sceivers. The number of filters M should be greater than or equal to the number of Lrdnsceivers N so that each of the M desired operating frequency bands will only be used by one transceiver at a time.
The band pass filters ideally present, within their p~ssban~ an impedance subst~nti~lly the same as the characteristic impedance ofthe tr~ncmiecion metlillm (e.g., 50 ohms for a coaxial line). Outside the passband the impedance is ve~y high, effectively an open circuit. Accordingly, when a plurality of contiguous b~ndp~cs filters are conne~,Led to a common antenna, as in the present invention, only one of the filters pr~,se."s the characteristic impedance at any given frequency. The r~rn~inder of the filters ideally present an open circuit and draw no power from the ~nt.o~n~
Accordingly, the present invention permits interconnection of a plurality of filters to the co~ --on ~ntenna, effectively in parallel with one another, without the necç$~ for a power co.l~ lcr with its conco"uL~It combiner power loss. It is to be understood that the lowest frequency filter may be a low pass filter instead of a b~ld~cs filter, if signals or inl~.r~...nce below the lowest desired frequency band are not ~nticiF~e l, while still ol~t~ling the ror~goii~ benefits. Similarly, if signals or i"te,r~,rence above 10 the highest desired frequency band are not anticipated, the highest frequency filter may be a high pass filter.
Still referring to Figure 1, the appar~ s 10 also includes a switch matrix 20, which has M first ports 22 which are electrically interconnected with the M filters of the filter matrix, and N second ports 24. Preferably, the filters are coMected in a 15 st~ P~I (i.e., electrically parallel) arrangement between the common ~ntenn~ 14 and the M first ports 22 of switch matrix 20. Switch matrix 20 provides selective electrical il-tercoMection between any of the M first ports and N second ports, through any of a number of techniques well-known in the art. Accordingly, at least one, and preferably each of, the N second ports 24 which correspond to the N transceivers 12, may be20 selectively electrically in~er~,ol-nected with the common antenn~ through at least one, and preferably any desired one, of the M filters of the filter bank for ~ s.~;on or reception in the desired frequency band to which the filter col I ~sponds. Out-of-band signals are thus att~n~l~te~ It will be apprec;ated that switch matrix 20 can have any suitable constmction. Typically, a plurality of diodes are provided for illLer~iolule-;Lion 25- purposes. They can be individually biased on or offby control signals, thereby present;.-p a short or open circuit and e~iLing a selected interconnection between any one of the M first ports and any one of the N second ports. A suitable switch matrix which may be used is described in U.S. Patent No. 5,446,424, entitled "MicrowaveCrosspoint Blocking Switch Matrix and Assembly Employing Multilayer Stripline and 21!~7693 Pin Diode Switching Elements".
The N second ports 24 of s~vitch matrix 20 may in turn be selectively S elect~ically illter~ol~n~led with the N transceivers 12 through N L,Anc~.~;cc:on path pairs. At least one of, and pr.,~er_bly each, trAncmisciQrl path pair i~rlud~s aL,n~ ed signal l,A~ -.;on line 26 and a received signal Llnllc~ cc:on path (a pr~ ,d cG~ gv~ion of which will be described in greater detail below). When a given l~ sce;ver 12 is in ~ lUl mode, it is co.lilected to its corresponding switch 10 matrLx second port through the associated l,n~ ed signal ~IA~s~ c~;on line 26.
When in receiw mode, a t~anscei~er 12 is connecte~l to its corresponding switch matriY second port through the associated received signal trAncmicsion path.
Apparatus 10 also preferably includes cArlc~ tion device 28. The cAnc~llA~ion device is electrically coupled to each of the L~ A ~lc~ l led signal trAncmission lines 26, preferably with directional couplers 30, in order to receive a sample ofthe l,A~.c.,l;lled signal from each ofthe N l~lsceivers that is opel~ lg in ~ sl~u~ mode. The cancellation device 28 is also electrically interconnected with each of the received signal ~rArs..l~icsion paths ofthe N tr~ncmis.sion path pairs forboth receipt of a received signal sample and injection of an interference cancellation signal. A pi~;Çe~, ed method of i~ler~;onllection of c~nce~lation device 28 with the received signal trAn~mi~sion paths will be diccllssed below.
The received signal sarnple includes both an interference portion and a non-interference portion. The cAncell~tion device 28 is electrically configured to co~ -e the transrnitted signal samples with the received signal sample and to produce an interference cancellation signal that has substAntiAlly the same frequency and arnplitude characteristics as the interference portion of the received signal sarnple but is substantially 180~ out of phase with it, so as to result in destructive interference, effectively canceling the interference portion of the received signal.
Still referring to Figure 1, a prefel -ed form of received signal trancmission path hldes N first tr~ncmicr;on line se~ynentc 32 having first and second ends. The first ends are selectively electrically interconnected with the N second ports 24 of switch matrix 20 through switches 36. The second ends are selectively electrically S inLe~w~ne~led to a main power combiner 38 having N input ports, through switches 40. Preferably, the input ports of main power col"biner 38 can also be ~on~e~ledthrough a~ilches 40 to il.lpedance matched t~,l...inalions, in order to prevent rPfle~honc Main power combiner 38 comb;ncs the received signals from all Op~lalillg 10 frequency bands. An error correction tr~nsmission line 42 is coupled to the output of co~,l)iner 38 to calTy the colllbu~ed slgnals. The prere.. ed form of received signal ;c~;on path also incl~ldes main power splitter 44 having N output ports and an input port. The coll-bined signals enter the input port of splitter 44. N secondC...:c.cion line s~.~e~s 46 have first ends which are selectively electrically 15 intercGn-le~ with the N output ports of spliKer 44 via switches 48, and also have second ends which are selectively electrically i"lerco~ ecled with transceivers 12 via switches 50. Pl~,f~-~bly, the output ports of spliKer 44 can also be connected to imred~nce~ hed te,lll-na~ions through switches 48 to prevent reflections. Switches 50 are electrically configured to perrnit selective electrical i.lLerco~ ection of 20 l-~nscei~ers 12 with either tr~nsmiScion lines 26 or the received signal ~ .C;c.i;on paths just described, i.e., the first and second tr~ncmicsion line segments 32 and 46, error correction tr~ncmiscion line 42, main power colllbincr 38, and main power spliKer 44.
Contin-lin~ to refer to Figure 1, the ~ fel,ed i~,~ere~m~ection between inte.ft:rence rqnc~ tion device 28 and the received signal tr~nsmiSsion paths incl~des error correction signal injection directional coupler 52 coupled to error correction hi~ ;csion line 42 for injection ofthe inte-rerence ç~nc~ tion signal, and also includes error sampling directional coupler 54, also coupled to error correctiontr~ncmicsion line 42. Preferably, error sampling directional coupler 54 is interconnected with error correction transmission line 42 at a point where it samples the received signals after the error correction signal injection directional coupler 52 has injected the interference c~llcell~tion (error correction) signal. In this way, adaptive il.le.rclence cAncellAtion is achieved, i.e., the corrected signal is sampled for the portions that are coherent with the tr~nsmitted signals. In order to make up for at least a portion of power losses incurred in the received signals between the çGm.llon A.~tellnA
14 and the main power splitter 44, low noise amplifier 56 îs pl~ef~;lably provided in error correction h ~ .. s~;on line 42, to amplify the col .~ ,d received signal.
In opelal;on, the ll~lc-";ll;n~ transceiver(s) (TR(l) and TR(N) in Figure 1) are10 electricaUy ~le~onne~led with corresponding second ports 24 of switch matrix 20 through ~vvil~ Les 50, 1l ;..,cn,;l le~ signal trAncmicsiQn lines 26 and switches 36. Second ports 24 are then in turn ele~,ll;cally inlercon~le.,led with co.lll..on ~ntenn~ 14 through switch matrix 20 and app~opliale filters 18 of filter bank 16. Each port 24 is coi-l-e~,led to ~nt~nn~ 14 through only one filter 18, co-,~ onding to the desired tr~n.cmithnp frequency band of its coll.,sponding tr~nsmitting ~nsceiver. Accordingly, each "n~,..;lled signal is filtered to att~nl.~te out-of-band noise.
The receiving transceiver(s) (TR(2) in Figure 1) are electrically interconnectedto collt~onding second ports 24 of switch matrix 20 through the previously-described received signal ~ ,e...is~;on path inclllding switches 36, first tr~ncmicsion line se~g" - .~s 32, main power co.llbiner 38, error correction ll~ s~;on line 42, low noise amplifier 56, main power splitter 44, switches 48, second h~,.c...;c~;on line se~n~ntS
46 and switches 50. Second ports 24 of switch matrix 20 are in turn electrical~yinterconnected with cormnon ~ntçnna 14 through switch matrix 20 and appropriate filters 18 of filter bank 16. Each port 24 is connected to ~ntenn~ 14 through only one filter 18, co-l~,~ponding to the desired receive frequency band of its corresponding receiving llansceiver. Accor-lingly, each receive signal is filtered to attçnn~te out-of-band noise. The filtering of the transmitted and received signals to P~ ;n~te out-of-band noise reduces the power required for the interference cancellation signal.
C~ncellAtion device 28 samples each trAnsmitted signal through directional couplers 30 and col-lpares the ~lA~ ed signals to a received signal sample from directional coupler 54. Those portions of the IlAns...;~ed and received signals that are coherent ~pr~nl inte~r~re.lce. Based on the ~letection of the coherent signals, the 5 ~,Ail~P1lA1;~n device 28 effectively modifies a portion ofthe sampled t~An~ (ed signals and gc~c~atcs an error c~ ,lion signal (also ~er~ ,d to as an u~l~,.r~ ce c~ncPllA~ion signal) which is c~ie l;Ally equal in ATnrlit~e and 180~ out-of-phase with the ull~r~i-u~g signals on the received signal path. This cAnC~ll-Ation signat is injected via error co"~,~lion signal ~"e~ioll directional coupler 52 (also rere,~d to as a sl~mmi~
coupler) into error correction line 42 where it cancels or at least .. ,in;~ 5 the ulLelr~rulg signat portion ofthe received signat to form a cGl~ d signal. Low noise amplifier 56 -Amrlifi~s the coll~led signal to make up for losses. As mentioned above, because both reception and l A~ s~;on are filtered, the amount of intelre~j1ce to be c~ncPled by c~An~ Ation device 28 is redl-ce-l thereby cutting its power requir~.nellLs.
A pler~ -~td form of ~ncellAtion device 28 wilt be ~lisa~sse~ in greater detail below.
Rert;llu~g now to Figure 2, wherein like elements have been given the same r~Ç~r~l1ce numbers as in Figure 1 incremented by 100, there is shown an embodiment of the invention employing a modified electrical i.~Lercon.~ection between the filter bank 116 and tolll.u~n antenna 114. In this embodiment, filter bank 116 is divided into two sep~te filter banks, odd filter bank 166 and even filter bank 168. The odd filter bank 166 Colllaills those of the M fitters that are odd-numbered and the even filter bank COIllaills those of the M filters that are even numbered. The odd and even numbering ofthe filters 118 refers to the frequenGy position ofthe individuat filters in the operating band of filter banks 166, 168 in relati'on to all other filters.
The odd filter bank 166 and even filter bank 168 are electrically interconnectedwith comrnon antenna 114 via circulator 170. The book Microwave Receivers and Related Components. by Jarnes B. Tsui, Peninsula Publishing, 1985, desclibes (atpages 296-97) the interco~ e~;iion of a circulator with odd and even filter banks, Circulator 170 includes an input port 172 and first f 2197693 and second output ports 174 and 176 respectively. First output port 174 is electrically interco~u~ected with one of the odd and even filter banks, for example, the even filter bank 168 as shown in Figure 2, while second output port 176 is electrically inte. conne~ led with the other of the odd and even filter banks, for example, the odd filter bank 166 as shown in Figure 2. The input signal from common ~ntenn~ 114 is fed into input port 172 of circulator 170. It first reaches first output port 174, where it will pass through the even fi ter bank 168 if it ,~ f 5 any of the characteristic freql~enl ies ofthe filters 118 in even filter bank 168. If it does not match any ofthose frequencies, it will reflect and reach second output port 176 where it will pass through an app,oytiate filter 118 in odd filter bank 166.
The purpose of using circulator 170 with odd and even filter banks 166 and 168 is to achieve a better voltage st~n~ing wave ratio (VSWR) than is possible with the confi~ration shown in Figure 1. In Figure 1, there is potential for signals at the edge of a given desired frequency band to be partially passed by an adjac~nt filter, due to overlap in the pA~b~n~ls of neighboring filters. This is ~ n~ted in the configuration of Figure 2, wherein the adjacent filters are separated into odd and even banks. It is to be understood that the filters are numbered consecutively (from lowest frequency to highest) in accordance with their desired frequency band. Losses incirculator 170 are generally on the order of 0.2-0.3 dB. The r~m~ind~r of the apy~l~s of Figure 2 is identical to that of Figure 1.
At low frequencie~ on the order of 50-100 MHz, circulators are either unavailable, or otherwise bulky and expensive. For operation at these frequencies, another alternative configuration, shown in Figure 3, is possible. In Figure 3, like clP ..c..l~ have received the same numbers as in Figure 2, il1crellle.,led by 100. In the configuration shown in Figure 3, circulator 170 of Figure 2 is replaced by filter bank power splitter 286. Operation is similar to the configuration of Figure 2, except that a 3 dB power loss is encountered in the filter bank power splitter 286. Thus, at frequencies where a circulator is available, the configuration of Figure 2 is prefelled.
. . ~ 2197693 Figure S depicts an altemative embodiment of the present invention which does not employ a switch matrix. Like parts have the same ~;çc;r(~nce numbers as in Figure 1, incrPrnented by 300. Instead of the switch matrix, tunable b~ndp~s filters 390 are interposed between switches 336 and comrnon ~nt~nn~ 314~ Rather than colu~e~,l each hansceiver 312 to ~ntçnn~ 314 via a fixed filter co-.~,sponding to the l.~1sceiver's Ope~alin~3 frequency band (by use of a switch matrix), in the embodiment of Figure 5, each ~1sce;ver is provided with its own tunable ~ndp~c~ filter which is adjusted by control signals to the desired OpC~al;ng frequency of the L~sc~ er. In all other~spe~,ls, the embodiment of Figure 5 is similar to that of Figures 1-3.
Referring now to Figure 4, a prèrellèd embodiment ofthe c~ncell~tion device 28 will be described. Preferably, c~ncell~tion device 28 inrludes N c-~nc~ tion loops co,. e;~ponding to each of the l. ~nc~ ed signal tr~mmi~sion lines of the N tr~n.cmiC~ion path pairs and the number of l.a,~scei~ers. Each loop incl~ldes a t.i...c,.,;l~ed signal sample input port S8 electrically interconnected by one ofthe directional couplers 30 (shown in Figure 1) to its co--~s~ondil1g ll~nclil;~led signal tl~ncl~l;ssion line 26 (shown in Figure 1). Each loop also in~ des a received signal sarnple input port 59 and an interference c~ncçll~tion signal output port 60.
Each loop also includes a phase detector 61 (also referred to as a synchronous detector) and a vector modulator 62 (also refe.led to as a signal controller). Phase detector 61 has a first input port electrically interconnected ~.vith l~ s~.. ;l led signal sarnple input port 58 via directional coupler 63 for input of a sarnple of the l, ~n~...;Lled signal from the co.~e~pondil-g lr~r,smilling transceiver. Phase detector 61 also has a second input port which is the same as received signal sarnple input port 59. Phase detector 61 also has I and Q output ports respectively connected to the inputs of I and Q loop integrators and/or amplifiers 6i and 65 respectively. Phase detector 61 cG".pares the received and ll;~ns~ ed signal samples in order to detect in-phase(coherent) portions of the received and transrnitted signal samples and then supplies I
(in-phase) and Q (quadrature phase) DC signals to the I and Q output ports respectively. The I and Q signals are then amplified and/or integrated by components 64 and 65 to create control signals provided to the vector modulator.
Vector modulator 62 has a first input port (which is the same as l~ s~;Lled signal sarnple input port 58), and also has I and Q control signal input ports conne~e~
S to the outputs of I and Q loop ;nleg~alo~J~lpl;~e~ 64 and 65 res~Je~ ely. Vector modulator 62 also has an output port (which is the same as illlel r~nce c~nc~ tion signal output port 60). Based on the I and Q control signals provided to it, vector modulator 62 effectively modifies a portion ofthe sample signal ofthe Ll~n~ èd signal to produce an i~llelre.~nce c~ncell~tion signal that is essenti~lly equal in ~mrlitude and 180~ out of phase with the L~llelr~;lu~g signal in the received signal path (on lt~n~ ;on line 42).
The operation of the c~nc~ tion loop ~iscussed above is described in greater detail in U.S. Patent No. 5,117,50S, entitled ~Inte~,rerei1ce C~ncell~l;on System Having Noise Reduction Features and Method". It is to be understood that, although Figure 4 shows only a single cancellation loop, one is provided for each of the N
transceivers.
Still refe~ g to Figure 4, cancellation device 28 also includes error s~mrlin~
power splitter 78 having an input port electrically i.llel~;olule~iled with error sarnpling directional coupler 54, and having N output ports, each electrically illlercounected with the received signal samp!e input port 59 of one of the N cancellation loops.
C~ncPll~tion device 28 also includes an u-le.r~ ce cancellation signal power combiner 79 having N input ports each electrically interconnected with the interference cancellation system output port 60 of one of the N canceler loops. Interference cancellation system power co"~binef 79 combines the interference cancellation signals ~om all the loops to produce a colubined interference cancellation signal at its output port, which is electrically interconnected with the error correction signal injection directional coupler 52 for injection of the combined interference cancellation signal into error correction transrnission line 42.
It is to be understood that the embodiments of the invention shown in Figures 1, 2, 3 and 5 may be provided with control circuits (not shown) for adjusting the ope~dLing frequency bands of the tl~sceivers; controlling the various switches and switch l..al~;ces to conn~ct the lr~lsceivers to corresponding filters (Figures 1, 2 and 3) or tuning the ~o~tPd tunable filter (Figure 5); and C1~A~ the l A~ s~:on pathbetween Ant~nn~ and ll~nâeeiver depending on whether the ha~sceiver is op~"dlillg in the ll An~ or receiving mode. Suitable control signals for the control circuits can be g~n~aled by a control computer or microprocessor such as described in United States Patent No. 5,140,699.
The present invention provides a method for miti~ tin~ inlelre,cnce b~lweell N
collocated radio t~lsceivers opeldL,ng through a common ~nt~nn~, where each l- -dnsce;ver has a ll ~alnll and a receive mode and an associated frequency band. In this method, a main output signal of each ofthe N l-~nscei~rers operating in ~ slllil mode is s~mpled to provide a sarnpled ~ n~ ed output signal. Each of the main output signals is filtered through a filter CGI res~,onding to the associated frequency band of the Ll~lsceiver that has produced the signal in order to substantially prevent subsequent ~ ... cC;on of out-of-band interference. Subsequent to the scullpli~lg step, after the signals have been filtered, they are tr~n~mitted through the common ~ntenn~
The number ofthe N lld~lsceivers opel dlillg in receive mode can be. design~ted as X.
A main received signal is filtered through a filter bank having a filter set to receive in each of the asso.,;dled frequency bands of the X receiving transceivers. The main received signa~ will have an ulterference component (caused by the tr~nS~
tl~lâcei~ers and any other interference) and a non-interference component (i.e., the desired signal received by the ~nt~nn~) The filtering step removes substantially all out-of-band interference from the main received signal. The method further includes sampling the main received signal to provide a sampled received signal and comparing the sampled ll~la.~ ed output signals and the sampled receive signals in a cancellat;on device. The r~ncPll~tion device generates an error correction signal which is subst~nti~lly identical to but is 180~ out of phase with the interference component of ~ ~ 2197693 the main received signal f~ ini~lg in the received signal path. The final steps include co"lb;ning the main received signal (in the received signal path) and the error correction signal to produce an error-co- re~iLed received signal that is subst~lti~lly free of interference, and dividing the received signal X-ways for distribution to the X
5 Llai~sceivers op~alihg in receive mode.
As a result ofthe present invention, it is possible to provide an ,.lle~ref~.lcamitig~tion method and app~allls for multiple collocated ll ~ sce;vas which permit operation through a co.. on ~ntPnn~ while .. ;.-;.. ;,;~g power loss. The present invendon provides protection against both in-band and out-of-band inte, e~fence. The ~ ;on of potential priority conflicts on a given band prevents the loss of critical data. The use of filters in conjunction with a cancPll~tion device results in an"llel~renca mitig~tion method and app~al.ls which afford protection even againststrong illL~Ir~fence. The col"bu~aLion of interference cancellation with band pass filters is achieved, in the present invention, using relatively compact and ine~ens;~e hardware.
Although illustrative embodil"el,Ls ofthe present invention have been desclil)cdherein with ,efefence to the acco,.~pan~ing drawings, it is to be understood that the invention is not limited to those precise embo~ c and that various other r.l~ ges and morlific~tions may be effected therein by one skilled in the art without departing from the scope or spirit of the invention.
Claims (12)
1. Apparatus for mitigating interference between a plurality of collocated radio transceivers operating through a common antenna, at least some of said transceivers having both a transmit mode and a receive mode, said apparatus . comprising:
(a) a filter bank having a plurality of filters, said filter bank being electrically coupled to said common antenna, each of said plurality of filters corresponding to one of a plurality of desired operating frequency bands;
(b) a switch matrix having a plurality of first ports electrically connected to said plurality of filters and a plurality of second ports corresponding to said plurality of transceivers, each of said plurality of second ports being capable of selective electrical interconnection with each of said plurality of first ports, whereby at least one of said plurality of second ports may be electrically interconnected with said common antenna through at least one of said plurality of filters of said filter bank, for at least one of transmission and reception in the desired frequency band to which said filter corresponds;
(c) a plurality of transmission path pairs for selective electrical interconnection of said plurality of transceivers and said plurality of corresponding second ports, at least one of said plurality of transmission path pairs including a transmitted signal transmission line and a received signal transmission path, each of said transceivers being connected to its corresponding switch matrix second portthrough said transmitted signal transmission line when in transmit mode and through said received signal transmission path when in receive mode; and (d) a cancellation device, said cancellation device being electrically coupled to each of said transmitted signal transmission lines of said plurality of transmission path pairs for receipt of a transmitted signal sample from each of said plurality of transceivers that is operating in said transmit mode, said cancellation device being electrically coupled to said received signal transmission paths of said plurality of transmission path pairs for both receipt of a received signal sample and injection of an interference cancellation signal, said received signal sample having an interference portion and a non-interference portion, said cancellation device being responsive to said transmitted signal samples and said received signal sample and generating in response thereto said interference cancellation signal, said interference cancellation signal having substantially the same frequency and amplitude as said interference portion of said received signal sample, said interference cancellation signal being substantially 180° out-of-phase with said interference portion of said received signal sample.
(a) a filter bank having a plurality of filters, said filter bank being electrically coupled to said common antenna, each of said plurality of filters corresponding to one of a plurality of desired operating frequency bands;
(b) a switch matrix having a plurality of first ports electrically connected to said plurality of filters and a plurality of second ports corresponding to said plurality of transceivers, each of said plurality of second ports being capable of selective electrical interconnection with each of said plurality of first ports, whereby at least one of said plurality of second ports may be electrically interconnected with said common antenna through at least one of said plurality of filters of said filter bank, for at least one of transmission and reception in the desired frequency band to which said filter corresponds;
(c) a plurality of transmission path pairs for selective electrical interconnection of said plurality of transceivers and said plurality of corresponding second ports, at least one of said plurality of transmission path pairs including a transmitted signal transmission line and a received signal transmission path, each of said transceivers being connected to its corresponding switch matrix second portthrough said transmitted signal transmission line when in transmit mode and through said received signal transmission path when in receive mode; and (d) a cancellation device, said cancellation device being electrically coupled to each of said transmitted signal transmission lines of said plurality of transmission path pairs for receipt of a transmitted signal sample from each of said plurality of transceivers that is operating in said transmit mode, said cancellation device being electrically coupled to said received signal transmission paths of said plurality of transmission path pairs for both receipt of a received signal sample and injection of an interference cancellation signal, said received signal sample having an interference portion and a non-interference portion, said cancellation device being responsive to said transmitted signal samples and said received signal sample and generating in response thereto said interference cancellation signal, said interference cancellation signal having substantially the same frequency and amplitude as said interference portion of said received signal sample, said interference cancellation signal being substantially 180° out-of-phase with said interference portion of said received signal sample.
2. Apparatus as defined in Claim 1, wheren:
said plurality of collocated radio transceivers includes N of said transceivers,said plurality of second ports of said switch matrix includes N of said ports, and said plurality of transmission path pairs includes N of said transmission path pairs, N being an integer greater than 1;
said plurality of filters includes M of said filters, said plurality of desired operating frequency bands includes M of said bands, and said plurality of first ports of said switch matrix includes M of said ports, M being an integer greater than l;
each of said N transceivers has both a transmit mode and a receive mode;
any given one of said N second ports of said switch matrix may be selectively interconnected with said common antenna through any given one of said M filters of said filter bank; and each of said N transmission path pairs includes both a transmitted signal transmission line and a received signal transmission path.
said plurality of collocated radio transceivers includes N of said transceivers,said plurality of second ports of said switch matrix includes N of said ports, and said plurality of transmission path pairs includes N of said transmission path pairs, N being an integer greater than 1;
said plurality of filters includes M of said filters, said plurality of desired operating frequency bands includes M of said bands, and said plurality of first ports of said switch matrix includes M of said ports, M being an integer greater than l;
each of said N transceivers has both a transmit mode and a receive mode;
any given one of said N second ports of said switch matrix may be selectively interconnected with said common antenna through any given one of said M filters of said filter bank; and each of said N transmission path pairs includes both a transmitted signal transmission line and a received signal transmission path.
3. Apparatus as defined in Claim 2, wherein each of said received signal transmission paths of said N transmission path pairs includes first and second transmission line segments having first and second ends, said first ends of said first segments being selectively electrically interconnected with said N second ports of said switch matrix, said second ends of said second segments being selectively electrically interconnected with said transceivers, and further comprising:
a main power combiner having N input ports and an output port, said input ports of said main power combiner being selectively electrically interconnected with said second ends of said first segments for combination of received signals carried in said received signal transmission paths into a combined signal, said received signals having passed through those of said M filters corresponding to those of said M desired operating frequency bands in which those of said N transceivers that are operating in said receive mode are operating;
an error correction transmission line from which said cancellation device receives said received signal sample and into which said cancellation device injects said interference cancellation signal, said error correction transmission line having a first end electrically interconnected with said output port of said main power combiner and also having a second end; and a main power splitter having an input port electrically interconnected to said second end of said error correction transmission line and also having N output ports, said N output ports being selectively electrically interconnected with said first ends of said second segments, whereby said received signal transmission paths extend through said first transmission line segments, said main power combiner, said error correction transmission line, said main power splitter, and said second transmission line segments, for said combination of said received signals, for sampling and interference cancellation, of said combined signal, and for splitting and distributing of said combined signal to each of said N transceivers that is operating in said receive mode.
a main power combiner having N input ports and an output port, said input ports of said main power combiner being selectively electrically interconnected with said second ends of said first segments for combination of received signals carried in said received signal transmission paths into a combined signal, said received signals having passed through those of said M filters corresponding to those of said M desired operating frequency bands in which those of said N transceivers that are operating in said receive mode are operating;
an error correction transmission line from which said cancellation device receives said received signal sample and into which said cancellation device injects said interference cancellation signal, said error correction transmission line having a first end electrically interconnected with said output port of said main power combiner and also having a second end; and a main power splitter having an input port electrically interconnected to said second end of said error correction transmission line and also having N output ports, said N output ports being selectively electrically interconnected with said first ends of said second segments, whereby said received signal transmission paths extend through said first transmission line segments, said main power combiner, said error correction transmission line, said main power splitter, and said second transmission line segments, for said combination of said received signals, for sampling and interference cancellation, of said combined signal, and for splitting and distributing of said combined signal to each of said N transceivers that is operating in said receive mode.
4. Apparatus as defined in Claim 3, wherein said received signal sample is received from said error correction transmission line by said cancellation device after said cancellation device has injected said interference cancellation signal into said error correction transmission line, thereby providing adaptive interference cancellation.
5. Apparatus as defined in Claim 4, further comprising a low noise amplifier electrically connected between said second end of said error correction transmission line and said input port of said main power splitter to amplify said combined signal to make up for at least a portion of losses between said common antenna and said main power splitter.
6. Apparatus as defined in Claim 5, wherein said cancellation device includes:
N cancellation loops corresponding to each of said transmitted signal transmission lines of said N transmission path pairs, each of said loops having a transmitted signal sample input port electrically interconnected to said corresponding one of said transmitted signal transmission lines of said N transmission path pairs, a received signal sample input port, and an interference cancellation signal output port;
an error sampling power splitter having an input port and N output ports electrically interconnected to one each of said received signal sample input ports of said N cancellation loops;
an error coupler connected between said input port of said error sampling power splitter and said error correction transmission line for tapping said received signal sample;
an interference cancellation signal power combiner having N input ports and an output port, said N input ports of said interference cancellation signal power combiner being electrically interconnected with one each of said interference cancellation signal output ports of said N cancellation loops to produce a combined interference cancellation signal; and a summing coupler connected between said output port of said interference cancellation signal power combiner and said error correction transmission line for injecting said combined interference cancellation signal.
N cancellation loops corresponding to each of said transmitted signal transmission lines of said N transmission path pairs, each of said loops having a transmitted signal sample input port electrically interconnected to said corresponding one of said transmitted signal transmission lines of said N transmission path pairs, a received signal sample input port, and an interference cancellation signal output port;
an error sampling power splitter having an input port and N output ports electrically interconnected to one each of said received signal sample input ports of said N cancellation loops;
an error coupler connected between said input port of said error sampling power splitter and said error correction transmission line for tapping said received signal sample;
an interference cancellation signal power combiner having N input ports and an output port, said N input ports of said interference cancellation signal power combiner being electrically interconnected with one each of said interference cancellation signal output ports of said N cancellation loops to produce a combined interference cancellation signal; and a summing coupler connected between said output port of said interference cancellation signal power combiner and said error correction transmission line for injecting said combined interference cancellation signal.
7. Apparatus as defined in Claim 6, wherein each of said N cancellation loops includes:
a phase detector having first and second input ports and I and Q output ports, said first input port of said phase detector being electrically interconnected with said transmitted signal sample input port for input of said transmitted signal sample, said second input port of said phase detector being electrically interconnected with a corresponding one of said N output ports of said error sampling power splitter, said phase detector comparing said transmitted signal sample and said received signal sample, said phase detector detecting in-phase components of said transmitted signal sample and said received signal sample and supplying to said I and Q output ports respectively I and Q components of said in-phase components.
I and Q loop amplifiers each having input and output ports, said input ports of said I and Q loop amplifiers being electrically interconnected respectively with said I
and Q output ports of said phase detector, said I and Q loop amplifiers amplifying respectively said I and Q components of said in-phase components from said phasedetector;
a vector modulator having a first input port, an I input port, a Q input port, and an output port, said first input port of said vector modulator being electrically interconnected with said transmitted signal sample input port for input of said transmitted signal sample, said I and Q input ports being electrically interconnected with said output ports of said I and Q loop amplifiers respectively, said output port of said vector modulator being electrically interconnected with a corresponding one of said N input ports of said interference cancellation signal power combiner, said vector modulator shifting said phase of said interference cancellation signal to be substantially 180° out-of-phase with said interference portion of said received signal sample.
a phase detector having first and second input ports and I and Q output ports, said first input port of said phase detector being electrically interconnected with said transmitted signal sample input port for input of said transmitted signal sample, said second input port of said phase detector being electrically interconnected with a corresponding one of said N output ports of said error sampling power splitter, said phase detector comparing said transmitted signal sample and said received signal sample, said phase detector detecting in-phase components of said transmitted signal sample and said received signal sample and supplying to said I and Q output ports respectively I and Q components of said in-phase components.
I and Q loop amplifiers each having input and output ports, said input ports of said I and Q loop amplifiers being electrically interconnected respectively with said I
and Q output ports of said phase detector, said I and Q loop amplifiers amplifying respectively said I and Q components of said in-phase components from said phasedetector;
a vector modulator having a first input port, an I input port, a Q input port, and an output port, said first input port of said vector modulator being electrically interconnected with said transmitted signal sample input port for input of said transmitted signal sample, said I and Q input ports being electrically interconnected with said output ports of said I and Q loop amplifiers respectively, said output port of said vector modulator being electrically interconnected with a corresponding one of said N input ports of said interference cancellation signal power combiner, said vector modulator shifting said phase of said interference cancellation signal to be substantially 180° out-of-phase with said interference portion of said received signal sample.
8. Apparatus as defined in Claim 2, wherein said M filters of said filter bank are electrically connected in a stacked arrangement between said common antenna and said M first ports of said switch matrix.
9. Apparatus as defined in Claim 2, wherein:
said M filters of said filter bank are sub-divided into odd and even filter banks;
said M operating frequency bands and filters are numbered consecutively from 1 to M;
said odd filter bank contains those of said M filters that are odd-numbered; andsaid even numbered bank contains those of said M filters that are even-numbered;
further comprising a circulator, said circulator having an input port and first and second output ports, said input port of said circulator being electrically interconnected to said common antenna, said first output port of said circulator being electrically interconnected with a first one of said odd and even filter banks, said second output port of said circulator being electrically connected to a second one of said odd and even filter banks, whereby received signals input from said common antenna matching the frequency bands in said first one of said odd and even filter banks are transmitted thereby and received signals not matching the frequency bands in said first one of said odd and even filter banks are reflected and routed to said second output port for transmission through said filters of said second of said odd and even filter banks.
said M filters of said filter bank are sub-divided into odd and even filter banks;
said M operating frequency bands and filters are numbered consecutively from 1 to M;
said odd filter bank contains those of said M filters that are odd-numbered; andsaid even numbered bank contains those of said M filters that are even-numbered;
further comprising a circulator, said circulator having an input port and first and second output ports, said input port of said circulator being electrically interconnected to said common antenna, said first output port of said circulator being electrically interconnected with a first one of said odd and even filter banks, said second output port of said circulator being electrically connected to a second one of said odd and even filter banks, whereby received signals input from said common antenna matching the frequency bands in said first one of said odd and even filter banks are transmitted thereby and received signals not matching the frequency bands in said first one of said odd and even filter banks are reflected and routed to said second output port for transmission through said filters of said second of said odd and even filter banks.
10. Apparatus as defined in Claim 2, wherein:
said M filters of said filter bank are sub-divided into odd and even filter banks;
said M operating frequency bands and filters are numbered consecutively from 1 to M;
said odd filter bank contains those of said M filters that are odd-numbered; andsaid even numbered bank contains those of said M filters that are even-numbered;
further comprising a filter bank power splitter, said filter bank power splitterhaving an input port and first and second output ports, said input port of said filter bank power splitter being electrically interconnected to said common antenna, said first output port of said filter bank power splitter being electrically interconnected to a first one of said odd and even filter banks, said second output port of said filter bank power splitter being electrically interconnected to a second one of said odd and even filter banks, whereby received signals input from said common antenna are routed to those of said filters having matching frequency bands with reflection of non-matching signals.
said M filters of said filter bank are sub-divided into odd and even filter banks;
said M operating frequency bands and filters are numbered consecutively from 1 to M;
said odd filter bank contains those of said M filters that are odd-numbered; andsaid even numbered bank contains those of said M filters that are even-numbered;
further comprising a filter bank power splitter, said filter bank power splitterhaving an input port and first and second output ports, said input port of said filter bank power splitter being electrically interconnected to said common antenna, said first output port of said filter bank power splitter being electrically interconnected to a first one of said odd and even filter banks, said second output port of said filter bank power splitter being electrically interconnected to a second one of said odd and even filter banks, whereby received signals input from said common antenna are routed to those of said filters having matching frequency bands with reflection of non-matching signals.
11. Apparatus for mitigating interference between N collocated radio transceivers operating through a common antenna, each of said transceivers having a transmit mode and a receive mode, said apparatus comprising.
(a) a filter bank having a group of N tunable bandpass filters, each of said filters corresponding to one of said N transceivers, each of said filters being tuned to a desired operating frequency of its corresponding transceiver, each of said filters having a first port electrically coupled to said common antenna and having a second port;
(b) a group of N transmission path pairs for selective electrical interconnection of said N transceivers and said second ports of said corresponding filters, each of said N transmission path pairs including a transmitted signal transmission line and a received signal transmission path, each of said transceivers being connected to the second port of its corresponding bandpass filter through said transmitted signal transmission line when in said transmit mode and through saidreceived signal transmission path when in said receive mode; and (c) a cancellation device, said cancellation device being electrically coupled to each of said transmitted signal transmission lines of said N transmission path pairs for receipt of a transmitted signal sample from each of said N transceivers that is operating in said transmit mode, said cancellation device being electrically coupled to said received signal transmission paths of said N transmission path pairs for both receipt of a received signal sample and injection of an interference cancellation signal, said received signal sample having an interference portion and a non-interference portion, said cancellation device being electrically configured to compare said transmitted signal samples with said received signal sample to produce said interference cancellation signal, said interference cancellation signal having substantially the same frequency and amplitude as said interference portion of said received signal sample, said interference cancellation signal being substantially 180°
out-of-phase with said interference portion of said received signal sample.
(a) a filter bank having a group of N tunable bandpass filters, each of said filters corresponding to one of said N transceivers, each of said filters being tuned to a desired operating frequency of its corresponding transceiver, each of said filters having a first port electrically coupled to said common antenna and having a second port;
(b) a group of N transmission path pairs for selective electrical interconnection of said N transceivers and said second ports of said corresponding filters, each of said N transmission path pairs including a transmitted signal transmission line and a received signal transmission path, each of said transceivers being connected to the second port of its corresponding bandpass filter through said transmitted signal transmission line when in said transmit mode and through saidreceived signal transmission path when in said receive mode; and (c) a cancellation device, said cancellation device being electrically coupled to each of said transmitted signal transmission lines of said N transmission path pairs for receipt of a transmitted signal sample from each of said N transceivers that is operating in said transmit mode, said cancellation device being electrically coupled to said received signal transmission paths of said N transmission path pairs for both receipt of a received signal sample and injection of an interference cancellation signal, said received signal sample having an interference portion and a non-interference portion, said cancellation device being electrically configured to compare said transmitted signal samples with said received signal sample to produce said interference cancellation signal, said interference cancellation signal having substantially the same frequency and amplitude as said interference portion of said received signal sample, said interference cancellation signal being substantially 180°
out-of-phase with said interference portion of said received signal sample.
12. A method for mitigating interference between N collocated radio transceivers operating through a common antenna, each of said transceivers having a transmit mode and a receive mode and having an associated frequency band, said method comprising the steps of:
(a) sampling a main output signal of each of those said N transceivers operating in transmit mode to provide sampled output signals;
(b) filtering each of said main output signals through a filter corresponding to the associated frequency band of the transceiver producing said one of said main output signals to substantially prevent subsequent transmission of out-of-band interference, said filtering step being performed after said sampling step (a);
(c) transmitting said main output signals through said common antenna after said step of filtering said main output signals;
(d) filtering a main received signal through a filter bank having a filter set to receive in each of said associated frequency bands of those of said N transceivers operating in receive mode, said main received signal having an interference portion and a non-interference portion, the number of those of said N transceivers operating in receive mode being designated as X, said filtering of said main received signal filtering out substantially all out-of-band interference from said main received signal;
(e) sampling said main received signal to provide a sampled received signal;
(f) comparing said sampled output signals and said sampled received signal in a cancellation device and generating an error correction signal which is substantially identical to but is 180° out of phase with said interference portion of said main received signal;
(g) combining said main received signal and said error correction signal to produce an error-corrected received signal that is substantially free of interference; and (h) dividing said received signal X ways for distribution to said X
transceivers operating in receive mode.
(a) sampling a main output signal of each of those said N transceivers operating in transmit mode to provide sampled output signals;
(b) filtering each of said main output signals through a filter corresponding to the associated frequency band of the transceiver producing said one of said main output signals to substantially prevent subsequent transmission of out-of-band interference, said filtering step being performed after said sampling step (a);
(c) transmitting said main output signals through said common antenna after said step of filtering said main output signals;
(d) filtering a main received signal through a filter bank having a filter set to receive in each of said associated frequency bands of those of said N transceivers operating in receive mode, said main received signal having an interference portion and a non-interference portion, the number of those of said N transceivers operating in receive mode being designated as X, said filtering of said main received signal filtering out substantially all out-of-band interference from said main received signal;
(e) sampling said main received signal to provide a sampled received signal;
(f) comparing said sampled output signals and said sampled received signal in a cancellation device and generating an error correction signal which is substantially identical to but is 180° out of phase with said interference portion of said main received signal;
(g) combining said main received signal and said error correction signal to produce an error-corrected received signal that is substantially free of interference; and (h) dividing said received signal X ways for distribution to said X
transceivers operating in receive mode.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US609,042 | 1996-02-29 | ||
| US08/609,042 US5729829A (en) | 1996-02-29 | 1996-02-29 | Interference mitigation method and apparatus for multiple collocated transceivers |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2197693A1 CA2197693A1 (en) | 1997-08-29 |
| CA2197693C true CA2197693C (en) | 2003-01-07 |
Family
ID=24439128
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002197693A Expired - Lifetime CA2197693C (en) | 1996-02-29 | 1997-02-13 | Interference mitigation method and apparatus for multiple collocated transceivers |
Country Status (2)
| Country | Link |
|---|---|
| US (1) | US5729829A (en) |
| CA (1) | CA2197693C (en) |
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Also Published As
| Publication number | Publication date |
|---|---|
| CA2197693A1 (en) | 1997-08-29 |
| US5729829A (en) | 1998-03-17 |
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