CA2094710C - Method and apparatus for establishing spread spectrum communications - Google Patents

Abstract

A method for establishing communications between a master unit (50) and a plurality of node units (51-55). Of the plurality of node units, K node units are assumed to have established communications with a master unit. A first (K+ 1) node unit of the plurality of node units desires to establish communications with the master unit. The method includes transmitting from the master unit a base-station spread spectrum signal (CSn1) having a common-signalling chip code, transmitting from the first node unit a second spread spectrum signal (CSm) with a first identification code using the common-signalling chip code, transmitting from the master unit a third spread spectrum signal (CSn2) with a master unit identification code, using the common-signalling chip code. The method further includes generating at the first node unit using the master unit identification signal (CSn2) a master unit chip code for transmitting spread spectrum signals (CNMK+1) to the master unit. Additionally, the method includes generating at the master unit using the first identification code, a first node unit chip code for transmitting spread spectrum signals (CMNk+1) to the first node unit.

Description

W092/074~ 2 0 9 ~ 7 1 0 PCT/US91/07~2 ._ DES~$2TPTTON

Method and Apparatus for ~ctabl ich~nq SDread Spectrum Communications Bac~rou,.d of the Invention This invention relates to spread spectrum communica-tions, and more particularly to a method for establi~ing spread spectrum communications between a base station and 5 a hAn~s~t.

Descri~tion of the Prior Art A spread spectrum system is one in which the signal energy is distributed over a frequency spectrum that is much wider than the maximum bandwidth required to transmit the information being sent. Techniques for direct sequence spread spectrum modulation have been developed for several years to ensure, among other benefits, secure communica-tions. Modulation is achieved by mixing the information to be sent with a periodic pseudo-noise (PN) code. The spectral density function for the resulting signal has a sin(X)/X shape with a very wide bandwidth, as compared to the information, and a lower spectral density function amplitude as compared to the information. This modifica-tion of the original spectral density function reduces the signal's sensitivity to in-band interference and jamming, as well as reducing interference to other equipment that is sensitive to radio frequencies. Among the other advan-tages inherent to a spread spectrum system are selective addressing capabilities, code division multiplexing for multiple access, and highly accurate ranging capabilities.
n~e t~ the-~..~~d_d ..atu.~ h~ sig..al, demvdulatio.l is a more involved process compared with demodulation schemes associated with traditional communications systems. In this case, demodulation involves a receiver reference code, identical to that transmitted, that synchronizes the receiver with the transmitter. The difficulty with this process is that there is no indication of the degree of non-synchronization between received and reference codes until a very high degree of synchronization is achieved. Additionally, mismatches between transmit and receive oscillators used to generate PN codes tend to cause drift in the synchronization between transmitter and receiver.
A prior art communications system using two pseudo-random waveforms and two correlators for designating a MARK
and a SPACE, is disclosed in U.S. Patent No. 4,247,942, to Hauer, issued January 27, 1981. Hauer discloses in a communication system, a first delay line having multiple spaced taps for supplying successive input pulses to the delay line. In response to each input impulse, variously delayed pulses appear at the taps of the delay line, which are used to generate pulses representing a MARK or a SPACE. His disclosure includes synchronous detectors, and means for supplying the carrier-transmitted pulses to the detectors.
The prior art does not teach a method for establishing spread spectrum communications using a spread spectrum signal which allows the use of one or more common signalling spectrum spreading codes to manage handshaking from a master unit to a plurality of node units, without the use of a separate frequency channel for com~on signalling, and without requiring a separate time channel for common signalling.
Obiects and Summary of the Invention An object of the invention is to provide a method for establishing communications using spread spectrum signals ~J - 2 -4 ~ 1! n to communicate between a master unit and a plurality of remote units.
Another object of the invention is to provide for a method for using spread spectrum signals to communicate - 2a -W092/07434 2 0 9 4: 7 1 0~ PCr/USgl/07382 between a master unit and a plurality of remote units requiring a minimum amount of digital signal ~oc~ssing.
A ~urther object of the invention is to aliow use of the same frequency for both common signalling as well as communications.
An additional object of the invention i~ to allow use of the same frequency and same time slot for both common signalling and communications.
Another object of the invention is to allow access and h~n~chAking of a plurality of node units to a single master unit when no node unit has a-priori knowledge of spectrum spreading or identification codes, time slots, synchronization parameters, or frequencies utilized at the master unit to be acc~c~e~.
A still further object of the invention is to allow use of a collision avoidance protocol.
Another object of the invention is to allow the management of simultaneous users on a single master unit on a common signalling and communication time slot and frequency basis.
Another object of the invention is to allow the node units to have a minimal need for intelligence, processing power, or local synchronized clock sou~es.
Another object of the invention is to allow use of spectrum spreading codes as address codes.
Another object of the invention is to allow node response to a valid signal within a time slot through CDMA
only, eliminating the need for a highly accurate clock and a level of node complexity and intelligence.
Another object of the invention is to allow half-duplex communication between master unit and node unit in the _-me Tn~ time slct.
According to the present invention as embodied and broadly described herein, a method and apparatus for establishing and maintaining h~n~h~king and communica-tions between a master unit and a plurality of N node units, with multiple configurations, is provided. Of the W092/074~ 2 0 9 4 7 1 0 PCT/US91/07~2 plurality of N node units, K node units, where K < N, are a~sumed to have e~tablished 2K communications links with a master unit, using up to ~K different spectrum spre~
codes to generate up to 2K different spread ~e_LL~m sig-nals to transmit from the node units to the master unit.
A time slot for each of the K linked node units is pro-vided for transmitting and receiving in each of the first K time slot~. A total of N time slots, const~tuting a time frame, are a~gumed available for communicating and/or initializing with the master unit by using time division multiple access. While system capacity allows N node units to establish and maintain simul~n~us communica-tions, with a single master unit, the number of node units which may access the master unit is not limited to N, but may be much greater.
In this invention, transmitting and/or receiving in a time slot may include transmitting and/or receiving in a plurality of time slots in a slot position within a frame and/or from frame to frame. Transmitting and/or receiving in a particular time slot also does not limit a time slot to a particular slot position within a frame.
A first (K+1) node unit of the plurality of the N
node units, of the plurality of X node units able to access the master unit, is assumed to desire to establish communications with, or access, the master unit. The method constitutes hAn~chAking between the (K+l)th node unit and the master unit in an access time slot.
A first embodiment of the present invention implements the (K+l)th time slot as the access slot and (K+l)th communication slot. The (K+l)th time slot may occupy, or float to, any open time slot within the time fr3me Qf the N-X open slQtc, and ma,T char.ge t ime slots as the number, K, of node units which have established communications links with the master unit, changes. This embodiment comprises several steps, the first of which is transmitting in a (K+l)th time slot from the master unit W092/074~ 2 0 9 4 7 1 0 ~ PCT/USgl/07~2 .~ .

a master-initialization spread spectrum signal, CSnl, common to the plurality of X node units.
In r~-~On-? tO receiving the master-initialization spread spectrum signal, CSnl, in the tK+l)th time slot, the (K~l)th node unit transmits in the (K+l)th time slot a first node-initialization spread ~ L~m signal, CSml, which may be the same as, and thus a node retransmission of, the master-initialization ~pread ~e_LL~m signal, CSnl, or which may be a spread ~e_L~m signal having a chip code distinct from the master-initialization spread spectrum signal, CSnl, and common to all master units that the (K+l)th node unit may acc6--. The first node-initialization spread spectrum signal, CSml, may contain the (K+l)th node unit's identification code as data information modulating the chip sequence for the (K+l)th node-initialization spread spectrum signal.
The master unit receives the first node-initialization spread ~e~L~um signal, CSml, from the (K+l)th node unit in the (K+l)th time slot, and, in reply, transmits in the (K+l)th time slot a master-identification spread spectrum signal, CSn2, which may be distinct from spread spectrum signal CSnl but common to all X node units. The master-identification spread ~e~LL~m signal contains the master unit's (K+l)th slot identification code as data information modulating the chip sequence for the master-identification spread ~e_L-~m signal.
In response to receiving the master-identification spread spectrum signal, CSn2, the (K+l)th node unit may transmit in the (K+l)th time slot a second node-initialization spread spectrum signal, CSm2. The secondnode-initialization spread spectrum signal, CSm2, may ~~n~air. tR+l~th. r.ode-identificz'i~n ~~de -s dat2 information modulating the chip sequence from the node-initialization spread spectrum signal. The node-identification spread spectrum signal may have a highdegree of uniqueness to the plurality of the N-l other node units.

W092/074~ 2 0 9 4 7 1 0 ~ ~ PCT/US91/07~2 The master unit receives the (K+l)th node unit's identification code, and tran~mits in the (K+l)th time siot a master unit (K+l)th clot communicaiion spread spectrum signal, CMNk+l, generated from a spectrum spread-ing code derived from the (K+l)th node unit'sidentification code.
In ~ o--se to receiving the (K+l)th master identification code in the (K+l)th time slot from the master unit the (K+l)th node unit transmits in the (K+l)th time slot a (K+l)th node unit communication spread spectrum signal, CNNk+l, generated from a spectrum spreading code derived from the (K+l)th master-identification code.
In a second emho~iment of the present invention, a fixed, or Fth, time slot, such as the 1st or Nth slots of the plurality of N time slots in a time frame, serves as the access slot. The coc~n~ embodiment comprises of the steps of transmitting in the Fth time slot from the master unit a master-initialization spread spectrum signal, CSnl, common to all node units. The Fth time slot may occupy a fixed time slot within the time frame of the N-K unused time slots, and does not change slots as the number, K, of node units which have established communications links with the master unit, changes.
In response to receiving the master-initialization spread spectrum signal, CSnl, in the Fth time slot, the (K+l)th node unit transmits in the Fth time slot a first and second code-initialization spread spectrum signal, CSml, CSm2, having the characteristics and properties previously discussed.
The master unit receives the node-initialization ~:nrP~A CpP~trl~m si nnal; Csm, in tho Fth t-imo clo1- fro~ t ho (K+l)th node unit, and transmits in the Fth time slot a master-identification spread spectrum signal, CSn2, which may be distinct from the master-initialization spread spectrum signal, CSnl, but common to all X node units, and cont~ining the master unit's (K+l)th slot identification W092/074~ 2 0 9 ~ 7 I Q PCT/US91/07~2 code. The master-identification spread ~e~Llum signal, CSn2, may include information directing the (K+l)th node unit as to which time siot and spec~rum spr~A~ing code to use for communication from the (K+l)th node unit to the master unit.
In responce to receiving the master-identification spread spectrum signal, CSn2, the (K+l)th node unit trans-mits in the Fth time slot the eeco~A node-initialization spread spectrum signal, CSm2. The -econA node-initialization spread spectrum signal, CSm2, is common toall master units that (K+l)th node unit may access, and may contain its (K+l)th node-unit-identification code.
The ~econ~ node-initialization spread spectrum signal, CSm2, may have a high degree of uni~n~sC to the plurality of the N-l other node units.
The master unit receives the (K+l)th node unit's identification code from the (K+l)th node unit in the Fth time slot, and transmits in the (K+l)th time slot a master unit (K+l)th slot communication spread spectrum signal, CMNk+l, generated from a spectrum spreading code derived from the (K+l)th node unit's identification code.
In response to receiving the (K+l)th master unit identification code from the master unit in the Fth time slot via the CSn2 spread spectrum signal, the (K+l)th node unit transmits in the (K+l)th time slot a (K+l)th node unit communication spread spectrum signal, CNMk+l, generated from a spectrum spreading code derived from the (K+l)th master unit identification code.
As an alternative architecture in this configuration, the (K+l)th node unit may transmit the (K+l)th node unit communication spread spectrum signal in the (K+l)th time c~ ~t in r~cnQnse 1-n rC~c~it.~in.~ t~ ~n2e~ _~ un.it (~ ) th el~~
communication signal in the (K+l)th time slot. In this case, the master unit (K+l)th slot identification signal transmitted in the Fth time slot would not nececcArily contain information detailing which time slot of the N-K
time slots to use for communication transmissions.

W092/074~ 2 0 9 4 71 0 ~ PCT/US91/07~2 In a third embodiment of~the invention, the master unit may function with the initialization, identification, and communication protocols detailed in first and -econh embodiments, but may be configured to transmit the master-initialization spread ~e~ m signal, CSnl, in a plural-ity of vacant (N-X) time slots. If the master unit does transmit in a plurality of vacant (N-X) time slots, then node units (K+l), (K+2), (K+3),..., (K+(N-K)) (or N) may access the master unit in the (K+l)th, (K+2)th, (K+3)th, ..., (K+(N-K))th (or Nth) time slots, respectively or randomly. Therefore, the (K+l)th node unit trying to access the master unit would access the first time slot immediately available after its initiation of the access attempt, instead of waiting for the (K+l)th or Fth time slot to occur in the next frame.
Thus, if K users are present, the master unit transmits in the 1st through Kth time slots the master unit communication spread spectrum signals, CMN1 through CMNk, pertaining to the 1st through Kth node units, and in the (K+l)th through Nth time slots a master-initialization spread spectrum signal, CSnl, which is common to the plurality, X, of node units that may access the master unit. The master-initialization spread spectrum signal may be distinct from all master or node unit communication and identification spread spectrum signals.
In all three embodiments, if a plurality of up to N-K node units tries to access the master unit sequentially in time, with the period between access attempts being greater than or equal to the slot period, upon reception of the master-initialization spread spectrum signal, CSnl, each node unit will access the open time slot available ~ '~ly f~ll~-~-r.s ~L~ r.-'ia_ c.. ~f 'h_ Z_C6SS
attempt. When the first (K+l)th node unit has accecc~A
the master unit (master unit slot and (K+l)th node unit identification signals are being transmitted in the (K+l)th time slot), the master unit may wait to transmit the (K+2)th through Nth master-identification signals W092/074~ 2 0 9 4 71 0 PCT/US91/07~2 ,~

until the (K+l)th slot is occupied with master unit-to-(K+l)th node unit and/or (K+l)th node unit-to-master unit communication signal~.
If a plurality of up to N-K node units tries to acce~s the ma~ter unit instantaneou~ly (the time period between node unit access attempts being less than the slot period), upon ~ece~Lion of the master-initialization spread ~e~L~m signal, CSnl, each node unit of this plurality of node units will transmit a node-initialization spread spectrum signal, CSm, within thesame time slot, thus jamming at least one of the node-initialization spread a~e~L~um signals, CSm, at the master unit. If the master unit does not receive a valid node-initialization spread ~e~ m signal, CSm, or identifica-tion code from a node unit during the time slot, it maycease to transmit any signal in that time slot for a predetermined period of time, or it may transmit a "jammed signal alarm" code through the master unit slot identifi-cation signal, CSn2. When a lack of response or a jammed signal alarm code from the master unit is encountered, the node units which tried to access the master unit instan-taneously, of the plurality, N - K, of node units, may initiate a node unit internal "wait" state, whose period may be derived from each node nit's identification code.
After the wait state period, the plurality of node units which failed to access the master unit may attempt to access it again. Since wait states may be highly unique to each node unit, it is unlikely that the same plurality of node units will jam each other again.
If all N time slots are being used for communication or initialization functions by N node units, then the master-initiali7ati~r.spreaA spe~trum _igr.al, ~Snl, ~_ not transmitted by the master unit, and no new node units of the plurality of X - N node units may access the master unit. The master unit may operate such that the Nth time slot may transmit a "busy" alarm to the plurality of N-K
node units having not established communications with the ., r ~ i 4 ' ~ '5 ~ Q ~ 4 ~ 1 0 ~

" ~
master unit such that it informs them that no further access is available at that master unit, thereby allowing only N-l node units to access the master unit.
Additional objects of the invention and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description or may be learned by practice of the invention.
The objects and advantages of the invention also may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.
Brief Description of the drawinqs The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate preferred embodiments of the invention, and together with the description serve to explain the principles of the invention.
FIG. 1 illustrates a master unit with a plurality of remote units;
FIG. 2A and 2B illustrate the protocol of the method of the present invention;
FIG. 3 illustrates time slots;
FIG. 4 illustrates the multiple access system timing diagram of a preferred embodiment using binary signalling techniques;
FIG. 5 illustrates the multiple access system timing diagram of a second preferred embodiment using M-ary signalling techniques; and FIG. 6 illustrates an FDMA three frequency master unit network.

~ 60724-2117 7~3~7 ~ -.. ", Detailed Description of the Preferred Embodiments Reference will now be made to the present preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings.
In the exemplary arrangement shown in FIG. 1, the present invention includes a method and apparatus for establishing communications between a master unit 50 and N
node units. The master unit 50 may be a base station, PBX, file server or other central controlling device serving as the center of a star network, and the node units may be any type of computer, communications, telephone, video or other data device serving as a node point in the star network. While the system capacity allows N node units to establish simultaneous communications with a single master unit, the number, X, of node units that may access the master unit is not limited to N
node units, but may be much larger than N.
As illustratively shown in FIG. 1, a master unit 50 is shown with a plurality of N node units 51, 52, 53, 54, 55, where N = 5, and a plurality of X node units 56, of which the plurality of N node units is a subset. Of the plurality of N
node units 51, 52, 53, 54, 55, three node units (K = 3), are assumed to already have established communications channels with the master unit 50 using up to six different spectrum spreading chip codes to generate up to six different spread spectrum signals.
A particular node unit and master unit use two of the six spectrum spreading chip codes during communications.
A first of the two spectrum spreading chip codes is used while .~ ~
~ 60724-2117 7 ~
.,.
communicating from the master unit to the particular node unit. A second of the two spectrum spreading chip codes is used while communicating from the particular node unit to the master unit. The spectrum spreading chip codes may be embodied as a pseudo-random sequence, and the - lla -~., W092/074~ 2 0 9 4 7 1~ PCT/US91/07~2 spectrum spr~A~ing chip;codes typically modulate informa-tion data which may be'embodied as a data bit sequence, as is well known in the art.
A total of five time slots (N = 5), which constitute a time frame, are assumed available for communicating with the master unit by use of time division multiple access.
Each of the three node units 51, S2, 53, communicates with the master unit 50 in a time slot, which may be the first three of five time slots. Alternatively, each of the three node units may communicate with the master unit 50 in three time slots which have any predetermined order.
Additionally, a (X+l)th time slot, which by way of example is the fourth time slot (K + 1 = 4), may G~u~y, or "float" to, any open time slot within the time frame of the two unused time slots, and may change time slots as the number, K, of node units which have established communications links with the master unit, changes. A
node unit, which of the five node units is the fourth node unit, desires to establish communications with, or access the master unit 50.
In the present invention, transmitting and/or receiving in a time slot may include transmitting and/or receiving in a plurality of time slots in a slot position within a frame and/or from frame to frame. Transmitting and/or receiving in a particular time slot also does not limit a time slot to a particular slot position within a frame.
In a first embodiment of the invention, the apparatus and method comprises the steps of transmitting in a (K+l)th time slot from the master unit 50, a master-initialization spread spectrum signal, CSnl. The master-initializatior. epread spoctr--~ sign21 ~ee_ a ~o-~er-common-signalling chip code which is known and stored in all the node units able to access the master unit. All of the node units have means responsive to the master-initialization spread spectrum signal, for correlating with the master-common-signalling chip code of the master W092/074~ 2 0 9 4 71~0 ~ PCT/US91/07~2 "

unit 50. The correlating means may be embodied as a surface acoustic wave device (SAW), digital device, or any other device which can perform the required function. The master-common-signalling chip code may, but is not required, to modulate information data embodied as a data bit sequence or data symbol sequence. The information data may include i nA~Yi ng or other data pertinent to the (K+l)th time slot. The entire chip ~equence of the master-common-signalling chip code is transmitted per data bit or data symbol during the (K+l)th time slot from the master unit.
In response to receiving the master-initialization spread spectrum signal, CSnl, at the (K+l)th node unit, the method and apparatus include transmitting from the (K+l)th node unit in the (K+l)th time slot a first node-initialization spread spectrum signal, CSml. The first node-initialization spread spectrum signal may, but is not required,retransmit the master-common-signalling chip code which was transmitted from the master unit during the (K+l)th time slot. Alternatively, the first node-initialization spread spectrum signal, CSml, may use a node-common-signalling chip code which can be received by all master units that the (K+l)th node unit may access.
The first node-initialization spread spectrum, CSml, signal additionally may be modulated by information data, such as the (K+l)th node unit's identification code. The entire chip sequence of the master-common-signalling chip code or node-common-signalling chip code modulates each bit, or symbol, of the information data, i.e., the node unit's identification code, using spread spectrum modulation.
~ he maste~ ~-nit 50 rece--.es the r- rs' n_de-initialization spread spectrum signal, CSml, from the (K+l)th node unit in the (K+l)th time slot, and transmits in the (K+l)th time slot a master-identification spread spectrum signal, CSn2. The master-identification spread spectrum signal uses a master-identification code which is W092/074~ 2 0 9 4 71 0 PCT/US91/07~2 common to all X node units.~ The master-identification code is modulated by the mas~er-common-signalling chip code or node common-signal~ing chip code to produce the master-identification spread D~e~Ll~m signal.
The master-identification code may be unique to the (K+l)th master unit slot, and may be unique to a minimum of N master-identification codes available at the master unit 50. The master-identification code, which may be distinct from all other master-identification codes and node-identification codes, is used by the node unit for generating a chip code for a spread spectrum signal used to communicate with the master unit 50. The chip code is generated from an algorithm ~.o~e_sing the master-identification code, which may include, for example, a one-to-one relationship for setting taps on a set of shift registers.
In response to receiving the master-identification spread spectrum signal, CSn2, from the master unit 50 in the (K+l)th time slot, the (K+l)th node unit transmits in the (K+l)th time slot its node-identification code to the master unit using a second node-initialization spread spectrum signal, CSm2. As described previously for the first node-initialization spread spectrum signal, the second node-initialization spread spectrum signal, CSm2, uses a master-common-signalling chip code, or a node-common-signalling chip code which is common to all master units to which the (K+l) node unit may access for modulating the node-identification code. The tK+l) node-identification code has a high degree of uniqueness compared with node unit identification codes by which the plurality of other node units may access the master unit.
The m2ster unit 50 re~eives the 'K l)th r.~de-identification code, and establishes the master-unit-to-(K+l)th-node-unit communication channel by transmitting in the (K+l)th time slot a master-unit-(K+l)th-slot communi-cation spread spectrum signal, CMNK+l. The spectrum spreading chip code for the master-unit-(K+l)th-slot-WOg2/074~ 2 0 9 4 71~ PCT/US91/07~2 .

communication spread spectrum signal is generated from the(K+l)th node unit identification code.
In le~ e to receiving the (K~l)th master-identification code-, the (K+l)th node unit establishes the (K+l)th node-unit-to-master un~t communication ch-nnel by transmitting in the (K+l)th time slot a (K+l)th node-unit-communication spread ~e_~lum ~ignal, CNMK+l. The spectrum spr~i nq chip code for the (R+l)th node unit communication spread spectrum signal is generated from the (K+l)th master-identification code.
In the explanatory emho~iment ~i~cl~sse~ herein, the master unit may operate such that it does not transmit in a time slot except to send a plurality of K master unit slot communication spread spectrum signals, CNNl to CMNK, in K time slots, to K node units which have established communications links with the master unit, plus a master-initialization spread spectrum signal, CSnl, in the case of a search for a new node unit trying to access the master unit, or a master unit slot identification signal, CSn2, in the case of a node unit being in the process of accessing a master unit, leaving N-K-l time slots unused.
If the master unit is transmitting a master-identification spread spectrum signal, CSn2, in the (K+l)th time slot (the (K+l)th node unit is in the process of accessing the master unit), it then may transmit a master-initialization spread spectrum signal, CSnl, in the (K+2)th time slot, in order to allow the (K+2)th node unit to access the master unit through the same method.
If a plurality of up to N-K node units tries to access the master unit sequentially in time, with the period between access attempts being greater than or equal to the t~mc rr~me pericd, ~pcr. recep'ion cf tho m-s_er-initialization spread spectrum signal, CSnl, each node unit of the plurality of N - K node units will access the time slot immediately available following its initiation of the access attempt. When the first (K+l)th node unit has ac~e~se~ the master unit (master unit (K+l)th slot and WOg2/074~ PCT/US91/07~2 (K+l)th node unit identification signals are being trans-mitted in the (K+l)th time slot), the macter unit may wait to transmit the (K+2)th master unit slot identification signal until the (K+l)th slot is occupied with master unit-to-(K+l)th node unit and/or (K+l)th node unit-to-master unit communication signals.
If a plurality of up to N-K node units tries to access the master unit instantaneously (the time period between node unit access attempts being less than the frame period), upon reception of the master-initialization spread spectrum signal, CSnl, each node unit of this plurality of node units will transmit a first node initialization spread ~e~L~m signal, CSml, within the same time slot, thus jamming at least one of the node unit initialization signals, CSm, at the master unit. If the master unit does not receive a valid node-initialization spread spectrum signal, CSm, or identification code from a node unit during the time slot, it may cease to transmit any signal in that time slot for a predetermined period of time, or it may transmit a "jammed signal alarm" code through the master-identification spread spectrum signal, CSn2. When a lack of response or a jammed signal alarm code from the master unit is encountered, the node units which tried to access the master unit instantaneously, of the plurality, N - K, of node units, may then initiate a node unit internal "wait" state, whose period may be derived from each node unit's identification code. After the wait state period, the plurality of node units which failed to access the master unit may attempt to access it again. Since wait states may be highly unique to each node unit, it is unlikely that the same plurality of node uni' e will iam each o'h2r '~oin.
If all N time slots are being used for communication or initialization functions by N node units, then the master-initialization spread spectrum signal, CSnl, is not transmitted by the master unit, and no new node units of the plurality of X - N node units may access the master W092/074~ 2 0 9 4 7 1 0 PCT/US91/07~2 unit until a time slot opens up through one or more of the N node units Ah~nAon;~g communications with -the master unit.
As an alternative archit~_Lule to the present embodiment, the master unit may operate such that the Nth time slot may be held in reserve to transmit a "busy"
alarm to the plurality of N-R node units having not established communications with the master unit such that it informs them that no further acce~s is available at that master unit, thereby allowing only N-l node units to access the master unit.
The time division multiple access frame and time slots of the present invention are illustratively shown in FIG.

2. There are N time slots, with N = 5, available for N
node units to communicate with the master unit, with K = 3 time slots already being used by the first K node units which are communicating with the master unit. During any one or all of the available N-X ~ 2 time slots, the master unit transmits a master-initialization spread spectrum signal, CSnl, common to the set of X node units that may access the master unit, of which the N = 5 node units is a subset. Since all node units which may access the master unit recognize the first master-initialization spread spectrum signal, CSnl, the 4th node unit trying to access the master unit will know that this time slot is available for communicating. In response to receiving the master-initialization spread spectrum signal, CSnl, in the 4th time slot, the 4th node unit may transmit in the 4th time slot to the master unit its identification code or a simple acknowledgment ("ACK") through a first node-initialization spread spectrum signal, CSml, common to all ma~' cr uni' s i' may ~~ces-, but d s' -.c_ _ro- th~ -astsr-initialization spread s~e~L~m signal, CSnl.
In response to receiving the first node-initialization spread spectrum signal, CSml, in the 4th time slot from the 4th node unit, the master unit transmits its 4th master-identification code, which may be distinct from all W092/074~ PCT/USgl/07~2 209~1~ ~

other master and node unit identification codes, with a master-identification spread pectrum signal, CSn2, common to the plurality of node units that may A~ceCc tne master unit and distinct from~the master-initialization spread spectrum signal, CSnl, and the first node-initialization spread ~e~.~m signal, CSml. In LF.~u.~? to receiving the 4th master-identification spread spectrum signal, CSn2, the 4th node unit may transmit in the 4th time slot its identification code through the -?~on~ node-initialization spread spectrum signal, CSm2. In r~spons~to receiving the 4th node-identification code, the master unit derives a master unit spectrum spreA~in~ communica-tion code for the 4th slot from the 4th node-identification code, and uses it to generate a master unit 4th slot communication spread spectrum signal, CMN4. The 4th master unit slot communication signal, CMN4, is then used for all transmissions from the master unit to the 4th node unit.
In response to receiving the master-identification code for the 4th time slot, the 4th node unit derives a 4th node unit spectrum spreading communication code from the master-identification code, and uses it to generate a 4th node unit communication spread spectrum signal, CNM4.
The 4th node unit communication signal, CNM4, is then used for all transmissions from the 4th node unit to the master unit.
In a particular embodiment, there may be 4K samples per second, divided into K frames of four time slots of one milliseconds each, allowing N = 4 users to use one time slot 1000 times per second. The master unit trans-mits eighteen bits (two addressing, sixteen data) in each time sl~' i' ~ses, yielding 16 ~s thr~ughp~t f~cm _he master unit to each node unit per slot. In initialization or identification modes, the eighteen bits may be used differently. Node units, which may be embodied as hand-sets as illustrated in FIG. 1, transmit eighteen bits per time slot only in response to receiving a spread spectrum WOg2/074~ 2 0 9 4 71 0 PCT/US91/07~2 .~

initialization, identification, or communication signal from the master unit. The mast~r unit transmission frame comprises four time slots, and is configured such that it does not transmit in a time-slot except to send a spread spectrum communication signal to K ufiers who are on line, plus an initialization (in the case of a search for a new node unit trying to access the ma~ter unit) or identifica-tion (in the case of a new node unit in the ~G~Q~S of accessing a master unit) signal, leaving N-K-l time slots open. If the master unit is transmitting a master-identification spread ~e_L-~m signal in the (K+l)th time slot (i.e. the (K+l)th node unit is accessing the system), it then may transmit a master-initialization spread spectrum signal in the (K+2)th time slot, in order to allow the (K~2)th node unit to access the master unit.
Thus, if two node units are present, then the master unit transmits in the 1st through ~?CQ~ time slots the communication spread spectrum signals per~ ng to the 1st through second nodes, and in the third time slot an initialization spread spectrum signal common to all node units that may access the master unit, which may be distinct from all communication and identification spread spectrum signals.
If, with N = 4 and K = 2 node units, a plurality of up to 2 node units try to access the master unit sequentially in time, with the period between access attempts being greater than or equal to the frame period, or one milli-second, upon reception of the master-initialization spread spectrum signal, CSnl, the third and fourth node units will access the third and fourth time slots, respectively, immediately available in the first time frame following th_-r rcspectiYe initi~t O..S _ r th~ ~~~~SS 'tt~-pt. ~.'.~,6..
the third node unit has acceC~e~ the system (master unit slot and third node unit identification signals are being transmitted in the third time slot), the master unit may wait to transmit the fourth master unit slot identifica-tion signal until the third slot is occupied with master unit-to-3rd node unit and/or 3rd node unit-to-master unit communication signals. If, with N = 4 and K = 2 node units, a plurality of up to 2 node units tries to access the master unit instantaneously (the time period between node unit access attempts being less than the frame period, or one millisecond), upon reception of the master-initialization spread spectrum signal, CSnl, in the third time slot, the third and fourth node units will transmit a first node-initialization spread spectrum signal, CSml, within the third time slot, thus jamming at least one of the first node-initialization signals, CSnl, at the master unit. If the master unit does not receive a valid initialization signal, CSm, or identification code from a node unit during the thlrd slot, it may cease to transmit any signal in the third time slot for a predetermined period of time, or it may transmit a "jammed signal alarm" code through the master-identification spread spectrum signal, CSn2. When a lack of response or a jammed signal alarm code from the master unit is encountered, the third and fourth node units may then initiate a node unit internal ~wait~ state, whose period may be derived from each node unit's identification code. After the wait state period, the third and fourth node units may attempt to access it again. Since wait states may be highly unique to each node unit, it is unlikely that the third and fourth node units will jam each other again. If all four time slots are being used for communication or initialization functions by four node units, then the initialization spread spectrum signal, CSnl, is not transmitted by the master unit, and no new node units ~ ~ ~ 4 ~

: Y~r of the plurality of X - 4 node units may access the master unit.
With N = 4 and K = 2, the master unit may function with the initialization, identification, and communication procedures detailed above, but may be configured to transmit the master-initialization spread spectrum signal, CSnl, in the vacant third and fourth time slots. If - 20a -W092/074~ 2 09 4 710~ : ' PCT/US91/07~2 the master unit does transmit the third and fourth vacant time slots, node units three and four may access the master unit in the third and fourth time slots, respect-ively or randomly. -Therefore, the third node unit trying to access the master unit would access the first time slot immediately available after its initiation of the access attempt, instead of waiting for the third time slot to occur in the next frame.
Thus, if two users are present, the master unit lo transmits in the 1st through second time slots the master unit communication spread spectrum signals, CMNl through CMN2, pertaining to the first through sQcon~ node units, and in the third through fourth time slots a master initialization spread spectrum signal, CSnl, common to the plurality, X, of node units that may access the master unit, which may be distinct from all master or node unit communication and identification spread spectrum signals.
If 2 node units try to access the master unit sequentially in time, with the period between access attempts being greater than or equal to the slot period of 250 micro-seconds, upon reception of the master-initialization spread spectrum signal, CSnl, each node unit will access the open time slot available immediately following its initiation of the access attempt. When the third node unit has acreCc~ the master unit (master unit slot and third node unit identification signals are being trans-mitted in the third time slot), the master unit may wait to transmit the fourth master unit slot identification signal until the third slot is occupied with master unit-to-4th node unit and/or third node unit-to-master unit communication signals.
Tf :- p~ ty of Up t~ ~ node units t~_es t- --_es., the master unit instantaneously (the time period between node unit access attempts being less than the slot period, or 250 microseconds), upon reception of the master-initialization spread spectrum signal, CSnl, the third and fourth node units will transmit a first node-WOg2/074~ PCT/US91/07~2 initialization spread spectrum signal, CSNl, or ~?cQnAnode-initialization spread pectrum signal, CSm2, within the same time slot, thus jamming at least one of the node-initialization spread D~e_Ll~m signal or node-identification spread ~ ~m signal, CSm, at the masterunit. If the master unit does not receive a valid node-initialization spread ~e_L.um signal or node-identification spread ~e~LL~m signal, CSml, or identifi-cation code from a node unit during the time slot, it may cease to transmit any signal in that time slot for a predetermined period of time, or it may transmit a ~jammed signal alarm" code through the master-identification spread spectrum signal, CSn2. When a lack of r~spo~? or a jammed signal alarm code from the master unit is Pnco~ntered, the third and fourth node units may initiate a node unit internal "wait" state, whose period may be derived from each node unit's identification code. After the wait state period, the third and fourth node units may attempt to access it again. Since wait states may be highly unique to each node unit, it is unlikely that the third and fourth node units will jam each other again.
FIG. 3 illustratively shows the foregoing protocol of the present invention.
- In a second embodiment of the present invention, a fixed, or Fth, time slot, such as the 1st or Nth slots of the plurality of N time slots in a time frame, serves as the access slot. The cecQn~ method and apparatus comprises the steps of transmitting in the Fth time slot from the master unit the master-initialization spread spectrum signal, CSnl, common to all node units. The Fth time slot may occupy a fixed time slot within the time f-am~ o the ~-K unu-s~d 'im_ _lct-, -r.d dc~s nc' ch-r.g~
slots as the number, K, of node units which have estab-lished communications links with the master unit, changes.
In response to receiving the master-initialization spread spectrum signal, CSnl, in the Fth time slot, the (K+l)th node unit transmits in the Fth time slot a (X+l)th node-W092/074~ 2 0 9 4 71 0 PCT/US91/07382 . .

initialization spread spectrum signal, CSm, which may be the same as CSnl, common to all master units that the (K+l)th node unit may Acce~, which may contain the (K+l)th node unit's identification code.
The master unit receives the node-initialization spread ~e~L~m signal, CSm, in the Fth time slot from the (K+l)th node unit, and tran~mits in the Fth time slot a master-identification spread sp._LLum signal, CSn2, which may be distinct from spread spectrum signal CSnl but common to all X node units, containing the master unit's (K+l)th slot identification code, which may include information directing the (K+l)th node unit as to which time slot and spectrum spreA~ i ng code to use for communi-cation from the (K+l)th node unit to the master unit.
In response to receiving the master-identification spread spectrum signal, CSn2, the (K+l)th node unit may transmit in the Fth time slot the (K+l)th node-initialization spread spectrum signal, CSm, common to all master units that it may access, which may contain its (K+l)th node unit identification code, which may have a high degree of uniqueness to the plurality of the N-l other node units.
The master unit receives the (K+l)th node unit's identification code from the (K+l)th node unit in the Fth time slot via the node-initialization spread spectrum signal, CSm, common to all master units accessible by the (K+l)th node unit, and transmits in the (K+l)th time slot a master unit (K+l)th slot communication spread spectrum signal, CMNk+l, generated from a spectrum spre~ing code derived from the (K+l)th node unit's identification code.
In ~ea~G"se to receiving the (K+l)th master unit ~dar.tiPicativr. __Aa Prvm tha mastar unit ir. the Fth timê
slot via the master-identification spread spectrum signal, CSn2, common to all X node units, the (K+l)th node unit transmits in the (K+l)th time slot a (K+l)th node unit communication spread spectrum signal, CNMk+l, generated from a spectrum spreading code derived from the (K+l) th master-identification code.
As an alternative architecture of the second embodiment, the (K+l) th node unit may transmit the (K+l)th node communication spread spectrum signal in the (K+l) th time slot in response to receiving the master unit (K+l) th slot communication signal in the (K+l)th time slot. In this case, the master-identification spread spectrum signal transmitted in the Fth time slot would not necessarily contain information detailing which time slot of the N-K time slots to use for communication transmissions.
In the second embodiment, the master unit may operate such that it does not transmlt in a time slot except to send a plurality of K master unit slot communication spread spectrum signals, CMNl to CMNK, to K node units which have established communications links with the master unit, plus a master-initialization spread spectrum signal, CSnl, in the case of a search for a new node unit trying to access the master unit, or a master-identification spread spectrum signal, CSn2, in the case of a node unit being in the process of accessing a master unit, in the Fth time slot, leaving N-K-l time slots unused. If the master unit is transmitting a master-identification spread spectrum signal, CSn2, in the Fth time slot (assuming the (K+l)th node unit is in the process of accessing the system), it then may transmit a master-initialization spread spectrum signal, CSnl, in one of the N-K-l unused time slots, in order to allow the (K+2)th node unit to access the master unit.

If a plurality of up to N-K node units tries to access the master unit sequentially in time, with the period between access attempts being greater than or equal to the frame period, upon reception of the master-initialization spread spectrum signal, CSnl, each node unit of the plurality of N - K node units will access the (K+l)th time slot through the Fth time slot immediately available - 24a -WOg2/074~ 2 0 9 4 710 PCT/US91/07~2 i,~

following its initiation of the AccesC attempt. When the first (K+l)th node unit hac ~c~c~~~ the system (assuming the master-identification and (K+~ node-identification spread spe~Ll~m signals are being transmitted in the Fth time slot), the master unit may wait to transmit the (K+2)th master-identification spread ~e_L~um signal until the (K+l)th slot is occupied with master unit-to-(K+l)th node unit and/or (K+l)th node unit-to-master unit communication signals.
If a plurality of up to N-K node units tries to access the master unit instantaneously (the time period between node unit access attempts being less than the frame period), upon reception of the master-initialization spread spectrum signal, CSnl, in the Fth time slot, each node unit of this plurality of node units will transmit a node-initialization spread spectrum signal, CSm, within the same time slot, thus jamming at least one of the node-initialization spread spectrum signals, CSm, at the master unit. If the master unit does not receive a valid initialization signal, CSm, or identification code from a node unit during the time slot, it may cease to transmit any signal in the Fth time slot for a predetermined period of time, or it may transmit a "jammed signal alarm" code through the master-identification spread spectrum signal, CSn2. When a lack of response or a jammed signal alarm code from the master unit is encountered, the node units which tried to access the master unit instantaneously, of the plurality, N - K, of node units, may then initiate a node unit internal "wait" state, whose period may be derived from each node unit's identification code. After the wait state period, the plurality of node units which f2iled to a~cess the maste_ uni t m y -ttempt t~ --cess i ' again. Since wait states may be highly unique to each node unit, it is unlikely that the same plurality of node units will jam each other again.
If all N-1 time slots are being used for communication or initialization functions by N-l node units, then the master-initialization spread spectrum signal, CSnl, is not transmitted. The master unit may operate such that the Fth time slot may transmit a "busy" alarm to the plurality of N-K
node units having not established communications with the master unit such that it informs them that no further access is available at that master unit, thereby allowing only N-1 node units to access the master unit.
In a third embodiment of the present invention, the master unit may function with the initialization, identification and communication protocols as set forth in the first and second embodiments, but may be configured to transmit the master-initialization spread spectrum signal, CSnl, in a plurality of vacant (N-K) time slots, simultaneously. If the master unit does transmit in a plurality of vacant (N-K) time slots, node units (K+l), (K+2), (K+3), ..., (K+(N-K)) (or N) may access the master unit in the (K+l) th, (K+2) th, (K+3)th, ..., (K+ (N-K))th (or Nth) time slots, respectively or randomly. Therefore, the (K+l)th node unit trying to access the master unit would access the first time slot immediately available after its initiation of the access attempt, instead of waiting for the (K+l)th or Fth time slot to occur in the next frame.
Thus, if K users are present, the master unit transmits in the 1st through Kth time slots the master unit communication spread spectrum signals, CMNl through CMNK, pertaining to the 1st through Kth node units, and in the (K+l)th through Nth time slots a master-initialization spread spectrum signal, CSnl, common to the plurality, X, of node .~

7 ~ ~ 4 7 ~ O

units that may access the master unit, which may be distinct from all master or node unit communication and identification spread spectrum signals.
If a plurality of up to N-K node units tries to access the master unit sequentially in time, with the period between access attempts being greater than or equal to the slot period, upon reception of the master-initialization spread spectrum signal, CSnl, each node unit will access the open time slot available immediately following its - 26a -';: 60724-2117 ' ~:

WOg2/074~ 2 0 9 4 71 0 PCT/US91/07~2 initiation of the ~ .r attempt. When the first (K+l)th node unit has ~cce~-?~ the master unit (maste~ unit slot and (K+l)th node unit identification signals are being transmitted in the ~K+l)th time slot), the master unit may wait to transmit the (K+2)th through Nth master unit slot identification signals until the (K+l)th slot is occupied with master unit-to-(K+l)th node unit and/or (K+l)th node unit-to-master unit communication ci~nal~.
If a plurality of up to N-K node units tries to access the master unit instantaneously (the time period between node unit access attempts being less than the slot period), upon reception of the master-initialization spread spectrum signal, CSnl, each node unit of this plurality of node units will transmit a node-initialization spread spectrum signal, CSm, within thesame time slot, thus jamming at least one of the node-initialization spread spectrum cignals, CSm, at the master unit. If the master unit does not receive a valid node-initialization spread spectrum signal, CSm, or identifi-cation code from a node unit during the time slot, it maycease to transmit any signal in that time slot for a predetermined period of time, or it may transmit a "jammed signal alarm" code through the master unit slot identifi-cation signal, CSn2. When a lack of ~e~unse or a jammed signal alarm code from the master unit is encountered, the node units which tried to access the master unit instan-taneously, of the plurality, N - K, of node units, may initiate a node unit internal "wait" state, whose period may be derived from each node unit's identification code.
After the wait state period, the plurality of node units which failed to access the master unit may attempt to -cc~ss it again. Since wait ~tates m-y be h ~h y u..i~e to each node unit, it is unlikely that the same plurality of node units will jam each other again.
If all N time slots are being used for communication or initialization functions by N node units, then the initialization spread spectrum signal, CSnl, is not W092/074~ PCT/US91/07~2 transmitted by the master unit, and no new node units of the plurality of X - N node units may ~cce-s the master unit. The master unit may operate~sùch that the Nth time slot may transmit a "busy" alarm to the plurality of N-K
node units having not established communications with the master unit ~uch that it informs them that no further access is available at that master unit, thereby allowing only N-l node units to ~c~c the maeter unit.
It will be apparent to tho~e skilled in the art that various modifications can be made to the method for estab-1i chi~g spread spectrum communications between a master unit and a plurality of node units of the present inven-tion, without departing from the scope or spirit of the invention, and it is int~nAe~ that the ~ ent invention cover modifications and variations of the method for establi ch i ng spread spectrum communications as described herein, provided they come within the scope of the app~nA~ claims and their equivalents.

Claims (50)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A method for establishing wireless communication using spread spectrum signals to communicate between a master unit and at least one remote unit, comprising the steps of:
transmitting a first master-initialization spread spectrum signal from said master unit in a first available time slot in a time frame, wherein said time frame is periodic and is comprised of a plurality of time slots and in which some of said time slots are available for communication and some of said time slots are unavailable for communication;
receiving said master-initialization spread spectrum signal at a first remote unit seeking to establish communication with said master unit in said first available time slot;
transmitting a first node-initialization spread spectrum signal from said first remote unit seeking to establish communication with said master unit in said first available time slot in response to receiving said master-initialization spread spectrum signal at said first remote unit;
receiving said first node-initialization spread spectrum signal at said master unit in said first available time slot;
transmitting a master-identification spread spectrum signal from said master unit, in said first available time slot in response to receiving said first node-initialization spread spectrum signal;
receiving said master-initialization spread spectrum signal at said first remote unit seeking to establish communication with said master unit in said first available time slot;
transmitting a second node-initialization spread spectrum signal from said first remote unit seeking to establish communication with said master unit in response to receiving said master-identification spread spectrum signal;
receiving said second node-initialization spread spectrum signal at said master unit in said first available time slot;
transmitting a first communication spread spectrum signal from said master unit to said first remote unit seeking to establish communication with said master unit in said first available time slot;
receiving said first communication spread spectrum signal at said first remote unit seeking to establish communication with said master unit in said first available time slot;
transmitting a second communication spread spectrum signal from said first remote unit to said master unit in said first available time slot in response to said first communication spread spectrum signal;
communicating between said master unit and said first remote unit in said first available time slot.

2. The method of claim 1 wherein said first accessing spread spectrum signal is encoded using a first spectrum code, said first spectrum code resident in all of said remote units.

3. The method of claim 2 wherein said first spectrum code is an M-ary code.

4. The method of claim 2 wherein said first node-initialization spread spectrum signal is encoded using said first spread spectrum spreading code, said first spectrum spreading code resident in said master unit.

5. The method of claim 2 wherein said first node-initialization spread spectrum signal comprises information data modulated by said first spectrum spreading code, said information data comprising information identifying said first remote unit.

6. The method of claim 2 wherein said first node-initialization spread spectrum signal comprises information data modulated by said first spectrum spreading code, said information data comprising an acknowledgement signal.

7. The method of claim 2 wherein said first node-initialization spread spectrum signal comprises unique information for identifying said master unit modulated by said first spectrum spreading code.

8. The method of claim 7 further comprising the step of using said unique information for identifying said master unit contained in said master identification spread spectrum signal to select a third spectrum spreading code for communicating with said master unit.

9. The method of claim 8 wherein said third spread spectrum code is an M-ary code.

10. The method of claim 2 wherein said second node-initialization spread spectrum signal comprises unique information for identifying said first remote unit modulated by said first spread spectrum spreading code.

11. The method of claim 10 further comprising the step of using said unique information for identifying said first remote to select a fourth spectrum spreading code for communicating with said remote unit.

12. The method of claim 11 wherein said fourth spread spectrum code is an M-ary code.

13. The method of claim 1 wherein said first master-initialization spread spectrum signal comprises information data comprising indexing and addressing information for said first available time slot.

14. The method of claim 1 wherein said first node-initialization spread spectrum signal is encoded using a second spread spectrum spreading code, said second spread spectrum spreading code resident in said master unit.

15. The method of claim 14 wherein said second spreading code is an M-ary code.

16. The method of claim 14 wherein said first node-initialization spread spectrum signal comprises information data modulated by said second spectrum spreading code, said information data comprising an acknowledgment signal.

17. The method of claim 14 wherein said first node-initialization spread spectrum signal comprises information data contained in said master-initialization spread spectrum signal received from said master unit, said information data comprising an acknowledgment signal.

18. The method of claim 14 wherein said master identification spread spectrum signal comprises unique information for identifying said master unit modulated by said second spread spectrum spreading code.

19. The method of claim 18 further comprising the step of using said unique information for identifying said master unit contained in said master identification spread spectrum signal to select a third spectrum spreading code for communicating with said master unit.

20. The method of claim 19 wherein said second spreading code is an M-ary code.

21. The method of claim 11 wherein said second node-initialization spread spectrum signal comprises unique information for identifying said first remote unit modulated by said first spectrum spreading code.

22. The method of claim 21 further comprising the step of using said unique information for identifying said first unit to select a fourth spectrum spreading code for communicating with said node unit.

23. The method of claim 22 wherein said fourth spectrum spreading code is an M-ary code.

24. The method of claim 1 wherein said master identification spread spectrum signal comprises unique information for identifying said master unit.

25. A method for establishing communications between a master unit and a node unit by using time division multiple access, wherein a plurality of time slots comprise a time frame, comprising the steps of:
transmitting from said master unit an initialization signal in a time slot in a first time frame;
transmitting in said same time slot in said first time frame from a node unit desiring to establish communication with said master unit, responsive to receiving said initialization signal at said node unit, an initialization acknowledgment signal identifying said node unit;
transmitting in said same time slot in a second time frame from said master unit, responsive to receiving said initialization acknowledgment signal at said master unit, an identification signal identifying a slot position comprising one or more available vacant time slots; and communicating from said master unit to said node unit within said slot position using a first spread spectrum code, and communicating from said node unit to said master unit within said slot position using a second spread spectrum code.

26. The method of claim 25 wherein at least one of said initialization signal, said initialization acknowledgment signal, and said identification signal comprises a spread spectrum signal.

27. The method of claim 25 wherein said first spread spectrum code is an M-ary code.

28. The method of claim 25 wherein said second spread spectrum code is an M-ary code.

29. A method for establishing communications between a master unit and a node unit by using time division multiple access, wherein a plurality of time slots comprise a time frame, comprising the steps of:
transmitting from said master unit an initialization signal in an original time slot in a first time frame;
transmitting in said original time slot in said first time frame from a node unit desiring to establish communication with the master unit, responsive to receiving said initialization signal at said node unit, an initialization acknowledgment signal identifying said node unit;
transmitting in an available time slot in said first time frame different from said original time slot from said master unit, responsive to receiving said initialization acknowledgment signal at said master unit, a master identification signal; and communicating from said master unit to said node unit and said node unit to said master unit in said available time slot using a first spread spectrum code.

30. A method for establishing communications between a master unit and a node unit by using time division multiple access, wherein a plurality of time slots comprise a time frame, comprising the steps of:
transmitting from said master unit an initialization signal in an unused time slot;
transmitting in said unused time slot from a node unit desiring to establish communication with the master unit, responsive to receiving said initialization signal at said node unit, an initialization acknowledgment signal identifying said node unit, transmitting from said master unit, responsive to receiving said initialization acknowledgment signal at said master unit, a master identification signal identifying said master unit; and communicating from said master unit to said node unit using a spread spectrum signal including address bits for accessing said node unit, said node unit having a unique address corresponding to said address bits, and communicating from said node unit to said master unit using a spread spectrum code selected based on the identity of said master unit.

31. The method of claim 30 wherein at least one of said initialization signal, said initialization acknowledgment signal and said master initialization signal comprises a spread spectrum signal.

32. A method for establishing communications between a master unit and a node unit using time division multiple access, comprising the steps of:
transmitting from said master unit, using a first selected time slot and a first spread spectrum signal, an initialization signal, transmitting from a first node unit seeking to communicate with said master unit, using said first selected time slot, an initialization acknowledgment signal in response to said initialization signal;
transmitting from said master unit using said first selected time slot identification signal comprising a master unit identifier;
transmitting from said first node unit, in response to said identification signal, using said first selected time slot and identification acknowledgment signal comprising a node unit identifier, and communicating from said master unit to said node unit using a spread spectrum code selected based upon said node unit identifier, and communicating from said first node unit to said master unit using said first selected time slot and a spread spectrum code selected based on said master unit identifier.

33. The method of claim 32 wherein at least one of said initialization signal, said initialization acknowledgment signal and said master initialization signal comprises a spread spectrum signal.

34. A method for establishing communications between a master unit and a node unit by using time division multiple access, comprising the steps of:
transmitting from said master unit an initialization signal;
in response to said initialization signal, transmitting from said node unit desiring to establish communication with the master unit an initialization acknowledgment signal identifying said node unit, said initialization acknowledgment signal transmitted in a designated time slot;
in response to said initialization acknowledgment signal, transmitting from said master unit a master identification signal identifying said master unit in said designated time slot; and communicating from said node unit to said master unit in said designated time slot using an M-ary spread spectrum code.

35. The method of claim 34 further comprising the step of communicating from said master unit to said node unit using a second M-ary spread spectrum code.

36. The method of claim 34 wherein said second spread spectrum code is selected based upon the identify of said master unit.

37. The method of claim 34 wherein said second spread spectrum code is common to a plurality of node units accessible to said master unit.

38. A method for establishing wireless communications between a master unit and a node unit using time division multiple access, wherein a plurality of time slots comprise a time frame, and wherein a first time slot is used for establishing communication between said master unit and said node unit, comprising the steps of:
transmitting from said master unit a master initialization signal in said first time slot;
transmitting, from a node unit desiring to establish communication with said master unit, subsequent to receiving said master initialization signal at said node unit, a first node-initialization signal in said first time slot;
transmitting from said master unit, subsequent to receiving said first node-initialization signal at said master unit, a master identification signal in said first time slot, said master identification signal comprising information data identifying one or more available time slots for communicating between said master unit and said node unit;
transmitting from said node unit, subsequent to receiving said master identification signal at said node unit, a seconde node-initialization signal in said first time slot;
and communicating between said master unit and said node unit in said one or more available time slots.

39. The method of claim 38 wherein at least one of said master initialization signal, said first node-initialization signal, said second node-initialization signal and said master identification signal comprises a spread spectrum signal.

40. The method of claim 39 wherein said second node-initialization signal comprises information data identifying said node unit.

41. The method of claim 39 wherein said first node-initialization signal comprises information data identifying said node unit.

42. The method of claim 38 wherein said first node-initialization signal comprises information data comprising an acknowledgment signal.

43. A method for establishing wireless communication using spread spectrum signals to communicate between a first unit and a second unit using time division multiple access, wherein a plurality of time slots comprise a time frame, said time frame being periodic, comprising the steps of:
transmitting a first spread spectrum signal from said first unit in a first available time slot in a first time frame;
receiving said first spread spectrum signal at said second unit in a said first time slot in said first time frame;
transmitting a second spread spectrum signal from said second unit in said first time slot in said first time frame, subsequent to receiving said first spread spectrum signal at said second unit;
receiving said second spread spectrum signal at said first unit in said first time slot in said first time frame;
transmitting a third spread spectrum signal from said first unit in any available time slot in a second time frame, subsequent to receiving said second spread spectrum signal at said first unit;
receiving said third spread spectrum signal at said second unit in the same time slot in which said third spread spectrum signal was transmitted, in said second time frame;
transmitting a fourth spread spectrum signal from said second unit in said same time slot in which said third spread spectrum signal was transmitted, in said second time frame, subsequent to receiving said third spread spectrum signal at said second unit; and receiving said fourth spread spectrum signal at said first unit in said same time slot in which said third spread spectrum signal was transmitted, in said second time frame.

44. The method in claim 43 wherein said third and fourth spread spectrum signals are transmitted in said first time slot in said second time frame, and wherein said third and fourth spread spectrum signals are received in said first time slot in said second time frame.

45. The method of claim 43, further comprising the step of communicating between said first unit and said second unit in said first time slot.

46. A method for initialization between a master unit and a node unit, comprising the steps of:
in response to the transmission of an initialization signal, transmitting from said node unit a node-initialization signal;

transmitting from said master unit a master identification signal, in response to receiving the node-initialization signal; and transmitting from said node unit a node identification signal, in response to receiving the node-initialization signal.

47. The method of claim 46 further comprising a step of initiating communication by said master unit by transmitting a master communication signal from said master unit.

48. The method of claim 47 further comprising a step of transmitting from said node unit a node communication signal in a designated time slot.

49. The method of claim 46 wherein said master-initialization signal comprises a spread spectrum signal.

50. The method of claim 46 wherein a time frame comprises a plurality of time slots and wherein said node-initialization signal is transmitted in a time slot of said plurality of time slots that is designated by said master-initialization signal.