CA1214215A - Frequency-hopping radio communications system - Google Patents
Frequency-hopping radio communications systemInfo
- Publication number
- CA1214215A CA1214215A CA000428751A CA428751A CA1214215A CA 1214215 A CA1214215 A CA 1214215A CA 000428751 A CA000428751 A CA 000428751A CA 428751 A CA428751 A CA 428751A CA 1214215 A CA1214215 A CA 1214215A
- Authority
- CA
- Canada
- Prior art keywords
- frequency
- transmission
- station
- stations
- frequencies
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Classifications
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B7/00—Radio transmission systems, i.e. using radiation field
- H04B7/24—Radio transmission systems, i.e. using radiation field for communication between two or more posts
- H04B7/26—Radio transmission systems, i.e. using radiation field for communication between two or more posts at least one of which is mobile
- H04B7/2628—Radio transmission systems, i.e. using radiation field for communication between two or more posts at least one of which is mobile using code-division multiple access [CDMA] or spread spectrum multiple access [SSMA]
- H04B7/2634—Radio transmission systems, i.e. using radiation field for communication between two or more posts at least one of which is mobile using code-division multiple access [CDMA] or spread spectrum multiple access [SSMA] for channel frequency control
-
- 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
- H04B1/69—Spread spectrum techniques
- H04B1/713—Spread spectrum techniques using frequency hopping
- H04B1/7143—Arrangements for generation of hop patterns
Abstract
A B S T R A C T
A radio communications system comprising at least one master station and a plurality of slave stations in two-way frequency-hopping communication therewith. For telephony, speech is digitally encoded . Digital data is transmitted in packets using successive bursts at diffe-rent frequencies separated by intervals of silence. Each slave station has its own frequency-hopping pattern in-dependent of the patterns of the other slave stations but sharing a common pool of available frequencies. The master stations are capable of generating any of the slave station patterns instantly. The master stations broad-cast network time information for synchronization purposes, and the slave station patterns are determined by a combi-nation of a slave station identification number and network time.
A radio communications system comprising at least one master station and a plurality of slave stations in two-way frequency-hopping communication therewith. For telephony, speech is digitally encoded . Digital data is transmitted in packets using successive bursts at diffe-rent frequencies separated by intervals of silence. Each slave station has its own frequency-hopping pattern in-dependent of the patterns of the other slave stations but sharing a common pool of available frequencies. The master stations are capable of generating any of the slave station patterns instantly. The master stations broad-cast network time information for synchronization purposes, and the slave station patterns are determined by a combi-nation of a slave station identification number and network time.
Description
~REQUE~ICY-HOPPING Radio COY n~ICATIONS SWEPT
he invention relate to radio communications network (radio nets), to. to any system using Tory radio links for transmitting telephony or data between two or more stations, and it royalty particularly, but not exclusively, to radio links between mobile subscribers and one or more fixed master station.
BACKGROUND I THE INVENTION
So-called "cellular" nets have fixed stations spread out over the ground, with each fixed station being responsible for establishing communication with mobiles in a region, known as a "cell" 9 surrounding each fixed station.
Conventional radio nets use channels which are defined by the values of their center frequencies; information is transmitted by narrow band analog modulation, frequency modulation, amplitude modulation, or single side band. In nets having a large number of mobile subscribers, the frequency channels are no-t allocated to specific groups of links, but are held in common to be allocated to a calling mobile as a function of traffic. In such a system, channel management is important, since the bulk of the protection against inter-furriness between different calls is obtained by allocating different frequencies to links which are geographically close to one another.
the increasing numbers of customers applying to be connected as mobile radiotelephone subscribers require new radio net structures that enable greater density in the use of the available spectrum, or more precisely that provide greater spectrum efficiency which by reference to telephony, can be measured in erlangs/hertz/km2^
A first method of increasing spectrum efficiency consists in reducing the range between the mobiles and the nearest fixed station, but there is a limit to the improvement which can be obtained in this manner. Present systems are moving in this direction.
Preferred embodiments of the present invention provide a radio communications system which is capable of obtaining greater spectrum efficiency, which is highly flexible in installation and use, and which reduces infrastructure costs.
To do this, radio communications systems in accordance with the invention use a system of dispersing power by frequency spreading which enables higher spectrum efficiency to be obtained in spite of the apparent chaos caused by sup purposing signals from different links in the same space-time-frequency continuum Without constraint. The power dispersion technique used in radio communications systems in accordance with the present invention is frequency hopping, with each mobile station having its own frequency-hopping pattern known to the fixed stations. When there are several fixed or master stations they may readily be synchronized by simple means.
Summary OF THE INVENTION
. _ .. _ . _ _ .... .
The present invention provides a radio communications system comprising at least one master station and a plurality of slave stations, wherein information to be transmitted is in digital form, wherein a Tao link between any of the slave stations and a master station it established over a frequency-hopping channel in which -transmission takes place in bursts of predetermined duration at different frequencies with said frequency-hopping channel being determined by a frequency-hopping pattern which is associated with the slave station, each slave station having an independent frequency-hopping pattern associated therewith and all of the frequent swooping channels using frequencies selected from a pool of frequencies common to all of the channels, and wherein the useful transmission bursts are synchronized for the system as a whole with each slave station being synchronized from data received from a master station.
BRIEF DESCRIPTION OF THE DRAWINGS
......... , ,,, _,, Embodiments of the invention are described by way of example with reference to the accompanying drawings, in which:
Figure 1 is a block diagram of a link between a master station and a slave station in a radio communications system in accordance with the invention; and Figure 2 is a block diagram of a variant of the system shown in Figure 1.
I
MOVE D~TAIIED DESCRIPTION
In some type of radio communication system, and in particular those which require protection against jamming, channel are no longer defined in terms of center frequencies, nor are they associated with narrow band modulation. The main kind of system are either phase await system in which wide band mogul lion it obtained at a given ~requenc~, so else they are rapid or ~requenc~-hopping systems in which a packet of information it transmitted for a short period on a carrier of given frequency, and in which the next packet it transmitted on a carrier of different frequency chosen according to a predetermined code. Such oysters require the use of complex ~nchronizing means at the beginning ox a call, wince the ; brevity of the tranæmi sons and the lack of any idea infer-structure prevent prior synchronization. further, the number of stations connected in a single net is generally limited 7 and stations in the same net generally follow the same frequency-hopping pattern.
Completely different problems are encountered when designing a radio communications system having a large number of mobile subscribers each of which may be connected to any fixed infrastructure station. the main problem is to increase the net's spectrum efficiency by limiting likely interference to acceptable values. further, the synchronizing system in each station must be as simple as possible.
As outlined above the improvement in spectrum efficiency provide din a radio communications system in accordance with the invention is obtained by employing a frequency spreading technique. The technique used is frequency-hopping trays-mission as defined above, in which information is transmitted in packets in successive bursts at different frequencies. Each subscriber has a particular frequency-hopping pattern, with the allowable frequencies being chosen from a predetermined pool of frequencies common to all of the subscribers and with the master stations being capable of generating the same patterns on the basis of simple data. the bursts are separated by short intervals of dead time in order to facilitate frequency changing, and burst duration it large relative to the dead time and to the propagation time. The reasons for this choice are as follows: Trio technique require least modification of the existing conventional structure of transmitters and receivers.
Further, provided useful burst duration is long enough, this technique is no more sensitive to multiple path propagation than it fixed frequency transmission. Since the dead time it relatively short, the data transmission rate it increased very little (and remains less than 100 Kbits/s)- It it shown below that the synchronization does not need to be particularly accurate provided that the dead time can be large relative to the propagation time between a fixed station and various mobiles inlay this technique it readily adaptable to non-linear processing which can be most beneficial to this type of channel. The discontinuities due to the frequency hops and to the dead time makes it necessary to encode the information digitally. Digital data for transmission is already in digital form; speech for transmission needs to be encoded by a speech eroding system.
further, all the stations on the net change frequency at the same instant To do this, all the stations must be synchronized to a reference time common to all the elements of the system, with the master stations being directly synchrony iced to the reference time and with the slave stations synch-running themselves on data received from the master stations.
Consequently, a frequency-hopping channel is defined in the space-time-frequency continuum by its own frequency-hopping pattern. The number of "independent" patterns which can be defined in said continuum is much larger than the number of different frequencies. In this system, one or more successive bursts on different channels may have the same frequencies. In which case there it "intrinsic" interference of the weaker channel by the stronger. The frequency-hopping patterns are said to be independent when the conditional probability of interference in n successive bursts at a given level of traffic is substantially equal to the probability of interference in one burst raised to the power n. This result is obtained by .~,....
using a gamily of codes having this independence property or generating the frequenc~-hopping patterns.
Codes of this type are known, and are described, for example, in the following documents:
DO Surety and MOB. Purely in "Hopping Patterns for ~requency-hopped, Multiple Access Communication" Into Con.
Commune ICC 78 Toronto, Canada, June 4-7, 1978 pp. 741/743; and Go Einarsson in "Address assignment for a time-~requency coded ~pread-spectrum system STOWAGE vow 59, No Sept. 1980, pp. 124~/1255.
Thus the channel reserved or a particular subscriber is permanently defined regardless of the subscribers position, there being a one-to-one correspondence between each subscriber number and it frequency-hopping pattern. further, said correspondence may be made public without inconvenience. The frequency Jo be used at each hop is completely determined both at the master station and at the slave (or subscriber) station by a knowledge of network time and the subscriber's identific-anion number. further, by means of a simple frequency scrambling technique, it can be arranged for information accidentally received by a third party to be incomprehensible.
Thus, a complete non-blocking matrix of ~requency-hopping patterns can be defined for all the traffic and the calls from the fixed infrastructure to the mobiles, which matrix can become saturated only as a function of local traffic.
These choices considerably simplify the methods used to manage the radio nets.
he following explanations outline the increase in spectrum efficiency obtainable by such a system relative to a system having a pool of fixed frequencies.
Assume that there are two duplex bands each of 5 I band-width, giving N = 200 channels at 25 KHz spacing; the attenuation as a function of the distance d varies as 1/d4 and has a log normal law of = 10 dub.
I In a prior art system using a common pool of single frequency channels and a repeated pattern of sixteen hexagonal cells, interference is determined by the six nearest hexagons ~',;~,-..
in which the same frequencies are used, each of which is situated at a distance of tight times the cell radius. Since the attenuation it proportional, on average 7 to 1/d4, the field received by the central elation from a mobile in it own cell it 36 dub up on the interference (again on average).
Assuming that the modulation used require a signal to be 12 do up on the interference to provide adequate protection therefrom (a reasonable assumption *or analog modulation), the time during which the signal received by a mobile is degraded by 1 interference can be calculated a the sum of the occasions on which the attenuation it less than (36-12~ = 24 do, to. lets than a value equivalent to 2.4 I. hi is 1% of the time. or all six potential interfering hexagons) the probable inter-furriness time is thus 6~9 assuming uniform terrain and treating frequency distribution as being the same as time distribution.
Prior art spectrum efficiency is thus determined by the size of the pattern which enables 200/16 frequencies to be used per cell, to. 12 frequencies which correspond to a traffic of 7.2 erlangs with a loss rate of I for 12 sender-receivers per cell.
In a frequency-hopping system using coded access in accordance with the invention, let the average number of calls be _ and let the number of distinct channels be N.
The probability of intrinsic interference on any given channel from within the same cell can be calculated as :
nun x (owe x 0.8 The term (0.3)2 corresponds to voice activity, and the term 0.8 stems from the fact that the power from the mobiles is regulated in such a manner that in the event of conflict, there it a beneficial capture effect for the useful station in 20~ of cases where the received field is at least 6dH stronger than the interference.
To a first approximation the traffic in the six adjacent cells can be considered as being concentrated at a distance equal to the distance of the centers of the cells to. at twice the cell range. this gives an average attenuation proportional to 1/d4 equal to 12 do) which means that the reference field strength is exceeded for 0.6 or 0.27 of the time and per cell taking into account the 6 dub margin necessary for canceling the code conflict equity which gives an overall probability of intrinsic interference ox no x (owe x 1.62 or the six adjacent cell (where 1.62 = 0.27 x 6).
likewise, for the 12 cells at a distance of 4 radii the figure it (n/N) x (owe 0.43 and for the 18 cells at a distance of 6 radii the figure lo (n/N) x (o 3)2 x I
Given the various approximations made, the overall probab-islet of intrinsic interference (includir~ the contributions prom more distant cells) converges on value which it less than (n/N) (owe x To be comparable with the prior art system calculated above, the interference must remain less than I on average, to. (n/N) must not be greater than 0.22.
Since digital modulation requires a greater bandwidth than analog modulation, the number of available channels in a given frequency band is less than the number available to a prior art system using a pool of fixed frequencies. Assume that there only half as many channels available, giving N = 100. Then for n/N = 0.22 the value of n is 22 calls which 1.8 times as many as the number of calls possible using a prior art system in which a pool of fixed frequency channels are held in common in a given frequency band.
inure 1 is a block diagram of a portion of such a frequency-hopping radio communications system. the diagram show a portion 100 of a fixed or master station and a slave station 200 which may be a mobile subscriber. Identical components in both stations are referenced by numbers having the same tens and unit digits but preceded by the digit 1 for master station components or by the digit 2 for slave station components.
he master station comprises a plurality of transmitter-receiver subassemblies such as the portion 100, each of which comprises a transmitter 101 having a modulation signal input and a carrier signal input, and a receiver 102 having a carrier signal input and a modulated signal output. Each transmitter-receiver subassembly further includes a synthesizer 103 having two outputs respectively connected to the carrier frequency inputs ox the transmitter 101 and the receiver 102. The synthesizer ha a driver signal input connected to thy output from a driver oscillator 1069 and a frequency hopping control input connected to the output prom a frequency hopping pattern generator 104. The driver oscillator 104 it a highly stable oscillator and also serve to drive a clock 107. The clock comprises, or example, a o'er of divider stage, and us capable of being reset to a given time via a shift control input 113 connected to means outside the station, ego to a receiver tuned to receive "pips" from a broadcast time signal.
the clock 107 ha an output connected to a control input of a sequencer 108 which generates signal based on the clock-determined time to define the beginning of each burst ox transmission and the beginning of each intervening period of dead time. The period of dead time is used to set the synthesizer 10~ to the frequency of the next burst of trays-mission, and to attenuate transient effects in the equipment due to steep fronts at the beginning and end of each burst.
The frequency generated by the synthesizer during each burst is defined by the frequency pattern generator 104 which derives the frequency from the time as defined by the sequencer 108 and from an identifying reference number which is different for each link. or example, there may be one reference number for each slave station and another one for a common signaling channel. Such frequency pattern generators are known see above) and may operate according to algorithms of varying degrees of complexity.
The master station has a signal input 114. For a radio telephone station, the station further includes a speech coder 112. The speech coder includes a voice activity detector function and has a first output for digitized speech signal and a second output DAY connected to a transmitter inhibit circuit 120 to apply a voice activity detection signal thereto. the inhibit circuit 1~0 applies a suitable voltage to the transmitter 101 to prevent it from transmitting during silences in the speech signal. The first output from the speech coder 112 is applied to a first in first out It buffer memory 105 }. ..
. g which alto hugs a control lout connected to a Canada output prom the sequencer 108, The signal to be transmitted arrives in the form of a errs ox bits at the input to the buyer memory 105 Where it it stored. The memory is then read at hither speed under the control ox the agonizer in order to be able to past all the bite during the ~ransmisBiOn bursts.
On the receiver ode, the output prom the receiver 102 1B
connected to the input ox a demodulator 110. During reception, each burst I demodulated as a whole and synchronization is sought on a per burst basis, ego by storing the entire received burst end then jig a demodulator which includes a eynchron-icing circuit of the type described in the present Assignee's US Patent 4 263 672 . The output prom the demodulator it connected to the input ox buffer memory 109 which performs the inverse junction ox the buffer memory 105, it delivering data at a constant rate prom each valid burst. To validate each burst, the master station further includes a validating circuit 111 which has one input connected to a third output from the sequencer 108 and another input connected to an output from the demodulator 110. The validating circuit checks that the bursts actually correspond to the call in progre 8, ego by each burst including a signal characteristic of the channel being used, and hence of the expected mobile. bursts which do not meet the validity criteria are eliminated and are replaced by an interpolation signal, ego by an alternating series of Ox and us, supposing the speech it delta coded In other embodiments the validation decision may be based on an analysis of redundant information in the transmitted burst.
The output 115 prom the buffer memory 109 is thus the signal output prom the master station.
The circuit of the slave station 200 is very similar It comprises a transmitter 201 and a receiver 202 having carrier frequency inputs connected to outputs from a synthesizer 203.
A frequency hopping pattern generator 204 is controlled by a sequencer 208 and has it output connected to a control input of the synthesizer 203. The synthesizer also receives a driver signal from a highly stable driver oscillator 206, which oscillator alto has an output connected to a clock 207. The output from the clock 207 it connected to the input to the sequencer 208 which has a second output connected to control a buffer memory 205 which receives an input signal prom the stations signal input 214 via speech coding circuit 212. the speech coder has a voice activity detection output DAY
connected to an input of a transmitter inhibiter circuit 220 whose output inhibits transmission by uprising the carrier during periods of silence in the speech input oign~l During reception, the output prom the receiver 202 it connected to the input ox a demodulator 210 having it output connected to an input of a buffer memory 209 whose output constitutes the signal output 215 prom the slave station.
he main difference between the master station and the slave station lies in -their synchronization. The shift input to the clock 207 is connected to receive a control signal prom a validating and synchronizing circuit 221. The validating and synchronizing circuit 221 has a second output connected to a control input of the buffer memory 209. The validating portion of this circuit 221 operates in the same Jay as the validating circuit 111 in the master station to ignore some packets of data in the memory 205 on -the basis of the signal demodulated by the demodulator 210. In addition, the validating and synch-ionizing circuit 221 synchronizes the clock 207. To do this it measures the instant of arrival of each burst on the basis of the rising front of the burst pulse and the synchronization bit, and corrects the clock by bringing it into phase with the received burst each time a burst is validated. So long as the control it both Asiatic and sufficiently rapid, the slave stations operate at a time which is offset relative to the master station by an amount equal to the propagation time between the stations, which depends on the position of the mobile. Since the slave station is synchronized on data transmitted by the master station, only the master station is capable if initiating a call in such a system Possible transmission modes include frequency duplex, time duplex, and alternating simplex mode, provided that the duration of transmission in each direction is short enough to enable the muster station to wend a return signal necessary for eynchroni2ation.
When using frequency duplex mode, the master station sends packets of data in successive bursts at the frequencies determined by the pattern corresponding to the called slave station. the slave elation receives the data packets from the master station, with the signal applied by the synthesizer 203 to the demodulator 210 hollowing the tame pattern ox frequency hops. The slave station transmits corresponding packets ox data in the opposite direction in Burt at successive frequencies which are derived prom the same pattern by a constant frequency offset, with the offset advantageously being equal to the receiver intermediate frequency, At the master station, the same offset is used on the frequency applied by the synthesizer 103 to the demodulator 110. this is the preferred mode of transmission for a radio communications system in accordance with the invention.
When using time duplex transmission mode, two-burst cyclic operation is provided with the first burst in each cycle corresponding to transmission in one direction and the second burst corresponding to transmission in the other direction.
The synthesizer switches on the transmitter and the receiver in each of the stations alternately under the control of the frequency-hopping pattern generator 104 or 204 as the case may be. This mode of transmission requires the data to be compressed and then decompressed which has the effect of doubling the data transmission rate required during the useful periods of the bursts. Nonetheless, this mode remains usable I so long as the data rate used does not exceed the values at which multiple path propagation becomes a hindrance.
finally, it is naturally possible to use an alternating mode with transmission or reception taking place on a single frequency, in which case the circuits 112 and 212 provide voice operated transmitter switching.
inure 2 shows an embodiment ox a radio communications system in accordance with the invention in which A common ~ignalling channel it provided and alto used for synchrony it ion in which case a Levi elation may initiate a ash. In this figure, component which are the same I components shown in Figure 1 have been designated by the came reverences. Tic embodiment it intended to enable a periodic a~nchroni~ing signal to be transmitted to all the slave station, even when the meeter station has a call jet up on a code defined by the identification number ox the corresponding subscriber To do this the matter talon include a second connoisseur 116 in addition to the sequencer 108. Similarly the Allah station includes a second sequencer 21S in addition to the sequencer 208. The second sequencers 116 and 216 determine the periodicity at which the stations switch over to the common or general channel ego one burst in every 100 bursts. For this particular burst 7 the frequency is not determined by the identification number of a particular subscriber but by a general number associated with the common channel, whereby all the slave stations can receive a time message in the clear. To do this, the matter station further includes a time memory 117 having an input connected to the clock 107. Thus the time memory 117 is permanently updated by the clock 107. The use o*
network time as identifying the common channel has several advantages. firstly, slave stations which are already in synchronization with the network can identify the common channel without ambiguity, and can therefore keep in synchronization by listening preferentially or exclusively to said time signals. Secondly, a non-synchronized slave station can use the time signals to get into synchronization, in which case all it has to do it listen on some pattern, ego its own 7 provided there it a high enough probability of interference between its own *requenc~-hopping pattern and the common channel frequency-hopping pattern to. a probability of interference such that two successive interferences between the two channels are likely to occur in less than a tolerable waiting period for establishing synchronization In the master station, the frequenc~-hopping pattern generator 104 thus receives the general number which is I".
,~,,, 13 lo associated with the common channel or a particular identification number associated with a culled caption, depending on whether the second sequencer 116 wish one or another of said numbers to the pattern generator. A switch 118 pe~orm~ the required ewitchin~ junction. likewise the transmitter 101 receive data to be transmitter from the buffer memory 105 or from the time memory 117 pa a witch 119 under the control of the second sequencer 116.
In the slave station the second sequencer 216 control a switch 218 which applies the general number ox the common channel or the reverence number us the station in question to the frequency-hopping pattern venerator 204. At the irrupt interference in the receiver, the receiver clock 207 it forced to the received time by the validating and synchronizing circuit 221. Next time the second sequencers 116 and 216 switch to the general number, the presumed synchronization can be verified. If verification fails, a new search is begun or the time signal.
The presence of a duplex common channel also makes it possible for the slave stations to send signals to the master station In particular the slave stations can send signals requesting that a call be set up. Such a request is transmitted simply by sending the identification number of the calling slave station during a reference burst of the common channel. the ensuing dialog, if any, then takes place on the channel defined by the identification number transmitted by the calling slave station.
If there are several master stations in a network, the system adapts readily to coordinating traffic between the entire group of stations.
To do this, a periodic reference frame defined relative to the common time of the group of networks it defined as follows:
the bursts for sending timing data from each of -the stations as defined by their respective second sequencers 116 are offset in time. Thus, while each master station having a call in progress cannot transmit on the common channel, synchronization is ensured by master stations which are not engaged on calls I,.
transmitting packet ox time data on the common channel. In this way, c ifs from a master elation are not interrupted.
this arrangement not only get rid ox the corresponding intrinsic interference but alto ha the advantage of enabling a elate station which dazzlers to set up a call to select the "but" available matter elation by transmitting its ash request in synchronization with the bet quality received time word, to. in synchronization with the lime Ford having the highest amplitude received idea strength.
By Jay of example, the hollowing numerical values can be used in a radio communication stem in accordance with the invention. The frequency range may be 900 My The frequency oft between transmission and reception may be 45 MHz. the number of frequency channels in the net may be 100, at 50 KHz spacing. Each burst may last 2 millisecond, with a dead time of 1 millisecond between bursts For a continuous input digital data rate of 76 Kbits/aecond, the data rate during each burst it 24 Kbits/~econd~ with 48 bits being transmitted in each burst.
There it little difficulty in storing the frequency-hopping pattern of a subscriber or slave station in memory, however, each master station capable of communicating with any of the subscriber stations must be capable of instantly generating the frequency-hopping pattern of any subscriber. Jo do this it is sufficient for all the patterns to be chosen from the same code family, and to establish a one-to-one relationship between each subscriber number and the corresponding frequency-hopping pattern.
-
he invention relate to radio communications network (radio nets), to. to any system using Tory radio links for transmitting telephony or data between two or more stations, and it royalty particularly, but not exclusively, to radio links between mobile subscribers and one or more fixed master station.
BACKGROUND I THE INVENTION
So-called "cellular" nets have fixed stations spread out over the ground, with each fixed station being responsible for establishing communication with mobiles in a region, known as a "cell" 9 surrounding each fixed station.
Conventional radio nets use channels which are defined by the values of their center frequencies; information is transmitted by narrow band analog modulation, frequency modulation, amplitude modulation, or single side band. In nets having a large number of mobile subscribers, the frequency channels are no-t allocated to specific groups of links, but are held in common to be allocated to a calling mobile as a function of traffic. In such a system, channel management is important, since the bulk of the protection against inter-furriness between different calls is obtained by allocating different frequencies to links which are geographically close to one another.
the increasing numbers of customers applying to be connected as mobile radiotelephone subscribers require new radio net structures that enable greater density in the use of the available spectrum, or more precisely that provide greater spectrum efficiency which by reference to telephony, can be measured in erlangs/hertz/km2^
A first method of increasing spectrum efficiency consists in reducing the range between the mobiles and the nearest fixed station, but there is a limit to the improvement which can be obtained in this manner. Present systems are moving in this direction.
Preferred embodiments of the present invention provide a radio communications system which is capable of obtaining greater spectrum efficiency, which is highly flexible in installation and use, and which reduces infrastructure costs.
To do this, radio communications systems in accordance with the invention use a system of dispersing power by frequency spreading which enables higher spectrum efficiency to be obtained in spite of the apparent chaos caused by sup purposing signals from different links in the same space-time-frequency continuum Without constraint. The power dispersion technique used in radio communications systems in accordance with the present invention is frequency hopping, with each mobile station having its own frequency-hopping pattern known to the fixed stations. When there are several fixed or master stations they may readily be synchronized by simple means.
Summary OF THE INVENTION
. _ .. _ . _ _ .... .
The present invention provides a radio communications system comprising at least one master station and a plurality of slave stations, wherein information to be transmitted is in digital form, wherein a Tao link between any of the slave stations and a master station it established over a frequency-hopping channel in which -transmission takes place in bursts of predetermined duration at different frequencies with said frequency-hopping channel being determined by a frequency-hopping pattern which is associated with the slave station, each slave station having an independent frequency-hopping pattern associated therewith and all of the frequent swooping channels using frequencies selected from a pool of frequencies common to all of the channels, and wherein the useful transmission bursts are synchronized for the system as a whole with each slave station being synchronized from data received from a master station.
BRIEF DESCRIPTION OF THE DRAWINGS
......... , ,,, _,, Embodiments of the invention are described by way of example with reference to the accompanying drawings, in which:
Figure 1 is a block diagram of a link between a master station and a slave station in a radio communications system in accordance with the invention; and Figure 2 is a block diagram of a variant of the system shown in Figure 1.
I
MOVE D~TAIIED DESCRIPTION
In some type of radio communication system, and in particular those which require protection against jamming, channel are no longer defined in terms of center frequencies, nor are they associated with narrow band modulation. The main kind of system are either phase await system in which wide band mogul lion it obtained at a given ~requenc~, so else they are rapid or ~requenc~-hopping systems in which a packet of information it transmitted for a short period on a carrier of given frequency, and in which the next packet it transmitted on a carrier of different frequency chosen according to a predetermined code. Such oysters require the use of complex ~nchronizing means at the beginning ox a call, wince the ; brevity of the tranæmi sons and the lack of any idea infer-structure prevent prior synchronization. further, the number of stations connected in a single net is generally limited 7 and stations in the same net generally follow the same frequency-hopping pattern.
Completely different problems are encountered when designing a radio communications system having a large number of mobile subscribers each of which may be connected to any fixed infrastructure station. the main problem is to increase the net's spectrum efficiency by limiting likely interference to acceptable values. further, the synchronizing system in each station must be as simple as possible.
As outlined above the improvement in spectrum efficiency provide din a radio communications system in accordance with the invention is obtained by employing a frequency spreading technique. The technique used is frequency-hopping trays-mission as defined above, in which information is transmitted in packets in successive bursts at different frequencies. Each subscriber has a particular frequency-hopping pattern, with the allowable frequencies being chosen from a predetermined pool of frequencies common to all of the subscribers and with the master stations being capable of generating the same patterns on the basis of simple data. the bursts are separated by short intervals of dead time in order to facilitate frequency changing, and burst duration it large relative to the dead time and to the propagation time. The reasons for this choice are as follows: Trio technique require least modification of the existing conventional structure of transmitters and receivers.
Further, provided useful burst duration is long enough, this technique is no more sensitive to multiple path propagation than it fixed frequency transmission. Since the dead time it relatively short, the data transmission rate it increased very little (and remains less than 100 Kbits/s)- It it shown below that the synchronization does not need to be particularly accurate provided that the dead time can be large relative to the propagation time between a fixed station and various mobiles inlay this technique it readily adaptable to non-linear processing which can be most beneficial to this type of channel. The discontinuities due to the frequency hops and to the dead time makes it necessary to encode the information digitally. Digital data for transmission is already in digital form; speech for transmission needs to be encoded by a speech eroding system.
further, all the stations on the net change frequency at the same instant To do this, all the stations must be synchronized to a reference time common to all the elements of the system, with the master stations being directly synchrony iced to the reference time and with the slave stations synch-running themselves on data received from the master stations.
Consequently, a frequency-hopping channel is defined in the space-time-frequency continuum by its own frequency-hopping pattern. The number of "independent" patterns which can be defined in said continuum is much larger than the number of different frequencies. In this system, one or more successive bursts on different channels may have the same frequencies. In which case there it "intrinsic" interference of the weaker channel by the stronger. The frequency-hopping patterns are said to be independent when the conditional probability of interference in n successive bursts at a given level of traffic is substantially equal to the probability of interference in one burst raised to the power n. This result is obtained by .~,....
using a gamily of codes having this independence property or generating the frequenc~-hopping patterns.
Codes of this type are known, and are described, for example, in the following documents:
DO Surety and MOB. Purely in "Hopping Patterns for ~requency-hopped, Multiple Access Communication" Into Con.
Commune ICC 78 Toronto, Canada, June 4-7, 1978 pp. 741/743; and Go Einarsson in "Address assignment for a time-~requency coded ~pread-spectrum system STOWAGE vow 59, No Sept. 1980, pp. 124~/1255.
Thus the channel reserved or a particular subscriber is permanently defined regardless of the subscribers position, there being a one-to-one correspondence between each subscriber number and it frequency-hopping pattern. further, said correspondence may be made public without inconvenience. The frequency Jo be used at each hop is completely determined both at the master station and at the slave (or subscriber) station by a knowledge of network time and the subscriber's identific-anion number. further, by means of a simple frequency scrambling technique, it can be arranged for information accidentally received by a third party to be incomprehensible.
Thus, a complete non-blocking matrix of ~requency-hopping patterns can be defined for all the traffic and the calls from the fixed infrastructure to the mobiles, which matrix can become saturated only as a function of local traffic.
These choices considerably simplify the methods used to manage the radio nets.
he following explanations outline the increase in spectrum efficiency obtainable by such a system relative to a system having a pool of fixed frequencies.
Assume that there are two duplex bands each of 5 I band-width, giving N = 200 channels at 25 KHz spacing; the attenuation as a function of the distance d varies as 1/d4 and has a log normal law of = 10 dub.
I In a prior art system using a common pool of single frequency channels and a repeated pattern of sixteen hexagonal cells, interference is determined by the six nearest hexagons ~',;~,-..
in which the same frequencies are used, each of which is situated at a distance of tight times the cell radius. Since the attenuation it proportional, on average 7 to 1/d4, the field received by the central elation from a mobile in it own cell it 36 dub up on the interference (again on average).
Assuming that the modulation used require a signal to be 12 do up on the interference to provide adequate protection therefrom (a reasonable assumption *or analog modulation), the time during which the signal received by a mobile is degraded by 1 interference can be calculated a the sum of the occasions on which the attenuation it less than (36-12~ = 24 do, to. lets than a value equivalent to 2.4 I. hi is 1% of the time. or all six potential interfering hexagons) the probable inter-furriness time is thus 6~9 assuming uniform terrain and treating frequency distribution as being the same as time distribution.
Prior art spectrum efficiency is thus determined by the size of the pattern which enables 200/16 frequencies to be used per cell, to. 12 frequencies which correspond to a traffic of 7.2 erlangs with a loss rate of I for 12 sender-receivers per cell.
In a frequency-hopping system using coded access in accordance with the invention, let the average number of calls be _ and let the number of distinct channels be N.
The probability of intrinsic interference on any given channel from within the same cell can be calculated as :
nun x (owe x 0.8 The term (0.3)2 corresponds to voice activity, and the term 0.8 stems from the fact that the power from the mobiles is regulated in such a manner that in the event of conflict, there it a beneficial capture effect for the useful station in 20~ of cases where the received field is at least 6dH stronger than the interference.
To a first approximation the traffic in the six adjacent cells can be considered as being concentrated at a distance equal to the distance of the centers of the cells to. at twice the cell range. this gives an average attenuation proportional to 1/d4 equal to 12 do) which means that the reference field strength is exceeded for 0.6 or 0.27 of the time and per cell taking into account the 6 dub margin necessary for canceling the code conflict equity which gives an overall probability of intrinsic interference ox no x (owe x 1.62 or the six adjacent cell (where 1.62 = 0.27 x 6).
likewise, for the 12 cells at a distance of 4 radii the figure it (n/N) x (owe 0.43 and for the 18 cells at a distance of 6 radii the figure lo (n/N) x (o 3)2 x I
Given the various approximations made, the overall probab-islet of intrinsic interference (includir~ the contributions prom more distant cells) converges on value which it less than (n/N) (owe x To be comparable with the prior art system calculated above, the interference must remain less than I on average, to. (n/N) must not be greater than 0.22.
Since digital modulation requires a greater bandwidth than analog modulation, the number of available channels in a given frequency band is less than the number available to a prior art system using a pool of fixed frequencies. Assume that there only half as many channels available, giving N = 100. Then for n/N = 0.22 the value of n is 22 calls which 1.8 times as many as the number of calls possible using a prior art system in which a pool of fixed frequency channels are held in common in a given frequency band.
inure 1 is a block diagram of a portion of such a frequency-hopping radio communications system. the diagram show a portion 100 of a fixed or master station and a slave station 200 which may be a mobile subscriber. Identical components in both stations are referenced by numbers having the same tens and unit digits but preceded by the digit 1 for master station components or by the digit 2 for slave station components.
he master station comprises a plurality of transmitter-receiver subassemblies such as the portion 100, each of which comprises a transmitter 101 having a modulation signal input and a carrier signal input, and a receiver 102 having a carrier signal input and a modulated signal output. Each transmitter-receiver subassembly further includes a synthesizer 103 having two outputs respectively connected to the carrier frequency inputs ox the transmitter 101 and the receiver 102. The synthesizer ha a driver signal input connected to thy output from a driver oscillator 1069 and a frequency hopping control input connected to the output prom a frequency hopping pattern generator 104. The driver oscillator 104 it a highly stable oscillator and also serve to drive a clock 107. The clock comprises, or example, a o'er of divider stage, and us capable of being reset to a given time via a shift control input 113 connected to means outside the station, ego to a receiver tuned to receive "pips" from a broadcast time signal.
the clock 107 ha an output connected to a control input of a sequencer 108 which generates signal based on the clock-determined time to define the beginning of each burst ox transmission and the beginning of each intervening period of dead time. The period of dead time is used to set the synthesizer 10~ to the frequency of the next burst of trays-mission, and to attenuate transient effects in the equipment due to steep fronts at the beginning and end of each burst.
The frequency generated by the synthesizer during each burst is defined by the frequency pattern generator 104 which derives the frequency from the time as defined by the sequencer 108 and from an identifying reference number which is different for each link. or example, there may be one reference number for each slave station and another one for a common signaling channel. Such frequency pattern generators are known see above) and may operate according to algorithms of varying degrees of complexity.
The master station has a signal input 114. For a radio telephone station, the station further includes a speech coder 112. The speech coder includes a voice activity detector function and has a first output for digitized speech signal and a second output DAY connected to a transmitter inhibit circuit 120 to apply a voice activity detection signal thereto. the inhibit circuit 1~0 applies a suitable voltage to the transmitter 101 to prevent it from transmitting during silences in the speech signal. The first output from the speech coder 112 is applied to a first in first out It buffer memory 105 }. ..
. g which alto hugs a control lout connected to a Canada output prom the sequencer 108, The signal to be transmitted arrives in the form of a errs ox bits at the input to the buyer memory 105 Where it it stored. The memory is then read at hither speed under the control ox the agonizer in order to be able to past all the bite during the ~ransmisBiOn bursts.
On the receiver ode, the output prom the receiver 102 1B
connected to the input ox a demodulator 110. During reception, each burst I demodulated as a whole and synchronization is sought on a per burst basis, ego by storing the entire received burst end then jig a demodulator which includes a eynchron-icing circuit of the type described in the present Assignee's US Patent 4 263 672 . The output prom the demodulator it connected to the input ox buffer memory 109 which performs the inverse junction ox the buffer memory 105, it delivering data at a constant rate prom each valid burst. To validate each burst, the master station further includes a validating circuit 111 which has one input connected to a third output from the sequencer 108 and another input connected to an output from the demodulator 110. The validating circuit checks that the bursts actually correspond to the call in progre 8, ego by each burst including a signal characteristic of the channel being used, and hence of the expected mobile. bursts which do not meet the validity criteria are eliminated and are replaced by an interpolation signal, ego by an alternating series of Ox and us, supposing the speech it delta coded In other embodiments the validation decision may be based on an analysis of redundant information in the transmitted burst.
The output 115 prom the buffer memory 109 is thus the signal output prom the master station.
The circuit of the slave station 200 is very similar It comprises a transmitter 201 and a receiver 202 having carrier frequency inputs connected to outputs from a synthesizer 203.
A frequency hopping pattern generator 204 is controlled by a sequencer 208 and has it output connected to a control input of the synthesizer 203. The synthesizer also receives a driver signal from a highly stable driver oscillator 206, which oscillator alto has an output connected to a clock 207. The output from the clock 207 it connected to the input to the sequencer 208 which has a second output connected to control a buffer memory 205 which receives an input signal prom the stations signal input 214 via speech coding circuit 212. the speech coder has a voice activity detection output DAY
connected to an input of a transmitter inhibiter circuit 220 whose output inhibits transmission by uprising the carrier during periods of silence in the speech input oign~l During reception, the output prom the receiver 202 it connected to the input ox a demodulator 210 having it output connected to an input of a buffer memory 209 whose output constitutes the signal output 215 prom the slave station.
he main difference between the master station and the slave station lies in -their synchronization. The shift input to the clock 207 is connected to receive a control signal prom a validating and synchronizing circuit 221. The validating and synchronizing circuit 221 has a second output connected to a control input of the buffer memory 209. The validating portion of this circuit 221 operates in the same Jay as the validating circuit 111 in the master station to ignore some packets of data in the memory 205 on -the basis of the signal demodulated by the demodulator 210. In addition, the validating and synch-ionizing circuit 221 synchronizes the clock 207. To do this it measures the instant of arrival of each burst on the basis of the rising front of the burst pulse and the synchronization bit, and corrects the clock by bringing it into phase with the received burst each time a burst is validated. So long as the control it both Asiatic and sufficiently rapid, the slave stations operate at a time which is offset relative to the master station by an amount equal to the propagation time between the stations, which depends on the position of the mobile. Since the slave station is synchronized on data transmitted by the master station, only the master station is capable if initiating a call in such a system Possible transmission modes include frequency duplex, time duplex, and alternating simplex mode, provided that the duration of transmission in each direction is short enough to enable the muster station to wend a return signal necessary for eynchroni2ation.
When using frequency duplex mode, the master station sends packets of data in successive bursts at the frequencies determined by the pattern corresponding to the called slave station. the slave elation receives the data packets from the master station, with the signal applied by the synthesizer 203 to the demodulator 210 hollowing the tame pattern ox frequency hops. The slave station transmits corresponding packets ox data in the opposite direction in Burt at successive frequencies which are derived prom the same pattern by a constant frequency offset, with the offset advantageously being equal to the receiver intermediate frequency, At the master station, the same offset is used on the frequency applied by the synthesizer 103 to the demodulator 110. this is the preferred mode of transmission for a radio communications system in accordance with the invention.
When using time duplex transmission mode, two-burst cyclic operation is provided with the first burst in each cycle corresponding to transmission in one direction and the second burst corresponding to transmission in the other direction.
The synthesizer switches on the transmitter and the receiver in each of the stations alternately under the control of the frequency-hopping pattern generator 104 or 204 as the case may be. This mode of transmission requires the data to be compressed and then decompressed which has the effect of doubling the data transmission rate required during the useful periods of the bursts. Nonetheless, this mode remains usable I so long as the data rate used does not exceed the values at which multiple path propagation becomes a hindrance.
finally, it is naturally possible to use an alternating mode with transmission or reception taking place on a single frequency, in which case the circuits 112 and 212 provide voice operated transmitter switching.
inure 2 shows an embodiment ox a radio communications system in accordance with the invention in which A common ~ignalling channel it provided and alto used for synchrony it ion in which case a Levi elation may initiate a ash. In this figure, component which are the same I components shown in Figure 1 have been designated by the came reverences. Tic embodiment it intended to enable a periodic a~nchroni~ing signal to be transmitted to all the slave station, even when the meeter station has a call jet up on a code defined by the identification number ox the corresponding subscriber To do this the matter talon include a second connoisseur 116 in addition to the sequencer 108. Similarly the Allah station includes a second sequencer 21S in addition to the sequencer 208. The second sequencers 116 and 216 determine the periodicity at which the stations switch over to the common or general channel ego one burst in every 100 bursts. For this particular burst 7 the frequency is not determined by the identification number of a particular subscriber but by a general number associated with the common channel, whereby all the slave stations can receive a time message in the clear. To do this, the matter station further includes a time memory 117 having an input connected to the clock 107. Thus the time memory 117 is permanently updated by the clock 107. The use o*
network time as identifying the common channel has several advantages. firstly, slave stations which are already in synchronization with the network can identify the common channel without ambiguity, and can therefore keep in synchronization by listening preferentially or exclusively to said time signals. Secondly, a non-synchronized slave station can use the time signals to get into synchronization, in which case all it has to do it listen on some pattern, ego its own 7 provided there it a high enough probability of interference between its own *requenc~-hopping pattern and the common channel frequency-hopping pattern to. a probability of interference such that two successive interferences between the two channels are likely to occur in less than a tolerable waiting period for establishing synchronization In the master station, the frequenc~-hopping pattern generator 104 thus receives the general number which is I".
,~,,, 13 lo associated with the common channel or a particular identification number associated with a culled caption, depending on whether the second sequencer 116 wish one or another of said numbers to the pattern generator. A switch 118 pe~orm~ the required ewitchin~ junction. likewise the transmitter 101 receive data to be transmitter from the buffer memory 105 or from the time memory 117 pa a witch 119 under the control of the second sequencer 116.
In the slave station the second sequencer 216 control a switch 218 which applies the general number ox the common channel or the reverence number us the station in question to the frequency-hopping pattern venerator 204. At the irrupt interference in the receiver, the receiver clock 207 it forced to the received time by the validating and synchronizing circuit 221. Next time the second sequencers 116 and 216 switch to the general number, the presumed synchronization can be verified. If verification fails, a new search is begun or the time signal.
The presence of a duplex common channel also makes it possible for the slave stations to send signals to the master station In particular the slave stations can send signals requesting that a call be set up. Such a request is transmitted simply by sending the identification number of the calling slave station during a reference burst of the common channel. the ensuing dialog, if any, then takes place on the channel defined by the identification number transmitted by the calling slave station.
If there are several master stations in a network, the system adapts readily to coordinating traffic between the entire group of stations.
To do this, a periodic reference frame defined relative to the common time of the group of networks it defined as follows:
the bursts for sending timing data from each of -the stations as defined by their respective second sequencers 116 are offset in time. Thus, while each master station having a call in progress cannot transmit on the common channel, synchronization is ensured by master stations which are not engaged on calls I,.
transmitting packet ox time data on the common channel. In this way, c ifs from a master elation are not interrupted.
this arrangement not only get rid ox the corresponding intrinsic interference but alto ha the advantage of enabling a elate station which dazzlers to set up a call to select the "but" available matter elation by transmitting its ash request in synchronization with the bet quality received time word, to. in synchronization with the lime Ford having the highest amplitude received idea strength.
By Jay of example, the hollowing numerical values can be used in a radio communication stem in accordance with the invention. The frequency range may be 900 My The frequency oft between transmission and reception may be 45 MHz. the number of frequency channels in the net may be 100, at 50 KHz spacing. Each burst may last 2 millisecond, with a dead time of 1 millisecond between bursts For a continuous input digital data rate of 76 Kbits/aecond, the data rate during each burst it 24 Kbits/~econd~ with 48 bits being transmitted in each burst.
There it little difficulty in storing the frequency-hopping pattern of a subscriber or slave station in memory, however, each master station capable of communicating with any of the subscriber stations must be capable of instantly generating the frequency-hopping pattern of any subscriber. Jo do this it is sufficient for all the patterns to be chosen from the same code family, and to establish a one-to-one relationship between each subscriber number and the corresponding frequency-hopping pattern.
-
Claims (12)
- The embodiments of the invention in which an exclusi-ve property or privilege is claimed are defined as follows:
l. A radio communications system comprising at least one master station and a plurality of slave stations, wherein information to be transmitted between said stations is in digital form, wherein a two-way link between any of said slave stations and a master station is established over a frequency-hopping channel, in which trasnmission takes place in bursts of predetermined duration at different frequencies, with said frequency-hopping channel being determined by a frequency-hopping pattern which is asso-ciated with each slave station, each slave station having an independent frequency-hopping pattern associated there-with and all of said frequency-hopping channels using fre-quencies selected from a pool of frequencies common to all of said channels, and wherein useful transmission bursts are synchronized for the system as a whole with each slave station being synchronized from data received from a master station. - 2. A system according to claim 1, wherein each master station is synchronized on an external time signal common to the entire system.
- 3. A system according to claim 1, wherein said useful transmission bursts are separated by intervals of dead time which are short in duration relative to a duration of the useful bursts, thereby facilitating frequency changing without greatly increasing data rate during transmission and hence without greatly increasing sensitivity to multiple path propagation, all said stations including means for compressing data to be transmitted by a factor equal to a period of time between starts of two successive bursts divided by a period of time of a useful duration of a burst, together with corresponding means for decompressing received data.
- 4. A system according to claim 1, wherein transmission in each frequency-hopping channel is established in fre-quency duplex, with transmission frequencies in one di-rection being determined by the frequency-hopping pattern associated with one slave station and with transmission frequencies in the opposite direction being offset from said transmission frequencies in said one direction by a predetermined fixed frequency value.
- 5. A system according to claim 4, wherein the fixed offset frequency between the two directions of transmission is equal to a receiver intermediate frequency.
- 6. A system according to claim 1, wherein transmission in each frequency-hopping channel is established in time duplex, with transmission in each direction using the same pattern of frequencies.
- 7. A system according to claim 1, wherein transmission in each frequency-hopping channel is established with automatic alternation of transmission direction taking place on the same pattern of frequencies, switching to transmission being under control of a signal activity detector circuit.
- 8. A system according to claim 1, wherein said bursts are of a predetermined duration which is long enough relative to propagation delays between stations to avoid the need for synchronization accuracy to take said propagation delays into account.
- 9. A system according to claim 1, wherein the frequency-hopping pattern associated with a slave station is established in the master station and said slave station involved in a call on the basis of time of transmission and of an identi-fication number associated with said slave station, each station being provided with a pattern generator, and said time of transmission being measured relative to a number of bursts in a cycle whose duration is a function of a number of frequencies available in said common pool of frequencies.
- 10. A system according to claim 1, further including a common signalling channel having its own frequency-hopping pattern associated therewith, said common signal frequency-hopping pattern being available at all of said stations and being switchably selectable via switching means provided at all of said stations, each master station being further provided with a time memory and means for periodically transmitting data contained in said time memory in trans-mission bursts at frequencies determined by said common signal frequency-hopping pattern.
- 11. A system according to claim 10, including a plurality of master stations, and wherein different master stations transmit on said common signalling channel at different instants,
- 12. A system according to claim 1, wherein said system transmits telephony, and wherein each station transmitter is provided with a trasnmitter inhibit circuit connected to turn off a transmitter carrier during periods of silence in between periods of active speech, and wherein each station receiver is provided with means for rejecting interference and interpolating between bursts effectively received from a station with which it is in communication.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| FR8209258A FR2527871B1 (en) | 1982-05-27 | 1982-05-27 | RADIOCOMMUNICATION SYSTEM, FREQUENCY HOPPING |
| FR8209258 | 1982-05-27 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1214215A true CA1214215A (en) | 1986-11-18 |
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| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000428751A Expired CA1214215A (en) | 1982-05-27 | 1983-05-24 | Frequency-hopping radio communications system |
Country Status (8)
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| US (1) | US4554668A (en) |
| EP (1) | EP0095959B1 (en) |
| JP (1) | JPS58219845A (en) |
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| DE (1) | DE3363259D1 (en) |
| DK (1) | DK233783A (en) |
| FR (1) | FR2527871B1 (en) |
| GR (1) | GR77474B (en) |
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-
1982
- 1982-05-27 FR FR8209258A patent/FR2527871B1/en not_active Expired
-
1983
- 1983-05-17 EP EP83400986A patent/EP0095959B1/en not_active Expired
- 1983-05-17 DE DE8383400986T patent/DE3363259D1/en not_active Expired
- 1983-05-20 US US06/496,564 patent/US4554668A/en not_active Expired - Fee Related
- 1983-05-24 CA CA000428751A patent/CA1214215A/en not_active Expired
- 1983-05-25 DK DK233783A patent/DK233783A/en not_active Application Discontinuation
- 1983-05-27 GR GR71481A patent/GR77474B/el unknown
- 1983-05-27 JP JP58093892A patent/JPS58219845A/en active Pending
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| Publication number | Publication date |
|---|---|
| FR2527871B1 (en) | 1986-04-11 |
| DE3363259D1 (en) | 1986-06-05 |
| GR77474B (en) | 1984-09-24 |
| DK233783A (en) | 1983-11-28 |
| JPS58219845A (en) | 1983-12-21 |
| FR2527871A1 (en) | 1983-12-02 |
| DK233783D0 (en) | 1983-05-25 |
| EP0095959A1 (en) | 1983-12-07 |
| EP0095959B1 (en) | 1986-04-30 |
| US4554668A (en) | 1985-11-19 |
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