EP0084967B1 - Radio communication system - Google Patents

Radio communication system Download PDF

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Publication number
EP0084967B1
EP0084967B1 EP83300320A EP83300320A EP0084967B1 EP 0084967 B1 EP0084967 B1 EP 0084967B1 EP 83300320 A EP83300320 A EP 83300320A EP 83300320 A EP83300320 A EP 83300320A EP 0084967 B1 EP0084967 B1 EP 0084967B1
Authority
EP
European Patent Office
Prior art keywords
radio
sequence
frequency
pseudo
sets
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.)
Expired
Application number
EP83300320A
Other languages
German (de)
English (en)
French (fr)
Other versions
EP0084967A3 (en
EP0084967A2 (en
Inventor
Paul Wilkinson Dent
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
BAE Systems Electronics Ltd
Original Assignee
Marconi Co Ltd
Priority date (The priority date 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 date listed.)
Filing date
Publication date
Application filed by Marconi Co Ltd filed Critical Marconi Co Ltd
Priority to AT83300320T priority Critical patent/ATE13789T1/de
Publication of EP0084967A2 publication Critical patent/EP0084967A2/en
Publication of EP0084967A3 publication Critical patent/EP0084967A3/en
Application granted granted Critical
Publication of EP0084967B1 publication Critical patent/EP0084967B1/en
Expired legal-status Critical Current

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Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04K—SECRET COMMUNICATION; JAMMING OF COMMUNICATION
    • H04K1/00—Secret communication
    • H04K1/003—Secret communication by varying carrier frequency at or within predetermined or random intervals

Definitions

  • This invention relates to radio communication apparatus and particularly to such apparatus in which the carrier frequency is changed periodically in an attempt to maintain security and overcome jamming of the radio transmission.
  • Such periodic frequency changing is called hopping.
  • Each radio set in the network may be adapted to operate on a common hop-set according to its own pseudo-random sequence thus giving what is called a random hopping system.
  • statistically predictable interference occurs as a result of random frequency coincidences when two communications are being conducted simultaneously.
  • orthogonal system is one in which both the hop-set and the pseudo-random sequence is common to each radio set in the network. Some means then has to be employed to prevent continuous interference between the channels used in simultaneous communications.
  • An object of the present invention is to provide a random frequency hopping system which permits simultaneous non-interfering conversations in a radio network.
  • a frequency-hopping radio communication system comprises a plurality of radio transmitter/receiver sets having means for changing their operating frequencies periodically, in synchronism, and according to a common main-line pseudo-random channel sequence, each radio set having means for modifying its operating channel sequence to a side track sequence which is dependent upon the point in said main line sequence at which the modification is initiated, and means for transmitting a signal to a selected other radio set to initiate said side track sequence in the receiving radio set at the same instant as in the transmitting radio set, both radio sets being arranged to revert to the main-line channel sequence on termination of transmission.
  • the modification may be effected by a change in a feedback path of a pseudo-random number generator in each radio set which generator determines the operating channel sequence of a radio set.
  • a real time clock 1 steps a random number generator 2 through a pseudo-random number sequence, the output number at any instant being determined by the original number, i.e. the key variable, with which the random number generator was loaded, and the time elapsed since that occurrence.
  • All radio sets in the network are loaded with the same key variable and their clocks are initially synchronised, so that all radio sets will produce the same pseudo-random number sequence in synchronism. There may be a very slight phase drift between the number sequences of the different radio sets if they should run on for a substantial time without communication but this is accommodated as will be seen.
  • Each radio set has a stored table 3 of permitted frequencies, i.e. a large random selection of the total possible channels in the band. This hop-set is again common to all radios of the network.
  • the table 3 is addressed by each multi-digit random number as it arises and the resulting channel frequency identity is applied to a transmitter/receiver radio 14 which is frequency agile and electronically tunable.
  • the operating frequency thus changes periodically and synchronously for all radios of the network in accordance with the number sequence provided by a number generator. This common basic sequence will be referred to as the main-line sequence.
  • the key variable initially loaded into each random number generator 2 can be changed periodically for different networks on a geographical or other basis.
  • the random number generator 2 consists of a shift register with predetermined feedback in known manner.
  • a controllable feedback path 4 which, when effective, changes the pattern generated in a predetermined manner.
  • This feedback path is controlled by a switch 6, the modified number sequence produced by the generator then depending upon the content of the generator when the modification is initiated.
  • a bistable 8 determines the condition of the switch 6, the switch being closed when the bistable is 'set'.
  • an absolute time marker is transmitted, a so-called 'bingo' signal. It is the transmission and reception of this signal which initiates the modification of the random number generator 2 in the transmitting and receiving radios.
  • the bistable 8 has a set input derived by way of an OR-gate 10 from a 'bingo' detector 12 which monitors the signal received by the basic radio 14. Immediately therefore, on reception of the 'bingo' signal the bistable 8 is set, the switch 6 is closed, and a modified random number sequence is generated dependent upon the content of the generator at the instant of switch closure. At the transmitting radio the bistable 8 is set at the same instant by a signal following the synchronising and addressing preamble. This post-transmission synchronising signal is applied by way of the OR-gate 10.
  • Both transmitting and receiving radios are thus modified at the same instant and with the same content in their random number generators.
  • the resulting modified sequences which bear no relation to the main-line sequence, are therefore identical and communication can proceed between these two radios. If, of course, transmission to two or more other radios is required this is easily accommodated, by transmission of the respective addresses on the main line sequence.
  • Figure 2 shows the effect of closure of the switch 6 on the operating frequency sequences.
  • the upper horizontal line indicates the main-line frequency sequence F 5 F, 8 F 6 etc. (a typical part of the sequence), the frequency changes occurring at regular intervals determined by the clock. If, for example radio 1 calls radio 2, and the 'bingo' signal arises at the instant of the main-line change to F 4 , then a sidetrack sequence will occur in radios 1 and 2 having typical frequencies F 15 F 10 F 3 etc. as shown. These latter changes will occur in synchronism with the main-line changes F 1 F 3 F 10 etc. Radios 1 and 2 will then operate on the modified or sidetrack sequence while the remainder of the radios in the network carry on passively on the main-line sequence.
  • radio 3 should call radio 4 and emit a 'bingo' signal at F 12 in the main-line sequence then the content of the random number generators of radios 3 and 4 will at that instant be different from the content of the generators of radios 1 and 2 and consequently a new sidetrack sequence will arise for the operation of radios 3 and 4. No interference between the two communications will arise other than the predictable statistical coincidence of frequencies.
  • an 'end-of- message' code is transmitted, which is detected by a detector 16.
  • An output from the detector 16 resets the bistable 8 by way of an OR-gate 18, the switch 6 opens, and the generator 2 reverts to the production of the main-line sequence in the same phase as if it had not been interrupted.
  • a transmit key input 20 also serves to reset the bistable 8 by way of OR-gate 18 to ensure that on transmission the radio is operating on the main-line sequence i.e. on which all other (passive) radios are listening for their address code.
  • the system described has the significant feature, in contrast with fixed frequency radio systems, that an ongoing selective communication does not prevent the rest of the net communicating, or setting up selective calls of their own, since the sequence of frequencies used to set up calls, the main line sequence, is unrelated to the sequence of frequencies used for the message, the sidetrack sequence. Furthermore, there are as many different sidetrack sequences as there are points of departure from the main line sequence, the only limiting factor to their use being the acceptability of interference caused by the statistical probability that two or more sequences will alight on the same frequency at the same time.
  • the system makes this virtually impossible. If the captured radio is switched permanently to 'transmit' in an attempt to jam, it will, after the short initial preamble, switch to the sidetrack sequence of frequencies which will then not interfere with any other transmission. Even if a receiver is addressed, and follows the spurious transmission, the operator can, upon determining that the message is of not value, switch the receiver back to the main line by pressing the transmit switch 20 momentarily.
  • the main-line sequence could be rendered unavailable to a large extent by constantly switching a captured radio between transmit and receive.
  • Software or hardware traps may be built into the radio to prevent a captured radio being switched in this way. Such a trap may for instance cause erasure of the key variable upon detection of such behaviour.
  • a captured radio may, of course, be modified by the enemy to bypass these traps; but that would involve laboratory work, and by the time the radio was returned to the field, the key variable would no longer be current. It may also be made extremely difficult to extract the key variable from one radio in order to transfer it to a modified radio.
  • retransmission is often employed, whereby the signal is received from the initiating transmitter on one frequency, and relayed on another frequency.
  • Two conventional radio sets may be connected back-to-back to provide such an automatic relay station, as illustrated diagrammatically in Figure 3.
  • single frequency simplex is used on each leg of the path, and the relaying transmitter is keyed only when the receiver detects the presence of a valid signal. Since the two legs of the relay path must be on different frequencies to provide adequate isolation between the co-sited transmitter and receiver, the frequency on which a receiving station should best listen depends on its geographical position, i.e., whether it is nearer to the initiating station or the appropriate relay site.
  • a mobile station may have to change frequency according to position.
  • the relay station may comprise two radio sets B and C each as aforesaid but modified in that set B is made receptive to all transmission irrespective of address, any valid transmission so received on the main line sequence causing conversion to a sidetrack sequence at the BINGO code reception.
  • the first radio link in the relay process i.e. between the originating station A and the relay station B/C is then operated on a first side track sequence.
  • the transmitting set C of the relay station is caused to initiate re-transmission on the main line sequence, of the synchronising and address preamble, the address being that of the out-station D, relayed from the originating station A.
  • both set C and out-station set D switch to a side- track sequence which is different from that in operation between the AB link since it arises at a later time. There is again, therefore, no interference between the AB transmission and the CD transmission.
  • the mobile radio set D will lock onto the first synchronisation preamble which is receives successfully whether from the initiating station A or the relay station B/C. As it moves out of range of one relay site and into the coverage zone of another, no action is thus required by the operator to pick up the new relay link.

Landscapes

  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Mobile Radio Communication Systems (AREA)
  • Reduction Or Emphasis Of Bandwidth Of Signals (AREA)
  • Input Circuits Of Receivers And Coupling Of Receivers And Audio Equipment (AREA)
  • Radio Relay Systems (AREA)
EP83300320A 1982-01-27 1983-01-21 Radio communication system Expired EP0084967B1 (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AT83300320T ATE13789T1 (de) 1982-01-27 1983-01-21 Funkverbindungssystem.

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB8202357 1982-01-27
GB8202357 1982-01-27

Publications (3)

Publication Number Publication Date
EP0084967A2 EP0084967A2 (en) 1983-08-03
EP0084967A3 EP0084967A3 (en) 1983-08-10
EP0084967B1 true EP0084967B1 (en) 1985-06-12

Family

ID=10527920

Family Applications (1)

Application Number Title Priority Date Filing Date
EP83300320A Expired EP0084967B1 (en) 1982-01-27 1983-01-21 Radio communication system

Country Status (7)

Country Link
EP (1) EP0084967B1 (enrdf_load_stackoverflow)
JP (1) JPS58161438A (enrdf_load_stackoverflow)
AT (1) ATE13789T1 (enrdf_load_stackoverflow)
AU (1) AU553652B2 (enrdf_load_stackoverflow)
DE (1) DE3360246D1 (enrdf_load_stackoverflow)
GB (1) GB2114402B (enrdf_load_stackoverflow)
IN (1) IN159180B (enrdf_load_stackoverflow)

Families Citing this family (17)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2129655B (en) * 1982-09-08 1986-02-05 Racal Res Ltd Improvements in and relating to radio communications
IL82561A (en) * 1986-05-27 1991-12-15 Fairchild Weston Systems Inc Secure communication system for multiple remote units
US5056108A (en) * 1990-04-04 1991-10-08 Van Metre Lund Communication system
US5561686A (en) * 1991-08-23 1996-10-01 Kabushiki Kaisha Toshiba Radio information communication system using multi-carrier spread spectrum transmission system
CN1088035A (zh) * 1992-04-15 1994-06-15 客运电迅传送有限公司 信号分配系统
US5533046A (en) * 1992-10-08 1996-07-02 Lund; Vanmetre Spread spectrum communication system
US5809417A (en) * 1994-07-05 1998-09-15 Lucent Technologies Inc. Cordless telephone arranged for operating with multiple portable units in a frequency hopping system
US5463659A (en) * 1994-07-05 1995-10-31 At&T Ipm Corp. Apparatus and method of configuring a cordless telephone for operating in a frequency hopping system
GB9508885D0 (en) * 1995-05-02 1995-06-21 Plessey Semiconductors Ltd Wireless local area networks
GB2300547B (en) * 1995-05-02 1999-08-25 Plessey Semiconductors Ltd Wireless local area neworks
GB9513398D0 (en) * 1995-06-30 1995-09-27 Boateng Jacob K Automatic exchangeless universal radio phone
CA2300064A1 (en) * 1997-08-14 1999-02-25 Siemens Aktiengesellschaft Method and device for generating a random number sequence for carrier frequencies of a mobile radio transmission
CA2335302A1 (en) * 1998-06-18 1999-12-23 Siemens Aktiengesellschaft Method and apparatus for converting a random number sequence into carrier frequencies for a mobile radiotelephone transmission
US8069468B1 (en) * 2000-04-18 2011-11-29 Oracle America, Inc. Controlling access to information over a multiband network
US20220395193A1 (en) * 2019-06-26 2022-12-15 Nec Corporation Height estimation apparatus, height estimation method, and non-transitory computer readable medium storing program
US20240087353A1 (en) * 2019-10-31 2024-03-14 Nec Corporation Image processing apparatus, image processing method, and non-transitory computer readable medium storing image processing program
JP7355674B2 (ja) 2020-02-18 2023-10-03 株式会社日立製作所 映像監視システムおよび映像監視方法

Family Cites Families (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CH499931A (de) * 1968-02-12 1970-11-30 Patelhold Patentverwertung Synchronisierverfahren für programmgesteuerte Trägerumtastung
DE1939975A1 (de) * 1969-08-06 1971-02-18 Licentia Gmbh System zur UEbertragung von binaercodierten Nachrichten
DE2457027B2 (de) * 1974-12-03 1977-02-03 Licentia Patent-Verwaltungs-Gmbh, 6000 Frankfurt Verfahren zum programmieren von anordnungen zum erzeugen zufallsaehnlicher binaerzeichenfolgen

Also Published As

Publication number Publication date
JPS58161438A (ja) 1983-09-26
EP0084967A3 (en) 1983-08-10
GB2114402A (en) 1983-08-17
JPH0234499B2 (enrdf_load_stackoverflow) 1990-08-03
AU553652B2 (en) 1986-07-24
GB2114402B (en) 1985-06-05
EP0084967A2 (en) 1983-08-03
DE3360246D1 (en) 1985-07-18
ATE13789T1 (de) 1985-06-15
AU1062383A (en) 1983-08-04
IN159180B (enrdf_load_stackoverflow) 1987-04-04

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