Time division duplex telecommunication system

• US 5,416,779 A
• Filed: 07/13/1994
• Issued: 05/16/1995
• Est. Priority Date: 01/27/1989
• Status: Expired due to Fees

• Current Assignee: Shaye Communications Ltd (AT&T, Inc.), NT Corporation (Brunswick Corporation), British Telecommunications PLC (BT Group PLC), Ferranti Creditphone Limited, GEC Plessey Telecommunications Limited, GPT Ltd., Kenwood Corporation (JVC Kenwood Corporation), Kc, Lucent Technologies Wireless Limited Capital House (Nokia Corporation), Northern Telecom Limited (Nortel Networks Corporation), Orbitel Mobile Communications Ltd., Phonepoint Limited, Mercury Communications Ltd. (Siemens AG), The Courtyard Co.
• Original Assignee: British Telecommunications PLC (BT Group PLC), GPT Ltd., Kenwood Corporation (JVC Kenwood Corporation), AT&T Wireless Communications Products Ltd. (Nokia Corporation), Northern Telecom Limited (Nortel Networks Corporation), Orbitel Mobile Communications Ltd.
• Inventors: Rodgers, Ian, Dudek, Michael T., Proctor, Peter N., Bidwell, Brian A., Goodings, Rupert, Barnes, Nigel E., Crisp, Malcolm, Odhams, David C., Bud, Andrew
• Primary Examiner(s): Olms, Douglas W.
• Assistant Examiner(s): TON, DANG T
• Application Number:
  US08/274,581
• Time in Patent Office: 307 Days
• Field of Search: 370/95.1, 370/24, 370/110.1, 370/109, 370/105.4, 370/105.5, 370/106, 370/24, 370/31, 370/95.2, 370/95.3, 379/61, 379/63, 379/58, 379/59, 379/60, 455/14, 455/15, 455/5.1, 455/33.1, 455/33.2, 455/49.1, 455/51.1, 455/53.1, 455/54.1, 455/56.1, 455/73, 455/78, 455/88, 371/5.4, 371/5.5, 371/47.1, 371/441, 371/45, 371/43
• US Class Current: 370/280
• CPC Class Codes: H04L 7/041 using special codes as synchronising signal
• CPC Class Codes: H04M 1/72505 Radio link set-up procedures
• CPC Class Codes: H04M 1/733 with a plurality of base stations connected to a plurality of lines for selection in cordless PBX H04W84/16

Abstract

A communication procedure suitable for a cordless telephone system involves time division duplex radio communication between a handset 11 and a base station 3 using alternating bursts of transmission over a single radio channel. Once a radio link has been set up, initial transmissions carry a synchronisation logical channel S and a signalling logical channel D multiplexed together, but the link may switch to bursts carrying a communications logical channel B for the speech data and the signalling logical channel D. Burst synchronisation is achieved by the asynchronous detection of words in a synchronisation channel S. These words have bit patterns reducing the probability of incorrect asynchronous detection of them. If one part ceases to receive handset signals from the other, it transmits a special signal, informing the other part. This enables both parts to detect the failure of a link at substantially the same time, so that their actions to re-establish the link are synchronised.

Claims

1. A telecommunication system, comprising:

first and second devices having communication means for providing time-division two-way communication between said devices over a radio channel by exchanging radio signals in alternating bursts carrying digital data, such that during the time-division two-way communication, transmission of one of said alternating bursts from one of the first and second devices is completed before transmission of the next of said alternating bursts by the other of the first and second devices is begun;

burst producing means in each of said devices for producing at least some of said alternating bursts in a predetermined format such that each burst in said predetermined format comprises digital data for a first logical channel (D) and digital data for a second logical channel (B) at different times in the burst in said predetermined format, the digital data of the first logical channel (D) including error detection codes; and

each of said devices having means for using said error detection codes to detect errors in the first logical channel (D) in bursts received by the respective one of said devices, and for using said errors detected in the first logical channel (D) as an indication of the quality of transmission of the second logical channel (B).

2. A system according to claim 1 wherein said burst producing means produces at least some of which comprise digital data for the first logical channel (D) followed by digital data for the second logical channel (B) followed by digital data for the first logical channel (D).

3. A method of telecommunication in which first and second devices communicate with each other, comprising the steps of:

performing time-division two-way communication between said devices over a radio channel by exchanging radio signals in alternating bursts carrying digital data, such that during t he time-division two-way communication, transmission of one of said alternating bursts from one of the first and second devices is completed before transmission of the next of said alternating bursts by the other of the first and second devices in begun;

producing at least some of said alternating bursts in a predetermined format such that each burst in said predetermined format comprises digital data for a first logical channel (D) and digital data for a second logical channel (B) at different times in the burst in said predetermined format, the digital data of the first logical channel (D) including error detection codes; and

using, in each of said devices, said error detection codes to detect errors in the first logical channel (D) in bursts received by the respective one of said devices; and

using said errors detected in the first logical channel (D) as an indication of the quality of transmission of the second logical channel (B).

4. A method according to claim 3, wherein said step of producing at least some of said alternating bursts comprises producing bursts at least some of which comprise digital data for the first logical channel (D) followed by digital data for the second logical channel (B) followed by digital data for said first logical channel (D).

5. A telecommunication system, comprising:

first and second devices having communication means for providing time-division two-way communication between said devices over a radio channel by exchanging radio signals in alternating bursts carrying digital data, such that during the time-division two-way communication, transmission of one of said alternating bursts from one of the first and second devices is completed before transmission of the next of said alternating bursts by the other of the first and second devices is begun;

means in each of the first and second devices for repeatedly sending one of a pre-set group of signal codes while they are exchanging said radio signals, such repetition being at a rate such that the period, beginning with a transmission by either one of the pre-set group of signal codes and ending with the next transmission by said one of said first and second devices of any one of the pre-set group of signal codes, does not exceed a first predetermined length of time, and at a time when one of said first and second devices sends one of said pre-set groups of signal codes, a first code of said pre-set group of signal codes normally being sent if said one of said first and second devices has received any of said pre-set group of signal codes within the first predetermined length of time before said time when said one device sends one of said pre-set group of signal codes and a second code of said pre-set group of signal codes normally being sent otherwise; and

means for controlling each of the first and second devices such that if either of said first and second devices has not received said first code for a second predetermined length of time greater than the first predetermined length of time, said one of said first and second devices which has not received said first code enters a mode for causing re-establishment of the time-deviation two-way communication,

wherein re-establishment of the time-division two-way communication is a procedure following a period of said time-division two-way communication for bringing the first and second devices, without relying on the existence of said time-division two-way communication at the time the procedure is initiated, to a state in which (i) each of the first and second devices has synchronized its decoding of received said alternating bursts with the ones of said alternating bursts received from the other of the first and second devices; and

(ii) each of the first and second devices has transmitted a signal and has received from the other of the first and second devices a reply to the transmitted signal to enable the respective one of said first and second devices to confirm that the other of the first and second devices received the signal, whereby the first and second devices are enabled to communicate with each other in said time-division two-way communication by exchanging radio signals in said alternating bursts, and one of said first and second devices has transmitted a signal to the other of said first and second devices identifying the period of said time-division two-way communication following the procedure as a continuation of a period of said time-division two-way communication before the procedure.

6. A method of telecommunication in which first and second devices communicate with each other, comprising the steps of:

performing time-division two-way communication between said devices over a radio channel by exchanging radio signals in alternating bursts carrying digital data, such that during the time-division two-way communication, transmission of one of said alternating bursts from one of the first and second devices is completed before transmission of the next of said alternating bursts by the other of the first and second devices is begun;

each of the first and second devices repeatedly sending one of a pre-set group of signal codes while they are exchanging said radio signals, such repetition being at a rate such that the period, beginning with a transmission by either one of the pre-set group of signal codes and ending with the next transmission by said one of said first and second devices of any one of the pre-set group of signal codes, does not exceed a first predetermined length of time, and at a time when one of said first and second devices sends one of said pre-set groups of signal codes, a first code of said pre-set group of signal codes normally being sent if said one of said first and second devices has received any of said pre-set group of signal codes within the first predetermined length of time before said time when said one device sends one of said pre-set groups of signal codes and a second code of said pre-set group of signal codes normally being sent otherwise, and

controlling each of the first and second devices such that if either of said first and second devices has not received said first code for a second predetermined length of time greater than the first predetermined length of time, said one of said first and second devices which has not received said first code enters a mode for causing re-establishment of the time-division two-way communication,

wherein re-establishment of the time-division two-way communication is a procedure following a period of said time-division two-way communication for bringing the first and second devices, without relying on the existence of said time-division two-way communication at the time the procedure is initiated, to a state in which (i) each of the first and second devices has synchronized its decoding of received said alternating bursts with the ones of said alternating bursts received from the other of the first and second devices; and

(ii) each of the first and second devices has transmitted a signal and has received from the other of the first and second devices a reply to the transmitted signal to enable the respective one of said first and second devices to confirm that the other of the first and second devices received the signal, whereby the first and second devices are enabled to communicate with each other in said time-division two-way communication by exchanging radio signals in said alternating bursts, and one of said first and second devices has transmitted a signal to the other of said first and second devices identifying the period of said time-division two-way communication following the procedure as a continuation of a period of said time-division two-way communication before the procedure.

7. A telecommunication system, comprising:

a remote unit having communication means capable of time-division two-way communication with a base station over a radio channel by exchanging radio signals in alternating bursts carrying digital data, such that during the time-division two-way communication, transmission of one of said alternating bursts from one of the remote unit and the base station is completed before transmission of the next of said alternating bursts by the other of the remote unit and the base station is begun, to enable the remote unit to communicate via the base station with a further device;

means in the remote unit for instructing re-establishment of the time-division two way communication; and

means in the base station for instructing re-establishment of the time-division two-way communication,

wherein re-establishment of the time-division two-way communication is a procedure following a period of said time-division two-way communication for bringing the remote unit and the base station, without relying on the existence of said time-division two-way communication at the time the procedure is initiated, to a state in which (i) each of the remote unit and the base station has synchronized its decoding of received said alternating bursts with the ones of said alternating bursts received from the other of the remote unit and the base station; and

(ii) each of the remote unit and the base station has transmitted a signal and has received from the other of the remote unit and the base station a reply to the transmitted signal to enable the respective one of the remote unit and the base station to confirm that the other of the remote unit and the base station received the signal, whereby the remote unit and base station are enabled to communicate with each other in said time-division two-way communication by exchanging radio signals in said alternating bursts, and the remote unit has transmitted a link continuation signal to the base station identifying the period of said time-division two-way communication following the procedure as a continuation of a period of said time-division two-way communication before the procedure,

the telecommunication system also comprising;

responsive means which is responsive to the instructing means in said remote unit and to the instructing means in said base station to cause the remote unit to transmit radio signals to initiate said re-establishment.

8. A system according to claim 7 wherein said communication means of said remote unit is capable of said time-division two-way communication with a plurality of base stations, and

wherein said responsive means causes said re-establishment to take place between said remote unit and one of said plurality of base stations which is not necessarily the base station with which the remote unit was in communication during said period of said time-division two-way communication before the procedure.

9. A system according to claim 7 or claim 8 wherein said responsive means causes the remote unit to transmit radio signals to initiate said re-establishment which comprise radio signals transmitted by the remote unit to initiate the establishment of said time-division two-way communication when the remote unit has not been in said time-division two-way communication immediately beforehand, modified so as to include as said link continuation signal a signal identifying the period of said time-division two-way communication before the procedure,

wherein establishment of the time-division two-way communication is a procedure for bringing the remote unit and the base station, without relying on the existence of said time-division two-way communication at the time the procedure is initiated, to a state in which (i) each of the remote unit and the base station has synchronized its decoding of received said alternating bursts with the ones of said alternating bursts received from the other of the remote unit and the base station;

and (ii) each of the remote unit and the base station has transmitted a signal and has received from the other of the remote unit and the base station a reply to the transmitted signal to enable the respective one of the remote unit and the base station to confirm that the other of the remote unit and the base station are enabled to communicate with each other in said time-division two-way communication by exchanging radio signals in said alternating bursts.

10. A method of telecommunication in which a remote unit and a base station are in communication with each other, comprising the steps of:

performing time-division two-way communication between a remote unit and a base station over a radio channel by exchanging radio signals in alternating bursts carrying digital data, such that during the time-division two-way communication, transmission of one of said alternating bursts from one of the remote unit and the base station is completed before transmission of the next of said alternating bursts by the other of the remote unit and the base station is begun, to enable the remote unit to communicate via the base station with a further device;

determining when the remote unit or the base station with which the remote unit is in said time-division two-way communication requires re-establishment of the time-division two-way communication; and

in response to a determination made in said determining step that either of the base station and remote unit requires re-establishment of the time-division two-way communication, causing the remote unit to transmit radio signals to initiate said re-establishment,

wherein re-establishment of the time-division two-way communication is a procedure following a period of said time-division two-way communication for bringing the remote unit and the base station, without relying on the existence of said time-division two-way communication at the time the procedure is initiated, to a state in which (i) each of the remote unit and the base station has synchronized its decoding of said received said alternating bursts with the ones of said alternating bursts received from the other of the remote unit and the base station; and

(ii) each of the remote unit and the base station has transmitted a signal and has received from the other of the remote unit and the base station a reply to the transmitted signal to enable the respective one of the remote unit and the base station to confirm that the other of the remote unit and the base station received the signal, whereby the remote unit and base station are enabled to communicate with each other in said time-division two-way communication by exchanging radio signals in said alternating bursts, and the remote unit has transmitted a link continuation signal to the base station identifying the period of said time-division two-way communication following the procedure as a continuation of a period of said time-division two-way communication before the procedure.

11. A method according to claim 10, wherein said step of performing communication between a remote unit and a base station is performed with a remote unit capable of communication with a plurality of base stations, and wherein the step of causing re-establishment to be initiated causes re-establishment to take place between said remote unit and a base station from said plurality of base stations which is not necessarily the base station with which the remote unit was previously in said communication during said period of said time-division two-way communication before the procedure.

12. A method according to claim 10 or claim 11, wherein said step of causing initiation of re-establishment comprises transmitting radio signals by the remote unit to initiate said re-establishment which comprise radio signals transmitted by the remote unit to initiate the establishment of said time-division two-way communication when the remote unit has not been in said time-division two-way communication immediately beforehand, modified so as to include as said link continuation signal a signal identifying the period of said time-division two-way communication before the procedure,

wherein establishment of the time-division two-way communication is a procedure for bringing the remote unit and the base station, without relying on the existence of said time-division two-way communication at the time the procedure is initiated, to a state in which (i) each of the remote unit and the base station has synchronized its decoding of received said alternating bursts with the ones of said alternating bursts received from the other of the remote unit and the base station;

and (ii) each of the remote unit and the base station has transmitted a signal and has received from the other of the remote unit and the base station a reply to the transmitted signal to enable the respective one of the remote unit and the base station to confirm that the other of the remote unit and the base station received the signal, whereby the remote unit and base station are enabled to communicate with each other in said time-division two-way communication by exchanging radio signals in said alternating bursts.

13. A telecommunication system, comprising:

first and second devices having communication means for providing time-division two-way communication between said devices over a radio channel by exchanging radio signals in alternating bursts carrying digital data, such that during the time-division two-way communication, transmission of one of said alternating bursts from one of the first and second devices is completed before transmission of the next of said alternating bursts by the other of the first and second devices is begun;

means in each of said devices for producing said alternating bursts such that at least some of the information communicated between the devices over a first logical channel (D) is arranged in words which include an error detection code and an information portion for carrying said information; and

means in each of said devices to arrange a predetermined word for communication between the devices over said first logical channel, said predetermined word including an error detection code and an information portion comprising data sequence which does not communicate any information from the one of said first and second devices which is transmitting to the other of said first and second devices which is receiving.

14. A system according to claim 13, wherein said producing means produces said alternating bursts such that communication of at least some of said words over said first logical channel is preceded by communication of a set pattern over said first logical channel, said set pattern indicating the timing in said first logical channel of a word which is preceded in the first logical channel by the set pattern, and no part of said predetermined word comprising said set pattern.

15. A method of telecommunication in which first and second devices communicate with each other, comprising the steps of:

performing time-division two-way communication between said devices over a radio channel by exchanging radio signals in alternating bursts carrying digital data, such that during the time-division two-way communication, transmission of one of said alternating bursts from one of the first and second devices is completed before transmission of the next of said alternating bursts by the other of the first and second devices is begun;

producing said alternating bursts such that at least some of the information communicated between the devices over a first logical channel (D) is arranged in words which include an error detection code and an information portion for carrying said information; and

arranging a predetermined word for communication between the devices over said first logical channel, said predetermined word including an error detection code and an information portion comprising a data sequence which does not communicate any information from the one of said first and second devices which is transmitting to the other of said first and second devices which is receiving.

16. A method according to claim 15, wherein said step of producing bursts includes preceding communication of at least some of said words over said first logical channel by communication of a set pattern over said first logical channel, said set pattern indicating the timing in the first logical channel of a word which is preceded in the first logical channel by the set pattern, and no part of said predetermined word comprising said set pattern.

17. A telecommunication system, comprising:

first and second devices having communication means for providing time-division two-way communication between said devices over a radio channel by exchanging radio signals in alternating bursts carrying digital data, such that during the time-division two-way communication, transmission of one of said alternating bursts from one of the first and second devices is completed before transmission of the next of said alternating bursts by the other of the first and second devices is begun;

means in each of said devices for producing said alternating bursts such that at least some of the information communicated between the devices over a first logical channel (D) is arranged in words, and communication of at least some of said words over said first logical channel is preceded by communication over the first logical channel of a set pattern indicating the timing in said first logical channel of a word which is preceded in the first logical channel by the set pattern;

means in each of said devices for transmitting over said first logical channel, in between repetitions of a word preceded by communication of said set pattern, either a different word preceded by said set pattern or a predefined sequence which does not include said set pattern such that if said repeated word includes said set pattern and the one of said first and second devices which receives said repeated word incorrectly identifies said set pattern in an occurrence of said repeated word as an occurrence of said set pattern preceding a word, said repeated word is repeated sufficiently infrequently to allow said one of the first and second devices to identify said set pattern correctly in the communication of the set pattern before the next communication of the repeated word.

18. A method of telecommunication in which first and second devices communicate with each other, comprising the steps of:

performing time-division two-way communication between said devices over a radio channel by exchanging radio signals in alternating bursts carrying digital data, such that during the time-division two-way communication, transmission of one of said alternating bursts from one of the first and second devices is completed before transmission of the next of said alternating bursts by the other of the first and second devices is begun;

producing said alternating bursts such that at least some of the information communicated between the devices over a first logical channel (D) is arranged in words, and communication of at least some of said words over said first logical channel is preceded by communication over the first logical channel of a set pattern indicating the timing in said first logical channel of a word which is preceded in the first logical channel by the set pattern; and

transmitting over said first logical channel, in between repetitions of a word preceded by transmissions of said set pattern, either a different word preceded by said set pattern or a predefined sequence which does not include said set pattern such that if said repeated word includes said set pattern and the one of said first and second devices which receives said repeated word incorrectly identifies said set pattern in an occurrence of said repeated word as an occurrence of said set pattern preceding a word, said repeated word is repeated sufficiently infrequently to allow said one of said first and second devices to identify said set pattern correctly in the communication of the set pattern before the next communication of the repeated word.

19. A telecommunication device for establishing synchronous time-division two-way communication with an other device over a radio channel by exchanging radio signals in alternating bursts carrying digital data such that, during the time-division two-way communication, reception of one of said alternating bursts from said other device is completed before transmission of the next of said alternating bursts by said telecommunication device is begun,

said telecommunication device comprising:

means for producing at least some of said alternating bursts in a predetermined format such that each burst in said predetermined format comprises digital data for a first logical channel (D) and digital data for a second logical channel (B) at different times in the first in said predetermined format, the digital data of the first logical channel (D) including error detection codes; and

means for using said error detection codes to detect errors in the first logical channel (D) in bursts received by the telecommunication device, and for using said errors in the first logical channel (D) as an indication of the quality of transmission of the second logical channel (B).

20. A telecommunication device for establishing time-division two-way communication with an other device over a radio channel by exchanging radio signals in alternating bursts carrying digital data such that, during the time-division two-way communication, reception of one of said alternating bursts from said other device is completed before transmission of the next of said alternating bursts by said telecommunication device is begun,

said telecommunication device comprising:

means for repeatedly sending one of a pre-set group of signal codes while the telecommunication device is exchanging said radio signals with said other device, such repetition being at a rate such that the period, beginning with a transmission by the telecommunication device of any one of said pre-set group of signal codes and ending with the next transmission by the telecommunication device of any one of said pre-set group of signal codes does not exceed a first predetermined length of time, and at a time when said telecommunication device sends one of said pre-set group of signal codes a first code of said pre-set group of signal codes normally being sent if the telecommunication device has received any of said pre-set group of signal codes within the first predetermined length of time before said time when said telecommunication device sends one of said pre-set group of signal codes and a second code of said pre-set group of signal codes normally being sent otherwise; and

means for controlling the telecommunication device to cause it to enter a mode for causing re-establishment of the time-division two-way communication if it has not received said first code for a second predetermined length of time greater than the first predetermined length of time,

wherein re-establishment of the time-division two-way communication is a procedure following a period of said time-division two-way communication for bringing said telecommunication device and said other device, without relying on the existence of said time-division two-way communication at the time the procedure is initiated, to a state in which (i) each of said telecommunication device and said other device has synchronized its decoding of received said alternating bursts with the ones of said alternating bursts received from the other of said telecommunication device and said other device; and

(ii) each of said telecommunication device and said other device has transmitted a signal and has received from the other of said telecommunication device and said other device a reply to the transmitted signal to enable the respective one of said telecommunication device and said other device to confirm that the other of said telecommunication device and said other device received the signal, whereby said telecommunication device and said other device are enabled to communicate with each other in said time-division two-way communication by exchanging radio signals in said alternating bursts, and one of said telecommunication device and said other device has transmitted a signal to the other of said telecommunication device and said other device identifying the period of time-division two-way communication following the procedure as a continuation of a period of said time-division two-way communication before the procedure.

21. A telecommunication remote unit for establishing time-division two-way communication with a base unit over a radio channel by exchanging radio signals in alternating bursts carrying digital data such that, during the time-division two-way communication, reception of one of said alternating bursts from said base unit is completed before transmission of the next of said alternating bursts by said remote unit is begun, to enable said remote unit to communicate via the base unit with a further device,

said remote unit comprising:

decision means for decoding when to cause re-establishment of the time-division two-way communication wherein re-establishment of the time-division two-way communication is a procedure following a period of said time-division two-way communication for bringing the remote unit and the base unit, without relying on the existence of said time-division two-way communication at the time the procedure is initiated, to a state in which (i) each of the remote unit and the base unit has synchronized its decoding of received said alternating bursts with the ones of said alternating bursts received from the other of the remote unit and the base unit; and

(ii) each of the remote unit and the base unit has transmitted a signal and has received from the other of the remote unit and the base unit a reply to the transmitted signal to enable the respective one of the remote unit and the base unit to confirm that the other of the remote unit and base unit received the signal, whereby the remote unit and base unit are enabled to communicate with each other in said time-division two-way communication by exchanging radio signals in said alternating bursts, and the remote unit has transmitted a link continuation signal to the base unit identifying the period of said time-division two-way communication following the procedure as a continuation of a period of said time-division two-way communication before the procedure,

said remote unit also comprising;

means responsive to said decision means for causing the remote unit to transmit radio signals to initiate said re-establishment.

22. A telecommunication base unit for establishing time-division two-way communication with a remote unit over a radio channel by exchanging radio signals in alternating bursts carrying digital data such that, during the time-division two-way communication, reception of one of said alternating bursts from said remote unit is completed before transmission of the next of said alternating bursts by said base unit is begun, to enable said remote unit to communicate via the base unit with a further device,

said base unit comprising:

decision means for deciding when the cause re-establishment of the time-division two-way communication,

wherein re-establishment of the time-division two-way communication is a procedure following a period of said time-division two-way communication for bringing the remote unit and the base unit, without relying on the existence of said time-division two-way communication at the time the procedure is initiated, to a state in which (i) each of the remote unit and the base unit has synchronized its decoding of received said alternating bursts with the ones of said alternating bursts received from the other of the remote unit and the base unit; and

(ii) each of the remote unit and the base unit has transmitted a signal and has received from the other of the remote unit and the base unit a reply to the transmitted signal to enable the respective one of the remote unit and the base unit to confirm that the other of the remote unit and the base unit received the signal, whereby the remote unit and base unit are enabled to communicate with each other in said time-division two-way communication by exchanging radio signals in said alternating bursts, and the remote unit has transmitted a link continuation signal to the base unit identifying the period of said time-division two-way communication following the procedure as a continuation of a period of said time-division two-way communication before the procedure,

said remote unit also comprising;

means responsive to said decision means for causing the remote unit to transmit radio signals to initiate said re-establishment.

23. A telecommunication device for establishing time-division two-way communication with an other device over a radio channel by exchanging radio signals in alternating bursts carrying digital data such that, during the time-division two-way communication, reception of one of said alternating bursts from said other device is completed before transmission of the next of said alternating bursts by said telecommunication device is begun,

said telecommunication device comprising:

means for producing said alternating bursts such that at least some of the information communicated from the telecommunication device to said other device over a first logical channel (D) is communicated in words which include an error detection code and an information portion for carrying said information; and

means to arrange a predetermined word for communication from the telecommunication device to said other device over said first logical channel, said predetermined word including an error detection code and an information portion comprising a data sequence which does not communicate any information from the telecommunication device to said other device.

24. A telecommunication device for establishing time-division two-way communication with an other device over a radio channel by exchanging radio signals in alternating bursts carrying digital data such that, during the time-division two-way communication, reception of one of said alternating bursts from said other device is completed before transmission of the next of said alternating bursts by said telecommunication device is begun,

said telecommunication device comprising:

means for producing said alternating bursts such that at least some of the information communicated from the telecommunication device to said other device over a first logical channel (D) is communicated in words, and communication of at least some of said words over said logical channel is preceded by communication over the first logical channel (D) of a set pattern indicating the timing in the first logical channel of a word which is preceded in the first logical channel by the set pattern; and

means for transmitting over said first logical channel, in between repetitions of a word preceded by communication of said set pattern, either a different word preceded by said set pattern or a predefined sequence which does not include said set pattern such that if said repeated word includes said set pattern and said other device incorrectly identifies said set pattern in an occurrence of said repeated word as an occurrence of said set pattern preceding a word, said repeated word is repeated sufficiently infrequently to allow said other device to identify said set pattern correctly in the communication of the set pattern before the next communication of the repeated word.