Spectrally efficient TDM duplex communication system

• US 5,001,703 A
• Filed: 01/23/1989
• Issued: 03/19/1991
• Est. Priority Date: 01/23/1989
• Status: Expired due to Fees

• Current Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: Johnson, Brian K. A., Patsiokas, Stelios J.
• Primary Examiner(s): Olms, Douglas W.
• Assistant Examiner(s): Jung, Min
• Application Number:
  US07/300,993
• Time in Patent Office: 785 Days
• Field of Search: 370/79, 370/24, 370/26, 370/29, 370/32, 370/95, 370/84
• US Class Current: 370/280
• CPC Class Codes: H04J 3/1688 the demands of the users being taken into account after redundancy removal, e.g. by predictive coding, by variable sampling reducing bandwidth of signals in general H04B1/66; in PCM-systems H04B14/046; removal of redundancy in telegraph communication H03M7/30
• CPC Class Codes: H04L 5/1484 operating bytewise

Abstract

An improved duplex time division multiplexed (TDM) communication system is provided while conserving spectrum and efficiency. To accommodate two voice signals on one channel, the time allocated in a channel for brief listener voice acknowledgements is short; the time allocated for talker transmission is long. Moreover, the coding rate for the listener is slower than for the talker. The slot allocation can be switched whereby whoever is the dominant talker will maintain the longer slot.

Claims

1. A method for communication between at least a first unit and a second unit via a time division multiplexed communciation channel, comprising the steps of:

(a) transmitting an information signal from said first unit to at least said second unit in a first slot encoded at a first rate allocated to said first unit, said first slot having a first duration;

(b) detecting by said first unit an information signal from said second unit in a second slot encoded at a second rate allocated to said second unit, said second rate being slower than said first rate, and said second slot having a second duration smaller than said first duration;

(c) exchanging slot rate allocation for converting said first slot to said second duration to accommodate information encoded at said second rate re-allocated to said first unit in response to detecting activity of said second unit;

(d) exchanging slot rate allocation for adapting said second slot to said first duration to accommodate information encoded at said first rate re-allocated to said second unit; and

(e) operating, thereafter, to receive an information signal from said second unit in said second slot encoded at said first rate re-allocated to said second unit.

2. The method of claim 1, wherein step (b) comprises:

(b1) detecting a voice signal from said second unit;

(b2) detecting silence of said first unit.

3. The method of claim 1, wherein said step (b) comprises:

(b1) detecting an information signal over a predefined period of time from said second unit; and

(b2) detecting silence of said first unit.

4. The method of claim 1, wherein said detecting step comprises receiving a command.

5. The method of claim 1, wherein said detecting step comprises detecting a voice signal.

6. The method of claim 1, wherein said detecting step comprises detecting a data information signal.

7. The method of claim 1, wherein said detecting step comprises detecting a control signal.

8. A method for communication between at least a first unit and a second unit via a time division multiplexed communication channel, comprising the steps of:

transmitting an information signal from said first unit to at least said second unit in a first slot encoded at a first rate allocated to said first unit, said first slot having a first duration;

decoding information by said first unit from said second unit in a second slot encoded at a second rate allocated to said second unit, said second rate being slower than said first rate, and said second slot having a second duration smaller than said first duration;

exchanging slot rate allocation for converting said first slot to said second duration to accommodate information encoded at said second rate re-allocated to said first unit in response to decoding information from said second unit;

exchanging slot rate allocation for adapting said second slot to said first duration to accommodate information encoded at said first rate re-allocated to said second unit; and

thereafter, receiving an information signal from said second unit in said second slot encoded at said first rate re-allocated to said second unit until transmission of activity from said first unit in said first slot encoded at said second rate is received.

9. The method of claim 8, wherein said decoding step comprises monitoring said second slot to determine whether said second unit has transmitted.

10. A method for communication between at least a first unit and a second unit via a time division multiplexed communication channel, comprising the steps of:

in at least said first unit;

(a) encoding an information signal at a first rate allocated to said first unit;

(b) transmitting said information signal in a first slot having a first duration;

(c) monitoring a second slot encoded at a second rate allocated to said second unit, said second rate being slower than said first rate, and said second slot having a second duration being shorter than said first duration;

(d) exchanging slot rate allocation for converting said first to said second duration to accommodate information encoded at said second rate re-allocated to said first unit in response to step (c);

(e) adapting said second slot to said first duration to accommodate information encoded at said first rate re-allocated to said second unit; and

(f) operating, thereafter, to receive an information signal from said second unit in said second slot encoded at said first rate re-allocated to said second unit.

11. The method of claim 10, wherein said encoding step comprises encripting an information signal.

12. The method of claim 10, wherein said encoding step comprises vocoding an information signal.

13. A method for communication between at least a first unit and a second unit via a control station on a time division multiple access communication channel partitioned into a plurality of logical channels each selectively having variable encoding rates and slot durations, comprising the steps of:

at said first unit;

transmitting information signals from said first unit to at least said control station in a first slot encoded at a first rate, said first slot having a first duration;

receiving in a second slot information signals encoded at said first rate, said second slot having said first duration;

adapting in response to a command signal to adapt said first slot to have a third duration being at most equal to said first duration to accommodate information encoded at a third rate being at most equal to said first rate, while adapting said second slot to have a fourth duration smaller than said third duration to accommodate information encoded at a fourth rate being slower than said third rate;

transmitting information signals to at least said control station in said first slot encoded at said third rate, said first slot having said third duration;

detecting information signals from said control station in said second slot encoded at said fourth rate, said fourth rate being slower than said third rate, and said second slot having said fourth duration smaller than said third duration;

converting said first slot to said fourth duration to accommodate information encoded at said fourth rate in response to detecting activity of said control station;

adapting said second slot to said third duration to accommodate information encoded at said third rate; and

operating, thereafter, to receive information signals from said control station in said second slot encoded at said third rate, and

receiving information signals from said first unit;

repeating information signals to at least said second unit;

receiving information signals from said second unit;

repeating information signals to at least said first unit;

determining a value representing a total quantity of a plurality of logical channels in use; and

comparing said value to a threshold representing a predetermined number of said plurality of logical channels and transmitting said command signal when said value is at least equal to said threshold.

14. The method of claim 13, wherein said comparing step comprises comparing said value to a threshold representing a total quantity of said plurality of logical channels presently available having equal slot durations and coding rates.

15. A method for communication between at least a first unit and a second unit via a control station on a time division multiple access communication channel selectively having variable encoding rates and slot durations, comprising the steps of:

at said first unit;

transmitting an information signal to at least said control station in a first slot encoded at a first rate, said first slot having a first duration;

receiving in a second slot an information signal encoded at said first rate, said second slot having said first duration;

adapting in response to a command signal to provide said first slot having a third duration being at most equal to said first duration to accommodate information encoded at a third rate being at most equal to said first rate, while providing said second slot to have a fourth duration smaller than said third duration to accommodate information encoded at a fourth rate being slower than said third rate; and

transmitting an information signal to at least said control station in said first slot encoded at said third rate, said first slot having said third duration, and

at said control station;

receiving said information signal from said first unit;

repeating said information signal to at least said second unit;

receiving said information signal from said second unit;

repeating said information signal to at least said first unit;

determining a value representing a total quantity of information carried over said channel; and

comparing said value to a threshold representing a normal quantity of information and transmitting said command signal when said value is at least equal to said threshold.

16. The method of claim 15, wherein said adapting step comprises providing said second slot to have a fourth duration smaller than said third duration to accommodate information encoded at a fourth rate being slower than said third rate, irregardless of audio quality.

17. In a TDM communication system operating between at least a first unit and a second unit via a time division multiplexed communication channel, a device capable of communicating within said system, comprising:

means for transmitting an information signal from said first unit to at least said second unit in a first slot encoded at a first rate allocated to a first unit, said first slot having a first duration;

means for detecting activity of said second unit in a second slot encoded at a second rate allocated to a second unit, said second rate being slower than said first rate, and said second slot having a second duration smaller than said first duration;

means responsive to means for detecting activity of said second unit for exchanging slot rate allocation by converting said first slot to said second duration to accommodate information encoded at said second rate re-allocated to said first unit while adapting said second slot to said first duration to accommodate information encoded at said first rate re-allocated to said second unit; and

means to receive an information signal from said second unit in said second slot encoded at said first rate re-allocated to said second unit.

18. The device of claim 17, wherein said transmitting means comprises means for digitally analyzing a voice signal encoded at said first rate to provide said information signal in said first slot.

19. The device of claim 18, wherein said means for detecting comprises means for decoding at said second rate to recover said voice signal from said activity received in said second slot.

20. A method for communication between at least a first unit and a second unit via a time division multiplexed communication channel, comprising the steps of:

at a first unit;

(a) transmitting an information signal from said first unit to at least said second unit in a first slot encoded at a first rate, said first slot having a first duration;

(b) detecting activity of said second unit in a second slot encoded at a second rate, said second rate being slower than said first rate, and said second slot having a duration smaller than said first duration;

(c) converting said first slot to said second duration to accommodate information encoded at said second rate in response to detecting activity of said second unit;

(d) adapting said second slot to said first duration to accommodate information encoded at said first rate; and

(e) operating, thereafter, to receive an information signal from said second unit in said second slot encoded at said first rate, and

at a second unit;

(a) receiving said information signal in said first slot encoded at said first rate, said first slot having said first duration;

(b) transmitting a signal representing activity in a second slot encoded at said second rate, said second rate being slower than said first rate, and said second slot having said second duration smaller than said first duration;

(c) converting said first slot to said second duration to accommodate information received at said second rate in response to step (b);

(d) adapting said second slot to said first duration to accommodate information encoded at said first rate; and

(e) operating, thereafter, to transmit said information signal in said second slot encoded at said first rate.