Fully meshed CDMA network for personal communications terminals

• US 5,481,561 A
• Filed: 10/26/1993
• Issued: 01/02/1996
• Est. Priority Date: 05/29/1991
• Status: Expired due to Fees

• Current Assignee: COMSAT Corporation (Reorganized ISA SA)
• Original Assignee: COMSAT Corporation (Reorganized ISA SA)
• Inventors: Fang, Russell J.
• Primary Examiner(s): Gregory, Bernarr E.
• Application Number:
  US08/141,721
• Time in Patent Office: 798 Days
• Field of Search: 375/1, 375/76, 375/97, 375/98, 375/200-210, 375/317, 375/344, 375/345, 380/18, 380/30, 380/34, 380/49, 370/110.1, 370/111, 455/9, 455/67, 455/4, 455/69, 455/70, 455/71
• US Class Current: 370/320
• CPC Class Codes: H04B 7/216 Code division or spread-spectrum multiple access [CDMA, SSMA]
• CPC Class Codes: H04J 13/00 Code division multiplex systems for frequency hopping H04B1/713
• CPC Class Codes: H04L 2007/045 Fill bit or bits, idle words
• CPC Class Codes: H04L 5/02 Channels characterised by the type of signal
• CPC Class Codes: Y02D 30/70 in wireless communication networks

Abstract

A network of personal communications terminals communicating in a CDMA mode includes a reference station for transmitting a pilot tone that is pre-corrected at the reference station and is used at the remaining stations for frequency control, transmit power control and antenna acquisition and tracking. Voice activation is employed to permit the CDMA system to share the satellite transponder power and bandwidth in a fully Demand-Assignment-Multiple-Accessing (DAMA) manner. Burst-mode operation of a voice activated CDMA system is permitted by sending dummy data in the speech pausing period at a reduced (but not zero) power level, and the "near-far" problem inherent in a CDMA system is mitigated by the use of uplink power control.

Claims

1. A communications system, comprising a plurality of terminals communicating with one another in a code division multiple access (CDMA) manner over a communications medium, said system including a modulator at each of said terminals for modulating signals being transmitted to another terminal in accordance with a PN code associated with communications between said each terminal and said another terminal, and a demodulator at said another terminal for demodulating received signals in accordance with said PN code, said system further comprising reference means at at least one of said plural terminals for transmitting a pilot tone to others of said terminals for controlling at least one parameter at said other terminals, and means at said other terminals for receiving said pilot tone and controlling said at least one parameter in accordance with said pilot tone, said system further comprising means for automatically periodically changing said PN codes associated with said terminals.

2. A system as defined in claim 1, further comprising means for assigning said PN codes on a demand assigned basis.

3. A communications system, comprising a plurality of terminals communicating with one another in a code division multiple access (CDMA) manner over a communications medium, said system including a modulator at each of said terminals for modulating signals being transmitted to another terminal in accordance with a PN code associated with communications between said each terminal and said another terminal, and a demodulator at said another terminal for demodulating received signals in accordance with said PN code, said system further comprising reference means at at least one of said plural terminals for transmitting a pilot tone to others of said terminals for controlling at least one parameter at said other terminals, and means at said other terminals for receiving said pilot tone and controlling said at least one parameter in accordance with said pilot tone, said system further comprising means for determining said PN codes in accordance with a public key cryptosystem.

4. A communications system, comprising a plurality of terminals communicating with one another over a communications medium, said system including a modulator at each of said terminals for modulating signals to be transmitted to a particular one of said terminals in accordance with a PN code assigned to communications between said each terminal and said particular terminal, and a demodulator at said particular terminal for demodulating signals in accordance with said PN code, with each terminal transmitting information separated by pauses, with each terminal transmitting other signals during said pauses in the transmission of said information, and wherein each terminal transmits at a lower power level during said pauses than during transmission of said information.

14. A system as defined in claim 4, wherein said reference means at said one terminal transmits said pilot tone onto said communications medium, and wherein said one terminal includes means for monitoring the return of said pilot tone to said one terminal, and means for adjusting the frequency of transmission of said pilot tone by said one terminal to obtain a desired received pilot tone frequency.

5. A communications system, comprising a plurality of terminals communicating with one another over a communications medium, said system including a modulator at each of said terminals for modulating signals being transmitted over said communications medium and a demodulator for demodulating signals received over said communications medium, said system further comprising:

reference means at at least one of said plural terminals for transmitting a pilot tone to others of said terminals for controlling at least one parameter at said other terminals;

means at said other terminals for receiving said pilot tone and controlling said at least one parameter in accordance with said pilot tone;

means at each of said terminals for storing data relating to the amount of information transmitted; and

means for polling each terminal to retrieve said stored data for billing purposes.

6. A communications system, comprising a plurality of terminals communicating with one another over a communications medium, said system including a modulator at each of said terminals for modulating signals being transmitted over said communications medium and a demodulator for demodulating signals received over said communications medium, said system further comprising:

reference means at at least one of said plural terminals for transmitting a pilot tone to others of said terminals for controlling at least one parameter at said other terminals;

means at said other terminals for receiving said pilot tone and controlling said at least one parameter in accordance with said pilot tone;

means at each of said terminals for storing a credit value corresponding to an amount of preauthorized credit; and

means at each of said terminals for subtracting from said stored credit value in accordance with an amount of information transmitted by said terminal.

7. A communications system, comprising a plurality of terminals communicating with one another over a communications medium, said system including a modulator at each of said terminals for modulating signals being transmitted over said communications medium and a demodulator for demodulating signals received over said communications medium, said system further comprising:

reference means at at least one of said plural terminals for transmitting a pilot tone to others of said terminals for controlling a pointing direction of an antenna at said other terminals; and

means at said other terminals for receiving said pilot tone and controlling said antenna pointing direction in accordance with said pilot tone.

8. A system as defined in claim 7, wherein said reference means at said one terminal transmits said pilot tone onto said communications medium, and wherein said one terminal includes means for monitoring the return of said pilot tone to said one terminal, and means for adjusting the amplitude of the transmission of said pilot tone by said one terminal to obtain a desired received pilot tone amplitude, each terminal other than said one terminal including means for adjusting a transmit power level in accordance with the amplitude of said received pilot tone.

9. A system as defined in claim 7, wherein said terminals are portable.

10. A system as defined in claim 7, wherein said information includes speech information.

11. A system as defined in claim 7, wherein said information includes facsimile information.

12. A system as defined in claim 7, wherein said information includes data.

13. A communications system, comprising a plurality of terminals communicating with one another over a communications medium, said system including a modulator at each of said terminals for modulating signals being transmitted over said communications medium and a demodulator for demodulating signals received over said communications medium, said system further comprising:

reference means at at least one of said plural terminals for transmitting a pilot tone to others of said terminals for controlling a carrier frequency at said other terminals; and

means at said other terminals for receiving said pilot tone and controlling said carrier frequency in accordance with said pilot tone.