Methods and apparatus for mobile station to mobile station communications in a mobile satellite communication system

• US 5,943,324 A
• Filed: 04/13/1998
• Issued: 08/24/1999
• Est. Priority Date: 01/11/1994
• Status: Expired due to Term

• Current Assignee: Ericsson, Inc. (Telefonaktiebolaget LM Ericsson)
• Original Assignee: Ericsson, Inc. (Telefonaktiebolaget LM Ericsson)
• Inventors: Reinhold, Stanley L., Dent, Paul W., Ramesh, Rajaram
• Primary Examiner(s): Olms, Douglas W.
• Assistant Examiner(s): RAO, SEEMA SRINIVAS
• Application Number:
  US09/059,045
• Time in Patent Office: 498 Days
• Field of Search: 370/310, 370/315, 370/316, 370/319, 370/321, 370/323, 370/324-326, 370/345, 370/347, 370/464, 370/465, 370/468, 370/477, 370/498, 370/501, 370/545, 370/521, 455/12.1, 455/11.1, 375/211, 375/213, 340/825.18, 379/338
• US Class Current: 370/321
• CPC Class Codes: H04B 7/18558 Arrangements for managing communications, i.e. for setting up, maintaining or releasing a call between stations

Abstract

Methods and apparatus for mobile station to mobile station communications in a mobile satellite communications system include an asymmetrical TDMA formatting scheme. According to exemplary embodiments, a first mobile station broadcasts a first signal to an orbiting satellite using a first TDMA format. The satellite receives the first signal, maps the first TDMA format to a second TDMA format and broadcasts a second signal having the second TDMA format to a second mobile station. Advantageously, exemplary embodiments utilize an elastic buffer to allow the satellite to map the uplink TDMA format to the downlink TDMA format without having to demodulate and re-modulate communications signals.

Claims

1. In a mobile satellite communications system, a method for providing communications via a communications satellite relay station between a first mobile station conditioned to transmit a first signal having a first TDMA signal format and a first bandwidth and a second mobile station conditioned to receive a second signal having a second TDMA signal format, the method comprising:

receiving in the satellite relay station the first signal having the first TDMA signal format and the first bandwidth from the first mobile station;

sampling the received first signal at a first rate to produce a first bitstream having a first number of samples per second;

storing, in a buffer, the first bitstream;

clocking out of the buffer the first bitstream at a second rate, which is different from the first rate, to produce a second bitstream having a second number of samples per second which is different from the first number of samples per second of the first bitstream, the samples in both the first and second bitstreams being representative of the received first signal; and

transmitting from the satellite relay station to the second mobile station the second bitstream as the second signal using the second TDMA format at a second bandwidth which is different from the first bandwidth of the first signal.

2. The method of claim 1, wherein the number of time slots in the first TDMA format and the second TDMA format may be varied with different frames.

3. A method according to claim 1, wherein the second bitstream is multiplexed with Slow Associated Control Channel (SACCH) information to provide the second signal using the second TDMA format.

4. A method according to claim 3, wherein the SACCH information is provided to the satellite relay station by a ground station in the mobile satellite communications system.

5. A communications satellite relay station for providing communications between a first mobile station conditioned to transmit a first signal having a first TDMA format and a first bandwidth and a second mobile station conditioned to receive a second signal having a second TDMA format, the satellite relay station comprising:

a receiver for receiving the first signal having the first TDMA signal format and the first bandwidth;

an analog to digital converter for sampling the received first signal at a first rate to produce a first bitstream having a first number of samples per second;

a buffer for receiving the first bitstream and clocking out the first bitstream at a second rate, which is different from the first rate, to produce a second bitstream having a second number of samples per second which is different from the first number of samples per second of the first bitstream, the samples in both the first and second bitstreams being representative of the received first signal; and

a transmitter for transmitting the second bitstream as the second signal using the second TDMA format at a second bandwidth which is different from the first bandwidth of the first signal.

6. The satellite relay station of claim 5, where said buffer is a shift register.

7. The satellite relay station of claim 5, where said second TDMA format is a GSM format.

8. A satellite relay station according to claim 5, wherein the second bitstream is multiplexed with Slow Associated Control Channel (SACCH) information to provide the second signal using the second TDMA format.

9. A satellite relay station according to claim 8, wherein the SACCH information is provided to the satellite relay station by a ground station in the mobile satellite communications system.

10. In a mobile satellite communications system, a method for providing communications via a communications satellite relay station between a first mobile station conditioned to transmit a first signal having a first TDMA format and a first bandwidth BW and a second mobile station conditioned to receive a second signal having a second TDMA format, the method comprising:

receiving, in the satellite relay station the first signal having the first TDMA signal format and the first bandwidth BW from the first mobile station;

downconverting the first signal to a first IF signal;

sampling the first IF signal at a rate N×

BW, where N is greater than or equal to 2, to produce a first bitstream having at least N×

BW samples per second with the samples being representative of the received first signal;

storing, in a buffer, the first bitstream;

clocking out of the buffer the first bitstream at a rate M×

N×

BW, where M is greater than or equal to 2 to produce a second bitstream having at least M×

N×

BW samples per second with the samples being representative of the received first signal;

filtering the second bitstream to produce a second IF signal;

upconverting the second IF signal to produce an output signal;

formatting the output signal into the second TDMA format to produce the second signal; and

transmitting the second signal from the satellite relay station to the second mobile station.

11. The method of claim 10, wherein the number of time slots in the first TDMA format and the second TDMA format may be varied with different frames.

12. The method of claim 10, wherein N, in the sampling rate of the first IF signal, is an integer.

13. The method of claim 10, wherein M, in the rate at which the first bitstream is clocked out of the buffer, is an integer.

14. A method according to claim 10, wherein the second bitstream is multiplexed with Slow Associated Control Channel (SACCH) information to provide the second signal using the second TDMA format.

15. A method according to claim 14, wherein the SACCH information is provided to the satellite relay station by a ground station in the mobile satellite communications system.

16. A method for supporting calls between two mobile stations within a satellite communication system, comprising the steps of:

transmitting signals from a first mobile station to a satellite relay station using a narrowband time division multiple access transmission format;

sampling and digitizing signals received from said first mobile station;

storing said sampled and digitized signals in a buffer means at a first rate;

reading out of said buffer means said stored signals at a faster rate than said first rate and modulating said stored signals onto a downlink frequency to create a wideband time division multiple access transmission format;

transmitting said modulated signals to a second mobile station;

receiving and decoding said modulated signals at said second mobile station.

17. A method according to claim 16, wherein the stored signals are multiplexed with Slow Associated Control Channel (SACCH) information to provide the wideband time division multiple access format.

18. A method according to claim 17, wherein the SACCH information is provided to the satellite relay station by a ground station in the satellite communication system.

19. A satellite transponder for supporting calls between two mobile stations within a satellite communication system, comprising:

receiving means for receiving signals being transmitted using a narrowband time division multiple access transmission format;

means for sampling and digitizing said received signals;

means for storing said sampled and digitized signals at a first rate;

means for reading out said stored signals at a faster rate than said first rate and modulating said stored signals onto a downlink frequency to create a wideband time division multiple access transmission format; and

transmitting means for transmitting said modulated signals to a second mobile station.

20. A satellite transponder according to claim 19, wherein the stored signals are multiplexed with Slow Associated Control Channel (SACCH) information to provide the wideband time division multiple access format.

21. A satellite transponder according to claim 20, wherein the SACCH information is provided to the satellite transponder by a ground station in the satellite communication system.

22. A method for supporting calls between two mobile stations within a satellite communication system, comprising the steps of:

receiving narrow band time division multiple access (TDMA) signals from said mobile stations at a satellite relay station;

relaying the received narrowband TDMA signals to at least one ground station;

digitizing some of the received narrowband signals;

time compressing said digitized signals;

multiplexing said time compressed signals into a wideband TDMA downlink format along with other signals from said at least one ground station; and

transmitting said multiplexed signals to one of said mobile stations.

23. A method according to claim 22, wherein said other signals from said at least one ground station are Slow Associated Control Channel Information (SACCH) signals.

24. A method according to claim 23, wherein said SACCH signals are computed based upon the received narrowband signals relayed to said at least one ground station.

25. A method according to claim 23, wherein said SACCH signals control transmit timing at said mobile stations.

26. A communications satellite relay station for providing communications between a first mobile station conditioned to transmit a first signal having a first TDMA format and a second mobile station conditioned to receive a second signal having a second TDMA format, the satellite relay station comprising:

a receiver for receiving the first signal having the first TDMA signal format and a first bandwidth BW and downconverting the first signal to a first IF signal;

an analog to digital converter for sampling the first IF signal at a rate N×

BW, where N is greater than or equal to 2 to produce a first bitstream having at least N×

BW samples per second with the samples being representative of the received first signal;

a buffer for receiving the first bitstream and clocking out the first bitstream at a rate M×

N×

BW, where M is greater than or equal to 2 to produce a second bitstream having at least M×

N×

BW samples per second with the samples being representative of the received first signal;

a low pass filter for filtering the second bitstream to produce a second IF signal;

an upconverter for upconverting the second IF signal to produce an upconverted output signal; and

a transmitter for transmitting the upconverted output signal using the second TDMA format.

27. The satellite relay station of claim 26, where said buffer is a shift register.

28. The satellite relay station of claim 26, where said second TDMA format is a GSM format.

29. The satellite relay station of claim 26, wherein the number of time slots in the first TDMA format and the second TDMA format may be varied with different frames.

30. The satellite relay station of claim 26, wherein N, in the sampling rate of the first IF signal, is an integer.

31. The satellite relay station of claim 26, wherein M, in the rate at which the first bitstream is clocked out of the buffer, is an integer.

32. A satellite relay station according to claim 26, wherein the second bitstream is multiplexed with Slow Associated Control Channel (SACCH) information to provide the second signal using the second TDMA format.

33. A satellite relay station according to claim 32, wherein the SACCH information is provided to the satellite relay station by a ground station in the mobile satellite communications system.

34. A satellite transponder for supporting calls between two mobile stations within a satellite communication system, comprising:

means for receiving narrow band time division multiple access (TDMA) signals from said mobile stations at a satellite relay station;

means for relaying the received narrowband TDMA signals to at least one ground station;

means for digitizing some of the received narrowband signals;

means for time compressing said digitized signals;

means for multiplexing said time compressed signals into a wideband TDMA downlink format along with other signals from said at least one ground station; and

means for transmitting said multiplexed signals to one of said mobile stations.

35. A satellite transponder according to claim 34, wherein said other signals from said at least one ground station are Slow Associated Control Channel Information (SACCH) signals.

36. A satellite transponder according to claim 35, wherein said SACCH signals are computed based upon the received narrowband signals relayed to said at least one ground station.

37. A satellite transponder according to claim 35, wherein said SACCH signals control transmit timing at said mobile stations.