Duplex satellite communication using a single frequency or pair

• US 6,430,391 B1
• Filed: 11/29/1999
• Issued: 08/06/2002
• Est. Priority Date: 11/29/1999
• Status: Expired due to Term

• Current Assignee: Ericsson, Inc. (Telefonaktiebolaget LM Ericsson)
• Original Assignee: Ericsson, Inc. (Telefonaktiebolaget LM Ericsson)
• Inventors: Dent, Paul W., Ottoson, Tony
• Primary Examiner(s): Maung, Nay
• Assistant Examiner(s): GELIN, JEAN ALLAND
• Application Number:
  US09/451,210
• Time in Patent Office: 981 Days
• Field of Search: 455/11.1, 455/443, 455/445, 455/446, 455/447, 455/450, 455/451, 455/452, 455/455, 455/464, 455/7.427, 455/8, 455/9, 455/10, 455/13.1, 455/12.1, 455/16, 455/504, 455/511, 455/517, 455/61, 455/118, 455/131, 455/207, 370/315, 370/276, 370/277, 370/279, 370/280, 370/281, 370/316, 370/319, 370/328, 370/329, 370/330, 370/344, 370/437, 370/529
• US Class Current: 455/11.1
• CPC Class Codes: H04B 7/18513 Transmission in a satellite or space-based system
• CPC Class Codes: H04B 7/216 Code division or spread-spectrum multiple access [CDMA, SSMA]
• CPC Class Codes: H04L 5/06 the signals being represented by different frequencies combined with time-division multiplexing H04L5/26

Abstract

An improved satellite communications system allows for greater spectral efficiency by requiring just two frequencies for wireless communications between a first ground-based station and a second ground-based station via a satellite. Both the first station and the second station use the first frequency to transmit signals to the satellite; the satellite transponds the signals it receives on the first frequency to the second frequency and transmits the signals to the first and second stations on the second frequency. Use of two frequencies in such a manner results in some own-signal interference. The first station preferably stores its outgoing signals in memory and then subtracts out these stored signals to eliminate the its own-signal interference. The second station may likewise store and subtract out its transmissions, but this is not required. The present invention also contemplates that each satellite beam cell will have its own network station, thereby allowing for simpler antenna configurations to be used.

Claims

1. A method of communicating information signals simultaneously between a first station and a second station with the aid of an intervening repeater, comprising:

a) transmitting a first information-modulated signal from said first station to said repeater using a first communications channel;

b) transmitting a second information-modulated signal from said second station to said repeater using said first communications channel;

c) receiving said first and second signals superimposed at said repeater;

d) translating said received superimposed signals to a second communications channel and transmitting said translated superimposed signals on said second communications channel;

e) receiving said translated superimposed signals on said second communications channel at said first station;

f) processing, at said first station, said received signal to decode said second information-modulated signal by compensating for said superimposed first information-modulated signal transmitted by said first station.

2. The method of claim 1 wherein said compensating includes said first station retaining delayed information transmitted by itself and jointly processing the received signal together with said delayed information.

3. The method of claim 2 wherein said joint processing includes weighting said delayed information using weighting coefficients and subtracting weighted delayed information from the received signal.

4. The method of claim 3 wherein said weighting coefficients are determined by correlating the received signal with said delayed information.

5. The method of claim 2 wherein said joint processing includes using said delayed information to form a stop-filter adapted to reject said first information-modulated signal and filtering the received signal using said stop-filter to remove said first information-modulated signal.

6. The method of claim 3 wherein said weighting coefficients are determined by a method of least squares equation solving.

7. The method of claim 6 wherein said method of least squares equation solving is a sequential least squares method.

8. The method of claim 7 wherein said sequential least squares method is a Kalman filter.

9. The method of claim 7 wherein said sequential least squares method exponentially de-emphasizes older information samples.

10. The method of claim 7 wherein said sequential least squares method subtracts the influence of the oldest information sample in a rectangular time window.

11. The method of claim 3 wherein said weighting coefficients are estimates of the propagation channel from said first station'"'"'s transmitter input through said repeater to said first station'"'"'s receiver output.

12. The method of claim 1 wherein said compensating includes delaying, at said first station, a baseband representation of said first information-modulated signal transmitted by said first station and jointly processing the received signal together with said delayed baseband representation.

13. The method of claim 12 wherein said baseband representation is a complex number stream.

14. The method of claim 12 wherein said joint processing includes weighting said delayed baseband representation using weighting coefficients and subtracting the weighted delayed baseband representation from the received signal.

15. The method of claim 14 wherein said weighting coefficients are determined by correlating the received signal with said delayed baseband representation.

16. The method of claim 12 wherein said joint processing includes using said delayed baseband representation to form a stop-filter adapted to reject said first information-modulated signal and filtering the received signal using said stop-filter to remove said first information-modulated signal.

17. The method of claim 14 wherein said weighting coefficients are determined by a method of least squares equation solving.

18. The method of claim 17 wherein said method of least squares equation solving is a sequential least squares method.

19. The method of claim 18 wherein said sequential least squares method is a Kalman filter.

20. The method of claim 18 wherein said sequential least squares method exponentially de-emphasizes older signal samples.

21. The method of claim 18 wherein said sequential least squares method subtracts the influence of the oldest signal sample in a rectangular time window.

22. The method of claim 14 wherein said weighting coefficients are estimates of the propagation channel from said first station'"'"'s transmitter output through said repeater to said first station'"'"'s receiver output.

23. The method of claim 1 wherein said first information-modulated signal includes information-modulated signals intended for said second station and information-modulated signals intended for other stations.

24. The method of claim 23 wherein the first station decodes the signal received from said repeater by compensating for all of the information-modulated signals transmitted from said first station whether or not they were intended for reception by said second station.

25. The method of claim 1 wherein said first communications channel is a first radio frequency in a first frequency band and said second communications channel is a second radio frequency in a second radio frequency band.

26. The method of claim 1 wherein said first communications channel is a first timeslot on a first radio frequency and said second communications channel is a second timeslot on a second radio frequency.

27. The method of claim 1 wherein said first communications channel is a first timeslot on a first radio frequency and said second communications channel is a second timeslot on said first radio frequency and said first and second timeslots do not overlap at said repeater.

28. The method of claim 1 wherein said first and second information-modulated signals have different bandwidths.

29. A method for communicating information using a repeater with a multi-beam antenna between a first station in a first beam and a second station in a second beam, comprising

a) transmitting a first information-modulated signal from said first station to said repeater using a first communications channel in said first beam;

b) transmitting a second information-modulated signal from said second station to said repeater using a second communications channel in said second beam;

c) transmitting a third information-modulated signal from a third station to said repeater using said second communications channel in said second beam;

d) receiving said first and second and third signals at said repeater;

e) translating said received signals in said second beam, including said second and third signals, to a third communications channel and transmitting said translated signals on said third communications channel in said first beam;

f) receiving said translated signals on said third communications channel at said first station; and

g) processing, at said first station, said received signal to decode said second information-modulated signal from said second station by compensating for the interfering signal transmitted by said third station.

30. The method of claim 29 further comprising transmitting from said third station to said first station a copy of said third information-modulated signal.

31. The method of claim 29 further comprising transmitting from said third station to said first station a copy of the information used to modulate said third information-modulated signal.

32. The method of claim 29 further comprising jointly demodulating said second information-modulated signal with said third information-modulated signal at said first station.

33. The method of claim 32 wherein said joint demodulation uses a Joint Maximum Likelihood Sequence Estimator.

34. The method of claim 33 wherein said third information-modulated signal includes known symbols transmitted by said third station for synchronization purposes and wherein said known symbols are exploited to reduce complexity of said joint demodulation.

35. The method of claim 29 further comprising jointly and simultaneously demodulating and decoding said second and third information-modulated signals.

36. A method of communicating information signals simultaneously between a first station and a second station with the aid of an intervening repeater, comprising:

a) at a first station,

i) modulating a first information signal based on a first set of data;

ii) transmitting said first information signal to said repeater using a first communications channel;

iii) temporarily buffering said first information signal at said first station;

b) transmitting a second information signal from said second station to said repeater using said first communications channel;

c) receiving a combined signal at said repeater on said first communications channel representing said first and second information signals superimposed together;

d) translating said combined signal to a second communications channel and transmitting said translated combined signal on said second communications channel;

e) receiving said translated combined signal on said second communications channel at said first station;

f) processing, at said first station, said received signal to decode said second information signal by subtracting said first information signal transmitted by said first station from said received signal.

37. The method of claim 36 wherein said buffering terminates no later than immediately after said second information signal is decoded from said received signal.

38. The method of claim 36 wherein said processing of said received signal includes subtracting a weighted version of said first information signal from the received signal.

39. The method of claim 38 wherein said weighted version depends on a plurality of weighting coefficients and wherein said weighting coefficients are determined by correlating the received signal with said buffered representation.