Method and System for Cooperative Communications with Minimal Coordination

• US 20090313528A1
• Filed: 10/06/2008
• Published: 12/17/2009
• Est. Priority Date: 10/19/2007
• Status: Active Grant

• Current Assignee: Trellisware Technologies, Inc. (ViaSat Incorporated)
• Original Assignee: Trellisware Technologies, Inc. (ViaSat Incorporated)
• Inventors: Johnson, Mark, Chugg, Keith M.
• Granted Patent: US 8,576,946 B2
• Time in Patent Office: Days
• US Class Current: 714/758
• CPC Class Codes: H04B 7/026 Co-operative diversity, e.g. using fixed or mobile stations as relays

Abstract

A method and system are provided in a wireless communications system comprising a plurality of nodes (users) working cooperatively. The system provides cooperative diversity by allowing nodes to actively share their antennas and other resources to obtain spatial diversity. The nodes receive the same message (information data) from a common source. Each node enhances the reliability of the message with a modern forward error correction (FEC) code, converts the FEC encoded message into an ensemble of symbols, divides the ensemble of symbols into packets, modulates, dithers and transmits the packets to a receiving node. The dithering process is performed by varying the signal amplitude, phase, frequency and/or symbol timing of the modulated packets. A unique dither pattern is assigned to each node. The receiving node captures a composite signal comprising the transmitted packets of all or most of the transmitting nodes in the cooperative communications system. Because the transmitted packets are dithered independently in phase and/or amplitude, spatial diversity is transformed into temporal diversity.

Claims

1. A cooperative communication system for communicating information in a multiple-node environment comprising:

At least one source transmitter sending information data;

a plurality of transceivers working in cooperation, with each transceiver receiving the information data, modulating the information data, dithering the modulated information data with a dithering mechanism, and relaying the modulated and dithered information data; and

at least one sink receiver receiving a composite signal comprising a plurality of modulated and dithered information data relayed from the plurality of transceivers.

2. The cooperative communication system of claim 1 wherein the modulated and dithered information data comprises a B number of packets, with each packet including a D number of symbols.

3. The cooperative communication system of claim 2 wherein the B number and the D number are positive integers.

4. The cooperative communication system of claim 2 wherein each one of the B number of packets is dithered with a constant (time-invariant) dither value.

5. The cooperative communication system of claim 1 wherein each one of the plurality of transceivers computes a cyclic redundant check (CRC) on the received information data for verifying an error-free reception.

6. The cooperative communication system of claim 1 wherein each one of the plurality of transceivers further comprises:

a forward error correction (FEC) encoder for encoding the received information data; and

a training pattern generator for adding a training sequence to each packet.

7. The cooperative communication system of claim 6 wherein the FEC encoder is one of the Reed-Solomon block code, a convolutional code, or a low density parity-check code.

8. The cooperative communication system of claim 6 wherein the training sequence is the same for the plurality of transceivers working in cooperation.

9. The cooperative communication system of claim 1 wherein the dithering mechanism comprises a pseudo-random number generator or pseudo-noise generator having a plurality of distinct dithering values.

10. The cooperative communication system of claim 9 wherein a first dithering value of the plurality of distinct dithering values is coupled to a first packet of the B number of packets.

11. The cooperative communication system of claim 1 wherein the dithering mechanism further comprises a plurality of dithering modules.

12. The cooperative communication system of claim 11 wherein one of the plurality of dithering modules comprises a linear feedback shift register coupled with the pseudo-random number generator having an initialization seed.

13. The cooperative communication system of claim 12 wherein the initialization seed is stored in a memory.

14. The cooperative communication system of claim 13 wherein the memory is one of the ROM, EPROM, EEPROM, SRAM, Flash memory or registers.

15. The cooperative communication system of claim 12 wherein the initialization seed is user configurable.

16. The cooperative communication system of claim 11 wherein a first dithering module of the plurality of dithering modules is a phase dithering module.

17. The cooperative communication system of claim 16 wherein the phase dithering module comprises a plurality of discrete phase values.

18. The cooperative communication system of claim 11 wherein a second dithering module of the plurality of dithering modules is an amplitude dithering module having a plurality of discrete amplitude values.

19. The cooperative communication system of claim 14 wherein a third dithering module is a symbol-time dithering module having a plurality of discrete symbol-time values.

20. The cooperative communication system of claim 14 wherein a fourth dithering module is a phase-and-amplitude dithering module.

21. The cooperative communication system of claim 1 wherein the composite signal has a time-varying signal-to-noise ratio (SNR).

22. The cooperative communication system of claim 1 wherein the at least one sink receiver is configured to capture the composite signal having a training sequence and estimate a channel response based on a portion of the training sequence.

23. A method of relaying information in a cooperative network having a plurality of nodes, the network including at least one source node transmitting information data, a plurality of hop-nodes working in cooperation, and at least one destination node, the method comprising:

at each one of the plurality of hop-nodes, receiving the transmitted information data, modulating and dithering the information data;

at each one of the plurality of hop-nodes, transmitting the modulated and dithered information data; and

at the at least one destination node, receiving a composite signal comprising a plurality of the modulated and dithered information data from the plurality of hop-nodes.

24. The method of claim 23, wherein the method further comprises, at each one of the plurality of hop-nodes:

encoding the received information data with an FEC (forward error correction) code;

mapping the encoded information data into an ensemble of symbols;

dividing the ensemble of symbols into a plurality of packets, wherein each packet includes a plurality of symbols; and

inserting a training sequence to each one of the plurality of packets.

25. The method of claim 24 wherein the FEC code is a low density parity-check code.

26. The method of claim 24 wherein the training sequence is the same for each packet.

27. The method of claim 24 wherein the training sequence is known a priori to the at least one destination node.

28. The method of claim 23 wherein the modulating of the information data comprises a multi-level phase and/or amplitude modulation (mQAM).

29. The method of claim 28 wherein the mQAM modulation is one of:

binary phase shift keying (BPSK), quadrature phase shift keying (QPSK), multi-level phase shift keying (mPSK), and multi-level amplitude shift keying (mASK).

30. The method of claim 23 wherein the dithering of the information data is performed at each one of the plurality of packets, each packet being associated with a distinctively unique time-invariant dither value.

31. The method of claim 23 wherein the dithering is a phase dithering having discrete phase values.

32. The method of claim 23 wherein the dithering is an amplitude and phase dithering.

33. The method of claim 23 wherein the dithering comprises a pseudo-random number generator.

34. The method of claim 23 wherein the composite signal has a time-varying signal-to-noise ratio (SNR).

35. The method of claim 23 wherein the method further comprises, at the destination node:

a) receiving the composite signal;

b) processing a training sequence portion of a first packet to estimate a channel response;

c) demodulating the plurality of symbols in the first packet;

d) repeating the steps of b) and c) until the plurality of packets are demodulated; and

e) FEC decoding the plurality of packets to obtain a original transmitted information data.