Space-time doppler coding schemes for time-selective wireless communication channels
Space-time Doppler (STDO) coding techniques are describe for time-selective channels. In particular, a STDO coded system is capable of achieving a maximum Doppler diversity for time-selective frequency-flat channels. As demonstrated herein, this maximum diversity may be represented as Q+1, where Q is the number of bases in a generalized Basis Expansion Model (BEM) for time-frequency selective channels. In addition, linearly precoded transmissions are described to collect this maximum diversity gain.
1. A wireless communication device comprising:
a first coder that linearly precodes a data stream to produce a precoded data stream;
a second coder that processes the precoded data stream in accordance with a doppler spread of time-selective communication channels to produce a transformed data stream; and
an antenna to output a waveform in accordance with the transformed data stream.
2. The wireless communication device of claim 1 , wherein the second coder processes the precoded data stream in accordance with a Basis Expansion Model (BEM) for the channels to produce the transformed data stream.
3. The wireless communication device of claim 2 , wherein the second coder samples the data stream to collect blocks of frequency-domain samples, and processes the collected blocks of samples to transform the frequency-domain samples to time-domain samples for the transformed data stream.
4. The wireless communication device of claim 3 , wherein the second coder collects blocks of Q+1 frequency-domain samples, wherein Q is a selected as a function of the doppler spread of the channels.
5. The wireless communication device of claim 3 , further comprising a modulator to process blocks of N symbols within the transformed data stream at a symbol period T s to produce the waveform for transmission with the antennas, and wherein the second coder samples the precoded data stream with a period of 1/N*T s to collect the samples.
6. The wireless communication device of claim 5 , wherein Q=2*┌f max *T s N┐, where f max represents the doppler spread of the channels.
7. The wireless communication device of claim 5 , further comprising a power splitter to produce a plurality of mirrored data streams from the transformed data stream, and wherein the antenna comprises one of a plurality of antennas to output waveforms in accordance with the mirrored data streams.
8. The wireless communication device of claim 7 , further comprising a digital phase sweeping module that computes a single channel vector from estimates of doppler offset for the channels, and process the mirrored data streams with the single channel vector to shift a basis of each of the channels so that the basis become consecutive within a Fast Fourier Transform (FFT) grid.
9. The wireless communication device of claim 7 , further comprising a modulator to modulate each mirrored data stream and produce the waveforms for transmission with the respective antennas.
10. The wireless communication device of claim 1 , wherein the first coder comprises a linear constellation precoder.
11. The wireless communication device of claim 1 , wherein the first coder applies a unitary matrix to blocks of M symbols of the data stream.
12. The wireless communication device of claim 1 , wherein the waveform is a multi-carrier waveform.
13. The wireless communication device of claim 1 , wherein the waveform is single-carrier waveform.
14. The wireless communication device of claim 1 , wherein the first coder linearly precedes the data stream by applying a matrix to symbols blocks of the data stream, wherein the matrix has a size that is an integer function of the number of antennas and the doppler spread.
15. The wireless communication device of claim 14 , wherein the blocks include N symbols, where N is selected as a function of the number of antennas N t and the doppler spread of the channels.
16. The wireless communication device of claim 14 , wherein the first coder divides each of the symbol blocks of the data stream into N g groups, where each group has N sub symbols, and N sub is an integer function of the number of antennas and the doppler spread.
17. The wireless communication device of claim 16 , wherein the matrix applied by the linear precoder has a size of N sub ×N sub .
18. The wireless communication device of claim 1 , wherein the wireless communication device comprises one of a base station and a mobile device.
19. A wireless communication device comprising:
a demodulator that receives a waveform from a plurality of time-selective multipath communication channels and produces a demodulated data stream; and
a decoder that decodes the demodulated data in accordance with a Basis Expansion Model (BEM) that parameterizes time-selective communication multi-path channels as a function of frequency-selective multi-path communication channels.
20. The wireless communication device of claim 19 , wherein the decoder applies an N×N matrix to the demodulated data, wherein the N is selected as a function of a doppler spread of the frequency-selective multi-path communication channels.
21. A method comprising:
estimating a doppler spread for a plurality of channels from a transmitter to a receiver;
applying a linear precoder to a data stream to form a precoded data stream;
processing the precoded data stream in accordance with the doppler spread to produce a transformed data stream; and
transmitting a waveform with an antenna in accordance with the transformed data stream.
22. The method of claim 21 , wherein processing the precoded data stream comprise processing the precoded data stream in accordance with a Basis Expansion Model (BEM) for the channels to produce the transformed data stream.
23. The method of claim 21 , wherein processing the precoded data stream comprises:
sampling the data stream to collect blocks of frequency-domain samples;
processing the collected blocks of samples to transform the frequency-domain samples to time-domain samples; and
outputting the transformed data stream based on the time-domain samples.
24. The method of claim 23 , wherein sampling the precoded data stream comprises collecting blocks of Q+1 frequency-domain samples, wherein Q is a selected as a function of the doppler spread of the channels.
25. The method of claim 23 , further comprising modulating blocks of N symbols within the transformed data stream at a symbol period T s to produce the waveform for transmission with the antennas.
26. The method of claim 25 , wherein sampling the precoded data stream comprises sampling the precoded data stream with a period of 1/N*T s to collect the samples.
27. The method of claim 25 , wherein Q=2*[f max *T s *N], where f max represents the doppler spread of the channels.
28. The method of claim 21 , further comprising:
splitting the power of the transformed data stream to produce a plurality of mirrored data streams; and
transmitting the mirrored data stream with respective antennas.
29. The method of claim 28 , further comprising:
computing a single channel vector from the estimated doppler offset; and
processing the mirrored data streams with the single channel vector to shift a basis of each of the channels so that basis become consecutive within a Fast Fourier Transform (FFT) grid.
30. The method of claim 21 , wherein applying a linear precoder comprises applying a linear constellation precoder.
31. The method of claim 21 , wherein the waveform is a multi-carrier waveform.
32. The method of claim 21 , wherein the waveform is a single-carrier waveform.
33. The method of claim 21 , wherein applying a linear precoder comprises:
selecting a block size N as a function of the number of antennas N t and the doppler spread; and
applying a matrix to symbol blocks of the data stream, wherein the matrix has a size that is selected as a function of the number of antennas and the doppler spread.
34. The method of claim 33 , wherein applying a linear precoder comprises:
dividing each of the blocks of the data stream into N g groups, where each group has N sub symbols, and N sub is selected as a function of the number of antennas and the doppler spread; and
applying the matrix to each of the symbol groups within the blocks, wherein the matrix has a dimension that is a function of the number of symbols N sub within the groups.
35. The method of claim 34 , wherein the size of the matrix is N sub ×N sub .
36. A computer-readable medium comprising instructions to cause a programmable processor of a wireless communication device to:
estimate a doppler spread for a plurality of channels from a transmitter to a receiver;
apply a linear precoder to a data stream to form a precoded data stream;
process the precoded data stream in accordance with the doppler spread to produce a transformed data stream; and
transmit a waveform with an antenna in accordance with the transformed data stream.
37. The computer-readable medium of claim 36 , further comprising instructions to cause the programmable processor to process the precoded data stream comprise processing the precoded data stream in accordance with a Basis Expansion Model (BEM) for the channels to produce the transformed data stream.
38. The computer-readable medium of claim 36 , further comprising instructions to cause the programmable processor to:
sample the data stream to collect blocks of frequency-domain samples;
process the collected blocks of samples to transform the frequency-domain samples to time-domain samples; and
output the transformed data stream based on the time-domain samples.