Space-time transmit diversity scheme for time-dispersive propagation media
View Patent ↗This invention extends Alamouti's scheme for wideband TDMA systems; it then works in conjunction with time-domain equalization. In fact, the present invention envisages time-domain DFE or MLSE equalization (which is more robust than linear frequency-domain equalization) via the use of a training mid-amble to separate adjacent sub-blocks; this mid-amble is used in equalizer training and its direct and inter-symbol interference contributions to the received signal, are subtractively eliminated to facilitate the detection process itself. This approach may be applied to all systems in time-dispersive propagation media, where the burst or slot length is short enough that the fading can be considered time-invariant over its duration.
1. A method for recovering a symbol block comprising:
receiving the symbol block (x) via a first wireless channel and a second wireless channel, wherein the symbol block comprises a first sub-block (x 0 ), a predefined mid-amble, and a second sub-block (x 1 );
estimating a first impulse response (h (0) ) of the first wireless channel and a second impulse response (h (1) ), of the second wireless channel using the received predefined mid-amble;
demodulating the received symbol block using h (0) and h (1) to produce processed vectors r 0 and r 1 , wherein
r 0 =h (0)F {circle around (x)}x 0 +h (1) {circle around (x)}x 1 F and
r 1 =h (0)F {circle around (x)}x 1 −h (1) {circle around (x)}x 0 F
where “{circle around (x)}” denotes convolution and “F” denotes time-reversal and complex conjugation;
equalizing the processed vectors r 0 and r 1 to recover transmitted symbol blocks s 0 and s 1 wherein s 0 corresponds to x 0 and s 1 corresponds to x 1 and wherein
x 0 =h (0) {circle around (x)}s 0 −h (1) {circle around (x)}s 1 F +v 0 and
x 1 =h (0) {circle around (x)}s 1 +h (1) {circle around (x)}s 0 F +v 1
so that
r 0 =( h (0) {circle around (x)}h (0)F +h (1) {circle around (x)}h (1)F ){circle around (x)} s 0 +w 0 and
r 1 =( h (0) {circle around (x)}h (0)F +h (1) {circle around (x)}h (1)F ){circle around (x)} s 1 +w 1
where w 0 , w 1 , v 0 , and v 1 are noise components.
2. The method of claim 1 further comprising subtracting an estimate of the received mid-amble component,
x uest =h (0) {circle around (x)}u 0 +h (1) {circle around (x)}u 1
from received burst (x), wherein u 0 is a predefined mid-amble of the first wireless channel and u 1 is a predefined mid-amble of the second wireless channel.
3. The method of claim 1 wherein a joint least squares technique is used to estimate h (0) and h (1) .
4. The method of claim 1 wherein linear equalization is used to equalize the processed vectors r 0 and r 1 to recover transmitted symbol blocks s 0 and s 1 .
5. The method of claim 1 wherein decision feedback is used to equalize the processed vectors r 0 and r 1 to recover transmitted symbol blocks s 0 and s 1 .
6. The method of claim 1 wherein maximum likelihood sequence estimation (MLSE) is used to equalize the processed vectors r 0 and r 1 to recover transmitted symbol blocks s 0 and s 1 .
7. A receiver comprising:
a means for receiving a symbol block via a first wireless channel and a second wireless channel, wherein the symbol block comprises a first sub-block (x 0 ), a predefined mid-amble, and a second sub-block (x 1 );
a means for estimating a first impulse response (h (0) ) of the first wireless channel and a second impulse response (h (1) ), of the second wireless channel using the received predefined mid-amble;
a means for demodulating the received symbol block using h (0) and h (1) to produce processed vectors r 0 and r 1 , wherein
r 0 =h (0)F {circle around (x)}x 0 +h (1) {circle around (x)}x 1 F and
r 1 =h (0)F {circle around (x)}x 1 +h (1) {circle around (x)}x 0 F
where “{circle around (x)}” denotes convolution and “F” denotes time-reversal and complex conjugation;
a means for equalizing the processed vectors r 0 and r 1 to recover transmitted symbol blocks s 0 and s 1 , wherein s 0 corresponds to x 0 and s 1 corresponds to x 1 and wherein
x 0 =h (0) {circle around (x)}s 0 −h (1) {circle around (x)}s 1 F +v 0 and
x 1 =h (0) {circle around (x)}s 1 −h (1) {circle around (x)}s 0 F +v 1
so that
r 0 =( h (0) {circle around (x)}h (0)F +h (1) {circle around (x)}h (1)F ){circle around (x)}s 0 +w 0 and
r 1 =( h (0) {circle around (x)}h (0)F +h (1) {circle around (x)}h (1)F ){circle around (x)}s 1 +w 1
where w 0 , w 1 , v 0 , and v 1 are noise components.