Iterative channel estimation and equalization with superimposed reference signals
In a transmitter apparatus, a known reference signal is superimposed on top of a data signal that is typically not known a priori to a receiver and the combined signal is transmitted. At a receiver, an iterative channel estimation and equalization technique is used to recover the reference signal and the unknown data signal. In the initial iteration, the known reference signal is recovered by treating the data signal as noise. Subsequent iterations are used to improve estimation of received reference signal and the unknown data signal.
1. A receiver-side apparatus for wireless communication, comprising:
a reception circuitry configured to receive, over a channel, a signal comprising a known reference signal superimposed on an unknown data signal; and
a processor, coupled to the reception circuitry, configured to:
(A) generate a channel estimate using the known reference signal and by demodulating the signal;
(B) use the channel estimate to equalize the channel, thereby producing an estimation of the data symbols and the superimposed reference signal;
(C) remove the known reference signal from the estimation obtained in Step (B);
(D) decode data output after removing the known reference signal in Step (C) thereby generating estimation of the unknown data signal and extrinsic estimations of encoded symbols in the signal;
(E) apply the channel estimate to the estimation of the unknown data signal and subtracting resulting signal from the received signal to generate a revised estimate of the received reference signal;
(F) generate a new channel estimation using the revised estimate of the received reference signal; and
(G) iterate Step (B) to step (G) until an exit criteria is met.
2. The apparatus of claim 1 , wherein the exit criteria comprises exceeding a number of iterations.
3. The apparatus of claim 1 , wherein the exit criteria comprises achieving an error-free decoding of the unknown data signal.
4. The apparatus of claim 1 , wherein in Step (A), the unknown data signal superimposed on the known reference signal are treated as noise.
5. The apparatus of claim 1 , wherein, in Step (A), the processor is further configured, as part of generating the channel estimate, to:
interpolate estimates at time-frequency locations where there is no known reference signal present.
6. The apparatus of claim 5 , wherein the interpolating includes using feedback information from a prior iteration to estimate the channel at the time-frequency locations where there is no known reference signal present.
7. A receiver-side apparatus for wireless communication, comprising:
a reception circuitry configured to receive, over a channel, a signal comprising a known reference signal superimposed on an unknown data signal; and
a processor, coupled to the reception circuitry, configured to:
(A) generate a channel estimate using the known reference signal and by demodulating the signal;
(B) apply the channel estimate obtained in Step (A) to the known reference signal and subtracting the result from the received signal;
(C) use the channel estimate to equalize the signal obtained in Step (B), thereby producing an estimation of the data symbols;
(D) decode data output thereby generating estimation of the unknown data signal and extrinsic estimations of encoded symbols in the signal;
(E) apply the channel estimate to the estimation of the unknown data signal and subtracting resulting signal from the received signal to generate a revised estimate of the received reference signal;
(F) generate a new channel estimation using the revised estimate of the received reference signal; and
(G) iterate Step (B) to step (G) until an exit criteria is met.
8. The apparatus of claim 7 , wherein the exit criteria comprises exceeding a number of iterations.
9. The apparatus of claim 7 , wherein the exit criteria comprises achieving an error-free decoding of the unknown data signal.
10. The apparatus of claim 7 , wherein in Step (A), the unknown data signal superimposed on the known reference signal are treated as noise.
11. The apparatus of claim 7 , wherein, in Step (A), the processor is further configured, as part of generating the channel estimate, to:
interpolate estimates at time-frequency locations where there is no known reference signal present.
12. The apparatus of claim 11 , wherein the interpolating includes using feedback information from a prior iteration to estimate the channel at the time-frequency locations where there is no known reference signal present.
13. A receiver-side apparatus for wireless communication, comprising:
a reception circuitry configured to receive, over a channel, a signal comprising a known reference signal superimposed on an unknown data signal over a channel; and
a processor, coupled to the reception circuitry, configured to:
(A) generate a channel estimate using the known reference signal and by demodulating the signal;
(B) use the channel estimate to equalize the channel, and subtracting the known reference signal therefrom;
(C) produce an estimation of the data symbols from signal resulting from subtracting in in Step (B);
(D) decode data output from the estimation of the data symbols obtained in step (C), thereby generating estimation on the unknown data signal and extrinsic estimations of encoded symbols in the signal;
(E) apply the channel estimate on the estimation of the unknown data signal and subtracting resulting signal from the received samples to generate a revised estimate of the received reference signal;
(F) generate a new channel estimation using the revised estimate of the received reference signal; and
(G) iterate Step (B) to step (G) until an exit criteria is met.
14. The apparatus of claim 13 , wherein the exit criteria comprises exceeding a number of iterations.
15. The apparatus of claim 13 , wherein the exit criteria comprises achieving an error-free decoding of the unknown data signal.
16. The apparatus of claim 13 , wherein in Step (A), the unknown data signal superimposed on the known reference signal are treated as noise.
17. A receiver-side apparatus for wireless communication, comprising:
a reception circuitry configured to receive, over a channel, a signal comprising a known reference signal superimposed on an unknown data signal; and
a processor, coupled to the reception circuitry, configured to:
(A) generate a channel estimate using the known reference signal and by demodulating the signal;
(B) apply the channel estimate obtained in Step (A) to the known reference signal and subtracting the result from the received signal;
(C) use the channel estimate to equalize the signal obtained in Step (B), thereby producing an estimation of the data symbols;
(D) decode data output from the estimation of the data symbols obtained in step (C), thereby generating estimation on the unknown data signal and extrinsic estimations of encoded symbols in the signal;
(E) apply the channel estimate on the estimation of the unknown data signal and subtracting resulting signal from the received samples to generate a revised estimate of the received reference signal;
(F) generate a new channel estimation using the revised estimate of the received reference signal; and
(G) iterate Step (B) to step (G) until an exit criteria is met.
18. The apparatus of claim 17 , wherein the exit criteria comprises exceeding a number of iterations.
19. The apparatus of claim 17 , wherein the exit criteria comprises achieving an error-free decoding of the unknown data signal.
20. The apparatus of claim 17 , wherein in Step (A), the unknown data signal superimposed on the known reference signal are treated as noise.