Systems and methods for multistage signal detection in mimo transmissions and iterative detection of precoded OFDM
Systems and methods for multi-stage signal detection in MIMO transmission including Bernoulli-Gaussian detection are provided. A multistage iterative signal decoder is provided that exploits the property that in a relatively simply decoding scheme such as mean square error (MSE) or zero-forcing (ZF) only a small portion of the total symbols are mis-detected. Therefore, an optimality test is performed on the output of a relatively low complexity decoder unit. If the symbol passes the optimality test, it is presumed to be correctly decoded. Otherwise, the symbol is sent for further processing to a relatively higher complexity decoding unit such as a sphere decoder. In this way, processing efficiency is increased, because only those symbols requiring additional processing are processed by the high complexity processing unit.
1. A multistage system for signal detection comprising:
a first relatively low complexity detection unit configured to detect received symbols;
an optimality test unit configured to test the output of the first detection unit; and
a second relatively high complexity detection unit configured to reprocess those received symbols that fail a condition of the optimality test unit.
2. The system of claim 1 , wherein the system is part of a multi-carrier transmission system having a plurality of different sub-channels each carrying bits of data.
3. The system of claim 1 , wherein the received symbols are precoded QAM symbols.
4. The system of claim 1 , wherein the first relatively low complexity detection unit is a minimum MSE detection unit.
5. The system of claim 1 , wherein only symbols transmitted on tones presenting a SNR below a predetermined threshold are subjected to the optimality test.
6. The system of claim 1 , further comprising a second detecting unit interposed between an output of the optimality test unit and an input of a second optimality test unit, adapted to perform reprocessing on symbol output by the first detecting unit.
7. The system of claim 1 , wherein the optimality test unit determines whether a symbol has been detected correctly or if it needs further processing by the second detection unit or modification as determined by the optimality test.
8. The system of claim 7 , wherein the optimality test unit determines that a symbol has been detected correctly if syndrome value is less than zero.
9. The system of claim 8 , wherein the syndrome is defined as the vector Q, where
Q
=
A
-
Γ
⊗
d
2
diag
(
R
H
)
,
where {circle around (X)} denotes the element-wise product.
10. A method of detecting signals comprising:
detecting a received signal containing at least one symbol with a first detector;
performing an optimality test on the output of the first detector; and
for those symbols passing the optimality test, outputting the symbols, otherwise, processing the symbols with a second detector.
11. The method of claim 10 , wherein detecting with a first detector comprises detecting with a zero-forcing (ZF) detecting unit.
12. The method of claim 10 , further comprising performing a nulling and canceling operation on symbols failing the optimality test prior to subjecting those symbols to the a second optimality test.
13. The method of claim 10 , wherein the received signal is a symbol carried over a communication channel having a plurality of sub-carriers each carrying information.
14. The method of claim 13 , wherein only symbols transmitted on sub-carriers presenting an SNR below a predetermined threshold are subjected to the optimality test.
15. The method of claim 10 , wherein the received signal comprises precoded QAM symbols.
16. The method of claim 15 , wherein detecting with a first detector comprises decoding with an MSE detecting unit.
17. The method of claim 10 , wherein the optimality test unit determines that a symbol has passed the optimality test if a syndrome value is less than zero.
18. The method of claim 17 , wherein the syndrome is defined as the vector Q, where
Q
=
A
-
Γ
⊗
d
2
diag
(
R
H
)
,
where {circle around (X)} denotes the element-wise product.
19. An iterative method of detecting blindly precoded OFDM symbols comprising:
performing a first iteration of a B-G algorithm approximating a joint M-L detection on received; and
iteratively running the B-G algorithm updating the data with the results of the previous iteration using update equations (37), (38) and (39).