Method and apparatus providing an advanced MIMO receiver that includes a signal-plus-residual-interference (SPRI) detector
View Patent ↗A method is disclosed to obtain M final symbol decisions for signals received through N receive antennas that were transmitted in M parallel data layers, using a same spreading code from M transmit antennas. The method includes space-time equalizing the N received signals to generate M output signals from which at least inter-symbol interference is substantially removed and inter-layer interference is suppressed; despreading each of the M output signals for generating M soft symbol estimates; and processing the M soft symbol estimates to derive M final symbol decisions that are made in consideration of modeled residual inter-layer interference present in the space-time equalized M output signals. Processing includes operating a signal-plus-residual-interference (SPRI) detector that operates in accordance with a maximum likelihood (ML) technique, while space-time equalizing employs a linear minimum mean-square error (LMMSE) criterion. Transmitting may occur at a base station having the M transmit antennas, and receiving may occur at a mobile station having the N receive antennas.
1. A method, comprising:
space-time equalizing N received signals to generate M output signals from which at least inter-symbol interference is substantially removed and inter-layer interference is suppressed;
despreading each of the M output signals for generating M soft symbol estimates; and
processing the M soft symbol estimates to derive M final symbol decisions that are made in consideration of modeled residual inter-layer interference present in the space-time equalized M output signals.
2. A method as in claim 1 , where processing includes operating a signal-plus-residual interference (SPRI) detector that operates in accordance with a maximum likelihood (ML) technique.
3. A method as in claim 1 , where space-time equalizing employs a linear minimum mean-square error (LMMSE) criterion.
4. A method as in claim 1 , where transmitting occurs at a base station having the M transmit antennas, where receiving occurs at a mobile station having the N receive antennas, and where N<M.
5. A system to obtain M final symbol decisions for signals received through N receive antennas that were transmitted in M parallel data layers, using a same spreading code from M transmit antennas, comprising:
a space-time equalizer configured to operate on the N received signals to generate M output signals from which at least inter-symbol interference is substantially removed and interlayer interference is suppressed;
a plurality of despreaders configured to despread each of the M output signals to generate M soft symbol estimates; and
processing apparatus configured to process the M soft symbol estimates to derive M final symbol decisions that are made in consideration of modeled residual inter-layer interference present in the M output signals of said space-time equalizer.
6. A system as in claim 5 , where said processing apparatus comprises a signal-plus-residual-interference (SPRI) detector that operates in accordance with a maximum likelihood (ML) technique.
7. A system as in claim 5 , where said space-time equalizer employs a linear minimum mean-square error (LMMSE) criterion.
8. A system as in claim 5 , where the M transmit antennas are associated with a base station, where the N receive antennas are associated with a mobile station, and where N<M.
9. A Multiple Input, Multiple Output (MIMO) RF receiver, configured to receive M symbols transmitted in M parallel data layers through N receive antennas, using a same spreading code, c(k), from M transmit antennas; a space-time equalizer having N inputs coupled to said N receive antennas and M outputs coupled to individual ones of M code correlators; a signal model generator having an input coupled to a channel estimator and an output for outputting at least a model of residual inter-layer interference; and a signal-plus-residual-interference (SPRI) detector having M inputs coupled to outputs of said M code correlators configured to receive M soft symbol estimates there from, a further input coupled to said output of said signal model generator, and M outputs configured to output M final symbol decisions that are made taking into account the residual inter-layer interference that was not removed by said space-time equalizer.
10. A MIMO RF receiver as in claim 9 , where said signal model generator computes:
A
jm
=
w
m
H
(
h
j1
h
j2
⋮
h
jM
)
,
j
=
1
,
2
,
…
,
M
,
where A jm is the residual amplitude of the symbol from transmit antenna j when a symbol from transmit antenna m is detected by said space-time equalizer.
11. A MIMO RF receiver as in claim 10 , where said SPRI detector uses a maximum-likelihood (ML) criterion to obtain the final symbol decisions as:
(
s
_
1
s
_
2
⋮
s
_
M
)
=
arg
min
u
1
,
u
2
,
…
u
M
{
∑
m
=
1
M
s
^
m
-
(
A
1
m
A
2
m
…
A
Mm
)
(
u
1
u
2
⋮
u
M
)
2
}
,
where detection of an mth data layer is based on the outputs of all of said M code correlators.
12. A MIMO RF receiver as in claim 9 , where said signal model generator generates signal models for both desired signals and for interfering signals appearing at said M outputs of said space-time equalizer.
13. A MIMO RF receiver as in claim 9 , where said space-time equalizer operates with a linear minimum mean-square error (LMMSE) criterion.
14. A MIMO RF receiver as in claim 9 , where N<M.
15. A received signal-plus-residual-interference (SPRI) detector comprising M inputs configured to be coupled to M sources of soft symbol estimates, a further input configured to be coupled to an output of a signal model generator that models residual inter-layer interference present in an equalized received signal, and M outputs configured to output M final symbol decisions that are made taking into account the residual inter-layer interference.
16. The SPRI detector as in claim 15 , where the signal model generator computes:
A
jm
=
w
M
H
(
h
j1
h
j2
⋮
h
jM
)
,
j
=
1
,
2
,
…
,
M
,
where A jm is the residual amplitude of a symbol from transmit antenna j when a symbol from transmit antenna m is detected by a space-time equalizer that generates the equalized received signal, and where said SPRI detector uses a maximum-likelihood (ML) criterion to obtain the final symbol decisions as:
(
s
_
1
s
_
2
⋮
s
_
M
)
=
arg
min
u
1
,
u
2
,
⋯
u
-
M
{
∑
m
=
1
M
s
^
m
-
(
A
1
m
A
2
m
⋯
A
Mm
)
(
u
1
u
2
⋮
u
M
)
2
}
,
where detection of an mth data layer is based on all said M sources of soft symbol estimates.
17. The SPRI detector as in claim 15 , where the received signal is received through N receive antennas from M transmit antennas, where N≦M.
18. A system to obtain M final symbol decisions for signals received through N receive antennas that were transmitted in M parallel data layers, using a same spreading code from M transmit antennas, comprising:
an equalizer configured to operate on the N received signals to generate M output signals from which at least inter-symbol interference is substantially removed and inter-layer interference is suppressed;
a plurality of despreaders arranged to despread each of the M output signals for generating M soft symbol estimates; and
processing apparatus configured to process the M soft symbol estimates to derive M final symbol decisions that are made in consideration of modeled residual inter-layer interference present in the M output signals of said equalizer.
19. A system as in claim 18 , where said processing apparatus comprises a signal-plus-residual-interference (SPRD detector.
20. A system as in claim 19 , where said SPRI detector operates in accordance with a maximum likelihood (ML) technique.
21. A system as in claim 19 , where said SPRI detector operates in accordance with a Maximum a posteriori (MAP) technique.
22. A system as in claim 19 , where said system forms a part of an ordered successive interference canceller (OSIC) receiver.