Spatial mapping of an OFDM signal to reduce attenuation from an individual transmit antenna in a MIMO transmitter
View Patent ↗A method is provided for transmitting a digital signal. The method includes generating a plurality of spatial streams from a digital signal and transforming the spatial streams into a plurality of space-time streams. Each of the space-time streams are cycled in the frequency domain among each of a plurality of transmit antennas. The space-time streams are wirelessly transmitted from the plurality of transmit antennas.
1. A method of transmitting a digital signal, comprising:
generating a plurality of spatial streams from a digital signal;
transforming the spatial streams into a plurality of space-time streams;
cycling in a frequency domain each of the space-time streams among each of a plurality of transmit antennas, including a first antenna and a second antenna, so each space-time stream is successively transmitted by each of the transmit antennas, wherein at least two spatial mapping matrices are selected for the cycling, including a first matrix for use with a first subcarrier and a second matrix, which is different from the first matrix, for use with a second subcarrier, the first matrix mapping each space-time stream entirely to the first antenna, and the second matrix mapping each space-time stream entirely to the second antenna; and
wirelessly transmitting each of the space-time streams from each of the plurality of transmit antennas.
2. The method of claim 1 wherein cycling in the frequency domain comprises applying a rotation matrix to each of the space-time streams.
3. The method of claim 2 wherein the rotation matrix is applied by spatially mapping the space-time streams.
4. The method of claim 3 wherein the plurality of space-time streams each include data and a preamble for estimating a channel transfer function, and further comprising applying spatial mapping by rotating both the data and the preamble of the space-time streams.
5. The method of claim 2 wherein a number of transmit chains is equal to 3 and rotation of the space-time streams to subcarriers k, k+1 and k+2 is performed by applying spatial mapping matrices Q k , Q k+1 , and Q k+2 , respectively, where
Q
k
=
[
1
0
0
0
1
0
0
0
1
]
Q
k
+
1
=
[
0
0
1
1
0
0
0
1
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Q
k
+
2
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1
0
0
0
0
1
0
1
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]
.
6. The method of claim 3 wherein the spatial mapping further comprises encoding the space-time streams using space time block coding (STBC).
7. The method of claim 1 wherein the digital signal employs a multicarrier modulation scheme.
8. The method of claim 7 wherein the multicarrier modulated digital signal has a plurality of subcarriers and the space-time streams are rotated in a manner that varies from subcarrier to subcarrier.
9. The method of claim 7 wherein the multicarrier digital signal is an Orthogonal Frequency Division Multiplexing (OFDM) signal.
10. The method of claim 9 wherein the OFDM signal is compatible with at least one IEEE 802.11 standard.
11. A wireless Multiple-Input-Multiple-Output (MIMO) transmitter, comprising:
a stream parser for generating a plurality of spatial streams from a digital signal;
a space time block coder (STBC) for mapping each of the spatial streams to a plurality of space-time streams;
a spatial mapper for spatially expanding each of the space-time streams by rotating the space-time streams in a frequency domain; and
an analog front end for modulating the spatially expanded space-time streams onto a wireless carrier, the analog front end including a plurality of transmit antennas, including a first antenna and a second antenna, and rotation of the space-time streams in the frequency domain including use of a first spatial mapping matrix with a first subcarrier and a second spatial mapping matrix with a second subcarrier, the second matrix being different from the first matrix;
wherein the first matrix maps each space-time stream entirely to the first antenna, and the second matrix maps each space-time stream entirely to the second antenna.
12. The MIMO transmitter of claim 11 wherein the digital signal is an OFDM signal and further comprising a QAM mapping element mapping data bits in the spatial streams to constellation points.
13. The MIMO transmitter of claim 11 wherein the space-time streams are rotated in a manner that varies from subcarrier to subcarrier.
14. The MIMO transmitter of claim 11 wherein a number of transmit chains employed by the analog front end is equal to 3 and rotation of the space-time streams to subcarriers k, k+1 and k+2 is performed by applying spatial mapping matrices Q k , Q k+1 , and Q k+2 , respectively, where
Q
k
=
[
1
0
0
0
1
0
0
0
1
]
Q
k
+
1
=
[
0
0
1
1
0
0
0
1
0
]
Q
k
+
2
=
[
1
0
0
0
0
1
0
1
0
]
.
15. At least one non-transitory computer-readable medium encoded with instructions which, when executed by a processor, performs a method including:
dividing a multicarrier digital signal having a plurality of subcarriers into a plurality of spatial streams;
mapping the spatial streams into a plurality of space-time streams; and
spatially mapping the space time streams by rotating the space-time streams in a frequency domain so each space-time stream is successively transmitted by each of a plurality of transmit antennas, including a first antenna and a second antenna;
wherein at least two spatial mapping matrices are selected for the rotating, including a first matrix for use with a first subcarrier and a second matrix, which is different from the first matrix, for use with a second subcarrier, the first matrix mapping each space-time stream entirely to the first antenna, and the second matrix mapping each space-time stream entirely to the second antenna.
16. The non-transitory computer-readable medium of claim 15 wherein the space-time streams are rotated in a manner that varies from subcarrier to subcarrier.
17. The non-transitory computer-readable medium of claim 15 wherein the plurality of space-time streams each include packets having data and a preamble for estimating a channel transfer function, and further comprising applying spatial mapping by rotating both the data and the preamble of packets in the space-time streams.
18. The non-transitory computer-readable medium of claim 15 wherein a number of transmit chains is equal to 3 and rotation of the space-time streams to subcarriers k, k+1 and k+2 is performed by applying spatial mapping matrices Q k , Q k+1 , and Q k+2 , respectively, where
Q
k
=
[
1
0
0
0
1
0
0
0
1
]
Q
k
+
1
=
[
0
0
1
1
0
0
0
1
0
]
Q
k
+
2
=
[
1
0
0
0
0
1
0
1
0
]
.
19. The non-transitory computer-readable medium of claim 15 wherein the multicarrier digital signal is an Orthogonal Frequency Division Multiplexing (OFDM) signal.
20. The non-transitory computer-readable medium of claim 19 wherein the OFDM signal is compatible with at least one IEEE 802.11 standard.
21. The non-transitory computer-readable medium of claim 15 wherein the spatial mapping further comprises encoding the space-time streams using space time block coding (STBC).