Method and apparatus using sounding PPDUs to provide range extension to IEEE 802.11n signals
View Patent ↗A wireless transmitter includes a stream parser for generating a plurality of spatial streams from a digital signal and a space time block coder (STBC) for mapping each of the spatial streams to a plurality of space-time streams that each include data and a preamble for estimating a channel transfer function. The transmitter also includes a spatial mapper for spatially expanding each of the space-time streams by applying a spatial expansion matrix to data and to first training symbols used in the preamble to probe a channel experienced by the data and by applying an extension matrix to second training symbols used in the preamble to probe at least one additional dimension of the channel to enable use of beamforming to achieve range extension The spatial expansion matrix and the extension matrix form an overall matrix that has at least two orthogonal columns with different norms. The wireless transmitter also includes an analog front end for modulating the spatially expanded space-time streams onto a wireless carrier.
1. A wireless 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 that each include data and a preamble for estimating a channel transfer function;
a spatial mapper for spatially expanding each of the space-time streams by applying a spatial expansion matrix to data and to first training symbols used in the preamble to probe a channel experienced by the data and by applying an extension matrix to second training symbols used in the preamble to probe at least one additional dimension of the channel to enable use of beamforming to achieve range extension, wherein the spatial expansion matrix and the extension matrix form an overall matrix that has at least two orthogonal columns with different norms; and
an analog front end for modulating the spatially expanded space-time streams onto a wireless carrier.
2. The wireless transmitter of claim 1 wherein the number of space-time streams is equal to 2 and a number of transmit chains is equal to 3, and wherein the spatial expansion matrix Q D and the extension matrix Q E are as follows:
D
1
,
1
,
ⅇ
j
θ
k
[
1
0
0
1
1
0
]
Q
D
2
3
D
1
,
1
,
ⅇ
j
θ
k
[
-
1
0
1
]
Q
E
1
2
D
α
1
,
…
,
α
n
=
diag
(
α
1
,
…
,
α
n
)
is a diagonal matrix
θ k =−2πkΔ F τ CS where Δ F is the subcarrier frequency spacing and τ CS is related to a delay applied to a transmit chain.
3. The wireless transmitter of claim 1 wherein the number of space-time streams is equal to 2 and a number of transmit chains is equal to 4, and wherein the spatial expansion matrix Q D and the extension matrix Q E are as follows:
D
1
,
1
,
ⅇ
j
θ
k
,
ⅇ
j
θ
k
[
1
0
0
1
1
0
0
1
]
Q
D
1
2
D
1
,
1
,
ⅇ
j
θ
k
,
ⅇ
j
θ
k
[
-
1
0
0
-
1
1
0
0
1
]
Q
E
1
2
α
1
,
…
D
,
α
n
=
diag
(
α
1
,
…
,
α
n
)
is a diagonal matrix
θ k =−2πkΔ F τ CS where Δ F is the subcarrier frequency spacing and τ CS is related to a delay applied to a transmit chain.
4. The wireless transmitter of claim 1 wherein the number of space-time streams is equal to 3 and a number of transmit chains is equal to 4, and wherein the spatial expansion matrix Q D and the extension matrix Q E are as follows:
D
1
,
1
,
1
,
ⅇ
j
θ
k
[
1
0
0
0
1
0
0
0
1
1
0
0
]
Q
D
3
2
D
1
,
1
,
1
,
ⅇ
j
θ
k
[
-
1
0
0
1
]
Q
E
1
2
α
1
,
…
D
,
α
n
=
diag
(
α
1
,
…
,
α
n
)
is a diagonal matrix
θ k =−2πkΔ F τ CS where Δ F is the subcarrier frequency spacing and τ CS , is related to a delay applied to a transmit chain.
5. The wireless transmitter of claim 1 wherein the STBC is further configured to apply cyclic shifts to each transmit chain.
6. The wireless transmitter of claim 1 wherein the spatial streams generated by the stream parser include sounding physical layer protocol data units (PPDUs) that are used to measure channel characteristics.
7. The wireless transmitter of claim 6 wherein the sounding PPDUs are compatible with IEEE 802.11 standards.
8. A non-transitory computer-readable medium encoded with instructions which, when executed by a processor, performs a method including:
dividing a digital signal into a plurality of spatial streams;
mapping the spatial streams into a plurality of space-time streams that each include data and a preamble for estimating a channel transfer function;
spatially mapping the space time streams by applying a spatial expansion matrix to data and to first training symbols used in the preamble to probe a channel experienced by the data and by applying an extension matrix to second training symbols used in the preamble to probe at least one additional dimension of the channel to enable use of beamforming to achieve range extension, wherein the spatial expansion matrix and the extension matrix form an overall matrix that has at least two orthogonal columns with different norms; and
wirelessly transmitting each of the spatially mapped space-time streams.
9. The non-transitory computer-readable medium of claim 8 wherein the number of space-time streams is equal to 2 and a number of transmit chains is equal to 3, and wherein the spatial expansion matrix Q D and the extension matrix Q E are as follows:
D
1
,
1
,
ⅇ
j
θ
k
[
1
0
0
1
1
0
]
Q
D
2
3
D
1
,
1
,
ⅇ
j
θ
k
[
-
1
0
1
]
Q
E
1
2
D
α
1
,
…
,
α
n
=
diag
(
α
1
,
…
,
α
n
)
is a diagonal matrix
θ k =−2πkΔ F τ CS where Δ F is the subcarrier frequency spacing and τ CS is related to a delay applied to a transmit chain.
10. The non-transitory computer-readable medium of claim 8 wherein the number of space-time streams is equal to 2 and a number of transmit chains is equal to 4, and wherein the spatial expansion matrix Q D and the extension matrix Q E are as follows:
D
1
,
1
,
ⅇ
j
θ
k
,
ⅇ
j
θ
k
[
1
0
0
1
1
0
0
1
]
Q
D
1
2
D
1
,
1
,
ⅇ
j
θ
k
,
ⅇ
j
θ
k
[
-
1
0
0
-
1
1
0
0
1
]
Q
E
1
2
α
1
,
…
D
,
α
n
=
diag
(
α
1
,
…
,
α
n
)
is a diagonal matrix
θ k =−2πkΔ F τ CS where Δ F is the subcarrier frequency spacing and τ CS is related to a delay applied to a transmit chain.
11. The non-transitory computer-readable medium of claim 8 wherein the number of space-time streams is equal to 3 and a number of transmit chains is equal to 4, and wherein the spatial expansion matrix Q D and the extension matrix Q E are as follows:
D
1
,
1
,
1
,
ⅇ
j
θ
k
[
1
0
0
0
1
0
0
0
1
1
0
0
]
Q
D
3
2
D
1
,
1
,
1
,
ⅇ
j
θ
k
[
-
1
0
0
1
]
Q
E
1
2
α
1
,
…
D
,
α
n
=
diag
(
α
1
,
…
,
α
n
)
is a diagonal matrix
θ k =−2πkΔ F τ CS where Δ F is the subcarrier frequency spacing and τ CS is related to a delay applied to a transmit chain.
12. The non-transitory computer-readable medium of claim 8 further comprising applying cyclic shifts to each transmit chain.
13. The non-transitory computer-readable medium of claim 8 wherein the spatial streams include sounding physical layer protocol data units (PPDUs) that are used to measure channel characteristics.
14. The non-transitory computer-readable medium of claim 13 wherein the sounding PPDUs are compatible with IEEE 802.11 standards.
15. A non-transitory computer-readable medium encoded with instructions which, when executed by a processor, performs a method including:
receiving a wireless signal that includes a preamble used to estimate a channel transfer function H of a channel experienced by the wireless signal during transmission thereof, wherein the preamble includes first training symbols to which a spatial expansion matrix Q D is applied and second training symbols to which an extension matrix Q E is applied, wherein the first training symbols probe the channel experienced by the wireless signal and the second training symbols probe at least one additional dimension of the channel and wherein the spatial expansion matrix Q D and the extension matrix Q E form an overall matrix that has at least two orthogonal columns with different norms;
estimating values for HQ E and HQ D using known values for Q D and Q E ; and
obtaining a value for the channel transfer function H from the estimated values of HQ E and HQ D .
16. The non-transitory computer-readable medium of claim 15 further comprising forwarding to a source of the wireless signal channel state information acquired from the value of the channel transfer function to enhance the signal quality of wireless signal.
17. The non-transitory computer-readable medium of claim 16 wherein the channel state information is sufficient to allow use of beamforming at the source.
18. The non-transitory computer-readable medium of claim 16 wherein the channel state information is sufficient to use for calibration to thereby restore reciprocity between downlink and uplink channels.
19. The non-transitory computer-readable medium of claim 15 wherein the spatial expansion matrix Q D is a matrix having columns orthogonal to one another and the channel transfer function H is obtained from the relation [HQ D HQ E ]=HQ, where Q=[Q D Q E ].