Wireless system having channel fading compensation using zero-forcing
View Patent ↗A MISO wireless LAN includes multiple inputs and a single output. The present invention includes a method and apparatus of compensating for time sensitive or frequency sensitive channel fading using zero forcing. The time sensitive channel fading is represented by the vector [H(t)], and the interference compensation is performed by multiplying the incoming data by a zero forcing factor that is determined as [(H*·H) −1 ·H*]. More specifically, the H* represents channel matching and (H*·H) −1 represents interference cancellation due to channel fading over time or frequency.
1. A method of processing a signal transmitted over a communication link, comprising:
receiving a data stream; and
multiplying the received data stream by a zero-forcing factor [(H*·H) −1 ·H*], wherein H represents channel effects on the received data stream, including time-sensitive channel fading effects, and is represented by
H
=
[
h
1
(
t
1
)
h
2
(
t
1
)
h
2
*
(
t
2
)
-
h
1
*
(
t
2
)
]
,
and
wherein t 1 and t 2 comprise adjacent time periods over which a plurality of data symbols in the data stream is received by a receiver.
2. The method according to claim 1 , wherein said receiving comprises:
receiving data symbols through a first channel, wherein the data symbols are separated in time;
determining h 1 from a preamble of the data symbols received through the first channel;
receiving the data symbols through a second channel, wherein the data symbols are separated in time;
determining h 2 from the preamble of the data symbols received through the second channel;
wherein h 1 and h 2 are subject to changes over time; and
determining H from h 1 and h 2 .
3. The method according to claim 2 , wherein said receiving comprises:
receiving a first data symbol C 1 through the first channel;
receiving a second data symbol C 2 through the second channel;
receiving the negative complex conjugate of the second data symbol C 2 through the first channel;
receiving the complex conjugate of the first data symbol C 1 through the second channel; and
generating
Y
1
=
h
1
C
1
+
h
2
C
2
Y
2
=
-
h
1
C
2
*
+
h
2
C
1
*
Y
2
*
=
h
2
*
C
1
-
h
1
*
C
2
;
wherein
[
Y
1
Y
2
*
]
=
[
h
1
(
t
1
)
h
2
(
t
1
)
h
2
*
(
t
2
)
-
h
1
*
(
t
2
)
]
·
[
C
1
C
2
]
,
and
wherein t 1 and t 2 comprise adjacent time periods over which the first and second data symbols, C 1 and C 2 respectively, are received by the first and second channels.
4. The method according to claim 3 , wherein said multiplying comprises multiplying Y 1 and Y 2 * by the zero-forcing factor [(H*·H) −1 ·H*], wherein
H* is the complex conjugate of H.
5. The method of claim 1 , further comprising:
bypassing multiplication by the zero-forcing factor to reduce at least one of battery power and processing time in a receiver configured to receive the data stream.
6. The method of claim 5 , wherein bypassing multiplication by the zero-forcing factor comprises bypassing multiplication when there is little or no channel fading over time.
7. The method of claim 6 , wherein bypassing multiplication by the zero-forcing factor comprises multiplying the received data stream by a constant scaling factor for unity gain.
8. A method of processing a signal transmitted over a communication link, comprising:
receiving a data stream; and
multiplying the received data stream by a zero-forcing factor [(H*·H) −1 ·H*], wherein H represents channel effects on the received data, including frequency-sensitive channel fading effects, and is represented by
H
=
[
h
1
(
f
1
)
h
2
(
f
1
)
h
2
*
(
f
2
)
-
h
1
*
(
f
2
)
]
,
and
wherein f 1 and f 2 comprise adjacent frequency channels over which a plurality of data symbols in the data stream is received by a receiver.
9. The method according to claim 8 , wherein said receiving comprises:
receiving data symbols spread out over multiple frequencies through a first channel;
determining h 1 from a preamble of the data symbols received through the first channel;
receiving the data symbols spread out over multiple frequencies through a second channel;
determining h 2 from the preamble of the data symbols received through the second channel;
wherein h 1 and h 2 are subject to changes over frequency; and
determining H from h 1 and h 2 .
10. The method according to claim 9 , wherein said receiving comprises:
receiving a first data symbol C 1 through the first channel;
receiving a second data symbol C 2 through the second channel;
receiving the negative complex conjugate of the second data symbol C 2 through the first channel;
receiving the complex conjugate of the first data symbol C 1 through the second channel; and
generating
Y
1
=
h
1
C
1
+
h
2
C
2
Y
2
=
-
h
1
C
2
*
+
h
2
C
1
*
Y
2
*
=
h
2
*
C
1
-
h
1
*
C
2
;
wherein
[
Y
1
Y
2
*
]
=
[
h
1
(
f
1
)
h
2
(
f
1
)
h
2
*
(
f
2
)
-
h
1
*
(
f
2
)
]
·
[
C
1
C
2
]
,
and
wherein f 1 and f 2 comprise adjacent frequency channels over which the first and second data symbols, C 1 and C 2 respectively, are received by the first and second channels.
11. The method according to claim 10 , wherein said multiplying comprises multiplying Y 1 and Y 2 * by the zero-forcing factor [(H*·H) −1 ·H*], wherein
H* is the complex conjugate of H.
12. A local area network receiver configured to process a signal transmitted over a communication link, comprising:
means for receiving a data stream; and
means for multiplying the received data stream by a zero-forcing factor [(H*·H) −1 ·H*], wherein H represents channel effects on the received data stream, including time-sensitive channel fading effects, and is represented by
H
=
[
h
1
(
t
1
)
h
2
(
t
1
)
h
2
*
(
t
2
)
-
h
1
*
(
t
2
)
]
,
and
wherein t 1 and t 2 comprise adjacent time periods over which a plurality of data symbols in the data stream is received by a receiver.
13. The apparatus according to claim 12 , wherein said means for receiving comprises:
a first antenna that receives data symbols from a first channel, wherein the data symbols are separated in time;
means for determining h 1 and an associated first channel noise figure from a preamble of the data symbols received through the first channel;
a second antenna that receives the data symbols from a second channel, wherein the data symbols are separated in time;
means for determining h 2 and an associated second channel noise figure from the preamble of the data symbols received through the second channel;
wherein h 1 and h 2 are subject to changes over time;
means for determining H from h 1 and h 2 ; and
means for determining a signal-to-noise ratio from the first and second noise figures.
14. The apparatus according to claim 13 , wherein:
said first antenna receives a first data symbol C 1 and a negative complex conjugate of a second data symbol C 2 through the first channel;
said second antenna receives a second data symbol C 2 and the complex conjugate of the first data symbol C 1 through the second channel; and
said means for receiving comprises means for generating
Y
1
=
h
1
C
1
+
h
2
C
2
Y
2
=
-
h
1
C
2
*
+
h
2
C
1
*
Y
2
*
=
h
2
*
C
1
-
h
1
*
C
2
;
wherein
[
Y
1
Y
2
*
]
=
[
h
1
(
t
1
)
h
2
(
t
1
)
h
2
*
(
t
2
)
-
h
1
*
(
t
2
)
]
·
[
C
1
C
2
]
,
and
wherein t 1 and t 2 comprise adjacent time periods over which the first and second data symbols, C 1 and C 2 respectively, are received by the first and second channels.
15. The apparatus according to claim 14 , wherein said means for multiplying comprises:
means for multiplying Y 1 and Y 2 * by the zero-forcing factor [(H*·H) −1 ·H*].
16. A local area network receiver configured to process a signal transmitted over a communication link, comprising:
means for receiving a data stream; and
means for multiplying the received data stream by a mean square error [(H*·H) −1 ·H*], wherein H represents channel effects on the received data, including frequency-sensitive channel fading effects, and is represented by
H
=
[
h
1
(
f
1
)
h
2
(
f
1
)
h
2
*
(
f
2
)
-
h
1
*
(
f
2
)
]
,
and
wherein f 1 and f 2 comprise adjacent frequency channels over which a plurality of data symbols in the data stream is received by a receiver.
17. The apparatus according to claim 16 , wherein said means for receiving comprises:
a first antenna that receives data symbols from a first channel, wherein the data symbols are separated in frequency;
means for determining h 1 and an associated first channel noise figure from a preamble of the data symbols received through the first channel;
a second antenna that receives the data symbols from a second channel, wherein the data symbols are separated in frequency;
means for determining h 2 and an associated second channel noise figure from the preamble of the data symbols received through the second channel;
wherein h 1 and h 2 are subject to changes over frequency;
means for determining H from h 1 and h 2 ; and
means for determining a signal-to-noise ratio from the first and second noise figures.
18. The apparatus according to claim 17 , wherein:
said first antenna receives a first data symbol C 1 and a negative complex conjugate of a second data symbol C 2 through the first channel;
said second antenna receives a second data symbol C 2 and the complex conjugate of the first data symbol C 1 through the second channel;
said means for receiving comprises means for generating
Y
1
=
h
1
C
1
+
h
2
C
2
Y
2
=
-
h
1
C
2
*
+
h
2
C
1
*
Y
2
*
=
h
2
*
C
1
-
h
1
*
C
2
;
wherein
[
Y
1
Y
2
*
]
=
[
h
1
(
f
1
)
h
2
(
f
1
)
h
2
*
(
f
2
)
-
h
1
*
(
f
2
)
]
·
[
C
1
C
2
]
,
and
wherein f 1 and f 2 comprise adjacent frequency channels over which the first and second data symbols, C 1 and C 2 respectively, are received by the first and second channels.
19. The apparatus according to claim 18 , wherein said means for multiplying comprises:
means for multiplying Y 1 and Y 2 * by the zero-forcing factor [(H*·H) −1 ·H*].
20. The apparatus according to claim 17 , wherein said means for receiving comprises:
the first antenna receiving the data symbols spread out over multiple frequencies from the first channel;
means for determining h 1 from a preamble of the data symbols received from the first channel;
the second antenna receiving the data symbols spread out over multiple frequencies from the second channel;
means for determining h 2 from the preamble of the data symbols received from the second channel.