Wireless system having channel fading compensation using minimum mean square error
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 minimum mean square error. 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 minimum mean square error factor that is determined as [(H*·H+1/SNR) −1 ·H*]. More specifically, the H* represents channel matching and (H*·H+1/SNR) −1 represents interference cancellation due to channel fading over time or frequency.
1. A method for processing a diversity signal transmitted over a plurality of time-sensitive channel fading communication links, comprising:
receiving a first data stream transmitted over a first time-sensitive communication link during a first time period (t 1 ) and a second data stream transmitted over a second time-sensitive communication link during a second time period (t 2 ), wherein the first and second data streams correspond to the transmit-diversity signal;
multiplying said received first and second data streams by a mean square error [(H*·H+1/SNR) −1 ·H*], wherein H represents channel effects on the received first and second data streams and is represented by
H
=
[
h
1
(
t
1
)
h
2
(
t
1
)
h
2
*
(
t
2
)
-
h
1
*
(
t
2
)
]
,
where
h 1 (t 1 ) represents time-sensitive channel fading in the first communication link (h 1 ) during the first time period (t 1 ),
h 2 (t 1 ) represents time-sensitive channel fading in the second communication link (h 2 ) during the first time period (t 1 ),
h 2 *(t 2 ) is a complex conjugate of h 2 (t 2 ), which represents time-sensitive channel fading in the second communication link (h 2 ) during the second time period (t 2 ), and
−h 1 *(t 2 ) is a negative complex conjugate of h 1 (t 2 ), which represents time-sensitive channel fading in the first communication link (h 1 ) during the second time period (t 2 ); and
bypassing multiplication by the mean square error when substantially zero time-sensitive channel fading is present on the plurality of communication links.
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 and an associated first channel noise figure 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 and an associated second channel noise figure from the preamble of the data symbols received through the second channel;
determining an overall channel characteristic H from h 1 and h 2 ; and
determining a signal-to-noise ratio from the first and second noise figures.
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
]
.
4. The method according to claim 3 , wherein said multiplying comprises:
multiplying Y 1 and Y 2 * by the mean square error [(H*·H+1/SNR) −1 ·H*], where
H
=
[
h
1
(
t
1
)
h
2
(
t
1
)
h
2
*
(
t
2
)
-
h
1
*
(
t
2
)
]
and H* is the complex conjugate of H.
5. The method of claim 1 , wherein bypassing multiplication by the mean square error comprises multiplying the data stream by a constant scaling factor for unity gain.
6. A method for processing a diversity signal transmitted over a plurality of frequency-sensitive channel fading communication links, comprising:
receiving a first data stream transmitted over a first frequency-sensitive communication link in a first frequency range (f 1 ) and a second data stream transmitted over a second frequency-sensitive communication link in a second frequency range (f 2 ), wherein the first and second data streams correspond to the transmit-diversity signal;
multiplying said received first and second data streams by a mean square error [(H*·H+1/SNR) −1 ·H*], wherein H represents channel effects on the received first and second data streams and is represented by
H
=
[
h
1
(
f
1
)
h
2
(
f
1
)
h
2
*
(
f
2
)
-
h
1
*
(
f
2
)
]
,
where
h 1 (f 1 ) represents frequency-sensitive channel fading in the first communication link (h 1 ) over the first frequency range (f 1 ),
h 2 (f 1 ) represents frequency-sensitive channel fading in the second communication link (h 2 ) over the first frequency range (f 1 ),
h 2 *(f 2 ) is a complex conjugate of h 2 (f 2 ), which represents frequency-sensitive channel fading in the second communication link (h 2 ) over the second frequency range (f 2 ), and
−h 1 *(f 2 ) is a negative complex conjugate of h 1 (f 2 ), which represents frequency-sensitive channel fading in the first communication link (h 1 ) over the second frequency range (f 2 ); and
bypassing multiplication by the mean square error when substantially zero frequency-sensitive channel fading is present on the plurality of communication links.
7. The method according to claim 6 , wherein said receiving comprises:
receiving data symbols spread out over multiple frequencies through a first channel;
determining h 1 and an associated first channel noise figure 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 and an associated second channel noise figure from the preamble of the data symbols received through the second channel;
determining an overall channel characteristic H from h 1 and h 2 ; and
determining a signal-to-noise ratio from the first and second noise figures.
8. The method according to claim 7 , 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 C2 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
]
.
9. The method according to claim 8 , wherein said multiplying comprises multiplying Y 1 and Y 2 * by the mean square error [(H*·H +1/SNR) −1 ·H*], wherein
H
=
[
h
1
(
f
1
)
h
2
(
f
1
)
h
2
*
(
f
2
)
-
h
1
*
(
f
2
)
]
and H* is the complex conjugate of H.
10. A local area network receiver configured to process a diversity signal, comprising:
means for receiving a first data stream transmitted over a first time-sensitive communication link during a first time period (t 1 ) and a second data steam transmitted over a second time-sensitive communication link during a second time period (t 2 ), wherein the first and second data streams correspond to the transmit-diversity signal;
means for multiplying said received data stream by a mean square error [(H*·H+1/SNR) −1 ·H*], wherein H represents channel effects on the received first and second data streams and H is represented by
H
=
[
h
1
(
t
1
)
h
2
(
t
1
)
h
2
*
(
t
2
)
-
h
1
*
(
t
2
)
]
,
where
h 1 (t 1 ) represents time-sensitive channel fading in the first communication link (h 1 ) during the first time period (t 1 ),
h 2 (t 1 ) represents time-sensitive channel fading in the second communication link (h 2 ) during the first time period (t 1 ),
h 2 *(t 2 ) is a complex conjugate of h 2 (t 2 ), which represents time-sensitive channel fading in the second communication link (h 2 ) during the second time period (t 2 ), and
−h 1 *(t 2 ) is a negative complex conjugate of h 1 (t 2 ), which represents time-sensitive channel fading in the first communication link (h 1 ) during the second time period (t 2 ); and
means for bypassing multiplication by the mean square error when substantially zero time-sensitive channel fading is present on the plurality of communication links.
11. The local area network receiver according to claim 10 , 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;
means for determining an overall channel characteristic H from h 1 and h 2 ; and
means for determining a signal-to-noise ratio from the first and second noise figures.
12. The local area network receiver according to claim 11 , 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 wherein 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
]
.
13. The local area network receiver according to claim 12 , wherein said means for multiplying comprises means for multiplying Y 1 and y 2 * by the mean square error [(H*·H+1/SNR) −1 ·H*].
14. A local area network receiver configured to process a diversity signal, comprising:
means for receiving a first data stream transmitted over a frequency-sensitive communication link in a first frequency range (f 1 ) and a second data stream transmitted over a second frequency-sensitive communication link in a second frequency range (f 2 ), wherein the first and second data streams correspond to the transmit-diversity signal;
means for multiplying said received first and second data streams by a mean square error [(H*·H+1/SNR) −1 ·H*], wherein H represents channel effects on the received first and second data streams and is represented by
H
=
[
h
1
(
f
1
)
h
2
(
f
1
)
h
2
*
(
f
2
)
-
h
1
*
(
f
2
)
]
,
where
h 1 (f 1 ) represents frequency-sensitive channel fading in the first communication link (h 1 ) over the first frequency range (f 1 ),
h 2 (f 1 ) represents frequency-sensitive channel fading in the second communication link (h 2 ) over the first frequency range (f 1 ),
h 2 *(f 2 ) is a complex conjugate of h 2 (f 2 ), which represents frequency-sensitive channel fading in the second communication link (h 2 ) over the second frequency range (f 2 ), and
−h 2 *(f 2 ) is a negative complex conjugate of h 1 (f 2 ), which represents frequency-sensitive channel fading in the first communication link (h 1 ) over the second frequency range (f 2 ); and
means for bypassing multiplication by the mean square error when substantially zero frequency-sensitive channel fading is present on the plurality of communication links.
15. The local area network receiver according to claim 14 , 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 a second channel characteristic h 2 and an associated second channel noise figure from the preamble of the data symbols received through the second channel;
means for determining an overall channel characteristic H from h 1 and h 2 ; and
means for determining a signal-to-noise ratio from the first and second noise figures.
16. The local area network receiver according to claim 15 , 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 wherein 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
]
.
17. The local area network receiver according to claim 16 , wherein said means for multiplying comprises means for multiplying Y 1 and Y 2 * by the mean square error [(H*·H+1/SNR) −1 ·H*].