Multiplex communications – Communication over free space – Having a plurality of contiguous regions served by...
Reexamination Certificate
1998-10-22
2001-05-15
Nguyen, Chau (Department: 2663)
Multiplex communications
Communication over free space
Having a plurality of contiguous regions served by...
C370S342000, C370S441000, C370S479000, C370S468000
Reexamination Certificate
active
06233230
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to decoding in a spread spectrum, code division, multiple access (CDMA) communication system and, more particularly, to an apparatus and method of determining a data rate of an encoded user communication for purposes of controlling decoding of the user communication using a viterbi decoder.
2. Related Art
The CDMA system is interference limited, i.e. signals from one user create interference to the other users. Performance of the system depends on the total interference level. The system is designed so that every user transmits as little power as possible and only when it is necessary, thereby allowing the whole system to support more users.
In the IS-95 standard, the data rate depends on the speech activity and can change from frame to frame. However, the receiver does not know the data rates of the received frames. Referring to
FIG. 1
, a prior art CDMA receiver is shown. The user communication signal is received by a RAKE receiver and passed to three averaging circuits
14
a
,
14
b
, and
14
c
connected in parallel where an average of pairs, 4 tuples, and 8 tuples, respectively, is made. The output of the RAKE receiver is also supplied to the input of a first viterbi decoder
16
a
. The output of the averaging circuit
14
a
is supplied to the input of a viterbi decoder
16
b
. The output of the averaging circuit
14
b
is supplied to the input of a viterbi decoder
16
c
. The output of the averaging circuit
14
c
is supplied to the input of a viterbi decoder
16
d
. One output from each of the viterbi decoders
16
a
,
16
b
,
16
c
, and
16
d
is supplied to a selector circuit
24
. Another output from each of the viterbi decoders
16
a
,
16
b
,
16
c
, and
16
d
is supplied through a separate encoder
18
a
,
18
b
,
18
c
and
18
d
and a separate bit error counter
20
a
,
20
b
,
20
c
and
20
d
, respectively, to a comparator
22
. The comparator
22
outputs a signal to the selector
24
indicative of the which bit error counter has the least bit errors and the selector
24
then selects the output of the corresponding viterbi decoder
16
a
,
16
b
,
16
c
, and
16
d
as the output.
Therefore, conventionally, in order to decode the received frame correctly, the received frame has to be decoded four times using viterbi decoding for the four data rates 1.2 kbps, 2.4 kbps, 4.8 kbps and 9.6 kbps in rate set 1 or 1.8 kbps, 3.6 kbps, 7.2 kbps and 14.4 kbps in rate set 2. Then the four decoded frames are re-encoded and the re-encoded frames are compared with the original received frame. The embedded CRC bits or the number of bit corrections will then tell which sub-rate was transmitted. However, this method requires high complexity and power consumption because the receiver has to decode the received frame four times.
Various attempts to avoid this problem have been proposed. Channel decoding power consumption at the mobile station can be reduced by determining the sub-rate (“rate determination”) prior to applying the viterbi decoder. For such methods, the viterbi decoder is applied once per frame. Papers which describe these methods are: E. Cohen and H. Lou, “Multi-rate Detection for the IS-95 CDMA forward traffic channels”,
IEEE Global Telecommunications Conference,
November 1995 (hereinafter referred to as the “Cohen-Lou method”); E. Cohen and H. Lou, “Multi-rate Detection for the IS-95A CDMA Forward Traffic Channels Using The 13 kbps Speech Coder”,
IEEE International Conference on Communications,
1996; H. Kwon, S. Ratanamahatana, and J. Shim, “One Viterbi Decoder with Data Rate Estimation for IS-95 CDMA Wireless Communications”,
IEEE,
1997. Patents which describe such processes are U.S. Pat. Nos. 5,509,020 and 5,796,757. However, such prior art methods are often complex, requiring many arithmetic operations which require more power and are difficult to implement in actual practice with acceptable accuracy.
SUMMARY OF THE INVENTION
An apparatus for determining a data rate of a received, encoded signal, according to the invention includes a deinterleaver for deinterleaving the recorded, encoded signal and outputting a frame of deinterleaved symbols, a feature calculation circuit for applying a plurality of different algorithms to the frame of deinterleaved symbols to produce a corresponding plurality of output feature values which are indicative of a degree of repetition of the deinterleaved symbols, and a neural network for processing the plurality of output feature values according to a predetermined set of weights to produce a plurality of output rate determination values y
1
, y
2
, . . . y
n
, each of which corresponds to a different data rate, where m≦y≦M, n is an integer and m and M are predetermined minimum and maximum values, respectively. A rate detection circuit compares the plurality of output rate determination values y
1
, y
2
, . . . y
n
and selects a rate corresponding to the largest output rate determination value y
1
, y
2
, . . . y
n
. Where the encoded signal is a CDMA signal, then there are 384 deinterleaved symbols per frame and m=0 and M=1.
Preferably, the data rates include a full data rate, a half data rate, a quarter data rate, and an eighth data rate. The feature calculation circuit calculates four output feature values, x
1
, x
2
, x
3
, and x
4
according to the following algorithms:
x
1
=
∑
k
=
0
191
&LeftBracketingBar;
b
2
k
+
b
2
k
+
1
&RightBracketingBar;
∑
k
=
0
383
&LeftBracketingBar;
b
k
&RightBracketingBar;
x
2
=
∑
k
=
0
95
&LeftBracketingBar;
b
4
k
+
b
4
k
+
1
+
b
4
k
+
2
+
b
4
k
+
3
&RightBracketingBar;
∑
k
=
0
383
&LeftBracketingBar;
b
k
&RightBracketingBar;
x
3
=
∑
k
=
0
47
&LeftBracketingBar;
b
8
k
+
b
8
k
+
1
+
b
8
k
+
2
+
b
8
k
+
3
+
b
8
k
+
4
+
b
8
k
+
5
+
b
8
k
+
6
+
b
8
k
+
7
&RightBracketingBar;
∑
k
=
0
383
&LeftBracketingBar;
b
k
&RightBracketingBar;
x
4
=
∑
k
=
0
383
&LeftBracketingBar;
&LeftBracketingBar;
b
k
&RightBracketingBar;
-
1
384
∑
j
=
0
383
&LeftBracketingBar;
b
j
&RightBracketingBar;
&RightBracketingBar;
∑
k
=
0
383
&LeftBracketingBar;
b
k
&RightBracketingBar;
where x
1
indicates the degree of consistent repetition within every 2 deinterleaved symbols, x
2
indicates the degree of consistent repetition within every 4 deinterleaved symbols, x
3
indicates the degree of consistent repetition within every 8 deinterleaved symbols, and x
4
indicates a noise to signal+noise ratio.
In the preferred embodiment, each weight in the neural network between x
j
; and a sigmoid function representative of y
i
is w
ij
(i references the row, j the column):
W
ij
=
−14.8069
0.446381
−7.97306
−11.3604
34.818
−19.103
−0.950632
1.12659
−20.101
41.8083
−22.1198
8.47819
−6.93596
−19.5672
27.6596
12.6207
c
i
=
20.1445
−17.2149
−5.694
−3.85499
where c
i
is a bias value.
where c
i
is a bias value.
Another embodiment of the invention is an apparatus for decoding a received, encoded data signal having a plurality of data rates and which includes the above described rate determination apparatus.
Still another embodiment of the invention is an improved user terminal for receiving a radio frequency (RF) signal that conveys a spread spectrum, code division, multiple access (CDMA) user communication, the user communication being transmitted in frames of data bits, individual ones of the frames being transmitted with different data rates which are selected from a plurality of data rates, the user terminal including a deinterleaver for deinterleaving the recorded, encoded signal and outputting frames of deinterleaved symbols, and a decoder for decoding each frame of the user communication at an appropriate data rate, wherein the improvement is an apparatus for determining a data
Crosby, Heafey Roach & May
Hyun Soon-Dong
Nguyen Chau
Sony Corporation
Wigert, Jr. J. William
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