Multiplex communications – Generalized orthogonal or special mathematical techniques
Reexamination Certificate
1999-12-08
2004-03-16
Urban, Edward F. (Department: 2685)
Multiplex communications
Generalized orthogonal or special mathematical techniques
C370S209000, C375S142000, C375S150000
Reexamination Certificate
active
06707788
ABSTRACT:
PRIORITY
This application claims priority to an application entitled “Channel Spreading Device and Method in CDMA Communication System” filed in the Korean Industrial Property Office on Dec. 8, 1998 and assigned Serial No. 98-54296, the contents of which are hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to a channel spreading device and method in a CDMA (Code Division Multiple Access) communication system, and in particular, to a device and method for spreading a channel signal using a Walsh code.
2. Description of the Related Art
As one way to increase system capacity in a CDMA communication system, channelization is provided by use of orthogonal codes. The orthogonal codes can be Walsh codes. The orthogonal channelization is applied to a forward link in the IS-95 standard, for example. A reverse link can be orthogonally channelized by time alignment.
Orthogonal channelization is provided to the forward link in an IS-95 communication system. In
FIG. 1
, W
0
-W
63
denotes orthogonal codes and each channel is distinguished by its assigned orthogonal code. The orthogonal codes W
0
-W
63
can be Walsh codes. Each channel on the IS-95 forward link is convolutionally encoded and a modulator performs BPSK (Bi-Phase Shift Keying) modulation. The bandwidth used is 1.2288 MHz and the data rate is 9.6 kbps in the IS-95 communication system. Thus, 64 channels (=1.2288 M/(9.6 k×2)) on an IS-95/IS-95A forward link are distinguished by the 64 orthogonal codes W
0
-W
63
, as shown in FIG.
1
.
The number of available orthogonal codes is obtained after the modulation scheme and the minimum data rate is determined. Future CDMA communication systems will improve system performance by increasing the number of channels available to users.
However, the above IS-95 scheme limits the number of available channels, due to the limited number of Walsh codes available. Consequently, the capacity of channels available to users is limited. It is preferable to use a variable data rate and quasi-orthogonal codes due to their minimal interference with orthogonal codes.
The structure and generation of the quasi-orthogonal codes is disclosed in detail in Korea Application No. 97-47457. The application is for BPSK modulation and sequences have a correlation value of 2
m+1
(>{square root over (L)}) for an odd power of length 2, L=2
2m+1
. A complex quasi-orthogonal function for QPSK (Quadrature Phase Shift Keying) modulation is described in detail in Korea Application No. 98-37453. The complex quasi-orthogonal function is excellent in terms of a correlation value since a correlation value is given {square root over (L)} for L=2
2m+1
, thereby overcoming the correlation value-related problem of quasi-orthogonal functions in BPSK modulation.
In IMT-2000 systems, QPSK modulation is implemented to utilize the above complex quasi-orthogonal function. The resulting QPSK modulation of Walsh codes makes it impossible to achieve backward compatibility between an IMT-2000 system and an existing IS-95 system that employs BPSK modulation to spread specific common channels such as a pilot channel or a sync channel.
The incompatibility between the conventional IS-95 CDMA communication system and the IMT-2000 CDMA communication system will be described in detail. In the following description, the orthogonal code index k, which is applied to the orthogonal code spreader/despreader, is an index used for generating a specific Walsh code and thus the orthogonal code spreader/despreader is a Walsh code modulator/demodulator.
FIG. 2
is a block diagram of a spreading device in a base station using QPSK modulation according to a preferred embodiment of the present invention.
Referring to
FIG. 2
, after channel encoding, rate matching, and interleaving, odd data a
I
and even data a
Q
are applied to the input of signal mappers
211
and
213
, respectively. The signal mapper
211
converts 0s and 1s of the odd data a
I
to +1s and −1s, respectively, and outputs the converted data as d
I
. The signal mapper
213
converts 0s and 1s of the even data a
Q
to +1s and −1s, respectively and outputs the converted data as d
Q
. An orthogonal code spreader
215
receives the signals d
I
and d
Q
from the signal mappers
211
and
213
and an orthogonal code index k, multiplies the signals d
I
and d
Q
by the Walsh code W
k
corresponding to the orthogonal code index k, and outputs signals X
I
and X
Q
[X
I
+j X
Q
=(d
I
+jd
Q
)*(W
k
+jW
k
)].
A PN code generator
217
generates PN codes PN
I
and PN
Q
for spectrum-spreading the orthogonally spread signals X
I
and X
Q
. Here, the PN codes can be short PN sequences. A PN masking portion
219
generates spread spectrum signals Y
I
and Y
Q
by multiplying the orthogonally spread signals X
I
and X
Q
by their corresponding PN codes PN
I
and PN
Q
[Y
I
+jY
Q
=(PN
I
+jPN
Q
)*(X
I
+jX
Q
)]. Baseband filters
221
and
223
baseband-pass-filter the spread spectrum signals Y
I
and Y
Q
, respectively. A mixer
225
converts the output of the baseband filter
221
to an RF signal by multiplying it by a carrier cos 2&pgr;f
c
t and a mixer
227
converts the output of the baseband filter
223
to an RF signal by multiplying it by a carrier sin 2&pgr;f
c
t. An adder
229
sums the outputs of the mixers
225
and
227
and outputs the sum as a transmission signal.
As shown in
FIG. 2
, the signal mappers
211
and
213
convert the signals a
I
and a
Q
having 0s and 1s to the signals d
I
and d
Q
having 1s and −1s, respectively. The orthogonal code spreader
215
receives the orthogonal code index k as well as the signals d
I
and d
Q
to orthogonally spread the signals d
I
and d
Q
. The signals d
I
and d
Q
can be expressed as a complex number d
I
+jd
Q
, which is complex multiplied by the Walsh code in its complex form W
k
+jW
k
. This multiplication, which results in X
I
+jX
Q
(=(d
I
+jd
Q
)*(W
k
+jW
k
)), occurs N times (N is the number of chips in the Walsh code).
FIG. 3
is a block diagram of a mobile station receiver for receiving and demodulating a signal from the base station transmitter shown in
FIG. 2
according to a preferred embodiment of the present invention.
Referring to
FIG. 3
, a mixer
311
mixes a received signal with the carrier cos 2&pgr;f
c
t and a mixer
313
mixes the received signal with the carrier sin 2&pgr;f
c
t. Baseband filters
315
and
317
baseband-pass-filter the outputs of the mixers
311
and
313
.
A PN code generator
318
generates the PN codes PN
I
and PN
Q
for despreading the received signal. A PN masking portion
319
generates the despread signals X
I
and X
Q
by multiplying the signals Y
I
and Y
Q
received from the baseband filters
315
and
317
by the complex conjugate of PN codes PN
I
and PN
Q
[X
I
+jX
Q
=(PN
I
−jPN
Q
)*(Y
I
+jY
Q
)]. An orthogonal code despreader
321
receives the despread signals X
I
and X
Q
and the orthogonal code index k and generates the despread channel signals d
I
and d
Q
by multiplying the signals X
I
and X
Q
by the complex conjugate of the orthogonal code W
k
corresponding to orthogonal code index k [2*(d
I
+jd
Q
)=&Sgr;(X
I
+jX
Q
)*(W
k
−jW
k
)]. A signal mapper
323
converts +1s and −1s of the signal d
I
received from the orthogonal code despreader
321
to 0s and 1s, respectively. A signal mapper
325
converts +1s and −1s of the signal d
Q
received from the orthogonal code despreader
321
to 0s and 1s, respectively. The output signals of the signal mappers
323
and
325
are applied to a combiner (not shown) for use as a channel estimation signal.
In
FIG. 3
, the PN masking portion
319
and the orthogonal code despreader
321
form a single finger. To estimate channels, the mobile station receiver is provided with a plurality of such fingers.
In the despreadi
Kang Hee-Won
Kim Jae-Yoel
Kim Young-Ky
Maeng Seung-Joo
Dilworth & Barrese LLP
Nguyen Simon D
Samsung Electronics Co,. Ltd.
Urban Edward F.
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