Multiplex communications – Communication over free space – Combining or distributing information via code word channels...
Reexamination Certificate
1999-07-07
2002-10-01
Maung, Nay (Department: 2681)
Multiplex communications
Communication over free space
Combining or distributing information via code word channels...
C370S208000, C375S144000, C375S148000
Reexamination Certificate
active
06459693
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a device and method for cancelling code interference in a CDMA (Code Division Multiple Access) communication system, and more particularly, to a device and method for cancelling mutual interference between orthogonal codes and quasi-orthogonal codes (QOCs) in a CDMA communication system where the orthogonal codes coexist with the quasi-orthogonal codes.
2. Description of the Related Art
In a CDMA communication system, orthogonal codes provide orthogonal channelization among all code channels, and the maximum number of available code channels is determined by the length of the longest orthogonal code. Walsh codes are typical orthogonal codes used in a CDMA system, and thus any reference to orthogonal codes herein below refers to Walsh codes. If an orthogonal channel with orthogonality is assigned as dedicated to a transmitter/receiver from a call set-up to a call release, the number of available channels becomes limited and channels may not be available for assignment to every subscriber. To allow all subscribers to use the CDMA system, quasi-orthogonal codes are used due to their minimal loss of orthogonality relative to other codes, even though they lack full orthogonality.
A quasi-orthogonal code is generated by EX-ORing the longest orthogonal code used in the system with a quasi-orthogonal code mask as long as the longest orthogonal code in order to minimize orthogonality loss. U.S. Ser. No. 09/149,924 filed on Sep. 9, 1998 describes binary Quasi-orthogonal code mask generation, quasi-orthogonal code generation and the usage of Quasi-orthogonal codes. Quasi-orthogonal codes are characterized in that orthogonality between orthogonal code symbols using the same quasi-orthogonal code mask is maintained and orthogonality loss between quasi-orthogonal codes using different quasi-orthogonal code masks is minimized.
W
F1 XOR W
F2 XOR W
F3 XOR W
•
•
•
FM XOR W
where W=an N×N Walsh matrix and F
i=a
1×N row vector.
(1) 16-ary quasi-orthogonal masks of size 512 are:
F1=77B4B477 774BB488 87BB4478 78BBBB78 77B44B88 774B4B7778444478 8744BB78
77B4B477 774BB488 87BB4478 78BBBB78 77B44B88 774B4B77 78444478 8744BB78
F2=7E4DDBE8 17244D7E D41871BD 428E18D4 D4E77142 BD8EE7D4 7EB2DB17 E824B27E
7E4DDBE8 17244D7E D41871BD 428E18D4 D4E77142 BD8EE7D4 7EB2DB17 E824B27E
F3=417214D8 7DB1281B EB274172 D7E47DB1 B17DE4D7 8DBED814 1B28B17D 27EB8DBE
417214D8 7DB1281B EB274172 D7E47DB1 B17DE4D7 8DBED814 1B28B17D 27EB8DBE
F4=144EE441 B114BEE4 4EEBBEE4 144E1BBE 8D287D27 D78DD87D D78D2782 72D77D27
144EE441 B114BEE4 4EEBBEE4 144E1BBE 8D287D27 D78DD87D D78D2782 72D77D27
F5=488B7B47 IDDEDlED B88474B7 EDDIDE1D 122EDE1D 477B74B7 1DDE2EI2 488B84B8
488B7B47 1DDED1ED B88474B7 EDD1DE1D 122EDE1D 477B74B7 1DDE2E12 488B84B8
F6=1DB78BDE D17B4712 1D488B21 2E7BB812 2E7B47ED 1D4874DE D17BB8ED IDB77421
1DB78BDE D17B4712 ID488B21 2E7BB812 2E7B47ED 1D4874DE D17BB8ED 1DB77421
(2) 16-ary quasi-orthogonal code masks of size 256 are:
F1=77B4B477 774BB488 87BB4478 78BBBB78 77B44B88 774B4B77 78444478 8744BB78
F2=7E4DDBE8 17244D7E D41871BD 428E18D4 D4277142 BD8EE7D4 7EB2DB17 E824B27E
F3=417214D8 7DB1281B EB274172 D7E47DB1 B17DE4D7 8DBED814 1B28B17D 27EB8DBE
F4=144EE441 B114BEE4 4EEBBEE4 144E1BBE 8D287D27 D78DD87D D78D2782 72D77D27
F5=488B7B47 1DDED1ED B88474B7 EDD1DE1D 122EDE1D 477B74B7 1DDE2E12 488B84B8
F6=1DB78BDE D17B4712 1D488B21 2E7BB812 2E7B47ED 1D4874DE D17BB8ED 1DB77421
(3) 16-ary quasi-orthogonal masks of size 128 are:
F1=17DBBD71 E8DB4271 17DBBD71 E8DB4271
F2=72824EBE BEB17D72 72824EBE BEB17D72
F3=2DEE87BB 8744D2EE 2DEE87BB 8744D2EE
(4) 16-ary quasi-orthogonal masks of size 64 are:
F1=17DBBD71 E8DB4271
F2=72824EBE BEB17D72
F3=2DEE87BB 8744D2EE
Correlation values between quasi-orthogonal codes generated by using the above quasi-orthogonal code masks and Walsh codes are listed in Table 1.
TABLE 1
Walsh codes
QOCS
512
256
128
64
32
16
8
4
512
0, ∓32
∓16
0, ∓16
∓8
0, ∓8
∓4
0, ∓4
∓2
256
—
∓16
0, ∓16
∓8
0, ∓8
∓4
0, ∓4
∓2
128
—
—
0, ∓16
∓8
0, ∓8
∓4
0, ∓4
∓2
64
—
—
—
∓8
0, ∓8
∓4
0, ∓4
∓2
Basic orthogonal codes are defined as orthogonal codes EX-ORed with the quasi-orthogonal code masks to generate quasi-orthogonal codes and to indicate Walsh codes. The Walsh codes may be from different layers of different lengths only if they ensure orthogonal channelization among code channels. However, to make the best use of the correlation characteristics as given by Table 1, it is preferable that the lowest-layer Walsh codes or longest Walsh codes be used as the basic orthogonal codes. Herein, the length of the basic orthogonal codes is defined as L.
FIG. 1
is a schematic block diagram of a transmitter in a CDMA communications system using the above quasi-orthogonal codes. Referring to
FIG. 1
, reference numerals
140
and
170
denote typical channel encoders and interleavers. Signal mappers
112
,
142
, and
172
change 0s and 1s of input data to signal levels +1s and −1s, respectively. Demultiplexers
144
and
174
separate traffic channel data into I-channel data and Q-channel data for QPSK (Quadrature Phase Shift Keying) transmission. The demultiplexers
144
and
174
may be serial-to-parallel converters (SPCs). In the case of BPSK (Binary Phase Shift Keying) modulation of the traffic channel data, the demultiplexers
144
and
174
are omitted and data is sent on an I channel and a Q channel.
A Walsh code symbol W #
0
generator
116
generates a Walsh code symbol W #
0
as being a basic orthogonal code to spread a pilot channel. The pilot channel is used for channel estimation in a receiver. A mixer
118
multiplies the output of the Walsh code symbol W #
0
generator
116
by the output of the signal mapper
112
for orthogonal spreading of the pilot channel signal, and feeds the orthogonally spread pilot channel signal to an adder
162
. A Walsh code symbol W #A generator
146
generates a Walsh code symbol W #A as being a basic orthogonal code. Mixers
148
and
158
multiply the output of the Walsh code symbol W #A generator
146
by I channel data and Q channel data received from the demultiplexer
144
to produce a spread signal. Gain controllers
150
and
160
control the relative gain of a traffic channel relative to the pilot channel.
A Walsh code symbol W #a generator
176
generates a Walsh code symbol W #a as being a basic orthogonal code. A quasi-orthogonal code mask M #m generator
186
generates a quasi-orthogonal code mask used to generate a quasi-orthogonal code from a basic orthogonal code. Mixers
178
and
188
multiply the outputs of the Walsh code symbol W #a generator
176
and the quasi-orthogonal code mask M #m generator
186
, thereby producing a quasi-orthogonal code symbol Q[m]#a which belongs to a quasi-orthogonal code Q[m] and spreads the quasi-orthogonal code symbol Q[m] by multiplying the quasi-orthogonal code symbol Q[m] by the I channel and Q channel data received from the demultiplexer
174
. Gain controllers
180
and
190
control the relative gain of the traffic channel spread by a quasi-orthogonal code relative to the pilot channel. Adders
162
and
192
add the I channel signals and Q channel signals, respectively, and output S_I[n] and S_Q[n]. A PN (Pseudo Noise) code generator
120
generates two PN sequences PN_I[n] and PN_Q[n] for complex PN spreading. A complex PN spreader
130
performs the following complex PN spreading on the outputs of the adders
162
and
192
with the output of the PN code generator
120
.
(
S
—
I[n]+jS
—
Q[n]
)(
PN
—
I[n]+jPN
—
Q[n]
)=(
Ahn Jae-Min
Kim Young-Ky
Park Su-Won
Dilworth & Barrese LLP
Maung Nay
Samsung Electronics Co,. Ltd.
Vuong Quochien B.
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