Multiplex communications – Communication over free space – Combining or distributing information via code word channels...
Reexamination Certificate
1999-09-29
2002-12-03
Maung, Nay (Department: 2681)
Multiplex communications
Communication over free space
Combining or distributing information via code word channels...
C370S335000, C375S146000, C375S140000
Reexamination Certificate
active
06490267
ABSTRACT:
PRIORITY
This application claims priority to an application entitled “Device and Method for Generating Spreading Code and Spreading Channel Signals Using Spreading Code in CDMA Communication System” filed in the Korean Industrial Property Office on Sept. 29, 1998 and assigned Ser. No. 98-40507, 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 spread spectrum device and method for a CDMA communication system, and in particular, to a device and method for generating spreading sequences.
2. Description of the Related Art
Code Division Multiple Access (CDMA) mobile communication systems have developed from an existing mobile communication standard which mainly provides voice service into the IMT-2000 standard which can provide not only voice service but also high speed data transmission service. For example, the IMT-2000 standard can provide high quality voice, moving picture, and Internet search services. In CDMA communication systems, communication links between a base station and a mobile station include a forward link for transmitting from the base station to the mobile station and a reverse link for transmitting from the mobile station to the base station.
In CDMA communication systems, the reverse link typically employs a PN (Pseudorandom Noise) code complex spreading scheme as the spread spectrum method. However, the PN code complex spreading scheme has a problem when the power amplifier has an increase in the peak-to-average power ratio (PAR) because of user data. In the reverse link, an increase in the peak-to-average ratio of transmission power causes ‘re-growth,’ described below, which affects the design and performance of the power amplifier in the mobile stations. The characteristic curve of the power amplifier in the mobile station has a linear area and a non-linear area. When the transmission power of the mobile station increases, the signal of the mobile station will enter the non-linear area, interfering with the frequency areas of other users, which is called the “re-growth” phenomenon. In order not to interfere with the frequency areas of the other users, the cell area should be reduced in size and mobile stations in a cell area should transmit to the corresponding base station at a lower transmission power. Therefore, there is a need for a spreading method which decreases PAR while minimizing the degradation of bit error rate (BER) performance which affects the overall system performance.
A description of the PN complex spreading scheme will be made herein below with reference to a transmitter in a conventional CDMA communication system.
FIG. 1
illustrates a channel transmitter, including a spread spectrum device, for a CDMA communication system. As illustrated, the channel transmitter includes an orthogonal spreader
101
, a complex multiplier
102
, a PN sequence generator
103
and a lowpass filtering and modulation part
104
.
Referring to
FIG. 1
, the transmission data of each channel is applied to the orthogonal spreader
101
after channel coding, repetition and interleaving through corresponding channel coders (not shown). The orthogonal spreader
101
then multiplies the input channel data by a unique orthogonal code assigned to the corresponding channel to orthogonally spread the input channel data. Walsh codes are typically used for the orthogonal codes. The PN sequence generator
103
generates spreading sequences for spreading the transmission signals of the respective channels. PN sequences are typically used for the spreading sequences. The complex multiplier
102
complex multiplies the signals output from the orthogonal spreader
101
by the spreading sequences output from the PN sequence generator
103
to generate complex spread signals. The lowpass filtering and modulation part
104
baseband filters the complex spread signals output from the complex multiplier
102
and then converts the baseband filtered signals to RF (Radio Frequency) signals.
FIG. 2
is a detailed diagram illustrating the channel transmitter of
FIG. 1
for the reverse link.
Referring to
FIG. 2
, the transmission data of each channel undergoes channel coding, repeating, channel interleaving and binary mapping in such a manner that a signal “0” is mapped to “+1” and a signal “1” to “−1”, prior to being input to the corresponding channel. The data of the respective channels is multiplied by unique orthogonal codes in multipliers
111
,
121
,
131
and
141
. In
FIG. 2
, channel transmitters include a pilot channel transmitter, a control channel transmitter, a supplemental channel transmitter and a fundamental channel transmitter. As stated above, Walsh codes are typically used for the orthogonal codes that spread the respective channels. The orthogonally spread data of the control channel, the supplemental channel and the fundamental channel is multiplied by gains appropriate for each channel by the first to third gain controllers
122
,
132
and
142
. The channel data is added by binary adders
112
and
133
and then applied to the complex multiplier
102
. Herein, the outputs of the binary adders
112
and
133
will be referred to as “channelized data”.
The complex multiplier
102
multiplies the outputs of the adders
112
and
133
by spreading codes to perform spreading. As stated above, the PN codes output from the PN sequence generator
103
are used for the spreading codes. The PN codes input to the complex multiplier
102
have a rate equal to a chip rate and may have a value comprised of “+1” and “−1”. Herein, unless otherwise stated, the PN codes are assumed to have a value of “+1” and “−1”.
With regard to the complex multiplier
102
, channelized data output from the adder
112
is applied to multipliers
113
and
143
, and channelized data output from the adder
133
is applied to multipliers
123
and
134
. Further, a spreading code PN
i
output from the PN sequence generator
103
is applied to the multipliers
113
and
123
and a spreading code PN
q
output from the PN sequence generator
103
is applied to the multipliers
134
and
143
. In addition, outputs of the multipliers
113
and
134
are subtracted from each other by an adder
114
and then applied to a first lowpass filter
115
; and outputs of the multipliers
123
and
143
are added to each other by an adder
135
and then applied to a second lowpass filter
136
.
A real signal out of the outputs from the binary adder
114
is input to the first lowpass filter
115
and an imaginary signal is input to the second lowpass filter
136
. Output signals of the lowpass filters
115
and
136
are gain controlled by fourth and fifth gain controllers
116
and
137
, respectively, then modulated, added together, and transmitted through a transmission channel. The lowpass filtering and modulation part
104
lowpass filters and modulates the output data of the binary adders
114
and
135
, and then outputs the modulated data from a binary adder
118
.
Several methods have been proposed for reducing the PAR of the signals output from the first and second lowpass filters
115
and
136
, and those methods are based on how the PN sequence generator
103
generates the spreading codes PN
i
and PN
q
. In general, the peak-to-average power ratio PAR depends on both zero-crossings, which occur when the signs of PN
i
and PN
q
are simultaneously changed, and hold-phase-state, which occurs when the signs of both PN
i
and PN
q
are not changed. More specifically, zero-crossings (ZC) happen when, for example, an initial state in the first quadrant transitions to the third quadrant, causing a phase shift of &pgr;. Further, a hold-phase-state, or “hold,” happens when, for example, an initial state in the first quadrant remains in the first quadrant, causing no phase shift.
As stated above, in conventional QPSK (Quadrature Phase Shift Keying) spreading, a phase of the generated spreading codes can transition from the first quadrant to any of the second, third
Ahn Jae-Min
Kim Je-Woo
Park Chang-Soo
Woo Jung-Hyo
Dilworth & Barrese LLP
Lele Tanmay
Maung Nay
Samsung Electronics Co,. Ltd.
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