Multiplex communications – Communication techniques for information carried in plural... – Combining or distributing information via code word channels
Reexamination Certificate
1999-08-18
2003-09-23
Vanderpuye, Kenneth (Department: 2661)
Multiplex communications
Communication techniques for information carried in plural...
Combining or distributing information via code word channels
C370S335000, C370S498000, C370S535000
Reexamination Certificate
active
06625173
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a base station transmitter employing a CDMA (Code Division Multiple Access) scheme as a multiple access scheme, and more particularly to a power controlling method for transmission signals in a plurality of communication channels in the base station transmitter.
2. Description of the Prior Art
In a communication system with the CDMA, data to be transmitted is spectrum-spread modulated using a spread code (i.e., a pseudorandom noise (PN) sequence) in a transmitter and the spread modulated data is transmitted to a receiving side. In a receiver, the received data is demodulated by despreading the received data using the same spread code as the spread code used in the transmitter. In the CDMA communication system, since each communication channel is specified by selecting the spread code for use in despreading on the receiving side, a plurality of communication channels can be established in the same frequency band by a plurality of transmitting sides using different spread codes orthogonal to one another for spreading.
However, since it is difficult to completely maintain orthogonality between all of used spread codes, actually the respective spread codes are not completely orthogonal to one another but have components correlated with the other codes. These correlated components act as interference components for their own communication to contribute to deteriorated communication quality. Since such a factor causes interference components, the interference components are increased as the number of communication channels is increased. Thus, in the CDMA communication system, Eb/Io (ratio of desired received wave power to interference wave power) can be most effectively ensured when all of a plurality of signals to be received in a receiver has the same power. Therefore, the CDMA communication system must control transmission power on each transmitting side.
A base station in the CDMA communication system controls transmission power of each mobile station such that the reception power at the base station from each mobile station is equal to one another.
Additionally, a base station spread modulates transmission signals destined for each mobile station and then combines the spread modulated signals into a combined spread signal which is then transmitted to each mobile station. When a base station combines the plurality of signals, it controls the amplitudes of transmission signals destined for each mobile station in accordance with an amplitude controlling signal included in an upward channel from each mobile station, as opposed to the power control as described above.
To control the amplitudes of a plurality of signals and combine them in this manner, a conventional CDMA base station transmitter changes the amplitudes of spread modulated transmission signals with a variable gain amplifier or the like, and then combines the respective transmission signals. However, according to this method, since many variable gain amplifiers are required as communication channels, thereby having a disadvantage that an increased number of communication channels causes an increase in the scale of a circuit of a CDMA base station transmitter. Also, an analog circuit such as a variable gain amplifier requires considerable adjustment, maintenance, or the like, which involves time and effort. In view of the situation, a CDMA base station transmitter having transmission power controlling function such that an amplitude of each channel is controlled with digital processing without requiring a variable gain amplifier or the like has been employed.
As a CDMA base station transmitter having such a transmission power controlling function, a base station transmitter as described in Japanese Patent Laid-open Application No.
10-22977
(JP, 10022977, A) has been proposed, for example.
FIG. 1
is a block diagram showing a configuration of a conventional CDMA base station transmitter having the transmission power controlling function.
The conventional CDMA base station transmitter shown in
FIG. 1
spreads respective transmission signals for n communication channels #
1
to #n with different spread codes, and then combines the respective signals into a combined spread signal which is then transmitted to receivers. The CDMA base station transmitter uses orthogonal modulation as a primary modulation before the spread modulation. Each transmission signal can be divided into an in-phase component I and a quadrature component Q. The CDMA base station transmitter, as shown in
FIG. 1
, has channel signal processing units
21
1
to
21
n
provided for respective communication channels, spread code generator
12
for generating spread codes for respective communication channels, spreading and combining unit
83
for performing spread modulation and combination, and amplitude controlling signal decoder
14
.
Amplitude controlling signal decoder
14
is supplied with received signal
101
as an input which has been transmitted from each mobile station, and decodes and outputs amplitude controlling signals
102
1
to
102
n
for respective communication channels #
1
to #n included in received signal
101
. Amplitude controlling signals
102
1
to
102
n
indicate whether the transmission power of the CDMA base station transmitter is to be increased or to be reduced.
Channel signal processing unit
21
1
, as shown in
FIG. 2
, comprises amplitude correction value generator
211
, adder
212
, memory
214
, and parallel-to-serial converter
213
. The configurations of channel signal processing units
21
2
to
21
n
are the same as that of channel signal processing unit
21
1
. Amplitude correction value generator
211
receives amplitude controlling signal
102
1
from amplitude controlling signal decoder
14
and calculates a correction value for correcting amplitude signal
104
in accordance with the direction of amplitude controlling signal
102
1
. More specifically, since amplitude controlling signal
102
1
is provided for directing an increase or decrease in the amplitude of a transmission signal for communication channel #
1
, amplitude correction value generator
211
generates as a correction value a signal for increasing or decreasing the amplitude signal by a predetermined value in accordance with the direction of amplitude controlling signal
102
. For example, when amplitude controlling signal
102
1
directs an increase, a signal “+1.0 dB” is generated, while a signal “−1.0 dB” is generated when amplitude controlling signal
102
1
directs a decrease.
Adder
212
adds the correction value calculated at amplitude correction value generator
211
to amplitude signal
104
before correction stored in memory
214
to provide the result as amplitude signal
104
after correction. Memory
214
temporarily stores amplitude signal
104
provided from adder
212
and provides the signal to adder
212
after holding the signal for a predetermined time period. Parallel-to-serial converter
213
converts amplitude signal
104
provided from adder
212
and transmission signal
103
1
into one serial signal and outputs the signal. The format of the serial signal is shown in FIG.
3
.
The processing with channel signal processing unit
21
1
shown in
FIG. 2
may be also realized with a DSP (Digital Signal Processor) using software.
Spreading and combining unit
83
comprises serial-to-parallel converters
32
1
to
32
n
for receiving the serial signals from the channel signal processing units, spread modulation circuit
132
for performing spread modulation, and combining circuit
133
for generating a combined spread signal. In spreading and combining unit
83
, each of the serial signals from respective channel signal processing units
21
1
to
21
n
is applied to each of serial-to-parallel converters
32
1
to
32
n
, converted to a parallel signal, and separated into a transmission signal (I component and Q component) and an amplitude signal. The transmission signal separated from the serial signal wit
Nguyen Brian
Vanderpuye Kenneth
LandOfFree
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