Pulse or digital communications – Spread spectrum – Direct sequence
Reexamination Certificate
2001-02-23
2002-12-31
Pham, Chi (Department: 2631)
Pulse or digital communications
Spread spectrum
Direct sequence
C370S320000
Reexamination Certificate
active
06501789
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a CDMA receiving apparatus in a CDMA communication system for transmitting a transmit data which are subjected to a spread modulation processing with a predetermined spreading factor and demodulating the transmit data by subjecting the received signal to a despread processing and, more particularly, to a CDMA receiving apparatus provided with a function of estimating the error rate in a plurality of energy power ratios Eb/N0s which are lower than the Eb/N0 in the current communication.
As a modulation system in mobile communication, digital systems are now mainly used in place of the conventionally used analog systems. Analog cellular systems are generally called a first generation, while digital cellular systems such as PDC (Japanese standard), GSM (European standard), IS54 (US TDMA standard) and IS95 (US CDMA standard) are called a second generation. The systems of the first and second generations are mainly used for voice service, and effectively utilize limited radio bands for communication by making the most use of the analog/digital narrow-band modulation demodulation system.
In a next generation, however, not only telephone communication but communication through a FAX and an electric mail, and communication of inter-computer etc. are possible. In a next generation, therefore, there is a demand for a communication system which enables service of various types of information (multimedia information) such as a motion picture and a still picture in addition to sound and information through the above-described communication means, and which has such a high quality that a user is not aware that communication is performed in a mobile network. A DS-CDMA (direct sequence code division multiple access) system attracts attention as a promising radio access system which will satisfy the above-described demand. The DS-CDMA system is a system for realizing spread spectrum by directly multiplying the signal which is to be spread its spectrum by a signal in a much wider band.
FIG. 12
shows the structure of a CDMA transmitter in a mobile station. In a pilot channel signals are subjected to a BPSK modulation processing by a first modulator
1
a
and thereafter spread and modulated with a spreading code for the pilot channel by a first spreader
1
b
. On the other hand, in a data channel, after signals are subjected to an appropriate coding processing such as CRC coding and convolutional coding by an encoder
1
c
, they are subjected to a BPSK modulation processing by a second modulator
1
d
, and then spread and modulated with a spreading code for the data channel by a second spreader
1
e
. A multiplexer
1
f
combines these signals spread by the first and second spreaders
1
b
and
1
e
, respectively, into a vector. The combined signals are then mapped in I channel and Q channel In-phase channel and Quadrature channel which are orthogonal to each other, subjected to frequency conversion and high-frequency amplification by a radio transmitter
1
g
, and transmitted from an antenna
1
h.
FIG. 13
shows the structure of a CDMA receiving unit for 1 channel in a CDMA receiver at a base station. A radio receiver
2
a
converts the frequency of the high-frequency signal received from an antenna into the frequency of baseband signals, and inputs the baseband signals into a searcher
2
b
and each of finger portions
2
c
1
to
2
c
n
. When the direct sequence signal (DS signal) which is influenced by the multi paths are input, the searcher
2
b
detects the multi paths by autocorrelation using a matched filter (not shown), and inputs the timing data for starting despread and delayed time adjusting data in each path into each of the finger portions
2
c
1
to
2
c
n
. A despreader
3
a
in the pilot channel of each of the finger portions
2
c
1
to
2
c
n
subjects the direct wave or delayed wave which arrives through a predetermined path to a despread processing by using the same code as the spreading code in the pilot channel, integrates the result of the despread processing, thereafter subjects the integrated signal to a delay processing corresponding to its own path, and outputs a pilot channel signal. A despreader
3
b
in the data channel of each finger portion subjects the direct wave or delayed wave which arrives through a predetermined path to a despread processing by using the same code as the spreading code in the data channel, integrates the result of the despread processing, thereafter subjects the integrated signal to a delay processing corresponding to its own path, and outputs a data channel signal.
A channel estimating portion
3
c
estimates a channel for compensating for the influence of fading in a communication path by using the despread pilot channel signal, and outputs a channel estimation signal. A fading compensator
3
d
compensates for the fading of the despread data channel signal by using the channel estimation signal. A RAKE combiner
2
d
combines the signal output from each of the finger portions
2
c
1
to
2
c
n
, and outputs the combined signals to a decoder
2
e
for soft decision error correction as a soft decision data train. The decoder
2
e
decodes and outputs the transmitted data by soft decision error correction, and inputs the decoded data into an encoder
2
f
. The encoder
2
f
subjects the decoded data with an error corrected to the same encoding processing as the encoder
1
c
(
FIG. 12
) in the transmitter, and a error rate estimator
2
g
estimates a bit error rate BER by comparing the result of encoding with the data before decoding. The bit error rate BER is usable for the control of transmission power.
FIG. 14
is an explanatory view of the transmission power control in a closed loop of an uplink. In a mobile station
1
, a spread modulator
1
1
spreads and modulates a transmit data by using a spreading code which corresponds to a predetermined channel designated by a base station
2
, and a power amplifier
1
2
amplifies the input signal which is subjected to a processing such as orthogonal modulation and frequency conversion after the spread modulation, and transmits the amplified signal from an antenna to the base station
2
. In the base station
2
, a despreader
2
1
which corresponds to each path subjects a delayed signal which arrives through an allocated path to a despead modulation processing, and a RAKE combiner/demodulator
2
2
combines the signal output from each finger.
An Eb/N0 measuring portion
2
3
measures the ratio Eb/N0 which is the ratio of the signal energy per bit Eb to the noise power N0 of a received signal. A comparator
2
4
compares the target Eb/N0 with the measured Eb/N0 and if the measured Eb/N0 is larger than the target Eb/N0, it creates a command for lowering the transmission power by TPC (Transmission Power Control) bits, while if the measured Eb/N0 is smaller than the target one, it creates a command for raising the transmission power by TPC bits. The target Eb/N0 is a value necessary for obtaining a bit error rate BER of, for example, 10
−3
(an error occurs once in 1000 times), and it is input into the comparator
2
4
from a target Eb/N0 setting portion
2
5
. A spread modulator
2
6
spreads and modulates the transmit data and the TPC bits. After the spread modulation, the base station
2
subjects them to processing such as DA conversion, orthogonal modulation, frequency conversion and power amplification, and transmits them from the antenna to the mobile station
1
. A despreader
1
3
in the mobile station
1
subjects the signal received from the base station
2
to a despread processing, and a RAKE combiner/demodulator
1
4
decodes the received data and the TPC bits and controls the transmission power of the power amplifier
1
2
in accordance with the command designated by the TPC bits. The mobile station
1
and the base station
2
perform the above-described power control in every slot.
In the above-described transmission power control, it is necessary to determine and set the target Eb/N0 in such a manner as to obtain
Obuchi Kazuhisa
Yano Tetsuya
Fujitsu Limited
Katten Muchin Zavis & Rosenman
Pham Chi
Tran Khanh Cong
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