Pulse or digital communications – Spread spectrum – Direct sequence
Reexamination Certificate
2000-03-03
2004-04-27
Chin, Stephen (Department: 2734)
Pulse or digital communications
Spread spectrum
Direct sequence
Reexamination Certificate
active
06728298
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a spread spectrum communication system and a method for the same in which spread spectrum modulation using a direct spread (DS) method is carried out by using the same spread code list for a parallel data list, spread spectrum modulation signals are multiplexed and transmitted, and the transmitted spread spectrum modulation signals are demodulated to receive the parallel data list.
BACKGROUND OF THE INVENTION
In recent years, Code Division Multiple Access (CDMA) communicating method using a spread spectrum method as one of traffic transmitting methods such as images, voices, data and the like have been put into practical use in a mobile communication system and a satellite communication system.
The spread spectrum communicating method includes a direct spread (DS) method, a frequency hopping (FH) method and the like. In the DS method, a spread code list having a much wider band than the band of an information signal is directly multiplied by the information signal, thereby performing the spread spectrum of the information signal to carry out communication.
FIG. 17
is a block diagram showing the structure of a conventional spread spectrum communication system in which spread spectrum is carried out by using the same spread code list for parallel data, different time delays are given to spectrum spread signals to be multiplexed and transmitted. In
FIG. 17
, a data generating section
101
generates a binary digital information signal having a value of “1” or “−1”. In the following description, the speed at which the digital information signal is generated will be referred to as a bit rate and it is denoted as “R
b
”. A serial/parallel converting section
102
converts the digital information signal input from the data generating section
101
into parallel information signal having n channels. A multiplex number n is equal to or less than spread code length L (bit). In the following description, the speed at which the parallel information signal in each channel is generated will be referred to as a parallel bit rate and it is denoted as “R
p
” (=R
b
).
A spread code generating section
104
generates a spread code list. The spread code list has a value of a “1” or “−1” and a spread code list having a spread code length L (bit) which is generated by a clock generating section
103
and has a clock frequency band that is spread code length L times as much as the parallel bit rate R
p
. It is desirable that the circuit used for creating the codes has a simple structure and that the codes have great auto-correlation characteristics and small cross-correlation therebetween. Therefore, as a proper code list, for example, M list, Gold code and the like are used. In the following description, a clock rate generated by the clock generating section
103
will be referred to as a chip rate R
c
(=R
p
×L) and a clock cycle having the chip rate R
c
will be referred to as a chip cycle T
c
(=1/R
c
).
Each one of the n channel parallel information signal converted by the serial/parallel converting section
102
is input into the spread modulating sections
105
-
1
to
105
-n, respectively. The spread modulating sections
105
-
1
to
105
-n multiply the parallel information signal and a spread code input from the spread code generating section
104
, thereby generating parallel spectrum spread signals for n channels. As a result, each of the parallel spectrum spread signal has the chip rate R
c
.
Each parallel spectrum spread signal is input into each of the delay sections
107
-
1
to
107
-n. Each of the delay sections
107
-
1
to
107
-n delays the parallel spectrum spread signal by times {b
1
, b
2
, b
3
, . . . b
n
} respectively and output the same signals to a multiplexing section
108
. The multiplexing section
108
performs multiplexing by adding each of the parallel spectrum spread signal which have been delayed differently, and a multiplexed spectrum spread signal thus obtained is sent to a frequency converting section
109
. Although each of the parallel spectrum spread signal is spectrum-spread by the same spread code list in the spread modulating sections
105
-
1
to
105
-n, they have been delayed differently in the delay sections
107
-
1
to
107
-n. Therefore, a small cross-correlation is obtained between data lists at the time of the code synchronization of the data list corresponding to each of the parallel spectrum spread signal on the receiving side for receiving the multiplexed parallel spectrum spread signal.
A frequency converting section
109
frequency-converts the input multiplexed spectrum spread signal to obtain the radio frequency (RF), then generates a multiplexed RF signal is power-amplified by a power amplifying section
110
and transmitted using an antenna
111
.
FIG. 18
is a block diagram showing the structure of a conventional spread spectrum communication system for receiving the multiplexed RF signal. In
FIG. 18
, an RF amplifying section
122
receives the multiplexed RF signal from an antenna
121
and amplifies the multiplexed RF signal. A quadrature detecting section
123
causes a multiplier
141
to multiply a local carrier signal output from a voltage-controlled oscillator (VCO)
143
and the multiplexed RF signal input from the RF amplifying section
122
, causes a low-pass filter
145
to remove the high-frequency component of the multiplied signal, and furthermore, causes an A/D converter
147
to convert the multiplied signal into digital data, thereby generating the in-phase component of the complex spectrum spread signal having the frequency band of the chip rate R
c
. On the other hand, a multiplier
142
also multiplies the local carrier signal which is phase-shifted by &pgr;/2 by means of a &pgr;/2 phase shifter
144
and the multiplexed RF signal input from the RF amplifying section
122
for a signal output from the voltage-controlled oscillator
143
, a low-pass filter
146
removes the high-frequency component of the multiplied signal, and furthermore, an A/D converter
148
converts the multiplied signal into digital data, thereby generating the orthogonal component of the complex spectrum spread signal having a frequency band of a chip rate R
c
.
A correlation value calculating section
124
obtains a correlation between the complex spectrum spread signal input from the quadrature detecting section
123
and a spread code list which is the same as the spread code list generated by the spread code generating section
104
. More specifically, an in-phase correlation value calculating section
149
in the correlation value calculating section
124
outputs, as an in-phase correlation value, a correlation value of the complex spectrum spread signal and the spread code list which is the same as a spread code multiplied to the multiplexed RF signal. Further, an orthogonal correlation value calculating section
150
in the correlation value calculating section
124
outputs, as an orthogonal correlation value, a correlation value of the complex spectrum spread signal and the spread code list which is the same as the spread code multiplied to the multiplexed RF signal. The correlation in the in-phase correlation value calculating section
149
and the orthogonal correlation value calculating section
150
can be implemented by using a matched filter and the like.
A code synchronizing section
125
generates a symbol clock CK synchronized with the cycle of the spread code list multiplied by the multiplexed RF signal from the in-phase correlation value and the orthogonal correlation value which are output from the correlation value calculating section
124
, and outputs the symbol clock CK to data demodulating sections
128
-
1
to
128
-n.
Delay correcting sections
126
-
1
to
126
-n perform delay correction in such a manner that the timings of the peak values of the in-phase correlation value and the orthogonal correlation value for corresponding parallel spectrum spread signals match respectively. More specifically, the sh
Fujimura Akinori
Kojima Toshiharu
Okubo Seiji
Chin Stephen
Kim Kevin
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