Initial acquisition circuit

Details Initial acquisition circuit Initial acquisition circuit

2000-01-14

2001-04-03

Ghebretinsae, Temesghen (Department: 2734)

Pulse or digital communications

Spread spectrum

Direct sequence

C375S147000

Reexamination Certificate

active

06212222

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to an initial acquisition circuit in which, in a direct sequence spread spectrum communication scheme, spectrum spreading is performed on parallel data sequences by using identical spread code sequences, and, thereafter, code synchronization between a spread code sequence multiplied by a transmission signal multiplexed with a time offset and a spread code sequence used in a correlator on a reception device side is performed.
BACKGROUND OF THE INVENTION
In recent years, in a mobile communication system or a satellite communication system, there is considered a code division multiplex connection communication scheme using a spread spectrum scheme serving as one of the traffic transmission schemes of images, voice, data, or the like.
The direct sequence scheme, which is one of the spread spectrum communication schemes, is a scheme in which a spread code sequence in a band considerably wider than that of an information signal is directly multiplied by the information signal to spread the information signal during communication.
An initial acquisition circuit is used to establish a code synchronization between a spread code sequence multiplied on transmission side and a spread code sequence used in a correlator on a reception side. In the following explanation, a code synchronization state is a state in which the phase of a spread code multiplied by a reception signal and the phase of a spread code used in a correlator are equal to each other in data demodulation.
FIG. 8
is a block diagram of a transmission device and
FIG. 9
is a block diagram of a reception device of a spread spectrum communication system (to be referred to as the identical spread code multiplex SS system hereinafter), described in Japanese Patent Application Laid-Open No. 6-197096, in which spectrum spreading is performed on conventional parallel data by using identical spread codes, and, thereafter, multiplexing is performed with a time offset.
FIG. 8
is a block diagram showing a transmission device of a conventional identical spread code multiplex SS system. In
FIG. 8
, reference numeral
211
denotes a data generator; reference numeral
212
denotes a serial/parallel converter; reference numeral
213
denotes a clock generator; reference numeral
214
denotes a spread code generator; reference numerals
22
(
1
) to
22
(n) denote spread modulators; reference numerals
23
(
1
) to
23
(n) denote delays; reference numeral
241
denotes a multiplexer; reference numeral
242
denotes a frequency converter; reference numeral
243
denotes a power amplifier; and reference numeral
244
denotes a transmission antenna.
Operation of the transmission device of the conventional identical spread code multiplex SS system will be explained below. The data generator
211
of the transmission device of the conventional identical spread code multiplex SS system generates a digital information signal having a value of “1” or “−1”. In the following explanation, a generation rate of digital information signals is called a bit rate, and the value of the bit rate of the digital information signals is expressed as R
b
. The digital information signal is converted by the serial/parallel converter
212
into parallel information signals of n channels. The multiplex number n is equal or smaller than a spread code length L [bit]. In addition, in the following explanation, a generation rate of parallel information signals in each channel is called a parallel bit rate, and the value of the parallel bit rate is expressed as R
p
(=R
b

). Thus, a spread code sequence used in the transmission device of the conventional identical spread code multiplex SS system is generated by the spread code generator
214
, which generates values of “1” or “−1”. The spread code sequence has a code length L [bit], and a clock frequency band of R
p
×L generated by the clock generator
213
.
Codes such as M-sequence codes or Gold codes which are formed by a simple code forming circuit configuration in which autocorrelation and cross correlation between the codes are small, are used as the spread code sequence. In the following explanation, a clock rate generated by the clock generator
213
is called a chip rate R
c
(=R
p
×L), and a clock cycle having the chip rate R
c
is called a chip cycle T
c
(=1/R
c
). In the spread modulators
22
(
1
) to
22
(n), the parallel information signals of the n channels are multiplied by the spread code generated by the spread code generator
214
to generate parallel spread spectrum signals of n channels. Each parallel spread spectrum signal has the chip rate R
c
.
N different delay times {&tgr;
1
T
c
, &tgr;
2
T
c
, &tgr;
3
T
c
, . . . , &tgr;
n
T
c
} are given in the delay units
23
(
1
) to
23
(n) to the parallel spread spectrum signal sequence of the n channels. In the following description, {&tgr;
1
, &tgr;
2
, &tgr;
3
, . . . , &tgr;
n
} are called delay coefficients, and the delay coefficients {&tgr;
1
, &tgr;
2
, &tgr;
3
, . . . , &tgr;
n
} are integers which satisfy 0≦&tgr;
1
<&tgr;
2
<&tgr;
3
< . . . <&tgr;
n
<L. Thereafter, all the delayed parallel spread spectrum signals of the n channels are added to each other by the multiplexer
241
to generate a multiplexed spread spectrum signal. Although the parallel information signals of the parallel spread spectrum signal sequence of the n channels are spectrum-spread by identical spread code sequences, since the parallel spread spectrum signal sequence is multiplexed with different delay times, crosscorrelation between the signals of data sequence in code synchronization of the data sequence have small values.
Further, the frequency of the multiplexed spread spectrum signal is converted into a radio frequency (RF) by the frequency converter
242
. Thereafter, the power of the multiplexed spread spectrum signal is amplified by the power amplifier
243
to generate a multiplexed RF signal. The multiplexed RF signal is transmitted to a communication destination using the transmission antenna
244
.
FIG. 9
is a block diagram showing a reception device of a conventional identical spread code multiplex SS system. In
FIG. 9
, reference numeral
311
denotes a reception antenna; reference numeral
312
denotes an RF amplifier; reference numeral
111
denotes a quasi-coherent detector; reference numeral
112
denotes a correlation value calculator; reference numeral
141
denotes an initial acquisition unit; reference numeral
313
denotes a parallel/serial converter; reference numerals
32
(
1
) to
32
(n) denote delay correcting units; and reference numerals
33
(
1
) to
33
(n) denote data demodulators. The quasi-coherent detector
111
comprises a voltage controlled oscillator (VCO)
341
, a &pgr;/2-phase shifter
342
, multiplexers
343
and
344
, lowpass filters
345
and
346
, and A/D converters
347
and
348
, and the correlation calculator
112
comprises an in-phase correlation calculator
351
and an orthogonal correlation value calculator
352
.
Operation of a reception device of a conventional identical spread code multiplex SS system will be described below. In
FIG. 9
, the RF amplifier
312
in the reception device of the conventional identical spread code multiplex SS system RF-amplifies a multiplexed RF signal transmitted from the transmission device of the conventional identical spread code multiplex SS system explained above received through the reception antenna
311
. In the quasi-coherent detector
111
, a local carrier wave having a frequency band of a chip rate R
c
output from the VCO
341
and the RF-amplified multiplexed RF signal are multiplied together by the multiplexer
343
. A harmonic component is removed from the resultant signal by the lowpass filter
345
. This signal is then converted into digital data by the A/D converter
347
, so that an in-phase component of a complex spread spectrum signal included in the frequency band of the chip rate R
c
is generated.
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