Pulse or digital communications – Spread spectrum – Direct sequence
Reexamination Certificate
1999-12-27
2004-01-13
Bayard, Emmanuel (Department: 2731)
Pulse or digital communications
Spread spectrum
Direct sequence
Reexamination Certificate
active
06678313
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a correlator for spread spectrum communication for use on the side of a receiver of a spread spectrum communication system in mobile communication, radio LAN, and the like.
2. Description of the Related Art
Generally in a spread spectrum (SS) communication system for use in mobile communication or radio LAN, two-stage modulations, that is, narrow band modulation (primary modulation) and further spread modulation (secondary modulation) are performed on transmission data and the data is transmitted on the transmission side, while on the reception side, inverse spreading is performed on the received data, thereby returning to the primary modulation, and base band signals are reproduced in a usual wave detector circuit.
Furthermore, a conventional correlator for spread spectrum communication to obtain correlation for modulating received signals with spread spectra is constituted of an inverse spread circuit, and a modulation circuit for code division multiple access modulation waves. Specifically, a sliding correlator (SC) constituted of a logical circuit is used in the spread spectrum communication correlator in order to perform synchronous capturing and subsequently take correlation with a detected synchronous phase.
The sliding correlator uses one correlator of one to shift station issued code series (spread codes) by each bit, and obtains the correlation with each received code series. When the correlation is obtained with respect to the number of chips corresponding to the length of one symbol, the synchronous phase in which the correlation reaches its peak is obtained, and the synchronous capturing is performed.
Here the sliding correlator as one conventional inverse spread circuit will be described with reference to FIG.
14
.
FIG. 14
is a block diagram of one part of the conventional sliding correlator.
In the conventional sliding correlator a section for obtaining a correlation output is constituted of an A/D converter
31
, a multiplier
32
, a PN code register
33
, an adder
34
, and a delay circuit
35
.
Each component of the conventional sliding correlator will be described.
The A/D converter
31
is a high precision analog/digital converter which converts an analog signal subjected to code division multiple access (CDMA) modulation, transmitted, and received by an antenna (not shown) into a digital signal.
The PN code register
33
is a register for outputting a pseudo random noise (PN) code which is the same spread code as the code used in the CDMA modulation on the transmission side.
The multiplier
32
is a multiplier which multiplies the digital reception data outputted from the A/D converter
31
by the PN code outputted from the PN code register
33
.
The adder
34
and the delay circuit
35
accumulate/add multiplication results outputted from the multiplier
32
for one symbol period and output the integration value as the correlation output.
The operation of the conventional sliding correlator comprises converting the analog signal of the reception data received by the antenna into the digital signal by the A/D converter
31
, multiplying the digital signal by the PN code outputted from the PN code register
33
by the multiplier
32
, performing accumulation/addition by the adder
34
and the delay circuit
35
, and outputting the addition result for one symbol as the correlation output.
Subsequently, the accumulation/addition is repeated by shifting the multiplication timing in the multiplier
32
by one chip(more precisely, an interval of sample in the A/D converter) to change the phase, and the synchronous phase in which the correlation output reaches its peak is detected.
This constitution using the sliding correlator as the inverse spread circuit is relatively simple, has a small number of gates, and has little power consumption. However, since the time for the time of one symbol×the number of chips in one symbol is necessary until the synchronous capturing is performed, there is a problem that much time is necessary until the correlation output is obtained.
To solve the problem that much time is required until the correlation output is obtained, the use of a matched filter (MF) in the spread spectrum communication correlator instead of the sliding correlator is proposed.
The matched filter performs the synchronous capturing within one symbol time by collectively taking the correlation when the phase is shifted.
Here the matched filter as another example of the conventional inverse spread circuit will be described with reference to FIG.
15
.
FIG. 15
is a block diagram showing the constitution example of the conventional matched filter.
The conventional matched filter is constituted of an A/D converter
41
, a multiplier
42
, a PN code register
43
, an adder
44
, and a sample hold (S/H) circuit
45
.
Each component of the conventional matched filter will be described.
The A/D converter
41
is a converter which converts an analog input signal subjected to the CDMA modulation, transmitted to a digital signal.
The sample hold (S/H) circuit
45
comprises a plurality of circuits for successively taking and holding the digital signals from the A/D converter
41
.
The PN code register
43
is a register for outputting the PN code which is a spread code.
The multiplier.
42
is a multiplier which multiplies the digital signal held by each sample hold circuit
45
by the PN code from the PN code register
43
.
The adder
44
is an adder for collectively adding the outputs from the multiplier
42
.
The operation of the conventional matched filter comprises successively holding the input signals subjected to digital conversion in the A/D converter
41
by a plurality of S/H circuits
45
, multiplying the output from the S/H circuit
45
by the PN code outputted from the PN code register
43
by the multiplier
42
, further collectively adding the multiplication result of the multiplier
42
by the adder
44
, and outputting the addition result. The correlation output is obtained from the addition result.
In the general matched filter, however, in order to take the correlation when the phase is collectively shifted, different from the above-described sliding correlator, for example, the number of gates multiplied by the number of chips in one symbol is necessary, and the gate scale is enlarged, thereby causing the increase of LSI price and power consumption, so that it is actually difficult to use the matched filter in a mobile terminal receiver.
As described above, the conventional sliding correlator has a problem that much time is required until the correlation output is obtained, and the conventional matched filter has a problem that the number of gates is increased, thereby resulting in the increase of LSI price and power consumption.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a correlation circuit for spread spectrum communication, which reduces the number of constituting elements to achieve a low LSI price and can obtain correlation outputs.
According to the present invention, in the spread spectrum communication correlation circuit, a processing is repeated a plurality of times, comprising writing a spectrum spread reception signal into a memory, reading the written spread spectrum signal from the memory at a speed higher than the writing speed and performing product sum operation with a spread code at a high speed, the number of constituting elements is reduced, and the correlation output can be obtained in a short time as compared with the matched filter.
Moreover, according to the present invention, there is provided a correlation circuit for spread spectrum communication, comprising one or more receiving sections for receiving spread spectrum signals, one or more memory sections for holding the received spread spectrum signals, one or more multipliers for multiplying the signal held in the memory section and a spread code, and one or more adding sections for adding multiplication results. The spread spectrum signal inputte
Hoshina Kouya
Imaizumi Ichiro
Yasunari Kenjiro
Bayard Emmanuel
Jacobson & Holman PLLC
Kokusai Electric Co. Ltd.
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