Multiplex communications – Communication over free space – Combining or distributing information via code word channels...
Reexamination Certificate
1998-05-05
2001-04-24
Vincent, David R. (Department: 2661)
Multiplex communications
Communication over free space
Combining or distributing information via code word channels...
C375S149000
Reexamination Certificate
active
06222834
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a spread spectrum communication receiver and, more particularly, to a synchronizer circuit based on a correlation demodulation scheme.
FIG. 7
shows a spread spectrum communication receiver based on a conventional correlation demodulation scheme. Referring to
FIG. 7
, a received signal is input to a detection correlator
11
and a plurality of peak detection correlators
20
. The detection correlator
11
outputs a correlation value relative to a spread code in the chip phase designated by an up-down counter
80
. A detector
12
detects the output signal from the detection correlator
11
. A decoder
13
decodes the output signal from the detector
12
.
The peak detection correlator
20
calculates a correlation value at each sampling point within one period of the spread code. The output from the peak detection correlator
20
is input to an integration circuit constituted by a plurality of adders
30
and a plurality of memories
40
. The output from the integration circuit is input to a peak position detector
50
. The detected peak position is input, through a switch
60
, to a peak position memory
70
in the initial mode, and to a peak comparator
71
in the steady mode.
In this case, the peak comparator
71
performs control to minimize the difference between the peak position within one period of the spread code and the value stored in the peak position memory
70
. More specifically, the peak comparator
71
outputs “+1” when the peak position within one period of the spread code is larger than the value in the peak position memory
70
; outputs “−1” when the peak value is smaller than the stored value. The up-down counter
80
sequentially adds the outputs from the peak comparator
71
. The value in the up-down counter
80
is output to the detection correlator
11
. The chip phase of the detection correlator
11
is controlled in accordance with this value, thereby holding synchronization.
A synchronization device for a spread spectrum communication receiver using such a correlation demodulation scheme is disclosed in Japanese Patent Laid-Open No. 7-50613.
In a conventional spread spectrum communication receiver having such an arrangement, when a path for a received signal is to be detected, the reception levels in the entire search range are integrated over a plurality of periods, thereby facilitating detection of a path.
According to this method, however, when a plurality of paths in a multipath fading state in which the reception levels are low and greatly vary are to be detected, detection errors cannot be satisfactorily suppressed. For this reason, erroneously detected paths are also demodulated.
Assume that the correlation level of a received signal is as low as a noise level. In this case, if an instantaneous peak is set as a chip phase for correlation demodulation, a correlation peak cannot be detected owing to the influences of noise and fading. For this reason, peaks based on noise without any correlation component are frequently detected, resulting in a deterioration in demodulation characteristics.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a spread spectrum communication receiver which suppresses erroneous detection of correlation peaks and prevents a deterioration in demodulation characteristics even if a correlation level is as small as a noise level.
It is another object of the present invention to provide a spread spectrum communication receiver which efficiently selects paths to be used for correlation demodulation when a plurality of paths are to be subjected to correlation modulation.
In order to achieve the above objects, according to the present invention, there is provided a spread spectrum communication receiver comprising spread code generating means for generating a spread code, demodulation means for demodulating a received signal and outputting a demodulated signal, searcher means for obtaining a plurality of search paths separated from each other by not less than one chip from a search range on the basis of the demodulated signal output from the demodulation means and the spread code output from the spread code generating means, tracking means for tracking a plurality of tracking paths separated from each other by not less than one chip on the basis of the demodulated signal output from the demodulation means and the spread code output from the spread code generating means, and obtaining correlation levels of the tracking paths, path capturing/holding means for comparing the search paths output from the searcher means with the tracking paths output from the tracking means, and capturing/holding a plurality of paths on the basis of the comparison result, the path capturing/holding means performing backward protection in detecting coincidence between paths, performing forward protection in detecting loss of a path, and classifying path captured/held states of tracking paths into a complete incoincident state, a forward protection state, a complete protection state, and a forward protection state, thereby obtaining a path state, correlation demodulation path selection means for selecting paths to be subjected to correlation demodulation on the basis of the path state output from the path capturing/holding means and the correlation levels output from the tracking means, rake means for detecting demodulated paths designated by the correlation demodulation path selection means on the basis of a correlation between the demodulated signal output from the demodulation means and the spread code output from the spread code generating means, and performing rake synthesis of the demodulated paths, thereby outputting demodulated data, and decoding means for decoding the demodulated data output from the rake means, and outputting decoded data.
REFERENCES:
patent: 5982763 (1999-11-01), Sato
patent: 0 718 998 A2 (1996-06-01), None
patent: 3-3530 (1991-01-01), None
patent: 5-175935 (1993-07-01), None
patent: 5-327688 (1993-12-01), None
patent: 6-37736 (1994-02-01), None
patent: 7-50613 (1995-02-01), None
patent: WO 95/12262 (1995-05-01), None
McGinn & Gibb PLLC
NEC Corporation
Vincent David R.
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