Pulse or digital communications – Spread spectrum – Direct sequence
Reexamination Certificate
1998-02-09
2001-01-30
Chin, Stephen (Department: 2734)
Pulse or digital communications
Spread spectrum
Direct sequence
C375S148000, C375S346000, C375S350000
Reexamination Certificate
active
06181731
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a spread spectrum communication device, and more particularly to a spread spectrum communication device having the capability of removing a narrow-band interfering signal present in a frequency band of a spread signal.
2. Description of the Related Art
FIG. 12
illustrates an example of a narrow-band interference signal elimination circuit used in a conventional spread spectrum communication device.
As shown in
FIG. 12
, the narrow-band interference signal elimination circuit
100
comprises a switch
101
, a band-rejection filter
102
, a bandpass filter
103
, a detector
104
, a maximum level detection circuit
105
, a switch control circuit
106
, an input signal terminal
107
, and an output signal terminal
108
. The bandpass filter
103
comprises a plurality of filters BPF1, BPF2, . . . , BPFn. The input of each of these filters is connected to the input signal terminal
107
, and the output of each of these filters is connected to the maximum level detection circuit
105
via the corresponding one of the detectors DFT1, DFT2, . . . , DFTn. The output of the maximum level detection circuit
105
is connected to the switch
101
via the switch control circuit
106
. The input terminal of the switch
101
is connected to the input signal terminal
107
. The switch
101
has a plurality of output terminals which are connected to the filters BEF1, BEF2, . . . , BEFn, respectively, of the band-rejection filter
102
. The outputs of the filters BEF1, BEF2, . . . , BEFn are combined together and connected to the output signal terminal
108
. The band-rejection filter
102
, the bandpass filter
103
, and the detector
104
are each include an equal number of elements.
In the narrow-band interference signal elimination circuit
100
, the frequency bands of the respective filter elements of the band-rejection filter
102
and those of the respective filter elements of the bandpass filter
103
correspond to the frequency subbands used in the spread spectrum communication. When a signal is input to the input signal terminal
107
, the input signal is applied to the switch
101
and also to the detector
104
via the bandpass filter
103
. The detector
104
detects the signal level for each frequency band. The maximum level detection circuit
105
evaluates the signals output from the respective elements of the detector
104
, and determines the frequency band having a maximum signal level. The maximum level detection circuit
105
operates the switch
101
via the switch control circuit
106
so that the input signal is coupled to a band-rejection filter element having a frequency band corresponding to that of the bandpass filter element regarded as having the maximum signal level and thus the input signal components except for the signal component corresponding to the frequency band of the selected band-rejection filter element are output via the output signal terminal
108
. When a narrow-band interfering signal is present within a communication frequency band, the signal component having a frequency band including the frequency of the interfering signal is removed by the narrow-band interference signal elimination circuit
100
described above.
The narrow-band interference signal elimination circuit
100
described above has a problem that a great number of bandpass filter elements and band-rejection filter elements are required, and thus a large installation area for them is required. This causes an increase in cost. Another problem is that when there are two or more narrow-band interfering signals having different frequencies, only one narrow-band interfering signal having the highest signal level is removed.
Thus it is an object of the present invention to provide a small-sized low-cost spread spectrum communication device having a narrow-band interference signal elimination circuit capable of covering all spread signal frequency bands.
SUMMARY OF THE INVENTION
According to an aspect of the invention, to achieve the above object, there is provided a spread spectrum communication device including signal receiving means for receiving a spread signal having a spread spectrum and also including a narrow-band interference signal elimination circuit for removing a narrow-band interfering signal contained in the spread signal received via the signal receiving means and having a level higher than a predetermined value in the frequency domain, the spread spectrum communication device being characterized in that the narrow-band interference signal elimination circuit limits the narrow-band interfering signal a plurality of times so as to successively limit the level in the frequency domain.
In a preferable mode of the spread spectrum communication device, the narrow-band interference signal elimination circuit includes a magnetostatic filter for limiting the level of a signal whose level in the frequency domain is higher than a predetermined level.
In another preferable mode of the spread spectrum communication device, the narrow-band interference signal elimination circuit includes: a plurality of magnetostatic filters connected in series in such a manner that the saturation level thereof decreases with the position of the magnetostatic filters in the series connection; and a variable amplifier for amplifying the level of the spread signal input to the plurality of magnetostatic filters.
In still another preferable mode of the spread spectrum communication device, the narrow-band interference signal elimination circuit includes: a plurality of magnetostatic filters connected in series; a plurality of amplifiers respectively disposed between adjacent magnetostatic filters; and a variable amplifier for amplifying the level of the spread signal input to the plurality of magnetostatic filters.
In still another preferable mode of the spread spectrum communication device, the narrow-band interference signal elimination circuit includes: a plurality of magnetostatic filters connected in series; a plurality of variable amplifiers each disposed at an input of a the respective one of the magnetostatic filters; a level detection circuit for detecting the level of the spread signal and also the maximum level of the narrow-band interfering signal contained in the spread signal; and an amplification factor control circuit connected to the level detection circuit and serving to control the amplification factor of the plurality of variable amplifiers.
According to another aspect of the invention, there is provided a spread spectrum communication device including signal receiving means for receiving a spread signal having a spread spectrum and also including a narrow-band interference signal elimination circuit for removing a narrow-band interfering signal contained in the spread signal received via the signal receiving means and having a level higher than a predetermined value in the frequency domain, the spread spectrum communication device being characterized in that: the narrow-band inference signal elimination circuit includes: a gradient saturation magnetostatic filter whose saturation level decreases with the propagation of the signal; and a variable amplifier for amplifying the level of the spread signal input to the gradient saturation magnetostatic filter.
With the spread spectrum communication device constructed in the above-described manner according to the invention, when the spread signal includes a narrow-band interfering signal having a level in the frequency domain higher than the predetermined value, the level of the narrow-band interfering signal is limited to a predetermined value.
Other features and advantages of the present invention will become apparent from the following description of the invention which refers to the accompanying drawings.
REFERENCES:
patent: 4613978 (1986-09-01), Kurth et al.
patent: 5467368 (1995-11-01), Takeuchi
patent: 5564095 (1996-10-01), Arnstein et al.
patent: 5844936 (1998-12-01), Lesthievent
patent: 5930287 (1999-07-01), Kochi et al.
Kanaya Fumio
Kochi Tetsuya
Tanaka Hiroaki
Chin Stephen
Deppe Betsy L.
Murata Manufacturing Co. Ltd.
Ostrolenk Faber Gerb & Soffen, LLP
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