Pulse or digital communications – Repeaters – Testing
Patent
1995-05-30
1998-05-26
Chin, Stephen
Pulse or digital communications
Repeaters
Testing
375206, 375207, 370342, H04B 1500, H04K 100, H04L 2730
Patent
active
057578451
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a receiver for use in a direct sequence code division multiple access in spread spectrum communications, designed to adaptively remove interference signals.
With a view to implementing efficient utilization of frequency, a variety of spread spectrum systems have been studied in recent years (M. K. Simon, J. K. Omura, R. A. Scholtz and B. K. Levitt, "Spread Spectrum Communication," Computer Science Press, 1985). A CDMA (Code Division Multiple Access) system using a DS (Direct Sequence) scheme, in particular, is now being studied for practical use because of its relatively simple configuration.
With a conventional DS-CDMA receiver, a received wave from an antenna is amplified by an amplifier and is then input into a quasi-coherent detector circuit. The quasi-coherent detector circuit quadrature-detects the received signal, using, as a reference signal, a local carrier signal which is not synchronized with the received signal in phase but synchronized therewith in frequency, and outputs the amplitudes I(t) and Q(t) of in-phase and quadrature components of the received signal. The components I(t) and Q(t) will hereinafter be generically referred to as a received signal. The received signal will normally be identified with I(t) as the real part and jQ(t) as an imaginary part (j being an imaginary unit); therefore, various operation involved are complex ones. In the DS system, the received signal is subjected to despread-processing to extract therefrom a despread signal of a desired signal. Two methods are available for this despread-processing. One is a method that employs a matched filter with a spreading code; the output signal of the filter is used as the despread signal. The other method is one that multiplies the received signal by a spreading code in synchronization with the timing of the former and then extracts a DC component of the received signal by means of a low-pass filter; the DC component is used as the despread signal. While the method using the matched filter will hereinbelow be described, the same results as those obtainable therewith could also be produced by the other methods as well. The despread signal is demodulated in the baseband domain, by which a transmitted symbol sequence is extracted.
In such a DS-CDMA system, a plurality of users simultaneously utilize the same carrier frequency. The users use different spreading codes, but the spreading codes have some cross-correlation. Therefore, even if each user despreads the received signal by the spreading code of the particular desired signal, components of other users' signals get mixed into the despread signal. Thus, when the number of other users is large, the level of interfering signal components that get mixed into the despread signal of each user increases, causing significant degradation of the transmission performance. This degradation becomes increasingly serious when the received signal levels of other users exceed the received level of the desired signal at each users One possible solution to this problem is to control the power of transmission to each user to keep the level at the receiving point of each user constant, but it is very difficult to perfectly realize this transmission power control. The degradation of the transmission performance due to the cross-correlation between the spreading codes could be avoided by additionally equipping the receiver with an interference cancelling function. Conventional solutions and their defects will hereinbelow be described.
PRIOR ART EXAMPLE 1
In FIG. 1, there is shown a prior art configuration in which received signals by receiving antennas of plural branches are each despread by a spreading code of a desired signal and the resulting despread signals are linearly combined to cancel interference (Winters, J. H., "Spread Spectrum in a Four-Phase Communication Systems Employing Adaptive Antenna," IEEE Trans. on Comm., vol. COM-30, No. 5, pp. 929-936, May 1982). This example employs a four-branch configuration.
Sampled signals, by samp
REFERENCES:
patent: 4550414 (1985-10-01), Guinon et al.
patent: 5293398 (1994-03-01), Hamao et al.
patent: 5359624 (1994-10-01), Lee et al.
patent: 5414699 (1995-05-01), Lee
patent: 5511068 (1996-04-01), Sato
patent: 5583884 (1996-12-01), Maruyama et al.
patent: 5590160 (1996-12-01), Ostman
patent: 5592506 (1997-01-01), Omura et al.
patent: 5594754 (1997-01-01), Dohi et al.
Fukawa Kazuhiko
Suzuki Hiroshi
Chin Stephen
Ghayour Mohammad
NTT Mobile Communications Network
LandOfFree
Adaptive spread spectrum receiver does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Adaptive spread spectrum receiver, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Adaptive spread spectrum receiver will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-1972664