Multiplex communications – Communication over free space – Combining or distributing information via code word channels...
Patent
1995-08-28
1997-06-10
Hsu, Alpus H.
Multiplex communications
Communication over free space
Combining or distributing information via code word channels...
370441, 375210, 375346, H04J 1302
Patent
active
056383762
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a receiving method which is applied, for example, to mobile communications and by which a base station receives from L (where L is an integer equal to or greater than 2) communicators signals spectrum-spread by short- and long-period spreading code sequences and separates at least one of the received signals and, more particularly, to a receiving method which subjects a despreading code sequence of the received signal to decorrelation to obtain an interference-cancelled despread output.
PRIOR ART
Because of excellent interference resistance and security protection features of spread spectrum communication techniques, a code division multiple access (CDMA) communication system employing the spread spectrum communication scheme is now being studied more and more actively toward practical utilization in various communication systems. A problem of the CDMA system is a near-far problem that the power of a signal received by the district center greatly varies with the location of the communicator. In the CDMA system, since a plurality of communicators share the same frequency band, a signal transmitted from one of them becomes an interference wave which degrades the speech quality of a transmitted signal from another communicator.
For example, when a communicator near the base station and a communicator at a remote place simultaneously conduct communications, the signal from the former is received by the base station at a high power level, whereas the signal from the latter is received at a low power level. This means that the communication between the communicator at the remote location and the base station is seriously degraded by interference from the communication with the nearby communicator. As a solution to this near-far problem, there has been studied a transmitter power control scheme. With the transmitter power control scheme, the power of the signal that the receiving station receives, or the signal power versus interference power ratio which is determined by the received power, is controlled to be constant regardless of the location of the communicator, by which uniform speech quality can be obtained in the service area.
A typical communication system in which the near-far problem constitutes a main factor of the degradation of characteristics is a mobile communication system. In W. C. Y. Lee, "Overview of Cellular CDMA", IEEE Trans. VT, Vol. VT-40, pp. 291-302, 1991, there is analyzed how the ratio of areas in a zone over which communications can be made with predetermined speech quality (which ratio will hereinafter be referred to as a site ratio) is improved by the above-mentioned transmitter power control in the mobile communication system. Moreover, there has also been reported a trial calculation that the frequency utilization factor could be increased up to about 20 times higher than in the North American AMPS mobile communication system by the implementation of high-speed transmitter power control responsive to variations of fading which occurs in radio wave propagation environments of mobile communications (For more detailed information, see K. S. Gilhousen, I. M. Jacobs, R. Padovani, A. J. Viterbi, L. A. Weaver, Jr. and C. E. Wheatly III, "On the Capacity of a Cellular CDMA system," IEEE Trans. VT, Vol. VT-40, pp. 303-312, 1992).
However, the site ratio after the transmitter power control is greatly affected by control errors which are caused by various factors. For example, in E. Kudoh and T. Matsumoto, "Effect of Transmitter Power Control Imperfections on Capacity in DS/CDMA Cellular Mobile Radios," Proc. of IEEE ICC '92, Chicago, pp. 310.1.1-6, 1992, there is discussed the influence of control error on the relative frequency utilization factor in the aforementioned mobile communication system. This literature states that a 1 dB control error would decrease the relative frequency utilization factor down to 29% (up link) and 31% (down link).
On the other hand, Ruxandra Lupas and Sergio Verdu at Princeton University of the United States h
REFERENCES:
patent: 5341395 (1994-08-01), Bi
patent: 5345468 (1994-09-01), Bi
patent: 5377225 (1994-12-01), Davis
patent: 5500856 (1996-03-01), Nagase et al.
Asymptotic normality of the crosscorrelation of a CDMA system with phase drift, L.A. Rush and H.V. Poor, Proceedings of the Twenty-eighth Annual Conference on Information and Systems, Princeton, NJ Mar. 1994.
Narrowband Interference Suppression in CDMA Spread Spectrum Communications, L.A. Rush and H. V. Poor, IEEE Transactions on Communications, vol. 42, No. Feb. 3, 1994, part 3, pp. 1969-1979 Apr. 1994.
optimum Bandwidth for CDMA, Klein S. Gilhousen, International Conference on Personal, Mobile Radio, and Spread Spectrum Communications, Beijing, China. Oct. 1994.
Kawahara Toshirou
Matsumoto Tadashi
Miki Yoshinori
Hsu Alpus H.
NTT Mobile Communications Network
Rao Seema S.
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