Multiplex communications – Communication over free space – Combining or distributing information via code word channels...
Patent
1997-02-12
2000-10-24
Ton, Dang
Multiplex communications
Communication over free space
Combining or distributing information via code word channels...
370442, 370479, 375200, H04J 1300
Patent
active
061377880
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a code division multiple access (CDMA) demodulating apparatus used for receiving signals of a CDMA system using spread spectrum, and more specifically to a CDMA demodulating apparatus suitable for a mobile communication system which uses a cellular configuration.
BACKGROUND ART
DS (Direct Sequence)--CDMA is a system in which a plurality of users carry out communications using a same frequency band, and each user is identified by a spreading code. As a spreading code for each user, a spreading code such as Gold code is used. Interference signal power of another user is a reciprocal of average spreading factor (PG) in the despreading process of a receiver. However, each user, especially under asynchronous environment in ascendant mobile communications, is subject to momentary variation, short section variation, and distance variation due to independent fading.
Therefore, to satisfy a predetermined reception quality determined by the system by each user at the receiving side, it is necessary to control the transmission power to achieve a constant SIR (Signal-to-Interference Ratio) in the receiver input at the base station. Here, SIR is a ratio of the reception signal power at the user of the desired wave to the interference signal power received from another user. However, even though the transmission power control is perfect, and the SIR in the base station receiver input is maintained at a constant value, under multipath environment of mobile communications, spreading codes will never quadrate completely with each other. Therefore, the user is subject to interference due to cross-correlation of the power of a reciprocal of spreading factor at an average per one of other users.
As shown above, since the interference signal level increases with increasing number of users communicating in the same frequency band, to increase the user capacity per cell, an interference canceling technique to reduce interference from other users is required.
As interference canceling techniques, a multi-user type interference canceler and a single user type interference canceler are known. The multi-user type interference canceler not only demodulates a desired wave signal of its own channel, but also demodulates a signal of another user using spreading code information and reception signal timing of the other user. The single user type interference canceler, on the other hand, uses only the spreading code of own channel to minimize an average cross-correlation and noise component from the other user.
The multi-user type canceler includes a linear processing type (decorrelator or the like) and a nonlinear processing type. The decorrelator calculates mutual correlation of the spreading code of own channel and all other spreading codes of receiver input to determine an inverse matrix composed of the cross-correlation, and the cross-correlation is canceled by compensating for the output signal of a matched filter using this inverse matrix. Where K is a number of users, and Lk is a number of reception paths to individual users, dimension Dm of the decorrelator matrix is given by the following equation. ##EQU1##
Therefore, realization of the above technique becomes difficult as the number of users increases, which increases the circuit scale.
A nonlinear multi-user type interference canceler is a replica reproduction type interference canceler. This canceler demodulates interference signal from other user's channel, decides it to reproduce transmission information data replica, calculates an interference signal replica of each channel from this replica, and subtracts the interference replica from the reception signal, thereby demodulating the desired wave signal with enhanced SIR.
FIG. 1 shows a replica reproduction type multi-stage interference canceler (serial interference canceler) proposed in the document "Serial interference cancellation method for CDMA", IEE, Electronics Letters Vol. 30, No. 19, pp. 1581-1582, Sept. 1994.
In FIG. 1, the numeral 11 indicates a spread signal, 1
REFERENCES:
patent: 5105435 (1992-04-01), Stilwell
patent: 5224122 (1993-06-01), Bruckert
patent: 5235612 (1993-08-01), Stilwell et al.
patent: 5325394 (1994-06-01), Bruckert
patent: 5418814 (1995-05-01), Hulbert
patent: 5787112 (1998-07-01), Murai
patent: 5872776 (1999-02-01), Yang
patent: 5926471 (1999-07-01), Shoji
Andou Hidehiro
Higuchi Kenichi
Miki Yoshinori
Sawahashi Mamoru
Ho Tuan Q.
NTT Mobile Communications Network Inc.
Ton Dang
LandOfFree
CDMA demodulating apparatus does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with CDMA demodulating apparatus, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and CDMA demodulating apparatus will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-1972011