Pulse or digital communications – Repeaters – Testing
Patent
1995-07-18
1998-05-26
Bocure, Tesfaldet
Pulse or digital communications
Repeaters
Testing
35202, H04K 100
Patent
active
057578443
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Technical Field of the Invention
This invention is utilized for digital communications, and relates, in particular, to techniques for canceling interference signals in the received signal, and receiving under conditions of fast varying fading fluctuation, in spread spectrum communications.
2. Background of the Related Art
In recent years, in order to achieve effective utilization of frequency in digital mobile communications, code division multiple access systems which employ spread spectrum techniques have been studied. These spread spectrum techniques can be broadly divided into direct sequence systems and frequency hopping systems.
First, the configuration of an adaptive RAKE receiver will be explained with reference to FIG. 7. The receiver is a prior art example of a direct sequence receiver (see IEEE Journal on Selected Areas in Communications, Vol. 11, No. 7, September 1993). FIG. 7 is a block diagram of a prior art example of a direct sequence receiver. The explanation given here will assume a two-path model in which the propagation path is composed of a first arrival path and a delayed arrival path.
The received signal is inputted from inputted terminal 1. This received signal has been spread by a spreading code, such as a PN sequence, and in order to demodulate it, it has to be despread by the same spreading code. Multiplier 2 multiplies the received signal by the PN sequence outputted by PN sequence generator 5, and feeds the outputted to integrating circuit 6. This operation is equivalent to despreading. The PN sequence has a sharp autocorrelation, and if the timings of the PN sequences used in the transmitter and receiver do not coincide, despreading will not be successful. In this case, if the timing of the PN sequence outputted by PN sequence generator 5 coincides with that of the PN sequence of the first arrival path, the signal component corresponding to the first arrival path will be extracted from integrating circuit 6 and outputted as a despread signal.
Likewise, multiplier 3 multiplies the received signal by the delayed PN sequence that is outputted by delay circuit 4, and feeds the output integrating circuit 7. This operation is equivalent to despreading. If the timing of the PN sequence delayed by delay circuit 4 coincides with that of the PN sequence of the delayed arrival path, the signal component corresponding to the delayed arrival path will be extracted from integrating circuit 7 and outputted as a despread signal. Here, multipliers 2 and 3, delay circuit 4, PN sequence generator 5, and integrating circuits 6 and 7 correspond to a despreading and receiving means.
The despread signals are respectively multiplied by tap coefficients in multipliers 8 and 9, and are then added together by adder 10. The added signal that is outputted by adder 10 is fed to decision circuit 11, which corresponds to a signal decision means. Decision circuit 11 performs signal decision and outputs the decision signal from terminal 12. Subtraction circuit 14 calculates and outputs the difference between this decision signal and the added signal, i.e., the a priori estimation error. Note, that when a known training signal is contained in the received signal, the training signal outputted by training signal memory 15 is used instead of the decision signal during the training signal interval.
Switch circuit 13 performs this switching operation. Tap coefficient control circuit 16, which corresponds to a tap coefficient estimation means, receives as input the difference outputted by subtraction circuit 14, and the despread signals, and outputs the tap coefficients mentioned above.
Tap coefficient control circuit 16 employs a least mean square algorithm, for example, a recursive least mean square (RLS) algorithm in order to estimate the tap coefficients that minimize the square of the estimation error. This operation will be explained with reference to FIG. 8, which is a block diagram of a prior art example of tap coefficient control circuit 16.
The despread signals are inputted
REFERENCES:
patent: 5305349 (1994-04-01), Dent
patent: 5349609 (1994-09-01), Tsujimoto
patent: 5504783 (1996-04-01), Tomisato et al.
Higashi, Akihiro and Matsumoto, Tadashi, IEEE Journal on Selected Areas in Communications, vol. 11, No. 7, Sep. 1993, pp. 1076-1084.
Tomisato, Shigeru, Fukawa, Kazuhiko and Suzuki, Hiroshi, Technical Report of IEICE, Jan. 1993, pp. 61-66.
Tomisato, Shigeru, Fukawa, Kazuhiko and Suzuki, Hiroshi, Technical Report of IEICE, Jun. 1993, pp. 7-12.
Fukawa, Kazuhiko and Suzuki, Hiroshi, Technical Report of IEICE, Jul. 1989, pp. 415-421.
Qiu, Zhong-Qi, USUI, Shiro and Abe, Kenichi, Technical Report of IEICE, Jul. 1989, pp. 1038-1044.
Yoon, Young C., Kohno, Ryuji and Imai, Hideki, IEEE Second International Symposium on Spread Spectrum Techniques and Applications, Nov./Dec. 1992, pp. 87-90.
Fukawa Kazuhiko
Suzuki Hiroshi
Bocure Tesfaldet
NTT Mobile Communications Network Inc
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