Pulse or digital communications – Spread spectrum
Reexamination Certificate
1998-08-05
2001-03-20
Chin, Stephen (Department: 2634)
Pulse or digital communications
Spread spectrum
C375S147000, C375S345000, C370S342000
Reexamination Certificate
active
06205166
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to spread spectrum communication systems and more specifically to a code division multiple access (CDMA) communication receiver having an array of antennas whose directivity pattern is adaptively controlled.
2. Description of the Related Art
For CDMA communication receivers, it is known to use an adaptive array of antennas for receiving user signals. Each of the received user signals is separated into multipath components, which are supplied respectively to adaptive processing units so that each unit receives a set of multipath components of same arrival time. In each processing unit, the input signals are respectively multiplied with weight coefficients and summed together to produce a weighted sum signal. This signal is despread with a chip sequence and demodulated. The demodulated signals from the processing units are combined in an adder and a threshold decision is performed on the output of the adder to produce a symbol output. Each processing unit detects a decision error of the symbol output and produces the weight coefficient by detecting correlations between the set of multipath components and the decision error.
However, since the adaptive processing units are provided in number corresponding to the number of multipath components, and each unit performs weighting and summing operations and updating the weight coefficients, implementation of the prior art system suffers from hardware complexity. Additionally, difficulty is encountered for the prior art antenna array to create a distinct directivity pattern when the signals received by the antennas contain numerous multipath components, particularly when they contain weak components, due to decreased reliability of the decision errors.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a code division multiple access communication receiver having an adaptive array of antennas which can be implemented with reduced hardware and which is capable of adaptively controlling the antenna pattern even when the received signal contains numerous multipath components.
According to a first aspect of the present invention, there is provided a code division multiple access communication receiver comprising a plurality of antennas spaced a correlation distance apart from each other, and multiply-and-add circuitry for respectively weighting signals from the antennas with weight coefficients and summing the weighted signals to produce a weighted sum signal. Separation circuitry separates the weighted sum signal into multipath components which respectively correspond to propagation paths of a signal transmitted from a user station. A plurality of despreaders are provided for respectively despreading the separated multipath components with a chip sequence assigned to the user station to produce a plurality of despread signals at symbol intervals. Error detection circuitry detects a plurality of errors between a symbol output and the despread signals and combines the errors to produce a combined error signal. Weight control circuitry produces the weight coefficients from the signals detected by the antennas and updates the weight coefficients according to the combined error signal.
Preferably, the receiver includes a plurality of demodulators for estimating channel responses of the propagation paths from the despread signals and multiplying the despread signals by the estimated channel responses to produce a plurality of demodulated signals. The demodulated signals are summed and threshold decision is made on the sum of the demodulated signals to produce a decision output. The error detection circuitry is arranged to multiply the decision output by the estimated channel responses to produce a plurality of multiplied decision outputs, and detect a plurality of differences between the multiplied decision outputs and the despread signals to produce the errors.
According to a second aspect, the present invention provides a code division multiple access communication receiver comprising a plurality of antennas spaced a correlation distance apart from each other, and a plurality of despreaders for respectively despreading signals detected by the antennas with a chip sequence assigned to a user station to produce a plurality of despread signals at chip intervals. Multiply-and-add circuitry is connected to the despreaders for respectively weighting the despread signals by weight coefficients, separating each of the weighted despread signals into a plurality of multipath components which respectively correspond to propagation paths of a signal transmitted from the user station and summing the seperated multipath components to produce a plurality of weighted sum signals each representative of the sum of the multipath components of same arrival time. Error detection circuitry detects a plurality of errors between a symbol output and the weighted sum signals, and combining the errors to produce a combined error signal, and weight control circuitry produces the weight coefficients from the despread signals and updates the weight coefficients according to the combined error signal.
Preferably, a plurality of demodulators are provided for estimating channel responses of the propagation paths from the weighted sum signals and respectively multiplying the weighted sum signals by the estimated channel responses to produce a plurality of demodulated signals. The demodulated signals are summed and a threshold decision is made on the sum of the demodulated signals to produce a decision output. The error detection circuitry is arranged to multiply the decision output by the estimated channel responses to produce a plurality of multiplied decision outputs, and detect a plurality of differences between the multiplied decision outputs and the despread signals to produce the errors.
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Tanaka, S. Et al.: “Pilot Symbol-Assisted Decision-Directed Coherent Adaptive Array Diversity for DS-CDMA mobile Radio Reverse Link” IEICE Transactions on Fundamentals Electronics, Communications and Computer Sciences, JP, Institute of Electronics Information and Comm. Eng., Tokyo, vol. E80-A, No. 12, Dec. 1, 1997, pp. 2445-2453, XP000768670.
Maruta Yasushi
Ushirokawa Akihisa
Yoshida Shousei
Chin Stephen
Deppe Betsy L.
NEC Corporation
Sughrue Mion Zinn Macpeak & Seas, PLLC
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