Adaptive receiver for CDMA base stations

Details Adaptive receiver for CDMA base stations Adaptive receiver for CDMA base stations

1998-09-23

2001-11-27

Ngo, Ricky (Department: 2731)

Multiplex communications

Generalized orthogonal or special mathematical techniques

Particular set of orthogonal functions

C370S335000, C370S334000, C370S342000, C375S349000

Reexamination Certificate

active

06324160

ABSTRACT:

FIELD OF THE INVENTION
The present invention concerns an adaptive receiver for base stations of CDMA mobile wireless systems.
RELATED TECHNOLOGY
Rake receivers are used to ensure optimum reception at base stations in the uplink of CDMA mobile wireless systems corresponding to the IS-95 Standard and thus to contribute to the ability of a base station to service a maximum possible area and/or a maximum number of subscribers. In particular, in urban areas, for example, there is often no visual contact between the transmitting mobile station and the base station and only reflected components of the emitted signals are received. Rake receivers make it possible to process transmitted signal components, received from generally different directions and with a time offset at the receiver's antenna array, individually and subsequently recombine them to evaluate the information received.
Such a receiver is described, for example, in A. F. Naguib and A. Paulraj, “Performance of Wireless CDMA with M-ary Orthogonal Modulation and Cell Site Antenna Arrays,” IEEE Journal on Selected Areas in Communications, Vol. 14, No. 9, December 1996, pp. 1770-1783. In order to estimate the control parameters (channel vectors, weight vectors) for the individual rake processing paths, which take the angles of incidence of the signal components into account, the receiver requires the antenna correlation matrices calculated from the HF-demodulated reception signals of the antenna elements before and after despreading, as described on p. 1773, left column of the article. In particular, the computation of correlation matrices from signals which have not yet been despread requires substantial amounts of time and computing capacity due to the large amount of information to be processed. In addition, with the known circuit it is not clear whether the sturdiness to ensure the consistent reception quality required for such systems is guaranteed when erroneously restituted individual Walsh symbols result in an incorrect selection of the despread reception signals for computing the required correlation matrices.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an adaptive receiver for antenna arrays in CDMA base stations of mobile wireless systems designed according to the IS-95 Standard having a highly effective adaptively controllable antenna directivity capable of amplifying the useful portion of several components of the same signal received on different signal paths and, in general, with a time offset, and capable of considerably weakening noise signals, which also exhibits sufficient sturdiness against erroneous decisions when demodulating individual Walsh symbols, and which can be implemented at the lowest possible cost.
The present invention provides a receiver for a base stations in CDMA mobile wireless systems operated according to the IS-95 Standard, comprising an antenna array (
10
) having a plurality of antenna elements (
11
through
18
) and I/Q demodulators connected downstream from the antenna elements, and a demodulator module (
2
) having a plurality of processing paths (
21
a
through
24
a;
21
d
through
24
d
), in which components of individual signals transmitted from mobile stations and arriving at the antenna array via different signal paths can be processed independently of one another prior to being combined in a downstream incoherent rake combiner (
25
,
26
), at whose output restituted Walsh symbols containing useful signals can be picked up for further processing. Each of the individual processing paths forms reception channels optimally set in space and time to the most important signal paths, changes in these signal paths being tracked by the fact that a complex vector combination of the I/Q-demodulated in-phase and quadrature signals (x(i)) with direction signature vectors (â
&mgr;
) estimated for individual signal paths to be analyzed is performed in the individual processing paths. A circuit arrangement (
3
) is provided for estimating the required direction signature vectors using antenna correlation matrices (R
zz,&mgr;
(k)) obtained from a plurality of consecutive possible signal propagation times, characterized in that in order to estimate the direction signature vectors, the circuit arrangement (
3
) correlates the I/Q-demodulated signals (x(i)) received by the antenna elements with transmission signals recovered from restituted Walsh symbols by remodulation at consecutive points in time that mark possible signal propagation times to obtain pulse response vectors of the antenna array. The circuit contains a correlator (
32
) and a remodulator (
33
) for this purpose, a circuit (
34
) for recursively forming antenna correlation matrices from the coefficients (z
&mgr;
(k)) of the pulse response vectors being connected downstream from the correlator, the estimation accuracy and the rate of change being set via the selection of an averaging parameter (&eegr;). The direction signature vectors (â
&mgr;
) are calculated in additional circuits (
35
,
36
,
37
) from the antenna correlation matrices by iteration, and the average path powers (p
&mgr;
(k)) and the component propagation times (&tgr;
&mgr;
) for the signal paths producing the strongest path powers are determined by calculating the trace of the antenna correlation matrices. The estimated direction signature vector together with the component propagation time relevant for the respective signal path are made available on the processing paths set to the respective signal paths for a predefined number of signal paths producing the strongest signal powers.
The receiver according to the present invention needs no complex computations of antenna correlation matrices from not yet despread reception signals.


REFERENCES:
patent: 5218619 (1993-06-01), Dent
patent: 5563610 (1996-10-01), Reudink
patent: 5652765 (1997-07-01), Adachi et al.
patent: 5905721 (1999-05-01), Liu et al.
patent: 6067292 (2000-05-01), Huang et al.
patent: 6078573 (2000-06-01), Batalama et al.
patent: 44 41 543 (1995-05-01), None
patent: 0 756 391 (1997-01-01), None
Ayman F. Naguib et al., “Performance of Wireless CDMA with M -ary Orthogonal Modulation and Cell Site Antenna Arrays,” IEEE Journal on Selected Areas in Communications. Vol. 14 No.9, Dec. 1996 pp. 1770-1783.

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