Data detection for codes with non-uniform spreading factors

Details Data detection for codes with non-uniform spreading factors Data detection for codes with non-uniform spreading factors

2002-07-01

2004-05-25

Chin, Stephen (Department: 2634)

Pulse or digital communications

Bandwidth reduction or expansion

Television or motion video signal

C375S140000, C375S146000, C375S240000

Reexamination Certificate

active

06741653

ABSTRACT:

BACKGROUND OF THE INVENTION
This invention generally relates to wireless code division multiple access communication systems. In particular, the invention relates to data detection of communications having non-uniform spreading factors in such systems.
In code division multiple access (CDMA) communication systems, multiple communications may be simultaneously sent over a shared frequency spectrum. Each communication is distinguished by the code used to transmit the communication. Data symbols of a communication are spread using chips of the code. The number of chips used to transmit a particular symbol is referred to as the spreading factor. To illustrate, for a spreading factor of sixteen (16), sixteen chips are used to transmit one symbol. Typical spreading factors (SF) are 16, 8, 4, 2 and 1 in TDD/CDMA communication systems.
In some CDMA communication systems to better utilize the shared spectrum, the spectrum is time divided into frames having a predetermined number of time slots, such as fifteen time slots. This type of system is referred to as a hybrid CDMA/time division multiple access (TDMA) communication system. One such system, which restricts uplink communications and downlink communications to particular time slots, is a time division duplex communication (TDD) system.
One approach to receive the multiple communications transmitted within the shared spectrum is joint detection. In joint detection, the data from the multiple communications is determined together. The joint detector uses the, known or determined, codes of the multiple communications and estimates the data of the multiple communications as soft symbols. Some typical implementations for joint detectors use zero forcing block linear equalizers (ZF-BLE) applying Cholesky or approximate Cholesky decomposition or fast Fourier transforms.
These implementations are typically designed for all the communications to have the same spreading factor. Simultaneously handling communications having differing spreading factors is a problem for such systems.
Accordingly, it is desirable to be able to handle differing spreading factors in joint detection.
SUMMARY OF THE INVENTION
A plurality of communication signals is received. Each communication signal has an associated code. At least two of the communication signals has a different spreading factor. The associated codes have a scrambling code period. A total system response matrix has blocks. Each block has one dimension of a length M and another dimension of a length based on in part M and the spreading factor of each communication. M is based on the scrambling code period. Data of the received plurality of communication signals is received using the constructed system response matrix.


REFERENCES:
patent: 2002/0176392 (2002-11-01), Reznik et al.
A. Klein et al., “Zero Forcing and Minimum Mean-Square-Error Equalization for Multiuser Detection in Code-Division Multiple-Access Channels,” IEEE Transactions on Vehicular Technology, US, IEEE Inc. New York, vol. 45, No. 2, May 1, 1996 pp. 276-287.
H. R. Karimi et al., “A Novel and Efficient Solution to Block-Based Joint-Detection Using Approximate Cholesky Factorization,” IEEE International Symposium on Personal, Indoor and Mobile Radio Communications, vol. 3, 1998, pps. 1340-1345.
J. Mayer et al., “Realtime Feasibility of Joint Detetion CDMA,” EPMCC, European Personal Mobile Communications Conference Together with Kommunikation, vol. 145, No. 145, 1997, pp. 245-252.
Benvenuto et al., “Joint Detection with Low Computational Complexity for Hybrid TD-CDMA Systems,” IEEE Journal on Selected Areas in Communications, vol. 19, No. 1, Jan. 2001 pp. 245-253.
Klein et al., “Linear Unbiased Data Estimation in Mobile Radio Systems Applying CDMA,” IEEE Journal on Selected Areas in Communications, vol. 11, No. 7, Sep. 11, 1993, pp. 1058-1066.

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