Cancellation of interference in a communication system with application to S-CDMA

Abstract

Cancellation of interference in a communication system with application to S-CDMA. A relatively straight-forward implemented, and computationally efficient approach of selecting a predetermined number of unused codes is used to perform weighted linear combination selectively with each of the input spread signals in a multiple access communication system. If desired, the predetermined number of unused codes is always the same in each implementation. Alternatively, the predetermined number of unused codes are selected from within a reordered code matrix using knowledge that is shared between the two ends of a communication system, such as between the CMs and a CMTS. While the context of an S-CDMA communication system having CMs and a CMTS is used, the solution is generally applicable to any communication system that seeks to cancel narrowband interference. Several embodiments are also described that show the generic applicability of the solution across a wide variety of systems.

Description

CROSS REFERENCE TO RELATED APPLICATIONS [0001] The present U.S. Utility Patent Application claims priority pursuant to 35 U.S.C. §119(e) to U.S. Provisional Patent Application Serial No. 60 / 367,564, entitled “CANCELLATION OF INTERFERENCE IN A COMMUNICATION SYSTEM WITH APPLICATION TO S-CDMA,” (Attorney Docket No. BP 2285), filed Mar. 26, 2002, pending, which is hereby incorporated herein by reference in its entirety and is made part of the present U.S. Utility Patent Application for all purposes.TECHNICAL FIELD OF THE INVENTION [0002] The invention relates generally to communication systems; and, more particularly, it relates to communication systems that may be affected by undesirable interference. BACKGROUND OF THE INVENTION [0003] Signal processing within communication systems having a communication channel, in an effort to improve the quality of signals passing through the communication channel, has been under development for many years. In the past several years, emphasis has mo...

AI Technical Summary

Benefits of technology

[0007] Various aspects of the invention can be found in a communication receiver that supports interference cancellation functionality. The present invention uses a linear combination of the unused dimensions (for example, the unused codes) to cancel the interference. This may be done after the de-spreader, or, equivalently, as part of the de-spreading process. There is no appreciable inter-code interference introduced and no decision errors are made as part of this process. The allocation of unused codes reduces the capacity of the system by a small amount. In one embodiment, the reduction of capacity of the system will be to 120/128 of the original capacity for a system of 128 codes where 8 unused codes are employed. Clearly, other numbers of available codes may also be employed without departing from the scope and spirit of the invention.

[0008] It is noted that the present invention may be extended across a wide variety of application contexts. The present technique can be applied to cancel not only narrowband interference, but any interference that occupies a small number of dimensions in the signal space. The narrowband interference includes just one of the many types of interferences that may be substantially cancelled according to the present invention. A narrowband signal occupies a small number of DFT (discrete Fourier transform) bins, showing that it occupies a small number of dimensions in signal space. An extremely simple example is a CW (Continuous Wave) signal whose frequency is an integer multiple of the de-spread symbol rate; this CW signal occupies only a single bin in the DFT, or only one dimension in the signal space, where ea...

Problems solved by technology

The allocation of unused codes reduces ...

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