Blind source separation for interference cancellation in CDMA systems

Communication is the science of "reliable" transfer of information between two parties, in the sense that the information reaches the intended party with as few errors as possible. Modern wireless systems have many interfering sources that hinder reliable communication. The performance of receivers severely deteriorates in the presence of unknown or unaccounted interference. The goal of a receiver is then to combat these sources of interference in a robust manner while trying to optimize the trade-off between gain and computational complexity. Conventional methods mitigate these sources of interference by taking into account all available information and at times seeking additional information e.g., channel characteristics, direction of arrival, etc. This usually costs bandwidth. This thesis examines the issue of developing mitigating algorithms that utilize as little as possible or no prior information about the nature of the interference. These methods are either semi-blind, in the former case, or blind in the latter case. Blind source separation (BSS) involves solving a source separation problem with very little prior information. A popular framework for solving the BSS problem is independent component analysis (ICA). This thesis combines techniques of ICA with conventional signal detection to cancel out unaccounted sources of interference. Combining an ICA element to standard techniques enables a robust and computationally efficient structure. This thesis proposes switching techniques based on BSS/ICA effectively to combat interference. Additionally, a structure based on a generalized framework termed as denoising source separation (DSS) is presented. In cases where more information is known about the nature of interference, it is natural to incorporate this knowledge in the separation process, so finally this thesis looks at the issue of using some prior knowledge in these techniques. In the simple case, the advantage of using priors should at least lead to faster algorithms.reviewe

SEMI-BLIND INTERFERENCE SUPPRESSION ON COHERENT MULTIPATH ENVIRONMENTS

Blind source separation (BSS) can be used to separate an interfering source from a set of desired signals. By exploiting the statistical independence between the source signals and the interference, we present an alternative to the blind beamformer for suppressing the interference. [1, 2] presented the concept of combining Independent Component Analysis (ICA) with a conventional detection for suppressing jammers in a single-path environment. This paper address a broader view of interference suppression in coherent multipath environment. Computer simulations demonstrate the performance and applicability of our structure. 1

Jammer Mitigation In Ds-Cdma Array System Using Independent

In this paper we consider blind interference mitigation in direct sequence spread spectrum communication system under intentional jamming. Recent work [1] presents a general framework in which blind source separation (BSS) techniques are utilized to enhance conventional detection. However, only second order statistics were utilized which makes the scheme vulnerable to temporally uncorrelated information or jamming signals. In this paper we remove this disadvantage by utilizing BSS based on independent component analysis (ICA). Numerical examples are given to evaluate achieved performance gains

Inter-Cell Interference Cancellation in CDMA Array Systems by

The most important use of a spread spectrum communication system is that of interference mitigation. In fact, a spread spectrum communication system has an inherent temporal interference mitigation capability, usually called a processing gain. This gain enables the system to work properly in many cases. At times, however, the interference can be too strong, or the requirements for the link quality are more stringent, so that additional interference mitigation is needed

Suppression Of Bit-Pulsed Jammer Signals In Ds-Cdma Array System

In this paper, Independent Component Analysis is considered for blind suppression of interference caused by bit-pulsed jamming in a direct sequence spread spectrum communication system. A framework for applying blind techniques to the jammer mitigation problem was earlier introduced in [1]. However, the scheme proposed there is based on second-order statistics only, and has serious practical limitations. For example, it fails for temporally uncorrelated data which is commonplace in CDMA communications. This paper extends the framework by taking into account both data modulation and temporally uncorrelated jamming, and removes the uncorrelatedness limitation by employing independent component analysis instead of second-order statistics. Computer simulations show that the proposed method performs better than the well-known RAKE method, which is the standard choice for suppressing jammer signals