The performance of the minimum variance distortionless response (MVDR) estimator is studied by simulations if the estimator is applied for delay estimation of a direct sequence spread spectrum (DS/SS) signal corrupted by interference. The results show that the MVDR estimator can mitigate the effects of strong tone interferences and other DS/SS signals, under the condition that the number of other DS/SS signals is limited to one third of the code length. However, the estimator is quite sensitive to a highly correlated multipath signal.

A number of different techniques for the suppression of narrowband interference due to overlay in CDMA systems have been studied. This paper describes the relative performance of three such techniques for a fading channel, multi-user CDMA system. Personal Communication Network systems using suppression filters based on the symmetric transversal LMS, the lattice and transform domain algorithms are studied. Bit error rates are found by simulation for different suppression filters. The overlay signal is assumed to be narrowband BPSK and the performance of these systems is studied for varying BPSK carrier frequency offsets. Since both the lattice and LMS filters produce a notch filter after convergence, their relative performance is also studied as a function of the bandwidth of the BPSK interference signal. It is found that the lattice filters are better able to suppress a narrowband interference, but as the bandwidth of the interference increases, their performance degrades more than the...

Ultra Wide-band (UWB) radio systems have drawn attention during the last few years. These systems use low transmission power, spread over a bandwidth of several gigahertz, which enable them to co-exist with other narrow band systems over the same frequency band without interfering them. Nevertheless, the narrow band systems can cause interference which may jam the UWB receiver completely. This paper presents novel narrow band interference suppression algorithms for UWB radio systems, where standard narrow band interference suppression techniques cannot be applied. The presented algorithms use a RAKE receiver with MMSE weights and correlators at delays that does not correspond to channel taps. Theoretical analysis of these algorithms reveal that they can eliminate the narrow band interference almost completely. Simulation results support the theoretical ones.

This paper analyzes the effects of narrowband interferences (NBI) on the performance of a multi-band orthogonal frequency division multiplexing (MB-OFDM) Ultra-wideband (UWB) receiver and proposes efficient schemes for signal reception and extraction of information in the presence of NBI. A study to assess the effects of NBI on the quantization noise in the analog to digital converter (ADC) is conducted. It is found that a reduced-complexity digital frequency excision method is sufficient to compensate weak NBI (with signal-to-interference ratio (SIR) larger than 0 dB). To combat efficiently strong NBI (with SIR less than 0 dB), this paper proposes a novel mixed interference suppression scheme that relies on the joint cooperation between a digital NBI detector and an adaptive analog notch filter. Simulation results show that the proposed mixed suppression scheme improves the performance of the digital frequency excision scheme by as much as 9 dB. 1.

of two-stage detection in mismatched AWGN channels. reprint.

This paper studies the performance of a two dimensional least mean square (TDLMS) adaptive filter as a prewhitening filter for the detection of small signals in infrared image data. The spatially broad clutter with long correlation length is seen to be narrowband in the two dimensional frequency domain. This narrowband clutter is predicted and subtracted from the input, leaving the spatially small signal in the residual output. The output energy in the residual and prediction channels of such a filter is seen to depend on the correlation length of the various components in the input signal, thus permitting the separation of short correlation targets from the longer correlation clutter. False alarm improvements and detection gains obtained by using this detection scheme on thermal infrared sensor data with known target points is presented. 1 Introduction This paper addresses the problem of detecting small objects of very small spatial extent masked by This work was supported by the ...

This paper chronicles more than 40 years of evolution in the design of such modems.

Two delay estimators that mitigate effects of a tone jammer are presented. They are based on the phase interference extractor (PIE) and auxiliary-vector (AV) data detection principles. The estimators are analyzed by computer simulations and shown to tolerate more powerful jammers than the conventional correlator estimator does.

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.

In this paper Independent Component Analysis (ICA) is considered for blind interference cancellation in a direct sequence spread spectrum communication system utilizing antenna arrays. Recently, an ICA-assisted interference canceler was proposed [1]. This receiver structure is an extension to the framework proposed in [2], in which blind source separation (BSS) techniques were utilized to the jammer mitigation problem. A common feature for both is that they apply an advanced pre-processing tool to o#er an unjammed signal for conventional detection. However, it is not always desirable to apply the pre-processing tool, since it might even cause additional interference if the jammer is weak or absent. What would make the receivers more practical is to switch the additional canceler active only whenever it is expected to improve conventional detection. In this paper we compare two possible switching strategies at both ends of the receiver chain, pre and post switching schemes, and evaluate their impacts to the overall performance improvement of the array receiver.