Presence detection of long-and-short-code DS-SS signals using the phase linearity of multichannel sensors

Abstract

Abstract —In this study, the detection of direct sequence spreadspectrum (DS-SS) signals in white Gaussian noise without priorknowledge is investigated for spatially distributed multichannelwideband sensor array. A novel technique for the presence detec-tion of both the long-and-short-code DS-SS signals is proposedwhich uses the frequency domain spatial covariance matrix of thesensor array. The technique is based on the linearity of the phaseresponse of the wideband spatial covariances of cross sensorsalong the bandwidth of the signal. It is shown in simulationsthat the technique can detect DS-SS signals in a stable way atlow signal to noise ratio (SNR) without any prior informationand assumption on target. In addition, the proposed method candetect DS-SS signals in the presence of narrow band interferenceand multipath reflections. Index Terms —spread spectrum communication, signal detec-tion, sensor arrays, covariance matrices, phase linearity I. I NTRODUCTION DS-SS signals are widely preferred for secure wirelesscommunications in both military and civilian applications [1].The non-cooperative detection of DS-SS signals at low SNRis challenging and important problem for the applications suchas spectrum surveillance, source localization, etc. [7].In this paper, we propose a new DS-SS signal detectionmethod which has certain advantages and privileges. Theproposed method, which is based on the wideband spatialcovariance matrix of the received signals, does not requireany prior information and assumption on target signal. Theproposed method can detect both the long-and-short-codeDS-SS signals at low SNR with a superior’s performance. It isalso possible to detect DS-SS signals in the presence of narrowband interferences and multipath reflections.In literature, the detection methods are extensively studiedfor short-code DS-SS signals [2-6]. These methods are usuallybased on the cycle feature of the transmitted signal and somespecific assumptions [4]. For example, in [5] the temporalwindow durations should be larger than the length of thespreading sequence which is not a priori information. Onthe other hand, there are limited number of studies for thedetection of the long-code DS-SS signals, where the chipperiod is quite larger than the data symbol duration [7-9].The above property of the long spreading codes destroys thesymbol-interval cyclostationary properties of the transmittedsignal [8]. In this paper, the proposed method which uses thephase linearity between the cross channels can be applied forthe presence detection of both the long-and-short code DS-SSsignals. Many applications in literature, the phase data is usedfor the parameter estimation [10-13]. Furthermore, in [3], twochannel non-cooperative DS-SS detection approach that usesthe phase linearity is proposed. But the used algorithm andperformance details are not clear.