Radio frequency sources are observed at a fusion center via sensor measurements made over slow flat-fading channels. The number of sources may be larger than the number of sensors, but their activity is sparse and intermittent with bursty transmission patterns. To account for this, sources are modeled as hidden Markov models with known or unknown parameters. The problem of blind source estimation in the absence of channel state information is tackled via a novel algorithm, consisting of a dictionary learning (DL) stage and a per-source stochastic filtering (PSF) stage. The two stages work in tandem, with the latter operating on the output produced by the former. Both stages are designed so as to account for the sparsity and memory of the sources. To this end, smooth LASSO is integrated with DL, while the forward-backward algorithm and Expectation Maximization (EM) algorithm are leveraged for PSF. It is shown that the proposed algorithm can enhance the detection and the estimation performance of the sources, and that it is robust to the sparsity level.
Index TermsBlind source separation, Wireless networks, Dictionary learning, Intermittent and sparse sources, Hidden Markov model
I. INTRODUCTIONBlind source separation (BSS) refers to the separation of a set of source signals from a set of mixed signals, without resorting to any a priori information about the source signals or the mixing process [1]. BSS exploits only the information carried by the received signals themselves, hence the term blind. BSS has numerous applications in speech recognition [2,3], image extraction [4,5], and surveillance [6,7]. Different metrics are used to evaluate the performance of BSS methods depending on the applications. For example, signal-to-interference ratio is used in [2] for speech separation, and a performance index is introduced in [4] for image feature extraction. Based on these metrics, many approaches have been proposed to solve BSS problems, such as independent component analysis (ICA) [8], principal component analysis (PCA) [9], and singular value decomposition (SVD) [10].This paper addresses BSS in wireless networks. We are specifically interested in the set-up illustrated in Fig. 1, in which a fusion center observes a number of radio sources via noisy sensor measurements over unknown channels. The system may model an Internet-of-Things (IoT) system, such as LoRa, Sigfox, or Narrow Band-IoT (NB-IoT) [11,12].In wireless networks involving multiple terminals operating over flat fading channels, the signals received at a terminal are linear mixtures of the signals emitted by the transmitting terminals. The need for BSS arises in non-collaborative applications in which the signals and the channels through which they are received at a terminal are both unknown. ICA has been widely applied to solve BSS problems in wireless networks [13][14][15][16], since it yields a useful decomposition with only scaling, and permutation ambiguities [17]. To achieve signal separation, ICA relies on the statistical independence and on the non-...