Browsing by Author "Crespo, Pedro M."
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Item Concurrent and distributed projection through local interference for wireless sensor networks(2012) Insausti, Xabier; Crespo, Pedro M.; Beferull, Baltasar; Del Ser, Javier; IAIn this paper we use a gossip algorithm to obtain the projection of the observed signal into a subspace of lower dimension. Gossip algorithms allow distributed, fast and efficient computations on a Wireless Sensor Network and they can be properly modified to evaluate the sought projection. By combining computation coding with gossip algorithms we proposed a novel strategy that leads to important saving on convergence time as well as exponentially decreasing energy consumption, as the size of the network increases.Item A decode-and-forward scheme for multihop wireless networks(2013) Hernaez, Mikel; Alustiza, Iker; Crespo, Pedro M.; Del Ser, Javier; IAIn this paper, we propose a Decode-and-Forward (DF) relaying scheme for the multihop transmission in wireless networks, where the information generated by an independent source has to be sent to a far destination based on multiplerelay cooperation. The proposed DF scheme blends together convolutional channel coding with linear combination of blocks of data over a finite field. The performance of the proposed system is compared with reference schemes previously proposed in the literature. We provide simulation results showing that using blocks of K = 13 information bits, our scheme clearly outperforms these reference schemes that use blocks of K = 1500 information bits. Moreover, we show that the proposed DF scheme is suitable for large multi-hop networks with relays that share their resources with other networks since: 1) a negligible performance degradation is obtained for adding more hops; and 2) most of the iterative gain at the decoding is achieved in less than 10 iterations.Item Flexible channel coding approach for short-length codewords(2012) Hernaez, Mikel; Crespo, Pedro M.; Del Ser, Javier; IAThis letter introduces a channel coding design framework for short-length codewords which can achieve lower error floor than previous approaches. The proposed code is based on combining convolutional coding with a q-ary linear combination and unequal energy allocation. Simulation results suggest that for very low Bit Error Rates (BER) the proposed system will exhibit lower error floors than previous approaches, with a small performance penalty at mid-range BERs. On the other hand, when selecting an error floor higher than the previous approaches, the loss in performance at mid-range BERs is negligible.Item Iterative concatenated zigzag decoding and blind data fusion of correlated sensors(2009) Del Ser, Javier; Garcia-Frias, Javier; Crespo, Pedro M.; IAThis paper addresses the sensor network scenario where several nodes sense a common information source S. When such sensors forward their correlated observations to a common shared receiver, it is necessary to combine the received information in order to obtain an estimation of S with high reliability. In this manuscript we propose the use of low-complexity concatenated Zigzag codes for the transmission of correlated sensors through orthogonal AWGN channels. In reception, a novel albeit simple correlation estimation procedure is integrated into the iterative decoding and data fusion algorithm, which is based on the Sum-Product Algorithm applied over the factor graph describing the system. Fundamental limits are also derived for the end-to-end probability of error. Simulation results verify that the Bit Error Rate (BER) performance of the proposed receiver is very close to the aforementioned fundamental limits, while requiring less decoding complexity than other capacity-approaching codes.Item Iterative fusion of distributed decisions over the gaussian multiple-access channel using concatenated BCH-LDGM codes(2011) Del Ser, Javier; Manjarres, Diana; Crespo, Pedro M.; Gil-Lopez, Sergio; Garcia-Frias, Javier; IAThis paper focuses on the data fusion scenario where N nodes sense and transmit the data generated by a source S to a common destination, which estimates the original information from S more accurately than in the case of a single sensor. This work joins the upsurge of research interest in this topic by addressing the setup where the sensed information is transmitted over a Gaussian Multiple-Access Channel (MAC). We use Low Density Generator Matrix (LDGM) codes in order to keep the correlation between the transmitted codewords, which leads to an improved received Signal-to-Noise Ratio (SNR) thanks to the constructive signal addition at the receiver front-end. At reception, we propose a joint decoder and estimator that exchanges soft information between the N LDGM decoders and a data fusion stage. An error-correcting Bose, Ray-Chaudhuri, Hocquenghem (BCH) code is further applied suppress the error floor derived from the ambiguity of the MAC channel when dealing with correlated sources. Simulation results are presented for several values of N and diverse LDGM and BCH codes, based on which we conclude that the proposed scheme outperforms significantly (by up to 6.3dB) the suboptimum limit assuming separation between Slepian-Wolf source coding and capacity-achieving channel coding.Item Joint non-binary LDPC-BICM and network coding with iterative decoding for the multiple access relay channel(2011) Hernaez, Mikel; Crespo, Pedro M.; Del Ser, Javier; IAIn this paper we present a novel joint network-channel coding scheme for the time-division Multiple Access Relay Channel (MARC), which combines Bit-Interleaved Coded Modulation with iterative decoding (BICM-ID) based on nonbinary Low-Density Parity Check (LDPC) codes, along with the linear combination of blocks of data at the relay. The common receiver iteratively exchanges soft information between a joint soft demapper and the LDPC decoder associated to the transmitting nodes. The performance of the proposed system is compared, in terms of Frame Error Rate (FER) and through intensive Monte Carlo simulations, with the corresponding theoretical outage rate for different values of the spectral efficiency ρs of the overall setup. Two main conclusions are drawn: 1) small FER degradation is obtained as ρs increases; and 2) no diversity is lost with respect to the theoretical outage rate.Item Joint source-channel coding of sources with memory using turbo codes and the burrows-wheeler transform(2010-07) Del Ser, Javier; Crespo, Pedro M.; Esnaola, Inaki; Garcia-Frias, Javier; IAThe Burrows-Wheeler Transform (BWT) [1] is a block sorting algorithm which has been proven to be useful in compressing text data [2]. More recently, schemes based on the BWT have been proposed for lossless data compression using LDPC [3]-[5] and Fountain [6] codes, as well as for joint source-channel coding of sources with memory [7],[8]. In this paper we propose a source-controlled Turbo coding scheme for the transmission of sources with memory over AWGN channels also based on the Burrows-Wheeler Transform. Our approach combines the BWT with a Turbo code and employs different energy allocation techniques for the encoded symbols before their transmission. Simulation results show that the performance of the designed scheme is close (within 1.5 dB) to the theoretical Shannon limit.Item Joint source-channel-network decoding and blind estimation of correlated sensors using concatenated zigzag codes(2009) Del Ser, Javier; Mendicute, Mikel; Crespo, Pedro M.; Gil-Lopez, Sergio; Olabarrieta, Ignacio; IAFocusing on densely deployed wireless sensor networks, this paper presents a novel method for joint source-channel-network coding of distributed correlated sources through multiple access relay channels. In such networks, the role of intermediate sensors as relay nodes permits to achieve enhanced end-to-end error performance and increased spatial diversity in presence of channel fading. This paper addresses this scenario for a two source, single relay architecture by proposing a novel coding approach based on concatenated Zigzag codes, whose low complexity is specially suitable for energy-constrained autonomous systems. Joint decoding and estimation of the parameters defining the correlation between sensors is iteratively performed at the receiver side. Simulation results show that the proposed joint coding scheme attains significant energy gains with respect to traditional routing techniques, specially at high signal to noise ratios.Item Joint Turbo coding and source-controlled modulation of cycle-stationary sources in the bandwidth-limited regime(2010) Ochoa, Idoia; Crespo, Pedro M.; Del Ser, Javier; Hernaez, Mikel; IAIn this paper we propose a novel one-layer coding/shaping transmission system for the bandwidth-limited regime based on singlelevel codes and sigma-mapping [1]. Specifically, we focus on cyclestationary information sources with independent symbols. High spectral efficiencies can be achieved by combine at the transmitter a Turbo code with a sigma-mapper. Furthermore, the encoded symbols are modulated by using an asymmetric energy allocation technique before entering the aforementioned sigma-mapper. The corresponding decoder iterates between the Turbo decoder and the sigma-demapper, which exchange progressively refined extrinsic probabilities of the encoded symbols. For the Additive White Gaussian Noise (AWGN) channel, simulation results obtained for very simple Turbo codes show that the proposed system attains low bit error rates at signal-to-noise ratios relatively close to the corresponding Shannon limit. These promising results pave the way for future investigations towards reducing the aforementioned energy gap, e.g. by utilizing more powerful Turbo codes.Item On the design of a novel joint network-channel coding scheme for the multiple access relay channel(2013) Hernaez, Mikel; Crespo, Pedro M.; Del Ser, Javier; IAThis paper proposes a novel joint non-binary network-channel code for the Time-Division Decode-and-Forward Multiple Access Relay Channel (TD-DF-MARC), where the relay linearly combines - over a non-binary finite field - the coded sequences from the source nodes. A method based on an EXIT chart analysis is derived for selecting the best coefficients of the linear combination. Moreover, it is shown that for different setups of the system, different coefficients should be chosen in order to improve the performance. This conclusion contrasts with previous works where a random selection was considered. Monte Carlo simulations show that the proposed scheme outperforms, in terms of its gap to the outage probabilities, the previously published joint network-channel coding approaches. Besides, this gain is achieved by using very short-length codewords, which makes the scheme particularly attractive for low-latency applications.Item On the performance of single LDGM codes for iterative data fusion over the multiple access channel(2010) Del Ser, Javier; Garcia-Frias, Javier; Crespo, Pedro M.; Manjarres, Diana; Olabarrieta, Ignacio; IAOne of the applications of wireless sensor networks currently undergoing active research focuses on the scenario where the information generated by a data source S is simultaneously sensed by N nodes and therefrom transmitted to a common receiver. Based on the received information from such N nodes, such receiver infers the original information from S potentially more accurately than in the case of a single sensor. Often referred to as the CEO (Central Estimating Officer) problem [1], in this scenario we propose the use of single Low Density Generator Matrix (LDGM) codes for the transmission of the information registered by the nodes over the Multiple Access Channel (MAC). The corresponding receiver iterates between a soft demodulator, the set of N LDGM decoders and a soft-information fusion stage. Simulation results for the AWGN MAC channel show that 1) the proposed coding scheme outperforms the suboptimum limit assuming separated Slepian-Wolf distributed coding and capacity-approaching codes; and 2) the end-to-end Bit Error Rate (BER) performance is lower bounded, for increasing N, by the error floor due to the inherent ambiguity of the MAC channel when dealing with correlated sources. This paves the way for future research aimed at applying concatenated coding schemes to this setup.Item Signal shaping scheme based on the BWT for the transmission of non-binary sources with memory over the AWGN channel(2010) Crespo, Pedro M.; Insausti, Xabier; Del Ser, Javier; Gutiérrez-Gutiérrez, Jesús; IAThis paper proposes a low-complexity signal shaping scheme for the transmission of non-binary symbols generated by sources with memory over the AWGN channel. It is based on using the Burrows-Wheeler Transform (BWT) [1] and standard two dimensional (QAM) constellations. The constellation points are driven based on the first order probabilities of the BWT output symbols so that shaping gain is maximized. The proposed system is an extension of the one introduced in [2] for binary sources. To evaluate its performance, the corresponding average energy per transmitted symbol is compared with that obtained when using an ideal source encoder followed by a standard uncoded QAM transmission scheme. In addition, it is shown that the power gain ratio between both systems can be assessed based on the Kullback-Leibler divergence between the first order probability distributions of the BWT output symbols and the Maxwell-Boltzmann probability distribution, obtained under the constraint of achieving an entropy equal to the entropy-rate of the original source.