Browsing by Author "Hernaez, Mikel"
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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 Erratum: Serially-concatenated LDGM codes for correlated sources over Gaussian broadcast channels (IEEE Communications Letters (2009) 13:10 (788-790))(2010-03) Hernaez, Mikel; Crespo, Pedro; Ser, Javier Del; Garcia-Frias, Javier; IAItem 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 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 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 Serially-concatenated LDGM codes for correlated sources over gaussian broadcast channels(2009) Hernaez, Mikel; Crespo, Pedro; Del Ser, Javier; Garcia-Frias, Javier; IAWe propose a superposition scheme, based on the use of serially-concatenated LDGM codes, for the transmission of spatially correlated sources over Gaussian broadcast channels. The messages intended for each receiver are independently encoded using the same code. In this manner, a strong degree of correlation is kept between the encoded sequences,which are then modulated with different energies and symbolwise added. By properly designing the encoding process, simulation results show that our proposed scheme easily outperforms the suboptimal theoretical limit assuming separation between source and channel coding.Item Turbo joint source-channel coding of non-uniform memoryless sources in the bandwidth-limited regime(2010-04) Ochoa, Idoia; Crespo, Pedro; Ser, Javier Del; Hernaez, Mikel; IAThis letter proposes a novel one-layer coding/ shaping scheme with single-level codes and sigma-mapping for the bandwidth-limited regime. Specifically, we consider nonuniform memoryless sources sent over AWGN channels. At the transmitter, binary data are encoded by a Turbo code composed of two identical RSC (Recursive Systematic Convolutional) encoders. The encoded bits are randomly interleaved and modulated before entering the sigma-mapper. The modulation employed in this system follows the unequal energy allocation scheme first introduced in [1]. The receiver consists of an iterative demapping/decoding algorithm, which incorporates the a priori probabilities of the source symbols. To the authors knowledge, work in this area has only been done for the power-limited regime. In particular, the authors in [2] proposed a scheme based on a Turbo code with RSC encoders and unequal energy allocation. Therefore, it is reasonable to compare the performance with respect to the Shannon limit of our proposed bandwidthlimited regime scheme with this former power-limited regime scheme. Simulation results show that our performance is as good or slightly better than that of the system in [2].