Óscar Fresnedo

Low-Complexity Near-Optimal Decoding for Analog Joint Source Channel Coding Using Space-Filling Curves

Analog Joint Source-Channel Coding (JSCC) is a communication strategy that does not follow the separation principle of conventional digital systems but approaches the optimal distortion-cost tradeoff over AWGN channels. Conventional Maximum Likelihood (ML) analog JSCC decoding schemes suffer performance degradation at low Channel Signal to Noise Ratio (CSNR) values, while Minimum Mean Square Error (MMSE) decoding presents high complexity. In this letter we propose an alternative two step decoding approach which achieves the near-optimal performance of MMSE decoding at all CSNR values while maintaining a low complexity comparable to that of ML decoding. An additional advantage of the proposed analog JSCC decoding approach is that it can also be used in Multiple Input Multiple Output (MIMO) fading channels.

Experimental Evaluation of Analog Joint Source-Channel Coding in Indoor Environments

Recently, analog joint source-channel coding has been proposed as a means of achieving near-optimum performance for high data rates with a very low complexity. However, no experimental evaluation showing the practical feasibility of this scheme has been performed to date. In this paper, we describe a software-defined radio implementation of an analog joint source-channel coded wireless transmission system. Experimental evaluation carried out in an indoor environment making use of a wireless testbed show that the performance perfectly matches that originally reported by simulations in additive white Gaussian noise channels for signal-to-noise ratio values below 20 dB.

Analog joint source-channel coding over MIMO channels

Analog joint source-channel coding (JSCC) is a communication strategy that does not follow the separation principle of conventional digital systems but has been shown to approach the optimal distortion-cost tradeoff over additive white Gaussian noise channels. In this work, we investigate the feasibility of analog JSCC over multiple-input multiple-output (MIMO) fading channels. Since, due to complexity constraints, directly recovering the analog source information from the MIMO channel output is not possible, we propose the utilization of low-complexity two-stage receivers that separately perform detection and analog JSCC maximum likelihood decoding. We study analog JSCC MIMO receivers that utilize either linear minimum mean square error or decision feedback MIMO detection. Computer experiments show the ability of the proposed analog JSCC receivers to approach the optimal distortion-cost tradeoff both in the low and high channel signal-to-noise ratio regimes. Performance is analyzed over both synthetically computer-generated Rayleigh fading channels and real indoor wireless measured channels.

Analog Joint Source-Channel Coding for OFDM systems

Recently, analog Joint Source-Channel Coding (JSCC) has been shown to approach the optimal distortion-cost trade-off when transmitting over AWGN channels. In this work we consider analog JSCC over frequency-selective channels using Orthogonal Frequency Division Multiplexing (OFDM) modulation. Due to its high complexity, optimal MMSE analog JSCC decoding is infeasible in OFDM, hence a practical two-stage decoding approach made up of a MMSE estimator followed by a Maximum Likelihood (ML) decoder is proposed. Three different alternatives for system optimization are considered: non-adaptive coding, adaptive coding, and adaptive coding with precoding. We show that the three analog JSCC transmission strategies approach the optimal distortion-cost trade-off although much better performance is obtained with the adaptive coding with precoding method, specially in Multiple Input Multiple Output (MIMO) OFDM systems.

Evaluation of Analog Joint Source-Channel Coding Systems for Multiple Access Channels

We address the evaluation of low-complexity analog Joint Source Channel Coding (JSCC) methods for the transmission of discrete-time analog symbols over Multiple-Input Multiple-Output (MIMO) Multiple Access Channels (MAC). Analog JSCC is employed to encode the source information at each transmitter prior to be directly input to the MAC access scheme. Three channel access methods are considered to ensure the receiver is able to recover the user information: Code Division Multiple Access (CDMA), linear MMSE access codes and opportunistic access. CDMA allows the orthogonal transmission of the user data requiring only Channel State Information (CSI) at reception. On the other hand, linear MMSE access codes exploit CSI knowledge at transmission and exhibit better performance. Finally, opportunistic access also exploits CSI at transmission and allocates all MAC resources to the user with the strongest channel. This latter access scheme exhibits the best performance in terms of sum distortion although it may lead to unfair rate distributions among users.

Analog Joint Source Channel Coding for Gaussian Multiple Access Channels

We investigate the problem of transmiting independent sources over the Gaussian Multiple Access Channel (MAC) using a CDMA-like access scheme that allows users to transmit at different rates. Rather than using standard digital communications systems, we focus on analog joint source-channel coding techniques to encode each users source. We analyze the performance of the proposed scheme and demonstrate its optimality. Simulation results with practical analog joint source-channel codes optimized for point-to-point communications show that the resulting performance is very close to the theoretical limits.

Comparison between Analog Joint Source-Channel Coded and Digital BICM Systems

Recently, the use of analog joint source-channel coding for the transmission of data samples at high rates over AWGN channels has been proposed in the literature. Simulation results have shown that this analog scheme performs close to the theoretical limits for several source distributions and transmission rates. In this paper we study the performance of such a system in comparison with optimized capacity approaching digital Bit Interleaved Coded Modulation (BICM) schemes. We show that in practical situations the analog transmission performs better than the digital scheme with a much lower encoding and decoding complexity when considering Gaussian and Laplacian source distributions.

Analogue joint source-channel coding for multiple input multiple output-orthogonal frequency division multiplexing systems

Analogue joint source-channel coding JSCC has been shown to approach the optimal distortion-cost trade-off when transmitting over additive white Gaussian noise channels. In this work, we consider analogue JSCC over frequency-selective channels using orthogonal frequency division multiplexing OFDM modulation and multiple antennas at transmission and/or reception, that is, using a multiple input multiple outputMIMO-OFDM system. Because of its high complexity, optimal Minimum Mean Square Error MMSE analogue JSCC decoding is infeasible in MIMO-OFDM systems and a practical two-stage decoding approach made up of an MMSE estimator followed by a maximum likelihood decoder is proposed instead. Three different alternatives for system optimisation are considered: non-adaptive coding, adaptive coding and adaptive coding with precoding. We show that the three considered strategies approach the optimal distortion-cost trade-off, but the best performance is obtained with the adaptive coding scheme when precoding is utilised. Copyright

Design of MAC access schemes for analog joint source channel coding

We address the transmission of discrete-time analog samples over a block fading Multiple Access Channel (MAC). At each transmitter, the source information is first encoded using analog Joint Source Channel Coding (JSCC) and then input to a MAC access scheme. We consider three different access schemes: Code Division Multiple Access (CDMA), linear MMSE access codes and opportunistic communication. CDMA allows the orthogonal transmission of the user information requiring only Channel State Information (CSI) at reception. Linear MMSE access strategy exploits the CSI knowledge at transmission to obtain the optimal linear access codes that minimize the MSE at the output of a linear receiver. Finally, opportunistic access allocates all the transmit power to the user with the strongest channel. Although opportunistic is the optimal access strategy when the CSI is available at transmission, it can lead to an unfair allocation of the power and transmission rates of the users.

Analog distributed coding of correlated sources for fading multiple access channels

In this work, we address the analog transmission of correlated information over fading Multiple Access Channels (MACs) using analog Joint Source Channel Coding (JSCC). We consider module-like mappings to encode the source data and the utilization of different orthogonal access schemes. The user information is individually mapped at each transmitter and the receiver exploits the source correlation and the properties of the module mappings to decode the received symbols. We also propose a Maximum-A-Posteriori (MAP) method which achieves similar performance to that of the optimal decoding with significantly lower complexity. The obtained results confirm the potential of using analog JSCC techniques to transmit correlated data over fading MACs.