Rate compatible modulation for non-orthogonal multiple access

We propose a new Non-Orthogonal Multiple Access (NOMA) coding scheme based on the use of a Rate Compatible Modulation (RCM) encoder for each user. By properly designing the encoders and taking advantage of the additive nature of the Multiple Access Channel (MAC), the joint decoder from the inputs of all the users can be represented by a bipartite graph corresponding to a standard point-topoint RCM structure with certain constraints. Decoding is performed over this bipartite graph utilizing the sum-product algorithm. The proposed scheme allows the simultaneous transmission of a large number of uncorrelated users at high rates, while the decoding complexity is the same as that of standard point-to-point RCM schemes. When Rayleigh fast fading channels are considered, the BER vs SNR performance improves as the number of simultaneous users increases, as a result of the averaging effect

Combining the Burrows-Wheeler Transform and RCM-LDGM Codes for the Transmission of Sources with Memory at High Spectral Efficiencies

In this paper, we look at the problem of implementing high-throughput Joint SourceChannel (JSC) coding schemes for the transmission of binary sources with memory over AWGN channels. The sources are modeled either by a Markov chain (MC) or a hidden Markov model (HMM). We propose a coding scheme based on the Burrows-Wheeler Transform (BWT) and the parallel concatenation of Rate-Compatible Modulation and Low-Density Generator Matrix (RCM-LDGM) codes. The proposed scheme uses the BWT to convert the original source with memory into a set of independent non-uniform Discrete Memoryless (DMS) binary sources, which are then separately encoded, with optimal rates, using RCM-LDGM codes

Rate compatible joint source-channel coding for point-to-point and multiple access channels.

In this Thesis we consider high-throughput rate compatible Joint Source-Channel Coding (JSCC) schemes based on Rate Compatible Modulation (RCM) codes. These codes achieve JSCC capabilities by embedding source compression into modulation through the generation of multi-level symbols from weighted linear combinations of the input bits. The smooth rate adaptation is achieved seamlessly by varying the number of generated symbols. These two properties make them advantageous over conventional Adaptive Coded Modulation (ACM) techniques, which usually rely on unrealistic instant and accurate channel estimations, and a limited set of coding and modulation combinations to choose from. The main drawback of RCM codes is that they experience performance degradation due to the presence of error floors at high Signal-to-Noise Ratios (SNRs). These error floors can be substantially improved by substituting a few RCM symbols by LDGM coded bits, forming an hybrid coding scheme in which the LDGM symbols correct residual errors produced by the RCM. This work investigates new applications and design techniques of these family of codes for point-to-point and multi-user communications. For the point-to-point case, we propose an EXIT chart analysis and a bit error rate prediction procedure suitable for implementing RCM-LDGM codes. The developed EXIT charts speed up the design method of good codes, which otherwise requires the use of time-consuming simulations. We continue by considering the problem of implementing high-throughput JSCC schemes for the transmission of binary sources with memory over AWGN channels, for which we propose a coding scheme that makes use of the Burrows-Wheeler Transform (BWT) and the rate compatible RCM-LDGM codes. Finally, for the first time in the literature, we propose the use of RCM-LDGM codes for additive impulsive noise channels. For multi-user communications we begin by considering that the information sources are uncorrelated and propose a new coding scheme based on the use of an irregular RCM encoder for each user. By properly designing the encoders and taking advantage of the additive nature of the MAC, the proposed scheme allows the simultaneous transmission of a large number of uncorrelated users at high rates, while the decoding complexity is the same as that of standard point-to-point RCM schemes. In the last part of the Thesis, we tackle the multi-user communication scenario in which the transmitted information sources are spatially correlated and also extend the use of LDGM codes in parallel with the proposed RCM systems in the MAC.Esta Tesis estudia esquemas de comunicación con tasas de transmisión altas y adaptables basados en códigos RCM y cuya codificación de fuente y canal es conjunta. La compresión de fuente se incorpora en la modulación mediante la generación de símbolos multi-nivel a partir de combinaciones lineales ponderadas de los bits de entrada, mientras que la adaptación de la tasa de transmisión se logra variando el número de símbolos generados. Estas dos propiedades son ventajosas frente las técnicas convencionales de modulación codificada adaptativa, que generalmente se basan en estimaciones precisas e instantáneas del canal, lo cual, es poco realista. Además, estas técnicas tienen un conjunto limitado de combinaciones de codificación y modulación para elegir. El principal inconveniente de los códigos RCM es que experimentan una degradación del rendimiento debido a la presencia de altos suelos de error. Una solución consiste en sustituir algunos símbolos RCM por LDGM, formando un esquema de codificación híbrido en el que los símbolos LDGM corrigen errores residuales producidos por los RCM. En concreto, en esta Tesis buscamos nuevas técnicas de diseño y aplicaciones para esta familia de códigos tanto en comunicaciones punto a punto como en comunicaciones multi-usuario. Para el caso punto a punto, proponemos un análisis llamado EXIT chart y un procedimiento de predicción de la tasa de error. Las técnicas desarrolladas aceleran el diseño de buenos códigos, ahorrando simulaciones que requieren de mucho tiempo. A continuación, consideramos la transmisión de fuentes binarias con memoria sobre canales AWGN, para lo cual proponemos un esquema de codificación que hace uso de la Transformada de Burrows-Wheeler y los códigos RCM-LDGM. Finalmente, por primera vez en la literatura, proponemos el uso de estos códigos para canales de ruido impulsivo aditivo. Para las comunicaciones multi-usuario empezamos considerando que las fuentes de información a transmitir por los usuarios son independientes y proponemos un nuevo esquema de codificación basado en el uso de un codificador RCM irregular para cada usuario. Al diseñar apropiadamente los codificadores individuales y aprovechando la naturaleza aditiva del canal, el esquema propuesto permite la transmisión simultánea de un gran número de usuarios a altas tasas de transmisión manteniendo la complejidad de decodificación tradicional. En la última parte de la Tesis abordamos el escenario de comunicación multi-usuario en el que las fuentes de información transmitidas están correlacionadas espacialmente y también ampliamos el uso de códigos LDGM en paralelo con los sistemas RCM propuestos para el MAC

Design of High Rate RCM-LDGM Codes

This master thesis is studies the design of High Rate RCM-LDGM codes and it is divided in two parts: In the rst part, it proposes an EXIT chart analysis and a Bit Error Rate (BER) prediction procedure suitable for implementing high rate codes based on the parallel concatenation of a Rate Compatible Modulation (RCM) code with a Low Density Generator Matrix (LDGM) code. The decoder of a parallel RCMLDGM code is based on the iterative Sum-Product algorithm which exchange information between variable nodes (VN) and the corresponding two types of check nodes: RCM-CN and LDGM-CN. To obtain good codes that achieve near Shannon limit performance one is required to obtain BER versus SNR behaviors for di erent families of possible code design parameters. For large input block lengths, this could take large amount of simulation time. To overcome this design drawback, the proposed EXIT-BER chart procedure predicts in a much faster way this BER versus SNR behavior, and consequently speeds up their design procedure. In the second part, it studies two di erent strategies for transmitting sources with memory. The rst strategy consists on exploiting the source statistics in the decoding process by attaching the factor graph of the source to the RCMLDGM one and running the Sum-Product Algorithm to the entire factor graph. On the other hand, the second strategy uses the Burrows-Wheeler Transform to convert the source with memory into several independent Discrete Memoryless (DMS) binary Sources and encodes them separately

Design of High Rate RCM-LDGM Codes

This master thesis is studies the design of High Rate RCM-LDGM codes and it is divided in two parts: In the rst part, it proposes an EXIT chart analysis and a Bit Error Rate (BER) prediction procedure suitable for implementing high rate codes based on the parallel concatenation of a Rate Compatible Modulation (RCM) code with a Low Density Generator Matrix (LDGM) code. The decoder of a parallel RCMLDGM code is based on the iterative Sum-Product algorithm which exchange information between variable nodes (VN) and the corresponding two types of check nodes: RCM-CN and LDGM-CN. To obtain good codes that achieve near Shannon limit performance one is required to obtain BER versus SNR behaviors for di erent families of possible code design parameters. For large input block lengths, this could take large amount of simulation time. To overcome this design drawback, the proposed EXIT-BER chart procedure predicts in a much faster way this BER versus SNR behavior, and consequently speeds up their design procedure. In the second part, it studies two di erent strategies for transmitting sources with memory. The rst strategy consists on exploiting the source statistics in the decoding process by attaching the factor graph of the source to the RCMLDGM one and running the Sum-Product Algorithm to the entire factor graph. On the other hand, the second strategy uses the Burrows-Wheeler Transform to convert the source with memory into several independent Discrete Memoryless (DMS) binary Sources and encodes them separately

Asymptotic BER EXIT chart analysis for high rate codes based on the parallel concatenation of analog RCM and digital LDGM codes

This paper proposes an extrinsic information transfer (EXIT) chart analysis and an asymptotic bit error rate (BER) prediction method to speed up the design of high rate RCM-LDGM hybrid codes over AWGN and fast Rayleigh channels. These codes are based on a parallel concatenation of a rate compatible modulation (RCM) code with a lowdensity generator matrix (LDGM) code. The decoder uses the iterative sum-product algorithm to exchange information between the variable nodes (VNs) and the two types of constituent check nodes: RCM-CN and LDGM-CN. The novelty of the proposed EXIT chart procedure lies on the fact that it mixes together the analog RCM check nodes with the digital LDGM check nodes, something not possible in previous multi-edge EXIT charts proposed in the literature

Rate compatible modulation for non-orthogonal multiple access

We propose a new Non-Orthogonal Multiple Access (NOMA) coding scheme based on the use of a Rate Compatible Modulation (RCM) encoder for each user. By properly designing the encoders and taking advantage of the additive nature of the Multiple Access Channel (MAC), the joint decoder from the inputs of all the users can be represented by a bipartite graph corresponding to a standard point-topoint RCM structure with certain constraints. Decoding is performed over this bipartite graph utilizing the sum-product algorithm. The proposed scheme allows the simultaneous transmission of a large number of uncorrelated users at high rates, while the decoding complexity is the same as that of standard point-to-point RCM schemes. When Rayleigh fast fading channels are considered, the BER vs SNR performance improves as the number of simultaneous users increases, as a result of the averaging effect

Asymptotic BER EXIT chart analysis for high rate codes based on the parallel concatenation of analog RCM and digital LDGM codes

This paper proposes an extrinsic information transfer (EXIT) chart analysis and an asymptotic bit error rate (BER) prediction method to speed up the design of high rate RCM-LDGM hybrid codes over AWGN and fast Rayleigh channels. These codes are based on a parallel concatenation of a rate compatible modulation (RCM) code with a lowdensity generator matrix (LDGM) code. The decoder uses the iterative sum-product algorithm to exchange information between the variable nodes (VNs) and the two types of constituent check nodes: RCM-CN and LDGM-CN. The novelty of the proposed EXIT chart procedure lies on the fact that it mixes together the analog RCM check nodes with the digital LDGM check nodes, something not possible in previous multi-edge EXIT charts proposed in the literature

Rate compatible joint source-channel coding for point-to-point and multiple access channels.

In this Thesis we consider high-throughput rate compatible Joint Source-Channel Coding (JSCC) schemes based on Rate Compatible Modulation (RCM) codes. These codes achieve JSCC capabilities by embedding source compression into modulation through the generation of multi-level symbols from weighted linear combinations of the input bits. The smooth rate adaptation is achieved seamlessly by varying the number of generated symbols. These two properties make them advantageous over conventional Adaptive Coded Modulation (ACM) techniques, which usually rely on unrealistic instant and accurate channel estimations, and a limited set of coding and modulation combinations to choose from. The main drawback of RCM codes is that they experience performance degradation due to the presence of error floors at high Signal-to-Noise Ratios (SNRs). These error floors can be substantially improved by substituting a few RCM symbols by LDGM coded bits, forming an hybrid coding scheme in which the LDGM symbols correct residual errors produced by the RCM. This work investigates new applications and design techniques of these family of codes for point-to-point and multi-user communications. For the point-to-point case, we propose an EXIT chart analysis and a bit error rate prediction procedure suitable for implementing RCM-LDGM codes. The developed EXIT charts speed up the design method of good codes, which otherwise requires the use of time-consuming simulations. We continue by considering the problem of implementing high-throughput JSCC schemes for the transmission of binary sources with memory over AWGN channels, for which we propose a coding scheme that makes use of the Burrows-Wheeler Transform (BWT) and the rate compatible RCM-LDGM codes. Finally, for the first time in the literature, we propose the use of RCM-LDGM codes for additive impulsive noise channels. For multi-user communications we begin by considering that the information sources are uncorrelated and propose a new coding scheme based on the use of an irregular RCM encoder for each user. By properly designing the encoders and taking advantage of the additive nature of the MAC, the proposed scheme allows the simultaneous transmission of a large number of uncorrelated users at high rates, while the decoding complexity is the same as that of standard point-to-point RCM schemes. In the last part of the Thesis, we tackle the multi-user communication scenario in which the transmitted information sources are spatially correlated and also extend the use of LDGM codes in parallel with the proposed RCM systems in the MAC.Esta Tesis estudia esquemas de comunicación con tasas de transmisión altas y adaptables basados en códigos RCM y cuya codificación de fuente y canal es conjunta. La compresión de fuente se incorpora en la modulación mediante la generación de símbolos multi-nivel a partir de combinaciones lineales ponderadas de los bits de entrada, mientras que la adaptación de la tasa de transmisión se logra variando el número de símbolos generados. Estas dos propiedades son ventajosas frente las técnicas convencionales de modulación codificada adaptativa, que generalmente se basan en estimaciones precisas e instantáneas del canal, lo cual, es poco realista. Además, estas técnicas tienen un conjunto limitado de combinaciones de codificación y modulación para elegir. El principal inconveniente de los códigos RCM es que experimentan una degradación del rendimiento debido a la presencia de altos suelos de error. Una solución consiste en sustituir algunos símbolos RCM por LDGM, formando un esquema de codificación híbrido en el que los símbolos LDGM corrigen errores residuales producidos por los RCM. En concreto, en esta Tesis buscamos nuevas técnicas de diseño y aplicaciones para esta familia de códigos tanto en comunicaciones punto a punto como en comunicaciones multi-usuario. Para el caso punto a punto, proponemos un análisis llamado EXIT chart y un procedimiento de predicción de la tasa de error. Las técnicas desarrolladas aceleran el diseño de buenos códigos, ahorrando simulaciones que requieren de mucho tiempo. A continuación, consideramos la transmisión de fuentes binarias con memoria sobre canales AWGN, para lo cual proponemos un esquema de codificación que hace uso de la Transformada de Burrows-Wheeler y los códigos RCM-LDGM. Finalmente, por primera vez en la literatura, proponemos el uso de estos códigos para canales de ruido impulsivo aditivo. Para las comunicaciones multi-usuario empezamos considerando que las fuentes de información a transmitir por los usuarios son independientes y proponemos un nuevo esquema de codificación basado en el uso de un codificador RCM irregular para cada usuario. Al diseñar apropiadamente los codificadores individuales y aprovechando la naturaleza aditiva del canal, el esquema propuesto permite la transmisión simultánea de un gran número de usuarios a altas tasas de transmisión manteniendo la complejidad de decodificación tradicional. En la última parte de la Tesis abordamos el escenario de comunicación multi-usuario en el que las fuentes de información transmitidas están correlacionadas espacialmente y también ampliamos el uso de códigos LDGM en paralelo con los sistemas RCM propuestos para el MAC