Abstract
A communications system for mobile wireless networks based on concatenation of code NRZ, irregular LDPC code and equalizer of two bits is studied. The transmitter is composed of a NRZ line coder and irregular LDPC coder with a low error threshold. The receiver is composed of the sum-product decoder and low complexity equalizer with a maximum probability estimation sequence algorithm. The communication system is simulated on an AWGN channel and fast fading with Rayleigh distribution, for different word sizes. A mobile speed of 150 Km/h is considered. System performance in terms of the bit error probability (BER) and signal-to-noise (SNR) is calculated for NRZ-LDPC codes, achieving to BER of 10-5 a SNR of 9 dB without equalizer and a SNR of 4.5 dB with equalizer. The results of the performance study indicate that system with NRZ-LDPC codes and equalizer achieves a considerable reduction of the SNR.
Highlights
A communications system for mobile wireless networks based on concatenation of code NRZ, irregular LDPC code and equalizer of two bits is studied
The transmitter is composed of a NRZ line coder and irregular LDPC coder with a low error threshold
The receiver is composed of the sum-product decoder and low complexity equalizer with a maximum probability estimation sequence algorithm
Summary
Un ciclo en un grafo de Tanner es una secuencia de nodos formando una ruta que comienza y termina en el mismo nodo incluyendo a cada uno de los nodos una única vez. Entonces la construcción del código se determina por medio de las funciones generatrices de distribución de grado λ(x) y ρ(x) para el nodo de bits y de chequeo, respectivamente, esto es: El código de chequeo de paridad de baja densidad irregular se construye mediante el método dado en [11], el que permite obtener un código LDPC irregular con bajo umbral de error y una matriz H con ciclos de la mayor longitud posible. A continuación se describe el algoritmo que se utiliza en este trabajo: Algoritmo MLSE: En la minimización del MLSE los coeficientes óptimos del ecualizador se determinan de la solución del conjunto de ecuaciones lineales, dados en forma matricial como: Γc = ξ (8). La ecuación recursiva para descargar los coeficientes del ecualizador una vez cada N iteraciones es: c(k+1)N = ckN − ΔgkN (16).
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