Study of the Noise Immunity of the Iterative Symbol-by-Symbol Decoding Algorithm for Decoding Signal Constructions Based on OFDM Signals

An algorithm is proposed for iterative symbol-by-symbol decoding of signal constructions based on orthogonal frequency-division multiplexing signals with the base increased using pseudorandom sequences and noise-immunity coding. The algorithm is based on the nonlinear transformation of the spectral components of the input implementation (constraining the spectral component amplitudes or their switching-off) in combination with the symbol-by-symbol decoding of the used class of noise-immune block codes. The results of the simulation of this decoding algorithm for the investigated signal constructions in the presence of the channel of narrow-band noise are reported and the stability of the signal constructions against the distorting effect of the discussed interference class is demonstrated. It is shown that a signal construction based on a low-density code in combination with the iterative symbol-by-symbol decoding algorithm is more efficient in terms of the noise immunity than a convolutional code in combination with the Viterbi decoding algorithm that implements the maximum likelihood rule. It is shown that the operation of switching-off the spectral components relative to their constraining is more efficient in terms of suppressing the distorting effect of the investigated noise complex.