The fast frequency hopping spread-spectrum system investigated has signal structure,
which is characterized by a frequency-time matrix of size Q x L. The Q-ary source
symbols are encoded into such binary signal matrices. This matrices are transmitted
using on-off FSK modulation, i.e. sending a short sine wave packet in frequency-time
cells (chips) corresponding to the one valued elements of the matrix. At the receiving
end the elements of the matrix are hard (0-1) detected, resulting in a received binary
matrix. The usual symbol detection rule decides on a symbol (matrix) having maximal
Hamming-correlation with the received matrix. This paper deals with the question of
exploiting side information from the received binary matrix in order to measure the
reliability of the reception. This reliability information can be used to improve
the error rate performance of a concatenated coding scheme, where the symbol-to-matrix
code is the inner code and an appropriate Q-ary block code is used for outer code.
In the analysis partially jammed channels are considered, where a given percent of
symbols from the words of the outer code are supposed to be corrupted by jamming.
Binary asymmetric channel with crossover probabilities p(d) and p(f) is chosen as
the model of the chip-channel under jamming.