Satellite communications modeled by a feedforward random multiple-access system are considered. The transmission times of the users are governed by protocol signals. The authors consider the model of a slot-synchronized collision channel without feedback, proposed by J.L. Massey and P. Mathys (1985), augmented by interleavers that are essential for enabling the use of practical short codes. They assess the throughput of the channel on the basis of a short-coding error parameter. The set of parameters of all users characterizes the rate region achievable by employing short block codes with nonideal interleaving. The short-coding error parameter corresponds to a bound on the probability of error which is tighter than the bound expressed with the aid of the conventional cut-off rate. The analysis takes into account practical communication aspects, such as the effect of interleaving span and noise in noninterfered slots.>

The interleaving span of coded frequency-hopped (FH) systems is often constrained to be smaller than the decoder memory length, i.e. nonideal interleaving is performed. An upper bound on the performance of a Viterbi decoder of a convolutional code with nonideal interleaving is presented. A soft decision diversity combining technique is introduced, and the performance of combined convolutional and diversity coding subject to worst-case partial band noise jamming is investigated. Optimization of the FH system performance subject to constraints of allowed delay and synthesizer settling time provides the best combination of interleaving span and hopping rate. The FH system considered employs M-ary frequency-shift key (MFSK) modulation and noncoherent demodulation with 2-b soft decision based on Viterbi's ratio-threshold technique.>

This paper deals with the optimization of coherent generalized tamed frequency modulation (GTFM). The optimization is carried out over certain parameters of the modulation scheme to give the best BER (bit error rate) performance, subject to a bandwidth constraint. The optimization is done by an algorithm which uses the upper bound on the squared Euclidean distance as a metric of the BER performance and the power spectra at a certain frequency as a metric of the bandwidth. It is concluded that when the modulation index is not restricted to 0.5, a theoretic improvement of 1.9 dB over the BER performance of GTFM is achievable, with equal bandwidths as a basis of comparison.