A performance comparison of control policies for slotted Aloha frequency-hopped multiple access systems

A performance analysis of slotted Aloha with frequency-hopped code-division multiple access is presented, with emphasis on the effects of the retransmission control policy. Static and dynamic control policies are considered. Performance using static control is shown to be highly sensitive to the relationship between the packet generation process and the chosen retransmission probability. Dynamic control, on the other hand, is very robust in that it provides high throughput over wide ranges of arrival rates. Delays are generally quite small when system parameters are properly set. A simple rule for computing the retransmission probability as a function of the backlog is provided and gives a result very close to the analytically derived optimal value. Numerical performance evaluation is given for the case of a network of 250 users and a spread factor (number of hopping positions) of 100, where the other system parameters are varied.<>