The effects of slotting, burstiness, and jamming in frequency-hopped random access systems

A model is defined for a frequency-hopped spread-spectrum system, and performance is derived for the aspects of system variables by both mathematical analysis and simulation. Interference is characterized at both the symbol level and the packet levels. Values for the jamming parameters a, ρ_t and ρ_f that cause maximum degradation in the users´ throughput are determined. A number of specific examples are presented to illustrate the results. It is shown that, unlike the case of unspread systems, performance does not depend heavily on the burstiness of the user traffic or on whether slotted operation is used. As the number of frequency bins q increases, the difference in performance between slotted and unslotted operation becomes insignificant. For large q, only slightly less throughput is obtainable when the traffic is bursty as compared with continuous transmission by the users; this fact justifies the consideration of random-access techniques in a spread-spectrum environment. The effect of the jamming pulse length a is closely related to γ, the amount of the interference that a symbol can tolerate. If the jamming pulse length is large, the effect of the jammer is similar to additional user traffic of an equal load