Idle signal multiple-access (ISMA) scheme for terrestrial packet radio networks

This report proposes a new random-access packet communication system which is appropriately applied to terrestrial radio and called the idle signal multiple-access (ISMA) scheme. The characteristics of the system and its realization are studied. In this field, the CSMA system has received particular attention as a system with large channel capacity which can substitute for the ALOHA system. However, an assumption for this system is that all terminal pairs can observe each other's transmitted signals, thus imposing a severe requirement on a centralized system, which does not take into account direct communication between terminals. To cope with this problem, the BTMA system was proposed, but the ISMA system proposed herein shows its superiority to the BTMA system (a frequency-division method) in such aspects as channel capacity and structural simplicity because the entire frequency band can be used owing to the application of time division to the transmitted control signals. The channel capacity of the ISMA system is generally close to that of the CSMA system and it can be applied to a system operating with dynamic time division of channels for calls in both directions, upward and downward.