ISA2: a “two-phase” MAC protocol for multimedia wireless networks

A new MAC-level protocol is introduced and investigated, operating in a cellular environment, where a base station co-ordinates mobile users within each cell. The channel multiplexing structure is based on time division (TDM), and the slots in each frame are dynamically assigned to the users and their service classes by the cell base station. Decisions are taken on the basis of binary channel feedback information (collision/no collision), by assuming independence in the presence of packets at the mobile stations (whence the name ISA, independent stations algorithm), and aim at maximizing the one-step throughput in the current frame. The frame is divided into two periods: the first (short) one contains a number of mini-slots, equal to the number of “real” slots (i.e., those capable of containing a fixed size packet) of the second part. At the beginning of the frame, the access rights are computed and broadcast to the users; the enabled stations that have a packet to transmit respond, by sending a short burst that contains their ID in a mini-slot. This most recent feedback is used at the base station to update the parameters of the decision algorithm, which is then re-applied to yield the final access rights for the second part of the frame. The performance of the scheme is analyzed by simulation in the presence of mixed voice and data traffic, and compared with those of RRA-ISA (a reservation random access protocol using the same algorithm in a single-phase fashion) and PRMA