ABSTRACT
Signal insulation is easily attainable by using a scheduling procedure in which signals are allowed to access the medium according to a predefined plan. Signal contention occurs if a signal insulation mechanism is not used. Certainly, access coordination must be exercised in each direction of the communication: from the central point, hereinafter referred to as access point, down to the terminals (users)—downlink or forward link-and from the terminals (users) up to the access point-uplink or reverse link. Similarly, it must be performed in both directions for a two-way communication. Access control in the downlink direction can be implemented with techniques simpler than those used to control access in the uplink direction. The reason is obvious: because, in the first case, the communication is characterized by a point-to-multipoint transmission mechanism, the access point may exercise complete control over the access; in the second case, the communication is
multipoint-to-point, therefore rendering the coordination among independent terminals more complex.
