TABLE OF CONTENTS The increasing demand for communication links is making the radio spectrum a scarce resource that has to be managed as efficiently as possible. Different services, such as cellular systems, wireless LAN, radio and television broadcasting, and satellite communications are usually allocated over nonoverlapping frequency bands. However, within each kind of service, there are several users who share the same frequency spectrum. One of the most challenging tasks of modern communications is then the search for the best possible strategies for making many potential users share a communication medium and still guarantee the required quality of service (QoS).
The choice among the available alternatives is not unique and it is typically dictated by the QoS and by the traffic properties. The parameters assessing the QoS depend, on their turn, on the kind of message transmitted through the network. Typically, voice transmission is delay- sensitive, as an excessive delay is considered a very annoying factor. To give some figures of merit, interpacket delays in excess of 100 ms are perceived as rather annoying for the listener. Conversely, the delay is not as important in data transmissions. However, the bit error rate (BER) is a crucial parameter for data communications. As an example, in 3G cellular systems, the maximum tolerable BER for voice links is 10 -3, whereas the target BER for data links is 10 -6.
As a consequence of these different QoS requirements, it is customary to distinguish between two main classes of...
