Thus, multipath fading doesn’t greatly affect the received signal within a wideband channel, and frequency selective fades occur only in a small fraction of the signal bandwidth. In wideband systems, the transmission bandwidth of a single channel is much larger than the coherence bandwidth of the channel. Narrow band TDMA allows users to use the same channel but allocates a unique time slot to each user on the channel, thus separating a small number of users in time on a single channel. Systems operating with channels substantially narrower than the coherence bandwidth are called as Narrow band systems. Frequency division multiple-access (FDMA)ĭepending on how the available bandwidth is allocated to the users, these techniques can be classified as narrowband and wideband systems.There are several different ways to allow access to the channel. The main aim in the cellular system design is to be able to increase the capacity of the channel, i.e., to handle as many calls as possible in a given bandwidth with a sufficient level of quality of service. In wireless communication systems, it is often desirable to allow the subscriber to send information simultaneously from the mobile station to the base station while receiving information from the base station to the mobile station.Ī cellular system divides any given area into cells where a mobile unit in each cell communicates with a base station. Multiple access schemes are used to allow many mobile users to share simultaneously a finite amount of radio spectrum.
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