Traffic Capacity Versus Coverage
Cellular systems use one or more of four different techniques of access (TDMA, FDMA, CDMA, SDMA). See Cellular concepts. Let a case of Code Division Multiple Access be considered for the relationship between traffic capacity and coverage (area covered by cells). CDMA cellular systems can allow an increase in traffic capacity at the expense of the quality of service.
In TDMA/FDMA cellular radio systems, Fixed Channel Allocation (FCA) is used to allocate channels to customers. In FCA the number of channels in the cell remains constant irrespective of the number of customers in that cell. This results in traffic congestion and some calls being lost when traffic gets heavy.
A better way of channel allocation in cellular systems is Dynamic Channel Allocation (DCA) which is supported by the GSM, DCS and other systems. DCA is a better way not only for handling bursty cell traffic but also in efficiently utilising the cellular radio resources. DCA allows the number of channels in a cell to vary with the traffic load, hence increasing channel capacity with little costs. Since a cell is allocated a group of frequency carries (e.g. f1-f7) for each user, this range of frequencies is the bandwidth of that cell, BW. If that cell covers an area Ac, and each user has bandwidth B then the number of channels will be BW/B. The density of channels will be . This formula shows that as the coverage area Ac is increased, the channel density decreases.
Read more about this topic: Cellular Traffic
Famous quotes containing the words traffic and/or capacity:
“If you don’t have a policeman to stop traffic and let you walk across the street like you are somebody, how are you going to know you are somebody?”
—John C. White (b. 1924)
“Mankind’s common instinct for reality ... has always held the world to be essentially a theatre for heroism. In heroism, we feel, life’s supreme mystery is hidden. We tolerate no one who has no capacity whatever for it in any direction. On the other hand, no matter what a man’s frailties otherwise may be, if he be willing to risk death, and still more if he suffer it heroically, in the service he has chosen, the fact consecrates him forever.”
—William James (1842–1910)