The main objective of channel-assignment techniques is to stabilize the fluctuations in the probability of call blockage over the entire coverage area of a cellular network over a period of time. A classical approach to frequency-assignment problems does not enable this task to be performed in an efficient way when applied to the frequency planning of cellular networks since it does not consider the cumulative effect of co-channel interferers. The criteria of frequency planning in a cellular system includes how to allocate (or assign) channels to each cell, and then how to re-assign channels with varying traffic load, while maintaining the desired signal quality.
Channel assignment refers to the allocation of specific (fixed) channels to cell-sites on long-term basis, and the allocation of specific channels to mobile united on a short- term basis during a call. One way is fixed(static) channel assignment in which the set of all channels is partitioned intoʽnʼ groups of frequency channels (fixed) and each cell is assigned to one of these ʽnʼ groups of frequency channels .This arrangement is acceptable as far as…show more content… An underlaid small cell is sometimes commissioned at the same cell-site over a large cell. This permits the two frequency groups to reuse the channels in two different cell-reuse patterns of the same cluster size. The channels assigned in the small cells have more protection against cochannel interference. A set of frequencies used in an overlay area (coverage area of large cell) will differ from a set of frequencies used in an underlay area (coverage area of small cell) in order to avoid cochannel and adjacent-channel interference. The hand-offs are implemented between the large cells and small cells. An example of overlapped cells-based cellular system is shown in Fig
