Hierarchical TDMA Cellular Network with Distributed Coverage for High Traffic Capacity

Several multi-dimensional trade-offs between coverage area, capacity, quality of service, required bandwidth and cost need to beconsidered for the deployment of cellular networks. Typically, large cells (radius of several kilometers) guarantee continuous coverage in low traffic service areas, while small cells (radius less than 1 kilometer) are deployed to achieve higher capacity. Due to the tremendous success of cellular systems network planning to cater for the traffic capacity requirements of “hot spots” becomes a critical issue. Techniques such as deployment of small cells (micro-cells) and efficient management of radio resources are used to manage high traffic density with limited available spectrum bandwidth. In TDMA cellular systems suchas GSM (900 or 1800 MHz), PCS 1900 or D-AMPS, reduction in cell size means a more frequent spatial reuse of frequencies and hence a higher spectral efficiency. However, the increasing difficulty of ensuring good quality handovers with decreasing cell sizes imposes an asymptotic limit for this method of performance enhancement. This chapter, first describes the “conventional methods” for capacity enhancement of TDMA based cellular systems and then develops the principle of hierarchical networks useful for very high density networks. It corresponds to a network organization where at least two different cell types (e.g. macro-cells and micro-cells) operate in an overlapping coverage and employing special means of interlayer resource management (directed retry). Finally, the idea of “distributed coverage” in the micro-cell layer is introduced. It is demonstrated that the communication quality is improved, of fered traffic is increased and the accuracy of mobile speed estimation is also enhanced, further improving the spectrum efficiency in the service area.