High capacity cellular mobile radio systems

The design of high capacity mobile radio systems is addressed. Key to high capacity is the deployment of microcells and this necessitated an in-depth radio propagation measurement programme to establish the bit rates that could be supported in microcellular environments. Armed with this knowledge, the network capacity of time division multiple access (TDMA) and code division multiple access (CDMA) in microcellular networks can be established.In the radio propagation experiments, a basic modem was used to transmit data at rates of 2, 4 or 8 Mb/s and at carrier frequencies of 1.8, 2.4 or 3.5 GHz. Consistently high bit error ratios (BERs) were recorded for all but line-of-sight (LOS) indoor environments, even when the received signal levels were high. A wideband channel sounder was therefore constructed and measurements made to quantify the extent of the channel dispersion and the likely requirements of the BER mitigating procedures that would be needed.An analytical model was then introduced to show that directed retry should be used to significantly improve microcell utilisation in TDMA systems. It was found that microcells should be sited on street corners to maximise capacity, and between seven and nine RF carriers were required to plan contiguous microcell networks. An automatic frequency planning (AFP) algorithm based on a modified simulated annealing method was developed that can plan microcell networks of one hundred cells in less than one minute, so that channel allocations can be changed in response to changes in the traffic distribution across the network.Analytical models for calculating the uplink and downlink capacities of a multiple rate DS-CDMA system are presented. These models include the implementation of voice activity detection and the effect of lognormally distributed errors in the uplink power control. For an exponential path loss exponent of 3.6 and lognormal shadow fading with a standard deviation of 8 dB, a power control error of 1 dB reduces the uplink capacity of a 5 MHz single cell system by one-third.