Capacity of advanced TDMA systems for fixed radio access

We review the potential of advanced TDMA systems for fixed radio access. We highlight the differences between the fixed radio access (FRA) environment and the cellular mobile environment, and show that there are significant advantages in a system designed specifically for FRA over mobile and personal systems adapted for this purpose. The features of an advanced TDMA system for FRA are discussed, including the use of directional antennas, and adaptive rate coding and modulation. In particular we consider the capacity improvement possible by the use of directional antennas. Even if 99.9% availability is required, a system spectral efficiency of 0.7 bits/s/Hz/cell is possible, a factor of two improvement on a system with isotropic antennas. The advantages of adaptivity are shown by considering a simple adaptive protocol which is able to improve on this figure by a factor of four