A New Approach to High-Capacity Digital Mobile Radio

Space diversity (adaptive phased-array antennas) is an effective weapon against the cochannel interference encountered in cellular mobile radio systems. High-order diversity, and hence, strong interference suppression, can be achieved with modest hardware complexity by using time-division retransmission. With this technique, which is especially well-suited to digital modulation methods, the adaptive signal processing required for space diversity can be performed at just one end of the communication link, namely, the base station. At the other end (the mobile unit) only a single-element antenna is needed. Moreover, the use of coherent phase-shift keying in such a system allows simple RF circuity, because the adaptive processing is done at baseband. In the context of cellular mobile radio, the combination of space diversity, time-division retransmission and 120-degree corner illumination of each cell can yield a reliable communication channel even in the presence of intercell interference, Ray leigh fading (both flat and frequency-selective), and shadow fading. The use of these techniques allows approximately 130 two-way channels per cell (at 32 kb/s each) to be accommodated in the 40-MHz bandwidth of the 850-MHz mobile radio band.