High-user-density digital cellular mobile radio systems

Digital cellular mobile radio systems are described having partially overlapping cells that are based on road configurations, and in which the energy is radiated along the road from approximately street lamp elevations. One proposed system uses propagation frequencies in the vicinity of 900 MHz, employs adaptive differential pulse code modulation at 32 kbit/s and a minimum shift keying modem enabling a channel spacing of 25 kHz. One example of system performance shows that, for clusters of ten cells along a six-lane highway, the signal/interference ratio is 20 dB, the probability of error is 10−3, and the channel SNR is 10.8 dB. Given an allocated mobile radio bandwidth of 20 MHz, the system can support 80 users per cell. If the vehicles are travelling at 88 km/h (55 miles/h) and 10% of the drivers make a telephone call, the cell length is 4.8 km (3 miles), and the cochannel distance is 48 km (30 miles). In our deliberations we made comparisons with conventional analogue FM systems, and showed that they have approximately half the user density capacity of the new system. A digital microcellular mobile radio systems employing 60 GHz is also considered. The bit rate per segment of road was found to be vast, e. g. 100 Mbit/s per 100 m of road. This system is capable of providing portable communications to large numbers of pedestrians and drivers in congested city streets. Because of the configuration of the proposed cell structure, shadow fading is conjectured to have very little impact on system performance.