A system plan for a 900-MHz portable radio telephone

The system concepts for a high capacity personal radio telephone system are described. Previous systems for mobile radio telephone service have been based on a rigid assignment of frequencies to specific small geographic areas within the total coverage area. This approach has led to conservative geographic frequency reuse constraints and the requirement for accurate location techniques in the system. Through the utilization of the power imbalance that exists in the proposed portable radio telephone system between base and portable unit transmitters these constraints are eliminated. It will be shown how this power imbalance allows the selection of the optimum signal for the portable unit and relaxed requirements on location and reuse of frequencies. The required signal-to-interference ratios must be obtained within a design reliability level over the coverage area. Computer simulation of the frequency reuse plan and the propagation variability over the area indicates the nominal repeat intervals necessary as a function of this reliability level. A reuse plan that obtains the required repeat intervals with a high degree of spectral efficiency, through the combined use of geographic and frequency separation, will be presented. This system called tertiary offset, achieves a significant increase in interference protection by splitting each channel into a group of three channels and utilizing each subgroup in a different pattern of reuse over the area. The improvement due to this plan will be shown.