Alternatives in cellular system design for serving portables

Abstract

System design alternatives for serving low-power hand-held portable radiotelephones in cellular systems are explored. Two popular designs are considered for systems with little or no frequency reuse. In one design, omnidirectional antennas are used with full-coverage space diversity and receivers with high sensitivity. In the other design, 60-degree sector receive antennas are used with sectorized space diversity. Although both designs are able to compensate for the low radiated power (0.6 watts) of hand-held portables, the more complex sectorized scheme shows somewhat greater variability in service quality because it combines signals from antennas looking into different sectors. With both methods, quality in the portable-to-land direction will generally be better than quality in the land-to-portable direction despite the low radiated power of the portable. The major difficulty with serving portables in systems that have significant frequency reuse is co-channel interference. Cell sectorization, RF power balancing, and dynamic RF power control are needed to control interference and allow portables and vehicular mobiles to operate on the same set of channels. Diversity combining arrangements at the cell site that provide full diversity coverage over the serving sector (i.e., two antennas per sector) offer better protection against interference than do those that combine signals coming from antennas that are looking into different sectors. With the latter arrangement, the full benefit of cell sectorization cannot be realized since the cell-site receiver is susceptible to interference coming into adjacent sector antennas as well as interference coming into the serving sector antenna.