Smart antennas-the practical realities

Cellular communications systems performance can be improved through the application of novel antenna techniques. Such improvements may be necessary to enhance coverage in buildings and for portable hand-held units, to extend cell-site range and coverage at reduced infrastructure cost, and to increase the capacity of existing cell sites. Often, these benefits can be made available at a fraction of the cost of new cell sites. Improvements in range and coverage can be achieved with intelligent multibeam antenna systems that provide greater antenna gain and discrimination against interference. Range improvements for intelligent antenna systems, when compared to the performance of conventional sector antennas, have been demonstrated to exceed 40%. Increased capacity can be achieved when the carrier-to-interference ratio (CIR) level is improved through digital signal processing techniques that place desired signals in or near the narrower main beam of the multibeam antenna and place interferers into the pattern sidelobes and/or nulls. Hazeltine and other vendors have demonstrated CIR improvements of at least 6 dB in field trials. Analysis, as well as computer simulation, using terrain-based propagation models and a real cellular system lay-down, predicts that a 6-dB improvement in carrier-to-interference can nearly double capacity while maintaining the same quality of service. However, this superior performance requires the system designer to develop solutions for practical problems in propagation and operation. Key areas to be considered include diversity, beam tracking, and installation.