CHAPTER 10 CONCLUSIONS AND FUTURE WORK

This dissertation reported results of an investigation into the performance of antenna arrays that can be mounted on handheld radios. Handheld arrays show great promise for improving the coverage, capacity, and power efficiency of wireless communication systems. As shown in Chapter 8, the signals received by the antennas in these handheld antenna arrays can be combined to provide 7-9 dB diversity gain against fading at the 99% reliability level in non line-of-sight multipath channels. Thus, peer-to-peer systems of handheld transceivers that use antenna arrays can achieve reliability comparable to systems of single-antenna handheld units, with only one-fifth the transmitter power, resulting in lower overall power consumption and increased battery life. Through the use of adaptive beamforming techniques, a handheld radio with an antenna array can receive a desired signal while rejecting interfering signals that occupy the same frequency and time, but have different spatial or polarization characteristics. This can allow more than one user to share the frequency and time channel within a cell, in spatial-division multiple access (SDMA) or a combination of SDMA and code division multiple access (CDMA). Commercial cellular and PCS systems in which the handheld units are equipped with array antennas can use SDMA or SDMA/CDMA to serve more subscribers within the constraints of limited frequency spectrum. In military systems, the interference rejection capability of handheld arrays can provide protection against hostile jammers. The investigations reported in this dissertation have shown that two-element arrays with closely spaced elements can provide substantial diversity gain of 7 to 9 dB in non line-of-sight Ricean fading multipath channels (see Section 8.4). This means that if handheld antenna arrays are used with receive diversity combining, the power of the transmitting base station or peer handheld unit can be reduced by 7-9 dB from the power required to maintain a comparable level of reliability in a system that uses single-antenna handheld radios. This represents a significant savings in power, and a substantial reduction in interference to nearby co-channel units. In addition, as reported in Sections 9.6-9.9, four-element arrays of closely spaced elements used with adaptive beamforming 222 algorithms were shown to provide 25 dB or more of interference rejection in the presence of a single interferer. This interference rejection capability could potentially allow two separate spatial channels to coexist in the same time/frequency channel, doubling system capacity. Chapters 2-5 included background information that provides a context for the development of the …