 further. 3.8 SUMMARY A wide range of commercial wireless products are being developed in response to the 1985 FCC Part 15 ruling which eliminates the need for licens- ing in specific bands for operation with spread-spectrum radios with up to 1 W of power. The FCC Part 15 rule has been a catalyst for many innova- tive wireless applications. Qualcomm's application of spread-spectrum radios for a digital cellular phone system also served to stimulate interest in spread-spectrum radios. It introduced a new way of designing high-density multicell digital voice net- works [41]. More research is being devoted to the use of new types of optimal receivers that take advantage of the fact that the "interference" is not ran- dom noise but rather other CDMA signals with characteristics that can be exploited to achieve better performance and higher capacity. Most of this work has been directed to direct-sequence spread-spectrum systems, with most of the complexity in the form of digital signal processing. The key issues associated with commercial applications of spread-spec- trum radios are complexity and cost. As pointed out by Viterbi [2], "Doubtless, CDMA is conceptually more difficult to understand. But diffi- culty of concept should not be confused with difficulty of implementation." Indeed, most of the complexity in direct-sequence spread-spectrum radios in a CDMA network resides in the digital processing, which is imple- mentable in digital chips. Today, all kinds of complex processing are readily available in the form of low-cost digital chips in everyday products. Practical commercial applications for spread-spectrum radios are now becoming better understood. Their primary advantages are their greater robustness compared to narrowband radios and their potentially higher overall capacity in multicell networks. Spread-spectrum radios are well suited to play key roles in a world becoming increasingly wireless. Commercial Applications 3.9 REFERENCES [1] A. J. Viterbi, "When not to spread spectrum-A sequel," IEEE Comm. Ma