 large multipath delays (delays greater than a chip time), direct- sequence spread-spectrum radios can be more robust since they can better overcome the effects of multipath. Commercial slow frequency-hopping Commercial Applications radios behave as narrowband radios. Thus, for higher data rates, the impact of multipath tends to degrade frequency-hopping radios more than direct- sequence radios. The issue of mutual interference resulting from many spread-spectrum radios independently operating in a given area is very interesting. In a sys- tem in which many such spread-spectrum radios co-exist in the same area, it is difficult to compare the performances of these two types of radios, which depend largely on the application. With frequency-hopping radio, for each hop, radio performance is "good" or "bad," depending on whether any other similar radio signal hops into the same band at the same time. The probability of this occurring depends on the number of hopping radios in the area and the availability of non-over- lapping hopping bands. Multipath conditions are likely to be different in each hopped frequency, even without interference, SO performance during each hop can vary greatly, owing to different multipath conditions. Thus, frequency-hopping radios result in a channel that is time-varying, with changes in channel conditions occurring at each hop transition, somewhat like a fading channel in which fades occur at discrete times. As in any fading channel, coding with inter- leaving can dramatically improve performance (see Part 1, Chapter 3, Sections 3.7 and 3.8). Unfortunately, it is impractical to interleave data when the hop rate is slow, as is true for most commercial frequency-hopping sys- tems. Thus, the major difference between the two types of spread-spectrum radio is that frequency-hopping radios experience occasional strong bursty errors, while direct-sequence radios experience continuous but lower-level random errors. In direct-sequence radios, errors can be considered to be scat- tered randomly ove