From the discussion above it is obvious that FDMA is a good candidate for applications like cordless telephone. In particular the simple signal processing make it a good choice for inexpensive implementation in the benign cordless environment. The possibility to concentrate signal processing functions in the base station strengthens this aspect.
In the cellular application, on the other hand, FDMA is inappropriate because of the lack of ``built-in'' diversity, and the potential for severe intra-cell interference between base stations. A further complication arises from the difficulty of performing hand-overs if base-stations are not tightly synchronized.
For PCS the decision is not as obvious. Depending on whether the envisioned PCS application resembles more a cordless PBX than a cellular system FDMA may be an appropriate choice. We will see below that it is probably better to opt for a combined TDMA/FDMA or a CDMA based system to avoid the pitfalls of pure FDMA systems and still achieve moderate equipment complexities.
Finally, there is the problem of channel assignment. Clearly, it is not reasonable to assign a unique frequency to each user as there are not sufficiently many frequencies and the spectral resource would be unused whenever the user is idle. Instead, methods which allocate channels on demand can make much more efficient use of the spectrum. Such methods will be discussed further during the description of TDMA systems.
