Recent Progress in Time-Slotted CDMA

Abstract

As a vital issue when designing mobile radio systems, the multiple-access (MA) scheme underlying the air interface has to be defined. There are three basic MA schemes available, namely frequency-division MA (FDMA), time-division MA (TDMA), and code-division MA (CDMA). Each of these schemes has its specific pros and cons, as discussed in detail in [1, 2]. In the first generation (1G) mobile radio systems the transmission was analog, and as a consequence, these systems were restricted to the use of FDMA. The second generation (2G) mobile radio systems introduced in the early 1990s and the forthcoming third generation (3G) systems apply digital transmission technology, which allows the use of TDMA and CDMA as well as combinations of the three basic MA schemes. The idea behind such hybrids consists of retaining the advantages of the contained basic MA schemes and simultaneously circumventing their disadvantages in the combinations. Virtually all modern mobile radio systems apply hybrid MA schemes, with all those schemes comprising an FDMA component, which facilitates frequency planning and enables cluster sizes larger than one with a view to reduce intercell and adjacent channel multiple-access interference (MAI). For instance, the MA scheme of the de facto 2G world standard, GSM (Global System for Mobile Communications), is the hybrid FDMA+TDMA.