The radio technology on which WLANs are based is known as Spread Spectrum modulation and has its origins in the military. Among the advantages of Spread Spectrum technologies, one can mention the inherent transmission security, resistance to interference from other radio sources, redundancy, resistance to multipath and fading effects, etc. As a result, Spread Spectrum systems can coexist with other radio systems, without being disturbed by their presence and without disturbing their activity. The immediate effect of this elegant behavior is that Spread Spectrum systems may be operated without the need for license, and that made the Spread Spectrum modulation to be the chosen technology for license-free WLAN operation.


There are two types of Spread Spectrum modulation techniques:
Frequency Hopping (FHSS) and Direct Sequence (DSSS).

DSSS has the advantage of providing higher capacities than FHSS, but it is influenced by many environment factors (mainly reflections). The best way to minimize such influences is to use the technology in either (i) point to multipoint, short distances applications or (ii) long distance applications, but point to point topologies. In both cases the systems can take advantage of the high capacity offered by DSSS technology, without paying the price of being disturbed by the effect of reflections. As so, typical DSSS applications include indoor wireless LAN in offices (i), building to building links (ii), Point of Presence (PoP) to Base Station links (in cellular deployment systems) (ii), etc.

FHSS is a very robust technology, with little influence from noises, reflections, other radio stations or other environment factors. In addition, the number of simultaneously active systems in the same geographic area (collocated systems) is significantly higher than the equivalent number for DSSS systems. All these features make the FHSS technology the one to be selected for installations designed to cover big areas where a big number of collocated systems is required and where the use of directional antennas in order to minimize environment factors influence is impossible.