Wireless LANs; why IEEE 802.11 DSSS?

Now the IEEE 802.11 standard for wireless LANs (WLANs) has become a fact, choices for designers are simplified. As the implementation of IEEE 802.11 is a must dictated by the industry, the only choice left is the PHY (physical layer). The standard defines three choices in PHY including DSSS (direct sequence spread spectrum) and FHSS (frequency hopping spread spectrum) RF PHYs and an infrared PHY. To choose the best PHY for the design, one should carefully consider characteristics such as peak bandwidth, aggregate throughput, cost of implementation, immunity to noise, and range. In offering multiple PHY choices, the IEEE 802.11 committee has followed the trend set by standards such as Ethernet that includes PHY choices such as 10BaseT, 10Base5, 100BaseT, and many others. In the successful Ethernet arena, multiple PHYs have allowed designers to match price and performance to applications. WLANs perform an analogous role to wired Ethernet networks, simply using RF or optical data transmission in stead of wiring. Evaluating WLAN technologies requires a look at all of the PHY choices. In most cases, the choice between infrared and RF should be straightforward. The infrared option will likely be used in cost sensitive office applications with short line-of-sight links. RF-based WLANs, however, have wide applicability in a range of office, warehouse, factory, medical and retail applications