[Before we talk about HomeRF (SWAP) and WECA (Wi-Fi), we need to understand the original standard that both of these new specifications are based on. The original Institute of Electrical and Electronics Engineers wireless-Ethernet specification, known as IEEE 802.11, designated two ways of communicating between devices and allowed for speeds of upto 2 Mbps. Both communication methods, Direct-Sequence Spread Spectrum (DSSS) and Frequency-Hopping Spread Spectrum (FHSS), use the frequency-shift keying (FSK) technology. FSK is the technology that was originally used to connect computers through power/electricity-lines (commonly referred to as Power-Line Networking). In frequency-shift keying (FSK) data is sent back and forth over the electrical wires connecting the various computer terminals in one's network. FSK uses two frequencies, one for '1s' and the other for '0s', to send digital information between the computers on the network. The frequencies used are in a narrow band just above the level where most line noise occurs.Also, both DSSS and FHSS are based on spread-spectrum radio waves in the 2.4-gigahertz (GHz) range. Spread spectrum simply means that data is sent in small pieces over a number of the discrete frequencies available for use at any time in the specified range. Devices using direct-sequence spread spectrum (DSSS) communicate by splitting each byte of data into several parts and sending them concurrently on different frequencies. DSSS uses a lot of the available bandwidth, about 22 megahertz (MHz). Devices using frequency-hopping spread spectrum (FHSS) send a short burst of data, shift frequencies (hop) and then send another short burst. Since the FHSS devices that are communicating agree on which frequencies to hop to, and use each frequency for a brief period of time (less than 400 milliseconds) before moving on, several independent FHSS networks can exist in the same physical area without interfering with each other. Also, due to FCC (Federal Communications Commission) restrictions, as well as the fact that FHSS devices generally send data on just two to four frequencies simultaneously, they only use 1 MHz or less of the available bandwidth. Because they use any given frequency for such a short time, FHSS devices are less prone to interference than DSSS devices. But DSSS is capable of much greater speed than FHSS since these devices can send a lot more data at the same time. Currently, FHSS-based devices are easier and cheaper to produce, which has led the HomeRF group to adopt FHSS as the method of communication for their products.]
Prof. Ashay Dharwadker