As various wireless networking technologies have advanced over time, several WLAN technologies have emerged, including: narrowband, spread spectrum, frequency hopping spread spectrum, and direct sequence spread spectrum.
Narrowband
As the name suggests, narrowband technology uses a specific radio frequency (in the range of 50 cps to 64 Kbps) for data transmission.
Spread Spectrum
Originally developed for military use, spread spectrum technology allows for greater bandwidth by continually altering the frequency of the transmitted signal, thus spreading the transmission across multiple frequencies.
Spread spectrum uses more bandwidth than narrowband, but the transmission is more secure, reliable, and easier to detect.
Frequency Hopping Spread Spectrum (FHSS)
Frequency hopping spread spectrum (FHSS) technology synchronizes the changing frequency of both the transmitter and receiver (using a narrowband carrier) to, in effect, produce a single transmission signal. This frequency “hopping” can occur as often as several times a second; it is constantly changing from one
frequency to another, transmitting data for a certain period of time before changing frequency again. Like spread spectrum technology, FHSS technology consumes additional bandwidth, however, this is over the course of multiple carrier frequencies.
Direct Sequence Spread Spectrum (DSSS)
Direct sequence spread spectrum (DSSS) technology breaks down the transmitted stream of data into small pieces across a frequency channel. A redundant bit pattern (known as a chipping code) is generated for each bit transmitted. Generally, the longer the chipping code, the more likely it is that the original transmitted data will be properly received. DSSS technology uses more bandwidth than FHSS, but DSSS is considered more reliable and resists interference. Because of the chipping code, data can still be recovered without retransmission of the signal, even in the case of damaged data bits. U.S. Robotics wireless networking products utilize DSSS technology.