The technologies available for use in a WLAN include infrared, UHF (narrowband) and spread spectrum implementation.

1. Infrared Technology:

i. Infrared is an invisible band of radiation that exists at lower end of visible electromagnetic spectrum.

ii. There are two types of infrared WLAN solutions: Direct beam (or line-of-sight) and diffused beam (uses reflected rays)

iii. Direct beam WLANs offer faster data rates while diffused beam technology achieves lower data rates in 1-2 Mbps range.

iv. The advantage of using this technology is that there are no government regulations on its use and also it is immune to EM and RF interference.

v. The disadvantage is that it is a short range technology (30-50 ft radius under ideal conditions).

vi. Also, it requires line-of-sight. The signal gets affected by solid objects like doors, walls, etc.

vii. The signal gets affected by light in presence of sunlight, fluorescent bulb, etc. this can be avoided by using high signal power and an optimal bandwidth filter.

viii. The signal is also affected by fog, dirt, ice, snow

2. UHF Narrowband technology:

i. The frequency range is 430 to 470 MHZ and rarely segments in 800 MHZ range. The portion 430-450 MHZ is unlicensed while 450-470 MHZ band is licensed.

ii. The term narrow band is used because RF signal is sent in a very narrow band width, typically 12.5 KHz or 25 KHz.

iii. Power levels range from 1 to 2 Watts. The transmission distances of this technology is more than that available from 900 MHZ or 2.4 GHZ spread spectrum systems.

iv. There are two systems: Synthesized and Un-synthesized system uses crystal controlled frequency operation. There can be frequency drift problem in crystal.

v. The synthesized uses single, standard crystal. Multiple frequencies are achieved using dividing the crystal frequency and then multiplying it to desired channel frequency. The factors are programmed in to digital memory in radio.

vi. The advantage of this technology is that it has longest range and its low cost for large sites where throughput required is only low to medium. vii. The disadvantages of this include the need of license, no multivendor inter operability and interference potential.

3. Spread Spectrum Technology:

i. In this technique, the entire allotted bandwidth is shared instead of dividing it into discreet private parts.

ii. The spread spectrum spreads the transmission power over entire usable spectrum. Thus, though bandwidth efficiency decreases; reliability, integrity and security increase.

iii. In commercial applications, spread spectrum techniques currently offer data rates up to 2Mbps.

iv. Two modulation schemes are used to encode spread spectrum signals : frequency hopping spread spectrum (FHSS) and direct sequence spread spectrum (DSSS)

v. FHSS uses a narrowband carrier that changes frequency in a pattern known to both transmitter and receiver. To some other receiver, FHSS appears to be a short-duration impulse noise. Thus, the data security increases.

vi. Similarly, DSSS generates redundant bit pattern for every bit to be transmitted, known as spreading code, known only to transmitter and receiver. To some other receiver, DSSS appears as low-power, wideband noise and is rejected.