The of different wireless technologies that WLANs use

An Overview of Wireless Technologies

Now that you understand the different frequencies on which radio waves can travel, take a look at the three technologies WLANs use:●  Infrared—Infrared light can’t be seen by the human eye. Infrared (IR) technology is restricted to a single room or line of sight because IR light can’t penetrate walls, ceilings, or floors. This technology is used for most remote controls and for syncing PDAs.

●  Narrowband—Narrowband technology uses microwave radio band frequencies to transmit data. The most common uses of this technology are cordless phones and garage door openers.

●  Spread spectrum—For data to be moved over radio waves, it must be modulated on the carrier signal or channel. Modulation defines how data is placed on a carrier sig- nal. For example, spread spectrum modulation means data is spread across a large- frequency bandwidth instead of traveling across just one frequency band. In other words, a group of radio frequencies is selected, and the data is “spread” across this group. Spread spectrum, the most widely used WLAN technology, uses the following methods:

●  Frequency-hopping spread spectrum (FHSS): Data hops to other frequencies to avoid interference that might occur over a frequency band. This hopping from one frequency to another occurs at split-second intervals and makes it difficult for an intruder or attacker to jam the communication channel.

●  Direct sequence spread spectrum (DSSS): DSSS differs from FHSS, in that it spreads data packets simultaneously over multiple frequencies instead of hopping to other frequencies. Sub-bits are added to a packet as it travels across the frequency band and are used for recovery, in much the same way RAID-5 uses parity bits to rebuild a hard disk that crashes. Sub-bits are called “chips,” and every bit of the original message is represented by multiple bits, called the chipping code.

●  Orthogonal frequency division multiplexing (OFDM): The bandwidth is divided into a series of frequencies called tones, which allows a higher throughput (data transfer rate) than FHSS and DSSS do.