WIRELESS NETWORKING (Part 4)

RF Channelling

All RF communications require a fairly small segment of the total RF spectrum is available. One segment is called the channel (Channel). To allow for multiple signals are used simultaneously, each channel requires a separate frequency with the help of FDMA. The frequency of one channel is the center frequency of a single spectrum canal. The width of the channel spectrum is called the channel bandwidth.

The use of such channel, highly depends on the type communication. In the CB radio (handy talky), using a type halfduplex, so it is quite necessary one channel only. In multi-channel systems, such as mobile phones, used for supports full-duplex type. In order to implement full-duplex, then The second channel is made in addition to the main channel, which allows two-way can dirambatkan simultaneously. Another example is the two-channel receiver in a stereo system (the left channel and right channel) FM radio. With the increasingly widespread use of RF for many purposes, then the channel utilization is considered, so that later emerged concept of frequency reuse (Frequency Reuse). Examples of the use of frequencies between the radio station in Yogyakarta with at jakarta could use the same single frequency. This probably because of the distance that had exceeded the scope of the ability of the FM signal.

On a mobile phone communication, also applied the concept of frequency reuse This, first pioneered by the AMPS (Advanced Mobile Phone Service). Time Division Multiple Accessing (TDMA) TDMA is used to add capabilities FDMA. Each channel is divided into several time slots, where each one slot used by one user. An example is the GSM (Global System for Mobile Communication) is a type of TDMA. Code Division Multiple Access (CDMA) CDMA is the latest technology for multiple access. CDMA is not divide a set of frequencies used to be several channels. CDMA gives a unique code for each signal and then combines all the signals into one large channel. CDMA wireless technology known as 3G phones because of very efficient in bandwidth usage and also very secret because uniquely encoded communications.