WiMAX

Standards does not define any uniform global licensed spectrum for WiMax, however the WiMax forum has published 3 licensed spectrum profiles 2.3 GHz, 2.5 GHz and 3.5 GHz, in an effort to drive standardization and decrease cost. Also plans for use of analog TV spectrum (700 MHz) await the complete deployment of digital TV.

The following modulation schemes are supported by WiMAX:

★ Binary phase shift keying modulation

★ Quadrature phase shift keying modulation

★ Quadrature amplitude modulation

WiMAX supports the following for encryption:

★Advanced encryption standard

★Triple data encryption standard

In wimax system, ranging procedure is initiated by SS(Subscriber Station) to establish connection with BS(Base Station). This ranging procedure are of many types mainly available for synchronization and maintenance of RF link. After Ranging is completed Base station waits for SBC REQ message transmitted by the Wimax SS. Using SBC REQ message SS informs BS of its basic capabilities. Unlike ranging request(RNG REQ) there is no dedicated slot for bandwidth request and SBC REQ. Bandwidth request can be transmitted any where in the uplink subframe except the reserved ranging slot.

The procedure helps wimax subscriber camp on to wimax compliant base station. Following are the summarized steps for network entry. Please note that this procedure is as per IEEE 802.16-2004 OFDM PHY and MAC layer specifications. This version of wimax is also referred as fixed wimax due to non-mobility of subscriber stations. The procedure for mobile version of wimax i.e. mobile wimax is similar to this but there are few changes to MAPs/channel descriptors and header format as well as addition in MAC messages.

The central radio transmitter/receiver installed by service provider to broadcasts WiMax signals. These transmitters are typically mounted on towers or tall buildings. Cellular networks are based on the concept of cells (a logical division of geographical area), each such cell is allocated a frequency and is served by a base station.

Base station consists of a receiver, transmitter and a control unit. Adjacent base stations use different frequencies to avoid cross-talk.

WiMax combines the advantages of favorite Wi-Fi and a wide coverage of cellular network. It takes a best part of wi-fi networks, the fast speed and broadband internet experience. WiMax is a WAN technology, service providers will deploy a wimax network that enables access over long distance. Coverage for a geographical area is divided into a series of overlapping areas called cells. Each cell provides coverage for users within that immediate vicinity. When you travel from one cell to another, the wireless connection is handed off from one cell to another.