WiMAX (IEEE 802.16-2004)

WiMAX (IEEE 802.16-2004)

WiMAX is short for Worldwide Interoperability for Microwave Access and it is defined by the IEEE 802.16 Working Group. Although first intended for fixed applications, the initial WiMAX standards have evolved to form the basis for mobile WiMAX as well.

The current version of the fixed WiMAX standard is 802.16-2004, sometimes also referred to as 802.16d. It is essentially frequency independent, allowing also nonline-of-sight (NLOS) operation in the lower end of the frequency range (frequencies below 3 GHz, according to Richardson (2006)). The radio access interface is based on orthogonal frequency division multiplexing (OFDM) with 256 subcarriers, although OFDMA2048 and single carrier access modes are included in the 802.16-2004 standard as alternatives. OFDM allows good resistance to interference and multipath fading.

Channel bandwidth ranges from 1.25 to 20 MHz, and either FDD or TDD may be used for duplexing. WiMAX cell size is dependent on the used frequency band, but coverage radiuses of 1 to 2 km for NLOS and 10 to 16 km for LoS are typical with standard base station equipment. With some optional enhancements, however, the figures are 4 to 9 km (NLOS) and 30 to 50 km (LOS) (Baines 2005). Actual data rates are also highly variable and depend on a number of factors.

Although rates as high as 75 Mbit/s have been advertised, according to results of trials conducted by AT&T in late 2005, 2 Mbit/s over a range of roughly 5 to 10 km is closer to reality. For a comprehensive performance analysis, one may refer to, e.g., Ball et al. (2005).

Fixed WiMAX, as defined in 802.16-2004, does not support handovers or any other basic mobility mechanisms. As such, it lends itself only to fixed or, at most, nomadic applications.

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What is Mobile Broadband?

Mobile broadband is defined as broadband access (e.g. cable and DSL) in the cellular environment. The term is synonymous with FLASH-OFDM, a 3G alternative system.

Just as the cellular phone revolutionized voice telephony by freeing the user from wires and stationary constraints, mobile broadband is doing the same for high-speed data. Users are no longer confined to desks, no longer tethered to wires, no longer restricted to a stationary environment.

Mobile broadband is a step up from local wireless data applications like WiFi (and eventually WiMax), which gets rid of the wire, but not the confinement. Users still must be stationary and in a certain area (mostly inside) when using such technologies. One can think of WiFi as the data equivalent of the cordless phone, whereas mobile broadband is analogous to the cell phone, enabling everywhere access to high speed data – at any range of motion.

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