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• Optimal transport for VBR traffic (e.g. video)
• Data prioritization
• Improves end-to-end performance by hiding RF layer-induced errors from upper layer protocols
• Enables highest data rates allowed by channel conditions, improving system capacity
• Protects user privacy
• Enables cellular deployments by minimizing self interference
develop and extend to support other PHY specifications. Hence, the modular nature of the standard is helpful in this aspect. For example, the very first version of the standard only supported single carrier modulation. Since that time, orthogonal frequency division multiplexing (OFDM) has been added (Table 2.3; Figure 2.8).
2.6 WiMAX STANDARDS
The IEEE 802.16, the ‘Air Interface for Fixed Broadband Wireless Access Systems’, also known as the IEEE WirelessMAN air interface, is an emerging suite of standards for fixed, portable and mobile BWA in MAN.
These standards are issued by IEEE 802.16 work group that originally covered the wireless local loop (WLL) technologies in the 10-66 GHz radio spectrum, which were later extended through amendment projects to include both licensed and unlicensed spectra from 2 to 11 GHz.
Although the term WiMAX is only a few years old, 802.16 has been around since the late 1990s, first with the adoption of the 802.16
WiMAX STANDARDS Table 2.3 802.16 PHY features
256-point FFT OFDM waveform
Adaptive modulation and variable error correction encoding per RF burst
TDD and FDD duplexing support
Flexible Channel sizes (e.g. 3.5,
5, 10 MHz.)
Designed to support smart antenna systems
Built-in support for addressing multipath in outdoor LOS and NLOS environments Ensures a robust RF link while maximizing the number of bps for each subscriber unit Addresses varying worldwide regulations where one or both may be allowed Provides the flexibility necessary to operate in many different frequency bands with varying channel requirements around the world Smart antennas are fast becoming more affordable, and as these costs come down their ability to suppress interference and increase system gain will become important to BWA deployments
Figure 2.8 WiMAX standards
WiMAX IN DEPTH
standard (10-66GHz) and then with 802.16a (2-11 GHz). Although the work on IEEE 802.16 standard started in 1999, it was only during 2003 that the standard received wide attention when the IEEE 802.16a standard was ratified in January.
Developing a new technical standard in the telecommunications field is never an easy process, but the growth of wireless LANs and WiFi hotspots has shown that there is a huge demand for wireless services that allow people to connect to the Internet and business networks from anywhere at any time. That has provided equipment makers and service providers with the incentive to cooperate on developing standards for WiMAX in order to grow the market. Standardization efforts have been underway for almost 6 years and momentum is building for multivendor interoperability.
The IEEE 802.16 standards for BWA provide the possibility for interoperability between equipment from different vendors, which is in contrast to the previous BWA industry, where proprietary products with high prices are dominant in the market. The IEEE 802.16 standards have received wide support from major equipment manufacturers like Intel and Nokia.
Furthermore, a nonprofit organization called WiMAX Forum was formed in 2001, with the aim of harmonizing standards, and testing and certifying interoperability between equipment from different manufacturers. Systems conforming to the test specifications will receive a ‘WiMAX certified’ label. This standardized solution is expected to bring beneficial economical effects such as mass production and cost reduction.
The stage is set for a paradigm-shift in the communications industry that could well result in a completely new equipment deployment cycle, firmly grounded in the wide-based adoption of Ethernet technologies. This BWA network architecture promises to become a significant means of delivering bundled voice, data and video services over a single network.
It is often thought that WiMAX is one homogenous technology when in fact it is a trade name for a group of IEEE wireless standards. In that respect, WiMAX and WiFi are analogous. WiFi is not a standard, but a trade name that can be applied to a series of 802.11 IEEE standards, including 802.11b, 802.11a and 802.11g. It is assumed that the term WiFi will be applied to 802.11n once that standard is ratified.
The WiMAX umbrella currently includes 802.16-2004 and 802.16e.
802.16-2004 utilizes OFDM to serve multiple users in a time division
fashion in a sort of a round-robin technique, but done extremely quickly so that users have the perception that they are always transmitting/ receiving. 802.16e utilizes OFDMA and can serve multiple users simultaneously by allocating sets of ‘tones’ to each user (Table 2.4).