Data Acquisition Web

The IEEE 802 group initiated the IEEE 802.16 Working Group to create standards for broadband wireless access in order to offer a high speed/capacity, low cost, and a scalable solution to extend fiber optic backbones. IEEE 802.16 is a unit of the IEEE 802 LAN/MAN Standards Committee, the premier transnational forum for wireless networking standardization.

802.16 promises to overcome all of the shortcomings of long-distance applications encountered by people using 802.11 protocols. The 802.11 family was never intended to provide long-distance, metropolitan-area coverage (in spite of some examples of people doing exactly that).

The 802.16 specification is designed for wireless infrastructures that will cover entire cities, with typical ranges measured in kilometers and to provide commercial-quality services to stationary locations as an alternative to traditional wired connections.

The first IEEE 802.16 standard, published in April 2002, defines the WirelessMAN Air Interface for wireless MANs. These systems are meant to provide network access to homes, small businesses, and commercial buildings.

802.16 supports point-to-multipoint architecture in the 10-66 GHz range, transmitting at data rates up to 120Mbps. At those frequencies, transmission requires line-of-sight, and roofs of buildings provide the best mounting locations for base and subscriber stations. The base station connects to a wired backbone and can transmit wirelessly up to 90 Km to a large number of stationary subscriber stations, possibly hundreds.

To accommodate non-line-of-sight access over lower frequencies, IEEE published 802.16a in January 2003, which includes support for mesh architecture. 802.16a operates in the licensed and unlicensed frequencies between 2GHz and 11GHz using orthogonal frequency division multiplexing (OFDM), which is similar to 802.11a and 802.11g.

The 802.16 medium access control (MAC) layer supports many different physical layer specifications, both licensed and unlicensed. Through the 802.16 MAC, every base station dynamically distributes uplink and downlink bandwidth to subscriber stations using time-division multiple access (TDMA). This is a dramatic difference from the 802.11 MAC, with current implementations operating through the use of carrier sensing mechanisms that don't provide effective bandwidth control over the radio link.