802.16, also referred to as IEEE 802.16, "WirelessMAN," or "WiMAX" (which stands for "Worldwide Interoperability for Microwave Access"), is a family of standards developed by the Institute of Electrical and Electronics Engineers (IEEE) 802.16 Working Group on Broadband Wireless Access Standards.
The workgroup, a unit of the IEEE 802 LAN/MAN Standards Committee, was established by the IEEE Standards Board in 1999. In keeping with its objective of preparing formal specifications for the global deployment of broadband Wireless Metropolitan Area Networks, the workgroup created the 802.16 family of standards.
December 2001 marked the release of the first 802.16 standard, which uses a single-carrier (SC) physical (PHY) standard. The first version of 802.16 delivered a standard for point-to-multipoint broadband wireless transmission in the 10-66 GHz band. It featured only a line-of-sight (LOS) capability.
The amendment succeeding the first version of 802.16 was known as 802.16a. This amendment was ratified in January 2003. It was intended to provide "last mile" fixed broadband access. It delivered a point-to-multipoint capability in the 2-11 GHz band, which required a non-line-of-sight (NLOS) capability to function.
The PHY was extended to include Orthogonal Frequency Division Multiplex (OFDM) and Orthogonal Frequency Division Multiple Access (OFDMA) as modulation schemes.
802.16c delivered a system profile for the 10-66 GHz 802.16 standard.
802.16d was an amendment created with the objective of being aligned with the European Telecommunications Standards Institute (ETSI) HIPERMAN standard, and laying down conformance and test specifications. Development began in September 2003 and concluded in 2004. With its release, the earlier documents, 802.11a-c, were withdrawn.
802.16e, alternately known as "Mobile WiMAX," comes with a number of enhancements, including better support for Quality of Service (QoS) and the use of Scalable OFDMA. Concluded in 2005, 802.16e is the latest amendment of the 802.16 family to have been released so far. It uses Scalable OFDMA for data transmission, supporting channel bandwidths from 1.25 MHz up to 20 MHz, with up to 2048 sub-carriers.
Under good conditions, a highly efficient 64 quadrature amplitude modulation (64 QAM) coding scheme is used; in intermediate conditions, 16 QAM and quadrature phase-shift keying (QPSK) is used; while under less favorable conditions, binary phase-shift keying (BPSK) is used. This is because the physical layer (PHY) of an 802.16 system supports adaptive modulation and coding. It also supports Multiple-in Multiple-out (MIMO) antennas for good NLOS characteristics (or higher bandwidth) and hybrid automatic repeat request (HARQ) for ample performance in error-correction.
Features in the media access control (MAC) layer include Convergence Sub-layers, power-saving mechanisms such as "idle" and "sleep mode," and handover mechanisms. 802.16e provides strong support for QoS because it is a connection-oriented technology, and the subscriber station (SS) needs to be allocated a channel by the base station (BS) before it can begin to transmit data.
A number of amendments, 802.16f-m, have yet to be released. 802.16f (Management Information Base) is active. 802.16g (Management Plane Procedures and Services) is under development. 802.16h (Improved Coexistence Mechanisms for License-Exempt Operation), 802.16i (Mobile Management Information Base), 802.16j (Multihop Relay Specification), 802.16k (Bridging of 802.16) and 802.16m (Advanced Air Interface) are all at pre-draft stage.