IEEE 802.16

The IEEE 802.16 Working Group on Broadband Wireless Access Standards, which was established by IEEE Standards Board in 1999, aims to prepare formal specifications for the global deployment of broadband Wireless Metropolitan Area Networks. The Workgroup is a unit of the IEEE 802 LAN/MAN Standards Committee. A related future technology Mobile Broadband Wireless Access (MBWA) is under development in IEEE 802.20.

Although the 802.16 family of standards is officially called WirelessMAN, it has been dubbed “WiMAX” (from "Worldwide Interoperability for Microwave Access") by an industry group called the WiMAX Forum. The mission of the Forum is to promote and certify compatibility and interoperability of broadband wireless products.

802.16 Standards

The first 802.16 standard was approved in December 2001. It delivered a standard for point to multipoint Broadband Wireless transmission in the 10-66 GHz band, with only a line-of-sight (LOS) capability. It uses a single carrier (SC) physical (PHY) standard.

IEEE 802.16 standardizes the air interface and related functions associated with wireless local loop. Three working groups have been chartered to produce standards:

• IEEE 802.16.1 - Air interface for 10 to 66 GHz, also known as Local Multipoint Distribution Service.
• IEEE 802.16.2 - Coexistence of broadband wireless access systems.
• IEEE 802.16.3 - Air interface for licensed frequencies, 2 to 11 GHz, also known as 802.16a

802.16a was an amendment to 802.16 and delivered a point to multipoint capability in the 2-11 GHz band. For this to be of use, it also required a non-line-of-sight (NLOS) capability, and the PHY standard was therefore extended to include Orthogonal Frequency Division Multiplex (OFDM) and Orthogonal Frequency Division Multiple Access (OFDMA). 802.16a was ratified in January 2003 and was intended to provide "last mile" fixed broadband access.

802.16c, a further amendment to 802.16, delivered a system profile for the 10-66 GHz 802.16 standard.

In September 2003, a revision project called 802.16d commenced aiming to align the standard with aspects of the European Telecommunications Standards Institute (ETSI) HIPERMAN standard as well as lay down conformance and test specifications. This project concluded in 2004 with the release of 802.16-2004 which superseded the earlier 802.16 documents, including the a/b/c amendments.

An amendment to 802.16-2004, IEEE 802.16e-2005 (formerly known as IEEE 802.16e), addressing mobility, was concluded in 2005. This implemented a number of enhancements to 802.16-2004, including better support for Quality of Service and the use of Scalable OFDMA, and is sometimes called “Mobile WiMAX”, after the WiMAX forum for interoperability.

Amendments in progress

Active amendments:

• 802.16e-2005 — Mobile 802.16
• 802.16f-2005 — Management Information Base
• 802.16g-2007 — Management Plane Procedures and Services
• 802.16k-2007 — Bridging of 802.16 (an amendment to 802.1D)

Amendments under development:

• 802.16h — Improved Coexistence Mechanisms for License-Exempt Operation
• 802.16i — Mobile Management Information Base
• 802.16j — Multihop Relay Specification
• 802.16Rev2 — Consolidate 802.16-2004, 802.16e, 802.16f, 802.16g and possibly 802.16i into a new document.

Amendments at pre-draft stage:

• 802.16m — Advanced Air Interface. Data rates of 100 Mbit/s for mobile applications and 1 Gbit/s for fixed applications, cellular, macro and micro cell coverage, with currently no restrictions on the RF bandwidth (which is expected to be 20 MHz or higher). The proposed work plan would allow completion of the standard by December 2009 for approval by March 2010.

802.16e-2005 Technology

The 802.16 standard essentially standardizes 2 aspects of the air interface - the physical layer (PHY) and the Media Access Control layer (MAC). This section provides an overview of the technology employed in these 2 layers in the current version of the 802.16 specification (which is strictly 802.16-2004 as amended by 802.16e-2005, but which will be referred to as 802.16e for brevity).

PHY

802.16e uses Scalable OFDMA to carry data, supporting channel bandwidths of between 1.25 MHz and 20 MHz, with up to 2048 sub-carriers. It supports adaptive modulation and coding, so that in conditions of good signal, a highly efficient 64 QAM coding scheme is used, whereas where the signal is poorer, a more robust BPSK coding mechanism is used. In intermediate conditions, 16 QAM and QPSK can also be employed. Other PHY features include support for Multiple-in Multiple-out (MIMO) antennas in order to provide good NLOS (Non-line-of-sight) characteristics (or higher bandwidth) and Hybrid automatic repeat request (HARQ) for good error correction performance.

MAC

The 802.16 MAC describes a number of Convergence Sublayers which describe how wireline technologies such as Ethernet, ATM and IP are encapsulated on the air interface, and how data is classified, etc. It also describes how secure communications are delivered, by using secure key exchange during authentication, and encryption using AES or DES (as the encryption mechanism) during data transfer. Further features of the MAC layer include power saving mechanisms (using Sleep Mode and Idle Mode) and handover mechanisms.

A key feature of 802.16 is that it is a connection oriented technology. The subscriber station (SS) cannot transmit data until it has been allocated a channel by the Base Station (BS). This allows 802.16e to provide strong support for Quality of Service (QoS).

QoS

QoS in 802.16e is supported by allocating each connection between the SS and the BS (called a service flow in 802.16 terminology) to a specific QoS class. In 802.16e, there are 5 QoS classes:

802.16e-2005 QoS classes

Service	Abbrev	Definition	Typical Applications
Unsolicited Grant Service	UGS	Real-time data streams comprising fixed-size data packets issued at periodic intervals	T1/E1 transport
Extended Real-time Polling Service	ertPS	Real-time service flows that generate variable-sized data packets on a periodic basis	VoIP
Real-time Polling Service	rtPS	Real-time data streams comprising variable-sized data packets that are issued at periodic intervals	MPEG Video
Non-real-time Polling Service	nrtPS	Delay-tolerant data streams comprising variable-sized data packets for which a minimum data rate is required	FTP with guaranteed minimum throughput
Best Effort	BE	Data streams for which no minimum service level is required and therefore may be handled on a space-available basis	HTTP

The BS and the SS use a service flow with an appropriate QoS class (plus other parameters, such as bandwidth and delay) to ensure that application data receives QoS treatment appropriate to the application.

Certification

Because the IEEE only sets specifications but does not test equipment for compliance with them, the WiMAX Forum runs a certification program wherein members pay for certification. WiMAX certification by this group is intended to guarantee compliance with the standard and interoperability with equipment from other manufacturers. The mission of the Forum is to promote and certify compatibility and interoperability of broadband wireless products.

See also

• WiBro
• WiMAX
• WiBAS

External links

• IEEE Std 802.16-2004
• IEEE Std 802.16e-2005
• ITU Radiocommunication Assembly approves new developments for its 3G standards
• IEEE website for 802.16
• Get IEEE 802 (IEEE 802.16)
• The WiMAX Forum
• WiMAX: Opportunity or Hype? A paper presented at the ITERA 2006 academic conference discussing the standardization process
• European Telecommunications Standards Institute
• The implications of WiMAX for competition and regulation A paper of the OECD, Organisation for Economic Co-operation and Development