IEEE Communications Magazine • February 20051290163-6804/05/$20.00 © 2005 IEEETOPICS IN BROADBAND ACCESSINTRODUCTIONIEEE standard 802.16, the first version of whichwas completed in October 2001, defines the airinterface and medium access control (MAC) pro-tocol for a wireless metropolitan area network(WMAN™), intended for providing high-band-width wireless voice and data for residential andenterprise use. This is the first industry-wide stan-dard that can be used for fixed wireless accesswith substantially higher bandwidth than most cel-lular networks. The IEEE 802.16 standard, oftenreferred to as WiMax, heralds the entry of broad-band wireless access as a major new tool in theeffort to link homes and businesses to coretelecommunications networks worldwide.In the near future 802.16 will offer a mobileand quickly deployable alternative to cabledaccess networks, such as fiber optic links, coaxialsystems using cable modems, and digital sub-scriber line (DSL) links. Because wireless sys-tems have the capacity to address broadgeographic areas without the costly infrastructurerequired to deploy cable links to individual sites,the technology may prove less expensive todeploy and should lead to more ubiquitousbroadband access. Wireless broadband systemshave been in use for several years, but the devel-opment of this new standard marks the matura-tion of the industry and a new level ofcompetitiveness for non-line of sight (NLOS)wireless broadband services.Historically, 802.16 activities were initiated atan August 1998 meeting called by the NationalWireless Electronics Systems Testbed (N-WEST)of the U.S. National Institute of Standards andTechnology. The effort was welcomed in IEEE802, which led to the formation of the 802.16Working Group, which has held weeklong meet-ings at least bimonthly since July 1999. Develop-ment of 802.16 and the included WirelessMAN™air interface, along with associated standards andamendments, is the responsibility of IEEE Work-ing Group 802.16 on Broadband Wireless Access(BWA) Standards [1]. The Working Group’s initialinterest was in the 10–66 GHz range, but morerecent interest is behind the 2–11 GHz amendmentproject that led to IEEE 802.16a and was complet-ed in January 2001. The new 802.16d upgrade tothe 802.16a standard was recently approved inJune 2004 (now named 802.16-2004), and primarilyintroduces some performance enhancement fea-tures in the uplink. Equipment based on this stan-dard is expected to be dominant in the first versionof products. Currently the standardization of802.16e is underway, which promises to supportmobility up to speeds of 70–80 mi/h and an asym-metrical link structure that will enable the sub-scriber station to have a handheld form factor forPDAs, phones, or laptops.In order to rapidly converge on a worldwidestandard, a staggering number of options areprovided in the various 802.16 standards forArunabha Ghosh and David R. Wolter, SBC Laboratories Inc.Jeffrey G. Andrews and Runhua Chen, The University of Texas at AustinABSTRACTThe IEEE 802.16 family of standards and itsassociated industry consortium, WiMax, promiseto deliver high data rates over large areas to alarge number of users in the near future. Thisexciting addition to current broadband optionssuch as DSL, cable, and WiFi promises to rapid-ly provide broadband access to locations in theworld’s rural and developing areas where broad-band is currently unavailable, as well as compet-ing for urban market share. WiMax’scompetitiveness in the marketplace largelydepends on the actual data rates and rangesthat are achieved, but this has been difficult tojudge due to the large number of possibleoptions and competing marketing claims. Thisarticle first provides a tutorial overview of802.16. Then, based on extensive recent studies,this article presents the realistic attainablethroughput and performance of expectedWiMax compatible systems based on the 802.16dstandard approved in June 2004 (now named802.16-2004). We also suggest future enhance-ments to the standard that could at least quadru-ple the achievable data rate, while alsoincreasing the robustness and coverage, withonly moderate complexity increases.Broadband Wireless Access withWiMax/8O2.16: Current PerformanceBenchmarks and Future PotentialANDREWS LAYOUT 1/28/05 2:19 PM Page 129IEEE Communications Magazine • February 2005130parameters related to the MAC and physical(PHY) layers. In order to ensure that resulting802.16-based devices are in fact interoperable,an industry consortium called the WiMax Forumwas created. The WiMax Forum develops guide-lines known as profiles, which specify the fre-quency band of operation, the PHY to be used,and a number of other parameters. Adherenceto a given profile should enable interoperabilitybetween vendor products. The WiMax Forumhas identified several frequency bands for theinitial 802.16d products, notably in both licensed(2.5–2.69 and 3.4–3.6 GHz) and unlicensedspectrum (5.725–5.850 GHz). Due to all thepotential options in the standards, as well as thehuge ranges of data rates, ranges, and otherperformance measures that are being quoted asachievable for 802.16, there is presently a signif-icant amount of confusion about what type ofperformance can really be expected fromWiMax-compliant systems in the near future.This article will distill the important featuresof WiMax/802.16 systems and give well supportedpredictions on the performance that can beexpected from 802.16d-compliant systems, with aparticular focus on the downlink. Since it is prob-able that many potential customers will wanthigher performance than we demonstrate as feasi-ble, we also outline suggestions for enhancementsto 802.16 that could significantly increase perfor-mance while not radically altering the standard.OVERVIEW OF THE PHYSICAL LAYERWe begin by providing an overview of the IEEE802.16 PHY and MAC subsystems. This can beconsidered an update of [2], although we adopta higher-level approach in order to emphasizethe key parameters that will affect the perfor-mance of upcoming 802.16 systems. Design ofthe 2–11 GHz PHY is driven by the need forNLOS operation, which allows inexpensive andflexible consumer deployment and operation.The IEEE 802.l6a/d standard defines three dif-ferent PHYs that can be used in conjunctionwith the MAC layer to provide a reliable end-to-end link. These air interface specifications are:• WirelessMAN-SCa: A single-carrier modu-lated air