WiMax
WiMAX, is defined as Worldwide Interoperability for Microwave Access by the WiMAX Forum, formed in April 2001 to promote conformance and interoperability of the standard IEEE 802.16, also known as WirelessMAN. The Forum describes WiMAX as "a standards-based technology enabling the delivery of last mile wireless broadband access as an alternative to cable and DSL. WiMAX has a range of up to 30 miles. One of its promoted uses are for PDAs.
The WiMAX Forum is "the exclusive organization dedicated to certifying the interoperability of BWA products, the WiMAX Forum defines and conducts conformance and interoperability testing to ensure that different vendor systems work seamlessly with one another." Those that pass conformance and interoperability testing achieve the "WiMAX Forum Certified" designation and display this mark on their products and marketing materials. Vendors claiming their equipment is "WiMAX-ready", "WiMAX-compliant", or "pre-WiMAX" are not WiMAX Forum Certified, according to the Forum.
Introduction
The IEEE 802.16 media access controller (MAC) is significantly different from that of IEEE 802.11 Wi-Fi MAC. In Wi-Fi, the MAC uses contention access — all subscriber stations wishing to pass data through an access point are competing for the AP's attention on a random basis. This can cause distant nodes from the AP to be repeatedly interrupted by less sensitive, closer nodes, greatly reducing their throughput. And this makes services, such as VoIP or IPTV which depend on a determined level of quality of service (QoS) difficult to maintain for large numbers of users.
In contrast, the 802.16 MAC is a scheduling MAC where the subscriber station only has to compete once (for initial entry into the network). After that it is allocated a time slot by the base station. The time slot can enlarge and constrict, but it remains assigned to the subscriber station meaning that other subscribers are not supposed to use it but take their turn. This scheduling algorithm is stable under overload and over-subscription (unlike 802.11). It is also much more bandwidth efficient. The scheduling algorithm also allows the base station to control Quality of Service by balancing the assignments among the needs of the subscriber stations.
A recent addition to the WiMAX standard is underway which will add full mesh networking capability by enabling WiMAX nodes to simultaneously operate in "subscriber station" and "base station" mode. This will blur that initial distinction and allow for widespread adoption of WiMAX based mesh networks and promises widespread WiMAX adoption. WiMAX/802.16's use of OFDMA and scheduled MAC allows wireless mesh networks to be much more robust and reliable.
The original WiMAX standard, IEEE 802.16, specifies WiMAX in the 10 to 66 GHz range. 802.16a, updated in 2004 to 802.16-2004, added support for the 2 to 11 GHz range, of which most parts are already unlicensed internationally and only very few still require domestic licenses. Most business interest will probably be in the 802.16-2004 standard, as opposed to licensed frequencies. The WiMAX specification improves upon many of the limitations of the Wi-Fi standard by providing increased bandwidth and stronger encryption. It also aims to provide connectivity between network endpoints without direct line of sight in some circumstances. The details of performance under non-line of sight (NLOS) circumstances are unclear as they have yet to be demonstrated. It is commonly considered that spectrum under 5-6 GHz is needed to provide reasonable NLOS performance and cost effectiveness for PtM (point to multi-point) deployments. WiMAX makes clever use of multi-path signals but does not defy the laws of physics.
Uses for WiMAX
WiMAX is a framework for wireless development based on a forward-looking core set of technologies. More recently 3GPP cellular's 4G, 802.22 Cognitive Radio RAN (Rural Area Network), and 802.20, the High Speed Mobile Broadband Wireless Access (MBWA) Working Group, have shifted toward use of similar constructs of multi-channel scalable OFDM, HARQ, FEC, MIMO-AAS and other complementary technologies as are part of WiMAX. WiMAX is designated as the metropolitan area network (MAN) technology that can connect IEEE 802.11 (Wi-Fi) hotspots with each other and to other parts of the Internet and provide a wireless alternative to cable and DSL for last mile (last km) broadband access. However, the field of uses is broader and overlaps those for mobile WAN (wide area networks) and WLANs. IEEE 802.16 provides up to 50 km (31 miles) of linear service area range and allows connectivity between users without a direct line of sight.
Note that this should not be taken to mean that users 50 km (31 miles) away without line of sight will have connectivity. Practical limits from real world tests seem to be around 5-8 km (3-5 miles). The technology has been claimed to provide shared data rates up to 70 Mbit/s, which, according to WiMAX proponents, is enough bandwidth to simultaneously support more than 60 businesses with T1-type connectivity and well over a thousand homes at 1Mbit/s DSL-level connectivity. Real world tests, however, show practical maximum data rates between 500kbit/s and 2 Mbit/s, depending on conditions at a given site.
It is also anticipated that WiMAX will allow inter-penetration for broadband service provision of VoIP, video, and Internet access—simultaneously. Most cable and traditional telephone companies are closely examining or actively trial-testing the potential of WiMAX for "last mile" connectivity. This should result in better price-points for both home and business customers as competition results from the elimination of the "captive" customer bases both telephone and cable networks traditionally enjoyed. Even in areas without preexisting physical cable or telephone networks, WiMAX could allow access between anyone within range of each other. Home units the size of a paperback book that provide both phone and network connection points are already available and easy to install.
There is also interesting potential for interoperability of WiMAX with legacy cellular networks. WiMAX antennas can "share" a cell tower without compromising the function of cellular arrays already in place. Companies that already lease cell sites in widespread service areas have a unique opportunity to diversify, and often already have the necessary spectrum available to them (i.e. they own the licenses for radio frequencies important to increased speed and/or range of a WiMAX connection). WiMAX antennae may be even connected to an Internet backbone via either a light fiber optics cable or a directional microwave link. Some cellular companies are evaluating WiMAX as a means of increasing bandwidth for a variety of data-intensive applications. In line with these possible applications is the technology's ability to serve as a very high bandwidth "back-haul" for Internet or cellular phone traffic from remote areas back to a backbone. Although the cost-effectiveness of WiMAX in a remote application will be higher, it is definitely not limited to such applications, and may in fact be an answer to expensive urban deployments of T1 back-hauls as well. Given developing countries' (such as in Africa) limited wired infrastructure, the costs to install a WiMAX station in conjunction with an existing cellular tower or even as a solitary hub will be diminutive in comparison to developing a wired solution. The wide, flat expanses and low population density of such an area lends itself well to WiMAX and its current diametrical range of 30 miles. For countries that have skipped wired infrastructure as a result of inhibitive costs and unsympathetic geography, WiMAX can enhance wireless infrastructure in an inexpensive, decentralized, deployment-friendly and effective manner.
Spectrum Allocations for WiMAX
The 802.16 specification applies across a wide swath of RF spectrum, but specification is not the same as permission to use. There is no uniform global licensed spectrum for WiMAX. In the US, the biggest segment available is around 2.5 GHz, and is already assigned, primarily to Sprint Nextel. Elsewhere in the world, the most likely bands used will be around 3.5 GHz, 2.3/2.5 GHz, or 5 GHz, with 2.3/2.5 GHz probably being most important in Asia.
There is some prospect that some of a 700 MHz band might be made available for WiMAX use, but it is currently assigned to the analog TV and awaits the complete rollout of HD digital TV before it can become available, likely by 2009. And, in any case, there will be other uses suggested for that spectrum if and when it actually becomes open.
It seems likely that there will be several variants of 802.16, depending on local regulatory conditions and thus on which spectrum is used. Even if everything but the underlying radio frequencies is the same. WiMAX equipment will not, therefore, be as portable as it might have been. And perhaps even less so than WiFi, whose assigned channels in unlicensed spectrum varies more than a little from jurisdiction to jurisdiction.
Fixed and mobile
April 2006 is seeing the first releases of two, mutually incompatible, versions of WiMAX creating a challenge for everyone in the industry, namely, picking the version that will fare best in the long run. 802.16-2004 WiMAX only supports fixed access, but products are already available. 802.16e WiMAX supports mobile and fixed access but products are still at least a year away.
In one of the most significant WiMAX deployments to date, regional service provider Arialink Broadband says it is building out a broadband wireless network for all of Muskegon County, Mich., using 802.16e equipment from Samsung Corp. Competition from wired technologies (DSL, cable modem, fiber-to-the-home) and from wireless technologies (Wi-Fi, 3G including WCDMA, HSDPA, EV-DO, TD-CDMA, and proprietary solutions like Qualcomm's FLASH-OFDM) has made it a very broad connectivity market.
Recently announced in Red Herring.com, Clearwire, a so called 'start-up', is looking to invest about $1 billion in funds to build its own WiMAX network. Towerstream has continued to service large cities in the United States, testing and installing WiMAX certified equipment as it is officially released.
The WiMAX Forum member companies and products to complete certification and interoperability testing include Airspan's MacroMAX base station and EasyST subscriber station solution, Axxcelera's ExcelMax base station, Sequans Communications' SQN1010-RD subscriber station solution, Siemens AG WayMAX@vantage base station and subscriber station solutions, Aperto's Packetmax 5000 base station, Redline Communication's RedMAX base station and subscriber unit, Proxim Wireless Tsunami MP16 3500, and Wavesat's miniMAX subscriber station solution.
WiBro: South Korean version
Perhaps the most telling deployments for WiMAX will be for the WiBro mobile derivative: WiBro has South Korean government support with the requirement for each carrier to spend over US$1 billion for deployments. The Koreans sought to develop WiBro as a regional and potentially international alternative to 3.5-4G systems. But given the lack of self-developed momentum as a standard, WiBro has joined WiMAX and agreed to harmonize with the similar OFDMA 802.16e version of the standard. What makes WiBro roll-outs, which will start in April 2006, a good 'test case' for the overall WiMAX effort is that it is mobile, well thought out for delivery of wireless broadband services, and the fact that the deployment is taking place in a highly sophisticated, broadband-saturated market. WiBro will go up against 3G and very high bandwidth wire-line services rather than as gap-filler or rural under-served market deployments as is often exampled as the 'best fit' markets for WiMAX. WiBro goes much more "in your face" in direct competition with 3G and high bandwidth wired services which pose tough competition. Telecom Italia, the dominant telephony and internet service provider in Italy has announced it will test, together with Korean Samsung Electronics, a WiBro network service, starting with the Winter Olympic Games 2006, held in Turin.
