WiMAX has shown to be one of the most popular “standards” for broadband wireless access to the internet.
Technical overview
WiMAX is a term coined to describe standard, interoperable implementations of IEEE 802.16 wireless networks, in a rather similar way to Wi-Fi being interoperable implementations of the IEEE 802.11 Wireless LAN standard. However, WiMAX is very different from Wi-Fi in the way it works.
In Wi-Fi, the media access controller (MAC) uses contention access — all subscriber stations that wish to pass data through a wireless access point (AP) are competing for the AP’s attention on a random interrupt basis. This can cause subscriber stations distant from the AP to be repeatedly interrupted by closer stations, greatly reducing their throughput. This makes services such as Voice over IP (VoIP) or IPTV, which depend on a predetermined type of Quality of Service (QoS), difficult to maintain for large numbers of users.
In contrast, the 802.16 MAC uses a scheduling algorithm, 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 contract, but it remains assigned to the subscriber station, meaning that other subscribers cannot use it. This scheduling algorithm is stable under overload and over-subscription (unlike 802.11). It can also be more bandwidth efficient. The scheduling algorithm also allows the base station to control QoS parameters by balancing the time-slot assignments among the application needs of the subscriber stations.
The original WiMAX standard (IEEE 802.16) specified WiMAX in the 10 to 66 GHz range. 802.16a, updated in 2004 to 802.16-2004 (also known as 802.16d), added support for the 2 to 11 GHz range. 802.16d was updated to 802.16e in 2005. Revision 802.16e uses scalable orthogonal frequency-division multiplexing (OFDM) as opposed to the non-scalable version used in revision .16d. This brings potential benefits in terms of coverage, self installation, power consumption, frequency re-use and bandwidth efficiency. Revision .16e also adds a capability for full mobility support.
Most interest will probably be in the 802.16d and .16e standards, since the lower frequencies suffer less from signal attenuation and therefore give improved range and in-building penetration.
The WiMAX specification improves upon many of the limitations of the Wi-Fi standard by providing increased bandwidth and range and stronger encryption. It provides connectivity between network endpoints without need for direct line of sight in favourable circumstances. The non-line-of-sight propagation (NLOS) performance requires the .16d or .16e revisions, since the lower frequencies are needed. It relies upon clever use of multi-path signals.
[edit]Uses for WiMAX
A commonly held misconception is that WiMAX will deliver 70 Mbit/s, over 70 miles. Each of these may be true individually, given ideal circumstances, but they are not simultaneously true. WiMAX has some similarities to DSL in this respect, where one can either have high bandwidth or long reach, but not both simultaneously. The other feature to consider with WiMAX is that the bandwidth is shared between users in a given radio sector, so if there are many active users in a single sector, each will get reduced bandwidth.
The bandwidth and reach of WiMAX make it suitable for the following potential applications:
- Connecting Wi-Fi hotspots with each other and to other parts of the Internet
- Providing a wireless alternative to cable and DSL for last mile (last km) broadband access.
- Providing high-speed mobile data and telecommunications services (4G)
[edit]Broadband Access
Many cable and traditional telephone companies are closely examining, in active trials or small scale deployments of WiMAX for “last mile” connectivity. This could result in better price-points for both home and business customers as based on the benefits of competition. In areas without pre-existing physical cable or telephone networks, WiMAX is a viable alternative for broadband access that has hitherto been unavailable. Prior to WiMax, many operators have been using proprietary fixed wireless technologies to offer broadband services. Subscriber units are available both in indoor and outdoor models by various manufactures. Self install indoor units are convenient but the subscriber must be significantly closer to the WiMax base station. The indoor units are comparable in size to a cable modem or DSL modem. Outdoor units allow for the subscriber to be much further away from the WiMax base station but usually require professional installation. Outdoor units are roughly the size of textbook.
[edit]Mobile applications
There is potential for using WiMAX with legacy cellular networks. WiMAX antennas can “share” a cell tower without compromising the function of cellular arrays already in place. Some cellular companies are evaluating WiMAX as a means of increasing bandwidth for a variety of data-intensive applications; indeed, Sprint Nextel has announced in mid-2006 that it will be investing about US$ 3 billion in a WiMAX technology buildout over the next few years. In line with these possible applications is the technology’s ability to serve as a high bandwidth “backhaul” for Internet or cellular phone traffic from remote areas back to an internet 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 reducing the cost of T1/E1 backhaul as well. Given the limited wired infrastructure in some developing countries, the costs to install a WiMAX station in conjunction with an existing cellular tower or even as a solitary hub are likely to be small in comparison to developing a wired solution. Areas of low population density and flat terrain are particularily suited to WiMAX and its range. 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.
WiMAX. (2006, October 4). In Wikipedia, The Free Encyclopedia. Retrieved 04:27, October 7, 2006, from http://en.wikipedia.org/w/index.php?title=WiMAX&oldid=79500211