WiMax, or Worldwide Interoperability for Microwave Access, is described on the www.WiMax.com website as being a standards initiative to ensure broadband wireless radios interoperate from vendor to vendor. The website states that WiMax has the potential to replace telephone company’s copper wire networks, cable TV’s coaxial cable infrastructure, as well as cellular networks. WiMax is the IEEE standard 802.16, and has gone through many updates. IEEE has just recently approved 802.16m – Advanced Air Interface for Broadband Wireless Access Systems, also called Mobile WiMax Release 2. WiMax is intended for use in Metropolitan Area Networks.
This technology is touted as offering a six mile range and throughput of 72 Mbps using one base station, although it is admitted that in real world applications, a fixed broadband set up would offer a maximum of 45 Mbps, and a mobile set up would have a spectral efficiency of 5bps/Hz, which is still considered better than 3G. The WiMax website compares this service to a coffee shop wi-fi range of 100 yards and a throughput of 11 Mbps. However the WiMax offers the security of multi-level encryption and QoS (Quality of Service) dynamic bandwidth allocation.
A WiMax radio contains a transmitter and receiver and generates electrical oscillations in the carrier frequency between 2 and 11 GHz. Most solutions use separate radios and antennas. While traditional wireless networks require antennas to be on the highest point such as a mountain top or skyscraper, for WiMax the line of sight (LOS) is most important. With a LOS solution the range for reception is about 10 miles, while non line of sight (NLOS) set ups offer a range of about 4 to 5 miles. WiMax solutions include point to point (P2P) with one sender and one receiver, and point to multi point (PMP) distribution in which one base station can service hundreds of dissimilar subscribers. The website describes LOS as offering the best function, while NLOS is described as “acceptable” and “adequate”.
WiMax offers three types of antennas. Omni-directional antennas broadcast 360 degrees from base stations and are used in PMP configurations. The drawback is that as the energy is diffused, the range and signal strength become limited. Sector antennas focus the beam on a smaller area, usually 60, 90 or 120 degrees, which offers a greater range and throughput. Panel antennas are powered by Ethernet cable, called Power over Ethernet (PoE) and are typically used for P2P solutions. The subscriber station, or CPE (Customer Premise Equipment) can be outdoors or indoors. Outdoors CPE offers somewhat better performance as the reception is not impeded by walls, but the installation costs more and it must be weather resistant. An indoor CPE is installed by the subscriber so easier and quicker to obtain.
802.16e adds Scalable Orthogonal frequency-division multiple access (OFDMA) and Multiple In and Multiple Out (MIMO) antenna systems to the Physical Layer. OFDMA and MIMO can help users avoid interference by changing frequencies. For the MAC Layer 802.16e uses Convergence Sublayers as wireline technologies such as Ethernet, ATM and IP are encapsulated in the air interface. Secure communications are delivered by using secure key exchange during authentication and encryption with AES or DES during data transfer.
Whether WiMax can beat wi-fi remains to be seen. A recent news article in ars technica states that the WiMax operator Clearwire is being sued by users for “throttling” or usage caps, that keep internet connections to much lower speeds than advertised. Some think that Clearwire accepted more new customers than they had the infrastructure to handle, in the hopes that they could use the subscriber fees to build up their network. This type of incident could cause individuals and companies to think twice before trying this technology.
References
WiMax.com. 2011. WiMax.com Broadband Solutions, Inc. 13 Jul. 2011. <http://www.WiMax.com/>
Cheng, J. (2011). Wimax throttling lawsuit. ars technica, Retrieved from http://arstechnica.com/telecom/news/2011/03/wimax-throttling-lawsuit-clearwire-cant-deliver-the-goods.ars
Sojourn 