Wimax Technology Overview

WiMAX: An Information Study

WiMAX: An Information Study

This study will define what WiMAX is; provide a brief history of the technology; describe how WiMAX works and discuss its uses and potential benefits. WiMAX has the potential to become an extension to the reach of broadband solutions. WiMAX is still emerging and growing but shows signs of picking up a wider acceptance in the broadband marketplace. Could WiMAX be the broadband of the future?

What is WiMAX?

WiMAX, short for Worldwide Interoperability for Microwave Access or the Air Interface Standard and designated as 802.16 by the Institute of Electrical and Electronics Engineers (IEEE), is considered to be a broadband wireless technology (BWA) used to create metropolitan area networks (MAN). The standard covers both the Media Access Control (MAC) and the physical (PHY) layers

According to WiMAX Forum, the consortium behind WiMAX, "WiMAX is a standards-based technology enabling the delivery of last mile wireless broadband access as an alternative to cable and DSL. WiMAX will provide fixed, nomadic, portable, and eventually, mobile wireless broadband connectivity without the need for direct line-of-sight with a base station."

A number of PHY considerations were taken into account in the development of WiMAX. At higher frequencies, line of sight eases the effect of multipath, allowing for wide channels, typically greater than 10 MHz in bandwidth. This provides very high capacity links on both the uplink and the downlink. For sub 11 GHz non line of sight capability is a requirement. The original IEEE 802.16 MAC was enhanced to accommodate different PHYs and services, which address the needs of different environments. The standard is designed to accommodate either Time Division Duplexing (TDD) or Frequency Division Duplexing (FDD) deployments, allowing for both full and half-duplex terminals in the FDD case.

The MAC was designed specifically for point-to-multipoint (PMP) wireless access environment. It supports higher layer or transport protocols such as ATM, Ethernet or Internet Protocol (IP), and is designed to easily accommodate future protocols that have not yet been developed. The MAC is designed for very high bit rates (up to 268 mbps each way) of the truly broadband physical layer, while delivering ATM compatible Quality of Service (QoS); UGS, rtPS, nrtPS, and Best Effort.

The frame structure allows terminals to be dynamically assigned uplink and downlink burst profiles according to their link conditions. This allows a trade-off between capacity and robustness in real-time, and provides roughly a two times increase in capacity on average when compared to non-adaptive systems, while maintaining appropriate link availability.

The 802.16 MAC uses a variable length Protocol Data Unit (PDU) along with a number of other concepts that greatly increase the efficiency of the standard. Multiple MAC PDUs may be concatenated into a single burst to save PHY overhead. Additionally, multiple Service Data Units (SDU) for the same service may be concatenated into a single MAC PDU, saving on MAC header overhead. Fragmentation allows very large SDUs to be sent across frame boundaries to guarantee the QoS of competing services. And, payload header suppression can be used to reduce the overhead caused by the redundant portions of SDU headers.

The MAC uses a self-correcting bandwidth request/grant scheme that eliminates the overhead and delay of acknowledgements, while simultaneously allowing better QoS handling than traditional acknowledged schemes. Terminals have a variety of options available to them for requesting bandwidth depending upon the QoS and traffic parameters of their services. They can be polled individually or in groups. They can steal bandwidth already allocated to make requests for more. They can signal the need to be polled, and they can piggyback requests for bandwidth.

According to WiMAX Forum, the consortium behind WiMAX, "WiMAX is a standards-based technology enabling the delivery of last mile wireless broadband access as an alternative to cable and DSL. WiMAX will provide fixed, nomadic, portable, and eventually, mobile wireless broadband connectivity without the need for direct line-of-sight with a base station."

The versatility of both the PHY and Mac allow WiMAX networks, a range of 50 km, without line of site, provide data rates up 70 Mb/s. They are able to connect and extend WiFi (802.11) hotspots and provide wireless Internet access over a large area.

Figure 1:

History of the technology.

The IEEE approved the initial 802.16 standard for wireless MAN for the 10-66 GHz frequency range in December 2001. The 802.16a extension for sub-11 GHz was approved in January 2003. Amendment 802.16c, approved in December of 2002, "updates and expands Clause 12 of IEEE Std 802.16-2001, which concerns system profiles that list sets of features and functions to be used in typical implementation cases. Errors and inconsistencies in IEEE Std 802.16-2001 are also corrected. The scope is limited to 10-66 GH." The 802.16-2004 standard was ratified by the IEEE in June 2004 and includes 802.16a and 802.11c. The 802.16e standard, which adds mobility, is being reviewed by IEEE and expects approval in mid-2005.

The growth of WiMAX?

WiMAX is being implemented all over the globe with a US company leading the way. Clearwire a company headquartered out of Kirkland has been buying spectrum in the US and in Europe with 34 million dollars of spectrum purchased in the last 2 months. They are delivering wireless solutions for backhauls and for wireless home services that compare to DSL and Cable.

Figure 2: Clearwire's recent coverage in the United States.

AT&T in Atlanta, right now, is testing WiMAX. They are looking to the broadband solution to bypass local carriers and bring the last mile to the customers themselves. This could be a huge savings to AT&T with local carriers costing them around 10 billion. The last mile, which is the most expensive for ISP's and carriers, can be done rather inexpensively with WiMAX technology. This is achieved from not needing to run cable or wire and tear up streets to get to the customers doorstep.

With 70 mbps throughput WiMAX will be a good solution for getting companies up and running fast on the Internet. WiMAX technology will improve wireless distances, rates, and bandwidth to areas