WiMAX IEEE 802.16 technology tutorial

WiMAX Wireless Broadband Technology Includes:
Basics & introduction     RF interface     WiMAX frequencies     MAC layer     Network architecture    

WiMAX technology is a wireless broadband communications technology based around the IEE 802.16 standard providing high speed data over a wide area.

The letters of WiMAX stand for Worldwide Interoperability for Microwave Access (AXess), and it is a technology for point to multipoint wireless networking.

WiMAX technology is able to meet the needs of a large variety of users from those in developed nations wanting to install a new high speed data network very cheaply without the cost and time required to install a wired network, to those in rural areas needing fast access where wired solutions may not be viable because of the distances and costs involved - effectively providing WiMAX broadband. Additionally it is being used for mobile applications, providing high speed data to users on the move.

What is WiMAX technology? - basics

The standard for WiMAX technology is a standard for Wireless Metropolitan Area Networks (WMANs) that has been developed by working group number 16 of IEEE 802, specializing in point-to-multipoint broadband wireless access. Initially 802.16a was developed and launched, but now it has been further refined. 802.16d or 802.16-2004 was released as a refined version of the 802.16a standard aimed at fixed applications. Another version of the standard, 802.16e or 802.16-2005 was also released and aimed at the roaming and mobile markets.

WiMAX broadband technology uses some key technologies to enable it to provide the high speed data rates:

• OFDM (Orthogonal Frequency Division Multiplex):   OFDM has been incorporated into WiMAX technology to enable it to provide high speed data without the selective fading and other issues of other forms of signal format.
  
  

  Note on OFDM:

  Orthogonal Frequency Division Multiplex, OFDM is a form of signal format that uses a large number of close spaced carriers that are each modulated with low rate data stream. The close spaced signals would normally be expected to interfere with each other, but by making the signals orthogonal to each other there is no mutual interference. The data to be transmitted is shared across all the carriers and this provides resilience against selective fading from multi-path effects.

  Read more about OFDM, Orthogonal Frequency Division Multiplexing.

• MIMO (Multiple Input Multiple Output):   WiMAX technology makes use of multipath propagation using MIMO. By utilising the multiple signal paths that exist, the use of MIMO either enables operation with lower signal strength levels, or it allows for higher data rates.
  
  

  Note on MIMO:

  MIMO is a form of antenna technology that uses multiple antennas to enable signals travelling via different paths as a result of reflections, etc., to be separated and their capability used to improve the data throughput and / or the signal to noise ratio, thereby improving system performance.

  Read more about MIMO technology

WiMAX Forum

The WiMAX Forum is a wireless industry consortium with a growing number of members including many industry leaders. It has been set up to support and develop WiMAX technology worldwide, bring common standards across the globe to enable the technology to become an established worldwide technology.

One of the aims of the forum is to enable a standard to be adopted that will enable full interoperability between products. Learning from the problems of poor interoperability experienced with previous wireless standards, and the impact that this had on take up, the WiMAX Forum aims to prevent this from happening. Ultimately vendors will be able to have products certified under the auspices of the Forum, and then be able to advertise their products as "Forum Certified".

Although WiMAX technology will support traffic based on transport technologies ranging from Ethernet, Internet Protocol (IP), and Asynchronous Transfer Mode (ATM), the Forum will only certify the IP-related elements of the 802.16 products. The focus is on IP operations because this is the now the main protocol that is used.

WiMAX history

The history of WiMAX starts back in the 1990s with the realisation that there would be a significant increase in data traffic over telecommunications networks. With wired telecommunications networks being very expensive, especially in outlying areas and not installed in many countries, methods of providing wireless broadband were investigated.

WiMAX history started with these investigations into what was termed the last mile connectivity - methods of delivering high speed data to a large number of users who may have no existing wired connection.

The possibility of low cost last mile connectivity along with the possibility of a system that could handle backhaul over a wireless link proved to be a compelling argument to develop a new wireless data link system.

The next major phase in WiMAX history was the development of the standards by the IEEE.

The 802.16 standards working group was set up by the IEEE in 1999 under the IEEE 802 LAN/MAN Standards Committee. The first 802.16 standard was approved in December 2001and this was followed by two amendments to the basic 802.16 standard. These amendments addressed issues of radio spectrum and interoperability and came under the designations 802.16a and 802.16c.

In September 2003 a major revision project was commenced. This had the aim of aligning the standard with the European / ETSI HIPERMAN standard. It was also intended to incorporate conformance test specifications within the overall standard. The project was completed in 2004 and the standard was released as 802.16d, although it is often referred to as 802.16-2004 in view of the release date. With the release of the 802.16-2004 standard, the previous 802.16 documents, including the a, b, and c amendments were withdrawn.

WiMAX versions

Since its initial conception, new applications for WiMAX have been developed and as a result there are two "flavours" of WiMAX technology that are available:

The two flavours of WiMAX broadband technology are used for different applications and although they are based on the same standard, the implementation of each has been optimised to suit its particular application.

• 802.16d - DSL replacement     The 802.16d version is often referred to as 802.16-2004 and it is closer to what may be termed the original version of WiMAX defined under 802.16a. It is aimed at fixed applications and providing a wireless equivalent of DSL broadband data - often called WiMAX broadband. In fact the WiMAX Forum describes the technology as "a standards-based technology enabling the delivery of last mile wireless broadband access as an alternative to cable and DSL."
  
  802.16d is able to provide data rates of up to 75 Mbps and as a result it is ideal for fixed, DSL replacement applications as WiMAX broadband. It may also be used for backhaul where the final data may be distributed further to individual users. Cell radii are typically up to 75 km.
• 802.16e - Nomadic / Mobile     While 802.16 / WiMAX was originally envisaged as being a fixed only technology, with the need for people on the move requiring high speed data at a cost less than that provided by cellular services and opportunity for a mobile version was seen and 802.16e was developed. This standard is also widely known as 802.16-2005. It currently provides the ability for users to connect to a WiMAX cell from a variety of locations, and there are future enhancements to provide cell handover.
  
  802.16e is able to provide data rates up to 15 Mbps and the cell radius distances are typically between 2 and 4 km.

Competition

The competition with WiMAX, 802.16 depends upon the type or version being used. Although initially it was thought that there could be significant competition with Wi-Fi, there are other areas to which WiMAX is posing a threat.

• DSL cable lines     WiMAX is able to provide high speed data links to users and in this way it can pose a threat to DSL cable operators.
• Cell phone operators     As LTE was being developed and the initial roll-outs were taking place, cell phone operators saw the mobile version of WiMAX as a significant threat. It was even considered for adoption as the IMT 4G standard, but LTE was adopted as the standard, leaving WiMAX for fixed WiMAX braodband, last mile links and a variety of other point to point applications.

WiMAX technology has been deployed in many areas. Although initially seen as a candidate for 4G, its use is decreasing, although it is used as WiMAX broadband and also for last mile links.

  Written by Ian Poole .
  Experienced electronics engineer and author.

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