Worldwide Interoperability for Microwave Access “Wimax”

December 31, 2007 | By archives | Filed in: Blogging.

WiMAXWiMAX, the Worldwide Interoperability for Microwave Access, is a telecommunications technology aimed at providing wireless data over long distances in a variety of ways, from point-to-point links to full mobile cellular type access. It is based on the IEEE 802.16 standard, which is also called WirelessMAN. The name WiMAX was created by the WiMAX Forum, which was formed in June 2001 to promote conformance and interoperability of the standard. 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

The terms “fixed WiMAX”, “mobile WiMAX”, “802.16d” and “802.16e” are frequently used incorrectly. Correct definitions are:
802.16dStrictly speaking, 802.16d has never existed as a standard. The standard is correctly called 802.16-2004 and was developed by the IEEE 802.16802.16d, but the standard never was. However, since this standard is frequently called 802.16d, that term is also used in this article to assist readability. Task Group d. Therefore the project was called802.16eJust as 802.16d has never existed as a standard, neither has 802.16e. 802.16e is an amendment to 802.16-2004, and the amendment is properly referred to as 802.16e-2005. 802.16e-2005 is not a standard in its own right – since it is only an amendment, the original document (802.16-2004) has to be read and then the amendments added to it.Fixed WiMAX

This is a phrase frequently used to refer to systems built using 802.16-2004 (‘802.16d‘) and the OFDM PHY as the air interface technology. Fixed WiMAX deployments do not cater for handoff between Base Stations, therefore the service provider cannot offer mobility.

Mobile WiMAX

A phrase frequently used to refer to systems built using 802.16e-2005 and the OFDMA PHY as the air interface technology. “Mobile WiMAX” implementations can be used to deliver both fixed and mobile services.

Uses

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 broadband access.
  • Providing high-speed data and telecommunications services.
  • Providing a diverse source of Internet connectivity as part of a business continuity plan. That is, if a business has a fixed and a wireless Internet connection, especially from unrelated providers, they are unlikely to be affected by the same service outage.
  • Providing nomadic connectivity.

Broadband access

Many companies are closely examining WiMAX for “last mile” connectivity at high data rates. The resulting competition may bring lower pricing for both home and business customers or bring broadband access to places where it has been economically unavailable. Prior to WiMAX, many operators have been using proprietary fixed wireless technologies for broadband services.

WiMAX access was used to assist with communications in Aceh, Indonesia, after the tsunami in December 2004. All communication infrastructure in the area, other than Ham Radio, was destroyed, making the survivors unable to communicate with people outside the disaster area and vice versa. WiMAX provided broadband access that helped regenerate communication to and from Aceh.

WiMAX was used by Intel to assist the FCC and FEMA in their communications efforts in the areas affected by Hurricane Katrina.

Subscriber units

WiMAX subscriber units are available in both indoor and outdoor versions from several manufacturers. Self-install indoor units are convenient, but radio losses mean that the subscriber must be significantly closer to the WiMAX base station than with professionally-installed external units.

As such, indoor-installed units require a much higher infrastructure investment as well as operational cost (site lease, backhaul, maintenance) due to the high number of base stations required to cover a given area. Indoor units are comparable in size to a cable modem or DSL modem. Outdoor units are roughly the size of a laptop PC, and their installation is comparable to a residential satellite dish.

With the advent of mobile WiMAX, there is an increasing focus on portable units. This includes handsets (similar to cellular smartphones) and PC peripherals (PC Cards or USB dongles). In addition, there is much emphasis from operators on consumer electronics devices (games terminals, MP3 players and the like); it is notable this is more similar to WiFi than 3G cellular technologies.

Mobile applications

Some cellular companies are evaluating WiMAX as a means of increasing bandwidth for a variety of data-intensive applications; Sprint Nextel announced in mid-2006 that it would invest about US$ 5 billion in a WiMAX technology buildout over the next few years. As of Friday, November 9, 2007, this project in partnership with Clearwire has been shelved, but the project could be revived with or without Clearwire once Sprint hires a new CEO.

On December 5, 2007, Bin Shen, Sprint’s VP of Product Management and Partnership Development, announced that Sprint’s WiMAX network will go live in a soft launch in Chicago, Baltimore, and Washington DC. Full commercial launch is still expected to be approximately spring of 2008. In December 2007 Wateen Telecom Pakistan Deployed the largest and the first in the world to roll-out WiMAX 802.16e network nationwide in 22 cities. 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 per user/point of WiMAX in a remote application will be higher, it is not limited to such applications, and may 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 WiMAXWiMAX and its range. For countries that have skipped wired infrastructure as a result of prohibitive costs and unsympathetic geography, WiMAX can enhance wireless infrastructure in an inexpensive, decentralized, deployment-friendly and effective manner. 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 particularly suited to

Technical information

WiMAX is a term coined to describe standard, interoperable implementations of IEEE 802.16 wireless networks, similar to the way the term Wi-Fi is used for interoperable implementations of the IEEE 802.11 Wireless LAN standard. However, WiMAX is very different from Wi-Fi in the way it works.
Standards

The current WiMAX incarnation, Mobile WiMAX, is based upon IEEE Std 802.16e-2005, approved in December 2005. It is an amendment of IEEE Std 802.16-2004 and so the actual standard is 802.16-2004 as amended by 802.16e-2005 – the specifications need to be read together to understand them.

IEEE Std 802.16-2004 addresses only fixed systems. It replaced IEEE Standards 802.16-2001, 802.16c-2002, and 802.16a-2003.

IEEE 802.16e-2005

IEEE 802.16e-2005 improves upon IEEE 802.16-2004 by:

  • Adding support for mobility (soft and hard handover between base stations). This is seen as one of the most important aspects of 802.16e-2005, and is the very basis of ‘Mobile WiMAX’.
  • Scaling of the Fast Fourier Transform (FFT) to the channel bandwidth in order to keep the carrier spacing constant across different channel bandwidths (1.25-20 MHz). Constant carrier spacing results in a higher spectrum efficiency in wide channels, and a cost reduction in narrow channels. Also known as Scalable OFDMA (SOFDMA).
  • Improving NLOS coverage by utilizing advanced antenna diversity schemes, and hybrid-Automatic Retransmission Request (HARQ)
  • Improving capacity and coverage by introducing Adaptive Antenna Systems (AAS) and Multiple Input Multiple Output (MIMO) technology
  • Increasing system gain by use of denser sub-channelization, thereby improving indoor penetration
  • Introducing high-performance coding techniques such as Turbo Coding and Low-Density Parity Check (LDPC), enhancing security and NLOS performance
  • Introducing downlink sub-channelization, allowing administrators to trade coverage for capacity or vice versa
  • Enhanced Fast Fourier Transform algorithm can tolerate larger delay spreads, increasing resistance to multipath interference
  • Adding an extra QoS class (enhanced real-time Polling Service) more appropriate for VoIP applications.

802.16d vendors point out that fixed WiMAX offers the benefit of available commercial products and implementations optimized for fixed access. It is a popular standard among alternative service providers and operators in developing areas due to its low cost of deployment and advanced performance in a fixed environment. Fixed WiMAX is also seen as a potential standard for backhaul of wireless base stations such as cellular, WiFi or even Mobile WiMAX.

SOFDMA (used in 802.16e-2005) and OFDM256 (802.16d) are not compatible so most equipment will have to be replaced if an operator wants or needs to move to the later standard. However, some manufacturers are planning to provide a migration path for older equipment to SOFDMA compatibility which would ease the transition for those networks which have already made the OFDM256 investment. Intel provides a dual-mode 802.16-2004 802.16-2005 chipset for subscriber units. This affects a relatively small number users and operators.

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