Overview WIMAX

wimax

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WiMAX (Worldwide Interoperability for Microwave Access) is a telecommunications protocol that provides fixed and fully mobile internet access. The current WiMAX revision provides up to 40 Mbit/s with the IEEE 802.16m update expected offer up to 1 Gbit/s fixed speeds. The name “WiMAX” was created by the WiMAX Forum, which was formed in June 2001 to promote conformity 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”.

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WiMAX base station equipment with a sector antenna and wireless modem on top

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    Terminology

WiMAX refers to interoperable implementations of the IEEE 802.16 wireless-networks standard (ratified by the WiMAX Forum), in similarity with Wi-Fi, which refers to interoperable implementations of the IEEE 802.11  Wireless LAN standard (ratified by the Wi-Fi Alliance). The WiMAX Forum  certification allows vendors to sell their equipment as WiMAX (Fixed or  Mobile) certified, thus ensuring a level of interoperability with other  certified products, as long as they fit the same profile.

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The IEEE 802.16 standard forms the basis of ‘WiMAX’ and is sometimes  referred to colloquially as “WiMAX”, “Fixed WiMAX”, “Mobile WiMAX”,  ”802.16d” and “802.16e.”Clarification of the formal names are as follow:

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  • 802.16-2004 is also known as 802.16d, which refers to the  working party that has developed that standard. It is sometimes referred  to as “Fixed WiMAX,” since it has no support for mobility.
  • 802.16e-2005, often abbreviated to 802.16e, is an amendment  to 802.16-2004. It introduced support for mobility, among other things  and is therefore also known as “Mobile WiMAX”.

 

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Mobile WiMAX is the WiMAX incarnation that has the most commercial  interest to date and is being actively deployed in many countries.

 Mobile WiMAX is also the basis of future revisions of WiMAX. As such,  references to and comparisons with “WiMAX” in this Wikipedia article  mean “Mobile WiMAX.

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 Uses

The bandwidth and range of WiMAX make it suitable for the following potential applications:

  • Providing portable mobile broadband connectivity across cities and countries through a variety of devices.
  • Providing a wireless alternative to cable and DSL for “last mile” broadband access.
  • Providing data, telecommunications (VoIP) and IPTV services (triple play).
  • Providing a source of Internet connectivity as part of a business continuity plan.
  • .Providing a network to facilitate machine to machine communications, such as for Smart Metering

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Broadband

Companies are deploying WiMAX to provide mobile broadband or at-home  broadband connectivity across whole cities or countries. In many cases  this has resulted in competition in markets which typically only had  access to broadband through an existing incumbent DSL (or alike)  operator.
Additionally, given the relatively low cost to deploy a WiMAX network  (in comparison to GSM, DSL or Fiber-Optic), it is now possible to  provide broadband in places where it may have not been economically  viable

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Back-haul

WiMAX is a possible replacement candidate for cellular phone technologies such as GSM and CDMA, or can be used as an overlay to increase capacity. Fixed WiMAX is also considered as a wireless backhaul technology for 2G, 3G, and 4G networks in both developed and developing nations.

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In North America, backhaul for urban cellular operations is typically provided via one or more copper wire  line T1 connections, whereas remote cellular operations are sometimes  backhauled via satellite. In most other regions, urban and rural  backhaul is usually provided by microwave links.

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))The exception to this is where the network is operated by an incumbent  with ready access to the copper network, in which case T1 lines may be  used). WiMAX is a broadband platform and as such has much more  substantial backhaul bandwidth requirements than legacy cellular  applications. Therefore, traditional copper wire line backhaul solutions  are not appropriate.

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Consequently the use of wireless microwave  backhaul is on the rise in North America and existing microwave backhaul  links in all regions are being upgraded.

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Capacities of between 34 Mbit/s and 1 Gbit/s[citation needed]  are routinely being deployed with latencies in the order of 1 ms. In  many cases, operators are aggregating sites using wireless technology  and then presenting traffic on to fiber networks where convenient.

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Triple-play

WiMAX supports the technologies that make triple-play service offerings possible (such as Quality of Service and Multicasting).
As a result, it is possible for a WiMAX operator to not only provide high-speed broadband internet access, but also VoIP and IPTV  services to customers with relative ease. This enables a WiMAX service  to be a replacement for DSL, Cable and Telephony services.

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On May 7, 2008 in the United States, Sprint Nextel, Google, Intel, Comcast, Bright House, and Time Warner announced a pooling of an average of 120 MHz of spectrum and merged with Clearwire  to form a company which will take the name Clear.

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The new company hopes  to benefit from combined services offerings and network resources as a  springboard past its competitors. The cable companies will provide media  services to other partners while gaining access to the wireless network  as a Mobile virtual network operator to provide triple-play services.

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Some analysts have questioned how the deal will work out: Although  fixed-mobile convergence has been a recognized factor in the industry,  prior attempts to form partnerships among wireless and cable companies  have generally failed to lead to significant benefits to the  participants.

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Other analysts point out that as wireless progresses to  higher bandwidth, it inevitably competes more directly with cable and  DSL, inspiring competitors into collaboration.

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Also, as wireless  broadband networks grow denser and usage habits shift, the need for  increased backhaul and media service will accelerate, therefore the  opportunity to leverage cable assets is expected to increase.

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 Rapid deployment

  • 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 amateur 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 hardware was donated by Intel Corporation to assist the Federal Communications Commission (FCC) and FEMA in their communications efforts in the areas affected by Hurricane Katrina. In practice, volunteers used mainly self-healing mesh, Voice over Internet Protocol (VoIP), and a satellite uplink combined with Wi-Fi on the local link.

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Connecting to WiMAX

A WiMAX Gateway which provides VoIP, Ethernet and WiFi connectivity

There are numerous devices on the market that provide connectivity to a WiMAX network. These are known as the “subscriber unit” (SU).
There is an increasing focus on portable units. This includes handsets (similar to cellular smartphones);  PC peripherals (PC Cards or USB dongles); and embedded devices in  laptops, which are now available for Wi-Fi services.

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In addition, there  is much emphasis by operators on consumer electronics devices such as  Gaming consoles, MP3 players and similar devices. It is notable that  WiMAX is more similar to Wi-Fi than to 3G cellular technologies.

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The WiMAX Forum website provides a list of certified devices.  However, this is not a complete list of devices available as certified  modules are embedded into laptops, MIDs (Mobile internet devices), and other private labeled devices

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WiMAX Gateways

WiMAX gateway devices are available as both indoor and outdoor  versions from several manufacturers. Many of the WiMAX gateways that are  offered by manufactures such as ZyXEL, Motorola, and Greenpacket  are stand-alone self-install indoor units. Such devices typically sit  near the customer’s window with the best WiMAX signal, and provide:

  • An integrated Wi-Fi access point to provide the WiMAX Internet connectivity to multiple devices throughout the home or business.
  • Ethernet ports should you wish to connect directly to your computer or DVR instead.
  • One or two PSTN telephone jacks to connect your land-line phone and take advantage of VoIP.

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Indoor gateways are convenient, but radio losses mean that the  subscriber may need to be significantly closer to the WiMAX base station  than with professionally-installed external units.

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Outdoor units are roughly the size of a laptop PC, and their installation is comparable to the installation of a residential satellite dish.  A higher-gain directional outdoor unit will generally result in greatly  increased range and throughput but with the obvious loss of practical  mobility of the unit.

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WiMAX Dongles

There are a variety of USB dongles on the market which provide  connectivity to a WiMAX network. Generally these devices are connected  to a notebook or netbook whilst on the go. Dongles typically have  omnidirectional antennae which are of lower-gain compared to other  devices, as such these devices are best used in areas of good coverage.

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WiMAX Mobiles

HTC announced the first WiMAX enabled mobile phone, the Max 4G, on Nov 12th 2008. The device was only available to certain markets in Russia on the Yota network.

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HTC released the second WiMAX enabled mobile phone, the EVO 4G, March 23, 2010 at the CTIA conference in Las Vegas. The device made available on June 4, 2010 is capable of both EV-DO(3G) and WiMAX(4G) as well as simultaneous data  & voice sessions. The device also has a front-facing camera  enabling the use of video conversations. A number of WiMAX Mobiles are expected to hit the US market in 2010.

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Technical information

 
Illustration of a WiMAX MIMO board

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WiMAX and the IEEE 802.16 Standard

The current WiMAX revision is based upon IEEE Std 802.16e-2005, approved in December 2005. It is a supplement to the IEEE Std 802.16-2004, and so the actual standard is 802.16-2004 as amended by 802.16e-2005.  Thus, these specifications need to be considered together.
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 (typically 1.25 MHz, 5 MHz,  10 MHz or 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). Other bands not  multiples of 1.25 MHz are defined in the standard, but because the  allowed FFT subcarrier numbers are only 128, 512, 1024 and 2048, other  frequency bands will not have exactly the same carrier spacing, which  might not be optimal for implementations.
  • Advanced antenna diversity schemes, and hybrid automatic repeat-request (HARQ)
  • Adaptive Antenna Systems (AAS) and MIMO technology
  • Denser sub-channelization, thereby improving indoor penetration
  • Introducing Turbo Coding and Low-Density Parity Check (LDPC)
  • Introducing downlink sub-channelization, allowing administrators to trade coverage for capacity or vice versa
  • Fast Fourier transform algorithm
  • Adding an extra QoS class for VoIP applications.

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SOFDMA (used in 802.16e-2005) and OFDM256 (802.16d) are not  compatible thus equipment will have to be replaced if an operator is to  move to the later standard (e.g., Fixed WiMAX to Mobile WiMAX).

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Physical layer

The original version of the standard on which WiMAX is based (IEEE 802.16)  specified a physical layer operating in the 10 to 66 GHz range.  802.16a, updated in 2004 to 802.16-2004, added specifications for the 2  to 11 GHz range.

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802.16-2004 was updated by 802.16e-2005 in 2005 and  uses scalable orthogonal frequency-division multiple access (SOFDMA) as opposed to the fixed orthogonal frequency-division multiplexing  (OFDM) version with 256 sub-carriers (of which 200 are used) in  802.16d. More advanced versions, including 802.16e, also bring multiple  antenna support through MIMO (See WiMAX MIMO).

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This brings potential benefits in terms of coverage, self installation,  power consumption, frequency re-use and bandwidth efficiency.

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MAC (data link) layer

The WiMAX MAC uses a scheduling algorithm  for which the subscriber station needs to compete only once for initial  entry into the network. After network entry is allowed, the subscriber  station is allocated an access slot by the base station.

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The time slot  can enlarge and contract, but remains assigned to the subscriber  station, which means that other subscribers cannot use it. In addition  to being stable under overload and over-subscription, the scheduling  algorithm can also be more bandwidth efficient.

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The scheduling algorithm also allows the base station to control Quality of service (QoS) parameters by balancing the time-slot assignments among the application needs of the subscriber stations.

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Deployment

As a standard intended to satisfy needs of next-generation data networks (4G),  WiMAX is distinguished by its dynamic burst algorithm modulation  adaptive to the physical environment the RF signal travels through.

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Modulation is chosen to be more spectrally efficient (more bits per OFDM/SOFDMA symbol). That is, when the bursts have a high signal strength and a carrier to noise plus interference ratio (CINR), they can be more easily decoded using digital signal processing  (DSP).

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In contrast, operating in less favorable environments for RF  communication, the system automatically steps down to a more robust mode  (burst profile) which means fewer bits per OFDM/SOFDMA symbol; with the  advantage that power per bit is higher and therefore simpler accurate  signal processing can be performed.

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Burst profiles are used inverse (algorithmically dynamic) to low  signal attenuation; meaning throughput between clients and the base  station is determined largely by distance. Maximum distance is achieved  by the use of the most robust burst setting; that is, the profile with  the largest MAC frame allocation trade-off requiring more symbols (a  larger portion of the MAC frame) to be allocated in transmitting a given  amount of data than if the client were closer to the base station.

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The client’s MAC frame and their individual burst profiles are  defined as well as the specific time allocation. However, even if this  is done automatically then the practical deployment should avoid high  interference and multipath environments. The reason for which is  obviously that too much interference causes the network function poorly  and can also misrepresent the capability of the network.

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The system is complex to deploy as it is necessary to track not only the signal strength and CINR (as in systems like GSM)  but also how the available frequencies will be dynamically assigned  (resulting in dynamic changes to the available bandwidth.) This could  lead to cluttered frequencies with slow response times or lost frames.

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As a result the system has to be initially designed in consensus with  the base station product team to accurately project frequency use,  interference, and general product functionality.

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Integration with an IP-based network


The WiMAX Forum WiMAX Architecture

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The WiMAX Forum has proposed an architecture that defines how a WiMAX  network can be connected with an IP based core network, which is  typically chosen by operators that serve as Internet Service Providers  (ISP); Nevertheless the WiMAX BS provide seamless integration  capabilities with other types of architectures as with packet switched  Mobile Networks.

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The WiMAX forum proposal defines a number of components, plus some of  the interconnections (or reference points) between these, labeled R1 to  R5 and R8:

  • SS/MS: the Subscriber Station/Mobile Station
  • ASN: the Access Service Network[17]
  • BS: Base station, part of the ASN
  • ASN-GW: the ASN Gateway, part of the ASN
  • CSN: the Connectivity Service Network
  • HA: Home Agent, part of the CSN
  • AAA: Authentication, Authorization and Accounting Server, part of the CSN
  • NAP: a Network Access Provider
  • NSP: a Network Service Provider

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It is important to note that the functional architecture can be  designed into various hardware configurations rather than fixed  configurations. For example, the architecture is flexible enough to  allow remote/mobile stations of varying scale and functionality and Base  Stations of varying size – e.g. femto, pico, and mini BS as well as  macros.

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Spectrum allocation

There is no uniform global licensed spectrum for WiMAX, however the  WiMAX Forum has published three licensed spectrum profiles: 2.3 GHz,  2.5 GHz and 3.5 GHz, in an effort to drive standardisation and decrease  cost.

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In the USA, the biggest segment available is around 2.5 GHz, and is already assigned, primarily to Sprint Nextel and Clearwire.  Elsewhere in the world, the most-likely bands used will be the Forum  approved ones, with 2.3 GHz probably being most important in Asia. Some  countries in Asia like India and Indonesia will use a mix of 2.5 GHz, 3.3 GHz and other frequencies. Pakistan’s Wateen Telecom uses 3.5 GHz.

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Analog TV bands (700 MHz) may become available for WiMAX usage, but await the complete roll out of digital TV, and there will be other uses suggested for that spectrum. In the USA the FCC auction for this spectrum  began in January 2008 and, as a result, the biggest share of the  spectrum went to Verizon Wireless and the next biggest to AT&T.

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Both of these companies have stated their intention of supporting LTE, a technology which competes directly with WiMAX. EU commissioner Viviane Reding has suggested re-allocation of 500–800 MHz spectrum for wireless communication, including WiMAX.

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WiMAX profiles define channel size, TDD/FDD  and other necessary attributes in order to have inter-operating  products. The current fixed profiles are defined for both TDD and FDD  profiles. At this point, all of the mobile profiles are TDD only. The  fixed profiles have channel sizes of 3.5 MHz, 5 MHz, 7 MHz and 10 MHz.  The mobile profiles are 5 MHz, 8.75 MHz and 10 MHz. (Note: the 802.16  standard allows a far wider variety of channels, but only the above  subsets are supported as WiMAX profiles.)

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Since October 2007, the Radio communication Sector of the  International Telecommunication Union (ITU-R) has decided to include  WiMAX technology in the IMT-2000 set of standards.

*This enables spectrum owners (specifically in the 2.5-2.69 GHz band at  this stage) to use WiMAX equipment in any country that recognizes the  IMT-2000.

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Spectral efficiency

One of the significant advantages of advanced wireless systems such as WiMAX is spectral efficiency. For example, 802.16-2004 (fixed) has a spectral efficiency of 3.7 (bit/s)/Hertz,  and other 3.5–4G wireless systems offer spectral efficiencies that are  similar to within a few tenths of a percent.

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The notable advantage of  WiMAX comes from combining SOFDMA with smart antenna  technologies. This multiplies the effective spectral efficiency through  multiple reuse and smart network deployment topologies.

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The direct use  of frequency domain organization simplifies designs using MIMO-AAS  compared to CDMA/WCDMA methods, resulting in more effective systems.

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Inherent Limitations

A commonly-held misconception is that WiMAX will deliver 70 Mbit/s  over 50 kilometers. Like all wireless technologies, WiMAX can either  operate at higher bitrates or over longer distances but not both:  operating at the maximum range of 50 km (31 miles) increases bit error rate  and thus results in a much lower bitrate. Conversely, reducing the  range (to under 1 km) allows a device to operate at higher bitrates.

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A recent city-wide deployment of WiMAX in Perth, Australia, has  demonstrated that customers at the cell-edge with an indoor CPE  typically obtain speeds of around 1–4 Mbit/s, with users closer to the  cell tower obtaining speeds of up to 30 Mbit/s.

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Like all wireless systems, available bandwidth is shared between  users in a given radio sector, so performance could deteriorate in the  case of many active users in a single sector. However, with adequate  capacity planning and the use of WiMAX’s Quality of Service, a minimum  guaranteed throughput for each subscriber can be put in place.

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In  practice, most users will have a range of 4-8 Mbit/s services and  additional radio cards will be added to the base station to increase the  number of users that may be served as required.

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Silicon implementations

A critical requirement for the success of a new technology is the availability of low-cost chipsets and silicon implementations.
WiMAX has a strong silicon ecosystem with a number of specialized  companies producing baseband ICs and integrated RFICs for implementing  full-featured WiMAX Subscriber Stations in the 2.3, 2.5 and 3.5Ghz band  (refer to ‘Spectrum allocation’ above).

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It is notable that most of the  major semiconductor companies have not developed WiMAX chipsets of their  own and have instead chosen to invest in and/or utilise the well  developed products from smaller specialists or start-up suppliers.

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These  companies include but not limited to Beceem, Sequans and PicoChip. The  chipsets from these companies are used in the majority of WiMAX devices.

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Intel Corporation  is a leader in promoting WiMAX, but has limited its WiMAX chipset  development and instead chosen to invest in these specialized companies  producing silicon compatible with the various WiMAX deployments  throughout the globe.

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Comparison with Wi-Fi

Comparisons and confusion between WiMAX and Wi-Fi are frequent because both are related to wireless connectivity and Internet access.

  • WiMAX is a long range system, covering many kilometres, that uses  licensed or unlicensed spectrum to deliver connection to a network, in  most cases the Internet.
  • Wi-Fi uses unlicensed spectrum to provide access to a local network.
  • Wi-Fi is more popular in end user devices.
  • Wi-Fi runs on the Media Access Control’s CSMA/CA protocol, which is connectionless and contention based, whereas WiMAX runs a connection-oriented MAC.
  • WiMAX and Wi-Fi have quite different quality of service (QoS) mechanisms:
    • WiMAX uses a QoS mechanism based on connections between the base  station and the user device. Each connection is based on specific  scheduling algorithms.
    • Wi-Fi 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.
  • Both 802.11 and 802.16 define Peer-to-Peer (P2P) and ad hoc networks, where an end user communicates to users or servers on another Local Area Network (LAN) using its access point or base station.  However, 802.11 supports also direct ad hoc or peer to peer networking  between end user devices without an access point while 802.16 end user  devices must be in range of the base station.

Wi-Fi and WiMAX are complementary. WiMAX network operators typically  provide a WiMAX Subscriber Unit which connects to the metropolitan WiMAX  network and provides Wi-Fi within the home or business for local  devices (e.g., Laptops, Wi-Fi Handsets, smartphones) for connectivity.

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This enables the user to place the WiMAX Subscriber Unit in the best  reception area (such as a window), and still be able to use the WiMAX  network from any place within their residence.

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Conformance testing

TTCN-3  test specification language is used for the purposes of specifying  conformance tests for WiMAX implementations. The WiMAX test suite is  being developed by a Specialist Task Force at ETSI (STF 252).

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Associations

WiMAX Forum

The WiMAX Forum is a non profit organization formed to promote the adoption of WiMAX compatible products and services.
A major role for the organization is to certify the interoperability of WiMAX products.

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Those that pass conformance and interoperability testing achieve the  ”WiMAX Forum Certified” designation, and can display this mark on their  products and marketing materials. Some vendors claim that their  equipment is “WiMAX-ready”, “WiMAX-compliant”, or “pre-WiMAX”, if they  are not officially WiMAX Forum Certified.
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Another role of the WiMAX Forum is to promote the spread of knowledge  about WiMAX. In order to do so, it has a certified training program  that is currently offered in English and French. It also offers a series  of member events and endorses some industry events.

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Competing technologies

Speed vs. Mobility of wireless systems: Wi-Fi, HSPA, UMTS, GSM

Within the marketplace, WiMAX’s main competition comes from existing, widely deployed wireless systems such as UMTS, CDMA2000, existing Wi-Fi and mesh networking.

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In the future, competition will be from the evolution of the major cellular standards to so-called 4G, high-bandwidth, low-latency, all-IP networks with voice services built on top. The worldwide move to 4G for GSM/UMTS and AMPS/TIA (including CDMA2000) is the 3GPP Long Term Evolution  effort.

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However, it has been noted that the likely performance  difference between WiMAX as it stands today and LTE when it is  eventually commercially available in 2–3 years time, will be negligible.[citation needed]

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LTE is expected to be ratified at the end of 2010, with commercial  implementations becoming viable within the next two years.. End of 2009  TeliaSonera started commercial deployment in Oslo and Stockholm, In  Denmark the 3 big telecoms are upgrading their network, and will make  LTE available during 2010.

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In some areas of the world, the wide availability of UMTS and a  general desire for standardization has meant spectrum has not been  allocated for WiMAX: in July 2005, the EU-wide frequency allocation for WiMAX was blocked.