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Wimax

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WIMAX

Ainda pouco conhecido no Mercado, o padrão wireless IEEE802.16 está a caminho de revolucionar a indústria de acesso de Broadband Wireless. O padrão 802.16 é também conhecido como a interface aérea da IEEE para Wireless MAN, isto é, da rede metropolitana sem fios. Esta tecnologia está sendo especificada pelo grupo do IEEE que trata de acessos de banda larga para última milha em áreas metropolitanas, com padrões de desempenho equivalentes aos dos tradicionais meios tais como DSL, Cable modem ou E1/T1.

A figura abaixo apresenta o posicionamento de cada um dos padrões de acesso wireless, mostrando do lado esquerdo o padrão IEEE e do lado direito o padrão ETSI equivalente.
 

Fonte: Intel

Originalmente, o padrão 802.16, que foi ratificado em Dezembro de 2001, estava focando basicamente as faixas de freqüências situadas entre 10GHz e 66GHz considerando sempre aplicações com linha de visada.

A versão 802.16a, que foi concluída em 2003, passou a focar as aplicações sem linha de visada, dentro das faixas de freqüência entre 2GHZ e 11GHZ, considerando também os aspectos de interoperabilidade. A tabela que se segue, apresenta a evolução das especificações do IEEE para a Wireless MAN.


IEEE 802.16
Dezembro de 2001 IEEE 802.16c
Dezembro de 2002 IEEE 802.16a
Janeiro de 2003 IEEE 802.16d
1º Trimestre de 2004
WIMAX IEEE 802.16e
4º Trimestre de 2004
10-66 GHz
Linha de visada
Até 34 Mbps (canalização de 28 MHz)
Interoperabilidade 2-11 GHZ
Sem linha de visada
Até 75Mbps
(canalização de 20 MHz) Modificações na 802.16a e interoperabilidade Mobilidade Nomândica
802.11/16
 
Wimax: Forum

O WIMAX Fórum (Worldwide Interoperability for Microwave Access) www.wimaxforum.org é uma organização sem fins lucrativos, formada por empresas fabricantes de equipamentos e de componentes, e tem por objetivo promover em larga escala a utilização de redes ponto multiponto, operando em freqüências entre 2GHz e 11GHz, alavancando a padronização IEEE 802.16 e garantindo a compatibilidade e interoperabilidade dos equipamentos que adotarem este padrão.

O WIMAX Fórum é o equivalente, ao Wi-Fi Alliance, responsável pelo grande desenvolvimento e sucesso do Wi-Fi em todo o mundo .

O WIMAX é constituído pelas indústrias líderes do setor, que estão comprometidas com as interfaces abertas e com a interoperabilidade entre os diversos produtos utilizados no Acesso Broadband Wireless:

O WIMAX pretende motivar um mercado de Acesso Broadband mais competitivo, através de um conjunto mínimo de especificações de performance da interface aérea entre os produtos dos diversos fabricantes, certificando os produtos que atendem a estas especificações.

•  Para os operadores de rede, esta interoperabilidade entre equipamentos significa a não dependência de um fornecedor para o desenvolvimento de sua rede.
•  Para os fabricantes de equipamentos significa menos tipos diferentes de produtos a desenvolver e a produzir.
•  Para os Fabricantes de componentes, significa uma escala de produção muito maior.
•  Para o usuário final significa acessos Broadband mais velozes e mais baratos.

Participantes:

Os participantes atuais do WIMAX Fórum estão relacionados a seguir:

Advantech AMT   l   AirXstream   l   Analog  Devices   l   Arris   l   AT&T   l   Axxcelera Broadband Wireless   l   Bandai Wireless   l   BeamReach Networks   l   Comtech AHA   l   Covad   l   CTS Communications Components   l   Cushcraft Corporation   l   Daintree Networks Inc.   l   Elcotez   l  Engim   l   Filtronics   l   First Avenue Networks    l   Gradiente Electronica S.A.   l   Inphi Corporation   l   Intracom   l   K&L Microwave   l   KarlNet   l  L3 PrimeWave  l Micom Labs   l   MTI   l   M-Web   l   NextWave Telecom   l  NextNet Wirelss   l   Nozema   l   Orthogon Systems   l   Pronto Networks   l  PCCW   l  picoChip   l  Radwin l  Remec l   SGS   l   Siemens Mobile   l   Unwired Australia   l   Vcom   l   Vyyo   l   ZTE  Corporation  

Wimax: Aplicações

O WIMAX irá facilitar o desenvolvimento de uma série de aplicações de Wireless Broadband, conforme a figura que se segue .

Fonte: WIMAX Forum

Estas aplicações são possíveis pelas seguintes características do WIMAX:

•  Fornecimento de link de dados de NxE1 (com garantia de banda).
•  Fornecimento de link de dados de fração de E1 (com garantia de banda).
•  Fornecimento de link de dados em um padrão equivalente ao ADSL /Cable Modem.
•  Portabilidade, isto é, o usuário pode transportar sua CPE (customer premise equipment) e utilizar o serviço em local diferente do usual.
•  Instalação da CPE no modo plug and play.
•  Cobertura sem linha de visada. 

Wimax: Características Técnicas

Modulação

O WIMAX apresenta três modos de operação, todos os três PHY, quais sejam: single carrier, OFDM 256, ou OFDMA 2K. O modo mais comumente utilizado é o OFDM 256 .

Throughput

Com o esquema de modulação robusto, o WIMAX entrega elevadas taxas de throughput com longo alcance e uma grande eficiência espectral e que é também tolerante às reflexões de sinais. A velocidade de transmissão dos dados varia entre 1 Mbps e 75 Mbps (cerca de 8 a 11Mbps para Pré WiMax), dependendo das condições de propagação, sendo que raio típico de uma célula WIMAX é de 6 Km a 9 Km .

Uma modulação dinâmica adaptativa permite que uma estação radio base negocie o throughput e o alcance do sinal. Por exemplo, se a estação radio base não pode estabelecer um link robusto com um assinante localizado a uma grande distância, utilizando o esquema de modulação de maior ordem, 64 QAM (Quadrature Amplitude Modulation), a modulação é reduzida para 16 QAM ou QPSK (Quadrature Phase Shift Keying), o que reduz o throughput , porém aumenta o alcance do sinal.

Escalabilidade

Para acomodar com facilidade o planejamento da célula WIMAX, tanto nas faixas licenciadas quanto nas não licenciadas, o 802.16a/d suporta diversas larguras de banda. Por exemplo, se um operador tem disponível 20 MHz de espectro, ele pode dividi-lo em dois setores de 10 MHz ou 4 setores de 5 MHz cada.

O operador pode crescer a quantidade de usuários mantendo um bom alcance do sinal e um bom throughput .

O operador pode reusar o mesmo espectro em dois ou mais setores, criando uma isolação entre as antenas da estação radio base.

Cobertura

O padrão 802.16 também suporta tecnologias que permitem a expansão de cobertura, incluindo as tecnologias de "smart antenna" assim como as tecnologias MESH.

Qualidade de Serviço

O padrão 802.16 apresenta qualidade de serviço que permite a transmissão de voz e vídeo, que requerem redes de baixa latência.

O MAC (Media Access Control) do 802.16 provê níveis de serviço "Premium" para clientes corporativos, assim como um alto volume de serviços em um padrão equivalente aos serviços hoje oferecidos pelos serviços de ADSL e de Cable Modem, tudo dentro da mesma estação radio base.

Segurança

Características de privacidade e criptografia estão previstos no padrão 802.16 permitindo transmissões seguras incluindo os procedimentos de autenticação.  

Wimax: Espectro Previsto

Oficialmente o padrão 802.16a/d está sendo estabelecido para faixa de freqüências entre 2GHz e 11 GHz, porém existe interesse de utilizá-lo também em bandas inferiores a 2GHz. Abaixo são relacionadas algumas das bandas, conforme definido pelo FCC dos Estados Unidos, que poderão ser utilizadas pelo padrão 802.16a/d.

UHF 0,75 - 0,8 GHZ -
ISM 0,9 - 0,93 GHZ Banda não licenciada, para utilização em aplicações industriais, científicas e médicas
UPCS 1,91 - 1,93 GHZ Banda não licenciada para utilização em serviços de comunicação pessoal
WCS 2,3 GHZ Wireless Communications Service
ISM 2,4 - 2,48 GHZ Banda não licenciada, para utilização em aplicações industriais, científicas e médicas
MMDS 2,5 - 2,7 GHZ Multi-Channel Multipoint Distribution Service
Internacional 3,4 - 3,7 GHZ 4,8 - 5,0 GHZ Banda licenciada na Europa, América Latina e Asia Banda licenciada no Japão
UNII 5,15 - 5,35; 5,725 - 5,85 GHZ Banda não licenciada, para uso do serviço nacional de informação de infra-estrutura
Novo Espectro 5,470 - 5,725 GHZ -
 
Wimax: Referências

Este tutorial apresentou o WIMAX, para aplicação nas Redes Broadband Metropoltanas Wireless-WMAN, utilizando as especificações do padrão IEEE 802.16.

Referências

•  IEEE 802.16 and WiMAX - Intel
•  WIMAX Fórum web page
•  802.16 and 802.11: The right technology in the right place - Jeff Orr - Proxim
•  802.16: Broadband Wireless Access: The Next Big thing in Wireless - Hassan Yaghoobi - Intel

   
WiMAX

WiMAX is defined as Worldwide Interoperability for Microwave Access by the WiMAX Forum, formed in April 2001 to promote conformance and interoperability of the IEEE 802.16 standard, officially known as WirelessMAN. 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 is not a technology, but rather a certification mark, or 'stamp of approval' given to equipment that meets certain conformity and interoperability tests for the IEEE 802.16 family of standards. A similar confusion surrounds the term Wi-Fi (Wireless Fidelity), which like WiMAX, is a certification mark for equipment based on a different set of IEEE standards from the 802.11 working group for wireless local area networks (WLAN). Neither WiMAX, nor Wi-Fi is a technology but their names have been adopted in popular usage to denote the technologies behind them. This is likely due to the difficulty of using terms like 'IEEE 802.16' in common speech and writing." - OECD [1]

Contents

1 Technical overview
2 Uses for WiMAX
2.1 Broadband Access
2.2 Mobile applications
3 Spectrum Allocations for WiMAX
4 Standards
4.1 IEEE 802.16e
4.2 HIPERMAN
4.3 WiBro
5 WiMAX Forum
6 Competing technologies
6.1 UMTS
6.2 EV-DO
6.3 Wi-Fi
7 External links

Technical overview

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

In Wi-Fi, the media access controller ("MAC") 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 distant nodes from the AP to be repeatedly interrupted by closer nodes, greatly reducing their throughput. This makes services such as Voice over IP (VoIP) or IPTV, which depend on a predetermined type of "quality of service" (QoS), difficult to maintain for large numbers of users.

In contrast, the 802.16 MAC uses a scheduling algorithm, where the subscriber station only has to compete once (for initial entry into the network). After that it is allocated a time slot by the base station. The time slot can enlarge and contract, but it remains assigned to the subscriber station, meaning that other subscribers cannot use it. This scheduling algorithm is stable under overload and over-subscription (unlike 802.11). It can also be more bandwidth efficient. The scheduling algorithm also allows the base station to control Quality of Service parameters by balancing the time-slot assignments among the application needs of the subscriber stations.

The original WiMAX standard (IEEE 802.16) specified WiMAX in the 10 to 66 GHz range. 802.16a, updated in 2004 to 802.16-2004 (also known as 802.16d), added support for the 2 to 11 GHz range. 802.16d was updated to 802.16e in 2005. 802.16e uses scalable orthogonal frequency-division multiplexing (OFDM) as opposed to the non-scalable version in .16d. This brings potential benefits in terms of coverage, self installation, power consumption, frequency re-use and bandwidth efficiency. .16e also adds a capability for full mobility support.

Most interest will probably be in the 802.16d and .16e standards, since the lower frequencies suffer less from signal attenuation and therefore give improved range and in-building penetration.

The WiMAX specification improves upon many of the limitations of the Wi-Fi standard by providing increased bandwidth and range and stronger encryption. It provides connectivity between network endpoints without need for direct line of sight in favourable circumstances. The non-line-of-sight propagation (NLOS) performance requires the .16d or .16e variants, since the lower frequencies are needed. It relies upon clever use of multi-path signals.


Uses for WiMAX

A commonly held misconception is that WiMAX will deliver 70 Mbit/s, over 70 miles. Each of these may be true individually, given ideal circumstances, but they are not simultaneously true. WiMAX has some similarities to DSL in this respect, where one can either have high bandwidth or long reach, but not both simultaneously. The other feature to consider with WiMAX is that the bandwidth is shared between users in a given radio sector, so if there are many active users in a single sector, each will get reduced bandwidth.

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 (last km) broadband access.
Providing high-speed mobile data and telecommunications services (4G)

Broadband Access

Many cable and traditional telephone companies are closely examining or actively trialling the potential of WiMAX for "last mile" connectivity. This could result in better price-points for both home and business customers as based on the benefits of competition. In areas without pre-existing physical cable or telephone networks, WiMAX could allow broadband access that has hitherto been unavailable. Home units the size of a paperback book that provide both phone and network connection points are already available and easy to install.


Mobile applications

There is potential for using WiMAX with legacy cellular networks. WiMAX antennas can "share" a cell tower without compromising the function of cellular arrays already in place. Some cellular companies are evaluating WiMAX as a means of increasing bandwidth for a variety of data-intensive applications; indeed, Sprint/Nextel has announced in mid-2006 that it will be investing about US$ 3 billion in a WiMAX technology buildout over the next few years. 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-effectiveness of WiMAX in a remote application will be higher, it is definitely not limited to such applications, and may in fact be an answer to reducing the cost of T1/E1backhaul as well. Given the limited wired infrastructure in some developing countries, the costs to install a WiMAX 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 particularily suited to WiMAX and its range. For countries that have skipped wired infrastructure as a result of inhibitive costs and unsympathetic geography, WiMAX can enhance wireless infrastructure in an inexpensive, decentralized, deployment-friendly and effective manner.


Spectrum Allocations for WiMAX

The 802.16 specification applies across a wide swath of RF spectrum. However, specification is not the same as permission to use! There is no uniform global licensed spectrum for WiMAX. In the US, the biggest segment available is around 2.5 GHz, and is already assigned, primarily to Sprint Nextel, along with Clearwire in more rural areas. Elsewhere in the world, the most likely bands used will be around 3.5 GHz, 2.3/2.5 GHz, or 5 GHz, with 2.3/2.5 GHz probably being most important in Asia.

There is some prospect in the U. S. that some of a 700 MHz band might be made available for WiMAX use, but it is currently assigned to analog TV and awaits the complete rollout of digital TV before it can become available, likely by 2009. In any case, there will be other uses suggested for that spectrum if and when it actually becomes open.

It seems likely that there will be several variants of 802.16, depending on local regulatory conditions and thus on which spectrum is used, even if everything but the underlying radio frequencies is the same. WiMAX equipment will not, therefore, be as portable as it might have been - perhaps even less so than WiFi, whose assigned channels in unlicensed spectrum varies little from jurisdiction to jurisdiction.

The actual radio bandwidth of spectrum allocations is also likely to vary. Typical allocations are likely to provide channels of 5 MHz or 7 MHz. In principle the larger the bandwidth allocation of the spectrum, the higher the bandwidth that WiMAX can support for user traffic.


Standards

The current 802.16 standard is IEEE Std 802.16e-2005, approved in December 2005. It followed on from IEEE Std 802.16-2004, which replaced IEEE Standards 802.16-2001, 802.16c-2002, and 802.16a-2003.

IEEE Std 802.16-2004 (802.16d) addresses only fixed systems. 802.16e adds mobility components to the standard.


IEEE 802.16e

IEEE 802.16-2005 (formerly named, but still best known as, 802.16e or Mobile WiMAX) provides an improvement on the modulation schemes stipulated in the original (fixed) WiMAX standard. It allows for fixed wireless and mobile Non Line of Sight (NLOS) applications primarily by enhancing the OFDMA (Orthogonal Frequency Division Multiple Access).

SOFDMA improves upon OFDM256 for NLOS applications by:

Improving NLOS coverage by utilizing advanced antenna diversity schemes, and hybrid-Automatic Retransmission Request (hARQ)
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
Improving coverage by introducing Adaptive Antenna Systems (AAS) and Multiple Input Multiple Output (MIMO) technology
Eliminating channel bandwidth dependencies on sub-carrier spacing, allowing for equal performance under any RF channel spacing (1.25-14 MHz)
Enhanced Fast Fourier transform (FFT) algorithm can tolerate larger delay spreads, increasing resistance to multipath interference
SOFDMA and OFDMA256 are not compatible so most equipment will have to be replaced. 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 OFDMA256 investment.


HIPERMAN

The equivalent of 802.16 in Europe is HIPERMAN. The WiMAX Forum is working to ensure that 802.16 and HIPERMAN inter-operate seamlessly.


WiBro

Korea's telecoms industry has developed its own standard, WiBro. In late 2004, Intel and LG Electronics have agreed on interoperability between WiBro and WiMAX.

WiBro has South Korean government support with the requirement for each carrier to spend over US$1 billion for deployments. The Koreans sought to develop WiBro as a regional and potentially international alternative to 3.5-4G systems. But given the lack of self-developed momentum as a standard, WiBro has joined WiMAX and agreed to harmonize with the similar OFDMA 802.16e version of the standard. What makes WiBro roll-outs, which will start in April 2006, a good 'test case' for the overall WiMAX effort is that it is mobile, well thought out for delivery of wireless broadband services, and the fact that the deployment is taking place in a highly sophisticated, broadband-saturated market. WiBro will go up against 3G and very high bandwidth wire-line services rather than as gap-filler or rural under-served market deployments as is often exampled as the 'best fit' markets for WiMAX.


WiMAX Forum
WiMAX Forum logo

The WiMAX Forum is "the exclusive organization dedicated to certifying the interoperability of BWA products, the WiMAX Forum defines and conducts conformance and interoperability testing to ensure that different vendor systems work seamlessly with one another." Those that pass conformance and interoperability testing achieve the "WiMAX Forum Certified" designation and display this mark on their products and marketing materials. Vendors claiming their equipment is "WiMAX-ready", "WiMAX-compliant", or "pre-WiMAX" are not WiMAX Forum Certified, according to the Forum.


Competing technologies

WiMAX is a framework for wireless development based on a forward-looking core set of technologies. More recently 3GPP cellular's 4G, 802.22 Cognitive Radio RAN (Rural Area Network), and 802.20, the High Speed Mobile Broadband Wireless Access (MBWA) Working Group, have shifted toward use of similar constructs of multi-channel scalable OFDM, HARQ, FEC, MIMO-AAS and other complementary technologies as are part of WiMAX.


UMTS

For some applications, UMTS could be a direct competitor to WiMAX. UMTS has been deployed in Europe and elsewhere mostly by Mobile Telephone operators. The HSDPA technology enables down-link with data transmission up to 8-10 Mbit/s (see above for comparison). UMTS also provides a circuit channel optimized for voice and video traffic. In July 2005 EU frequency allocation for WiMAX was blocked by France and Finland, where manufacturers have invested heavily in UMTS technology.

The most recent 3GPP standardization activities are development of advanced systems based on OFDM rather than CDMA. The 3G Long Term Evolution (LTE) platform will be based on MIMO-OFDM similar to WiMAX/802.16e-2005.


EV-DO

Evolution-Data Optimized is a wireless radio broadband data standard adopted by many CDMA mobile phone service providers around the globe. It is standardized by3GPP2, as part of the CDMA family of standards.


Wi-Fi

Wi-Fi is a Wireless Local Area Network (LAN) technology that works in unlicensed spectrum, using the 2.4GHz and 5 GHz bands. Wi-Fi is a cheap and easy way of providing local connectivity at high speed. WiMAX uses licenced spectrum and has strong authentication mechanisms built in. It has considerably greater range than Wi-Fi. Taken together, this means that WiMAX and Wi-Fi are generally complementary rather than competing.