what is a wimax ?
- Posts : 38
Reputation : 7
Join date : 2009-11-22
WiMAX is an IP based, wireless broadband access technology that provides performance similar to 802.11/Wi-Fi networks with the coverage and QOS (quality of service) of cellular networks. WiMAX is also an acronym meaning "Worldwide Interoperability for Microwave Access (WiMAX).
WiMAX is a wireless digital communications system, also known as IEEE 802.16,(live example in-foris and Broadband uganda) that is intended for wireless "metropolitan area networks". WiMAX can provide broadband wireless access (BWA) up to 30 miles (50 km) for fixed stations, and 3 - 10 miles (5 - 15 km) for mobile stations. In contrast, the WiFi/802.11 wireless local area network standard is limited in most cases to only 100 - 300 feet (30 - 100m).
With WiMAX, WiFi-like data rates are easily supported, but the issue of interference is lessened. WiMAX operates on both licensed and non-licensed frequencies, providing a regulated environment and viable economic model for wireless carriers.
At its heart, however, WiMAX is a standards initiative. Its purpose is to ensure that the broadband wireless radios manufactured for customer use interoperate from vendor to vendor. The primary advantages of the WiMAX standard are to enable the adoption of advanced radio features in a uniform fashion and reduce costs for all of the radios made by companies, who are part of the WiMAX Forum™ - a standards body formed to ensure interoperability via testing. The more recent Long Term Evolution (LTE) standard is a similar term describing a parallel technology to WiMAX that is being developed by vendors and carriers as a counterpoint to WiMAX.
What is the Range of WiMAX?
The answer to this question probably generates more confusion than any other single aspect of WiMAX. In the early days of WiMAX it was common to see statements in the media describing WiMAX multipoint coverage extending 30 miles. In a strict technical sense (in some spectrum ranges) this is correct, with even greater ranges being possible in point to point links. In practice (and especially in the license-free bands) this is wildly overstated especially where non line of sight (NLOS) reception is concerned.
Due to a variety of factors explained in more detail in other FAQ answers, the average cell ranges for most WiMAX networks will likely boast 4-5 mile range (in NLOS capable frequencies) even through tree cover and building walls. Service ranges up to 10 miles (16 Kilometers) are very likely in line of sight (LOS) applications (once again depending upon frequency). Ranges beyond 10 miles are certainly possible, but for scalability purposes may not be desirable for heavily loaded networks. In most cases, additional cells are indicated to sustain high quality of service (QOS) capability. For the carrier class approach, especially in regards to mobility, cells larger than this seem unlikely in the near future. The primary WiMAX focused US carrier Clearwire has stated that its cell sites are planned at about 1.5 miles apart for mobile purposes. This choice is clearly one intended to meet NLOS requirements. In licensed frequencies, expect similar performance or better for WiMAX than in traditional cellular systems.
What RF Frequencies does WiMAX work in?
The most recent versions of both WiMAX standards in 802.16 cover spectrum ranges from at least the 2 GHz range through the 66 GHz range. This is an enormous spectrum range. However, the practical market considerations of the Forum members dictated that the first product profiles focus on spectrum ranges that offered Forum vendors the most utility and sales potential.
The International standard of 3.5 GHz spectrum was the first to enjoy WiMAX products. The US license free spectrum at 5.8 GHz has a few WiMAX vendors building products. Licensed spectrum at 2.5 GHz used both domestically in the US and fairly widely abroad is the largest block in the US. Also, in the US and in Korea products are shipping for the 2.3 GHz spectrum range. Also in the US the 3.65 GHz band of frequencies now has WiMAX gear shipping to carriers.
The technology appears easily extensible to lower frequencies including the valuable 700 MHz spectrum range at which the nation's largest auction (in terms of money spent) concluded in 2008. More likely near term frequencies likely to be supported include the new 4.9 GHz public safety band (sometimes described as a Homeland security band).
The second largest block of frequencies ever auctioned (in terms of money spent) occurred in the summer of 2006 with the AWS auction from the FCC. This spectrum was split with the bulk being at 1.7 GHz and the rest at 2.1 GHz. At this point, the Forum is not expected to develop a product profile for this range as most licensees have announced support for LTE systems or plan to use it for existing GSM/UMTS networks.
The physics of radio signals typically place two primary constrictions on spectrum. To generalize, the higher the spectrum frequency the greater the amount of bandwidth that can be transported---lower frequencies transport less bandwidth. Secondly, the lower the frequency the greater the carry range and penetration of a signal. For example: A 900 MHz license free radio will travel farther and penetrate some tree cover fairly easily at ranges up to one to two miles. But it can carry much less bandwidth than a 2.4 GHz signal which cannot penetrate any tree cover whatsoever, but can deliver a lot more data. The caveat that can somewhat alter this equation is power. Licensed band spectrum such as 2.5 GHz by virtue of being dedicated to one user is allotted significantly higher power levels which aids in tree and building wall penetration.
Where did the idea of WiMAX come from?
Much of the credit for the formation of the WiMAX Forum™ and to the founding members of the WiMAX Forum, which committed themselves early to the process of creating a collaborative standards body. As a founding member of the WiMAX Forum, Intel recognized that a well developed ecosystem was necessary to drive adoption and thereby drive lower hardware costs. Intel was also instrumental in getting other silicon chip manufacturers involved whose products would form the core of WiMAX technology.
What factors will most greatly affect range for WiMAX products?
Many factors affect range for any broadband wireless product. Some factors include the terrain and density/height of tree cover. Hills and valleys can block or partially reflect signals. Bodies of water such as rivers and lakes are highly reflective of RF transmissions. Fortunately OFDM can often turn this to an advantage---but not always. The RF shadow of large buildings can create dead spots directly behind them, particularly if license-free spectrums are being used (with their attendant lower power allotments). How busy the RF environment of a city or town is can greatly degrade signals---meaning that properly designed and well thought out networks are always desired.
The physics of radio transmission dictate that the greater the range between the base station and customer radio, the lower the amount of bandwidth that can be delivered, even in an extremely well-designed network. The climate can affect radio performance---despite this there are ubiquitous wireless networks deployed today with great success in frozen Alaskan oil fields as well as lush South American and Asian climates. And increasingly WiMAX radio antenna technology coupled with the inherent advantages of OFDM/OFDMA based radios can be a major factor in range and bandwidth capability. The new multiple input multiple output (MIMO) and adaptive antenna systems (AAS) based antenna systems promise to maintain and even link connection and link budgets with much higher bandwidth than older technology.
No two cities are exactly alike in terms of the challenges and opportunities presented. In many respects, broadband wireless remains very much an art form. However, this is also true for the cellular carriers most of us use daily. It can be done quite well. Mobile broadband wireless will be more difficult. Achieving high quality of service (QOS) will be easier with fixed broadband wireless. Despite all of these challenges, current broadband wireless is very effectively serving customers even in the most challenging environments.
- Posts : 129
Reputation : 6
Join date : 2009-11-29
Permissions in this forum:You cannot reply to topics in this forum