WIMAX is Coming !
What is WIMAX?
WiMax is a new broadband wireless data communications technology based around the IEE 802.16 standard that will provide high speed data communications over a wide area. The letters of WiMax stand for Worldwide Interoperability for Microwave Access (X), and it is a technology for point to multipoint wireless networking. It is designed to help facilitate the install of a new high speed data network very cheaply without the cost and time required to install a wired network, It will greatly benefit those in rural areas needing fast access where wired solutions may not be viable because of the distances and costs involved in providing other 'last mile' services.
What about the WiMax Forum?
The WiMax Forum is a wireless industry consortium with over a hundred members including many industry leaders. It has been set up to support and develop WiMax technology worldwide.
One of the aims of the forum is to enable a standard to be adopted that will enable full interoperability between products. This is a different approcah from previous wireless standards. The WiMax Forum aims to prevent the errors of the earlier wireless standards 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".
WIMAX Interface
The IEEE 802.16 / HiperMAN WiMax standard allows data transmission using multiple broadband frequency ranges. The fact that the technology can work in multiple frequency ranges allows it to avoid interference with other wireless applications, thereby being able to operate satisfactorily in the presence of other transmissions. This will help to greatly reduce some of the problems with the earlier 802.11 standards.
The frequency bands that are chosen for a particular system affect a number of factors including the data rate that can be carried and the range that can be achieved. Thus it is possible to choose the frequency band to be used according to the prevailing conditions and the requirements for the system. The system designers wil have great flexibility in their planning designs.
WiMax technology uses a form of modulation known as Orthogonal Frequency Division Multiplex (OFDM). It is the fact that WiMax uses OFDM that enables it to occupy a wide bandwidth and carry the very high data rates. OFDM uses a large number of close spaced carriers, each modulated with a fraction of the data payload. The carriers are orthogonal to each other and in this way they do not interfere with each other, and in this way the bandwidth used by the overall signal is minimised and makes efficient use of the available spectrum. The other advantage is that if interference is present, either in the form of other signals, or multipath interference, then only a small number of the carriers will be affected. The data allocations are set up so that when this occurs the error correction systems are able to detect the errors and normally replace the corrupt data. How efficient this is in actual applications is still being studied, but early adopters will see a tremendous improvement over the protocols used previously and deployed currently by other broadband providers using 802.11 standards based equipment.
Frequencies used and speed of the resulting networks.
The basic 802.16 WiMax standard uses frequencies in the range 10 to 66 GHz, although extensions to the standard allow for the use of other frequencies. At these frequencies, particularly those in the range between 10 and 66 GHz, the transmission path is essentially line of sight. By having both transmitter and receiver in sight of each other the direct path can be taken and multipath reflections are reduced. This speeds the rate at which data can be sent.
When multiple paths are present because the signal is reflected, the total received signal is the sum of several signals that travel via different paths and over different lengths. This can cause problems in a number of ways. The first is that the signals arriving via the different paths will take a different amount of time such that they will tend to cancel each other out and the strength of the particular carrier is reduced. Another problem occurs when longer delays are experienced. Here the delays may mean that adjacent data symbols interfere, and the receiver cannot decipher the correct data to be decoded. Fortunately when using OFDM, the data rate of the modulation on each carrier is generally quite low and delays have to be significant for this to occur.
It can be seen that reducing multipath distortion enables a higher data rate to be carried. Theoretically WiMax 802.16 / HiperMAN can carry up to 75 Mbps in both the uplink and downlink directions, although in many instances speeds will be less.
WiMax applications
WiMax 802.16 / HiperMAN has a tremendous number of possible applications. The initial plans are to use WiMax as a point to multi-point broadband technology to provide individual users with access to broadband data services. In this way it would provide an attractive alternative to technologies such as DSL. Typically providers would want to limit the number of subscribers to any one base station to around 500 to preserve the bandwidth needed by each user. In this application it is unlikely that ranges will exceed 10 miles.
The maximum range of WIMAX is up to 31 miles. WiMax could achieve widespread use as provide a backbone for other services when no other 'last mile' service exists. WIMAX may also be used as part of the service providers' infrastructure. As it is anticipated that services will use directional antennas and in this way several services could share the same frequency bands with minimum levels of interference. The applications available through this technology will most likely insure quick adoption of the standards and a quick proliferation of the equipment.
Check back here in the next couple of weeks for updates