Wimax, drives from the words "Worldwide Interoperability for Microwave Access" and is the system of wide area wireless connection that complies with IEEE 802.16 standard. It is still at the stage of improvement spread. Products with this technology make use of the licensed 2.5 GHz and 3.5 GHz frequency bands.

The main purpose of Wimax is to provide wireless network services in wide areas. It is designed to enable maximum 70 Mbps communication speed, depending on the distance, within a radius of up to 10 Km, depending on the antenna used. Connection is possible even if the antennas of the net work devices are not in the direct sight of each other. For this reason this feature stands up as an advantage especially at city centers.

A Comparison of Wimax & Wi-Fi

When compared with the, 802.11 a/b/g standard, wireless networks (Wi-Fi) widely used today it is seen that the bands used for Wimax brings about extra installation and running costs since it is subject to licensing, whereas the band used for Wi-Fi networks does not need any applications or licenses. This situation, however, makes Wimax advantageous as the products provide high power transmission without being susceptible to any negative interference from other devices broadcasting on the same band. The other important difference stems in the distances the signals can cover. While the Wimax devices can provide services in areas pronounced in kilometers, the distance for 802.11 a/b/g Wi-Fi devices is in the magnitude of 30 - 50 meters on the average. The recently developing 802.11n technology, which is foreseen as the future of 802.11 a/b/g networks, will serve much longer distances with much higher bandwidths, when it becomes the standard, compared to the classical Wi-Fi. Even so, distances that can be covered by 802.11n will be a lot less than that of Wimax. This advantage of Wimax, however, becomes secondary when the bandwidth, within its area of service it provides, is considered; it is much smaller compared to Wi-Fi networks. The bandwidth capacity of Wimax remains narrow, especially when set beside the 300 Mbps bandwidth of the 802.11n technology which is expected to be the standard by the end of 2009 and be compatible with the earlier 802.11a/b/g supporting devices.

Figure-1: Speed vs. Mobility for wireless technologies
(Resource: http://commons.wikimedia.org/wiki/File:Wimax-speed.jpg)

Considering the user; those who would wish to make use of the advantages of either the 802.11n or the Wimax have to procure extra hardware. Both technologies need self specific hardware. Here, the advantage of networks set with the 802.11n network infrastructure, that the Wimax does not have, is that all the network cards of the earlier 802.11 a/b/g technology runs with 802.11n type networking devices. So, the users who do not have the new hardware and thus cannot make use of the speed and coverage advantages of 802.11n are able to use the existing network cards, within their limited capacity, until they procure the additional hardware. In other words, the users can get services from networks set up with 802.11n even if they do not invest on any new hardware.

Today, the greatest obstacle for Wimax to be wide spread on the user side in Türkiye is that license allotment for the frequency band that Wimax devices operate in is not being granted and only trial licenses of six months period are provided for two times only. And in this situation the firms to set up Wimax infrastructure are reluctant to invest permanently and even if Wimax support exists on the user side the spread of the technology become difficult.

Today, 802.11 a/b/g/n cards are plentiful with reasonable pricing. Now, most of the newly produced laptop computers automatically come with these cards. The sale of Wimax featured devices and laptops are not so wide spread on the Wimax scene. The company Intel which is the largest chip producer for laptop computers has included both 802.11a/g/n and Wimax features on the recently produced chips. We can say that with the spread of these laptop computers Wimax technology may also take on momentum.

Work at METU

The Wimax trial set up work in METU started in the beginning of 2008 and was completed at the end of August and various trials have been carried out with the temporary six month license until it expired. Within the scope of this work, a central antenna on the roof of the CC and two more antennas on the 6^th dorm and METU MEMS (Micro-Electro-Mechanical Systems) facility were placed and coverage area and signal strength tests were conducted. Furthermore, data from various locations have been collected with a mobile antenna.

With the experiments we have done it has been assessed that an antenna placed at the CC roof can cover a wide area in METU but with a low speed and an even wider area if the antennas were in sight of each other. Getting a connection with the CC roof antenna from the bus stop region below the hill from the A4 gate of the (METU) campus where the antennas were in no position in sight of each other showed the possibility of getting connected even with the antennas not in sight of each other.

Conclusion

After the user side hardware becomes wide spread and the obstacles in getting a license for that frequency band are settled, Wimax can be regarded as an alternative to Wi-Fi technologies for providing mobile services for cases where reaching with cabling is especially difficult and taking under coverage the wider areas with Wi-Fi devices is costly. Bearing in mind that Wi-Fi technologies provide high bandwidth in a limited area and Wimax technologies provide wide area coverage but have low bandwidth, having Wimax infra structure set up in METU can provide users - who have Wimax hardware - with access to network services from outside buildings, at locations where Wi-Fi signal strength is poor and at locations that are not fully covered by Wi-Fi. Therefore Wimax can be considered as a supplement for Wi-Fi devices. It can provide net work services for field cameras, and for systems (transformers, generators, water pumps, heat exchangers, various hardware on roofs, traffic light automation etc.) that the substructure units have.

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