What is WiMAX ?

In the world of wireless networks WiMAX is a dominant technology. WiMAX (Worldwide Interoperability for Microwave Access) technology is a worldwide wireless networking standard that addresses interoperability across IEEE 802.16* standard-based product. WiMAX is a standards-based technology enabling the delivery of last mile wireless broadband access as an alternative to cable and DSL(Digital Subscriber Line).Mainly it is a telecommunications technology that provides wireless transmission of data using a variety of transmission modes, from point-to-multipoint links to portable and fully mobile internet access.

WiMAX in Bangladesh

Perspective of Bangladesh WiMAX technology is very effective, because Bangladesh is a small but largely populated country and rivers are situated here like a net. Buildup a cable network all over the country is very difficult because of those rivers. Though WiMAX technology is not cheap, but after installation its maintenance cost is low. So if we install it one time then cost becomes less. So country like Bangladesh can buildup network with WiMAX technology and can provide better service in telecommunication and high speed Internet.

Applications of WiMAX

The main application of WiMAX technology is transmition of data at high rate over a long distance. It is used for high speed broad band internet service. 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. It has also been considered as a wireless backhaul technology for 2G, 3G, and 4G networks in both developed and poor nations. Multi-player Interactive Gaming, VOIP and Video Conference are also some application of WiMAX technology

How WiMAX works ?

In practical terms, WiMAX would operate similar to WiFi but at higher speeds, over greater distances and for a greater number of users. WiMAX could potentially erase the suburban and rural blackout areas that currently have no broadband Internet accessbecause phone and cable companies have not yet run the necessary wires to those remote locations.WiMAX is designed to support high speed broadband services. It has two parts:
  WiMAX base station:      WiMAX base station is similar to a cellular network base station which consists of a  WiMAX tower and indoor electronics. Base station performs the MAC and PHY  features. It also handles the signaling and user scheduling. It is also responsible for uplink and downlink bandwidth management on a real time basis and frequency reuse.  
  WiMAX receiver: WiMAX receiver could be a WiMAX enabled computer, PCMCIA card, WiMAX modem, mobile internet devices or a standalone box. It works like a Wi-Fi network but in a broader coverage area.
            A WiMAX tower station can connect directly to the Internet using a high-bandwidth wired connection. It can also connect to another WiMAX tower using a line-of-sight, microwave link. This connection to a backhaul, along with the ability of a single tower to cover up to 3,000 square miles, is what allows WiMAX to provide coverage to remote rural areas. WiMAX actually can provide two forms of wireless service:There is the non-line-of-sight, where a small antenna on your computer connects to the tower. In this mode, WiMAX uses a lower frequency range 2 GHz to 11 GHz.Lower-wavelength transmissions are not as easily disrupted by physical obstructions,they are better able to diffract, or bend, around obstacles.
There is line-of-sight service, where a fixed dish antenna points straight at the WiMAX tower from a rooftop or pole. The line-of-sight connection is stronger and more stable, so it's able to send a lot of data with fewer errors. Line-of-sight transmissions use higher frequencies, with ranges reaching a possible 66 GHz. At higher frequencies, there is less interference and lots more bandwidth. WiFi-style access will be limited to a4-to-6 mile radius. Through the stronger line-of- sight antennas, the WiMAX transmitting station would send data to WiMAX enabled computers or routers set up within the transmitter's 30-mile radius. The fastest WiMAX handles up to 70 megabits per second, which, according to WiMAX proponents, is enough bandwidth to simultaneously support more than 60 businesses with T1-type connectivity and well over a thousand homes at 1Mbit/s DSL-level connectivity

Some drawbacks and Suggested Solutions of WiMax

There are some drawbacks of this Technology; we must consider those when going to the phase of implementation of this technology. Some important objections to WiMAX are:

Interference: The interference from other broadcasters may degrade the quality of the WiMAX service.

1. Quality of Service (QoS): Wireless is inherently unstable so this can affect voice and video services.

2. Security: As it is believed that Wireless medium is less secure so Security of WiMax can be big question.

3. Reliability: Also reliability of any wireless technology isn’t that much as compare to cable network, so reliability of Wimax can be a question too.

The solutions to these drawbacks are best understood through the Physical (PHY) and Medium Access Control (MAC) Layers. The WiMax Working Group no doubt were aware of these objections based on experiences with earlier wireless technologies (Wi-Fi, LMDS, MMDS,CDMA, GSM) and they made Wimax to fix failures of past wireless technologies.

Spectrum Allocation Problem

A major problem with WiMax is Spectrum Allocation; there are two main types of spectrum Allocation. Licensed and unlicensed, the unlicensed bands such as 2.4 GHz and 5.8 GHz, which are used for some applications, may reduce the performance and QoS of WiMax, which may affect the commercial viability of the service. And for the licensed bands 2.5 GHz and 3.5 GHz  bands, they are currently occupied by some other services such as fixed-satellite, broadcasting satellite, etc. in some countries. The scarcity of suitable spectrum for WiMax may not be a problem which can be satisfactorily resolved in the short term.

Peak to average power Ratio

One problem with OFDM systems is the high peak-to-average power Ratio (PAPR), which significantly reduces the efficiency of the transmitter high power amplifier (HPA). Many solutions have been suggested to reduce the peak power of OFDM signals. Using typical HPA models and spectral masks, these PAPR reduction methods are evaluated in terms of the total system degradation.

Limitation or disadvantages of WiMAX

One of the major problem with WiMax is Spectrum Allocation; there are two main types of spectrum Allocation. Licensed and unlicensed, the unlicensed bands such as 2.4 GHz and 5.8 GHz, which are used for some applications, may reduce the performance and QoS of WiMax, which may affect the commercial viability of the service. And for the licensed bands 2.5 GHz and 3.5 GHz bands, they are currently occupied by some other services such as fixed-satellite, broadcasting satellite, etc. in some countries. The scarcity of suitable spectrum for WiMax may not be a problem which can be satisfactorily resolved in the short term. 

 One problem with OFDM systems is the high peak-to-average power Ratio (PAPR), which significantly reduces the efficiency of the transmitter high power amplifier (HPA). Many solutions have been suggested to reduce the peak power of OFDM signals. Using typical HPA models and spectral masks, these PAPR reduction methods are evaluated in terms of the total system degradation.
 

Advantages of WiMAX

WiMAX technology can reach theoretically 30-mile coverage radius and achieve data rates up to 70 Mbps. This technology is very efficient, because it provide non-line-of-sight communication. As a result line-of-sight not needed between base station and user. WiMAX technology supports both of licensed and unlicensed frequency bands. There are some limitations of this technology that must be considered before implementation. WiMAX suffer from interference from other broadcasters of wireless devices. Wireless is inherently unstable so this can affect voice and video services. Also reliability of any wireless technology isn’t that much as compare to cable network, so reliability of WiMAX can be a question. As it is believed that Wireless medium is less secure so Security of WiMAX can be big question too. A commonly-held misconception is that WiMAX will deliver 70 Mbit/s over 50 kilometers (~31 miles). In reality, WiMAX can either operate at higher bitrates or over longer distances but not both: operating at the maximum range of 50 km increases bit error rate and thus results in a much lower bitrate. Conversely, reducing the range (to <1 km) allows a device to operate at higher bitrates.