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WiMAX, which stands for Worldwide Interoperability for Microwave Access, is a new technology which has been under development since 1991 and aims to provide "point-to-multipoint wireless networking" . This new technology is aiming to solve network problems which are faced with the computer communication technology used today, the Wi-Fi (IEEE 802.11) These problems are mostly concentrating in terms of security (where WLAN is considered rather vulnerable)  and of course in order to provide services to areas which lack infrastructure for broadband services or to remote and/or rural areas where provides hesitate to provide their services since it is not profitable for them .
WiMAX is the developing technology which can provide extremely high speed network connections by the use transceivers to user's antennas. The protocol that WiMAX is based on is the IEEE 802.16 protocol which supports a variety of transport technologies such as IPv4, IPv6, Ethernet and asynchronous transfer mode .
Contrast between Wireless Broadband Access and IEEE 802.16
In order to understand better the improvements and differences that WiMAX has to offer, one should compare the previous technology and compare them. In the Wi-Fi technology and the IEEE 802.11 standards, the wireless broadband access is configured within cellular systems with a "central" (this is not always the case) Base Station which covers a large area (of few kilometers) . The antenna of the Base Station can be situated anywhere, whether on a tall building or a tower or any tall infrastructure. In order for a user to achieve connectivity, he or she must obtain a premise unit so the connectivity can be achieved. This connectivity may be possible either by routing the signal with an Ethernet cable either straight to a computer, or connecting the user via Wi-Fi (802.11) or a Wired Ethernet Lan .
The design of IEEE 802.16 as aforementioned is designed to offer point-to-multipoint broadband wireless access. What is most important though, in order to achieve transmission, is the requirement of Line of Sight (LoS). Furthermore, IEEE 802.16 operates in a spectrum of 10-66 GHz (though there are several types of IEEE 802.16 which will be briefly mentioned in a later stage) and determines the Physical Layer (PHY) and the Medium Access Control (MAC) of the Broadband Wireless Access .The Broadband Wireless Access (BWA) is the way a range of fixed radio systems are transporting and delivering broadband services; services between users' location and the main networks .
The evolution of WiMAX can offer high speed and low cost broadband wireless access. In addition, it can be flexible to future changes (extending and improving the fiber-optic infrastructure) and also what is very important, it can easily be deployed. The Base Station of a WiMAX can cover up to 5 kilometers and providing bandwidth up to 70Mbps, as long Line of Sight is possible  . Furthermore, the WiMAX is being modified and altered in order to cover Non-Line-of-Sight applications ("in licensed and unlicensed bands in the sub 11 GHz frequency range") .
IEEE 802.16 Extensions
The IEEE.16 Working Group has proceeded in several extensions of the initial standard in order to provide some improvements needed for the better use of the IEEE 802.16.
IEEE 802.16a: The reason for this development is for the use of licensed lower frequencies (from 2-11GHz) which will resolve the issue of Line of Sight. Lower frequencies can penetrate obstacles therefore no Line of Sight is needed between the transceiver and the receiver (antenna). The basic transmission range (of the IEEE 802.16) can be extended with the capability of one transceiver being able to pass on communication to other transceivers.
IEEE 802.16b: With IEEE 802.16b, the 5 and 6GHz frequency band spectrum is increased, and offers QoS (Quality of Service) which guarantees transmission which may have priority such as real time voice and video.
IEEE 802.16c: This extension standardizes more details of the IEEE 802.16 in the frequency bands between 10 - 66GHz. This way it may be maintained more reliable implementation and in addition interoperability.
IEEE 802.16d: The specific extension only gives minor improvements and fixes to the 802.16a and also creates system profiles for compliance testing of 802.16a devices.
IEEE 802.16e: it's the extension which aims to offer standardization in networking between base stations and mobile devices (instead of just static users). This would be possible by providing high-speed signal handoffs which are extremely necessary when users are on the move .
Major Principles of WiMAX network
WiMax is using two MAC system profiles; one is the Asynchronous Transfer Mode (ATM) transport protocol and the other is the basic IP. In addition, two basic PHY system profiles have been defined; one of the United States, which uses the 25 MHz wide channel in 10,66 GHz range and one for Europe, which uses the 28MHz wide channel in the 10,66 GHz range.
The main principles of the WiMAX network are the following:
Spectrum: can be deployed in licensed but also unlicensed spectra.
Topology: can support various Radio Access Network (RAN) topologies.
Interworking: unified integration via independent Radio Access Network to support and interwork with WiFi, 3GPP and 3GPP2 networks and IP operator core network.
IP Connectivity: can support IPv4 and IPv6 joined networks in clients and application servers.
Mobility Management: may also provide services to fixed access but also deliver services to mobile and broadband multimedia .
Architecture of WiMAX Technology
The architecture of WiMAX can be divided in three units. One is the Mobile Station (MS), the second is the Access Service Network (ASN) and the third is the Connectivity Service Network (CSN). Its main goal is to provide a mixed support to a range of network models. All the aforementioned units interconnect with a reference point and may be either grouped into functional entities which can be either single or distributed physical devices over a variety of other physical devices; this depends on the choice made on implementation. This choice is up to the manufacturer who may decide whether an implementation should be individual or combined.
The three main entities in more details are:
Base Station (BS): it is the unit responsible to provide air interface with the Mobile Station (MS). It is also responsible for handoffs, radio resource supervision, and classification of traffic, DHCP, session and multicast management.
Access Service Network (ASN): is the unit responsible for connecting users to their service provider. It includes one or maybe more Base Stations and one or more Access Service Network Gateways to form the RAN (Radio Access Network). In one hand the Access Service Network is connected with several Mobile Stations while on the other side is connected with the IP Network.
Connectivity Service Network (CSN): it is a set of functions which are responsible into connecting WiMAX clients with the network by offering IP services. It may include servers, routers and gateway devices and so on in order to support authentication either of the user or to other devices and/or services. It also supports roaming, IP addresses and location management and also mobility between Access Service Networks .
WiMAX Reference Network
Wireless Services of WiMAX
The WiMAX can provide two wireless services which are the Non-Line-of-Sight and the Line-of-Sight services.
Non-Line-of-Sight: With the Non-Line-of-Sight service, the user connects via a small antenna attached to his/hers personal computer to a tower. This service is similar to Wi-Fi. In order to achieve that, WiMAX is using frequency ranges from 2GHz up to 11GHz. The reason why lower frequencies are used is because lower frequencies transmissions to not get easily disturbed by any physical obstacles that might be in the way of transmission. Lower frequency transmissions are easily diffracted on obstacles or go around physical obstacles .
Line-of-Sight: in this service, there are stronger and more stable connections which are possible by pointing a fixed dish antenna to the WiMAX tower. This way there is a reduction in the number of errors during transmission while the number of data is far greater. Unlike the Non-Line-of-Sight, in this service, the range of frequency bands used goes up to 66GHz. One huge benefit of higher frequencies is the extremely low interfere that someone might get and in addition, the achievement of having a lot more bandwidth. Another significant benefit of WiMAX is the range of coverage that can cover which goes up to 9,300 square kilometers of coverage with Line-of-Sight service in contradiction of the 65 square kilometers of range that the Wi-Fi is offering .
The Architecture of IEEE 802.16
The IEEE 802.16 standard includes a stack of protocols with interfaces witch are precise. In the Medium Access Control Layer we meet three sub layers; the Service Specific Convergence Sub layer (MAC CS), the MAC Common Part Sub layer (MAC CPS) and the privacy sub layer.
The Service Specific Convergence Sub Layer allows communication with higher layers and the transformation of higher-level data services to MAC Layer service flows and connections. The two types met in a Convergence Sub Layer are the Asynchronous Transfer Mode (ATM CS) used as implied to ATM networks and services while the second type is the Packet Convergence Sub layer which is responsible for services using packets (Ethernet, Point to Point Protocol, IP version 4 and 6 and also Virtual LANs) .
Moving on to the MAC Common Part Sub layer (MAC CPS), can be described as the heart of the 802.16 standard. Here there is a variety of rules dictated which deal with connection management, bandwidth allocation and system access mechanisms. In addition, other functions are met in MAC CPS such as uplink scheduling, bandwidth request, connection control and so on. The MAC Service Access Point (MAC SAP) is responsible for the communication of CS and MAC CPS. In order to achieve this communication between the two, four steps must be followed; creating a connection, modifying it, deleting it and transport the data over the connection .
The Privacy Sub Layer is the sub layer dividing the MAC CPS and the Physical Layer (PHY). The Privacy Sub layer is the one responsible for data encryption and decryption when entering or leaving the Physical Layer. It is also responsible for secure key-exchange and authentication (Either using 56-bit DES encryption or AES) .
Moving lower to the Physical Layer, it is important to notice that since many modes are supported, therefore, the protocol must be adjustable and flexible to changes by designers when it comes to controlling the multiplexing. So the Physical Layer can sustain more changes in comparison with the rest of the standard .
Why Using WiMAX?
So what makes WiMAX so special? Well, the answer is simple; WiMAX can give solutions in a variety of access needs. It can be for sure more affordable for subscribers, with less cabling and much better speeds and bandwidth and also security. It can be based in the already existing infrastructure, which means no excessive cost for subscribers (since they do not have to discard their current infrastructure because WiMAX can interoperate between different types of networks) while at the same time they can enjoy a full range of high value multimedia services by the supported bandwidth .
Another huge plus of WiMAX is that it can provide a better and larger area coverage with full services such as Voice over IP (VoIP), video conferencing, non-real times downloads; and all these with the best performance ensured.
Last but not least, the WiMAX is the evolution of the 3G in mobile phones; with the combination of WiMAX and CDMA standards, the next step can be ensured to the fourth generation mobile phones communications; to what is known as 4G .