Introduction to the Wimax and Its Related Issues and Its Comparison with Wi-Fi

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1 Introduction to the Wimax and Its Related Issues and Its Comparison with Wi-Fi Puram Ashok, pulipati manas, Rayala Ravi Kumar Students of K L University, Associate Professor of K L University, Department of ECE, Vaddeswaram, India. ABSTRACT: One of the developing technologies in the recent times which are not yet fully implemented and which requires a lot of research work is WIMAX which was proposed for a goal of bringing the usage of broadband till the LAST MILE. A lot of concerns and issues regarding this technology and this paper will mainly discuss about the basics and types of WIMAX and also deals with some of questions regarding the safety in using WIMAX. This paper is focused on description of static wimax and mobile wimax and also describes about the handover policies which is the major advantage in mobile wimax in addition to the major drawbacks in this issue and some comparisons are made with WIFI. Keywords:Fixed wimax,mobile wimax,handover,backhaul NEED FOR WIMAX: In recent years, Broadband technology has been required by a high percentage of the people. In the recent years, the demand has risen rapidly.dsl operators, who initially focused their deployments in densely-populated urban areas, now wimax technology is available forsuburban and rural areas where new markets are quickly taking root. The DSL market, which is based on the wire line infrastructure, can provide this service to the millions of business subscribers and private subscribers and havind a huge growth rate. But supplying the quick rollout of infrastructure to the last mile has become a difficult and expensive challenge for carriers who cannot possibly keep pace with the demand.this made the subscibers provide this technology only to the urban areas with broadband ready infrastructure have the benefits of DSl services they do not require any technology to fill the void.the introduction of the new WiMAX standard - fits this agenda perfectly. INTRODUCTION: World wide Interoperability for Microwave access which is referred to as WIMAX. It can provide a lowcost, locally managed, wireless metropolitan area network (MAN) infrastructure with capabilities that can equal or surpass those of 3G/3G+/4G public wireless networks. WiMAX networks can be deployed for temporary or permanent use and can be much more easily isolated from large-scale failures in the electric power or telephone grids. WiMAX is a MAC and physical layer wireless communications technology. WiMAX was designed to provide outdoor broadband wireless access.the set of standards that define WiMAX are developed and maintained by the IEEE Theoretically IEEE can provide single channel data rates up to 75 Mbps on both the Uplink and downlink..two major variants of WiMAX have emerged: d standard supports fixed or slowly moving users; e standard supports mobile users. There is non line of sight, WiFi sort of service, a small antenna on your computer connects to tower. In this mode, It uses a lower frequency range - 2GHz ISSN: Page 218

2 to 11GHz. They can able to diffract, bend around the obstacles. There is a line-of-sight service, a fixed dish antenna points straight towards at the WiMAX tower from a rooftop. It is stronger and more stable, so it can able to send a lot of data with few errors. Line-of-sight transmissions uses higher frequencies with ranges reaching 66 GHz. At the higher frequencies, there is possible of less interference and lot more of bandwidth. WiFi access is to 4 to 6 mile of radius. BASIC OPERATION AND REQUIREMENT FOR WIMAX: Typical point to multipoint Broadband Wireless Access (BWA) systems are composed of two key elements: base station and subscriber equipment. The base station connects to network backbone and uses an outdoor antenna to send and receive high-speed data and voice to subscriber equipment, thereby eliminating the need of extensive and expensive wireline infrastructure and providing highly flexible and cost-effective last-mile solutions. A wimax base station serves subscriber stations using Non-Line-of-Sight (NLOS) or LOS Point-to-Multi- Point connectivity; and this connection is referred to as the last mile communication. Ideally, Wimax (802.16) should use NLOS Point-to-Multi-Point antennas to connect residential or business subscribers to the Wimax Base Station (BS). A Subscriber Station (Wimax CPE-Customer Premise Equipment)typically serves a building using wired or wireless LAN. TYPES OF WIMAX: The WIMAX has been classified into two types- FIXED and STATIC WIMAX. FIXED WIMAX: Based on IEEE d standard, this type of wimax is used for point to point data transformation, generally when the user is stable or when there is a minimum movement for example within a room in the house. This fixed wimax uses Orthogonal Frequency Division Multiplexing(OFDM).The fixed wimax can support both Frequency Division Duplexing and Time Division Duplexing. CHALLENGES IN FIXED WIMAX: 1.The communication will be taking place between WIMAX CPE and NLOS(Non Line Of Sight) basestation and so the requirements for the link security are greater than those required for a wireless technology 2.Another challenge is setting up high performance radio links which are capable of providing data rates comparable to wired broadband service, using equipment that can self installed indoors by users, like that of Digital Subscriber Line (DSL) and cable modems so as to increase the data rate in non line of sight environment. MOBILE WIMAX: Based on IEEE e standard, this type of wimax is used to provide the internet acess to vehicular class, where the user can move from one location to another location which uses base station hand off techniques, the major advantage of mobile wimax when compared with fixed wimax. It uses a low frequency of 2-11 GHz.It is based on Orthogonal Frequency Division Multiple Acess(OFDMA) and mainly uses Time Division Duplexing Mode(TDD). HANDOVER TYPES: The basic role of WiMAX handover is to provide the continuous connection when a Mobile Station (MS) migrates from the coverage area of one BS to the coverage area of another BS.In the IEEE e,three types of handover are described: 1. Hard handover, 2. Macro Diversity Handover (MDHO) and 3. Fast Base Station Switching (FBSS). ISSN: Page 219

3 Hard handover is mandatory in WiMAX systems. Other two types of handover are optional. Hard Handover: During hard handover the MS communicates with only just one BS in each time. Connection with the old BS is broken before the new connection is established. Handover is executed after the signal strength from the neighbor s cell is exceeding the signal strength from the current cell. TERMINOLOGY IN WIMAX: FREQUENCY DIVISION DUPLEXING(FDD): Transmission and receiving of signal from base station and subscriber station will take place in different channels. TIME DIVISION DUPLEXING(TDD): Unlike in FDD, instead of two different channels which are used by FDD for transmitting and receiving signals, only one channel is used for both. BACKHAUL: Interconnection of one base station with another base station with the help of microwave links which enables the roaming feature for wimax user from one base station coverage to another just like in the case of cellular roaming is known as backhaul. ORTHOGONAL FREQUENCY DIVISION MULTIPLEXING(OFDM): This technology is generally used for facing the challenges that are present in the non line of sight transmission where it uses a large number of sub carriers to carry the data on several parallel channels. It uses mainly slow modulated narrow band signals instead of rapidly modulated wideband signal. The low symbol rate gives the added advantage of eliminating the Inter Symbol Interface(ISI). Channel equalization is simplified because OFDM uses many slowly modulated narrowband signals rather than one rapidly modulated wideband signal. As a result this method is mainly preferred in the Fixed Wimax. ORTHOGONAL FREQUENCY DIVISION MULTIPLE ACCESS(OFDMA): Achieving multiple access to the above discussed OFDM technique is known as OFDMA. It is a multi user version which can be achieved by subsets of subcarriers to individual users in order to get simultaneous low data transmission to various users is known as OFDMA. Its main advantage is the low data rate transmission for several users and also the delay will be reduced and it will be maintained constant. This type of technique will be used in Mobile WIMAX. SECURITY ISSUES: As we all know that the security concerns are more in wireless technologies when compared with wired technologies. The security issues can be classified under two categories where the first one relates to the user and other relating to the service provider. Issues relating to user: Eavesdropping and data destruction are the two major issues related to the end user. Each layer handles different aspects of security and the data encryption must be taken place at the link layer so as to provide a security from eavesdropping. Issues relating to the service provider: Authentication and access control are the two major security issues in wimax relating to the service provider. Unauthorized access should be prevented by the service provider and it can be implemented at various levels of network such as physical layer etc in order to avoid any inconvenience to the users. At the transport layer Secure Sockets layer (SSL) may be used to add security to transport layer protocols and packets. PROTOCCOLS USED IN WIMAX: 1.RADIUS(Remote Authentication Dial-In User Service): It is client/server protocol used in the link layer where the remote access servers communicate with the central server so as to check and verify the authentication of that particular user and if the user is eligible to access the requested service or not. This consists of a central database where it has the details of all the users and it can be shared by the remote servers.the RADIUS server returns one of three responses to the RAS : 1) Access Reject, 2) Access Challenge, 3) Access Accept. Access Reject -- The user is unconditionally denied access to all requested network resources. ISSN: Page 220

4 Access Challenge -- Requests additional information from the user such as a secondary password, PIN, token, or card. Access Accept -- The user is granted access. Once the user is authenticated, the Remote Authentication Dial-In User Service(RADIUS) server will check that the user is authorized to use network service requested. 2.Secure Socket Layer(SSL): This protocol is mainly used in the transport layer regarding the management of security in the message transmission on the internet. SSL has recently succeeded by TLS(Transport Layer Security).SSL uses a program layer located between the Internet's Hypertext Transfer Protocol (HTTP) and (TCP)Transport Control Protocol layers. SSL uses public and private key encryption system from the RSA, which also includes the use of digital certificate. Digital certificate are implemented at application layer which is depending on the network sensitivity. TLS and SSL are an integral part of most Web browsers and the Web servers. If a Website is on a server that supports Secure socket layer, SSL can be enabled and specific Web pages can be identified as requiring SSL access. 4. Extensible Authentication Protocol(EAP): EAP authentication potocol is used in wireless and point to point protocol connections. During the link establishment phase of the PPP connection specific authentication mechanism is not chosen with this EAP.Instead of this during the connection authentication phase the PPP peers negotiate to perform EAP. When the connection authentication phase is reached, the peers negotiate the use of specific EAP authentication scheme known as an EAP method. By using a supplicant --a software component, the EAP peer and the EAP authenticator send EAP messages supplicant uses EAP to authenticate network access and a data link layer transport protocol such as PPP. The authentication server and the EAP authenticator send EAP messages using Remote Authentication Dial-In User Service (RADIUS). The end result EAP messages are exchanged between EAP components on the EAP peer and the authentication server. EAP infrastructure is as shown in figure 3.Privacy Key Management(PKM): The PKM protocol will be used in WIMAX between the customer premise equipment(cpe) and the base station(bs). The CPE will act as a client requesting the keying material to the base station which acts as a server and acts according to the requests made from the CPE and allows only the requested keying material to be reached to the CPE and also sees that the CPE receives only the keying material for which they are authorized. The Privacy Key Management (PKM) Protocol first creates an Authorization Key (AK), which is a secret symmetric key shared between the Wimax CPE (Customer Premise Equipment) and BS. This protocol uses X.059 digital certificates which is send by CPE to the BS. The BS then authenticates the syntax and information and validates the certificate, if properly verified,it will encrypt the Authorization Key (AK). Since only the Wimax CPE device contains the matching private key, only that Wimax CPE device can de-crypt the message and obtain the AK assigned to it. ADVANTAGES OF WIMAX : Coverage: It can provide coverage to hundreds of users at a time and can manage of receiving and sending of data at very high speed with full of network security. High Speed: The High speed voice and high speed of connectivity over the long distances makes it more demanded in urban and rural areas. ISSN: Page 221

5 Multi-functionality within the Wimax Technology: It can perform a variety of task at a time such as video streaming and offering high speed internet voice application, transformation of data, providing telephone service, etc. DIADVANTAGES: 1.Lack of Quality It is difficult to provide high quality to each and every user because they can access from the same tower. 2.Expensive network Its installation and operational cost are more and due to heavy structure, tower and antennas makes the Wimax network high cost network. 3.Bad Weather The quality of this wimax services varies in rainy season because of the weather condition interrupt the signal which causes bad signal and broadcasting may stops COMPARISION BETWEEN WIMAX AND WI- FI: Wi-Fi is intended for LAN applications, scale from one to tens with one subscriber, for the each CPE device. Fixed channel sizes (20MHz). WiMAX can efficiently support from one to hundreds of Consumer premises equipments (CPE), with the unlimited subscribers behind each consumer premises equipments(cpe). Flexible channel sizes are from 1.5MHz to 20MHz. Bit rate: Wi-Fi works at 2.7 bps/hz and peak up to 54 Mbps in 20 MHz channel.but WiMAX works at 5 bps/hz and peak up to 100 Mbps in 20 MHz channel. Quality of Service: Wi-Fi does not guarantee any Quality of service but WiMax will provide several level of QoS.WiMAX provides ubiquitous broadband while Wi-Fi does not. Reference: [1] WiMAX taking wireless to the MAX by Deepak Pareek [2] WiMAX a wireless technology revolution by G.S.V.Radha Krishna Rao [3] Internet (Google and Wikipedia). IEEE Standards: WiMAX technology is based on IEEE and Wi-Fi is based on IEEE standard Both are IEEE standards. Range: Wi-Fi provides local network access for a few hundred feet with speeds of 54 Mbps, But WiMAX antenna is expected to have a range of 40 miles with speed of 70 Mbps. Scalability: ISSN: Page 222