An Introduction To Wimax Technology Computer Science Essay
One of the general forms of wireless networking is wireless metropolitan area network (WMAN) and that has a projected coverage region, range is approximately the size of the metropolitan city. A wireless metropolitan area network (WMAN) covers a large geographical region than a wireless local area network (WLAN). However, it is smaller than a wireless wide area network. Basically WMAN is possessed by a distinct entity and this entity should be a government, an Internet service provider (ISP) or outsized corporation.
The most extensively used structure of wireless metropolitan area network (WMAN) is IEEE 802.16 or WiMAX. Near the beginning, iterations of the IEEE 802.16 standards or WiAMX were designed to provide last mile broadband wireless access and it was denoted by the 802.16-2004. In 2005, IEEE designed another version of IEEE 802.16 standard named IEEE 802.16e-2005. In this version improvements were added for enhanced user mobility. The latest version of IEEE 802.16 was designed in 2009 name IEEE 802.16j-2009. Actually it is the combination of IEEE 802.16-2004 and IEEE 802.16e-2005. This standard provides a framework for multi-hop relay (also called mesh networking) networking. Actually this segment elucidates the basic concepts of WiMAX as well as its topologies also.
Basic components of WiMAX
WiMAX has four basic components that is essential to design the framework of WiMAX
Base Station (BS): The BS station is one kinds of node that makes a logical connection between the wireless subscriber devices and the operator networks. Basically the fundamental work of base station is to maintain the subscriber devices and also administrate access to the operator networks. To enable wireless communication a base station consists dissimilar types of infrastructural components and these components
should be transceivers, antennas and as well as other equipment for transmitting electromagnetic wave. Although BS is working as fixed nodes but sometimes it can be used as a part of mobile solutions. On the contrary, in multi-hop relay topology a BS serves as a master relay base station.
Subscriber Station (SS): The subscriber station (SS) is one kind of fixed wireless nodes is used by the subscriber those who wants to communicate with the base station. In point of fact a subscriber station usually just communicates only with the base station, apart from multi-hop relay network operations.
Mobile Subscriber (MS): In 2005, IEEE designed another latest 802.16 standard called 802.16e-2005 where multi-hop relay (or mesh network architecture) was added to make a logical connection between the SS and the BS. Conversely, MS is a fixed node which is working with the connection provided by the architecture of multi-hop relay network. On the other hand, MS supports different types of operational modes to manage the enhanced power scheme. MS is particularly designed for small and self-powered device such as- mobile phones, laptops and other kinds of portable electronic devices.
Relay Station (RS): RS was defined in IEEE 802.16j-2009 and it is working like SS which is used to forward traffic to other SSs, RSs or MSs that are in a multi-hop security zone.
In the time of communication WiMAX devices use two different types of message such as- data message and management message. Data message is used to move data transversely the WiMAX network and to maintain the communication between the BS and SS management message is used. Depending on signal propagation IEEE 802.16 standard delineates
different frequency bands for WiMAX operations. Suppose to propagate signal between various nodes WiMAX utilizes a radio frequency (RF) beam but this beam is highly susceptible to RF barriers if the propagation is over this beam. So it is important to select the nodes that are barrier less. To fixed operations this type of signal propagation is limited and it is called line-of-site (LOS) and its frequency range is 10-66 GHz. However, the other types of signal propagation are called non-line-of-sight (NLOS) and it uses advanced RF modulation methods that is used to recompense for RF signal changes and would avoid the LOS communications. NLOS is more usually used if we compared it to the LOS because of its barriers.
Network architecture of WiMAX.
In WiMAX network there are four topologies:
Multi-hop relay (mesh networking) and
Here we describe the above topologies
Point-to-Multipoint: A point-to-multipoint topology provides network access services from one location to another. It is constructed of a central BS which supports multiple SSs. Basically it is used remote office confidential scheme connectivity, wireless backhaul services in long range and as well as last mile broadband access. This network topology can operate with both LOS and NLOS signal propagation. PMP network structure in a BS that has a distinctive operating range of 8 km.
Figure: PMP technology (Reference?).
Point-to-Point: A point-to-point (P2P) network topology provides high facility wireless links that is used to make a communication between two sites. This technology works with a enthusiastic elongated range and used for wireless backhaul services with high bandwidth. In this topology, BS considers as a central site host and SS consider as a remote site host. For establishing link between BS and SS, BS controls different types of security parameters and as well as controls the whole communication process. Maximum operating range of this topology is approximately 48 km. By using LOS and NLOS signal propagation this topology provides high bandwidth wireless services.
Figure: P2P Topology (Need reference and also reconstruction?)
Multi-Hop Relay: In 2009, IEEE designed a new WiMAX standard called 802.16j-2009 and multi-hop relay was added with that standard. Basically, it is used to expand BS coverage area by authorizing SS or MS to perform specific function for traffic relay and by acting as RS. Outer surface of the base station range data is predetermined to an MS/SS and relayed throughout adjoining RS. In security region RS can forward traffic to SS or RS. A trusted relationship among a BS and a set of RS is denoted by a security zone. To enlarge the geological area of a network, the coverage area of BS that is routed over the multiple RS and data is deriving outside the BS. To enlarge network geographical area including different RF barriers, usually multi-hop relay network infrastructure uses NLOS signal propagation. On the contrary, sometimes this topology uses LOS signal propagation in a technical form. In multi-hop relay topology, utmost operating range is approximately 8 km for each node.
Figure: Multi-Hop Relay (Reference and Reconstruction is needed).
Mobile: In mobile topology, several BSs that are worked together to offer flawless communication over a sprinkled network to MSs and BSs. A mobile topology has a similarity to a mobile or cellular network. For cellular operation this it uses progressed RF signalling which sustains the enhanced RF complexity. This topology is used to merge each member BS within a large coverage area and it also handoffs the MSs in between the coverage areas of BSs. NLOS signal propagation is used to perform the operations of mobile WiMAX and operational frequency range is between 2 and 6 GHz. The maximum operating range of this topology is approximately 8 km.
Figure: Mobile Topology (Reference and Reconstruction is needed?)
WiMAX Protocol Architecture
Open Systems Interconnection (OSI) is a seven layer model that is often used to describe the network technology in different aspect. The IEEE 802.16 broadband wireless access standard follows the seven layer OSI model. The top layer of the OSI model is called the application layer and the bottom layer of the OSI model is called the physical layer. In OSI model different protocols are divided into a sequence of layers and each layer transfers data to upper layer and also utilizes the function of lower layer. Suppose session layer (Layer 3) transfer data to the higher layer which is called transport layer. Basically, in OSI model bottom layers are executed in hardware. However, top layers are executed in software. Two lowest layers of OSI model is physical layer and the data link layer and this two layers are denoted by tha layer 1 and layer 2.
Figure: IEEE 802.16 Protocol Layer
In OSI model data link layer is divided into two sub layers and these are media access control (MAC) layer and logical link layer (LLC). Physical layer establishes physical connection between two entities those who are in communications and MAC layer is liable to maintenance that connection. The IEEE 802.16 or WiMAX broadband wireless access standard just follow the first two layers (Physical layer and Data link layer) of the OSI model.
2.2.1 Physical Layer
The IEEE 802.16 standards or WiMAX technology is a broadband wireless access (BWA) system data is transmitted at high speed over the air circumference by using electromagnetic waves and a given operating frequency is used in here. Physical layer make a connection between two entities those who are in the communication and the connection should be in two directions- downlink and uplink.
Actually, the IEEE 801.16 standards or WiMAX is a digital technology and the physical layer is maintaining and transmitting the digital bit sequences. This layer also categorized the type of modulation and demodulation, signal type, transmitting power and different types of physical features. The IEEE 802.16 standards or WiMAX network technology allows a frequency bandwidth from 2 to 66 GHz. This frequency can be divided into two parts-
Usually, the first range of frequency is designed for NLOS transmission and the first frequency range is started from 2 GHz and it finishes at 11 GHZ. At this present time this frequency range is used in WiMAX network.
And the other frequency range is designed for LOS transmissions and the frequency range is started from 11 GHz and it finishes at 66 GHz. But in this moment this frequency range is not used for WiMAX network.
The 802.16 standards or WiMAX technology characterized five different physical interfaces and each of these physical interfaces is defined in different sections. 802.16 standard supports two different duplexing mode like as- frequency division duplexing (FDD) and time division duplexing (TDD). The WMAN supports LOS transmission techniques and is précised for a frequency range from 10 to 66 GHz. The source of this standard is coding format and the carrier modulation. To break up downlink and uplink it supports time division duplexing (TDD) and as well as frequency division duplexing (FDD
Band of Operation
technique for NLOS
OFDM for NLOS
OFDM Broken into
subgroups to provide
multiple access in a
single frequency band.
May be SC, OFDM,
OFDMA. Must include
Selection to mitigate
Table 2.1: Physical Interfaces that is defined in the 802.16 standard.
IEEE 802.16 or WiMAX network uses orthogonal frequency division multiplexing (OFDM) technology that allows and allocating subcarriers for different users. When multiple signals hitting the receiver then this technology can help to overcome that signals.
The IEEE 802.16 standard allows scalable OFDM and the OFDM is divided into 256 different subcarriers. Physical layer contains different types of multiplexing and modulation techniques and WiMAX or IEEE 802.16 standard sustains frequencies of wide range. The modulation method can be used in the uplink and conversely downlink also. Uplinks are quaternary PSK (QPSK), phase shift keying (PSK), binary phase shift keying (BPSK), 64 QAM and 16 quartered amplitude modulation.
The IEEE 802.16 standards also support half and full duplex station. TDD framing has a time duration that is fixed and it is adaptive also. It has one down link frame and as well as one uplink frames also. BS sends two different types of downlink sub frame named DLMAP and ULMAP. Same frequency is shared by the down link and up link transmission but they are separated depending on time. If we consider FDD, transmissions are scheduled based on ULMAP and DLMAP. Depending on different frequencies downlink and uplink communications occurs at the same time.
One of the most appropriate inclinations is WMAN-OFDM which provides fixed support in NLOS situation. Sometimes WMAN-OFDM is also known as OFDM and for data transmission this technology used OFDM transmission.
WMAN-OFDMA using orthogonal frequency division multiple access (OFDMA). It is also called OFDMA and which is working with the physical layer. This layer uses OFDMA access which indicates multi-point transform and to provide mobile broadband wireless access. Operations of this technology are limited and the operation band is less than 11 GHz licensed band. However, depending on single carrier modulation WirelessMAN-SCa works and its aimed frequency range is 2 to 11 GHz. To make access in uplink and downlink TDMA technique is applied and another technique is TDM that is also supported in downlink.
The final arrangement is Wireless High-Speed Unlicensed Metropolitan Area Network (WirelessHUMAN) and its aimed frequency range is below 11 GHz in license band. For duplexing it supports TDD technique and for this technique air interfaces can be specified form 2 to 11 GHz frequency band. Finally, the IEEE 802.16 or WiMAX network only supports OFDM and 802.16 standards physical layers.
2.2.2 Media Access Control Layer (MAC)
One of the most important protocol layer of IEEE 802.16 standard or WiMAX network is MAC and this layer related to the connection. When IEEE 802.16-2004 standard was
designed then MAC layer was added to that standard for broadband wireless PMP access applications. Depending on a protocol stack IEEE 802.16 standard is designed with suitably defined interfaces. In IEEE 802.11 standard, a number of Subscriber Station (SS), Access Point (AP) and a Base Station (BS) are available. BS is broadcasted to the SS and it is mainly wired. On the contrary, to validate access that is conflict free 802.16 standard uses downlink and uplink. To build a communication between BS and SS, BS exploits TDM (Time Division Multiplexing). However, to share the uplink SS exploits TDMA (Time Division Multiple Access) technique.
Figure: IEEE 802.16 MAC Layer Overview
The MAC layer is designed with three important sub layers and they are Security Sublayer (SS), Convergence Sublayer (CS) and as well as Common Part Sublayer (CPS). Previously I defined MAC layer is connection oriented and to indicate the connection it’s needed a connection identifiers that is 16 bit where a bandwidth is needed continuously. Connection Identifier (CID) is used to make a distinction between Upper Link (UL) and Down Link (DL) channels. CID is checked by the SS and SS receives the Protocol Data Unit (PDUs). Finally, SS addressed those PDUs and preserve them.
Figure: Synopsis of MAC Layer functions.
18.104.22.168 Convergence Sublayer (CS)
Convergence Sublayer is placed above the Mac Common Part Sublayer (CPS) and it is also called the service specific Convergence Sublayer (CS). Depending on MAC Service Access Point (SAP) CS provides different types of services. When CS provides services then it also performs different types of functions and these are as follows:
In IEEE 802.16-2004, the CS specifies two different types of higher layers. Form the higher layers, CS recognizes higher layer PDUs. If we consider IEEE 802.16 standard then two CSs are presented and they are- packet CS mode and the ATM (Asynchronous Transfer Mode). The higher layer protocol that is supported by packet CS is IPv4 or IPv6.
Figure: Communication between sending and receiving entity by transferring SDUs and PDUs
One of the indispensable functions of IEEE 802.16 broadband wireless access is Quality of Service (QoS) management mechanism. The appropriate Connection Identifier (CID) where MAC service data units are mapped and categorized.
An optional function that is used in CS is Payload Header Suppression. Actually, it is a process of payload headers where suppressing repetitive parts are included and this process restoring and includes these headers at the receiver end.
CS PDUs is received from the peer entity and the CS PDUs that is delivered to the MAC SAP. PDUs and SDUs are receiving and transferring between receiving and sending entity.
22.214.171.124 Medium Access Control Common Part Sublayer (MAC CPS)
The middle of the MAC layer is called the Common Part Sublayer (CPS). CPS is responsible for different types of functions such as- connection establishment, bandwidth allocation and maintenance the connection between two different sides and those are executed in the MAC layer.
In IEEE 802.16-2004, a no. of messages is delineated in the CPS and these messages are also called management messages. During the time of connection establishment messages are swapped among the BS and SS. After the connection establishment transfer messages are swapped between the BS and SS and finally to make a permission for data transmission.
By using MAC SAP, CPS receives various types of data that are available in different CSs. MAC connections are established by using those data collected from the CSs. For data transmission and data scheduling, QoS is captured into account of data over the physical layer. Different types of procedures that is included to the CPS is QoS management, allocation of bandwidths, demands of bandwidth and as well as the management of radio resource.
126.96.36.199 Security Sublayer
Security Sublayer provides authentication mechanism for the MAC layer and it is presented in the MAC sublayer. This sublayer also provides different types of encryption mechanism, secure key exchange and integrity control transversely the broadband wireless access system. Authentication mechanism and encryption mechanism is the part of network security. Security algorithms are designed based on these two important mechanisms (authentication and encryption) and this algorithm should prevents different types of security attacks such as- theft of services, man in the middle attack, denial of services of attack etc.
To establish encryption connection between BS and SS, an encryption mechanism is used. However, to authenticate BS and SS an authentication mechanism can be used. In 802.16 standards, if we considered authentication and encryption mechanism then cryptographic suites those are defined in that mechanism and this mechanism should be pairings of encryption and the authentication algorithm.
To provide protected allocation of keying data between BS and SS, an authentication protocol can be used that is called Privacy Key Management Protocol (PKM). By using protected key allocation system, BS and SS synchronized those keying data for the PKM protocol. The privacy mechanism can be more secure if the digital certificate is included to the SS authentication mechanism related to key management protocol. Furthermore, BS uses PKM protocol which ensures and controls access to the network.
Security Features of WiMAX
Base Station (BS) and Subscriber Station (SS) are the main entities of IEEE 802.16 or WiMAX network. These entities are protected by different security measures and these are as follows:
Public Key Infrastructure.
User Authentication and Authorization.
Data Integrity and Privacy.
Security association (SA) is a no. of parameters that holds a set of security information. It is shared by the SS and BS. Every SA holds different traffic encryption key, an initialization vectors and a cryptographic identifier that is designed for selected algorithms. Depending on security association identifier (SAID) it identifies SS and BS.
Public Key Infrastructure
Secure key management is one of the key functions of 802.16 or WiMAX network. In WiMAX network, secure key is transmitted and exchanged between different mobile stations. For this key exchange WiMAX uses Privacy and Key Management Protocol (PKM). To perform secure key management and other functions PKM protocol uses two types of strong encryption algorithm such as- RSA (Rivest-Shamir-Adleman) algorithm) and AES (Advanced Encryption Standard) and it also uses X.509 digital certificates to perform authentication functions.
Figure: Public Key Infrastructure of IEEE 802.16 standards or WiMAX network. (Ref.)
At the initial stage of WiMAX technology, PKMv1 protocol was used for authentication mechanism but it was a one way authentication method. For this reason, this one way authentication method has a risk for Man-in-the-middle (MITM) attack. If we considered IEEE 802.16e standard, then this problem is solved. Because in this standard PKMv2 method is used for authentication and it is a two way authentication method. The above figure shows the public key infrastructure of WiMAX network.
User Authentication and Authorization
WiMAX technology sustains different types of authentication mechanism and security sub-layer handles those types of mechanism.
The first mechanism is RSA based authentication where an X.509 directory authentication certificate is used with RSA encryption. This certificate includes the MAC address and the public key of SS which is issued by the manufacturer of SS. In this mechanism, digital certificate of SS is verified by the BS. According to the request of BS, SS transfers its certificate to the BS then BS checks the validity of this certificate and encrypts the Authorization Key (AK) by using PK which is verified previously.
The second mechanism is third party based authentication where a trusted third party is used as an Authentication Server (AS) which must have the knowledge about SS. During the time of authentication, SS sends its certificates and others authentication requirement to BS the BS verifies that certificate and sends a reply to the SS. it is important to check that the BS is legitimate or rogue but the SS is unable to check the BS. However, AS and BS recognize each other. When SS receives authentication reply from BS then sends it to the AS. After that SS will send the credentials of SS, SSID and its own ID to the AS. Finally, AS will verify the
information of both sides and send the authentication message to the SS. If the BS is legitimate then SS will continue the communication. Conversely, if the BS is rogue then SS will stop the communication.
Another authentication mechanism is Extensive Authentication Protocol (EAP) based authentication. At the time of communication SS is authenticated by different types of credential such as user name/password, USIM, ad SIM issued by the operator or an X.509 certificate. Different types of authentication protocols are involved with this mechanism such as- Tunnelled Transport Layer Security with Microsoft Challenge-Handshake Authentication Protocol version 2 (EAP-TTLS MS-CHAP v2), Extensible Authentication Protocol-Authentication and Key Agreement (EAP-AKA) and EAP-Transport Layer Security (EAP-TLS) and the operator can choose any one of them for authentication.
After the authentication, authorization process will start. At the time of authorization, SS sends an authorization message request to BS for a SAID and an AK. This authorization message includes cryptographic ID, encryption algorithm and X.509 certificate and these involves with the SS. After receiving the authorization message of SS, BS interacts with the authentication server and the authentication server may be a RADIUS server (AAA server) or a trusted third party or Kerberos or others is used for authentication. Finally, AS checks and authenticates the request and forwards an authorization reply to the SS which contains the public key of SS that encrypts the AK, SAIS and a lifetime key.
Data Integrity and Privacy
For encryption, WiMAX technology supports Advanced Encryption Standard (AES) algorithm. This algorithm converts the plain text into the form of cipher text that can be used as a final output and a no. of conversion round is repeated by the AES cipher. Several progressing stages are required for that conversion round and an encryption key is involved with each stage.
On the contrary, to converts the cipher texts into the form of plain text, a no. of reverse stages are included with this conversion. For each stage, same key is used as decryption key. While DES is one of the secure algorithm for encryption and decryption but it is not well enough and more secure for WiMAX network. AES is a strongly suggested standard for WiMAX network which supports different modes such as- Cipher Block Chaining (CBC) mode, ECB mode, CCM mode and as well as CTR mode.
Evolution of IEEE 802.16 or WiMAX Network
At the end of twentieth century several telecommunication companies those who are the manufacturers of telecommunication equipment were started to present their artefacts for Broadband Wireless Access (BWA). At that time a standard was needed which must be interoperable. In August 1998, a meeting was called by the U.S National Institute of Standards and Technology (NIST) and the National Wireless Electronic Systems Testbed (N-WEST) to converse about that standard. The meeting was ended with a fruitful decision and it was to organize a standard named IEEE 802.16. At the same time a group was formed to develop the standard and they have been working a lot to develop that standard for mobile and fixed BWA. The working group of IEEE 802.16 standard is responsible for the overall development of that standard and associated with the air interface of WirelessMan.
For BWA, the IEEE 802.16 standard includes the measurement of MAC layer and the Physical Layer. On December 2001, the first version of IEEE 802.16 standard was established which was included with some new functionalities and features. In 2004, the working group of IEEE 802.16 was designed a new standard namely called IEEE 802.16-2004 based on the previous standard. This standard includes the air interface of WirelessMan and supporting multimedia services for fixed BWA system. On February 2006, the working group granted a new standard named IEEE 802.16e- 2005 based on the combination of previous standard.
The evolution of IEEE 802.16 standard is presented below-
This standard includes with a no. of Physical layer and MAC layer to present fixed broadband wireless access. Basically, this standard is working with PMP and P2P topology. At the time of communication, the Physical layer of this standard uses a modulation technique which is single carrier with a frequency range 10-66 GHz. At the same time, BS allocates the time duration of data transmission and the modulation time, shared by the all nodes connected to a network. Simultaneously, a broadcast downlink and uplink map is formed in the network. Here, BS is only the subscriber is connected to the network and do not need to eavesdrop another node which is connected to the same network. To provide the flexibility of scheduling SS have the negotiation capability for the allocation of transmission bandwidth.
Different types of modulation standards are included with this standard such as- 64-QAM, QPSK and 16-QAM. Based on the connection which must be vigorous, these modulation standards are varied from Subscriber Station to Subscriber Station and different frame to frame. According to the duplexing system, this standard supports different duplexing system such as- Frequency Division Duplexing (FDD) and Time Division Duplexing (TDD).
One of the valuable features of this standard is to provide discrepancy Quality of Service (QoS) and this feature is included with the MAC layer. A service flow ID which is included with the QoS check because this ID actually performs the QoS check. Either SS or BS can be generated the service flow ID. The IEEE 802.16-2001 standard supports Line of Sight (LOS) conditions that are included with the Customer Premises Equipment (CPE).
On December 2002, another standard was approved by the IEEE standards board named IEEE 802.16c-2002. Different types of errors and indiscretions of previous standard were solved in this standard and the signal frequency range was added from 10-66 GHz.
On January 2003, another new version of IEEE 802.16 standard was approved by the IEEE standard board depending on the changing characteristics of previous standard. This standard is included with the physical layer conditions that support multiple physical layer conditions. It improves the MAC layer that can sustain multiple physical layers. Frequency range 2-11 GHz that is included with the physical layer was added with this standard. License exempt band with a frequency range below 11 GHz is also incorporated with this standard. NLOS (Non Line of Sight) operation is feasible for this feature which enlarges the geological area of the network. For NLOS operation multiple transmission is a common issue includes with this specification. Different technical issues are included with specification such as- power management method, intrusion mitigation, multiple transmissions and as well as satellite dish array which is adaptive. In previous standard single carrier modulation technique was involved but in this specification single carrier modulation is replaced by the Orthogonal Frequency Division Multiplexing (OFDM). Different types of security issues and security features are already improved with this vision. One of the discretionary supports of this specification was Mesh topology that is included with the PMP.
UP to 134 Mbps
UP to 75 Mbps
UP to 75 Mbps
UP to 15 Mbps
(optional in UL),
Table 2.2: Comparison of different IEEE 802.16 BWA standard.
On September 2004, another version of IEEE 802.16 standard was invented by the IEEE standard board name IEEE 802.16-2004. Basically, this version was created depending on the previous three versions (802.16-2001, 802.16c-2002 and 802.16a-2003). All features of previous versions were merged in this specification. At first, when this version was created then it was denoted by a name called 802.16REVd. But, after some up gradation a new dimension was published named 802.16-2004. A new feature was added with this specification that is certification and basically this feature is used for WiMAX certification.
In the middle of 2005, another new specification of IEEE 802.16 was published by the IEEE 802.16 working group namely called IEEE 802.16e-2005. An extension was added with this standard that was mobility that supports mobile subscriber station. In this specification different methodology was tested in a manner. Actually, this standard was formulated based on the revisions of IEEE 802.16f and IEEE 802.16g standard which support network management plane.
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