Conclusion

In this webblog, we outlined a high-level overview of WiMAX technology by presenting its explanation, standards, benefits, features, security, threats, future, enhancement, as well as its challenges.

WiMAX technology could be a significant growth market for the telecom industry.
Broadband wireless has had a checkered history, and the emergence of the WiMAX standard offers a significant new opportunity for success.
Broadband wireless systems can be used to deliver a variety of applications and services to both fixed and mobile users.
WiMAX could potentially be deployed in a variety of spectrum bands: 2.3GHz, 2.5GHz, 3.5GHz, and 5.8GHz.
WiMAX faces a number of competitive challenges from both fixed-line and third-generation mobile broadband alternatives.
The service requirements and special constraints of wireless broadband make the technical design of broadband wireless quite challenging.

WiMAX Technology at Home

Now let's have a close look to the WiMAX technology when we are using it at home.

Here's what would happen if you got WiMAX. An Internet service provider sets up a WiMAX base station 10 miles from your home. You would buy a WiMAX-enabled computer or upgrade your old computer to add WiMAX capability. You would receive a special encryption code that would give you access to the base station. The base station would beam data from the Internet to your computer (at speeds potentially higher than today's cable modems), for which you would pay the provider a monthly fee. The cost for this service could be much lower than current high-speed Internet-subscription fees because the provider never had to run cables.

If you have a home network, things wouldn't change much. The WiMAX base station would send data to a WiMAX-enabled router, which would then send the data to the different computers on your network. You could even combine WiFi with WiMAX by having the router send the data to the computers via WiFi.
WiMAX doesn't just pose a threat to providers of DSL and cable-modem service. The WiMAX protocol is designed to accommodate several different methods of data transmission, one of which is Voice Over Internet Protocol (VoIP). VoIP allows people to make local, long-distance and even international calls through a broadband Internet connection, bypassing phone companies entirely. If WiMAX-compatible computers become very common, the use of VoIP could increase dramatically. Almost anyone with a laptop could make VoIP calls.

WiMAX Cost

During this section we will try to answer the cost issue concerning the WiMAX technology. A citywide blanket coverage of wireless Internet access sounds great, but companies aren't going to go around setting up WiMAX base stations out of sheer kindness. Who's going to pay for WiMAX?
It depends how it will be used. There are two ways WiMAX can be implemented -- as a zone for wireless connections that single users go to when they want to connect to the Internet on a laptop (the non-line-of-sight "super WiFi" implementation), or as a line-of-sight hub used to connect hundreds of customers to a steady, always-on, high-speed wireless Internet connection.
Under the "super WiFi" plan, cities might pay to have WiMAX base stations set up in key areas for business and commerce and then allow people to use them for free. They already do this with WiFi, but instead of putting in a bunch of WiFi hot spots that cover a few hundred square yards, a city could pay for one WiMAX base station and cover an entire financial district. This could provide a strong draw when city leaders try to attract businesses to their area.
Some companies might set up WiMAX transmitters and then make people pay for access. Again, this is similar to strategies used for WiFi, but a much wider area would be covered. Instead of hopping from one hot spot to another, WiMAX-enabled users could have Internet access anywhere within 30 miles of the WiMAX base station. These companies might offer unlimited access for a monthly fee or a "pay as you go" plan that charges on a per-minute or per-hour basis.
The high-speed wireless hub plan has the potential to be far more revolutionary. If you have high-speed Internet access now, it probably works something like this: The cable (or phone) company has a line that runs into your home. That line goes to a cable modem, and another line runs from the modem to your computer. If you have a home network, first it goes to a router and then on to the other computers on the network. You pay the cable company a monthly fee, which reflects in part the expense of running cable lines to every single home in the neighborhood.

WiMAX Enhancement

After discussing the threats to WiMAX technology, during this section we will introduce the enhancements that can reduce these threats. These enhancements includes power control, error detection techniques, sub-channelization, transmission diversity, antennas for fixed WiMAX applications, and adaptive modulation.

Power Control

Algorithms of power control are applied to enhance the general performance of the system, it is deployed by the base station sending power control information to every Customer Premise Equipments (CPEs) to control the transmit power level so that the level inward bound at the base station is at a fixed level. In a dynamical changing fading environment this pre-determined performance level indicates that the CPE only broadcasts sufficient power to meet this constraint. The communication would be that the CPE broadcast level is supported on worst case circumstances. The power control decreases the general power consumption of the CPE and the possible interference with other base stations. For Line-of-Sight (LOS) the transmission power of the CPE is approximately comparative to its distance from the base station, for Non-Line-Of-Sight (NLOS) it is also closely dependant on the clearance and barriers.

Error Detection Techniques

WiMAX have built-in error detection techniques to reduce the system Signal to Noise Ratio (SNR) obligations. Convolutional Encoding, Strong Reed Solomon FEC, and interleaving algorithms are used to identify and correct errors to enhance throughput. These strong error correction techniques assist to recover corrupted frames that may have been missing due to frequency selective fading or burst errors. To remove the errors, Automatic Repeat Request (ARQ) is used that cannot be corrected by the FEC by resending the error-ed information again. This notably improves the Bit Error Rate (BER) performance for a similar maximum level.

Sub Channelization

Another option within WiMAX in the uplink is Sub Channelization. Without sub channelization, narrow restrictions and requirement for cost effective Customer Premise Equipments (CPEs), usually cause the link budget to be unbalanced, for that reason the system range to be up link is restricted. Sub channeling allows the link budget to be objective such that the system gains are parallel for both the up and down links. Sub channeling focuses the broadcasting power into fewer OFDM carriers; this is what boosts the system gain that can either be applied to widen the reach of the system, overcome the infrastructure penetration losses, and or lessen the power consumption of the CPE. The use of sub channeling is promoted expansion in Orthogonal Frequency Division Multiple Access (OFDMA) to permit a more flexible use of resources that can maintain roaming or mobile operation.

Transmission Diversity

Diversity formats are used for improvement of multi-path and reflections signals that arise in Non-Line-of-Sight (NLOS) environment. Diversity is an optional element in WiMAX. The diversity algorithms presented by WiMAX in both the transmitter and receiver significantly enhances the system accessibility. The WiMAX transmit diversity option uses space time coding to offer transmit source freedom; this decreases the weaken margin requirement and resist the interference with other devices. For receive diversity, a variety of joining techniques are present to increase the accessibility of the system. For example, Maximum Ratio Combining (MRC) takes benefit of two separate receive chains to prevent fading and decrease path loss. Diversity has verified to be a helpful tool for coping with the challenges of NLOS transmission.

Antennas For Fixed WiMAX Applications

Directional antennas enhance the fade margin by adding together extra gain. This increases the link accessibility comparisons between directional and omni-directional antennas. Delay spread is further reduced by directional antennas at both the Base Station and Customer Premise Equipment (CPE). The antenna pattern restrains any multi-path signals that appear in the sidelobes and backlobes. The efficiency of these methods has been verified and demonstrated in booming deployments, in which the service operates under considerable NLOS fading.

Adaptive Modulation

WiMAX system supports adaptive modulation to regulate the Signal Modulation Scheme (SMC) depending on the Signal to Noise Ratio (SNR) state of the radio link. When the radio link is soaring in quality, the peak modulation scheme is used, offering the system additional capacity. During a signal fade, the WiMAX system can move to a lower modulation scheme to keep the connection quality and link permanence. This element allows the system to overcome time-selective fading. The key element of adaptive modulation is that it enhances the range that a higher modulation scheme can be used over, because the system can bend to the actual fading circumstances, as opposed to having a fixed scheme that is planned for the worst case situations.

WiMAX Future

Public broadband access via wireless is not only a benefit to business travellers but is also an interesting business opportunities in itself. Broadband wireless internet access via hot spots in hotels, airports, convention centres, coffee shops, restaurants, etc. is a fast growing trend. Hot spots provide internet access for hire. Relatively economical to set up, all that is required to create a simple hot spot is a broadband connection and a wireless router. May hot spots use T1 for its high bandwidth, but DSL, cable and fixed wireless can also be used.

WiMAX can make high speed wireless internet services available to much larger areas than can typical Wi-Fi hot spots. WiMAX implementations can provide a wireless range of up to 30 miles or 50 kilometres, much greater than the physical distance limitations of Wi-Fi hot spots or DSL, WiMAX can also be used to interconnect existing Wi-Fi networks.

WiMAX promises many strategic opportunities, not just as a backhaul solution for Wi-Fi delivering additional bandwidth to hot spots, but potentially for 3G networks too. WiMAX initially may be deployed as a wireless backhaul solution, but will be upgraded to a mobility application, once the 802.16e standard is approved and WiMAX-capable client devices enter the market, marking a major increase in the anticipated market.

WiMAX can compliment existing and emerging 3G mobile and wired networks, and can play a significant role in helping service providers deliver converged services that can be accessed using a broad range of devices on a wide variety of networks.

At the technical level, 3G and WiMAX solutions fit well together by providing different capabilities while allowing for seamless integration. 3G technologies have evolved over many years to become highly spectrally efficient, allowing operators to take advantage of costly spectrum dedicated to mobile services. 3G CDMA technologies such as W-CDMA and CDMA 2000 1xEV-DO provide high through puts in low bandwidths as 5 MHz and 1.25 MHz, respectively

Threats to WiMAX

Most of the experts and professionals claiming that broadband data delivered over 3G cellular networks will choke the hope of the WiMAX industry for the standard to become worldwide significant. There are too many factors involved in weakening WiMax security, stability, Quality of service etc. In this chapter I am going to discuss the threats involved in WiMax deployment and in the infrastructure after that.

Since there are many threats to WiMAX, therefore we will restrict our discussion on the most important aspects, and those are the application layer threat, the physical layer threat, the sub-privacy layer threat and the data link layer.

Application Layer Threats to WiMAX

software based threat management and secure access solutions will be as essential as ever, with a typical security infrastructure comprising components such as firewalls, virtual private networking (VPN), Internet key exchange (IKE) tunnelling, and intrusion prevention systems (IPS), each of which reside at the application layer.

For example, in an WiMax mesh network installation where routers or gateways will operate as intermediaries, or hot spots linking client and base station, there is an increased potential of security vulnerabilities, as the intermediary routers that reside between base station and client are presentable and vulnerable to attacks. Popular application level services, such as voice over Internet protocol (VoIP), could be broken by hackers who can initiate the download of remote configuration settings and resynchronize clients’ CPE settings to their specifications. Hackers may also replicate, or spoof the address of the intermediary router or server and deceive other clients into believing their connection is secure, thus opening them up to malicious attack. These routers and gateways will require robust security measures to ensure that unprotected clients remain protected behind the intermediary access point.

The majority of existing routers will have their own firewall components that provide Application Layer Gateway (ALG) functionality for the signalling protocols that support and keep multiple sessions. Any deficiency in the ALG functionality could result in diminished QoS for low latency applications, such as VoIP and videoconferencing. OEMs must develop devices with ALGs that permit inward call requests to the devices only from the device registered with the server and endpoints, while dynamically allowing inward media packets only on call set up. These media sessions are to be disabled on termination of the connection.

Physical Layer Threats to WiMAX

Privacy Sub-layer resides on the top of Physical layer in IEEE 802.16 standard, therefore, WiMax networks are open to to physical layer attacks for example, blocking and rushing. Blocking is done by activating a source of strong noise to significantly lowering the capacity of the channel, therefore denying services (DoS) to all stations. However, blocking or jamming is detectable with radio analyzer devices. Rushing or scrambling is another type of jamming, but it takes place for a short interval of time aimed at particular frames. Control or management messages could be jumbled, but it is not possible with delay sensitive message i.e., scrambling Uplink slots are comparatively hard, because attacker has to interpret control information and to send noise during a particular interval.

Privacy Sub Layer Threats to WiMAX

Privacy Sub-layer’s main objective was to protect service providers against theft of service, rather than securing network users. It is obvious that the privacy layer only secures data at the data link layer, but it does not ensure complete encryption of user data. Furthermore, it does not protect physical layer from being interrupted. It is essential to include technologies to secure physical layer and higher layer security for a converged routable network and devices within the system.

Data Link Layer Threats to WiMAX

In a typical Wi-Fi mechanism, a digital subscriber line (DSL) feeds a packet-ized bit stream into a modem or access point, which in turn broadcasts a radio signal; often encrypted to Wi-Fi enabled clients that de-packet this data into information. In a WiMAX installation, a fixed wireless base station, similar in concept to a cell phone tower, serves an always-on radio signal directly accessible by WiMAX enabled clients, with no need for leased lines or an intermediate access point.

Like Wi-Fi, the WiMax Media Access Control (MAC) protocol, a sub layer of the data link layer, manage the consumer’s access to the physical layer. However, the scheduling algorithm within the WiMAX MAC protocol offers optimal prioritization of this traffic based on First-In First-Out (FIFO) scheduling, in which clients seeking access to the base station are allocated bandwidth upon time of initial access, instead of random queue assignment based on order of MAC address as in Wi-Fi. Furthermore, the WiMax MAC protocol ensures optimal quality of service (QoS) over its WiFi predecessor, allocating bandwidth effectively by balancing client’s needs instead of best effort service; that is, equal distribution of what remains after allocation to other consumers.

In addition, before encrypting the radio signal with Wired Equivalent Privacy (WEP), WPA/PSK, or any other existing Layer 2 security protocol, WiMax basic authentication architecture, by default, employs X.509-based public key infrastructure (PKI) certificate authorization, in which the base station authenticates the client’s digital certificate prior to granting access to the physical layer.

WiMAX Security

Wireless systems always make some people worried when speaking of security. After all, every wireless system broadcasts, by definition, everything you’re doing on the network to the world or at least the part of the world within range. Security is an important consideration in any communication system design but is particularly so in wireless communication systems. The fact that connection can be established in a loosen fashion makes it easier to intrude in an ordinary and undetectable manner than is the case for wired access. Further, the shared wireless medium is often perceived by the general public to be somewhat less secure than its wired counterpart. Therefore, a robust level of security must be built into the design of wireless systems.

From the point of view of an end user, the primary security concerns are privacy and data integrity. Users need assurance that no one can eavesdrop on their sessions and that the data sent across the communication link is not tampered. This is usually achieved through the use of encryption.

From the service provider’s point of view, an important security consideration is preventing unauthorized use of the network services. This is usually done using strong authentication and access control methods. Authentication and access control can be implemented at various levels of the network such as the physical layer, and the service layer. The service provider’s need to prevent fraud should be balanced against the inconvenience that it may impose on the user.

WiMAX systems were designed at the outset with robust security in mind. The standard includes state-of-the-art methods for ensuring user data privacy and preventing unauthorized access, with additional protocol optimization for mobility.
Security is handled by a privacy sublayer within the WiMAX MAC. The key aspects of WiMAX security are as follow:

Encryption In WiMAX

Encryption is the method used to protect the confidentiality of data flowing between a transmitter and a receiver. Encryption involves taking a stream or block of data to be protected, called plain text, and using another stream or block of data, called the encryption key, to perform a reversible mathematical operation to generate a ciphertext. The ciphertext is unintelligible and hence can be sent across the network without fear of being eavesdropped. The receiver does an operation called decryption to extract the plaintext from the ciphertext, using the same or different key. When the same key is used for encryption and decryption, the process is called symmetric keyencryption. This key is typically derived from a shared secret between the transmitter and the receiver and for strong encryption typically should be at least 64 bytes long. When different keys are used for encryption and decryption, the process is called asymmetrickeyencryption. Both symmetric and asymmetric key encryptions are typically used in broadband wireless communication systems, each serving different needs.

Device/user authentication

WiMAX provides a flexible means for authenticating subscriber stations and users to prevent unauthorized use. The authentication framework is based on the Internet Engineering Task Force (IETF) EAP, which supports a variety of credentials, such as username/password, digital certificates, and smart cards.
WiMAX terminal devices come with built-in X.509 digital certificates that contain their public key and MAC address. WiMAX operators can use the certificates for device authentication and use a username/password or smart card authentication on top of it for user authentication.

Flexible key-management protocol

The Privacy and Key Management Protocol Version 2 (PKMv2) is used for securely transferring keying material from the base station to the mobile station, periodically reauthorizing and refreshing the keys.

Protection of control messages

The integrity of over-the-air control messages is protected by using message digest schemes, such as AES-based CMAC or MD5-based HMAC.

Support for fast handover

To support fast handovers, WiMAX allows the MS to use preauthentication with a particular target BS to facilitate accelerated reentry.
A three-way handshake scheme is supported to optimize the reauthentication mechanisms for supporting fast handovers, while simultaneously preventing any man-in-the-middle attacks.