Brief Introduction of WiMAX Technology

Hochschule Darmstadt

M. Sc. In Electrical Engineering & Information Technology

(Communication)

Submitted to: Professors Shun Ping Chen

Prepared by: Md. Tamim Haider

AKM Faisal Islam

Brief Introduction of WiMAX Technology

Introduction Since the final decades of the twentieth century, data networks have known steadily growing success. After the installation of fixed Internet networks in many places all over the planet and their now large expansion, the need is now becoming more important for wireless access. Already high-speed wireless data access, i.e. in Mb/s, has been largely deployed most part of the world. WiMAX stands for “Worldwide Interoperability for Microwave Access”. The technology is presently one of the most promising global telecommunication systems. Great hopes and important investments have been made for WiMAX, which is a Broadband Wireless Access System having many applications: fixed or last-mile wireless access, backhauling, mobile cellular network, telemetering, etc. WiMAX is based on the IEEE 802.16 standard, having a rich set of features.

Additional Wireless Communication Systems In the 1970s, the Bell Labs proposed the cellular concept, a magic idea that allowed the coverage of a zone as large as needed using a fixed frequency bandwidth. Since then, many wireless technologies had large utilization, the most successful until now being GSM, the Global System for Mobile, originally European second generation cellular system. GSM is a technology mainly used for voice transmission in addition to low-speed data transmission such as the Short Message Service (SMS). In addition to GSM, third-generation (3G) cellular systems, originally European and Japanese UMTS (Universal Mobile Telecommunication System) technology and originally American cdma2000 technology, are already deployed and are promising wireless communication systems. Beside this LTE is knocking at the door to be deployed rapidly.

Different Types of Data Networks

A large number of wireless transmission technologies exist, other systems still being under design. These technologies can be distributed over different network families, based on a network scale. In Figure-1, is shown of wireless network categories, with the most famous technologies for each type of network. Personal Area Network (PAN) PAN is a (generally wireless) data network used for communication among data devices close to one person. The scope of a PAN is then of the order of a few meters, generally assumed to be less than 10 m, although some WPAN may have a greater reach. Examples of WPAN technologies are Bluetooth, UWB and Zigbee. Local Area Network (LAN) LAN is a data network used for communication among data devices like computers, telephones, printer and personal digital assistants (PDAs). This network covers a relatively small area, like a home, an office or a small campus. The scope of a LAN is of the order of 100 meters. The most presently used LANs are Ethernet (fixed LAN) and WiFi (Wireless LAN or WLAN).

Metropolitan Area Network (MAN) MAN is a data network that may cover up to several kilometers, typically a large campus or a city. For instance, a university may have a MAN that joins together many of its LANs situated around the site, each LAN being of the order of half a square kilometer. Examples of MAN technologies are FDDI, DQDB and Ethernet-based MAN. Fixed WiMAX can be considered as a Wireless MAN (WMAN). Wide Area Network (WAN) WAN is a data network covering a wide geographical area, as big as the Planet. WANs are based on the connection of LANs, allowing users in one location to communicate with users in other locations. The most (by far) presently used WAN is the Internet network. Other examples are 3G and mobile WiMAX networks, which are Wireless WANs.

WiMAX Application The bandwidth and reach of WiMAX make it suitable for the following potential applications:

Connecting Wi-Fi hotspots

Providing Broadband Access

Providing a wireless alternative to cable and DSL

Providing high-speed mobile data and telecommunications services (4G).

Providing a diverse source of Internet connectivity as part of a business continuity plan

Providing Nomadic connectivity.

WiMAX Associations

WiMAX Forum The WiMAX Forum is a not for profit consortium of industry leaders representing the entire mobile internet ecosystem. With over 580 WiMAX networks active in 149 countries, the WiMAX Forum and its members are committed to the global adoption of 4G mobile broadband.

The WiMAX Forum’s primary goal is to accelerate the adoption, deployment and expansion of WiMAX technologies across the globe while facilitating roaming agreements, sharing best practices within our membership and certifying products. WiMAX Forum Certified products are interoperable and support broadband fixed, nomadic, portable and mobile services. The WiMAX Forum works closely with service providers and regulators to ensure that WiMAX Forum Certified systems meet customer and government requirements.

WiMAX Spectrum Owners Alliance (WiSOA) WiSOA was the first global organization composed exclusively of owners of WiMAX spectrum. WiSOA focused on the regulation, commercialization, and deployment of WiMAX spectrum in the 2.3–2.5 GHz and the 3.4–3.5 GHz ranges. WiSOA merged with the Wireless Broadband Alliance in April 2008.

WiMAX Standards The below table is the summarization of most important features WiMAX 802.16standards.

Standard name Date Published Frequency Goals

802.16 Apr 2002 10-66 GHz Original standard, line of sight, fixed-

fixed point wireless

802.16a Jan 2003 2-11 GHz Added non line of sight extension. Now

supplanted by the 802.16d variant

802.16d Jun 2004 2-11 GHz

10-66 GHz

supports fixed and nomadic access in Line of Sight and Non Line of Sight

environments

802.16e Feb 2006 2-6 GHz Optimized for dynamic mobile radio

channels, provides support for handoffs and roaming

As the table above shows, the standards went through many phases of evolution, it started as a

line of sight, last mile fixed-to-fixed point, it evolved to near line of sight fixed-to-fixed point,

then to near line of sight roaming friendly standard. This evolution becomes important as we

consider the security of this standard.

Fixed versus Mobile WiMAX It is unfortunate that 802.16d fixed WiMAX and 802.16e mobile WiMAX share the same last name. There is virtually no relevant relationship between the two technologies. They are the broadband equivalent of apples and oranges. 802.16d was developed specifically for fixed wireless applications. Because it does not attempt to support mobility, the terminal devices or Customer Premise Equipment are not constrained by battery operation or small form factor for handheld operation. 802.16e or mobile WiMAX was developed to compete with existing cellular solutions. Cellular industry started with voice and is adding data service whereas 802.16e started with data and is attempting to add voice. 802.16e was developed specifically for mobility. Therefore the terminal device is constrained by battery life and a small form factor to enable handheld devices. The terminal device requires a great deal of additional signal processing to overcome the limited power and antenna gain of the small form factor device and thus base station also has added complexity. In this competitive market business cases justify that a single wireless solution serving both mobile and fixed wireless customers and in these cases 16e is a viable solution over 16d. In these markets, the question is not 16d versus 16e, but rather 16e versus LTE (Long Term Evolution). It is beyond the scope of this discussion to delve into the merits of 16e and LTE. However, with the continued delay of 16e consumer devices and services, LTE has the opportunity to catch up to 16e and surpass it in market adoption. Many large corporations are taking sides on this debate with the outcome to be determined over the next several years.

LOS and NLOS Propagation

Coverage from a BS is linked to several radio parameters. The first one is the propagation environment. Depending on the relative locations of the BS and the terminal, several models can be used to evaluate the losses due to propagation.

LOS and Near LOS Propagation Line-of-Sight (LoS) and Near Line-of-Sight (NLoS) propagations may happen when the BS and the MS are deployed outdoor, above the average height of the environment. This may be the case of the deployment of a fixed WiMAX solution in a rural environment with the BS located on a high altitude point and the SS deployed on the rooftop of the customer’s house. LOS requires the obstacle free propagation. In that case, the propagation losses are proportional to the square of the distance between the BS and the SS.

NLOS Propagation NLOS (Non-Line-of-Sight) propagation occurs when the terminal is located indoor and/or at ground level. In this situation, there is in most cases no direct path between the BS and the terminal, there is a high number of obstacles on the BS to MS path (buildings, trees, cars, etc.) and the receiver may receive several copies of signal that experienced several reflections/diffractions on different obstacles.

Licensed and Unlicensed WiMAX Spectrum As with any other spectrum based technology, successful WiMAX deployment will depend largely on the availability and suitability of spectrum resources. For entities providing wireless communications services, two sources of spectrum are available:

Licensed spectrum

Unlicensed spectrum

Licensed spectrum requires an authorization/license from the Commission, which offers that individual user an exclusive right to operate on a specific frequency (or frequencies) at a particular location or within a defined geographic area. 2.3 GHz, 2.5 GHz 3.3 GHz and 3.5 GHz, the latter being the most (geographically) widely announced WiMAX frequency band. Unlicensed spectrum permits any user to access specific frequencies within any geographic area inside the United States without prior Commission authorization. While users of this spectrum do not have to apply for individual licenses or pay to use the spectrum. 5 GHz spectrum is the License-exempt bands. In the future, various bands between 5 GHz and 6 GHz can be used for unlicensed WiMAX, depending on the country involved. They are still subject to certain rules. First, unlicensed users must not cause interference to licensed users and must accept any interference they receive. Second, any equipment that will be utilized on unlicensed spectrum must be approved in advance by the Commission.

Interoperability in a WiMAX network Technology for wireless networks with interoperability develops the concept of "communications anytime anywhere". Within the WiMAX industry there is a strong commitment to ensuring full interoperability, both through certification and ad-hoc testing between vendors. It is important for network operators to realize how interoperability is established and what it covers so that they understand how different products, solutions and applications from different vendors can coexist in the same WiMAX network. The WiMAX Forum Certification program verifies interoperability at the PHY and MAC layers.

WiMAX Architecture

The architecture of a typical Mobile WiMAX network is shown in the below Figure. MSs and BTSs sit at the network edge and responsible for over-the-air transmissions. Further into the network, the ASN interfaces the BTS and the all-IP core network, the CSN. Typically the ASN includes numerous BTSs with one or more ASN gateways. The ASN manages radio resources, MS access, mobility, security and QoS. It acts as a relay for the CSN for IP address allocation and AAA functions. The ASN gateway hosts the Mobile IP Foreign Agent (FA). The CSN performs core network functions, including policy and admission control, IP address allocation, billing and settlement. It hosts the Mobile IP Home Agent (HA), the IP and AAA servers, and PSTN and VoIP gateways. The CSN is also responsible for internetworking with non-WiMAX networks (e.g. 3G, DSL) and for roaming through links to other CSNs.

Figure: WiMAX architecture

WiMAX Reference Network Model with Interface & Functionality

Reference network model

Interfaces Functionality

R1 Interface between the MS and the ASN Air interface

R2 Interface between the MS and the CSN AAA, IP host configuration, mobility management

R3 Interface between the ASN and CSN AAA, policy enforcement, mobility management

R4 Interface between ASNs Mobility management

R5 Interface between CSNs Internetworking, roaming

R6 Interface between BTS and ASN gateway IP tunnel management to establish and release MS connection

R8 Interface between BTSs Handoffs

WiMAX security architecture

The security architecture of IEEE 802.16 is comprised of five components:

1. Security associations A context to maintain the security state relevant to a connection between a base station (BS)

and a subscriber station (SS). The role of security associations (SA) is to maintain the security

state/context relevant to a connection; it operates at MAC layer or layer 2 of the network stack.

There are two SA types in 802.16, data SA and authorization SA.

2. Certificate profile The standard uses X.509v3 certificates to identify communicating parties. The standard defines

two certificate types: manufacture certificates and subscriber station (SS) certificates. The

manufacture certificate identifies the manufacture of 802.16 devices (network card, base

station etc.). An SS certificate identifies the subscriber station and includes its MAC address in

the subject field. Manufacturers typically create and sign SS certificates. The design assumes

the SS maintains the private key corresponding to its public key in sealed tamper resistant

storages.

3. PKM authorization PKM stands for Privacy and Key Management. The PKM authorization protocol is used to distribute an authorization token or key to an authorized SS. This step involves three messages exchanges. The SS uses its RSA private key to retrieve the AK. Correct use of the AK demonstrates authorization to access the network. 4. Privacy and key management It is the protocol to rekey the SA. Once authorized to the network, the SS can now establish a data SA between it and the BS, for that it again uses the PKM protocol. The phase can have two or three message exchanges. BS never uses message 1 unless it wants to rekey a data SA or create a new SA. SS uses message 2 to request SA parameters. It is noteworthy that the PKM protocol is one side authentication from the BS side, there is no comparable authentication from the SS side. 5. Encryption By default the 802.16d standard supports DES-CBC encryption operating over the payload field

of the MAC protocol data unit. Neither the MAC header nor the packet CRC is encrypted. It is

noteworthy that the 802.16d version of the standard doesn’t provide any means for data

authenticity. And in 802.16e payload field encryption is using DES-CBC and AES.

WiMAX Performance Indicator To evaluate and optimize the performance of WiMAX systems radio resource management Procedures are implemented. For radio resource management (power control, selection of the modulation and coding scheme and use of advanced antenna technology), the standard defines a set of channel quality indicators are available.

• RSSI (Received Signal Strength Indicator) • CINR (Carrier-to-Interference-and-Noise Ratio)

A vibrant WiMAX ecosystem is rapidly emerging to address the needs of network operators. It

includes a wide range of players: content providers and application developers, device

manufacturers, solution providers and equipment vendors. Many have started to work together

to ensure that operators can fully exploit WiMAX.