WiMAX IEEE 802.16 technology tutorial- IEEE 802.16, WiMAX, Wireless Microwave Access technology is able to provide 4G levels of Broadband Wireless Access for both mobile and fixed applications.In this section WiMAX IEEE 802.16 tutorial WiMAX history WiMAX IEEE 802.16 standards WiMAX physical layer, & modulation WiMAX frequencies & spectrum WiMAX MAC layer WiMAX QoS WiMAX network architecture WiMAX security WiMAX testing WiMAX TDD and FDD comparisonWiMAX technology is a broadband wireless data communications technology based around the IEE 802.16 standard providing high speed data over a wide area.The letters of WiMAX stand for Worldwide Interoperability for Microwave Access (AXess), and it is a technology for point to multipoint wireless networking.WiMAX technology is able to meet the needs of a large variety of users from those in developed nations wanting to install a new high speed data network very cheaply without the cost and time required to install a wired network, to those in rural areas needing fast access where wired solutions may not be viable because of the distances and costs involved. Additionally it is being used for mobile applications, providing high speed data to users on the move.What is WiMAX technology? - basicsThe standard for WiMAX technology is a standard for Wireless Metropolitan Area Networks (WMANs) that has been developed by working group number 16 of IEEE 802, specializing in point-to-multipoint broadband wireless access. Initially 802.16a was developed and launched, but now it has been further refined. 802.16d or 802.16-2004 was released as a refined version of the 802.16a standard aimed at fixed applications. Another version of the standard, 802.16e or 802.16-2005 was also released and aimed at the roaming and mobile markets.WiMAX technology uses some key technologies to enable it to provide the high speed data rates: OFDM (Orthogonal Frequency Division Multiplex): OFDM has been incorporated into WiMAX technology to enable it to provide high speed data without the selective fading and other issues of other forms of signal format.

Note on OFDM:Orthogonal Frequency Division Multiplex (OFDM) is a form of transmission that uses a large number of close spaced carriers that are modulated with low rate data. Normally these signals would be expected to interfere with each other, but by making the signals orthogonal to each other there is no mutual interference. The data to be transmitted is split across all the carriers to give resilience against selective fading from multi-path effects..Click on the link for an OFDM tutorial

MIMO (Multiple Input Multiple Output): WiMAX technology makes use of multipath propagation using MIMO. By utilising the multiple signal paths that exist, the use of MIMO either enables operation with lower signal strength levels, or it allows for higher data rates.

Note on MIMO:Two major limitations in communications channels can be multipath interference, and the data throughput limitations as a result of Shannon's Law. MIMO provides a way of utilising the multiple signal paths that exist between a transmitter and receiver to significantly improve the data throughput available on a given channel with its defined bandwidth. By using multiple antennas at the transmitter and receiver along with some complex digital signal processing, MIMO technology enables the system to set up multiple data streams on the same channel, thereby increasing the data capacity of a channel.Click on the link for a MIMO tutorialWiMAX ForumThe WiMAX Forum is a wireless industry consortium with a growing number of members including many industry leaders. It has been set up to support and develop WiMAX technology worldwide, bring common standards across the globe to enable the technology to become an established worldwide technology.One of the aims of the forum is to enable a standard to be adopted that will enable full interoperability between products. Learning from the problems of poor interoperability experienced with previous wireless standards, and the impact that this had on take up, the WiMAX Forum aims to prevent this from happening. Ultimately vendors will be able to have products certified under the auspices of the Forum, and then be able to advertise their products as "Forum Certified".Although WiMAX technology will support traffic based on transport technologies ranging from Ethernet, Internet Protocol (IP), and Asynchronous Transfer Mode (ATM), the Forum will only certify the IP-related elements of the 802.16 products. The focus is on IP operations because this is the now the main protocol that is used.WiMAX versionsSince its initial conception, new applications for WiMAX have been developed and as a result there are two "flavours" of WiMAX technology that are available: 802.16d (802.16-2004) 802.16e (802.16-2005)The two flavours of WiMAX technology are used for different applications and although they are based on the same standard, the implementation of each has been optimised to suit its particular application.1. 802.16d - DSL replacement The 802.16d version is often referred to as 802.16-2004 and it is closer to what may be termed the original version of WiMAX defined under 802.16a. It is aimed at fixed applications and providing a wireless equivalent of DSL broadband data. In fact the WiMAX Forum describes the technology as "a standards-based technology enabling the delivery of last mile wireless broadband access as an alternative to cable and DSL."

802.16d is able to provide data rates of up to 75 Mbps and as a result it is ideal for fixed, DSL replacement applications. It may also be used for backhaul where the final data may be distributed further to individual users. Cell radii are typically up to 75 km.

2. 802.16e - Nomadic / Mobile While 802.16 / WiMAX was originally envisaged as being a fixed only technology, with the need for people on the move requiring high speed data at a cost less than that provided by cellular services and opportunity for a mobile version was seen and 802.16e was developed. This standard is also widely known as 802.16-2005. It currently provides the ability for users to connect to a WiMAX cell from a variety of locations, and there are future enhancements to provide cell handover.

802.16e is able to provide data rates up to 15 Mbps and the cell radius distances are typically between 2 and 4 km.

CompetitionThe competition with WiMAX, 802.16 depends upon the type or version being used. Although initially it was thought that there could be significant competition with Wi-Fi, there are other areas to which WiMAX is posing a threat.1. DSL cable lines WiMAX is able to provide high speed data links to users and in this way it can pose a threat to DSL cable operators.

2. Cell phone operators Cell phone operators saw the mobile version of WiMAX as a significant threat. It is offering data download speeds in excess of those that can be offered even using the cellular UMTS HSPA (High Speed Packet Access) However LTE has gained acceptance as the global cellular telecommunications system.WiMAX technology is now being deployed in many areas and while it was initially seen as yet another wireless standard that might fall into the background, it is now emerging as a major front runner and posing threats to other areas of the industry.WiMAX history- overview of WiMAX history and how the IEEE 802.16 standard has developed from its early beginnings.In this section WiMAX IEEE 802.16 tutorial WiMAX history WiMAX IEEE 802.16 standards WiMAX physical layer, & modulation WiMAX frequencies & spectrum WiMAX MAC layer WiMAX QoS WiMAX network architecture WiMAX security WiMAX testing WiMAX TDD and FDD comparisonThe history of WiMAX starts back in the 1990s with the realisation that there would be a significant increase in data traffic over telecommunications networks. With wired telecommunications networks being very expensive, especially I outlying areas and not installed in many countries, wire-less methods were investigated.WiMAX history started with these investigations into what was termed the last mile connectivity - methods of delivering high speed data to a large number of users who may have no existing wired connection.The possibility of low cost last mile connectivity along with the possibility of a system that could handle backhaul over a wireless link proved to be a compelling argument to develop a new wireless data link system.IEEE standard developedThe next major phase in WiMAX history was the development of the standards by the IEEE.The 802.16 standards working group was set up by the IEEE in 1999 under the IEEE 802 LAN/MAN Standards Committee. The first 802.16 standard was approved in December 2001and this was followed by two amendments to the basic 802.16 standard. These amendments addressed issues of radio spectrum and interoperability and came under the designations 802.16a and 802.16c.In September 2003 a major revision project was commenced. This had the aim of aligning the standard with the European / ETSI HIPERMAN standard. It was also intended to incorporate conformance test specifications within the overall standard. The project was completed in 2004 and the standard was released as 802.16d, although it is often referred to as 802.16-2004 in view of the release date. With the release of the 802.16-2004 standard, the previous 802.16 documents, including the a, b, and c amendments were withdrawn.Wireless technologies IEEE 802.16 WiMAX standards- overview, information or tutorial about the WiMAX IEEE 802.16 standards, including 802.16d (802.16-2004) and 802.16e (802.16-2005).In this section WiMAX IEEE 802.16 tutorial WiMAX history WiMAX IEEE 802.16 standards WiMAX physical layer, & modulation WiMAX frequencies & spectrum WiMAX MAC layer WiMAX QoS WiMAX network architecture WiMAX security WiMAX testing WiMAX TDD and FDD comparisonThe standards board of the IEEE (Institute of Electrical and Electronics Engineers) based in the USA set up a working group to address Broadband Wireless Access Standards under the 802.16 banner. Its aim was to prepare formal standards that would be used for the deployment of broadband metropolitan area networks around the world.Although the standards for the physical and MAC layers are defined under 802.16, the technology has been named WiMAX (Worldwide interoperability of Microwave Access) and issues, including interoperability, certification and promotion of the system are handled by the WiMAX Forum.Relationship with WiMAX ForumThe WiMAX Forum was formed in June 2001. Its aim is to promote and certify compatibility and interoperability of broadband wireless products. In particular its focus is on the IEEE 802.16 standard which has been aligned with the ETSI HiperMAN standard. In this role the WiMAX Forum works with the IEEE 802.16 working group.802.16 Standards and AmendmentsAlthough the original 802.16 standard along with amendments a, b, and c are now withdrawn, there are still many documents that are being used for defining and evolving the 802.16 standard. A summary of the major documents, including those that have been withdrawn is given below:Standard / amendment Comments

802.16 Now withdrawn. This is the basic 802.16 standard that was released in 2001. It provided for basic high data links at frequencies between 11 and 60 GHz.

802.16a Now withdrawn. This amendment addressed certain spectrum issues and enabled the standard to be used at frequencies below the 11 GHz minimum of the original standard.

802.16b Now withdrawn. It increased the spectrum that was specified to include frequencies between 5 and 6 GHz while also providing for Quality of Service aspects.

802.16c Now withdrawn. This amendment to 802.16 provided a system profile for operating between 10 and 66 GHz and provided more details for operations within this range. The aim was to enable greater levels of interoperability.

802.16d(802.16-2004) This amendment was also known as 802.16-2004 in view of the fact that it was released in 2004. It was a major revision of the 802.16 standard and upon its release, all previous documents were withdrawn. The standard / amendment provided a number of fixes and improvements to 802.16a including the use of 256 carrier OFDM. Profiles for compliance testing are also provided, and the standard was aligned with the ETSI HiperMAN standard to allow for global deployment. The standard only addressed fixed operation.

802.16e(802.16-2005) This standard, also known as 802.16-2005 in view of its release date, provided for nomadic and mobile use. With lower data rates of 15 Mbps against to 70 Mbps of 802.16d, it enabled full nomadic and mobile use including handover.

802.16f Management information base

802.16g Management plane procedures and services

802.16h Improved coexistence mechanisms for license-exempt operation

802.16j Multi-hop relay specification

802.16k 802.16 bridging

802.16m Advanced air interface. This amendment is looking toth e future and it is anticipated it will provide data rates of 100 Mbps for mobile applications and 1 Gbps for fixed applications. It will allow cellular, macro and micro cell coverage, with currently there are no restrictions on the RF bandwidth although it is expected to be 20 MHz or more.

Summary of the IEEE 802.16 standardsIn view of the fact that it is necessary for standards such as 802.16 to continually move forward, further amendments and documents will be issued as new development take place. Only by taking account of the way in which technology is moving and the new requirements for 802.16, can it keep pace with the needs of the users. One good example of a standard that has evolved is Ethernet. This standard has remained in use for many years, and will do so for many years to come. This has been achieved by simply upgrading the standard to keep pace with the needs of the users. In this way it has been the major networking standard for over 30 years. This too could be true for the IEEE 802.16 standard.WiMAX RF physical layer, & modulation- an overview, summary or tutorial about the WiMAX RF physical layer with the use of WiMAX, OFDM, WiMAX MIMO and modulation In this section WiMAX IEEE 802.16 tutorial WiMAX history WiMAX IEEE 802.16 standards WiMAX physical layer, & modulation WiMAX frequencies & spectrum WiMAX MAC layer WiMAX QoS WiMAX network architecture WiMAX security WiMAX testing WiMAX TDD and FDD comparisonThe use of WiMAX is starting to grow rapidly, and many manufacturers are producing WiMAX equipment. One of the areas of particular interest is the WiMAX RF physical layer, or air interface as this governs the radio signal that is transmitted and received.The WiMAX, 802.16-2004 standard describes four different RF or air interfaces dependent upon the application envisaged. Of these the one that is intended for non-line of sight applications up to 30 km and for frequencies below 11 GHz is the most widely implemented at the moment. As a result it is often thought of as the WiMAX air interface.Basics of the WiMAX air interfaceThe WiMAX RF signal uses OFDM (orthogonal frequency division multiplex) techniques and the signal incorporates multiples of 128 carriers in a total signal bandwidth that may range from 1.25 to 20 MHz.

Note on OFDM:Orthogonal Frequency Division Multiplex (OFDM) is a form of transmission that uses a large number of close spaced carriers that are modulated with low rate data. Normally these signals would be expected to interfere with each other, but by making the signals orthogonal to each other there is no mutual interference. The data to be transmitted is split across all the carriers to give resilience against selective fading from multi-path effects..Click on the link for an OFDM tutorial

The WiMAX signal bandwidth can be set to a figure between 1.25 and 20 MHz. To maintain orthogonality between the individual carriers the symbol period must be the reciprocal of the carrier spacing. As a result narrow bandwidth WiMAX systems have a longer symbol period. The advantage of a longer symbol period is that this helps overcome problems such as multipath interference that is prevalent on non-line of sight applications. This is a great advantage that WiMAX systems possess.WiMAX MIMOMore advanced versions including 802.16e utilise MIMO (Multiple Input Multiple Output) and as a result they support multiple antennas. The use of these techniques provides potential benefits in terms of coverage, self installation, power consumption, frequency re-use and bandwidth efficiency.

Note on MIMO:Two major limitations in communications channels can be multipath interference, and the data throughput limitations as a result of Shannon's Law. MIMO provides a way of utilising the multiple signal paths that exist between a transmitter and receiver to significantly improve the data throughput available on a given channel with its defined bandwidth. By using multiple antennas at the transmitter and receiver along with some complex digital signal processing, MIMO technology enables the system to set up multiple data streams on the same channel, thereby increasing the data capacity of a channel.Click on the link for a MIMO tutorial

WiMAX adaptive modulation and codingWiMAX modulation and coding is adaptive, enabling it to vary these parameters according to prevailing conditions. WiMAx modulation and coding can be changed on a burst by burst basis per link. To determine the required WiMAX modulation and coding scheme the channel quality feedback indicator is used. The mobile can provide the base station with feedback on the downlink channel quality and for the uplink, the base station can estimate the channel quality, based on the received signal quality.

Parameter Downlink Uplink

Modulation BPSK, QPSK, 16 QAM, 64 QAM; BPSK optional for OFDMA-PHY BPSK, QPSK, 16 QAM; 64 QAM optional

Coding Mandatory: convolutional codes at rate 1/2, 2/3, 3/4, 5/6

Optional: convolutional turbo codes at rate 1/2, 2/3, 3/4, 5/6; repetition codes at rate 1/2, 1/3, 1/6, LDPC, RS-Codes for OFDM-PHY Mandatory: convolutional codes at rate 1/2, 2/3, 3/4, 5/6

Optional: convolutional turbo codes at rate 1/2, 2/3, 3/4, 5/6; repetition codes at rate 1/2, 1/3, 1/6, LDPC

WiMAX physical layer data ratesOne of the key performance factors of any wireless system is the data rates that can be achieved. As WiMAX is particularly flexible in terms of channel bandwidth, modulation and also the coding scheme, these can significantly vary the data rates that can be achieved.A summary of the different modulation access / modulation technologies and oversampling rates is given in the table below:

Channel Bandwidth (MHz)

Attribute 1.25 3.5 5 10

Physical layer modulation / access mode 128 OFDMA 256 OFDM 512 OFDMA 1024 OFDMA

Oversampling 28/25 8/7 28/25 28/25

The table below gives a summary of the physical later data rates that may be achieved using different WiMAX modulation, coding and channel bandwidths.

Physical layer data rate (kbps)

Channel B/W 1.25 3.5 5 10

Modulation & code rate Downlink Uplink Downlink Uplink Downlink Uplink Downlink Uplink

BPSK1/2 -- -- 946 326 -- -- -- --

QPSK1/2 504 154 1882 653 2520 653 5040 1344

QPSK3/4 756 230 2822 979 3870 979 7560 2016

16QAM1/2 1008 307 3763 1306 5040 1306 10 080 2688

16QAM 3/4 1512 461 5645 1958 7560 1958 15 120 4032

64QAM 1/2 1512 461 5645 1958 7560 1958 15 120 4032

64QAM2/3 2016 614 7526 2611 10 080 2611 20 160 5376

64QAM3/4 2268 691 8467 2938 11 340 2938 22 680 6048

64QAM5/6 2520 768 9408 3264 12 600 3264 25 200 6720

WiMAX data structureAlthough WiMAX can be deployed as TDD (Time Division Duplex), FDD (Frequency Division Duplex) and half duplex FDD, the most common arrangement is the TDD mode. His allows for a greater efficiency in spectrum usage than FDD mode.Using TDD mode the WiMAX base station and the end users transmit on the same frequency, but to enable them not to interfere with each other their transmissions are separated in time. In order to achieve this the base station first transmits a subframe and this is followed by a short gap which is called the Transmit/receive Transition Gap (TTG). After this gap, the users or remote stations are able to transmit their subframes. The timing of these "uplink" subframes needs to be accurately controlled and synchronised so that they do not overlap whatever distance they are from the base station. Once all the uplink subframes have been transmitted, another short gap known as the Receive/transmit Transition Gap (RTG) is left before the basestation transmits again.There are slight differences between the WiMAX subframes transmitted on the uplink and downlink. The downlink subframe begins with a preamble, after which a header is transmitted and this is followed by one or more bursts of data. The modulation within a subframe may change, but it remains the same within an individual burst. Nevertheless it is possible for the modulation type to change from one burst to the next. The first bursts to be transmitted use the more resilient forms of modulation such as BPSK and QPSK. Later bursts may use the less resilient forms of modulation such as 16 QAM and 64 QAM that enable more data to be carried.By Ian PooleWiMAX Frequencies and Spectrum Allocations- summary of the WiMAX spectrum allocations and frequencies allocated around the globe.In this section WiMAX IEEE 802.16 tutorial WiMAX history WiMAX IEEE 802.16 standards WiMAX physical layer, & modulation WiMAX frequencies & spectrum WiMAX MAC layer WiMAX QoS WiMAX network architecture WiMAX security WiMAX testing WiMAX TDD and FDD comparisonThe IEEE 802.16 WiMAX standard allows data transmission using multiple broadband frequency ranges. The original 802.16a standard specified transmissions in the range 10 - 66 GHz, but 802.16d allowed lower frequencies in the range 2 to 11 GHz. The lower frequencies used in the later specifications means that the signals suffer less from attenuation and therefore they provide improved range and better coverage within buildings. This brings many benefits to those using these data links within buildings and means that external antennas are not required.Different bands are available for WiMAX applications in different parts of the world. The frequencies commonly used are 3.5 and 5.8 GHz for 802.16d and 2.3, 2.5 and 3.5 GHz for 802.16e but the use depends upon the countries:

Region FrequencyBands (GHz) Comments

Canada 2.32.53.55.8

USA 2.32.55.8

Central and South America 2.53.55.8 The spectrum is very fragmented and allocations vary from country to country

Europe 2.53.55.8 The spectrum is very fragmented and varies from country to country. The 2.5 GHz allocation is currently allocated to IMT 2000. 5.8 GHz is also not available in most European countries.

Middle East and Africa 2.55.8 The spectrum is very fragmented.

Russia 2.53.55.8 The 2.5 GHz allocation is currently allocated to IMT 2000.

Asia Pacific(inc China, India, Australia, etc) 2.32.53.33.55.8 The spectrum is very fragmented and varies between countries.

Current major spectrum allocations for WiMAX worldwideWiMAX MAC Layer- an overview of the essentials of the WiMAX MAC layer - the media access control layer for the IEEE 802.16 system.In this section WiMAX IEEE 802.16 tutorial WiMAX history WiMAX IEEE 802.16 standards WiMAX physical layer, & modulation WiMAX frequencies & spectrum WiMAX MAC layer WiMAX QoS WiMAX network architecture WiMAX security WiMAX testing WiMAX TDD and FDD comparisonThe WiMAX MAC layer, or IEEE 802.16 MAC is an essential elements within the overall WiMAX software stack.The WiMAX MAC layer is a form of MAC used for the WiMAX system.WiMAX MAC layer basicsA MAC layer or Media Access Control data communication protocol sub-layer may also be known as a Medium Access Control layer.A MAC layer is a sub-layer of the Data Link Layer. This is defined in the standard seven-layer OSI model as layer 2. The MAC layer provides addressing and channel access control mechanisms that make it possible for several terminals or network nodes to communicate within a multi-point network, typically a local area network (LAN) or metropolitan area network (MAN).The WiMAX MAC has been designed and optimised to enable point to multipoint wireless applications and the WiMAX MAC layer provides an interface between the physical layer and the higher application layers within the stack.The WiMAX MAC layer has to meet a number of requirements: Point to multipoint: One of the main requirements for WiMAX is that it must be possible for a base station to communicate with a number of different outlying users, either fixed or mobile. To achieve this, the IEEE 802.16, WiMAX MAC layer is based on collision sense multiple access with collision avoidance, CSMA/CA to provide the point to multipoint, PMP capability. Connection orientated: Supports communication in all conditions: The WiMAX MAC layer must be able to support a large number of users along with high data rates. As the traffic is packet data orientated it must be able to support both continuous and" bursty" traffic. Most data traffic is "bursty" in nature having short times of high data rates then remaining dormant for a short while. Efficient spectrum use: The WiMAX MAC must be capable of supporting methods that enable very efficient use of the spectrum. Variety of QoS options: To provide the support for different forms of traffic from voice data to Internet surfing, etc, a variety of different classes and forms of QoS support are needed. Support for QoS is a fundamental part of the WiMAX MAC-layer. The WiMAX MAC utilises some of the concepts that are embedded in the DOCSIS cable modem standard. Multiple WiMAX / IEEE 802.16 physical layers: With different variants, the WiMAX MAC layer must be able to provide support for the different PHYs. WiMAX MAC layer operationThe WiMAX MAC layer is primarily an adaptation layer between the physical layer and the upper layers within the overall stack.One of the main tasks of the WiMAX MAC layer is to transfer data between the various layers. Transmission of data - reception of MAC Service Data Units, MSDUs from the layer above. It then aggregates and encapsulates them into MAC Protocol Data Units, MPDUs, before passing them to the physical layer, PHY for transmission. Reception of data - the WiMAX MAC layer takes MPDUs from the physical layer. It decapsulates and reorganises them into MSDUs, and then passes them on to the upper-layer protocols. For the different formats: IEEE 802.16-2004 and IEEE 802.16e-2005, the WiMAX MAC design includes a convergence sublayer. This is used to interface with a variety of higher-layer protocols, such as ATM, Ethernet, IP, TDM Voice, and other future protocols that may arise.WiMAX defines a concept of a service flow and has an accompanying Service Flow Identifier, SFID. The service flow is a unidirectional flow of packets with a particular set of QoS parameters, and the identifier is used to identify the flow to enable operation.

WiMAX Protocol StackThere is an additional layer between the WiMAX MAC itself and the upper layers. This is called the Convergence Sublayer. For the upper protocol layers, the convergence sublayer acts as an interface to the WiMAX MAC. Currently the convergence sublayer only supports IP and Ethernet, although other protocols can be supported by encapsulating the data.The WiMAX MAC layer provides for a flexible allocation of capacity to different users. It is possible to use variably sized MPDUs from different flows - these can be included into one data burst before being handed over to the PHY layer for transmission. Also, multiple small MSDUs can be aggregated into one larger MPDU. Conversely, one big MSDU can be fragmented into multiple small ones in order to further enhance system performance. This level of flexibility gives significant improvements in overall efficiency.WiMAX MAC Connection IdentifierBefore any data is transferred over a WiMAX link, the user equipment or mobile station and the base station must create a connection between the WiMAX MAC layers of the two stations. To achieve this, an identifier known as a Connection Identifier, CID, is generated and assigned to each uplink / downlink connection. The CID serves as an intermediate address for the data packets transmitted over the WiMAX link.There is another identifier used within the WiMAX MAC layer. Known as the Service Flow Identifier, SFID, this is assigned to unidirectional packet data traffic by the base station. It is worth noting that the base station WiMAX MAC layer also handles the mapping of the SFIDs to CIDs to provide the required quality of service.The WiMAX MAC layer also incorporates a number of other features including power-management techniques and security features.The WiMAX MAC layer has been developed to provide the functionality required for a point to multipoint system. The WiMAX MAC layer is also able to provide support for the different physical layers needed for the different flavours of WiMAX that are in use.WiMAX QoS Quality of Service- an overview of the essentials of WiMAX QoS, Quality of service and the various WiMAX QoS Service Classes.In this section WiMAX IEEE 802.16 tutorial WiMAX history WiMAX IEEE 802.16 standards WiMAX physical layer, & modulation WiMAX frequencies & spectrum WiMAX MAC layer WiMAX QoS WiMAX network architecture WiMAX security WiMAX testing WiMAX TDD and FDD comparisonWiMAX QoS or WiMAX Quality of Service is a key element in the delivery of service over the WimAX medium. WiMAX QoS.With techniques such as Internet Protocol being used, delays or latency and jitter can be introduced into the data transmission arena. While IP techniques provide improved levels of efficiency, this comes at a cost.To overcome the effects of latency and jitter, the concept of quality of service is used. For WiMAX QoS several techniques and definitions are at the core of the implementation.WiMAX QoS basicsIn an ideal world it would be possible to send data over a network and gain the same performance as that achieved by a circuit switched network. However the nature of packet data means that the same channels are sued for data travelling to and from a variety of different sources and end points.Within a packet data network, there are three main parameters that are key to the performance of the network, and the WiMAX QoS. These three parameters are: Latency: Latency is a measure of time delay experienced in a system - in the case of a telecommunications system such as WiMAX it is the time that it takes from the initiation of sending data until it arrives at its destination. In a WiMAX system. The WiMAX system can be split into three major elements as far as latency is concerned: From the user to the base station via the WiMAX radio interface Over the IP network From the base station to the end user over the WiMAX radio interfaceTypically it is found that the maximum latency occurs within the IP network - this may be around 100ms in many instances with the WiMAX radio access network / interface introducing around 5ms. Jitter: In the context of computer networks and int hei case the WiMAX system, jitter is a measure of the variability over time of the packet latency across a network. A network with constant latency has no variation and hence no jitter. However as the levels of data are constantly varying, it takes a variable amount of time for a packet to arrive at its destination. Packet jitter is expressed as an average of the deviation from the network mean latency. Although the term jitter is often used, it is actually imprecise and a standards-based term, packet delay variation, PDV, is more correctly used. PDV is an important quality of service factor in assessment of network performance. Packet loss: Packet loss is the term used to indicate the loss of data packets during transmission over a network. Packet loss may occur for a variety of reasons but normally occurs as a result of high network latency or overloading of switches or routers that are unable to process or route all the incoming data.WiMAX QoS definitionsIn order to categorise the different types of quality of service, there are five WiMAX QoS classes that have been defined.These WiMAX QoS classes are defined in the table below:

WiMAX QoS ClassWiMAX QoS Class Details

Unsolicited Grant Service The Unsolicited Grant Service, UGS is used for real-time services such as Voice over IP, VoIP of for applications where WiMAX is used to replace fixed lines such as E1 and T1.

Real-time Packet Services This WiMAX QoS class is used for real-time services including video streaming. It is also used for enterprise access services where guaranteed E1/T1 rates are needed but with the possibility of higher bursts if network capacity is available. This WiMAX QoS class offers a variable bit rate but with guaranteed minimums for data rate and delay.

Extended Real Time Packet Services This WiMAX QoS class is referred to as the Enhanced Real Time Variable Rate, or Extended Real Time Packet Services. This WiMAX QoS class is used for applications where variable packet sizes are used - often where silence suppression is implemented in VoIP. One typical system is Skype.

Non-real time Packet Services This WiMAX QoS class is used for services where a guaranteed bit rate is required but the latency is not critical. It might be used for various forms of file transfer.

Best Effort This WiMAX QoS is that used for Internet services such as email and browsing. Data packets are carried as space becomes available. Delays may be incurred and jitter is not a problem.

WiMAX Network Architecture- summary, description or overview of the basics of the WiMAX network architecture, detailing the different elements / entities in the WiMAX network.In this section WiMAX IEEE 802.16 tutorial WiMAX history WiMAX IEEE 802.16 standards WiMAX physical layer, & modulation WiMAX frequencies & spectrum WiMAX MAC layer WiMAX QoS WiMAX network architecture WiMAX security WiMAX testing WiMAX TDD and FDD comparisonThe WiMAX network architecture defines the system after the air interface to enable a full end to end network to be achieved.In order that elements of network equipment can be used from different suppliers, it is necessary to define the WiMAX network architecture that is common to all WiMAX networks. In this way economies of scale can be gained along with robust networks that are able to perform reliably under all conditions.WiMAX network basicsThe basic WiMAX standard does not define the WiMAX network for end to end connectivity. However the need for a standard WiMAX network architecture is realised and the WiMAX Forum Network Working Group have developed a standard for defining the WiMAX network architecture.The standard now used is available from the WiMAX Forum as WiMAX Forum Network Architecture, document: WMF - T32-002-R010v04 and it is dated February 03, 2009.WiMAX network architecture major entitiesThe WiMAX architecture developed by the WiMAX form supports is a unified network architecture to support fixed, nomadic and mobile operation. The WiMAX network architecture is based upon an all-IP model.The WiMAX network architecture comprises three major elements or areas. Remote or Mobile stations: These are the user equipments that may be mobile or fixed and may be located in the premises of the user. Access Service Network, ASN : This is the area of the WiMAX network that forms the radio access network at the edge and it comprises one or more base stations and one or more ASN gateways. Connectivity Service Network, CSN: This part of the WiMAX network provides the IP connectivity and all the IP core network functions. It is what may be termed the core network in cellular parlance.

WiMAX Network Reference ModelWiMAX network architectureThe overall WiMAX network comprises a number of different entities that make up the different major areas described above. These include the following entities Subscriber Station, SS / Mobile Station, MS : The Subscriber station, SS may often be referred to as the Customer Premises Equipment, CPE. These take a variety of forms and these may be termed "indoor CPE" or "outdoor CPE" - the terminology is self-explanatory. The outdoor CPE has the advantage that it provides better performance as a result of the better position of the antenna, whereas the indoor CPE can be installed by the user. Mobile Stations may also be used. These are often in the form of a dongle for a laptop, etc. Base Station, BS: The base-station forms an essential element of the WiMAX network. It is responsible for providing the air interface to the subscriber and mobile stations. It provides additional functionality in terms of micro-mobility management functions, such as handoff triggering and tunnel establishment, radio resource management, QoS policy enforcement, traffic classification, DHCP (Dynamic Host Control Protocol) proxy, key management, session management, and multicast group management. ASN Gateway, ASN-GW: The ASN gateway within the WiMAX network architecture typically acts as a layer 2 traffic aggregation point within the overall ASN.

The ASN-GW may also provide additional functions that include: intra-ASN location management and paging, radio resource management and admission control, caching of subscriber profiles and encryption keys. The ASN-GW may also include the AAA client functionality(see below), establishment and management of mobility tunnel with base stations, QoS and policy enforcement, foreign agent functionality for mobile IP, and routing to the selected CSN. Home Agent, HA: The Home Agent within the WiMAX network is located within the CSN. With Mobile-IP forming a key element within WiMAX technology, the Home Agent works in conjunction with a "Foreign Agent", such as the ASN Gateway, to provide an efficient end-to-end Mobile IP solution. The Home Agent serves as an anchor point for subscribers, providing secure roaming with QOS capabilities. Authentication, Authorisation and Accounting Server, AAA: As with any communications or wireless system requiring subscription services, an Authentication, Authorisation and Accounting server is used. This is included within the CSN. WiMAX Security- an overview of the essential elements for WiMAX security including encryption and authentication and the ways they are implemented.In this section WiMAX IEEE 802.16 tutorial WiMAX history WiMAX IEEE 802.16 standards WiMAX physical layer, & modulation WiMAX frequencies & spectrum WiMAX MAC layer WiMAX QoS WiMAX network architecture WiMAX security WiMAX testing WiMAX TDD and FDD comparisonLike any system security is a key element within the overall WiMAX system. WiMAX security has to implemented in a way that provides sufficient protection against intrusion and other forms of unauthorised access without hindering the overall operation.Accordingly WiMAX security has been incorporated into the heart of the system to ensure that seamlessly integrated and provides an effective solution.WiMAX security utilises a number of advanced techniques including PKMv2 based authentication and over the air encryption. These considerable improve the level of security that is can be attained, but overall end-to-end security is still challenging and requires each network to adopt security within the overall network design and roll out as well as in the ways of working.WiMAX security basicsWiMAX uses Internet Protocol, IP as the core transport mechanism, and as a result, WiMAX security measures need to incorporate not only the traditional security requirements for a wireless telecommunications system, but also those relating to the use of IP systems.In view of the need for a high level of WiMAX security, the IEEE 802.16 working groups incorporated security measures into the standard during the concept stages to counteract WiMAX security threats. WiMAX security has been embedded into the standard from the beginning rather than being added as an extra at a later stage. By adopting this approach, WiMAX security has been made more effective while being less intrusive to the user.WiMAX security elements are included in the standard and fall under four main headings: Authentication of the user device Higher level user authentication Advanced over-the-air encryption Methods for securing the control and signalling within an IP scenario Each of these WiMAX security areas has been addressed within standards, but even so, it is still necessary for the network operators to use good practice to ensure that security is not compromised. It is quite possible to circumvent the best security technology if the correct operating procedures are not in place.WiMAX security threatsWhen developing any security system it is necessary to understand the means by which security could be compromised and in this way build in the relevant security measures.Some of the main threats to WiMAX security are summarised in the table below:

Type of security attack Description / details of the security attack

Man-in-the-middle This form of WiMAX security issue occurs when a base station is set up to impersonate a base station in the network, either just to a subscriber, or a two way impersonation between the subscriber and the base station.

Privacy compromise This type of security attack takes the form of the attacker capturing user and / or signalling traffic being conveyed over the wireless or the wired elements of the network. These packets can be analysed and information extracted at a later time.

Theft of service This occurs if users without authorised access are able to access the network and utilise it without payment.

Denial of service (physical) This is achieved by degrading the network performance by physically disrupting the physical elements of the network, e.g. by jamming the radio channels used.

Denial of service (protocol) This form of denial of service involves overloading the network or system resources by introducing new traffic or modifying existing traffic. This happens when Internet websites are maliciously targeted by millions of requests to overload their resources.

Replay This form of WiMAX security issue occurs if previously valid messages are injected into the system to exhaust resources or lock out valid users.

Although these are broad descriptions for the major forms of WiMAX security issue, they all need to be addressed so that malicious attempts cannot succeed in disrupting he network, obtaining user information or data, or gaining unauthorised access to the network.WiMAX security measuresThe WiMAX standard includes several security protection measures to address and overcome the various WiMAX security threats that are posed to the system. These include mutual device / user authentication techniques, a flexible key management tool, traffic encryption, and control and management message protection.There are several key protocols and standards that are used as part of the overall WiMAX security strategy: PKMv2: This is the Privacy Key Management Protocol version 2. This is used as a key management protocol for the encrypted and authorised exchange of crypto keys for multicast and broadcast traffic. EAP: This is the Internet Engineering Task Force, Extensible Authentication Protocol. This protocol is used for device and user authentication. EAS: This is the Advanced Encryption Standard. This is used for encrypting the over the air traffic. During the operation of the system, the various WiMAX security measures are brought in to play at the various required stages. WiMAX security authentication: Authentication is the ability of the network to ensure that the subscriber and subscriber devices are legitimate users and devices to be connected to the network.

Network entry authorisation uses EAP because it provides a flexible and scalable framework for authentication of the user and devices. WiMAX security encryption: The EAS encryption is used for encrypting over the air traffic. The WiMAX security approach utilises uses Counter Mode with Cipher Block Chaining Message, CCM, authentication code. With AES CCM, the sender generates a unique value per packet and sends this value to the receiver. This prevents man-in-the-middle attacks because they would have difficulty in substituting the traffic. An additional measure introduces the use of Traffic Encryption State machine which uses a periodic key refresh mechanism to provide for the continued transition of keys. WiMAX security is able to bring into play a number of security mechanisms to ensure a high level of security. Although no security measures can be deemed to be one hundred percent safe, the WiMAX security measures provide a very high level of security. Provided that the operator processes and procedures are also secure, the overall level of WiMAX security should be sufficiently high for most applications.WiMAX testing and WiMAX conformance test- an overview, summary or tutorial about WiMAX testing, conformance test, and WiMAX test equipment, including conformance test equipment.In this section WiMAX IEEE 802.16 tutorial WiMAX history WiMAX IEEE 802.16 standards WiMAX physical layer, & modulation WiMAX frequencies & spectrum WiMAX MAC layer WiMAX QoS WiMAX network architecture WiMAX security WiMAX testing WiMAX TDD and FDD comparisonWiMAX is a broadband wireless data communications technology based around the IEE 802.16 standard that is capable of providing high speed data communications (70 Mbps) over a wide area. The letters of WiMAX stand for Worldwide Interoperability for Microwave Access (X), and it is a technology for point to multipoint wireless networking. The technology is being deployed in a variety of applications from providing "the last mile" communications to users to supplying the backbone communications networks required in many developing countries.

Types of WiMAX testingWith many manufacturers now developing and supplying equipment, it is essential that they operate to their individual specifications and that they also interoperate with each other. To ensure that this can happen, manufacturers need to perform a variety of different types of test: Development testing Verification and Validation testing Conformance testing Production testingEach of these types of test has its place in the development of any product, and in this case in the development of WiMAX.WiMAX development testDuring the development of any product, test equipment is required to ensure that all the circuitry operates as it should. The test equipment that will typically be required will include items such as oscilloscopes, as well as RF measuring equipment including spectrum analyzers, RF power meters and the like. In addition to this test equipment will be needed to aid debugging the software. This is likely to include emulators of various types.During the development testing stage it is always wise to undertake testing of the product against the conformance tests (see later) as these will have to be undertaken later. By using the conformance test equipment along with the conformance test cases, the product can be made to work correctly and any bugs removed at this stage. Often the conformance test equipment will enable the test cases to be modified to enable development testing to be undertaken.Verification and Validation testingOnce the design of the product has been completed, in this case a WiMAX unit, it will be necessary to ensure that it meets its requirements the requirements set down in the development specification, and that it also operates satisfactorily. These tests need to be performed formally to ensure that the development has been satisfactorily completed. Test equipment here will include any equipment needed to test the interfaces to the overall unit. Typically the test equipment will include items from spectrum analyzers and power meters to check the RF performance to data communications analyzers to check the data interfaces.To ensure that some of this testing can be undertaken more easily, because the overall operation of WiMAX involves many complicated protocols, specialised WiMAX testers or WiMAX test equipment may be used. These items are supplied by a number of test equipment manufacturers and have been developed specifically for WiMAX testing. They are able to interface to both the RF and data interfaces of the unit, and provide a comprehensive test of its operation.WiMAX Conformance TestingOne of the major concerns for any organisation such as the WiMAX Forum, is that of ensuring that devices from a variety of different manufacturers operate satisfactorily together. With the size of specifications for standards such as WiMAX increasing along with their complexity, there is the possibility of areas being interpreted in different ways, or bugs being present that will prevent their interoperability. In addition to this, the 802.16 standard only specifies the Physical and MAC layers of the standard and this leaves many aspects open to the individual vendors. The WiMAX Forum seeks to address this, and ensure that interoperability issues do not arise. A large number of problems in this area would lead to a lack of confidence in the technology as a whole and would significantly decrease sales for all vendors.To ensure that interoperability issues do not occur, products must be run against a validated set of conformance test cases on a set of conformance test equipment that has been validated by the WiMAX Forum. Products that pass conformance and interoperability testing are able to claim they are: "WiMAX Forum Certified" and they can display this mark on their products and marketing materials. Some vendors may claim that their equipment is "WiMAX-ready", "WiMAX-compliant", or "pre-WiMAX", if they are not officially WiMAX Forum Certified. These products may not have been fully tested against the test cases and as a result they may have interoperability problems.There are two types of WiMAX conformance test equipment: 1. Base Station Emulator (BSE): - used for testing a mobile station (MS).

2. Mobile Station Emulator (MSE): - used for testing a base station (BS).There are also other distinctions between the testers. There are those that address the radio signal itself, and those that address the protocols. The radio tests typically take longer to perform as they look for the radio signal performance, addressing parameters such as the spectrum of the signal, power levels and the like. The protocol tests address the manner in which the WiMAX equipment communicates with other units, sending the messages and establishing a link.Although conformance test equipment will be able to run the conformance tests for WiMAX equipment, in view of the different bands that are in use, the conformance test equipment may need different options to enable it to cover the relevant bands.One major area of importance is the development of the test cases that are used for the certification process. The model used follows a similar process to that used for test cases for UMTS. The basic test procedures are written by the WiMAX Forum and these procedures describe the functionality to be tested and the test method. They also provide a priority for them. ETSI then take the test procedures and write the code in TTCN-3. This code is released to the test equipment vendors who analyse, integrate and if necessary raise "changes requests" if necessary. Once test cases are passing on real equipment, they can be submitted for validation. Only then can vendor equipment be tested for certification in a WiMAX Forum accredited test lab. New test cases are often developed as technologies evolve and the older ones can change.Production WiMAX testingOnce an item is in production, testing needs to be performed on it to ensure that each item leaving the production line performs correctly. The testing undertaken at this point in the process is aimed at checking that the unit is built correctly. As this testing adds no value, but only ensure things are correct, the testing needs to be as fast as possible while still ensuring that no faulty product leaves the factory. Accordingly this form of WiMAX testing should not include any development , verification, validation or conformance testing. Instead it should only concentrate on the tests needed to ensure the product has been correctly assembled.The type of test equipment used for production testing is quite different to that needed for, say, conformance testing. Tests need to be performed very quickly, and therefore the test equipment is honed to ensure that it can undertake a limited number of tests very quickly.WiMAX testing is an essential element of the WiMAX rollout. WiMAX products need to be correctly designed, verified and validated and then conformance tested. Once in production, they need to undergo the correct level of production testing. Although this testing can be costly, it is an essential element of the development and production process.WiMAX TDD FDD Comparison- an overview, summary or tutorial comparing WiMAX FDD and TDD duplex modes and giving the advantages and disadvantages of each for of WiMAX 802.16.In this section WiMAX IEEE 802.16 tutorial WiMAX history WiMAX IEEE 802.16 standards WiMAX physical layer, & modulation WiMAX frequencies & spectrum WiMAX MAC layer WiMAX QoS WiMAX network architecture WiMAX security WiMAX testing WiMAX TDD and FDD comparisonToday WiMAX is being deployed in many areas of the globe for a variety of applications. With these WiMAX deployments being aimed at different markets with different applications, the two flavours of duplex scheme available WiMAX, namely TDD and FDD WiMAX need to be considered to ensure that the correct option is taken. Accordingly it is necessary to undertake a WiMAX TDD FDD comparison and assess which option is best for each application within the regulatory limitations. This is in addition to assessing other WiMAX options including the fixed and mobile variants that are availableWith WiMAX offering a high level of service and considered by many as a 4G cellular technology, it is a certain option for deployment in many areas of the globe.Duplex modesThe WiMAX, 802.16 standard offers two forms of duplex transmission to separate the uplink and downlink messages. Both WiMAX TDD (time division duplex) and WiMAX FDD (frequency division duplex) are available. Each method offers its own advantages and disadvantages.

Note on TDD and FDD duplex schemes:In order for radio communications systems to be able to communicate in both directions it is necessary to have what is termed a duplex scheme. A duplex scheme provides a way of organizing the transmitter and receiver so that they can transmit and receive. There are several methods that can be adopted. For applications including wireless and cellular telecommunications, where it is required that the transmitter and receiver are able to operate simultaneously, two schemes are in use. One known as FDD or frequency division duplex uses two channels, one for transmit and the other for receiver. Another scheme known as TDD, time division duplex uses one frequency, but allocates different time slots for transmission and reception. Click on the link for more information on TDD FDD duplex schemes

Each of the two schemes is applicable for different types of service. Accordingly it is necessary to opt for the most effective form of duplex for the given application.WiMAX duplex requirementsIt is possible to use both FDD and TDD for WiMAX. However FDD transmissions require the use of two channels, one for the uplink and one for the downlink. These need to be separated sufficiently to enable the receiver to operate without being desensitised by the transmitter which needs to operate simultaneously. This not only requires there to be a separate frequency separation between uplink and downlink, but it is normally also necessary to incorporate additional filtering to remove the transmitter frequency from the receive band. This can add additional cost into consumer items that are normally very cost sensitive.Any paired spectrum allocated, is normally split such that there is equal bandwidth available in both directions. This is not ideal where the traffic may be asymmetric and the balance may be variable.Using WiMAX TDD it is possible to accommodate the asymmetry in the traffic balance. By altering the number of frames for traffic in each direction it is possible to make far more efficient use of the available spectrum. The balance of frames for each direction, and hence the capacity can be altered dynamically, enabling the system to respond the actual traffic travelling in each direction. Therefore TDD can handle both symmetric and asymmetric broadband traffic and therefore TDD therefore has higher spectral efficiency than FDD for these applications.With both types of WiMAX duplex scheme being available for use, it is necessary to choose the correct form of duplex scheme for the particular type of deployment. To achieve the optimum form, it is necessary to undertake a WiMAX TDD FDD comparison to ascertain the optimum version subject to any regulatory constraints. It is useful to note that the first release of fixed WiMAX support both TDD and FDD duplex modes, although Mobile WiMAX only includes TDD mode.Wireless technologies- resources and analysis covering wireless technologies including Bluetooth, IEEE 802.11 - Wi-Fi, WiMax, IEEE 802.15.4, Zigbee etc

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