3.3 Medium Access Control Common Part Sublayer

3.3 Medium Access Control Common Part Sublayer (MAC CPS)

The Common Part Sublayer (CPS) resides in the middle of the MAC layer. The CPS represents the core of the MAC protocol and is responsible for:

• bandwidth allocation;

• connection establishment;

• maintenance of the connection between the two sides.

The 802.16-2004 standard defines a set of management and transfer messages. The management messages are exchanged between the SS and the BS before and during the establishment of the connection. When the connection is realised, the transfer messages can be exchanged to allow the data transmission.

The CPS receives data from the various CSs, through the MAC SAP, classified to particular MAC connections. The QoS is taken into account for the transmission and scheduling of data over the PHY Layer. The CPS includes many procedures of different types: frame construction, multiple access, bandwidth demands and allocation, scheduling, radio resource management, QoS management, etc. These functions are detailed in Chapters 8 to 11.

3.2 Convergence Sublayer (CS)

3.2 Convergence Sublayer (CS)

The service-specific Convergence Sublayer (CS), often simply known as the CS, is just above the MAC CPS sublayer (see Figure 3.2). The CS uses the services provided by the MAC CPS, via the MAC Service Access Point (SAP). The CS performs the following functions:

• Accepting higher-layer PDUs from the higher layers. In the present version of the standard ^[1], CS specifications for two types of higher layers are provided: the asynchronous transfer mode (ATM) CS and the packet CS. For the packet CS, the higher-layer protocols may be IP v4 (version 4) or v6 (version 6).

• Classifying and mapping the MSDUs into appropriate CIDs (Connection IDentifier). This is a basic function of the Quality of Service (QoS) management mechanism of 802.16 BWA.

• Processing (if required) the higher-layer PDUs based on the classification.

• An optional function of the CS is PHS (Payload Header Suppression), the process of suppressing repetitive parts of payload headers at the sender and restoring these headers at the receiver.

• Delivering CS PDUs to the appropriate MAC SAP and receiving CS PDUs from the peer entity.

Chapter 3: Protocol Layers and Topologies

In this chapter, the protocol layer architecture of WiMAX/802.16 is introduced. The main objectives of each sublayer are given as well as the global functions that they realise. Links are provided to the chapters of this book where each of these sublayers or procedures are described in much more detail.

3.1 The Protocol Layers of WiMAX

The IEEE 802.16 BWA network standard applies the so-called Open Systems Interconnection (OSI) network reference seven-layer model, also called the OSI seven-layer model. This model is very often used to describe the different aspects of a network technology. It starts from the Application Layer, or Layer 7, on the top and ends with the PHYsical (PHY) Layer, or Layer 1, on the bottom (see Figure 3.1).

Figure 3.1: The seven-layer OSI model for networks. In WiMAX/802.16, only the two first layers are defined

The OSI model separates the functions of different protocols into a series of layers, each layer using only the functions of the layer below and exporting data to the layer above. For example, the IP (Internet Protocol) is in Layer 3, or the Routing Layer. Typically. only the lower layers are implemented in hardware while the higher layers are implemented in software.

The two lowest layers are then the Physical (PHY) Layer, or Layer 1, and the Data Link Layer, or Layer 2. IEEE 802 splits the OSI Data Link Layer into two sublayers named Logical Link Control (LLC) and Media Access Control (MAC). The PHY layer creates the physical connection between the two communicating entities (the peer entities), while the MAC layer is responsible for the establishment and maintenance of the connection (multiple access, scheduling, etc.).

The IEEE 802.16 standard specifies the air interface of a fixed BWA system supporting multimedia services. The Medium Access Control (MAC) Layer supports a primarily point to-multipoint (PMP) architecture, with an optional mesh topology (see Section 3.7). The MAC Layer is structured to support many physical layers (PHY) specified in the same standard. In fact, only two of them are used in WiMAX.

The protocol layers architecture defined in WiMAX/802.16 is shown in Figure 3.2. It can be seen that the 802.16 standard defines only the two lowest layers, the PHYsical Layer and the MAC Layer, which is the main part of the Data Link Layer, with the LLC layer very often applying the IEEE 802.2 standard. The MAC layer is itself made of three sublayers, the CS (Convergence Sublayer), the CPS (Common Part Sublayer) and the Security Sublayer.

Figure 3.2: Protocol layers of the 802.16 BWA standard. (From IEEE Std. 802.16-2004 ^[1]. Copyright IEEE 2004, IEEE. All rights reserved.)

The dialogue between corresponding protocol layers or entities is made as follows. A Layer X addresses an XPDU (Layer X Protocol Data Unit) to a corresponding Layer X (Layer X of the peer entity). This XPDU is received as an (X-1)SDU (Layer X-1 Service Data Unit) by Layer X-1 of the considered equipment. For example, when the MAC Layer of an equipment sends an MPDU (MAC PDU) to a corresponding equipment, this MPDU is received as a PSDU (PHYsical SDU) by the PHYsical Layer (see Figure 3.2).

In this chapter, the different layers are introduced. Each of these layers or sublayers and many of their functions are described in the following sections.

2.6 The Korean Cousin: WiBro

2.6 The Korean Cousin: WiBro

South Korea has definitely an advantage in modern telecommunication networks, whether in ADSL (Asymmetric Digital Subscriber Line) or 3G figures. The TTA PG302 BWA standard was approved in June 2004 by the TTA (Telecommunications Technology Association, the Korean standardisation organisation) and is known as WiBro (Wireless Broadband). This standard has the support of leading people in the Korean telecommunication industry.

Originally sought as a competitor of WiMAX, an agreement was found by the end of 2004, while 802.16e was still under preparation, between 802.16 backers (including Intel) and WiBro backers in order to have WiBro products certified as WiMAX equipments.

WiBro licenses were assigned in Korea in January 2005. The three operators are Korea Telecom (KT), SK Telecom (SKT) and Hanaro Telecom. Pilot networks are already in place (April 2006). Relatively broad coverage public commercial offers should start before the end of 2006. WiBro planned deployments in other countries have been reported (among others. Brazil). This should give WiBro an early large-scale BWA deployment and then provide important field technical and market observations.

2.5 Other 802.16 Standards

2.5 Other 802.16 Standards

In addition to the 802.16e amendment of the 802.16 standard, other amendments have been made or are still in preparation. The goal of these amendments is to improve certain aspects of the system (e.g. have a more efficient handover) or to clarify other aspects (e.g. management information).

The 802.16f amendment, entitled ‘Management Information Base’, was published in December 2005 and provides enhancements to IEEE 802.16-2004, defining a Management Information Base (MIB) for the MAC and PHY and the associated management procedures (see Section 3.6 for more details on 802.16f).

The 802.16g amendment was still at the draft stage in October 2006. The draft is entitled ‘Management Plane Procedures and Services’ and the amendment approval is planned for May 2007 (October 2006 information). It should provide the elements for efficient handover, high-performance QoS (Quality of Service) management and radio resource management procedures.

Other amendments at the draft stage are the following (from the IEEE 802.16 website, July 2006):

• 802.16/Conformance04 – Protocol Implementation Conformance Statement (PICS) proforma for frequencies below 11 GHz;

• 802.16k – Media Access Control (MAC) Bridges – Bridging of 802.16.

Amendments at the pre-draft stage are the following:

• 802.16h – Improved Coexistence Mechanisms for License-Exempt Operation;

• 802.16i – Mobile Management Information Base, where the objective is to add mobility support to the 802.16f fixed MIB standard.

Work on the 802.16j amendment draft has been reported, which concerns the Multi-hop Mobile Radio (MMR). Hence, 802.16j should provide some enhancement for the Mesh mode. The Project Authorization Request (PAR) of 802.16j was approved in March 2006.

2.4 Predicted Products and Deployment Evolution

2.4 Predicted Products and Deployment Evolution

2.4.1 Product Types

Different types of WiMAX products are expected.

First step: CPE products. These CPE products are first outdoor (see Figure 1.5) and then indoor. These are the products already certified (mainly outdoor for the moment). For CPEs WiMAX products, some providers may require that only authorised installers should install the equipment for subscribers. It can be expected that self-installed CPEs will quickly appear.

Second step: devices installed on portable equipments. These portable equipments will first be laptops. It is expected (and probably already realised by the time of publication of this book) that these laptop-installed WiMAX devices may have a USB (Universal Serial Bus) connection, PCMCIA (Personal Computer Memory Card International Association) (less probable), a PCI (Peripheral Component Interconnect) connection or another type of connection. In this case, a WiMAX subscriber can move in a limited area (the one covered by the BS) and then nomadicity will be realised.

Later, a WiMAX internal factory-installed device in laptops will probably appear, as is already the case for WiFi. This will clearly produce a situation where WiMAX will spread widely. The difficulties encountered are of two types:

• manufacturing devices small enough; this do not really seem to be a difficult problem:

• radio engineering and deployment considerations, where the technology and deployment techniques should be mature enough to have a high concentration of subscribers.

Final step: WiMAX devices in PDA and other handheld devices such as a mobile phone. For this, WiMAX devices need to be even smaller. They could take the shape of the SIM (Subscriber Identity Module) cards presently used for cellular systems (second and third generation). Thus WiMAX will be a mobile network and then a competitor for 3G systems.

2.4.2 Products and Deployment Timetable

Once WiMAX evolution is described, we need to know about the timetable of these products. What about the network deployments? As of today a large number of pre-WiMAX networks exist around the world, both in developed and developing countries. These deployments are often on a scale smaller than the whole country, typically limited to a region or an urban zone. For example, in France, Altitude Telecom operator proposes a BWA subscription in four geographic departments: Calvados, Orne, Seine-et-Marne and Vendée. The displayed data rate is 1 Mb/s (June 2006). Many fixed WiMAX networks (then using the recently certified products) are imminent, some of them belonging to pre-WiMAX operators planning to upgrade to certified WiMAX.

Table 2.5 is based on documents and conferences by WiMAX actors. The (e), expected, dates are only assumptions. Some of these previewed dates may be changed in the future.

Table 2.5: WiMAX products and networks timetable: (e), expected
Open table as spreadsheet

	Products	Certification	Networks
2005	Proprietary (pre-WiMAX); outdoor CPE		Fixed
2006	Pre-WiMAX equipments; first use of WiMAX certified products	Since January 2006, certification of fixed WiMAX equipments based on IEEE 802.16-2004 (see Section 2.3.1)	Launch of WiBro service in Korea; (e) first nomadic use of WiMAX?
2007	(e) Indoor, self-installed; (e) first use of mobile WiMAX, wave 1 (no MIMO and AAS, etc.)	(e) Certification of mobile WiMAX equipments based on IEEE 802.16e	(e) Nomadic use of WiMAX
2008	(e) Ramp-up of mobile WiMAX products, wave 1 and wave 2 (MIMO and AAS)		(e) Mobility

2.3 WiMAX Products Certification

The WiMAX forum first recognised the Centro de Tecnología de las Comunicaciones, (Cetecom Lab) (http://www.cetecom.es), located in Malaga, Spain, as the first certification lab of WiMAX products. In February 2006, the WiMAX Forum designated the Telecommunications Technology Association's (TTA) IT Testing and Certification Lab in Seoul, South Korea, as the second lab available to WiMAX Forum members to certify compatibility and interoperability of WiMAX products. The first certifications of this latter lab are expected in 2007. The process for selecting a third WiMAX certification lab in China has been reported.

WiMAX conformance should not be confused with interoperability ^[5]. The combination of these two types of testing make up certification testing. WiMAX conformance testing is a process where BS and SS manufacturers test units to ensure that they perform in accordance with the specifications called out in the WiMAX Protocol Implementation Conformance Specification (PICS) documents. The WiMAX PICS documents are proposed by the TWG (see the previous section). In the conformance test, the BS/SS units must pass all mandatory and prohibited test conditions called out by the test plan for a specific system profile. The WiMAX system profiles are also proposed by the TWG.

WiMAX interoperability is a multivendor (≥3) test process hosted by the certification lab to test the performance of the BS and/or SS from one vendor to transmit and receive data bursts of the BS and/or SS from another vendor based on the WiMAX PICS. Then, each SS, for example, is tested with three BSs, one from the same manufacturers, the two others being from different manufacturers. A group test, formally known as a plugfest ^[6], is a meeting where many vendors can verify the interoperability of their equipments.

2.3.1 WiMAX Certified Products

The certification process started in the summer of 2005 in Cetecom. The first equipment certification took place on 24 January 2006. The complete list of certified WiMAX equipments can be found on http://www.wimaxforum.org/kshowcase/view. All these equipments were certified for IEEE 802.16-2004 profiles (fixed WiMAX). Certification of equipments based on mobile WiMAX profiles (or, soon on mobile WiMAX equipments) should take place in the first half of 2007.

The certified equipments are from the three types of WiMAX manufacturers:

• pre-WiMAX experienced companies;

• companies initially more specialised in cellular network products, e.g. Motorola, which is in these two categories;

• newcomers that started business specifically for WiMAX products.

^[5]Agis, A. et al., Global, interoperable broadband wireless networks: extending WiMAX technology to mobility. Intel Technology Journal, August 2004.

^[6]WiMAX Forum White Paper, 3rd WiMAX Forum plugfest-test methodology and key learnings, March 2006.

2.2 WiMAX Forum

2.2 WiMAX Forum

IEEE 802 standards provide only the technology. It is then needed to have other organisms for the certification of conformity and the verification of interoperability. In the case of IEEE 802.11 WLAN, the Wireless Fidelity Alliance (WiFi or Wi-Fi) Consortium had a major role in the success of the WiFi technology, as it is now known. Indeed, the fact that two WiFi certified IEEE 802.11 WLAN devices are guaranteed to work together paved the way for the huge spread of WiFi products.

The certification problem was even more important for WiMAX as many product manufacturers claimed they had verified the 802.16 standard (for pre-WiMAX products, see Section 1.4.2). The WiMAX (Worldwide Interoperability for Microwave Access) Forum (http://www.wimaxforum.org) was created in June 2001 with the objective that the WiMAX Forum plays exactly the same role for IEEE 802.16 as WiFi for 802.11. The WiMAX Forum provides certification of conformity, compatibility and interoperability of IEEE 802.16 products. After a period of low-down, the WiMAX Forum was reactivated in April 2003. Some sources indicate this latter date as the date of the creation of the WiMAX Forum. Intel and Nokia, along with others, played a leading role in the creation of the Forum. Then Nokia became less active, claiming that it wished to concentrate on 3G. However, Nokia is again an active player of WiMAX.

WiMAX Forum members are system and semiconductors manufacturers, other equipment vendors, network operators, academics and other telecommunication actors. A complete list of the WiMAX Forum members can be found on the Forum Member Roster web page. A nonexhaustive list of WiMAX members is proposed in Table 2.2.

Table 2.2: Some WiMAX Forum members
Open table as spreadsheet

Manufacturers	Airspan, Alcatel, Alvarion, Broadcom, Cisco, Ericsson. Fujitsu, Huawei, Intel, LG, Lucent, Motorola, Navini, Nokia, Nortel, NEC Proxim, Sagem, Samsung, Sequans, Siemens, ZTE, etc.
Service providers	British Telecom, France Telecom, KT (Korea Telecom), PCCW, Sprint Nextel, Telmex, etc.

The site of the WiMAX Forum indicates that its objective is to facilitate the deployment of broadband wireless networks based on the IEEE 802.16 standard by ensuring the compatibility and interoperability of broadband wireless equipment. More details about WiMAX certification are given in Section 2.3.

2.2.1 WiMAX Forum Working Groups

The WiMAX Forum is organised into Working Groups (WGs). The scope of these WGs is given in Table 2.3, as indicated on the WiMAX Forum website.

Table 2.3: WiMAX Forum working groups. As of July 2006, the Forum website also indicates the Global Roaming Working Group (GRWG)
Open table as spreadsheet

Working group name	Scope
Application Working Group (AWG)	Defines applications over WiMAX that are necessary to meet core competitive offerings and are uniquely enhanced by WiMAX
Certification Working Group (CWG)	Handles the operational aspects of the WiMAX Forum certification program; interfaces with the certification lab(s); selects new certification lab(s).
Marketing Working Group (MWG)	Promotes the WiMAX Forum, its brands and the standards that form the basis for worldwide interoperability of BWA systems
Network Working Group (NWG)	Creates higher-level networking specifications for fixed, nomadic, portable and mobile WiMAX systems, beyond what is defined in the scope of 802.16; specifically, the NWG defines the architecture of a WiMAX network
Regulatory Working Group (RWG)	Influences worldwide regulatory agencies to promote WiMAX-friendly, globally harmonised spectrum allocations
Service Provider Working Group (SPWG)	Gives service providers a platform for influencing BWA product and spectrum requirements to ensure that their individual market needs are fulfilled
Technical Working Group (TWG)	Develops conformance test specifications and certification services and profiles based on globally accepted practices to achieve worldwide interoperability of BWA systems

The WiMAX network architecture as defined by the NWG is described in Chapter 13.

2.2.2 WiMAX Forum White Papers

The WiMAX Forum regularly publishes White Papers. These are a very useful information source about WiMAX, freely available on the Forum website. In Table 2.4, a nonexhaustive list of White Papers is proposed (until July 2006).

Table 2.4: WiMAX Forum (http://www.wimaxforum.org) White Papers, last update: July 2006. Table was drawn with the help of Ziad Noun
Open table as spreadsheet

Title	Date of latest version	Number of pages	Brief description
IEEE 802.16a standard and WiMAX -Igniting BWA	Date not mentioned	7	An overview of IEEE 802.16a standard, its PHY and MAC layers; talks also about the WiFi versus WiMAX scalability
Regulatory position and goals of the WiMAX Forum	August 2004	6	Describes the goals of WiMAX Forum (interoperability of broadband wireless products); describes also the initial frequency bands (license and license exempt)
Business case for fixed wireless access in emerging markets	June 2005	22	Describes the characteristics of emerging markets and discusses the service and revenue assumptions for business case analysis (urban, suburban, rural)
WiMAX deployment considerations for fixed wireless access in the 2.5 GHz and 3.5 GHz licensed bands	June 2005	21	About the licensed spectrum for WMAN, the radio characteristics, the range and the capacity of the system in different sccnarios (urban, suburban. etc.)
Business case models for fixed broadband wireless access based on WiMAX technology and the 802.16 standard	October 2004	24	Describes the WiMAX architecture and applications, the business case considerations and assumptions and the services oftered by WiMAX
Initial certification profiles and the European regulatory framework	September 2004	4	Describes the profiles currently identified for the initial certification process and the tentative profiles under consideration for the next round of the certification process
WiMAX's technology for LOS and NLOS environments.	August 2004	10	About the characteristics of OFDM and the other solutions used by WiMAX to solve the problems resulting from NLOS (subchannelisation, directional antennas, adaptive modulation, error correction techniques, power control, etc.)
Telephony's ‘Complete Guide to WiMAX’	May 2004	10	About WiMAX marketing and policy considerations
What WiMAX Forum certified products will bring to Wi-Fi	June 2004	10	Why WiFi is used in WiMAX, the OFDM basics, the 802.16/HiperMAN PHY and MAC layers, the operator requirements for BWA systems and the products certification
What WiMAX Forum certified products will bring to 802.16	June 2004	6	The certified products: where do WiMAX Forum certified products fit and why select them?
Fixed, nomadic, portable and mobile applications for 802.16-2004 and 802.16e WiMAX networks	November 2005	16	Compares the two possibilities of deployment for an operator: fixed WiMAX (802.16-2004) or mobile WiMAX (802.16e)
The WiMAX Forum certified program for fixed WiMAX	March 2006	15	Describes the general WiMAX certification process and specifically the fixed WiMAX system profiles certifications
Third WiMAX Forum plugfest - test methodology and key learnings	March 2006	18	Describes WiMAX March 2006 plugfest
Mobile WiMAX - Part I: a technical overview and performance evaluation	March 2006	53	Technical overview of 802.16e system (mobile WiMAX) and the corresponding WiMAX architecture
Mobile WiMAX - Part II: a comparative analysis	May 2006	47	Compares elements between mobile WiMAX and presently used 3G systems (1xEVDO and HSPA)
Mobile WiMAX: the best personal broadband experience!	June 2006	19	Provides mobile WiMAX advantages in the framework of mobile broadband access market
Executive summary: mobile WiMAX performance and comparative summary	July 2006	10	Brief overview of mobile WiMAX and summary of previous White Papcr performance data

Chapter 2: WiMAX Genesis and Framework

2.1 IEEE 802.16 Standard

The main features of IEEE 802.16/WiMAX technology are the following:

• (Carrier) frequency <11>

• OFDM. The 802.16 is (mainly) built on the Orthogonal Frequency Division Multiplexing (OFDM) transmission technique known for its high radio resource use efficiency.

• Data rates. A reasonable number is 10 Mb/s. Reports have given more ambitious figures going up to 70 Mb/s or even 100 Mb/s. These values would be for a very good state of the radio channel and for a very small cell capacity, making these values too optimistic for the moment.

• Distance. Up to 20 km, a little less for indoor equipments.

As mentioned in Chapter 1, the IEEE 802.16 standard is the network technology used for WiMAX. The IEEE 802.16 working group for BWA was created in 1999. It was divided into two working groups:

• 802.16a, centre frequency within the interval 2–11 GHz. This technology will then be used for WiMAX.

• 802.16, with a frequency value interval of 10–66 GHz.

Many documents were approved and published by 802.16 subcommittees. They are presented in Table 2.1.

Table 2.1: Main IEEE 802.16 documents
Open table as spreadsheet

Date and name of the document	Description
Dec. 2001, 802.16	10–66.GHz; line-of-sight (LOS); 2–5 km; channel bandwidth values: 20, 25 and 28 MHz
Jan. 2003, 802.16a	2-11 GHz; non-line-of-sight (NLOS)
Oct. 2004, 802.16-2004	Revises and consolidates previous 802.16 standards; replaces 16a and 16; 5–50km
7 Dec. 2005, 802.16 approves 802.16e amendment of 802.16-2004	Mobility; OFDMA (SOFDMA)
Other 802.16 amendments approved or at draft stage: 802.16f, 802.16g, 802.16f, etc.	See Section 2.5

As stated in 802.16-2004 ^[1], this standard revises and consolidates IEEE standards 802.16-2001, 802.16a-2003 and 802.16c-2002. Before getting to 802.16-2004, a revision called 802.16d was started in September 2003 with the objective of taking into account the ETSI HiperMAN BWA standard ^[3]. The 802.16d project was later concluded with the approval of the 802.16-2004 document and the withdrawal of the earlier 802.16 documents, including the a, b and c amendments. Confusingly enough, some people still refer to 802.16-2004 as 802.16d (or even 16d).

2.1.1 From 802.16-2004 to 802.16e

802.16-2004 was definitely very useful, replacing a set of documents all describing different parts of the same technology, with different modification directions. Yet, after its publication, it still needed an upgrade, mainly for the addition of mobility features. Other features were needed and some errors had to be corrected. This gave way to 802.16e amendment approved on December 7, 2005 and published in February 2006 ^[2].

It should be noted that 802.16e is not a standalone document. It only proposes (sometimes important) changes and additions to the 802.16-2004 text. Hence, a person wishing to read the details of specific information in 802.16, e.g. ‘What is the frame format in 802.16?’ has first to read the related part of 802.16-2004 and then go on to read the possible changes that took place in 802.16e. It was reported that the IEEE intention was to have a unique document resulting from 16-2004 and 16e fusion, called 802.16-2005. However, by summer 2006, this document does not exist (to the best of the author's knowledge). However, the 802.16-2004 standard and 802.16e amendment are sometimes referred to as the IEEE 802.16-2005 standard.

The main differences of 802.16e with regard to 802.16-2004 are the following (the list is not exhaustive):

• Mobile stations (MS) appear. A station in a mobile telecommunication service is intended to be used while in motion or during halts at unspecified points. However, a 802.16e MS is also a subscriber station (SS).

• MAC layer handover procedures. There are two types of handover (see Chapter 14).

• Power save modes (for mobility-supporting MSs): sleep mode and idle mode (see Chapter 14).

• SOFDMA (Scalable OFDMA). More generally, the OFDMA PHY layer, i.e. Section 8.4 of the 802.16 standard, was completely rewritten between 16-2004 and 16e. Although the word SOFDMA does not appear in the 802.16e document, it is the type of standardised OFDMA. For OFDMA and SOFDMA, see Chapter 5.

• Security (privacy sublayer). The security of 16-2004 is completely updated (see Chapter 15).

• Multiple-Input Multiple-Output (MIMO) and Adaptive Antenna System (AAS) techniques, both already introduced in 802.16-2004, have many enhancement and implementation details provided in 802.16e (see Chapter 12).

• Multicast and broadcast services (MBS) feature.

• A new (fifth) QoS class: ertPS. (In addition to 802.16-2004 rtPS), ertPS Class supports realtime service flows that generate variable-size data packets on a periodic basis, e.g. VoIP with silence suppression.

• Other: the Low-Density Parity Check (LDPC) code is an optional channel coding, etc.

^[1]IEEE 802.16-2004, IEEE Standard for Local and Metropolitan Area Networks, Air Interface for Fixed Broadband Wireless Access Systems, October 2004.

^[3]Wikipedia, the free encyclopedia, http://www.wikipedia.org.

^[2]IEEE 802.16e, IEEE Standard for Local and Metropolitan Area Networks, Air Interface for Fixed Broadband Wireless Access Systems, Amendment 2: Physical and Medium Access Control Layers for Combined Fixed and Mobile Operation in Licensed Bands and Corrigendum 1, February 2006 (Approved: 7 December 2005).

1.4 History of BWA Technologies

1.4 History of BWA Technologies

1.4.1 Video Distribution: LMDS, MMDS and DVB

The Local Multipoint Distribution Service (LMDS) is a fixed wireless access system specified in the United States by the Digital Audio-Visual Council (Davic), a consortium of video equipment suppliers, network operators and other telecommunication industries. Davic was created in 1993. LMDS is a broadband wireless point-to-multipoint communication technology. Originally designed for wireless digital television transmission, the target applications were then video and Internet in addition to phone.

The standard is rather open and many algorithms used for LMDS are proprietary. Depending on the frequency bandwidth allocated, data rates are of the order of tens of Mb/s in the downlink and Mb/s in the uplink. Link distance can go up to a few km. LMDS operates in the 28 GHz frequency band in the United States. This band is called the LMDS band. Higher frequencies can also be used.

The Multichannel Multipoint Distribution Service (MMDS), also known as wireless cable, is theoretically a BWA technology. It is mainly used as an alternative method of cable television. The MMDS operates on frequencies lower than the LMDS, 2.5 GHz, 2.7 GHz, etc., for lower data rates as channel frequency bandwidths are smaller.

Standardising for digital television started in Europe with the Digital Video Broadcasting (DVB) Project. This standardization was then continued by the European Telecommunications Standard Institute (ETSI). DVB systems distribute data by many mediums: terrestrial television (DVB-T), terrestrial television for handhelds (DVB-H), satellite (DVB-S) and cable (DVB-C). The DVB standards define the physical layer and data link layer of a television distribution system.

Many European countries aim to be fully covered with digital television by around 2010 and to switch off analogue television services by then. DVB will also be used in many places outside Europe, such as India and Australia.

1.4.2 Pre-WiMAX Systems

WiMAX and 802.16 systems will be described in detail in Chapter 2. In this subsection, the pre-WiMAX is introduced. The first version of the IEEE 802.16 standard appeared in 2001. The first complete version was published in 2004. There was evidently a need for wireless broadband much before these dates. Many companies had wireless broadband equipment using proprietary technology since the 1990s and even before. Evidently these products were not interoperable.

With the arrival of the 802.16 standard, many of these products claimed to be based on it. This was again not possible to verify as WiMAX/802.16 interoperability tests and plugfest started in 2006. These products were then known as pre-WiMAX products. Pre-WiMAX equipments were proposed by manufacturers often specialising in broadband wireless. Many of them had important markets in Mexico, Central Europe, China, Lebanon and elsewhere. Device prices were of the order of a few hundred euros. A nonexhaustive list of pre-WiMAX manufacturers contains the following: Airspan, Alvarion, Aperto, Motorola, Navini, NextNet, Proxim, Redline and SR Telecom. Intel and Sequans, among others, provide components.

The performances of pre-WiMAX systems are close to the expected ones of WiMAX, whose products should start to appear from the second part of 2006. Many of the pre-WiMAX equipments were later certified and more are in the process of being certified.

1.3 Applications of BWA

As already introduced above with IEEE 802.16, a BWA system is a high data rate (of the order of Mb/s) WMAN or WWAN. A BWA system can be seen as an evolution of WLL systems mainly featuring significantly higher data rates. While WLL systems are mainly destined for voice communications and low data rate (i.e. smaller than 50kb/s), BWAs' are intended to deliver data flows in Mb/s (or a little lower).

The first application of BWA is fixed-position high data rate access. This access can then evidently be used for Internet, TV and other expected high data rate applications such as Video-on-Demand (VoD). It will also surely be used for other applications that are not really apparent yet. In one word, the first target of BWA is to be a wireless DSL (Digital Subscriber Line, originally called the Digital Subscriber Loop) or also a wireless alternative for the cable. Some business analysts consider that this type of BWA application is interesting only in countries and regions having relatively underdeveloped telecommunications infrastructure. Indeed, using WiMAX for the fixed-position wireless Internet in Paris or New York does not seem economically viable.

Another possible use of high data rate access with BWA is WiFi Backhauling. As shown in Figure 1.4, the Internet so-called backbone is linked to a BS which may be in Line-of-Sight (LOS) of another BS. This has a Non-Line-of-Sight (NLOS) coverage of Subscriber Stations (SSs). The distinction between IEEE 802.16 NLOS and LOS technologies will be detailed in Chapter 2.

Figure 1.4: Broadband Wireless Access (BWA) applications with a fixed access. The two main applications of a fixed BWA are wireless last-mile for high data rate and (more specifically) WiFi backhauling

The SS in Figure 1.4 is a Consumer Premises Equipment (CPE). The CPE is a radio-including equipment that realises the link between the BS and the terminal equipment(s) of the user. After the CPE, the user may install a terminal such as a Personal Computer (PC) or a TV and may also connect a WiFi Access Point and then a WLAN (the BWA then realizing the WiFi network backhauling). Hence the two main applications of fixed BWA are the wireless last-mile for high data rate and (more specifically) WiFi backhauling. As shown in this figure, a wireless terminal can then be fixed (geographically) or not. This may be the case of a laptop connected to the CPE with a WiFi connection (see the figure).

The fixed access is the first use of BWA, the next step being nomadicity (see Section 1.3.1 for the difference between nomadicity and mobility). A first evolution of the SS will be the case when it is no longer a CPE but a card installed in some laptop. A nomadic access, shown in Figure 1.5, is an access where the user or the subscriber may move in a limited area, e.g. in an apartment or a small campus. This area is the one covered by a BS. Whenever the user moves out of the zone, the communication (or the session) is interrupted. A typical example of a portable access is WLAN/WiFi use in its first versions (802.11, 802.11b and 802.11a) where a session is interrupted when the terminal gets out of a WLAN coverage even if it enters a zone covered by another WLAN, e.g. in two neighbouring companies.

Figure 1.5: Nomadic or portable BWA

The nomadic access is very useful in some cases, such as campuses, company areas, compounds, etc. It can be observed that due to this position, which is not fixed, the link between the BS and the SS has to be NLOS (it can be LOS only in the case of fixed CPEs, theoretically). A nomadic access is also sometimes known as a wireless access. The final expected step of WiMAX is a mobile access. The difference between wireless and mobile will now be discussed.

1.3.1 Wireless is Not Mobile!

Different scenarios of mobility can be considered. The most simple one is when two neighbouring BSs belong to the same operator. Hence, the same billing system and customer care apply to the two BSs. In this case, a user moving from one cell to a neighbouring one has to start the session again. This feature is nomadicity rather than mobility. Mobility (or full mobility) is the scenario where the session is not interrupted, whether this is a data session, a voice communication (over IP or not), a video transmission, etc.

The distinction is made between wireless (but yet geographically) fixed access, nomadicity, portability and mobility. Portability is when a user can move with a reasonable speed over a large area, covered by many BSs, without interruption of an possible open session or communication. The value considered as a reasonable speed is of the order of 120km/h. Mobility is the same as portability but with no real limit for speed; i.e. if mobility is realised, a BWA can be used in some high-speed trains with speeds exceeding 350km/h.

In cellular systems, second generation or later, a voice communication is not interrupted when a mobile moves from one cell to another. This is the so-called ‘handover’. The cellular systems are then real mobile networks. Is WiMAX a cellular mobile network? Considering that a cell is the area covered by one BS, the only condition would be a high-speed handover feature. This should be realised with 802.16e evolution of 802.16. However, a WiMAX handover is not expected to occur at very high speeds to be precise, at speeds higher than a magnitude of 100km/h. The final objective of WiMAX is to be a mobile system. In this case, part or all of a territory or country will be covered by contiguous cells with a seamless session handover between cells, as in a cellular system (see Figure 1.6). It is evident that WiMAX will then become a rival to 3G cellular systems.

Figure 1.6: Mobile Broadband Wireless Access (BWA). A mobile WiMAX device can move over all the cells in a seamless session

Some service providers define triple play as the combination of data (Internet), voice (unlimited phone calls) and video (TV, video on demand). This evolves into quadruple play by adding mobility. In a first step, this mobility will in fact be only nomadicity, e.g. using the WiMAX subscription to have an Internet access in a caf&eU far away from home.

Another application sometimes mentioned for BWA is telemetering: using the BWA for reporting electricity, gas, water, etc. This should represent a small but yet perhaps interesting market. WiMAX telemetering products have already been reported. Evidently, WiMAX is not the only technology that can be used for telemetering.

1.3.2 Synthesis of WiMAX BWA Applications

To sum up, the applications known or expected today of WiMAX as a BWA system are:

• Broadband fixed wireless access. WiMAX would be a competitor for fixed-line high data rate providers in urban and rural environments.

• WiFi backhauling.

• Telemetering. This should represent a small but yet perhaps interesting market.

• Nomadic Internet access.

• Mobile (seamless sessions) high data rate access.

1.2 Wireless Networks and Broadband Wireless Access (BWA)

1.2 Wireless Networks and Broadband Wireless Access (BWA)

1.2.1 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 1.1, a now-classical representation (sometimes called the ‘eggs figure’) is shown of wireless network categories, with the most famous technologies for each type of network.

Figure 1.1: Illustration of network types. For each category, the most well known technologies are given. To this figure, some people add a smaller ‘egg’ in the WPAN (Wireless Personal Area Network), representing the WBAN (Wireless Body Area Network), with a coverage of the magnitude of a few metres, i.e. the proximity of a given person

A Personal Area Network (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 metres, generally assumed to be less than 10m, although some WPAN technologies may have a greater reach. Examples of WPAN technologies are Bluetooth, UWB and Zigbee.

A Local Area Network (LAN) is a data network used for communication among data devices: computer, telephones, printer and personal digital assistants (PDAs). This network covers a relatively small area, like a home, an office or a small campus (or part of a campus). The scope of a LAN is of the order of 100 metres. The most (by far) presently used LANs are Ethernet (fixed LAN) and WiFi (Wireless LAN, or WLAN).

A Metropolitan Area Network (MAN) is a data network that may cover up to several kilometres, 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 kilometre. Then from this MAN the university could have several links to other MANs that make up a WAN. Examples of MAN technologies are FDDI (Fiber-Distributed Data Interface), DQDB (Distributed Queue Dual Bus) and Ethernet-based MAN. Fixed WiMAX can be considered as a Wireless MAN (WMAN).

A Wide Area Network (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. Typically, a WAN consists of a number of interconnected switching nodes. These connections are made using leased lines and circuit-switched and packet-switched methods. The most (by far) presently used WAN is the Internet network. Other examples are 3G and mobile WiMAX networks, which are Wireless WANs. The WANs often have much smaller data rates than LANs (consider, for example, the Internet and Ethernet).

To this figure, some people add a smaller ‘egg’ in the WPAN, representing the WBAN, Wireless Body Area Network, with a coverage of the magnitude of a few metres, i.e. the near proximity of a given person. A WBAN may connect, for example, the handset to the earphone, to the ‘intelligent’ cloth, etc.

1.2.2 Some IEEE 802 Data Network Standards

WiMAX is based on the IEEE 802.16 standard ^[1],[2]. Standardisation efforts for local area data networks started in 1979 in the IEEE, the Institute of Electrical and Electronics Engineers. In February 1980 (80/2), the IEEE 802 working group (or committee) was founded, dedicated to the definition of IEEE standards for LANs and MANs. The protocols and services specified in IEEE 802 map to the lower two layers (Data Link and Physical) of the seven-layer OSI networking reference model ^[3],[4]. IEEE 802 splits the OSI Data Link Layer into two sublayers named Logical Link Control (LLC) and Media Access Control (MAC) (see Chapter 3).

Many subcommittees of IEEE 802 have since been created. The most widely used network technologies based on IEEE 802 subcommittees are the following:

• IEEE 802.2, Logical Link Control (LLC). The LLC sublayer presents a uniform interface to the user of the data link service, usually the network layer (Layer 3 of the OSI model).

• IEEE 802.3, Ethernet. The Ethernet, standardised by IEEE 802.3, is a family of network technologies for LANs, standardized by IEEE 802.3. It quickly became the most widespread LAN technology until the present time. Possible data rates are 100 Mb/s, 1 Gb/s and 10 Gb/s.

• IEEE 802.5, Token Ring. The Token Ring LAN technology was promoted by IBM in the early 1980s and standardised by IEEE 802.5. Initially rather successful, Token Ring lost ground after the introduction of the 10BASE-T evolution of Ethernet in the 1990s.

• IEEE 802.11, WLAN. IEEE 802.11 is the subcommittee that created what is now known as WiFi Technology. A Wireless Local Area Network (WLAN) system and many variants were proposed by the IEEE 802.11 working group (and subcommittees), founded in 1990. A WLAN covers an area whose radius is of the magnitude of 100 metres (300 feet). First, IEEE 802.11 (http://www.ieee802.org/11/) and its two physical radio link variants, 802.11a and 802.11b standards, were proposed by the end of the 1990s. IEEE 802.11b products, certified by WiFi (Wireless Fidelity) Consortium, were available soon after. These products have nearly always been known as being of WiFi Technology. These WiFi products quickly encountered a large success, mainly due to their simplicity but also the robustness of the technology, in addition to the relative low cost and the use of unlicensed 2.4 GHz and 5 GHz frequency bands. Other variants of the basic 802.11 standard are available (802.11e, 802.11g, 802.11h, 802.11i, etc.) or are at the draft stage (802.11n, etc.).

• IEEE 802.15, WPAN. Different WPAN technologies were or are defined in IEEE 802.15. IEEE 802.15.1 included Bluetooth, initially proposed by a consortium of manufacturers, and now studies the evolution of Bluetooth. Bluetooth is now a widely used (data) cable-replacement technology with a theoretical scope of up to 20m. IEEE 802.15.3a studied an Ultra-Wide Band (UWB) System, very high-speed and very low-distance network. The IEEE 802.15.3a draft has not yet been approved. IEEE 802.15.4 is about ZigBee, a lowcomplexity technology for automatic application and an industrial environment.

• IEEE 802.16, BWA. IEEE 802.16 is the working group of IEEE 802 dedicated to BWA. Its aim is to propose standards for (high data rate) WMAN. IEEE 802.16 standards are detailed in Section 2.2. As for 802.11 products a certification forum was created for IEEE 802.16 products, the WiMAX (Worldwide Interoperability for Microwave Access) forum, also described in Chapter 2. It can already be said that WiMAX is the name normally used for IEEE 802.16 products.

BWA networks have a much greater range than WLAN WiFi. In fact, IEEE 802.16 BWA has two variants: IEEE 802.16-2004, which defines a fixed wireless access WMAN technology, and IEEE 802.16e, which is an amendment of 802.16-2004 approved in December 2005. It included mobility and then fast handover, then becoming a Wireless WAN (see Figure 1.1).

• IEEE 802.20, Mobile Broadband Wireless Access (MBWA). The aim of this group is to define a technology for a packet-based air interface designed for IP (Internet Protocol) based services. This technology is destined for high-speed mobile devices. It was reported that MBWA will be based on the so-called Flash OFDM technology proposed by Flarion Company.

• A draft 802.20 specification was balloted and approved on 18 January 2006. On 8 June 2006, the IEEE Standards Board directed that all activities of the 802.20 working group be temporarily suspended ^[3].

• IEEE 802.21, Media Independent Handover (MIH). IEEE 802.21 is a new IEEE standard. It is definitely interesting for a telecommunication equipment to have the possibility of realising a handover between two different wireless technologies. A handover is the operation of changing the corresponding base station (the cell), the communication channel, the technology, etc., without interruption of an ongoing telecommunication session (conversation or other). IEEE 802.21 studies standards enabling handover and interoperability between different network types, which is called MIH. These network types can be of the IEEE 802 family or not. For example, the 802.21 standard would provide information to allow a handover between 3G and 802.11/WiFi networks.

1.2.3 Cordless WLL Phone Systems

Along with progress in cellular (or mobile) systems and wireless data networks, wireless phone systems have began to appear. An important budget for a phone operator or carrier has always been the local loop, also called the ‘last mile’, which connects the phone subscriber to the network last elements. It was seen for some configurations that a (radio) Wireless Local Loop (WLL) can be an interesting replacement solution for a fixed (mainly copper) local loop. These WLL systems had to provide a communication circuit, initially for voice, and some low-rate data services. The general principle of a local loop is shown in Figure 1.2.

Figure 1.2: Local loop of a classical (voice) phone system

In a WLL system, terminal stations are connected to a Base Station (BS) through the radio channel (see Figure 1.3). The main difference between WLL and cellular systems is the fact that in a cellular system a subscriber can be connected to one BS or another. A subscriber can also change the BS during a communication without causing an interruption, which is called the handover (or also handoff) procedure.

Figure 1.3: Coverage of a given zone by a BS

Several technologies have been proposed for WLL systems, also known as cordless phone systems (or also cordless systems). After analogue systems, mainly proprietary, a digital system was proposed, CT2/CAI (Cordless Telephone 2/Common Air Interface), in 1991. With CT2/CAI, the occupation of one (voice) user is 100kHz.

The European Telecommunications Standards Institute (ETSI) published a WLL cordless system in 1992 named DECT (Digital Enhanced Cordless Telecommunications). The range of DECT equipments is up to a few hundred metres. DECT works in the 1.9 GHz bandwidth.

DECT is a digital TDMA (Time Division Multiple Access) suited for voice and low data rate applications, in the order of tens of kb/s. Some evolutions of DECT, featuring many slots per user, propose higher data rates up to hundreds of kb/s. DECT has a relatively high success rate nowadays, yet it is a capacity-limited system as TDMA-only systems do not use the bandwidth very efficiently (a user taking many slots leaves very few resources for other users). The wide use of WLL systems for phone communications and some other low data rate communications gave way to high data rate BWA systems, introduced in Section 1.2.2 above and described in further detail in the next section.

^[1]IEEE 802.16-2004, IEEE Standard for Local and Metropolitan Area Networks, Air Interface for Fixed Broadband Wireless Access Systems, October 2004.

^[2]IEEE 802.16e, IEEE Standard for Local and Metropolitan Area Networks, Air Interface for Fixed Broadband Wireless Access Systems, Amendment 2: Physical and Medium Access Control Layers for Combined Fixed and Mobile Operation in Licensed Bands and Corrigendum 1, February 2006 (Approved: 7 December 2005).

^[3]Wikipedia, the free encyclopedia, http://www.wikipedia.org.

^[4]Tanenbaum, A. Computer Networks, Prentice-Hall, August 2002.

WiMAX Technology for Broadband

Chapter 1: Introduction to Broadband Wireless Access

1.1 The Need for Wireless Data Transmission

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. There is no doubt that by the end of the first decade of the twentieth century, high-speed wireless data access, i.e. in Mb/s, will be largely deployed worldwide.

Wireless communication dates back to the end of the nineteenth century when the Maxwell equations showed that the transmission of information could be achieved without the need for a wire. A few years later, experimentations such as those of Marconi proved that wireless transmission may be a reality and for rather long distances. Through the twentieth century, great electronic and propagation discoveries and inventions gave way to many wireless transmission 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 utilisation, the most successful until now being GSM, the Global System for Mobile communication (previously Groupe Sp&eUcial 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).

The GSM has evolutions that are already used in many countries. These evolutions are destined to facilitate relatively high-speed data communication in GSM-based networks. The most important evolutions are:

• GPRS (General Packet Radio Service), the packet-switched evolution of GSM;

• EDGE (Enhanced Data rates for GSM Evolution), which includes link or digital modulation efficiency adaptation, i.e. adaptation of transmission properties to the (quickly varying) radio channel state.

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.

Cellular systems have to cover wide areas, as large as countries. Another approach is to use wireless access networks, which were initially proposed for Local Area Networks (LANs) but can also be used for wide area networks.