Chapter 13: WiMAX Architecture

Jérôme Brouet,

Alcatel, France

13.1 The Need for a Standardised WiMAX Architecture

13.1.1 Supporting Working Groups and Documents

The IEEE 802.16 standard only defines the PHY and MAC layers. Consequently, in order to ensure intervendor internetwork interoperability, for operations such as roaming, it is important to define standards over the widest range of interfaces and equipments, as in 3GPP and 3GPP2 mobile standards. Then, in addition to the alignment of the radio access features for multivendor interworking between base stations and terminals based on the 802.16 standards ^[1],[2], the WiMAX Forum charter also aims to deliver a framework for a high-performance end-to-end IP network architecture to support fixed, nomadic, portable and mobile users (see Table 13.1 for service type definitions).

Table 13.1: WiMAX service definition. (Based on Reference ^[33].)
Open table as spreadsheet

Service type	Service area	Speed	Handover	Comment
Fixed	Single BS	Stationary	No; yet may involve BS reselection due to link conditions	Usually, fixed outdoor terminals
Nomadicity	Any BS	Stationary	No; yet may involve BS reselection due to link conditions	Indoor/Outdoor use; usually self-install
Portability	Any BS	Mobile	Yes	Session continuity for non-real-time applications
Simple mobility	Any BS	Mobile	Yes	Performance for non-real-time applications and some support of real-time applications
Full mobility	Any BS	Mobile	Yes	Session continuity for real-time applications
[33]WiMAX Forum White Paper, Fixed, nomadic, portable and mobile applications for 802.16-2004 and 802.16e WiMAX networks, November 2005.

The WiMAX architecture is based on the use of standardised IP protocols and is compatible with service frameworks such as the IP Multimedia Subsystem (IMS). Two working groups from the WiMAX Forum organisation (see Chapter 2) define the architecture and associated functionalities: the Network Working Group (NWG) creates the network specifications and the Service Provider Working Group (SPWG) helps to define requirements and priorities.

The set of specifications issued by these two groups includes several alternatives for mapping different required functionalities to physical equipments, allowing at the same time added value manufacturer-dependent implementation choices and also interoperability points at the network level, thanks to standardised open interfaces (or reference points in the WiMAX wording)^{[21],[10],[34]}. The latest NWG drafts are publicly accessible at http://www.wimaxforum.org/technology/documents.

The specifications are organised by release (currently, Release 1 will be finalised by Q3'06) and consists of a set of three-stage documents:

• Stage 1 document defines the requirements for the WiMAX architecture.

• Stage 2 documents describe the network reference model, the reference points and also include some informative parts for interworking between a WiMAX network and another network (e.g. a DSL network) ^[21]. The WiMAX network architecture is evidently also applicable to standalone deployments (not just for interworking scenarios).

• Stage 3 documents define the details of the protocols and other procedures to be implemented in a WiMAX end-to-end network ^[34].

13.1.2 High-level Architecture Requirements

The WiMAX reference architecture has been created having in mind various types of requirements:

• a high-performance packet-based network with functional split, ensuring maximum flexibility based on standard protocols from IEEE and IETF;

• the support of a full scale of services and applications;

• the support of roaming and interworking with other fixed/mobile networks.

In terms of services and applications, a WiMAX network is designed to be abie to support:

• voice (using VoIP), multimedia (using IMS) and other mandatory regulatory services such as emergency calls;

• access to a large variety of application service providers;

• interfacing with a variety of interworking and media gateways for translating legacy services (e.g. circuit voice, MMS) to IP and to transport them over WiMAX radio access networks;

• delivery of IP MBS, multicast and broadcast services (see Chapter 12).

In addition, considering network interworking and roaming, several deployment scenarios must be supported:

• loose coupling with existing wired (e.g. DSL) or wireless networks (e.g. 3GPP or 3GPP2 mobile networks);

• global roaming between WiMAX operators (this includes among others a consistent use of the AAA, Authentication Authorization and Accounting, among WiMAX operators for authentication and billing);

• a variety of user authentication methods (username/password, digital certificates, SIM based).

The resulting reference architecture and functional split is developed further in the next sections of this chapter.

^[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).

^[21]WiMAX Forum Document, WiMAX end-to-end network systems architecture; Stage 2, Release 1: architecture tenets, network reference architecture, reference points, April 2006.

^[10]WiMAX Forum White Paper, Mobile WiMAX - Part I: a technical overview and performance evaluation, March 2006.

^[34]WiMAX Forum Document, WiMAX end-to-end network systems architecture; Stage 3, Release 1: detailed protocols and procedures, April 2006.