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.

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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.

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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.

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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.