WiMAX Networks: Performance and Measurements

Introduction

Broadband communications can be considered one of the most significant steps in modern communications systems. The requirement for new services like video conferencing, fast Internet and Voice over IP (VoIP), has set new standards for both fixed and wireless technologies. WiMAX is a wireless technology that aims at providing broadband services to wireless users similar to those of xDSL technologies. WiMAX is required to cover the needs of both broadband and wireless markets, both of which are the major markets in communications while high potentials for the future are also foreseen.

Figure 1.

Global growth trend for mobile, internet and broadband markets (taken from ITU)

Figure 2.

Communications market statistics for 2007 (taken from ITU)

WiMAX is a point to multipoint wireless technology introduced by the Institute of Electrical and Electronics Engineers (IEEE) and it is described in the 802.16 framework of specifications. The first official meeting of the 802.16 group, took place in 1999 but the form of the technology was quite different than the one defined in latest standards. Since its first steps, WiMAX technology has gone through four development phases. The first phase was a narrowband version which was followed by the broadband edition for line-of-sight (LOS) conditions only. The third phase enhanced WiMAX for operation in non line-of-sight link conditions (NLOS) while the latest stage is the one that is described in the current standards of 802.16 group.

The latest standard of WiMAX is the 802.16e-2005 with a major emphasis in introducing mobility of users for speeds up to 120 km/h with full handover support between base stations. The transmission characteristics and handover times are within the required limits in order to support real time applications such as VoIP, video streaming and online gaming. The support of the aforementioned applications is a real challenge for all wireless technologies especially in meeting the high requirements and the quality of service that is necessary for delivering the above services. Those transmission characteristics can be achieved by means of offering the required Quality of Service (QoS) mechanisms that will assure prioritization in services that are sensitive to delays (e.g. VoIP) over other types of services that are not delay sensitive or are not real-time (e.g. file transfer).

History Of Wimax

The 802.16 standard was formed by IEEE in 1998 for defining and specifying the specs of a broadband wireless technology. The proposed technology would mostly fit LOS environments with frequencies ranging from 10-66GHz. The initial standard was to define the PHY and MAC layers including for single carries signals.

The next version of 802.16 was an amendment that allowed provision of services in NLOS environments by using frequencies from 2GHz up to 11GHz. This was the 802.16a standard that was published by IEEE in 2003. 802.16a was the first version of the standard that supported Orthogonal Frequency Division Multiplexing (OFDM) for the PHY layer as far as Orthogonal Frequency Division Multiple Access (OFDMA) for the MAC.

The revision that was published one year later (802.16d-2004), replaced all previous standards and came with the name of WiMAX. The 2004 version is also known as “Fixed WiMAX” since it did not support mobility functionality. This mobility functions were initiated with the version 2005.

802.16e-2005 is the latest version of WiMAX standards that is also known as “Mobile WiMAX”. Its major differences compared to 802.16d include support for nomadic users (fixed users that can be attached to different Base Stations without handover support) and also support for mobile users. Another feature of mobile WiMAX is full interoperability between equipment of different vendors, a feature that was not mandatory in all previous versions. The latter is also known as Wave 2 and refers to MAC interoperability as opposed to Wave 1 that refers to interoperability for the PHY layer only. Wave 2 certification is important in the case of mobile users that change Base Stations while moving (e.g. they could also use the Base Station of another service provider) [1-3].