Mobile WiMAX (IEEE 802.16e-2005)

Mobile WiMAX (IEEE 802.16e-2005)

Perhaps the biggest shortcoming of 802.16-2004 is the lack of support for mobility. IEEE addressed this issue by developing specifications for a separate version of the standard, the 802.16e, which was approved on December 7, 2005 (IEEE 2005).

Also known as mobile WiMAX, the standard is seen to be in competition with 3G cellular technologies. Its radio access method is even more sophisticated than that of fixed WiMAX, utilizing scalable OFDMA and thus achieving an even better link budget. The tradeoff is increased complexity in physical layer processing.

Fast handover signaling is supported, e.g., to allow users in moving vehicles to seamlessly switch between base stations. (Baines 2005) Mobile WiMAX operates in the 2 to 6 GHz range that mainly consists of licensed bands. Mobile applications are likely to operate in frequencies below 3 GHz, while even some fixed applications are expected to use 802.16e due to its better characteristics.

However, it should be noted that there is no backward compatibility with fixed WiMAX. Cell radiuses are expected to be typically 2 to 5 km, and user data rates up to 30 Mbit/s are achievable in theory with full 10 MHz channels. The first certified 802.16e products are expected to be available by late 2006, though wide scale commercial deployments are expected not earlier than 2008.

On a further note, South Korea has its own variant of mobile WiMAX called WiBro which is standardized by TTA. It uses 10 MHz channels in the 2.3 GHz band in Korea, and aims for interoperability with official 802.16e equipment. According to a recent performance analysis, WiBro performs favorably in comparison with 3G High-Speed Downlink Packet Access (HSDPA) in multipath fading channels (Shin et al. 2005).

WiMAX (IEEE 802.16-2004)

WiMAX (IEEE 802.16-2004)

WiMAX is short for Worldwide Interoperability for Microwave Access and it is defined by the IEEE 802.16 Working Group. Although first intended for fixed applications, the initial WiMAX standards have evolved to form the basis for mobile WiMAX as well.

The current version of the fixed WiMAX standard is 802.16-2004, sometimes also referred to as 802.16d. It is essentially frequency independent, allowing also nonline-of-sight (NLOS) operation in the lower end of the frequency range (frequencies below 3 GHz, according to Richardson (2006)). The radio access interface is based on orthogonal frequency division multiplexing (OFDM) with 256 subcarriers, although OFDMA2048 and single carrier access modes are included in the 802.16-2004 standard as alternatives. OFDM allows good resistance to interference and multipath fading.

Channel bandwidth ranges from 1.25 to 20 MHz, and either FDD or TDD may be used for duplexing. WiMAX cell size is dependent on the used frequency band, but coverage radiuses of 1 to 2 km for NLOS and 10 to 16 km for LoS are typical with standard base station equipment. With some optional enhancements, however, the figures are 4 to 9 km (NLOS) and 30 to 50 km (LOS) (Baines 2005). Actual data rates are also highly variable and depend on a number of factors.

Although rates as high as 75 Mbit/s have been advertised, according to results of trials conducted by AT&T in late 2005, 2 Mbit/s over a range of roughly 5 to 10 km is closer to reality. For a comprehensive performance analysis, one may refer to, e.g., Ball et al. (2005).

Fixed WiMAX, as defined in 802.16-2004, does not support handovers or any other basic mobility mechanisms. As such, it lends itself only to fixed or, at most, nomadic applications.

MOBILE BROADBAND WIRELESS ACCESS

Emerging telecommunications applications such as multimedia streaming, music download, on-line gaming and content browsing are popular examples of the digital revolution we have been facing as the world gets connected.Fixed broadband access has already become an urban commodity in the developed countries, but so far there have been few means of delivering these bandwidth-consuming services effectively and affordably to the significant number of rural and mobile users.

However, recent advances in e.g. signal processing, radio protocols, and mobile network infrastructure are now enabling the concept of mobile broadband for consumers around the world.

Mobile broadband is defined here as the potential to transfer low-latency user data with speeds exceeding 256 kbit/s while roaming the network with seamless handover between adjacent cells. This paper presents the different mobile broadband technologies with commercial availability already or within a few years.

Related regulation aspects are important factors affecting the regional markets. Analysis of the current market situation, significant vendors’ strategies and foreseen future developments are also used to draw the conclusions about the respective potential of these technologies.

Currently there are a number of different technologies for broadband wireless access for both fixed and mobile applications. Some of them are completely proprietary, based on vendor-specific solutions that are noninteroperable, while others are based on open standards developed by industry working groups. In the following subsections, we briefly describe the fundamental characteristics of the currently most significant wireless broadband technologies, focusing on key metrics such as operating frequencies, channel bandwidth, cell sizes, user data rates and latency, handover capabilities, and timeframe of availability.