IEEE 802.16 is a standards-based wireless technology that provides high- throughput broadband connections over long distances of up to 50 km (Gabriel, 2003; LAN/MAN Standards Committee of the IEEE Computer Society, 2004; Intel, 2006). It can be used for a number of applications, including last-mile broadband connections, hotspots, cellular backhaul and high-speed enterprise connectivity for business. This has certain conformity and interoperability tests for the IEEE 802.16 family standards.
The IEEE 802.16 specification was the first interface standard for broadband wireless access systems, approved in 2001. This utilizes point-to-multipoint (PMP) infrastructure designs operating at radio frequencies between 10 and 66 GHz addressing issues in the line-of-sight (LOS) environment (Worldwide Interoperability for Microwave Access Forum, 2003). The WiMAX base stations (BS) can offer greater wireless coverage of about 5 miles with LOS transmission, within a bandwidth of up to 70 Mbps (Wei et al., 2005). When the signal is propagated through the air there is an increase in attenuation; this occurs due to the amplitude of the wave changes. Trees and buildings are also problematic, contributing to signal degradation (Sweeny, 2004), but the IEEE 802.16 addressed the LOS environment. This led to the amendment of 802.16
(extension 802.16a) standards for use between 2 and 11 GHz, which provides support for non-line-of-sight (NLOS) operation at the lower frequencies, which is not possible in higher bands (Anderson, 2001).
HiperMAN is the ETSI standard-based equivalent of WiMAX (802.16.a) and it provides broadband wireless MAN connectivity to fixed, portable and nomadic users (Intel, 2006). This was achieved through the introduction of three new PHY layer specifications (i.e. new single-carrier PHY, a 256-point fast Fourier transformation [FFT] OFDM PHY and a 2048-point FFT OFDMA PHY). The orthogonal frequency division multiplexing (OFDM) signaling format has the ability to support NLOS performance while maintaining a high level of spectral efficiency, maximizing the use of available spectrum (Nuaymi, 2007). The other attributes of the PHY-layer features of 802.16a that enable the technology to deliver robust performance in a broad range of channel environments are: flexible channel widths, adaptive burst profiles forward error correction, with concatenated Reed-Solomon and convolutional encoding. The optional advanced antenna system (AAS) is responsible for the improvement in regard to range/capacity. Dynamic frequency selection helps in minimizing interference while space-time coding enhances performance in fading environments through spatial diversity (Wei et al., 2005).
The WiMAX-based solution is set up and deployed like cellular systems, using base stations that service a radius of several miles/kilometers. The most typical WiMAX-based architecture includes a base station mounted on a building, and it is responsible for communicating on a point-to-multipoint basis, with subscriber stations (the customer premise equipment CPE) located in business offices and homes. Voice and data from CPE are then routed through standard Ethernet cable, either directly to a single computer, or to an 802.11 hot-spot or a wired Ethernet LAN (Burrows et al., 2005). As noted above, the IEEE 802.16 can easily be integrated into most networks.
The 802.16d is the fixed WiMAX standard IEEE 802.16-2004, approved by the IEEE in June 2004. It provides fixed, point-to-multipoint, broadband wireless access service, and its product-profile utilizes the OFDM 256-FFT system profile (IEEE 802.16d, 2004).
In December 2005, the IEEE approved the mobile WiMAX standard, the 802.16- 2005 (also known as 802.16e). The IEEE 802.16e is based on the early WiMAX standard 802.16a, adds mobility features to WiMAX in the 2 to 11 GHz-licensed bands. 802.16e allows for fixed wireless and mobile NLOS applications, primarily by enhancing the orthogonal frequency-division multiple access (OFDMA).
IEEE 802.16f – Management Information Base for Fixed Services is an amendment to IEEE Standard 802.16-2004 which provides enhancements to IEEE Standard 802.16-2004. It defines a management information base (MIB) for the MAC and PHY and associated management procedures (IEEE 802.16f, 2005).
IEEE 802.16g – Management Plane Procedures and Services (amendment under development). This is an amendment to IEEE Standard 802.16-2004, which provides enhancements to the MAC and PHY management entities of IEEE Standard 802.16-2004, as amended by P802.16e, to create standardized procedures and interfaces for the management of conformant 802.16-devices (IEEE 802.16g, 2005).
Advantages of IEEE 802.16
The IEEE 802.16 has several advantages, especially in our mission of offering backhaul connectivity for a rural area outside PSTN coverage.
• The WiMAX standard recovers from many of the limitations of WiFi, thus providing increased shared bandwidth, larger coverage, and stronger encryption (triple-data-encryption standard [3DES] or advanced
encryption standard [AES]), and it aims to provide connectivity between the endpoints of a network without the necessity of direct LOS (Airband:
WiMAX: Navigating Between Hype and Reality, 2007). This makes
WiMAX an enhanced wireless technology.
• Continuous quality of service (QoS): This is built into the WiMAX MAC layer (WiMAX Forum, 2004). It provides essential support for applications such as voice-over IP (VoIP), which requires QoS for effective operation. This was found to be lacking in the earlier 802.11 standards (IEEE Std 802.11, 1999), and it has only been recently added to the 802.11e amendment (IEEE Std 802.11e, 2005).
• WiMAX is a WAN/MAN technology designed to provide up to 50 km of coverage with a throughput of 70 Mbps, making it the most ideal access technology for rural Internet connectivity (Wei et al., 2005; Sweeny, 2004).
• Throughput and performance are optimal within the typical cell radius of up to 10 km (Intel IEEE 802.16 and WiMAX).
• WiMAX will be able to connect to IEEE 802.11 (WiFi) hotspots to the Internet and provide a wireless extension to cable and DSL for last-mile broadband access. Also, a high tower is not needed for achieving adequate 5-km coverage in rural settings; and a single sector (Tx/Rx radio pair ) of 20 MHz of a BS may simultaneously connect more than 60 businesses with T1-level connectivity and hundreds of homes with DSL- rate connectivity (Intel, 2005).
• The ability to quickly offer service, even in areas that are hard for wired infrastructure to reach, helps operators to overcome problems associated with connectivity in remote, disadvantaged areas (Burrows et al., 2005). This is one major advantage, especially in our mission of providing rural connectivity.
• Greater reliability, since the technology is more robust and will improve network performance. The WiMAX equipment is able to manage spectrum
much more efficiently in a more automated fashion to eliminate potential interference issues (Airband: WiMAX: Navigating Between Hype and
Reality, 2007).
The advantages of IEEE 802.11 are similar to those of WiMAX. But one other advantage associated with fixed broadband wireless access over wired access technologies is the cost. The high costs from cables and the labor-intensive deployment of cables makes fixed broadband wireless access technology a cheaper option. WiMAX is also able to offer cost-efficient service supply in areas where traditional xDSL is not suitable due to a small number of customers per digital subscriber-line access multiplexer (DSLAM). These merits make WiMAX an access technology that can offer FBW services to disadvantaged rural areas in South Africa.
Limitations of IEEE 802.16
• IEEE 802.16 can offer Internet connectivity for long distances up to 50 km; however, there are drawbacks associated with the technology. Other wireless technologies operating in the vicinity can interfere with the WiMAX connection and cause a reduction in data throughput (WiMAX
Technology Brief, 2005). The issue of transmission being affected by
atmospheric conditions, such as rain, affects WiMAX performance. Buildings and trees attenuate the signal, contributing to signal degradation (Sweeny, 2004). This affects the performance of WiMAX technology overall.
• LOS is required for long-distance connection (5 to 30 miles) (WiMAX
Technology Brief, 2005). Without LOS backhaul, connectivity is not
possible for such long distances.
• The data rates being offered by WiMAX are not as high as some wired access counterparts, such as optical fiber (Sweeny, 2004).
• Currently, pre-WiMAX products are available on the market. This means time is needed for WiMAX to mature and offer products that offer long- distance connectivity.
• In South Africa, at present, few companies offer WiMAX products. Rather, they must be shipped from outside the country. Although the cost is still high, this should come down once these products are manufactured locally.