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In order to achieve this level of performance, a fixed wireless point to point technology with LOS (line-of-sight) locations and directional antennas is required, meaning that all of the power is essentially dedicated to supporting that one connection - a rather expensive and impractical application for WiMAX under most scenarios.
Wireless backhaul can have notable exception where the subscription cost of the service offering could justify the dedicated resources. Achieving 70 Mbps in a mobile environment with WiMAX will not be feasible or economical in the foreseeable future.
Additionally, there is still an inherent tradeoff between data rates and distance, with the higher data rates only achievable near the centre of
the cell. In other words, to achieve 70 Mbps data rates throughout an entire cell would require very small cell radii.
This level of performance is not extraordinary. There are also several non-WiMAX solutions, in particular microwave radio solutions, which can transmit a point-to-point signal that supports hundreds of Mbps or more. Simply crank up the power and allocate spectrum and virtually anything is possible. These high data rates may well be limited to fixed scenarios under certain special conditions, similar to those provided above. It is much more difficult to achieve high data rates in mobile environments.
3.2 THE ‘AHAA(S)’
WiMAX is designed to cover wide geographical areas serving large number of users at low cost and provides a wireless alternative to wired backhaul and last-mile deployments that use data over cable service interface specification (DOCSIS) cable modems, digital subscriber line technologies (xDSL), T-carrier and E-carrier (T-x/E-x) systems, and optical carrier level (OC-x) technologies. WiMAX is considered one of the best solutions for last-mile distribution due to its extraordinary performance characteristics (Figure 3.1).
Throughput and Coverage
WiMAX technology can reach a theoretical 30 mile coverage radius and achieve data rates up to 75 Mbps, although at extremely long range
Pico-cell pedestrian Range ~100 m
Mini-cell mobile oata _i-20 Mbps
Range -1 km Data -1 Mbps
Figure 3.1 Coverage vs throughput
throughput is closer to the 1.5 Mbps performance of typical broadband services (equivalent to a T1 line). Dynamic adaptive modulation allows the base station to trade off throughput for range so that service providers can provision rates based on a tiered pricing approach, similar to that used for wired broadband services.
WiMAX 802.16 equipment certified by the Forum supports shared throughput of up to 75 Mbps and a coverage radius of 5-8 km (licence-exempt), and depends on terrain and population density. By using a robust modulation scheme, IEEE 802.16 delivers high throughput at long ranges with a high level of spectral efficiency that is also tolerant of signal reflections.
In addition to supporting a robust and dynamic modulation scheme, the IEEE 802.16 standard also supports technologies that increase coverage, including mesh topology and ‘smart antenna’ techniques. As radio technology improves and costs drop, the ability to increase coverage and throughput by using multiple antennas to create ‘transmit’ and/or ‘receive diversity’ will greatly enhance coverage in extreme environments.
Flexibility and Scalability
The 802.16-2004 standard supports flexible radio frequency (RF) channel bandwidths and reuse of these frequency channels as a way to increase network capacity. The standard also specifies support for transmit power control (TPC) and channel quality measurements as additional tools to support efficient spectrum use.
Easy addition of new sectors supported with flexible channels maximizes cell capacity, allowing operators to scale the network as the customer base grows. Flexible channel bandwidths accommodate spectrum allocations for both licensed and unlicensed spectrum.
The standard has been designed to scale up to hundreds or even thousands of users within one RF channel. Operators can reallocate spectrum through sectoring as the number of subscribers grows. Support for multiple channels enables equipment makers to provide a means addressing the range of spectrum use and allocation regulations faced by operators in diverse international markets.
The 802.16 standard provides an important flexibility advantage to new businesses or businesses that move their operations frequently, like a construction company with offices at each building site. Unlike a T1 or
Figure 3.2 Coverage vs throughput
DSL line, wireless broadband access can be quickly and easily set up at new and temporary sites (Figure 3.2).
The wireless medium used by WiMAX enables service providers to circumvent costs associated with deploying wires, such as time and labour. Interoperable equipment allows operators to purchase WiMAX Certified™ equipment from more than one vendor. A stable, standard-based platform improves OpEx by sparking innovation at every layer, network management, antennas and more.