WiMax is not the only solution for delivering broadband wireless services. Several proprietary solutions, particularly for fixed applications, are already in the market. A few proprietary solutions, such as I-Burst technology from ArrayComm and Flash-OFDM from Flarion (acquired by QualComm) also support mobile applications. In addition to the proprietary solutions, there are standards-based alternative solutions that at least partially overlap with WiMax, particularly for the portable and mobile applications. In the near term, the most significant of these alternatives are third-generation cellular systems and IEEE802.11-based Wi-Fi systems. In this section, we compare and contrast the various standards-based broadband wireless technologies and highlight the differentiating aspects of WiMax.WiMax versus 3G and Wi-Fi]
How does WiMax compare with the existing and emerging capabilities of 3G and Wi-Fi? The throughput capabilities of WiMax depend on the channel bandwidth used. Unlike 3G systems, which have a fixed channel bandwidth, WiMax defines a selectable channel bandwidth from 1.25MHz to 20MHz, which allows for a very flexible deployment. When deployed using the more likely 10MHz TDD (time division duplexing) channel, assuming a 3:1 downlink-to-uplink split and 2 x 2 MIMO, WiMax offers 46Mbps peak downlink throughput and Mbps uplink.
The reliance of Wi-Fi and WiMax on OFDM modulation, as opposed to CDMA as in 3G,allows them to support very high peak rates. The need for spreading makes very high data rates more difficult in CDMA systems.
More important than peak data rate offered over an individual link is the average throughput and overall system capacity when deployed in a multicellular environment. From a capacity standpoint, the more pertinent measure of system performance is spectral efficiency.
WiMax specifications accommodated multiple antennas right from the start gives it a boost in spectral efficiency. In 3G systems, on the other hand, multiple-antenna support is being added in the form of revisions. Further, the OFDM physical
[layer used by WiMax is more amenable to MIMO implementations than are CDMA systems from the standpoint of the required complexity for comparable gain. OFDM also makes it easier to exploit frequency diversity and multi-user diversity to improve capacity. Therefore, when compared to 3G, WiMax offers higher peak data rates, greater flexibility, and higher average throughput and system capacity.
Another advantage of WiMax is its ability to efficiently support more symmetric links useful for fixed applications, such as T1 replacement and support for flexible and dynamic adjustment of the downlink-to-uplink data rate ratios. Typically, 3G systems have a fixed asymmetric data rate ratio between downlink and uplink.
What about in terms of supporting advanced IP applications, such as voice, video, and multimedia?
. How do the technologies compare in terms of prioritizing traffic and controlling quality?
The WiMax media access control layer (MAC layer) is built from the ground up to support a variety of traffic mixes, including real-time and non-real-time constant bit rate and variable bit rate traffic, prioritized data, and best-effort data. Such 3G solutions as HSDPA and 1x EV-DO were also designed for a variety of QoS levels.
Perhaps the most important advantage for WiMax may be the potential for lower cost owing to its lightweight IP architecture. Using an IP architecture simplifies the core network 3G has a complex and separate core network for voice and data and reduces the capital and operating expenses. IP also puts WiMax on a performance/price curve that is more in line with general-purpose processors (Moore’s Law), thereby providing greater capital and operational efficiencies. IP also allows for easier integration with third-party application developers and makes convergence with other networks and applications easier.
In terms of supporting roaming and high-speed vehicular mobility, WiMax capabilities are somewhat unproven when compared to those of 3G. In 3G, mobility was an integral part of the design, WiMax was designed as a fixed system, with mobility capabilities developed as an add-on feature.
In summary, WiMax occupies a somewhat middle ground between Wi-Fi and 3G technologies when compared in the key dimensions of data rate, coverage, QoS, mobility, and price..
Other Comparable Systems
So far, we have limited our comparison of WiMax to 3G and Wi-Fi technologies. Two other standards based-technology solutions could emerge in the future with some overlap with WiMax: the IEEE 802.20 and IEEE 802.22 standards under development. The IEEE 802.20 standard is aimed at broadband solutions specifically for vehicular mobility up to 250 kmph. This standard is likely to be defined for operation below 3.5GHz to deliver peak user data rates in excess of 4Mbps and 1.2Mbps in the downlink and uplink, respectively. This standards development effort began a few years ago but it has not made much progress, owing to lack of consensus on technology and issues with the standardization process. The IEEE 802.22 standard is aimed specifically at bringing broadband access to rural and remote areas through wireless regional area networks (WRAN). The basic goal of 802.22 is to define a cognitive radio that can take advantage of unused TV channels that exist in these sparsely populated areas. Operating in the VHF and low UHF bands provides favorable propagation conditions that can lead to greater range. This development effort is motivated by the fact that the FCC plans to allow the use of this spectrum without licenses as long as a cognitive radio solution that identifies and operates in unused portions of the spectrum is used. IEEE 802.22 is in early stages of development and is expected to provide fixed broadband applications over larger coverage areas with low user densities.
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