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The introduction of the IEEE 802.16 family of standards (a.k.a. WiMAX) has spurred the interest of organizations seeking to deploy high performance, cost-effective broadband wireless networks. The initial offering, 802.16d-2004 (commonly known as fixed WiMAX), addresses fixed and nomadic applications. The more recent 802.16e-2005 (Mobile WiMAX) is an amendment of the "d" standard and supports fixed, nomadic and truly mobile deployments.
It should be noted that 802.16e-2005 not only introduces mobility, it also provides better performance in fixed and nomadic deployments. While the 802.16d PHY is based on OFDM (Orthogonal Frequency Division Multiplexing) with 256 FFTs, 802.16e is based on S-OFDMA (Scalable Orthogonal Frequency Division Multiple Access) and uses 512 FFTs (3.5 and 5 MHz channels) and 1024 FFTs (7 and 10 MHz channels).
OFDMA technology also lowers the uplink PAPR (and thus the peak power needed), therefore reducing the PA linearity constraint. By using a greater number of pilot subcarriers and introducing sub-channelization to dynamically and randomly distribute subcarriers across the whole channel, 802.16e addresses a wide range of coverage and capacity needs and provides the best possible protection against frequency-selective channel and interference.
The OFDMA technology also allows the MAC scheduler to allocate the bandwidth resources in time and frequency domains, as opposed to time only for OFDM. 802.16e-2005 therefore allows truly full duplex communication where the base station can exchange with several subscriber stations at the same time. This translates into much less overall system latency.
Another 802.16e-2005 strong suit is its support for frequency reuse-1 deployments, which greatly simplifies network planning by allowing a much greater flexibility in frequency allocation.
These are but a few reasons why systems based on 802.16e.2005 have a marked advantage over 802.16d-2004 solutions. And we have not even broached the benefits of MIMO 2X2 Matrix A and B, Sleep and Idle modes power reduction, QoS, SFN operation for Multicast / Broadcast services, etc, etc.
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