Editing WiMAX (section)

=== The IEEE 802.16 standard ===
WiMAX is based upon [[IEEE]] [[IEEE 802.16|802.16e-2005]],<ref name=tge>{{cite web|title=IEEE 802.16e Task Group (Mobile WirelessMAN)|url=http://www.ieee802.org/16/tge/|website=Ieee802.org|access-date=2008-03-12|archive-url=https://web.archive.org/web/20080224040456/http://www.ieee802.org/16/tge/|archive-date=2008-02-24|url-status=live}}</ref> approved in December 2005. It is a supplement to the IEEE Std 802.16-2004,<ref name=tgd>{{cite web|title=IEEE 802.16 Task Group d|url=http://www.ieee802.org/16/tgd/|website=Ieee802.org|access-date=2008-03-12|archive-url=https://web.archive.org/web/20080224053608/http://www.ieee802.org/16/tgd/|archive-date=2008-02-24|url-status=live}}</ref> and so the actual standard is 802.16-2004 as amended by 802.16e-2005. Thus, these specifications need to be considered together.

IEEE 802.16e-2005 improves upon IEEE 802.16-2004 by:
* Adding support for mobility (soft and hard handover between base stations). This is seen as one of the most important aspects of 802.16e-2005, and is the basis of mobile WiMAX.
* Scaling of the [[fast Fourier transform]] (FFT) to the channel bandwidth in order to keep the carrier spacing constant across different channel bandwidths (typically 1.25&nbsp;MHz, 5&nbsp;MHz, 10&nbsp;MHz or 20&nbsp;MHz). Constant carrier spacing results in a higher spectrum efficiency in wide channels, and a cost reduction in narrow channels. Also known as scalable OFDMA (SOFDMA). Other bands not multiples of 1.25&nbsp;MHz are defined in the standard, but because the allowed FFT subcarrier numbers are only 128, 512, 1024 and 2048, other frequency bands will not have exactly the same carrier spacing, which might not be optimal for implementations. Carrier spacing is 10.94&nbsp;kHz.
* Advanced [[antenna diversity]] schemes, and [[hybrid automatic repeat-request]] (HARQ)
* [[Adaptive beamformer|Adaptive antenna system]]s (AAS) and [[MIMO]] technology
* Denser sub-channelization, thereby improving indoor penetration
* Intro and [[Low-density parity-check code|low-density parity check]] (LDPC)
* Introducing downlink sub-channelization, allowing administrators to trade coverage for capacity or vice versa
* Adding an extra [[quality of service]] (QoS) class for VoIP applications

SOFDMA (used in 802.16e-2005) and OFDM256 (802.16d) are not compatible thus equipment will have to be replaced if an operator is to move to the later standard (e.g., Fixed WiMAX to Mobile WiMAX).