To start with, .11 is used only in a few unlicensed shared spectrum. Nobody can provide wide area coverage with meaningful guarantees of quality of service. 802.11 is cheap and commonly available and does well over short distances. Whether the protocol can be modified to work over longer range or can be improved by using directional antennas is understood but provides only a limited capability: you cannot set up a link in a congested area that delivers that link quality unless you get above/around the common interference. Pedestrians or mobile users at ground level will share the spectrum with everyone else who wishes to use it. Municipalities, for example, can use WiFi for public access but they have no greater legal rights to use it than private individual or business owners who may also wish to have their own networks. That is the nature of license exempt spectrum.
WiMAX could be used in license exempt spectrum along with WiFi : there is an 802.16 standard working group that has worked on a MAC to do that... but has pretty well stalled for lack of interest and because of the knowledge that use of WiMAX would have to contend, and therefore, offer similar capabilities compared to WiFi.
WiFi has become very popular but growth has slowed. WiMAX has just started to deploy. It is now prescribed for use in 2.3, 2.5, 3.5 GHz with 1.7, 2.1 GHz and probably 700 MHz soon to follow. ITU is likely to include WiMAX as a sixth system under IMT-2000, calling it IP-OFDMA. And the future version of WiMAX, 802.16m is expected to be proposed for IMT-Advanced, which LTE will likely also be proposed. The goals for IMT-Advanced are 100 Mbps in mobile application and 1 Gbps in fixed-nomadic. The way both WiMAX II and LTE will achieve that
is through the use of MIMO-AAS and 'smart wireless broadband' network architecture which includes pico-cell/micro-cell granularity and distributed network intelligence (smart network management). Unlike WiFi junk, this is being done within the standard so that it doesn't come into play as a cadre of proprietary MESH/routing enhancements that provide no interoperability at the MESH network node level.
WiMAX is a managed network, WiFi is a contention based network (MAC). Big difference. The power of WiFi is that it can be randomly adopted by end users or organizations without having to buy spectrum licenses. And it takes advantage of advances in semiconductors making devices cheap. This leads to 'viral adoption' phenomena of open consumer products.
WiMAX, once volumes ramp, will have similar low cost for various scale of device. It has similar adoption patterns as cellular wireless: it takes scale of capital and needs large coverage areas to become attractive to mass markets. And the product, although sold through retail channels, will need 'market push' to gain broad appeal. However, some operators that I have interviewed say that they will offer corporate and government organizations the opportunity to deploy their own intra-cell/campus and in-building networks that operate over the licensed spectrum. This will allow these organizations to build high availability, secure networks that do not share spectrum with other groups locally. On a local level, the neworks will provide similar bandwidth as 802.11n. It could be higher if a broader band of spectrum is available - that depends on the spectrum the operator has licensed and how they wish to allocate it. 802.16j is working on sub-cell architecture that allows reuse of spectrum of 10X. Demonstrations and simulations of MIMO-OFDM systems have, whether that is WiMAX, LTE or something else, have been staged for up to 100X spectrum reuse. This can be envisioned as having many local n802.11n networks (back hauled via cable, DSL or fiber) within a few city blocks: if the local networks are deployed so they don't cause interference then each can operate at high bandwidth. In an organized network such as WiMAX or LTE, the task is much more difficult because of hand-off between base stations and need to organize and distribute management tasks including QoS.
WiFi and WiMAX have several similarities and much that is different between them. The use of WiMAX, just as has been the case for WiFi, won't be apparent until use flourishes - not for another 3-4 years. Only then will comparisons be on more equal commercial footing. |
