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Multichannel Multipoint Distribution Systems (MMDS) evolved from the North American educational service known as Instructional Television Fixed Service (ITFS). MMDS licenses provide sufficient bandwidth to deliver analog wireless TV services, and have widely been used to do so in competition with cable TV. Hence MMDS is also referred to as Wireless Cable. Over time, MMDS signal transmission systems have been modified so that they can provide digital data services, such as digital TV services and Internet access. An inherent advantage of MMDS is that it does not require the installation of costly cable networks.
MMDS operates on a number of independent, 4 to 6 MHz wide transmission channels scattered across the microwave frequency band from 2.1 GHz to 2.7 GHz. Many of these channels are separated from one another by frequency spans containing other types of radio services. The theoretical maximum bandwidth avialable with MMDS is 202 MHz; up to 33 video channels can be relayed to subscribers. However, in most markets not all of the MMDS channels are available for licensing. Consequently, the maximum practical MMDS operating bandwidth is less than 100 MHz and is usually limited to 16 independent narrow band signal transmission channels.
In September 1998 the FCC passed new rules that permit MMDS licensees to use all or part of any of their 6 MHz channels for two-way service. The Order adopted provides for flexibility in two-way system design by permitting licensees to combine multiple channels to accommodate wider bandwidth uses and the "subchannelizing" of 6 MHz channels for smaller bandwidth uses, and by allowing response stations and boosters to operate up to maximum permitted power levels.
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