MMDS and LMDS

Multichannel Multipoint Distribution Service (MMDS), also known as Wireless Cable, is a wireless telecommunications technology, used for general-purpose broadband networking or, more commonly, as an alternative method of cable television programming reception. It is also a digital wireless transmission system that works in the 2.2-2.4 GHz range. Also known as "Advanced Wireless Services" (AWS) and "wireless cable, it requires line of sight between transmitter and receiver, which can be 30 or more miles apart.

MMDS was designed initially as a one-way service for bringing cable TV to subscribers in remote areas or in locations that are difficult to install cable. It supports approximately 33 analog channels and more than 100 digital channels of TV. In late 1998, the FCC opened up the technology for two-way transmission, enabling MMDS to provide data and Internet services to subscribers.

Technology

The BRS band uses microwave frequencies at 2.1 GHz and from 2.5 GHz to 2.7 GHz. Reception of BRS-delivered television and data signals are done with a rooftop microwave antenna. The antenna is attached to a down-converter or transceiver to receive and transmit the microwave signal and convert them to frequencies compatible with standard TV tuners (much like on satellite dishes where the signals are converted down to frequencies more compatible with standard TV coaxial cabling), some antennas use an integrated down-converter or transceiver. Digital TV channels can then be decoded with a standard cable set-top box or directly for TVs with integrated digital tuners. Internet data can be received with a standard DOCSIS Cable Modem connected to the same antenna and transceiver.

            Local Multipoint Distribution Service (LMDS) is a digital wireless transmission system that works in the 28 GHz range in the U.S. and 24-40 GHz overseas. It requires line of sight between transmitter and receiving antenna, which can be from one to four miles apart depending on weather conditions. LMDS provides bandwidth in the OC-1 to OC-12 range, which is considerably greater than other wireless broadband services.

LMDS is a new type of stationary (fixed) broadband wireless access technology designed for a mass subscriber marketplace. Based on millimeter microwave frequencies - 24GHz and above - LMDS now offers a potential for cheaper in-building bandwidth than newly installed fiber or copper. In fact, it's the microwave technology that could make wireless data for the enterprise both cheap and ubiquitous.  While several vendors are offering products today, this technology is still in early development stages.

LMDS is a broadband wireless access technology originally designed for digital television transmission (DTV). It was conceived as a fixed wireless, point-to-multipoint technology for utilization in the last mile. LMDS commonly operates on microwave frequencies across the 26 GHz and 29 GHz bands. In the United States, frequencies from 31.0 through 31.3 GHz are also considered LMDS frequencies.

Throughput capacity and reliable distance of the link depends on common radio link constraints and the modulation method used - either phase-shift keying or amplitude modulation. Distance is typically limited to about 1.5 miles (2.4 km) due to rain fade attenuation constraints. Deployment links of up to 5 miles (8 km) from the base station are possible in some circumstances such as in point-to-point systems that can reach slightly farther distances due to increased antenna gain.

sources:

http://mobileinfo.com/Hot_Topics/LMDS&MMDS.htm

http://en.wikipedia.org/wiki/Multichannel_Multipoint_Distribution_Service

http://en.wikipedia.org/wiki/Local_Multipoint_Distribution_Service

http://www.answers.com/topic/local-multipoint-distribution-service