Chapter 18

MMDS and LMDS

      The  Multichannel Multipoint Distribution Service (MMDS) is a broadcasting and communications service that operates in the ultra-high-frequency (UHF) portion of the radio spectrum between 2.1 and 2.7 GHz. MMDS is also known as wireless cable. It was conceived as a substitute for conventional cable television (TV). However, it also has applications in telephone/fax and data communications. Allows two-way voice, data and video streaming. It operates at a lower frequency than LMDS (typically within specified bands in the 2-10GHz range) and therefore has a greater range and requires a less powerful signal than LMDS. MMDS is a less complicated, cheaper system to implement.

     

         MMDS band uses microwave frequencies from 2 GHz to 3 GHz in range. Reception of MMDS-delivered television signals is done with a special rooftop microwave antenna and a set-top box for the television receiving the signals. The antenna usually has an integrated down-converter to transmit the signals at frequencies compatible with terrestrial TV tuners down on the coax (much like on satellite dishes where the signals are converted down to frequencies more compatible with standard TV coaxial cabling), some larger antennas utilise an external down-converter. The receiver box is very similar in appearance to an analogue cable television receiver box. is a wireless telecommunications technology, used for general-purpose broadband networking or, more commonly, as an alternative method of cable television programming reception.

Transmission line

   Transmission line is a specialized cable designed to carry alternating current of radio frequency, that is, currents with a frequency high enough that their wave nature must be taken into account. Transmission lines are used for purposes such as connecting radio transmitters and receivers with their antennas, distributing cable television signals, and computer network connections.

        

          Local Multipoint Distribution Service (LMDS) is an ideal solution for bringing high-bandwidth services to homes and offices within the last-mile—an area where cable or optical fibre may not be convenient or economical. Having architectural similarities with cellular networks, LMDS is a fixed (non-mobile) point-to-multipoint wireless access technology that typically operates in the 28 GHz band and offers Line-of-Sight (LoS) coverage up to 3-5 km. Depending on the local licensing regulations in a country, such broadband wireless systems may operate anywhere from 2 to 42 GHz. Though data transfer rates for LMDS can reach 1.5 to 2 Gbps, in reality it is designed to deliver data at speeds between 64 Kbps to 155 Mbps (as against 9.6 Kbps offered by 2G cellular networks like GSM), a more realistic downstream average being around 38 Mbps. At such speeds, LMDS may be the key to bringing multimedia data—supporting voice connections, the Internet, videoconferencing, interactive gaming, video streaming and other high-speed data applications—to millions of customers worldwide over the air.

              

The services possible with LMDS include the following:

· Voice dial−up services

· Data

· Internet access

· Video

Head-End Equipment

The Head-End equipment can be broken down into two main categories:

Digital television equipment and Internet and VoIP equipment.

   

     The digital television equipment can provide MPEG-2 encoded video/audio streams from live television feeds, and optionally from video servers with VOD or other pre-recorded content.  The encoded streams are multiplexed into a DVB compliant MPEG-2 ASI transport stream and delivered to the transmission site through a variety of distribution networks including IP networks, microwave links and satellite delivery.

          The Internet and VoIP Head-End equipment requires a robust IP network connection to the DOCSIS 2.0/3.0 Wireless Modem Termination System at the transmission site.  The connection must exceed the total bandwidth   (>30Mbit/sec) of the wireless data network.

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

http://www.angelfire.com/nd/ramdinchacha/DEC00.html

http://www.uniquesys.com/MMDS/MMDS_Triple_Play.php

http://www.digital-kaos.co.uk/forums/f10/what-mmds-simple-explanation-23214/

http://www.mobilecomms-technology.com/projects/mmds/