Chapter 18: MMDS and LMDS

MMDS (Multichannel Multipoint Distribution Service) is a Multichannel broadcast service that operates in the 2.1 to 2.9 GHz. Frequency range. It’s designed to be a POINT to MULTIPOINT broadcast service that is capable of delivering multiple channels of television programming for digital or analogue mode together with internet access, telephone and data transfer services to individual receive sites. Channels containing video, audio and data transmitter from a central site to individual residences, multiple dwelling units, and business locations. MMDS systems, which can be configured to offer just television are commonly referred to as “ Wireless Cable Television”.

HOW DOES MMDS SYSTEM         

                    WORK?

The architecture of a typical wireless cable system can be divided into two basic nodes: transmitting sites and receiving sites. Transmitting sites are the main or “HUB” node of MMDS system.

Programming information is generally delivered to an MMDS system from satellites, it can also be generated locally or come from pre-recorded video tapes, these signals are fed into discrete transmitters where they are modulated up converted and amplified. Transmitter powers range 1 to 200 watts per channel and 15 to 100 watts average power per digital channel, individual microwave channels are then multiplexed or combined together and are passed to a transmitting antenna via low loss coaxial cable or waveguide. A centrally located transmitting antenna radiates the MMDS signal to the desired receiving sites, generally in an omni directional (360 degrees) pattern.

LMDS (Local Multipoint Distribution System)

LMDS (Local Multipoint Distribution System) is a system for broadband microwave transmission direct from a local antenna to homes and businesses within a line-of-sight radius, a solution to the so-called last-mile problem of economically bringing high-bandwidth services to users. LMDS is an alternative to installing optical fiber all the way to the user or to adapting cable TV for broadband Internet service. Depending on the implementation, LMDS offers a bandwidth of up to 1.5 Gbps downstream to users and 200 Mbps upstream from the user. A more typical data rate is 38 Mbps downstream. Some services offer both downstream and upstream service (symmetrical service); others offer downstream only (asymmetrical service) with upstream being obtained using wire connections. 

In addition to the investment by service providers for transmitters, users need to install transceivers costing about $125-225. However, the cost of installing LMDS is considered far lower than installing fiber optic cable or upgrading cable TV systems. The first markets for LMDS are seen as:

·         High-speed data transmission for businesses

·         Interactive television and streaming multimedia from Web sites

·         Voice service (usually as a supplement to other services) 

Because LMDS requires a more expensive and possibly larger transceiver than can conveniently be packaged in a handheld device, LMDS is not viewed as a replacement for or alternative to mobile wireless technologies such as cellular and GSM. On the other hand, LMDS offers much higher data rates because of its use of a higher range of frequencies with their wider bandwidths. In general, LMDS is for fixed locations and offers higher data rates; cellular digital such as GSM is for mobile users at lower data rates.

References:

http://searchnetworking.techtarget.com

http://wikipedia.com

http://multi-session.net

Broadband Telecommunication Handbook, 2nd edition by Regis J. "Bud" Bates