LMDS and MMDS share a number of common architectural features although they vary from one manufacturer to another according to features and capabilities. The core components are a base-station transceiver (transmitter and receiver), a customer-premise transceiver and some kind of CPE network interface unit (NIU) or card.
MMDS: Multichannel Multipoint Distribution Service
Multichannel multipoint distribution service (MMDS), also known wireless cable, is a wireless telecommunications technology, used for general-purpose broadband networking’s or, more commonly, as an alternative method of cable television programming reception. MMDS is a microwave technology that was originally designated for one-way transmission of wireless cable TV signals to rural areas. MMDS service is ideal for home users because the data rate and the cost of using the system are well matched to a home user's requirements.
LMDS: Local Multipoint Distribution Service
Local Multipoint Distribution Service(LMDS), is a broadband wireless point to multipoint communication system that provides reliable digital two-way voice, data and Internet services. The term "Local" indicates that the signals range limit. "Multipoint" indicates a broadcast signal from the subscribers, the term "distribution" defines the wide range of data that can be transmitted, data ranging anywhere from voice, or video to Internet and video traffic. It provides high capacity point to multipoint data access that is less investment intensive.
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Originally designed for wireless digital telivision transmission LMDS and MMDS(Microwave Multipoint Distribution System) were predicted to serve the wireless Subscription Television needs. MMDS is also a broadband wireless communication service which operates at lower frequencies. Usually, LMDS operates at frequencies above the 10Ghz range and MMDS at frequencies below the 10GHz range.
LMDS technical and design issues.
A normal LMDS setup has a central facility with a fiber-linked PSTN and internet connections relay signal via point to point microwave links which in turn pass the signal along to hubs, located on rooftops or as stand-alone towers, for Point to Multipoint (PMP) transport to the end site. Basically, four parts in the LMDS architecture are:
- Network operations center(NOC)
- Fiber based infrastructure
- Base station
- Customer Premise Equipment and NOC designs.
Synergy between MMDS and LMDS spectrum and applications
Same customers and applications-data, voice, video.
- similar needs for backhaul, CPE modem, base station gateways etc.
- MMDS spectrum is good for long distance communication- need few cells.
- LMDS spectrum is good for communication over short distances - need many cells.
- LMDS and MMDS spectrum used together can lower system deployment costs and increase coverage.
Advantages and disadvantages of MMDS spectrum
- Propagation over long distances up to 100 km. with single tower.
- Less attenuation due to rain, foliage.
- RF component costs lower at 2.5 GHz.
- Equipment readily available today.
- Limited capacity without sectorization, cellularization which adds complexity and cost.
- Interference issues with other MMDS and ITFS licensees.
- Large upstream bandwidth in MMDS band requires careful planning, filtering etc.
- Cellularization later on may require retuning the entire network (every CPE ).
Advantages and disadvantages of LMDS spectrum
- Very large bandwidth available for data, IP telephony, video conferencing services.
- Large capacity.
- Higher RF component costs.
- Small cell size, 2-8 Km.
- Does not cover entire metropolitan area of a large city without adding many cells at high cost .
Benefits of using MMDS, LMDS and unlicensed bands together
- Complete coverage of a large city right in the beginning.
- Lower infrastructure and deployment costs.
- More types of services can be offered ie. lower cost services with MMDS network and high bandwidth services with LMDS network.
- Can grow subscribers and services by adding additional LMDS cells.
- More options to address interference with other ITFS and MMDS licensees.
- Lower back haul costs - LMDS and MMDS cells can be used for back haul.
