MMDS and LMDS

The local multipoint distribution service (LMDS) and multichannel multipoint distribution service (MMDS) have their historical roots in television. MMDS's pre-cursor, the multipoint distribution service (MDS), was established by the Federal Communications Commission (FCC) in 1972. The Commission originally thought MDS would be used primarily to transmit business data. However, the service became increasingly popular for transmitting entertainment programming. Unlike conventional broadcast stations, whose transmissions are received universally, MDS programming is designed to reach only a subscriber-based audience. 

LMDS

LMDS is a fixed broadband line-of-sight, point-to-multipoint, microwave system, which operates at a high frequency (typically within specified bands in the 24-40GHz range) and can deliver at a very high capacity, depending on the associated technologies. Given the complexity of the equipment required (and the power needed to deliver signals) both of these technologies are regarded as prohibitively expensive for the consumer market. Therefore, LMDS operators will initially be targeting enterprises and network operators, although the consumer market is likely to emerge over time as the cost of CPE comes down (partly driven by the take-up of IP). It should be noted that CPE costs $5,000 for LMDS in the 26GHz range. 

Local multipoint distribution services (LMDS), a line-of-sight technology running in the 28 GHz band. LMDS is most suited for densely populated urban areas where it is difficult and expensive to deploy additional or new wired infrastructures. Typical speeds are 45M bit/sec downstream in a point-to-multipoint configuration. However, LMDS has the potential to exceed OC-3 (155M bit/sec) speeds. Distances between sites are limited to 4 kilometers. 

MMDS

MMDS 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. As a consequence, the CPE is cheaper, thus it has a wider potential addressable market. It is also less vulnerable to rain fade - the interference caused by adverse weather conditions that can undermine the quality of the microwave signal. However, the bandwidth offered by LMDS makes this the more viable option.

Multichannel multipoint distribution service (MMDS) operates in the 2 GHz to 3 GHz band, is less susceptible to interference than LMDS, and has no line-of-sight requirements. MMDS can support greater distances than LMDS - up to 30 miles between sites. The tradeoff is that MMDS is slower, delivering downstream speeds in the neighborhood of 10M bit/sec.  

TECHNOLOGY

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.

For downstream traffic to the customers' premises, the base station converts the digital bitstream containing voice, data and video information into microwaves that are transmitted to a small antenna on the customer's premises. The microwaves are then reconverted back into a digital bitstream by the NIU and delivered to the end-user. The process is reversed for upstream traffic. When the base station receives the microwave signal and has converted it into a digital bitstream, this is routed through, or 'backhauled' to, the wider network, through which the data or call is delivered to its destination.

Unlike the lower frequency cellular systems, LMDS and MMDS both require a line-of-sight between the base station and customer premise transceivers. This is a prerequisite for any system operating above approximately 2-3.5GHz. The base station is connected to the wide-area network switch or internet POP via either a high-capacity wireline (usually fibre optic) or wireless. Similarly, at the customer's premises, the signal can be delivered to the end-user terminals via either of these.

BENEFITS

Wireless systems are being deployed to fulfil a number of functions. On a network level they are suitable for both access and backbone infrastructure. It is generally agreed, however, that it is in the access market where the key advantages are held over wireline alternatives. The principal strengths of LMDS/MMDS are:

• Speed of network deployment is much quicker with wireless systems enabling rapid, early market entry
• Entry, deployment and upgrading costs are much lower than for wireline alternatives, for which engineering (cabling and trenching) costs are significantly higher
• The maintenance, management and operation expenditure is lower. Wireless systems can be rolled out much faster, enabling an earlier return on investment
• Scalable architectures enable expanded coverage and services in direct relation to the level of demand
• Only one network architecture is required to provide a full suite of interactive voice, video and data services that can be expanded as and when desired

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.

Difference between MMDS and LMDS technology:

 

MMDS uses the lower frequency range compared to LMDS, hence MMDS covers larger areas than LMDS but provides lower access speed. 

LMDS, MMDS race for low-cost implementation

 LMDS, MMDS race for low-cost implementation
Advocates for wireless residential broadband access had a busy November, as the millimeter-wave camp examining 28- and 38-GHz local multipoint distribution service (LMDS) networks raced to make consumer and business systems cost-effective for single-user Internet access. They faced an onslaught of new efforts from competing radio system specialists aiming to make the microwave networks known as multichannel multipoint distribution service (MMDS) at 2.5 GHz and 5 GHz easier to deploy. Cost-reduction efforts in both markets may result in making wireless "last-mile" access technologies viable alternatives to always-on Internet access technologies such as cable modems and digital subscriber lines.

The IEEE's new 802.16 working group for broadband wireless access networks is trying to hammer out common principles for both MMDS and LMDS systems. At a meeting in Koloa, Hawaii, in mid-November, the panel worked on physical-transceiver, Medium Access Control and frequency-coexistence standards for both camps. On Nov. 11, the working group approved an official study group extension to examine MMDS and similar networks that operate at less than 10 GHz. The existing 802.16.1 air interface project is for networks ranging in frequency from 10 GHz to 66 GHz.

With both technologies, an antenna and radio are installed on the roof of a business' site and are connected by coaxial cable to customer premises equipment in the LAN wiring closet. Commercial service availability is imminent. WorldCom has been conducting MMDS service trials with schools, residential and business customers in Boston; Dallas; Jackson, Miss.; Baton Rouge, La.; and Memphis, Tenn., using equipment from Cisco and Motorola. Meanwhile, Cisco has said it plans to begin commercially shipping LMDS and MMDS interfaces for its routers by midyear - which sounds like any day now. The move could prove to be a major stepping stone for service provider deployments. 


http://www.eetimes.com/electronics-news/4039196/LMDS-MMDS-race-for-low-cost-implementation


http://www.rficsolutions.com/publishedpapers/Broadbandwireless.pdf


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


http://www.networkworld.com/newsletters/wireless/2000/0626wire1.html