LMDS and MMDS in Wireless | Architectures, Advantages, Disadvantages

In the evolving landscape of broadband wireless communication technologies, LMDS (Local Multipoint Distribution Service) and MMDS (Multichannel Multipoint Distribution Service) have emerged as key players. These technologies serve as alternatives to DSL, such as ADSL and VDSL, offering robust solutions for video, voice, ATM and internet applications. This tutorial delves into the architectures of LMDS and MMDS, their advantages and disadvantages and a comparative analysis.

LMDS Architecture

The full form of LMDS is Local Multipoint Distribution Service. It is a P2MP (Point to Multi-Point) technology operating above 20 GHz. P2P (Point to Point) and TV systems can also be interfaced with LMDS.

LMDS architecture

The figure-1 depicts LMDS architecture. It consists of NOC (Network Operation Center), BS (Base Station), CPE (Customer Premises Equipment), fiber based infrastructure. Multiple NOCs are interconnected together. Fiber backbone infrastructure consists of SONET, OC-12, OC-3, DS3 optical links, CO equipments etc. Moreover NOC is interfaced with ATM, IP systems, PSTN and Internet.

BS is interfaced with optical equipments on one side and wireless on the other. It houses optical to electrical and electrical to optical interfaces as well as RF up/down converters. RF up converter is used to convert data to be transmitted on modulated RF waveforms. The RF down converter does the reverse operation.

CPEs are installed at customer premises and are linked with BS using wireless microwave links. They are available from multiple vendors. It consists of functionalities viz. modulation, demodulation, RF upconversion and RF downconversion etc. CPEs utilize multiple access schemes viz. TDMA, FDMA and CDMA for communication with BSs in the LMDS network.

Following are the key features of LMDS system:
• It operates at 28 GHz or 38 GHz frequency.
• It is installed similar to cellular system cell based layout.
• Cell size or range of BS is 5 miles.
• It uses P2MP and P2P topologies for end communication with CPEs.

LMDS Advantages and Disadvantages

LMDS provides high-bandwidth capabilities suitable for diverse applications such as voice, IP, and data, along with robust user capacity management through sectorization in densely populated areas. However, its implementation involves high costs due to the extensive RF equipment required and the need for numerous small cells, which can escalate installation expenses.

Advantages of LMDS

Following are the benefits or advantages of LMDS.
• It has larger bandwidth used for wide variety of applications such as voice, IP, data etc.
• It supports large capacity of users densely populated by way of sectorizing the area into cells.

Disadvantages of LMDS

Following are the drawbacks or disadvantages of LMDS.
• It has high RF equipment costs due to larger number needed.
• Smaller cell size (i.e. 2 to 8 Km) due to requirement of covering large capacity of users.
• Requires many cells to cover larger city areas. This increases installation cost for service providers.

MMDS Architecture

The full form of MMDS is Multichannel Multipoint Distribution Service. It is used for small business and home offices. It is not used for large customer requirements such as central offices. It is used where other broadband wireless technologies are difficult to be installed. It uses microwave tower installed on top of the mountains or tall buildings. It covers larger distance compare to LMDS which is about 35 miles.

MMDS architecture

The figure-2 depicts MMDS architecture. It consists of Hub equipment and customer side equipments. Hub consists of antenna tower, RF equipments, Modem, Router for connection with internet and network management system (i.e. NMS). Customer side equipments include antenna, wireless modem, ethernet switch, PCs etc. Hub antenna tower receives wireless signals from multiple users similar to P2MP topology. Each user premise antenna and Hub antenna is connected with P2P microwave link.

Following are the key features of MMDS system:
• It operates in 2.5 GHz and 3.5 GHz frequency bands.
• Hub tower has coverage distance of about 35 miles.
• It uses both P2MP and P2P topologies. P2MP from multiple users to Hub and P2P between individual user and Hub.

MMDS Advantages and Disadvantages

MMDS offers extensive coverage up to 100 km with lower equipment costs and minimal rain related signal loss due to its lower frequency usage. However, it supports fewer users due to the lack of sectorization, is prone to interference from other applications, and requires precise planning for upstream bandwidth management.

Advantages of MMDS

Following are the benefits or advantages of MMDS.
• The RF propagation covers 100 Km of region using single antenna tower.
• Due to smaller frequency of use compare to LMDS, MMDS does not suffer from rain attenuation.
• RF equipments are cheaper at lower frequency of 2.5GHz or 3.5 GHz and are available in large quantities.

Disadvantages of MMDS

Following are the drawbacks or disadvantages of MMDS.
• It does not support larger capacity due to lack of sectorization concept in MMDS.
• It suffers from interference from other MMDS and TV applications.
• Large upstream bandwidth needs more and accurate planning.

Comparison Between LMDS and MMDS

Let us compare LMDS Vs. MMDS and derive key differences between them in tabular form.

Features LMDS MMDS
Full Form Local Multipoint Distribution Service Multichannel Multipoint Distribution Service
Frequency range 28 GHz or 38 GHz 2.5 GHz and 3.5 GHz
Coverage area 5 miles 35 miles
Cell size Smaller, 2 to 8 Km Larger, upto 100 Km
RF Equipment Cost Higher Lower
Interference susceptibility Lower Higher (from other MMDS and TV applications)
Rain attenuation Higher Lower

Conclusion : In summary, LMDS and MMDS play crucial roles in expanding broadband wireless networks, offering viable alternatives to traditional DSL technologies. While LMDS is ideal for high-density urban environments requiring high bandwidth, MMDS excels in covering larger areas with lower equipment costs and minimal rain attenuation. By understanding the unique features, advantages, and limitations of LMDS and MMDS, businesses and service providers can make informed decisions about deploying these technologies to meet their specific broadband needs.

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