LMDS vs. MMDS: Comparing Broadband Wireless Technologies

LMDS (Local Multipoint Distribution Service) and MMDS (Multichannel Multipoint Distribution Service) are both broadband wireless technologies designed to deliver high-speed internet, voice, and video services. However, they differ significantly in their suitability for different environments. LMDS shines in urban areas with dense populations, offering high bandwidth and excellent sectorization. MMDS, on the other hand, is better suited for wider geographic coverage in suburban and rural areas, leveraging lower frequencies for extended reach and cost-effectiveness.

MMDS: Multichannel Multipoint Distribution Service

MMDS is often used as a replacement for cable TV service providers, particularly in rural or suburban areas where traditional cable infrastructure is not feasible.

Key Features of MMDS

• Frequency Range: Typically operates in the 2.5 GHz and 3.5 GHz bands.
• Architecture: Supports both Point-to-Multipoint (P2MP) and Point-to-Point (P2P) topologies.
• Coverage: Can cover larger geographical areas, with hub towers reaching approximately 35 miles.
• Cost: Uses less specialized RF equipment in larger quantities at lower frequencies, which helps reduce costs.
• Interference: More susceptible to interference from other MMDS and TV applications due to shared frequency bands.
• Deployment: Requires precise planning for large-scale deployments and upstream bandwidth management.

(Image: MMDS Architecture)

LMDS: Local Multipoint Distribution Service

LMDS provides TV and two-way internet service similar to MMDS, but it’s particularly well-suited for high-density urban environments that demand high bandwidth and extensive coverage management.

Key Features of LMDS

• Frequency Range: Operates above 20 GHz, typically at 28 GHz or 38 GHz.
• Architecture: Utilizes a Point-to-Multipoint (P2MP) topology, with the ability to interface with Point-to-Point (P2P) and TV systems.
• Coverage: Typically covers smaller areas, with a base station range of up to 5 miles.
• Bandwidth: Offers high bandwidth, suitable for a wide range of applications, including voice, IP, and data services.
• Network: Requires specialized RF equipment for operations, including RF Up/Down converters and optical interfaces. Supports sectorization to manage large user capacities in densely populated urban areas.
• Infrastructure: Requires a robust fiber-based infrastructure with SONET, optical links, and CO equipment.

(Image: LMDS Architecture)

Frequency Allocation

• MMDS: The 2.15 GHz to 2.68 GHz frequency band is allocated for MMDS. OFDM (Orthogonal Frequency-Division Multiplexing) modulation is used with a bandwidth of 6 MHz, composed of 512 sub-carriers. The sub-carrier spacing is about 12 KHz.

  $f\_{subcarrier} = 12 \text{ kHz}$

• LMDS: Approximately 30 GHz to 40 GHz bands are used for LMDS, mainly in the USA, Europe, and other countries.

Advantages and Disadvantages

• Both MMDS and LMDS are used for TV and two-way internet service using fixed wireless access.
• MMDS, due to its lower RF frequency range, provides less bandwidth compared to LMDS. However, advancements in OFDM technology are leading to higher achievable data rates with MMDS.
• MMDS is ideal for small business enterprises and residential users, while LMDS is often used for larger businesses, offering higher data rates.
• MMDS signals can cover longer distances, making them suitable for large cell network scenarios. LMDS signals cover shorter distances from base station equipment.
• Due to the larger wavelength, MMDS signals are less susceptible to rain and absorption losses compared to shorter wavelength LMDS signals.

LMDS vs. MMDS: A Tabular Comparison

Conclusion

The choice between LMDS and MMDS depends on a variety of factors: coverage requirements, bandwidth needs, cost considerations, deployment flexibility, interference levels, weather resilience, regulatory requirements, and specific application scenarios. Evaluating these parameters will help stakeholders determine the most suitable technology for their broadband deployment objectives.

For further information, refer to tutorials on LMDS and MMDS, which describe architectures, advantages, disadvantages, and system features.