Satellite spectrum refers to the range of electromagnetic frequencies used for communication between satellites and ground stations or other satellites. These frequencies are carefully allocated and regulated by international and national bodies to ensure interference-free operation across various services such as telecommunications, broadcasting, navigation, Earth observation, and scientific research.

Satellite communication primarily operates in the following frequency bands:

1. L-Band (1-2 GHz)
   • Uses: GPS, mobile satellite services, and aviation communication.
   • Advantages: Penetrates weather conditions; supports mobile applications.
   • Limitations: Lower bandwidth; supports fewer data-intensive applications.
2. S-Band (2-4 GHz)
   • Uses: Weather radar, satellite radio, and mobile communication.
   • Advantages: Moderate penetration and bandwidth.
   • Limitations: Limited spectrum availability for growth.
3. C-Band (4-8 GHz)
   • Uses: Satellite TV, fixed satellite services.
   • Advantages: Highly reliable for broadcasting; resists rain fade.
   • Limitations: Requires large antennas; competition from terrestrial services.
4. X-Band (8-12 GHz)
   • Uses: Military satellite communication, radar systems.
   • Advantages: Reserved for government and defense applications.
   • Limitations: Limited to specific users.
5. Ku-Band (12-18 GHz)
   • Uses: Direct-to-home (DTH) broadcasting, VSAT systems, and enterprise networks.
   • Advantages: Compact ground equipment; moderate data rates.
   • Limitations: Susceptible to rain fade.
6. Ka-Band (26-40 GHz)
   • Uses: High-throughput satellites (HTS), broadband internet services.
   • Advantages: High data rates and capacity.
   • Limitations: High susceptibility to rain fade.
7. V-Band (40-75 GHz) and Beyond
   • Uses: Emerging technologies, 5G backhaul, and advanced communications.
   • Advantages: Massive bandwidth for high-speed services.
   • Limitations: Requires advanced technology for signal management.

• International Telecommunication Union (ITU): The ITU coordinates global spectrum allocation and assigns frequency ranges to different services.
• National Regulatory Authorities: Countries have their own bodies (e.g., FCC in the U.S., TRAI in India) to manage spectrum within their territories.

• Spectrum Congestion: Increasing demand for communication services strains existing bands.
• Interference Management: Avoiding conflicts between satellites and terrestrial systems.
• Policy Harmonization: Aligning international and regional regulations.

• Dynamic Spectrum Sharing: Adaptive technologies that enable more efficient spectrum use.
• High-Frequency Bands: Expanding into millimetre-wave frequencies for advanced applications.
• New Constellations: Large satellite constellations (e.g., Starlink, OneWeb) are driving demand for innovative spectrum solutions.

The 687 MHz spectrum refers to a specific frequency range within the UHF (Ultra High Frequency) band. This range is part of the broader electromagnetic spectrum and is typically used for applications that require high-capacity data transmission, such as broadcasting, telecommunications, and certain defence applications.

Key Characteristics of the 687 MHz Spectrum

1. Frequency Range:
   • Falls within the UHF range (300 MHz to 3 GHz), which is known for its utility in communication and broadcasting.
2. Propagation Characteristics:
   • Good Coverage: The frequency range around 687 MHz allows for better penetration through obstacles like buildings and trees, making it suitable for urban environments.
   • Moderate Bandwidth: It supports moderate data rates, which is suitable for standard-definition broadcasting and some broadband applications.
3. Applications:
   • Telecommunications: Utilized for mobile communication services, including 4G LTE networks in some regions.
   • Broadcasting: Often used for TV broadcasting, especially for digital terrestrial television (DTT) services.
   • Military and Defence: Some portions may be allocated for secure communication or radar systems.
4. Regulatory Context:
   • The use of the 687 MHz spectrum varies by region and is regulated by national bodies like the FCC (in the U.S.) or TRAI (in India), in line with guidelines set by the ITU.

In recent years, many governments have been reallocating parts of the UHF band (including frequencies around 687 MHz) to support the growth of mobile broadband networks. This process, often called the digital dividend, involves repurposing spectrum previously used for analog broadcasting for more efficient digital communication technologies.

Challenges

• Interference: Ensuring coexistence with adjacent services such as broadcasting or military communication can be a challenge.