Satellite vs. Mobile Communication: A Detailed Comparison

This article compares satellite communication with cellular mobile communication, highlighting the key differences between the two using examples like C-band satellite and GSM cellular technologies.

Introduction:

Both satellite and mobile communication systems enable two-way communication, allowing users to transmit and receive voice, data, and multimedia content. These systems rely on Radio Frequency (RF) signals for operation. Operators can extend their services to users in regions served by both satellite and mobile cellular towers. Both satellite and mobile networks are designed to handle mobility, ensuring users stay connected while on the move, unlike traditional fixed-line telephones.

Satellite Communication

Satellite communication systems consist of a satellite in space and ground stations, also known as VSATs (Very Small Aperture Terminals) or satellite phones, on Earth. Communication occurs across various frequency bands (L, S, C, X, Ku, K, Ka) between ground stations and satellites in network configurations like star or mesh.

• Star Configuration: Communication traffic between VSATs and the satellite passes through a central Hub station.
• Mesh Configuration: VSATs can communicate directly with each other via the satellite.

Satellites are placed in different orbits depending on their applications, including:

• Geostationary Orbit (GEO)
• Medium Earth Orbit (MEO)
• Low Earth Orbit (LEO)
• Highly Elliptical Orbit (HEO)
• Sun Synchronous Orbit (SSO)
• Polar Orbit

These satellites are used for a variety of purposes, including telecommunications, weather monitoring, Earth observation, satellite internet, scientific research, surveillance, and satellite telephony.

Figure 1: Mesh topology-based satellite system.

As shown in Figure 1, in a mesh network, a call or data transfer between VSAT1 and VSAT2 requires a single hop via the satellite.

Here’s how voice and data travel through different subsystems at a VSAT or ground station:

1. Baseband Voice and Data: These signals are interfaced with a Multiplexer (MUX). The MUX output is fed into a satellite modem, which modulates the signal at an Intermediate Frequency (IF).
2. RF Upconversion: The IF modulated signal is then sent to an RF Upconverter, which translates it into an RF modulated signal. This RF signal is amplified and transmitted to the satellite using an aligned antenna.
3. Satellite Relay: The satellite receives the 6 GHz signal from the VSAT and down-converts it to a 4 GHz signal before relaying it back to Earth.
4. VSAT Reception: The receiving VSAT (VSAT2) performs the reverse operations:
   • Receives the 4 GHz signal using an antenna.
   • Passes the signal through a Low Noise Amplifier (LNA).
   • Down-converts the RF signal to an IF signal.
   • The IF signal is demodulated by a satellite modem back into the baseband signal.

Cellular Mobile Communication

Cellular mobile communication systems consist of:

• Base Stations located in different cells
• Mobile Subscriber Stations (mobile phones)
• Mobile Switching Center (MSC)
• A database of subscribers

The MSC interfaces with other telecom networks such as the Public Switched Telephone Network (PSTN) and the Public Switched Data Network (PSDN). Base Stations consist of a Base Transceiver Station (BTS) and a Base Station Controller (BSC), which interfaces with the MSC.

These components work together to provide seamless mobile communication services, enabling users to make and disconnect calls, browse the internet, send messages, and access other data services within the network’s coverage area.

Cellular network architecture varies based on the specific technology used, such as GSM, CDMA, UMTS, Mobile WiMAX, 4G LTE, 5G NR (New Radio), and 6G. However, the fundamental components and their functionalities remain consistent across these systems.

Figure 2: A cellular network consisting of BTS in different cells communicating with MS.

Let’s break down the functions of various components in a GSM cellular network:

• Mobile Station (MS): The mobile phone or handset used to communicate with the cellular network. It requires a SIM (Subscriber Identity Module) card from the cellular network operator to connect to the network and store user information.
• Base Transceiver Station (BTS): Responsible for establishing and maintaining radio communication with mobile stations within its coverage area. It transmits and receives RF signals to and from mobile phones using antennas.
• Base Station Controller (BSC): Manages and controls multiple BTSs within a specific geographical area known as “cells.” It handles tasks like call handover, resource allocation, and control of BTSs.
• Mobile Switching Center (MSC): Interfaces with PSTN or PSDN. It handles call routing, mobility management, authentication, and billing.
• Home Location Register (HLR) and Visitor Location Register (VLR):
  • HLR: Stores information about all registered users within the network, including subscriber identity, service profile, current location area, and supplementary service information.
  • VLR: A temporary database of subscribers when they roam into a new location from their home location, speeding up call setup and authentication by avoiding queries to the home network.
• Authentication Center (AuC): Authenticates users and enables secure communication between the mobile station and the cellular network by providing encryption keys.
• Equipment Identity Register (EIR): Stores information about mobile devices within the network, helping identify stolen or unauthorized devices using their IMEI numbers.
• Short Message Service Center (SMSC): Handles the storage, forwarding, and delivery of SMS messages between mobile devices.
• Gateway Mobile Switching Center (GMSC): A specialized MSC that handles calls between the cellular network and external networks, such as other mobile or landline networks.

Difference between Satellite Communication and Mobile Communication

The following table highlights the differences between satellite communication and mobile communication based on various parameters:

Conclusion:

Satellite and cellular mobile communication technologies are increasingly used together in hybrid communication systems. This combination provides extensive coverage, increased resilience, and enhanced connectivity in various scenarios, allowing users to benefit from both technologies. Satellite-based networks are used as terrestrial infrastructure and as backhaul connectivity for many telephony networks. They are also essential for maritime and aeronautical communication, disaster recovery and emergency services, IoT connectivity, remote monitoring and telemetry, and military and defense communication. Modern cellular mobile communication systems like 5G and 6G are also integrating satellite connectivity.