Understanding Satellite Gateways: Principles and Advantages

This page explains how a satellite gateway works and its fundamental principles. It also outlines the benefits or advantages of using a satellite gateway.

What is a Satellite Gateway?

A satellite gateway is a device that acts as an interface between a satellite and a Local Area Network (LAN).

Essentially, the satellite gateway contains an antenna and equipment that converts radio frequency (RF) signals to Internet Protocol (IP) signals, and vice versa, for terrestrial connections. IP is the foundation of internet access and data transfer. Voice information can also be transmitted using Voice over IP (VoIP) technology.

The major functions of a satellite gateway are:

• Connectivity: It provides a connection between the terrestrial backhaul network and the satellite, whether it’s a Geostationary Orbit (GEO) or Low Earth Orbit (LEO) satellite, using an RF antenna. LEO satellites orbit at lower altitudes (~500 to 1500 Km) compared to GEO satellites (~35,800 Km).
• Signal Conversion: It converts baseband data into an RF signal for transmission to the satellite.
• Signal Reception and Decoding: It converts received RF signals back to baseband for decoding data in various forms (voice, image, video, text).
• Content Delivery: Content is delivered to cache/storage either by satellite via gateway or through terrestrial connectivity to Evolved Packet Core (EPC) or Content Delivery Network (CDN).

Image courtesy: http://www.etsi.org/

Figure 1 illustrates a general hybrid network architecture. The access side and core side are interconnected via various resources to serve users or customers needing different services.

These resources can be satellite-based networks, fixed networks, and mobile networks, utilizing cellular technologies like GSM, CDMA, 4G LTE, and 5G.

An Intelligent User Gateway (IUG) provides secure broadband access, storage, and Quality of Service (QoS) provisions at the Customer Premises Equipment (CPE). An Intelligent Network Gateway (ING) handles different user traffic types using various access links like xDSL (e.g., ADSL, VDSL), satellite, terrestrial lines, and other mobile networks (e.g., EDGE (2G), UMTS (3G), HSPA (3G), LTE (4G)).

The IUG and ING work together to route different types of traffic. Here are some mobile communication scenarios using satellites and cellular mobile networks:

Landline subscribers are connected using PSTN (Public Switched Telephone Network) either through a cellular MSC (Mobile Switching Center) or through gateway terrestrial connectivity.

• Case #1: Two mobile users communicate directly via satellites (e.g., LEO).
• Case #2: Two mobile users communicate via a satellite gateway if they are in the vicinity of different satellites.
• Case #3: A mobile user and a PSTN user can communicate using a cellular mobile network like GSM or using a satellite via a gateway.

Satellite Gateway Working Operation

The satellite gateway needs a clear line of sight to the satellite from the ground.

It is the primary interface between the satellite and the earth for providing voice, data, and video services over IP. It must be maintained for many years to support the long lifespan (approximately 15 to 25 years) of the satellites.

The area around the antenna needs to be large enough to accommodate indoor equipment for future expansion and to withstand severe weather conditions. To avoid regulatory issues, the land where the satellite gateway is installed should ideally be owned by the gateway operator in that region.

Image courtesy: http://www.etsi.org/, document : ETSI TR 103 272 V1.1.1

Figure 2 shows the architecture of a satellite network that includes a satellite gateway. Let’s examine the functions of the different subsystems at the satellite ground station. In the figure, ING and IUG refer to Intelligent Network Gateway and Intelligent User Gateway, respectively.

• TTC (Telemetry Tracking and Control): Monitors and controls transmit/receive information to/from the space segment.
• SCC (Satellite Control Center): Monitors and controls the space segment.
• NCC (Network Control Center): Controls and synchronizes the entire satellite ground station network.
• NMS (Network Management System): Manages resources like time instants, frequencies, codes, and power levels for uplink and downlink signals in the network. Refer to the VSAT NMS tutorial.
• ST (Satellite Terminal): Small antenna terminals located directly at user or company premises. Refer to VSAT system basics for more information.
• GW (Gateway): The satellite gateway, featuring a large antenna and other components.

Figure 3 shows the internal modules of a satellite gateway and their functions. Let’s understand the functions of different modules in a satellite gateway (GW1) terminal:

• RF Antenna: During transmission, it relays the modulated RF signal into the air towards the satellite. During reception, it receives the satellite signal and passes it to the next module after applying gain for decoding the information.
• Diplexer or OMT: Separates transmit and receive signals to their respective chains.
• Transmit Chain Modules: Mux (Multiplexer), Modulator, Up converter, RF Power combiner, Power Amplifier.
• Receive Chain Modules: Low Noise Amplifier, RF divider, Down converter, demodulator, demultiplexer.
• Baseband Connectivity: Satellite modems like DMD2400/2401 provide baseband (voice/data) connections.

Refer to the article on Satellite Ground Station for more information.

Benefits or Advantages of Satellite Gateway

Here are the benefits or advantages of using a satellite gateway:

• Bidirectional Access: Offers two-way communication with the satellite from the ground.
• Connectivity: Connects access links and core networks via satellite where other transmission mediums are not feasible.
• Higher Gain: Provides higher system gain due to the large antenna size.
• Easy Installation: Can be easily installed on the ground or on a vehicle with sufficient battery power.