VSAT Tutorial : VSAT Network Architecture, System Components, Access Techniques and Protocols
VSAT (Very Small Aperture Terminal) technology plays a crucial role in satellite communication, providing reliable connectivity for a variety of applications, including remote internet access, enterprise networking, and military communications. This tutorial on VSAT covers its network architecture, system components (RF transceiver, LNA, PA, modem, antenna), access techniques and protocols used for satellite communication.
VSAT, or Very Small Aperture Terminal, is a type of satellite communication system that uses small, ground-based antennas to transmit and receive data from satellites in geostationary or low earth orbits. Typically, the antenna size ranges from 0.75 meters to 2.4 meters, making it ideal for remote and mobile communication. VSAT is used for many applications which include Internet access, distance education, telemedicine, telephony, banking, video conferencing and more. It is mainly used where traditional terrestrial communication infrastructure is not available or practical. The interface to satellite is through disc antenna and various frequency bands are used for its operation. The most common frequency bands used in VSAT include C band, Ku band and Ka band.
VSAT system components
As shown in the figure, VSAT system composed of two main parts ODU(Outdoor Unit) and IDU(Indoor Unit). ODU and IDU are interfaced using cable. ODU consists of LNA,PA,Transceiver,Antenna and OMT. IDU consists of Modem,MUX-DEMUX and interface to telephone/PC/EPABX. Refer VSAT system overview article for more details.

RF transceiver: RF Transceiver is basically a frequency converter. It consists of two parts frequency up converter and frequency down converter. Up converter converts modulator frequency usually in either 70/140 MHz to satellite frequency bands (C,Ku,Ka) as per satellite in use for particular location/application. Down converter does reverse of the up converter. In addition to frequency conversion both provide gain to the signal as per VSAT link budget and the same need to be adjusted as per need of the link using attenuation settings available in RF transceiver in both up/down link. Refer following links for RF trasceiver basics and for Rf transceiver design and development.
C band RF Transceiver Design and Development BUC-Block Up Converter basics
RF power amplifier (PA) :
RF Power amplifier is the unit which provide power amplification without any frequency change before signal is
transmitted to the antenna and consecutively to the air.
Refer RF Power Amplifier
to know more on its design basics, various PA stages, classes, specifications
and design of rf amplifier with example.
RF LNA: RF LNA is the low noise amplifier used in VSAT. As the signal is received by antenna is composed of noise as well as useful information signal part. In addition it is very low in the power level. LNA's job is to boost this low level of signal to the sufficient level considering less amplification of noise part, so that adequate C/N is maintained. For more on LNA and LNB refer following links.
Satellite modem:
Satellite modem provides two major functionalities in the VSAT. The first one is it makes link reliable by adding forward error correction functionality using various techniques such as convolution coding/turbo coding and so on.
The second one is that it does task of modulation and demodulation.
There are various modulation techniques used in modem, the most popular among them are QPSK/8PSK.
To know what is modulation,various modulation techniques and satellite modem design refer following links.
Antenna: Antenna is basically a electro-magnetic frequency transducer. It sends and receives EM waves of various frequency bands. Antenna diameter and aperture vary band to band. Hence C band antenna design is different than Ku band. The signal to be transmitted will be provided to antenna by Power Amplifier. The signal received by Antenna is fed to LNA/LNB through OMT as shown in the figure. For more on Antenna refer our Antenna tutorial.
VSAT network architecture
VSAT networks consist of three main components: a central hub station, a satellite, and multiple remote VSAT terminals. VSAT network architecture is the way Hub station and/or VSATs are interfaced with satellite to provide the service. There are five main topologies exist, viz. broadcast, point to point, point to multipoint(star), mesh, hybrid. The satellite itself operates as a relay, receiving signals from the ground terminals and transmitting them to the designated locations, ensuring long range connectivity and minimal signal loss. Let us understand each of this VSAT topology.

• In Broadcast type, there is a single broadcasting station interfaced with satellite and satellite will relay signals to all the VSATs.
Here broadcasting station-satellite-all VSATs link exist.
• In point to point type of topology, two VSATs communicate via satellite using dedicated assigned channel.
So here VSAT1-Satellite-VSAT2 dedicated link exist.
• In Star topology, there are three entities hub station(usually with larger antenna), VSATs and Satellite.
All the communications between VSATs happen through Hub station.
hence here if VSAT1 and VSAT2 need to communicate then,link is VSAT1-satellite-Hub-Satellite-VSAT2.
Hence two hop communication is needed to communicate between any two VSATs in the network.
• In Mesh type of topology, VSATs can communicate with one another directly and no Hub station is needed .
But each VSAT need to be complex owing to more functionalities required similar to the Hub station.
Also antenna specifications need to be different than star type of topology.
• In Hybrid type is the combination of both star and mesh type. Here few of the VSATs communicate via Hub
and few can communicate directly with one another.
VSAT Access Techniques
These techniques define how multiple VSAT terminals share the same satellite transponder frequency band without interference.
The most commonly used access techniques in VSAT are as follows.
1. FDMA (Frequency Division Multiple Access): In FDMA, different VSAT terminals are allocated distinct frequency
bands within the same transponder. Each terminal transmits on its unique frequency, enabling simultaneous communication.
However, it requires high-frequency stability and bandwidth management.
2. TDMA (Time Division Multiple Access): In TDMA, multiple terminals share the same frequency channel but transmit at
different time slots. This technique is efficient for data bursts and reduces bandwidth wastage, making it suitable
for applications with variable data rates.
3. DAMA (Demand Assigned Multiple Access): DAMA dynamically allocates bandwidth to VSAT terminals based on demand, ensuring
optimal use of the satellite’s capacity. It is ideal for networks with varying traffic patterns, as it assigns resources
only when needed, reducing idle channel time.
SCPC- Single Channel Per Carrier MCPC- Multiple Channels Per Carrier SCPC vs MCPC
VSAT Network Protocols
Protocols play a critical role in establishing and managing communication links in VSAT networks.
Some of the commonly used protocols include:
• TCP/IP (Transmission Control Protocol/Internet Protocol): Standard suite for internet and intranet communications,
facilitating data exchange between remote VSAT terminals and central hubs.
• MPLS (Multiprotocol Label Switching): Used in enterprise networks for efficient routing and network segmentation,
ensuring better performance and security.
• ATM (Asynchronous Transfer Mode): Supports data, voice, and video transmission over satellite links with high reliability
and quality of service (QoS).
• DVB-S2 (Digital Video Broadcasting - Satellite - Second Generation): A standard for satellite transmission that offers
improved bandwidth efficiency, error correction, and flexibility, commonly used for video broadcasting and IP data transmission.
VSAT NMS Protocol
The VSAT Network Management System (NMS) protocol is crucial for monitoring, controlling, and managing the entire VSAT network from a central location. It allows network operators to oversee remote VSAT terminals, hub stations, and the communication links in real-time, ensuring smooth operations and quick fault resolution.
The NMS protocol facilitates remote configuration, status monitoring, performance analysis, and diagnostics of VSAT components, such as RF transceivers, modems, and antennas
It uses standard management protocols like SNMP (Simple Network Management Protocol) or proprietary protocols tailored to specific network architectures to collect performance data and alarms from VSAT terminals. This centralized management capability improves network efficiency, reduces operational costs, and enhances service quality by providing operators with detailed visibility and control over the entire VSAT network.
To know more on NMS (Network Management System) basics for star configuration VSAT including NMS protocol used for local and remote NMS. Refer VSAT NMS protocol.
Conclusion
Understanding VSAT network architecture and its system components is essential for optimizing satellite communication performance. With a solid grasp of RF transceivers, LNAs, PAs, modems, and antennas, along with access techniques and protocols, you can design and deploy more efficient VSAT networks. This tutorial serves as a foundational resource for those looking to enhance their knowledge of satellite communication and leverage VSAT technology in various fields.