VSAT Internet System Block Diagram Explained

The VSAT (Very Small Aperture Terminal) internet system block diagram illustrates how satellite-based broadband connectivity operates. Each component, from the satellite dish to the modem, plays a crucial role in ensuring reliable internet access, especially in remote locations. This guide breaks down the system to provide a better understanding of its operation, including its advantages and disadvantages.

Internet service is delivered through various transmission mediums, including DSL, fiber optic, copper lines, cellular technologies (GSM, CDMA, LTE, etc.), and indoor technologies (LAN, WLAN, etc.). VSAT leverages satellites for internet applications and is ideally suited for locations where installing cellular towers or laying copper or fiber optic cables is difficult, such as hilly or geographically challenging terrain.

Because the internet signal relies on satellites positioned approximately 36,000 kilometers away, VSAT service is relatively easy to deploy. Like other internet systems, VSAT supports both upload and download activities. The internet relies on protocols like HTTP for browsing and FTP/TFTP for uploading and downloading files.

VSAT Internet Block Diagram

Figure 1: VSAT internet block diagram

The diagram above depicts a typical VSAT internet block diagram. As shown, it consists of the user’s computer or laptop, the VSAT unit itself, a satellite, a hub station, and the broader internet infrastructure, including servers. Let’s examine these subsystems with an example of downloading a file from the internet.

• Once the VSAT connection with the satellite and hub station is established, the VSAT link functions as a leased line for internet access.
• Common VSAT systems operate in C band, Ku band, and Ka band.
• In the C band, the downlink frequency is typically in the 6 GHz range, while the uplink frequency is in the 4 GHz range. File downloads occur on the downlink frequency, and file uploads occur on the uplink frequency.
• An ISP (Internet Service Provider) line is connected at the hub station, serving all VSATs within the network.

Advantages and Disadvantages of VSAT Internet

Here are the pros and cons of using VSAT for internet connectivity:

Advantages:

• VSAT provides internet access to areas where other methods, like fiber, copper, or cellular systems, are impractical or impossible to install.
• It offers a more secure communication channel. Encryption is often implemented before the satellite modem to enhance security.

Disadvantages:

• Download times or latency can be higher due to the multi-hop communication path between the VSAT and the hub station via the satellite. It takes approximately 120 ms for electromagnetic waves to travel from the VSAT to the satellite (at a distance of 36,000 km) at a rate of $3 \times 10^8$ m/s. A round trip (two hops) introduces a delay of around 240 ms.

  $$\text{Time} = \frac{\text{Distance}}{\text{Speed}} = \frac{36000 \times 10^3 \text{ m}}{3 \times 10^8 \text{ m/s}} = 0.12 \text{ s} = 120 \text{ ms}$$

• The system’s complexity means that troubleshooting can be difficult for end-users. It is generally recommended to contact the VSAT internet service provider for support in case of issues.

• The data rate in VSAT internet depends on the satellite bandwidth allocated to the specific VSAT and is not solely dependent on the internet connection’s bandwidth at the hub station.

Conclusion

By understanding the VSAT internet system block diagram, we can see how broadband connectivity is achieved through satellite communication. Each component plays a vital role in providing stable, high-speed internet, particularly in regions where traditional terrestrial networks are unavailable.