Satellite Communication Basics - Network Encyclopedia

Summary

This video explains the fundamentals of satellite communication, focusing on the use of geostationary orbit (GEO) satellites. It discusses key challenges such as propagation time, signal loss, and interference. Satellite communication is compared with line-of-sight (LOS) microwave technology, highlighting its advantages and limitations. The video also covers the importance of frequency bands, including the most desirable ranges for commercial use, and the issues related to power limitations and frequency congestion. It emphasizes the role of satellite systems in extending digital networks for various services like telephony, data, and video.

Takeaways

• 😀 Satellite communication is an extension of line-of-sight (LOS) microwave technology, requiring the satellite to be within line-of-sight of each earth terminal.
• 😀 Noise is a significant concern in satellite communication, often resulting in lower received signal levels compared to LOS microwave systems.
• 😀 In satellite systems operating below 10 GHz, very little link margin is required, and fading experienced in LOS microwave is not an issue.
• 😀 This discussion focuses on geostationary orbit (GEO) communication satellites, which are key for extending digital networks.
• 😀 Satellite communication is used for various digital services like telephony, data, the Internet, facsimile, and video, although fiber optics is a strong competitor.
• 😀 The distance between the earth station and the satellite, often on the order of 22,300 miles, results in higher propagation times, with a round-trip delay of around 500 ms.
• 😀 The propagation delay in satellite communication systems can cause issues like echo on telephone circuits and delays in data packet transmission.
• 😀 The free-space losses in satellite communication are much higher than in LOS microwave, with up to 207 dB loss at 14 GHz.
• 😀 Earth-to-satellite communications are power-limited, especially for downlinks, as satellites rely on solar cells to power RF transmissions.
• 😀 The growing number of geostationary satellites in equatorial orbit is leading to increased radio-frequency interference and congestion in the frequency spectrum.
• 😀 The most desirable frequency bands for satellite communication are in the 1000–10,000 MHz range, with specific bands for uplink and downlink communication that are preferred for less atmospheric absorption and noise.

Q & A

What is the main difference between satellite communication and Line-of-Sight (LOS) microwave communication?

Satellite communication is an extension of LOS microwave technology, but it involves the use of satellites as relay points to extend communication over longer distances, unlike LOS microwave, which typically involves direct communication between Earth stations within line of sight.

Why is noise more of a concern in satellite communication compared to LOS microwave?

In satellite communication, the received signals are often at much lower levels than in LOS microwave systems, which makes noise more impactful. The greater distance between the Earth station and satellite leads to signal degradation, increasing the influence of noise.

What is a significant challenge caused by the distance between Earth and the satellite in communication?

A major challenge is the propagation delay, which causes delays in communication. For example, the round-trip delay between Earth stations and a satellite can be as much as 500ms, which can affect real-time communication, such as telephone calls.

What is the typical range of free-space loss in satellite communication, and how does it vary with frequency?

Free-space loss in satellite communication can be significant. For example, at 4.2 GHz, the loss is 196 dB, while at 14 GHz, it increases to around 207 dB. Higher frequencies tend to experience greater free-space losses.

Why is the downlink (satellite to Earth) in satellite communication considered power-limited?

The downlink is power-limited because the satellite depends on solar cells for its power, which are insufficient to produce high RF power. As a result, the received signal levels on Earth can be very low, potentially as low as −150 dBW.

What is the issue with interference in geostationary satellite communication?

Interference is a significant issue because the equatorial orbit is becoming crowded with geostationary satellites. This leads to radio-frequency interference, especially for systems using smaller Earth station antennas with wider beamwidths, which are more prone to interference.

Which frequency bands are considered most desirable for commercial satellite communication?

The most desirable frequency bands for commercial satellite communication are 3700–4200 MHz (downlink), 5925–6425 MHz (uplink), 7250–7750 MHz (downlink), and 7900–8400 MHz (uplink). These bands are preferred due to less atmospheric absorption, minimal rainfall loss, and well-developed technology.

Why are the frequency bands of 1000–10,000 MHz ideal for satellite communication?

The 1000–10,000 MHz frequency range is ideal for satellite communication because it offers less atmospheric absorption compared to higher frequencies, has minimal rainfall loss, experiences lower noise levels, and benefits from well-established technology in this range.

What impact does the high distance between Earth and the satellite have on the communication time?

The high distance between Earth and the satellite leads to significant propagation times, with the round-trip delay between Earth station to satellite and back being approximately 500ms. This delay can affect communication, especially in systems requiring quick responses like telephony or data transmission.

How do fiber optics compare to satellite communication in terms of network extension?

Fiber optics has become a strong competitor to satellite communication due to its ability to provide higher bandwidth and lower costs in certain areas. However, satellite communication still plays a critical role, particularly in remote areas or for systems requiring global coverage, such as VSAT.