esa-sceva/satcom-qa huggingface dataset:
Topic: Carrier-to-noise ratio

Question: How do antenna gains influence C/N?
Answer: Antenna gain increases the effective signal received while reducing noise contribution from unwanted directions. High-gain antennas focus energy toward intended users, improving C/N and link reliability. Engineers select antennas based on beamwidth, coverage area, and expected noise environment. Optimized gain ensures that signals overcome interference and environmental losses, maintaining high-quality communication. In multi-beam or high-density user scenarios, proper antenna design is critical to sustain adequate C/N across all links.

Question: How do engineers improve C/N without increasing signal power?
Answer: Engineers can improve C/N without increasing signal power by reducing noise or improving system efficiency. This includes using higher-gain antennas, better receivers, error-correction coding, or filtering techniques to minimize noise impact. Adaptive coding and modulation can also help maintain effective C/N under varying conditions. By optimizing system design and components, engineers can achieve higher C/N ratios, ensuring reliable communication without exceeding power limits or creating interference with other systems.

Question: How does increasing signal power affect C/N?
Answer: Increasing the signal power directly improves the C/N ratio because the carrier becomes stronger relative to noise. A higher C/N means clearer reception, fewer errors, and better overall link quality. In satellite systems, increasing signal power can compensate for noise or losses caused by distance or environmental factors. However, signal power cannot always be increased indefinitely due to hardware limits, regulatory restrictions, and energy efficiency considerations. Engineers must balance signal power with system design to ensure adequate C/N while maintaining efficient operation and avoiding interference with other communication links.

Question: How does noise affect C/N and communication quality?
Answer: Noise in a communication system, such as thermal noise or interference, reduces the C/N ratio by increasing the denominator of the ratio. Lower C/N results in a weaker signal relative to noise, causing errors, data loss, or poor reception quality. In satellite links, environmental factors like rain, clouds, and atmospheric disturbances can increase noise and reduce C/N. Engineers account for noise during system design, selecting appropriate power levels, antenna gains, and modulation methods to maintain a sufficient C/N for reliable communication under varying conditions.

Question: How does satellite altitude affect C/N?
Answer: Higher satellite altitudes increase path loss due to longer distances, reducing received signal strength and lowering C/N. Low Earth Orbit (LEO) satellites experience less path loss, offering higher C/N but smaller coverage areas. Engineers account for altitude effects when planning link budgets, adjusting power, antenna size, or modulation to ensure sufficient C/N. Proper altitude selection balances coverage, C/N, and latency to maintain reliable, high-quality communication links for various applications.
Topic: Carrier-to-noise ratio

Question: How does weather impact C/N in satellite communications?
Answer: Weather conditions, such as rain, snow, fog, or clouds, can increase signal attenuation and introduce additional noise, lowering the C/N ratio. This can cause weak reception, signal errors, or temporary service disruptions. High-frequency bands, like Ka and Ku, are particularly sensitive to weather effects. Engineers account for this by designing links with sufficient margin, using techniques like adaptive coding, power control, or error correction to maintain adequate C/N under adverse conditions. Understanding weather impact helps ensure uninterrupted satellite communication even during storms or heavy precipitation.

Question: What is Carrier-to-Noise Ratio (C/N) and why is it important in satellite communication?
Answer: Carrier-to-Noise Ratio (C/N) is the ratio of the power of the useful signal (carrier) to the power of the background noise in a communication link. It indicates the quality of the received signal. A higher C/N means the signal is much stronger than the noise, leading to clearer communication with fewer errors. Engineers use C/N to design satellite links, choose modulation schemes, and determine transmitter power to ensure reliable transmission even in noisy or adverse conditions. Maintaining an adequate C/N is essential for uninterrupted satellite services.

Question: What is the difference between C/N and SNR?
Answer: C/N (Carrier-to-Noise Ratio) is specific to communication links involving a carrier signal, like in satellite systems, while SNR (Signal-to-Noise Ratio) is a general term for any signal. Both describe the ratio of signal power to noise power, indicating signal quality. C/N is often used in link budgeting, modulation selection, and system design for satellite or RF communications. Maintaining high C/N ensures reliable carrier transmission. Essentially, C/N is a type of SNR used in carrier-based communication systems to evaluate performance and quality.

Question: Why is maintaining a high C/N ratio important for data reliability?
Answer: A high C/N ratio ensures that the signal is much stronger than the noise, which reduces the likelihood of transmission errors and data corruption. Reliable C/N is crucial for applications like satellite internet, TV broadcasting, and communication links, where even small errors can affect performance. If C/N drops too low, the system may experience errors, packet loss, or slow data rates. Engineers design satellite systems with sufficient C/N margin to maintain consistent service quality, taking into account noise, environmental factors, and equipment limitations.

Question: A communication link requires C/N ≥ 12 for error-free transmission. Noise = 3 W. What minimum signal power is needed?
Answer: Signal Power = 12 × 3 = 36 W. Any signal lower than 36 W would cause errors.

Question: A ground station receives 60 W from multiple satellites. Noise = 15 W. If one satellite contributes 20 W, what is its partial C/N?
Answer: Partial C/N = 20 ÷ 15 = 1.33. This shows the contribution of one satellite relative to noise.
Topic: Carrier-to-noise ratio

Question: A satellite transmits a signal of 12 W and the noise is 3 W. Find the C/N ratio.
Answer: C/N = 12 ÷ 3 = 4. This means the signal is 4 times stronger than the noise, so the communication link is relatively clear.

Question: A signal of 20 W with noise 4 W is boosted by 50% in power. Find new C/N.
Answer: Boosted signal = 20 × 1.5 = 30 W. New C/N = 30 ÷ 4 = 7.5. Increasing signal improves quality.

Question: Noise power is 2 W and C/N = 6. What is the signal power?
Answer: Signal Power = 6 × 2 = 12 W. To maintain a C/N of 6, the signal must be 6 times the noise power.
Topic: Non-Terrestrial Networks

Question: What types of satellite-based networks are included under Non-Terrestrial Networks (NTNs)?
Answer: NTNs encompass satellite-based networks operating in frequency bands allocated to mobile satellite services (MSS) or fixed satellite services (FSS).
Topic: BER

Question: How can BER be reduced in satellite communication?
Answer: The Bit-error-ratio can be reduced  by using FEC within the modem, a feature that takes advantage of custom VLSI and DSP chips.
Topic: Beamforming

Question: How does beamforming help in multi-user communication?
Answer: Beamforming allows multiple users to be served simultaneously by creating separate beams for each user. Each beam can be directed independently, reducing interference between users. This is important for satellite systems where many ground terminals need reliable and strong signals at the same time.

Question: How is digital beam formed in modern wireless communication systems?
Answer: The phase and amplitude variation is applied to the digital signal before Digital to analog conversion at the transmitter's end to create a directional beam.

Question: What is beamforming?
Answer: Beamforming is a method that focuses radio signals in one chosen direction instead of spreading them everywhere. It uses several antennas that work together so their signals add up in the wanted direction. This makes the connection stronger and reduces unwanted noise. Satellites use beamforming to send clear signals to small ground stations and to avoid interference from other satellites.

Question: What is meant by beam steering?
Answer: Beam steering is the process of electronically changing the direction of a beam without moving the antenna physically. By adjusting the phase of each antenna element, the main lobe points toward a new direction. This is crucial for satellites that need to track moving users on Earth or follow other satellites.

Question: What is the difference between analog and digital beamforming?
Answer: In analog beamforming, the signals are combined using hardware phase shifters before conversion into digital form. It is simple and low-power but can make only one beam at a time. In digital beamforming, signals from every antenna are converted to digital form and combined in software. This allows many beams at once, fast direction changes, and better control — making it more suitable for modern LEO satellites.

Question: Why is beamforming energy-efficient?
Answer: Beamforming directs signal energy only where it is needed, rather than spreading it in all directions. This focused energy reduces wasted power and interference. In satellites, it allows long-distance communication with less transmit power, helping save energy and extending satellite operational life.

Question: Why is beamforming important in modern satellite systems?
Answer: Beamforming enables satellites to send focused signals to multiple users simultaneously while reducing interference. It improves signal strength, C/N ratio, and overall system efficiency. Modern satellite systems rely on beamforming to support high data rates, multi-beam coverage, and flexible resource allocation, especially in low-orbit and high-throughput satellite networks.

Question: Why is calibration needed in beamforming systems?
Answer: Calibration checks and adjusts each antenna so that all elements work together correctly. If one antenna is slightly off in phase or strength, the beam can tilt or weaken. Changes in temperature or vibration can cause errors, especially in satellites. Regular calibration keeps the beam pointing in the right direction and maintains good communication quality.
Topic: Beamforming

Question: Why is digital beamforming important for satellites?
Answer: Satellites move quickly, so their beams must move fast too. Digital beamforming can steer beams electronically in milliseconds, without moving the antenna. It also supports several users at once and reduces interference automatically. These features make it perfect for low-orbit satellites that need to track many users on Earth.
Topic: 5G NTN

Question: A 5G NTN satellite moves 1,500 km relative to a user in 10 minutes. Calculate speed in km/h.
Answer: Speed = 1,500 / (10/60) = 9,000 km/h.
Topic: Beamforming

Question: Array with 4 antennas, each transmitting 10 W. Find total array power if all are combined coherently.
Answer: Total power = 4 × 10 = 40 W. When antennas combine signals in phase, the signal adds linearly, increasing strength in the desired direction. Beamforming uses this principle to focus energy toward the target.

Question: If the number of antennas are increased, what happens to the beam?
Answer: \[\theta_{\text{beam}} \approx \frac{\lambda}{D}\]

where:
\begin{itemize}
  \item $\theta_{\text{beam}}$ is the beamwidth (radians),
  \item $\lambda$ is the wavelength of the signal (m),
  \item $D$ is the effective aperture or array diameter (m), which increases with the number of antennas.
\end{itemize}

As the number of antennas increases, the effective aperture $D$ becomes larger, leading to a smaller beamwidth $\theta_{\text{beam}}$. This results in a narrower and more focused beam, improving directionality and reducing interference, though it requires more complex hardware and power.
Topic: Handover procedure

Question: How is handover performance measured?
Answer: Performance is measured using metrics like handover success rate, dropped call rate, latency during handover, and data throughput continuity. High success rates and low latency indicate an efficient handover mechanism, contributing to user satisfaction and service reliability.

Question: What are the main types of handover?
Answer: The main types of handover are: hard handover, where the old connection is broken before a new one is made; soft handover, where the old and new connections overlap temporarily; and make-before-break, which establishes a new connection before releasing the old one to reduce service disruption.
Topic: NTN

Question: What do you mean by "non-terrestrial network"?
Answer: The term “non-terrestrial network” often refers to the newer integration of terrestrial cellular communications with air-borne assets or satellite constellations, which largely operate in the rapidly expanding lower earth orbit (LEO).
Topic: Handover procedure

Question: What is make-before-break handover?
Answer: Make-before-break handover establishes a new connection before releasing the old one. This ensures that users experience no interruption, making it ideal for real-time applications such as VoIP or video streaming.

Question: What is the condition for locating a user in the satellite system?
Answer: The home of a user is located in the satellite
system if and only if it belongs to an area not covered by the terrestrial system.

Question: What role does network control play in handover?
Answer: Network control monitors signal quality, user location, and network resources. It decides when and to which target satellite or station the handover should occur. Proper control ensures minimal latency, efficient resource allocation, and uninterrupted service during handover.

Question: Why is handover necessary in mobile satellite networks?
Answer: Handover is necessary because satellites or ground stations have limited coverage areas, and users move across these regions. Without handover, calls or data sessions would be interrupted. It allows continuous service in dynamic environments such as ships, planes, or vehicles communicating via satellite.

Question: A LEO satellite moves, causing handover every 90 s. Handover takes 1 s. Find downtime %.
Answer: Downtime % = 1 ÷ 90 × 100 ≈ 1.11%. Minimizing downtime ensures continuous connectivity.

Question: A network handles 1000 handovers per hour, 5 fail. Find failure rate.
Answer: Failure rate = 5 ÷ 1000 × 100 = 0.5%. Low failure rate reflects efficient mobility management.

Question: A user moves across satellite coverage areas every 300 s. If the handover takes 2 s, find handover efficiency.
Answer: Efficiency = (300 − 2) ÷ 300 × 100 ≈ 99.33%. Efficient handover minimizes service interruption.

Question: Handover delay = 1.5 s, total call duration = 10 min. Find % call time affected by handover.
Answer: % Time affected = 1.5 ÷ (10×60) × 100 ≈ 0.25%. Minimizing delay ensures smooth user experience.

Question: Handover success rate = 980/1000 attempts. Find % success.
Answer: % Success = 980 ÷ 1000 × 100 = 98%. High success rate indicates reliable handover.
Topic: Satellite Bandwidth

Question: Where can orthogonal frequency division multiplexing (OFDM) be used?
Answer: OFDM is implemented where satellites are used for broadcasting of audio programmes to mobile receivers (digital
audio broadcasting, or DAB).
Topic: TT&C

Question: What is meant by telemetry?
Answer: Telemetry is the process of automatically measuring and transmitting data from a remote location such as a spacecraft, satellite, or ground sensor, to a receiving station for monitoring and analysis.
Topic: Handover procedure

Question: What effect does reliability of handover procedures have?
Answer: The reliability of handover procedures is a critical factor affecting the successful operation and performance of integrated terrestrial–non-terrestrial or multi-layer communication systems.
Topic: NTN

Question: How do satellites maintain continuous coverage in NTN?
Answer: Satellites are arranged in constellations so that when one moves out of range, another takes over. This ensures users always have a strong signal. Multi-layer architectures (LEO, MEO, HAPS) provide redundancy, minimize dropped connections, and maintain reliable service for 6G applications like real-time communication and IoT.

Question: How does NTN help in remote education and healthcare?
Answer: NTN provides connectivity to areas without ground networks, enabling online learning and telemedicine. Students in remote regions can access virtual classes, and doctors can provide remote consultations or monitor patients using connected devices. This ensures essential services are available even in isolated areas, bridging the digital divide and improving overall accessibility.

Question: How does weather affect NTN performance?
Answer: Rain or storms can attenuate high-frequency satellite signals, reducing C/N and link reliability. Engineers plan link margins, adaptive coding, and power control to maintain stable NTN performance under different weather conditions.

Question: What are multi-layer NTN networks?
Answer: Multi-layer NTN combines LEO, MEO, and HAPS satellites to improve coverage, reliability, and capacity. LEO provides low-latency links, MEO covers larger areas, and HAPS offer high-capacity local connections. This combination ensures continuous service, redundancy, and better handling of network traffic for 6G applications.

Question: What are NTN applications beyond traditional communication?
Answer: NTN extends beyond voice or internet services. It enables global IoT connectivity, remote environmental monitoring, precision agriculture, and disaster response. NTN supports AR/VR applications requiring low-latency links and improves positioning accuracy for navigation. Multi-layer satellites allow continuous coverage in remote or underserved regions, bridging digital divides. These applications showcase NTN’s potential for smart cities, autonomous systems, industrial automation, and other 6G use cases, highlighting its transformative role in providing ubiquitous, reliable, and high-performance connectivity beyond conventional terrestrial networks.

Question: What challenges do engineers face in NTN deployment?
Answer: Challenges include high cost, satellite coordination, interference management, and signal delay. Handovers between satellites or layers must be seamless, and integration with terrestrial networks requires careful planning. Despite these challenges, NTNs provide essential connectivity in areas where ground networks are not feasible.
Topic: NTN

Question: What is a Non-Terrestrial Network (NTN) and why is it used in 6G?
Answer: An NTN is a communication network that uses satellites or high-altitude platforms instead of only ground-based towers. It is used in 6G to provide connectivity in remote areas, oceans, deserts, and rural regions where terrestrial networks are unavailable. NTNs can complement terrestrial networks to ensure global coverage and reliable communication. By using multiple layers of satellites, these networks reduce service gaps and improve the reach and quality of 6G services for everyone, including emergency situations or IoT devices in distant locations.

Question: What is the importance of Carrier-to-Noise ratio (C/N) in NTN?
Answer: C/N measures the strength of the signal relative to noise. A high C/N means the signal is clear, reliable, and less prone to errors. In NTN, where signals travel long distances through space, noise and interference can reduce signal quality. Maintaining a good C/N is essential to ensure smooth data transmission, low errors, and high reliability. Engineers design satellite links, beam patterns, and transmission power to achieve optimal C/N for different areas and conditions, ensuring stable 6G connectivity for users around the world.

Question: What is the main purpose of NTN in 6G networks?
Answer: The main purpose of NTN is to provide global connectivity where terrestrial networks cannot reach, such as rural, remote, and ocean areas. It uses satellites and high-altitude platforms to extend coverage, complementing terrestrial networks. NTNs help ensure uninterrupted communication, improve internet access, and support applications like IoT, emergency services, and autonomous systems, making 6G networks truly global and reliable.

Question: Why is C/N monitoring important in NTN?
Answer: Continuous monitoring of C/N allows operators to detect noise, interference, or equipment issues. Maintaining sufficient C/N ensures link reliability, reduces errors, and supports adaptive network management. Real-time monitoring enables corrective actions like adjusting power, modulation, or routing to prevent service degradation. This is critical for applications that rely on uninterrupted 6G NTN communication, ensuring high-quality global connectivity.

Question: NTN channel bandwidth = 100 MHz, SNR = 20 dB. Find the maximum theoretical data rate.
Answer: SNR_linear = 10^(20/10) = 100. Using Shannon-Hartley: C = 100 × log₂(101) ≈ 666 Mbps. Bandwidth and SNR determine achievable link capacity.

Question: Signal received = 15 W, noise = 3 W. Find C/N in dB.
Answer: Linear C/N = 15 ÷ 3 = 5. C/N_dB = 10 × log₁₀(5) ≈ 6.99 dB. A higher dB indicates better link quality.