esa-sceva/satcom-qa huggingface dataset:
Topic: Satellite broadcasting

Question: Calculate minimum C/N ratio for DVB-S2 to maintain BER of10-7 with 8PSK modulation.
Answer: Typically,C/N = 9.7dB from DVB-S2 tables

Question: Calculate symbol rate given bandwidth 36 MHz and roll-off factor 0.35.
Answer: Rs= B /(1+α ) = 36 /1.35 = 26.67 Msps

Question: Estimate satellite broadcast power flux density at Earth given transmitter power 100 W, antenna gain 30 dBi, and distance 40,000 km
Answer: The power flux density (PFD) at Earth from a satellite is calculated by the formula: PFD = (Pt*Gt )/4πR^2 where P is transmitter power in watts, Gt = 10^(GdBi/10) is antenna gain in linear scale, and R is the distance in meters.
 Pt = 100 W, GdBi  = 30, and R = 40,000 km = 4 x 10^7 m, convert gain: Gt = 10^3= 1000.
Surface area: 4πR² = 2.01 × 10^16 m².
 PFD = (100 x 1000)/( 2.01 x 10^16)= 4.98 x 10-12 W/m² Conversion to dBW/m² is about 113 dBW/m²
Topic: DVB-S2

Question: Find DVB-S2 throughput for symbol rate 28.8 Msps and modulation QPSK (2 bits/symbol) with coding rate 3/4.
Answer: Throughput = R X Bits/Symbol x Codingrate = 28.8 x 2 x 0.75 =  43.2 Mbps
Topic: Uplink

Question: Calculate uplink fade margin for link margin 10 dB and rain fade 7 dB.
Answer: Fade margin = Link margin - Rain fade = 10-7=3 dB
Topic: Handover procedure

Question: Calculate handover execution time given radio link failure timer 200 ms, preparation time 50 ms, actual handover 250 ms.
Answer: Total time = 200 + 50+250 = 500 ms

Question: Calculate handover success probability Ps = 1-e^- λt if rate λ = 0.2 sec^{-1} and time t = 3 sec.
Answer: Ps=1-e^-0.6= 1-0.5488 = 0.4512 or 45.12%

Question: Calculate required SINR for handover decision if threshold is 15 dB and current SINR is 12 dB.
Answer: Required increase = 15 - 12 = 3 dB

Question: Calculate total handover delay given preparation 10 ms, execution 15 ms, and completion 5 ms delays.
Answer: Total delay=10+15+5=30 ms

Question: Compute handover signaling load if average messages per handover are 10 and handover rate is 5/min.
Answer: Load = 10 × 5 = 50 messages/min

Question: Find average handover delay if signaling delay is 5 ms, processing delay is 20 ms, and response delay is 10 ms.
Answer: Total handover delay =  5+20+10 = 35 ms
Topic: Communication Latency

Question: Calculate effect of data rate on latency if packet size is 1,500 bytes and data rate is 10 Mbps.
Answer: Transmission delay = Packet size (bits) /Data rate (bps)= (1500*8)/(10*10^6)=1.2 x 10-3 s or 1.2 ms

Question: Calculate propagation delay for distance 3000 km assuming speed of light 3*10^8 m/s.
Answer: Propagation delay = Distance/Speed =  (3x10^6) / (3×10^8)= 0.01 s or 10 ms

Question: Calculate total latency if transmission delay is 5 ms, propagation delay is 20 ms, and processing delay is 10 ms.
Answer: Total latency =5+20+10=35 ms

Question: Find round trip time (RTT) if one-way latency is 30 ms.
Answer: RTT = 2× one-way latency = 2 x 30 = 60 ms
Topic: Link availability

Question: Calculate link availability if mean downtime per year is 5 minutes.
Answer: Availability =(365×24×60-5)/ (365×24×60)= 0.9999965 = 99.99965%

Question: Calculate MTBF (Mean Time Between Failures) if failure rate is 0.0001 failures/hour.
Answer: MTBF = 1/0.0001 =10,000 hours

Question: Calculate probability link is unavailable for 5 minutes if failure rate is 0.0001/hr and repair rate is 1/hr.
Answer: P unavailable =λ/( λ+μ)= 0.0001/1.0001 ≈ 0.0001

Question: Find link availability with MTBF 10,000 hours and MTTR 1 hour.
Answer: Availability = MTBF/( MTBF+MTTR) =10000/(10000+1) = 99.99%
Topic: Link Budget

Question: How do antenna types affect link budget?
Answer: Different antenna types have varying gains and radiation patterns, influencing how much the signal is amplified and directed at the receiver.

Question: How does antenna gain improve the link budget?
Answer: Antenna gain focuses the signal energy in preferred directions, increasing transmitted or received power, thereby improving overall link budget performance.

Question: How does link budget differ for uplink and downlink?
Answer: Uplink and downlink can have different power levels, antenna gains, and path losses, so separate link budgets are calculated for each direction.

Question: What is the significance of system losses in link budgets?
Answer: System losses cover non-idealities like cable attenuation, imperfect antenna connections, and equipment inefficiencies, influencing the actual signal power delivered.
Topic: Downlink

Question: Calculate received power in downlink if transmit power is 35 dBm, path loss 140 dB, antenna gains total 25 dB.
Answer: Prx = Ptx + Gtotal - Lpath = 35+25-140 = -80 dBm
Topic: 3gpp

Question: Calculate Signal to Interference plus Noise Ratio (SINR) if signal power is -60 dBm, interference power is -80 dBm, and noise power is -90 dBm as per 3GPP methods.
Answer: Convert powers to linear scale:
P signal = 10^-6, P interference = 10^-8, P noise = 10^-9 watts
SINR = P signal/(P interference+P noise)=10^-6/(10^-8+10^-9) = 90.9 (linear).
In dB 10log(90.9)=19.58 dB
Topic: Link Budget

Question: Calculate total cable and connector loss if each is 1 dB and total 3 cables.
Answer: Total loss =3* 1 =3dB

Question: Calculate total losses if cable attenuation is 1.5 dB per meter for 4 meter cable.
Answer: L=1.5*4=6 dB

Question: Calculate total system losses if cable loss is 2 dB on transmitter and 3 dB on receiver.
Answer: Total losses =2+3=5dB
Topic: Uplink

Question: Calculate uplink bit rate if bandwidth is 20 MHz and spectral efficiency is 4 bps/Hz.
Answer: Uplink bit rate R= Band width * spectral efficiency = 20 * 10^6 * 4 = 80 *10^6 bps = 80 Mbps

Question: Calculate uplink CNR if transmit power is 40 dBW, path loss is 210 dB, noise spectral density is -174 dBm/Hz, bandwidth 1 MHz and antenna gain 45 dB.
Answer: CNR = P tx + G ant - L path - N power, noise power N = N0 + 10 log B = -174 + 60= -114 dBm; CNR = 40 + 45 -210 (-114)= -11 dB

Question: Calculate uplink power needed for received power -85 dBm if path loss is 190 dB and antenna gain is 45 dB.
Answer: P tx= P rx + L path - G ant = -85-190-45 = 60 dBm = 1 kW
Topic: 3gpp

Question: How to calculate path loss according to the 3GPP model for a given distance of 1 km and frequency 2 GHz?
Answer: Using the 3GPP path loss model formula: PL=128.1 + 37.6 log(d)dB, where d is distance in km. For d=1, PL = 128.1+37.6*log (1)=128.1+0=128.1 dB
Topic: Link Budget

Question: How to calculate total system loss if cable loss is 2 dB and connector loss is 1 dB?
Answer: Total loss Ltotal = 2 + 1 = 3dB. Losses add up linearly in dB scale.
Topic: 3gpp

Question: What is the maximum throughput given bandwidth 10 MHz and spectral efficiency 5 bps/Hz in 3GPP standards?
Answer: Throughput T= Bandwidth*spectral efficiency
T= 10*10^6*5 = 50*10^6 bps
Topic: Telecommunication Payload

Question: Calculate power consumption if telecommunication payload transmits at 100 W with efficiency 60%.
Answer: Power input = Transmission/efficiency = 100/0.6 = 166.67 W

Question: Calculate required bandwidth for telecommunication payload data rate 2 Gbps and spectral efficiency 4 bps/Hz.
Answer: B = R/η = (2*10^9) / 4 = 500 * 10^6 Hz = 500 MHz

Question: Compute maximum data rate on telecommunication payload with 500 MHz bandwidth using 16QAM (4 bits/symbol) and 0.8 coding rate.
Answer: Throughput = 500 * 10 ^ 6 * 4 *0.8 = 1.6 * 10 ^ 9 bps = 1.6 Gbps

Question: Find noise temperature of payload if noise figure is 3 dB.
Answer: Te = (10^(NF/10)-1) x T0 = (10^0.3- 1) x 290 = (1.995-1) × 290 = 289 K approx.
Topic: Satellite Bandwidth

Question: Calculate bandwidth efficiency if bit rate is 25 Mbps and bandwidth is 20 MHz.
Answer: ɳ=Rb/B= (25×10^6) /(20×10^6) = 1.25 bps/Hz

Question: Calculate required bandwidth for a satellite link with data rate 40 Mbps and spectral efficiency 2 bps/Hz.
Answer: B = R/ η = (40×10^6 )/2= 20 MHz

Question: Calculate the max bit rate if bandwidth is 36 MHz with roll-off factor 0.25 and 8PSK modulation (3 bits/symbol).
Answer: Symbol rate Rs = B/(1 + alpha) = 36/1.25 = 28.8 Msps. Bit rate Rb =R s * bits/symbol = 28.8 * 3 = 86.4 Mbps
Topic: Satellite bus

Question: Calculate power budget for satellite bus if total power consumption is 2000 W and solar array efficiency is 25%.
Answer: Required solar array power = Total power consumption/solar array efficiency=2000/0.25 = 8000 W

Question: Calculate total mass of satellite bus if payload mass is 300 kg and bus-to-payload mass ratio is 2.5.
Answer: Bus mass = Payload mass X Ratio = 300 × 2.5 = 750 kg
Topic: Inter satellite Link

Question: Calculate inter-satellite distancedddif two satellites orbit at 36,000 km and angular difference is 2°.
Answer: d = 2 × πX 36000 × 2 /360 = 1256.6 km

Question: Calculate propagation delay between satellites separated by 5000 km.
Answer: Delay=Distance/speed of light = (5000×10^3)/(3x10^8)= 16.67 ms
Topic: Satellite gateway

Question: Calculate gateway throughput if transponder bandwidth is 500 MHz and spectral efficiency is 3 bps/Hz.
Answer: Throughput=Bandwidth*efficiency = 500*10^6*3=1.5Gbps

Question: Calculate link capacity if gateway has 32 carriers of 36 MHz each with 8PSK modulation (3 bits/symbol) and coding rate 3/4.
Answer: Symbol rate per carrier Rs = 36/1.25 = 28.8 Msps; Per carrier capacity = 28.8 × 3 × 0.75 = 64.8 Mbps; Total capacity = 64.8 × 32 = 2074 Mbps or 2.07 Gbps

Question: Find number of carriers needed if each carrier supports 100 MHz bandwidth and desired total bandwidth is 1 GHz.
Answer: Number of carriers = Total bandwith/ bandwidth of each carriers = 1000/100=10 carriers
Topic: IP over satellite

Question: Calculate IP packet delay over satellite if transmission time is 2 ms and propagation delay is 250 ms.
Answer: Total delay = Transmission time + propagation delay = 2 + 250= 252 ms

Question: Calculate throughput reduction over satellite link with 250 ms latency and window size 64 packets of 1500 bytes.
Answer: Max throughput = (64×1500×8 )/0.25 = 3.07 Mbps
Topic: Downlink

Question: Calculate downlink SINR if signal power is -70 dBm and interference plus noise is -90 dBm.
Answer: SINR = P signal - P interference + noise = -70-(-90) = 20 dB
Topic: SNR

Question: Calculate data throughput over satellite if SNR=15 dB and spectral efficiency is 4 bps/Hz with BW 36 MHz.
Answer: Throughput = BW × η = 36 × 106 × 4 = 144 Mbps
Topic: Signal-to-noise ratio

Question: Calculate noise power Pn in watts for bandwidth 10 MHz and noise spectral density N0 = 10^-20W/Hz
Answer: Pn=N0* B = 10^-20 * 10^7 = 10^-13 W

Question: Calculate required Eb/N0(dB) given data rate R=1Mbps and bandwidth B=1.5MHz with SNR=10dB.
Answer: Eb/N0= SNR*B/R, Linear SNR = 10, Eb/N0 =  10 * 1.5/1 = 15 linear or 10 * log (15) = 11.76 dB

Question: Calculate SNR if signal power is -80 dBm and noise power is -100 dBm.
Answer: SNR = P signal - P noise = -80- (- 100) = 20dB
Topic: SNR

Question: Calculate SNR margin if measured SNR is 18 dB and minimum required is 14 dB.
Answer: Margin= measured SNR -minimum requirement = 18 -14 = 4dB
Topic: Uplink

Question: Calculate uplink SNR if received power is -70 dBm and noise power is -110 dBm.
Answer: SNR= Received power- noise power= -70-(-110)=40 dB
Topic: Signal-to-noise ratio

Question: Convert SNR of 12 dB to a linear scale.
Answer: SNR (linear) = 10^(12/10) = 15.85
Topic: TCP over satellite

Question: Calculate TCP throughput for satellite with window size 64 KB and RTT 0.5 s.
Answer: Throughput = Window Size /RTT= (64 * 8 * 10 ^ 3)/0.5 = 1.024 * 10 ^ 6  bps = 1.024 Mbps

Question: Calculate TCP throughput if window size is 1 MB and RTT is 600 ms.
Answer: Throughput = Window Size*8 /RTT = (1 * 10 ^ 6 * 8)/0.6  = 13.33 * 10 ^ 6 bps = 13.33 Mbps

Question: Calculate TCP throughput if window size is 100 KB and RTT 450 ms.
Answer: Throughput = (100 * 8 * 10 ^ 3)/0.45 = 1.778 * 10 ^ 6 * bps = 1.778 Mbps

Question: Calculate TCP window size needed for 5 Mbps throughput with RTT 0.4 s.
Answer: Window size = Throughput × RTT = 5 * 10 ^ 6 * 0.4 = 2 * 10 ^ 6 bits= 250 KB

Question: Estimate TCP throughput if packet loss rate is 0.01 and RTT 0.6 s.
Answer: Throughput = MSS/ (RTT*√p). Assuming MSS=1500 bytes:(1500*8)/ (0.6*√0.01)= 12000/(0.6 * 0.1) = 200000 bps = 200 Kbps
Topic: Downlink

Question: For given bandwidth 20 MHz and spectral efficiency 4 bps/Hz, find downlink peak data rate.
Answer: R = B × η = 20 × 10^6 x 4 = 80 × 10^6 bps  = 80 Mbps
Topic: TT&C

Question: Calculate round trip time for TT&C if distance to GEO satellite is 36,000 km.
Answer: RTT = 2 * distance/ speed of light= (2*36,000*10^3)/3*10^8 = 0.24 s = 240 ms
Topic: Link Budget

Question: How does rain attenuation differ at various frequency bands in a link budget?
Answer: Rain attenuation increases with frequency. High-frequency bands like Ku, Ka, and V are more affected by rain, causing greater signal loss, while lower frequencies such as L and S bands experience minimal rain impact. In a link budget, expected rain attenuation must be included to maintain a positive link margin and ensure reliable communication during rainy conditions.

Question: A link has SNR = 20 dB. If noise power = -100 dBm, what is the received signal power?
Answer: Signal power = -100 + 20 = -80 dBm.

Question: A satellite has 20 dBW EIRP, free-space path loss 155 dB, receive antenna gain 25 dBi, receiver loss 2 dB. receiver sensitivity is -120 dBW, compute link margin.
Answer: LM=Pr−Pmin=−112−(−120) =8 dB. Positive margin ensures buffer against fading or additional losses.

Question: A satellite link requires 20 dB C/N. Received power is -105 dBW. What is the maximum allowable noise power?
Answer: C/N = Pr - N → N = Pr - C/N = -105 -20 = -125 dBW. Noise power must not exceed -125 dBW to maintain reliable link.

Question: A transmitter sends 10 W, antenna gain is 5 dB, and path loss is 10 dB. What is the received power in dB?
Answer: Convert 10 W to dBW: 10log (10) =10) dBW. Received power (Pr = 10 + 5 - 10 = 5) dBW. So the receiver gets 5 dBW. Simple addition/subtraction of gain and loss gives the received power.

Question: How do fade margins help in maintaining a reliable satellite link?
Answer: Fade margin represents the additional power included in the link budget to compensate for unpredictable losses such as rain, atmospheric absorption, or antenna misalignment.
It is calculated as the difference between the actual received power and the minimum required power for reliable communication:

Mf=Pr−Pmin
        
where
Mf is the fade margin (dB),
Pr is the received power (dB), and
Pmin is the minimum power required by the receiver for proper demodulation (dB).

For example, if Pr=−100 dBW
Pmin=−105 dBW=−105dBW, the fade margin is 
Mf=5 dB Including this margin ensures the link remains operational during temporary degradations, thereby enhancing link reliability.

Question: How do pointing losses affect a high-gain satellite antenna?
Answer: If a high-gain antenna is misaligned, its effective gain decreases due to pointing loss.
In the link budget, this is represented as a reduction in antenna gain:

Geff=Gt−Lp

where

Geff is the effective antenna gain (dB),

Gt is the nominal transmit antenna gain (dB), and

Lp is the pointing loss (dB).

For example, if Gt=45 dB =45dB and Lp=2 dB, then Geff=43 dB =43dB.
High-gain, narrow-beam antennas are particularly sensitive to such misalignment, so engineers include 
Lp in the link budget and design precise control systems to minimize pointing errors.
Topic: Link Budget

Question: How do you calculate Effective Isotropic Radiated Power (EIRP)?
Answer: The Effective Isotropic Radiated Power (EIRP) is a measure of how much power a transmitting antenna radiates in its most focused direction. It combines the effects of the transmitter’s power and antenna gain, while subtracting losses. It is given by EIRP=Pt+Gt−Lt where Pt is transmit power, Gt is antenna gain, and Lt represents system losses. EIRP allows engineers to compare different transmission systems and ensure the transmitted signal is strong enough to be received at a given distance with minimal distortion or loss.

Question: How does halving the distance between satellite and ground affect free-space path loss?
Answer: Halving the distance between the satellite and the ground reduces the free-space path loss (FSL). The FSL is given by the formula:

\[
\text{FSL} = 20 \log_{10} (d)
\]

where \( d \) is the distance between the satellite and the receiver. When the distance is halved, \( d' = \frac{d}{2} \), the change in FSL is:

\[
\Delta \text{FSL} = 20 \log_{10} \left( \frac{d}{2} \right) = 20 \log_{10} (d) - 20 \log_{10} (2)
\]

Thus, the reduction in FSL is approximately:

\[
\Delta \text{FSL} = - 20 \log_{10} (2) \approx -6 \, \text{dB}
\]

This means the received power increases by 6 dB when the distance is halved. Engineers can take advantage of shorter distances or lower orbits to improve signal strength.

Question: How is received power estimated in link budget analysis?
Answer: Received power (Pr) is the total signal power at the receiving antenna after accounting for all gains and losses in the system. It is calculated using the equation Pr=Pt+Gt+Gr−Lp, where Pt is the transmitted power, Gt and Gr are the transmitter and receiver antenna gains, and Lp is the path loss in dB. This simple relationship helps determine whether the signal level at the receiver is strong enough for correct detection. In practical terms, higher antenna gains or transmit power improve received signal levels.

Question: If a 15 W transmitter communicates through a lossy cable of 1.5 dB, how is EIRP affected?
Answer: Cable loss reduces the effective power reaching the antenna. P effective=Pt−L cable=15 W≈11.76W → 10.7 dBW. If antenna gain is 20 dBi, EIRP = 10.7 + 20 = 30.7 dBW. Including cable losses ensures the link budget accurately reflects real transmitted power, preventing overestimation of received power and link margin.

Question: If rain attenuation is 3 dB, how should the link budget be adjusted?
Answer: Rain attenuation adds extra loss to the link. In the budget, this 3 dB is added to total path loss, reducing received power. Engineers may compensate by increasing EIRP, using higher-gain antennas, or adding fade margin. For example, if FSL is 150 dB, EIRP 30 dBW, and receive antenna gain 20 dBi, the new Pr=30+20−(150+3) =−103 dBW. Proper adjustment ensures signal stays above minimum required power.
Topic: Link Budget

Question: If rain increases path loss by 3 dB, by how much should antenna gain be increased to maintain the same received power?
Answer: To compensate for 3 dB additional loss, the antenna gain should be increased by 3 dB. For example, if original Gr = 20 dBi, new Gr = 23 dBi. This keeps received power unchanged, maintaining link reliability without increasing transmitter power.

Question: Received power = -100 dBW, minimum required = -110 dBW. Find link margin.
Answer: Link Margin LM=Pr−Pmin=−100−(−110) =10 dB. Positive margin shows signal is strong enough.

Question: Transmit power = 5 W, transmitter gain = 3 dB, receiver gain = 2 dB, path loss = 8 dB. Find received power.
Answer: Convert 5 W: 10log10(5) = 6.99 ≈ 7dBW. Then (Pr = 7 + 3 + 2 - 8 = 4dBW. Received power is 4 dBW. Simple arithmetic gives an easy link budget result.

Question: Transmitter power = 20 W, antenna gain = 4 dB, path loss = 14 dB. Find received power.
Answer: Convert 20 W: 10log10(20) = 13 dBW. Then Pr = 13 + 4 - 14 = 3 dBW. Receiver gets 3 dBW. Very simple addition/subtraction problem.

Question: Using Pr=−108.45 dBW (Q13) and N=−126.05 dBW (Q14), compute C/N in dB.
Answer: C/N=Pr−N=−108.45−(−126.05) =17.60 dB (rounded). This means the carrier is ~17.6 dB above the noise floor — a healthy margin for many modulations. Link designers use C/N to predict bit error rates and choose modulation/coding. If C/N is too low, increase EIRP, antenna gain, or reduce bandwidth/noise to improve the link.

Question: What does free-space path loss represent in link budget analysis?
Answer: Free-space path loss (FSL) represents the weakening of a radio signal as it travels through space without obstacles. It increases with both distance and frequency. The FSL can be calculated using FSL=20log10(d)+20log10(f)+92.44 where d is distance in kilometres and f is frequency in gigahertz. This loss occurs naturally due to the spreading of the wavefront over distance. Understanding FSL helps engineers predict how much power is lost before the signal reaches the receiver, which is essential for maintaining reliable satellite and wireless communications.

Question: What is link margin in link budget analysis?
Answer: Link margin indicates the safety buffer or extra signal strength available above the minimum required level for proper reception. It is calculated using LM=Pr

Question: What is the importance of noise power in link budget analysis?
Answer: Noise power defines the amount of unwanted signal present in the receiver that can interfere with communication. It is an essential factor for determining the quality of the received signal. Noise power is given by N=kTB where k is Boltzmann’s constant, T is system temperature, and B is bandwidth. In link budget analysis, noise power helps calculate the signal-to-noise ratio (SNR), which directly affects system performance. Lower noise levels or narrower bandwidths help improve signal clarity and ensure better data accuracy in communication links.