Link budget quiz

Introduction

Exercise 81

Which is/are correct?

1. A link budget accounts for the losses and gains between the transmitter and the receiver.

2. Gains and losses are usually the same in both directions in a bidirectional wireless communication system.

3. Given two communicating nodes, the link budget is usually done four times for the following paths: A-B, B-A, A-A, B-B.

4. The result of a link budget is a signal-to-noise (SNR) ratio. One goal of the analysis is to check whether SNR is high enough.

Solution to Exercise 81

1, 4

Signal power budget

Exercise 82

Which of the following influence/s in the noise power budget calculation?

1. Shape of the receiver antenna

2. Distance between the transmitter and the receiver antenna

3. The cable between the antenna and the transceiver

4. Transmitter antenna gain

Solution to Exercise 82

1, 2, 3, 4

Transmit power

Exercise 83

Which is/are correct?

1. Transmit power can be measured in Watt.

2. Transmit power can be measured in dBm.

3. Transmit power can be measured in dBmW.

4. The higher the transmission power, the higher the SNR.

5. The lower the transmission power, the higher the noise.

6. A cellular base station typically has more transmit power than a Wi-Fi router.

7. Transmit power depends on how much the transceiver amplifies a signal.

Solution to Exercise 83

1, 2, 3, 4, 6, 7

Antenna gains

Exercise 84

Which is/are correct?

1. The higher the antenna power, the higher the antenna gain.

2. The antenna gain is partially based on the shape of the antenna.

3. The antenna gain stays the same for all frequencies.

4. The standard antenna of the PlutoSDR is directional, i.e., radiating in a specific direction.

5. A directional antenna focuses the transmit power in a specific direction

6. If an antenna does not point in the right direction, then the antenna gain decreases.

7. A smartphone should typically have an almost omnidirectional antenna because it needs to work reasonably well regardless of how the user holds the phone.

8. At higher frequency bands like 28 GHz, we can achieve greater directivity by controlling how multiple transmitted waves combine through beamforming techniques without physically changing the shape of individual antenna elements.

Solution to Exercise 84

2, 5, 6, 7, 8

Path loss

Exercise 85

Which is/are correct?

1. As an electromagnetic wave moves through space, its voltage decreases.

2. The energy flowing through a unit area typically increases if we near us to the antenna.

3. Path loss works against the transmit power in the link budget.

4. The linear path loss grows quadratically with increasing distance.

5. FSPL stands for free space path loss and is based on both signal frequency and distance of the transmission line.

6. Signal frequency in path loss is measured in .

7. FSPL should not be used indoors because the FSPL model does not capture the environmental properties of an indoor environment.

8. A non-free-space model should be used to model path loss for a case without LOS.

9. Okumura-Hata model can only model the path loss in large cities.

Solution to Exercise 85

2, 3, 4, 5, 7, 8

Miscellaneous losses

Exercise 86

Which is/are correct?

1. Rain can cause an extra loss and is typically accounted for in the miscellaneous loss.

2. Signal loss per distance monotonously (always) increases with increasing frequencies.

3. Compared to the free-space loss, e.g., FSPL, atmospheric loss is caused by the interaction between the electromagnetic wave and molecules in the air, such as oxygen and water, which absorb energy at specific frequencies.

4. We can account 1-3 dB for all miscellaneous losses when working with frequencies < 40 GHz.

5. A link budget usually assumes ideal conditions, while real-world factors are accounted for in miscellaneous losses.

Solution to Exercise 86

1, 3, 4, 5

Signal power equation

Exercise 87

You want to calculate the received power by the receiver. Which of the following affect/s the received power positively?

1. Transmit power

2. Antenna gain

3. Path loss

4. Miscellaneous losses

Solution to Exercise 87

1, 2

Exercise 88

You have two of the same wireless transceiver with a single omnidirectional antenna. Given the following data, what is the received power in dBW?

• miscellaneous loss: 3 dB

• path loss: 10 dB

• antenna gain: 1 dB

• transmission power: 1 W

Solution to Exercise 88

0 (1W) -3 +1 -10 = -12 dBW

EIRP

Exercise 89

Which is/are correct?

1. Effective isotropic radiated power (EIRP) applies only if the antenna is pointed towards the sky.

2. EIRP is only based on antenna properties like cables and directivity.

3. EIRP can be used as a compact metric describing the transmitting device in the link budget.

Solution to Exercise 89

3

Noise power budget

Exercise 90

Which is/are correct?

1. The R in the abbreviation SNR stands for radiation because noise is based on the radiated heat of the receiver, which affects the reception.

2. We start to account for the noise in the path loss due to the interference in the air through other radio signals.

3. Every receiver suffers from thermal noise because the receiving device operates at temperatures above 0 Kelvin.

4. The noise directly depends on the data rate.

5. Physical temperature contributes to the system noise temperature. However, a system could have a noise temperature of 100K even though all its physical components are at room temperature (~290 K).

Solution to Exercise 90

3, 5

The noise depends on the bandwidth but not data rate.

SNR

Exercise 91

Which is/are correct?

1. SNR in dB is calculated by subtracting the noise from the signal power.

2. We typically want an SNR of 10 dBW (100 mW).

3. One way to get the SNR is to calculate the received power with and without the signal present.

4. A communication system is using 16-QAM. If the SNR decreases, we could change to QPSK to maintain data transfer.

Solution to Exercise 91

1, 3, 4

SNR is in dB, not dBW

Example Link Budget: ADS-B

Exercise 92

Which is/are correct?

1. ADS-B messages may collide. ADS-B features randomization of the transmission period to decrease the probability of collision.

2. The path loss of ADS-B only depends on how far away an aircraft is from the next obstacle.

3. If there is a base station in the receiver’s proximity, then the base station may cause interference. This interference leads to less signal power in the SNR link budget calculation.

Solution to Exercise 92

1

Interference leads to more noise, not less signal power.