EM3: Car-to-X Communication at Karlsruher Institut Für Technologie | Flashcards & Summaries

# Lernmaterialien für EM3: Car-to-X Communication an der Karlsruher Institut für Technologie

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TESTE DEIN WISSEN

Explain the CSMA/CA principle

Lösung anzeigen
TESTE DEIN WISSEN

CSMA/CA = Carrier Sense Multiple Access / Collision Avoidance

Listen to the channel before starting transmission. Transmission is only started if channel is free.

• 1-persistent: Transmit as soon as channel gets free
• Non-persistent: If channel is free transmit immediately, else wait random time
• p-persistant: If channel is free transmit with probability p or wait with probability (1-p)

Lösung ausblenden
TESTE DEIN WISSEN

What are typical applications based on CAM?

Lösung anzeigen
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CAM = Cooperative Awareness Message

- Intersection assis

- Slow vehicle warning

- Blind spot detection

- Connected ACC

- Automatic driving

Lösung ausblenden
TESTE DEIN WISSEN

Which limitations have the free-space model and the two-way model

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TESTE DEIN WISSEN

Free-space model

calculation based on direct path

- inaccurate in rural area

Two-way model

Additionally consider reflection off ground and hight of antenna.

Leads to constructive and destructive interference based on distance.

Lösung ausblenden
TESTE DEIN WISSEN

What are the advantages of C-ACC over ACC?

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- Higher accuracy control of vehicle following gap

- Significantly faster responses to speed changes by observing multiple forward vehicles

- Early detection of cut-ins

- Cooperative adaption of speed to increase traffic volume

Lösung ausblenden
TESTE DEIN WISSEN

Which factors influence the communication range?

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TESTE DEIN WISSEN

- Required packet reception success rate by application

- System (modulation & coding)

- Channel characteristics

- Interference (packet collisions)

- Transmission power

- Antenna and vehicle body

Lösung ausblenden
TESTE DEIN WISSEN

What are typical effects influencing the propagation of electromagnetic waves?

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TESTE DEIN WISSEN
• Free-space path loss
• no obstruction
• attenuation dependent on distance
• Reflection
• change in direction of wave
• vehicles, building, street signs, ...
• Diffraction
• waves propagated around object
• vehicles, buildings, ...
• Scattering
• wave encountering object with rough surface
• Penetration
• wave penetrates through material
• window, vegetation, ...
Lösung ausblenden
TESTE DEIN WISSEN

What are typical applications based on infrastructure messages?

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- Green light optimal speed advisory

- Signal violation warning

- Remaining red and green traffic times

Lösung ausblenden
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Which factors influence the free-space path loss?

Lösung anzeigen
TESTE DEIN WISSEN

loss is

• quadratic with frequency (antenna effectivity)
Lösung ausblenden
TESTE DEIN WISSEN

How do you expect the free-space transmission range for commercial Wi-Fi at 2.4 GHz in comparison to 5.9 GHz?

Lösung anzeigen
TESTE DEIN WISSEN

2.4 GHz has higher range since 5.9 GHz has higher frequency and therefore higher loss.

~ double frequency ➔ 6 dB higher loss

Lösung ausblenden
TESTE DEIN WISSEN

Explain the parameters of statistical channel models

Lösung anzeigen
TESTE DEIN WISSEN
• Path loss (free space, ...)
• Fading statistics (small-scale) fluctuations in the received power due to interference
• Fading statistics (large scale) fluctuations due to obstructions in path
• Delay spread - Average power delivered by multi path components
• Doppler spread - Widening of spectrum due to different Doppler effects caused by multi path components

Lösung ausblenden
TESTE DEIN WISSEN

What is the principle of link budget calculation?

Lösung anzeigen
TESTE DEIN WISSEN
• Starting with the output power adding all the changes in power gain or loss in transmitter, channel and receiver. The result is the receive power.
• Calculate noise power based on temperature and bandwidth.
• Calculate signal to noise ration based on receive power and noise power.
• Subtract receiver noise from SNR

Based on SNR packet error rate for given modulation sheme can be found in charts.

Lösung ausblenden
TESTE DEIN WISSEN

What are the main differences between CAM and DENM?

Lösung anzeigen
TESTE DEIN WISSEN

CAM

• sent always
• contains general information about vehicle

DENM

• sent only when hazard occurs
• contains specific information about hazard
Lösung ausblenden
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Q:

Explain the CSMA/CA principle

A:

CSMA/CA = Carrier Sense Multiple Access / Collision Avoidance

Listen to the channel before starting transmission. Transmission is only started if channel is free.

• 1-persistent: Transmit as soon as channel gets free
• Non-persistent: If channel is free transmit immediately, else wait random time
• p-persistant: If channel is free transmit with probability p or wait with probability (1-p)

Q:

What are typical applications based on CAM?

A:

CAM = Cooperative Awareness Message

- Intersection assis

- Slow vehicle warning

- Blind spot detection

- Connected ACC

- Automatic driving

Q:

Which limitations have the free-space model and the two-way model

A:

Free-space model

calculation based on direct path

- inaccurate in rural area

Two-way model

Additionally consider reflection off ground and hight of antenna.

Leads to constructive and destructive interference based on distance.

Q:

What are the advantages of C-ACC over ACC?

A:

- Higher accuracy control of vehicle following gap

- Significantly faster responses to speed changes by observing multiple forward vehicles

- Early detection of cut-ins

- Cooperative adaption of speed to increase traffic volume

Q:

Which factors influence the communication range?

A:

- Required packet reception success rate by application

- System (modulation & coding)

- Channel characteristics

- Interference (packet collisions)

- Transmission power

- Antenna and vehicle body

Q:

What are typical effects influencing the propagation of electromagnetic waves?

A:
• Free-space path loss
• no obstruction
• attenuation dependent on distance
• Reflection
• change in direction of wave
• vehicles, building, street signs, ...
• Diffraction
• waves propagated around object
• vehicles, buildings, ...
• Scattering
• wave encountering object with rough surface
• Penetration
• wave penetrates through material
• window, vegetation, ...
Q:

What are typical applications based on infrastructure messages?

A:

- Green light optimal speed advisory

- Signal violation warning

- Remaining red and green traffic times

Q:

Which factors influence the free-space path loss?

A:

loss is

• quadratic with frequency (antenna effectivity)
Q:

How do you expect the free-space transmission range for commercial Wi-Fi at 2.4 GHz in comparison to 5.9 GHz?

A:

2.4 GHz has higher range since 5.9 GHz has higher frequency and therefore higher loss.

~ double frequency ➔ 6 dB higher loss

Q:

Explain the parameters of statistical channel models

A:
• Path loss (free space, ...)
• Fading statistics (small-scale) fluctuations in the received power due to interference
• Fading statistics (large scale) fluctuations due to obstructions in path
• Delay spread - Average power delivered by multi path components
• Doppler spread - Widening of spectrum due to different Doppler effects caused by multi path components

Q:

What is the principle of link budget calculation?

A:
• Starting with the output power adding all the changes in power gain or loss in transmitter, channel and receiver. The result is the receive power.
• Calculate noise power based on temperature and bandwidth.
• Calculate signal to noise ration based on receive power and noise power.
• Subtract receiver noise from SNR

Based on SNR packet error rate for given modulation sheme can be found in charts.

Q:

What are the main differences between CAM and DENM?

A:

CAM

• sent always
• contains general information about vehicle

DENM

• sent only when hazard occurs
• contains specific information about hazard

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