Difference between Doppler spread and Coherence time

This page defines Doppler spread vs Coherence time and mentions difference between Doppler spread and Coherence time.

These terms are related to characteristics of wireless channel.

Doppler spread

• Doppler shift is the random changes in a channel introduced as a result of a mobile user's mobility.
• Doppler spread has the effect of shifting or spreading the frequency components of a signal.
• It is caused by time selective fading. i.e. for a particular instance of time channel behaves as a fading channel and for rest it behaves as FLAT channel.
• Types of fading on the basis of doppler spread are fast fading and slow fading.
• Fast fading : Channel impulse response changes rapidly within the symbol duration.
• Slow fading : Channel impulse response changes at a rate much slower than the transmitted symbol bandwidth.
• Doppler spread is expressed in the following formula. As mentioned, doppler spread is defined as maximum doppler shift (fm).

Doppler spread formula

Coherence time

• The coherence time of the channel is the inverse of the Doppler spread.
• It is the measure of the speed at which channel characteristics change.
• This determines the rate at which fading occurs. When channel changes are higher than modulated symbol rate, fast fading occurs. When channel changes are slower than the symbol rate, slow fading occurs.
• Coherence time is expressed in the following formula.

Coherence time formula


Signalling Types
EPABX system basics
Circuit Switching vs Packet Switching
Telephone system tutorial
2W circuit vs 4W circuit

5G NR Numerology | 5G NR Terminology

5G NR Control channels | 5G NR Traffic Channels | 5G NR Reference Signals and sequences


This 5G tutorial also covers following sub topics on the 5G technology:
5G basic tutorial
5G Frequency Bands
5G millimeter wave tutorial
5G mm wave frame
5G millimeter wave channel sounding
Difference between 4G and 5G
5G testing and test equipments
5G network architecture
5G NR Physical layer
5G NR MAC layer
5G NR RLC layer
5G NR PDCP layer

LoRaWAN related links

The LoRaWAN Wireless tutorial covers following sub topics:
LoRaWAN Smart Parking   LoRaWAN sensor design   LoRaWAN smart healthcare system   LoRaWAN smart water metering   LoRaWAN architecture   LoRaWAN Interface Types   LoRaWAN roaming types   LoRa tutorial   LoRa Frequency Bands   LoRa protocol stack   LoRa MAC layer   LoRaWAN classes   LoRa features   LoRa Transceiver module  

What is Difference between

difference between FDM and OFDM
Difference between SC-FDMA and OFDM
Difference between SISO and MIMO
Difference between TDD and FDD
Difference between 802.11 standards viz.11-a,11-b,11-g and 11-n
Bluetooth vs zigbee
Fixed wimax vs mobile

RF and Wireless Terminologies