What is Doppler spread in wireless communication?
One of the challenging issues is the large Doppler spread, which is caused by the high mobility of a wireless terminal and may lead to severe communication per- formance loss. Doppler spread is a measure of spectral broadening of the rate of change in a mobile fading channel which is proportional to the mobile speed.
Besides sound and radio waves, the Doppler effect also affects the light emitted by other bodies in space. If a body in space is "blue shifted," its light waves are compacted and it is coming towards us. If it is "red shifted" the light waves are spread apart, and it is traveling away from us.
- Astronomers use Doppler shifts to calculate precisely how fast stars and other astronomical objects move toward or away from Earth. For example the spectral lines emitted by hydrogen gas in distant galaxies is often observed to be considerably redshifted.
- The doppler effect just states that, to an observer, a sound appears to sound higher in pitch (frequency) as it gets closer to them and lower in pitch (frequency) as it moves farther away. Astronomers can use this because you can use emitted sounds to calculate the distance or velocity of an object.
Is there a Doppler shift if the source and the observer move in the same direction with the same velocity?If the source and observer move in the same direction with the same velocity, their separaton can't be changing—so they can't be getting closer together or farther apart. Therefore a Doppler shift can't occur in this case.
The Doppler effect (or the Doppler shift) is the change in frequency or wavelength of a wave in relation to observer who is moving relative to the wave source. It is named after the Austrian physicist Christian Doppler, who described the phenomenon in 1842.
- Doppler blueshift is caused by movement of a source towards the observer. The term applies to any decrease in wavelength and increase in frequency caused by relative motion, even outside the visible spectrum. Nearby stars such as Barnard's Star are moving toward us, resulting in a very small blueshift.
- A Doppler ultrasound is a test that uses high-frequency sound waves to measure the amount of blood flow through your arteries and veins, usually those that supply blood to your arms and legs. Vascular flow studies, also known as blood flow studies, can detect abnormal flow within an artery or blood vessel.
- The pitch of the siren of a Fire truck appears to change as the truck passes us due to the Doppler effect. Of course, to an observer on the truck, the pitch does not change at all. Since the speed of sound in air is essentially fixed, the perceived pitch of a tone is related to the wavelength of the sound.
A blueshift is any decrease in wavelength, with a corresponding increase in frequency, of an electromagnetic wave; the opposite effect is referred to as redshift. In visible light, this shifts the color from the red end of the spectrum to the blue end.
- Redshift and blueshift describe how light shifts toward shorter or longer wavelengths as objects in space (such as stars or galaxies) move closer or farther away from us. If an object moves closer, the light moves to the blue end of the spectrum, as its wavelengths get shorter.
- Accelerating expansion of the universe. The accelerating expansion of the universe is the observation that the universe appears to be expanding at an increasing rate, so that the velocity at which a distant galaxy is receding from the observer is continuously increasing with time.
- The cosmological redshift is a redshift caused by the expansion of space. As a result of the Big Bang (the tremendous explosion which marked the beginning of our Universe), the Universe is expanding and most of the galaxies within it are moving away from each other.
Updated: 21st October 2019