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Multipath channels
The document discusses key parameters for characterizing multipath channels: 1) Coherence bandwidth is the range of frequencies over which the channel can be considered flat and two frequency components will be correlated. It is inversely proportional to the root mean square (RMS) delay spread. 2) Doppler spread is the range of frequencies over which the received Doppler spectrum is non-zero. It characterizes the time-varying nature of the channel. 3) Coherence time is the duration over which the amplitude of two received signals will be correlated. It is inversely proportional to the maximum Doppler shift and characterizes the time-varying nature of the channel.
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Multipath channels
- 1. Parameters of Multipathchannels M.Vignesh pandi A.Vijayasekhar
- 2. Coherence Bandwidth Itis a measure of range frequencies over which the channel is considered flat. Otherwise it is range frequencies over which two frequency component have a strong potential for amplitude correlation.
- 3. It is usedto characterize the channel in the frequency domain It is inversely proportional to the rms delay spread B c =1/ σ ז Two sinusoidal with frequency separation greater than Bc are affected quite differently by the channel. If the frequency correlation function is above 0.9, than the correlation bandwidth is B c =1/50 σ ז If the frequency correlation function is above 0.5 than the coherence bandwidth is approximately B c =1/5 σ ז
- 4. Doppler spread andcoherence time are parameters are describes the time varying nature of the channel in a small- scale region. It is defined as the range of frequency over which the received Doppler spectrum is essentially non-zero Doppler spread and Doppler frequency: Doppler spread B d is defined as the range of frequencies over which the received Doppler spectrum is essentially non-zero. Doppler spread and coherence time
- 5. The maximum Dopplerfrequency f d is give by f d =v/ λ λ =c/f f d =v/ λ = v/(c/f) f d =vf/c Where C-velocity of light V-speed of the mobile, including the speed of the mobile environment in m/s λ - wavelength of the radio signal in meters and F- radio frequency When a pure sinusoidal tone of frequency fc is transmitted the received signal spectrum, will have components in the range fc-fd to fc+fd where fd is the Doppler shift.
- 6. Coherence Time (Tc ) Coherence time is the time duration over which two received signal have a strong potential for amplitude correlation Distortion is occurred at the receiver, if the reciprocal bandwidth of signal is greater than the coherence time for the channel The Doppler spread & coherence time are inversely proportional to each other T c ≈1/f m
- 7. If the timecorrelation function is above 0.5 than the coherence time is given as T c ≈9/(16 π f m ) where f m =maximum Doppler shift f m =v/ λ If the digital transmission system is used,than the coherence time as geometric mean of above two equation T c =√(9/(16 π f m 2 ))
- 8.