The Wireless Channel. Lecture 3. Area 1. Area 2. Short- term fading. Log-normal shadowing. Transmitter. Large and Small Scale Propagation Models. Wireless Mulipath Channel. Channel varies at two spatial scales: large scale fading small scale fading. Large-scale fading.
The Wireless Channel
Channel varies at two spatial scales:
large scale fading
small scale fading
where ai(t) and i(t) are the gain and delay of path i.
Time variations property
Time spreading property
Signal can take many different paths between sender and receiver
due to reflection, scattering, diffraction
• Due to the different paths taken by the multipath components, they may arrive at different times
• If the symbol period TS is smaller than the delay spread, i.e. TS< Tm, Inter-Symbol Interference (ISI) will occur
• The receiver cannot determine which symbol each multipath component belongs to:
The Delay Spread Tm is defined as the difference between times-of arrival
of the first and last multipath components Typical values are as follows:
Based on Time-Spreading
Based on Time-Variations
Complex circular symmetric Gaussian .
No fading, Constant power