| Communications Toolbox | |
The figure below depicts direct and major reflected paths between a stationary radio transmitter and a moving receiver. The shaded shapes represent reflectors such as buildings.
The major paths result in the arrival of delayed versions of the signal at the receiver. In addition, the radio signal undergoes scattering on a local scale for each major path. Such local scattering is typically characterized by a large number of reflections by objects near the mobile. These irresolvable components combine at the receiver and give rise to the phenomenon known as multipath fading. Due to this phenomenon, each major path behaves as a discrete fading path. Typically, the fading process is characterized by a Rayleigh distribution for a non-line-of-sight path and a Rician distribution for a line-of-sight path.
The relative motion between the transmitter and receiver causes Doppler shifts. Local scattering typically comes from many angles around the mobile. This scenario causes a range of Doppler shifts, known as the Doppler spectrum. The maximum Doppler shift corresponds to the local scattering components whose direction exactly opposes the mobile's trajectory.
The toolbox implements a baseband channel model for multipath propagation scenarios that include
Local scattering from all angles, with uniform power distribution, around the mobile. This scenario corresponds to what is known as the Jakes Doppler spectrum. The toolbox lets you specify the maximum Doppler shift of the Jakes Doppler spectrum. You can also omit a Doppler shift to model a static channel.
N discrete fading paths, each with its own delay and average power gain. A channel for which N = 1 is called a frequency-flat fading channel. A channel for which N > 1 is experienced as a frequency-selective fading channel by a signal of sufficiently wide bandwidth.
A Rayleigh or Rician model for the first major path. Any subsequent paths use a Rayleigh model.
Some additional information about typical values for delays and gains is in Choosing Realistic Channel Property Values.
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