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# doppler.flat

Construct flat Doppler spectrum object

## Syntax

dop = doppler.flat

## Description

dop = doppler.flat creates a flat Doppler spectrum object that is to be used for the DopplerSpectrum property of a channel object (created with either the rayleighchan or the ricianchan function). The maximum Doppler shift of the flat Doppler spectrum object is specified by the MaxDopplerShift property of the channel object.

## Properties

The flat Doppler spectrum object contains only one property, SpectrumType, which is read-only and has a fixed value of 'Flat'.

## Theory and Applications

In a 3-D isotropic scattering environment, where the angles of arrival are uniformly distributed in the azimuth and elevation planes, the Doppler spectrum is found theoretically to be flat [2]. A flat Doppler spectrum is also specified in some cases of the ANSI J-STD-008 reference channel models for PCS, for both outdoor (pedestrian) and indoor (commercial) [1] applications.

The normalized flat Doppler power spectrum is given analytically by:

where ${f}_{d}$ is the maximum Doppler frequency.

## Examples

expand all

### Create a Rayleigh Channel with Flat Doppler Spectrum

This example shows how to create a Rayleigh channel object with a flat Doppler spectrum.

Set the sample time and maximum Doppler shift.

```ts = 1e-6; % sec
fd = 50; % Hz
```

Create the Rayleigh channel object.

```chan = rayleighchan(ts,fd);
```

Observe that the default Doppler spectrum property, SpectrumType, is 'Jakes' .

```chan.DopplerSpectrum
```
```
ans =

SpectrumType: 'Jakes'

```

Change the Doppler spectrum property of the channel by using doppler.flat.

```chan.DopplerSpectrum = doppler.flat
```
```
chan =

ChannelType: 'Rayleigh'
InputSamplePeriod: 1.0000e-06
DopplerSpectrum: [1x1 doppler.flat]
MaxDopplerShift: 50
PathDelays: 0
AvgPathGaindB: 0
NormalizePathGains: 1
StoreHistory: 0
StorePathGains: 0
PathGains: -0.6760 + 0.6319i
ChannelFilterDelay: 0
ResetBeforeFiltering: 1
NumSamplesProcessed: 0

```