Communications Toolbox™

doppler.rounded - Construct rounded Doppler spectrum object

Syntax

dop = doppler.rounded dop = doppler.rounded(coeffrounded)

Description

The doppler.rounded function creates a rounded Doppler spectrum object that is used for the DopplerSpectrum property of a channel object (created with either the rayleighchan or the ricianchan function).

dop = doppler.rounded creates a rounded Doppler spectrum object with default polynomial coefficients , , (see Theory and Applications for the meaning of these coefficients). The maximum Doppler shift (in Hertz) is specified by the MaxDopplerShift property of the channel object.

dop = doppler.rounded(coeffrounded), where coeffrounded is a row vector of three finite real numbers, creates a rounded Doppler spectrum object with polynomial coefficients, , given by coeffrounded(1), coeffrounded(2), and coeffrounded(3), respectively.

Properties

The rounded Doppler spectrum object contains the following properties.

Property	Description
`SpectrumType`	Fixed value, `'Rounded'`
`CoeffRounded`	Vector of three polynomial coefficients (real finite numbers)

Theory and Applications

A rounded spectrum is proposed as an approximation to the measured Doppler spectrum of the scatter component of fixed wireless channels at 2.5 GHz [1]. However, the shape of the spectrum is influenced by the center carrier frequency.

The normalized rounded Doppler spectrum is given analytically by a polynomial in f of order four, where only the even powers of f are retained:

where

is the maximum Doppler shift, and are real finite coefficients. The fixed wireless channel model of IEEE 802.16 [1] uses the following parameters: , , and . Because the channel is modeled as Rician fading with a fixed line-of-sight (LOS) component, a Dirac delta is also present in the Doppler spectrum at .

Example

The following code creates a Rician channel object with a maximum Doppler shift of . It then creates a rounded Doppler spectrum object with polynomial coefficients , , , and assigns it to the DopplerSpectrum property of the channel object.

chan = ricianchan(1/1000,10,1);
dop_rounded = doppler.rounded([1.0 -0.5 1.5]);
chan.DopplerSpectrum = dop_rounded;

References

[1] IEEE 802.16 Broadband Wireless Access Working Group, "Channel models for fixed wireless applications," IEEE 802.16a-03/01, 2003-06-27.