Module imu mod SGSFR

Overview

This module is devoted to IMU signals sampling frequency reduction. This module is typically used when device sensor sampling rate is high, inducing adverse noise-signal ratio and large data load.

Module nomenclature

The module input consists in two physical streams that carry IMU gyroscopic velocities and translational accelerations.

After signal sampling frequency reduction, the module creates two identical physical streams as output that carry the downsampled input quantities.

Module interface

This section gives a summary of the module interface in terms of streams and devices. The order of devices and streams is given as waited by the module. The devices interface is given by :

device( Physical ) IMU sensor

The stream input interface is :

stream( Physical | IMU ) Gyroscopic velocities
stream( Physical | IMU ) Translational accelerations

and the stream output interface is :

stream( Physical | IMU ) Downsampled gyroscopic velocities
stream( Physical | IMU ) Downsampled translational accelerations

The two input streams are attached as well as the two output streams.

Module operation

The sampling frequency reduction algorithm operates through signal accumulation and averaging. For a given signal s = { s(i) } with i going from 1 to n, s(i) being the signal sample at time i, and a reduction factor of f, the length of the downsampled signal r is computed as follows :

    m = [n / f]

where [] designate the integer part. For a given j, the frequency reduced sample r(j) of r is computed as follows :

    r(j) = (1 / f) ∑(k = u,v) s(k);

with

    u = (j - 1) * f
    v = (j * f) - 1

Using this reduction algorithm, if the input signal length is not a multiple of f, the last incomplete segment is simply not considered.