njit-etd2003-081 - New Jersey Institute of Technology

101
The quantity C(ω) has a range of 0.0 to 1.0, where 1.0 indicates that all of the
measured output power is due to the input excitation. This is the most desirable
situation and will only be true at frequencies where the spectral energy of the noise
ny (t) is negligible. The coherence can therefore be viewed as a measurement quality
indicator. When a significant portion of the measured output is not related to the
excitation, a low coherence results. This indicates that for a given amount of averaging,
the variance of the transfer function at these frequencies will be higher than the variance
where there is good coherence (closer to 1.0).
It is important to recognize that since this estimator is unbiased, given sufficient
averaging, the transfer function estimate will converge to the system's actual transfer
function in spite of possibly low coherence.
The above transfer function and coherence estimation calculations are calculated
in Lab VIEW and/or MatLab System Identification Toolbox.
3.13.2 The ARX Models
The timing of electrical and mechanical events within the heart is vital to its function. In
"normal" healthy humans, a bundle of spontaneously depolarizing cells located on the
right atrium of the heart, called the sino-atrial (SA) node, acts as the pacemaker for the
heart. Through an upward drift in electrical potential, the cells spontaneously reach a
threshold potential, at which point the cells rapidly depolarize, or "fire", as a group. This
is followed by a reset which marks the start of a new cycle. The firing initiates the
spread of electrical activity through the heart, and therefore initiates the contraction that
is necessary for blood to be delivered to the rest of the body. Although temporal