Signals, systems,
and other curiosities.
Posts
Science and engineering are fascinating, and understanding how things work from the ground up never gets old. Here I write about technical topics that captivate me, from wireless systems and physics to AI and biomedical signal processing.
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When the airframe joins the array
On a small drone the airframe becomes part of the direction-finding array. A simulation study of what this does to bearings and to emitter localization, and of which calibration recovers them.
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What statistical physics sees in the heartbeat
Detrended fluctuation analysis (DFA) was invented to find long-range correlations in DNA. Applied to cardiac rhythm, it measures the fractal scaling that standard HRV metrics are blind to, and that deteriorates before the linear statistics change.
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OFDM vs OTFS: A pragmatic comparison
Fast fading breaks the orthogonality of OFDM subcarriers and creates inter-carrier interference, for which delay-Doppler waveforms such as OTFS are proposed as the remedy. However, a fair comparison shows that a properly designed OFDM performs on par with OTFS at much lower complexity.
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The geometry of long-range radio links
How far a beyond visual line of sight (BVLoS) radio link reaches is set mainly by geometry: the radio horizon, the antenna height that fixes it, and the diffraction that carries the signal past it.
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Operating beneath the noise floor
In long-range communications, a radio receiver decodes a signal whose power sits below the thermal noise. It breaks no law: what sets the limit is not the noise floor but the interplay between the signal-to-noise ratio and the energy per bit. That interplay governs the design of a weak-signal link.
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The geometry of the longest day
The summer solstice is the extremum of a deterministic signal: the Sun's apparent annual motion. The same spherical geometry that fixes the longest day also explains why, near it, the Sun appears to stand still, and why clock time and sundial time diverge.
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Reading the heart with a radio engineer's toolbox
An electrocardiogram is a noisy one-dimensional signal. The same signal processing used in radio receivers, filtering and spectral estimation, turns it into a measure of autonomic health.