Sponsor: San Diego Section
Speaker: Professor Fred Harris, University of California San Diego

Meeting Date: 23 Aug 2023
Time: 03:00 PM to 04:30 PM
Cost:
Location: San Diego, California
Reservations: IEEE
Summary:
An interesting experiment helps explain why we measure time. After seeing someone glancing at their watch, you can ask them if they know what time it is, and will be surprised to learn they don’t know and will have to look again at their timepiece to respond to the question. But you know they had just looked at it, why didn’t it register? It is interesting to note that we don’t look at our watch to know what the current time is, we look to learn how much time remains till an upcoming event; perhaps end of a lecture, or to a make a scheduled call. What we learn is time intervals are more important than time itself. We partition time into convenient intervals, such as second, minutes, days, weeks, months, years, and so on. The intervals allow us to schedule and coordinate activities. Christiaan Huygens invented the pendulum clock in 1656 which reduced clock errors from 15 minutes per day to 15 seconds per day.

A ship’s navigator could determine Latitude (north of equator) by measuring altitude of the North Star. They were not similarly able to determine their longitude. In old maps Latitudes of coastlines are accurate, but the Longitudes are off by hundreds of miles. Pendulum clocks cannot operate on board a ship and thus a navigator, without access to accurate time, could not determine Longitude.

In 1707, due to a poor estimate of longitude during a severe storm off the Isles of Scilly, the British Navy lost four ships, 1600 sailors, and an Admiral. This is considered the greatest maritime disaster in British history. In response to this loss, in 1714, Parliament offered a 20,000 Pound Sterling ($4.4 million today) prize to anyone who could find a way to determine a ship’s longitude within 0.5 degrees (30 nautical miles). Navigation is why we care “What time is it?”

This presentation will discuss the process of time keeping and in particular how we used DSP techniques to set the time and align the crystal-controlled clocks aboard the SpaceX Starlink Satellites. This proved to be an interesting task due to various design constraints.

Bio: Professor Fred Harris is at the University of California San Diego where he teaches and conducts research on Digital Signal Processing and Communication Systems. He holds 40 patents on digital receiver and DSP technology and lectures throughout the world on DSP applications. He consults for organizations requiring high performance, cost effective DSP solutions. He was an adjunct member at the Princeton Center for Communications Research and at the Communications and Signal Processing Research Group in the Department of Electrical and Electronic Engineering at Imperial College London.

He has written some 260 journal and conference papers, the most well-known being his 1978 paper “On the use of Windows for Harmonic Analysis with the Discrete Fourier Transform”. He is the author of the book Multirate Signal Processing for Communication Systems and has contributed to several other DSP books including the Sklar and harris 3-rd edition of Digital Communications the “Time Domain Signal Processing with the DFT” chapters in Doug Elliot’s 1987 book Handbook of Digital Signal Processing, and “A most Efficient Digital Filter: The Two-Path Recursive All-Pass Filter” and the “Ultra Low Phase Noise DSP Oscillator” Chapters in Rick Lyon’s 2012 book Streamlining Digital Signal Processing. He is co-author of the book Software Radio Sampling Rate Selection, Design and Synchronization.