STEM Blog
Understanding Cell Phone Technology: Lossless Data Compression
Claude Shannon proved that at least one code exists that allows data to be sent across a communications channel at rates up to the channel capacity C, assuming the entropy of the source is less than C. Unfortunately, his theory doesn’t completely explain what the code(s) might be. This week we’re going to begin talking…
Understanding Cell Phone Technology: Data Compression and Error Correction
Last week, we looked at noise on a communications channel. Why? Because such noise is always going to be present, and system designers have to compensate for it if the technology has any hope of working. How do they do that? Let’s begin by remembering that any message contains information. If every bit of the…
Understanding Cell Phone Technology: Noise
Today we’re going to talk about why noise on a communications channel is bad. Wait a minute, you say, I thought anything that increases uncertainty, including noise, increases information, and that’s a good thing. Who’s right? The nuance here is that we want the uncertainty we choose, not the uncertainty introduced by noise. The mathematician…
Understanding Cell Phone Technology: What’s RF?
The Electromagnetic (EM) spectrum refers to the complete range of electromagnetic radiation, typically described by frequency or wavelength. The frequencies of EM waves range from 3 to 300 * 10^18 Hertz (Hz), or wavelengths of 1 * 10^5 to 1 * 10^-12 meters (m). In a vacuum, all EM waves travel at the speed of…
Understanding Cell Phone Technology: Analog and Digital Signals
Since the invention of the telegraph, people have been transmitting messages using electrical signals. In early telegraph and telephone systems, the electrical signals traveled over physical wires. Over time, inventors found ways to harness the radio frequencies of the electromagnetic (EM) spectrum for wireless telegraphic and telephonic communications. The invented words – “telegraph” and “telephone”…
Understanding Cell Phone Technology: The Model
Finally, we are ready to talk about the components of the modern communications system. The diagram attached to the end of this blog is the model we will have in our heads as we investigate the main components of our digital cell phones. I’ve drawn two cell phones operating across the radio frequency (RF) spectrum….
Understanding Cell Phone Technology: Information Content
Every message begins with an information source, like someone talking on a cell phone, or a computer transmitting a file across the internet. A mathematician, Claude Shannon, came up with the idea in the 1940’s of the information content of a message, the essential elements of the message that have to be preserved in order…
Morse code transmitter
The J-38 telegraph code transmitter used during World War II. Morse code was the first data compression method for electric communications.
Understanding Cell Phone Technology: Data Compression
STEM education often stops short of explaining how mathematics underlies modern technologies. There’s a reason for that: it’s complicated. But students must be curious about how their cell phones manage to transmit their voices and data from and to anywhere on the planet, right? For the next several weeks, this blog will explore this subject….