Digital Communications

## Communications .. is the act of conveying meanings from one entity or group to another through the use of <span style="color:red">mutually understood</span> signs, <span style="color:red">symbols</span>, and semiotic rules.

## History Early means of communicating over a distance included ..

## History  #### Semaphore Flags

## History  #### Telegraph

## Modern Day 20th- and 21st-century technologies for long-distance communication usually involve electrical and electromagnetic technologies ..

## Modern Day  #### Radio

## Modern Day  #### Fiber Optics

## Modern Day  #### Satellites

## Wireless A revolution in wireless communication began in the first decade of the 20th century with the pioneering developments in radio communications by Guglielmo Marconi.

 ### Guglielmo Marconi

 ### Jagdis Chandra Bose

Analog - Digital

FM Radio Bluetooth Headset

## Digital Communications - Resilience to noise and errors - Features → song information, volume adjustment - [Compose anything from "0" and "1"](http://sticksandstones.kstrom.com/appen.html) - [0 , 1] → "Symbols"

Message → Encode → Transmit → Channel → Receive → Decode → Message

## Signal - Smoke - Light (Electromagnetic Radiation) - Radio Waves (Electromagnetic Radiation) - Sound Waves

## Frequency  <audio src="440Hz.wav" controls="controls"></audio> <audio src="1kHz.wav" controls="controls"></audio>

## Transmission Medium physical medium that carries a information between the transmitter and the receiver

## Transmission Medium  #### copper wire for electro-magnetic signals

## Transmission Medium  ### free space for radio signals

## Transmission Medium  #### glass optical fibers for optical communications

## Channel Effects - Spreading → Linear, Spherical - Noise → conversations in a bar - Echo/Multi-path/Reverberation

## Spreading 

## Noise 

## Multipath 

## Multipath - Impulse Response 

## More Channel Effects! - Propagation Delay - Doppler Effect

## Propagation Delay time taken for a communication signal to travel from the source to the destination

## Propagation Delay | | | |-------------------------------|---------------| | speed of radio waves in air | 299792458 m/s | | speed of sound waves in air | 343 m/s | | speed of sound waves in water | 1500 m/s |

## Propagation Delay  one-way trip takes over **1.3s**

## Doppler Effect apparent change in the frequency of a signal caused by relative motion between the transmitter and the receiver.

Doppler Effect

Doppler Effect

## Demo [https://chinmay.audio/digi-comms-playground/channel](https://chinmay.audio/digi-comms-playground/channel)

## Preamble 

Modulation

## On/Off Keying - "Smoke/No-Smoke" - the presence of a signal for a specific duration represents a 1, else 0

## Frequency Shift Keying (FSK) - One frequency for 0, and another for 1 → BFSK

## Other Modulations - Frequency Hopping (FH-FSK) - Phase Shift Keying (PSK) - Orthogonal frequency-division multiplexing (OFDM) - Orthogonal signal-division multiplexing (OSDM)

## Demo [https://chinmay.audio/digi-comms-playground](https://chinmay.audio/digi-comms-playground)

## Bit Rate | | | |----------------------------|---------| | WiFi (802.11n) | 600Mbps | | Bluetooth | 2Mbps | | UW Acoustic Modems | 2kbps |

## Bit Rate - Bandwidth(Frequency) | | Bandwith | Center Frequency | Bit rate | |----------------------------|----------|------------------|--------- | | WiFi (802.11n) | 40MHz | 2.4GHz | 600Mbps | | Bluetooth | 1MHz | 2.4GHz | 2Mbps | | UW Acoustic Modems | 18kHz | 24kHz | 2Kbps |

## Range - Spreading - Noise - Frequency

## Range - Frequency | | Bandwith | Center Frequency | Bit rate | Range | |----------------------------|----------|------------------|-----------|-------| | WiFi (802.11n) | 40MHz | 2400MHz | 600Mbps | ~100m | | Bluetooth | 1MHz | 2400MHz | 2Mbps | ~10m | | UMTS (3G) | 15MHz | 800MHz | 42Mbps | ~50km | | UW Acoustic Modems | 18kHz | 24kHz | 2Kbps | ~3km |

## Localization 

# Questions ?