Data Signal Combinations

Prelim topic

Transmit Analog Data with Analog Signals

• To send analog data over an analog medium, you MODULATE the data onto a set of analog carrier signals

• This MODULATION allows multiple different channels to coexist simultaneously at different frequencies.

• Ex: AM/FM broadcast radio and older broadcast television are classic examples.

Transmitting Digital Data with Digital Signals

• This process uses digital encoding schemes to convert digital data (1s and 0s) into digital signal voltage pulses

• Rely on encoding techniques like:
  - NRZ-L, NRZI, Manchester, Differential Manchester, Bipolar AMI, and 4B/5B

• Because these signals degrade rapidly over long distances, these methods are USED in LANs

NZR-L (Nonreturn to zero-level)

• This digital encoding scheme transmits a binary 1 as zero voltage and a binary 0 as a positive voltage
  - 0 → + V
  - 1 → - V

• Is susceptible to synchronization loss

NZRI (Nonreturn to zero inverted)

• This digital encoding scheme creates a voltage change at the start of a 1 and no voltage change at the start of a 0
  - 0 → No V change
  - 1 → V change

• Better synchronization and improved reliability over NZR-L

Differential Manchester

• In this digital encoding scheme, every single bit has at least one significant voltage change in the middle of the bit window

• Ensures constant synchronization between the sender and receiver

Bipolar-AMI

• This digital encoding scheme uses 3 unique voltage levels: positive, zero, and negative. A binary 0 is a zero voltage, while a binary 1 alternates back and forth between positive and negative voltages.

4B/5B Encoding

• This digital encoding scheme translates 4 bits of data into a specific 5-bit quantity. This design ensures that no 5-bit code contains more than 2 consecutive zeroes

• Once converted, the new code is transmitted using an NZRI encoded signal

Transmitting Digital Data with Analog Signals

• To transmit digital data over analog mediums, the data must undergo SHIFT KEYING (modulation)

• Ex: Amplitude Shift Keying, Frequency Shift Keying, Phase Shift Keying

• Dial-up internet, DSL, and cable modems historically used these techniques to send digital traffic over traditional analog telephone or coaxial cable lines

Analog Shift Keying (ASK)

• The simplest modulation technique where one specific amplitude encodes a binary 0, while a different amplitude encodes a binary 1, keeping frequency and phase constant

Frequency Shift Keying (FSK)

• This technique modulates by changing the frequency of the carrier wave. One specific frequency modulates a 0, and another distinct frequency encodes a 1.

• This modulation technique is generally less susceptible to noise than ASK

Phase Shift Keying (PSK)

• This modulates by having one phase change representing a 0, while a different phase change represents a 1.

Transmitting Analog Data with Digital Signals

• To safely send analog data across modern digital infrastructure, the continuous analog waveform must be digitized

• 2 Techniques: Pulse Code Modulation and Delta Modulation

• Telephone networks use these techniques to digitize the human voice at the source, allowing it to be reliably routed through digital fiber-optic networks across the globe without degradation.

Pulse Code Modulation (PCM)

• This modulation technique works by taking periodic “snapshots” (samples) of a continuous analog waveform at regular intervals

• These physical voltage snapshots are then translated into standard binary values (quantization)

• Taking more snapshots in a given time frame, or utilizing more quantization levels (more bits per sample) creates a significantly higher-resolution digital representation.

Delta Modulation

• This modulation offers a simpler digitization technique that tracks the continuous analog waveform by logging relative changes rather than absolute values

• It uses a single bit for tracking: a binary 1 signifies a rise in voltage from the previous sample, and a binary 0 signifies a drop in voltage

ASCII (American Standard Code for Information Interchange)

• A widely used 7-bit (or 8-bit extended) code supporting foundational English characters and control symbols

EBCDIC (Extended Binary Coded Decimal Interchange Code)

• An 8-bit code primarily used on IBM mainframe and midrange computer systems for enterprise processing

Unicode

• A massive encoding standard that assigns a unique number to every character across hundreds of different languages and scripts

• Every basic character in this utilize 16 bits = allowing it to support a massive number of diverse character sets.

• Ex:
  - T equals 0000 0000 0101 0100
  - r equals 0000 0000 0111 0010
  - a equals 0000 0000 0110 0001