Fundamentals of Data and Signals

Data vs. Signals

  • Data: raw facts/meaningful content (text, image, numbers, audio, video)
  • Signal: physical form (electrical, optical, electromagnetic) that carries data across a medium
  • Data is the message; signal is the carrier

Analog vs. Digital

  • Analog: continuous values; infinite possibilities between min & max
  • Digital: discrete values; typically binary 0,1{0,1}
  • Both data and signals can be analog or digital → 4 possible pairings

Four Data–Signal Combinations

  • Analog data → Analog signal: amplitude/frequency modulation (AM, FM)
  • Digital data → Digital (square-wave) signal: encoding schemes (NRZ-L, NRZI, Manchester, etc.)
  • Digital data → Analog (discrete) signal: modulation (ASK, FSK, PSK; e.g., modem)
  • Analog data → Digital signal: digitization (PCM, Delta; codec)

Signal Fundamentals

  • Amplitude: height above/below reference (volts/amps/watts)
  • Frequency ff: cycles per second (Hz); Period T=1fT = \frac{1}{f}
  • Phase: relative position within one cycle (degrees/radians)
  • Spectrum: range f<em>min→f</em>maxf<em>{min} \rightarrow f</em>{max}
  • Bandwidth BW=f<em>max−f</em>minBW = f<em>{max} - f</em>{min} (e.g., telephone voice 300 Hz−3400 Hz⇒3100 Hz300\,\text{Hz} - 3400\,\text{Hz} \Rightarrow 3100\,\text{Hz})

Attenuation & Gain

  • Signals lose strength while travelling → attenuation (dB)
  • dB=10log⁡<em>10(P</em>outPin)dB = 10 \log<em>{10} \left( \frac{P</em>{out}}{P_{in}} \right)
  • Amplification = negative attenuation (gain)

Noise (Interference Sources)

  • Thermal (Johnson/white noise): random electron motion
  • Intermodulation: mixing of multiple signals in non-linear circuits
  • Crosstalk: leakage between adjacent channels/cables
  • Impulse: sudden spikes (lightning, switching)
  • Atmospheric: natural phenomena (sunspots, storms)
  • Echo: reflections from impedance mismatch/long lines

Modulation (Analog Data → Analog Signal)

  • Vary carrier amplitude (AM), frequency (FM), or phase to embed data
  • Example: AM radio combines voice waveform with carrier wave

Digital Encoding (Digital Data → Digital Signal)

  • Map bits to voltage levels or transitions
    • NRZ-L: level high for 1, low for 0 (or inverse)
    • NRZI, Manchester, Differential Manchester, Bipolar-AMI, 4B/5B: enhance synchronization & error handling

Key Takeaways

  • Understand distinctions: data vs. signal; analog vs. digital
  • Core signal parameters: amplitude, frequency, phase, bandwidth
  • Conversion techniques allow any data type over any medium
  • Noise & attenuation limit performance; encoding/modulation mitigate issues