Noise in Communication Systems

Noise in Telecommunication Engineering

  • Definition of Noise

    • Noise refers to unwanted signals that are present in conjunction with the desired signal in a communication system.
    • It corrupts and distorts the desired signals.
    • Noise is a random signal and cannot be represented with a simple equation.
    • The presence of noise degrades the quality of the received signal at the receiver, affecting overall communication performance.

  • Effects of Noise

    • Noise degrades system performance for both analog and digital systems.
    • The receiver may fail to understand the original signal.
    • This impairs the functionality of the receiver.
    • Overall, noise reduces the efficiency of the communication system.

  • Types of Noise

    • Internal Noise: Noise generated within the components of the circuit.
    • Shot Noise: Caused by the random emission of electrons.
    • Partition Noise: Occurs when a circuit is divided into multiple paths.
    • Frequency Noise: Can occur at low (below a few kHz) or high frequencies.
    • Thermal Noise (Johnson Noise): Results from the random motion of charged particles in a conductor; increases with temperature.
    • External Noise: Noise coming from outside the circuit.
    • Atmospheric Noise: Generated by lightning and other atmospheric conditions.
    • Galactic Noise: Stemmed from disturbances outside the Earth's atmosphere.
    • Impulse Noise: Results from sudden changes in voltage and current.
    • Interference: Noise from nearby communication systems affecting signal quality.

  • Noise Measurement

    • Noise effects can be quantified using:
    • Signal to Noise Ratio (SNR): Measures the ratio of signal power (S) to noise power (N) and is typically expressed in dB.
    • Bit Error Rate (BER): Probability of error in digital transmissions.
    • Noise Factor (F) and Noise Temperature (Te): Used to characterize the noise performance of receivers.

  • Calculating Noise Power and Resistor Values

    • Noise power can be calculated with the formula involving noise resistance, Boltzmann's constant, absolute temperature, and bandwidth:
    • Noise Power: P_n = kTB
    • Noise Voltage: Vn = ext{sqrt}(PnR)

  • Decibels (dB)

    • Decibels measure the ratio of one signal against another, useful in telecommunications to express gains and losses.
    • dB can be negative (loss of signal) or zero (equal powers).

  • Examples of dB Calculations

    • Example 2.1: Calculate the noise power at room temperature (25 °C) for a bandwidth of 1 kHz.
    • Example 2.2: Determine equivalent noise resistance with given conditions of voltage, temperature, and bandwidth.
    • Additional examples illustrate how to compute dB values for power and voltage ratios, considering gains and losses in circuits.

  • System Level Decibels Analysis

    • In a communication system, signals pass through multiple stages, each affecting signal level and characteristics. For instance:
    • Pre Amplifier gain: +20 dB
    • Main Amplifier gain: +10 dB to +20 dB
    • Power Amplifier gain: +15 dB

  • Next Chapter: Chapter 3

    • Focus on Amplitude Modulation, outlining the importance and applications in telecommunication engineering.