Signal Transmission and Reception

Why it matters

Signal transmission and reception are fundamental to all communication systems, enabling the transfer of information over distances. Understanding these processes is crucial for designing efficient and reliable communication networks, which are integral to modern technology and connectivity.

Key ideas

• Signal Transmission: The process of sending information from a source to a destination through a communication channel. It involves modulation, amplification, and transmission of signals.
• Signal Reception: The process of receiving transmitted signals at the destination, involving demodulation, filtering, and amplification to retrieve the original information.
• Communication Channel: The medium through which the signal travels, which can be wired (like coaxial cables) or wireless (like radio waves).
• Modulation and Demodulation: Modulation is the process of varying a carrier signal to encode information, while demodulation is the reverse process at the receiver end.
• Noise and Interference: Unwanted disturbances that affect signal quality. Understanding noise is crucial for improving signal reception.

Formulas

The link budget below neglects feeder, mismatch, polarization and implementation losses; include these as extra dB subtractions when specified. G_t and G_r are antenna gains relative to isotropic antennas.

• P_r = P_t + G_t + G_r - L_p

  • P_r: Received power (dBm)
  • P_t: Transmitted power (dBm)
  • G_t: Transmitter gain (dBi)
  • G_r: Receiver gain (dBi)
  • L_p: Path loss (dB)

• SNR = P_signal / P_noise

  • SNR: Signal-to-noise ratio (dimensionless)
  • P_signal: Power of the signal (W)
  • P_noise: Power of the noise (W)

Worked example

Given:

• Transmitted power, P_t = 10 dBm
• Transmitter gain, G_t = 15 dBi
• Receiver gain, G_r = 10 dBi
• Path loss, L_p = 100 dB

Find: Received power, P_r

1. Use the formula: P_r = P_t + G_t + G_r - L_p
2. Substitute the given values: P_r = 10 + 15 + 10 - 100
3. Calculate: P_r = -65 dBm

Final Answer: -65 dBm

Common mistakes

• Confusing dBm and dB: dBm is an absolute power level, while dB is a relative measure.
• Ignoring the effects of noise and interference on signal quality.
• Miscalculating path loss, which can significantly affect received power.

For GATE EC

Questions often involve calculating received power, signal-to-noise ratio, and understanding the effects of noise and interference. Practice problems on modulation techniques and their impact on signal transmission and reception.

Quick check

1. What is the role of modulation in signal transmission?
2. How does path loss affect received power?
3. What is the difference between dBm and dB?

Answers: 1. To encode information onto a carrier signal. 2. It reduces the received power. 3. dBm is an absolute power level, dB is a relative measure.