Electronic communication links signals, channels and information reliability. PSC Computer Engineer questions can ask modulation types, bandwidth, noise, SNR, BER, multiplexing and error detection/correction methods. This note connects communication theory with network and electronics concepts.

Concept Teaching

Communication engineering asks three questions: how to represent information as a signal, how to transmit it through a noisy channel, and how to recover it with acceptable error. Modulation adapts signal to channel, multiplexing shares channel, and error control improves reliability.

Analog and Digital Communication

Analog communication sends continuously varying signals; digital communication sends discrete symbols/bits.

• Analog systems include AM and FM broadcast concepts.
• Digital systems represent information using bits and symbols.
• Digital communication is more noise-tolerant with regeneration and coding.
• Sampling converts analog signal to discrete-time signal.
• Quantization maps sample amplitudes to discrete levels.
• Line coding represents digital bits as physical waveforms.

Analog Modulation

Analog modulation varies one carrier parameter.

Digital Modulation

Digital modulation maps bits to signal symbols.

• ASK changes carrier amplitude according to bits.
• FSK changes carrier frequency according to bits.
• PSK changes carrier phase according to bits.
• QPSK sends two bits per symbol using four phase states.
• QAM combines amplitude and phase changes to increase spectral efficiency.
• Higher-order modulation carries more bits per symbol but needs better SNR.

Multiplexing

Multiplexing allows multiple signals/users to share one communication medium.

Noise, SNR and BER

Noise reduces the receiver’s ability to decide transmitted symbols correctly.

• Higher SNR generally reduces BER.
• SNR in dB = 10 log10(signal power/noise power).
• BER = error bits / total transmitted bits.
• Thermal noise, interference and attenuation affect channel quality.
• Regeneration in digital systems helps restore clean logic levels.
• Eye diagram concept shows timing/noise margin in digital communication.

Bandwidth and Channel Capacity

Capacity links bandwidth and SNR to maximum reliable data rate.

• Bandwidth is frequency range occupied or supported by channel.
• Nyquist criterion relates symbol rate to bandwidth for noiseless channel.
• Shannon capacity gives theoretical maximum data rate for noisy channel.
• Increasing bandwidth or SNR can increase capacity.
• Practical systems operate below theoretical capacity due to coding/modulation limits.

Error Detection and Correction

Error control is essential in digital systems.

• Parity bit detects odd number of bit errors in simple form.
• Checksum detects errors by arithmetic sum-style redundancy.
• CRC uses polynomial division and is strong for burst error detection.
• Hamming code can correct single-bit error and detect certain multiple-bit errors.
• Forward Error Correction adds redundancy so receiver can correct without retransmission.
• ARQ uses detection plus retransmission request.

Engineering Mechanism

• Source information is encoded into analog or digital signal.
• Modulator maps message onto carrier or symbols.
• Channel adds attenuation, distortion and noise.
• Receiver filters, amplifies and demodulates signal.
• Decision circuit estimates transmitted bits/symbols.
• Error control detects or corrects corrupted data.
• Performance is measured using SNR, BER, bandwidth and throughput.

Diagrams / Models To Draw

• Draw basic communication system: source, transmitter, channel, noise, receiver, destination.
• Draw AM/FM/PM concept waveforms.
• Draw ASK/FSK/PSK symbol difference.
• Draw FDM and TDM sharing diagrams.
• Draw CRC/error-control block: data, encoder, channel, decoder.

Formulas, Tables and Algorithms

• SNR = Signal power / Noise power.
• SNR(dB) = 10 log10(S/N).
• BER = number of erroneous bits / total transmitted bits.
• Shannon capacity: C = B log2(1 + S/N).
• Nyquist noiseless bit rate idea: maximum bit rate depends on bandwidth and signal levels.
• QPSK carries 2 bits per symbol.

Worked Example

If signal power is 100 mW and noise power is 1 mW, SNR = 100. In dB, SNR = 10 log10(100) = 20 dB. If 50 bits are wrong out of 1,000,000 transmitted bits, BER = 50/1,000,000 = 5 x 10^-5.

Subjective Answer Pattern

• Define communication system and modulation.
• Compare analog and digital modulation methods.
• Explain multiplexing techniques.
• Discuss noise, SNR and BER.
• Add capacity/bandwidth relation.
• Explain error detection and correction methods.
• Conclude with practical reliability tradeoff.

Common Engineering Mistakes

• Confusing SNR with BER.
• Saying modulation and multiplexing are the same.
• Using 20 log for power ratio instead of 10 log.
• Saying CRC corrects errors generally; CRC mainly detects.
• Ignoring bandwidth requirement of FM/high-order schemes.
• Assuming higher data rate always means lower BER.

MCQ Revision

• Which modulation varies amplitude?
• What does FDM share by?
• Write SNR in dB formula.
• What does BER measure?
• Which code can correct single-bit error?
• What is Shannon capacity formula?

Final Summary

• Communication systems transmit information through noisy channels.
• Modulation maps information onto carrier/symbols.
• Multiplexing shares channel resources.
• SNR and BER measure signal quality and digital reliability.
• Error control uses detection, correction or retransmission.
• Capacity depends on bandwidth and SNR.