Digital Communication
71 articles • Complete guide
Get ready for 5G, IoT & wireless with ASK, QAM, error correction, MIMO, spread spectrum, and channel coding.
Live constellation diagrams and BER curves make modern communication crystal clear. Interactive modulators, equalizer & constellation visualizers, virtual labs, quizzes coming soon.
Curriculum
Select an article below to start learning
Digital Modulation
ASK, FSK, PSK, QAM, QPSK, constellation diagrams
Digital Modulation Overview
Coherent vs non-coherent, power vs bandwidth efficiency.
ASK Modulation
Amplitude shift keying, OOK, bandwidth, probability of error.
FSK Modulation
Frequency shift keying, BFSK, orthogonality, bandwidth.
BPSK Modulation
Binary phase shift keying, constellation, BER = Q(sqrt(2Eb/N0)).
QPSK Modulation
Quadrature PSK, 2 bits/symbol, bandwidth efficiency.
QAM Basics
Quadrature Amplitude Modulation, 16-QAM, 64-QAM constellations.
Constellation Diagrams
Signal space representation, Euclidean distance.
M-ary Modulation
M-PSK, M-QAM, symbol rate vs bit rate, trade-offs.
MSK Modulation
Minimum shift keying, CPFSK, constant envelope.
GMSK Modulation
Gaussian MSK, pulse shaping, GSM standard usage.
OFDM Basics
Orthogonal Frequency Division Multiplexing, subcarriers.
Differential PSK
DPSK modulation and demodulation, non-coherent advantage.
OQPSK
Offset QPSK, avoiding 180 degree phase jumps.
Power Spectral Density
PSD of digital modulation schemes.
Baseband Transmission
Line coding, ISI, eye diagrams, equalizers
Baseband Transmission Basics
Digital signals over low-pass channels, limitations.
NRZ Line Coding
Non-return to zero, unipolar, polar, bipolar variants.
RZ Line Coding
Return to zero, wider bandwidth, self-clocking properties.
Manchester Encoding
Biphase coding, self-clocking, IEEE 802.3 Ethernet standard.
AMI Line Coding
Alternate mark inversion, pseudo-ternary, zero DC component.
HDB3 and B8ZS
High density bipolar 3, scrambling techniques.
Inter Symbol Interference
ISI definition, channel bandwidth limits, pulse spreading.
Nyquist Criterion
Pulse shaping, raised cosine filter, roll-off factor.
Eye Diagram
ISI visualization, eye opening, noise margin, jitter analysis.
Matched Filter
Maximizes SNR at sampling instant, impulse response h(t) = s(T-t).
Equalization Basics
Zero forcing, MMSE equalizers, adaptive equalization overview.
Correlative Coding
Duobinary signaling, controlled ISI.
Scrambling Techniques
Ensuring transition density for clock recovery.
Information Theory
Entropy, mutual information, channel capacity
Information Theory Basics
Entropy, information content I = -log2(P), Shannon.
Source Entropy
Entropy H = -sum P*log2(P), maximum entropy conditions.
Joint and Conditional Entropy
H(X,Y), H(Y|X), chain rule for entropy.
Mutual Information
I(X;Y) = H(X) - H(X|Y), channel relationship.
Channel Capacity
Shannon capacity C = B*log2(1+SNR).
Shannon Limit
Implications of Shannon-Hartley theorem.
BSC Channel
Binary Symmetric Channel, capacity calculation.
BEC Channel
Binary Erasure Channel properties.
Differential Entropy
Entropy of continuous random variables.
Source Coding
Huffman, Shannon-Fano, LZW, arithmetic coding
Source Coding Theorem
Shannon first theorem, entropy rate, limits of compression.
Huffman Coding
Variable length codes, optimal prefix codes, algorithm construction.
Shannon-Fano Coding
Top-down code assignment, comparison with Huffman efficiency.
Lempel-Ziv Coding
Dictionary based, LZW algorithm, lossless compression.
Run Length Encoding
Compression of repetitive data, simple algorithm.
Arithmetic Coding
Concept of coding entire message as a number.
Lossy vs Lossless
Subjective fidelity criteria, JPEG/MPEG examples.
Error Control
Hamming, cyclic, convolutional, turbo codes
Error Control Basics
Detection vs correction, ARQ vs FEC, code rate.
Linear Block Codes
Generator matrix G, parity check matrix H, syndrome decoding.
Hamming Code
(7,4) Hamming code, single error correction.
Cyclic Codes
Polynomial representation, systematic generation, CRC.
Convolutional Codes
Encoder structure, constraint length, code rate.
Viterbi Decoding
Maximum likelihood decoding algorithm, path metric.
Turbo Codes
Parallel concatenated codes, iterative decoding.
LDPC Codes
Low Density Parity Check codes, near-Shannon limit performance.
Trellis Coded Modulation
Combined coding and modulation, Ungerboeck optimization.
Interleaving
Handling burst errors, block vs convolutional interleavers.
BCH Codes
Bose-Chaudhuri-Hocquenghem codes overview.
Reed-Solomon Codes
Non-binary cyclic codes, application in storage.
Spread Spectrum
FHSS, DSSS, CDMA, PN sequences
Spread Spectrum Intro
Processing gain, anti-jamming, low probability of intercept.
PN Sequences
Maximal length sequences, m-sequences, autocorrelation properties.
Direct Sequence Spread Spectrum
DSSS, chip rate, spreading code, CDMA basis.
Frequency Hopping Spread Spectrum
FHSS, slow vs fast hopping, Bluetooth application.
Rake Receiver
Multipath diversity combining in CDMA.
Synchronization
Code acquisition and tracking.
Multiple Access
FDMA, TDMA, CDMA, OFDMA, random access
Multiple Access Techniques
FDMA, TDMA, CDMA overview.
CDMA Details
Code Division Multiple Access, orthogonality, near-far problem.
OFDMA
Orthogonal Frequency Division Multiple Access, 4G/5G usage.
SDMA
Space Division Multiple Access, smart antennas.
CSMA/CD and CA
Carrier Sense Multiple Access basics.
Other Topics
MIMO, beamforming, advanced techniques
MIMO Technology
Multiple Input Multiple Output, spatial multiplexing.
Beamforming
Directional transmission, antenna arrays.
5G New Radio
Key technologies in 5G standards.
Software Defined Radio
SDR architecture, reconfigurability.
Cognitive Radio
Spectrum sensing, dynamic spectrum access.