FFT spectral leakage — causes, scalloping, and how windows help
Why FFT bins leak when tones miss bin centers, what scalloping loss is, and how windowing + ENBW trade leakage against noise bandwidth.
Understand Moving Average Filter with Python & Matlab
This post contains interactive python code which you can execute in the browser itself. The moving average filter is a simple Low Pass FIR (Finite Impulse Response) filter commonly used for smoothing an array of sampled data/signal. It takes \(L\) samples of input at a time and takes the average of those \(L\)-samples and produces … Read more
Random Interleaver
Random Interleaver: The Random Interleaver rearranges the elements of its input vector using a random permutation. The incoming data is rearranged using a series of generated permuter indices. A permuter is essentially a device that generates pseudo-random permutation of given memory addresses. The data is arranged according to the pseudo-random order of memory addresses. The … Read more
Block Interleaver Design for RS codes
Reed-Solomon (RS) codes are powerhouse error-correcting tools, but they have a specific Achilles’ heel: if a burst inside one codeword exceeds the correction radius \(t = \lfloor (n-k)/2 \rfloor\), a bounded-distance decoder fails on that codeword. Block Interleaving is the mathematical bridge that allows RS codes to survive massive, contiguous bursts by spreading the damage … Read more
Interleavers and deinterleavers
Random errors and burst errors An interleaver is there because of the way errors arrive, not because of the code itself. Two patterns matter. Random errors. Error locations are independent. A channel that does this has no memory: an error in one position says nothing about the next. Burst errors. Errors arrive in runs. A … Read more
QPSK modulation and demodulation — two bits per symbol and the shared BPSK BER curve
QPSK maps two bits per symbol on four phases; how modulation/demodulation work, constellation geometry, and links to BER tools and BPSK/M-PSK.
Spread Spectrum Communications – Introduction
Spread spectrum system, originally developed for military applications, is extremely resistant to unauthorized detection, jamming, interference and noise. It converts a narrowband signal to wideband signal by the means of spreading. The original 802.11 and 802.11b used direct-sequence spreading. From 802.11a onward, Wi-Fi is OFDM. Bluetooth Classic hops; Bluetooth Low Energy hops as well, on … Read more
Demystifying Error Correction: Convolutional Codes and the Viterbi Algorithm
Convolutional Encoding Unlike block codes (like Reed-Solomon), Convolutional Codes do not have a fixed block size. Instead, they process a continuous stream of bits. The output at any given time depends not only on the current input bit but also on the previous $K-1$ bits, where $K$ is the Constraint Length.+1. Convolutional codes are a … Read more
Performance comparison of digital modulation techniques — BER trade-offs at a glance
Digital Modulations 101 — 5 lessons (same on every page in this path) 1. BPSK → 2. QPSK → 3. M-PSK sim (you are here) → 4. QAM sim → 5. EVM Tools: BER vs Eb/N0 · EVM → SNR · Eb/N0 ↔ SNR Side reading for Digital Modulations 101. Use this comparison after QPSK … Read more
BPSK modulation and demodulation — constellation, decision rule, and BER intuition
BPSK maps bits to opposite phases; coherent demodulation, decision rule, and links to the Q-function BER formula and interactive calculator.