Maximum-length sequences (m-sequences) — LFSR properties and autocorrelation
m-sequences from linear feedback shift registers: period 2ⁿ−1, two-level autocorrelation, and their role as parents of Gold codes.
Spread Spectrum
Gold code generator — preferred pairs, correlation, and CDMA use
How Gold codes are built from preferred m-sequence pairs, their three-valued cross-correlation, and why they are used in CDMA/GNSS spreading.
Walsh Hadamard Code – Matlab Simulation
Walsh–Hadamard codes of length \(N = 2^k\) are the rows of the Sylvester Hadamard matrix. Mapped to \(\pm 1\) they are mutually orthogonal. The listing builds that matrix, checks the Gram matrix, and plots the periodic cross-correlation of the first row against the others. Python Matlab The original Matlab helper is unchanged in spirit. bitand(codeSize,codeSize-1)==0 … Read more
Codes used in CDMA
IS-95 uses three families of sequences at once: a long code for scrambling, a short code for cell identity and quadrature spreading, and a set of Walsh–Hadamard codes for the forward channels under one base station. Long code The long code is an m-sequence from a 42-stage LFSR, clocked at the chip rate 1.2288 Mc/s. … Read more
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