72 articles
Adaptive equalization
Adaptive equalization is a signal processing method that automatically adjusts a digital filter's tap coefficients to remove intersymbol interference from unknown or time-varying communication channels.
BCJR algorithm
The BCJR algorithm (Bahl–Cocke–Jelinek–Raviv) computes the probability of each bit in decoded data; it was published at IBM in 1974 and became the decoding engine of turbo codes.
Bit-interleaved coded modulation with iterative decoding
Bit-interleaved coded modulation with iterative decoding (BICM-ID) is a bandwidth-efficient coded-modulation scheme, introduced by Xiaodong Li and James A. Ritcey at the University of Washington in 1997.
Blind equalization
Blind equalization is the recovery of a transmitted data signal from a distorted received signal without a known training sequence, relying instead on the signal's statistical properties; its principal algorithm is the Constant Modulus Algorithm.
Blind multiuser detection
Blind multiuser detection is a set of CDMA receiver techniques that suppress multiple-access interference without training sequences or knowledge of interferers, introduced by Honig, Madhow, and Verdú in 1995.
Carrier frequency offset estimation
Carrier frequency offset (CFO) estimation is the process by which a radio receiver measures the frequency difference between a received signal and its local oscillator.
Carrier recovery
Carrier recovery is the process by which a receiver estimates the frequency and phase of the transmitter's carrier to allow coherent signal demodulation.
Constant false alarm rate detection
Constant false alarm rate (CFAR) detection, first described in 1968 by H. M. Finn and R. S. Johnson, is a radar signal-processing technique that adapts the detection threshold to local noise, keeping false alarms constant.
Constant modulus algorithm
The constant modulus algorithm (CMA) is a blind adaptive equalization algorithm, proposed by Dominique Godard in 1980, that equalizes a channel without a known training sequence.
Correlation receiver
A correlation receiver is a digital-communication receiver that decides which known signal was sent by cross-correlating the received waveform with stored copies of each candidate, equivalent to a matched filter.
Costas loop
A Costas loop is a phase-locked loop circuit that recovers the carrier of a suppressed-carrier signal while demodulating its data, invented by John P. Costas in 1956.
Cyclic-prefixed single-carrier equalization
Cyclic-prefixed single-carrier equalization (SC-FDE) is a transmission technique in which single-carrier blocks sent with a cyclic prefix are equalized at the receiver by FFT-based frequency-domain processing.
Decision-directed equalization
Decision-directed equalization is an adaptive equalization mode in which a receiver replaces the training sequence with its own detected symbols as the reference for continued adaptation, letting the equalizer track the channel without repeated known data.
Decorrelating detector
The decorrelating detector is a linear multiuser detector for CDMA systems, developed by Ruxandra Lupas and Sergio Verdú, that removes multiple-access interference at the price of amplified noise.
Delay-locked loop
A delay-locked loop is a feedback control loop that keeps a local copy of a PRN code aligned with the incoming signal, the code-tracking loop of GPS receivers.
Digital down converter
A digital down converter (DDC) is a digital signal processing block that selects a frequency band from digitized samples, shifts it to baseband, and reduces the sample rate.
Diversity reception
Diversity reception is a wireless technique in which a receiver combines two or more independent copies of the same signal to reduce fading and improve reliability.
DOCSIS 3.1
DOCSIS 3.1 is a cable broadband specification released by CableLabs in 2013 that uses OFDM to deliver downstream speeds of up to 10 Gbps over existing hybrid fiber-coaxial networks.
Early–late gate synchronizer
The early–late gate synchronizer is a symbol-timing recovery method that compares samples taken before and after a pulse's peak to steer the receiver's sampling clock.
Equal-gain combining
Equal-gain combining (EGC) is a linear diversity-combining technique used in wireless receivers with multiple antennas, where branch signals are aligned in phase and summed with equal weights.
Extrinsic information transfer chart
An extrinsic information transfer (EXIT) chart is a graphical tool introduced by Stephan ten Brink in 1999 that predicts the convergence behavior of iterative decoding schemes such as turbo codes.
Four-level pulse-amplitude modulation
Four-level pulse-amplitude modulation (PAM4, also written PAM-4) encodes two bits per symbol using four amplitude levels, doubling throughput over NRZ at the same symbol rate.
Fractionally spaced equalization
Fractionally spaced equalization is an adaptive equalization technique whose filter taps are spaced at a fraction of the symbol period, sampling faster than the symbol rate.
Fractionally spaced equalizer
A fractionally spaced equalizer is an adaptive equalizer whose filter taps are spaced at a fraction of the symbol period, typically half, rather than a full symbol period.
Frame synchronization
Frame synchronization is the receiver task of locating where data frames begin and end in a received bit or symbol stream, so the payload can be correctly segmented and decoded.
Frequency-domain equalizer
A frequency-domain equalizer (FDE) is a receiver technique that compensates for intersymbol interference by equalizing each FFT-transformed block of samples, one coefficient per frequency bin.
Gardner timing recovery
Gardner timing recovery is a feedback method for recovering symbol timing in digital receivers, based on the detector Floyd Gardner proposed in 1986 using two samples per symbol.
Generalized selection combining
Generalized selection combining (GSC), or hybrid selection/maximum ratio combining, is a diversity technique in which wireless receivers combine the strongest subset of available signal branches, balancing performance and complexity.
Gold code
A Gold code is a binary pseudorandom sequence formed by exclusive-oring two shifted m-sequences from a preferred pair, proposed by Robert Gold in 1967 and widely used in CDMA.
I/Q imbalance compensation
I/Q imbalance compensation is the DSP and calibration techniques that correct amplitude and phase mismatches between the in-phase and quadrature branches of a modulator or demodulator.