Feedback AGC block diagram

How Automatic Gain Control (AGC) Works

Alfred North Whitehead said, "Civilization advances by extending the number of important operations which we can perform without thinking of them." In today’s world, it is easy to take no notice of the level of process automation integrated into our lives. To have an idea of how things were in the early days, signal processing technology to sort out the radar picture on a map was not available and only a dot or a line could be generated on the screen representing a detected target. A radar operator had to stare at a screen for their whole shift to raise

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DDS waveform and spectrum after dithering

Direct Digital Synthesizer (DDS)

A Direct Digital Synthesizer (DDS) is an integral part of all modern communication systems. It is a technique to produce a desired waveform, usually a sinusoid, through employing digital signal processing algorithms. As an example, in the transmitter (Tx) of a digital communication system, a Local Oscillator (LO) is required to generate a carrier sinusoid that upconverts the modulated signal to its allocated frequency in the spectrum. On the receive (Rx) side, another local oscillator downconverts this high frequency signal to baseband for further processing. Such a process is shown in the Tx and Rx block diagrams of a Quadrature

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A discrete-time FM demodulator block diagram with atan2 and derivative filter

Frequency Modulation (FM) and Demodulation Using DSP Techniques

Frequency Modulation (FM) is as old as the history of wireless communications itself. The past few decades saw the rise of digital signal processing in all spheres of life that pervaded even the implementation of analog modulation schemes. Today many of the FM systems are built using discrete-time techniques instead of the conventional circuitry as described below. Frequency Modulation In digital communications, data is sent through altering a characteristic of an electromagnetic wave such as amplitude, frequency or phase in discrete steps (e.g., $M$ number of levels). Such systems are known as Amplitude Shift Keying (ASK), Frequency Shift Keying (FSK)

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Working of an Early-Late TED

On the Link Between Gardner Timing Error Detector and Early-Late Timing Error Detector

This post is written on an advanced topic mainly for practitioners and researchers in the design of wireless systems. For learning about wireless communication systems from a DSP perspective (the idea behind SDRs), I recommend you have a look at my book. F. M. Gardner described his well known Timing Error Detector (TED) — known as Gardner TED — in his often cited article [1]. Gardner was a pioneer in the area of synchronization and Phase Locked Loops (PLL). Later, M. Oerder (a student of Heinrich Meyr) derived this scheme from the maximum likelihood principle in [2]. Heinrich Meyr is

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Output from the Costas Loop block after phase convergence

Costas Loop for Carrier Phase Synchronization

Costas loop is a carrier phase synchronization solution devised by John Costas at General Electric Company in 1956 [1]. It had an enormous impact on modem signal processing in general and carrier synchronization in particular. At that time, it was customary to send a pilot tone for carrier synchronization along with the data signal which consumed a significant amount of power. Costas was one of the earliest scientists to demonstrate that the carrier phase could be reliably recovered from the Rx signal without the need of a pilot tone. In words of Costas, "It is unfortunate that many engineers tend

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