A figurative example of IQ imbalance depicting potential sources of mismatches
Wireless and SDR

Direct Conversion (Zero-IF) Receiver

The frontend of the transceiver plays a crucial role in determining the ultimate system performance. In a previous article, we described how a superheterodyne architecture helps in enhancing the selectivity and sensitivity of the receiver. Some of the main issues with a superheterydone receiver are the image frequency and a large form factor due to multiple conversion stages. Today we discuss a direct conversion architecture, also known as zero-IF and homodyne. Recall from the concept of frequency domain that a real sinusoid at the Local Oscillator (LO) output has two impulses in its spectrum, one at a positive frequency $+F_{\text{LO}}$

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DDS waveform and spectrum after dithering
DSP / Wireless and SDR

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
DSP / Wireless and SDR

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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Spectrum of the cascade of CIC filters with a wideband compensation filter for rate change factor 10, unit differential delay and 4 stages
DSP / Wireless and SDR

Cascaded Integrator Comb (CIC) Filters – A Staircase of DSP

In olden days, people used to have lots of kids. A famous Urdu satirist once wrote: "It has been observed that the last kid is usually the most mischievous of them all. Therefore, there should be no last kid in a family!" I remembered this line today because I have observed that starting a write-up is the most difficult task of them all. Therefore, there is no introductory paragraph in this article. Suffice it to say that this is the only topic I have found that takes you from a very small first step (just two additions) to really advanced

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Cell Averaging CFAR (CA-CFAR)
Radar and Localization / Wireless and SDR

Adaptive Thresholding in Radar Detection Using Constant False Alarm Rate (CFAR) Techniques

Target detection is one of the most important and challenging tasks in a radar system. After transmitting a pulse, the radar receives echoed or reflected signals and begins processing them. A fundamental difficulty is that the received signal may originate from a genuine target, from static objects such as terrain or buildings, or from various noise and interference sources. The primary objective of radar signal processing is therefore to reliably distinguish true targets from these unwanted returns and to maximize the probability of detection. Background Figure 1 illustrates a typical radar detection chain. In a conventional RADAR receiver, the incoming

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