Frequency response of a moving average filter
DSP

Moving Average Filter

The most commonly used filter in DSP applications is a moving average filter. In today’s world with extremely fast clock speeds of the microprocessors, it seems strange that an application would require simple operations. But that is exactly the case with most applications in embedded systems that run on limited battery power and consequently host small microcontrollers. For noise reduction, it can be implemented with a few adders and delay elements. For lowpass filtering, an excellent frequency domain response and substantial suppression of stopband sidelobes are less important than having a basic filtering functionality, which is where a moving average

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OFDM slices the spectrum just like a bread
Wireless and SDR

A Beginner’s Guide to OFDM

In the recent past, high data rate wireless communications is often considered synonymous to an Orthogonal Frequency Division Multiplexing (OFDM) system. OFDM is a special case of multi-carrier communication as opposed to a conventional single-carrier system.  The concepts on which OFDM is based are so simple that almost everyone in the wireless community is a technical expert in this subject. However, I have always felt an absence of a really simple guide on how OFDM works which can prove useful for technical persons not wanting to deal with too much technicalities, such as DSP experts outside communications, computer programmers, ham

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Multipath components with large Doppler shifts compared to the signal bandwidth
Wireless and SDR

Slow and Fast Fading in Wireless Channels

We discussed the idea of fading in wireless channels in a previous article. To understand different types of fading in the context of time variations, refer to the figure below that shows a multipath channel. Slow Fading A slow motion scenario is illustrated in the figure below where three multipath components are arriving with Doppler shifts $F_{D,i}$ from the carrier frequency. In this scenario, the magnitudes of $F_{D,i}$ are small and hence observe very little spreading of the cumulative spectrum. This can be understood by recalling that when two sinusoids with two different frequencies $F_1$ and $F_2$ are added, the

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A discrete-time PLL with a PI loop filter and an NCO consisting of a phase accumulator and a Look-Up Table (LUT)
Wireless and SDR

Phase Locked Loop (PLL) in a Software Defined Radio (SDR)

IBM Watson and Google DeepMind are the most complex computers that, some believe, will try to run the world in a distant future. A PLL on the other hand is the simplest computer that actually runs so much of the world as a fundamental component of intelligent electronic circuits. The PLL was invented by the French engineer Henri de Bellescize in 1932 when he published his first implementation in the French journal L’Onde Electrique. A Phase Locked Loop (PLL) is a device used to synchronize a periodic waveform with a reference periodic waveform. In essence, it is an automatic control

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Future predictions
Machine Learning

Machine Learning – The Big Picture

Machine learning is probably the defining technology of the past decade. As with all walks of life, it is playing an increasingly significant role in existing and future wireless networks. In this article, we explore the big picture of this exciting field. Nature vs Man Humans have always been interested in the workings of a mind, replicated by machines in many science fiction stories. During their investigations on Artificial Intelligence (AI, of which machine learning is a subset), many scientists observed that the machines need not copy the exact brain but a functional level performance is good enough that can

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