Articles | Page 26 of 35

December 9, 2021 Wireless/SDR

What is the Difference between Analog, Digital and Hybrid Beamforming?

Beamforming is one of the most practical solutions to overcome higher path loss and atmospheric attenuation in mmWave bands. How it is implemented is a matter of great interest to RF industry due to the conflicting requirements of efficiency and flexibility. In a tradeoff between cost, size and complexity, analog beamforming is combined with digital beamforming to give rise to a hybrid solution, an architecture of choice in current 5G mmWave systems. Nevertheless, digital beamforming is inevitably the direction of future and it is only a matter of time before it will be used in 5G networks in high bands

November 29, 2021 DSP / Wireless/SDR

DFT-Precoded OFDM

One of the drawbacks of an OFDM waveform is its high Peak to Average Power Ratio (PAPR). This high PAPR arises from the fact that a set of $N$ QAM symbols are taken into time domain through an inverse Fourier Transform (iFFT) operation that basically generates a combination of complex sinusoids scaled by those symbols. Due to the variations between the symbol values and the sinusoids with different frequencies, the output waveform can have a large variance in amplitudes. This reduces the power amplifier efficiency that results in faster battery drainage in a mobile terminal. The effect on base station

A trellis for implementing Viterbi algorithm

May 23, 2022 Wireless/SDR

Maximum Likelihood Sequence Estimation (MLSE Equalizer)

In the discussion on a wireless channel, we saw that an increased amount of Inter-Symbol Interference (ISI) occurs for high data-rate wireless systems that impacts the system performance to a significant extent. The performance of a linear equalizer suffers from spectral nulls. A Decision Feedback Equalizer (DFE) recovers much of the performance losses due to ISI but it is susceptible to error propagation. In 1972, David Forney published a paper titled "Maximum-likelihood sequence estimation of digital sequences in the presence of intersymbol interference" in which he proposed the idea of sequence estimation. For this purpose, there was an implicit assumption

Channel hardening implies the channel flutucations due to small-scale fading smooth out

December 3, 2021 Wireless/SDR

On Massive MIMO, Channel Hardening and Favorable Propagation

Imagine an alien race looking at our planet from outside the solar system through a lens of time. They will notice one unmistakable direction. Our pursuit of MORE in everything. This tendency might be ingrained in the fundamental idea of life itself. To live is to grow. While our dreams for faster transportation face mechanical roadblocks from the laws of physics, technologies for faster communication are only bound by the laws of electromagnetics. Ever since we linked digital electronics to information exchange from one point to another without any physical medium, on-demand reception and transmission of data at any place

August 26, 2016 DSP

The Concept of Frequency

A wireless signal from one device to another travels through the use of electromagnetic waves propagated by an antenna. Electromagnetic waves have different frequencies and one can pick up a specific signal by tuning a radio Rx to a specific frequency. But what is a frequency anyway? Watch the video below for an interesting description of actual time domain samples and how to interpret their frequency domain representation. A Complex Sinusoid Consider a complex number $V$ in an $IQ$-plane. A complex number is defined as a pair of real numbers in $(x,y)$-plane similar to the vectors but with different arithmetic