There has been a continuous debate about harmful effects of Electromagnetic Radiations ever since they came into existence. Most of the research results suggest that there are no harmful effects, if the rules and regulations are followed. But there is a small body of research that suggests that there might be some harmful effects and more research needs to be carried out. This is particularly important now as 5G Wireless Technology is being rolled out around the world and it uses millimeter waves for which we have limited data. Also, 5G would be using much smaller cells meaning that base stations would be closer to human beings.
Continue reading 5G Millimeter Waves: Are They Really Harmful
previously discussed Block Codes and Convolutional Codes and their coding and
decoding techniques particularly syndrome-based decoding and Viterbi decoding.
Now we discuss an advanced form of Block Codes known as Low Density Parity
Check (LDPC) codes. These codes were first proposed by Robert Gallager in 1960
but they did not get immediate recognition as they were quite cumbersome to
code and decode. But in 1995 the interest in these codes was revived, after
discovery of Turbo Codes. Both these codes achieve the Shannon Limit and have
been adopted in many wireless communication systems including 5G.
Continue reading Low Density Parity Check Codes
In the previous post we discussed
block codes and their decoding mechanisms. It was observed that with syndrome-based
decoding there is only a minimal advantage over the no coding case. With
Maximal Likelihood (ML) decoding there is significant improvement in
performance but computational complexity increases exponentially with length of
the code and alphabet size. This is where convolutional codes come to the
Continue reading Convolutional Codes and Viterbi Decoding
previously discussed modulation and demodulation in wireless communications,
now we turn our attention to channel coding. We know that in a wireless channel
the transmitted information gets corrupted due to noise and fading and we get
what are called bit errors. One way to overcome this problem is to transmit the
same information multiple times. In coding terminology this is called a
repetition code. But this is not recommended as it results in reduced data rate
and reduced spectral efficiency.
Continue reading Hamming Codes
Phase Lock Loops (PLLs) are an important
component of communication systems, where they are used for carrier phase and
frequency synchronization. They are also used in test and measurement equipment
such as in Signal Generators and Vector Network Analyzers (VNAs) for frequency
synthesis. Although not discussed here in detail but PLLs are also quite adept
at generating multiples of a base frequency e.g. if you have a reference signal
at 10MHz then a PLL can be used to generate a 100MHz signal (X=10) or even a
1GHz signal (X=100). In fact, you can also divide the frequency to get low
frequency signals. In the first case the feedback frequency is divided by X and
in the second case the reference or input frequency is divided by X.
Continue reading Phase Lock Loop – Explained
As previously discussed, finding the
frequency of a complex sinusoid embedded in noise is a classical problem in
Signal Processing. The problem is compounded by the fact that number of samples
available is usually quite small. So far, we have discussed Zero Crossing, FFT,
MUSIC and ESPRIT methods of frequency estimation. Zero Crossing method is
simplest of the above four but it can detect only one sinusoid at a time. Advantage
of Zero Crossing method is that it is computationally not that complex. It does
not require complex matrix manipulations as some of the other methods do.
Continue reading KAY’s Single Frequency Estimator