<<<All Things Wireless>>>
LDPC 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.
Read moreConvolutional codes when decoded using Viterbi Algorithm (VA) provide significant gains over the no coding case. The performance is further improved by using soft metrics instead of hard metrics (Euclidean distance is used in this case instead of Hamming distance). In fact, the performance is even better than brute force ML decoded Hamming (7,4) Code discussed in the previous section.
Read moreIn this post we discuss Hamming (7,4) Code which transmits 4 information bits for every 7 bits transmitted, resulting in a code rate of 4/7. The 3 additional bits are called parity bits and these protect against single bit errors in the channel. This is called a systematic code since after performing the coding operation the information bits are preserved, parity bits are only appended to the information bits.
Read morePhase 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.
Read moreThe basic concept of Kay’s estimator is quite simple. It finds the phase advanced from one sample to the next and this gives us the frequency. Averaging is performed over the time window to get more accurate results. Averaging can be performed using uniform weighting or a weighting function defined by Kay in [1].
Read moreAs discussed in previous posts it is frequently required in communications and signal processing to estimate the frequency of a signal embedded in noise and interference. The problem becomes more complicated when the number of observations (samples) is quite limited. Typically, the resolution in the frequency domain is inversely proportional to the window size in the time domain.
Read moreIn this post we present the simplest method of frequency estimation that is called the Zero Crossing (ZC) method. Since a sine wave crosses the x-axis twice during each cycle, we can simply count the number of crossings and divide it by two and again divide it by the observation window size, giving us the frequency in Hertz.
Read moreCarrier phase or frequency synchronization is a common problem in wireless communication systems. These two problems are interrelated as instantaneous frequency is just the rate of change of phase.
Read moreA relatively new technique to improve the spectral efficiency and the energy efficiency of wireless communication system is called Index Modulation (IM). There are two main types of IM, one that uses multiple transmit antennas (Spatial Modulation) and one that uses multiple carriers (OFDM-IM). We will focus here on Spatial Modulation also known as SM.
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