Signal Processing for Communication Systems
Mathuranathan In the previous article, the architecture of an OFDM transmitter was described using sinusoidal components. Generally, an OFDM signal can be represented as \(s(t)\) = symbols mapped to chosen constellation (BPSK/QPSK/QAM etc..,) \(f_n\) = orthogonal frequency This equation can be thought of as an IFFT process ( Inverse Fast Fourier Transform). The Fourier transform breaks a … Read more
Article moved to new pages The article has been consolidated into these following pages. Please refer these links. If you are looking for Matlab code refer this ebook : Simulation of Digital Communication Systems by Mathuranathan Viswanathan (1) Introduction to OFDM – Orthogonal Frequency Division Multiplexing (2) An OFDM Communication System – Implementation Details (3) … Read more
In modulations, information is mapped on to changes in frequency, phase or amplitude (or a combination of them) of a carrier signal. Multiplexing deals with allocation/accommodation of users in a given bandwidth (i.e. it deals with allocation of available resource).OFDM is a combination of modulation and multiplexing. In this technique, the given resource (bandwidth) is … Read more
The phenomenon of Rayleigh Flat fading and its simulation using Clarke’s model and Young’s model were discussed in the previous posts. The performance (Eb/N0 Vs BER) of BPSK modulation (with coherent detection) over Rayleigh Fading channel and its comparison over AWGN channel is discussed in this post. We first investigate the non-coherent detection of BPSK … Read more
A multipath fading channel can be modeled as a FIR (Finite Impulse Response) filter with the following impulse response. $$ h( \tau ; t ) = h_{0}(t) \delta ( \tau – \tau_{0}(t)) + h_{1}(t) \delta ( \tau – \tau_{1}(t)) + . . . + h_{L-1}(t) \delta ( \tau – \tau_{L-1}(t)) $$ where h(τ,t) is the … Read more
Modified Duobinary Signaling is an extension of duobinary signaling. It has the advantage of zero PSD at low frequencies (especially at DC ) that is suitable for channels with poor DC response. It correlates two symbols that are 2T time instants apart, whereas in duobinary signaling, symbols that are 1T apart are correlated. The general … Read more
The condition for zero ISI (Inter Symbol Interference) is which states that when sampling a particular symbol (at time instant nT=0), the effect of all other symbols on the current sampled symbol is zero. As discussed in the previous article, one of the practical ways to mitigate ISI is to use partial response signaling technique … Read more
The following is a function to generate a Walsh Hadamard Matrix of given codeword size. The codeword size has to be a power of 2. function [H]=generateHadamardMatrix(codeSize) %[H]=generateHadamardMatrix(codeSize); % Function to generate Walsh-Hadamard Matrix where “codeSize” is the code % length of walsh code. The first matrix gives us two codes; 00, 01. The second … Read more
IS-95 CDMA Standard uses three types of codes namely 1) Long code 2) Short code and 3) Walsh Hadamard codes. Long Code: Long codes run at 1.2288 Mb/s and are 42 bits longs (created using a 42 bits LFSR register). It takes approx 41.2 days to repeat a long code at this rate. It is … Read more
Spectral leakage due to FFT is caused by: mismatch between desired tone and chosen frequency resolution, time limiting an observation. Understand the concept using hands-on examples. Limits of frequency domain studies Frequency Transform is used to study a signal’s frequency domain characteristics. When using FFT to study the frequency domain characteristics of a signal, there … Read more