Introduction to OFDM – orthogonal Frequency division multiplexing – part 4 – Cyclic Prefix

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[ratings] Consider a non-ideal channel h(t)≠δ(t), that causes delay dispersion. Delay dispersion manifests itself as Inter Symbol Interference (ISI)on each subcarrier channel due to pulse overlapping. It will also cause ICC (Inter Carrier Interference ) due to the non-orthogonality of the received signal. Adding cyclic prefix to each OFDM symbol mitigates the problems of ISI … Read more

Introduction to OFDM – orthogonal Frequency division multiplexing – part 3

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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

Introduction to OFDM – orthogonal Frequency division multiplexing – part 2

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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

Introduction to OFDM – orthogonal Frequency division multiplexing

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[ratings] 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) … Read more

Eb/N0 Vs BER for BPSK over Rayleigh Channel and AWGN Channel

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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

Simulation of Rayleigh Fading ( Clarke’s Model – sum of sinusoids method)

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[ratings] 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 … Read more

Correlative Coding – Modified Duobinary Signaling

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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

Correlative coding – Duobinary Signaling

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The condition for zero ISI (Inter Symbol Interference) is $latex p(nT)= \begin{cases} 1, & n=0 \\ 0, & n\neq 0 \end{cases} &s=1$ 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 … Read more

Walsh Hadamard Code – Matlab Simulation

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[ratings] 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 … Read more