Signal Processing for Communication Systems
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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
The moving average filter is a simple Low Pass FIR (Finite Impulse Response) filter commonly used for smoothing an array of sampled data/signal. It takes samples of input at a time and takes the average of those -samples and produces a single output point. It is a very simple LPF (Low Pass Filter) structure that … Read more
Random Interleaver: The Random Interleaver rearranges the elements of its input vector using a random permutation. The incoming data is rearranged using a series of generated permuter indices. A permuter is essentially a device that generates pseudo-random permutation of given memory addresses. The data is arranged according to the pseudo-random order of memory addresses. The … Read more
Introduction: A Reed Solomon (RS) encoder, takes user data symbols and converts it into a n symbol wide codeword, by adding parity symbols. The error correcting capability of the RS code is computed as . That is, a RS code with parity symbols can correct a burst error of upto symbol errors. Block Interleavers: Suppose, … Read more
Interleavers and Deinterleavers are designed and used in the context of characteristics of the errors that might occur when the message bits are transmitted through a noisy channel. To understand the functions of an interleaver/deinterleaver, understanding of error characteristics is essential. Two types are errors concern communication system design engineer. They are burst error and … Read more
Quadrature Phase Shift Keying (QPSK) is a form of phase modulation technique, in which two information bits (combined as one symbol) are modulated at once, selecting one of the four possible carrier phase shift states. The QPSK signal within a symbol duration \(T_{sym}\) is defined as where the signal phase is given by Therefore, the … Read more
Spread spectrum system, originally developed for military applications, is extremely resistant to unauthorized detection, jamming, interference and noise. It converts a narrowband signal to wideband signal by the means of spreading. Standards like WiFi and bluetooth use spread spectrum technology such as direct sequence spread spectrum and frequency hopping spread spectrum respectively. Spread spectrum techniques … Read more
Viterbi algorithm is utilized to decode the convolutional codes. Again the decoding can be done in two approaches. One approach is called hard decision decoding which uses Hamming distance as a metric to perform the decoding operation, whereas, the soft decision decoding uses Euclidean distance as a metric. As stated in one of the previous … Read more
Key focus: Compare Performance and spectral efficiency of bandwidth-efficient digital modulation techniques (BPSK,QPSK and QAM) on their theoretical BER over AWGN. More detailed analysis of Shannon’s theorem and Channel capacity is available in the following book● Wireless Communication Systems in Matlab (second edition), ISBN: 979-8648350779 available in ebook (PDF) format and Paperback (hardcopy) format. Simulation of various … Read more