Worst-Case Error Probability of a Spread-Spectrum System in Energy-Limited Interference

We consider a communication channel corrupted by thermal noise and by an unknown and arbitrary interference of bounded energy. For this channel, we derive a simple upper bound to the worst-case error probability suffered by a direct sequence (DS) communication system with error-correction coding, pseudorandom interleaving, and a correlation receiver. This bound is exponentially tight as the block length of the error correcting code becomes large. Numerical examples are given that illustrate the dependence of the bound on the choice of error correcting code, the type of interleaving used, and the relative energy of the Gaussian noise and arbitrary interferenc

Convolutional Coded Generalized Direct Sequence Spread Spectrum

In this thesis we investigate the worst-case performance of coded ordinary and coded generalized direct sequence spread spectrum (DSSS) systems in a communication channel corrupted by an unknown and arbitrary interfering signal of bounded power. We consider convolutional codes with Viterbi decoding in order to compare the performance of coded ordinary and coded generalized DSSS systems. For the generalized DSSS system, we use a pulse stream of +1,-1 and 0 as the spreading sequence, which is different from ordinary DSSS system which uses the typical sequence with pulse values of +1 and -1. A C program for performing Monte-Carlo simulations is written in order to evaluate and compare the performance of coded ordinary and coded generalized DSSS systems. Plots of the worst-case error probability versus signal-to-interference ratio are presented for different code rates and constraint lengths of the convolutional code. Simulation results of the worst-case performance of ordinary and generalized DSSS show that generalized DSSS consistently performs appreciably better than ordinary DSSS. Simulation is performed for various code rates, various constraint lengths of the convolutional code and various lengths of the convolutional interleaver. Over all these simulations, it is observed that the difference between ordinary and generalized DSSS gets more pronounced as the channel gets wors

Convolutional Coded Generalized Direct Sequence Spread Spectrum

In this thesis we investigate the worst-case performance of coded ordinary and coded generalized direct sequence spread spectrum (DSSS) systems in a communication channel corrupted by an unknown and arbitrary interfering signal of bounded power. We consider convolutional codes with Viterbi decoding in order to compare the performance of coded ordinary and coded generalized DSSS systems. For the generalized DSSS system, we use a pulse stream of +1,-1 and 0 as the spreading sequence, which is different from ordinary DSSS system which uses the typical sequence with pulse values of +1 and -1. A C program for performing Monte-Carlo simulations is written in order to evaluate and compare the performance of coded ordinary and coded generalized DSSS systems. Plots of the worst-case error probability versus signal-to-interference ratio are presented for different code rates and constraint lengths of the convolutional code. Simulation results of the worst-case performance of ordinary and generalized DSSS show that generalized DSSS consistently performs appreciably better than ordinary DSSS. Simulation is performed for various code rates, various constraint lengths of the convolutional code and various lengths of the convolutional interleaver. Over all these simulations, it is observed that the difference between ordinary and generalized DSSS gets more pronounced as the channel gets wors

Convolutional Coded Generalized Direct Sequence Spread Spectrum

In this thesis we investigate the worst-case performance of coded ordinary and coded generalized direct sequence spread spectrum (DSSS) systems in a communication channel corrupted by an unknown and arbitrary interfering signal of bounded power. We consider convolutional codes with Viterbi decoding in order to compare the performance of coded ordinary and coded generalized DSSS systems. For the generalized DSSS system, we use a pulse stream of +1,-1 and 0 as the spreading sequence, which is different from ordinary DSSS system which uses the typical sequence with pulse values of +1 and -1. A C program for performing Monte-Carlo simulations is written in order to evaluate and compare the performance of coded ordinary and coded generalized DSSS systems. Plots of the worst-case error probability versus signal-to-interference ratio are presented for different code rates and constraint lengths of the convolutional code. Simulation results of the worst-case performance of ordinary and generalized DSSS show that generalized DSSS consistently performs appreciably better than ordinary DSSS. Simulation is performed for various code rates, various constraint lengths of the convolutional code and various lengths of the convolutional interleaver. Over all these simulations, it is observed that the difference between ordinary and generalized DSSS gets more pronounced as the channel gets wors

Code Design for Non-Coherent Detection of Frame Headers in Precoded Satellite Systems

In this paper we propose a simple method for generating short-length rate-compatible codes over $\mathbb{Z}_M$ that are robust to non-coherent detection for $M$-PSK constellations. First, a greedy algorithm is used to construct a family of rotationally invariant codes for a given constellation. Then, by properly modifying such codes we obtain codes that are robust to non-coherent detection. We briefly discuss the optimality of the constructed codes for special cases of BPSK and QPSK constellations. Our method provides an upper bound for the length of optimal codes with a given desired non-coherent distance. We also derive a simple asymptotic upper bound on the frame error rate (FER) of such codes and provide the simulation results for a selected set of proposed codes. Finally, we briefly discuss the problem of designing binary codes that are robust to non-coherent detection for QPSK constellation.Comment: 11 pages, 5 figure

Constellation Design for Channels Affected by Phase Noise

In this paper we optimize constellation sets to be used for channels affected by phase noise. The main objective is to maximize the achievable mutual information of the constellation under a given power constraint. The mutual information and pragmatic mutual information of a given constellation is calculated approximately assuming that both the channel and phase noise are white. Then a simulated annealing algorithm is used to jointly optimize the constellation and the binary labeling. The performance of optimized constellations is compared with conventional constellations showing considerable gains in all system scenarios.Comment: 5 pages, 6 figures, submitted to IEEE Int. Conf. on Communications (ICC) 201

Investigation of Generalized DSSS Under Multiple Access and Multipath

In this thesis we investigate and compare the average performances of ordinary and generalized direct sequence spread spectrum (DSSS) systems under multi-path fading and multiple-access interference. As part of multiple access performance, we also consider generation of orthogonal and semi-orthogonal codes using various algorithms, and compare cross correlation properties of codes formed by 2-level and 3-level signature sequences. In order to simulate ordinary and generalized DSSS performance under various scenarios, we develop a complete Java library with classes that are well encapsulated with regard to communication modules and loosely coupled so that we can reuse them to create any type of DSSS communication model. We verify the library under Gaussian noise before performing simulations under multi-path fading and multiple-access interference. We find with regards to multi-path fading that generalized DSSS does not perform any better than ordinary DSSS, regardless of how the signature sequences are generated. For multiple access, when using perfectly orthogonal signature sequences, we observe that ordinary and generalized DSSS perform exactly the same. We investigate semi-orthogonal sequences in great detail, and observe that generalized DSSS can accommodate more users than ordinary DSSS for the same performanc

Improving the Spectral Efficiency of Nonlinear Satellite Systems through Time-Frequency Packing and Advanced Processing

We consider realistic satellite communications systems for broadband and broadcasting applications, based on frequency-division-multiplexed linear modulations, where spectral efficiency is one of the main figures of merit. For these systems, we investigate their ultimate performance limits by using a framework to compute the spectral efficiency when suboptimal receivers are adopted and evaluating the performance improvements that can be obtained through the adoption of the time-frequency packing technique. Our analysis reveals that introducing controlled interference can significantly increase the efficiency of these systems. Moreover, if a receiver which is able to account for the interference and the nonlinear impairments is adopted, rather than a classical predistorter at the transmitter coupled with a simpler receiver, the benefits in terms of spectral efficiency can be even larger. Finally, we consider practical coded schemes and show the potential advantages of the optimized signaling formats when combined with iterative detection/decoding.Comment: 8 pages, 8 figure

Investigation of Generalized DSSS Under Multiple Access and Multipath

In this thesis we investigate and compare the average performances of ordinary and generalized direct sequence spread spectrum (DSSS) systems under multi-path fading and multiple-access interference. As part of multiple access performance, we also consider generation of orthogonal and semi-orthogonal codes using various algorithms, and compare cross correlation properties of codes formed by 2-level and 3-level signature sequences. In order to simulate ordinary and generalized DSSS performance under various scenarios, we develop a complete Java library with classes that are well encapsulated with regard to communication modules and loosely coupled so that we can reuse them to create any type of DSSS communication model. We verify the library under Gaussian noise before performing simulations under multi-path fading and multiple-access interference. We find with regards to multi-path fading that generalized DSSS does not perform any better than ordinary DSSS, regardless of how the signature sequences are generated. For multiple access, when using perfectly orthogonal signature sequences, we observe that ordinary and generalized DSSS perform exactly the same. We investigate semi-orthogonal sequences in great detail, and observe that generalized DSSS can accommodate more users than ordinary DSSS for the same performanc

An efficient receiver structure for sweep-spread-carrier underwater acoustic links

In this paper, we present an improved receiver architecture for sweep-spread-carrier modulation, a spread-spectrum technique proposed to effectively contrast the effects of time dispersion over multipath propagation channels in underwater acoustic wireless links. The proposed structure is capable of taking advantage of the energy received from all propagation paths rather than only from the strongest path, as envisaged in the pioneering paper introducing this modulation technique. A hardware version of the modem was implemented in the laboratory and its behavior was assessed and compared, using standard propagation models, to that exhibited by the traditional single-path-based scheme in terms of bit error rate. Results are presented showing that gains of a few decibels can be achieved in signal-to-noise-plus-interference ratio. Issues relevant to carrier/symbol synchronization, channel estimation, and sensitivity to Doppler distortion are also addressed