Optimal and suboptimal receivers for code-multiplexed transmitted-reference ultra-wideband systems

Cataloged from PDF version of article.In this study, optimal and suboptimal receivers are investigated for code-multiplexed transmitted-reference (CM-TR) ultra-wideband systems. First, a single-user scenario is considered, and a CM-TR system is modeled as a generalized noncoherent pulse-position modulated system. Based on that model, the optimal receiver that minimizes the bit error probability is derived. Then, it is shown that the conventional CM-TR receiver converges to the optimal receiver under certain conditions and achieves close-to-optimal performance in practical cases. Next, multi-user systems are considered, and the conventional receiver, blinking receiver, and chip discriminator are investigated. Also, the linear minimum mean-squared error (MMSE) receiver is derived for the downlink of a multi-user CM-TR system. In addition, the maximum likelihood receiver is obtained as a performance benchmark. The practicality and the computational complexity of the receivers are discussed, and their performance is evaluated via simulations. The linear MMSE receiver is observed to provide the best trade-off between performance and complexity/practicality. Copyright © 2011 John Wiley & Sons, Lt

Optimal and suboptimal receivers for code-multiplexed transmitted-reference ultra-wideband systems

In this study, optimal and suboptimal receivers are investigated for code-multiplexed transmitted-reference (CM-TR) ultra-wideband systems. First, a single-user scenario is considered, and a CM-TR system is modeled as a generalized noncoherent pulse-position modulated system. Based on that model, the optimal receiver that minimizes the bit error probability is derived. Then, it is shown that the conventional CM-TR receiver converges to the optimal receiver under certain conditions and achieves close-to-optimal performance in practical cases. Next, multi-user systems are considered, and the conventional receiver, blinking receiver, and chip discriminator are investigated. Also, the linear minimum mean-squared error (MMSE) receiver is derived for the downlink of a multi-user CM-TR system. In addition, the maximum likelihood receiver is obtained as a performance benchmark. The practicality and the computational complexity of the receivers are discussed, and their performance is evaluated via simulations. The linear MMSE receiver is observed to provide the best trade-off between performance and complexity/practicality. © 2012 John Wiley & Sons, Ltd

Generalized Code-Multiplexing for UWB Communications

Code-multiplexed transmitted reference (CM-TR) and code-shifted reference (CSR) have recently drawn attention in the field of ultra-wideband communications mainly because they enable noncoherent detection without requiring either a delay component, as in transmitted reference, or an analog car- rier, as in frequency-shifted reference, to separate the reference and data-modulated signals at the receiver. In this paper, we propose a generalized code-multiplexing (GCM) system based on the formulation of a constrained mixed-integer optimization problem. The GCM extends the concept of CM-TR and CSR while retaining their simple receiver structure, even offering better bit-error-rate performance and a higher data rate in the sense that more data symbols can be embedded in each transmitted block. The GCM framework is further extended to the cases when peak power constraint is considered and when inter-frame interference exists, as typically occurs in high data-rate transmissions. Numerical simulations performed over demanding wireless environments corroborate the effectiveness of the proposed approach

Coded-reference ultra-wideband systems

Transmitted-reference (TR) and frequency-shifted reference (FSR) ultra-wideband (UWB) systems employ pairs of reference and data signals, which are shifted in the time and frequency domains, respectively, to facilitate low-to-medium data rate communications without the need for complex channel estimation and template signal generation. On the other hand, the recently proposed coded-reference (CR) UWB systems provide orthogonalization of the reference and data signals in the code domain, which has advantages in terms of performance and/or implementation complexity. In this paper, CR UWB systems are investigated. First, it is shown that a CR UWB system can be considered as a generalized non-coherent pulse-position modulated system. Then, an optimal receiver according to the Bayes decision rule is derived for CR UWB systems. In addition, the asymptotic optimality properties of the conventional CR UWB receivers are investigated. Finally, simulation results are presented to compare the performance of the optimal and conventional CR UWB receivers. ©2008 IEEE

Performance analysis of code-multiplexed transmitted-reference ultra-wideband systems

In code-multiplexed transmitted-reference (CM-TR) ultra-wideband (UWB) systems, data signals and reference signals are transmitted using two distinct orthogonal codes. In this way, performance improvements and/or implementation advantages are obtained compared to transmitted-reference (TR) and frequency-shifted reference (FSR) ultra-wideband (UWB) systems. In this study, performance of CM-TR systems is investigated, and probability of error expressions are obtained. For the single user case, a closed-form expression for the exact probability of error is derived, whereas a Gaussian approximation, the accuracy of which depends on the number of frames per symbol, is considered for the multiuser case. Also, the maximum likelihood detector is derived, and numerical examples are presented. © 2011 IEEE

Performance Analysis and Optimization of Tc-DTR IR-UWB Receivers over Multipath Fading Channels with Tone Interference

International audienceIn this paper, we analyze the performance of a particular class of transmitted-reference receivers for impulse radio ultra wideband communication systems, which is called chip-time differential transmitted-reference (Tc-DTR). The analysis aims at investigating the robustness of this receiver to single-tone and multi-tone narrowband interference (NBI) and comparing its performance with other non-coherent receivers that are proposed in the literature. It is shown that the Tc-DTR scheme provides more degrees of freedom for performance optimization and that it is inherently more robust to NBI than other non-coherent receivers. More specifically, it is analytically proved that the performance improvement is due to the chip-time-level differential encoding/decoding of the direct sequence (DS) code and to an adequate design of DS code and average pulse repetition time. The analysis encompasses performance metrics that are useful for both data detection (i.e., average bit error probability) and timing acquisition (i.e., false-alarm probability Pfa and detection probability Pd). Moving from the proposed sem-analytical framework, the optimal code design and system parameters are derived, and it is highlighted that the same optimization criteria can be applied to all the performance metrics considered in this paper. In addition, analytical frameworks and theoretical findings are substantiated through Monte Carlo simulations

Receiver design and performance analysis for code-multiplexed transmitted-reference ultra-wideband systems

Ankara : The Department of Electrical and Electronics Engineering and the Institute of Engineering and Sciences of Bilkent University, 2010.Thesis (Master's) -- Bilkent University, 2010.Includes bibliographical references leaves 70-74.In transmitted-reference (TR) and frequency-shifted reference (FSR) ultrawideband (UWB) systems, data and reference signals are shifted relative to each other in time and frequency domains, respectively. The main advantage of these systems is that they remove strict requirements of channel estimation. In order to implement TR UWB systems, an analog delay line, which is difficult to build in an integrated fashion, is needed. Although FSR systems require frequency conversion at the receiver, which is much simpler in practice, they have data rate limitations. Instead, a code-multiplexed transmitted-reference (CM-TR) UWB system that transmits data and reference signals using two distinct orthogonal codes can be considered. This system requires a simpler receiver and has better performance than TR and FSR. In the first part of the thesis, CM-TR systems are investigated and probability of error expressions are obtained. For the single user case, a closed-form expression for the exact probability of error is derived. For the multiuser case, a closed-form expression is derived based on the Gaussian approximation, and the results are compared in different scenarios. In the second part of the thesis, some optimal and suboptimal receivers are studied. First, low complexity receivers, such as the blinking receiver (BR) and the chip discriminator, are presented. The requirements for these types of receivers are explained, and the conditions under which their performance can be improved are discussed. Then, an analytical analysis of the linear minimum mean-squared error (MMSE) receiver and the requirements to implement this MMSE receiver are provided. Lastly, the optimal maximum-likelihood (ML) detector is derived, which has higher computational complexity and more strict requirements than the other receivers. Finally, simulation results are presented in order to verify the theoretical results and to compare the performance of the receivers.Tutay, Mehmet EminM.S

Receiver Design and Security for Low Power Wireless Communications Systems

This dissertation focuses on two important areas in wireless communications: receiver design and security. In the first part of this dissertation we consider low data rate receiver design for ultra-wideband (UWB), a wideband radio technology that promises to help solve the frequency allocation problem that often inhibits narrowband systems. Reference-based receivers are promising candidates in the UWB regime, because the conventional rake receiver designs suffers from complexity limitations and inaccuracies in channel estimation. Many reference-based systems have arisen as viable solutions for receivers. We unify these systems as well as other systems into the general framework for performance analysis to suggest the optimal system for varying constraints. We improve the performance of frequency-shifted reference (FSR-UWB) for an average power constraint by halving the frequency offset and employing a sample-and-hold approach across the frame period. Also, we introduce a novel peak mitigation technique; tone reservation, for the multi-differential (MD) version of FSR-UWB, to reduce the high peak-to-average power ratio observed as the data carriers increase. The next part of this dissertation is about wireless security which is ubiquitous in modern news. Cryptography is widely use for security but it assumes limited computational abilities of an eavesdropper, is based on the unproven hardness of the underlying primitives, and allows for the message to be recorded and decrypted later. In this dissertation we consider an information-theoretic security approach to guaranteeing everlasting secrecy. We contribute a new secrecy rate pair outage formulation, where an outage event is based on the instantaneous rates of the destination and the eavesdropper being below and above desired thresholds, respectively. In our new secrecy rate pair outage formulation, two new unaccounted outage events emerge: secrecy breach, where the eavesdropper is above the targeted threshold; unreliable, where the destination is unable to successfully decode the message. The former case must be carefully avoided, while for the latter case we can exploit automatic retransmissions (ARQ) while maintaining the eavesdropper intercept probability below the target threshold. We look at both ``simple\u27\u27 receivers and also complex receivers that use a buffer to store previous messages to maximally combine signal-to-noise ratio (SNR). Then we extend these results to the two-hop case where we maximize the end-to-end secure throughput by optimizing the intercept probability at each eavesdropper given a total end-to-end intercept constraint. Lastly, we consider the difficult case in information-theoretic security: the near eavesdropper case, where we contribute an optimal power allocation algorithm that leverages nearby chatter nodes to generate noise to reduce the probability of intercept by the eavesdropper while minimally impeding the source-to-destination communication. As shown in both one-hop and two-hop cases, allowing a slight outage at the destination for cases of when the eavesdropper is above a specific threshold greatly improves secrecy performance