Low Complexity Rate Compatible Puncturing Patterns Design for LDPC Codes

In contemporary digital communications design, two major challenges should be addressed: adaptability and flexibility. The system should be capable of flexible and efficient use of all available spectrums and should be adaptable to provide efficient support for the diverse set of service characteristics. These needs imply the necessity of limit-achieving and flexible channel coding techniques, to improve system reliability. Low Density Parity Check (LDPC) codes fit such requirements well, since they are capacity-achieving. Moreover, through puncturing, allowing the adaption of the coding rate to different channel conditions with a single encoder/decoder pair, adaptability and flexibility can be obtained at a low computational cost.In this paper, the design of rate-compatible puncturing patterns for LDPCs is addressed. We use a previously defined formal analysis of a class of punctured LDPC codes through their equivalent parity check matrices. We address a new design criterion for the puncturing patterns using a simplified analysis of the decoding belief propagation algorithm, i.e., considering a Gaussian approximation for message densities under density evolution, and a simple algorithmic method, recently defined by the Authors, to estimate the threshold for regular and irregular LDPC codes on memoryless binary-input continuous-output Additive White Gaussian Noise (AWGN) channels

Estimation of LTE Signals' Time of Arrival in a Multi-Band Environment

This thesis summarizes the research work on the estimation of the Time of Arrival (ToA) of signals in Orthogonal Frequency Division Multiplexing (OFDM) based communication systems. The estimated ToA values can be employed for positioning purposes, thus providing an alternative mean of localization to satellite-based technologies. By employing signals of oppor- tunity (SoP), this information can be obtained without the need to allocate transmission resources specifically for positioning purposes. The OFDM multiplexing technique is widely employed in modern telecom- munication standards and presents interesting properties with regard to ToA estimation. In particular, the Third Generation Partnership Project (3GPP) Long Term Evolution is interesting for its diffusion, geographical coverage, and wide transmission bandwidth, making it a prime candidate for research. The upcoming fifth generation (5G) mobile systems are also expected to employ an OFDM-based physical layer, leading to further possibilities of ap- plication and development. In the first part of the work, novel algorithms for the estimation of ToA in OFDM-based systems have been developed. The slope-based algorithm exploits the phase rotation of sub-carriers to obtain the estimation with sim- ple unwrap and linear fitting operations. It can be shown that if the Direct Path (DP) is also the stronger one, the ToA can be inferred from slope of the phase rotation even when secondary paths are presents. A piecewise variant with outliers removal is also introduced to reduce the effects of noise and phase jumps on the final estimation. The Difference-Based algorithm (DBTE) instead relies on a rough first estimate of the channel parameters to obtain an estimation of the first prop- agation path delay even when secondary paths present, on average, larger amplitudes than the direct one. Multiple consecutive symbols can be aggre- gated to achieve a more accurate and reliable estimate. The DBTE method achieves good performance at the cost of a greater computational complexity than the slope-based method. The second part of the work focused on exploiting multiple transmission bands at the same time for ToA estimation. The developed research is based on the assumption that the propagation environment is highly correlated be- tween the transmission bands, which is reasonable if the carrier frequencies are relatively close to each other. This allows one to make full use of the higher bandwidth occupied by the set of signals as a whole, rather than just the bandwidth of each signal on its own, to achieve improved precision and multi-path robustness. The Space-Alternating Generalized Expectation-Maximization (SAGE) algorithm has been chosen for its versatility and good performance in com- plex propagation environments. SAGE presents the advantage of being appli- cable to multi-band scenarios without the need of significant modifications to its basic formulation. A simulator has been implemented in Matlab to evaluate the possible benefits of dual-band usage. In the LTE network multiple transmitter can be allocated on the same physical base station mast, in order to decrease deployment costs and im- prove the network coverage and quality of service. To this end, a set of live measurements on downlink LTE signals has been performed in Monfalcone, Italy. The considered cellular mast carries 3 cell IDs for each operator and transmits on LTE band 20. The Cell-Specific Reference Signal (CRS) has been used as the reference signal of choice. The CRS is always transmitted, allowing it to be used in a fully opportunistic way. The ToA is derived from the gathered data, showing (in agreement with simulations) that the combi- nation of signals from multiple bands leads to a reduced range and standard deviation in the estimations.This thesis summarizes the research work on the estimation of the Time of Arrival (ToA) of signals in Orthogonal Frequency Division Multiplexing (OFDM) based communication systems. The estimated ToA values can be employed for positioning purposes, thus providing an alternative mean of localization to satellite-based technologies. By employing signals of oppor- tunity (SoP), this information can be obtained without the need to allocate transmission resources specifically for positioning purposes. The OFDM multiplexing technique is widely employed in modern telecom- munication standards and presents interesting properties with regard to ToA estimation. In particular, the Third Generation Partnership Project (3GPP) Long Term Evolution is interesting for its diffusion, geographical coverage, and wide transmission bandwidth, making it a prime candidate for research. The upcoming fifth generation (5G) mobile systems are also expected to employ an OFDM-based physical layer, leading to further possibilities of ap- plication and development. In the first part of the work, novel algorithms for the estimation of ToA in OFDM-based systems have been developed. The slope-based algorithm exploits the phase rotation of sub-carriers to obtain the estimation with sim- ple unwrap and linear fitting operations. It can be shown that if the Direct Path (DP) is also the stronger one, the ToA can be inferred from slope of the phase rotation even when secondary paths are presents. A piecewise variant with outliers removal is also introduced to reduce the effects of noise and phase jumps on the final estimation. The Difference-Based algorithm (DBTE) instead relies on a rough first estimate of the channel parameters to obtain an estimation of the first prop- agation path delay even when secondary paths present, on average, larger amplitudes than the direct one. Multiple consecutive symbols can be aggre- gated to achieve a more accurate and reliable estimate. The DBTE method achieves good performance at the cost of a greater computational complexity than the slope-based method. The second part of the work focused on exploiting multiple transmission bands at the same time for ToA estimation. The developed research is based on the assumption that the propagation environment is highly correlated be- tween the transmission bands, which is reasonable if the carrier frequencies are relatively close to each other. This allows one to make full use of the higher bandwidth occupied by the set of signals as a whole, rather than just the bandwidth of each signal on its own, to achieve improved precision and multi-path robustness. The Space-Alternating Generalized Expectation-Maximization (SAGE) algorithm has been chosen for its versatility and good performance in com- plex propagation environments. SAGE presents the advantage of being appli- cable to multi-band scenarios without the need of significant modifications to its basic formulation. A simulator has been implemented in Matlab to evaluate the possible benefits of dual-band usage. In the LTE network multiple transmitter can be allocated on the same physical base station mast, in order to decrease deployment costs and im- prove the network coverage and quality of service. To this end, a set of live measurements on downlink LTE signals has been performed in Monfalcone, Italy. The considered cellular mast carries 3 cell IDs for each operator and transmits on LTE band 20. The Cell-Specific Reference Signal (CRS) has been used as the reference signal of choice. The CRS is always transmitted, allowing it to be used in a fully opportunistic way. The ToA is derived from the gathered data, showing (in agreement with simulations) that the combi- nation of signals from multiple bands leads to a reduced range and standard deviation in the estimations

Analysis and design of rate compatible LDPC codes

The main concern in nowadays digital communications standards, such as IEEE802.11n, 802.16e (Wi-MAX), 100BaseT Ethernet, and Digital Video Broadcasting (DVB), is the need of adaptive and flexible communication techniques. The request for higher efficiency, both in bandwidth use and power consumption, increases the need for limit-achieving, flexible techniques of channel coding. Low Density Parity Check (LDPC) Codes are very interesting because of their high performances and potential flexibility introduced by puncturing. In this paper, the design of rate-compatible LDPC is addressed. A class of punctured LDPC codes is defined through their equivalent parity check matrices. A formal analysis is provided, based on a simplified approach on the decoding belief propagation algorithm, i.e., considering a Gaussian approximation for message densities under density evolution. A suitable design criterion for the puncturing patterns is then addressed

On the Performance of SAGE Algorithm for ToA Estimation in Dual-Band OFDM Systems

This paper discusses the use of the Space-Alternating Generalized Expectation-maximization (SAGE) algorithm for Time of Arrival (ToA) estimation in Orthogonal Frequency Division Multiplexing (OFDM) systems. This algorithm, which is an extension of the expectation-maximization approach, can exploit the intrinsic properties of a multi-carrier OFDM system to achieve the estimation of a number of parameters of each incoming signal replica, such as its amplitude, ToA, Doppler shift, and angle of arrival. The SAGE method can also be easily tailored to estimate only a desired subset of these parameters. Accordingly, this study focuses on the sole ToA estimation, but extending the SAGE functionalities to dual-band OFDM systems. This extension is achieved by exploiting the availability at the receiver of more than one band from the same transmitter, and combining the derived channel information to increase the bandwidth available for estimation. It will be shown that, in highly correlated scenarios, the performance of the SAGE algorithm for ToA estimation in a dual-band system is comparable to that of a single-band system with equivalent total bandwidth

A simple method for TOA estimation in OFDM systems

In this paper a simple algorithm for the estimation of the Direct Path (DP) Time of Arrival (TOA) in an OFDM-based telecommunications system is proposed. It is shown that, under certain conditions, it is possible to infer the TOA of the direct path by estimating the phase slope across the subcarriers. The proposed algorithm exploits the intrinsic properties of a multi-carrier OFDM system to perform the estimation, and it can be employed in a fully opportunistic way if known reference signals (intended for purposes other than TOA estimation) are available. The obtained TOA estimations can be used to calculate the pseudo-ranges that can be employed for trilateration-based positioning. The performance of the proposed algorithm and its variants are assessed with simulations

A low-complexity approach for time of arrival estimation in OFDM systems

This paper proposes a novel algorithm for Time of Arrival (ToA) estimation in Orthogonal Frequency Division Multiplexing (OFDM) systems. The algorithm performs the estimation starting from the channel frequency samples, in a fully opportunistic way when some known reference signals are already available for operations different from ToA estimation itself. The developed solution, named Difference-Based ToA Estimation (DBTE), exploits the intrinsic properties of a multi-carrier OFDM system to calculate the ToA with a low computational cost. The conceived technique is compared with other existing methods in terms of performance and computational time, in order to outline the interesting accuracy/complexity trade-off that characterizes the presented approach

Cave canem: HBO\u2082 therapy efficacy on Capnocytophaga canimorsus infections: a case series

Dog bites are a frequent injury, but the incidence and type of lesions vary across countries. Although only few patients develop complications, the treatment of advanced injuries has a considerable medical, social and economic impact. A frequently isolated pathogen in dog bite wounds is Capnocytophaga canimorsus, a bacterium that can cause sepsis or meningitis. Hyperbaric oxygen (HBO\u2082) therapy has been shown to be useful in treating anaerobic infections, most likely because it creates an inhospitable environment for the bacterium and enhances the patient's immune response