Initial synchronisation of wideband and UWB direct sequence systems: single- and multiple-antenna aided solutions

This survey guides the reader through the open literature on the principle of initial synchronisation in single-antenna-assisted single- and multi-carrier Code Division Multiple Access (CDMA) as well as Direct Sequence-Ultra WideBand (DS-UWB) systems, with special emphasis on the DownLink (DL). There is a paucity of up-to-date surveys and review articles on initial synchronization solutions for MIMO-aided and cooperative systems - even though there is a plethora of papers on both MIMOs and on cooperative systems, which assume perfect synchronization. Hence this paper aims to ?ll the related gap in the literature

Two-stage code acquisition in wireless optical CDMA communications using optical orthogonal codes

In this paper, we analyze the performance of code acquisition system in atmospheric optical code division multiple access (OCDMA) communications using optical orthogonal codes. Memory introduced by temporal correlation of optical fading process precludes us from using the Markov chain model for a code acquisition analysis. By considering this issue, we discuss how to extend the applicability of the Markov chain model to the atmospheric OCDMA communications. We analyze and compare the performance of correlator and chip level detector (CLD) structures in the acquisition system. In our analysis, we consider the effects of free space optical channel impairments, multiple access interference, and receiver thermal noise in the context of semi-classical photon-counting approach. Furthermore, we evaluate the performance of various two stage schemes that utilize different combinations of active correlator, matched filter, and CLD in search and verification stages, and we find the optimum acquisition scheme among them. Numerical results show significant improvement in reducing the acquisition time and required power for synchronization using our optimum scheme in the wireless OCDMA communications

PN Code Acquisition Using Smart Antennas and Adaptive Thresholding for Spread Spectrum Communications;

In this paper, we consider a pseudo-noise (PN) code acquisition for direct sequence spread spectrum communication in a Rayleigh fading multipath channel environment using smart antenna and adaptive thresholding automatic trimmed-mean constant false alarm rate (ATM-CFAR) processing. A smart antenna is an array of antenna elements that can modify the array pattern adaptively to minimize the effect of multiple access interference (MAI) from other users and multipath. PN code acquisition using a fixed threshold may lead to an excessive number of false alarms, and thus, adaptive thresholding ATM-CFAR processing is considered. In addition, since the interference (MAI and multipath) can be considered as outliers, an outlier determiner is embedded to the proposed system based on the interquartile range. This novel approach of combining smart antennas and adaptive thresholding ATMCFAR detection with an outlier determiner proved to be very robust since it resulted in a serious enhancement of the probability of detection

Adaptive DS-CDMA multiuser detection for time variant frequency selective Rayleigh fading channel

The current digital wireless mobile system such as IS-95, which is based on direct sequence Code Division Multiple Access (DS-CDMA) technology, will not be able to meet the growing demands for multimedia service due to low information exchanging rate. Its capacity is also limited by multiple accessed interference (MAI) signals. This work focuses on the development of adaptive algorithms for multiuser detection (MUD) and interference suppression for wideband direct sequence code division multiple access (DS-CDMA) systems over time-variant frequency selective fading channels. In addition, channel acquisition and delay estimation techniques are developed to combat the uncertainty introduced by the wireless propagation channel. This work emphasizes fast and simple techniques that can meet practical needs for high data rate signal detection. Most existing literature is not suitable for the large delay spread in wideband systems due to high computational/ hardware complexity. A de-biasing decorrelator is developed whose computational complexity is greatly reduced without sacrificing performance. An adaptive bootstrap symbolbased signal separator is also proposed for a time-variant channel. These detectors achieve MUD for asynchronous, large delay spread, fading channels without training sequences. To achieve high data rate communication, a finite impulse response (FIR) filter based detector is presented for M-ary QAM modulated signals in a multipath Rayleigh fading channel. It is shown that the proposed detector provides a stable performance for QAM signal detection with unknown fading and phase shift. It is also shown that this detector can be easily extended to the reception of any M-ary quadrature modulated signal. A minimum variance decorrelating (MVD) receiver with adaptive channel estimator is presented in this dissertation. It provides comparable performance to a linear MMSE receiver even in a deep fading environment and can be implemented blindly. Using the MVD receiver as a building-block, an adaptive multistage parallel interference cancellation (PIC) scheme and a successive interference cancellation (SIC) scheme were developed. The total number of stages is kept at a minimum as a result of the accurate estimating of the interfering users at the earliest stages, which reduces the implementation complexity, as well as the processing delay. Jointly with the MVD receiver, a new transmit diversity (TD) scheme, called TD-MVD, is proposed. This scheme improves the performance without increasing the bandwidth. Unlike other TD techniques, this TDMVD scheme has the inherent advantage to overcome asynchronous multipath transmission. It brings flexibility in the design of TD antenna systems without restrict signal coordination among those multiple transmissions, and applicable for both existing and next generation of CDMA systems. A maximum likelihood based delay and channel estimation algorithm with reduced computational complexity is proposed. This algorithm uses a diagonal simplicity technique as well as the asymptotically uncorrelated property of the received signal in the frequency domain. In combination with oversampling, this scheme does not suffer from a singularity problem and the performance quickly approaches the Cramer-Rao lower bound (CRLB) while maintaining a computational complexity that is as low as the order of the signal dimension

An Assessment of Indoor Geolocation Systems

Currently there is a need to design, develop, and deploy autonomous and portable indoor geolocation systems to fulfil the needs of military, civilian, governmental and commercial customers where GPS and GLONASS signals are not available due to the limitations of both GPS and GLONASS signal structure designs. The goal of this dissertation is (1) to introduce geolocation systems; (2) to classify the state of the art geolocation systems; (3) to identify the issues with the state of the art indoor geolocation systems; and (4) to propose and assess four WPI indoor geolocation systems. It is assessed that the current GPS and GLONASS signal structures are inadequate to overcome two main design concerns; namely, (1) the near-far effect and (2) the multipath effect. We propose four WPI indoor geolocation systems as an alternative solution to near-far and multipath effects. The WPI indoor geolocation systems are (1) a DSSS/CDMA indoor geolocation system, (2) a DSSS/CDMA/FDMA indoor geolocation system, (3) a DSSS/OFDM/CDMA/FDMA indoor geolocation system, and (4) an OFDM/FDMA indoor geolocation system. Each system is researched, discussed, and analyzed based on its principle of operation, its transmitter, the indoor channel, and its receiver design and issues associated with obtaining an observable to achieve indoor navigation. Our assessment of these systems concludes the following. First, a DSSS/CDMA indoor geolocation system is inadequate to neither overcome the near-far effect not mitigate cross-channel interference due to the multipath. Second, a DSSS/CDMA/FDMA indoor geolocation system is a potential candidate for indoor positioning, with data rate up to 3.2 KBPS, pseudorange error, less than to 2 m and phase error less than 5 mm. Third, a DSSS/OFDM/CDMA/FDMA indoor geolocation system is a potential candidate to achieve similar or better navigation accuracy than a DSSS/CDMA indoor geolocation system and data rate up to 5 MBPS. Fourth, an OFDM/FDMA indoor geolocation system is another potential candidate with a totally different signal structure than the pervious three WPI indoor geolocation systems, but with similar pseudorange error performance

Two-Stage Code Acquisition Employing Search Space Reduction and Iterative Detection in the DS-UWB Downlink

Abstract—In this paper we propose and investigate an iterative code acquisition scheme assisted by both search space reduction and iterative Massage Passing (MP), which was designed for the Direct Sequence-Ultra WideBand (DS-UWB) DownLink (DL). The performance of this iterative code acquisition scheme is analysed in terms of both the correct detection probability and the achievable Mean Acquisition Time (MAT). We propose an improved criterion for designing the iterative MP based twostage acquisition regime. Our proposed scheme is capable of reducing the MAT by several orders of magnitude compared to the benchmark scenarios, when considering the employment of long PseudoNoise (PN) codes suitable for a variety of applications

Online circuit breaker monitoring system

Circuit breakers are used in a power system to break or make current flow through power system apparatus. Reliable operation of circuit breakers is very important to the well-being of the power system. Historically this is achieved by regular inspection and maintenance of the circuit breakers. An automated online circuit breaker monitoring system is proposed to monitor condition, operation and status of high and medium voltage circuit breakers. By tracking equipment condition, this system could be used to perform maintenance only when it is needed. This could decrease overall maintenance cost and increase equipment reliability. Using high accurate time synchronization, this system should enable development of system-wide applications that utilize the data recorded by the system. This makes possible tracking sequence of events and making conclusions about their effect on-line. This solution also enables reliable topology analysis, which can be used to improve power flow analysis, state estimation and alarm processing

Optimum SINR receiver in dispersive CDMA channels

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