Communication Systems Design for Downhole Acoustic Telemetry

The goal of this dissertation is to design a reliable and efficient communication system for downhole acoustic communication. This system is expected to operate in two different modes. A broadband high data rate mode in case of transmission of an image or a video file and a narrowband low data rate mode in case of transmission of sensor readings. This communication system functions by acoustic vibration of the pipes and uses them as the channel instead of installing long cables in areas that are hard to reach. However, this channel has unique characteristics where it exhibits several passbands and stopbands across the frequency spectrum. The communication system is expected to get around those challenges in both modes of operation. In the broadband case, the system uses Orthogonal Frequency Division Multiplexing to transmit data across multiple orthogonal frequencies spanning multiple passbands combined with an error-correction code to recover some of the losses caused by the channel. In the narrowband case, a short packet is transmitted at a low data rate where the signal spectrum can fit inside one passband. However, transmitting short packets induces a new synchronization problem. This dissertation investigates and explores in detail the problem of synchronization on short packets where each synchronization stage is examined. A simple algorithm that exploits the presence of error-correction codes is proposed for the frame synchronization stage and demonstrated to approach the optimal solution. Then, all synchronization stages are combined in order to study the effect of propagated errors caused by imperfect synchronization from one stage to the next and what can be done in the design of the packet and the receiver structure to mitigate those losses. The resulting synchronization procedure is applied to the pipe strings and demonstrated to achieve desirable levels of performance with the assistance of equalization at the receiver

Navigation system and method

In a global positioning system (GPS), such as the NAVSTAR/GPS system, wherein the position coordinates of user terminals are obtained by processing multiple signals transmitted by a constellation of orbiting satellites, an acquisition-aiding signal generated by an earth-based control station is relayed to user terminals via a geostationary satellite to simplify user equipment. The aiding signal is FSK modulated on a reference channel slightly offset from the standard GPS channel. The aiding signal identifies satellites in view having best geometry and includes Doppler prediction data as well as GPS satellite coordinates and identification data associated with user terminals within an area being served by the control station and relay satellite. The aiding signal significantly reduces user equipment by simplifying spread spectrum signal demodulation and reducing data processing functions previously carried out at the user terminals

An Architecture for High Data Rate Very Low Frequency Communication

Very low frequency (VLF) communication is used for long range shore-to-ship broadcasting applications. This paper proposes an architecture for high data rate VLF communication using Gaussian minimum shift keying (GMSK) modulation and low delay parity check (LDPC) channel coding. Non-data aided techniques are designed and used for carrier phase synchronization, symbol timing recovery, and LDPC code frame synchronization. These require the estimation of the operative Eb/N0 for which a kurtosis based algorithm is used. Also, a method for modeling the probability density function of the received signal under the bit condition is presented in this regard. The modeling of atmospheric radio noise (ARN) that corrupts VLF signals is described and an algorithm for signal enhancement in the presence of ARN in given. The BER performance of the communication system is evaluated for bit rates of 400 bps, 600 bps, and 800 bps for communication bandwidth of ~200 Hz.Defence Science Journal, 2013, 63(1), pp.25-33, DOI:http://dx.doi.org/10.14429/dsj.63.376

Feasibility study of 5G low-latency packet radio communications without preambles

This thesis deals with the feasibility of having lower latency for radio communication of short packets, which is the major traffic in the fifth generation (5G) of cellular systems. We will examine the possibility of using turbo synchronization instead of using a long preamble, which is needed for Data-Aided (DA) synchronization. The idea behind this is that short packets are required in low-latency applications. The overhead of preambles is very significant in case of short packets. Turbo synchronization allows to work with short or null preambles. The simulations will be run for a turbo synchronizer which has been implemented according to the Expectation Maximization (EM) formulation of the problem. The simulation results show that the implemented turbo synchronizer outperforms or attains the DA synchronizer in terms of reliability, accuracy and acquisition range for carrier phase synchronization. It means that the idea of eliminating the preamble from the short packet seems practical. The only downward is that there is a packet size limitation for the effective functionality of turbo synchronizer. Simulations indicate that the number of transmitted symbols should be higher than 128 coded symbols

Orbiter global positioning system design and Ku-band problems investigation, exhibit B, revision 1

The LinCom effort in supporting the JSC study of the use of the Global Positioning System (GPS) on the space shuttle and in Ku-band problem investigation is documented. LinCom was tasked to evaluate system implementation, performance, and integration aspects of the shuttle GPS and to provide independent technical assessment of reports submitted to JSC regarding integration studies, system studies and navigation analyses

Code-aided Maximum-likelihood Ambiguity Resolution Through Free-energy Minimization

International audienceIn digital communication receivers, ambiguities in terms of timing and phase need to be resolved prior to data detection. In the presence of powerful error-correcting codes, which operate in low signal to noise ratios (SNR), long training sequences are needed to achieve good performance. In this contribution, we develop a new class of code-aided ambiguity resolution algorithms, which require no training sequence and achieve good performance with reasonable complexity. In particular, we focus on algorithms that compute the maximum-likelihood (ML) solution (exactly or in good approximation) with a tractable complexity, using a factor-graph representation. The complexity of the proposed algorithm is discussed, and reduced complexity variations, including stopping criteria and sequential implementation, are developed

Study of a navigation and traffic control technique employing satellites. Volume 3 - User hardware Interim report

User hardware configurations and requirements for navigation and air traffic control technique using satellite