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As diverse and data-heavy underwater applications emerge, demanding requirements are further imposed on underwater wireless communication systems. Future underwater wireless communication networks might consist of both mobile and stationary nodes which exchange data such as control, telemetry, speech, and video signals among themselves as well as a central node located at a ship or onshore. The submerged nodes, which can, for example, take the form of an autonomous underwater vehicle/robot or diver, can be equipped with various sensors, sonars, video cameras, or other types of data acquisition instruments. Innovative physical layer solutions are therefore required to develop efficient, reliable, and high-speed transmission solutions tailored for challenging and diverse requirements of underwater applications. Building on the promising combination of multi-carrier and cooperative communication techniques, this dissertation investigates the fundamental performance bounds of cooperative underwater acoustic (UWA) communication systems taking into account the inherent unique characteristics of the UWA channel. We derive outage probability and capacity expressions for cooperative multi-carrier UWA systems with amplify-and-forward and decode-and-forward relaying. Through the derived expressions, we demonstrate the effect of several system and channel parameters on the performance. Furthermore, we investigate the performance of cooperative UWA systems in the presence of non-uniform Doppler distortion and propose receiver designs to mitigate the degrading Doppler effects.

Mémoire (M.P.M.O.)--Université du Québec à Chicoutimi, 1990. / "Maîtrise en gestion des PMO" CaQCU Document électronique également accessible en format PDF. CaQCU

The demand for access to information when and where you need has motivated the transition of wireless communications from a fixed infrastructure based cellular communications technology to a more pervasive adhoc wireless networking technology. Challenges still remain in wireless adhoc networks in terms of meeting higher capacity demands, improved reliability and longer connectivity before it becomes a viable widespread commercial technology. Present day wireless mesh networking uses node-to-node serial multi-hop communication to convey information from source to destination in the network. The performance of such a network depends on finding the best possible route between the source and destination nodes. However the end-to-end performance can only be as good as the weakest link within a chosen route. Unlike wired networks, the quality of point-to-point links in a wireless mesh network is subject to random fluctuations. This adversely affects the performance resulting in poor throughput and poor energy efficiency. In recent years, a new paradigm for communication called cooperative communications has been proposed for which initial information theoretic studies have shown the potential for improvements in capacity over traditional multi-hop wireless networks. Cooperative communication involves exploiting the broadcast nature of the wireless medium to form virtual antenna arrays out of independent single-antenna network nodes for transmission. In this research we explore the fundamental performance limits of cooperative communication under more practical operating scenarios. Specifically we provide a framework for computing the outage and ergodic capacities of non identical distributed MIMO links, study the effect of time synchronization error on system performance, analyze the end-to-end average bit error rate (ABER) performance under imperfect relaying, and study range extension and energy efficiency offered by the system when compared to a traditional system. / Ph. D.

We consider the problem of allocating resources in large wireless net- works in which multiple information flows must be accommodated. In particular, we seek a method for selecting schedules, routes, and power allocations for networks with terminals capable of user-cooperation at the signal level. To that end, we adopt a general information-theoretic communications model, in which the datarate of a wireless link is purely a function of transmission power, pathloss and interference. We begin by studying the case of resource allocation when only point-to-point links are available. The problem is NP-hard in this case, requiring an exponentially-complex exhaustive search to guarantee an optimal solution. This is prohibitively difficult for anything but the smallest of networks, leading us to approximate the problem using a decomposition approach. We construct the solution iteratively, developing polynomial-time algorithms to optimally allocate resources on a per-frame basis. We then update the network graph to reflect the resources consumed by the allocated frame. To manage this decomposition, we present a novel tool, termed the Network-Flow Interaction Chart. By representing the network in both space and time, our techniques trade off interference with throughput for each frame, offering considerable performance gains over schemes of similar complexity. Recognizing that our approach requires a large amount of overhead, we go on to develop a method in which it may be decentralized. We find that while the overhead is considerably lower, the limited solution space results in suboptimal solutions in a throughput sense. We conclude with a generalization of the Network-Flow Interaction Chart to address cooperative resource allocation. We represent cooperative links using "metanodes," which are made available to the allocation algorithms alongside point-to-point links and will be selected only if they offer higher throughput. The data-carrying capability of the cooperative links is modeled using Decode-and-Forward achievable rates, which are functions of transmit power and interference, and so may be incorporated directly into our framework. We demonstrate that allocations incorporating cooperation results in significant performance gains as compared to using point-to-point links alone.

Grice (1982) and Bar-On and Green (2010) each provide 'continuity stories' which attempt to explain how a human-like language could emerge from the primitive communication practices of non-human animals. I offer desiderata for a proper account of linguistic continuity in order to argue that these previous accounts fall short in important ways. I then introduce the recent evolutionary literature on non-cooperative communication in order to construct a continuity story which better satisfies the proposed desiderata while retaining the positive aspects of the proposals of Grice and Bar-On and Green. The outcome of this project is a more tenable and empirically investigable framework chronicling the evolution of human-like language from communicative abilities currently found in non-human animals.

In this paper, we consider the code division multiple access of the multiuser cooperative network system, all sources transmit signals using assigned spreading waveforms in first phase, and all relays transmit precoded signals using a common spreading waveform to help send signals to all destinations in second phase, in order to improve the performance. In this paper, we proposed the precoding strategy of relay point and the decoding strategy of destination point; at first we use the zero-forcing to eliminate the multi-user interferen- ce at the destination, and then joint design of the precoding vector at relay point and the decoding vector at destination point to achieve different optimization objectives. In this paper, we consider the power constraints to optimal the average SNR for the precoding vector and decoding vector, but the precoding vector favors the source-destination pairs with better channel quality in this condition, we also present the design of fairness, joint design of the precoding vector and the decoding vector to make the worst SNR can have the best signal-to-noise ratio after the design, and also consider the power constrain.

Cooperative communication has been shown that it is an effective way to combat the outage caused by channel fading; that is, it provides the spatial diversity for communication. Except for amplify-and-forward (AF) and decode-and-forward (DF), compressed-and-forward (CF) is also an efficient forwarding strategy. In this thesis, we proposed a new CF scheme. In the existing CF protocol, the relay will switch to the DF mode when the source transmitted signal can be recovered by the relay completely; no further compression is made in this scheme. In our proposed, the relay will estimate if the codeword in a block is succeeded decoded, choose the corresponding forwarding methods with LDPC coding; those are based on joint source-channel coding or compressive sensing. At the decode side, a joint decoder with side information that performs sum-product algorithm (SPA) to decode the source message. Simulation results show that the proposed CF scheme can acquire the spatial diversity and outperform AF and DF schemes.

In this paper, the channel estimation problem for a two-way relay network (TWRN) based on two different wireless channel assumptions is considered. Previous works have proposed a training-based channel estimation method to obtain the channel state information (CSI). But in practice the channel change from one data block to another, which may cause the performance degradation due to the outdated CSI. To enhance the performance, the system has to insert more training signal. In order to improve the bandwidth efficiency, we propose a joint channel estimation and data detection method based on expectation-maximization (EM) algorithm. From the simulation results, the proposed method can combat the effect of fading channel and still the MSE results are very close to Cramer-Rao Lower Bound (CRLB) at the high signal-to-noise ratio (SNR) region. Additionally, as compare with the previous work, the proposed scheme also has a better detection performance for both time-varying and time-invariant channels.

For wireless communication systems, due to broadcasting nature of wireless medium, how to keep eavesdroppers from wiretapping messages is worth investigated. In addition to encryption techniques applied in application layer, physical layer secrecy techniques have been studied in literature. Under the premise that eavesdropper cannot steal any information, physical layer secrecy focus on maximizing the capacity of legal transmission, and make it more reliable by using physical properties of wireless channel. This thesis considers an amplify-and-forward (AF) multiple-input multiple-output (MIMO) cooperative communication network with an untrusted relay (UR), and linear precoders are employed at source, relay, and destination. The relay here serves as a bridge of transmission 1 between the source and the destination. However, assume that the untrusted relay may wiretap information from the source without authorization. In order to prevent relay from wiretapping information, the destination generates artificial noise (AN) to interfere the relay, when the relay is receiving information from the source. Since AN is generated by the destination, the destination can eliminate AN by itself after receiving signal from the relay without corrupting signals of legal transmission. We propose precoder design for source, relay and destination to maximize secrecy capacity under the power constraint of three nodes. By utilizing singular value decomposition (SVD) of all channel matrices and Hadamard inequality, we simplify the optimization problem of precoding matrices to scalar optimization problem, and optimization can be accomplished recursively.