Analysis of hybrid-ARQ based relaying protocols under modulation constraints

In a seminal paper published in 2001, Caire and Tuninetti derived an information theoretic bound on the throughput of hybrid-ARQ in the presence of block fading. However, the results placed no constraints on the modulation used, and therefore the input to the channel was Gaussian. The purpose of this thesis is to investigate the impact of modulation constraints on the throughput of hybrid-ARQ in a block fading environment. First, we consider the impact of modulation constraints on information outage probability for a block fading channel with a fixed length codeword. Then, we consider the effect of modulation constraints upon the throughput of hybrid-ARQ, where the rate of the codeword varies depending on the instantaneous channel conditions. These theoretical bounds are compared against the simulated performance of HSDPA, a newly standardized hybrid-ARQ protocol that uses QPSK and 16-QAM bit interleaved turbo-coded modulation. The results indicate how much of the difference between HSDPA and the previous unconstrained modulation bound is due to the use of the turbo-code and how much is due to the modulation constraints. (Abstract shortened by UMI.)

Smart Wireless Sensor Networks

The recent development of communication and sensor technology results in the growth of a new attractive and challenging area - wireless sensor networks (WSNs). A wireless sensor network which consists of a large number of sensor nodes is deployed in environmental fields to serve various applications. Facilitated with the ability of wireless communication and intelligent computation, these nodes become smart sensors which do not only perceive ambient physical parameters but also be able to process information, cooperate with each other and self-organize into the network. These new features assist the sensor nodes as well as the network to operate more efficiently in terms of both data acquisition and energy consumption. Special purposes of the applications require design and operation of WSNs different from conventional networks such as the internet. The network design must take into account of the objectives of specific applications. The nature of deployed environment must be considered. The limited of sensor nodes� resources such as memory, computational ability, communication bandwidth and energy source are the challenges in network design. A smart wireless sensor network must be able to deal with these constraints as well as to guarantee the connectivity, coverage, reliability and security of network's operation for a maximized lifetime. This book discusses various aspects of designing such smart wireless sensor networks. Main topics includes: design methodologies, network protocols and algorithms, quality of service management, coverage optimization, time synchronization and security techniques for sensor networks

Performance Study of Shared Versus Nonshared Bandwidth on a Packet-Switched Network

In wide area computer data communications, many networks have evolved by satisfying increased user demands in the most expedient manner. In some cases, new users’ demands are satisfied by installing a new link, rather than sharing the links that are already in place. This research investigates the differences in performance between using a dedicated link for each source destination pair (nonshared bandwidth) and using a single link to be used by all source destination pairs (shared bandwidth). Simulation models are developed for a wide area network using shared bandwidth, and a wide area network using nonshared bandwidth. The quality of service offered by each network is based on its responsiveness and productivity. Responsiveness will be measured in terms of average end to end delay of packet transmission, and productivity will be measured in terms of percent bandwidth utilization. The networks are modeled under a common set of operating assumptions and system environment. This allows for accurate comparison of packet delay and bandwidth utilization. Two variable input parameters are used in the simulation: intensity of input traffic load, and amount of link capacity. Provided that the intensity of the input traffic load remains below the network saturation level, it is shown that the shared system clearly outperforms the nonshared system. This result occurs for both a uniform and a nonuniform traffic load destination distribution

Adaptive scheduling in cellular access, wireless mesh and IP networks

Networking scenarios in the future will be complex and will include fixed networks and hybrid Fourth Generation (4G) networks, consisting of both infrastructure-based and infrastructureless, wireless parts. In such scenarios, adaptive provisioning and management of network resources becomes of critical importance. Adaptive mechanisms are desirable since they enable a self-configurable network that is able to adjust itself to varying traffic and channel conditions. The operation of adaptive mechanisms is heavily based on measurements. The aim of this thesis is to investigate how measurement based, adaptive packet scheduling algorithms can be utilized in different networking environments. The first part of this thesis is a proposal for a new delay-based scheduling algorithm, known as Delay-Bounded Hybrid Proportional Delay (DBHPD), for delay adaptive provisioning in DiffServ-based fixed IP networks. This DBHPD algorithm is thoroughly evaluated by ns2-simulations and measurements in a FreeBSD prototype router network. It is shown that DBHPD results in considerably more controllable differentiation than basic static bandwidth sharing algorithms. The prototype router measurements also prove that a DBHPD algorithm can be easily implemented in practice, causing less processing overheads than a well known CBQ algorithm. The second part of this thesis discusses specific scheduling requirements set by hybrid 4G networking scenarios. Firstly, methods for joint scheduling and transmit beamforming in 3.9G or 4G networks are described and quantitatively analyzed using statistical methods. The analysis reveals that the combined gain of channel-adaptive scheduling and transmit beamforming is substantial and that an On-off strategy can achieve the performance of an ideal Max SNR strategy if the feedback threshold is optimized. Finally, a novel cross-layer energy-adaptive scheduling and queue management framework EAED (Energy Aware Early Detection), for preserving delay bounds and minimizing energy consumption in WLAN mesh networks, is proposed and evaluated with simulations. The simulations show that our scheme can save considerable amounts of transmission energy without violating application level QoS requirements when traffic load and distances are reasonable

Push-to-Talk över Bluetooth

Push-to-Talk over Cellular (PoC) är en teknologi som möjliggör en radiotelefonlik service över GPRS vilken väckt ökande popularitet. I skrivande stund pågår specifiering av en öppen PoC-standard inom Open Mobile Alliance (OMA). OMA planerar att baser PoC på en IP/UDP/RTP protokollstack samt en server-clientarkitektur. Systemet utnyttjar även SIP-signaleringsegenskaperna hos IP Multimedia Subsystem (IMS). PoC-nätelement handhar bl.a. gruppförvaltning och taltursfördelning. Forskningsproblemet för denna avhandling är: "Hur kan en PoC-liknande service erbjudas gratis åt mobiltelefonsanvändare med hjälp av Bluetooth-teknologi?" Den primära målsättningen för detta arbete är därmed att skissa upp ett förslag för hur man kunde utveckla en Push-to-Talk (PTT)-funktion som utnyttjar ett Bluetooth scatternet-nät samt PAN-profilen för att överföra data. En måttlig räckvidd kan uppnås med hjälp av Bluetooth apparater av effektklass 1 vars räckvidd kan vara t.o.m. 100 m. En sekundär målsättning är att beskriva PoC samt de protokoll PoC utnyttjar (t.ex. SIP och SDP). Denna beskrivning utgör både en utgångspunkt för att uppnå den primära målsättningen och erbjuder även en introduktion till OMA PoC som lämpar sig för både studeranden och yrkesmän. Det uppskissade förslaget för Push-to-Talk över Bluetooth (PoB) innefattar metoder för skapande av grupper och nät, dataöverföring samt taltursfördelning. Metoden för nätskapande (som kan vara användbar även för andra ändamål) baserar sig på att skapa ett scatternet emellan apparater som tillhör en på förhand specifierad grupp av apparater samt på att undvika slingor. Detta möjliggör enkel kommunikation genom att skicka data till alla apparater inom nätet, förutsatt att de apparater som sammanbinder piconet-näten till ett scatternet fungerar som repeterare. Ytterligare uppskissas en metod för att kombinera PoB och PoC. Avsikten med detta är att möjliggöra PTT-kommunikation med både lokalt och avlägset belägna gruppmedlemmar med hjälp av Bluetooth respektive GPRS.Push-to-Talk over Cellular (PoC) is an emerging technology enabling a walkie-talkie-like service over GPRS. At the time of writing, an open standard for PoC is being specified by the Open Mobile Alliance (OMA). As specified by the OMA standard drafts, PoC is based on an IP/UDP/RTP protocol stack and a client-server based architecture. The systems exploits the SIP signalling capabilities of the the IP Multimedia Subsystem (IMS). Group management, floor control etc are administered by the network elements of PoC. The research problem of this thesis is: "How can mobile phone users be provided with a free-of-charge PTT-feature with PoC-like user experience by means of Bluetooth technology?" The primary objective of the study is thus to propose an outline for developing a Push-to-Talk (PTT) feature that utilizes a Bluetooth scatternet and the PAN profile for data communications. A reasonable range can be obtained with Bluetooth class 1 devices, which provide a range of up to 100 m. A subsidiary objective is to provide a description of OMA PoC and the protocols it relies upon. The description serves both as a basis for pursuing the primary objective and as a tutorial, which is suitable for students or professionals desiring to acquaint themselves with OMA PoC. The proposed outline for Push-to-Talk over Bluetooth (PoB) comprises e.g. methods for group formation, network formation, communication, and floor control. The network formation method, which can be utilized in other applications as well, is based on creating a scatternet among a predefined set of devices and on avoiding loops. This approach enables usage of a simple broadcasting based communication method, in which the devices bridging the piconets into a scatternet act as repeaters. A method for combining PoB and PoC is also outlined. It is intended for enabling PTT-communication with both local and distant group members over Bluetooth and GPRS respectively

A NEUROMORPHIC APPROACH TO TACTILE PERCEPTION

Ph.DDOCTOR OF PHILOSOPH

Variable Rate Transmission Over Noisy Channels

Hybrid automatic repeat request transmission (hybrid ARQ) schemes aim to provide system reliability for transmissions over noisy channels while still maintaining a reasonably high throughput efficiency by combining retransmissions of automatic repeat requests with forward error correction (FEC) coding methods. In type-II hybrid ARQ schemes, the additional parity information required by channel codes to achieve forward error correction is provided only when errors have been detected. Hence, the available bits are partitioned into segments, some of which are sent to the receiver immediately, others are held back and only transmitted upon the detection of errors. This scheme raises two questions. Firstly, how should the available bits be ordered for optimal partitioning into consecutive segments? Secondly, how large should the individual segments be? This thesis aims to provide an answer to both of these questions for the transmission of convolutional and Turbo Codes over additive white Gaussian noise (AWGN), inter-symbol interference (ISI) and Rayleigh channels. Firstly, the ordering of bits is investigated by simulating the transmission of packets split into segments with a size of 1 bit and finding the critical number of bits, i.e. the number of bits where the output of the decoder is error-free. This approach provides a maximum, practical performance limit over a range of signal-to-noise levels. With these practical performance limits, the attention is turned to the size of the individual segments, since packets of 1 bit cause an intolerable overhead and delay. An adaptive, hybrid ARQ system is investigated, in which the transmitter uses the number of bits sent to the receiver and the receiver decoding results to adjust the size of the first, initial, packet and subsequent segments to the conditions of a stationary channel

Coding Theory For Security And Reliability In Wireless Networks

Wireless networks hold many applications and are an integral part of our lives. Security and reliability are extremely important in wireless networks. These networks must be reliable so that data can be conveyed from transmitters to receivers. Data sent across wireless networks must be kept confidential from unintended users and it is necessary that false packets generated by illegitimate users are rejected by the receiver. Another important task is for the network to determine which network components can be trusted and to what degree. The work presented in this dissertation addresses the security and reliability issues in wireless networks through the use of coding theory. The network is composed of numerous nodes and we consider a classical point to point communication problem. We explore the network reliability issue and develop two algorithms (exponential and polynomial time) which determine minimum redundancy and optimal symbol allocation to assure that the probability of successful decoding is greater than or equal to a specified threshold. The performance of the algorithms is compared with each other, and MDS, LT, and Raptor codes are compared using the exponential algorithm. We also consider the security problem of keeping a message confidential from an illegitimate eavesdropper in a multiple path network. Carefully crafted Raptor codes are shown to asymptotically achieve perfect secrecy and zero-error probability, and a bit allocation method across the paths is developed. Lastly, we look into the problem of determining the integrity of nodes in the network. In particular, we show how the malicious nodes can be localized in the network through the use of ReedMuller codes. The Reed-Muller codes represent the paths that are necessary in the network. For the case where a path is not realizable according to the network connectivity matrix, we conceived an algorithm to treat the non-realizable paths as erasures and decode to localize malicious nodes. The performance of the algorithm is compared to several techniques

Blockchain security and applications

Cryptocurrencies, such as Bitcoin and Ethereum, have proven to be highly successful. In a cryptocurrency system, transactions and ownership data are stored digitally in a ledger that uses blockchain technology. This technology has the potential to revolutionize the future of financial transactions and decentralized applications. Blockchains have a layered architecture that enables their unique method of authenticating transactions. In this research, we examine three layers, each with its own distinct functionality: the network layer, consensus layer, and application layer. The network layer is responsible for exchanging data via a peer-to-peer (P2P) network. In this work, we present a practical yet secure network design. We also study the security and performance of the network and how it affects the overall security and performance of blockchain systems. The consensus layer is in charge of generating and ordering the blocks, as well as guaranteeing that everyone agrees. We study the existing Proof-of-stake (PoS) protocols, which follow a single-extension design framework. We present an impossibility result showing that those single-extension protocols cannot achieve standard security properties (e.g., common prefix) and the best possible unpredictability if the honest players control less than 73\% stake. To overcome this, we propose a new multi-extension design framework. The application layer consists of programs (e.g., smart contracts) that users can use to build decentralized applications. We construct a protocol on the application layer to enhance the security of federated learning

Operational support systems for satellite communications

The role of satellite communications is changing from providing bandwidth linking network operators interconnections towards providing IP enabled communications to end users. This migration from few high-value routes towards many low-value routes means that integration and automation of processes with terrestrial networks becomes critical in driving down unit costs. Integration and automation is necessary on all planes: user, control and management. In satellite communications, management aspects, underpinned by Operational Support Systems (OSS) have received the least research attention, making this a valuable topic for study. In most areas, OSS for satellite systems are similar to other domains. However there are some notable areas of difference which have been the focus of this research. The eTOM business framework, developed by the TMF, has been used to highlight aspects of OSS unique to satellite. Since satellite capacity represents the highest operational cost of a satellite route, effective management while minimising the overhead traffic is critical. The transmission of IP packets is assumed and the real-time measurement of QoS parameters such as packet delay and loss emerged as the most important differences. A number of approaches to QoS measurement are feasible, however the use of trace packets is most promising especially for high network loads. An experiment compares the results from simulations, mathematical models and from a test network, using Poisson and self-similar traffic flows. The relationship between measurement accuracy and trace packet intensity is explored and the measurement response time to steps in traffic load is estimated. It is discovered that measurement accuracy improves as the queue load increases, in contrast to alternative approaches such as sampling of user packets. The response time to steps depends upon the degree of self-similarity and is generally longer than the times recommended by standards. A pragmatic approach to management of different modes is proposed where the measurement method is changed depending on the load