1,007 research outputs found
Distributed space-time block coding in cooperative relay networks with application in cognitive radio
Spatial diversity is an effective technique to combat the effects of severe fading in wireless environments. Recently, cooperative communications has emerged as an attractive communications paradigm that can introduce a new form of spatial diversity which is known as cooperative diversity, that can enhance system reliability without sacrificing the scarce bandwidth resource or consuming more transmit power. It enables single-antenna terminals in a wireless relay network to share their antennas to form a virtual antenna array on the basis of their distributed locations. As such, the same diversity gains as in multi-input multi-output systems can be achieved without requiring multiple-antenna terminals.
In this thesis, a new approach to cooperative communications via distributed extended orthogonal space-time block coding (D-EO-STBC) based on limited partial feedback is proposed for cooperative relay networks with three and four relay nodes and then generalized for an arbitrary number of relay nodes. This scheme can achieve full cooperative diversity and full transmission rate in addition to array gain, and it has certain properties that make it alluring for practical systems such as orthogonality, flexibility, low computational complexity and decoding delay, and high robustness to node failure. Versions of the closed-loop D-EO-STBC scheme based on cooperative orthogonal frequency division multiplexing type transmission are also proposed for both flat and frequency-selective fading channels which can overcome imperfect synchronization in the network. As such, this proposed technique can effectively cope with the effects of fading and timing errors. Moreover, to increase the end-to-end data rate, this scheme is extended for two-way relay networks through a three-time slot framework. On the other hand, to substantially reduce the feedback channel overhead, limited feedback approaches based on parameter quantization are proposed. In particular, an optimal one-bit partial feedback approach is proposed for the generalized D-O-STBC scheme to maximize the array gain. To further enhance the end-to-end bit error rate performance of the cooperative relay system, a relay selection scheme based on D-EO-STBC is then proposed. Finally, to highlight the utility of the proposed D-EO-STBC scheme, an application to cognitive radio is studied
Joint Source and Relay Precoding Designs for MIMO Two-Way Relaying Based on MSE Criterion
Properly designed precoders can significantly improve the spectral efficiency
of multiple-input multiple-output (MIMO) relay systems. In this paper, we
investigate joint source and relay precoding design based on the
mean-square-error (MSE) criterion in MIMO two-way relay systems, where two
multi-antenna source nodes exchange information via a multi-antenna
amplify-and-forward relay node. This problem is non-convex and its optimal
solution remains unsolved. Aiming to find an efficient way to solve the
problem, we first decouple the primal problem into three tractable
sub-problems, and then propose an iterative precoding design algorithm based on
alternating optimization. The solution to each sub-problem is optimal and
unique, thus the convergence of the iterative algorithm is guaranteed.
Secondly, we propose a structured precoding design to lower the computational
complexity. The proposed precoding structure is able to parallelize the
channels in the multiple access (MAC) phase and broadcast (BC) phase. It thus
reduces the precoding design to a simple power allocation problem. Lastly, for
the special case where only a single data stream is transmitted from each
source node, we present a source-antenna-selection (SAS) based precoding design
algorithm. This algorithm selects only one antenna for transmission from each
source and thus requires lower signalling overhead. Comprehensive simulation is
conducted to evaluate the effectiveness of all the proposed precoding designs.Comment: 32 pages, 10 figure
Physical-Layer Cooperation in Coded OFDM Relaying Systems
Mobile communication systems nowadays require ever-increasing data rate and coverage of wide areas. One promising approach to achieve this goal is the application of cooperative communications enabled by introducing intermediate nodes known as relays to support the transmission between terminals. By processing and forwarding the receive message at the relays, the path-loss effect between the source and the destination is mitigated. One major limit factor for relay assisted communications is that a relay cannot transmit and receive using the same physical resources. Therefore, a half-duplex constraint is commonly assumed resulting in halved spectral efficiency. To combat this drawback, two-way relaying is introduced, where two sources exchange information with each. On the other hand, due to the physical limitation of the relays, e.g., wireless sensor nodes, it's not possible to implement multiple antennas at one relay, which prohibits the application of multiple-input multiple-output (MIMO) techniques. However, when treating multiple relays as a cluster, a virtual antenna array is formed to perform MIMO techniques in a distributed manner. %This thesis aims at designing efficient one-way and two-way relaying schemes. Specifically, existing schemes from the literature are improved and new schemes are developed with the emphasis on coded orthogonal frequency division multiplexing (OFDM) transmissions. Of special interest is the application of physical-layer network coding (PLNC) for two-phase two-way relaying. In this case, a network coded message is estimated from the superimposed receive signal at the relay using PLNC schemes. The schemes are investigated based on a mutual information analysis and their performance are improved by a newly proposed phase control strategy. Furthermore, performance degradation due to system asynchrony is mitigated depending on different PLNC schemes. When multiple relays are available, novel cooperation schemes allowing information exchange within the relay cluster are proposed that facilitate distributed MIMO reception and transmission. Additionally, smart signaling approaches are presented to enable the cooperation at different levels with the cooperation overhead taken into account adequately in system performance evaluation
Distributed space time block coding and application in cooperative cognitive relay networks
The design and analysis of various distributed space time block coding
schemes for cooperative relay networks is considered in this thesis.
Rayleigh frequency flat and selective fading channels are assumed to
model the links in the networks, and interference suppression techniques
together with an orthogonal frequency division multiplexing (OFDM)
type transmission approach are employed to mitigate synchronization
errors at the destination node induced by the different delays through
the relay nodes.
Closed-loop space time block coding is first considered in the context
of decode-and-forward (regenerative) networks. In particular, quasi orthogonal
and extended orthogonal coding techniques are employed for
transmission from four relay nodes and parallel interference cancellation
detection is exploited to mitigate synchronization errors. Availability
of a direct link between the source and destination nodes is studied.
Outer coding is then added to gain further improvement in end-to-end
performance and amplify-and-forward (non regenerative) type networks
together with distributed space time coding are considered to reduce
relay node complexity. A novel detection scheme is then proposed
for decode-and-forward and amplify-and-forward networks with closed-loop
extended orthogonal coding and closed-loop quasi-orthogonal coding
which reduce the computational complexity of the parallel interference cancellation. The near-optimum detector is presented for relay
nodes with single or dual antennas. End-to-end bit error rate simulations
confirm the potential of the approach and its ability to mitigate
synchronization errors
Distributed space time block coding in asynchronous cooperative relay networks
The design and analysis of various distributed space time block coding
schemes for asynchronous cooperative relay networks is considered
in this thesis. Rayleigh frequency flat fading channels are assumed to
model the links in the networks, and interference suppression techniques
together with an orthogonal frequency division multiplexing type transmission
approach are employed to mitigate the synchronization errors
at the destination node induced by the different delays through the
relay nodes.
Closed-loop space time block coding is first considered in the context
of decode-and-forward (regenerative) networks. In particular, quasi orthogonal
and extended orthogonal coding techniques are employed for
transmission from four relay nodes and parallel interference cancellation
detection is exploited to mitigate synchronization errors. Availability
of a direct link between the source and destination nodes is studied,
and a new Alamouti space time block coding technique with parallel
interference cancellation detection which does not require such a direct
link connection and employs two relay nodes is proposed. Outer
coding is then added to gain further improvement in end-to-end performance
and amplify-and-forward (non regenerative) type networks
together with distributed space time coding are considered to reduce
relay node complexity.
Novel detection schemes are then proposed for decode-and-forward
networks with closed-loop extended orthogonal coding which reduce
the computational complexity of the parallel interference cancellation.
Both sub-optimum and near-optimum detectors are presented for relay
nodes with single or dual antennas. End-to-end bit error rate simulations
confirm the potential of the approaches and their ability to
mitigate synchronization errors. A relay selection approach is also formulated
which maximizes spatial diversity gain and attains robustness
to timing errors.
Finally, a new closed-loop distributed extended orthogonal space
time block coding solution for amplify-and-forward type networks which
minimizes the number of feedback bits by using a cyclic rotation phase
is presented. This approach utilizes an orthogonal frequency division
multiplexing type transmission structure with a cyclic prefix to mitigate
synchronization errors. End-to-end bit error performance evaluations
verify the efficacy of the scheme and its success in overcoming synchronization
errors
Mitigating PAPR in cooperative wireless networks with frequency selective channels and relay selection
The focus of this thesis is peak-to-average power ratio (PAPR) reduction in cooperative wireless networks which exploit orthogonal frequency division multiplexing in transmission. To reduce the PAPR clipping is employed at the source node. The first contribution focuses
upon an amplify-and-forward (AF) type network with four relay nodes which exploits distributed closed loop extended orthogonal space frequency block coding to improve end-to-end performance. Oversampling and filtering are used at the source node to reduce out-of-band interference and the iterative amplitude reconstruction decoding technique is used at the destination node to mitigate in-band distortion which is introduced by the clipping process. In addition, by exploiting quantized group feedback and phase rotation at two of the relay nodes, the system achieves full cooperative diversity in addition to array gain.
The second contribution area is outage probability analysis in the context of multi-relay selection in a cooperative AF network with frequency selective fading channels. The gains of time domain multi-path fading channels with L paths are modeled with an Erlang distribution.
General closed form expressions for the lower and upper bounds of outage probability are derived for arbitrary channel length L as a function of end-to-end signal to noise ratio. This analysis is then extended for the case when single relay selection from an arbitrary number of relay nodes M is performed. The spatial and temporal cooperative diversity gain is then analysed. In addition, exact form of outage probability for multi-path channel length L = 2 and selecting the best single relay from an arbitrary number of relay nodes M is obtained. Moreover, selecting a pair of relays when L = 2 or 3 is additionally analysed.
Finally, the third contribution context is outage probability analysis of a cooperative AF network with single and two relay pair selection from M available relay nodes together with clipping at the source node, which is explicitly modelled. MATLAB and Maple software based simulations are employed throughout the thesis to support the analytical results and assess the performance of algorithms and methods
Two–Way Relaying Communications with OFDM and BICM/BICM-ID
Relay-aided communication methods have gained strong interests in academic community
and been applied in various wireless communication scenarios. Among different techniques
in relay-aided communication system, two-way relaying communication (TWRC) achieves
the highest spectral efficiency due to its bi-directional transmission capability. Nevertheless,
different from the conventional point-to-point communication system, TWRC suffers from
detection quality degradation caused by the multiple-access interference (MAI). In addition,
because of the propagation characteristics of wireless channels, fading and multipath
dispersion also contribute strongly to detection errors. Therefore, this thesis is mainly concerned
with designing transmission and detection schemes to provide good detection quality
of TWRC while taking into account the negative impacts of fading, multipath dispersion
and multiple-access interference.
First, a TWRC system operating over multipath fading channels is considered and orthogonal
frequency-division multiplexing (OFDM) is adopted to handle the inter-symbol
interference (ISI) caused by the multipath dispersion. In particular, adaptive physical-layer
network coding (PNC) is employed to address the MAI issue. By analyzing the detection
error probability, various adaptive PNC schemes are discussed for using with OFDM and
the scheme achieving the best trade-off among performance, overhead and complexity is
suggested.
In the second part of the thesis, the design of distributed precoding in TWRC using
OFDM under multipath fading channels is studied. The objective is to design a distributed
precoding scheme which can alleviate MAI and achieve multipath diversity to combat fading.
Specifically, three types of errors are introduced when analyzing the error probability in the
multiple access (MA) phase. Through analysis and simulation, the scheme that performs
precoding in both time and frequency domains is demonstrated to achieve the maximum
diversity gains under all types of errors.
Finally, the last part of the thesis examines a communication system incorporating forward
error correction (FEC) codes. Specifically, bit-interleaved code modulation (BICM)
without and with iterative decoding (BICM-ID) are investigated in a TWRC system. Distributed
linear constellation precoding (DLCP) is applied to handle MAI and the design
of DLCP in a TWRC system using BICM/BICM-ID is discussed. Taking into account the
multiple access channel from the terminal nodes to the relay node, decoding based on the
quaternary code representation is introduced. Several error probability bounds are derived
to aid in the design of DLCP. Based on these bounds, optimal parameters of DLCP are
obtained through analysis and computer search. It is also found that, by combining XORbased
network coding with successful iterative decoding, the MAI is eliminated and thus
DLCP is not required in a BICM-ID system
Power Optimisation and Relay Selection in Cooperative Wireless Communication Networks
Cooperative communications have emerged as a significant concept to improve reliability and throughput in wireless systems. In cooperative networks, the idea is to implement a scheme in wireless systems where the nodes can harmonize their resources thereby enhancing the network performance in different aspects such as latency, BER and throughput. As cooperation spans from the basic idea of transmit diversity achieved via MIMO techniques and the relay channel, it aims to reap somewhat multiple benefits of combating fading/burst errors, increasing throughput and reducing energy use. Another major benefit of cooperation in wireless networks is that since the concept only requires neighbouring nodes to act as virtual relay antennas, the concept evades the negative impacts of deployment costs of multiple physical antennas for network operators especially in areas where they are difficult to deploy. In cooperative communications energy efficiency and long network lifetimes are very important design issues, the focus in this work is on ad hoc and sensor network varieties where the nodes integrate sensing, processing and communication such that their cooperation capabilities are subject to power optimisation. As cooperation communications leads to trade-offs in Quality of Services and transmit power, the key design issue is power optimisation to dynamically combat channel fluctuations and achieve a net reduction of transmit power with the goal of saving battery life. Recent researches in cooperative communications focus on power optimisation achieved via power control at the PHY layer, and/or scheduling mechanism at the MAC layer. The approach for this work will be to review the power control strategy at the PHY layer, identify their associated trade-offs, and use this as a basis to propose a power control strategy that offers adaptability to channel conditions, the road to novelty in this work is a channel adaptable power control algorithm that jointly optimise power allocation, modulation strategy and relay selection.
Thus, a novel relay selection method is developed and implemented to improve the performance of cooperative wireless networks in terms of energy consumption. The relay selection method revolves on selection the node with minimum distance to the source and destination. The design is valid to any wireless network setting especially Ad-hoc and sensor networks where space limitations preclude the implementation of bigger capacity battery. The thesis first investigates the design of relay selection schemes in cooperative networks and the associated protocols. Besides, modulation strategy and error correction code impact on energy consumption are investigated and the optimal solution is proposed and jointly implemented with the relay selection method. The proposed algorithm is extended to cooperative networks in which multiple nodes participate in cooperation in fixed and variable rate system. Thus, multi relay selection algorithm is proposed to improve virtual MIMO performance in terms of energy consumption. Furthermore, motivated by the trend of cell size optimisation in wireless networks, the proposed relay selection method is extended to clustered wireless networks, and jointly implemented with virtual clustering technique.
The work will encompass three main stages: First, the cooperative system is designed and two major protocols Decode and Forward (DF) and amplify and forward (AF) are investigated. Second, the proposed algorithm is modelled and tested under different channel conditions with emphasis on its performance using different modulation strategies for different cooperative wireless networks. Finally, the performance of the proposed algorithm is illustrated and verified via computer simulations. Simulation results show that the distance based relay selection algorithm exhibits an improved performance in terms of energy consumption compared to the conventional cooperative schemes under different cooperative communication scenarios
Analysis and Ad-hoc Networking Solutions for Cooperative Relaying Systems
Users of mobile networks are increasingly demanding higher data rates from
their service providers. To cater to this demand, various signal processing
and networking algorithms have been proposed. Amongst them the multiple
input multiple output (MIMO) scheme of wireless communications is one of
the most promising options. However, due to certain physical restrictions,
e.g., size, it is not possible for many devices to have multiple antennas
on them. Also, most of the devices currently in use are single-antenna
devices. Such devices can make use of the MIMO scheme by employing
cooperative MIMO methods. This involves nearby nodes utilizing the antennas
of each other to form virtual antenna arrays (VAAs). Nodes with limited
communication ranges can further employ multi-hopping to be able to
communicate with far away nodes. However, an ad-hoc communications scheme
with cooperative MIMO multi-hopping can be challenging to implement because
of its de-centralized nature and lack of a centralized controling entity
such as a base-station. This thesis looks at methods to alleviate the
problems faced by such networks.In the first part of this thesis, we look,
analytically, at the relaying scheme under consideration and derive closed
form expressions for certain performance measures (signal to noise ratio
(SNR), symbol error rate (SER), bit error rate (BER), and capacity) for the
co-located and cooperative multiple antenna schemes in different relaying
configurations (amplify-and-forward and decode-and-forward) and different
antenna configurations (single input single output (SISO), single input
multiple output (SIMO) and MIMO). These expressions show the importance of
reducing the number of hops in multi-hop communications to achieve a better
performance. We can also see the impact of different antenna configurations
and different transmit powers on the number of hops through these
simplified expressions.We also look at the impact of synchronization errors
on the cooperative MIMO communications scheme and derive a lower bound of
the SINR and an expression for the BER in the high SNR regime. These
expressions can help the network designers to ensure that the quality of
service (QoS) is satisfied even in the worst-case scenarios. In the second
part of the thesis we present some algorithms developed by us to help the
set-up and functioning of cluster-based ad-hoc networks that employ
cooperative relaying. We present a clustering algorithm that takes into
account the battery status of nodes in order to ensure a longer network
life-time. We also present a routing mechanism that is tailored for use in
cooperative MIMO multi-hop relaying. The benefits of both schemes are shown
through simulations.A method to handle data in ad-hoc networks using
distributed hash tables (DHTs) is also presented. Moreover, we also present
a physical layer security mechanism for multi-hop relaying. We also analyze
the physical layer security mechanism for the cooperative MIMO scheme. This
analysis shows that the cooperative MIMO scheme is more beneficial than
co-located MIMO in terms of the information theoretic limits of the
physical layer security.Nutzer mobiler Netzwerke fordern zunehmend höhere Datenraten von ihren
Dienstleistern. Um diesem Bedarf gerecht zu werden, wurden verschiedene
Signalverarbeitungsalgorithmen entwickelt. Dabei ist das "Multiple input
multiple output" (MIMO)-Verfahren für die drahtlose Kommunikation eine der
vielversprechendsten Techniken. Jedoch ist aufgrund bestimmter
physikalischer Beschränkungen, wie zum Beispiel die Baugröße, die
Verwendung von mehreren Antennen für viele Endgeräte nicht möglich. Dennoch
können solche Ein-Antennen-Geräte durch den Einsatz kooperativer
MIMO-Verfahren von den Vorteilen des MIMO-Prinzips profitieren.
Dabei schließen sich naheliegende Knoten zusammen um ein sogenanntes
virtuelles Antennen-Array zu bilden. Weiterhin können Knoten mit
beschränktem Kommunikationsbereich durch mehrere Hops mit weiter
entfernten Knoten kommunizieren. Allerdings stellt der Aufbau eines solchen
Ad-hoc-Netzwerks mit kooperativen MIMO-Fähigkeiten aufgrund der dezentralen
Natur und das Fehlen einer zentral-steuernden Einheit, wie einer
Basisstation, eine große Herausforderung dar. Diese Arbeit befasst sich mit
den Problemstellungen dieser Netzwerke und bietet verschiedene
Lösungsansätze.Im ersten Teil dieser Arbeit werden analytisch in
sich geschlossene Ausdrücke für ein kooperatives
Relaying-System bezüglicher verschiedener Metriken, wie das
Signal-Rausch-Verhältnis, die Symbolfehlerrate, die Bitfehlerrate und die
Kapazität, hergeleitet. Dabei werden die "Amplify-and forward" und
"Decode-and-forward" Relaying-Protokolle, sowie unterschiedliche
Mehrantennen-Konfigurationen, wie "Single input single output" (SISO),
"Single input multiple output" (SIMO) und MIMO betrachtet. Diese Ausdrücke
zeigen die Bedeutung der Reduzierung der Hop-Anzahl in Mehr-Hop-Systemen,
um eine höhere Leistung zu erzielen. Zudem werden die Auswirkungen
verschiedener Antennen-Konfigurationen und Sendeleistungen auf die Anzahl
der Hops analysiert. Weiterhin wird der Einfluss von
Synchronisationsfehlern auf das kooperative MIMO-Verfahren herausgestellt
und daraus eine untere Grenze für das
Signal-zu-Interferenz-und-Rausch-Verhältnis, sowie ein Ausdruck für die
Bitfehlerrate bei hohem Signal-Rausch-Verhältnis entwickelt.
Diese Zusammenhänge sollen Netzwerk-Designern helfen die Qualität des
Services auch in den Worst-Case-Szenarien sicherzustellen.
Im zweiten Teil der Arbeit werden einige innovative
Algorithmen vorgestellt, die die Einrichtung und die Funktionsweise von
Cluster-basierten Ad-hoc-Netzwerken, die kooperative Relays verwenden,
erleichtern und verbessern. Darunter befinden sich ein
Clustering-Algorithmus, der den Batteriestatus der Knoten berücksichtigt,
um eine längere Lebensdauer des Netzwerks zu gewährleisten und ein
Routing-Mechanismus, der auf den Einsatz in kooperativen MIMO
Mehr-Hop-Systemen zugeschnitten ist. Die Vorteile beider Algorithmen werden
durch Simulationen veranschaulicht.
Eine Methode, die Daten in Ad-hoc-Netzwerken mit verteilten Hash-Tabellen
behandelt wird ebenfalls vorgestellt. Darüber hinaus wird auch
ein Sicherheitsmechanismus für die physikalische Schicht in
Multi-Hop-Systemen und kooperativen MIMO-Systemen präsentiert. Eine Analyse
zeigt, dass das kooperative MIMO-Verfahren deutliche Vorteile gegenüber dem
konventionellen MIMO-Verfahren hinsichtlich der informationstheoretischen
Grenzen der Sicherheit auf der physikalischen Schicht aufweist
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