71 research outputs found
Optimal space-time codes for the MIMO amplify-and-forward cooperative channel
In this work, we extend the non-orthogonal amplify-and-forward (NAF)
cooperative diversity scheme to the MIMO channel. A family of space-time block
codes for a half-duplex MIMO NAF fading cooperative channel with N relays is
constructed. The code construction is based on the non-vanishing determinant
criterion (NVD) and is shown to achieve the optimal diversity-multiplexing
tradeoff (DMT) of the channel. We provide a general explicit algebraic
construction, followed by some examples. In particular, in the single relay
case, it is proved that the Golden code and the 4x4 Perfect code are optimal
for the single-antenna and two-antenna case, respectively. Simulation results
reveal that a significant gain (up to 10dB) can be obtained with the proposed
codes, especially in the single-antenna case.Comment: submitted to IEEE Transactions on Information Theory, revised versio
Enhancing diversity and multiplexing gains in multi-user wireless relay systems
The demand for higher transmission rates and better quality of service in modern wireless
communications is endless. The use of multiple transmit or /and receive antennas has been
considered as one of the most powerful approaches to facilitate high -speed and high -quality
communications. However, in practical cellular systems, mobile terminals may not be able to
support a multiple- antenna setup. Thus an emerging technique called cooperative diversity is
under consideration to utilize the multi -hop relay concept to realize the advantages of multiple - antenna systems in multi -user single- antenna networks. Cooperative diversity has attracted
much interest in recent years as a very promising direction for future wireless communication
evolution.Due to the fact that in practice terminals cannot transmit and receive simultaneously (i.e. the
half -duplex limitation), the diversity improvement brought by the standard cooperative diversity
transmission protocols is in general accompanied by a multiplexing loss (equivalent to a
reduction in transmission data rate in high signal -to -nose ratio (SNR)). The purpose of this
thesis is to use advanced transmission protocols to provide both good diversity and multiplexing
performance when using the practical repetition -coded decode - and -forward (DF) relaying
strategy in uplink mobile -to -base station transmission of cellular systems.The task is fulfilled by relaxing the orthogonal channel allocation requirement of the standard
protocols and by using two relays to take turns forwarding source information to destination.
We start our analysis from an M- source two -relay one -destination network. Through
diversity -multiplexing tradeoff (DMT) analysis, we prove that for an isolated -relay scenario
and a strong -interference scenario, the considered approach effectively recovers the multiplexing
loss induced by the standard protocols while still obtaining diversity improvement over
direct source -destination transmission without considering relaying.In addition, since the optimal multiplexing gain of the considered system can be achieved by the
above approach, we study further improving diversity performance for a two -source network.
We analyze taking full advantage of the multiple- source structure, multiple -relay structure, and
the capability of affording complex signal processing at the destination (base station). For all
three cases, we prove that the diversity performance of the above approach can be enhanced
without a significant loss of multiplexing performance or using complex coding strategies at
relays. Since the good DMT performance is not affected by source -relay channel conditions,
the protocols discussed in this thesis make relaying more beneficial
Propagation measurement based study on relay networks
Von der nächsten Generation von Mobilfunksystemen erwartet man eine
umfassende Versorgung mit breitbandigen Multimediadiensten. Um die dafĂĽr
erforderliche flächendeckende Versorgung mit hohen Datenraten zu
gewährleisten, können Relay-Netzwerke einen wesentlichen Beitrag liefern.
Hierbei werden Netzwerkstationen mit Relay-Funktionalität in zellulare
Netzwerke integriert.
Diese Dissertation befasst sich mit der Untersuchung Relay-basierter
Netzwerke unter Verwendung von Ausbreitungsmessungen. Die Arbeit deckt
Fragen zur Kanalmodellierung, Systemevaluierung bis hin zur
Systemverifikation ab. - Zunächst wird ein auf Funkkanalmessungen
beruhendes experimentelles Kanalmodell fĂĽr Relay-Netzwerke vorgestellt. Im
Weiteren werden technische Verfahren fĂĽr Mehrfachzugriffs-Relay-Netzwerke
MARN diskutiert. Die erreichbare Systemleistung wurde unter Verwendung von
Rayleigh-Kanälen innerhalb einer Systemsimulation bestimmt und im Anschluss
mit realen Kanälen, die sowohl direkt aus Funkkanalmessungen als auch
indirekt aus dem bereits erwähnten Kanalmodell abgeleitet wurden,
verifiziert.
Bisherige Arbeiten zur Modellierung breitbandiger Multiple-Input
Multiple-Output (MIMO) Kanäle berücksichtigen nicht oder nur sehr stark
vereinfacht die Langzeitkorrelationseigenschaften zwischen den Links und
werden damit der vermaschten und räumlich weit verteilten Topologie von
Relay-Netzwerken gerecht. In der vorliegenden Dissertation erfolgte daher
eine experimentelle Untersuchung zu den Korrelationseigenschaften von
Large-Scale-Parametern LSP, die unter Verwendung von Funkkanalmessdaten aus
urbanen Umgebungen und aus Innenräumen abgeleitet wurden. Die Ergebnisse
hierzu fanden Eingang in das vom WINNER-Projekt entwickelte Kanalmodell.
Sie erlauben damit eine realistischere Simulation von Relay-unterstĂĽtzten
Netzen.
Einen weiteren Schwerpunkt dieser Arbeit stellen technische Verfahren dar,
die eine Erhöhung der Systemleistung in MARN mit unbekannter Interferenz
UKIF versprechen. Im Einzelnen handelt es sich um die
Mehrfachzugriffs-Kodierung MAC - die eine verbesserte Signaltrennung auf
der Empfängerseite und eine Erhöhung des Datendurchsatzes erlaubt, den
Entwurf eines Relay-Protokolls zur Erhöhung der Systemeffizienz, einen
Minimum Mean Square Error (MMSE) Algorithmus zur UnterdrĂĽckung unbekannter
Interferenzen bei Erhaltung der MAC-Signalstruktur mehrerer Mobilstationen
MS, und ein fehlererkennungsbasiertes Signalauswahlverfahren zur
Diversitätserhöhung.
Die vorgenannten Verfahren werden in einer Systemsimulation zunächst mit
Rayleigh-Kanälen evaluiert und demonstrieren die erzielbare theoretische
Leistungssteigerung. Die Berücksichtigung realer Funkkanäle innerhalb der
Systemsimulation zeigt allerdings, dass die theoretische Systemleistung so
in der Realität nicht erreichbar ist. Die Ursache hierfür ist in den
idealisierten Annahmen theoretischer Kanäle zu suchen.
FĂĽr die Entwicklung kĂĽnftiger Relay-Netzwerke bieten die in dieser Arbeit
aufbereiteten Erkenntnisse hinsichtlich der
Langzeitkorrelationseigenschaften zwischen den Links einen wertvollen
Beitrag für die Abschätzung ihrer Systemleistung auf der Basis eines
verbesserten Kanalmodells.Considering technological bases of next generation wireless systems, it is
expected that systems can provide a variety of coverage requirements to
support ubiquitous communications. To satisfy the requirements, an
innovative idea, integrating network elements with a relaying capability
into cellular networks, is one of the most promising solutions.
The main topic of this dissertation is a propagation measurement based
study on relay networks. The study includes three parts: channel modeling,
performance evaluation, and verification. First of all, an empirical
channel model for relay networks is proposed based on statistical analyses
of measurement data. Then, advanced techniques for the throughput
improvement and interference cancellation are proposed for Multiple Access
Relay Networks (MARN) which are used as an example of relay networks. The
performance of the considered MARN is evaluated for Rayleigh channels, and
then verified for realistic channels, obtained from measurement data and
from the experimental relay channel model as well.
For relay channel modeling, the long-term correlation properties between
links are of crucial importance due to the meshed-network topology.
Although, there is a wide variety of research results for Multiple-Input
Multiple-Output (MIMO) channel modeling available, the characterization of
correlation properties has been significantly simplified or even completely
ignored which motivates this research to be performed. In this
dissertation, the experimental results of the correlation properties of
Large Scale Parameters (LSP) are presented through the analysis on the
real-field measurement data for both the urban and indoor scenarios.
furthermore, the correlation properties have been fully introduced into the
WINNER channel Model (WIM) for realistic relay channel simulations.
As a further contribution of this dissertation, various advanced techniques
are proposed for MARN in the presence of Unknown Interference (UKIF).
Multiple Access Coding (MAC) is introduced as a multiple access technique.
The use of MAC provides the signal separability at the receiver and
improves throughput. Thereafter, high system resource efficiency can be
achieved through relay protocol design. At the receiver, Minimum Mean
Square Error (MMSE)-based spatial filtering is used to suppress UKIF while
preserving multiple Mobile Station (MS)s’ MAC-encoded signal structure.
Furthermore, an error detection aided signal selection technique is
proposed for diversity increasing.
The theoretical system performance with aforementioned techniques is
simulated for Rayleigh channels. Thereafter, realistic channels are
exploited for the performance verification. The gap between the theoretical
performance and the realistic performance indicates that the assumptions
made to the simplified Rayleigh-channels do not fully hold in reality.
For the future relay system design, this work provides valuable information
about the performance evaluation of relay networks in consideration of the
correlation properties between links
Analysis and Design of Non-Orthogonal Multiple Access (NOMA) Techniques for Next Generation Wireless Communication Systems
The current surge in wireless connectivity, anticipated to amplify significantly in future wireless technologies, brings a new wave of users. Given the impracticality of an endlessly expanding bandwidth, there’s a pressing need for communication techniques that efficiently serve this burgeoning user base with limited resources. Multiple Access (MA) techniques, notably Orthogonal Multiple Access (OMA), have long addressed bandwidth constraints. However, with escalating user numbers, OMA’s orthogonality becomes limiting for emerging wireless technologies. Non-Orthogonal Multiple Access (NOMA), employing superposition coding, serves more users within the same bandwidth as OMA by allocating different power levels to users whose signals can then be detected using the gap between them, thus offering superior spectral efficiency and massive connectivity. This thesis examines the integration of NOMA techniques with cooperative relaying, EXtrinsic Information Transfer (EXIT) chart analysis, and deep learning for enhancing 6G and beyond communication systems. The adopted methodology aims to optimize the systems’ performance, spanning from bit-error rate (BER) versus signal to noise ratio (SNR) to overall system efficiency and data rates. The primary focus of this thesis is the investigation of the integration of NOMA with cooperative relaying, EXIT chart analysis, and deep learning techniques. In the cooperative relaying context, NOMA notably improved diversity gains, thereby proving the superiority of combining NOMA with cooperative relaying over just NOMA. With EXIT chart analysis, NOMA achieved low BER at mid-range SNR as well as achieved optimal user fairness in the power allocation stage. Additionally, employing a trained neural network enhanced signal detection for NOMA in the deep learning scenario, thereby producing a simpler signal detection for NOMA which addresses NOMAs’ complex receiver problem
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