3,112 research outputs found
Permutation Trellis Coded Multi-level FSK Signaling to Mitigate Primary User Interference in Cognitive Radio Networks
We employ Permutation Trellis Code (PTC) based multi-level Frequency Shift
Keying signaling to mitigate the impact of Primary Users (PUs) on the
performance of Secondary Users (SUs) in Cognitive Radio Networks (CRNs). The
PUs are assumed to be dynamic in that they appear intermittently and stay
active for an unknown duration. Our approach is based on the use of PTC
combined with multi-level FSK modulation so that an SU can improve its data
rate by increasing its transmission bandwidth while operating at low power and
not creating destructive interference for PUs. We evaluate system performance
by obtaining an approximation for the actual Bit Error Rate (BER) using
properties of the Viterbi decoder and carry out a thorough performance analysis
in terms of BER and throughput. The results show that the proposed coded system
achieves i) robustness by ensuring that SUs have stable throughput in the
presence of heavy PU interference and ii) improved resiliency of SU links to
interference in the presence of multiple dynamic PUs.Comment: 30 pages, 12 figure
Performance enhancement solutions in wireless communication networks
In this dissertation thesis, we study the new relaying protocols for different wireless network systems. We analyze and evaluate an efficiency of the transmission in terms of the outage probability over Rayleigh fading channels by mathematical analyses. The theoretical analyses are verified by performing Monte Carlo simulations.
First, we study the cooperative relaying in the Two-Way Decode-and-Forward (DF) and multi-relay DF scheme for a secondary system to obtain spectrum access along with a primary system. In particular, we proposed the Two-Way DF scheme with Energy Harvesting, and the Two-Way DF Non-orthogonal Multiple Access (NOMA) scheme with digital network coding. Besides, we also investigate the wireless systems with multi-relay; the best relay selection is presented to optimize the effect of the proposed scheme. The transmission protocols of the proposed schemes EHAF (Energy Harvesting Amplify and Forward) and EHDF (Energy Harvesting Decode and Forward) are compared together in the same environment and in term of outage probability. Hence, with the obtained results, we conclude that the proposed schemes improve the performance of the wireless cooperative relaying systems, particularly their throughput.
Second, we focus on investigating the NOMA technology and proposing the optimal solutions (protocols) to advance the data rate and to ensure the Quality of Service (QoS) for the users in the next generation of wireless communications. In this thesis, we propose a Two-Way DF NOMA scheme (called a TWNOMA protocol) in which an intermediate relay helps two source nodes to communicate with each other. Simulation and analysis results show that the proposed protocol TWNOMA is improving the data rate when comparing with a conventional Two-Way scheme using digital network coding (DNC) (called a TWDNC protocol), Two-Way scheme without using DNC (called a TWNDNC protocol) and Two-Way scheme in amplify-and-forward(AF) relay systems (called a TWANC protocol).
Finally, we considered the combination of the NOMA and physical layer security (PLS) in the Underlay Cooperative Cognitive Network (UCCN). The best relay selection strategy is investigated, which uses the NOMA and considers the PLS to enhance the transmission efficiency and secrecy of the new generation wireless networks.V této dizertační práci je provedena studie nových přenosových protokolů pro různé bezdrátové síťové systémy. S využitím matematické analýzy jsme analyzovali a vyhodnotili efektivitu přenosu z hlediska pravděpodobnosti výpadku přes Rayleighův kanál. Teoretické analýzy jsou ověřeny provedenými simulacemi metodou Monte Carlo.
Nejprve došlo ke studii kooperativního přenosu ve dvoucestném dekóduj-a-předej (Two-Way Decode-and-Forward–TWDF) a vícecestném DF schématu s větším počtem přenosových uzlů pro sekundární systém, kdy takto byl získán přístup ke spektru spolu s primárním systémem. Konkrétně jsme navrhli dvoucestné DF schéma se získáváním energie a dvoucestné DF neortogonální schéma s mnohonásobným přístupem (Non-orthogonal Multiple Access–NOMA) s digitálním síťovým kódováním. Kromě toho rovněž zkoumáme bezdrátové systémy s větším počtem přenosových uzlů, kde je přítomen výběr nejlepšího přenosového uzlu pro optimalizaci efektivnosti navrženého schématu. Přenosové protokoly navržených schémat EHAF (Energy Harvesting Amplify and Forward) a EHDF(Energy Harvesting Decode and Forward) jsou společně porovnány v identickém prostředí z pohledu pravděpodobnosti výpadku. Následně, na základě získaných výsledků, jsme dospěli k závěru, že navržená schémata vylepšují výkonnost bezdrátových kooperativních systémů, konkrétně jejich propustnost.
Dále jsme se zaměřili na zkoumání NOMA technologie a navrhli optimální řešení (protokoly) pro urychlení datového přenosu a zajištění QoS v další generaci bezdrátových komunikací. V této práci jsme navrhli dvoucestné DF NOMA schéma (nazýváno jako TWNOMA protokol), ve kterém mezilehlý přenosový uzel napomáhá dvěma zdrojovým uzlům komunikovat mezi sebou. Výsledky simulace a analýzy ukazují, že navržený protokol TWNOMA vylepšuje dosaženou přenosovou rychlost v porovnání s konvenčním dvoucestným schématem používajícím DNC (TWDNC protokol), dvoucestným schématem bez použití DNC (TWNDNC protokol) a dvoucestným schématem v zesil-a-předej (amplify-and-forward) přenosových systémech (TWANC protokol).
Nakonec jsme zvážili využití kombinace NOMA a zabezpečení fyzické vrstvy (Physical Layer Security–PLS) v podpůrné kooperativní kognitivní síti (Underlay Cooperative Cognitive Network–UCCN). Zde je zde zkoumán výběr nejlepšího přenosového uzlu, který užívá NOMA a bere v úvahu PLS pro efektivnější přenos a zabezpečení nové generace bezdrátových sítí.440 - Katedra telekomunikační technikyvyhově
Adaptive Randomized Distributed Space-Time Coding in Cooperative MIMO Relay Systems
An adaptive randomized distributed space-time coding (DSTC) scheme and
algorithms are proposed for two-hop cooperative MIMO networks. Linear minimum
mean square error (MMSE) receivers and an amplify-and-forward (AF) cooperation
strategy are considered. In the proposed DSTC scheme, a randomized matrix
obtained by a feedback channel is employed to transform the space-time coded
matrix at the relay node. Linear MMSE expressions are devised to compute the
parameters of the adaptive randomized matrix and the linear receive filter. A
stochastic gradient algorithm is also developed to compute the parameters of
the adaptive randomized matrix with reduced computational complexity. We also
derive the upper bound of the error probability of a cooperative MIMO system
employing the randomized space-time coding scheme first. The simulation results
show that the proposed algorithms obtain significant performance gains as
compared to existing DSTC schemes.Comment: 4 figure
Constellation Mapping for Physical-Layer Network Coding with M-QAM Modulation
The denoise-and-forward (DNF) method of physical-layer network coding (PNC)
is a promising approach for wireless relaying networks. In this paper, we
consider DNF-based PNC with M-ary quadrature amplitude modulation (M-QAM) and
propose a mapping scheme that maps the superposed M-QAM signal to coded
symbols. The mapping scheme supports both square and non-square M-QAM
modulations, with various original constellation mappings (e.g. binary-coded or
Gray-coded). Subsequently, we evaluate the symbol error rate and bit error rate
(BER) of M-QAM modulated PNC that uses the proposed mapping scheme. Afterwards,
as an application, a rate adaptation scheme for the DNF method of PNC is
proposed. Simulation results show that the rate-adaptive PNC is advantageous in
various scenarios.Comment: Final version at IEEE GLOBECOM 201
STiCMAC: A MAC Protocol for Robust Space-Time Coding in Cooperative Wireless LANs
Relay-assisted cooperative wireless communication has been shown to have
significant performance gains over the legacy direct transmission scheme.
Compared with single relay based cooperation schemes, utilizing multiple relays
further improves the reliability and rate of transmissions. Distributed
space-time coding (DSTC), as one of the schemes to utilize multiple relays,
requires tight coordination between relays and does not perform well in a
distributed environment with mobility. In this paper, a cooperative medium
access control (MAC) layer protocol, called \emph{STiCMAC}, is designed to
allow multiple relays to transmit at the same time in an IEEE 802.11 network.
The transmission is based on a novel DSTC scheme called \emph{randomized
distributed space-time coding} (\emph{R-DSTC}), which requires minimum
coordination. Unlike conventional cooperation schemes that pick nodes with good
links, \emph{STiCMAC} picks a \emph{transmission mode} that could most improve
the end-to-end data rate. Any station that correctly receives from the source
can act as a relay and participate in forwarding. The MAC protocol is
implemented in a fully decentralized manner and is able to opportunistically
recruit relays on the fly, thus making it \emph{robust} to channel variations
and user mobility. Simulation results show that the network capacity and delay
performance are greatly improved, especially in a mobile environment.Comment: This paper is a revised version of a paper with the same name
submitted to IEEE Transaction on Wireless Communications. STiCMAC protocol
with RTS/CTS turned off is presented in the appendix of this draf
Adaptive Network Coding Schemes for Satellite Communications
In this paper, we propose two novel physical layer aware adaptive network
coding and coded modulation schemes for time variant channels. The proposed
schemes have been applied to different satellite communications scenarios with
different Round Trip Times (RTT). Compared to adaptive network coding, and
classical non-adaptive network coding schemes for time variant channels, as
benchmarks, the proposed schemes demonstrate that adaptation of packet
transmission based on the channel variation and corresponding erasures allows
for significant gains in terms of throughput, delay and energy efficiency. We
shed light on the trade-off between energy efficiency and delay-throughput
gains, demonstrating that conservative adaptive approaches that favors less
transmission under high erasures, might cause higher delay and less throughput
gains in comparison to non-conservative approaches that favor more transmission
to account for high erasures.Comment: IEEE Advanced Satellite Multimedia Systems Conference and the 14th
Signal Processing for Space Communications Workshop (ASMS/SPSC), 201
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