30 research outputs found
A secure network coding based modify-and-forward scheme for cooperative wireless relay networks
This paper investigates the security at the physical layer of cooperative relay communications. Inspired by the principle of physical-layer network coding (PNC), we propose a new secure relaying scheme, namely secure PNC-based modify-and-forward (SPMF). In the proposed scheme, the relay node linearly combines the decoded data from the source node with an encrypted key before conveying the mixed data to the destination node. As both the linear PNC operation and encrypted key at the relay are unknown to the eavesdropper, the SPMF scheme provides a double security level in the system. Particularly, taking into account the practical scenario of the imperfect knowledge shared between the relay and destination, the secrecy outage probability (SOP) of the proposed SPMF scheme is analysed and evaluated in comparison with modify-and-forward, cooperative jamming, decode-and-forward and direct transmission schemes. The proposed scheme is shown to achieve a performance improvement of up to 3 dB when compared to the conventional schemes under imperfect knowledge of shared information between the nodes
Theoretical predictions of melting behaviors of hcp iron up to 4000 GPa
The high-pressure melting diagram of iron is a vital ingredient for the
geodynamic modeling of planetary interiors. Nonetheless, available data for
molten iron show an alarming discrepancy. Herein, we propose an efficient
one-phase approach to capture the solid-liquid transition of iron under extreme
conditions. Our basic idea is to extend the statistical moment method to
determine the density of iron in the TPa region. On that basis, we adapt the
work-heat equivalence principle to appropriately link equation-of-state
parameters with melting properties. This strategy allows explaining
cutting-edge experimental and ab initio results without massive computational
workloads. Our theoretical calculations would be helpful to constrain the
chemical composition, internal dynamics, and thermal evolution of the Earth and
super-Earths
Преподавание медицинской реабилитации: фокус на физические аспекты
ВУЗЫВЫСШИЕ УЧЕБНЫЕ ЗАВЕДЕНИЯОБРАЗОВАНИЕ МЕДИЦИНСКОЕМЕДИЦИНСКАЯ РЕАБИЛИТАЦИЯМЕТОДИКА ПРЕПОДАВАНИ
Hybrid spectrum access with relay assisting both primary and secondary networks under imperfect spectrum sensing
This paper proposes a novel hybrid interweave-underlay spectrum access for a cognitive amplify-and-forward relay network where the relay forwards the signals of both the primary and secondary networks. In particular, the secondary network (SN) opportunistically operates in interweave spectrum access mode when the primary network (PN) is sensed to be inactive and switches to underlay spectrum access mode if the SN detects that the PN is active. A continuous-time Markov chain approach is utilized to model the state transitions of the system. This enables us to obtain the probability of each state in the Markov chain. Based on these probabilities and taking into account the impact of imperfect spectrum sensing of the SN, the probability of each operation mode of the hybrid scheme is obtained. To assess the performance of the PN and SN, we derive analytical expressions for the outage probability, outage capacity, and symbol error rate over Nakagami-m fading channels. Furthermore, we present comparisons between the performance of underlay cognitive cooperative radio networks (CCRNs) and the performance of the considered hybrid interweave-underlay CCRN in order to reveal the advantages of the proposed hybrid spectrum access scheme. Eventually, with the assistance of the secondary relay, performance improvements for the PN are illustrated by means of selected numerical results
Performance Assessment of Cooperative Relay Networks with Advanced Radio Transmission Techniques
In the past decade, cooperative communications has been emerging as a pertinent
technology for the current and upcoming generations of mobile communication
infrastructure. The indispensable benefits of this technology have motivated
numerous studies from both academia and industry on this area. In particular,
cooperative communications has been developed as a means of alleviating the
effect of fading and hence improve the reliability of wireless communications.
The key idea behind this technique is that communication between the source and
destination can be assisted by several intermediate nodes, so-called relay
nodes. As a result, cooperative communication networks can enhance the
reliability of wireless communications where the transmitted signals are
severely impaired because of fading. In addition, through relaying
transmission, communication range can be extended and transmit power of each
radio terminal can be reduced as well.
The objective of this thesis is to analyze the system performance of
cooperative relay networks integrating advanced radio transmission techniques
and using the two major relaying protocols, i.e., decode-and-forward (DF) and
amplify-and-forward (AF). In particular, the radio transmission techniques that
are considered in this thesis include multiple-input multiple-output (MIMO)
systems and orthogonal space-time block coding (OSTBC) transmission, adaptive
transmission, beamforming transmission, coded cooperation, and cognitive radio
transmission.
The thesis is divided into an introduction section and six parts based on
peer-reviewed journal articles and conference papers. The introduction provides
the readers with some fundamental background on cooperative communications
along with several key concepts of cognitive radio systems. In the first part,
performance analysis of cooperative single and multiple relay networks using
MIMO and OSTBC transmission is presented wherein the diversity gain, coding
gain, outage probability, symbol error rate, and channel capacity are assessed.
It is shown that integrating MIMO and OSTBC transmission into cooperative relay
networks provides full diversity gain. In the second part, the performance
benefits of MIMO relay networks with OSTBC and adaptive transmission strategies
are investigated. In the third part, the performance improvement with respect
to outage probability of coded cooperation applied to opportunistic DF relay
networks over conventional cooperative networks is shown. In the fourth part,
the effects of delay of channel state information feedback from the destination
to the source and co-channel interference on system performance is analyzed for
beamforming AF relay networks. In the fifth part, cooperative diversity is
investigated in the context of an underlay cognitive AF relay network with
beamforming. In the sixth part, finally, the impact of the interference power
constraint on the system performance of multi-hop cognitive AF relay networks
is investigated
Adaptive Modulation and Coding with Queue Awareness in Cognitive Incremental Decode-and-Forward Relay Networks
This paper studies the performance of adaptive modulation and coding in a
cognitive incremental decode-and-forward relaying network where a secondary
source can directly communicate with a secondary destination or via an
intermediate relay. To maximize transmission efficiency, a policy which
flexibly switches between the relaying and direct transmission is proposed. In
particular, the transmission, which gives higher average transmission
efficiency, will be selected for the communication. Specifically, the direct
transmission will be chosen if its instantaneous signal-to-noise ratio (SNR) is
higher than one half of that of the relaying transmission. In this case, the
appropriate modulation and coding scheme (MCS) of the direct transmission is
selected only based on its instantaneous SNR. In the relaying transmission,
since the MCS of the transmissions from the source to the relay and from the
relay to the destination are implemented independently to each other, buffering
of packets at the relay is necessary. To avoid buffer overflow at the relay,
the MCS for the relaying transmission is selected by considering both the queue
state and the respective instantaneous SNR. Finally, a finite-state Markov
chain is modeled to analyze key performance indicators such as outage
probability and average transmission efficiency of the cognitive relay network
Amplify-and-Forward Relay Assisting both Primary and Secondary Transmissions in Cognitive Radio Networks over Nakagami-m Fading
In this paper, we study the performance for the primary and secondary
transmissions in cognitive radio networks
where the amplify-and-forward (AF) secondary relay helps to transmit the
signals for both the primary and secondary transmitters over independent
Nakagami-m fading. First, we derive exact closed-form expressions for outage
probability and symbol error rate (SER) of the primary network. Then, we derive
an exact closed-form expression for outage probability and a closed-form
expression of a tight upper bound for SER of the secondary network.
Furthermore, we also make a comparison for the performance of the primary
system with and without the
help of the secondary relay