Nhu Tri Do

Outage Performance Analysis of Relay Selection Schemes in Wireless Energy Harvesting Cooperative Networks over Non-Identical Rayleigh Fading Channels

In this paper, we study relay selection in decode-and-forward wireless energy harvesting cooperative networks. In contrast to conventional cooperative networks, the relays harvest energy from the source’s radio-frequency radiation and then use that energy to forward the source information. Considering power splitting receiver architecture used at relays to harvest energy, we are concerned with the performance of two popular relay selection schemes, namely, partial relay selection (PRS) scheme and optimal relay selection (ORS) scheme. In particular, we analyze the system performance in terms of outage probability (OP) over independent and non-identical (i.n.i.d.) Rayleigh fading channels. We derive the closed-form approximations for the system outage probabilities of both schemes and validate the analysis by the Monte-Carlo simulation. The numerical results provide comprehensive performance comparison between the PRS and ORS schemes and reveal the effect of wireless energy harvesting on the outage performances of both schemes. Additionally, we also show the advantages and drawbacks of the wireless energy harvesting cooperative networks and compare to the conventional cooperative networks.

A Soft-Hard Combination-Based Cooperative Spectrum Sensing Scheme for Cognitive Radio Networks

In this paper we propose a soft-hard combination scheme, called SHC scheme, for cooperative spectrum sensing in cognitive radio networks. The SHC scheme deploys a cluster based network in which Likelihood Ratio Test (LRT)-based soft combination is applied at each cluster, and weighted decision fusion rule-based hard combination is utilized at the fusion center. The novelties of the SHC scheme are as follows: the structure of the SHC scheme reduces the complexity of cooperative detection which is an inherent limitation of soft combination schemes. By using the LRT, we can detect primary signals in a low signal-to-noise ratio regime (around an average of −15 dB). In addition, the computational complexity of the LRT is reduced since we derive the closed-form expression of the probability density function of LRT value. The SHC scheme also takes into account the different effects of large scale fading on different users in the wide area network. The simulation results show that the SHC scheme not only provides the better sensing performance compared to the conventional hard combination schemes, but also reduces sensing overhead in terms of reporting time compared to the conventional soft combination scheme using the LRT.

Performance analysis of multirelay RF energy harvesting cooperative networks with hardware impairments

In this study, the authors analyse the outage performance of multirelay decode-and-forward cooperative networks subject to two joint practical issues of wireless communications, namely, energy constraints and transceiver hardware impairment (HI). To deal with energy constraints at relay nodes, radio-frequency (RF) energy harvesting (EH) technique is adopted. Considering the joint impacts of RF EH technique and HI, two relay selection schemes, namely, harvested energy-based relay selection (HEbS) scheme and channel quality-base relay selection (CQbS) scheme are proposed. Tight closed-form approximate expressions for the outage probability of each scheme are derived and corroborated through Monte Carlo simulations. Some representative performance comparisons are carried out and show that the diversity order achieved by the HEbS scheme is 1 and is independent of the number of relays, K, whereas that achieved by the CQbS scheme is K, which is full diversity.

Secure transmission using decode-and-forward protocol for underlay cognitive radio networks

In this paper, we study the physical layer security for underlay cognitive radio network in the presence of an eavesdropper that tries to intercept the secondary transmission. Specifically, a transmission at each hop uses a same frequency band of a primary user as long as the interference that caused by the secondary transmission at a primary receiver does not excess a maximum tolerable interference level. We investigate the secrecy outage probability (SOP) for a cognitive decode-and-forward (DF) relay network. Moreover, we drive a closed-form expression of the SOP of the considered system. Simulation results validate our theoretical results under three distinct cases as follows: the signal-to-noise ratio (SNR) of the main link between a secondary transmitter and a corresponding receiver is, respectively, smaller, equal to, or larger than the SNR of the eavesdropper link between the same secondary transmitter and the eavesdropper.

A relay selection protocol for wireless energy harvesting relay networks

In this paper, we consider a dual-hop decode-and-forward (DF) relaying network, where relays operate based on harvested energy from radio frequency (RF) radiation. Considering time switching-based relaying mechanism, we propose a relay selection protocol, where the relay having the highest harvested energy will forward the received signal towards the destination. We investigate the system performance in terms of outage probability over Rayleigh fading channels. In particular, we derive the analytical expression of the system outage probability and the closed-form expression of its lower bound of the proposed protocol. The analysis results are validated by the Monte-Carlo simulation results. The numerical results show that the proposed relay selection and the number of relays have significant impacts on the system outage probability.

Outage performance of physical layer security for multi-hop underlay cognitive radio networks with imperfect channel state information

In this paper, we consider a multi-hop decode-and-forward (DF) relaying transmission in underlay cognitive radio networks. Considering the presence of an eavesdropper that overhears the transmission, we address secure communications of multi-hop wireless communications in terms of physical layer security. In addition, we take in to account the effect of imperfect channel state information (CSI) which is of importance issue in underlay cognitive radio. We analyze the secrecy outage performance of the system over Rayleigh fading channels. In particular, we derive the closed-form expression of the system secrecy outage probability. The analysis results are validated by the Monte-Carlo simulation results. The numerical results show that the imperfect CSI issue does not effect on the security issue of the transmission in underlay cognitive radio networks. On the other hand, the number of hops plays a key role in the physical layer security.

Transmit antenna selection schemes for MISO-NOMA cooperative downlink transmissions with hybrid SWIPT protocol

In this paper, we investigate outage performance and diversity gain of transmit antenna selection (TAS) schemes in two-user multiple-input single-output non-orthogonal multiple access (MISO-NOMA) cooperative downlink transmissions. To this end, two TAS criteria, namely Criterion I and Criterion II, are proposed, which select an antenna that experiences the best fading condition of the channel from the source to the far user and to the near user, respectively. Additionally, considering the near user as a relay to help improve the reliability of the far user, hybrid simultaneous wireless information and power transfer (SWIPT) architecture is adopted to power the near users relaying operation. Tight closed-form approximate expressions for the outage probability (OP) of both users are derived. Numerical results reveal that Criterion I and II achieve, respectively, the diversity order of K + 1 and 2 at the far user, and 1 and K at the near user, where K denotes the number of transmit antennas at the base station.

Performance Analysis of Physical Layer Security of Opportunistic Scheduling in Multiuser Multirelay Cooperative Networks

In this paper, we study the physical layer security (PLS) of opportunistic scheduling for uplink scenarios of multiuser multirelay cooperative networks. To this end, we propose a low-complexity, yet comparable secrecy performance source relay selection scheme, called the proposed source relay selection (PSRS) scheme. Specifically, the PSRS scheme first selects the least vulnerable source and then selects the relay that maximizes the system secrecy capacity for the given selected source. Additionally, the maximal ratio combining (MRC) technique and the selection combining (SC) technique are considered at the eavesdropper, respectively. Investigating the system performance in terms of secrecy outage probability (SOP), closed-form expressions of the SOP are derived. The developed analysis is corroborated through Monte Carlo simulation. Numerical results show that the PSRS scheme significantly improves the secure ability of the system compared to that of the random source relay selection scheme, but does not outperform the optimal joint source relay selection (OJSRS) scheme. However, the PSRS scheme drastically reduces the required amount of channel state information (CSI) estimations compared to that required by the OJSRS scheme, specially in dense cooperative networks.

Opportunistic scheduling for fixed-gain amplify-and-forward-based multiuser multirelay SWIPT cooperative networks

In this paper, we analyze the downlink outage performance of opportunistic scheduling in dual-hop fixed-gain amplify-and-forward (FG-AF) cooperative networks consisting of one source, multiple radio-frequency (RF) energy harvesting relays, and multiple destinations. To this end, a relay-destination selection scheme named direct links plus opportunistic channel state information (CSI)-based selection (DOS) scheme is proposed. The performance analysis in terms of outage probability (OP) is carried out for the proposed DOS scheme. In particular, an exact closed-form expression for the OP is provided. The developed analysis is corroborated through Monte-Carlo simulation. Numerical results show that the DOS scheme achieves full diversity gain, i.e., K + M, where K and M are the numbers of relays and destinations, respectively.

Connectivity of hybrid overlay/underlay cognitive radio ad hoc networks

In this paper, we study the connectivity of a hybrid cognitive radio ad hoc network (H-CRAHN) in which each secondary user can be able to use either overlay cognitive radio or underlay cognitive radio paradigms to access a licensed spectrum. Specifically, we carry out a simulation-based analysis to investigate the connectedness between two arbitrary nodes in the H-CRAHN. Considering such a hybrid network, we propose an algorithm to calculate the path probability which measures the connectivity of the network. We then exam what network parameters that impact on the connectivity of the H-CRAHN. The simulation results show that by using the hybrid underlay/overlay transmission mode at the SUs, the path probability increases compared to the use of only underlay mode or overlay mode. In addition, active rate of primary user, node density, and transmit power play key roles in the study of the network connectivity.