Long Yang

Outage Performance of DF-Based Cooperative Multicast in Spectrum-Sharing Cognitive Relay Networks

This letter investigates the outage performance of decode-and-forward-based cooperative multicast (CM) in spectrum-sharing cognitive relay networks (CRNs). Considering a CRN coexisted with multiple primary users, a closed-form expression for the exact outage probability of CM is derived over independently and non-identically distributed Rayleigh fading channels. The asymptotic analysis is also presented to reveal that the diversity gain of CM in CRNs is determined by the number of relays, and the spectrum-sharing scenario only has impact on coding gain. Simulation results corroborate our theoretical analysis.

Optimal Relay Selection for Secure Cooperative Communications With an Adaptive Eavesdropper

Optimal relay selection is investigated for secure cooperative communications against an adaptive eavesdropper that can perform eavesdropping if the eavesdropping link has good channel quality or perform jamming otherwise. A number of decode-and-forward relays are available for legitimate communications, among which one relay can be selected to help. For legitimate communications, three cases for availability of the eavesdropping channel information are considered: full channel knowledge, partial channel knowledge, and statistical channel knowledge. An optimal relay selection scheme is proposed for each case. For the first and third cases, exact secrecy outage probability expressions in closed form are derived, and for the second case, an approximate secrecy outage probability is derived, which is tight in the high main-to-eavesdropper ratio regime. Moreover, secrecy diversity order for the proposed relay selection scheme in each case is also derived, which is shown to be a full secrecy diversity. Finally, numerical results are given to verify the theoretical analysis derived in this paper.

Improving physical-layer security in untrusted relay networks: cooperative jamming and power allocation

The inherent broadcast characteristics of wireless medium make wireless data transmission difficult to be shielded from unintended recipients. As such, secure communication over wireless channels becomes a critical issue in the design of wireless networks. In this study, the authors study cooperative jamming and power optimisation in untrusted relay networks to improve physical layer security. By exploiting the direct link, a source-based jamming (SBJ) scheme is proposed to hinder the untrusted relay from intercepting the confidential message. Considering the total power budget, a power allocation strategy is also proposed to optimally determine the power of source and untrusted relay as well as the power of information and jamming signals. Furthermore, to evaluate the secrecy performance of the proposed SBJ scheme with the power allocation strategy, tight lower bound of ergodic secrecy capacity and asymptotic secrecy outage probability are derived in closed form. Simulation verifies the advantages of the proposed SBJ scheme and the power allocation strategy.

Cooperative Wireless Multicast: Performance Analysis and Time Allocation

Cooperative wireless multicast is investigated, in which a source sends multicast messages to a number of users. For a multicast message from the source, some users do not successfully receive the message (called unsuccessful users). For a successful user (who successfully receives the message from the source), we define its worst relaying channel gain as the smallest channel gain among its channel gains to all unsuccessful users. It is proposed that the successful user whose worst relaying channel gain is the highest among the worst relaying channel gains of all successful users is selected to serve as a relay. Considering that the channels in the system are independent but nonidentically distributed Rayleigh fading, we derive a closed-form outage probability expression for the proposed scheme. It is shown that the proposed scheme can achieve full diversity, and thus, having a larger number of users can improve the outage performance. Furthermore, we study the time allocation strategy that determines the durations used by the source and the selected relay for their transmissions, respectively. An approximate optimal time allocation is derived. In addition, we also investigate the case with relay selection error and the case with mixed Rayleigh/Rician fading. Simulation results verify the performance of the proposed cooperative multicast scheme and time allocation strategy.

Secure Communications in Underlay Cognitive Radio Networks: User Scheduling and Performance Analysis

This letter investigates secure communications against eavesdropping in an underlay cognitive radio network. The secondary users do not know the interference level that they receive from the primary transmitter, and thus, secondary transmissions may experience outages. We consider an outage probability threshold for secondary transmissions, and propose secondary user scheduling schemes for downlink and uplink, targeting at maximizing the achievable secrecy rate. We derive closed-form secrecy outage probability and show that the proposed user scheduling schemes can achieve full secrecy diversity.

Differential successive relaying scheme for fast and reliable data delivery in vehicular ad hoc networks

The high-speed mobility of modern transportation worsens the situation of unstable direct links and imprecise channel estimation, which poses challenges on fast and reliable data delivery in vehicular ad hoc networks (VANETs). The goal of the proposed scheme is to provide high-speed full-duplex relaying connectivity for unstable direct links, and reliable information detection without precise channel state information (CSI) in VANETs. In the proposed scheme, full-duplex relaying connectivity is provided by differential successive relays (DSRs) at roadside or inside other vehicles. To improve robustness of DSR without specific CSI, efficient blind interference cancellation is presented to mitigate inter-relay interference. Meanwhile, reliable information detection without precise CSI is enabled by superposition coding with differential modulation. Furthermore, the advantages, applications of DSR and complexities for real-world implementation are discussed, and the decision rule, bit error probability and ergodic capacity are theoretically obtained. Numerical results verify significant improvements in the performance of the proposed scheme when compared with conventional schemes with half-duplex relays and frequent channel estimation in VANETs.

Three‐path successive relaying protocol with blind inter‐relay interference cancellation and cooperative non‐coherent detection

Successive relaying has recently emerged as a spectral-efficient technique for cooperative wireless communications. However, in scenarios with uncertain accuracy of instantaneous channel state information (CSI), the scope of conventional two-path successive relaying protocol shrinks. This is due to the challenges of cancelling inter-relay interference (IRI) and detecting signals efficiently without specific CSI. The two challenges motivate us to propose a novel double listening 3-path successive relaying (DL3PSR) protocol to mitigate the successive relayings dependence on accurate instantaneous CSI. We overcome the first challenge by proposing a blind IRI cancellation technique, and its effectiveness is proven. After blind IRI cancellation, the challenge of efficient signal detection is overcome by robust cooperative non-coherent detection, which consists of exclusive OR (XOR) demodulation and joint decoding. Based on constellation mapping, XOR demodulation is designed to demodulate M-ary phase-shift keying symbols without instantaneous CSI. Moreover, joint forward and backward decoding strategy is proposed to improve the robustness of data detection by retrieving two independent versions of the original data. Furthermore, the detection threshold, bit error probability, and achievable rate of DL3PSR are theoretically obtained. Simulations verify that in scenarios without full knowledge of CSI, DL3PSR protocol outperforms conventional two-path successive relaying in bit error performance and that the rate of DL3PSR is close to that of the full-duplex relaying. Copyright

NOMA-Enabled Cooperative Unicast–Multicast: Design and Outage Analysis

This paper designs a novel non-orthogonal multiple access (NOMA) unicast–multicast system, where a number of unicast users (those who require different messages) and a group of multicast users (those who require identical message) share the same time/space/frequency resource. For the designed NOMA unicast–multicast system, an efficient two-phase cooperation strategy is proposed to improve the reliability of all users. In the first phase, the base station (BS) broadcasts a superposed message consisting of all users’ information. In the second phase, a multicast user is selected to forward the information intended by unsuccessfully decoded unicast and/or multicast users. Moreover, the multicast user selection is investigated under two different power allocation (PA) approaches: 1) fixed PA (FPA), in which the PA coefficients for both the phases are predetermined, and 2) dynamic PA (DPA), in which the PA coefficients for the first phase are predetermined, while the PA coefficients for the second phase are dynamically determined based on instantaneous channel information. Under the FPA approach, a best user selection (BUS) scheme (called F-BUS) is proposed to minimize the outage probability. Under the DPA approach, the local optimal PA coefficients for the second phase are derived in closed form first. Based on the derived PA coefficients, a BUS scheme (called D-BUS) is then proposed for outage probability minimization. To verify the reliability of the proposed cooperation strategy with employing the BUS schemes, we theoretically analyze the outage probability as well as diversity orders. It is shown that the proposed cooperation strategy achieves diversity orders equal to the number of multicast users, indicating that the inherent diversity orders offered by the multicast users are fully exploited. Finally, simulation results are presented to validate the theoretical results and demonstrate the advantages of the proposed cooperation strategy and the BUS schemes.

Cooperative jamming for energy harvesting multicast networks with an untrusted relay

Recently, there are increasing requirements of security in wireless communications, especially for the multiuser systems. In this study, the authors consider the security of two-hop cooperative multicast networks with an untrusted relay. An energy harvesting destination aided cooperative jamming framework is proposed to protect information from being intercepted by the untrusted relay. For the multiple destinations, a maximum interference jammer selection (MIJS) scheme is proposed to further improve physical layer security. Then the ergodic secrecy rate (ESR) for MIJS scheme is investigated and both the lower bound of ESR and the approximation of ESR are obtained. Finally, the effect of both the energy arrival rate and the number of destination nodes on ESR has been shown via numerical simulations. It can be revealed that as the number of destinations increases, the ESR is determined with two common behaviours regarding the multicast nature and energy arrival rate: (i) multicast nature forces the secrecy rate to decrease with the increasing number of destinations and (ii) the probability that a jammer exists increases with the increasing number of destinations but limited to one.