Yueying Zhang

Secrecy Capacity Enhancement With Distributed Precoding in Multirelay Wiretap Systems

The secrecy capacity of relay communications is investigated in this paper, where an eavesdropper is present. Distributed precoding through multiple relay nodes can be used to enhance the received signal power at the destination node and to mitigate the signal leakage to the eavesdropper, simultaneously. Due to individual power constraints at relay nodes, the distributed precoding scalar at each relay node is equivalent to a distributed precoding angle. An iterative algorithm is proposed to find the suboptimum distributed precoding angles at all the relay nodes, where the channel state information (CSI) sharing overhead among the relay nodes can also be substantially reduced. Each relay node receives the equivalent CSI from its preceding relay node, computes its distributed precoding angle, and updates the equivalent CSI for the next relay node. Compared with the simple decode-and-forward relaying protocol with random distributed precoding, the proposed iterative distributed precoding algorithm is able to further improve on the secrecy capacity of the multirelay wiretap system with an acceptable CSI sharing overhead.

Cooperative jamming and power allocation with untrusty two-way relay nodes

This study investigates the security of the two-way relaying system with untrusty relay nodes. Cooperative jamming schemes are considered for bi-directional secrecy communications. The transmit power of each source node is divided into two parts corresponding to the user and jamming signals, respectively. Two different assumptions of the jamming signals are considered. When the jamming signals are a priori known at the two source nodes, closed-form power allocation expressions at two source nodes are derived. Under the assumption of unknown jamming signals, it is proven that the cooperative jamming is useless for the system secrecy capacity, because that all the power should be allocated to the user signals at each source node. Relay selection is also investigated based on the analysis of cooperative jamming. Simulation results are presented to compare the system secrecy capacities under the two jamming signal assumptions.

Cooperative jamming and power allocation in three-phase two-way relaying wiretap systems

The security of the three-phase two-way relaying system with an eavesdropper is investigated in this paper. A cooperative jamming and power allocation scheme is proposed to enhance the system secrecy capacity. When a source node transmits user signals to the relay node, the other source node interferes the relay node with pre-defined jamming signals simultaneously. Optimum power allocation between the user and jamming signals at each source node is analyzed. Our analytical results suggest that the proposed cooperative jamming scheme improves on the system secrecy capacity, especially when the channel gains of the two source-relay links are of large difference. Simulation results in close agreement with analytical results clearly demonstrate the advantage of the proposed cooperative jamming scheme.

A Novel QoE-Based Carrier Scheduling Scheme in LTE-Advanced Networks with Multi-Service

Carrier aggregation is one of the key techniques for the advancement of long-term evolution (LTE- Advanced) networks. This article proposes a quality- of-experience (QoE)-based carrier scheduling scheme for networks with multiple services. The proposed scheme aims at maximizing the user QoE, which is determined by both the application-level and network-level quality of services. Packet delay, as an essential factor affecting QoE, is first discussed under the context of QoE optimization as well as the data rate. The component carriers are dynamically scheduled according to the network traffic load by the proposed novel scheme. Simulation results show that our approach can achieve significant improvement in QoE and fairness over conventional approaches.

Analysis of Conditional Error Rate and Combining Schemes in HARQ

In hybrid automatic repeat request (HARQ), maximum ratio combining (MRC) is usually employed at the receiver if the retransmission signal is the same as that in the first transmission. However, conventional performance analysis of HARQ and MRC does not consider that all previous transmissions fail. In this paper, we analyze the conditional error rate of HARQ with arbitrary combining schemes. Both the theoretical and approximate expressions of the conditional error rate are derived. Our analytical and simulation results reveal that conventional MRC is not optimum for HARQ, especially when the packet is short or the channel gain of the first transmission is much better than that of retransmission.

QoE and energy efficiency aware resource allocation for OFDM systems in group mobility environments

The global information and communication technology industry is a fast growing contributor to the electrical energy consumption, especially for the base stations, accounting for a substantial amount of the energy use. Inherently, a resource allocation strategy including subchannels blackout would reduce energy consumption. In this paper, energy efficient resource allocation algorithms are addressed for the OFDM system in group mobility environments, suffering from high intercarrier interference. We first propose the subchannels blackout scheme to save energy implicitly without performance degradation by turning off certain subchannels when transmitting signals. Then, resource allocation scheme in combination with subchannels blackout scheme is developed, consisting of intergroup subchannels allocation and inner-group subchannels blackout. Its advantage is twofold. i Energy consumption is reduced obviously; ii intercarrier interference is decreased and channel quality is enhanced simultaneously. However, the original transmit rate decreases with the decrease of active resources. We also prove under subchannels blackout scheme, achieved throughput and perceptual quality of experience QoE are quasiconcave in energy saving percentage, which reflects the number of blackout subchannels. We then present two energy efficient resource allocation algorithms. Both algorithms focus on the optimal solution by using an iteration method. The difference lies in the objective. One tries for energy consumption minimization above the satisfactory QoE level, but the other aims to maximize QoE perceived by users. Numerical results confirm the theoretical findings and demonstrate the promising energy-saving capability with satisfying QoE of the proposed resource allocation schemes. Copyright

A novel codebook design with the LBG algorithm in precoding systems under spatial correlated channel

Precoding is an efficient approach to obtain high channel capacities and high quality in multiple-input-multiple-output systems and draws much attention in recent researches. In the codebook-based precoding systems, the tradeoff between performance and feedback overhead should be considered. In this paper, a novel version of the Linde-Buzo-Gray (LBG) algorithm is first utilized in the codebook design by redefining a set of operations in the conventional LBG algorithm. Moreover, the codebook can be trained online under spatial correlated channel adapting to the channel variation. Simulation results demonstrate that the proposed codebook design achieves better robustness, smaller quantization error and higher capacity than the traditional fixed uniform codebook design does.

Cross-Layer Design for TCP Throughput Optimization in Cooperative Relaying Networks

In this paper, we investigate the transmission control protocol (TCP) throughput in cooperative relaying networks and take an cross-layer design approach when selecting a relay to optimize the TCP throughput. A first-order finite-sate Markov channel (FSMC) is used to model the wireless time varying channels, and the TCP throughput is estimated as a function of physical layer signal-to-noise ratio (SNR) and link-layer frame size and retransmission times. Since relay selection is crucial in improving the TCP performance, we proposed a stochastic decision making approach to select the optimal relay for every TCP packet according to the states of each relay. We formulated the cross-layer TCP throughput optimization problem as a restless bandit system and obtained the statistically optimal relay selection policy, which has an indexability property and can be easily implemented in real system. We compare the proposed scheme through simulations under different parameters of physical layer and link-layer, simulation results show that the TCP throughput can be improved significantly by the optimal relay selection scheme.

Successive Phase Sharing and Distributed Multiuser Precoding in Multirelay Systems

In wireless sensor networks, several relay nodes can be used to support multiple transmission links between source and destination nodes simultaneously to achieve higher spectral efficiency. A channel state information sharing scheme among multiple relay nodes is presented in this letter, where only one angle per source-destination pair is sent from one relay node to another. Then, to enhance received signal powers, a distributed multiuser precoding scheme is presented to be used at each relay node with the angles sent by another relay node. Simulation results demonstrate that the proposed distributed precoding scheme enhances the capacity performance with slight overhead.

Cooperative Jamming and Power Allocation in Two-Way Relaying System with Eavesdropper

The security of the two-way relaying system with an eavesdropper is investigated in this paper. A cooperative jamming and power allocation scheme is proposed to enhance the system secrecy capacity. Both user and pre-defined jamming signals are transmitted by each source node simultaneously. The optimum power allocation between the user and jamming signals at each source node is derived. Our analytical results suggest that the proposed cooperative jamming scheme improves on the system secrecy capacity, especially when the channel gains of the two source-relay links are of large difference. Simulation results in close agreement with analytical results clearly demonstrate the advantage of the proposed cooperative jamming scheme.