Cai Yueming

A Game-Theoretic Dynamic Power Management Policy on Wireless Sensor Network

Game theory is a set of tools developed to model interactions between agents with conflicting interests, and is thus well-suited to address some problems in communications systems. In this paper we apply game theory to wireless sensor network power saving problem, and designed a dynamic power management policy for the nodes in the network. The policy has good effects on power saving while the complexity is low.

Cooperative Spectrum Sensing Technique

Cognitive Radios (CRs), which sense the spectrum and implement opportunistic sharing when no licensed user is found to use it, are able to improve the efficiency of spectrum. Spectrum sensing must be firstly solved in CRs. Cooperative sensing can make good use of network resources, obtain higher gain and make the network steadier. In this paper we give a brief introduction of the principle of cooperative sensing and discuss the cooperative sensing techniques in CRs. Simulation results show that cooperative sensing can improve the detection probability, improve the agility gain and thus help to improve the efficiency of spectrum.

An improved channel estimation scheme for OFDM systems by tracking the subspace

Channel parameters in OFDM systems over fading channels are generally obtained by transmitting pilot symbols in given positions of the time-frequency grid. The pilot-based method usually involves the LS estimation step on the pilot subcarriers and the interpolation step over the entire time-frequency grid. Increasing the accuracy of the pilot estimation will accordingly increase the precision in the interpolation step. This can be achieved by subspace tracking method. We propose in this paper an improved subspace-tracking algorithm by the Givens plane rotation based delay-subspace tracking and the RLS filtering based amplitude tracking. Performed on a parameterized model of the channel, simulations prove that our channel estimation is more robust and accurate while the complexity of the algorithm is low.

An Adaptive Non-Orthogonal Cooperation Scheme Based on Channel Quality Information

We consider cooperative relay communication in a wireless network composed of three nodes and limited by the half-duplex and total power constrained. Here we focused on the non-orthogonal transmission of relay node to achieve higher spectrum efficiency. Based on the channel quality information (CQI) at the relay node, an adaptive non- orthogonal cooperative scheme is proposed which combines the benefit of the amplify-and-forward and decode-and- forward strategies. The relay node adoptively chooses one of these two strategies to cooperate in order to obtain larger average mutual information between the source and destination node. When the CQI is available at the source node, the power allocation is utilized to improve the performance of the adaptive cooperation scheme.

A SISO Iterative Probabilistic Data Association Detector for MIMO Systems

In this paper, the Probabilistic Data Association (PDA) detection method for Multiple-Input Multiple-Output (MIMO) detection in V-BLAST systems is extended to the Soft-In-Soft-Out (SISO) iterative signal detection problem between PDA detector and channel decoder. The SISO PDA detector can considerably reduce the PDA internal iteration numbers and avoid the near singularity problem of the effective noise covariance matrix in high signal to noise ratio (SNR). Simulations under a multiple antenna Rayleigh fading scenario show that the SISO iterative PDA detector attains a better performance.

Space diversity schemes for STBC-based MIMO systems and pre-FDE SIMO systems

In wireless communications, multiple receive antennas can be used with orthogonal frequency division multiplexing (OFDM) or single-carrier (SC), and frequency domain equalization (FDE) or frequency domain pre-equalization (pre-FDE) to significantly improve system capacity and performance. However, the complexity of such combination can be very large because multiple discrete Fourier transform (DFT) blocks, each for one receive antenna, are required to fully take advantage of the space diversity. Reference Defeng Huang et al., (2004) proposed a receive space diversity architecture for OFDM systems using orthogonal designs. Using this architecture, the number of DFT blocks can be reduced but performance degradation will be introduced. In this paper, we propose space diversity schemes for space-time block coding (STBC) based multiple-input multiple-output (MIMO) systems and frequency domain pre-equalization single-input multiple-output (SIMO) systems. These schemes can be used with OFDM and SC transmission techniques. Using these schemes, the total number of Fourier transform (FT) blocks can be further reduced and the performance can be significantly improved at higher signal-to-noise ratio. Simulation results show the benefits of the proposed schemes

Space diversity schemes for STBC-based SC/FDE systems and SC/Pre-FDE systems

In wireless communications, multiple receive antennas can be used with orthogonal frequency division multiplexing (OFDM) or single-carrier (SC) frequency domain equalization (FDE) and frequency domain pre-equalization (Pre-FDE) to significantly improve system capacity and performance. However, the complexity of such combination can be very large because multiple discrete Fourier transform (DFT) blocks, each for one receive antenna, are required to fully take advantage of the space diversity. A receive space diversity architecture was proposed in previous paper for OFDM systems using orthogonal designs. Using this architecture, the number of DFT blocks can be reduced but performance degradation will be introduced. In this paper, we propose two space diversity schemes for SC systems; one uses pre-FDE technique and the other uses FDE and space-time block coding (STBC) technique to compose a multiple-input multiple-output (MIMO) system. Using these schemes, the total number of Fourier transform (FT) blocks can be further reduced but the performance can be significantly improved. Simulation results show that the proposed SC system schemes exceed the corresponding OFDM schemes at high signal-to-noise ratio (SNR).

Bargaining-based jammer power allocation for dynamic eavesdropping scenario

This paper proposes a bargaining-based jammer power allocation scheme for multi-source multi-destination wireless network in the presence of a friendly jammer and a malicious node which eavesdrops erratically. We formulate the erratic behavior of the eavesdropper as a novel model where the eavesdropper wiretaps the message of the legitimate sources with a certain probability in a time slot. Moreover, in order to obtain a fair and efficient solution, the jammer power allocation problem is modeled as a Nash bargaining game under the constraint of maximum transmit power of a friendly jammer, which is a convex optimization problem. Then, the closed form of the Nash bargaining solution (NBS) is derived, and a simple but effective centralized algorithm is proposed. Besides, we find that the even power allocation solution and the sum-secrecy-rate optimal solution are the special cases of the NBS, when the bargaining power is properly selected. Simulation results demonstrate that the NBS achieves a good performance in terms of both effectiveness and fairness.This paper proposes a bargaining-based jammer power allocation scheme for multi-source multi-destination wireless network in the presence of a friendly jammer and a malicious node which eavesdrops erratically. We formulate the erratic behavior of the eavesdropper as a novel model where the eavesdropper wiretaps the message of the legitimate sources with a certain probability in a time slot. Moreover, in order to obtain a fair and efficient solution, the jammer power allocation problem is modeled as a Nash bargaining game under the constraint of maximum transmit power of a friendly jammer, which is a convex optimization problem. Then, the closed form of the Nash bargaining solution (NBS) is derived, and a simple but effective centralized algorithm is proposed. Besides, we find that the even power allocation solution and the sum-secrecy-rate optimal solution are the special cases of the NBS, when the bargaining power is properly selected. Simulation results demonstrate that the NBS achieves a good performance in terms of both effectiveness and fairness.

Energy efficiency of distributed switch and stay combining system in WSNs

Wireless sensor network is a kind of network which usually consists of many energy-limited sensor nodes. Its important to enhance the energy efficiency. In this paper we describe a virtual switch and stay system called distributed switch and stay system with a single amplify and forward relay to simplify the scenario of wireless sensor networks. From the respect of outage probability, we compute the energy efficiency of the system. The result shows that the outage probability and energy efficiency is largely influenced by the value of the switching threshold. The superiority of the system can be seen especially in low SNR region.

Maximum-likelihood detection based on branch and bound algorithm for MIMO systems

Maximum likelihood detection for MIMO systems can be formulated as an integer quadratic programming problem. In this paper, we introduce depth-first branch and bound algorithm with variable dichotomy into MIMO detection. More nodes may be pruned with this structure. At each stage of the branch and bound algorithm, active set algorithm is adopted to solve the dual subproblem. In order to reduce the complexity further, the Cholesky factorization update is presented to solve the linear system at each iteration of active set algorithm efficiently. By relaxing the pruning conditions, we also present the quasi branch and bound algorithm which implements a good tradeoff between performance and complexity. Numerical results show that the complexity of MIMO detection based on branch and bound algorithm is very low, especially in low SNR and large constellations.