Lei Wang

Cooperative MIMO Spectrum Sensing Using Free Probability Theory

In this paper, using free probability theory, which is a valuable tool for describing the asymptotic behavior of multiple systems, especially for large matrices, a new cooperative MIMO scheme for spectrum sensing is proposed, which shows how asymptotic free property of random matrices and the property of Wishart distribution can be used to assist spectrum sensing in MIMO system for cognitive radios. Simulations over Rayleigh fading and AWGN channels demonstrate the proposed scheme has better detection performance compared with the energy detection techniques even for the case of a small sample of observations.

Two-way relay channel estimation based on compressive sensing

A method of two-way relay sparse channel estimation based on compressive sensing (CS) is designed. We specifically introduce the orthogonal matching pursuit (OMP) algorithm to reconstruct the channel impulse response of orthogonal frequency division multiplexing (OFDM) system. The introduced method can fully exploit the potential sparsity of two-way relay channels (TWRC). By contrast to traditional linear estimation methods, the introduced method needs much less training sequences under the same estimation performance, thus improving the utilization of communication resources such as spectrum and energy effectively. At the same time, the computational efficiency of the introduced method is always higher than traditional methods as its computational complexity mainly relies on the sparse degree of multipath channels. Simulation results confirm the introduced method.

Association analysis and prediction for IPTV service data and user's QoE

In order to provide good service and improve users feeling and degree of satisfaction, video service providers are now interested in understanding the influence of attributes on Quality of Experience (QoE). In this paper, based on IPTV business, we study the relationship between alarming data from IPTV set-top boxes and the users QoE. First, data cleaning and analysis are performed. After these procedures, the important attributes influencing QoE are selected. Then decision tree is used for modeling dataset. Here information entropy minimization heuristic is adopted to discretize continuous-valued attributes and the improved C4.5 algorithm is designed to fastly and accurately build the tree. Experimental results show that the proposed scheme can indeed improve the prediction accuracy when compared with other competing schemes.

QoE-driven scheme for multimedia content dissemination in Device-to-Device communication

Device-to-Device (D2D) communication has been proposed to be a promising data offloading solution in the coming big data age, with multimedia dominating the digital contents. As quality of experience (QoE) is the major determining factor in the success of new multimedia applications, we novelly propose a QoE-driven cooperative content dissemination (QeCS) scheme in the paper. Specifically, all the users predict the QoE of the potential connections characterized by mean opinion score (MOS) and send the results to the content provider (CP). Then CP formulates a weighted oriented graph based on the network topology and MOS of each potential connection. By factorizing the graph, the content dissemination fashion is established through seeking 1-factor with the maximum weight thus achieving maximum total user MOS.

Active tracking using color silhouettes for indoor surveillance

Pan-Tilt-Zoom (PTZ) cameras play an important role in surveillance systems. In this paper, we propose an active tracker using color silhouettes with a single camera. We firstly apply dilation and erosion operators of morphology to binary difference image to get color silhouettes. We also record the color silhouette of the target which we are interested in. Secondly, we measure the similarity of color silhouette between the observation and the candidates of silhouettes. We exploit the most similar one to update that of the tracked target. Finally, we control the PTZ camera to move according to the location of the tracked target. The experimental results show that the proposed algorithm can effectively track people even though she/he is fully occluded.

Spectrum sensing using non-asymptotic behavior of eigenvalues

The classical random matrix theory is mainly focused on asymptotic spectral properties of random matrices when their dimensions tend to infinity. At the same time, many recent applications, like convex geometry, functional analysis and information theory, operate with random matrices of fixed dimensions. In this paper, we investigate a recently developed non-asymptotic behavior of eigenvalues of random matrices, which is about spectral properties of random sub-Gaussian matrices of fixed dimensions. Then, a new spectrum sensing scheme for cognitive radio is proposed by using the non-asymptotic behavior of eigenvalues. Simulation results show that the proposed scheme has a better detection performance than the classical energy detection technique and the scheme based on asymptotic behavior of eigenvalues of random matrices, even in the case of a small sample of observations.

Location-based distributed caching for device-to-device communications underlaying cellular networks

Device-to-device D2D communications have been viewed as a promising data offloading solution in cellular networks because of the explosive growth of multimedia applications. Because of the nature of distributed device location, distributed caching becomes an important function of D2D communications. By taking advantage of the caching capacity of the device, in this work, we explore the device storage and file frequent reuse to realize distributed content dissemination, that is, storing contents in mobile devices named helpers. Specifically, we first investigate the average and lower bound of helper amount by dividing the network into small areas where the nodes are within each others communication radius. Then, optimal helper amount is derived based on average helper amount and network topology. Subsequently, a location-based distributed helper selection scheme for distributed caching is proposed based on the given optimal helper amount. In particular, nodes are selected as helpers according to their locations and degrees, and contents are placed in the manner for maximizing total user utility. Extensive simulation results demonstrate the factors that affect the optimal helper amount and the total user utility. Copyright

Secure content sharing protocol for D2D users based on profile matching in social networks

With the increasing of mobile devices, Device-to-Device(D2D) communication is considered as a promising technology for achieving direct communication of devices. But the security issues still remain to be solved. In this paper, We utilize D2D communication between UEs in proximity to share epidemic media contents. We propose a Secure Content Sharing Protocol(SCSP) that combine with the credibility between users. The credibility involves users interest, interaction and geographical location. By means of encryption, signature and authentication in SCSP, the data confidentiality, non-repudiation and mutual authentication can be guaranteed. Furthermore, the users privacy can be protected based on Pallier Homomorphic Encryption. At last, it is shown that the proposed SCSP can meet the security requirements and have lower computation cost in comparison with other related works through security analysis and quantitative evaluation.

Sidelobe interference reduced scheduling algorithm for device-to-device communication in millimeter wave networks

With the combination of device-to-device (D2D) communication and millimeter wave (mmWave) technology, the density of communication devices increases greatly and the communication environment becomes more complicated. A key challenge in such networks is interference, which is not only from main lobe, but also from the sidelobe power accumulation. However, the approaches for resource allocation in traditional wireless networks may not be efficient for this complex environment. In this paper, we first introduce a new scenario that employs time and space division for scheduling in mmWave and D2D networks. Then, we propose a resource allocation algorithm based on vertex coloring and redefine concurrent transmission conditions by defining a power decision threshold, which is designed to further reduce the sidelobe interference. Simulation results present that our scheduling algorithm outperforms traditional time division multiple access (TDMA) and traditional vertex coloring algorithm.

Physical layer security in D2D communication system underlying cellular networks

Due to the openness of the physical layer, the physical layer security has been widely discussed. It is considered as an effective way to improve the secrecy rate that we add artificial noise to D2D communications underlaying cellular networks. Compared to previous studies, in this paper we not only think of the situation where artificial noise is added to the original communication signal between the base station and the cellular user, but also consider the design of the intended information signal and artificial noise signal between corresponding D2D pair. In order to improve system secret rate under limited resources, we propose an idea of the power distribution coefficient for two legitimate communication links(one link between BS and CU and the other link between a D2D pair). Then we build convex optimization model and adopt a mixed penalty function algorithm to obtain optimal value of power distribution coefficient. On this basis, a joint optimization allocation scheme for transmit power between BS and DU-T is proposed, which satisfies the best security mechanism of physical layer in D2D communication underlying cellular networks. Simulation results show that as taking the optimal solution, system secret rate is clearly improved.