Showing papers by "Beijing University of Posts and Telecommunications published in 2010"

Research on the architecture of Internet of Things

Abstract: The Internet of Things is a technological revolution that represents the future of computing and communications. It is not the simple extension of the Internet or the Telecommunications Network. It has the features of both the Internet and the Telecommunications Network, and also has its own distinguishing feature. Through analysing the current accepted three-layer structure of the Internet of things, we suggest that the three-layer structure can't express the whole features and connotation of the Internet of Things. After reanalysing the technical framework of the Internet and the Logical Layered Architecture of the Telecommunication Management Network, we establish new five-layer architecture of the Internet of Things. We believe this architecture is more helpful to understand the essence of the Internet of Things, and we hope it is helpful to develop the Internet of Things.

Carrier aggregation for LTE-advanced mobile communication systems

Abstract: In order to achieve up to 1 Gb/s peak data rate in future IMT-Advanced mobile systems, carrier aggregation technology is introduced by the 3GPP to support very-high-data-rate transmissions over wide frequency bandwidths (e.g., up to 100 MHz) in its new LTE-Advanced standards. This article first gives a brief review of continuous and non-continuous CA techniques, followed by two data aggregation schemes in physical and medium access control layers. Some technical challenges for implementing CA technique in LTE-Advanced systems, with the requirements of backward compatibility to LTE systems, are highlighted and discussed. Possible technical solutions for the asymmetric CA problem, control signaling design, handover control, and guard band setting are reviewed. Simulation results show Doppler frequency shift has only limited impact on data transmission performance over wide frequency bands in a high-speed mobile environment when the component carriers are time synchronized. The frequency aliasing will generate much more interference between adjacent component carriers and therefore greatly degrades the bit error rate performance of downlink data transmissions.

Evidence for a bimodal distribution in human communication.

Abstract: Interacting human activities underlie the patterns of many social, technological, and economic phenomena. Here we present clear empirical evidence from Short Message correspondence that observed human actions are the result of the interplay of three basic ingredients: Poisson initiation of tasks and decision making for task execution in individual humans as well as interaction among individuals. This interplay leads to new types of interevent time distribution, neither completely Poisson nor power-law, but a bimodal combination of them. We show that the events can be separated into independent bursts which are generated by frequent mutual interactions in short times following random initiations of communications in longer times by the individuals. We introduce a minimal model of two interacting priority queues incorporating the three basic ingredients which fits well the distributions using the parameters extracted from the empirical data. The model can also embrace a range of realistic social interacting systems such as e-mail and letter communications when taking the time scale of processing into account. Our findings provide insight into various human activities both at the individual and network level. Our analysis and modeling of bimodal activity in human communication from the viewpoint of the interplay between processes of different time scales is likely to shed light on bimodal phenomena in other complex systems, such as interevent times in earthquakes, rainfall, forest fire, and economic systems, etc.

A perturbed particle swarm algorithm for numerical optimization

Abstract: The canonical particle swarm optimization (PSO) has its own disadvantages, such as the high speed of convergence which often implies a rapid loss of diversity during the optimization process, which inevitably leads to undesirable premature convergence. In order to overcome the disadvantage of PSO, a perturbed particle swarm algorithm (pPSA) is presented based on the new particle updating strategy which is based upon the concept of perturbed global best to deal with the problem of premature convergence and diversity maintenance within the swarm. A linear model and a random model together with the initial max-min model are provided to understand and analyze the uncertainty of perturbed particle updating strategy. pPSA is validated using 12 standard test functions. The preliminary results indicate that pPSO performs much better than PSO both in quality of solutions and robustness and comparable with GCPSO. The experiments confirm us that the perturbed particle updating strategy is an encouraging strategy for stochastic heuristic algorithms and the max-min model is a promising model on the concept of possibility measure.

Effective Interference Cancellation Scheme for Device-to-Device Communication Underlaying Cellular Networks

Abstract: It is expected that Device-to-Device (D2D) communication is allowed to underlay future cellular networks such as IMT-Advanced for spectrum efficiency. However, by reusing the uplink spectrums with the cellular system, the interference to D2D users has to be addressed to maximize the overall system performance. In this paper, a novel method to deal with the resource allocation and interference avoidance issues by utilizing the network peculiarity of a hybrid network to share the uplink resource is proposed and the implementation details are described in a real cellular system. Simulation results prove that satisfying performance can be achieved by using the proposed mechanism.

Fast and Robust Modulation Classification via Kolmogorov-Smirnov Test

Abstract: A new approach to modulation classification based on the Kolmogorov-Smirnov (K-S) test is proposed. The K-S test is a non-parametric method to measure the goodness of fit. The basic procedure involves computing the empirical cumulative distribution function (ECDF) of some decision statistic derived from the received signal, and comparing it with the CDFs or the ECDFs of the signal under each candidate modulation format. The K-S-based modulation classifiers are developed for various channels, including the AWGN channel, the flat-fading channel, the OFDM channel, and the channel with unknown phase and frequency offsets, as well as the non-Gaussian noise channel, for both QAM and PSK modulations. Extensive simulation results demonstrate that compared with the traditional cumulant-based classifiers, the proposed K-S classifiers offer superior classification performance, require less number of signal samples (thus is fast), and is more robust to various channel impairments.

Distributed Optimal Relay Selection in Wireless Cooperative Networks With Finite-State Markov Channels

Abstract: Relay selection is crucial in improving the performance of wireless cooperative networks. Most previous works for relay selection use the current observed channel conditions to make the relay-selection decision for the subsequent frame. However, this memoryless channel assumption is often not realistic given the time-varying nature of some mobile environments. In this paper, we consider finite-state Markov channels in the relay-selection problem. Moreover, we also incorporate adaptive modulation and coding, as well as residual relay energy in the relay-selection process. The objectives of the proposed scheme are to increase spectral efficiency, mitigate error propagation, and maximize the network lifetime. The formulation of the proposed relay-selection scheme is based on recent advances in stochastic control algorithms. The obtained relay-selection policy has an indexability property that dramatically reduces the computation and implementation complexity. In addition, there is no need for a centralized control point in the network, and relays can freely join and leave from the set of potential relays. Simulation results are presented to show the effectiveness of the proposed scheme.

A Novel Handover Mechanism Between Femtocell and Macrocell for LTE Based Networks

Abstract: The femtocell networks that use Home eNodeB and existing networks as backhaul connectivity can fulfill the upcoming demand of high data rate for wireless communication system as well as can extend the coverage area. It is also of interest to minimize operational effort by introducing self-optimizing mechanisms, and the optimization of the Home eNodeB involved handover is an important goal of LTE-Advanced. Since the different network architecture and functionality between Home eNodeB and LTE eNodeB, the handover procedure between the femtocell and macrocell should be modified in LTE network. In this paper, modified signaling procedure of handover is presented in the Home eNodeB gateway based femtocell network architecture. A new handover algorithm based on the UE’s speed and QoS is proposed. The comparison between the proposed algorithm and the traditional handover algorithm shows that the algorithms proposed in this paper have a better performance in the reducing of unnecessary handovers and the number of handovers.

Accelerometer Based Transportation Mode Recognition on Mobile Phones

Abstract: Recognizing the transportation modes of people’s daily living is an important research issue in the pervasive computing. Prior research in this field mainly uses Global Positioning System (GPS), Global System for Mobile Communications (GSM) or their combination with accelerometer to recognize transportation modes, such as walking, driving, etc. In this paper, we will introduce transportation mode recognition on mobile phones only using embedded accelerometer. In order to deal with uncertainty of position and orientation of mobile phone, acceleration synthesization based method and acceleration decomposition based method are introduced. Performance comparison indicates that acceleration synthesization based method outperforms acceleration decomposition based method. We will discuss the factors affect the recognition accuracy of acceleration decomposition based method and present potential improvements.

Robust Head-Shoulder Detection by PCA-Based Multilevel HOG-LBP Detector for People Counting

Abstract: Robustly counting the number of people for surveillance systems has widespread applications. In this paper, we propose a robust and rapid head-shoulder detector for people counting. By combining the multilevel HOG (Histograms of Oriented Gradients) with the multilevel LBP (Local Binary Pattern) as the feature set, we can detect the head-shoulders of people robustly, even though there are partial occlusions occurred. To further improve the detection performance, Principal Components Analysis (PCA) is used to reduce the dimension of the multilevel HOG-LBP feature set. Our experiments show that the PCA based multilevel HOG-LBP descriptors are more discriminative, more robust than the state-of-the-art algorithms. For the application of the real-time people-flow estimation, we also incorporate our detector into the particle filter tracking and achieve convincing accuracy

Outage performance of relay-assisted cognitive-radio system under spectrum-sharing constraints

Abstract: Investigated is the outage performance of cognitive wireless relay networks in a fading environment, where the secondary users including the source and relays may take advantage of a frequency band of a licensed (primary) user by opportunistically transmitting with high power as long as the interference it incurs is not deemed harmful by the licensee. The relation between the secondary channel performance and the interference inflicted on the primary user is quantified.

Cross-Layer Design for TCP Performance Improvement in Cognitive Radio Networks

Abstract: In cognitive radio (CR) networks, the end-to-end transmission-control protocol (TCP) performance experienced by secondary users is a very important factor that evaluates the secondary user perceived quality of service (QoS). Most previous works in CR networks ignore the TCP performance. In this paper, we take a cross-layer design approach to jointly consider the spectrum sensing, access decision, physical-layer modulation and coding scheme, and data-link layer frame size in CR networks to maximize the TCP throughput in CR networks. The wireless channel and the primary network usage are modeled as a finite-state Markov process. Due to the miss detection and the estimation error experienced by secondary users, the system state cannot be directly observed. Consequently, we formulate the cross-layer TCP throughput optimization problem as a partially observable Markov decision process (POMDP). Simulation results show that the design parameters in CR networks have a significant impact on the TCP throughput, and the TCP throughput can be substantially improved if the low-layer parameters in CR networks are optimized jointly.

Spreading and direction of Gaussian-Schell model beam through a non-Kolmogorov turbulence

Abstract: We show that the far-field beam spreading and direction of partially coherent Gaussian–Schell model (GSM) beams are independent on the spatial coherence of the source through non-Kolmogorov atmospheric turbulence, which has potential applications in long-distance free-space optical communication. The effects of spatial coherence, exponent value α, and inner scale and outer scale of atmospheric turbulence on beam spreading are studied in details. The GSM beam has greater spreading for smaller inner scale or bigger outer scale through non-Kolmogorov turbulent atmosphere.

Analytical Design Method of Multiway Dual-Band Planar Power Dividers With Arbitrary Power Division

Abstract: In this paper, a novel closed-form design method of generalized Wilkinson power dividers is proposed. By using this method, the power divider could be designed to be arbitrary-way (N-way) with arbitrary power division, and arbitrary dual-band operations in a pure planar structure. A previous dual-band unequal Wilkinson power divider is extended to arbitrary terminal impedances case, thus, it can be used to construct multiway planar power dividers through the combination of the two-section dual-frequency transformers. To obtain three-way (or any odd-way) power dividers with dual-band and unequal power division features, a new developed recombinant structure is employed. This recombinant structure consists of a two-way dual-band unequal power divider/combiner without any isolation structures. Furthermore, the complete design procedures and analytical equations of these proposed generalized power dividers are presented. To verify our proposed design approach in theory, several three-way and four-way power dividers with different dual-band applications and various power divisions are designed and simulated. Finally, a practical three-way power divider operating at both 0.6 and 2.45 GHz with a power dividing ratio of 3:5:1 is fabricated in microstrip technology as a typical example. The measured results of the fabricated power divider verify our proposed idea.

Scaling laws for overlaid wireless networks: a cognitive radio network versus a primary network

Abstract: We study the scaling laws for the throughputs and delays of two coexisting wireless networks that operate in the same geographic region. The primary network consists of Poisson distributed legacy users of density n, and the secondary network consists of Poisson distributed cognitive users of density m, with m >n. The primary users have a higher priority to access the spectrum without particular considerations for the secondary users, while the secondary users have to act conservatively in order to limit the interference to the primary users. With a practical assumption that the secondary users only know the locations of the primary transmitters (not the primary receivers), we first show that both networks can achieve the same throughput scaling law as what Gupta and Kumar (IEEE Trans. Inf. Theory, vol. 46, no. 2, pp. 388-404, Mar. 2000) established for a standalone wireless network if proper transmission schemes are deployed, where a certain throughput is achievable for each individual secondary user (i.e., zero outage) with high probability. By using a fluid model, we also show that both networks can achieve the same delay-throughput tradeoff as the optimal one established by El Gamal et al. (IEEE Trans. Inf. Theory, vol. 52, no. 6, pp. 2568-2592, Jun. 2006) for a standalone wireless network.

Internet of Things: Summarize on Concepts, Architecture and Key Technology Problem

Abstract: Internet of things is closely related to numerous fields.We first analyze basic concepts and features of Internet of things,and compare the relationships among Internet of things,the ubiquitous network,machine to machine,and the cyber physics system.Then,we introduce the ubiquitous sensor network(USN) architecture designed by the International Telecommunication Union,and present research proposals for Internet of things architecture.Furthermore,we summarize the key technologies of Internet of things and propose the model of Internet of things technology system.Finally,the status of standardization is concluded and several development proposals are suggested for Internet of things.

Performance Analysis of OSTBC Transmission in Amplify-and-Forward Cooperative Relay Networks

Abstract: A performance analysis is presented for amplify-and-forward (AF) cooperative relay networks employing transmit antenna diversity with orthogonal space-time block codes (OSTBCs), where multiple antennas are equipped at the transmitter. We develop a symbol-error-rate (SER) and outage performance analysis for OSTBC transmissions with and without cooperative diversity over flat Rayleigh fading channels. We first derive exact probability density functions (pdf's) and cumulative distribution functions (cdf's) for the system SNR without direct transmission with an arbitrary number of transmit antennas and then present the exact closed-form SER and outage probability expressions. Next, we derive the moment-generating function (MGF) for the overall system SNR with direct transmission and present the exact SER and outage probability with joint transmit antenna diversity and cooperative diversity. The theoretical analysis is validated by simulations, which indicate an exact match between them. The results also show how the transmit antenna diversity and the cooperative diversity affect the overall system performance.

Optimal Node Selection for Target Localization in Wireless Camera Sensor Networks

Abstract: This paper studies the node-selection problem for target localization in wireless camera sensor networks. The goal of node selection is to optimize the tradeoff between the energy consumption of wireless camera sensor networks and the quality of target localization. We propose a cooperative target localization algorithm, which is implemented by two phases: 1) target detecting phase and 2) target locating phase. For the target detecting phase, we develop a probing environment and adaptive sleeping (PEAS)-based density control algorithm to select the proper subset of deployed camera sensors for maintaining the desired density of nodes in the detecting mode. For the locating phase, we map the node-selection problem into an optimization problem and then propose an optimal node-selection algorithm to select a subset of camera sensors for estimating the location of a target while minimizing the energy cost. We conduct extensive experiments and simulations to validate and evaluate our proposed schemes.

Mining dependency in distributed systems through unstructured logs analysis

Abstract: Dependencies among system components are crucial to locating root errors in a distributed system. In this paper, we propose an approach to mine intercomponent dependencies from unstructured logs. The technique requires neither additional system instrumentation nor any application specific knowledge. In the approach, we first parse each log message into its log key and parameters. Then, we find dependent log key pairs belong to different components by leveraging co-occurrence analysis and parameter correspondence. After that, we use Bayesian decision theory to estimate the dependency direction of each dependent log key pair. We further apply time delay consistency to remove false positive detections. Case studies on Hadoop show that the technique successfully identifies the dependencies among the distributed system components.

Variational methods to Sturm–Liouville boundary value problem for impulsive differential equations☆

Abstract: In this paper, we study a linear Sturm–Liouville impulsive problem and a nonlinear Sturm–Liouville impulsive problem. By applying a new approach via critical point theory and variational methods, the existence results of positive solutions are obtained.

An Energy-Efficient n-Epidemic Routing Protocol for Delay Tolerant Networks

Abstract: In Delay Tolerant Networks (DTN), as disconnections between nodes are frequent, establishing routing path from the source node to the destination node may not be possible. However, if a node transmits packets to all its encounters, its batteries will be used up quickly. Many researches have been done on routing and forwarding algorithms in DTN, but few of them have explicitly address the energy issue. In this paper, we propose n-epidemic routing protocol, an energy-efficient routing protocol for DTN. The n-epidemic routing protocol is based on the reasoning that in order to reach a large audiences with low number of transmissions, it is better to transmit only when the number of neighbors reaching a certain threshold. We compare the delivery performance of n-epidemic routing protocol with basic epidemic routing protocol using both analytical approach and empirical approach with real experimental dataset. The experiment shows that n-epidemic routing protocol can increase the delivery performance of basic epidemic-routing by 434% averagely.

Performance Analysis of Selective Opportunistic Spectrum Access With Traffic Prediction

Abstract: In cognitive radio (CR) networks, the ability to capture a frequency slot for transmission in an idle channel has a significant impact on the spectrum efficiency and quality of service (QoS) of a secondary user (SU). The radio frequency (RF) front-ends of an SU have limited bandwidth for spectrum sensing with the target frequency bands dispersed in a discontinuous manner. This results in the SU having to sense multiple target frequency bands in a short period of time before selecting an appropriate idle channel for transmission. This paper addresses this technical challenge by proposing a selective opportunistic spectrum access (SOSA) scheme. With the aid of statistical data and traffic prediction techniques, our SOSA scheme can estimate the probability of a channel appearing idle based on the statistics and choose the best spectrum-sensing order to maximize spectrum efficiency and maintain an SU's connection. By means of doing so, this SOSA scheme can preserve the QoS of an SU while improving the system efficiency. In contrast to previous work, we consider the practical issues encountered by an SU in a wireless environment, such as discontinuous target frequency bands and limited spectrum-sensing ability. We examine the spectrum-sensing scheme in terms of packet loss ratio (PLR) and throughput. The simulation results show that the proposed SOSA scheme can decrease the probability of packet losses in the discontinuous spectrum environment and improve the spectrum efficiency.