Shin-Ming Cheng

On exploiting cognitive radio to mitigate interference in macro/femto heterogeneous networks

To successfully deploy femtocells underlaying the macrocell as a heterogeneous network, which has been proven to greatly improve indoor coverage and system capacity, the cross-tier interference among the macrocell and femtocells as well as the intratier interference among femtocells must be mitigated. However, some unique features present a challenge in interference mitigation in a two-tier heterogeneous network such as random deployment for femtocells, nonexistence of macro-femto backhaul coordination, and mandates allowing no modifications of existing macrocells. Carefully examining the existing distributed information acquisition mechanisms, cognitive radio is the most promising solution for two-tier heterogeneous networks. We therefore study possible interference mitigation approaches, including orthogonal radio resource assignment in the time-frequency and antenna spatial domains, as well as interference cancellation via novel decoding techniques. According to the information acquired by cognitive radio technology, recent innovations such as game theory and the Gibbs sampler have been explored to mitigate both cross-tier and intratier interferences. Performance evaluations show that considerable performance improvement can be generally achieved, and thus demonstrate the potential of applying cognitive radio in mitigating interference.

Smart attacks in smart grid communication networks

The operations of a smart grid heavily rely on the support of communication infrastructures for efficient electricity management and reliable power distribution. Due to the strong dependency, the robustness of a smart grid communication network against attack is of the utmost importance for the deployment of the smart grid. Notably, the large scale and autonomous features of a smart grid render its cyber security quite vulnerable to adversaries. In this article, we introduce several intelligent attacks and countermeasures in smart grid communication networks, which aim for maximal damage or benefits by taking advantage of the network structure as well as the protocol functionality. We adopt the percolation-based connectivity in statistic mechanics to quantitatively analyze the network robustness. If the attack and defense strategies are involved, the attack can be further smart and complicated. Consequently, a twoplayer zero-sum game is introduced between the adversary and the defender, and the outcome of the game equilibrium is used to evaluate the performance of defense mechanisms with different network configurations. This article therefore offers novel insights and comprehensive analysis on the cyber security of a smart grid.

On Modeling Malware Propagation in Generalized Social Networks

A hybrid malware on smart phones can be propagated by both end-to-end messaging services via personal social communications and short-range wireless communication services via spatial social interactions. Inspired from epidemiology, we propose a novel differential equation-based model to analyze the mixed behaviors of delocalized infection and ripple-based propagation for the hybrid malware in generalized social networks consisting of personal and spatial social relations. Validated by simulations, our model serves as the very first analytical model successfully approximating the complicated propagation behaviors of the hybrid malware.

Design and Analysis of Downlink Spectrum Sharing in Two-Tier Cognitive Femto Networks

In two-tier networks consisting of a macrocell overlaid with femtocells in cochannel deployment and closed-access policy, spatial reuse is achieved at the price of severe intratier and cross-tier interference from concurrent transmissions. The interference causes significant performance degradation, particularly when coordination among base stations (BSs) is infeasible. Cognitive radio (CR) is a promising technique for interference mitigation, where femto-BSs with cognitive information accomplish concurrent transmissions while meeting a per-tier outage constraint. This paper studies the role of information sensed at femto-BSs on the transmission capacity. By exploiting different cognitive information, we propose spectrum-sharing schemes between macrocell and femtocell, as well as among femtocells, to improve spatial reuse gain. Bounds on the maximum intensity of simultaneously transmitting femtocells that satisfy a given per-tier outage constraint in these schemes are theoretically derived via a stochastic geometry model. We conduct simulations to evaluate the performance of the proposed schemes in terms of transmission capacity. The results confirm that, when femto-BSs acquire the knowledge of user channel statistics or user location information, significant spatial reuse gain can be achieved by exploiting the avoidance region and multiuser diversity.

A study on distributed/centralized scheduling for wireless mesh network

The IEEE 802.16 standard proposes the Media Access Control (MAC) protocol for the Wireless Metropolitan Area Network (WMAN). Two transmission modes are defined in the IEEE 802.16, including Point-to-Multipoint (PMP) mode and mesh mode. In the 802.16 mesh mode, allocation of minislots can be handled by the centralized and distributed scheduling mechanisms. This paper proposes the Combined Distributed and Centralized (CDC) scheme to combine the distributed scheduling and centralized scheduling mechanisms so that the minislot allocation can be more flexible, and the utilization is increased. Two scheduling algorithms, Round Robin (RR) and Greedy, are proposed as the baseline algorithms for the centralized scheduling mechanism. We conduct simulation experiments to investigate the performance of the CDC scheme with the RR and Greedy algorithms. Our study indicates that with CDC scheme, the minislot utilization can be significantly increased.

Radio Resource Management for QoS Guarantees in Cyber-Physical Systems

The recent deployment of Cyber-Physical Systems (CPS) has emerged as a promising approach to provide extensive interaction between computational and physical worlds. For a large-scale distributed CPS comprising of numerous machines, sharing radio resource efficiently with the existing wireless networks while maintaining sufficient quality of service (QoS) for machine-to-machine (M2M) communications becomes an essential and challenging requirement. By clustering CPS machines as a swarm with the cluster head managing radio resources inside the swarm, spectrum sharing among numerous machines can be achieved in a distributed and scalable fashion. Specifically, we apply the recent innovation, cognitive radio, and a special mode in cognitive radio, interweave coexistence, to leverage machines to collect radio resource usage information for autonomous and interference-free radio resource management in the CPS. To reduce the communication overheads of channel sensing feed backing from machines, we apply compressive sensing to construct a spectrum map indicating the radio resource availability on any given locations within the CPS coverage. Such spectrum map resource management (SMRM) only utilizes a small portion of machines to perform channel sensing but enables distributed cluster-based spectrum sharing in an efficient way. Through the concept of effective capacity, the SMRM controls available resources to guarantee the QoS for communications of CPS. By evaluating the performance of the proposed SMRM in the most promising realization of CPS based on LTE-Advanced machine-type communications coexisting with LTE-Advanced Macrocells to utilize identical spectrum, the simulation results show effective QoS guarantees of CPS by SMRM in the realistic environments.

Cognitive Radio Network Tomography

The cognitive radio network (CRN), as a promising technique in future wireless communication networks, shall execute some critical functionalities to enhance existing wireless networks, such as network reconfigurability to adaptively select networks (e.g., in IEEE P1900.4 and ETSI-RSS), spectrum opportunity utilization for transmissions over opportunistic links to enhance spectrum efficiency (e.g., in IEEE 802.22), and further cooperative relays among cognitive radios (CRs) and nodes of coexisting multiradio systems, including heterogeneous primary systems. To support multilink operations and networking functions in CRN, traditional spectrum sensing is not enough, and we thus develop CRN tomography to meet the general needs of CRN operations at both the link and network levels. Borrowing the concept from medical/Internet tomography via statistical inferring, we establish the framework and methodology of CRN tomography that can be passive monitoring or active probing defined over link- or network-level parameter inference. Generally speaking, conventional CR spectrum-sensing techniques belong to the category of the passive link-level monitoring. Multiple-system sensing and identification can be considered as a sort of passive network-level CRN tomography. We further propose active link-level CRN tomography by examining the radio resource for transmissions. Finally, CRN tomography using active network-level probing is illustrated by the estimation of successful packet-transmission probability in network operations. This paper initiates explorations of CRN tomography obtaining the required parameters at the link and network levels for successful CRN operations.

Optimal Control of Epidemic Information Dissemination Over Networks

Information dissemination control is of crucial importance to facilitate reliable and efficient data delivery, especially in networks consisting of time-varying links or heterogeneous links. Since the abstraction of information dissemination much resembles the spread of epidemics, epidemic models are utilized to characterize the collective dynamics of information dissemination over networks. From a systematic point of view, we aim to explore the optimal control policy for information dissemination given that the control capability is a function of its distribution time, which is a more realistic model in many applications. The main contributions of this paper are to provide an analytically tractable model for information dissemination over networks, to solve the optimal control signal distribution time for minimizing the accumulated network cost via dynamic programming, and to establish a parametric plug-in model for information dissemination control. In particular, we evaluate its performance in mobile and generalized social networks as typical examples.

Multi-path routing with end-to-end statistical QoS Provisioning in Underlay Cognitive Radio Networks

Since the radio access of secondary users is typically confined to ensure sufficient operation for primary users in underlay cognitive radio networks (CRNs), the inevitably induced latency and interference pose new challenges on existing routing schemes for Quality-of-Service (QoS) provisioning. Due to stringent accessing and interference constraints, secondary users appeal to exploit multi-path routing based on multi-hop relaying protocol to support QoS requirements. Via our model, we derive the end-to-end delay statistics including medium access and retransmission delay, where we successfully relate path diversity to end-to-end reliability and optimize the delivery delay by adjusting transmission power. We analyze the performance of the duplication-based and coding-aided multi-path routing schemes, where opportunistic transmission is employed to improve the delivery delay due to channel awareness, and encoding packets on multiple paths further achieves throughput efficiency. This paper firstly presents insights and performance analysis to facilitate multi-path routing with QoS provisioning in underlay CRN.

Efficiency of a Cognitive Radio Link with Opportunistic Interference Mitigation

To increase spectrum utilization, cognitive radio allows concurrent secondary and primary transmissions as long as interference to primary users is constrained under a threshold. This research proposes an enhanced opportunistic interference mitigation scheme utilizing both successfully and unsuccessfully decoded primary packets to improve data rate of secondary transmission. Moreover, we propose an analytical model to investigate characteristic changes of the spectrum usage affected by the coexisting secondary transmission in terms of overall spectral efficiency. The interference mitigation scheme can be applied to realistic two-tier femtocell networks to enable robust communication against cross-tier interference thereby obtaining a substantial spectrum reuse gain.