Peter Han Joo Chong

Multihop cellular networks: Technology and economics

Recently, multihop cellular networks (MCNs) were proposed to preserve the advantages of traditional single-hop cellular networks with multihop ad hoc relaying networks, while minimizing the drawbacks that they involved. In this way, MCNs enhance the performance of both the existing cellular networks and ad hoc networks. Consequently, MCN-type system is considered as a promising candidate of fourth generation (4G) wireless network for future mobile communications. This paper surveys a number of MCN-type architectures in literature through a comprehensive comparison and discussion among the proposed architectures. The discussion is divided into two phases. In the first phase, we review the concept of MCN and compare the selected MCN-type architectures from a technology perspective. In the second phase, we further compare and discuss the economic perspective on the deployment of MCNs. Specifically, we focus on the economic considerations for deploying relays in MCN-type systems.

Modeling and Performance Analysis of Clustered Device-to-Device Networks

Device-to-device (D2D) communication enables direct communication between proximate devices thereby improving the overall spectrum utilization and off-loading traffic from cellular networks. This paper develops a new spatial model for D2D networks in which the device locations are modeled as a Poisson cluster process. Using this model, we study the performance of a typical D2D receiver in terms of coverage probability under two realistic content availability setups: 1) content of interest for a typical device is available at a device chosen uniformly at random from the same cluster, which we term uniform content availability, and 2) content of interest is available at the kth closest device from the typical device inside the same cluster, which we term k-closest content availability. Using these coverage probability results, we also characterize the area spectral efficiency (ASE) of the whole network for the two setups. A key intermediate step in this analysis is the derivation of the distributions of distances from a typical device to both the intra-and inter-cluster devices. Our analysis reveals that an optimum number of D2D transmitters must be simultaneously activated per cluster in order to maximize ASE. This can be interpreted as the classical tradeoff between more aggressive frequency reuse and higher interference power. The optimum number of simultaneously transmitting devices and the resulting ASE increase as the content is made available closer to the receivers. Our analysis also quantifies the best and worst case performance of clustered D2D networks both in terms of coverage and ASE.

Design and implementation of Bluetooth energy meter

Presently electronics energy measurement is continuously replacing existing technology of electro-mechanical meters especially in China and India. By the year 2004, digital meter has start replacing electromechanical meters in Singapore. A wireless digital energy meter would definitely offer greater convenience to the meter reading task. Bluetooth technology is chosen as a possible wireless solution to this issue. In this paper, we present the design and implementation issues of a Bluetooth-enabled energy meter. The energy reader can collect the energy consumption reading from the energy meter wirelessly based on Bluetooth. Two methods, which can retrieve the meter reading with little human intervention, are proposed and implemented in the targeted applications. They are AMR (automatic meter reading) and the APM (automatic polling mechanism). Few commercial applications are suggested to apply for the Bluetooth-enabled energy meter. We have successfully implemented the Bluetooth-enabled energy meter for these suggested commercial applications to demonstrate the advantage of reading the electricity consumption wirelessly via Bluetooth technology.

An efficient clustering scheme for large and dense mobile ad hoc networks (MANETs)

Large and dense MANETs often face scalability problem and need to achieve performance guarantee with the help of a hierarchical structure, typically a cluster control structure. In this paper, an efficient clustering scheme (ECS) is proposed for large and dense MANETs. Mechanisms for cluster formation and cluster maintenance are described and studied in detail. ECS can eliminate the frozen period requirement for cluster formation, reduce cluster overlapping and prolongs the cluster lifetime without producing excessive clustering overheads. The performance of ECS is compared with random competition-based clustering (RCC) and a modified version of highest connectivity clustering (HCC) in terms of clustering overheads, clusterhead lifetime, cluster number and cluster size. Simulation results show that ECS successfully achieves its targets at reducing the cluster overlapping, maintaining a stable cluster structure as well as producing moderate clustering overheads.

Fundamentals of Cluster-Centric Content Placement in Cache-Enabled Device-to-Device Networks

This paper develops a comprehensive analytical framework with foundations in stochastic geometry to characterize the performance of cluster-centric content placement in a cache-enabled device-to-device (D2D) network. Different from device-centric content placement, cluster-centric placement focuses on placing content in each cluster, such that the collective performance of all the devices in each cluster is optimized. Modeling the locations of the devices by a Poisson cluster process, we define and analyze the performance for three general cases: 1) k-Tx case: the receiver of interest is chosen uniformly at random in a cluster and its content of interest is available at the kth closest device to the cluster center; 2) 1-Rx case: the receiver of interest is the Ith closest device to the cluster center and its content of interest is available at a device chosen uniformly at random from the same cluster; and 3) baseline case: the receiver of interest is chosen uniformly at random in a cluster and its content of interest is available at a device chosen independently and uniformly at random from the same cluster. Easy-to-use expressions for the key performance metrics, such as coverage probability and area spectral efficiency of the whole network, are derived for all three cases. Our analysis concretely demonstrates significant improvement in the network performance when the device on which content is cached or device requesting content from cache is biased to lie closer to the cluster center compared with the baseline case. Based on this insight, we develop and analyze a new generative model for cluster-centric D2D networks that allows to study the effect of intra-cluster interfering devices that are more likely to lie closer to the cluster center.

Precise Two‐Photon Photodynamic Therapy using an Efficient Photosensitizer with Aggregation‐Induced Emission Characteristics

Two-photon photodynamic therapy (PDT) is able to offer precise 3D manipulation of treatment volumes, providing a target level that is unattainable with current therapeutic techniques. The advancement of this technique is greatly hampered by the availability of photosensitizers with large two-photon absorption (TPA) cross section, high reactive-oxygen-species (ROS) generation efficiency, and bright two-photon fluorescence. Here, an effective photosensitizer with aggregation-induced emission (AIE) characteristics is synthesized, characterized, and encapsulated into an amphiphilic block copolymer to form organic dots for two-photon PDT applications. The AIE dots possess large TPA cross section, high ROS generation efficiency, and excellent photostability and biocompatibility, which overcomes the limitations of many conventional two-photon photosensitizers. Outstanding therapeutic performance of the AIE dots in two-photon PDT is demonstrated using in vitro cancer cell ablation and in vivo brain-blood-vessel closure as examples. This shows therapy precision up to 5 µm under two-photon excitation.

Performance Comparison of Flat and Cluster-Based Hierarchical Ad Hoc Routing with Entity and Group Mobility

Ad hoc routing protocols can be divided into flat and hierarchical routing. One typical way to build hierarchy is to group mobile nodes into clusters, thus decrease routing space and improve network performance. Mobility models also affect the performance of ad hoc routing protocols and can be divided into entity mobility and group mobility models. This paper first studies the performance of flat routing, AODV and DSR, and cluster-based hierarchical routing, CBRP and ECBRP, on entity mobility, Random Waypoint, and group mobility, RPGM and RRGM. Performance comparisons between flat and cluster-based hierarchical routing protocols in different mobility models are analyzed. We have observed that the effects of group mobility on routing protocols are significantly different from that of entity mobility.

Design & implementation of user interface for mobile devices

The inspiration behind the wireless world came from the need to provide users with mobility and to offer an alternative to the limitations of wired medium. As a result, the user interface and the size of mobile devices in various wireless mobile technologies like GSM, GPRS, WLAN, and Bluetooth are the main concerns in the design of mobile devices. In this paper, we design a single-layered touch screen based user interface. Unlike conventional multi-layered user interface, a single-layered user interface makes the user interface more friendly and reduces the interface size. The memory requirements can be further reduced by implementing it in low-level languages. After design and implementation of user interface, we interface the user interface with the hardware of mobile devices through serial port with the help of AT commands.

Poisson Hole Process: Theory and Applications to Wireless Networks

Interference field in wireless networks is often modeled by a homogeneous Poisson point process (PPP). While it is realistic in modeling the inherent node irregularity and provides meaningful first-order results, it falls short in modeling the effect of interference management techniques, which typically introduces some form of spatial interaction among active transmitters. In some applications, such as cognitive radio and device-to-device networks, this interaction may result in the formation of holes in an otherwise homogeneous interference field. The resulting interference field can be accurately modeled as a Poisson hole process (PHP). Despite the importance of the PHP in many applications, the exact characterization of interference experienced by a typical node in the PHP is not known. In this paper, we derive several tight upper and lower bounds on the Laplace transform of this interference. Numerical comparisons reveal that the new bounds outperform all known bounds and approximations, and are remarkably tight in all operational regimes of interest. The key in deriving these tight and yet simple bounds is to capture the local neighborhood around the typical node accurately while simplifying the far field to attain tractability. Ideas for tightening these bounds further by incorporating the effect of overlaps in the holes are also discussed. These results immediately lead to an accurate characterization of the coverage probability of the typical node in the PHP under Rayleigh fading.

Efficient data dissemination in cooperative multi-RSU Vehicular Ad Hoc Networks (VANETs)

Enhanced Cooperative Load Balancing (ECLB) approach is proposed in VANETs.ECLB takes the advantages of fixed road layout and tolerable delay of requests.ECLB considers the mobility and the dynamic direction changes of vehicles.ECLB balances the workload among the junction-RSUs and edge-RSUs.ECLB outperforms the existing approaches. Many safety and non-safety related applications have been envisioned in VANETs. However, efficient data dissemination considering the mobility of vehicle is must for the success of these applications. Although the Road Side Unit (RSU) is a stationary unit, both RSU and vehicle have limited transmission range that restricts to shorter connection time. This endures a higher request drop rate especially at the overloaded RSUs. A cooperative load balancing (CLB) among the RSUs to use their residual bandwidth can be an effective solution to reduce the request drop rate. In this paper, we investigate that considering the remaining delay tolerance of submitted requests and the knowledge of fixed road layout, the performance of the cooperative load balancing system can be further improved significantly. We show that this performance gain comes from serving the requests based on the urgency and the efficient load balancing among the junction-RSUs and edge-RSUs. Based on the observations, we propose an Enhanced CLB (ECLB) approach in this paper. To demonstrate the efficiency of the ECLB approach a number of well-known scheduling algorithms are integrated and an extensive simulation experiments are conducted in the vehicular communication environment that supports the superiority of ECLB over the existing approaches.