Huai-Lei Fu

Group Mobility Management for Large-Scale Machine-to-Machine Mobile Networking

Machine-to-machine (M2M) communications have emerged as a new communication paradigm to support Internet of Things (IoT) applications. Millions to trillions of machines will connect to mobile communication networks (MCNs) to provide IoT applications. This group-based behavior is considered one of the features of M2M communications. That is, machines are likely with correlated mobility and may perform mobility management at the same time. As a result of this scenario, signaling exchanges for machines are more likely to occur at the same time, and the random access channel (RACH) for the signaling is more likely to be congested. In this paper, we propose a group mobility management (GMM) mechanism where machines are grouped based on the similarity of their mobility patterns at the location database (LDB), and only the leader machine performs mobility management on behalf of the other machines in the same group. The GMM mechanism attempts to mitigate the signaling congestion problem. Through our performance study, we show how the GMM mechanism can reduce registration signaling from machines.

Reducing Signaling Overhead for Femtocell/Macrocell Networks

Femtocell technology has been proposed to offload user data traffic from the macrocell to the femtocell and extend the limited coverage of the macrocell in mobile communications networks. In existing commercial femtocell/macrocell networks, a widely accepted solution to configure the location areas (LAs) is to partition the femtocells overlapped with a macrocell into small groups and to assign each group with a unique LA ID different from that of the macrocell. Such configuration can reduce the paging cost in the mobility management, but increases registration signaling overhead due to discontinuous coverage of femtocells. To reduce signaling overhead in the femtocell/macrocell network, we propose a delay registration (DR) algorithm that postpones the registration until the delay timer expires when the mobile station (MS) moves into the overlapped femtocell. Analytical models and simulation experiments are proposed to investigate the performance of the DR algorithm. Our analytical models are generally enough to accommodate various MS mobility behaviors. Our study can provide guidelines for the operators to set up a delay timer to reduce signaling overhead while sustaining the traffic offloading capability of the femtocell.

Energy-efficient reporting mechanisms for multi-type real-time monitoring in Machine-to-Machine communications networks

In Machine-to-Machine (M2M) communications, machines are wirelessly connected to accomplish collaborative tasks without human intervention, and provide ubiquitous solutions for real-time monitoring. The real-time monitoring application is one of the killer applications for M2M communications, where M2M nodes transmit sensed data to an M2M gateway, and then the M2M gateway can have real-time monitoring for each sensing region. In real-time monitoring application, the energy consumption for the M2M nodes to send sensed data to the M2M gateway is an important factor that significantly affects the performance of the system. In this paper, we first consider the energy consumption as well as the validity of sensed data to design either centralized or distributed energy-efficient reporting mechanisms. We then analyze the complexity of the reporting mechanisms. Simulation experiments are conducted to investigate the performance of the proposed mechanisms, and show that the distributed mechanism outperforms the centralized mechanism when the M2M nodes are mobile.

APS: Distributed air pollution sensing system on Wireless Sensor and Robot Networks

Rapid emergence of Wireless Sensor and Robot Networks (WSRNs) contributes to the deployment of an environmental monitoring system. Three challenging issues are critical to design of an environmental monitoring system, including energy efficiency of sensors, coverage of monitoring area, and validity of sensed data. In this paper, we design and implement an environmental monitoring system on the WSRN, namely distributed air pollution sensing (APS) system, to monitor the air quality in urban environment by taking the three issues into consideration. We apply the sensing region partition and monitoring period concepts for efficient sensed data transmission. We implement the energy-efficient reporting mechanism to prevent redundant transmissions of sensed data to save energy consumption of sensors and prolong network lifetime of the WSRN.

Performance Evaluation for Minislot Allocation for Wireless Mesh Networks

The IEEE 802.16 Standard defines the mesh mode for media access control for external and internal packet transmission. In the IEEE 802.16 mesh mode, the allocation of minislots is handled by centralized scheduling and distributed scheduling, which are independently exercised. This paper proposes the Combined Distributed and Centralized (CDC) and Combined Distributed and Centralized with Queue capability (CDCQ) schemes to combine distributed scheduling and centralized scheduling so that the minislot allocation can be more flexible and the utilization is increased. Two scheduling algorithms, i.e., the Round-Robin (RR) and Greedy algorithms, are used as the baseline algorithms for centralized scheduling. This paper proposes an analytical model and conducts simulation experiments to investigate the performance of the CDC-series schemes with the RR and Greedy algorithms in terms of the acceptance rate of both external and internal packet data. Our study indicates that the CDC-series schemes outperform the scheme proposed in the IEEE standard.

Laser action in Tb(OH) 3 /SiO 2 photonic crystals

Photonic crystals of Tb(OH)(3)/SiO(2) core/shell nanospheres with different periodicities were used as a resonant cavity to explore laser action. By changing the particle size, the optical stop band of the photonic crystals can be tuned to coincide with the multiple emission bands of terbium ions. An overlap of the stop band on the multiple emissions of the active materials embedded inside the photonic crystals offered a good chance for resonance. Lasing emissions arising from terbium ions occurred near the band edge of the PCs were demonstrated.

Electroluminescence enhancement in InGaN light-emitting diode during the electrical stressing process.

This study of the optoelectronic properties of blue light-emitting diodes under direct current stress. It is found that the electroluminescence intensity increases with duration of stress, and the efficiency droop curves illustrated that the peak-efficiency and the peak-efficiency-current increases and decreases, respectively. We hypothesize that these behaviors mainly result from the increased internal quantum efficiency.

A Study for Location Update Cost in a Femtocell Network

The indoor femtocell technology (known as femto BSs) with low power and low cost is proposed to provide comprehensive indoor wireless converge of macro BSs, which is known as the femtocell network. The Location Area ID for a femtocell is different from that for the macrocell that covers the femtocell, which results in frequent location update procedure (i.e., the location update cost increases) when the Mobile Station has a significant level of mobility between femtocells and macrocells. We propose the Cell Priority Transition (CPT) mechanism to reduce the location update cost for the femtocell network. The simulation experiments and analysis are conducted to investigate the performance of the CPT mechanism. Our study shows that the proposed CPT mechanism significantly reduces the location update cost for femtocell networks.

A Region-Based Reporting Scheme for Mobile Sensor Networks

The mobile sensor networks (MSNs) have been widely deployed to provide an ubiquitous solution for time-sensitive applications in a specific area with low deployment cost. The monitoring area of an MSN can be divided into several sensing regions (SRs). In an SR, the mobile sensor (MS) is responsible for reporting the sensed data to the sink node. For the time-sensitive applications on MSN, the time is divided into multiple monitoring periods (MPs). During every MP, a sensing report transmission in an SR is invalid if the sensing report is generated before the beginning of the MP. In this paper, we propose a region-based reporting mechanism, namely Energy-Efficient Distributed-Control Reporting (E²DCR) mechanism, for the MSNs. During every MP, the E²DCR mechanism attempts to have only one MS transmit the sensing report in an SR, and the other MSs in the same SR can stay in the sleep mode for power saving. Simulation experiments are conducted to investigate the performance of the proposed mechanism. Our study shows that E²DCR can meet the delay constraint of the time-sensitive applications with less power consumption.

MBS zone configuration schemes for wireless multicast and broadcast service

The Multicast Broadcast Service (MBS) zone technology is proposed to provide MBS with high QoS on Mobile Communications Networks (MCNs). An MBS zone consists of a group of Base Stations (BSs) synchronized to transmit the same MBS content using the same multicasting channel, which potentially reduces the time delay for Mobile Stations (MSs) to handoff between different BSs in the same MBS zone. However, significant time delay still incurs while MSs handoff between different BSs belonging to different MBS zones (i.e., the inter-MBS zone handoff). To reduce the possibility for the inter-MBS zone handoff, we may increase the size of an MBS zone (i.e., more BSs contained in an MBS zone), which may result in poor multicasting channel utilization. This paper proposes the OverLapping Scheme (OLS) and the Enhanced OverLapping Scheme (EOLS) for more flexible MBS zone configuration to get better performance for MBS in terms of QoS and radio resource utilization. We propose the analytical models for the original MBS zone technology (namely the Basic scheme), and the OLS scheme, which are validated against the simulation experiments. Based on the simulation results, we investigate the performance for the Basic scheme, the OLS scheme, and the EOLS scheme. Copyright