With the taxi playing an increasingly important role in the lives of people, we need further develop the understanding of taxi behavior to analyze the movement pattern of population and improve various intelligent transportation systems. Our work focus on building a new model for the vacant taxi movement pattern in town center of Beijing and we make contribution in three ways. Firstly, through studying foraging behavior of wild animals, we establish the model combined with Lévy flight and exponential distribution. The simulation result is approximate to actual data we collected. Secondly, unlike previous models, we add the time dimension into our model and show the time function of all parameters. Finally, we explain the physical significance and conversion relation of parameters in our model. With these relationship, we can calculate parameters by some small items of data, not the whole database.

Inspired by the migration and division in cells' life-time, we introduce an asynchronous cluster head rotation(ACR) scheme to address unbalanced load in large-scale wireless sensor network and prolong its lifetime. ACR provides an on-demand and low-overhead scheme to rotate CHs asynchronously. Clusters migrate or reproduce using a closed-loop and heuristic mechanism, according to their energy condition individually. Simulation experiments comparing ACR with several state-of-art clustering algorithms demonstrate that ACR obtains an extended lifetime while maintaining a harmonious topology. We probed further into the simulation results and reveal the distinctions between ACR and other clustering schemes.

In underwater wireless optical communication (UWOC) links, multiple scattering may cause temporal spread of beam pulse characterized by the impulse response, which therefore results in inter-symbol interference (ISI) and degrades system error performance. The impulse response of UWOC links has been investigated both theoretically and experimentally by researchers but has not been derived in simple closed-form to the best of our knowledge. In this paper, we analyze the optical characteristics of seawater and present a closed-form expression of double Gamma functions to model the channel impulse response. The double Gamma functions model fits well with Monte Carlo simulation results in turbid seawater such as coastal and harbor water. The bit-error-rate (BER) and channel bandwidth are further evaluated based on this model for various link ranges. Numerical results suggest that the temporal pulse spread strongly degrades the BER performance for high data rate UWOC systems with on-off keying (OOK) modulation and limits the channel bandwidth in turbid underwater environments. The zero-forcing (ZF) equalization designed based on our channel model has been adopted to overcome ISI and improve the system performance. It is plausible and convenient to utilize this impulse response model for performance analysis and system design of UWOC systems.

We consider the target coverage problem and lifetime performance of wireless sensor networks (WSNs). Traditional target coverage schemes only utilize the total energy and fixed/adjustable sensing range and have lower energy efficiency. In this paper, we propose an energy-efficient target coverage algorithm by taking into account the remaining energy and number of covered targets. Numerical results suggest that, regardless of the numbers of targets and sensors, the proposed algorithm achieves longer lifetime than traditional schemes.

We consider a clustered wireless sensor network where sensors are randomly distributed within a circle area with the only cluster head in the center. After the cluster head broadcasts source message to nearby sensor nodes, those neighboring nodes which have successfully decoded the message may help relay data for the head to the destination using space-time block coding (STBC) scheme to form a virtual multi-input-multi-output (vMIMO) system. We first analyze the average outage performance and overall energy consumption including transmission energy and the circuit energy. We then present a transmission scheme to maximize system throughput as well as its performance dependence on data rate and power allocation decisions. Numerical results have validated the proposed scheme and shown the significant throughput increment with appropriate data rate and power allocation decisions.

In traditional wireless sensor networks (WSNs), the power supply is a limiting factor on the lifetime of sensor nodes. Recently, energy harvesting technology has made it possible to develop autonomous WSNs with theoretical unlimited lifetimes. However, the change of power supply calls for a different version of network protocol. In this paper, we introduce Energy Potential Function which is utilized to measure the node's capability of enery harvesting and extend the traditional protocol LEACH to Energy Potential LEACH which is suitable for energy harvesting WSNs. Energy Potential LEACH can not only extend network lifetimes, but also improve the network throughput in energy harvesting WSNs. We evaluate the proposed protocol analytically and numerically, and find that it exhibits a better performance than previous work in terms of lifetimes and throughput.

This paper addresses the issue of transmission scheduling in multi-channel wireless ad hoc networks. The authors propose a multi-channel time division multiple access (TDMA) scheduling based on edge coloring and algebraic coding theory, called CC-TDMA. The authors categorized the conflicts suffered by wireless links into two types: explicit conflicts and implicit conflicts, and CC-TDMA utilize two different strategies to deal with them. Explicit conflicts are avoided completely by a simple distributed edge-coloring algorithm mu-M, and implicit conflicts are minimized by using coding theory to assign channels to links. The authors evaluate CC-TDMA analytically and numerically, and find that it exhibits a better performance than previous work in terms of throughput and delay.