Time Distribution Scheme Research Articles

Enabling Cost-effective Wireless Data Collection by Piggybacking on Delivery Drones in Agriculture

Drones have drawn considerable attention as the agents in wireless data collection for agricultural applications, by virtue of their three-dimensional mobility and dominant line-of-sight communication channels. Existing works mainly exploit dedicated drones via deployment and maintenance, which is insufficient regarding resource and cost-efficiency. In contrast, leveraging existing delivery drones for the data collection on their way of delivery, called delivery drones’ piggybacking , is a promising solution. For achieving such cost-efficiency, drone scheduling inevitably stands in front, but the delivery missions involved have escalated it to a wholly different and unexplored problem. As an attempt, we first survey 514 delivery workers and conduct field experiments; noticeably, the collection cost, which mostly comes from the energy consumption of drones’ piggybacking, is determined by the decisions on package-route scheduling and data collection time distribution . Based on such findings, we build a new model that jointly optimizes these two decisions to maximize data collection amount, subject to the collection budget and delivery constraints. Further model analysis finds it a Mixed Integer Non-Linear Programming problem, which is NP-hard. The major challenge stems from interdependence entangling the two decisions. For this point, we propose Delta , a \(\frac{1}{9+\delta } \) -approximation delivery drone scheduling algorithm. The key idea is to devise an approximate collection time distribution scheme leveraging energy slicing, which transforms the complex problem with two interdependent variables into a submodular function maximization problem only with one variable . The theoretical proofs and extensive evaluations verify the effectiveness and the near-optimal performance of Delta .

Two‐step method to reduce metro transit energy consumption by optimising speed profile and timetable

With the rising energy prices and increasing environmental awareness, the energy efficiency of metro transit system has attracted much attention in recent years. This study proposes a two-step optimisation method to optimise speed profile and timetable, aiming to reduce the operational energy consumption of metro transit system. First, a coasting point searching algorithm is designed to reduce tractive energy consumption by optimising speed profile and running time distribution scheme. Then, a mixed-integer linear programming model is constructed to maximise the overlap time between the accelerating and braking phases by optimising headway and dwell time, in order to improve the utilisation of regenerative braking energy (RBE). Furthermore, numerical simulations are presented based on the data from a Guangzhou Metro Line. The results show that the tractive energy consumption can be reduced by 8.46% and the utilisation of RBE can be improved by 11.6%.

Enhanced Timestamping Method for Subnanosecond Time Synchronization in IEEE 802.11 Over WLAN Standard Conditions

The time-sensitive network paradigm envisions the integration of operation technology and information technology in the same network. One of the requirements for building time-sensitive networks is sharing a global time along the network. This requirement is especially critical in wireless systems, where there are few robust methods to perform accurate time transfer. In this article, the problem of time transfer over realistic wireless channels is studied, and a time distribution scheme is proposed. The time distribution scheme has three components: Precision time protocol, a novel timestamping method (enhanced timestamps) and an algorithm to implement the enhanced timestamps. The performance of the proposed scheme has been evaluated in MATLAB using the IEEE 802.11n Standard under several standard wireless local area network channel models. The results show that the system can reach subnanosecond time transfer accuracy under non-line-of-sight and time-variant conditions, but its performance greatly depends on the signal-to-noise ratio and on the channel variation rate.

Low‐cost multi‐standard video transform core using time‐distribution scheme

Cost-effective two-dimensional (2D) discrete cosine transform (DCT) and inverse DCT architectures capable of supporting multiple standards of MPEG, H.264 and VC-1 are presented. The proposed core utilises a 1D core and a transposed memory to achieve a low cost design. Multi-level factor share is implemented in conjunction with distributed arithmetic in a system to enable the sharing of the coefficient matrix circuit in order to reduce hardware costs. The proposed approach employs a time-distribution scheme to enable the simultaneous processing of the first and second dimensions to enhance throughput. A high efficiency of this approach was verified by fabricating a test chip using the TSMC 0.18 μm CMOS process. The architecture has an operating frequency of 200 MHz, and throughput of 800 M-pixels/s with a gate count of 44.5 K.

Turnback Capacity Assessment and Delay Management at a Rail Transit Terminal with Two-Tail Tracks

Terminal capacity and performance have become a major concern for rail transit agencies in China due to the ever increasing passenger demand. This paper develops a mixed integer programming (MIP) optimization model to estimate the turnback capacity and performance of a rail transit terminal with two-tail tracks. The capacity evaluation and delay propagation are described and assessed as anN-track integrated model with minimal time span and train delay. Operations and design parameters such as tail track allocation strategies, maximum layover time, headway pattern, buffer time distribution scheme, and primary delay are also considered in this model. The effectiveness of the model is tested by a case study with computation results drawn from one terminal station in Shanghai, China. The case study results show that unfixed platform time and flexible tail track allocation strategies can improve the capacity of turnback operation, and the strategy of allowing swapping of the tail tracks has a significantly positive impact on delay absorption.

Field Application of the Multilinear Muskingum Discharge Routing Method

To implicitly model the nonlinear dynamics of flood wave propagation in rivers with floodplains, a multilinear discharge-hydrograph routing method based on time distribution scheme is proposed. The framework of this method is based on the variable parameter Muskingum-type routing method, which is used as the linear sub-model. The applicability limit and suitability of this flood routing method is verified using numerical experiments and field data, respectively.

Multilinear Muskingum Method for Stage-Hydrograph Routing in Compound Channels

A multilinear stage-hydrograph routing method based on time distribution scheme is analyzed. The framework of the multilinear method is based on the Muskingum-type routing method, which is used as the linear submodel. The proposed method can implicitly model the nonlinear dynamics of the flood wave propagation by varying the model parameters at each routing time step. The suitability of this flood routing method is verified using a set of laboratory experimental data and the field data of the Tiber River in central Italy.

Multilinear discrete cascade model for channel routing

A method for flood routing in rigid bed channels using multilinear modelling based on a time distribution scheme is presented. The discrete cascade model with its parameters related to channel and flow characteristics through a moment-matching technique is used as the linear submodel. The particular advantage of using this two-parameter submodel is that it simulates the outflow hydrograph in a realistic way unlike the Muskingum model which produces a ‘dip’ or ‘reduced outflow’ at the beginning of routing. The suitability of this method for routing floods in uniform rectangular channels is studied by routing a mathematically defined inflow hydrograph. The solutions obtained using this model are compared with the corresponding solutions of the St. Venant equations. The study reveals that the proposed multilinear model reproduces the St. Venant solutions closely when the rating curve corresponding to the inflow hydrograph is characterized by a narrow loop.

Multilinear muskingum flood routing method

In a study of multilinear modelling of flood wave propagation based on a time distribution scheme, an attempt is made to overcome certain limitations of the currently available multilinear models. The physically based Muskingum method is used as the linear sub-model. Unlike the currently available multilinear models, wherein the parameters are held constant for routing prescribed flow zones of the inflow hydrograph, in the proposed method they vary at each routing time step. This allows better modelling of the non-linear behaviour of the flood wave movement and eliminates the subjectivity of deciding on the number of flow zones to be used for routing the given inflow hydrograph. The suitability of this method for routing floods in wide uniform rectangular channels without lateral flow is studied using hypothetical data. The study reveals that the proposed method is capable of describing flood wave movement in open channels, as a result of a flood hydrograph characterized by narrow loop rating curve.