Time Slot Reuse Research Articles

Hybrid adaptive MAC scheme for the broadcast of vehicular safety beacons

SummaryVehicular safety applications are based on broadcasting periodic safety beacons on the IEE802.11p control channel. The CSMA MAC scheme adopted in the IEE802.11p cannot ensure the strict timeline and the high reliability when broadcasting these real time and critical messages since it does not consider the high mobility of vehicles, the limited network resources, and the variant traffic densities. Therefore, the design of an effective MAC scheme that takes in consideration these parameters represents a challenging task. Furthermore, the fixed beaconing rate results an overload on the commination channel and collisions especially in dense situations that delay beacons broadcast. In this paper, we propose a novel hybrid MAC scheme for fast and reliable broadcast of safety beacons. At first, it relies on a time slot reuse policy that considers the mobility features of vehicles while reducing transmission collisions. In addition, it adapts mathematically the beaconing rate to the traffic density based on vehicular velocity at the aim of optimizing the performance of the wireless channel. Simulation results show that our proposal outperforms significantly the IEEE802.11p CSMA MAC scheme and upgrades the performance of vehicular networks in broadcasting periodic safety beacons.

Fast and Reliable Dynamic Tag Estimation in Large-Scale RFID Systems

Radio-frequency identification (RFID) has been utilized in many applications, such as supply chain and stock management in supermarkets. RFID systems in such practical applications are inherently dynamic because tags may move in and out frequently. One important but challenging problem in such systems is how to estimate the number of dynamic tags fast and reliably. This article proposes effective solutions to this problem, which guarantee the accuracy of estimation and time efficiency. Especially, we want to simultaneously estimate the number of tags that moved out of the system (missing tags) and the number of tags that entered the system (unknown tags) in a specified time interval. We design a novel method called time slot reuse (TSR) that generates two logical frames corresponding to the two types of tags from only one physical frame. Based on TSR, we propose a protocol called SSR that can accurately estimate the number of dynamic tags by using the generated logic frames. However, the performance of SSR degrades significantly when the disparity between the number of the two types of tags is remarkable. We further propose an enhanced version of SSR (ESSR), which overcomes this drawback by partitioning the frame into ranges and mapping different types of tags into different ranges. Rigorous theoretical analysis is performed to tune parameters in SSR and ESSR to minimize the execution time. The simulation results demonstrate up to 80% improvement in time efficiency when compared with state-of-the-art solutions to the same problem.

A Bandwidth-Efficient MAC Scheme for Mission-Critical Applications in Industrial Wireless Sensor Networks

Industrial wireless sensor networks (IWSNs) have the potential to contribute significantly to a variety of wireless sensing endpoints, such as cable replacement, mobility, flexibility and cost reduction. However, the harsh and varied industrial environment entails addressing severe challenges, such as dust, heat, electromagnetic interference (EMI) and radio frequency interference from the other heterogeneous networks. One of the important challenges is the link burstiness in industrial wireless environments, which has not been heavily researched. In this paper, we propose a new timeslot scheduling algorithm to address this problem. The algorithm allows transmissions on the same link to be separated at least by a minimum timeslot distance. Moreover, to provide a synergistic complement to the timeslot scheduling, we also propose a timeslot reuse scheme, which facilitates improved efficiency and reliability in the bandwidth utilization and retransmission and decreases the average delay of the packet arrival. We evaluate the proposed algorithm and scheme by a real implementation, targeting a specific industrial application. The experimental results generally indicate that the proposed media access control (MAC) scheme greatly improves the reliability and decreases the packet arrival delay. Compared with the existing popular methods, the execution of our scheme indicates a minimal link burstiness influence and possesses more efficient bandwidth utilization.

Timeslot Management’s Design and Implementation of AIS Terminal Equipment

Our project team designed and realized an Automatic Identification System (AIS) terminal equipment specifically which is based on an ARM7 chip and compatible with a self-developed FPGA chip. The main research topic is about the timeslot management and implementation in this equipment. I designed a timeslot list in the form of an array, to storage every timeslot state in each channel and current frame real-time, intuitively, and conveniently. When there is a timeslot-occupied or a timeslot-reserved in the equipment, the timeslot list can storage the timeslot state real-time. This timeslot state is defined as whether each timeslot is currently occupied, what action occupied it, how long the timeout is. And manage the timeslot every timeslot by timeout, to realize each timeslot management in A/B channels. When the equipment will select candidate timeslots to send message, it could read the timeslot state by the timeslot number directly to know whether it can send message in this timeslot. Make sure its timeslot reuse, prevent its timeslot collision, and realize the communication real-time and effective.

Intertwined path formation and MAC scheduling for fast delivery of aggregated data in WSN

This paper studies the problem of data aggregation scheduling in wireless sensor networks (WSNs) to minimize time latency. In prior work on this problem, a node is assigned a parent from the set of unscheduled nodes in order to prevent the creation of cycles. However, using such a strategy reduces the time-slot reuse and consequently has a negative impact on the time latency. To address these shortcomings, we propose IPS (Interwined Path formation and MAC Scheduling), a novel cross-layer scheme for data aggregation scheduling that allows selecting a parent from all the node’s neighbors including the scheduled ones. IPS achieves reduced data delivery latency through three key design features, namely, (1) intertwining aggregation tree formation and scheduling, (2) for each node, a parent can be selected from already scheduled nodes so that the time latency is reduced and the cycles are prevented and (3) applying parent selection criteria that maximize the time slot reuse. We prove that the data delivery latency for IPS is upper-bounded by (⌊2πarccos(11+∊)⌋+3)R+Δ-4, where R is the network radius, Δ is the maximum node degree, and 0.05<∊⩽1. The simulation results show that IPS outperforms seven competing state-of-the-art aggregation scheduling algorithms in terms of latency and network lifetime.

Transmission scheduling for wireless mesh networks with temporal reuse

Link-assigned transmission schedules with timeslot reuse by multiple links in both the space and time domains are investigated in this study for stationary multihop wireless mesh networks with both rate and power adaptivity. Specifically, cross-layer optimised schedules with proportionally fair end-to-end flow rates and network coding capability are constructed for networks operating under the physical interference model with single-path minimum hop routing. Extending transmission rights in a link-assigned schedule allows for network coding and temporal reuse, which increases timeslot usage efficiency when a scheduled link experiences packet depletion. The schedules that suffer from packet depletion are characterised, and a generic temporal reuse-aware achievable rate region is derived. Extensive computational experiments show improved schedule capacity, quality of service, power efficiency and benefit from network coding accrued with schedules optimised in the proposed temporal reuse-aware convex rate region.

Performance Evaluation of Multi Hop Relay Network for Oceanic Air Traffic Control Communication

This paper proposes a new kind of communication system for air traffic control over the oceans; it is particularly effective at handling high air traffic loads due to many oceanic flights. In this system, each aircraft position report is sent to its relevant ground station by forwardly relaying them via a multi hop ad-hoc network that is formed by the aircraft between this aircraft and the ground station. In addition, an effective multiple access scheme with optimal values is also proposed. This scheme enables the various aircraft involved in relaying the signal to operate autonomously in a flight-route airspace. Furthermore, two useful schemes are proposed for efficient timeslot reuse and timeslot assignment in cases of low aircraft densities: the position aided timeslot reuse (PATR) and distance based timeslot assignment (DBTA), respectively. Finally, another scheme is proposed to improve the achievable relayed packet rate under low aircraft densities, which is called interference-based node selection (IB-NS). In all, the proposed system combined with those three schemes show the availability to utilize this system for air traffic control communications, specifically on high traffic ocean routes.

Iterative hybrid graph and interference aware scheduling algorithm for STDMA networks

An algorithm that combines graph colouring with signal-to-interference plus noise ratio information to allocate transmission rights in a spatial time division multiple access (STDMA) network is presented. The proposed iterative algorithm extends graph-based algorithms by allowing feasible schedules to be found with high spatial timeslot reuse.

Multi-rate power-controlled link scheduling for mesh broadband wireless access networks

The problem of multi-rate power-controlled collision-free scheduling in spatial time division multiple access (STDMA) wireless mesh networks is formulated as a mathematical program utilising cross layer information. As these mixed integer linear programs are intractable (${\cal NP}$-hard problems), optimal collision-free schedules can be found only for topologies consisting of a few nodes. To this end, approximation algorithms that are based on linear programming relaxation and randomised rounding are studied. The proposed framework, which aims to maximise the spatial timeslot reuse under predefined signal-to-interference noise ratio thresholds, is suitable for providing centralised scheduling in the mesh mode of the IEEE 802.16 standard. Performance aspects of the approximation algorithms under different scenarios are investigated.

A hexagonal-tree TDMA-based QoS multicasting protocol for wireless mobile ad hoc networks

The mobile multimedia applications have recently generated much interest in wireless ad hoc networks with supporting the quality-of-service (QoS) communications. The QoS metric considered in this work is the reserved bandwidth, i.e., the time slot reservation. We approach this problem by assuming a common channel shared by all hosts under a TDMA (Time Division Multiple Access) channel model. In this paper, we propose a new TDMA-based QoS multicast routing protocol, namely hexagonal-tree QoS multicast protocol, for a wireless mobile ad hoc network. Existing QoS routing solutions have addressed this problem by assuming a stronger multi-antenna model or a less-strong CDMA-over-TDMA channel model. While more practical and less costly, using a TDMA model needs to face the challenge of radio interference problems. The simpler TDMA model offers the power-saving nature. In this paper, we propose a new multicast tree structure, namely a hexagonal-tree, to serve as the QoS multicasting tree, where the MAC sub-layer adopts the TDMA channel model. In this work, both the hidden-terminal and exposed-terminal problems are taken into consideration to possibly exploit the time-slot reuse capability. The hexagonal-based scheme offers a higher success rate for constructing the QoS multicast tree due to the use of the hexagonal-tree. A hexagonal-tree is a tree whose sub-path is a hexagonal-path. A hexagonal-path is a special two-path structure. This greatly improves the success rate by means of multi-path routing. Performance analysis results are discussed to demonstrate the achievement of efficient QoS multicasting.

Resource assignment in a fixed broadband wireless system

We propose a time slot reuse partitioning (TRSP) scheme for resource assignment in packet-switched fixed TDMA wireless networks. The TSRP scheme is based upon two key ideas. The first one is for the system to have more than one coexisting reuse pattern in the time domain. The second is to match a terminal or application to an appropriate reuse pattern, so as to guarantee the required quality of service (QoS). We define and then simulate a specific implementation of the TRSP scheme for an integrated voice and broadband data system. The results show that this scheme provides good performance for both voice and data.