Self-organizing Time Division Multiple Access Research Articles

Self-Organizing TDMA: A Distributed Contention-Resolution MAC Protocol

This paper presents a self-organizing time division multiple access (SO-TDMA) protocol for contention resolution aiming to support delay-sensitive applications. The proposed SO-TDMA follows a cognition cycle where each node independently observes the operation environment, learns about the network traffic load, and then makes decisions to adapt the protocol for smart coexistence. Channel access operation in SO-TDMA is similar to carrier-sense multiple-access (CSMA) in the beginning, but then quickly converges to TDMA with an adaptive pseudo-frame structure. This approach has the benefits of TDMA in a high-load traffic condition, and overcomes its disadvantages in low-load, heterogeneous traffic scenarios. Furthermore, it supports distributed and asynchronous channel-access operation. These are achieved by adapting the transmission-opportunity duration to the common idle/busy channel state information acquired by each node, without any explicit message passing among nodes. The process of adjusting the transmission duration is modeled as a congestion control problem to develop an additive-increase-multiplicative-decrease (AIMD) algorithm, which monotonically converges to fairness. Furthermore, the initial access phase of SO-TDMA is modeled as a Markov chain with one absorbing state and its required convergence time is studied accordingly. Performance of SO-TDMA in terms of effective capacity, system throughput, collision probability, delay-outage probability and fairness is investigated. Simulation results illustrate its effectiveness in performance improvement, approaching the ideal case that needs complete and precise information about the queue length and the channel conditions of all nodes.

Scalable distributed model predictive control for constrained systems

A distributed model predictive control strategy is proposed for subsystems sharing a limited resource. Self-organized Time Division Multiple Access is used to coordinate subsystem controllers in a sequence such that no two re-optimize simultaneously. This new approach requires no central coordination or pre-organized optimizing sequence. The scheme guarantees satisfaction of coupled constraints despite dynamic entry and exit of subsystems.

An Improved MAC Protocol Design in VHF Data Exchange System (VDES) For Internet of Vessels

In recent year, the VDES (VHF Data Exchange System) has drawn extensive attention and admiration in the international maritime field and Internet of Vessels. It has been identified as a core data exchange platform for e-Navigation strategy in the future. However, the traditional Self-Organizing Time Division Multiple Access (SOTDMA) protocol of the Automatic Identification System (AIS) has not met the demands of the huge increases in VHF Data Link (VDL) loading. This paper proposes an improved SOTDMA (iSOTDMA) protocol for VDES to reduce the slot reservation collision rate, thereby improving the system performance. Finally, we present experimental results which show that the proposed iSOTDMA protocol can achieve better performance than the original SOTDMA in terms of slot reservation conflict rate.

Understanding STDMA via computer simulation: feasibility to vehicular safety applications, configurations, and time synchronization errors

Recently, several researchers have proposed to employ self-organized time division multiple access (STDMA) as an alternative Medium Access Control (MAC) protocol of vehicular communications and have studied STDMA to verify its feasibility to vehicular safety applications. However, most of studies have mainly focused on comparing STDMA with enhanced distributed channel access (EDCA) and have several limitations to reveal the feasibility: (1) they have not considered time synchronization error and (2) they have evaluated STDMA with only a single set of configurable parameters. Thus, the feasibility of STDMA to vehicular safety applications still remains unexplored and is an open issue. In this paper, we examine the performances of STDMA to confirm two points: (1) whether or not STDMA is feasible to safety applications even with time synchronization error and (2) whether or not proper configuration really helps to improve the performances. Our simulation results corroborate that current form of STDMA is not feasible to vehicular safety applications and we can improve STDMA via proper parameter configurations.

Real-time road traffic awareness model based on optimal multi-channel self-organized time division multiple access algorithm

Real-time road traffic awareness is a challenge in an intelligent transportation system or internet of vehicles. In this paper, we provide a real-time road traffic awareness model for vehicle drivers based on the optimal multi-channel self-organized time division multiple access algorithm. A system based on this model can be implemented in all kinds of road networks including urban and rural roads or highways and cover a large area. The results indicate that this system can identify more than 5000 vehicles within an identification radius of 40km on rural roads or highways and more than 8000 vehicles within an identification radius of 8km on urban roads. Simulation results show that a system based on this model can meet the drivers’ requirement of obtaining road traffic status in real time.

A MAC Protocol to Support Monitoring of Underwater Spaces.

Underwater sensor networks are becoming an important field of research, because of their everyday increasing application scope. Examples of their application areas are environmental and pollution monitoring (mainly oil spills), oceanographic data collection, support for submarine geolocalization, ocean sampling and early tsunamis alert. The challenge of performing underwater communications is well known, provided that radio signals are useless in this medium, and a wired solution is too expensive. Therefore, the sensors in these networks transmit their information using acoustic signals that propagate well under water. This data transmission type not only brings an opportunity, but also several challenges to the implementation of these networks, e.g., in terms of energy consumption, data transmission and signal interference. In order to help advance the knowledge in the design and implementation of these networks for monitoring underwater spaces, this paper proposes a MAC protocol for acoustic communications between the nodes, based on a self-organized time division multiple access mechanism. The proposal was evaluated using simulations of a real monitoring scenario, and the obtained results are highly encouraging.

How automatic identification system (AIS) antenna setup affects AIS signal quality

The AIS is mostly used to exchange different vessel data between vessels and AIS base stations. For mariners AIS data have become a useful complement to radar data since manual collision avoidance is supported by providing additional information via AIS. Furthermore AIS allows for implementing course prediction algorithms. However, AIS message losses have been confirmed by several studies affecting and restricting the AIS usage especially within vessel prediction algorithms. Several evaluations and simulations concerning the Self-Organized Time Division Multiple Access (SOTDMA) algorithm show that an AIS message loss caused by system overload is unlikely. However, in contrast to the SOTDMA evaluations there are no evaluations about the influence of the VHF medium and the AIS antenna setup on the AIS reception rate. Therefore, we intend to identify the VHF influence on the reception rate by using high quality AIS hardware and AIS antenna installations according to IMO guidelines to record and evaluate AIS data on a German Search and Rescue vessel. By using two different antennas we evaluate the meaning of the antenna height as well as of the general antenna setup for the AIS message reception rate and show the impact of measured reception rates for vessel prediction algorithms.

Ad Hoc Distributed Model Predictive Control of Air Traffic Management

This paper develops an ad hoc distributed control algorithm for air traffic management. The method is based on model predictive control, in which aircraft use optimization to determine their own flight trajectories. The coordination approach of Self-organized Time Division Multiple Access is used to ensure no two aircraft re-optimize simultaneously, thus ensuring collision avoidance. Unlike existing distributed predictive control, which requires a pre-organized optimizing sequence, this new approach requires no central coordinator.

A Scalable CSMA and Self-Organizing TDMA MAC for IEEE 802.11 p/1609.x in VANETs

vehicular ad hoc networks (VANETs) have been a key topic for research community and industry alike. The wireless access in vehicular environment standard employs the IEEE 802.11p/1609.4 for the Medium Access Control (MAC) layer implementation for VANETs. However, the carrier sense multiple access (CSMA) based mechanism cannot provide reliable broadcast services, and the multi-channel operation defined in IEEE 1609.4 divides the available access time into fixed alternating control channel intervals (CCH) and service channel (SCH) intervals, which may lead to the low utilization of the scarce resources. In this paper, a novel multichannel MAC protocol called CS-TDMA considering the channel access scheduling and channel switching concurrently is proposed. The protocol combines CSMA with the time division multiple access (TDMA) to improve the broadcast performance in VANETs. Meanwhile, the dwelling ratio between CCH and SCH changes dynamically according to the traffic density, resulting in the improvement of resource utilization efficiency. Simulation results are presented to verify the effectiveness of our mechanism and comparisons are made with three existing MAC protocols, IEEE MAC, SOFT MAC and VeMAC. The simulation results demonstrate the superiority of CS-TDMA in the reduction of transmission delay and packet collision rate and improvement of network throughput.

다중 홉 해양통신망에서 실시간 통합 서비스를 위한 MAC 프로토콜

In this paper, we propose a new frame structure and the underlying dynamic resource control mechanism to support an integrated service, including a real-time (RT) service that requires to serve the end-to-end delay performance, as well as non-real-time (NRT) service, using Self-Organizing Time Division Multiple Access (SO-TDMA)-based MAC protocol in a multi-hop ad-hoc maritime communication network. The underlying frame structure is dynamically configured by resource allocation to guarantee the average target outage performance of the real-time service. Toward this end, we analyze the average outage probability and its performance is verified for the proposed frame structure by simulation.

Simulation Based Evaluation of Highway Road Scenario between DSRC/802.11p MAC Protocol and STDMA for Vehicle-to-Vehicle Communication

In this paper the DSRC/IEEE 802.11p Medium Access Control (MAC) method of the vehicular communication has been simulated on highway road scenario with periodic broadcast of packets in a vehicle-to-vehicle situation. IEEE 802.11p MAC method is basically based on carrier sense multiple accesses (CSMA) where nodes listen to the wireless channel before sending the packets. If the channel is busy, the vehicle node must defer its access and during high utilization periods this could lead to unbounded delays. This well-known property of CSMA is undesirable for critical communications scenarios. The simulation results reveal that a specific vehicle is forced to drop over 80% of its packets/messages because no channel access was possible before the next message/packet was generated. To overcome this problem, we propose to use self-organizing time division multiple access (STDMA) for real-time data traffic between vehicles. Our initial results indicate that STDMA outperforms CSMA for time-critical traffic safety applications in ad- hoc vehicular networks.

선박자동식별장치를 이용한 ADS-B 개념 기반의 항공감시용 송수신기의 구현

국제해사기구(International Maritime Organization, IMO)에서는 선박의 해상 충돌을 방지하기 위하여 SOLAS의 요구조건에 따라 모든 선박에 대하여 선박자동식별장치(Automatic Identification System, AIS)를 의무적으로 장착하도록 권고하고 있다. AIS를 사용하면 타선에 대한 제원 및 항행정보의 획득이 가능하여 충돌방지뿐만 아니라 광역관제, 조난 선박의 탐색구조 등 안전관리에도 활용이 가능하다. 본 논문에서는 AIS 장비를 사용하여 ADS-B (Automatic Dependent Surveillance - Broadcast) 개념 기반의 항공감시용 송수신기를 구현한 결과에 대하여 살펴보도록 한다. 기본적으로 AIS는 해상에서 사용되기 때문에 고도 정보를 사용하지 않지만, AIS 장비 내부에 사용하는 GPS (Global Positioning System) 칩셋에서 제공하는 고도 정보의 추출이 가능하다. 고도 정보를 포함한 감시 메시지 형식을 정의하고, SOTDMA (Self-Organizing Time Division Multiple Access) 방식을 개선하여 ADS-B 송수신기를 구현하였다. 적용 결과를 확인하기 위하여 지상시험 및 비행시험을 수행하였다. International Maritime Organization (IMO) recommends the installation of an Automatic Identification System (AIS) according to requirements by SOLAS to avoid maritime collision. AIS provides traffic information of other ships that may be used for maritime traffic control, SAR (Search and Rescue) and collision avoidance to apply safety management. In this paper, preliminary results to implement an aeronautical surveillance transceiver using AIS transceiver based on ADS-B concepts are described. Although altitude information is not required for AIS since the AIS is operated at MSL (Mean Sea Level), altitude information can be extracted by a GPS (Global Positioning System) chip-set in the AIS transceiver. ADS-B transceiver is implemented by defining a surveillance message format including the altitude information and modifying SOTDMA (Self-Organizing Time Division Multiple Access) protocol. Ground tests and flight tests are performed to validate the implementation results.

NTS—A nanosatellite space trial

The COM DEV Mission Development Group has recently launched a nanosatellite mission called NTS (Nanosatellite Tracking of Ships). NTS is a space trial, intended to provide proof-of-concept validation for a COM DEV AIS (Automatic Identification System) radio that has been specifically designed to receive ship AIS transmissions from low Earth orbit. The AIS system uses the very high frequency (VHF) band and provides detailed information about each equipped vessel. Not only does this system provide information such as the location of a vessel, but it also provides heading, engine status and other crucial information about the ship. Designed for terrestrial use, the AIS system traditionally has a range of only 100 km and uses a local self-organized time-division multiple access (SO-TDMA) scheme to ensure transmissions from all ships in any self-organized cell do not overlap. Receiving these signals from a space platform presents an opportunity to provide wide area monitoring of shipping activity. Detection of AIS signals from space will provide a new capability to track and monitor large maritime vessels even when there are large distances from traditional shore based detection systems. The NTS program was designed to be a low cost demonstration satellite and provide rapid risk mitigation to assist in the development of a future constellation of spacecraft that could provide operational AIS from space (AIS-S) reception and dissemination. The scope of the NTS program was kept to a minimum with focus on the design, development and demonstration of a new payload. The nanosatellite bus was developed using a combination of pre-existing designs by the University of Toronto Institute of Aerospace Studies/Space Flight Laboratory (UTIAS/SFL). The resulting bus design was a combination of their CanX-2 and Generic Nanosatellite Bus. The NTS spacecraft is able to provide the capability to detect AIS signals from low earth orbit with multiple, short AIS signal collection cycles over its planned mission lifetime. The paper presents an overview of the NTS spacecraft, mission concept and preliminary results obtained from the flight.

On the Ability of the 802.11p MAC Method and STDMA to Support Real-Time Vehicle-to-Vehicle Communication

Traffic safety applications using vehicle-to-vehicle (V2V) communication is an emerging and promising area within the intelligent transportation systems (ITS) sphere. Many of these new applications require real-time communication with high reliability, meaning that packets must be successfully delivered before a certain deadline. Applications with early deadlines are expected to require direct V2V communications, and the only standard currently supporting this is the upcoming IEEE 802.11p, included in the wireless access in vehicular environment (WAVE) stack. To meet a real-time deadline, timely and predictable access to the channel is paramount. However, the medium access method used in 802.11p, carrier sense multiple access with collision avoidance (CSMA/CA), does not guarantee channel access before a finite deadline. In this paper, we analyze the communication requirements introduced by traffic safety applications, namely, low delay, reliable, real-time communications. We show by simulation of a simple, but realistic, highway scenario, that vehicles using CSMA/CA can experience unacceptable channel access delays and, therefore, 802.11p does not support real-time communications. In addition, we present a potential remedy for this problem, namely, the use of self-organizing time division multiple access (STDMA). The real-time properties of STDMA are investigated by means of the same highway simulation scenario, with promising results.