TDMA-based Protocol Research Articles

Full-Duplex UAV Relaying for Multiple User Pairs

Based on the advantages of small size, lightweight, as well as flexible deployment and recycling, unmanned aerial vehicle (UAV) has been more and more widely used in military and civilian. As flying relays, UAVs can quickly set up relay communication links for different missions, to enhance the receiving signal power, increase the system capacity, and expand the communication coverage. In this article, we investigate full-duplex (FD) UAV relaying for multiple source–destination pairs. To fully exploit the flying flexibility of the UAV in serving multiple source–destination pairs, we propose a scheduling protocol that exploits time-division multiple access (TDMA) to serve different source–destination pairs in turns when flying along an optimized trajectory. Then, we further formulate a joint optimization problem of the TDMA-based user scheduling, the dynamic UAV trajectory, and the UAV transmit power to maximize the system throughput. The formulated problem is nonconvex that makes it difficult to solve directly, hence we propose an iterative algorithm to obtain an approximate optimal solution based on block coordinate descent and successive convex optimization techniques. Simulation results demonstrate that our proposed FD-based UAV relaying network achieves significant throughput gains compared with the half-duplex (HD) baseline, and the TDMA-based protocol outperforms the OFDMA-based ones with fixed UAV position/trajectory when the UAV helps relay information for multiple source–destination pairs.

Empirical Performance Models of MAC Protocols for Cooperative Platooning Applications

Vehicular ad-hoc networks (VANET) enable vehicles to exchange information on traffic conditions, dynamic status and localization, to enhance road safety and transportation efficiency. A typical VANET application is platooning, which can take advantage of exchanging information on speed, heading and position to allow shorter inter-vehicle distances without compromising safety. However, the platooning performance depends drastically on the quality of the communication channel, which in turn is highly influenced by the medium access control protocol (MAC). Currently, VANETs use the IEEE 802.11p MAC, which follows a carrier sense multiple access with collision avoidance (CSMA/CA) policy that is prone to collisions and degrades significantly with network load. This has led to recent proposals for a time-division multiple access (TDMA)-based MAC that synchronize vehicles’ beacons to prevent or reduce collisions. In this paper, we take CSMA/CA and two TDMA-based overlay protocols, i.e., deployed over CSMA/CA, namely PLEXE-slotted and RA-TDMAp, and carry out extensive simulations with varying platoon sizes, number of occupied lanes and transmit power to deduce empirical models that provide estimates of average number of collisions per second and average busy time ratio. In particular, we show that these estimates can be obtained from observing the number of radio-frequency (RF) neighbours, i.e., number of distinct sources of the packets received by each vehicle per time unit. These estimates can enhance the online adaptation of distributed applications, particularly platooning control, to varying conditions of the communication channel.

Collision avoidance in shared slots in wireless devices of the Internet of Things: models and simulations

In this paper, we propose an analysis of a slot-based protocol designed for devices of the Internet of Things (IoT). In contrast to other TDMA-based protocols, this scheme uses a random technique to access shared slots, similarly to CSMA protocols. In practice, the transmissions are scheduled in a given backoff window of slots whose duration allows the transmission of a packet and its acknowledgment. Therefore, this protocol can be analyzed according to the methodology introduced by Bianchi for the IEEE 802.11 protocol even if the protocol studied differs in many aspects. The model we use is also particular because we succeed in obtaining a Markov model even though the scheme used to send a packet (in a node) may depend on the transmission of the previous packet. We distinguish two protocols; in the first one, at the initial stage or after a successful transmission, the packets are transmitted without any backoff, whereas in the second protocol each transmission is always preceded by the count down of a random backoff. Extensive simulations validate both protocols models. In addition, the performances of these protocols are compared with those of slotted Aloha and a protocol using a constant backoff window.

TDMA-based Low Power MAC Protocol Design of Wireless Sensor Networks for Vehicle Detection

TDMA-based Low Power MAC Protocol Design of Wireless Sensor Networks for Vehicle Detection

A TDMA-Based Hybrid Transmission MAC Protocol for Heterogeneous Vehicular Network

A TDMA-Based Hybrid Transmission MAC Protocol for Heterogeneous Vehicular Network

Synthesizing Existing CSMA and TDMA Based MAC Protocols for VANETs.

Many Carrier Sense Multiple Access (CSMA) and Time Division Multiple Access (TDMA) based medium access control (MAC) protocols for vehicular ad hoc networks (VANETs) have been proposed recently. Contrary to the common perception that they are competitors, we argue that the underlying strategies used in these MAC protocols are complementary. Based on this insight, we design CTMAC, a MAC protocol that synthesizes existing strategies; namely, random accessing channel (used in CSMA-style protocols) and arbitral reserving channel (used in TDMA-based protocols). CTMAC swiftly changes its strategy according to the vehicle density, and its performance is better than the state-of-the-art protocols. We evaluate CTMAC using at-scale simulations. Our results show that CTMAC reduces the channel completion time and increases the network goodput by 45% for a wide range of application workloads and network settings.

Medium Access Control for Wireless Body Area Networks with QoS Provisioning and Energy Efficient Design

With the promising applications in e-Health and entertainment services, wireless body area network (WBAN) has attracted significant interest. One critical challenge for WBAN is to track and maintain the quality of service (QoS), e.g., delivery probability and latency, under the dynamic environment dictated by human mobility. Another important issue is to ensure the energy efficiency within such a resource-constrained network. In this paper, a new medium access control (MAC) protocol is proposed to tackle these two important challenges. We adopt a TDMA-based protocol and dynamically adjust the transmission order and transmission duration of the nodes based on channel status and application context of WBAN. The slot allocation is optimized by minimizing energy consumption of the nodes, subject to the delivery probability and throughput constraints. Moreover, we design a new synchronization scheme to reduce the synchronization overhead. Through developing an analytical model, we analyze how the protocol can adapt to different latency requirements in the healthcare monitoring service. Simulations results show that the proposed protocol outperforms CA-MAC and IEEE 802.15.6 MAC in terms of QoS and energy efficiency under extensive conditions. It also demonstrates more effective performance in highly heterogeneous WBAN.

Time synchronisation attacks and defences in IEEE802.15.4e networks

Time synchronisation is very crucial in many wireless sensor network applications especially in industrial wireless networks. The current industrial wireless standards all use TDMA-based channel-sharing protocols on the medium access control (MAC) layer. If an adversary launches time synchronisation attacks to the industrial wireless networks, the whole networks communication will be paralysed. However, the time synchronisation is insufficient to be protected in the current industrial wireless standards which based on IEEE802.15.4e standard. So it is important to study in depth the time synchronisation method of attack and defense in IEEE802.15.4e networks. In this paper we give a survey of time synchronisation in IEEE802.15.4e networks and point out the possible attacks. They include ASN attack, message manipulation attack, node identity attack and pulse-delay attack. Then we propose some countermeasures against these attacks. Finally, we perform a series of experiments to evaluate the effectiveness of corresponding defences for the attacks. The experiment results show that the proposed mechanisms can successfully defend against these attacks. And the energy consumption of these defense methods are very low.

Reliability Evaluation of Broadcast Protocols for FlexRay

X-by-wire applications have extremely demanding reliability requirements that are increasingly being addressed through the adoption of distributed and fault-tolerant architectures. The development of these applications is facilitated by the availability of high-level services such as agreement or reliable broadcast (RB). Some dependable communication buses, e.g., TTP-C, already provide these services, whereas FlexRay does not. In this paper, we present an approach to evaluate the reliability of a family of RB protocols implemented both on top of FlexRay and on top of ordinary time-division multiple access (TDMA). In particular, we evaluate the impact of the acknowledgment policy on the reliability of these protocols. We express the reliability as the probability of violation of the agreement and validity properties of the protocol during a mission. For that, we develop an analytical model based on discrete-time Markov chains, which considers a comprehensive set of faults (permanent, transient, omissive, and asymmetric) affecting both nodes and channels, and their effects on the protocol execution. The structure of the model is quite flexible and easily adaptable to other TDMA-based protocols. To assess the sensitivity of the protocol to both internal and external factors, we carried out a large number of experiments considering several network configurations and fault rates. The results show that for FlexRay, the negative-acknowledgment policy provides the same reliability as the positive-acknowledgment policy. However, for TDMA-based protocols that lack FlexRay's ability to distinguish silence from the loss of a message, the negative-acknowledgment policy leads to lower reliability, and its fitness for safety-critical applications depends on the system configuration and environment conditions.

TDMA-Based IEEE 802.15.4 for Low-Latency Deterministic Control Applications

In this paper, we propose a technique for making IEEE 802.15.4 standard suitable for low-latency deterministic networks for wireless control applications where the cyclic update time of sensor's information is not more than 10 ms. The IEEE 802.15.4 has shown good characteristics for deterministic networks in beacon-enabled mode, but with minimum cyclic update time for personal area network devices not less than 15.36 ms. Moreover, it is unsuitable for hard real-time systems when used in nonbeacon-enabled mode due to the random nature of channel access protocol. The proposed technique employs time-division multiple access (TDMA)-based protocol that works on slightly modified IEEE 802.15.4 in star topology. Each end device in the network transmits its data frame after certain time delay in response to periodic requests from the coordinator. This time delay is optimized for better channel bandwidth utilization and reliable data exchange. While this TDMA-based protocol eliminates the risk of frame collisions to a great extent, medium-access control sublayer modifications reduce the nondeterminism of the network and increase the bandwidth efficiency. A mathematical model is proposed to design and develop a practical communication network with commercial off-the-shelf radios that can predict worst case arrival time of data frames. Experiments were conducted to evaluate the model for the proposed protocol.

Self Organized, Flexible, Latency and Energy Efficient Protocol for Wireless Sensor Networks

This paper presents Self Organized, Flexible, Latency and Energy Efficient (SOFLEE) Protocol, a cross-layer protocol for Wireless Sensor Networks that uses TDMA based medium access scheme combined with multi-hop routing information during time slot allocation. Time slot allocation is done centrally by Master Station (MS) to provide a collision-free and fair media access. MS allocates same transmission slot to nodes that are two hops apart to increase channel spatial reuse and decrease data latency. For data gathering at MS, SOFLEE uses parenthood willingness to forward data to MS through unidirectional tree rooted at MS. Parenthood willingness of a node is decided using: (i) its location with respect to MS, to forward data in correct direction; (ii) its number of children, to prevent local congestion; (iii) its residual energy, to uniformly distribute energy load of being a parent node and (iv) its parent–child communication link reliability to guarantee consistent data delivery. The parenthood willingness requires simple comparisons against thresholds, and thus, is very simple to implement on memory and computationally constrained nodes. Unlike a conventional TDMA-based protocol, SOFLEE provides flexibility to transfer data slots among nodes and priority based slot scheduling to adapt to dynamic traffic patterns of various Wireless Sensor Network applications. Finally, simple, memory and energy efficient techniques for: (i) hop-by-hop congestion control; (ii) catering to orphan nodes, link breakdowns and node deaths are incorporated in SOFLEE. A comparative analysis of SOFLEE, FlexiTP, self organized TDMA protocol, energy efficient fast forwarding and D-MAC show that SOFLEE is 25 to 61 % more energy efficient compared to FlexiTP. Data latency of SOFLEE is 32 to 68 % less, delivery ratio is 7 to 19 %, goodput is 3 % and network lifetime is 253.784 s to 448.440 s more compared to FlexiTP.

Token-MAC: A Fair MAC Protocol for Passive RFID Systems

Passive RFID systems used for inventory management and asset tracking typically utilize contention-based MAC protocols, such as the standard C1G2 protocol. Although the C1G2 protocol has the advantage that it is easy to implement, it suffers from unfairness and relatively low throughput when the number of tags in the network increases. This paper proposes a token-based MAC protocol called Token-MAC for passive RFID systems, which aims a) to provide a fair chance for tags in the network to access the medium without requiring synchronization of the tags, b) to increase the overall throughput, i.e., the tag rate, and c) to enable a high number of tags to be read under limited tag read time availability, which is an especially important challenge for mobile applications. We implement Token-MAC as well as C1G2 and a TDMA-based protocol using Intel WISP passive RFID tags and perform experiments. Additionally, based on our experimental results, we develop energy harvesting and communication models for tags that we then use in simulations of the three protocols. Our experimental and simulation results all show that Token-MAC can achieve a higher tag rate and better fairness than C1G2, and it can provide better performance over a longer range compared with the TDMA-based protocol. It is also shown that Token-MAC achieves much lower tag detection delay, especially for high numbers of tags. Token-MAC is, therefore, a promising solution for passive RFID systems.

Performance analysis of TDMA-based wireless network for safety-critical avionics

The opportunities and challenges for using wireless interconnects for safety-critical avionics have been discussed in our previous work. A Wireless Avionics Network (WAN) has been proposed based on hybrid architecture UWB and Switched Ethernet with adequate reliability and security mechanisms to increase scalability and reduce electromagnetic susceptibility (figure 1). Furthermore, a TDMA-based protocol was considered to guarantee a contention free access and enhance communication predictability. However, the use of wireless technologies may increase the communication latencies due to transmission errors, and real time constraints have to be verified. In order to deal with the worst case performance analysis of such network, an appropriate schedulability analysis based on Network Calculus formalism is presented in this paper and obtained results for a realistic case study are discussed herein.

A TDMA Scheme for Mobile Sensor Networks

We propose a TDMA-based protocol for mobile sensor networks. The proposed protocol overcomes the shortcomings of the other available TDMA-based protocols in a dynamic network where the cluster membership may change frequently. Unlike other existing TDMA-based protocols, we propose to vary the number of timeslots in the TDMA frame to allow underutilization of unused slots and successful allocation of timeslots to the newly joined sensors through minimizing collisions. The approach is fully decentralized and efficient to be used by the cluster head (leader) and the sensor nodes in a cluster. Simulations also show that the proposed mechanism provides significant performance improvements compared to the other existing approaches in terms of different network performance metrics.

Supporting bursty traffic in wireless sensor networks through a distributed advertisement-based TDMA protocol (ATMA)

Nodes in wireless sensor networks (WSNs) are battery powered and oftentimes deployed in remote and hostile locations. Energy conservation is, therefore, one of the primary goals of MAC protocols designed for these networks. Contention-based protocols employ static or variable duty cycles to minimize energy dissipated in idle listening. TDMA-based protocols, on the other hand, use reservation and scheduling to minimize energy loss. Further energy savings may be obtained by taking the nature of the network traffic into consideration. Several WSN applications such as surveillance applications and habitat monitoring applications generate bursty traffic. In this paper, we combine the advantages of contention-based and TDMA-based protocols to form Advertisement-based Time-division Multiple Access (ATMA), a distributed TDMA-based MAC protocol for WSNs, that utilizes the bursty nature of the traffic to prevent energy waste through advertisements and reservations for data slots. We provide detailed comparisons of the ATMA protocol with contention-based protocols (S-MAC, T-MAC and ADV-MAC), a TDMA-based protocol (TRAMA) and hybrid protocols (Z-MAC and IEEE 802.15.4) through extensive simulations and qualitative analysis. The simulation results show that with bursty traffic, ATMA outperforms these existing protocols in terms of energy consumption with reductions of up to 80%, while providing the best packet delivery ratio (close to 100%) and latency among all the investigated protocols for several simulation scenarios studied.

Ultra Low Power Signal Oriented Approach for Wireless Health Monitoring

In recent years there is growing pressure on the medical sector to reduce costs while maintaining or even improving the quality of care. A potential solution to this problem is real time and/or remote patient monitoring by using mobile devices. To achieve this, medical sensors with wireless communication, computational and energy harvesting capabilities are networked on, or in, the human body forming what is commonly called a Wireless Body Area Network (WBAN). We present the implementation of a novel Wake Up Receiver (WUR) in the context of standardised wireless protocols, in a signal-oriented WBAN environment and present a novel protocol intended for wireless health monitoring (WhMAC). WhMAC is a TDMA-based protocol with very low power consumption. It utilises WBAN-specific features and a novel ultra low power wake up receiver technology, to achieve flexible and at the same time very low power wireless data transfer of physiological signals. As the main application is in the medical domain, or personal health monitoring, the protocol caters for different types of medical sensors. We define four sensor modes, in which the sensors can transmit data, depending on the sensor type and emergency level. A full power dissipation model is provided for the protocol, with individual hardware and application parameters. Finally, an example application shows the reduction in the power consumption for different data monitoring scenarios.

An enhanced frame transmission method for medical devices with ultra low power operation

Radio modules for future medical devices are required to minimize their energy consumption while maximizing the reliability of frame transmission. For medical devices in wireless body network, TDMA-based protocols can be candidates, but they have low energy efficiency in a wireless interference environment. In this paper, we propose an enhanced continuous frame transmission (CFT) method which is a hybrid TDMA and random access MAC protocol with carrier sensing method. CFT controls the frame transmission epochs considering the effect of interference that changes according to the number of neighbor wireless devices. Simulation results show that CFT method has higher efficiency compared to conventional TDMA based methods in a interference environment.

A Lightweight Lap Time Measurement System for Alpine Ski Sport Using a TDMA-Based Linear Wireless Sensor Network

In Alpine ski sport, traditional lap time measurement systems record a skier's departure and arrival using time-of-day timers through wires, which is not cost effective in unofficial or training games. This paper develops a lightweight lap time measurement system using a wireless sensor network, which employs a practical TDMA-based linear wireless sensor network protocol for multihop communications in long strap-shaped environments where sensor nodes are linearly deployed. We evaluate the performance of this protocol through the implementation and deployment of the lap time measurement system. The experimental results show that the proposed protocol transmits data at a success rate of 99.66% and maintains the time synchronization errors between two adjacent nodes within 183 μs without using any other time synchronization protocols. In an experimental deployment for a 1.5 km ski slope covered by 31 nodes, the system provides lap time measurements with a measurement error of 1.255 ms, which satisfies the official measurement error of 5.0 ms.

Exploiting spatial correlation at the link layer for event-driven sensor networks

Wireless Sensor Networks (WSNs) can generally be classified into two categories: time-driven and event-driven. In an event-driven WSN, sensors report their readings only when they detect events. In such behaviour, sensors in the event area may suffer from higher contention. In this paper, we solve this problem by jointly considering two sub-issues. One is exploiting the spatial correlation of sensor data and the other is designing a specific MAC protocol. We propose a novel hybrid TDMA/CSMA protocol with the following interesting features that differentiate itself from traditional TDMA-based protocols: (1) the TDMA part is based on very loose time synchronisation and is triggered by the appearance of events; (2) the slot assignment strategy associated with the TDMA part takes the spatial correlation of sensor data into consideration and thus allows less strict slot allocation than conventional TDMA schemes. Simulation results show the efficiency of the proposed protocol.

Randomized Data-Gathering protocol for time-driven sensor networks

Proactive or time-driven sensor networks are devoted to the continuous reporting of environmental data to a sink or base station. An important issue associated with these networks is the management of a potentially large number of packets that are regularly generated by the set of nodes. A common solution at the MAC level is to use scheduled TDMA-based protocols, which minimize the communication duty cycle. However, TDMA schemes have strong synchronization requirements and exhibit low adaptability to changing traffic conditions. Thus, this paper proposes an alternative MAC protocol that overcomes the limitations of TDMA-based protocols while still approaching their performance in terms of lifetime. Essentially, this proposed solution combines randomization of the sensing and transmission process with a mechanism based on transmission announcements between adjacent nodes. The result is a lightweight protocol, called Randomized Data-Gathering (RDG), which exhibits desirable characteristics with respect to energy efficiency, synchronization avoidance, performance, scalability and adaptability to traffic changes in both time and space. The role of the randomization distribution is considered in detail, and an effective randomization scheme is selected. Both analytical and simulation methods are applied.