Guaranteed Time Slot Allocation Mechanism Research Articles

OGMAD: Optimal GTS-Allocation Mechanism for Adaptive Data Requirements in IEEE 802.15.4 Based Internet of Things

Future Internet of Things (IoT) will utilize IEEE 802.15.4 based low data rate communication for various applications. In the IEEE 802.15.4 standard, nodes send data to their Personal Area Network (PAN) coordinator using the Guaranteed Time Slot (GTS). The standard does not meet the adaptive data requirements of GTS requesting nodes in an efficient manner. If requesting GTSs in an active period are more or less than the available limit, either the requested nodes will not be entertained or GTSs remain underutilized. Consequently, it may cause unnecessary delay or poor GTS utilization. In this paper, an Optimal GTS allocation Mechanism for Adaptive Duty cycle (OGMAD) is proposed that adapts the active period of the superframe in accordance with the requested data. OGMAD also reduces GTS size to improve link utilization as well as accommodate more GTS requesting nodes. Simulation results verify that OGMAD improves link utilization, reduces network delay and offers more nodes to transmit their data as compared to the standard.

A GTS Allocation Scheme to Improve Multiple-Access Performance in Vehicular Sensor Networks

The IEEE 802.15.4 protocol is designed to flexibly support both real-time and contention-based services. When the beacon model is enabled, guaranteed time slot (GTS) scheduling can provide contention-free access to latency-sensitive services based on the time-division multiple-access mechanism. This characteristic makes IEEE 802.15.4 the appropriate candidate for vehicular sensor networks in which mobile nodes need to exchange packets with roadside units (RSUs) within a limited duration. In this paper, using network calculus theory, we analyzed the relationship between time-slot utilization and the corresponding access parameters, such as packet arrival rate, burst size, and vehicles' mobility extent. Then, for a given number of vehicles preparing to access an RSU, we proposed a time-sensitive weighted round-robin (TS-WRR) scheduler to improve the multiple-access performance, which can take the service delay requirement, packet arrival rate, and vehicular mobility level into account. Next, the weight determination and time-slot allocation strategy of the TS-WRR scheduler were issued in detail, which incorporate the special limitations and application requirements in a vehicle-to-infrastructure (V2I) communication environment. To make our model feasible for testing, we also elaborately demonstrated the implementation procedure with pseudocode and simulator design. Numerical results show that our TS-WRR scheduler outperforms some classic schedulers such as First-Come First-Served and WRR, as well as two latest works, i.e., implicit GTS allocation scheme and adaptive real-time GTS allocation mechanism in terms of delay guarantee and GTS utilization maximization in vehicular sensor networks.

Modeling and stability analysis of hybrid multiple access in the IEEE 802.15.4 protocol

To offer flexible quality of service to several classes of applications, the medium access control (MAC) protocol of IEEE 802.15.4 wireless sensor networks (WSNs) combines the advantages of a random access with contention with a time division multiple access (TDMA) without contention. Understanding reliability, delay, and throughput is essential to characterizing the fundamental limitations of the MAC and optimizing its parameters. Nevertheless, there is not yet a clear investigation of the achievable performance of hybrid MAC. In this article, an analytical framework for modeling the behavior of the hybrid MAC protocol of the IEEE 802.15.4 standard is proposed. The main challenge for an accurate analysis is the coexistence of the stochastic behavior of the random access and the deterministic behavior of the TDMA scheme. The analysis is done in three steps. First, the contention access scheme of the IEEE 802.15.4 exponential back-off process is modeled through an extended Markov chain that takes into account channel, retry limits, acknowledgements, unsaturated traffic, and superframe period. Second, the behavior of the TDMA access scheme is modeled by another Markov chain. Finally, the two chains are coupled to obtain a complete model of the hybrid MAC. By using this model, the network performance in terms of reliability, average packet delay, average queuing delay, and throughput is evaluated through both theoretical analysis and experiments. The protocol has been implemented and evaluated on a testbed with off-the-shelf wireless sensor devices to demonstrate the utility of the analysis in a practical setup. It is established that the probability density function of the number of received packets per superframe follows a Poisson distribution. It is determined under which conditions the guaranteed time slot allocation mechanism of IEEE 802.15.4 is stable. It is shown that the mutual effect between throughput of the random access and the TDMA scheme for a fixed superframe length is critical to maximizing the overall throughput of the hybrid MAC. In high traffic load, the throughput of the random access mechanism dominates over TDMA due to the constrained use of TDMA in the standard. Furthermore, it is shown that the effect of imperfect channels and carrier sensing on system performance heavily depends on the traffic load and limited range of the protocol parameters. Finally, it is argued that the traffic generation model established in this article may be used to design an activation timer mechanism in a modified version of the CSMA/CA algorithm that guarantees a stable network performance.

Energy and delay trade‐off of the GTS allocation mechanism in IEEE 802.15.4 for wireless sensor networks

AbstractThe IEEE 802.15.4 protocol proposes a flexible communication solution for low‐rate wireless personal area networks (LR‐WPAN) including wireless sensor networks (WSNs). It presents the advantage to fit different requirements of potential applications by adequately setting its parameters. When in beacon‐enabled mode, the protocol can provide timeliness guarantees by using its Guaranteed Time Slot (GTS) mechanism. However, power‐efficiency and timeliness guarantees are often two antagonistic requirements in wireless sensor networks. The purpose of this paper is to analyze and propose a methodology for setting the relevant parameters of IEEE 802.15.4‐compliant WSNs that takes into account a proper trade‐off between power‐efficiency and delay bound guarantees. First, we propose two accurate models of service curves for a GTS allocation as a function of the IEEE 802.15.4 parameters, using Network Calculus formalism. We then evaluate the delay bound guaranteed by a GTS allocation and express it as a function of the duty cycle. Based on the relation between the delay requirement and the duty cycle, we propose a power‐efficient superframe selection method that simultaneously reduces power consumption and enables meeting the delay requirements of real‐time flows allocating GTSs. The results of this work may pave the way for a power‐efficient management of the GTS mechanism in an IEEE 802.15.4 cluster. Copyright © 2006 John Wiley & Sons, Ltd.