An empirical study of the performance of IEEE 802.15.4e TSCH for wireless body area networks

Wireless Body Area Networks (WBANs) have made their way into many smart and ubiquitous healthcare and wellness applications. A low-power, efficient, and reliable communication protocol is of paramount importance for the success of WBANs in satisfying the requirements of the health applications. The IEEE 802.15.4 standard is always one of the main options due to its efficiency and low-complexity. However, it suffers from the impact of other wireless technologies using the same frequency band such as WiFi and Bluetooth. Time Slotted Channel Hoping (TSCH) is an operational mode of the IEEE 802.15.4e standard, which is originally developed for reliable industrial wireless networks. TSCH has Time Division Multiple Access (TDMA) and frequency hopping features, which increase the network robustness against effects such as noise, interference, and multi-path fading. This paper proposes to exploit TSCH for communications in WBANs, and studies its performance. The features of TSCH like power efficiency, TDMA-based operation, and heterogeneity support fit very well with the requirements of many health monitoring applications. The performance of the TSCH standard for WBAN communications is investigated through real-world experiments in various conditions. The results show that TSCH outperforms the basic IEEE 802.15.4 standard in terms of communication reliability against interferences from coexisting wireless devices

Time-domain cooperative coexistence of BLE and IEEE 802.15.4 networks

\u3cp\u3eWireless sensor networks have entered into our lives, and are expected to be even more widespread in the near future. Bluetooth Low Energy (BLE) and IEEE 802.15.4 are two low-power wireless standards that are widely used in sensor network applications. They share the same unlicensed 2.4 GHz ISM spectrum. To be able to employ both technologies in the same environment in a heterogeneous network, the creation of a proper coexistence mechanism is imperative. In this paper, we propose and develop a cooperative mechanism for the coexistence of co-located IEEE 802.15.4 and BLE networks in the time domain. This mechanism tries to avoid overlap of communications in these networks in order to decrease the chance of Cross-Technology Interference (CTI) and thus packet drops. The proposed mechanism does not impose any protocol change. The performance of the proposed mechanism is evaluated by using real hardware devices. The experimental results show that the overall packet reception ratio improves up to 12%.\u3c/p\u3

Cooperative coexistence of BLE and time slotted channel hopping networks

The Bluetooth Low Energy (BLE) and Time Slotted Channel Hopping (TSCH) mode of the IEEE 802.15.4 are two of the most widely used technology standards for Wireless Sensor Networks (WSNs). In many applications, both technologies need to be used in the same environment to fulfill application requirements. However, since they share the same 2.4 GHz ISM band, such networks may suffer from cross-technology interference, which decreases the reliability of the network. To solve this problem, we propose a cooperative coexistence solution for BLE and TSCH networks in which joint time-slot and channel hopping synchronization are performed. The proposed solution uses a scheduling matrix to model the resource usage of the networks. Following this, the overlaps in this matrix are eliminated by rescheduling the transmissions of the networks. The proposed solution does not require any protocol change. The performance of the proposed cooperative coexistence mechanism is evaluated using experiments with real wireless devices. The results of those show that our proposed solution considerably decreases Packet Error Rate (PER); an improvement of up to 45% PER is observed

Analysis of coexistence between IEEE 802.15. 4, BLE and IEEE 802.11 in the 2.4 GHz ISM band

The rapid growth of the Internet-of-Things (IoT) has led to a proliferation of low-power wireless technologies. A major challenge in designing an IoT network is to achieve coexistence between different wireless technologies sharing the unlicensed 2.4 GHz ISM spectrum. Although there is significant literature on coexistence between IEEE 802.15.4 and IEEE 802.11, the coexistence of Bluetooth Low Energy (BLE) with other technologies remains understudied. In this work, we examine coexistence between IEEE 802.15.4, BLE and IEEE 802.11, which are widely used in residential and industrial wireless applications. We perform a mathematical analysis of the effect of cross-technology interference on the reliability of the affected wireless network in the physical (PHY) layer. We also set up and perform PHY layer experiments to verify the analytical results. Finally, we extend the study to the Medium Access Control (MAC) layer. Our findings show that, even though the MAC layer mechanisms of IEEE 802.15.4 and BLE improve reliability, cooperative solutions are required to achieve coexistence

A scalable and fast model for performance analysis of IEEE 802.15.4 TSCH networks

\u3cp\u3eThe IEEE 802.15.4 Time-Slotted Channel Hopping (TSCH) protocol has received considerable attention in many industrial applications. However, analytical models for fast performance estimation of TSCH-based networks by considering the interaction between Medium Access Control (MAC) and Physical (PHY) layers is an open problem. In this paper, we propose a stochastic model for performance analysis of TSCH-based networks including dedicated and shared links with non-ideal wireless link properties. The proposed model is scalable and is able to evaluate the MAC performance of a large-scale network quickly. The developed model is verified by simulations and real-world experiments. The results confirm the accuracy of the proposed model for large-scale networks with orders of magnitude faster execution compared to the existing model in the literature. This confirms the speed and scalability of the model, which makes it a perfect tool for network design and optimization.\u3c/p\u3

LaDiS:a low-latency distributed scheduler for time-slotted channel hopping networks

Time-Slotted Channel Hopping (TSCH), as an operational mode of the IEEE 802.15.4 standard, is a promising medium access mechanism for industrial Wireless Sensor Networks (WSNs). However, efficient performance of such networks depends on the medium access scheduling scheme, which is not\u3cbr/\u3especified by the standard. This paper proposes a low-latency distributed scheduler, called LaDiS, for multi-hop tree-based TSCH networks. The main objective is to provide low end-to-end data latency in convergecast WSNs with very low communication overhead. The schedule of each node is determined by its parent based on the available local information about the routing structure and traffic requirement of that node. At the same time, LaDiS provides proper opportunity for data aggregation.\u3cbr/\u3eby relaying nodes in a multi-hop network leading to reduced\u3cbr/\u3etraffic. The performance of the proposed scheduler as well as\u3cbr/\u3ethe existing distributed TSCH schedulers is extensively evaluated\u3cbr/\u3ein various setups. The results show that LaDiS considerably\u3cbr/\u3eoutperforms others in terms of data latency in the networks\u3cbr/\u3eunder consideration in this work. LaDiS is implemented and\u3cbr/\u3eintegrated in the Contiki operating system

Guard-time design for symmetric synchronization in IEEE 802.15.4 time-slotted channel hopping

\u3cp\u3eTime-Slotted Channel Hopping (TSCH) is considered as one of the most reliable MAC solutions for low- power wireless networking. In order to establish time-slotted communications, this technique requires all nodes to remain synchronized. The synchronization is continuously done through normal communications to compensate the clock drift between different nodes. In this paper, we present a detailed look into the behavior of the IEEE 802.15.4 PHY and MAC in terms of the synchronization task. We show that the relation between timeslot offsets provided by the standard leads to different synchronization error margins for positive and negative relative clock drifts. This is due to the time required for detection of ongoing transmissions at receivers. This may lead to the situation that two nodes are able to communicate in only one direction. Depending on which node is the source node, the available margin to compensate the relative clock drift is different. Accordingly, we provide new values for timeslot offsets to compensate positive and negative relative clock drifts equally. Simulation results confirm that the standard offsets reduce the performance of TSCH due to asymmetric synchronization error handling. The results also show that this negative effect is mitigated by using the new offsets provided in this paper.\u3c/p\u3

Dependable interference-aware time-slotted channel hopping for wireless sensor networks

IEEE 802.15.4 Time-Slotted Channel Hopping (TSCH) aims to improve communication reliability in Wireless Sensor Networks (WSNs) by reducing the impact of the medium access contention, multipath fading, and blocking of wireless links. While TSCH outperforms single-channel communications, cross-technology interference on the license-free ISM bands may affect the performance of TSCH-based WSNs. For applications such as in-vehicle networks for which interference is dynamic over time, it leads to non-guaranteed reliability of the communications over time. This article proposes an Enhanced version of the TSCH protocol together with a Distributed Channel Sensing technique (ETSCH+DCS) that dynamically detects good quality channels to be used for communication. The quality of channels is extracted using a combination of a central and a distributed channel-quality estimation technique. The central technique uses Non-Intrusive Channel-quality Estimation (NICE) technique that proactively performs energy detections in the idle part of each timeslot at the coordinator of the network. NICE enables ETSCH to follow dynamic interference, while it does not reduce throughput of the network. The distributed channel quality estimation technique is executed by all the nodes in the network, based on their communication history, to detect interference sources that are hidden from the coordinator. We did two sets of lab experiments with controlled interferers and a number of simulations using real-world interference datasets to evaluate ETSCH. Experimental and simulation results show that ETSCH improves reliability of network communications, compared to basic TSCH and the state-of-the-art solution. In some experimental scenarios NICE itself has been able to increase the average packet reception ratio by 22% and shorten the length of burst packet losses by half, compared to the plain TSCH protocol. Further experiments show that DCS can reduce the effect of hidden interference (which is not detectable by NICE) on the packet reception ratio of the affected links by 50%

Topology management and TSCH scheduling for Low-Latency convergecast in in-vehicle WSNs

\u3cp\u3eWireless sensor networks (WSNs) are considered as a promising solution in intravehicle networking to reduce wiring and production costs. This application requires reliable and real-time data delivery, while the network is very dense. The time-slotted channel hopping (TSCH) mode of the IEEE 802.15.4 standard provides a reliable solution for low-power networks through guaranteed medium access and channel diversity. However, satisfying the stringent requirements of in-vehicle networks is challenging and demands for special consideration in network formation and TSCH scheduling. This paper targets convergecast in dense in-vehicle WSNs, in which all nodes can potentially directly reach the sink node. A cross-layer low-latency topology management and TSCH scheduling (LLTT) technique is proposed that provides a very high timeslot utilization for the TSCH schedule and minimizes communication latency. It first picks a topology for the network that increases the potential of parallel TSCH communications. Then, by using an optimized graph isomorphism algorithm, it extracts a proper match in the physical connectivity graph of the network for the selected topology. This network topology is used by a lightweight TSCH schedule generator to provide low data delivery latency. Two techniques, namely grouped retransmission and periodic aggregation, are exploited to increase the performance of the TSCH communications. The experimental results show that LLTT reduces the end-to-end communication latency compared to other approaches, while keeping the communications reliable by using dedicated links and grouped retransmissions.\u3c/p\u3