Kan Yu

Reliable and Low Latency Transmission in Industrial Wireless Sensor Networks

The major advantages with Industrial Wireless Sensor Networks (IWSNs) in process automation are cable cost reduction, enhanced flexibility and enabling new emerging applications such as wireless co ...

REALFLOW: Reliable Real-Time Flooding-Based Routing Protocol for Industrial Wireless Sensor Networks

Wireless technologies have been increasingly applied in industrial automation systems due to flexible installation, mobility, and cost reduction. Unlike traditional wireless sensor networks (WSNs), industrial wireless sensor networks (IWSNs), when expanding from wireless monitoring to wireless control, have more stringent requirements on reliability, real-time performance, and robustness in a number of industrial applications. Successive transmission failures or deadline misses in these applications may severely degrade the control quality and result in serious economic losses and safety problems. Therefore, when deploying IWSNs in harsh industrial environments, to achieve reliable and deterministic end-to-end transmissions is critically important. In this paper, we explain the primary challenges of designing appropriate routing protocols and present a reliable real-time flooding-based routing protocol for IWSNs (REALFLOW). Instead of traditional routing tables, related node lists are generated in a simple distributed manner, serving for packet forwarding. A controlled flooding mechanism is applied to improve both reliability and real-time performance. A seamless transition in the event of topology change can be achieved by REALFLOW. Performance evaluations via simulations verify that significant improvements of reliability, real-time performance, and network recovery time can be achieved by REALFLOW, compared with traditional routing protocols.

Adaptive forward error correction for best effort Wireless Sensor Networks

In this work we propose an Adaptive Forward Error Correction (AFEC) algorithm for best effort Wireless Sensor Networks. The switching model is described in terms of a finite-state Markov model and it is based on the channel behavior, observed via Packet Delivery Ratio in the recent past. We compare the performance of AFEC with static FEC, as well as uncoded transmissions. The results demonstrate a gain in PDR achieved by introducing FEC coding in uncoded IEEE 802.15.4 transmissions, as well as the advantages over static FEC schemes, namely increased throughput and reduced energy consumption. The proposed solution is IEEE 802.15.4-compliant and requires no additional feedback channels.

An RTOS-based architecture for industrial wireless sensor network stacks with multi-processor support

The design of industrial wireless sensor network (IWSN) stacks requires the adoption of real time operation system (RTOS). Challenges exist especially in timing integrity and multi-processor support. As a solution, we propose an RTOS-based architecture for IWSN stacks with multi-processor support. It offers benefits in terms of platform independency, product life cycle, safety and security, system integration complexity, and performance scalability. An implemented WirelessHART stack has proven the feasibility of the proposed architecture in practical product design. And future challenges as well as suggestions to standard improvement are discussed.

Implementation and Evaluation of Error Control Schemes in Industrial Wireless Sensor Networks

Industrial Wireless Sensor Networks (IWSNs) have been increasingly adopted in process automation due to a number of advantages such as cost reduction and enhanced flexibility. Nevertheless, transmission over wireless channels in industrial environments is prone to interference, resulting in frequent erroneous packet deliveries. Existing IWSN standards based on the IEEE 802.15.4 specification only prescribe Automatic Repeat Request (ARQ) for packet retransmission, without providing any means for error recovery, which leads to unexpected transmission delay. Forward Error Correction (FEC) code as an alternative approach is able to effectively improve reliability and reduce the number of retransmissions. However, FEC computation requires extra memory and processing time. In this paper, we discuss the timing constraints of employing FEC codes for IWSNs according to the IWSN standards. Then we benchmark a number of different FEC codes in a typical wireless sensor node in terms of memory consumption and processing time. Our results show that LDPC and Turbo code, as the state of the art FEC codes, fail to fulfill the requirement from the IWSN standards while other FEC candidates, such as RS code, are proven to be suitable for the practical implementation in IWSNs.

Reliable RSS-based routing protocol for Industrial Wireless Sensor Networks

High reliability and real-time performance are main research challenges in Industrial Wireless Sensor Networks (IWSNs). Existing routing protocols applied in IWSNs are either overcomplicated or fail to fulfill the stringent requirements. In this paper, we propose a reliable and flexible Received Signal Strength-based routing scheme. Our proposed solution can achieve a seamless transition in the event of topology change and can be applied in different industrial environments. The simulation results show that our solution outperforms conventional routing protocols in both reliability and latency. Furthermore, the result also proves that the changes of the network topology have no impact on data transmissions of other nodes by our scheme, whereas conventional routing protocols are shown to fail to recover the network in a short time. Finally, due to dynamic weighting mechanism, the proposed scheme is verified to achieve significantly higher reliability in scenarios with obstacles and avoid installation troubles, compared to location-based flooding scheme. Thus, our proposed scheme is considered to be more suitable for IWSNs than other routing protocols.

A flexible error correction scheme for IEEE 802.15.4-based industrial Wireless Sensor Networks

Noise and interference make a substantial impact on wireless transmissions in industrial environments, resulting in frequent erroneous packet deliveries. Existing industrial communication standards adopt the IEEE 802.15.4 specification, which provides no means to correct the detected errors. We propose an IEEE 802.15.4-compliant Forward Error Correction-based approach that can be easily retrofitted into the standard without the need for any kind of interaction with chip manufacturers or standardization bodies. We evaluate the approach on link- and network-level scenarios. Improvement of reliability by using FEC can yield multiple benefits: a reduced number of retransmissions, and lower average latency, to name a few. With respect to the uncoded system, the proposed solution provides identical coding gain as the traditional FEC method, at a significantly lower computational load of decoding.

Low jitter scheduling for Industrial Wireless Sensor and Actuator Networks

Applying Industrial Wireless Sensor and Actuator Networks (IWSANs) in the industrial automation is a growing trend due to flexibility, mobility and low cost. According to the current standards, such as WirelessHART and ISA100.11a, multi-channel TDMA transmission is included for reliable and deterministic communication. In this paper, we clarify the dependence of TDMA scheduling for sensors and actuators and point out the low correlation between the scheduling delay and the overall quality of control, and focus on reducing jitter in scheduling for improving quality of control and system stability. We propose a scheduling algorithm, aiming for lowing jitter and compare it with two traditional real-time scheduling schemes. Our simulation results exhibit significantly lower jitters by applying our scheduling policy than those two traditional scheduling schemes.

Reliable flooding-based downlink transmissions for Industrial Wireless Sensor and Actuator Networks

Reliable downlink transmissions from the sink to actuators for control data in Industrial Wireless Sensor and Actuator Networks (IWSANs) are extremely important for industrial control applications. However, on the network layer, existing routing protocols fail to fully support downlink transmissions for actuators, due to the insufficiency of reliability, robustness and real-time performance. In this paper, we propose a reliable flooding-based routing scheme focusing on downlink transmissions. Packets are forwarded to actuators according to weight values and the related node lists in intermediate nodes. Performance evaluations via simulations show that our protocol significantly outperforms traditional routing protocols in terms of reliability, transmission latency, network recovery time and network resource usage.

Towards reliable and lightweight communication in industrial wireless sensor networks

In this paper we address the issues of timeliness and transmission reliability of existing industrial communication standards. We combine a Forward Error Correction coding scheme on the Medium Access Control layer with a lightweight routing protocol to form an IEEE 802.15.4-conformable solution, which can be implemented into already existing hardware without violating the standard. After laying the theoretical foundations, we conduct a performance evaluation of the proposed solution. The results show a substantial gain in reliability and reduced latency, compared to the uncoded transmissions, as well as common Wireless Sensor Network routing protocols.