Empirical Study and Enhancements of Industrial Wireless Sensor-Actuator Network Protocols
Abstract:
Wireless sensor-actuator networks (WSANs) offer an appealing communication technology for process automation applications to incorporate the Internet of Things (IoT). In contrast to other IoT applications, process automation poses unique challenges for industrial WSAN due to its critical demands on reliable and real-time communication. While industrial WSANs have received increasing attention in the research community recently, most published results to date have focused on the theoretical aspects and were evaluated based on simulations. There is a critical need for experimental research on this important class of WSANs.We developed an experimental testbed by implementing several key network protocols ofWirelessHART, an open standard for WSANs that has been widely adopted in the process industries based on the Highway Addressable Remote Transducer Protocol (HART). We then performed a series of empirical studies showing that graph routing leads to significant improvement over source routing in terms of worstcase reliability, but at the cost of longer latency and higher energy consumption. It is therefore important to employ graph routing algorithms specifically designed to optimize latency and energy efficiency. Our studies also suggest that channel hopping can mitigate the burstiness of transmission failures; a larger channel distance can reduce consecutive transmission failures over links sharing a common receiver. Based on these insights, we developed a novel channel hopping algorithm that utilizes far away channels for transmissions. Furthermore, it prevents links sharing the same destination from using channels with strong correlations. Our experimental results demonstrate that our algorithm can significantly improve network reliability and energy efficiency.
Existing System:
A comparative study of the two routing approaches adopted by WirelessHART, namely source routing and graph routing1, and an empirical study on the impact of channel hopping on the burstiness of transmission failures. Our studies have led to two major insights on the development of resilient industrial WSANs: _ Graph routing leads to significant improvement over source routing in term of worst-case reliability, at the cost of longer latency and higher energy consumption. It is therefore important to employ graph routing algorithms specifically designed to optimize latency and energy efficiency. _ Channel hopping can mitigate the burstiness of transmission failures; a larger channel distance can reduce consecutive transmission failures over links sharing a common receiver. Based on these insights, we developed a novel channel hopping algorithm for graph routing that causes senders to utilize far-away channels between consecutive transmissions over the same link. It further prevents links sharing the same destination from using channels with strong correlations. Our experimental results demonstrate that our algorithm can significantly improve network reliability and energy efficiency.
Proposed system:
WirelessHART adopts a multi-channel TDMA at the MAC layer. Compared to CSMA/CA, TDMA can provide predictable packet latency, which makes it attractive for realtime communication. All devices’ clocks are synchronized, and time is divided into 10 ms slots that are classified into dedicated and shared slots. In a dedicated slot, only one sender is allowed to transmit. In a shared slot, multiple sensors can attempt to transmit, and these senders contend for the channel using CSMA/CA. To enhance network capacity and to combat interference, WirelessHART networks can use up to 16 channels operating in 2.4 GHz ISM band, which are specified in IEEE 802.15.4 standard, and each device switches its channel in every slot. Specifically, after transmitting a packet on channel x in time slot k, a device can hop to the channel corresponding to logical channel (x + 1) mod m, where m is the number of available channels, for the next transmission in time slot k+1. The logical channel is then mapped to a physical channel. Channel blacklisting is an optional feature that allows the network operator to restrict the channel hopping of field devices network-wide to selected channels in the wireless band. In each dedicated time slot, the total number of concurrent transmissions cannot exceed the number of available channels.
Conclusion:
Industrial WSANs offer an appealing communication technology for process automation applications to incorporate IoT while posing unique challenges due to their critical demands on reliable and real-time communication. Complementary to recent research on theoretical aspects of WSANs, we have implemented a suite of network protocols of the WirelessHART standard in TinyOS and TelosB motes and then performed a series of empirical studies on WSAN protocol designs. We further developed a novel channel hopping algorithm that prevents consecutive transmissions from using channels with strong correlations on a common link or to a common receiver. Experimental results demonstrate that our algorithm can significantly improve network reliability and energy efficiency.
References:
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