تجزیه و تحلیل مصرف انرژی پروتکل TDMA HART بی سیم

In this paper we analyze in detail the energy consumption characteristics of the Wireless HART protocol when operated with a popular transceiver, the ChipCon CC2420. We analyze how much various factors contribute to the overall energy consumption over a longer period of 12 h. These factors include the amount of management traffic and the power levels required for various transceiver activities (transmit, receive, listen, sleep). It turns out that in light traffic scenarios and with only a minimum-complexity level of exploitation of the transceivers sleeping capabilities the energy spent in the sleep state over 12 h is quite substantial. We then proceed to analyze the energy consumption characteristics with a more complex usage of the transceivers sleeping capabilities in which each node individually selects its next sleep state according to its transmission/reception schedule. With this scheme the energy consumption in the sleep state (over 12 h) can be reduced substantially.

In many application areas of embedded wireless networks, for instance in building automation or industrial control, source nodes send data frames periodically to a gateway or sink node across a set of forwarder nodes [32], [33] and [9]. For cost-effective, quick and scalable deployment, sensor nodes often run on batteries and therefore have only a limited amount of energy. The sensed data should be transported reliably and in a timely fashion to the sink. At the same time the operation of the whole network and of individual nodes should be energy-efficient. Therefore, reporting the sensed data reliably while consuming the minimum amount of energy is of great concern. In many sensor node designs the radio chip is the largest consumer of energy. Since the medium access layer usually controls the states of the radio, it has a large impact on overall energy-consumption. Different media access methods result in different trade-offs between end-to-end delay and energy-efficiency. From among the large number of existing MAC protocols for wireless sensor networks (contention-based protocols include [6], [27] and [38], contention-free protocols include [35] and [28], see [20] for a survey), a TDMA-based protocol has been chosen as a basis for the Wireless HART (WHART) standard [5]. A common view on TDMA-based protocols is that they offer good opportunities for energy-efficient operation of sensor nodes, as they allow nodes to enter a sleep state when they are not involved in any communications. Furthermore, TDMA is traditionally the method of choice for some of WHARTs major application areas like industrial and process automation, since it offers a level of determinism that is not achievable with other types of MAC protocols. WHART utilizes the physical layer of IEEE 802.15.4 and specifies a new MAC protocol. This new MAC protocol combines slow frequency hopping with a TDMA scheme. The TDMA slot allocation happens a priori at network configuration time. WHART supports multi-hop mesh topologies, and all devices must have routing capabilities.

A state-of-the-art solution for TDMA based system is the WHART standard. WHART is one of the first wireless communication standards specifically designed for process automation applications. The standard has been finalized in 2007, and at the beginning of 2010 it has been ratified as an IEC standard. In this paper we have analyzed the energy consumption of the WHART protocol when used with a popular transceiver. The main contributions were: (1) We have performed a sensitivity analysis using the response surface methodology to obtain some insights on how the overall energy consumption breaks down into different factors. By identifying the factors contributing most to the overall network energy consumption, one can obtain useful insights on where to start with any effort geared towards saving energy. (2) We have looked at two different strategies for exploiting the sleep modes of the CC2420 transceiver and have highlighted that significant savings can be achieved with only moderate increases in run-time complexity. (3) We have evaluated the impact of synchronization and management slots on the performance of WHART TDMA protocol. Future work will focus on the further improvement of WHART TDMA protocol itself and of TDMA scheduling methods. One particularly interesting area is the design of TDMA scheduling algorithms which explicitly take the presence of a local sleep scheduling algorithm and multiple sleep states into account by constructing schedules in which the slots of individual nodes have larger separations in time, so as to allow them to enter deeper sleep modes. We also plan to further explore energy consumption optimizations within the WHART protocol.