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BY 4.0 license Open Access Published by De Gruyter 2023

9 Energy Awareness

From the book Volume 1 Machine Learning under Resource Constraints - Fundamentals

  • Nico Piatkowski and Robert Falkenberg


In this contribution, we study how knowledge about the underlying compute architecture can be incorporated directly into the learning problem. More precisely, we consider the arithmetic limitations of Ultra-Low Power (ULP) Micro-Controller Units (MCU). Such systems do not contain arithmetic co-processors, which implies that most arithmetic computations must be emulated via integer logic. However, this creates a large performance penalty for any machine learning method that relies heavily on floating-point arithmetic. To mitigate this issue, we show how the model itself can be rephrased with integer-only operations such that floating point co-processors are no longer required. We exemplify this procedure with probabilistic undirected models, so-called Markov random fields. All steps of learning and inference are discussed. An approximate but integer-only probabilistic inference procedure called bit-length propagation (BL-Prop) is presented. BL-Prop is based on belief propagation, where instead of the full messages, only their bit-length is propagated along the models’ conditional independence structure. We analyze the algorithm and show what factors have the largest influence on the approximation quality. Furthermore,we derive IntGD-anumerical optimization method for convex objective functions with integrality constraints. The method is based on an accelerated proximal algorithm for non-smooth and non-convex penalty terms. For integer gradients computed via BL-Prop, IntGD is guaranteed to deliver an integer learning procedure in which the final parameter vector as well as all intermediate results are integers. Numerical experiments on benchmark data show that integer models allow us to achieve a competitive prediction quality on low-end hardware while maintaining a large speedup compared with its double precision counterpart-thus, completely mitigating the performance penalty that arose from the missing floating point unit.

The penetration of wireless communication systems in industrial and private environments is constantly increasing due to their flexible and mobile application possibilities. Wearables, smartphones, or industrial systems for tagging, tracking, and sensing are only a few examples from the tremendous variety of such systems. However, unleashing these systems from the power grid also means that the available energy is a limited resource that must be conserved and managed prudently. The estimation of energy consumption by the communication system differs significantly from the other components, as it is strongly dependent on external influences. These include the quality of the radio channel, the channel access scheme, and the utilization of the shared transmission medium by other participants, who are often not part of the actual system. Data transmissions can last longer, require a higher transmission power, or fail due to collisions, so that they have to be repeated. The consequence is a longer activity time of the transceiver and a shorter dwell time in the efficient power saving mode. Therefore, realistic simulation models are required at design time, which take into account the properties of the communication interface as well as the external environment. In the following, methods for modeling power consumption for different communication technologies are discussed. This includes decentralized narrow-band communication in the Short Range Devices (SRD) band and the comprehensive modeling of cellular technologies such as Long Term Evolution (LTE), LTE-Advanced (LTE-A) and Narrow Band Internet of Things (NB-IoT) by a Context-Aware Power Consumption Model (CoPoMo). It is shown that a decentralized channel access with brisk activity on the radio channel leads to an increased power consumption of all waiting subscribers, if the channel occupancy is to be tracked continuously to keep the transmission latency as low as possible. Conversely, in centrally organized cellular radio networks, the energy consumption of the User Equipment (UE) is dominated by uplink transmissions, especially when high transmission power is required. The proportion for reception, however, depends mainly on the duration of the transmission. In fact, adding an additional reception path via Carrier Aggregation (CA) not only increases the data rate, but also reduces the energy consumption of the UE . Since the knowledge of the transmit power is essential for the estimation of the power consumption, but most UEs do not provide this information to the application layer, a Machine Learning (ML)-based method for estimating the transmit power from the available parameters such as strength and quality of the received signal, is also


© 2022 Walter de Gruyter GmbH, Berlin/Boston
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