Work-in-Progress: Efficient Heuristics for Low Radiation Paths in Wireless Sensor Networks* Nikoletseas S., Patroumpa D., Raptopoulos C. Computer Technology Institute (CTI) and University of Patras, Greece Email: {nikole, patroumpa, raptopox}@ceid.upatras.gr Rolim Jose Centre Universitaire d Informatique Geneva, Switzerland Email: jose.rolim@unige.ch Abstract—We call radiation at a point of a wireless network the total amount of electromagnetic quantity (energy or power density) the point is exposed to. The impact of radiation can be high and we believe it is worth studying and control; towards radiation aware wireless networking we take (for the first time in the study of this aspect) a distributed computing, algorithmic approach. We exemplify this line of research by focusing on sensor networks, studying the minimum radiation path problem of finding the lowest radiation trajectory of a person moving from a source to a destination point in the network region. For this problem, we sketch the main ideas behind a linear program that can provide a tight approximation of the optimal solution, and then we discuss three heuristics that can lead to low radiation paths. We also plan to investigate the impact of diverse node mobility to the heuristics’ performance. I. I NTRODUCTION Imagine a person moving in a smart building with abundant heterogeneous wireless networking (such as WiFi, Blue-tooth, ZigBee and Cellular), carrying wearable, on-body or even implanted wireless devices (such as smart phones, medical equipment and tiny smart sensors). We call “radiation” at a target elementary surface the total amount of electromagnetic quantity (in terms of energy or power density) it is exposed to. The additive/correlated impact of electromagnetic radiation not only to the human itself but also to any carried sensitive nano-scale devices and vital equipment can be important; even if this impact can be considered controversial we believe it is worth studying and control. In particular, we note that almost all wireless devices operate in frequencies of the non-ionizing spectrum for the transmis- sion and reception of their signals. The impact of non-ionizing frequencies on humans is distinguished in thermal and non- thermal effects. It is true that safety levels for humans have been based on thermal effects of electromagnetic radiation. Yet, many scientists worry for non-thermal effects, since they can occur far below the established safety levels of radiation. In that field, mechanisms are still being investigated and there is not yet a well accepted link between some of the afore- mentioned effects and the radiation levels or radiation form. Several recent epidemiological studies in different areas as well as multidisciplinary experiments suggest that the radiation * This work was partially supported by EU/FIRE HOBNET project - STREP ICT-257466 aspect is important and worth further studying (for a partial list, see e.g. [1], [2], [3]). What also troubles scientists is that, while it is not clear how non-thermal effects occur, the radiation environment around human is being continuously enriched. This is enhanced by the fact that lately novel on-body or implanted wireless sensors and remotely controlled in-body medical devices are being introduced. Even if they operate at very low levels, nobody can really answer yet if there is an additive effect or what is the highest number of nodes/sensors a human can carry or what is the total “low level” electromagnetic power he/she can handle. While there are general standards that sensors need to satisfy, there are no measurements for radiation levels or any consideration on radiation levels when multiple sensors are being introduced. As has been explained above there is no causal link between the non-thermal effects and the radiating sources. Also, radiation can (potentially) influence nano-scale electronic devices. Because of all reasons above, even low levels of radiation are worth to investigate and control. In this paper, we begin the investigation of the aspect of electromagnetic radiation in modern and future heterogeneous wireless networks. In our long term vision, the network will be able to spatially quantify radiation and human presence and accordingly self-configure to automatically and dynamically reduce radiation, while maintaining satisfactory operation and performance. We exemplify our approach by focusing on wireless sensor networks; we are aware of the fact that the radiation of tiny wireless sensors is not very high but start this line of research with this network type as a first proof of concept for a broader, heterogeneous wireless network setting. Our broader goal is to come up with radiation awareness in an adaptive, distributed manner, by providing design princi- ples and studying key algorithmic and networking aspects of radiation aware wireless networking. In this work, we study the minimum radiation path problem of finding low radiation trajectories in a wireless sensor network. For this problem, we provide a linear program for the optimum, as well as efficient heuristics. We also plan to study the impact of mobility. A different, interesting problem is assuming a very general radiation field and deploy a sensor network as a measurement and guidance tool. We also note that known adaptive power control methods address similar issues but our methods man- age radiation explicitly.