Showing papers by "Swades De published in 2013"

Experimental demonstration of multi-hop RF energy transfer

Abstract: Batteries of field nodes in a wireless sensor network pose an upper limit on the network lifetime. Energy harvesting and harvesting aware medium access control protocols have the potential to provide uninterrupted network operation, as they aim to replenish the lost energy so that energy neutral operation of the energy harvesting nodes can be achieved. To further improve the energy harvesting process, there is a need for novel schemes so that maximum energy is harvested in a minimum possible time. Multi-hop radio frequency (RF) energy transfer is one such solution that addresses these needs. With the optimal placement of energy relay nodes, multi-hop RF energy transfer can save energy of the source as well as time for the harvesting process. In this work we experimentally demonstrate multi-hop RF energy transfer, wherein two-hop energy transfer is shown to achieve significant energy and time savings with respect to the single-hop case. It is also shown that the gain obtained can be translated to energy transfer range extension.

A receiver synchronized slotted Aloha for underwater wireless networks with imprecise propagation delay information

Abstract: In a wireless network, where propagation delay is high but known, slotted Aloha (S-Aloha) is synchronized with respect to the receiver's time slots. Since the transmitter knows the propagation delay to its receiver, after a frame is generated, the transmitter introduces a suitable delay before its transmission, such that the frame arrives exactly in a slot at the receiver. However, in an underwater wireless network, due to significantly less signal propagation speed, the channel dynamics has a significant effect on the time dispersion of propagation speed. Due to this uncertainty in propagation speed, even if the transmitter-receiver distance is exactly known, it is likely that a perfect synchronization at the receiver is not possible. In this paper, we first show that, even a little-less-than-perfect synchronization at the receiver reduces the throughput of receiver synchronized S-Aloha (RSS-Aloha) to that of pure Aloha. We modify the RSS-Aloha for underwater by accommodating the error in delay estimate while deciding the receiver-end slot size. Via probabilistic analysis, supported by simulations, we show that our proposed modified protocol offers a gradual increase in throughput as the propagation delay uncertainty decreases. We also show that the throughput of our proposed modified protocol is consistently higher compared to the transmitter synchronized S-Aloha when operating under the same propagation delay uncertainty. However, when the uncertainty is high, delay performance of the modified RSS-Aloha remains poorer than that of the transmitter synchronized S-Aloha in a system with smaller nodal communication range.

Feasibility analysis on integrated recharging and data collection in pollution sensor networks

Abstract: Uninterrupted network operation in field sensing activities such as pollution monitoring is a big challenge, as the pollution sensors could be quite power hungry. One way to keep the network functioning is to recharge the nodes periodically via radio frequency energy transfer, which can be achieved by using a mobile robot that acts as an energy source and a data sink. Given a set of sensors deployed in a geographic area, a mobile robot is required to visit all the sensors in a way so as to avoid a node's energy drainage and its buffer overflow. Before optimum path planning strategies depending on a set of given sensing and physical environmental constraints, a critical task is to investigate the components of energy consumed by a node on different activities. To this end, this work does an extensive study on the energy consumptions with a few chosen pollution sensor examples. Based on the energy consumption and rectification parameters, the required recharging periodicity is derived. This analysis forms the basis of constrained mobility and path planning of the mobile robot.

Contention based multi-channel MAC protocol for distributed cognitive radio networks

Abstract: Design of an efficient medium access control protocol is critical for proper functioning of a distributed cognitive radio network and better utilization of the available channels not being used by primary users. In this paper, we design a contention based distributed medium access control (MAC) protocol for the secondary users' channel access. The proposed MAC protocol allows collision-free access of the available channels and eventual utilization by secondary users, with spectrum sensing part being handled by exclusive sensing nodes. The effectiveness of the proposed MAC protocol is evaluated analytically and also through empirical simulations. We show how the protocol performs with respect to blocking probability, channel grabbing, and channel utilization1.

Assessment of health risk due to PM10 using fuzzy linear membership kriging with particle swarm optimization.

Abstract: Air quality is an important determinant of individu al as well as broader well-being. Major pollutants i clude gasses as well as assorted suspended particulate matter (P M). In this paper, we focus on PM10, which are a c olle tion of particles with median aerodynamic diameter less tha n 10 μm that remains suspended in the air for long periods. PM10, usually consist of smoke, dirt and dust parti cles, as well as spores and pollen, could easily be inhaled deep into lung. As a result, high outdoor PM10 concentra tion poses significant health hazard, and accurate modeling and prediction of health risk due to PM10 assume import ance in pollution and public health management. In his backdrop, we propose an improved health risk assessment technique, and demonstrate its efficacy using wide ly used California PM10 database. At the heart of the proposed m thod lies indicator kriging, a well-known risk es timation technique. However, improved assessment of subjective h ealt risk is achieved by posing the problem in a f uzzy setting, and optimizing the associated membership functions. In particular, we employ particle swarm optimizati on (PSO) algorithm, which has been motivated by natural beha vior of organisms such as fish-schooling and bird f locking, and proven effective in various optimization contexts. We apply the fuzzy PSO membership grade Kriging tec hnique to predict the PM10 spatial distribution over the enti re California state.

Revisiting distributed transmit power control in ad hoc wireless networks with ODC capability

Abstract: With a view to conserve energy, a basic power control (BPC) scheme was suggested in distributed control IEEE 802.11 wireless ad hoc networks, where a data frame is sent at the lowest permitted power. Past research showed that BPC works inefficiently in terms of throughput as well as energy consumption. In this paper we revisit the effects of BPC on the network performance with the nodes having frame arrival order dependent signal capture (ODC) capability. We first analyze the reasons for poor performance of basic power control without ODC. We then investigate the effect of ODC on system throughput as well as energy efficiency. Via intuitive arguments and network simulations we demonstrate that, in presence of ODC capability of the receivers, BPC can be highly effective in terms of throughput as well as energy efficiency.