Wireless Underground Channel Modeling

A comprehensive treatment of wireless underground channel modeling is presented in this chapter. The impacts of the soil on bandwidth and path loss are analyzed. A mechanism for the UG channel sounding and multipath characteristics analysis is discussed. Moreover, novel time-domain impulse response model for WUC is reviewed with the explanation of model parameters and statistics. Furthermore, different types of the through-the-soil wireless communications are surveyed. Finally, the chapter concludes with discussion of the UG wireless statistical model and path loss model for through-the-soil wireless communications in decision agriculture. The model presented in this chapter is also validated with empirical data

Signals in the Soil: An Introduction to Wireless Underground Communications

In this chapter, wireless underground (UG) communications are introduced. A detailed overview of WUC is given. A comprehensive review of research challenges in WUC is presented. The evolution of underground wireless is also discussed. Moreover, different component of UG communications is wireless. The WUC system architecture is explained with a detailed discussion of the anatomy of an underground mote. The examples of UG wireless communication systems are explored. Furthermore, the differences of UG wireless and over-the-air wireless are debated. Different types of wireless underground channel (e.g., In-Soil, Soil-to-Air, and Air-to-Soil) are reported as well

RF power source and estimation diversity in distributed sensing with passive wireless communications

Sensor nodes constitute a distributed wireless sensing architecture, such that, multiple sensors report their observations. However, sensor networks are comprised of energy-constrained nodes. Therefore, there have been many efforts to devise energy-efficient communication algorithms for sensor networks to achieve reliable and energy-efficient distributed wireless sensing. Recently, to mitigate battery depletion problem and extend network lifetime, wireless passive sensor networks (WPSN) have become a new field of interest. Modulated backscattering is an important communication technique in WPSN to alleviate reaching unlimited lifetime for sensor nodes. In this paper, we theoretically analyze event distortion in WPSN that is employing modulated backscattering for communication. First, we model backscattered power by sensor nodes at RF sources using log-normal channel model. Then, using the backscattered power gain of sensor nodes, the mean square error of estimated signal is analyzed for various number of RF sources and power levels in WPSN. The objective of this work is to reveal the impact of RF source diversity on event estimation distortion in WPSN. © 2011 IEEE

Cognitive radio sensor networks in industrial applications

The need for industrial monitoring and process control has arisen with the demand to overcome production capacity limitations, improve process efficiency, comply with the environmental regulations, predict machine failures, and precaution against natural accidents [14, 18]. Collected information from industrial equipment is used to diagnose efficiency decreases and faults in industrial applications. Therefore, reliable and timely information gathering from industrial equipment is extremely crucial to prevent possible inefficiencies and malfunctions in industrial applications

Energy-efficient RF source power control for opportunistic distributed sensing in wireless passive sensor networks

Energy limitation of sensor nodes is the main constraint to be addressed while designing and implementing algorithms for wireless sensor networks (WSN). Recently, to mitigate battery depletion problem and extend network lifetime, wireless passive sensor networks (WPSN) have become a new field of interest. Modulated backscattering is an important communication technique for WPSN to enable unlimited lifetime for sensor nodes. Determination of required number and power level of RF sources for wireless power transfer to sensor nodes is crucial for energy-efficient distributed sensing operation. Furthermore, deployed RF sources can share spectrum opportunistically via incorporation of cognitive radio capability such that desired distributed estimation distortion can be achieved with minimum spectrum utilization by WPSN. Employment of RF sources that radiate power only when spectrum opportunities are available unveils passive opportunistic distributed sensing (PODS). In this paper, first, we model intercepted power by passive sensor from RF sources and reflected power by passive sensor at the sink, and effect of opportunistic access to licensed spectrum bands on instantaneous throughput of sensor nodes. Then, a power level control scheme for RF sources is proposed to achieve desired distortion level with minimum energy consumption while using opportunistic distributed sensing in WPSN. Achieved estimation distortion at sink with respect to number and power level of RF sources, and available spectrum opportunities is investigated, and energy saving provided by proposed power control scheme is assessed for various distortion requirements, channel noise levels, and available spectrum opportunities via simulation experiments. © 2012 IEEE

Reliability and congestion control in cognitive radio sensor networks

Communication requirements for cognitive radio sensor networks (CRSN) necessitate addressing the problems posed by dynamic spectrum access (DSA) in an inherently resource-constrained sensor networks regime. In this paper, arising challenges for reliability and congestion control due to incorporation of cognitive radio capability into sensor networks are investigated along with the open research issues. Impact of DSA, i.e., activity of licensed users, intermittent spectrum sensing and spectrum handoff functionalities based on spectrum availability, on the performance of the existing transport protocols are inspected. The objective of this paper is to point out the urgent need for a novel reliability and congestion control mechanism for CRSN. To this end, CRSN challenges for transport layer are revealed and simulation experiments are performed to demonstrate the performance of the existing transport protocols in CRSN. © 2011 Elsevier B.V. All rights reserved

Spectrum-aware underwater networks: Cognitive acoustic communications

Communication capacity in underwater acoustic networks is severely limited by the uniquely challenging characteristics of underwater acoustic communications (UACs). In this article, dynamic spectrum sharing inspired from cognitive radio (CR) is applied to UAC networks, and spectrum-aware underwater networks (SUNs), i.e., cognitive acoustic communications (CACs), are proposed. First, the problem of spectrum scarcity in SUN is elaborately discussed by investigating the variation in acoustic channel capacity with respect to communication frequency and bandwidth. Then, the analysis of capacity gain via spectrum sharing in SUN is presented. To uncover the capacity gain via CAC, simulation experiments are performed, considering the effects of depth, distance, shipping, waves, spectrum management delay, and spectrum accessibility. The results of simulation experiments revealed a tradeoff between capacity gain and spectrum management delay. Furthermore, the tradeoff for capacity gain and spectrum accessibility period is also discussed. Here, our goal is to envision the potentials of CAC for mitigating spectrum scarcity in UAC. © 2012 IEEE