A. Ozan Bicen

Multi-Ray Channel Modeling and Wideband Characterization for Wireless Communications in the Terahertz Band

Terahertz (0.06-10 THz) Band communication is envisioned as a key technology for satisfying the increasing demand for ultra-high-speed wireless links. In this paper, first, a unified multi-ray channel model in the THz Band is developed based on ray tracing techniques, which incorporates the propagation models for the line-of-sight, reflected, scattered, and diffracted paths. The developed theoretical model is validated with the experimental measurements (0.06-1 THz) from the literature. Then, using the developed propagation models, an in-depth analysis on the THz channel characteristics is carried out. In particular, the distance-varying and frequency-selective nature of the Terahertz channel is analyzed. Moreover, the coherence bandwidth and the significance of the delay spread are studied. Furthermore, the wideband channel capacity using flat and water-filling power allocation strategies is characterized. Additionally, the temporal broadening effects of the Terahertz channel are studied. Finally, distance-adaptive and multi-carrier transmissions are suggested to best benefit from the unique relationship between distance and bandwidth. The provided analysis lays out the foundation for reliable and efficient ultra-high-speed wireless communications in the (0.06-10) THz Band.

Delay-sensitive and multimedia communication in cognitive radio sensor networks

Multimedia and delay-sensitive data applications in cognitive radio sensor networks (CRSN) require efficient real-time communication and dynamic spectrum access (DSA) capabilities. This requirement poses emerging problems to be addressed in inherently resource-constrained sensor networks, and needs investigation of CRSN challenges with real-time communication requirements. In this paper, the main design challenges and principles for multimedia and delay-sensitive data transport in CRSN are introduced. The existing transport protocols and algorithms devised for cognitive radio ad hoc networks and wireless sensor networks (WSN) are explored from the perspective of CRSN paradigm. Specifically, the challenges for real-time transport in CRSN are investigated in different spectrum environments of smart grid, e.g., 500kV substation, main power room and underground network transformer vaults. Open research issues for the realization of energy-efficient and real-time transport in CRSN are also presented. Overall, the performance evaluations provide valuable insights about real-time transport in CRSN and guide design decisions and trade-offs for CRSN applications in smart electric power grid.

Spectrum-aware and cognitive sensor networks for smart grid applications

Recently, wireless sensor networks have been considered as an opportunity to realize reliable and low-cost remote monitoring systems for smart grid. However, interference due to nonlinear electric power equipment and fading as a result of obstacles in various smart grid environments from generation to end-user sides make realization of reliable and energy-efficient communication a challenging task for WSNs in smart grid. In this article, spectrum-aware and cognitive sensor networks (SCSNs) are proposed to overcome spatio-temporally varying spectrum characteristics and harsh environmental conditions for WSN-based smart grid applications. Specifically, potential advantages, application areas, and protocol design principles of SCSN are introduced. The existing communication protocols and algorithms devised for dynamic spectrum management networks and WSNs are discussed along with the open research issues for the fulfillment of SCSNs. A case study is also presented to reveal the reliable transport performance in SCSNs for different smart grid environments. Lastly, different energy harvesting techniques for SCSN-based smart grid applications are reviewed. Here, our goal is to envision potentials of SCSNs for reliable and low-cost remote monitoring solutions for smart grid.

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.

System-Theoretic Analysis and Least-Squares Design of Microfluidic Channels for Flow-Induced Molecular Communication

Flow-induced Molecular Communication (FMC), where molecular transport is performed via flow, is utilized in microfluidic channels to enhance diffusion-based molecular communication. The incorporation of the microfluidic channel and the transport of molecules by flow, i.e., convection, require a rigorous analysis to develop an end-to-end concentration propagation model and a design for microfluidic channels. To the best of our knowledge, this is the first attempt to analyze concentration propagation in microfluidic channels from FMC perspective and devise them specifically to enhance the FMC. In this paper, a system-theoretic analysis of molecular transport is presented first. The system-theoretic model incorporates the solution of flow velocity in microfluidic channels and yields an end-to-end transfer function for concentration propagation based on building blocks of microfluidic channels. Then, the design of microfluidic channels is performed based on the least-squares Finite Impulse Response (FIR) filtering to achieve the desired end-to-end transfer function in FMC. According to the desired pass and stop bands, the required length and aspect-ratio parameters of the microfluidic channels are obtained for FIR filtering. The transfer functions for FMC is elaborated via numerical results. Furthermore, two example designs of microfluidic channels are presented for least-squares FIR band-pass and band-stop filtering in FMC.

Multi-Wideband Waveform Design for Distance-Adaptive Wireless Communications in the Terahertz Band

Terahertz band communication is envisioned as a key technology to satisfy the increasing demand for ultra-high-speed wireless links. In this paper, a multi-wideband waveform design for the THz band is proposed, by exploiting the channel peculiarities including the distance-varying spectral windows, the delay spread and the temporal broadening effects. This scheme allows the dynamical variation of the rate and the transmit power on each sub-window and improves the distance. Moreover, the closed-form expressions of the signal-to-interference-plus-the-noise and bit-error-rate for the multi-wideband waveform are derived, by considering the inter-symbol and inter-band interferences. Then, an optimization framework is formulated to solve for the multi-wideband waveform design parameters of the transmit power and the number of frames, with the aim to maximize the communication distance while satisfying the rate and the transmit power constraints. Four sub-optimal solutions are proposed and compared. The results show that the SINR increases with the transmit power and the number of frames, at the cost of the power consumption and the rate decrease. With the transmit power of 10 dBm, the largest distance to support 10 Gbps for the multi-path propagation is 4 m, which is realized via the power allocation scheme to minimize the power/bit on each sub-window and is 10% improvement over the fixed scheme. However, for the directional transmission, this scheme under-exploits the transmit power severely. Instead, the allocation scheme that minimizes the number of frames outperforms the other three schemes. In terms of the maximum distance that achieves 30 Gbps, this scheme reaches 22.5 m.

End-to-End Propagation Noise and Memory Analysis for Molecular Communication over Microfluidic Channels

Molecular communication (MC) between a transmitter and a receiver placed in the chambers attached to a microfluidic channel is investigated. A linear end-to-end channel model is developed capturing the effects of the diffusion and the junction transition at the chambers, as well as the microfluidic channel shapes and the fluid flow. The spectral density of the propagation noise is studied, and the flat frequency bands are identified for the chambers and the microfluidic channel. This suggests that in certain microfluidic design choices, the spectral density of noise may end up naturally being flat. Motivated by this result, the additive white Gaussian noise (AWGN) model is developed based on the chamber, the microfluidic channel, and the fluid flow parameters for the end-to-end propagation noise. Furthermore, the molecular memory is modeled due to inter-diffusion among transmitted molecular signals. The effect of the molecular memory on the end-to-end propagation noise is also analyzed. To substantiate our analytical results, the ranges of physical parameters that yield a linear end-to-end MC channel are investigated. These results show the validity of the AWGN model for MC over microfluidic channels and characterize the impact of the microfluidic channel and chamber geometry on the propagation noise and memory.

Genetically Engineered Bacteria-Based BioTransceivers for Molecular Communication

Molecular Communication (MC) is a nano-scale communication paradigm where the information is carried by molecular signals. To establish information transmission using molecules, biological nanomachines can be utilized as transmitters and receivers. A bacteria can be programmed as a biotransceiver by modifying their genetic code to implement biological circuits. In this paper, genetically engineered bacteria-based biotransceivers are investigated for MC, where bacteria can generate and respond to the molecular signals. A biochemical model of biological circuits is presented, and both analog and digital signaling are studied. The challenges in connecting basic biological circuits to build these blocks are revealed. A biotransceiver architecture is introduced that combines sensing, transmitting, receiving and processing blocks. Furthermore, biological circuit design framework is proposed for transmission of signals with M-ary pulse amplitude modulation. The biological circuits designed for biotransceiver are elaborated via numerical results based on biochemical parameters of the genetically engineered bacteria. The provided results show that using biological circuits, bacteria can function as a transmitter and receiver node for MC. Our work stands as a basis for future biotransceiver design for MC.

Dedicated Radio Utilization for Spectrum Handoff and Efficiency in Cognitive Radio Networks

To perform spectrum handoff, cognitive radio (CR) nodes communicating with each other need to exchange licensed user detection information, i.e., perform spectrum coordination, over a common control channel. The spectrum coordination can be fulfilled either via existing cognitive radio interface with time division or via a separate dedicated radio, i.e., a common control interface (CCI), continuously. CR nodes with CCI can instantly exchange licensed user detection information and cease frame transmission, while spectrum coordination can only be performed after the frame transmission period without CCI. Nevertheless, the impact of CCI incorporation into CR nodes in terms of common performance metrics must be thoroughly assessed to evaluate the worthiness of additional radio cost. In this paper, an analytical framework is presented to assess the impact of CCI incorporation into CR nodes for spectrum handoff. The developed framework enables analyzing potential benefits and disadvantages of employing CCI for spectrum handoff, in terms of achievable delay, energy consumption, spectrum utilization and event estimation performance. Extensive performance evaluations are presented to illustrate the impact of CCI utilization on efficiency of spectrum handoff. The network and communication regimes that would yield having CCI favorable are characterized in terms of spectrum conditions and CR parameters.

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.