There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

http://www.eecs.ucf.edu/~dcm/Teaching/COT4810-Spring2011/Literature/SensorNetworksSurvey.pdf

Wireless sensor networks: a survey

We develop and analyze low-complexity cooperative diversity protocols that combat fading induced by multipath propagation in wireless networks. The underlying techniques exploit space diversity available through cooperating terminals' relaying signals for one another. We outline several strategies employed by the cooperating radios, including fixed relaying schemes such as amplify-and-forward and decode-and-forward, selection relaying schemes that adapt based upon channel measurements between the cooperating terminals, and incremental relaying schemes that adapt based upon limited feedback from the destination terminal. We develop performance characterizations in terms of outage events and associated outage probabilities, which measure robustness of the transmissions to fading, focusing on the high signal-to-noise ratio (SNR) regime. Except for fixed decode-and-forward, all of our cooperative diversity protocols are efficient in the sense that they achieve full diversity (i.e., second-order diversity in the case of two terminals), and, moreover, are close to optimum (within 1.5 dB) in certain regimes. Thus, using distributed antennas, we can provide the powerful benefits of space diversity without need for physical arrays, though at a loss of spectral efficiency due to half-duplex operation and possibly at the cost of additional receive hardware. Applicable to any wireless setting, including cellular or ad hoc networks-wherever space constraints preclude the use of physical arrays-the performance characterizations reveal that large power or energy savings result from the use of these protocols.

Cooperative diversity in wireless networks: Efficient protocols and outage behavior

Cognitive radio is viewed as a novel approach for improving the utilization of a precious natural resource: the radio electromagnetic spectrum. The cognitive radio, built on a software-defined radio, is defined as an intelligent wireless communication system that is aware of its environment and uses the methodology of understanding-by-building to learn from the environment and adapt to statistical variations in the input stimuli, with two primary objectives in mind: /spl middot/ highly reliable communication whenever and wherever needed; /spl middot/ efficient utilization of the radio spectrum. Following the discussion of interference temperature as a new metric for the quantification and management of interference, the paper addresses three fundamental cognitive tasks. 1) Radio-scene analysis. 2) Channel-state estimation and predictive modeling. 3) Transmit-power control and dynamic spectrum management. This work also discusses the emergent behavior of cognitive radio.

/pdf/cognitive-radio-brain-empowered-wireless-communications-9m6gu0vz1z.pdf

Cognitive radio: brain-empowered wireless communications

Networking together hundreds or thousands of cheap microsensor nodes allows users to accurately monitor a remote environment by intelligently combining the data from the individual nodes. These networks require robust wireless communication protocols that are energy efficient and provide low latency. We develop and analyze low-energy adaptive clustering hierarchy (LEACH), a protocol architecture for microsensor networks that combines the ideas of energy-efficient cluster-based routing and media access together with application-specific data aggregation to achieve good performance in terms of system lifetime, latency, and application-perceived quality. LEACH includes a new, distributed cluster formation technique that enables self-organization of large numbers of nodes, algorithms for adapting clusters and rotating cluster head positions to evenly distribute the energy load among all the nodes, and techniques to enable distributed signal processing to save communication resources. Our results show that LEACH can improve system lifetime by an order of magnitude compared with general-purpose multihop approaches.

/pdf/an-application-specific-protocol-architecture-for-wireless-1s7y9fiv40.pdf

An application-specific protocol architecture for wireless microsensor networks

Millimeter wave wireless spectrum deployments will allow vehicular communications to share high data rate vehicular sensor data in real-time. The highly directional nature of wireless links in millimeter spectral bands will require continuous channel measurements to ensure the transmitter (TX) and receiver (RX) beams are aligned to provide the best channel. Using real-world vehicular mmWave measurement data at 28 GHz, we determine the optimal beam sweeping period, i.e. the frequency of the channel measurements, to align the RX beams to the best channel directions for maximizing the vehicle-to-infrastructure (V2I) throughput. We show that in a realistic vehicular traffic environment in Austin, TX, for a vehicle traveling at an average speed of 10.5 mph, a beam sweeping period of 300 ms in future V2I communication standards would maximize the V2I throughput, using a system of four RX phased arrays that scanned the channel 360 degrees in the azimuth and 30 degrees above and below the boresight. We also investigate the impact of the number of active RX chains controlling the steerable phased arrays on V2I throughput. Reducing the number of RX chains controlling the phased arrays helps reduce the cost of the vehicular mmWave hardware while multiple RX chains, although more expensive, provide more robustness to beam direction changes at the vehicle, allowing near maximum throughput over a wide range of beam sweep periods. We show that the overhead of utilizing one RX chain instead of four leads to a 10% drop in mean V2I throughput over six non-line-of-sight runs in real traffic conditions, with each run being 10 to 20 seconds long over a distance of 40 to 90 meters.

Performance Impact Analysis of Beam Switching in Millimeter Wave Vehicular Communications

This paper presents details of a simulation tool that generates statistical models of wideband channel impulse responses for indoor radio communication channels based on measured data. The simulator also recreates narrowband (CW) fading from the wideband spatially separated impulse responses. A carrier phase is calculated for each individual multipath component, and CW fading is recreated by calculating the phasor sum of all multipath components in each wideband impulse response snapshot at a fixed time and spatial position. We present a brief overview of the statistically based channel models, and then provide a theory to synthesize the phases of the individual multipath components in a simulator called SIRCIM Plus, based on work described by Rappaport et al. (1990, 1991). This technique may be used in conjunction with knowledge of the mobile velocity to provide accurate wideband and narrowband phase states over time and space.

Modeling and simulation of narrowband phase from the wideband channel impulse response

We study the distribution of the interference power in a millimeter wave (mmWave) cellular network. Such interference is random and highly dependent on the employed transmission technique, as well as the varying channel conditions and the varying association between users and base stations. Traditional networks at lower frequencies usually employ omnidirectional transmission which creates an (almost) equal amount of interference in any direction. MmWave networks, however, must employ directional beamforming transmission in order to compensate for the high path loss in mmWave frequency bands. These directional transmissions drastically change the network interference structure. We examine the interference power distributions in an mmWave network employing beamforming transmission under different user association schemes, and contrast with those under omnidirectional transmission. Numerical results using an analytical mmWave channel model and a measurement-based channel generator, NYUSIM, show that beamforming not only reduces the amount of strong interference and hence significantly enhances network throughput, but also user association can considerably alter network interference and throughput structures.

A Study of Interference Distributions in Millimeter Wave Cellular Networks

Preface. I: Evolution of Wireless Personal Communications. 1. Cellular for Personal Communications K. Raith, E. Lissakers, J. Uddenfeldt, J. Swerup. 2. British Telecom's Quest for Cordless Access in the United Kingdom R.G. Blake. II: Regulations and Standard Development. 3. From Wired to Wireless: Historical Lessons and Other Oxymorons G.J. Vogt. III: Code Division Multiple Access (CDMA) and Spectrum Sharing. 4. Personal Communication Networks of the Future: CDMA Digital Cellular & PCN Developments A. Salmasi. 5. Broadband-CDMA: A PCS Wireless Technology to Achieve Wireline Quality and Maximize Spectral Efficiency D.L. Schilling, T. Apelewicz, G.R. Lomp, V. Erceg. 6. Analysis of DS/CDMA: Use of Moments and Gaussian Approximations J.M. Holtzman. 7. Simulation Study of Spectrum Sharing Between Microwave Links and Personal Communications Systems B.K. Johnson, Z.S. Merchant. IV: Wireless Personal Communication System Design. 8. A Wireless Data Modem for Local Communications H. Kaufmann, R. Kung. 9. PCS Control Channel Considerations K.A. Felix. 10. Adaptive Equalization for Digital Wireless Data Transmission R.A. Aiegler, J.M. Cioffi. 11. Error Reduction of DMPSK Transmitted over Flat Fading Channels M. Fattouche, H. Zaglhoul. 12. A Non-Iterative Algorithm for Estimating the Impulse Response of ISI Channels K. Hamied, G.L. Stuber. 13. Simulation and Performance Analysis of Dynamic Channel Allocation Algorithms in DECT J.Z. Wang. V: Radiowave Propagation and Channel Characterization. 14. Theoretical Prediction of Propagation Over Buildings for Low Base Station Antennas H.L. Bertoni, L.R. Maciel, H.H. Xia. 15. Ray Model of Indoor Propagation P.F. Driessen, M. Gimersky, T. Rhodes. 16. Error Rate Prediction for High Data Rate Short Range Systems M.H. Barton, J.P. McGeehan, A.R. Nix, M.C. Lawton. 17. Site-Specific Propagation Prediction for PCS System Design T.S. Rappaport, S.Y. Seidel, K.R. Schaubach. Index.

https://www.springer.com/productFlyer_978-0-7923-7705-4.pdf?SGWID=0-0-1297-33342612-0

Wireless Personal Communications

Massive MIMO systems are well-suited for mm-Wave communications, as large arrays can be built with reasonable form factors, and the high array gains enable reasonable coverage even for outdoor communications. One of the main obstacles for using such systems in frequency-division duplex mode, namely the high overhead for the feedback of channel state information (CSI) to the transmitter, can be mitigated by the recently proposed JSDM (Joint Spatial Division and Multiplexing) algorithm. In this paper we analyze the performance of this algorithm in some realistic propagation channels that take into account the partial overlap of the angular spectra from different users, as well as the sparsity of mm-Wave channels. We formulate the problem of user grouping for two different objectives, namely maximizing spatial multiplexing, and maximizing total received power, in a graph-theoretic framework. As the resulting problems are numerically difficult, we proposed (sub optimum) greedy algorithms as efficient solution methods. Numerical examples show that the different algorithms may be superior in different settings.We furthermore develop a new, "degenerate" version of JSDM that only requires average CSI at the transmitter, and thus greatly reduces the computational burden. Evaluations in propagation channels obtained from ray tracing results, as well as in measured outdoor channels show that this low-complexity version performs surprisingly well in mm-Wave channels.

Theodore S. Rappaport

Papers

Performance Impact Analysis of Beam Switching in Millimeter Wave Vehicular Communications

Modeling and simulation of narrowband phase from the wideband channel impulse response

A Study of Interference Distributions in Millimeter Wave Cellular Networks

Wireless Personal Communications

Joint Spatial Division and Multiplexing for mm-Wave Channels