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

This letter demonstrates how spectrum up to 1 THz will support mobile communications beyond 5G in the coming decades. Results of rooftop surrogate satellite/tower base station measurements at 140 GHz show the natural isolation between terrestrial networks and surrogate satellite systems, as well as between terrestrial mobile users and co-channel fixed backhaul links. These first-of-their-kind measurements and accompanying analysis show that by keeping the energy radiated by terrestrial emitters on the horizon (e.g., elevation angles ≤ 15°), there will not likely be interference in the same or adjacent bands between passive satellite sensors and terrestrial terminals, or between mobile links and terrestrial backhaul links at frequencies above 100 GHz.

Terahertz Wireless Communications: Co-Sharing for Terrestrial and Satellite Systems Above 100 GHz

A Building Database Manipulator to build databases for a variety of physical environments including definitions of buildings, terrain and other site parameters, by scanning in or rapidly editing data. Raster scans may be entered or object files in various formats may be used as input. Detailed information is stored in the drawing database about the object's location, radio frequency attenuation, color, and other physical information such as electrical characteristics and intersections of the object with the ground, floors, ceilings, and other objects when objects are formatted in a drawing. The formatting process is strictly two-dimensional in nature, but the resulting drawing is a true three-dimensional environment. The user sees the three-dimensional building structure by altering the views. The resulting database may be used in a variety of modeling applications, but is especially useful for engineering, planning and management tools for in-building or microcell wireless systems.

Method and apparatus for a transportable environmental database for communications network management and engineering

We compare the performance of conventional subspace-based direction-of-arrival (DOA) estimation techniques such as ESPRIT and MUSIC with the integrated approaches that combine the constant modulus algorithm with subspace-based techniques. Simulated and measured results are presented for a variety of signal conditions. The integrated approach was found to perform significantly better than the conventional ESPRIT approach. Also, multipath present in the channel significantly degrades the performance of the DOA estimation algorithms, and this has been confirmed by measurement and ray tracing simulation. This work has application to smart antennas and position location.

http://faculty.poly.edu/~tsr/wp-content/uploads/CV/ICP/1996-10-Performance%20Comparison%20of%20Subspace-Based%20Algorithms%20and%20the%20Integrated%20Property-Restoral%20with%20Subspace-Based%20Algorithms%20for%20DOA%20Estimation.pdf

Comparison of conventional subspace based DOA estimation algorithms with those employing property-restoral techniques: simulation and measurements

Typical and worst case channel path loss, RMS delay spreads, and excess delay spreads (10dB down) at 900MHz in four European cities using typical cellular and microcellular antenna locations are presented. It is shown that a change in reference distance from 1 km to 100 m can change the perceived propagation power law exponent from 3.0 to 2.7, where free space propagation is assumed from the transmitter to the reference distance. This is a significant result, since the path loss directly affects the frequency reuse efficiency in CDMA spread spectrum systems. Measured data show that for microcellular sites, RMS delay spreads are less than 2 μs, with excess delay spreads (10dB) less than 6 μs. At typical cellular locations with high base antennas, RMS delay spreads are generally less than 8 μs and excess delay spreads (10dB) are less than 16 μs. Worst case measurements resulted in a RMS delay spread of 19.6 μs and an excess delay spread of 51.3 μs.

Path loss and multipath delay statistics in four European cities for 900 MHz cellular and microcellular communications

We present new frequency allocation schemes for wireless networks and show that they outperform all other published work. Two categories of schemes are presented: 1) those purely based on measurements and 2) those that use site-specific knowledge, which refers to knowledge of building layouts, the locations and electrical properties of access points (APs), users, and physical objects. In our site-specific knowledge-based algorithms, a central network controller communicates with all APs and has site-specific knowledge so that it can a priori predict the received power from any transmitter to any receiver. Optimal frequency assignments are based on predicted powers to minimize interference and maximize throughput. In our measurement-based algorithms, clients periodically report in situ interference measurements to their associated APs; then, the APs' frequency allocations are adjusted based on the reported measurements. Unlike other work, we minimize interference seen by both users and APs, use a physical model rather than a binary model for interference, and mitigate the impact of rogue interference. Our algorithms consistently yield high throughput gains, irrespective of the network topology, AP activity level, number of APs, rogue interferers, and available channels. Our algorithms outperform the best published work by 18.5%, 97.6%, and 1180% for median, 25th percentile, and 15th percentile user throughputs, respectively.

https://users.ece.utexas.edu/%7Egustavo/papers/Rappaport1269276163.pdf

Theodore S. Rappaport

Papers

Terahertz Wireless Communications: Co-Sharing for Terrestrial and Satellite Systems Above 100 GHz

Method and apparatus for a transportable environmental database for communications network management and engineering

Comparison of conventional subspace based DOA estimation algorithms with those employing property-restoral techniques: simulation and measurements

Path loss and multipath delay statistics in four European cities for 900 MHz cellular and microcellular communications

Site-Specific Knowledge and Interference Measurement for Improving Frequency Allocations in Wireless Networks