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

A real-time simulation tool called BERSIM is developed and used to study bit-by-bit errors, average bit error rate and block outage probabilities for pi /4 differential quadrature phase-shift keying (DQPSK) at megabit rates with raised-cosine pulse shaping. Simulation results show that when the ratio of RMS delay spread to bit duration is greater than about 0.02, the irreducible average BER is not only a function of RMS delay spread, but is also a function of the temporal and spatial distribution of individual multipath components in the complex channel impulse response. The results show that fading caused by multipath cancellation is the major error mechanism over a local area for RMS delay spreads smaller than 0.02-b duration. An example of BERSIM's real time output is shown for the transmission of a video image through a mobile radio system. The simulation methods are suited for evaluation and design of indoor wireless LANs, as well as paging and cellular systems. >

Simulation of bit error performance and outage probability of pi /4 DQPSK in frequency-selective indoor radio channels using a measurement-based channel model

This paper derives equations that describe level-crossing rates and average fade durations for mobile receivers operating in spatially complicated multipath channels. The results are useful for describing fading statistics for wireless systems that operate in realistic propagation channels or employ smart antennas, adaptive arrays, or other technologies that lead to a non-omnidirectional distribution of multipath power in space.

Level-crossing rates and average fade duration for wireless channels with spatially complicated multipath

The use of a building database and a three-dimensional formulation of the Fresnel-Kirchoff diffraction theory to compute the shadowing by buildings in the general situation where diffraction can occur by building edges of both horizontal and vertical orientation is described. The storage format of buildings in a geographic information system database is described. An algorithm for identifying the nearest diffracting building and deriving the necessary information for the evaluation of the diffraction integral is presented. Example results are presented to show the utility of this approach. >

Use of a building database in prediction of three-dimensional diffraction

It is well known that cellular capacity can be increased by reducing cell cluster size, since more channels may then be assigned to each cell. However, this reduction of cluster size leads to increased co-channel interference, requiring the use of some cochannel interference control techniques at the base stations or in the air interface. In this paper we analyse the combined application of "smart antennas" (narrowbeam antennas) and the fractional loading factor. We explore the effect of reducing the total co-channel interference, while simultaneously adjusting the cellular cluster size.

Combined effects of narrowbeam antennas and fractional loading factor in forward link cellular communication systems

The accurate classification of autocorre­ lation (second-order) small-scale fading statistics for mobile receivers over a local area is essential for stud­ ies involving equalization, diversity: adaptive arrays, and any other wireless concept affected by the time­ varying channel or multipath angle-of-arrival charac­ teristics. This paper establishes a relationship be­ tween small-scale fading and the directivity of im­ pinging waves at a mobile receiver by deriving second­ order fading statistics in terms of three new multi path angle-of-arrival parameters. receiver over a local area - and derives an equation for local area fading rate variance in terms of spatial channel parameters. Furthermore, these spatial pa­ rameters are shown to have basic physical meanings, related to the multipath angle-of-arrival characteris­ tics. Three examples of directional multipath mod­ els are presented to clarify this relationship. The key result is Eqn (1), an expression relating fading be­ havior to multipath propagation of arbitrary spatial complexity.

http://faculty.poly.edu/~tsr/wp-content/uploads/CV/ICP/1999-09-Three%20Parameters%20for%20Relating%20Small-Scale%20Temporal%20Fading%20Statistics%20to%20Multipath%20Angle-of-Arrival.pdf

Theodore S. Rappaport

Papers

Simulation of bit error performance and outage probability of pi /4 DQPSK in frequency-selective indoor radio channels using a measurement-based channel model

Level-crossing rates and average fade duration for wireless channels with spatially complicated multipath

Use of a building database in prediction of three-dimensional diffraction

Combined effects of narrowbeam antennas and fractional loading factor in forward link cellular communication systems

Three parameters for relating small-scale temporal fading statistics to multipath angles-of-arrival