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 paper presents directional and omnidirectional RMS delay spread statistics obtained from 28 GHz and 73 GHz ultrawideband propagation measurements carried out in New York City using a 400 Megachips per second broadband sliding correlator channel sounder and highly directional steerable horn antennas. The 28 GHz measurements did not systematically seek the optimum antenna pointing angles and resulted in 33% outage for 39 T-R separation distances within 200 m. The 73 GHz measurements systematically found the best antenna pointing angles and resulted in 14.3% outage for 35 T-R separation distances within 200 m, all for mobile height receivers. Pointing the antennas to yield the strongest received power is shown to significantly reduce RMS delay spreads in line-of-sight (LOS) environments. A new term, distance extension exponent (DEE) is defined, and used to mathematically describe the increase in coverage distance that results by combining beams from angles with the strongest received power at a given location. These results suggest that employing directionality in millimeter-wave communications systems will reduce inter-symbol interference, improve link margin at cell edges, and enhance overall system performance.

Exploiting Directionality for Millimeter-Wave Wireless System Improvement

This paper presents a 3-D statistical channel model of the impulse response with small-scale spatially correlated random coefficients for multi-element transmitter and receiver antenna arrays, derived using the physically-based time cluster - spatial lobe (TCSL) clustering scheme. The small-scale properties of multipath amplitudes are modeled based on 28 GHz outdoor millimeter-wave small-scale local area channel measurements. The wideband channel capacity is evaluated by considering measurement-based Rician-distributed voltage amplitudes, and the spatial autocorrelation of multipath amplitudes for each pair of transmitter and receiver antenna elements. Results indicate that Rician channels may exhibit equal or possibly greater capacity compared to Rayleigh channels, depending on the number of antennas.

MIMO channel modeling and capacity analysis for 5G millimeter-wave wireless systems

Measured impulse response estimates of radio channels have been used to determine time delay spread and path loss characteristics inside four buildings using different antenna heights at 1.3 GHz and 4.0 GHz. RMS delay spread values were found to be dependent on building and local topography, but generally independent of frequency and antenna height. Path loss values were found to be nearly independent of frequency.

Indoor wideband radiowave propagation measurements at 1.3 GHz and 4.0 GHz

This article demonstrates the performance of multi-beam antenna combining for improving link quality in future millimeter-wave cellular systems. Using experimental data obtained from 28 GHz propagation measurements in New York City [8], we demonstrate how the combination of two, three and four beams, either noncoherently or coherently at the mobile receiver antenna, can improve the propagation link substantially. The results reveal that an average of 28.1 dB improvement in path loss can be achieved via combining the strongest four received signals coherently, when compared to the case of randomly received signals using a single beam at the receiver. This paper is the first to present the potential of multi-beam combining for improving link budget (e.g., extending range) in future mm-wave urban cellular systems.

https://www.wireless.engineering.nyu.edu/wp-content/uploads/2013/12/Multi-beam-Antenna-Combining-for-28-GHz-Cellular-Link-Improvement-in-Urban-Environments.pdf

Multi-beam antenna combining for 28 GHz cellular link improvement in urban environments

Channel models describe how wireless channel parameters behave in a given scenario, and help evaluate link- and system-level performance. A proper channel model should be able to faithfully reproduce the channel parameters obtained in field measurements and accurately predict the spatial and temporal channel impulse response along with large-scale fading. This paper compares two popular channel models for next generation wireless communications: the 3rd Generation Partnership Project (3GPP) TR 38.900 Release 14 channel model and the statistical spatial channel model NYUSIM developed by New York University (NYU). The two channel models employ different modeling approaches in many aspects, such as the line-of-sight probability, path loss, and clustering methodology. Simulations are performed using the two channel models to analyze the channel eigenvalue distribution and spectral efficiency leveraging the analog/digital hybrid beamforming methods found in the literature. Simulation results show that the 3GPP model produces different eigenvalue and spectral efficiency distributions for mmWave bands, as compared to the outcome from NYUSIM that is based on massive amounts of real-world measured data in New York City. This work shows NYUSIM is more accurate for realistic simulations than 3GPP in urban environments.

Theodore S. Rappaport

Papers

Exploiting Directionality for Millimeter-Wave Wireless System Improvement

MIMO channel modeling and capacity analysis for 5G millimeter-wave wireless systems

Indoor wideband radiowave propagation measurements at 1.3 GHz and 4.0 GHz

Multi-beam antenna combining for 28 GHz cellular link improvement in urban environments

Investigation and Comparison of 3GPP and NYUSIM Channel Models for 5G Wireless Communications