Theodore S. Rappaport

Bio: Theodore S. Rappaport is an academic researcher from New York University. The author has contributed to research in topics: Path loss & Multipath propagation. The author has an hindex of 112, co-authored 490 publications receiving 68853 citations. Previous affiliations of Theodore S. Rappaport include University of Waterloo & University of Texas at Austin.

Improved spectral efficiency for CDMA systems

Abstract: Code Division Multiple Access (CDMA) · largely on frequency reuse and voice activity gating; based on spread-spectrum techniques finds increasing for. data transmission within a single cell environment,· use in commercial communications. Although CDMA the capacity of the current generation of CDMA sysoffers important advantages for wireless communicatems does ·not approach the capacity of Time or Fretions, current CDMA systems are less spectrally effi. quency Division Multiple Access. Furthermore, current . cient than ·systems employing orthogonal multiple acCDMA systems depend heavily on accurate power concess techniques in a single cell environment, and are detrol to avoid the near-far problem which arises when pendent on accurate power control. We survey research an interfering signal is received with higher power than into a variety of techniques which will increase the specthe desired signal. Even with an elaborate combinatral efficiency and robustness of subsequent generations tion of open~ loop and closed-loop power control, field of CDMA systems. These techriiques include multiuser trials indicate received signal powers will have a variand single user interference rejection techniques, the deance of 1-2 dB about their desired values in a mobile ployment of smart antenna technology, and the develenvironment[4]. This small variation can reduce the opment of advanced error correction coding techniques. capacity of by 15-30%~from the ideal case when conWe show how these techniques can be applied to inventional receivers· are employed[5]. crease the capacity of CDMA systems. New processing techniques· on the horizon will enable

Overview of wireless networks and security issues for wifi networks

Abstract: W . ireless local area networks (WLAN s) provide wireless connectivity between PCs, laptops and other equipment in corporate, public and home environments. Today, tens of millions of users rely on shortrange wireless connectivity between computers or automation equipment using WLAN modem gear that complies with well-known Figure 1. Evolution ofWLAN standards. standards such as IEEE 802.11, 802.11 a, 802.11 b and 802.llg. The first WLAN standard IEEE 802.11, initially contemplated in the late 1980's, was finalized in 1997 (10 years later!) and provided interoperability standards for equipment makers compatible 'with IEEE 802.11 b and 802.11 standards. · Figure 1 illustrates the evolution of IEEE WLAN · standards. An overview of the evolution of WiFi is

SISP-A software tool for propagation prediction

Abstract: Accurate modeling of radio propagation characteristics in and around built-up urban environments is vital to the successful functioning of ~urv~illance and tracking systems utilizing wireless technology. A vast majority of the software tools currently available to military and civilian users are based on very simple models with fairly limited accuracy and are closed architectures. We discuss the design and development of a software tool that prov~des: a) a framework for modelers to incorporate new models and test their hypotheses, and b) system designers and planners to obtain the propagation characteristics in any environment. The interactive software executes on a workstation, uses topographic maps with building overlays to predict signal coverage and channel characteristics for user-specified antenna locations. Work is in progress to improve the accuracy of the prediction software through better diffraction modeling.

I and i

Abstract: 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 …

Cooperative diversity in wireless networks: Efficient protocols and outage behavior

Abstract: 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.

Cognitive radio: brain-empowered wireless communications

Abstract: 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.

An application-specific protocol architecture for wireless microsensor networks

Abstract: 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.