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.

Multi-code multi-carrier code division multiple access (CDMA) system and method

Abstract: A multi-code multicarrier CDMA system and method for communicating data by transforming a stream of data into a plurality of code sequences selected from a code book by associating symbols of the data stream with the code sequences of the code book, wherein the codebook includes M code sequences and each of the code sequences has a length of N data symbols, copying each of the code sequences onto one or more of a plurality of subcarriers, transmitting the plurality of subcarriers, receiving the plurality of transmitted subcarriers, demodulating the received subcarriers to result in the code sequences, transforming the code sequences back into the stream of data based upon the associations between the code sequences of the code book and the symbols of the data stream, changing at least one of the number M and lengths N of the code sequences in the code book.

Application of narrow-beam antennas and fractional loading factor in cellular communication systems

Abstract: It is well known that cellular system capacity can be increased by reducing the cell cluster size N. Reducing the cluster size, however, increases cochannel interference. In the literature, several techniques have been proposed for controlling the cochannel interference and simultaneously reducing the cluster size. In this paper, we combine two proposed capacity improvement methods and explore the effectiveness of reducing cochannel interference using narrow-beam antennas ("smart antennas") with the fractional loading factor. As shown in this paper, it is possible to increase capacity by many times by decreasing the cluster size (i.e. increasing frequency reuse), although the proper combination of antenna specifications and fractional loading is surprisingly nonintuitive. The first cochannel mitigation technique uses base-station antennas with narrow beams in the direction of the desired mobile stations and significant side lobe attenuation in the direction of undesired users. The second technique exploits the fact that interference is related to the loading factor p/sub ch/, which defines the probability that a given channel is in use within a cell, We show that large capacity gains with respect to a reference cellular system (N=7, three sectors per cell) can be obtained by combining these two techniques. This paper provides insight for system-level deployment of high-capacity cellular systems and can be extended to fixed wireless systems as well.

Wireless channel prediction in a modern office building using an image-based ray tracing method

Abstract: The methodology of a three dimensional image-based ray tracing algorithm is presented. Building information and antenna properties are used to predict wideband channels in a modern office building. Comparisons between prediction results and measurement results are also given. >

Evaluation of several adaptive algorithms for canceling acoustic noise in mobile radio environments

Abstract: The authors investigate several adaptive noise-cancellation algorithms and their effectiveness in improving the quality of speech degraded by additive acoustic noise in mobile communications. A personal-computer system which was used to acquire test data and implement the algorithms is described. The algorithms studied include least mean squares (LMS), recursive least squares (RLS), a fast transversal filter (FTF) implementation of RLS, direct solution of the normal equation, and an adaptive notch filter. The results of a comparison of the algorithms based on various criteria are presented. The results of applying each of the algorithms to adaptive noise cancellation in mobile environments are described and evaluated. The FTF algorithm demonstrated excellent convergence qualities compared to the LMS algorithm. >

Effects of antenna polarization and beam pattern on multipath delay spread and path loss in indoor obstructed wireless channels

Abstract: The effects of different combinations of antenna patterns and polarizations on path loss and RMS delay spread in indoor obstructed channels at 245 GHz are treated Based on measurement results, and assuming the main beams of the antennas are lined up on boresight, it appears that using vertically polarized (VP) antennas at both the transmitter and the receiver can provide smaller delay spread and smaller path loss compared to those of other antenna combinations The correlation between path loss and RMS delay spread of different antenna combinations is presented It is found that path loss is uncorrelated with RMS delay spread when the antennas are omnidirectional However, strong correlations are found when the antennas are directional and both polarizations of the transmitter and receiver are vertically polarized (VP) or horizontally polarized (HP) >

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.