Showing papers by "Thomas L. Marzetta published in 2010"

Noncooperative Cellular Wireless with Unlimited Numbers of Base Station Antennas

Abstract: A cellular base station serves a multiplicity of single-antenna terminals over the same time-frequency interval. Time-division duplex operation combined with reverse-link pilots enables the base station to estimate the reciprocal forward- and reverse-link channels. The conjugate-transpose of the channel estimates are used as a linear precoder and combiner respectively on the forward and reverse links. Propagation, unknown to both terminals and base station, comprises fast fading, log-normal shadow fading, and geometric attenuation. In the limit of an infinite number of antennas a complete multi-cellular analysis, which accounts for inter-cellular interference and the overhead and errors associated with channel-state information, yields a number of mathematically exact conclusions and points to a desirable direction towards which cellular wireless could evolve. In particular the effects of uncorrelated noise and fast fading vanish, throughput and the number of terminals are independent of the size of the cells, spectral efficiency is independent of bandwidth, and the required transmitted energy per bit vanishes. The only remaining impairment is inter-cellular interference caused by re-use of the pilot sequences in other cells (pilot contamination) which does not vanish with unlimited number of antennas.

Pilot Contamination Reduction in Multi-User TDD Systems

Abstract: This paper considers the problem of interference mitigation in multi-cell multi-antenna time division duplex (TDD) wireless systems for downlink transmission. An efficient way to obtain channel state information (CSI) at the base station is by using uplink pilots and reciprocity of the downlink channel. At the same time, it has been shown that pilots from different cells contaminate each other, resulting in corruption of precoding matrices used by base stations, and high inter-cell interference. This paper studies the effects of shifting the location of pilots in time frames used in neighboring cells, and its effectiveness in obtaining better channel estimates, and, thereby, inter-cell interference reduction.

A Random Matrix--Theoretic Approach to Handling Singular Covariance Estimates

Abstract: In many practical situations we would like to estimate the covariance matrix of a set of variables from an insufficient amount of data. More specifically, if we have a set of $N$ independent, identically distributed measurements of an $M$ dimensional random vector the maximum likelihood estimate is the sample covariance matrix. Here we consider the case where $N

Secure compressive sampling using codebook of sampling matrices

Abstract: In one aspect, a compressive sampling encoder comprises matrix determination circuitry configured to determine a particular sampling matrix selected from a codebook comprising a plurality of sampling matrices. The compressive sampling encoder further comprises sampling circuitry coupled to the matrix determination circuitry and configured to apply the particular sampling matrix to a first signal to generate a second signal, and encryption circuitry configured to receive an identifier of the particular sampling matrix and to encrypt the identifier of the particular sampling matrix. The compressive sampling encoder provides at one or more outputs thereof the second signal and the encrypted identifier of the particular sampling matrix. Other aspects include a compressive sampling decoder, compressive sampling encoding and decoding methods, and associated computer program products.

Pilot signal allocation method and apparatus for multi-user wireless systems

Abstract: A construction is provided for uplink pilot signals in a cellular network Three sets of pilot signals are defined, having orthogonality properties that lead to reduced inter-cell interference In example embodiments, the network has a reuse factor of 3 for pilot signals, with sets U, V, and W of pilot signals assigned to cells in respective reuse classes The pilots of each set form an orthogonal basis Some pilots of each class, ie those which will generally be assigned to mobile stations near the cell edges, will also form an orthogonal basis with some pilots of each of the other classes

Interference reduction for wireless networks

Abstract: Embodiments are described to mitigate network interference issues and to enable a significant increase in the throughput of wireless systems. In one method, pilot transmissions of a first and second group of wireless units are synchronized. Each wireless unit of the first group and each wireless unit of the second group use a different orthogonal pilot (than others in their group) from the same group of orthogonal pilots. Also, the pilot transmissions of the second group of wireless units are synchronized so as to be shifted in time from the pilot transmissions of the first group. In another method, data from neighboring cells and pilots from wireless units are received at a cell. Channel vectors for the wireless units are then estimated using the received data from neighboring cells, the received pilots from the wireless units and previously estimated channel vectors between the cell and the neighboring cells.

Self steering directional loud speakers and a method of operation thereof

Abstract: A directional sound system, a method of transmitting sound to a spatial location determined by the gaze of a user and a directional communication system are disclosed. In one embodiment, the directional sound system includes: (1) a direction sensor configured to produce data for determining a direction in which attention of a user is directed, (2) a microphone configured to generate output signals indicative of sound received thereat, (3) loudspeakers configured to convert directed sound signals into directed sound and (4) an acoustic processor configured to be coupled to the direction sensor, the microphone, and the loudspeakers, the acoustic processor configured to convert the output signals to the directed sound signals and employ the loudspeakers to transmit the directed sound to a spatial location associated with the direction.

Multiple Antenna Method And Apparatus For Reducing Inter-Cell Interference In Multi-User Wireless Systems

Abstract: A method is provided to reduce inter-cell interference in mobile wireless systems, and particularly in TDD wireless systems. In an embodiment, a base station receives a pilot signal from at least one of the mobile terminals that it serves at a plurality of base station antennas, which include both main antennas and auxiliary antennas. In response, each of the base station antennas provides an output that is processed to obtain a set of precoding weights for a transmission from the main antennas. The processing includes nulling at least one interfering signal using the outputs from at least the auxiliary antennas.

Noninvasive characterization of electrical power distribution systems

Abstract: Embodiments of methods and apparatuses for characterizing an electrical power distribution system are disclosed. One method includes applying at least one test signal to at least one test point of the system, measuring a plurality of response signals at a plurality of test points, wherein the plurality of response signals are generated in response to the at least one test signal, and characterizing the system based on the plurality of response signals. One system includes a plurality of test/response units attached to a plurality of test points, the units configured to generate test signals and/or measure response signals at the test points. At least one controller coordinates application of the test signals and characterizes the electrical network based on the response signals. A communications link allows the test/response units to communicate with the at least one controller.