Showing papers by "Thomas L. Marzetta published in 2012"

Scaling up MIMO: Opportunities and Challenges with Very Large Arrays

Abstract: This paper surveys recent advances in the area of very large MIMO systems. With very large MIMO, we think of systems that use antenna arrays with an order of magnitude more elements than in systems being built today, say a hundred antennas or more. Very large MIMO entails an unprecedented number of antennas simultaneously serving a much smaller number of terminals. The disparity in number emerges as a desirable operating condition and a practical one as well. The number of terminals that can be simultaneously served is limited, not by the number of antennas, but rather by our inability to acquire channel-state information for an unlimited number of terminals. Larger numbers of terminals can always be accommodated by combining very large MIMO technology with conventional time- and frequency-division multiplexing via OFDM. Very large MIMO arrays is a new research field both in communication theory, propagation, and electronics and represents a paradigm shift in the way of thinking both with regards to theory, systems and implementation. The ultimate vision of very large MIMO systems is that the antenna array would consist of small active antenna units, plugged into an (optical) fieldbus.

Argos: practical many-antenna base stations

Abstract: Multi-user multiple-input multiple-output theory predicts manyfold capacity gains by leveraging many antennas on wireless base stations to serve multiple clients simultaneously through multi-user beamforming (MUBF). However, realizing a base station with a large number antennas is non-trivial, and has yet to be achieved in the real-world. We present the design, realization, and evaluation of Argos, the first reported base station architecture that is capable of serving many terminals simultaneously through MUBF with a large number of antennas (M >> 10). Designed for extreme flexibility and scalability, Argos exploits hierarchical and modular design principles, properly partitions baseband processing, and holistically considers real-time requirements of MUBF. Argos employs a novel, completely distributed, beamforming technique, as well as an internal calibration procedure to enable implicit beamforming with channel estimation cost independent of the number of base station antennas. We report an Argos prototype with 64 antennas and capable of serving 15 clients simultaneously. We experimentally demonstrate that by scaling from 1 to 64 antennas the prototype can achieve up to 6.7 fold capacity gains while using a mere 1/64th of the transmission power.

Pilot contamination precoding in multi-cell large scale antenna systems

Abstract: An LSAS entails a large number (tens or hundreds) of base station antennas serving a much smaller number of terminals, with large gains in spectral-efficiency and energy-efficiency compared with conventional MIMO technology. Until recently it was believed that in multi-cellular LSAS, even in the asymptotic regime, as the number of service antennas tends to infinity, the performance is limited by directed inter-cellular interference. The interference results from unavoidable re-use of reverse-link pilot sequences (pilot contamination) by terminals in different cells. We devise a new concept that leads to the effective elimination of inter-cell interference in TDD LSAS systems. This is achieved by outer multi-cellular pre-coding, which we call pilot contamination pre-coding (PCP). The main idea of PCP is that each base station linearly combines messages aimed to terminals from different cells that re-use the same pilot sequence. Crucially, the combining coefficients depend only on the slow-fading coefficients between the terminals and the base stations. Each base station independently transmits its PCP-combined symbols using conventional linear pre-coding that is based on estimated fast-fading coefficients. Further we derive estimates for SINRs and a capacity lower bound for the case of LSASs with PCP and finite number of antennas M.

Method for beamforming transmissions from a network element having a plurality of antennas, and the network element

Abstract: In one embodiment, the method includes receiving (S410) a pilot signal from a terminal (30) at a target antenna of the plurality of antennas (20) of the network element ( 10), determining (S420) an uplink channel estimate for the target antenna based on the received pilot signal, and obtaining (S430) a calibration coefficient associated with the target antenna. The calibration coefficient is based on a channel estimate between the target antenna and a different one of the plurality of antennas. The method further includes beamforming (S440) a transmission to the terminal using at least the target antenna based on the determined uplink channel estimate and the obtained calibration coefficient.

Method and apparatus of wireless communication using directional antennas

Abstract: A method is provided, in which a base station allocates pilot signals to mobile terminals in a cell, obtains CSI from uplink pilot signals transmitted by mobile terminals, uses the CSI to precode messages, and transmits the messages in conformance with a TDD protocol. The CSI is obtained by comparing the pilot signal received from each mobile terminal to a known pilot signal associated with that mobile terminal. The known pilot signals are associated with respective mobile terminals according to a pilot signal reuse pattern in which adjacent cells are allocated mutually orthogonal reuse groups of mutually orthogonal pilot signals, and mobile terminals within a given cell are limited to transmitting only pilot signals allocated to that cell.

Characterization of electrical power distribution systems using characterization matrices

Abstract: Embodiments of methods and apparatuses for characterizing an electrical power distribution system are disclosed. One method includes applying a plurality of test signals to a first plurality of test points of the electrical power distribution system, measuring a plurality of response signals at a second plurality of test points of the electrical distribution system, deriving a characterization matrix for the electrical power distribution system from the plurality of test signals and response signals, and characterizing the electrical power distribution system based on the derived characterization matrix.

Method and apparatus for self - interference cancellation

Abstract: Embodiments of the claimed subject matter provide methods and apparatuses for interference cancellation. One embodiment of a method includes estimating, for an antenna in an antenna array including a plurality of antennas, interference parameters using analog signals received at the antenna on each of a plurality of subcarriers. Each interference parameter is associated with one of a plurality of symbols transmitted to one of a plurality of users on one of the plurality of subcarriers. This embodiment also includes canceling interference from analog signals received by the antenna on the plurality of subcarriers using the estimated interference parameters.

Method and apparatus for power optimization in wireless systems with large antenna arrays

Abstract: A method and apparatus for communication between a wireless base station and a population of one or more terminals are provided, involving, in each of a plurality of iterations, transmitting a block of forward-link data from an array of multiple base station antennas to the terminal population. In each iteration, a forward-link power level is updated for each said terminal using a distributed algorithm and purely local information. Meanwhile, a set of beamforming coefficients based on channel state information (CSI) obtained from reverse-link pilot signals is periodically updated, and each data block is precoded with the most recently updated beamforming coefficients. Each data block is transmitted at the most recently updated forward-link power levels.

System and method of wireless fixed access using a multiple antenna array

Abstract: A new method is disclosed for providing wireless fixed access from an array of service antennas to a population of local terminals. In implementations, a service transceiver station (STS) performs beamform precoding using channel state information (CSI) obtained from transmissions by the local terminals, and the STS performs power allocation using slow fading coefficients which are static over the service antenna positions and over a frequency range spanning at least some carriers used for downlink transmission.

Method of improving transmission gain at a network element having a plurality of antennas

Abstract: In one embodiment, the method includes reducing (S220) a beam width of transmission to increase an open-loop beamforming gain, reducing (S230) a channel bandwidth of the transmission to increase a channel bandwidth gain, and increasing (S240) a sequence length of the transmission to increase a sequence length gain. In this embodiment, a gain improvement is based on the product of the open loop beamforming gain, the channel bandwidth gain and the sequence length gain.

Precoding apparatus for pilot contamination

Abstract: Methods are provided for mitigating interference due to pilot contamination in a cellular network in which there is reuse of pilot signals. In embodiments, forward- link signals are precoded, using knowledge of slow-fading coefficients, to mitigate the interference. In embodiments, interference in reverse-link signals destined for a given base station is mitigated by linearly combining reverse-link signals destined for the given base station and for other base stations of the network, using knowledge of slow-fading coefficients.

Interference alignment for channel-adaptive waveform modulation

Abstract: For communication channels with delay spreads that are longer than the symbol interval, orthogonal frequency-division multiplexing is unusable due to its redundant cyclic prefix. In this regime other techniques are therefore required to deal with inter-symbol interference. In this paper we introduce a new modulation scheme that achieves perfect immunity from inter-symbol interference and perfect diagonalization of the channel. A crucial component of this scheme is interference alignment: portions of the potential inter-symbol interference are arranged to lie in the same output subspace, thereby increasing the number of available interference-free input waveforms.