Showing papers by "Thomas L. Marzetta published in 2009"

Pilot Contamination and Precoding in Multi-Cell TDD Systems

Abstract: This paper considers a multi-cell multiple antenna system with precoding used at the base stations for downlink transmission. For precoding at the base stations, channel state information (CSI) is essential at the base stations. A popular technique for obtaining this CSI in time division duplex (TDD) systems is uplink training by utilizing the reciprocity of the wireless medium. This paper mathematically characterizes the impact that uplink training has on the performance of such multi-cell multiple antenna systems. When non-orthogonal training sequences are used for uplink training, the paper shows that the precoding matrix used by the base station in one cell becomes corrupted by the channel between that base station and the users in other cells in an undesirable manner. This paper analyzes this fundamental problem of pilot contamination in multi-cell systems. Furthermore, it develops a new multi-cell MMSE-based precoding method that mitigate this problem. In addition to being a linear precoding method, this precoding method has a simple closed-form expression that results from an intuitive optimization problem formulation. Numerical results show significant performance gains compared to certain popular single-cell precoding methods.

Pilot contamination problem in multi-cell TDD systems

Abstract: This paper considers a multi-cell multiple antenna system with precoding at the base stations for downlink transmission. To enable precoding, channel state information (CSI) is obtained via uplink training. This paper mathematically characterizes the impact that uplink training has on the performance of multi-cell multiple antenna systems. When non-orthogonal training sequences are used for uplink training, it is shown that the precoding matrix used by the base station in one cell becomes corrupted by the channel between that base station and the users in other cells. This problem of pilot contamination is analyzed in this paper. A multi-cell MMSE-based precoding is proposed that, when combined with frequency/time/pilot reuse techniques, mitigate this problem.

Security for wireless transfer of electrical power

Abstract: A security mechanism is provided for wireless power transfer applications including resonant source and device objects, wherein tuned resonance between source and device objects is necessary for efficient power transfer. Tuning parameters associated with the source object are periodically adjusted so as to require corresponding changes in tuning parameter(s) of the device object to maintain tuned resonance. The tuning parameters are communicated to authorized users such that only authorized users capable of matching the changes made by the transmitter would be capable of receiving power. Unauthorized users that are unaware of the transmit tuning parameters will be rendered unable to maintain tuned resonance and thus unable to receive power.

Automatic tuning for wireless power transfer

Abstract: In one embodiment, a wireless power transfer system has a wireless power transmitter and receiver. The transmitter has a transmitting resonant circuit that resonates at a first frequency and a signal generator that generates a signal at a second frequency. The transmitter also has a power detector that measures reflected power at the transmitting resonant circuit, and an auto-tuner that generates transmitter tuning parameters for adjusting the first and second frequencies to reduce reflected power. The receiver has a receiving resonant circuit that resonates at a third frequency based on a receiver tuning parameter. The receiver tuning parameter is generated by a power detector that measures power generated at the receiving resonant circuit, and an auto-tuner that generates the receiver tuning parameter to increase the load power.

Self-steering directional hearing aid and method of operation thereof

Abstract: A hearing aid and a method of enhancing sound. In one embodiment, the hearing aid includes: (1) a direction sensor configured to produce data for determining a direction in which attention of a user is directed, (2) microphones to provide output signals indicative of sound received at the user from a plurality of directions, (3) a speaker for converting an electrical signal into enhanced sound and (4) an acoustic processor configured to be coupled to the direction sensor, the microphones, and the speaker, the acoustic processor being configured to superpose the output signals based on the determined direction to yield an enhanced signal based on the received sound, the enhanced signal having a higher content of sound received from the direction than sound received at the user.

What is the value of joint processing of pilots and data in block-fading channels?

Abstract: The spectral efficiency achievable with joint processing of pilot and data symbol observations is compared with that achievable through the conventional (separate) approach of first estimating the channel on the basis of the pilot symbols alone, and subsequently detecting the data symbols. Studied on the basis of a mutual information lower bound, joint processing is found to provide a non-negligible advantage relative to separate processing, particularly for fast fading. It is shown that, regardless of the fading rate, only a very small number of pilot symbols (at most one per transmit antenna and per channel coherence interval) should be transmitted if joint processing is allowed.

Self-steering directional loudspeakers 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.

Pilot Contamination Problem in Multi-Cell TDD Systems

Abstract: This paper considers a multi-cell multiple antenna system with precoding at the base stations for downlink transmission. To enable precoding, channel state information (CSI) is obtained via uplink training. This paper mathematically characterizes the impact that uplink training has on the performance of multi-cell multiple antenna systems. When non-orthogonal training sequences are used for uplink training, it is shown that the precoding matrix used by the base station in one cell becomes corrupted by the channel between that base station and the users in other cells. This problem of pilot contamination is analyzed in this paper. A multi-cell MMSE-based precoding is proposed that, when combined with frequency/time/pilot reuse techniques, mitigate this problem.

What is the Value of Joint Processing of Pilots and Data in Block-Fading Channels?

Abstract: The spectral efficiency achievable with joint processing of pilot and data symbol observations is compared with that achievable through the conventional (separate) approach of first estimating the channel on the basis of the pilot symbols alone, and subsequently detecting the data symbols. Studied on the basis of a mutual information lower bound, joint processing is found to provide a non-negligible advantage relative to separate processing, particularly for fast fading. It is shown that, regardless of the fading rate, only a very small number of pilot symbols (at most one per transmit antenna and per channel coherence interval) should be transmitted if joint processing is allowed.

Methods for reducing inter-cell interference by precoding signals for transmission in wireless MIMO system

Abstract: Methods for suppressing inter-cell interference during data transmission using a preceding matrix are provided. Inter-cell interference is suppressed by precoding data (or information) signals for transmission from base station to mobile or vice versa. Methods according to example embodiments also increase intra-cell data transmission rates. The precoding matrix is generated based on estimated channel coefficients for propagation channels between a base station and mobiles inside and outside the base station's coverage area.

An IQML type algorithm for AR parameter estimation from noisy covariance sequences

Abstract: we deal with the problem of AR parameter estimation from noisy covariance sequences. An iterative quadratic maximum likelihood (IQML) type of algorithm is proposed to solve the problem. The convergence and consistency properties of the method are studied by carrying out several numerical simulations.