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Optimal Ranking of Test Items using the Rasch Model
(2016)2016 54th Annual Allerton Conference on Communication, Control, and Computing (Allerton)We study the problem of ranking test items, i.e., the ordering of items according to the amount of information they provide on the latent trait of the respondents. We focus on educational applications, where instructors are interested in ranking questions so as to select a small set of informative questions in order to efficiently assess the students' understanding on the course material. Using the Rasch model for modeling student responses, ...Conference Paper -
A 3.8Gb/s large-scale MIMO detector for 3GPP LTE-Advanced
(2014)2014 IEEE International Conference on Acoustics, Speech and Signal Processing (ICASSP)This paper proposes - to the best of our knowledge - the first ASIC design for high-throughput data detection in single carrier frequency division multiple access (SC-FDMA)-based large-scale MIMO systems, such as systems building on future 3GPP LTE-Advanced standards. In order to substantially reduce the complexity of linear soft-output data detection in systems having hundreds of antennas at the base station (BS), the proposed detector ...Conference Paper -
Recovery Guarantees for Restoration and Separation of Approximately Sparse Signals
(2011)2011 49th Annual Allerton Conference on Communication, Control, and Computing (Allerton)In this paper, we present performance guarantees for the recovery and separation of signals that are approximately sparse in some general (i.e., basis, frame, over-complete, or incomplete) dictionary but corrupted by a combination of measurement noise and interference that is sparse in a second general dictionary. Applications covered by this framework include the restoration of signals impaired by impulse noise, narrowband interference, ...Conference Paper -
Subset-Codebook Precoding for 1-bit Massive Multiuser MIMO
(2017)2017 51st Annual Conference on Information Sciences and Systems (CISS)We consider a massive multiuser MIMO downlink scenario with 1-bit digital-to-analog converters. QPSK information symbols are transmitted to the users by a channel-dependent mapping of the symbols to 1-bit DAC signals that are transmitted from each base station (BS) antenna. The mapping is selected to emulate the desired information bearing QPSK symbols at the users. Non-linear precoding is considered, where the mapping from the information ...Conference Paper -
VLSI Design of a Nonparametric Equalizer for Massive MU-MIMO
(2017)2017 51st Asilomar Conference on Signals, Systems, and ComputersLinear minimum mean-square error (L-MMSE) equalization is among the most popular methods for data detection in massive multi-user multiple-input multiple-output (MU-MIMO) wireless systems. While L-MMSE equalization enables near-optimal spectral efficiency, accurate knowledge of the signal and noise powers is necessary. Furthermore, corresponding VLSI designs must solve linear systems of equations, which requires high arithmetic precision, ...Conference Paper -
PAR-aware multi-user precoder for the large-scale MIMO-OFDM downlink
(2012)2012 International Symposium on Wireless Communication Systems (ISWCS)We consider an orthogonal frequency-division multiplexing (OFDM)-based downlink transmission scheme for large-scale multi-user (MU) multiple-input multiple-output (MIMO) wireless systems. In order to transmit signals with low peak-to-average (power) ratio (PAR), we propose to exploit the massive degrees-of-freedom available in large-scale MU-MIMO-OFDM systems. Specifically, we jointly perform MU precoding, OFDM modulation, and PAR reduction ...Conference Paper -
Optimal Large-MIMO Data Detection with Transmit Impairments
(2015)2015 53rd Annual Allerton Conference on Communication, Control, and Computing (Allerton)Real-world transceiver designs for multiple-input multiple-output (MIMO) wireless communication systems are affected by a number of hardware impairments that already appear at the transmit side, such as amplifier non-linearities, quantization artifacts, and phase noise. While such transmit-side impairments are routinely ignored in the data-detection literature, they often limit reliable communication in practical systems. In this paper, ...Conference Paper -
Time-varying Learning and Content Analytics via Sparse Factor Analysis
(2014)Proceedings of the 20th ACM SIGKDD international conference on Knowledge discovery and data miningWe propose SPARFA-Trace, a new machine learning-based framework for time-varying learning and content analytics for educational applications. We develop a novel message passing-based, blind, approximate Kalman filter for sparse factor analysis (SPARFA) that jointly traces learner concept knowledge over time, analyzes learner concept knowledge state transitions (induced by interacting with learning resources, such as textbook sections, ...Conference Paper -
Conjugate Gradient-based Soft-Output Detection and Precoding in Massive MIMO Systems
(2014)2014 IEEE Global Communications ConferenceMassive multiple-input multiple-output (MIMO) promises improved spectral efficiency, coverage, and range, compared to conventional (small-scale) MIMO wireless systems. Unfortunately, these benefits come at the cost of significantly increased computational complexity, especially for systems with realistic antenna configurations. To reduce the complexity of data detection (in the uplink) and precoding (in the downlink) in massive MIMO ...Conference Paper -
Nonlinear 1-Bit Precoding for Massive MU-MIMO with Higher-Order Modulation
(2016)2016 50th Asilomar Conference on Signals, Systems and ComputersMassive multi-user (MU) multiple-input multiple-output (MIMO) is widely believed to be a core technology for the upcoming fifth-generation (5G) wireless communication standards. The use of low-precision digital-to-analog converters (DACs) in MU-MIMO base stations is of interest because it reduces the power consumption, system costs, and raw baseband data rates. In this paper, we develop novel algorithms for downlink precoding in massive ...Conference Paper