196,797 research outputs found
Multiuser Mercury/waterfilling for Downlink OFDM with Arbitrary Signal Constellations
No full textThis paper formulates the power allocation policy that maximizes the region of mutual informations achievable in multiuser downlink OFDM channels. Arbitrary partitioning of the available tones among users and arbitrary modulation formats, possibly different for every user, are considered. The policy, derived for slowly fading channels tracked by the base station, adopts the form of a multiuser mercury/waterfilling procedure that generalizes the single-user mercury/waterfilling introduced in [1]. ©2006 IEEE
Design of MMSE multiuser detectors using random matrix techniques
No full textReduced-rank MMSE receivers using asymptotic weights reduce receiver complexity while maintaining good performance in long-sequence DS-CDMA systems. In this paper, we analyze such receivers in multipath fading channels and extend their design to multicarrier CDMA (both uplink and downlink). An explicit expression is obtained for the asymptotic eigenvalue moments of the interference autocorrelation matrix and for the asymptotic weights derived therefrom and used in the reduced-rank receiver. The full-rank MMSE receiver is also considered for multicarrier CDMA and a fixed point equation of the asymptotic maximum output SINR is derived which particularizes to the Tse-Hanly fixed point equation for the special case of DS-CDMA. An explicit expression of the MMSE spectral efficiency is proposed for multicarrier CDMA
Capacity of antenna arrays with space, polarization and pattern diversity
No full textWe present an analytical characterization of multi-antenna capacity in the limit of a large number of antennas. In contrast to previous studies, the entries of the channel matrix are not restricted to be identically distributed, thus incorporating diversity mechanisms that are otherwise excluded, such as those based on the use of antennas with distinct polarizations and radiation patterns. In addition to the capacity, first-order expressions in the low-and high-power regimes are also evaluated both asymptotically and non-asymptotically
Correlation number: A new design criterion in multi-antenna communication
No full textThis paper establishes a connection between antenna correlation and the Shannon capacity of multi-antenna channels. At low and moderate signal-to-noise ratios, which constitute the most relevant regime In contemporary mobile systems, a fundamental parameter emerges out of such connection. We illustrate how this parameter, for which we coin the term correlation number, can be used as a design criterion for diversity arrays. In addition, we present correlation numbers from experimental measurements conducted In New York City
Multiantenna capacity in interference-limited low-power conditions
No full textThis paper provides an analytical characterization of the multi-antenna capacity for scenarios where the noise is dominated by out-of-cell interference, spatially colored and subject to fading. The analysis is carried out in the region of energy per bit close to its minimum value
Dynamic forces produced by swinging bells
No full textThe swinging of bells on belfries is a classical problem in structural dynamics and has been addressed in the Central European specialized bibliography. To carry out our study, the different modalities of swinging bells have been classified in “systems” according to their most relevant characteristics in three groups: Central European, English and Spanish systems. Each group presents some singular characteristics of frequency and oscillation, unbalance and/or turning rate, which give rise to different forces variable in time on their supporting structures. We have analyzed the three systems and, compared the maximum values of the horizontal and vertical forces that appear on the structure as well as its main harmonics. Besides the parameters analyzed, the complete dynamic study of the structure, and therefore the evaluation of its dynamic amplification factor (D.A.F.), requires the knowledge of its dynamic characteristics: main frequencies and damping ratio
Optimum Power Allocation for Parallel Gaussian Channels with Arbitrary Input Distributions
No full textThe mutual information of independent parallel Gaussian-noise channels is maximized, under an average power constraint, by independent Gaussian inputs whose power is allocated according to the waterfilling policy. In practice, discrete signaling constellations with limited peak-to-average ratios (m-PSK, m-QAM, etc.) are used in lieu of the ideal Gaussian signals. This paper gives the power allocation policy that maximizes the mutual information over parallel channels with arbitrary input distributions. Such policy admits a graphical interpretation, referred to as mercury/waterfilling, which generalizes the waterfilling solution and allows retaining some of its intuition. The relationship between mutual information of Gaussian channels and nonlinear minimum mean-square error (MMSE) proves key to solving the power allocation problem
Dr. Duane M. Jackson, Morehouse College, July 2011
No full textThis video is a conversation with Dr. Duane M. Jackson. Dr. Jackson talks about his paper, "Recall and the Serial Position Effect: The Role of Primacy and Recency on Accounting Students' Performance." Jackie Daniel, AUC Woodruff Library, is the interviewer
Iterative multi-user detection for OFDM using biased mutation assisted genetic algorithms
No full textSpace Division Multiple Access (SDMA) aided Orthogonal Frequency Division Multiplexing (OFDM) systems assisted by efficient Multi-User Detection (MUD) techniques have recently attracted intensive research interests. As expected, Maximum Likelihood (ML) detection was found to attain the best performance, although this was achieved at the cost of a high computational complexity. Forward Error Correction (FEC) schemes such as Turbo Trellis Coded Modulation (TTCM) can be efficiently amalgamated with SDMA-OFDM systems for the sake of improving the achievable performance without bandwidth expansion. In this contribution, a MMSE-aided Iterative GA (IGA) MUD is proposed for employment in a TTCM-assisted SDMA-OFDM system, which is capable of achieving a similar performance to that attained by its optimum ML-aided counterpart at a significantly lower complexity, especially at high user loads. Moreover, when the proposed novel Biased Q-function Based Mutation (BQM) scheme is employed, the IGA-aided system’s performance can be further improved by achieving an Eb/N0 gain of about 6dB in comparison to the TTCM-aided MMSE-SDMA-OFDM benchmarker system both in low- and high-throughput modem scenarios, respectively, while still maintaining a modest complexity
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