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This paper is concerned with Single Carrier (SC)/Frequency Domain Equalization (FDE) for bandwidthefficient uplink block transmission, with Quadrature Amplitude Modulation (QAM) schemes, in a Multi-User (MU) Multi-Input Multi-Output (MIMO) system. The number of Base Station (BS) receiver antennas is assumed to be large, but not necessarily much larger than the overall number of transmitter antennas jointly using the same time/frequency resource at Mobile Terminals (MT).In this context, we consider several detection techniques and evaluate, in detail, the corresponding detection performances (discussed with the help of selected performance bounds), for a range of values regarding the number of available BS receiver antennas. From our performance results, we conclude that simple linear detection techniques, designed to avoid the need of complex matrix inversions, can lead to unacceptably high error floor levels. However, by combining the use of such simple linear detectors with an appropriate interference cancellation procedure -within an iterative Decision-Feedback (DF) technique -, a close approximation to the Single-Input Multi-Output (SIMO) Matched-Filter Bound (MFB) performance can be achieved after a few iterations, even for 64-QAM schemes, when the number of BS antennas is, at least, five times higher than the number of antennas which are jointly used at the user terminals.

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In this work, gamma‐ray burst (GRB) data are used to place constraints on a putative coupling between dark energy and dark matter. Type Ia supernovae constraints from the Sloan Digital Sky Survey II (SDSS‐II) first‐year results, the cosmic microwave background radiation shift parameter from Wilkinson Microwave Anisotropy Probe seven year results and the baryon acoustic oscillation peak from the SDSS are also discussed. The prospects for the field are assessed, as more GRB events become available.

Abstract-For conventional cyclic prefix (CP)-assisted single-carrier/frequency-domain equalization (SC/FDE) implementations, as well as for orthogonal frequency-division multiplexing (OFDM) implementations, the CP length is known to be selected on the basis of the expected maximum delay spread. Next, the data block size can be chosen to be large enough to minimize the CP overhead, yet small enough to make the channel variation over the block negligible. This paper considers the possibility of reducing the overall CP assistance, when transmitting sequences of SC blocks, while avoiding an excessively long fast Fourier transform window for FDE purposes and keeping good FDE performances through low-complexity, noniterative receiver techniques. These techniques, which take advantage of specially designed frame structures, rely on a basic algorithm for decision-directed correction (DDC) of the FDE inputs when the CP is not long enough to cope with the time-dispersive channel effects. More specifically, we present and evaluate a novel class of reduced-CP SC/FDE schemes, which takes advantage of a special frame structure for replacing "useless" CP redundancy by fully useful channel coding redundancy, with the help of the DDC algorithm. When using the DDC-FDE technique with these especially designed frame structures, the impact of previous decisions, which are not error-free, is shown to be rather small, thereby allowing a power-efficiency advantage (in addition to the obvious bandwidth-efficiency advantage) over conventional block transmission implementations under full-length CP. Additionally, the DDC algorithm is also shown to be useful to improve the power efficiency of these conventional implementations.

Abstract-This paper deals with Single Carrier (SC)/Frequency Domain Equalization (FDE) within a MultiUser (MU)-Multi-Input Multi-Output (MIMO) system where a large number of Base Station (BS) antennas is adopted. In this context, either linear or reduced-complexity iterative Decision-Feedback (DF) detection techniques are considered. Regarding performance evaluation by simulation, appropriate semi-analytical methods are proposed.This paper includes a detailed evaluation of Bit Error Rate (BER) performances for uncoded 4-Quadrature Amplitude Modulation (4-QAM) schemes and a MU-MIMO channel with uncorrelated Rayleigh fading. The accuracy of performance results obtained through the semi-analytical simulation methods is assessed by means of parallel conventional Monte Carlo simulations, under the assumptions of perfect power control and perfect channel estimation. The performance results are discussed in detail, with the help of selected performance bounds. We emphasize that a moderately large number of BS antennas is enough to closely approximate the Single-Input Multi-Output (SIMO) Matched-Filter Bound (MFB) performance, especially when using the suggested low-complexity iterative DF technique, which does not require matrix inversion operations. We also emphasize the achievable "massive MIMO" effects, even for strongly reduced-complexity linear detection techniques, provided that the number of BS antennas is much higher than the number of antennas which are jointly employed in the terminals of the multiple autonomous users.