1,721,008 research outputs found
Adaptive Pre- and Post-compensation of Nonlinear Distortions for High-level Data Modulations
No full textIn this letter, we show how different signal processing techniques can be combined to optimize the performance of a typical wideband nonlinear satellite link with spectrally efficient high-level modulation techniques. In particular, we follow two concurrent approaches: on one side, we pursue signal optimization in the form of special amplitude and phase shift keying (APSK) constellations to reduce the effect of nonlinear distortions, while on the other, we analyze the feasibility of adaptive data predistortion (DP) at the transmitter and adaptive nonlinear equalization (NLE) at the receiver. We demonstrate that the use of such optimized constellations relieves the complexity of the nonlinearity compensation techniques, and we also show that by clever adoption of these techniques the sensitivity to nonlinear distortion of both uncoded and turbo coded quadrature amplitude modulation and APSK constellations is greatly reduced
Blind Timing Synchronization for Filter-Bank Multicarrier Wireless Communications
No full textWe describe the performance of a blind timing recovery algorithm for filter bank multicarrier modulation (FBMCM) modems. Our starting point is a the maximum-likelihood criterion. From that, we present the derivation of a closed-loop tracker and demonstrate how to derive a relatively low-complexity scheme with reasonable performance loss. Unlike previously published works, a remarkable acquisition range equal to plus and minus one half the FBMCM signaling interval is achieved. We also show by simulation a significant robustness with respect to the multipath channel and non ideal carrier frequency estimation
Efficient Compensation of I-Q Phase Imbalance for Digital Receivers
No full textIn I/Q receivers characterized by direct conversion or low-IF operations, phase imbalance between the I and Q branches stands for a substantial issue which may degrade significantly the overall link performance. An alternative solution to high cost analog components with small tolerances which make the I/Q imbalance effect negligible is to estimate and compensate it digitally. In this paper we present a novel data aided (DA) joint estimator of the carrier phase offset and the I/Q phase imbalance derived following the maximum likelihood (ML) criterion. The performance accuracy analysis proves that the proposed estimator is efficient and achieves its vector Cramer-Rao lower bound (VCRLB). Simulation results in terms of BER performance of uncoded and turbo coded systems show that the proposed imbalance compensation method, at the cost of a low additional implementation complexity of the digital receiver, allows negligible performance degradation in the context of multi-level modulation formats, such as 16-QAM and 64-QAM
Another Turbo-Something: Carrier Synchronization
Full text linkPublication in the conference proceedings of EUSIPCO, Toulouse, France, 200
Some Results on Joint Iterative Channel Equalization and Turbo Decoding for OFDM Systems
No full textThe use of turbo/LDPC channel coding in wireless communication systems opens new avenues as far as the optimization of other signal detection functions are concerned. For instance, channel estimation/equalization may greatly benefit by the presence of high-efficiency channel coding with iterative decoding. In this paper we assume multicarrier (OFDM) transmission on a (time-invariant) frequency-selective wireless channel, and we show how to integrate soft-output iterative detection with (iterative) channel estimation. The conventional approach to channel estimation relies on pilot symbols suitably inserted in the data frame. We show here how to use the soft outputs produced by the iterative decoder at each iteration to "supplement" the pilot symbols and aid the function of channel estimation and equalization
Iterative Vector Tracking of Turbo- or LDPC- Coded High-level Constellations on a Nonlinear Satellite Channel
No full textInteractive multimedia wideband satellite services will require the adoption of Turbo or Low-Density Parity-Check (LDPC) coded spectrally-efficient high-level modulation techniques in future satellite transmission standards. In such a scenario nonlinear distortion caused by the on-board (nonlinear) high-power amplifier is quite a concern, so that countermeasures are to be properly adopted. The aim of this paper is to investigate the feasibility to use a low-complexity blind channel estimation algorithm, derived by means of the Expectation-Maximization (EM) approach, which makes iterative use of soft decisions provided by the SISO decoders within the overall decoding scheme. The performance of the proposed estimation scheme is evaluated over a nonlinear satellite channel for both Turbo and LDPC codes and compared with that of a conventional DA (Data Aided) vector tracker
The protective effect of caffeic acid phenethyl ester against cyclosporine A-induced cardiotoxicity in rats
No full textCyclosporine A (CsA) is the immunosuppressor, which is most frequently used in transplant surgery and in the treatment of autoimmune diseases. Oxidative stress has been considered as one of the possible mechanisms of CsA-induced cardiotoxicity.
The present investigation examines the ability of caffeic acid phenethyl ester (CAPE), which is an active component of propolis extracts, as a natural antioxidant to protect against CsA-induced oxidative stress and cardiotoxicity. CsA cardiotoxicity was
induced by subcutaneous injection of CsA at a dose of 15 mg/kg/body weight daily for 21 days in rats. Cardiotoxicity was evaluated by morphological and biochemical studies. CsA treated rats showed degenerative changes with cardiac fibrosis localized
around the fibers. These latters were disorganised and the network was disappeared. The ROS production was increased whereas cytochrome-c-oxidase decreased. The expression and levels of matrix metalloproteinase 2 (MMP2) were increased whereas those of its inhibitor were downregulated. CAPE subcutaneous administration (15 mol/kg/day) improved cardiac cytoarchitecture, decreased the levels and the expression of MMP2, and increased those of TIMP2 proteins. Moreover, it increased cytochrome-c oxidase activity and decreased ROS production. These results suggest that CAPE could have protective effect against CsA-induced
cardiotoxicity
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