Synchronisation de symbole et de chip dans le domaine fréquentiel pour les systèmes DS-CDMA et MC-CDMA

L'approche fréquentielle proposée conduit à des techniques simples et efficaces pour la synchronisation des symboles et des chips, applicable aux systèmes DS-CDMA et MC-CDMA. La technique de synchronisation des symboles présente une variance élevée et une non linéarité autour de la position du synchronisme de chip et doit être complétée. Les performances obtenues avec la méthode complémentaire proposée pour la synchronisation de chip sont équivalentes à celles de la technique Millier & Mueller Detector, et ainsi, la technique permet un traitement au débit de chip et non au double comme la méthode « early-late gate »

On the convergence of a new joint DFE & decoding procedure for blind decision directed

Abstract- Adaptive Equalization is a classical technique for mitigating ISI in unknown or time varying channels. Decisionfeedback equalizer (DFE) is considered to be an efficient approach in many types of channels where linear equalizers fail. Unfortunately, it suffers from error propagation phenomenon. In order to reduce such effect, the present paper deals with the joint application of both equalization and decoding process in the receiver. The main contributions are the proposal of a new joint DFE and decoding configuration which works in a blind decision directed (DD) context and the study of the corresponding error surfaces behavior, and the assessment of the convergence rate. The proposed technique has shown to be effective for the so-called bad channels class, which makes the conventional DD-DFE ill-converge when its weights are initialized with zeros. 1

Decoupled Space-Time Processing: Performance Evaluation for TDMA Cellular

Abstract- In this paper, we investigate the performance of a decoupled space-time processing technique in a TDMA cellular system. This structure has, as its main characteristic, the possibility of giving more degrees of freedom to an antenna array, and it can thereby provide better co-channel interference cancellation. We analyze its performance by link-level simulations and its sensitivity for parameters like delay spread, path angle separation and signal-to-interference ratio. The results show that the decoupled space-time structure can outperform the conventional linear space-time structure, especially in cases with a high level of CO-channel interference. 1

Design,Simulation and Hardware Implementation of a Digital Television System: Synchronization Techniques (Invited Paper)

supported many research consortia in order to develop a Digital Television System employing advanced technologies for multimedia broadcasting. One of the proposals for the physical layer of this system was entitled Innovative Modulation for the Brazilian Digital TV System (MI-SBTVD). The MI-SBTVD Project includes high performance error-correcting codes, transmit spatial diversity and multi-carrier modulation. The objective of this article is to present the synchronization techniques that were used in the first proof-of-concept for the MI-SBTVD System. We present the simulated performance results for both the AWGN and multipath channels. Finally, we also comment on the implementation details of the synchronization scheme using Field Programmable Gate Array (FPGA) devices

Immune-inspired Dynamic Optimization For Blind Spatial Equalization In Undermodeled Channels

In this work, we propose an evolutionary-like approach to the problem of blind adaptive spatial filtering that is based on the decision-directed criterion and on the doptaiNet, an artificial immune network conceived to perform multimodal search in dynamic environments. The proposal was tested under static and time-varying undermodeled channel models, and, in all cases, its ability to find and track a solution close to the Wiener global optimum was attested. The obtained results reveal that the dopt-aiNet may decisively enhance the performance of adaptive arrays in scenarios built from elements that are representative of some aspects of real-world communication systems. © 2006 IEEE.28962903Frost III, O.L., An Algorithm for Linearly Contained Adaptive Array Processing (1972) Proceedings of the IEEE, 60, pp. 926-935. , AugApplebaum, S., Adaptive Arrays (1976) IEEE Trans. on Antennas and Propagation, AP-24 (5), pp. 585-598Haykin, S., (1996) Adaptive Filter Theory, , 3rd edition, Prentice HallPapadias, C.B., Paulraj, A., A constant modulus algorithm for multiuser separation in the presence of delay spread using antenna arrays (1997) IEEE Signal Processing Letters, 4 (6), pp. 171-181(1994) Blind Deconvolution, , S. Haykin ed, Prentice HallYacoub, M.D., (1993) Foundations of Mobile Radio Engineering, , CRC Pressde França, F.O., Von Zuben, F.J., de Castro, L.N., An Artificial Immune Network for Multimodal Function Optimization on Dynamic Environments (2005) Proceedings of the Genetic and Evolutionary Computation Conference (GECCO, pp. 289-296Branke, J., (2001) Evolutionary Optimization in Dynamic Environments, , Kluwerde Castro, L.N., Timmis, J., (2002) Artificial Immune Systems: A New Computational Intelligence Approach, , Springer-Verlagde Castro, L.N., Timmis, J., An Artificial Immune Network for Multimodal Function Optimization (2002) Proc. of the IEEE Congress on Evolutionary Computation, 1, pp. 699-674de Castro, L.N., Von Zuben, F.J., Learning and Optimization Using the Clonal Selection Principle (2002) IEEE Transactions on Evolutionary Computation, 6 (3), pp. 239-251Gaspar, A., Collard, P., From GAs to Artificial Immune Systems: Improving Adaptation in Time Dependent Optimization (1999) Proc. of the IEEE Congress on Evolutionary Computation, pp. 1867-1874Bazaraa, M.S., Sherali, H.D., Shetty, C.M., (1993) Nonlinear Programming: Theory and Algorithms, , 2nd edition, Wile

MLP-BASED EQUALIZATION AND PRE-DISTORTION USING AN ARTIFICIAL IMMUNE NETWORK

Due to its universal approximation capability, the multilayer perceptron (MLP) neural network has been applied to several function approximation and classification tasks. Despite its success in solving these problems, its training, when performed by a gradientbased method, is sometimes hindered by the existence of unsatisfactory solutions (local minima). In order to overcome this difficulty, this paper proposes a novel approach to the training of a MLP based on a simple artificial immune network model. The application domain for assessing the performance of the proposed technique is that of digital communications, in particular, the problems of channel equalization and pre-distortion. The obtained simulation results demonstrate that the proposal is capable of efficiently solving the problems tackled. 1