KEYWORDS: Modulation, Receivers, Antennas, Error analysis, Global system for mobile communications, Phase shift keying, Gaussian filters, Deconvolution, Signal processing, Computer simulations
In this paper, multi-channel estimation schemes for a GMSK-based system with transmit diversity (space-time coding) are presented. For such a system, the channel information (impulse response) is critical for both space-time decoding and equalization at the receiver. Three non-blind estimation schemes, which decompose the channel in the process, are proposed for the GMSK receiver to obtain the impulse response of each of the multipath channels (i.e. transmit antennas): oversampling deconvolution, minimum mean-square error, and joint adaptive and correlation estimation. Since the received signal is the sum of emitted GMSK signals, interference cancellation is employed to facilitate the estimation process. Three cancellation algorithms, including direct cancellation, mean-square cancellation, and iterative cancellation, combined with each channel estimation method are investigated and compared. The estimated channel information will feed to the receiver consisting of space-time decoder and equalizer to decode the symbols of interest. Two receiver architectures are investigated in this paper, where the first design is the space-time decoder followed by the equalizer, the other is in the reverse way (equalizer followed by space-time decoder). In each of the two receiver architectures, the channel estimation needs additional modification and so does the equalizer. The equalizer in the design is a maximum likelihood sequence estimation (MLSE) based on Viterbi algorithm. To prove the concept and algorithms, both simulation and hardware implementation are performed. From the experimental results, it is shown that all the channel estimation algorithms can produce acceptable impulse response for space-time decoding and equalizer, in which the joint adaptive estimation with iterative cancellation is superior to the others. It is also shown that the diversity gain of this transmit diversity system is as good as a system with the same degree of receive diversity.
KEYWORDS: Computer programming, Modulation, Signal to noise ratio, Receivers, Error analysis, Global system for mobile communications, MATLAB, Computer simulations, Binary data, Phase shift keying
A new way of implementation of MMSE channel estimator for a GMSK signals with Turbo code over multipath fading channels is proposed in the paper. From the recent research results, it is clear that the usage of Turbo Codes with GMSK modulation is highly desirable because some signal processing modules in the receiver can be reused for both turbo decoder and equalization, and thus the receiving complexity can be reduced. Channel estimator is one of the modules that are required by the equalizer and the Turbo code decoder. In this paper we present an estimation technique, used for both GMSK equalization and Turbo decoder (SOVA/Log-MAP) over the multipath fading channel. The proposed MMSE estimator replaces the matched filters that are usually applied at the receiver end. The simulation results show that unified MMSE estimator gives us an edge over the disadvantages of the matched filter and conventional isolated estimators, such that the bit error rate performance is improved and the distorted data could be easily retrieved from the estimation technique.
KEYWORDS: Digital signal processing, Receivers, Signal processing, Signal detection, Computer architecture, Field programmable gate arrays, Filtering (signal processing), Analog electronics, Telecommunications, Antennas
In this paper, a re-programmable receiver architecture, based on software-defined-radio concept, for wireless signal interception is presented. The radio-frequency (RF) signal that the receiver would like to intercept may come from a terrestrial cellular network or communication satellites, which their carrier frequency are in the range from 800 MHz (civilian mobile) to 15 GHz (Ku band). To intercept signals from such a wide range of frequency in these variant communication systems, the traditional way is to deploy multiple receivers to scan and detect the desired signal. This traditional approach is obviously unattractive due to the cost, efficiency, and accuracy. Instead, we propose a universal receiver, which is software-driven and re-configurable, to intercept signals of interest. The software-defined-radio based receiver first intercepts RF energy of wide spectrum (25MHz) through antenna, performs zero-IF down conversion (homodyne architecture) to baseband, and digital channelizes the baseband signal. The channelization module is a bank of high performance digital filters. The bandwidth of the filter bank is programmable according to the wireless communication protocol under watch. In the baseband processing, high-performance digital signal processors carry out the detection process and microprocessors handle the communication protocols. The baseband processing is also re-configurable for different wireless standards and protocol. The advantages of the software-defined-radio architecture over traditional RF receiver make it a favorable technology for the communication signal interception and surveillance.
Severe environmental loads acting upon civil engineering structures can provide a significant hazard. Structural control, first formalized by Yao [10], is one tool that engineers today can use, especially in the retrofit of older existing structures that have been found to be deficient. Few active control strategies, however, can deal adequately with a lack of exact knowledge of system parameter values or nonlinear behavior. One strategy that appears to be effective is fuzzy logic control. Imprecise linguistic descriptions of system conditions (e.g., the velocity is slightly negative and the displacement is somewhat positive, so apply a small force in the negative direction) can be used as the basis for activating control forces through the mathematical rules created by Zadeh [11]. In this paper, we discuss some aspects of the application of fuzzy control to civil engineering problems and we present results from the control of linear, two-degree-of- freedom systems that are subjected to simulated seismic excitation.
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