This paper presents a newinterleaving scheme for efficient data transmission with Orthogonal Frequency Division Multiplexing (OFDM) over fading channels. This approach is based on the chaotic Baker map. The binary data is interleaved with the proposed approach prior to the modulation step. In addition to improve the system performance in fading channel, the proposed chaotic interleaving approach adds a degree of encryption to the transmitted data. The performance of the proposed approach is tested on the conventional Fast Fourier Transform OFDM (FFT-OFDM), Discrete Wavelet Transform OFDM (DWT-OFDM), and Discrete Cosine Transform OFDM (DCT-OFDM) with and without chaotic interleaving. Expectation-Maximization (EM) algorithm is also proposed to efficiently estimate the channel impulse response (CIR) of such a system operating on a channel with multipath fading. Starting from the Maximum Likelihood (ML) principle, we derive an iterative estimation algorithm based on the (EM) algorithm. This algorithm is capable of improving the channel estimate. In the initialization phase of this iterative algorithm, the initial channel estimate is based on the observation of the pilot carriers only. Then the EM algorithm updates the channel estimates until convergence is reached, the resulting bit error rate essentially coincides with the case of the perfectly known channel. By simulations, the efficiency of these algorithms can be investigated with simulation and the results of estimation will come to a comparison.
OFDM (orthogonal Frequency Division Multiplexing) is a basic element in the 4G mobile system. The OFDM performance can be improved using the channel coding. The channel coding is a class of signal transformations designed to improve communication system performance.The work presented in this paper discusses the performance improvement of OFDM communication system using different channel coding techniques through AWGN channel model. These coding techniques include Reed Solomon coding, Convolutional coding, Concatenated coding (by combining Reed Solomon with Convolutional), and Interleaved concatenated coding techniques. Besides, a new algorithm produced to choose a good convolutional encoder design for a certain rate and memory registers.
In this paper, design, simulation and implementation of Asymmetric Digital Subscriber Line (ADSL) modem is presented which can be applied to different telephone networks. Lhe ADSL modem is modeled and simulated under the MATLAB version 7.3 (R2006b) environments by which the simulation is achieved for both the downstream and upstream directions of the modem. The ADSL modem with a transmission throughput between 640 kbps and 6 Mbps operating over most of existing telephone subscriber loops has been implemented on TI TMS320C6713 DSP for consumer multimedia applications. Except the Analog Front End, all the basic building blocks of the ADSL modem functionalities are implemented with DSP platform. We use Real-Time Data Exchange (RTDX) as a way to debug and test our DSP designs.
This paper presents a new interleaving scheme for efficient data transmission with Orthogonal Frequency Division Multiplexing (OFDM) over fading channels. This approach is based on the chaotic Baker map. The binary data is interleaved with the proposed approach prior to the modulation step. In addition to reducing the channel effects on the transmitted data, the proposed chaotic interleaving approach adds a degree of encryption to the transmitted data. The performance of the proposed approach is tested on the Discrete Wavelet Transform OFDM (DWT-OFDM) and the conventional Fast Fourier Transform OFDM (FFT-OFDM) with and without chaotic interleaving. The proposed system comprises Frequency-Domain Equalization (FDE) to obtain high diversity gains over frequency selective multi-path fading channels. The simulation results show that the DWT-OFDM system implementing the new interleaving scheme provides better Bit Error Rate (BER) performance than the FFT-OFDM system.
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