SINR maximizing equalizer design for OFDM systems (original) (raw)
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Equalization for OFDM over doubly selective channels
IEEE Transactions on Signal Processing, 2000
In this paper, we propose a time-domain as well as a frequency-domain per-tone equalization for orthogonal frequency-division multiplexing (OFDM) over doubly selective channels. We consider the most general case, where the channel delay spread is larger than the cyclic prefix (CP), which results in interblock interference (IBI). IBI in conjunction with the Doppler effect destroys the orthogonality between subcarriers and, hence, results in severe intercarrier interference (ICI). In this paper, we propose a time-varying finite-impulse-response (TV-FIR) time-domain equalizer (TEQ) to restore the orthogonality between subcarriers, and hence to eliminate ICI/IBI. Due to the fact that the TEQ optimizes the performance over all subcarriers in a joint fashion, it has a poor performance. An optimal frequency-domain per-tone equalizer (PTEQ) is then obtained by transferring the TEQ operation to the frequency domain. Through computer simulations, we demonstrate the performance of the proposed equalization techniques. Index Terms-Basis expansion model (BEM), doubly selective channels, orthogonal frequency-division multiplexing (OFDM), per-tone equalization (PTEQ), time-domain equalization (TEQ).
Performance evaluation of various Channel Equalization Techniques in terms of BER for OFDM System
International Journal of Wireless and Mobile Communication for Industrial Systems, 2016
Orthogonal frequency division multiplexing is a type of multi-carrier transmission where all the subcarriers are orthogonal to each other. There is always a need for higher data rate and for this OFDM technique is used. At high data rates, the channel distortion to the data is very important and it is impossible to recover the transmitted data with a simple receiver. So, a complex receiver structure is needed which uses computationally expensive equalization and channel estimation algorithms to estimate the channel. These estimations can be used within the received data to recover the originally transmitted data. OFDM can simplify the equalization problem by changing the frequency-selective channel into a flat channel. The intersymbol interference (ISI) can occur in received signal due to multipath fading. In order to remove the ISI many kind of equalizers can be used. Equalizer is intend to work in such a way that Bit Error Rate (BER) should be low and Signal-to-Noise Ratio (SNR) should be high. An equalizer within a receiver compensates for the average range of expected channel amplitude and delay characteristics. This paper deals with the various equalization techniques (LMS, RLS and CMA) used for OFDM system. A comparative analysis of Bit error rate (BER) using different equalization technique along with different digital modulation is done using MATLAB Simulink. Simulation results shows that constant modulus algorithm (CMA) results in minimum value of BER which can be further used to enhance the performance of OFDM.
Joint Equalization and Interference Suppression in OFDM Systems
The paper deals with the joint equalization and narrowband interference (NBI) suppression in orthogonal frequency-division multiplexing (OFDM) systems. Since the conventional zero-forcing (ZF) receiver does not operate satisfactorily in interference-limited environments, we investigate the potential of the MMSE receiver, evaluating the advantage gained by exploiting the redundancy contained in the cyclic prefix (CP).
Indonesian Journal of Electrical Engineering and Computer Science
The nature of future wireless applications requires high data rates and for this OFDM technique is used. OFDM stands for orthogonal frequency division multiplexing and is a type of multi-carrier transmission where all the subcarriers are orthogonal to each other. At high data rates, the channel distortion to the data is very important and it is somewhat impossible to recover the transmitted data with a simple receiver. So a complex receiver structure is needed which uses computationally expensive equalization and channel estimation algorithms to estimate the channel. These estimations can be used within the received data to recover the originally transmitted data. OFDM can simplify the equalization problem by changing the frequency-selective channel into a flat channel. The radio channels in mobile radio systems are usually multipath fading channels that results in intersymbol interference (ISI) in the received signal. To remove ISI from the signal, many kind of equalizers can be used. The need for equalizers arises from the fact that the channel has amplitude and phase dispersion which results in the interference of the transmitted signals with one another which is known as ISI .So, to solve this problem equalizers are designed. Equalizer is intend to work in such a way that Bit Error Rate (BER) should be low and Signal-to-Noise Ratio (SNR) should be high. An equalizer within a receiver compensates for the average range of expected channel amplitude and delay characteristics. This paper deals with the various equalization techniques (LMS, RLS and CMA) used for OFDM system .A comparative analysis of different equalization technique in terms of BER is done using MATLAB Simulink.
Time-domain and frequency-domain per-tone equalization for OFDM over doubly selective channels
Signal Processing, 2004
In this paper, we propose new time-and frequency-domain per-tone equalization techniques for orthogonal frequency division multiplexing (OFDM) transmission over time-and frequency-selective channels. We present one mixed time-and frequency-domain equalizer (MTFEQ) and one frequency-domain per-tone equalizer. The MTFEQ consists of a one-tap time-varying (TV) time-domain equalizer (TEQ), which converts the doubly selective channel into a purely frequency-selective channel, followed by a one-tap frequency-domain equalizer (FEQ), which then equalizes the resulting frequency-selective channel in the frequency-domain. The frequency-domain per-tone equalizer (PTEQ) is then obtained by transferring the TEQ operation to the frequency-domain. While the one-tap TEQ of the MTFEQ optimizes the performance on all subcarriers in a joint fashion, the PTEQ optimizes the performance on each subcarrier separately. This results into a significant performance improvement of the PTEQ over the MTFEQ, at the cost of a slight increase in complexity. Through computer simulations we show that the MTFEQ suffers from an early and high error floor, while the PTEQ outperforms the MMSE equalizer for OFDM over purely frequency-selective channels, it
Joint equalisation and interference suppression in OFDM systems
Electronics Letters, 2003
We consider the problem of joint equalization and narrowband interference (NBI) suppression in orthogonal frequency-division multiplexing (OFDM) systems. Since the conventional zero-forcing (ZF) receiver does not operate satisfactorily in severe interference enviroments, we investigate the potential of the minimum mean square error (MMSE) receiver evaluating the advantage that can be achieved by exploiting the redundancy contained in the cyclic prefix (CP) of the OFDM signal.
Design of Time Domain Equalizers Incorporating Radio Frequency Interference Suppression
APCCAS 2006 - 2006 IEEE Asia Pacific Conference on Circuits and Systems, 2006
It is known that radio frequency interference (RFI) degrades the performance of DMT systems for digital subscriber loops. The RFI signal, though narrow band in nature, may be spread to subchannels around the RFI frequencies due to the large sidelobes of the receiving rectangular window. In this thesis, we propose a joint consideration of channel shortening and RFI suppression in the design of time domain equalizers (TEQ). We will design the TEQ by minimizing ISI, channel noise and RFI interference. Simulation results are given to show that the proposed method can considerably reduce interference around the RFI frequencies and increase the transmission rate.
Performance analysis of banded equalizers for OFDM systems in time-varying channels
2007 IEEE 8th Workshop on Signal Processing Advances in Wireless Communications, 2007
OFDM systems affected by severe time-varying channels greatly benefit from equalization schemes based on intercarrier interference (ICI) mitigation, which guarantee improved performance with respect to conventional one-tap equalizers. By exploiting a semianalytical approach, this paper assesses the BER performance of the so-called banded equalizers, i.e., those equalizers that take into account only the ICI produced by the closest subcarriers. Specifically, by exploiting the Gaussian approximation of the residual ICI at the equalizer output, we evaluate the BER of block linear equalizers designed under a minimum mean-squared error (MMSE) criterion. Simulation results show a very good agreement with the theoretical analysis. In addition, we derive a lower bound and an approximate upper bound for the BER of block decision-feedback equalizers.
Time domain equalization method for DFTS-OFDM signal without GI under high mobile environments
2015 12th International Conference on Electrical Engineering/Electronics, Computer, Telecommunications and Information Technology (ECTI-CON), 2015
In highly time-varying fading channel, the Discrete Fourier Transform Spreading Orthogonal Frequency Division Multiplexing (DFTS-OFDM) signal would be damaged significantly by the inter-channel interference (ICI) due to the loss of orthogonality among subcarriers which leads a fatal degradation of bit error rate (BER) performance. To solve this problem, this paper proposes a time domain equalization (TDE) technique in conjunction with a time domain channel impulse response (CIR) estimation method for the DFTS-OFDM signal without using a guard interval (GI). The features of proposed method is to employ a time domain training sequence (TS) both for the estimation of time domain CIR at every sampling time and for removing the inter-symbol interference (ISI) incurred in the multipath fading channel. The proposed method also employs the TDE with a maximum likelihood (ML) estimation method in the demodulation of received time domain signal at every symbol instead of using the conventional Minimum Mean Square Error-Frequency Domain Equalization (MMSE-FDE) method. This paper presents various simulation results to demonstrate the effectiveness of proposed demodulation method for the DFTS-OFDM signal without GI as comparing with the conventional MMSE-FDE and TDE methods both of using GI under highly mobile environments.