LMS-based Equalization in Filter Bank Multicarrier Wireless Communication Systems (original) (raw)
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LMS-based Equalization in Filter Bank Multicarrier Wireless Communication Systems Mashhoor
systems give many attractive characteristics for high data rates wireless communications. Filter bank multicarrier systems (FBMC) provide some advantages more than the traditional orthogonal frequency division multiplexing (OFDM) with cyclic prefix (CP). The most obvious difference between the two techniques is in frequency selectivity. In this paper, we will design adaptive channel equalization algorithms for FBMC system with offset QAM modulation(OQAM). Our proposed algorithms will be optimized based on well-known cost functions, which is the mean-squared error (MSE) criterion and it is based on least-mean-square (LMS) algorithm. Thus we will have an adaptive equalizer with lower complexity because of applying the equalizer to each sub-carrier. We have used in our simulation practical channel information based on the International Telecommunications Union ITU Standards. In this paper, we aim to optimize and evaluate the convergence characteristic curves of LMS equalization algorithm per-subcarrier.
ADAPTIVE CHANNEL EQUALIZATION FOR FBMC BASED ON VARIABLE LENGTH STEP SIZE AND MEAN-SQUARED ERROR
Recently, increasing data transmission rates and the demand of more bandwidth at the same time have been a challenge. The trend now is to support high data rates in wireless communications. Multicarrier systems have overcome many challenges of high bandwidth efficiency and at the same time provided also high spectral efficiency. Filter bank multicarrier systems (FBMC) provide some advantages more than the traditional orthogonal frequency division multiplexing (OFDM) with cyclic prefix (CP). FBMC systems provide a much better spectral shaping of the subcarriers than orthogonal frequency division multiplexing (OFDM). Therefore, the most obvious difference between the two techniques is in frequency selectivity. In this paper, we will present a least-meansquare (LMS) algorithm which is based on well-known cost functions, which is the mean-squared error (MSE) adapted for FBMC system with offset QAM modulation (OQAM). This leads to a per-subchannel adaptive equalizer solution with low complexity. The proposed simulations have used practical channel information based on the International Telecommunications Union (ITU) Standards. Moreover, we will discuss how the proposed algorithm will optimize and evaluate the convergence characteristic curves of LMS equalization algorithm per-subcarrier.
Channel Equalization in Filter Bank Based Multicarrier Modulation for Wireless Communications
EURASIP Journal on Advances in Signal Processing, 2007
Channel equalization in filter bank based multicarrier (FBMC) modulation is addressed. We utilize an efficient oversampled filter bank concept with 2x-oversampled subcarrier signals that can be equalized independently of each other. Due to Nyquist pulse shaping, consecutive symbol waveforms overlap in time, which calls for special means for equalization. Two alternative linear low-complexity subcarrier equalizer structures are developed together with straightforward channel estimation-based methods to calculate the equalizer coefficients using pointwise equalization within each subband (in a frequency-sampled manner). A novel structure, consisting of a linear-phase FIR amplitude equalizer and an allpass filter as phase equalizer, is found to provide enhanced robustness to timing estimation errors. This allows the receiver to be operated without time synchronization before the filter bank. The coded error-rate performance of FBMC with the studied equalization scheme is compared to a cyclic prefix OFDM reference in wireless mobile channel conditions, taking into account issues like spectral regrowth with practical nonlinear transmitters and sensitivity to frequency offsets. It is further emphasized that FBMC provides flexible means for high-quality frequency selective filtering in the receiver to suppress strong interfering spectral components within or close to the used frequency band.
Channel Equalization for Multi-Antenna FBMC/OQAM Receivers
IEEE Transactions on Vehicular Technology, 2000
In this paper, the problem of channel equalization in filter bank multicarrier (FBMC) transmission based on the offset QAM (OQAM) subcarrier modulation is addressed. Finite impulse response (FIR) per-subchannel equalizers are derived, based on the frequency sampling (FS) approach, both for the single-input multiple-output (SIMO) receive diversity and the multiple-input multiple-output (MIMO) spatially-multiplexed FBMC/OQAM systems. The FS design consists of computing the equalizer in the frequency domain at a number of frequency points within a subchannel bandwidth, based on which the coefficients of subcarrier-wise equalizers are derived. We evaluate the error rate performance and computational complexity of the proposed scheme for the both antenna configurations and compare them with those of the SIMO/MIMO OFDM equalizers. The obtained results confirm the effectiveness of the proposed technique with channels that exhibit significant frequency selectivity at subchannel level, and show a performance comparable to that of the optimum minimum mean squared error (MMSE) equalizer despite a significantly lower computational complexity. The possibility of tolerating a significant subchannel frequency selectivity gives more freedom in the multicarrier system parametrization. For example, it is possible to use a significantly wider subcarrier spacing than what is feasible in OFDM, thus relieving various critical design constraints.
ADAPTIVE CHANNEL EQUALIZER FOR WIRELESS COMMUNICATION SYSTEMS
The Data rates and spectrum efficiency of Wireless Mobile Communication have been significantly improved over the last decade or so. Recently, the advanced systems such as 3GPP LTE and terrestrial digital TV broadcasting have been sophisticatedly developed using OFDM and CDMA technology. In general, most mobile communication systems transmit bits of information in the radio space to receiver. The radio channels in mobile radio systems are usually multipath fading channels, which cause inter symbol interference (ISI) in the received signal. To remove ISI from the signal there is a need of strong equalizer which required the knowledge on the channel impulse response. (LMS) Least Mean Square, (RLS) Recursive Least squares and (PSO) Particle swarm optimization algorithms are used to implement the adaptive channel equalizer. The results are measured in terms of mean square error (MSE) and bit error rate (BER) Vs the number of iterations.
Convergence Analysis of Blind Equalizer in a Filter-Bank-Based Multicarrier Communication System
IEEE Transactions on Signal Processing, 2000
A recent development in the literature has proposed a cosine-modulated filter-bank-based multicarrier modulation (CMFB-MCM) system with blind equalization capability. However, convergence studies of the proposed blind equalizer have been carried out through computer simulations only. In this correspondence, we present a study of the blind equalizer by analyzing its associated cost function thoroughly. We show that the blind equalizer cost function is characterized by two global minima and two saddle points. We note that the presence of saddle points may result in occasional slow convergence of the adaptation algorithm and present a modified algorithm that avoids this problem.
Efficient Per-Carrier Channel Equalizer for Filter Bank Based Multicarrier Systems
—Filter bank-based multicarrier (FBMC) systems have a number of advantages over the OFDM modulation method. However, efficient channel equalization techniques for FBMC systems are not mature yet. In this paper a complex critically sampled filter bank, based on cosine-and sine-modulated filter banks, is used as a transmultiplexer and a low complexity equalizer called AP-ASCET is used to compensate the channel distortion. The use of oversampled receiver filter bank makes it possible to equalize successfully each subchannel independently of the others. Furthermore, the subchannel amplitude and phase responses are equalized independently using low-order linear-phase FIR and allpass IIR filter sections, respectively. The system performance is studied using the ITU-R Vehicular A channel model.
Comparison of LMS and FDAF Algorithms in Equalization of Fading Channel
International Journal of Engineering and Technology, 2011
Wireless link in mobile cellular communication system is experienced by large and small scale fading. Since the link is Non Line of Sight (NLOS), therefore, severely affected by multipath fading. Adaptive equalizer is a widely used technique to neutralize the effect of multipath fading. In this paper, Frequency Domain Adaptive Filer (FDAF) and Least Mean Square (LMS) algorithms are used to combat the effect of multipath fading for 16-QAM and QPSK modulated wave and the results are shown using constellation diagram and bit error rate (BER). Finally, a comparison is made between two algorithms in contexts of process time, mean BER, variance of BER and circuit complexity. Index Terms-Mobile cellular communications, fading channel, channel equalization, adaptive equalizer.
2012
Orthogonal Frequency Division Multiplexing (OFDM) has recently been applied in wireless communication systems due to its high data rate transmission capability with high bandwidth efficiency and its robustness to multi-path delay. Fading is the one of the major aspect which is considered in the receiver. To cancel the effect of fading, channel estimation and equalization procedure must be done at the receiver before data demodulation. This paper mainly deals with pilot based channel estimation techniques for OFDM communication over frequency selective fading channels. This paper proposes a specific approach to channel equalization for Orthogonal Frequency Division Multiplex (OFDM) systems. Inserting an equalizer realized as an adaptive system before the FFT processing, the influence of variable delay and multi path could be mitigated in order to remove or reduce considerably the guard interval and to gain some spectral efficiency. The adaptive algorithm is based on adaptive filtering with averaging (AFA) for parameter update. Based on the development of a model of the OFDM system, through extensive computer simulations, we investigate the performance of the channel equalized system. The results show much higher convergence and adaptation rate compared to one of the most frequently used algorithms -Least Mean Squares (LMS)
Equalization in filter bank based multicarrier systems
1999
In this paper we consider filter bank based multicarrier systems, which provide better spectral shaping than DFT-based Orthogonal Frequency Division Multiplexing (OFDM) or Discrete MultiTone (DMT) systems for the subchannels, as well as for the overall signal. Due to their better performance in case of narrowband interference, such techniques have received attention especially in the context of Very high-speed Digital Subscriber Line (VDSL) system development. However, the channel equalization for such systems is still an open problem. In this paper, it is demonstrated that filter bank based multicarrier systems are very sensitive to the nonlinear phase response of the channel. Alternative ways to perform the channel equalization are discussed. Also measurement results from real subscriber lines are presented and, based on these results, a two-step equalization approach is proposed.