An Improved DFT Channel Estimation Algorithm

Multi carrier modulation is Orthogonal Frequency Division Multiplexing (OFDM), dividing the large band spectrum into small (narrow) band spectrum.OFDM offers flexibility in adaptation to time varying channel condition by adopting the parameters at each subcarrier accurately.Due to the multipath effect the OFDM system suffers Inter Symbol Interference (ISI).ISI can be reduced by introducing the guard band (cyclic prefix).Time-varying channel estimation is an important activity in next generation wireless communication.Channel estimation is required mainly for the significant signal processing operation in multiple input multiple output MIMO-OFDM systems.In this project DFT -based channel estimation based on block type arrangement is implemented in MAT Lab.The bit error rate (BER) of DFT (Discrete Fourier Transform)based channel estimation is less than the BER of LS (Least Square) and MMSE (Minimum Mean Square Error) based channel estimation with same signal to noise ratio (SNR).

Orthogonal frequency division multiplexing (OFDM) is adopted in most wireless communication systems, and the performance of OFDM is affected by impulse noise (IN). Better channel estimation (CE) performance is required to detect the channel information on the receiving side. The OFDM system is considered with the number of subcarriers carrying the data and pilot symbols. In the OFDM modulator, the symbols of the frequency domain are transformed into the signals of the time domain using inverse discrete Fourier transformation (IDFT). Effective impulsive noise mitigation is crucial for improving the effectiveness of OFDM communication systems, and it improves the signal-to-noise ratio (SNR) at the receiver. A cyclic prefix is then appended before transmission through the channel. In the receiver noise, the effect of IN is mitigated jointly with CE using the Bayesian matching pursuit (BMP) and Moth-flame algorithm (MFA). In this approach, the IN and channel information is considered as a sparse vector. Here, the data symbols used are considered an unknown parameter. The approach incorporating all subcarriers has a lower mean square error (MSE) of IN estimate for impulsive noise reduction. The MFA algorithm is used to optimize the sensor matrix in BMP. The sparsity of the channel and the impulse response are observed in the time domain to represent the channel and IN together. It exactly recovers the sparse signal for finding the convex objectives of the sparse minimizer, and the sparse solution is obtained with fixed point updates. The proposed BMP algorithm improves the CE by explicitly considering the existence of IN. The BMP is a greedy algorithm that selects the most correlated residuals at each column. Under mutual incoherence, it recovers the signal with a higher probability. The simulated outcomes proved that the proposed CE and noise mitigation model achieved better performance based on the bit error rate (BER), throughput and MSE.

Filter bank multicarrier with offset quadrature amplitude modulation (FBMC-OQAM) system has low out-of-band emission but needs complex receiver for broadband channel. To address this problem, we propose a new cyclic prefix (CP)-based code FBMC-OQAM system (CC-FBMC-OQAM) with low complexity in this paper. CC-FBMC-OQAM system can be realized within the framework of the standard OFDM system, and perfect recovery (PR) condition is derived in the ideal channel. In order to reduce compute complexity, a low complexity transform of the Fast Walsh-Hadamard and Fourier transform (FWFT) is adopted and it uses a fast orthonormal unitary transform to calculate both the discrete Fourier transform (DFT) and the Walsh-Hadamard transform (WHT). Theoretical analysis and simulation results show that, compared to the C-FBMC-OQAM system and orthogonal frequency division multiplexing (OFDM) system, the computational complexity of proposed CC-FBMC-OQAM system is reduced substantially with almost same bit error rate (BER) performance in doubly-flat channel. Moreover, the BER performance of proposed CC-FBMC-OQAM system slightly outperform conventional C-FBMC-OQAM system in doubly-selective channel.

In this paper, an integrated Orthogonal Frequency Division Multiplexing (OFDM) system is developed to improve Bit Error Rate (BER) performance of communication systems in order to meet the requirements of advanced communication systems like long term evaluation advanced (LTE –A). The proposed OFDM system consists of channel estimation using comb type pilot arrangement and convolution encoder with the best known Coding Bounds and Maximum A Posteriori (MAP) decoder. Using pilot symbols, the channel quality is estimated. The BER performance of OFDM system is improved using pilot carriers, channel estimation schemes and MAP decoder at the best known coding bounds. The system performance is analyzed with recursive systematic and non-systematic convolution codes, ML and MAP decoders. From the results, it is evident that the proposed OFDM system with channel estimation and MAP decoder at the best known coding bounds improves the system performance significantly.

Conventional orthogonal frequency division multiplexing (OFDM) systems use discrete Fourier transform (DFT) as the basis function. Recently, it was shown that it is possible to use other sinusoidal transforms, e.g. discrete cosine transform (DCT), as OFDM basis functions. However, relative little is known regarding the performance of these alternative basis functions and how they compare with traditional DFT. This paper investigates the performance of OFDM modems employing alternative basis functions under different fading channel models in both double sideband and single sideband operation modes. A semi-analytical approach is also developed to predict and compare the error performance between different basis functions. The predicted results are close to the simulations thus verifying the simulation model. It was found that in general DFT has a better error performance, but interspersed basis is capable of offering a higher net throughout under certain channel conditions.

Cyclic Prefix (CP) based block Recursive Least Squares (RLS) channel estimation algorithms have been proposed for Orthogonal Frequency Division Multiplexing (OFDM) systems. In this paper, we investigate the performance of CP based exponentially weighted block RLS channel estimator. Our analysis and extensive simulation results show that smaller values of exponential forgetting weightings cause increase in convergence time and steady state performance error of the algorithm. Furthermore, performance of the approach degrades with the increase in channel nulls and constellation size.

Conventional orthogonal frequency division multiplexing (OFDM) system utilizes cyclic prefix (CP) to remove the channel-induced inter-symbol interference (ISI) at the cost of lower spectral efficiency. In this paper, a generalized sidelobe canceller (GSC) based equalizer for ISI suppression is proposed for uplink multi-antenna OFDM systems without CP. Based on the block representation of the CP-free OFDM system, there is a natural formulation of the ISI suppression problem under the GSC framework. By further exploiting the signal and ISI signature matrix structures, a computationally efficient partially adaptive (PA) implementation of the GSC-based equalizer is proposed for complexity reduction. The proposed scheme can be extended for the design of a pre-equalizer, which pre-suppresses the ISI and realizes CP-free downlink transmission to ease the computational burden of the mobile unit (MU). Simulation results show that the proposed GSC-based solutions yield equalization performances almost identical to that obtained by the conventional CP-based OFDM systems and are highly resistant to the increase in channel delay spread.

The nonlinearity of high power amplifiers (HPAs) exhibits amplitude and phase distortions, which cause loss of orthogonality among the subcarriers in orthogonal frequency division multiplexing (OFDM) systems, and hence, inter-carrier interference (ICI) is introduced in the transmitted signal. The ICI power is proportional to the amplitude of the signal at the amplifier input and it may cause a considerable bit error rate (BER) degradation. Due to the ICI is a random process and has unknown distribution function, it is difficult to evaluate the theoretical BER when the ICI is taken into account. This paper evaluates the BER analytically using sequence development approach (SDA) for OFDM systems perturbed by the HPA. In comparison to the state-of-the-art technique, the evaluation of the BER using this approach achieves superior approximation at the expense of additional computational complexity.

ABSTRACTWhile inter-symbol interference is not of concern, inter-carrier interference that is caused by carrier frequency offset (CFO) is more concerned in orthogonal frequency division multiplexing (OFDM) systems. The estimation of channel impulse response (CIR) is another important parameter of interest in the system. Recently, a number of approaches for the joint estimation of CFO and CIR in OFDM systems have been proposed in the literature, and most of them are traditional maximum-likelihood-based approaches. In this paper, we propose a number of mixture cost-reference particle filtering (CRPF) approaches for joint estimation of CIR and CFO, and a couple of them can be applied without the knowledge of both state and measurement noise statistics. Conventional least mean squares algorithm or recursive least squares algorithm is jointly employed with recently developed CRPF for nonlinear and multiple parameters estimation in OFDM systems. The computer simulation results show that mixture CRPFs are more robust against particle impoverishment (PI) problem than standard mixture particle filtering (PF) and mixture regularized PF (RPF) approaches although RPF was particularly developed to tackle the PI problem. In this paper, we investigate a number of mixture PF approaches including ones that do not need the information of noise statistics for the joint estimation of CFO and channel in OFDM systems.

Orthogonal frequency division multiplexing (OFDM) system has been widely used for the high speed digital communication area and it is very promising for the next generation communication standard because of high data rate capability. However, OFDM system has inherent serious problem of high peak-to-average power ratio (PAPR) that makes the OFDM signal be distorted in the nonlinear HPA (high power amplifier). In this paper, CI (carrier interferometry)-OFDM system is considered to overcome this problem and is newly analyzed in the selective fading and narrow-band interference channel. CI-OFDM system distributes each parallel data to all sub-carriers in differently phase-rotated form. So, PAPR becomes lowered and it shows the frequency diversity effects. BER (bit error rate) performance is analyzed in the selective fading and narrow-band interference environment. From the simulation results, it is confirmed that CI-OFDM system calms down the high PAPR problem and CI-OFDM system is more robust than the ordinary OFDM system in the selective fading and narrow-band interference channel.

Frequency offset (FO) introduces severe inter-symbol and inter-carrier interferences which will degrade the performances of orthogonal frequency division multiplexing (OFDM) system more adversely. To reduce the effect of CFO, an estimation algorithm has been proposed in this work which uses a turbo coding at the precoding section and Space time block coding techniques (alamouti code) for transmitting data. The turbo codes solve dilemma of structure and randomness through concatenation and interleaving and it will reduce bit error rate (BER) by error detection and error correction process. A fading channel has been modeled for evaluating the performance of the algorithm. Maximum likelihood (ML) estimation is used for the estimation that does take conditional probability into account. The offset estimation in OFDM is done by best linear unbiased estimator (BLUE) principle yet it has disadvantages that it is already sub optimal in nature and it is applicable only for linear observation models. So, ML technique is an alternative estimation criterion that can use as starting point of most of the statistical estimation and for nonlinear observations. The proposed system has improved BER while other methods supports BER of 25-30 dB and the proposed system shows improvement in spectral efficiency as well as the Power spectral density.

This paper presents the performance analysis of orthogonal frequency division multiplexing (OFDM) system using a mixed-scheduling belief propagation (MBP) algorithm for LDPC decoding where a double fading channels is considered. The MBP method is designed based on the LBP algorithm for the left-to-right direction (LBP-LR) and right-to-left direction (LBP-RL). Additionally, the bit error rate (BER) performance comparison of the BP, LBP, and MBP algorithms for LDPC decoding is proposed. The simulation results showed that the bit error rate (BER) performance of the MBP gave better BER than the BP and LBP algorithms, respectively.

In this paper, orthogonal frequency division multiplexing (OFDM) systems with coherent, incoherent and quasi-coherent demodulation schemes will be considered respectively. Resulting system performance figures will be compared in terms of bit error rate (BER) and hardware complexity. It is well known that non-differential modulation and coherent demodulation techniques have optimum BER performance but lead to a significantly increased system overhead due to pilot signals and system complexity due to channel estimation procedure. This paper describes differential modulation schemes, which do not require any radio channel estimation, and two related incoherent and quasi-coherent demodulation techniques. The resulting BER performance is nearly identical compared with coherent demodulation, but the computation complexity is drastically reduced. A field programmable gate array (FPGA) based experimental system has been developed, which is used for BER performance measurements and system complexity considerations

In this work, an efficient interleaving process is proposed for orthogonal frequency division multiplexing (OFDM) systems over impulsive noise channels. Unlike the conventional OFDM systems where the interleaving process is implemented before the inverse discrete Fourier transform (IDFT), the proposed scheme is based on performing the interleaving process post the IDFT. The aim of this process is to average the effect of the impulsive noise burst over a large number of OFDM symbols, which can reduce its impact on the bit error rate (BER) significantly. For the system and channel models considered in the work, simulation results have confirmed that the proposed system can effectively reduce the BER degradation due to the impulsive noise to about 1 dB as compared to the impulsive noise-free case.

This paper deals with channel estimation for orthogonal frequency-division multiplexing (OFDM) systems with transmit diversity. Space time coded OFDM systems, which can provide transmit diversity, require perfect channel estimation to improve communication quality. In actual OFDM systems, training sequences are usually used for channel estimation. The authors propose a training based channel estimation strategy suitable for space time coded OFDM systems. This novel strategy provides enhanced performance, high spectrum efficiency and relatively low computation complexity.