Efficient interleaving technique for OFDM system over impulsive noise channels

A weighted fractional Fourier transform (WFRFT) scheme is proposed for the orthogonal frequency division multiplexing (OFDM) system to combat impulsive noise (IN) in substation communications. According to the central limit theorem, the analytic expression of the real-valued IN probability density function (PDF) after WFRFT is derived and for ease of calculation, the closed form expression of the approximate PDF is also put forward. The PDF of IN shows that WFRFT makes IN more concentrated to the small amplitudes in the fractional Fourier transform domain than in the frequency domain at the receiver. As a result, the WFRFT scheme achieves a better bit error rate (BER) performance than the conventional OFDM system. In addition, the proposed scheme is also compatible with other existing IN mitigation techniques, such as dynamic peak-based threshold estimation-lookup table (DPTE-LUT) blanking. Simulation results have verified that the derived analytic and closed form PDF expressions of IN after WFRFT and the advantage of the proposed scheme over the counterpart OFDM system in the IN channels at high SNR with and without the DPTE-LUT blanking.

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.

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.

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.

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.

Broadband communications for indoor power-line networks with impulsive noise using orthogonal frequency division multiplexing (OFDM) is considered. From earlier investigations, it is known that this channel suffers from multipath fading and frequency selectivity along with man-made impulsive bursty noise. Nevertheless, the calculated channel capacity limit promises very high data rates over this channel. Enhancement techniques, such as coding can help an OFDM system to tackle impulsive noise burst. In this paper, the bit error rate (BER) performance of the OFDM system under impulsive noise and frequency fading is theoretically analyzed and closed form expression for the performance is derived. Two different impulsive noise environment models are studied and it is confirmed that both models represent the same environment. Furthermore, a theoretical upper bound on the performance of coded OFDM system is obtained, given perfect interleaving. The effect of the interleaver length on coding performance is also studied. Simulations show that the upper bound is quite tight for the case of employing a longer interleaver. The effect of interleaver size on the system performance is studied, as well

In this paper, we consider out-of-band radiations caused by high sidelobes in orthogonal frequency division multiplexing (OFDM) system. Suppression of sidelobes in OFDM system allows higher spectral efficiency and less interference with existing legacy systems in OFDM based overlay system. We combine different sidelobe suppression techniques to suppress the sidelobes in OFDM system. The multiple-choice sequence (MCS) is combined with cancellation carriers (CCs) and also MCS is combined with subcarrier weighting (SW) technique. MCS is applied prior to CCs or SW techniques. Simulation results show that combining MCS with CCs and MCS with SW techniques the sidelobes in OFDM system can be significantly reduced, which allow a successful co-existance between OFDM overlay system and an existing legacy system.

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) systems suffer from high sidelobes level. In some applications, as cognitive radios, this phenomenon can be a serious matter. This paper proposes Minimum shift keying (MSK)-OFDM to address this problem. The proposed method is an OFDM system using MSK modulation in each subcarrier. The corresponding transmitter and receiver are introduced. The method doesn't entail great changes in the main parts of OFDM. Like OFDM systems, the transceiver can be implemented using DFT/IDFT. Simulation results show great reduction in out of band radiation in comparison with conventional OFDM.

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.

Based on superposition of signals in the time domain, we propose a new low-complexity scheme for the reduction of the peak-to-average power ratio (PAPR) in orthogonal frequency division multiplexing (OFDM) systems. The proposed scheme first generates signal candidates by combining an OFDM signal and its cyclically delayed versions with different delays and phases, and then selects the candidate signal with minimum PAPR. It is shown that the complexity of the proposed scheme is significantly lower than that of the selective mapping (SLM) at the cost of some degradation in the bit error rate (BER) performance and, at similar PAPR and coded BER performance, is lower than that of the low-complexity SLM proposed recently.

Tone Reservation (TR) is a method used to reduce the Peak to Average Power Ratio (PAPR) in Orthogonal Frequency Division Multiplexing (OFDM) systems. In this paper, we assess the importance of considering an improved model of the power amplifier (PA) to accurately evaluate the performance of TR method based on Conjugate-Gradient algorithm. Simulation results were carried out in the context of WLAN IEEE 802.11a standard in presence of two memoryless models and nonlinear polynomial model with memory. These models are obtained by an experimental based method, including measurements and parameters identification with a 2.4 GHz class AB PA from RF Micro Devices. The evaluation results as well as the experimental comparison show that TR method considerably improves the transmission quality, in terms of Bit Error Rate (BER) and Error Vector Magnitude (EVM). These results highlight the importance of considering memory effects in PA modelling.

In visible light communications (VLCs), adaptive Orthogonal Frequency Division Multiplexing (OFDM) systems can adjust the transmission parameters according to channel estimation results to improve the system performance. Filtered-OFDM (F-OFDM) is a new flexible and adaptive technology based on OFDM systems and can further improve the system performance. In F-OFDM scheme, the out-of-band emission of OFDM signal is greatly inhibited by using the filter and the guard interval of the two subbands is reduced to save the spectrum resources. In this paper, we creatively apply the F-OFDM technology to visible light OFDM systems and derive the specific signal expression. Simulation results show that as the number of quadrature amplitude modulation (QAM) increases, the bit error rate (BER) performance of the F-OFDM system gets worse. Compared with asymmetrically clipped optical OFDM (ACO-OFDM) and direct current biased OFDM (DCO-OFDM) in VLCs, F-OFDM has better BER performance in 4QAM, 16QAM, and 64QAM schemes.

In this paper, a novel scheme of the weighted distortion-to-signal ratio (WDSR) based partial transmit sequence (PTS) is proposed to enhance the bit error rate (BER) performance in nonlinear distorted orthogonal frequency-division multiplexing (OFDM) systems, and its key idea is to employ the WDSR metric to predict the nonlinear distortion caused by high power amplifier (HPA). Furthermore, several alternative signals can be generated by the PTS technique, and the signal with the minimum WDSR is selected as the transmitted OFDM signal. Since the WDSR metric predicts the nonlinear distortion of OFDM systems, the BER performance of nonlinear distorted OFDM systems can be significantly improved. Simulation results show that the proposed WDSR-PTS scheme offers better BER performance than the conventional peak-to-average power ratio (PAPR) based PTS scheme.