Intercarrier Interference Reduction Research Articles

Inter-Carrier Interference Reduction Technique for Backscattered OFDM

Inter-Carrier Interference Reduction Technique for Backscattered OFDM

Design of nonlinear phase prototype filter based on coefficients symmetry for UFMC communication system

One of the candidates for short burst communication is universal filtering multicarrier (UFMC), which applies filters in each sub-band to reduce intercarrier interference. Compared with the linear phase FIR filter (LPFF), prototyping a nonlinear phase FIR filter (NLPFF) as the UFMC filter can benefit system performance by improving the filter magnitude response. However, the benefit, namely the tradeoff between phase response and better magnitude, is limited in previous NLPFF designs. Aiming at this problem, this paper has done the following works. First, we propose a new measure called sum of symmetric coefficient differences (SSCD) to represent the phase deviation. Furthermore, we propose a constrained least squares design for NLPFF, where constraints are imposed on the SSCD and squared magnitude. The design can be effectively realized under the second-order cone programming (SOCP) framework. Due to the significantly reduced constraint size and enhanced performance tradeoff area, the proposed SOCP-SSCD approach is the most competitive in effectiveness and efficiency. We have demonstrated this advantage by comparing with previous NLPFF methods. Consequently, by applying this method to design NLPFF as a prototype filter in the UFMC system, we have achieved better power spectral density, symbol error rate (SER), and demodulated constellation than previous prototype filters. For the SER indicator, Fig. 6(a) indicates an SNR gain of 1.2dB@{SER=0.001} between the designed NLPFFs and the previous prototype filters.

Low Complexity Non-Uniform FFT for Doppler Compensation in OFDM-Based Underwater Acoustic Communication Systems

The Doppler effect critically degrades the performance of orthogonal frequency division multiplexing (OFDM) systems in general. This problem is significantly worse for underwater acoustic (UWA) communication systems due to the distinct characteristics of the underwater channel, resulting in the loss of orthogonality among sub-carriers. In order to compensate Doppler shifts, including phase noise and multipath channels in realistic communication scenarios, the joint of channel estimation and ICI reduction is often performed. However, the accuracy depends on the channel estimation and the FFT size, while this leads to increased computational complexity at the receiver. To achieve this dual goal in the actual underwater communication environment, a novel pilot structure in the frequency domain has been applied to overcome the channel impulse response (CIR) variation in a block period. The coarse Doppler shift is firstly estimated by using the received pilot signal. Afterward, the study takes advantage of the flexibility provided by non-uniform fast Fourier transform (NFFT) in choosing the sampling points to construct a fast and stable Doppler frequency Compensation Matrix-based NFFT (DCMN) to fine compensate the Doppler phase shift. Finally, this study shows the improvement of the proposed method’s performance by actual experimental measurements and simulations.

A Performance Analysis of Wavelet based LTE-OFDM with Multi-equalizers

A rapid change in usage of mobile data and mobile based applications such as online gaming, mobile TV etc. motivates the mobile wireless communication system to work on new emerging trends Long Term Evolution (LTE). LTE-4G architecture provides an optimized packet based radio access technology. The basic signal format of LTE is Orthogonal Frequency Division Multiplexing (OFDM) Modulation. This modulation scheme satisfies the spectrum flexibility requirement in LTE. LTE-MIMO-OFDM with IFFT and FFT transform introduced to provide the cost-effective solution for very wide carriers with high PAPR. Inter-symbol Interference (ISI) and inter carrier interference (ICI) are predominant factors which exist in the wireless communication channel. Existing methods of ISI and ICI reduction to improve signal quality have been achieved using conventional OFDM techniques. However, a better modulation scheme is required to achieve high data rate, low latency and flexible bandwidth deployment. This paper has proposed a Wavelet based LTE-MIMO-OFDM modulation scheme with multi equalizer that improves the performance of system by reducing PAPR and BER in MCM. Experimental results show the performance of this scheme and the results is compared with existing MMSE and Multi equalizer MMSE and achieves a flexible spectral efficiency with reduction of PAPR and BER.

Pulse shaping methods for inter carrier interference reduction in OFDM system

The weakness of the orthogonal freuency division multiplexing (OFDM) system is susceptible to the existence of carrier frequency offset (CFO) which causes the emergence of inter carrier interference (ICI) which causes a degradation of performance OFDM systems. This study aims to apply the suggested rectangular (REC) pulse and improved sinc-power (ISP) pulse shaping methods on OFDM system and determines ICI reduction with the effects of CFO over flat fading Rayleigh channels. The performance of each pulse shaping method is evaluated and compared based on parameter ICI power vs. normalized frequency offset, signal to interference ratio (SIR) vs. normalized frequency offset and bit error rate (BER) vs. energy bit per noise (Eb/No). The simulation result in terms of BER vs. Eb/No indicated that REC and ISP pulse shaping has better performance dealing with ICI reduction compared to OFDM system no applied pulse shaping. In addition, the ISP is able to mitigate ICI better than REC.

Brain nitric oxide induces facilitation of the micturition reflex through brain glutamatergic receptors in rats.

Brain nitric oxide (NO) have been reported in regulation of the sympatho-adrenomedullary system, which can affect voiding and storage functions. Therefore, we investigated effects of intracerebroventricularly (icv) administered 3-(4-morpholinyl)sydnonimine, hydrochloride (SIN-1) (NO donor) on the micturition reflex, focusing on their dependence on the sympatho-adrenomedullary system and on brain N-methyl-D-aspartate (NMDA) and α-amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA) receptors in urethane-anesthetized (0.8 g/kg, ip) male Wistar rats. Plasma noradrenaline and adrenaline were measured just before and 5 minutes after SIN-1 administration. Evaluation of urodynamic parameters was started 1 hour before SIN-1 administration or intracerebroventricular pretreatment with other drugs. SIN-1 (100 and 250 µg/animal) elevated plasma adrenaline and reduced intercontraction interval([ICI]values; 110.5% [SIN-1, 0 µg]and 54.9% [SIN-1, 250 µg]during 15 minutes after SIN-1 administration [P < .05;η2 = 0.59]) without affecting plasma noradrenaline or maximal voiding pressure. SIN-1 (250 µg/animal) reduced single-voided volume and bladder capacity without affecting post-voiding residual volume. The SIN-1 (250 µg/animal)-induced adrenaline elevation and ICI reduction were attenuated by 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide, sodium salt (carboxy-PTIO) (NO scavenger, icv) (ICI values; 44.7% [vehicle + SIN-1]and 77.5% [carboxy-PTIO + SIN-1]during 15 minutes after SIN-1 administration [P < .05;η2 = 0.51]). Acute bilateral adrenalectomyabolished SIN-1-induced adrenaline elevation, while showed no effect on the SIN-1-induced ICI reduction. The ICI reduction was attenuated by MK-801 (NMDA receptor antagonist, icv) (ICI values; 47.0% [vehicle + SIN-1]and 87.6% [MK-801 + SIN-1]during 15 minutes after SIN-1 administration [P < .05;η2 = 0.61]), but not by DNQX (AMPA receptor antagonist, icv). Brain NO is involved in facilitation of the rat micturition reflex through brain NMDA receptors, independently of the sympatho-adrenomedullary outflow modulation.

EKF/UKF-based channel estimation for robust and reliable communications in V2V and IIoT

Cyber-physical systems (CPSs) are characterized by integrating computation, communication, and physical system. In typical CPS application scenarios, vehicle-to-vehicle (V2V) and Industry Internet of Things (IIoT), due to doubly selective fading and non-stationary channel characteristics, the robust and reliable end-to-end communication is extremely important. Channel estimation is a major signal processing technology to ensure robust and reliable communication. However, the existing channel estimation methods for V2V and IIoT cannot effectively reduce intercarrier interference (ICI) and lower the computation complexity, thus leading to poor robustness. Aiming at this challenge, according to the channel characteristics of V2V and IIoT, we design two channel estimation methods based on the Bayesian filter to promote the robustness and reliability of end-to-end communication. For the channels with doubly selective fading and non-stationary characteristics of V2V and IIoT scenarios, in the one hand, basis extended model (BEM) is used to further reduce the complexity of the channel estimation algorithm under the premise that ICI can be eliminated in the channel estimation. On the other hand, aiming at the non-stationary channel, a channel estimation and interpolation method based on extended Kalman filter (EKF) and unscented Kalman filter (UKF) Bayesian filters to jointly estimate the channel impulse response (CIR) and time-varying time domain autocorrelation coefficient is adopted. Through the MATLAB simulation, the robustness and reliability of end-to-end communication for V2V and IIoT are promoted by the proposed algorithms.

Beyond‐sparsity–based doubly selective channel estimation for high‐mobility multiuser MIMO‐OFDM systems

AbstractWireless communications in high‐mobility situations face with doubly selective (DS) fading. In addition, many practical wireless channels exhibit a sparse multipath structure. This paper investigates the DS multiuser multiple‐input–multiple‐output (MIMO) channel estimation via compressed sensing. The DS channel is characterized by a general sparse basis expansion model (BEM). This model reduces the channel estimation complexity as the channel estimation problem is reduced to estimating the BEM coefficients instead of numerous channel parameters. In addition, a pilot pattern is proposed for multiuser MIMO orthogonal frequency division multiplexing systems, which includes guard and silent pilots to reduce intercarrier interference and interuser interference, respectively. Then, two beyond‐sparsity features (ie, block and joint sparsity) of the BEM coefficients are exploited to propose a beyond‐sparsity–based channel estimation method. Moreover, a pilot design algorithm is proposed to optimize the pilot positions and enhance the estimator performance. Simulation results demonstrate that the proposed method significantly improves the estimation accuracy over the existing approaches, with a much smaller pilot overhead.

Location-Aware ICI Reduction in MIMO-OFDM Downlinks for High-Speed Railway Communication Systems

High mobility may destroy the orthogonality of subcarriers in OFDM systems, resulting in inter- carrier interference (ICI), which may greatly reduce the service quantity of high-speed railway (HSR) wireless communications. This paper focuses on ICI mitigation in the HSR downlinks with distributed transmit antennas.For such a system, its key feature is that the ICIs are caused by multiple carrier frequency offsets corresponding to multiple transmit antennas. Meanwhile, the channel of HSR is fast time varying, which is another big challenge in the system design. In order to get a good performance, low complexity real-time ICI reduction is necessary. To this end, we first analyzed the property of the ICI matrix in AWGN and Rician scenarios, respectively. Then, we propose corresponding low complexity ICI reduction methods based on location information. For evaluating the effectiveness of the proposed method, the expectation and variance of remaining interference after ICI reduction is analyzed with respect to Rician K-factor. In addition, the service quantity and the bandwidth and computation cost are also discussed. Numerical results are presented to verify our theoretical analysis and the effectiveness of proposed ICI reduction methods. One important observation is that our proposed ICI mitigation method can achieve almost the same service quantity with that obtained on the case without ICI at 300km/h,that is, ICI has been completely eliminated. Numerical results also show that the scenarios with Rician K-factors over 30dB can be considered as AWGN scenarios, which may provide valuable insights on future system designs.

Multimedia transmission in MC-CDMA using adaptive subcarrier power allocation and CFO compensation

ABSTRACTMulticarrier code division multiple access (MC-CDMA) system is one of the most effective techniques in fourth-generation (4G) wireless technology, due to its high data rate, high spectral efficiency and resistance to multipath fading. However, MC-CDMA systems are greatly deteriorated by carrier frequency offset (CFO) which is due to Doppler shift and oscillator instabilities. It leads to loss of orthogonality among the subcarriers and causes intercarrier interference (ICI). Water filling algorithm (WFA) is an efficient resource allocation algorithm to solve the power utilisation problems among the subcarriers in time-dispersive channels. The conventional WFA fails to consider the effect of CFO. To perform subcarrier power allocation with reduced CFO and to improve the capacity of MC-CDMA system, residual CFO compensated adaptive subcarrier power allocation algorithm is proposed in this paper. The proposed technique allocates power only to subcarriers with high channel to noise power ratio. The performance of the proposed method is evaluated using random binary data and image as source inputs. Simulation results depict that the bit error rate performance and ICI reduction capability of the proposed modified WFA offered superior performance in both power allocation and image compression for high-quality multimedia transmission in the presence of CFO and imperfect channel state information conditions.

A Review Paper on Analysis Of I/Q Imbalance and Impact of Timing Jitter and In OFDM Transmission Systems for ICI Reduction

A Review Paper on Analysis Of I/Q Imbalance and Impact of Timing Jitter and In OFDM Transmission Systems for ICI Reduction

ICI Reduction in Multicarrier Systems

Inter-Carrier Interference (ICI) is a major contribution to performance degradation in multicarrier systems. The main reason of the ICI is the Carrier Frequency Offset (CFO). Some researchers reduced the effect of this ICI by estimating the CFO value then compensating for it. The CFO estimation accuracy affects in turn the multicarrier system performance. The Repeated Prefix (RP) is a new technique that is recently proposed to reduce the ICI effect by estimating the CFO value without producing mathematical derivations. The drawback of this technique is its low performance at low guard interval values. This paper enhances the performance of this method at low guard interval values, giving the Maximum Likelihood Estimation (MLE) derivation for this process in addition to a derivation of the relative Cramer-Rao Lower Bound (CRLB). The proposed technique (RP-combined) reduces the effect of the residual ICI and can be used once in the transmitted frame with less data rate losses.Simulations show comparable results between both theoretical and simulated cases. Simulations also show the system performance with/without using channel estimation stage to show that, the channel estimator increases the immunity of the system performance to ICI for small offset values.

Enhanced Next Generation Millimeter-Wave Multicarrier System with Generalized Frequency Division Multiplexing

Orthogonal Frequency Division Multiplexing (OFDM) is a popular multicarrier technique used to attain high spectral efficiencies. It also has other advantages such as multipath tolerance and ease of implementation. However, OFDM based systems suffer from high Peak-to-Average Power Ratio (PAPR) problem. Because of the nonlinearity of the power amplifiers, the high PAPR causes significant distortion in the transmitted signal for millimeter-wave (mmWave) systems. To alleviate the high PAPR problem, this paper utilizes Generalized Frequency Division Multiplexing (GFDM) which can achieve high spectral efficiency as well as low PAPR. In this paper, we show the performance of GFDM using the IEEE 802.11ad multicarrier frame structures. IEEE 802.11ad is considered one of the most successful industry standards utilizing unlicensed mmWave frequency band. In addition, this paper indicates the feasibility of using GFDM for the future standards such as IEEE 802.11ay. This paper studies the performance improvements in terms of PAPR reduction for GFDM. Based on the performance results, the optimal numbers of subcarriers and subsymbols are calculated for PAPR reduction while minimizing the Bit Error Rate (BER) performance degradation. Moreover, transmitter side ICI (Intercarrier Interference) reduction is introduced to reduce the receiver load.

ICI Reduction in OFDM Systems Using a New Family of Nyquist-I Pulses

In this paper the parametric linear combination pulse (IPLCP) is proposed. The IPLCP is a new family of Nyquist-I pulses with two additional degrees of freedom to minimize the inter-carrier interference (ICI) power in orthogonal frequency-division multiplexing (OFDM) based systems due to frequency offset. Theoretical and numerical simulations are shown to verify that the performance of the IPLCP outperforms other existing pulses.

Low-Complexity ICI Reduction Method for OFDM Systems With Large Subcarrier Numbers

The intercarrier interference (ICI) resulting from the loss of orthogonality caused by the time-varying property of the propagation channels degrades the data detection performance of orthogonal frequency-division multiplexing (OFDM)-based wireless communication systems. Further, the severity of the problem increases when the mobile speed is relatively higher than the number of subcarriers. In this paper, a time-varying filtering method is proposed that reduces ICI by obtaining an approximation of linear system solutions such as zero-forcing (ZF) and minimum mean square error (MMSE). The update rates of the time-varying filter coefficients, which are actually the minimum phase versions of the channel impulse responses, are also minimized to reduce the computational complexity. The simulation results show that the proposed method with lower complexity effectively reduces ICI such that practical application is deemed feasible for OFDM systems with a large number of subcarriers.

PAPR and ICI Reduction of OFDM Signals Using New Weighting Factors from Riemann Matrix

Orthogonal frequency division multiplexing (OFDM) systems are significantly affected by peak-to-average-power ratio (PAPR). One of the straightforward methods to solve this problem is to use selected mapping (SLM) algorithm. The main idea of SLM scheme is to select the phase factors that minimize the PAPR and transmit these factors as side information (SI). In this paper, a new phase factors based on the diagonal elements of Riemann matrix is proposed. The results indicates that the introduced scheme has better PAPR reduction and power spectral density (PSD) performance compared to several SLM-based methods. Further, it does not need SI transmission. Also bit error rate (BER) of the proposed phase factor does not degrade with respect to conventional SLM.

Intercarrier interference reduction in MC-CDMA system through second order duobinary coded phase rotated conjugate cancellation scheme.

Multi-carrier code division multiple access (MC-CDMA) technique is one of the strong candidates for next generation wireless mobile communication systems. Multi-carrier systems are very much sensitive to carrier frequency offset (CFO) results in intercarrier interference (ICI). To mitigate ICI without any spectral loss, a second order duobinary coded phase rotated conjugate cancellation algorithm is proposed in this paper. In the conventional phase rotated conjugate cancellation (PRCC) technique, one path carries the MC-CDMA signal with a phase spin of ϕ and the other path carries the conjugate of the first path signal with -ϕ phase spin. This artificial phase rotation allows the transmitter to tune the transmitted signals so that the ICI effects could be mutually cancelled at the receiver. Although the PRCC technique reduces the spectral efficiency, the limitation can be overcome by the joint second order duobinary coding scheme with PRCC technique. In the proposed method, the correlative coding between the binary symbols modulated on adjacent subcarriers is used to reduce the ICI without any spectral loss. Simulation results show that the proposed PRCC method provides better carrier to interference ratio (CIR) and bit error rate (BER) performances compared to the conventional conjugate cancellation (CC) technique.

Transmitter Pulse Shaping to Reduce OOB Power and ICI in OFDM Systems

The goal of waveform shaping techniques in orthogonal frequency division multiplexing systems is reduction in out of band (OOB) transmit power as well as reduction in inter-carrier interference (IC...

Comparison of ICI Reduction and Fiber Nonlinearity Tolerance for DCS-OFDM and Conventional OFDM With Equal Spectrum Efficiency

Digital coherent superposition (DCS) for optical orthogonal frequency-division multiplexing (OFDM) subcarrier pairs with Hermitian symmetry can simultaneously reduce the inter-carrier interference (ICI) from laser phase noise and cancel the fiber nonlinearity to the first order. In this paper, we study an interesting scenario, where we upgrade the conventional OFDM with 4-quadrature amplitude modulation (QAM) to DCS-OFDM with 16-QAM, which have equal spectrum efficiency and require no change on hardware. We conduct a simulation to compare the tolerance to the laser phase noise and fiber nonlinearity, which are the main concerns for such an upgrading. First, the 16-QAM DCS-OFDM relaxes the laser linewidth requirement and performs better with a smaller fast Fourier transform size. Second, the nonlinear tolerance of 16-QAM DCS-OFDM is better when the nonlinear effects appear. The nonlinear tolerance of DCS-OFDM depends on the dispersion compensation scheme. The maximum SNR improvement is 3.4 dB with full post-dispersion compensation, and it can increase to 6.6 dB with symmetrical dispersion compensation at the launch power of 4 dBm. Finally, we verify that the maximum SNR improvement of 16-QAM DCS-OFDM with full post-dispersion compensation is 3.7 dB at the launch power of 6.2 dBm in the experiment.

Theoretical calculation on ICI reduction using digital coherent superposition of optical OFDM subcarrier pairs in the presence of laser phase noise.

Digital coherent superposition (DCS) of optical OFDM subcarrier pairs with Hermitian symmetry can reduce the inter-carrier-interference (ICI) noise resulted from phase noise. In this paper, we show two different implementations of DCS-OFDM that have the same performance in the presence of laser phase noise. We complete the theoretical calculation on ICI reduction by using the model of pure Wiener phase noise. By Taylor expansion of the ICI, we show that the ICI power is cancelled to the second order by DCS. The fourth order term is further derived out and only decided by the ratio of laser linewidth to OFDM subcarrier symbol rate, which can greatly simplify the system design. Finally, we verify our theoretical calculations in simulations and use the analytical results to predict the system performance. DCS-OFDM is expected to be beneficial to certain optical fiber transmissions.