Carrier Interference Research Articles

Fractional wavelet transform based OFDM system with cancellation of ICI

The future of wireless communication systems stimulate researchers to improve bandwidth efficiency and data rate by carrying out several analyses. The reliability of multiple input multiple output (MIMO) combined with orthogonal frequency division multiplexing (OFDM) in wireless communication is reduced by frequency error. This leads to damage of orthogonality between sub-carriers and induces inter carrier interference (ICI). To overcome this problem in conventional OFDM system, cyclic prefix is used. In this work, a novel technique named fractional wavelet transform (FrWT) is proposed. The FrWT reduces the effect of ICI in conventional system without any usage of cyclic prefix. Also, the bandwidth efficiency is improved due to its orthogonal wavelets and absence of cyclic prefix. The proposed work investigates the performance of FrWT-OFDM model and tested against carrier frequency offsets. The efficiency of ICI self cancellation technique in mitigating the effect of frequency offsets is analysed. The efficiency of proposed model is highlighted by comparing with existing FFT and wavelet based OFDM system by means of bit error rate (BER). Simulation results show reduced BER of 10−4.8 at 8 dB SNR for the proposed model with a normalized carrier frequency offset value of 0.1. Thus the effect of ICI is reduced efficiently for proposed transform in OFDM.

Effects of frequency and timing offsets in DCT-based multiple access system for VLC

Abstract Visible light communication (VLC) has gained a significant momentum in the recent times due to its distinctive characteristics of imparting concurrent ‘illumination’ and ‘communication’ by exploiting sustainable and energy-efficient opto-electronic devices like light emitting diodes (LEDs). Consequently, by utilizing the already installed LED lighting fixtures a small scale cellular communication network can be created within an indoor environment imparting economic and ubiquitous data transmission services to multitude of roaming mobile stations within the proximity of LEDs. Therefore, it is vital to address the detrimental aspects like carrier frequency offset (CFO) and symbol time offset (STO) which emanates predominantly in an uplink scenario. This paper evaluates the performance of DC offset optical fast orthogonal frequency division multiple access (DCO-FOFDMA) system in the presence of both CFO and STO and accomplishes a thorough mathematical analysis emphasizing the different interferences like inter carrier (ICI) and multi user interferences (MUI) emanating due to different timing disparities and frequency discrepancies. The simulation results evidences that, with the increase in sensitivity of CFO and timing misalignments, the system performance drastically deteriorates thereby hindering the detection capability of multiple users operating at the same time. In order to estimate the STO, synchronization algorithms like Maximum Likelihood (ML) and Classen are imposed to the developed system model. Additionally, Cramer Rao Lower Bound (CRLB) is derived for the estimation of CFO and STO.

A Review: Analysis of PAPR Reduction Techniques of OFDM System

Orthogonal Frequency Division Multiplexing (OFDM) is an efficient multicarrier modulation scheme in wireless communication. It is used in applications like 4G (fourth generation) mobile Communications, wireless networks, digital television, power line networks and audio Broadcasting. It offers both advantages and disadvantages for multicarrier transmission. The main advantages are the elimination of Inter Carrier Interference (ICI) and Inter Symbol Interference (ISI) in the signal. But OFDM’s one of the main detrimental aspects are high Peak-to-Average Power Ratio (PAPR) value of the transmitted signal which highly affects the power amplifiers complexity.

Downlink Design for Spectrum Efficient IoT Network

The Internet of Things (IoT) is a new network that connects massive devices which have the communication ability. With the requirement of various services and the wireless spectrums becoming increasingly scarce, we consider a nonorthogonal multicarrier transmission scheme that is spectrum efficient frequency division multiplexing (SEFDM) as the downlink transmission scheme for IoT network. SEFDM has the merit of improved bandwidth usage efficiency, but the serious inter carrier interference (ICI) will be introduced by multiplexing overlapped carriers. Thus, the signal detection is challenged for recovering the signal which is suffered from ICI due to the loss of the orthogonality. In this paper, a low complexity detector based on quasi-orthogonality compensation (QOC) is proposed in the downlink receiver. And the complexity of the QOC detector is also analyzed. Moreover, a novel detector which joint QOC and fixed sphere decoding (FSD) algorithm is proposed. The bit error rate performances of QOC and QOC-FSD detectors are evaluated by numerical simulations. Numerical results show that the QOC and QOC-FSD detectors can achieve better performance than conventional iterative detection (ID) and ID-FSD, respectively. Furthermore, QOC-FSD detector performs a lower complexity than ID-FSD detector.

A compensation method for the carrier interference of a three-component magnetic measurement system using a Cuckoo search algorithm

The magnetic interference field generated by ferromagnetic materials on the carrier decreases measurement precision, which has been a crucial factor limiting the application of three-component magnetic measurement. In this paper, a magnetic compensation method based on the Cuckoo search (CS) algorithm is proposed. The method can be separated into three steps. First, a measurement error model is established, based on which a formula of the absolute error sum will be derived. Then, compensation parameters are estimated using the CS algorithm by minimizing the absolute error sum. Finally, the geomagnetic intensity is calculated using estimates of the compensation parameters and measured data. As the CS algorithm possesses the advantages of insensitivity to iterative initial values and strong global search ability, optimal estimates of the compensation parameters can be obtained accurately using this method, which ensures high compensation precision. The experimental results show that, after compensation, the maximum error of the x-component can be reduced from 622 nT to 26 nT, the y-component from 329 nT to 19 nT, and the z-component from 669 nT to 15nT.

A MC-CDMA system based on orthogonal filter banks of wavelet transforms and partial combining

Multi Carrier Code Division Multiple Access (MC-CDMA) is an appropriate modulation technique for high data rates. In this modulation scheme, employing of combining techniques are unavoidable for restoring orthogonality between different user signals. In this paper, the combining techniques of a MC-CDMA based on wavelet transform are studied. The partial combining of the wavelet based MC-CDMA system is suggested and its performance is compared with the maximum ratio combining (MRC), equal gain combining (EGC), orthogonality restoring combining (ORC) and the minimum mean square error (MMSE) techniques. Orthogonal filter banks of the wavelet transforms provide orthogonality between the wavelets and scaling functions, subcarriers and spreading sequences. Therefore, they provide new dimensions in combatting multipath fading, inter carrier interference (ICI) and narrowband interference in MC-CDMA systems. Furthermore, analysis of partial combining shows that coefficients of this technique can be computed in a simple manner. Simulations results indicate that the bit error rate (BER) performance of the proposed scheme is almost comparable with the MMSE combining scheme and the proposed system has a proper performance in terms of BER versus the signal to noise ratio (SNR) in frequency selective fading channels.

A Diversity Enhanced-Particle Filter based Multiple Carrier Frequency Offset Estimation Using Hadamard Matching in CA-OFDM Based LTE-A System

Carrier aggregation (CA) is a promising bandwidth extension technique which in turn increases the data rate. A scalable and flexible Orthogonal frequency-division multiplexing (OFDM) can be considered as a key element in 5G wireless communications. The combination of CA and OFDM is a prominent factor in LTE-A system followed by strict synchronicity. So, carrier frequency offset (CFO) is an important parameter to be considered and corrected. In carrier-aggregated OFDM (CA-OFDM) systems, multiple carrier frequency offsets (MCFOs) are a non linear synchronization error that induces inter carrier interference (ICI) to the system. To solve this problem, our self proposed Diversity Enhanced Particle Filter (DE-PF) with a novel resampling algorithm is used in downlink CA-OFDM receiver structure with Hadamard sequence based prominent matching algorithm to match the estimated MCFO to its corresponding Component Carrier (CC). Simulations prove that with DE-PF algorithm and proposed Hadamard matching algorithm improves MCFO estimation accuracy to a greater extent than the existing linear and non linear algorithms.

Novel Adaptive Filter Design for Filter Bank Multicarrier System Under Doubly Dispersive Channel Conditions

ABSTRACTFilter bank multicarrier (FBMC) has emerged as the favourite multicarrier communication technique since it meets the demands of the next-generation standards, especially for communication under doubly dispersive channels. In order to combat the undesirable channel effects like inter symbol interference and inter carrier interference, the prototype filters used in FBMC systems must satisfy orthogonality conditions and be well localized simultaneously in both time and frequency domains. Even though conventional doubly localized filters are optimum in the absence of channel, they fail to satisfy orthogonality and localization criteria under doubly dispersive channels. In the present study, an adaptive filter design method is proposed in which the prototype filter is designed as the weighted sum of a time-limited Nyquist filter, a band-limited Nyquist filter, and doubly localized Gaussian filter based on the analysis of discrete ambiguity function (DAF). The filter is designed to vary its characteristics according to the maximum time and frequency domain dispersions of the channel, so that signal-to-interference ratio is maximized. In order to ensure distortion-less transmission, the perfect reconstruction criterion for distortion-less transmission is mapped to specific conditions for DAF according to two-dimensional channel scattering function. The superiority in performance of the proposed adaptive filter is analysed in terms of signal-to-interference ratio and bit error rate, and is compared with the conventional filters for various channel scattering conditions.

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.

A Comprehensive Performance Analysis of MIMO-OFDM Technology Using Different MIMO Configurations and M-QAM Modulation Schemes for LTE Cellular Network

MIMO-OFDM (Multiple Input Multiple Output-Orthogonal Frequency Division Multiplexing) uses multiple antennas at transmitter and receiver side to facilitate high throughput performance without needing additional bandwidth or transmission power. But frequency synchronization, Inter Carrier Interference (ICI) minimization and antenna diversity are the main challenges for MIMO-OFDM wireless technology. In this paper, a MIMO-OFDM hybrid model is designed with proper frequency synchronization and antenna diversity that minimizes ICI with improved signal strength. Using the model a comprehensive analysis in terms of Bit Error Rate (BER) performance with respect to Signal to Noise Ratio (SNR) and Bit Rate for different M-ary QAM modulation schemes and different MIMO configurations are presented over Rayleigh fading and AWGN channel. After an extensive analysis, it is found that the propose OFDM scheme shows better Bit Error rate (BER) performance for 64-QAM than any other M-ary QAM modulation schemes and the optimum MIMO configuration for this good quality performance is found to be 3×2 configuration.

Influence of spin–orbit coupling on spin-polarized electronic transport in magnetic semiconductor nanowires with nanosized sharp domain walls

Influence of spin–orbit coupling on spin-polarized electronic transport in magnetic semiconductor nanowires with nanosized sharp domain walls is investigated theoretically. It is shown that the Rashba spin–orbit coupling can enhance significantly the spin-flip scattering of charge carriers from a nanosized sharp domain wall whose extension is much smaller than the carrier’s Fermi wavelength. When there are more than one domain wall presented in a magnetic semiconductor nanowire, not only the spin-flip scattering of charge carriers from the domain walls but the quantum interference of charge carriers in the intermediate domain regions between neighboring domain walls may play important roles on spin-polarized electronic transport, and in such cases the influences of the Rashba spin–orbit coupling will depend sensitively both on the domain walls’ width and the domain walls’ separation.

Analysis of OFDM system using DCT-PTS-SLM based approach for multimedia applications

In last decade, wireless communications have observed a substantial development. However, wireless channels involve some disadvantages, like multipath fading, which make them hard to cope with. A modulation that efficiently deals with selective fading channels is an orthogonal frequency division multiplexing (OFDM), which consists on N orthogonal subcarriers generated and modulated when you look at the frequency domain. The orthogonal subcarriers allows, the use of the Fourier transform without introducing interference that is inter carrier interference. The advancements in digital signal processing and extremely large scale integrated circuits allow efficient and cost-effective utilization of the fast Fourier transform operations making OFDM an appealing solution for wireless channels. In OFDM system peak to average power ratio (PAPR) is a big risk which can be avoided using various techniques. This paper deals with performance analysis of multicarrier OFDM using combination of discrete cosine transform, partial transmit sequence and selective mapping. A video signal has been given as an input and MATLAB simulations were carried out. BER has been immensely improved and PAPR is reduced to 4 dB which is appreciable performance for multimedia devices.

Spectrum Efficient MIMO-FBMC System Using Filter Output Truncation

Due to the use of an appropriately designed pulse shaping prototype filter, filter bank multicarrier (FBMC) system can achieve low out of band (OoB) emissions and is also robust to the channel and synchronization errors. However, it comes at a cost of long filter tails which may reduce the spectral efficiency significantly when the block size is small. Filter output truncation (FOT) can reduce the overhead by discarding the filter tails but may also significantly destroy the orthogonality of FBMC system, by introducing inter carrier interference (ICI) and inter symbol interference (ISI) terms in the received signal. As a result, the signal to interference ratio (SIR) is degraded. In addition, the presence of intrinsic interference terms in FBMC also proves to be an obstacle in combining multiple input multiple output (MIMO) with FBMC. In this paper, we present a theoretical analysis on the effect of FOT in an MIMO-FBMC system. First, we derive the matrix model of MIMO-FBMC system which is subsequently used to analyze the impact of finite filter length and FOT on the system performance. The analysis reveals that FOT can avoid the overhead in time domain but also introduces extra interference in the received symbols. To combat the interference terms, we then propose a compensation algorithm that considers odd and even overlapping factors as two separate cases, where the signals are interfered by the truncation in different ways. The general form of the compensation algorithm can compensate all the symbols in a MIMO-FBMC block and can improve the SIR values of each symbol for better detection at the receiver. It is also shown that the proposed algorithm requires no overhead and can still achieve a comparable BER performance to the case with no filter truncation.

Performance Analysis of OFDM System with CP-Free STBC by using the Oblique Projection Technique

Background and Objective: This paper considers the model in which the digital feedback equalizer (DFE) together with oblique projection (OB) has been used to minimize the effect of Inter symbol Interference and Inter carrier Interference in multiple input multiple output orthogonal frequency division multiplexing system. The conventional MIMO-OFDM system uses cyclic prefix (CP) to remove ISI in received signals & this cyclic prefix is just an overhead on the transmitted data. In the proposed model CP has been removed and placed with Oblique Projection for saving the bandwidth. Usually by eliminating the CP in the system, the effect of ISI and ICI is not sufficiently removed. The frequency- domain block based decision feedback equalizer with oblique projection technique is proposing to dealing with this problem. This will also improve the spectral efficiency of the system. The proposed system has been able to give improvement of 12dB SNR at BER of 26dB in MMSE equalization and 27dB in zero forcing (ZF) decoding as compared to CP based conventional MIMO-OFDM system. Result and Conclusion: Further the proposed system has been able to increase the achievable rate at 0dB SNR the rate is 1.8 bits/sec/Hz. Keywords: MIMO, CP-OFDM, Decision Feedback Equalizer, Oblique Projection, STBC, ICI, ISI.

The Effect and Compensation of Phase Noise on Orthogonal Frequency Division Multiplexing (OFDM) System

Orthogonal Frequency Division Multiplexing (OFDM) is characterized by its high data rate. However, the modulation method used in the system is subject to the influence of phase noise due to the need of time synchronization. In this paper, an algorithm based on MMSE (minimum mean square error) is developed to compensate the influence of both the common phase error (CPE) and inter carrier interference (ICI), which are two aspects of phase noise, under common Gaussian white noise. The result of noise cancellation is presented in signal-to-noise ratio (SNR) and symbol error rate (SER). Like digital signal in general, SNR can reduce SER with or without phase noise compensation. The compensation of phase noise significantly reduces the SER of the decoded signal. However, the bandwidth of phase noise still determines the signal accuracy. Under high bandwidth of phase noise, increasing SNR will only slightly increase SER, which is not efficient.

Practical Evaluations of SEFDM: Timing Offset and Multipath Impairments

The non-orthogonal signal waveform spectrally efficient frequency division multiplexing (SEFDM) improves spectral efficiency at the cost of self-created inter carrier interference (ICI). As the orthogonal property, similar to orthogonal frequency division multiplexing (OFDM), no longer exists, the robustness of SEFDM in realistic wireless environments might be weakened. This work aims to evaluate the sensitivity of SEFDM to practical channel distortions using a professional experiment testbed. First, timing offset is studied in a bypass channel to locate the imperfection of the testbed and its impact on SEFDM signals. Then, the joint effect of a multipath frequency selective channel and additive white Gaussian noise (AWGN) is investigated in the testbed. Through practical experiments, we demonstrate the performance of SEFDM in realistic radio frequency (RF) environments and verify two compensation methods for SEFDM. Our results show first frequency-domain compensation works well in frequency non-selective channel conditions while time-domain compensation method is suitable for frequency selective channel conditions. This work paves the way for the application of SEFDM in different channel scenarios.

Temperature and impurity effect on parallel field magnetoconductance of bulk insulating topological insulator (Bi1−xSbx)2Te3

We have performed a systematic parallel field magnetotransport studies of (Bi1−xSbx)2Te3 to understand the temperature and impurity effect on the interference of bulk conductance on the surface states of highly insulating topologically insulating compound Bi2Te3. The compound exhibits a weak antilocalization effect (WAL) at low temperature and low magnetic field. WAL weakens and a weak localization effect is observed to be developed in the compound with the increase in temperature due to the creation of topologically trivial 2D electron gas states. Strong interlayer interference and coupling of bulk carriers with surface states are observed at low temperature. A similar temperature effect is observed for all concentrations of Sb. Topologically protected surface states enhance with the increase in Sb contents up to x = 0.3; however, a further increase in Sb concentration leads to a decrease in surface states. The data has been analysed via the generalised Altshuler and Aronov model for parallel field transport anticipating weak antilocalization and interlayer interference.

A novel energy-efficient ICI cancellation technique for bandwidth improvements through cyclic prefix reuse in an OFDM system

Orthogonal frequency division multiplexing (OFDM), a very promising technique that is leading the evolution in wireless mobile communication to sideline the bandwidth scarcity issue in spectrum allocation, is severely affected by the undesirable effects of the frequency offset error, which generates inter carrier interference (ICI) due to the Doppler shift and local oscillator frequency synchronization errors. There are many ICI cancellation techniques available in the literature, such as self-cancellation (SC), maximum likelihood estimation (MLE), and windowing, but they present a tradeoff between bandwidth redundancy and system complexity. In this study, a new energy-efficient, bandwidth-effective technique is proposed to mitigate ICI through cyclic prefix (CP) reuse at the receiver end. Unlike SC and MLE where the whole OFDM symbol data is transmitted in duplicate to create redundancy at the transmitter end, the proposed technique uses the CP data (which is only 20% of the total symbol bandwidth) to estimate the channel, and it produces similar results with a huge bandwidth saving. The simulation results show that the proposed technique has a significant improvement in error performance, and a comparative analysis demonstrates the substantial improvement in energy efficiency with high bandwidth gain. Therefore, it outperforms the legacy ICI cancellation schemes under consideration.

Feasibility of Single-Beam Interference Alignment in Multi-Carrier Interference Channels

Sun and Luo recently showed that if the vector-space single-beam interference alignment problem for a $K$ -user, $L$ -carrier interference channel is feasible, then $K\leq 2L-2$ . We prove the converse, that if $K\leq 2L-2$ , then the problem is feasible, i.e., that the requisite beamformers do exist.

A Magnetic-Balanced Inductive Link for the Simultaneous Uplink Data and Power Telemetry.

When using the conventional two-coil inductive link for the simultaneous wireless power and data transmissions in implantable biomedical sensor devices, the strong power carrier could overwhelm the uplink data signal and even saturate the external uplink receiver. To address this problem, we propose a new magnetic-balanced inductive link for our implantable glaucoma treatment device. In this inductive link, an extra coil is specially added for the uplink receiving. The strong power carrier interference is minimized to approach zero by balanced canceling of the magnetic field of the external power coil. The implant coil is shared by the wireless power harvesting and the uplink data transmitting. Two carriers (i.e., 2-MHz power carrier and 500-kHz uplink carrier) are used for the wireless power transmission and the uplink data transmission separately. In the experiments, the prototype of this link achieves as high as 65.72 dB improvement of the signal-to-interference ratio (SIR) compared with the conventional two-coil inductive link. Benefiting from the significant improvement of SIR, the implant transmitter costs only 0.2 mW of power carrying 50 kbps of binary phase shift keying data and gets a bit error rate of 1 × 10, even though the coupling coefficient is as low as 0.005. At the same time, 5 mW is delivered to the load with maximum power transfer efficiency of 58.8%. This magnetic-balanced inductive link is useful for small-sized biomedical sensor devices, which require transmitting data and power simultaneously under ultra-weak coupling.