Frequency Division Multiplexing Systems Research Articles

Effective Scheduling Policies to Optimize Radio Resources between NR-gNodeB and Device to Device Systems in 5G

Technology behind every communication systems, especially commercial applications requires periodic modifications to satisfy the subscriber’s desires. A bulk of handheld radio access devices are emerging in the market every day. Since radio resources are limited and expensive, Device to device communication underlying New Radio (NR-gNodeB) access network is encouraged in fifth generation (5G) systems. But such system may be a catalyst for interference. At present, the research hotspot is to find ideal solution for resource allocation and interference management. This paper emphasis the requirements of 5G system and its physical layer design. Further the intention is to mitigate interference in such system so that functionalities of scheduling schemes such as Greedy, Round Robin and Proportional fair algorithms are analyzed for efficient resource allocation. The simulation results explore that, the coded generalized frequency division multiplexing (GFDM) system results in higher transmission rate. Also, coded GFDM with proportional fair scheduler results in high throughput and reduced latency with no compromise in its fairness. In summary, the proposed scheme could be a wise choice for reliable communication in smart cities.

PAPR Reduction in OFDM System Using Hybrid OICF and Phase Rotation Scheme

Abstract Peak to average power ratio (PAPR) is one of the major limitations of orthogonal frequency division multiplexing (OFDM) systems because the higher PAPR induces the signal to get out of linear region of high power amplifier (HPA). In this article, a hybrid PAPR reduction scheme based on the combination of optimized iterative clipping and filtering (OICF) method and phase rotation is proposed. Using phase rotation, signal’s initial PAPR has been reduced by 14.23 dB and then OICF further reduces the final PAPR by 1.37 dB. Decreased PAPR will play an important role in reducing systems power consumption.

Efficient POPS-OFDM Waveform Design for Future Wireless Communication Systems

Future wireless networks are required to offer new applications and services, which will experience high dispersions in time and frequency, incurred mainly by coarse synchronization. Coarse synchronization is induced by signaling overhead reduction and dictated by the tremendous optimization of the radio interface efficiency. It is expected to dramatically damage waveform orthogonality in conventional orthogonal frequency-division multiplexing (OFDM) systems and to result in oppressive intercarrier interference (ICI). To alleviate the degradation in performance caused by ICI, the concept of nonorthogonal multiplexing has been promoted, as a serious alternative to strict orthogonal multiplexing, for guaranteeing the OFDM benefits without requiring high-level synchronization. Within this nonorthogonal multiplexing framework, ping-pong optimized pulse shaping-OFDM (POPS-OFDM) has been introduced as a powerful tool to efficiently design waveforms, which withstand future multicarrier systems’ dispersion impairments. In this paper, we investigate the discrete time version of the POPS-OFDM approach and study its sensitivity and robustness against estimation and synchronization errors. Based on numerical results, we show that POPS-OFDM provides an important gain in the signal-to-interference ratio, typically higher than 5 dB, with respect to conventional OFDM. We also demonstrate that POPS-OFDM brings an increased robustness against synchronization errors and ensures a dramatic reduction in out-of-band emissions, enabling flexible and improved spectrum utilization.

Performance Analysis of Relay Assisted Multihop Coherant OFDM System over Malaga Distribution with Pointing Errors

Abstract This paper presents a multi-hop coherent orthogonal frequency division multiplexing free space optical communication system (OFDM-FSO) model which includes a relay transmission mode of decode and forward (DF) over Malaga disrubution (M) and we analyse the results by deriving mathematical expressions for average bit error rate (BER) and outage probability. And the FSO link is characterized by path loss, pointing errors and atmospheric turbulence and also weather conditions like clear air, haze, light fog have been considered in the channel model. The BER and outage probability of the proposed system are examined including the effects of pointing errors and weather conditions. From this work, we can justify that with multi-hop configuration coverage area and signal power improves which bolsters the usage of relay in FSO communication for efficient and reliable system design.

Efficient Blind Adaptive CSE to Reduce Cyclic Prefix Length in Direct Detection Optical OFDM Systems

Abstract Direct detection optical orthogonal frequency division multiplexing (DDO-OFDM) systems for a long-reach of standard single mode fiber (SSMF) require a large length of cyclic prefix (CP) to avoid the inter-symbol interference (ISI) effect caused by group velocity dispersion (GVD). Unfortunately, this method is inefficient due to the energy wasted in CP samples. In order to reduce the CP length and to mitigate the residual ISI, a novel blind adaptive channel shortening equalizer (CSE) is proposed in this paper. Based on the orthogonality between subcarriers in the fast Fourier transform (FFT) property, the proposed algorithm attempts to minimize the sum-squared correlation (SSCM) between each sample located in a well-defined window to update the CSE coefficients. Thus, the combined channel-CSE response is shortened. Therefore, it can cancel the residual ISI effect due to the GVD and the short CP length. The performance of the system is evaluated on basis of bit error rate (BER) versus optical signal to noise ratio (OSNR) for different CP lengths. The simulation results validate the new algorithm SSCM and show that it can reduce the CP length with a much better system improvement than existing algorithms.

Unequal error protection technique for video streaming over MIMO-OFDM systems.

In this paper, a novel unequal error protection (UEP) technique is proposed for video streaming over multiple-input multiple-output orthogonal frequency-division multiplexing (MIMO-OFDM) systems. Based on the concept of hierarchical quadrature amplitude modulation (HQAM) UEP and multi-antenna UEP, the proposed technique combines the relative protection levels (PLs) of constellation symbols and the differentiated PLs of the transmit antennas. In the proposed technique, standard square quadrature amplitude modulation (QAM) constellations are used instead of HQAM so that the QAM mapper at the transmitter side and the soft decision calculation at the receiver side remain unchanged, but the UEP benefit of HQAM is retained. The superior performance of the proposed technique is explained by the improved connections between data with various priorities and data paths with various PLs. The assumed video compression method is H.264/AVC, which is known to be commercially successful. The IEEE802.16m system is adopted as a data transmission system. With the aid of realistic simulations in strict accordance with the standards of IEEE802.16m systems and H.264/AVC video compression systems, the proposed technique HQAM-multi-antenna UEP is shown to improve the video quality significantly for a given average bit error rate when compared with previous techniques.

Joint Mutual Coherence and Total Coherence Pilot Design for OFDM Channel Estimation

Existing works design the pilot based on the mutual coherence criterion or total coherence criterion alone. However, using the mutual coherence criterion or total coherence criterion alone to design the pilot will yield the sensing matrix which corresponds to a certain pilot with a large total coherence or mutual coherence. However, the sensing matrix with a large mutual coherence or total coherence will deteriorate the sparse recovery performance and is not optimal from the perspective of the sparse recovery. Therefore, in this paper, we jointly design the pilot based on both the mutual coherence criterion and the total coherence criterion for sparse channel estimation in orthogonal frequency division multiplexing (OFDM) systems. We first prove that the optimal pilot pattern with respect to the total coherence criterion is the cyclic difference set and given a pilot pattern, the pilot power allocation can be cast as a second order cone programming problem with respect to the total coherence criterion. A joint mutual coherence and total coherence pilot design algorithm is proposed to design the pilot jointly while cyclic difference set does not exist for practical OFDM systems. The proposed algorithm first optimizes the pilot pattern with the mutual coherence criterion assuming that the pilot power is equal. After obtaining the pilot pattern, the pilot power is allocated with the total coherence criterion. Simulation results have shown that the proposed pilot design algorithm can achieve the best performance in terms of normalized mean square error and bit error rate in comparison with existing pilot design methods.

Linear Precoded Index Modulation

Index modulation (IM) is an attractive concept for next generation communication systems. However, as an emerging technique, there are still some challenges need to be tackled in this frontier. In this paper, we consider two aspects of IM, which are diversity and detection complexity. Specifically, we propose a linear precoding assisted index modulation (LPIM) scheme for orthogonal frequency division multiplexing (OFDM) systems. We commence by analyzing the diversity and coding gains of the proposed scheme. Moreover, a detailed codebook design criterion is proposed. Then, our LPIM codebook is designed based on the maximum diversity and coding gain criteria. In contrast to the signaling model of the existing full diversity precoder designed for OFDM, we introduce a modeling method to link the zero-valued IM symbols to the origin of a Lattice for implementing our full diversity precoder designed for OFDM-IM. Both analytical and computer simulation results are provided for characterizing the attainable performance of OFDM-LPIM, demonstrating that it is capable of achieving full diversity as well as an attractive coding gain. However, the maximum-likelihood (ML) detection complexity of OFDM-LPIM is excessive, hence a low-complexity generalized iterative residual check detector (GIRCD) is proposed, which is inspired by the existing sparse recovery algorithms. Finally, computer simulation results are provided for demonstrating that GIRCD can provide a beneficial trade-off between bit error ratio performance and complexity.

A Compressed Sensing Estimation Technique for Doubly Selective Channel in OFDM Systems

In this work, an estimation algorithm based on the compressive sensing (CS) technique is proposed for an orthogonal frequency division multiplexing (OFDM) system applied to multi-path time-varying channels. A fitting polynomial is used to approximate each channel path, and full-band training symbols are adopted. The variation of the channel response can then be evaluated according to the observation on the inter-carrier interference (ICI) from the determinate signals. The CS-based technique is introduced to explore the sparsity of the double-selective channel and the usage of high-order fitting polynomials is allowed. The orthogonal matching pursuit (OMP) algorithm is designed to cooperate with the fitting polynomial model, and more accurate channel estimation results can be provided compared to those provided by conventional least-square (LS) algorithms. When multiple transmission antennas are required, the advantage of the proposed polynomial-fitting OMP (PF-OMP) algorithm is more obvious as more transmission antennas are used.

Gaussian Mixture Learning for LDPC Coded BICM Receivers With Blanking Nonlinearity

With the aid of blanking nonlinearity, the low density parity check (LDPC) coded bit-interleaved coded modulation (BICM) has been jointly considered as a robust mitigation for the impulsive interference in orthogonal frequency division multiplexing (OFDM) systems. However, the Gaussian assumption for the nonlinear channel conditional probability induces the mismatched L-values in the conventional MAP demodulator. In this paper, combined with the pulse blanking optimization via the PEXIT analysis, we propose a novel MAP demodulator based on the Gaussian mixture model (GMM) and estimate the parameters with the expectation-maximization (EM) algorithm. Taking the L-band Digital Aeronautical Communication System Type1 (L-DACS1) as an example, the GMM-based MAP demodulator can obtain the PEXIT thresholds that match the decoding curves well and provide the better BER performance in the interference-limit channel environment.

Efficient Compressed Sensing Based Non-Sample Spaced Sparse Channel Estimation in OFDM System

This paper aims to develop an efficient compressed sensing (CS) based channel estimation method for non-sample spaced sparse channels in orthogonal frequency division multiplexing (OFDM) systems, which can effectively balance the channel estimation performance, spectral efficiency and computational complexity. To realize this goal, a novel delay tracking and residual norm minimization (DTRNM) method is proposed. In this method, the idea of reference delay grids (RDG) inspired by the delay tracking (DT) method proposed in [1] is formulated, which is proven to be much more efficient than current algorithms in estimating non-sample spaced sparse channels. Both theoretical derivation and simulation results show the effectiveness of the proposed method.

Novel Joint Subcarrier and Power Allocation Method in SWIPT for WSNs Employing OFDM System

In recent research trends, simultaneous wireless information and power transfer (SWIPT) has proved to be an innovative technique to deal with limited energy problems in energy harvesting (EH) technologies for wireless sensor networks (WSNs). In this paper, a method of subcarrier and power allocation for both EH and information decoding (ID) operations is proposed under orthogonal frequency division multiplexing (OFDM) systems, with an improved the quality of service (QoS) parameters. This proposed method assigns one group of subcarriers for ID and remaining group of subcarriers is assigned for EH, despite of applying any splitting schemes. We achieved maximum EH under the ID and power constraints with an effective algorithm for the first time incorporating the dual decomposition technique which deals with power and subcarrier allocation problem jointly. The obtained simulation outcomes in relation to power allocation ratio, subcarrier allocation ratio and energy harvested (EH) at the destination node proved better when compared to the schemes that contain water filling, time switching (TS) or power splitting (PS) approaches under different target transmission rates and transmitter and receiver distances.

Posture-Specific Breathing Detection.

Human respiratory activity parameters are important indicators of vital signs. Most respiratory activity detection methods are naïve abd simple and use invasive detection technology. Non-invasive breathing detection methods are the solution to these limitations. In this research, we propose a non-invasive breathing activity detection method based on C-band sensing. Traditional non-invasive detection methods require special hardware facilities that cannot be used in ordinary environments. Based on this, a multi-input, multi-output orthogonal frequency division multiplexing (MIMO-OFDM) system based on 802.11n protocol is proposed in this paper. Our system improves the traditional data processing method and has stronger robustness and lower bit relative error. The system detects the respiratory activity of different body postures, captures and analyses the information, and determines the influence of different body postures on human respiratory activity.

Lagrange interpolation based extended Kalman filter for phase noise suppression in CO-OFDM system

Abstract In this paper, for the first time, a novel Lagrange interpolation (LRI) based extended Kalman filter (EKF) is proposed to compensate inter-carrier interference (ICI) in coherent optical orthogonal frequency division multiplexing (CO-OFDM) system. Owing to the features of Wiener distribution for laser phase noise, our proposed second-order or higher-order LRI is more suitable for phase fitting than sub-symbol block algorithm based on linear interpolation (LI-SCPEC). Furthermore, to compensate the common phase error (CPE), a modified iteration-free blind (MIFB) algorithm is also designed in this paper. Comparing with the existing common IFB scheme, our method avoids phase misjudgment. By combining the MIFB with the LRI scheme, the accuracy of phase noise estimation and spectrum utilization can be effectively improved. The results of Monte Carlo simulation prove that our proposed scheme is effective in phase noise suppression in CO-OFDM system

Deep clipping noise mitigation using ISTA with the specified observations for LED‐based DCO‐OFDM system

Deep clipping is beneficial for the optical orthogonal frequency division multiplexing (O-OFDM) system, since it can lower the peak-to-average power ratio, reduce the direct current requirement in light emitting diodes (LEDs), and relax the bit-resolution requirement in digital-to-analogue converters (DACs). However, it is accompanied by more signal distortions. In this study, a deep clipping noise mitigation scheme using iterative shrinkage/thresholding algorithm (ISTA) with three steps is proposed to improve bit error rate (BER) performance of the LED-based DCO-OFDM systems. In the first step, the estimated observation interference is eliminated from the received symbols to minimise the negative effect of channel noise. In the second step, two strategies are presented to generate the specified observations thus reduce the component of measurement noise in the whole observation vector. In the last step, combining the generalised cross validation and the estimation of observation interference, the appropriate regularisation parameter are calculated for ISTA to improve the robustness of the sparse recovery performance. They use simulations to show that the proposed scheme can correct the deep clipping noise with favourable reconstruction quality, which significantly improves the BER performance and therefore assist the LED non-linearity mitigation.

Performance Analysis of Semi-Coherent OFDM Systems With Imperfect Channel Estimates

This work presents the exact symbol error rate (SER) analysis of semi-coherent demodulated systems in the presence of imperfect knowledge of the channel estimates. The SER is derived in the context of orthogonal frequency division multiplexing (OFDM) systems where a modulation-hybrid frame structure is considered to enable blind channel estimation using a decision-directed approach. The exact SER is derived and presented in a closed-form analytical expression, which is then used to compute an accurate formula for the mean squared error (MSE) of the channel estimates. The obtained analytical and simulation results show that the SER and MSE are highly dependent on the channel correlation factor. However, reliable SER can still be obtained for most practical channel models, particularly when receiver diversity is incorporated.

Carrier Frequency Offset Estimation for OFDM With Generalized Index Modulation Systems Using Inactive Data Tones

As carrier frequency offset (CFO) causes the loss of orthogonality among subcarriers and further degrades the performance of orthogonal frequency division multiplexing (OFDM) systems, it is of vital importance to estimate and compensate for the CFO. In this letter, we develop a novel scheme to estimate the CFO for OFDM with generalized index modulation (OFDM-GIM) in which the variable inactive data tones are exploited to improve the accuracy of CFO estimation. Specifically, in the proposed scheme, the receiver first estimates and compensates for the CFO based on the pre-assigned null subcarriers. Since only partial subcarriers are activated in OFDM-GIM systems, the energy detection approach is applied to detect the inactive data tones. Finally, both the detected inactive data tones and the pre-assigned null subcarriers are exploited to re-estimate the CFO. We also derive the asymptotic analytical results that are validated by simulations and shown to achieve higher accuracy of the CFO estimation.

A Low Rank Channel Estimation Scheme in Massive Multiple-Input Multiple-Output

Aiming at the problem of computational complexity of channel estimation, this paper proposes a low-complexity block matching pursuit (BMP) algorithm based on antenna grouping and block sparsity for frequency division duplex (FDD) massive Multiple-input Multiple-output orthogonal frequency division multiplexing (OFDM) systems. The system coherence time may be exceeded as a result of time consumption when adopting an orthogonal pilot symbol in the time domain. To solve this problem, an antenna grouping transmission scheme is proposed to reduce the total channel estimation time by sacrificing the observed data length. The simulation results show that the proposed BMP algorithm has good anti-noise performance, and it can accurately determine the non-zero position of the sparse vector and adaptively determine the sparsity of the channel, which effectively translates to improved channel estimation performance and better overall system performance than the existing algorithms.

Joint window and filter optimization for new waveforms in multicarrier systems

One of the demands of the next-generation wireless communication systems is being supportive to asynchronous traffic types. In order to meet this demand, many waveform candidates for next-generation wireless communication systems have low out-of-subband emissions (OOSBE) of the transmitted signal, and the popular ones deploy either filtering or windowing at the transmitter. In this paper, a joint windowing and filtering multi-carrier waveform based on a generalized orthogonal frequency division multiplexing (OFDM) system is proposed. A joint window and filter optimization problem to minimize OOSBE is also formulated. The optimization problem is first divided into two solvable subproblems using interior-point methods, and then an iterative algorithm is proposed to obtain the optimal window and filter pair. Simulation results suggest that the proposed joint windowing and filtering waveform has an advantage in suppressing OOSBE or enhancing spectral efficiency, and is more robust to frequency asynchronism compared to waveforms deploying only either filtering or windowing.

Joint Power Allocation for OFDM-Based Non-Concurrent Two-Way AF Relaying

We consider an amplify-and-forward non-con-current two-way relaying for an orthogonal frequency division multiplexing (OFDM) system, where the base station (BS) serves a transmit-only user (TU) and a receive-only (RU) user, whose receive signal is interfered by the TU transmit signal. We design an overhearing-based interference cancellation scheme wherein the RU collects side-information by overhearing the TU transmit signal, and uses that to cancel its interference. We then jointly allocate power at the TU, BS, and the relay nodes across OFDM subbands to optimize the sum-rate, which is a non-convex problem. We solve it using successive convex approximation (SCA), which approximates the non-convex sum-rate optimization as a sequence of convex programs. The SCA approach is shown to converge within few iterations. Numerical results demonstrate the improved performance of the proposed algorithm over other state-of-the-art algorithms.