Non-contiguous Orthogonal Frequency Division Multiplexing Research Articles

Joint Sub-Band and Transmission Rate Selection for Anti-Jamming Non-Contiguous Orthogonal Frequency Division Multiplexing System: An Upper Confidence Bound Based Reinforcement Learning Approach

Reinforcement Learning (RL) has been employed to assign transmission parameters to all sub-carriers in a set frequency band for anti-jamming Orthogonal Frequency Division Multiplexing (OFDM) systems. However, prior works often overlooked the influence of wireless environment fading and convergence issues stemming from overly large parameter sets. To address these challenges, an anti-jamming scheme was proposed based on the Non-Contiguous Orthogonal Frequency Division Multiplexing (NC-OFDM) communication system integrated with reinforcement learning. First, all sub-carriers were divided into sub-bands, and a Finite State Markov Sub-bands (FSMS) model was established to describe the time-varying fading characteristics of each sub-band by combining Adaptive Modulation and Coding (AMC) technology. To mitigate instability due to the fading channel, a joint sub-band and modulation anti-jamming decision scheme was adopted, enabling the transmitter to select the optimal sub-band and transmission rate. Ultimately, this decision-making process was modeled as a Markov Decision Process (MDP), and an Upper Confidence Bound based Q-learning (UCB-Q) anti-jamming algorithm was proposed for obtaining the joint sub-band and transmission rate selection strategies. Simulation results indicate that the proposed algorithm demonstrates enhanced speed and superior average throughput. Additionally, the algorithm showcases the same commendable anti-jamming performance in scenarios with time-varying dynamic jamming.

Time-varying Metamaterial-enabled Directional Modulation Schemes for Physical Layer Security in Wireless Communication Links

Novel transmission schemes, enabled by recent advances in the fields of metamaterial (MTM), leaky-wave antenna (LWA) and directional modulation (DM), are proposed for enhancing the physical layer (PHY) security. MTM-LWAs, which offer compact, integrated, and cost-effective alternatives to the classic phased-array architectures, are particularly of interest for emerging wireless communication systems including Internet-of-Things. The proposed secure schemes are devised to accomplish the functionalities of directional modulation (DM) transmitters for orthogonal frequency-division multiplexing (OFDM) and non-contiguous OFDM transmissions, while enjoying the implementation benefits of MTM-LWAs. Specifically, transmitter architectures based on the idea of time-modulated MTM-LWA have been put forth as a promising solution for PHY security for the first time. The PHY security for the proposed schemes are investigated from the point of view of both passive and active attacks where an adversary aims to decode secret information and feed spurious data to the legitimate receiver, respectively. Numerical simulations reveal that even when the adversary employs sophisticated state-of-the-art deep learning based attacks, the proposed transmission schemes are resistant to these attacks and reliably guarantee system security.

Sidelobe Reduction in NC-OFDM-Based CRNs Using Differential Evolution-Assisted Generalized Sidelobe Canceller

Noncontiguous orthogonal frequency division multiplexing (NC-OFDM) is considered a suitable candidate for the cognitive radio network (CRN) to accomplish efficient data transmission. The NC-OFDM allows secondary users (SUs) to access the primary user (PU) spectrum while being detected idle. However, interference may occur in the adjacent frequency bands of the PU due to sidelobes of the SU transmission. The use of cancellation carriers (CCs) and generalized sidelobe canceller (GSC) is a widely adopted technique to tackle the sidelobes. To this end, this paper presents a differential evolution- (DE-) based GSC (DE-GSC) scheme to suppress unwanted sidelobes. At first, in the DE-GSC1 scheme, the adaptive weight vector is calculated using the DE algorithm while considering the complete samples of the sidelobes for optimization. The optimized weights are then added with the original weights to reduce the sidelobe issue. Next, in the DE-GSC2 scheme, selected elements for the adaptive weight vector near the main NC-OFDM signal are computed using the DE to reduce the search space. The performance of the proposed methods in terms of power spectral density (PSD) is compared with some of the recent techniques employing five different scenarios. Simulation results in the presence of single and multiple spectral hole scenarios validate that the proposed DE-GSC1 and DE-GSC2 methods result in enhanced suppression performance compared with the: original signal, simple CC, simple GSC, DE-based CC (DE-CC), and genetic algorithm- (GA-) based CC (GA-CC) schemes.

Robust time synchronization for NC-OFDM cognitive radio systems

In this paper, we propose a time-synchronization method for non-contiguous orthogonal frequency division multiplexing (NC-OFDM) systems. NC-OFDM is a modulation and multiplexing technique that is often used for cognitive radio (CR) systems. In OFDM-based CR systems, time synchronization is limited by a number of challenges: multipath channels with a high delay spread, a narrowband interference (NBI), and minimal number of subcarriers. Indeed, the proposed method addresses these problems since it does not require information on subcarriers nor the NBI center frequency; moreover, it works well on the multipath channel with a high delay spread.

Learning-Aided Physical Layer Attacks Against Multicarrier Communications in IoT

Internet-of-Things (IoT) devices that are limited in power and processing are susceptible to physical layer (PHY) spoofing (signal exploitation) attacks owing to their inability to implement a full-blown protocol stack for security. The overwhelming adoption of multicarrier techniques such as orthogonal frequency division multiplexing (OFDM) for the PHY layer makes IoT devices further vulnerable to PHY spoofing attacks. These attacks which aim at injecting bogus/spurious data into the receiver, involve inferring transmission parameters and finding PHY characteristics of the transmitted signals so as to spoof the received signal. Non-contiguous (NC) OFDM systems have been argued to have low probability of exploitation (LPE) characteristics against classic attacks based on cyclostationary analysis, and the corresponding PHY has been deemed to be secure. However, with the advent of machine learning (ML) algorithms, adversaries can devise data-driven attacks to compromise such systems. It is in this vein that PHY spoofing performance of adversaries equipped with supervised and unsupervised ML tools are investigated in this paper. The supervised ML approach is based on deep neural networks (DNN) while the unsupervised one employs variational autoencoders (VAEs). In particular, VAEs are shown to be capable of learning representations from NC-OFDM signals related to their PHY characteristics such as frequency pattern and modulation scheme, which are useful for PHY spoofing. In addition, a new metric based on the disentanglement principle is proposed to measure the quality of such learned representations. Simulation results demonstrate that the performance of the spoofing adversaries highly depends on the subcarriers' allocation patterns. Particularly, it is shown that utilizing a random subcarrier occupancy pattern secures NC-OFDM systems against ML-based attacks.

Spectrum shaping using NC‐OFDM for cognitive radio applications

Cognitive radio (CR) is an innovative technology that supports dynamic spectrum access to utilise the spectrum more efficiently in an opportunistic manner without interfering with the licensed users. Multi-carrier modulation techniques such as orthogonal frequency division multiplexing (OFDM) is identified as one of the suitable candidates for the design of CR systems. To provide high data rates while avoiding interference with licensed users, a variant of OFDM called non-contiguous OFDM (NC-OFDM) is used in CR. NC-OFDM is useful for dynamic shaping of spectrum based on the channel impairments, interference and jamming threats. In this work, the customised NC-OFDM transceiver link is simulated and compared with the customised OFDM link in the MATLAB environment. It is implemented in Zynq-7000 System-on-Chip (SoC) 7Z020 with radio-frequency front-end board, AD-FMCOMMS3-EBZ Software Defined Radio platform. Implementation of this link is carried out on Spartan-3A FPGA and compared the hardware resource utilisation with Zynq platform. It is observed that the Zynq platform utilises less hardware resources for the implementation. The transmitter spectrum, spectrum after de-activating unwanted sub-carriers, the spectrum shaping using raised cosine filtering, spectrum sensing using the correlation of known pattern and FFT-based spectrum sensing are also simulated in the MATLAB.

Simple metric to enhance multiple signaling techniques for nonlinear OFDM transmission

This paper proposes a simple and effective metric to choose the best orthogonal frequency division multiplexing (OFDM) signal within multiple signaling (MS) techniques such as PTS (Partial Transmit Sequence) or SLM (Selective Mapping), in order to reduce the deleterious effects of nonlinear amplification on the bit error rate (BER). The proposed metric is derived on the basis of a simplified mathematical analysis of the distortion produced by the nonlinear amplification and is calculated without the use of any mathematical model of the amplifier. This gives rise to lower computational cost in comparison to other metrics recently proposed with the same aim, besides reducing sensitivity to model mismatch. A simulation-based BER comparison over contiguous and non-contiguous OFDM shows that the advantages of the metrics here proposed are obtained without significant BER performance loss.

Optimization of Non-Contiguous OFDM based Data Transmission Schemes in Cognitive Radio Transceivers

Optimization of Non-Contiguous OFDM based Data Transmission Schemes in Cognitive Radio Transceivers

Dynamic spectrum access based simultaneous non-contiguous OFDM radar sensing and communication

With the concept of advanced intelligent transportation systems, the integration of data with technology underway with internet of things brings the concept of always connected and cognizant vehicles as an application area. The major constituents of internet of things are connection, convergence, convenience and the connected car. Road safety and vehicular infotainment are the most emerging issues for the automakers in this regard. Implementation of vehicular safety in urban lanes requires vehicle to vehicle sensing and data communication simultaneously. Because of operation spectrum scarcity, the requirement of vehicle to vehicle sensing and communication on a single platform simultaneously empowered with cognitive radio would be cost efficient. Dynamic Spectrum Access based integrated radar sensing and wireless communication transceiver is demonstrated in this work. In the proposed hardware model a direct sequence spread spectrum radar transceiver and an non contiguous orthogonal frequency division multiplexing communication transceiver is used.

Joint PAPR reduction and sidelobe suppression in NC-OFDM based cognitive radio using wavelet packet and SC techniques

Non-contiguous orthogonal frequency division multiplexing (NC-OFDM) is an appropriate transmission technique for cognitive radio (CR) systems. It guarantees an efficient spectrum utilization for high data rate wireless systems. However, NC-OFDM system suffers from two main problems, which are the high peak-to-average power ratio (PAPR) and the high sidelobe level. In this paper, two techniques are proposed to jointly reduce the PAPR and suppress the out-of-band (OOB) radiation caused by the high sidelobe levels. In both of the two proposed techniques, an inverse discrete wavelet packet transform (IDWPT) is used, once with the signal cancellation (SC) for the first proposed technique (IDWPT-SC), and once again with the sub-signal cancellation (Sub-SC) for the second proposed technique (IDWPT-Sub-SC). The use of the IDWPT helps decreasing the fluctuations in the transmitted signal, and hence reduces the PAPR and the OOB radiation. The simulation results show that, the proposed techniques provide better PAPR and sidelobe cancellation performance compared to the other techniques. Moreover, the two proposed techniques also conserve almost the same computational complexity as the other techniques.

A hybrid technique for joint PAPR reduction and sidelobe suppression in NC-OFDM based cognitive radio systems

Non-Contiguous Orthogonal Frequency Division Multiplexing (NC-OFDM) based Cognitive Radio (CR) system automatically identifies available frequency gaps in spectrum and utilize them to meet the requirement of higher data rates in 5G technology. It allocates some unauthorized users to access those frequency gaps without causing interference to the adjacent users. Besides the advantages of NC-OFDM based CR system, it suffers from two main drawbacks which are high Peak-to-Average Power Ratio (PAPR) and large spectrum sidelobe power. In order to overcome these drawbacks, we propose a hybrid technique that jointly reduces PAPR and sidelobe power. This technique involves a two level or modified clipping scheme for PAPR reduction. For sidelobe power suppression, signal cancellation symbols are generated by calculating Error Vector Magnitude (EVM) that are added to the original data bits. Here, the problem of sidelobe suppression can be formulated as a quadratically constrained quadratic program (QCQP), and the optimal solution can be obtained by the standard interior-point method. By combining two techniques we can solve these two issues in NC-OFDM based CR system simultaneously. From the simulation results, it is inferred that our proposed method outperforms interms of both PAPR, sidelobe power suppression over other existing methods and also improves the BER performance of the system.

Improved algorithms for interference suppression in non-contiguous orthogonal frequency division multiplexing-based cognitive radio systems

Non-contiguous orthogonal frequency division multiplexing is considered as an auspicious scheme for the cognitive radio (CR) systems. It has the abilities such as spectral efficiency, multiple path delay spread and robustness against channel fading. However, due to its high sidelobes, it distorts the signals of the neighboring users including cognitive radio users (CRUs) as well as licensed users. In this paper, we proposed two novel metaheuristic algorithms, i.e., Cuckoo search algorithm and Firefly algorithm, to estimate the amplitudes of cancelation carriers which are used for the suppression of sidelobes. The effectiveness of the proposed algorithms is shown in single as well as the multiple CRUs environment. Simulations results in terms of power spectral density show that with the help of proposed algorithms significant reduction in sidelobes is achieved as compared with the existing methods.

ML Detection and PAPR Reduction of NC-OFDM Signals Based on Clipping Noise Suppression for Cognitive Radio

We propose a new scheme based on clipping noise suppression to effectively reduce the peak-to-average power ratio (PAPR) of non-contiguous orthogonal frequency division multiplexing (NC-OFDM) signals that are used in dynamic spectrum access networks such as cognitive radio. Applying the conventional clipping method to NC-OFDM presents a problem in that not only the subcarriers used by secondary users (SUs) are affected, but the subcarriers of primary users (PUs) are also affected. This paper proposes a method for improving PAPR reduction performance by dividing the subcarriers, depending on the use of subcarriers by the SU, and applying suppression of different types of clipping noise to the subcarriers used by the SU and other subcarriers. Simulation results show that the lower the suppression of the clipping noise for subcarriers not used by the SU, the lower the PAPR of the NC-OFDM signal becomes.

Design of acoustic transmission along drill strings for logging while drilling data based on adaptive NC-OFDM

This paper represents a new scheme using the drill strings as the medium to deliver logging information via a compressional acoustic wave. Considering the comb-type frequency characteristics of an acoustic channel, non-contiguous orthogonal frequency division multiplexing (NC-OFDM) has been selected as a promising technique for achieving high-rate transmission with high spectral efficiency and immunity to multipath channels. However, the irregular pilot design and high peak-to-average power ratio (PAPR) halted the widespread application of NC-OFDM. To overcome these two disadvantages, we propose an adaptive pilot design scheme in which the dynamic range of available frequency is pre-simulated and an improved discrete Fourier transformation based least square (PDFT-LS) channel estimation scheme to obtain the channel characteristics and an improved selected mapping (PSLM) scheme with low-complexity to reduce the PAPR of the transmitter are applied. Computer simulation and circuit test results are presented to demonstrate that the data transmission rate can be in excess of 500bps along a 53.76m experimental channel under the conditions of the simulated impulse noise and surface noise with a low bit error rate (BER), and the PAPR reduction performance can reach almost the same as that of a conventional SLM (CSLM) scheme.

Analytical bound for the CCDF of Crest Factor in NC-OFDM Systems

Non-contiguous orthogonal frequency division multiplexing (NC-OFDM) is a promising framework for wireless communication systems due to OFDM characteristics like the spectral bandwidth efficiency, robustness to frequency selective fading channels, etc. However, it has been widely known that multicarrier signals generated by OFDM technique exhibit a large peak to average power ration (PAPR), one of the main impediment that has limited the applicability of OFDM systems. Several approaches are employed in literature to derive the PAPR distribution and thus try to reduce it in OFDM context, as Central limit theorem and modern extreme value theory. In new contexts like NC-OFDM systems when flexible access to spectrum is done with non-contiguous portions, the PAPR distribution remains generally unknown, and it is necessary to describe it, since this is one of the key design parameters. In this correspondence, we develop the PAPR bound expression in NC-OFDM context.

Color Image Transmission in Single-User Digitally Precoded Mmwave Non-Contiguous Orthogonal Frequency Division Multiplexing Wireless Communication System

Non-contiguous orthogonal frequency division multiplexing (NC-OFDM) has been considered as an outstanding technique for high data rate 5G and beyond 5G wireless communications. In this paper, we have made comprehensive performance evaluative study for a single user NC-OFDM scheme implemented wireless communication system under consideration of millimeter-wave (mmWave) large MIMO antenna configuration. In our 32×256 uniform linear antenna (ULA) configured simulated system under investigation, three selective modern channel coding (LDPC, Repeat and Accumulate and (3, 2) SPC) with a single higher order digital modulation (256-QAM)) and three signal detection (ZF, MMSE and LR-based linear detection) techniques have been utilized. On consideration of color image transmission in AWGN and Rayleigh fading channel, it is observable from MATLAB based simulation study that the Repeat and Accumulate channel encoded simulated system is very much robust and effective in retrieving color image under utilization of MMSE signal detection technique.

Minimizing the Error Vector Magnitude With Constrained Cubic Metric and Spectral Sidelobe in NC-OFDM-Based Cognitive Radio Systems

In this paper, we propose a minimized error vector magnitude (M-EVM) scheme to simultaneously reduce the cubic metric (CM) and spectral sidelobe in noncontiguous orthogonal frequency-division multiplexing (NC-OFDM)-based cognitive radio (CR) systems by modifying the constellations on the secondary user (SU) subcarriers and adding canceling symbols on the primary user (PU) subcarriers. The proposed M-EVM scheme formulates an optimization problem, which minimizes the EVM with constraints of the CM and spectral sidelobe. Furthermore, we propose an iterative approximation algorithm to solve the optimization problem. Simulation results show that the M-EVM scheme offers significant reductions of the CM and spectral sidelobe.

Iterative Reduction of Out-of-Band Power and Peak-to-Average Power Ratio for Non-Contiguous OFDM Systems Based on POCS

Iterative Reduction of Out-of-Band Power and Peak-to-Average Power Ratio for Non-Contiguous OFDM Systems Based on POCS

PAPR analysis in noncontiguous OFDM systems

AbstractNoncontiguous orthogonal frequency‐division multiplexing (NC‐OFDM) is a modulation technique suitable for 5G communications. It achieves high spectral efficiency due to aggregation and modulation with nonzero data symbols of only nonoccupied spectrum resources (subcarrier blocks). Similarly as in other multicarrier schemes, one of its main drawbacks is the high variation of instantaneous signal power measured typically by means of peak‐to‐average power ratio (PAPR). Although a lot of research effort has been put in OFDM PAPR characterization, there is a need for such work in the case of NC‐OFDM. This paper finds that PAPR distribution of NC‐OFDM is different than in the case of OFDM. The analysis was done by means of both simulations and analytical derivations. Lower and upper PAPR complementary cumulative distribution function bounds are provided for NC‐OFDM that are much tighter than state‐of‐the‐art solutions.

Cooperative subcarrier sensing using antenna diversity based weighted virtual sub clustering

The idea of cooperation and the clustering amongst cognitive radios (CRs) has recently been focus of attention of research community, owing to its potential to improve performance of spectrum sensing (SS) schemes. This focus has led to the paradigm of cluster based cooperative spectrum sensing (CBCSS). In perspective of high date rate 4th generation wireless systems, which are characterized by orthogonal frequency division multiplexing (OFDM) and spatial diversity, there is a need to devise effective SS strategies. A novel CBCSS scheme is proposed for OFDM subcarrier detection in order to enable the non-contiguous OFDM (NC-OFDM) at the physical layer of CRs for efficient utilization of spectrum holes. Proposed scheme is based on the energy detection in MIMO CR network, using equal gain combiner as diversity combining technique, hard combining (AND, OR and Majority) rule as data fusion technique and antenna diversity based weighted clustering as virtual sub clustering algorithm. Results of proposed CBCSS are compared with conventional CBCSS scheme for AND, OR and Majority data fusion rules. Moreover the effects of antenna diversity, cooperation and cooperating clusters are also discussed.