We propose and demonstrate a physical-layer security scheme using chaotic active constellation extension (ACE) in orthogonal frequency division multiplexing (OFDM). A super OFDM frame is generated by chaotic frame interleaving in ACE, where hyper digital chaos is applied to generate the chaotic interleaving vectors. A huge key space of size 2048! is provided via the multi-fold encryption to guarantee the secure OFDM data transmission, while the transmission performance is effectively improved via the chaotic ACE algorithm. Secure transmission of 8.9-Gb/s 16-QAM encrypted OFDM signals is demonstrated over a 20-km standard single-mode fiber, which shows reliable robustness against any exhaustive attacks. Moreover, the proposed chaotic ACE scheme improves the spectral efficiency of OFDM transmission, since it does not require any sideband to transmit the frame-interleaving information.

Performance-Improved Secure OFDM Transmission Using Chaotic Active Constellation Extension

In this paper, we develop an optimal perturbation approach to design companders to mitigate the peak-to-average power ratio problem experienced by orthogonal frequency division multiplexing (OFDM) signals. Specifically, we generalize single-linear component design approaches, which modify the Rayleigh-distributed OFDM signal amplitude tail, to use of multiple contiguous piecewise linear components. The new compander design approach defines and solves a constrained optimization problem to optimally perturb a given proposed multicomponent piecewise linear segment set to meet the power and probability density function constraints. The use of multiple piecewise linear components provides greater design flexibility to meet the constraints, thus providing solutions for pairs of inflection points and cutoff values where more rigidly designed companders fail to exist. We present examples of compander design, and demonstrate compander performance through numerical simulation. The new compander design approach can generate companders that offer performance improvements over current companders.

Compander Design for OFDM PAPR Reduction Using Optimal Perturbation of Piecewise Linear Segments

In this letter, we propose a machine learning (ML) approach to peak-to-average power ratio (PAPR) reduction in the downlink channel of the digital Massive Multiple Input Multiple Output (MIMO) system with orthogonal frequency division multiplexing (OFDM) signal. Naturally, substantial PAPR reduction is achieved when the noise after PAPR reduction is distributed in both frequency and spatial domains following the maximum allowed error vector magnitude (EVM). However, such an approach requires time-consuming manual tuning of hyperparameters for each scenario. To overcome this problem, we propose to compute an optimal hyperparameter function. Then we propose an efficient approximation for this function to enable the PAPR reduction based on the classical ML approaches.

Machine Learning-Assisted PAPR Reduction in Massive MIMO

The most famous and attractive strategy used in wireless communication for huge transmission of data with higher rate was orthogonal frequency division multiplexing (OFDM) approach. Efficient methods are important for PAPR reduction in high-speed wireless communication systems. The reduction of PAPR in OFDM system has been carried out with one of the most familiar approach called Partial transmit sequences (PTS). Various techniques are already presented for reducing the PAPR, some of them are, clipping, SLM, and PTS. From that PTS is considered as an efficient method because the PAPR was reduced by PTS without causing any signal distortion. In this work, PTS along with hybridization optimization algorithm named as PS–GW will be implemented to get the minimum performance on PAPR and computational complexity. The PS–GW is a combination of both the Particle Swarm Optimization (PSO) and Grey Wolf Optimizer (GWO) which search the optimal combination of phase rotational factors efficiently. A fundamental thought in this method was that the capacity of exploitation in PSO was enhanced with the capacity of investigation in GWO to create a two variations in quality. The results produced by this proposed method shows that the reduction was effectively determined in both PAPR and computational complexity.

https://ietresearch.onlinelibrary.wiley.com/doi/pdf/10.1049/iet-com.2019.0261

Hybrid PS–GW optimised PTS scheme for PAPR reduction in OFDM system

Selective mapping (SLM) is one of the core techniques to mitigate the problem of high PAPR in the MIMO-OFDM system. But the complexity of inverse fast Fourier transform (IFFT) increases with increase in the number of phase sequence in the conventional SLM (C-SLM) scheme. However, we can generate alternate signal sequences along with the OFDM sequence without increasing the number of IFFT. This can be achieved by combining in both SLM with additive mapping (SLM-AM) and U2 phase sequence (SLM-U2) respectively. The computational complexity of both (SLM-AM) and (SLM-U2) is comparatively lesser than the C-SLM without degradation the BER and PAPR performance. But these schemes require some extra memory to save the alternative sequences. In this paper we derive a new low computational complexity equation for combination of both (SLM-AM) and (SLM-U2) schemes using M-QAM and M-PSK modulation in MIMO-OFDM system. In the proposed MIMO-OFDM model, we also analyze the computational complexity and PAPR reduction performance of various schemes like C-SLM, SLM-U2, SLM-AM and SLM-AM-U2 respectively. It has been observed that proposed (SLM-AM-U2) provides best PAPR reduction performance. Also, the computational complexity is least in this case.

Performance Analysis of MIMO-OFDM System Using SLM with Additive Mapping and U 2 Phase Sequence for PAPR Reduction

The active constellation extension (ACE) scheme provides an effective means of reducing the peak-to-average power ratio (PAPR) without the need for side information. However, traditional ACE schemes involve a time-consuming iteration process. This letter proposes a novel ACE scheme, along with a low-complexity implementation, for orthogonal frequency division multiplexing (OFDM) systems, where the subcarrier grouping technique is adopted to increase the degrees of freedom in the optimization process. The simulation results show that for an OFDM system with 256 subcarriers and 16-ary quadrature amplitude modulation, the proposed scheme achieves a maximum performance gain of 4.3 dB compared with the original OFDM signal given that $\mathrm { Prob}(\mathrm {PAPR}(\mathbf {x})>\gamma )=10^{-3}$ .

PAPR Reduction in OFDM Systems Using Active Constellation Extension and Subcarrier Grouping Techniques

In this letter, the realizable direct-sequence code-division multiple-access (DS-CDMA) system occupying Nyquist bandwidth is developed Several frequently-adopted spreading codes are examined for realization feasibility in the bandlimited DS-CDMA system It is shown that Nyquist chip-rate transmission can be practically achieved for the bandlimited DS-CDMA system using frequently-adopted spreading codes at the sacrifice of very little user capacity

Realizable Bandlimited DS-CDMA System Occupying Nyquist Bandwidth

This paper considers the finite-order filter design problem for the source and multiple full-duplex (FD) relays in a cooperative communication system under frequency-selective fading channels. The goal is to optimize the source and relay filters such that the end-to-end signal-to-interference-plus-noise ratio (SINR) of minimum mean-squared error decision-feedback equalizer (MMSE-DFE) can be maximized. The resultant design problem is very difficult since we need to deal with self interference (SI), inter-relay interference (IRI), and inter-symbol interference (ISI) at the same time. Novel designs are then proposed to overcome the difficulty in this work. Transforming the signals into the frequency domain and using some optimization techniques, we first theoretically derive the power spectrum of the source filter and the spectrums of the relay filters. Then, the finite-order design is developed to approach the derived spectrums. Based on the weighted least-square (WLS) criterion, the Steiglitz-McBride method is exploited to obtain the filter coefficients in finite lengths. Numerical results demonstrated that complete removal of SI may not be a good strategy; preserving a certain amount of SI at each relay instead provides better SINR performance.

Finite-Order Filter Designs of Source and Multiple Full-Duplex Relays for Cooperative Communications in Presence of Frequency- Selective Fading and Inter-Relay Interference

This paper studies the joint common beamforming (CB) and the superposition coding (SC) design for a two-user massive multiple-input single-output (MISO) system with non-orthogonal multiple access (NOMA). Conventional beamforming design has to estimate the uplink channel state information (CSI) of the near and the far users separately. By the channel reciprocity, the CB is then constructed by combining two uplink CSIs together with certain rules. The design needs two training phases to separately estimate the CSI of the two users but combine them subsequently. In this paper, we propose a model adopting common pilots for the near and far users to estimate an uplink combined channel. In this model, only one training phase is required, and the CB is then constructed by the estimated combined channel directly. With the estimated combined channel, the joint CB and SC design is equivalent to optimizing the pilot power allocation and SC factor. However, the associated optimization is not convex. We then adopt the majorization-minimization approach to conduct the optimization problem and numerically find that the solutions meet the optimum points. Simulations verify the effectiveness of our joint design and show the superior performance not only for the transmission rate but also the reduced overhead.

A Novel Common Beamforming and Superposition Coding Design for Massive MISO-NOMA Systems

In this paper, novel finite-order filter designs for source and multiple full-duplex relays (FDRs) are proposed to improve the spectrum efficiency and link reliability of amplify-and-forward cooperative communication networks. In contrast to the single relay, FDRs suffer not only self-interference (SI), but inter-relay interference (IRI). By taking SI and IRI into consideration, this work aims at the joint design of the source filter, relay filters, and the linear minimum squared error (LMMSE) receiver. The finite-order filters are conducted in two stages. In the first stage, the spectrums of the source and FDRs are computed. Since the optimization problem involves the nonlinear equality constraint, we adopt the generic nonlinear equality alternating direction method of multipliers (neADMM) with a damping procedure to find the stationary solution. In the second stage, the filter coefficients are developed to approach the derived spectrums by using a weighted least square criterion. The numerical results justify the validity of the proposed designs. Interestingly, the results show that preserving a certain amount of SI at the FDRs not only reduces the implementation cost but improves the end-to-end signal-to-interference-plus-noise ratio (SINR).

Finite-Order Filter Designs for Source and Multiple FDRs in Wideband Cooperative Systems

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