Orthogonal time frequency space (OTFS) modulation has been proposed to achieve outstanding performances over delay-Doppler channels in comparison with orthogonal frequency division multiplexing (OFDM) systems. Particularly, transmitter and receiver structures of OTFS are same as those of asymmetric OFDM (A-OFDM) waveforms, and OTFS is simplified as A-OFDM over static multipath channels. In this paper, we propose an integrated waveform framework based on weighted-type fractional Fourier transform (WFRFT) with two-dimensional adjustable parameters and strong scalability, called as WFRFT-OTFS, which can be reduced to OTFS, A-OFDM, hybrid carrier (HC), OFDM and other waveforms. Basically, theoretical BER expressions of integrated WFRFT-OTFS framework over multipath channels with zero forcing (ZF) and minimum mean square error (MMSE) receivers are derived through fusing different waveform components and verified by simulation results.

In cognitive radio networks (CNRs), spectrum sensing data falsification (SSDF) attacks can severely deteriorate the performance of the collaborative spectrum sensing (CSS), which may be worse compared with the performance of the independent spectrum sensing (IndSS) under massive SSDF attacks. In this letter, a novel algorithm for defending against massive SSDF attacks is investigated from the perspective of honest secondary users (HSUs). In the proposed algorithm, each HSU evaluates the reliability of the CSS results. The CSS results with high reliability value are employed by secondary users (SUs) as final sensing results. However, its own sensing results are used if reliability value of CSS results is lower than the certain threshold. Theoretical derivation for the threshold of the reliability value is explained. Simulation results verify the effectiveness of the proposed scheme and indicate that our proposed algorithm can be considered as the extension of existing anti SSDF attacks algorithms.

Orthogonal Time Frequency Space (OTFS) has attracted the attention of researchers due to its excellent BER performance in high-speed mobile scenarios. In this paper, a low complexity Minimum Mean Square Error Serial Interference Cancellation (MMSE-SIC) receiver is proposed, which replaces the computationally intensive matrix inversion calculations in the symbol decision process with two low complexity algorithms. Firstly, a low complexity LDLH decomposition algorithm is proposed based on the properties of the equivalent channel matrix. Secondly, a low complexity algorithm is put forward for the inversion of lower triangular matrices. Finally, the concept of adjustable parameter is introduced to achieve dynamic adjustment of complexity. Simulation results demonstrate that the proposed algorithm achieves significant performance gains compared to the linear equalization algorithm and similar BER performance as the traditional SIC algorithm with reduced complexity.

Orthogonal time frequency space (OTFS) modulation has been put forward to achieve better performances over delay-Doppler channels in comparison with orthogonal frequency division multiplexing (OFDM) systems. In this paper, a nonlinear corrective active constellation expansion (NC-ACE) method is firstly proposed in OTFS waveform to achieve precise control of peak-to-average power ratio (PAPR) and BER performances due to its nonlinear compression characteristics. Compared to linear constraint of clipping and filtering process in traditional active constellation expansion (ACE) and bounded distortion ACE (BD-ACE) strategies, nonlinear compressed clipping noise is considered with a flexible curvature control coefficient. According to flexible features of NC-ACE, a bridge between optimal suppression and no reduction of PAPR performances is established in OTFS systems, where tradeoff between PAPR and BER performances can be further obtained.

Orthogonal Time Frequency Space (OTFS) is proposed to improve the performance of Orthogonal Frequency Division Multiplexing (OFDM) in time-variant channels. However, when Message Passing (MP) algorithm is utilized, the receiver always makes a tradeoff between BER performance and convergence speed due to the damping factor. In this letter, a Variable Damping factor Message Passing (VD-MP) algorithm is proposed to address this situation. This algorithm divides the range of the probability mass function (PMF) into multiple subintervals, with different damping factors in each subinterval. In addition, we also propose an iterative comparison algorithm to search the optimal damping factors for corresponding subintervals. Finally, simulation results show that in comparison with the MP algorithm, better BER performance with almost the same convergence speed can be obtained in proposed VD-MP algorithm with the same complexity.

This letter presents a novel index modulation framework called OFDM with Dual Frequency Index Modulation (OFDM-DFIM) to reduce the complexity of index modulation technology. We split subcarriers in subblock into two equal parts and original indices are derived from only one part. To compensate for lessened SE, the in-phase and quadrature components of $M$ -ary symbols are independently index modulated, which depends on indices and input strings, jointly. The OFDM-DFIM principle is applied in two different implementations, i.e., OFDM-DFIM-I and OFDM-DFIM-II. Specifically, all symbols in OFDM-DFIM-I share the same sequence to determine active positions, which can achieve diversity gain and result in better BER performance. In OFDM-DFIM-II, different symbols are controlled by different sequences to get higher SE. Moreover, a two-stage log-likelihood ratio detector is proposed to ease the computational burden. Simulation results show that the proposed two schemes exhibit promising results in both SE and BER performances.