Reflection modulation based on reconfigurable intelligent surface (RIS) is considered to be a promising information transfer mechanism, which does not require any additional radio frequency chains. However, existing reflection modulation schemes consider manipulating the ON/OFF states of RIS elements, which may result in some power loss. In this paper, we propose a new scheme, called RIS-aided quadrature reflection modulation (RIS-QRM), for better utilizing the reflection power in RIS-aided downlink multiple-input single-output (MISO) wireless systems. To this end, RIS-QRM partitions the RIS elements into two subsets in order to reflected the incident signals towards two orthogonal directions by using passive beamforming and encodes its local data onto the two partitions. A closed-form expression for the unconditional pairwise error probability of RIS-QRM in Rician fading is derived assuming maximum-likelihood detection at the receiver. Moreover, a low-complexity detection method that decouples the joint search of the constellation symbol and the RIS element partition is proposed. Computer simulation results corroborate the effectiveness of RIS-QRM and validate the analytical results. It is shown that RIS-QRM improves the error performance of the additional bits delivered by the RIS without deteriorating the error performance of the bits modulated on the constellation symbol, as compared to ON/OFF-based RIS-aided schemes.

In this paper, we investigate the performance of simultaneous wireless information and power transfer (SWIPT) cooperative amplify-and-forward (AF) communication systems in shadowed Nakagami- $m$ fading channels. Both coherent and non-coherent modulations, namely, binary phase-shift keying (BPSK) and binary differential phase-shift keying (BDPSK) are considered. We propose closed-form expressions of the moment generating function (MGF) and the probability density function (PDF) for the received signal-to-noise ratio (SNR) of the cooperative link. Based on this, we further derive the average bit-error-rate (BER) and the outage probability expressions for the systems with both BPSK and BDPSK modulations. All of these expressions are given in closed-form except one in single integral that can be easily evaluated using numerical integration methods. Numerical results are used to confirm the validity of the proposed analytical results. It is shown that the performance of the systems is more susceptible to the fading parameter $m$ than to the shadowing level $\sigma_s$ and does not change much with the power splitting ratio.

In this paper, we investigate the performance of simultaneous wireless information and power transfer cooperative amplify-and-forward communication systems with binary differential phase-shift keying modulation. The piece-wise linear energy harvesting (EH) model that captures the nonlinear input-output characteristic of the EH circuit is considered. We derive a novel and closed-form expression of the probability density function (PDF) for the harvested power of the nonlinear EH receiver. Based on this, we further derive the expressions for the PDF of the received signal-to-noise ratio of the cooperative link and the average biterror-rate of the systems. Numerical results confirm the validity of the proposed analytical results. It is shown that the system performance is significantly overestimated when the ideal linear EH model is used in the place of the practical nonlinear EH model. An opposite result to the linear EH model that the system performance is monotonically improved with the increase of the distance between the location of the relay node and the source node is also demonstrated.

In this paper, we present a secure transmission optimization scheme for intelligent reflecting surface (IRS) aided wireless powered communication networks (WPCNs) in the presence of eavesdropping in the uplink, where the linear energy harvesting (EH) model and imperfect channel state information (CSI) are considered. We aim to maximize the secrecy rate at the hybrid access point (HAP) by jointly optimizing the transmission time allocation factor, HAP transmit beamforming vector, IRS energy reflection coefficients, and IRS information reflection coefficients, which is formulated as a joint multivariate non-convex optimization problem. By using the alternatively iterative optimization method and after several manipulations on the subproblems, the optimal solutions of time allocation factor and HAP transmit beamforming vector are obtained with standard convex optimization tools, while the sub-optimal solutions of IRS energy and information reflection coefficients are obtained with semidefinite relaxation (SDR) and Gaussian randomization procedure. Numerical results show that the proposed algorithm achieves substantial performance enhancement while maintaining high robustness, and significantly outperforms the benchmark schemes under various CSI error variance. It is also shown that optimizing IRS phase shifts or increasing the number of IRS reflection elements is better than optimizing HAP transmit beamforming or increasing the number of HAP antennas, respectively.

In this paper, we study the outage and throughput performance for the simultaneous wireless information and power transfer (SWIPT) cooperative decode-and-forward (DF) communication systems. The hybrid receiver that uses both time switching (TS) and power splitting (PS) methods for energy harvesting (EH) and information decoding (ID), and the piece-wise linear EH model that captures the non-linear input-output characteristic of the EH circuit, are considered. We present exact analytical expressions of the outage probability (OP) and throughput, which are expressed as single definite integral on finite interval and can be easily evaluated, for the systems in Rayleigh fading channel. For further simplicity of calculation, we derive novel and closed-form approximate expressions of the OP and throughput. The impact of different system parameters on the system performance is investigated. Numerical results show the high accuracy of the proposed closed-form approximate expressions especially in the region of higher signal-to-noise ratio (SNR). It is also shown that the system performance is greatly overestimated when the ideal linear EH model is used instead of the practical non-linear EH model. A different result to the non-hybrid receiver with both linear EH model and non-linear EH model that there exists an optimal location to minimize the OP for the hybrid receiving relay node with non-linear EH model is also demonstrated.

Based on the characteristic function of the sum of correlated gamma random variables and an alternative expression of Q-function, a simple bit error rate (BER) expression is derived for the multicarrier code division multiple access (MC-CDMA) systems with maximal ratio combining (MRC) in correlated Nakagami-m fading channels. The much simpler approximate average BER expression using exponential approximation of the Q-function is also derived.