In this letter, we propose a deep learning-assisted approach for signal detection in uplink orthogonal frequency-division multiplexing (OFDM) systems over time-varying channels. In particular, we utilize a recurrent neural network (RNN) with bidirectional long short-term memory (LSTM) architecture to achieve signal detection. In addition, with the help of convolutional neural network (CNN) and batch normalization (BN), a new network structure CNN-BN-RNN Network (CBR-Net) is proposed to obtain better performance. The sequence feature information of the OFDM received signal is extracted from big data to successfully train a RNN-based signal detection model, which simplifies the architecture of OFDM systems and can adapt to the change of channel paths. Simulation results also demonstrate that the trained RNN model has the ability to recall the characteristics of wireless time-varying channels and provide accurate and robust signal recovery performance.

In this paper, we investigate security and energy efficiency of multicast communication in cognitive satellite terrestrial networks. To achieve high spectrum efficiency and low interference power transmissions in the cognitive terrestrial network, the rate splitting multiple access scheme (RSMA) is employed to prompt the massive access of the secondary users. In particular, we derive analytical and asymptotic closed-form expressions for secrecy outage probability of the satellite terrestrial network with eavesdropping, interfering, and imperfect channel state information. Hence, a beamforming (BF) scheme based on RSMA for secondary network is proposed to suppress eavesdropping, mitigate interference, and enhance energy efficiency of the proposed system model. Then, we transform non-convex optimization constraints into resoluble problems utilizing Taylor series expansion and successive convex approximation. Finally, simulation results corroborate the above theoretical analysis and highlight the superiority of the designed BF scheme on security and energy efficiency.

In this paper, a destination-assisted-jamming (DAJ)-based secure transmission is devised for an untrusted and energy harvesting relay network. In the proposed scheme, both source and destination split their energies into two parts for energy harvesting at the relay and transmissions of confidential and cooperative jamming signals, respectively. We formulate an optimization problem to maximize the achievable secrecy rate by jointly optimizing the energy splitting for the source and destination. The existence of the solution for the optimization is carefully analyzed. Due to high complexity of the joint optimization, an iterative optimization algorithm to obtain the near-optimal energy splitting policy is proposed. The numerical results validate that the optimized energy splitting policy leads to a higher achievable secrecy rate, and the iterative algorithm has a quick convergence rate.

In this paper, a joint beamforming alignment and suboptimal power allocation (Sub-OPA) for a two-way untrusted relay network is presented. Considering the link between users is established via only an untrusted relay because of either the shadowing fading or long distance between users, we utilize a destination-assisted-jamming (DAJ) technique to improve the security performance. In each time slot, a user transmits confidential signals and the other emits jamming signals simultaneously to prevent the untrusted relay from intercepting the confidential signals. First, we design a novel beamforming to align the confidential signal to the subspace corresponding to the confidential transmission channel and direct the cooperative jamming signal toward untrusted relay. Then, an iterative algorithm is presented to generate the Sub-OPA of each user for the transmission of confidential and cooperative jamming signal. The correctness and efficiency of the proposed beamforming scheme and the Sub-OPA are validated by numerical simulations and the results are compared via MatLab optimization toolbox. Moreover, the simulations show the iterative algorithm is converged after the fourth iteration at lower signal-to-noise ratios (SNRs) and rapidly converged with allocating more power to the confidential signals at higher SNRs.

Relay assisted communication helps to extend the transmission coverage area. In some realistic scenarios, the available relays are untrusted, which try to decode the confidential signals when relaying the signal. Thus, these untrusted relays are regarded as potential eavesdroppers, and the confidential signals is vulnerable. With physical layer security technology, a positive secrecy rate can be achieved at the physical layer without any cryptography. In particular, the mutual interference achieved from two way relaying network can be used to secure the confidential signals against eavesdroppers attack. In this paper, multiple untrusted relays are available in the ssyetm and relay selection must be performed. Here, three relay selection schemes are proposed with beamforming alignment to avoid information leakage to non-selected relays. Particularly, we propose an enhanced secure sum rate, which does not guarantee the fairness for both transmission links. Afterwards a max-min secure scheme is defined, which requires an exhaustive search. Then, the Lower Bound (LB) of the secrecy rate is introduced to reduce the complexity of the max-min secure scheme. The closed forms of the Secure Outage Probability (SOP) for the proposed schemes are formulated. The simulations results validate the proposed analytical forms, and the performance of max-min LB scheme appears to be quite close to that of max-min scheme with limited complexity.

For an energy harvesting relay network, an optimal secure transmission scheme is proposed. In the case of limited harvesting energy and total power, destination‐based jamming technique is applied to protect the confidential information from relay's jamming and eavesdropping. Moreover, the penalty function algorithm is utilised to obtain the optimal power allocation factor to maximise secure rate. The impacts of power allocation factor and energy transformation efficiency on the system secure rate are analysed. Simulation results validate the correctness and efficiency of the proposed scheme.