A joint continuous phase frequency shift keying (CPFSK) modulation and physical-layer network coding (PNC), i.e., CPFSK-PNC, is proposed for two-way relay channels (TWRCs). This letter discusses the signal detection of the CPFSK-PNC scheme with emphasis on the maximum-likelihood sequence detection (MLSD) algorithm for the relay receiver. The end-to-end error performance of the proposed CPFSK-PNC scheme is evaluated through simulations.

Compressive sensing (CS) exploits the sparsity or compressibility of signals to recover themselves from a small set of nonadaptive, linear measurements. The number of measurements is much smaller than Nyquist-rate, thus signal recovery is achieved at relatively expense. Thus, many signal processing problems which do not require exact signal recovery have attracted considerable attention recently. In this paper, we establish a framework for parameter estimation of a signal corrupted by additive colored Gaussian noise (ACGN) based on compressive measurements. We also derive the Cramer-Rao lower bound (CRB) for the frequency estimation problems in compressive domain and prove some useful properties of the CRB under different compressive measurements. Finally, we show that the theoretical conclusions are along with experimental results.

In this letter, we analyze the outage performance of decode-and-forward relay systems with imperfect MRC receiver at the destination. Unlike the conventional perfect MRC, the weight of each branch of the imperfect MRC receiver is only the conjugate of the channel impulse response, not being normalized by the noise variance. We derive an exact closed-form expression for the outage probability over dissimilar Nakagami-m fading channels. Various numerical examples confirm the proposed analysis.

Secrecy on the physical layer is receiving increased research interest due to its theoretical and practical importance. In this letter, a subcarrier allocation scheme is proposed for physical-layer security in cooperative orthogonal frequency division multiple access (OFDMA) networks that use the Amplify-and-Forward (AF) strategy. We consider the subcarrier pairing and assignment to maximize overall system rates subject to a secrecy level requirement. Monte Carlo simulations are carried out to validate our analysis.

In this letter, we combine minimum-shift keying (MSK) with physical-layer network coding (PNC) to form a new scheme, i.e., MSK-PNC, for two-way relay channels (TWRCs). The signal detection of the MSK-PNC scheme is investigated, and two detection methods are proposed. The first one is orthogonal demodulation and mapping (ODM), and the second one is two-state differential detection (TSDD). The error performance of the proposed MSK-PNC scheme is evaluated through simulations.

By exploiting the reciprocity and randomness properties of wireless channels, physical-layer-based key generation provides a stable secrecy channel even when the main channel suffers from a bad condition. Even though the channel variation due to the mobility of nodes in wireless channels provides an improvement of key generation rate (KGR), it decreases the key consistency probability (KCP) between the node pairs. Inspired by the received signal strength(RSS)-angle of arrival(AoA)-based geolocation research, in this work, we analyze the performance of the key extraction using the RSS and AoA. We aim to identify a way to utilize the high KGR of the AoA-based method to overcome the major drawback of having a low KGR in the most common RSS-based scheme. Specifically, we derive the KCP and KGR of the RSS-AoA-based key generation scheme. Further, we propose a new performance metric called effective key generation rate (EKGR), to evaluate the designed key generation scheme in practical scenarios. Finally, we provide numerical results to verify the accuracy of the presented theoretical analysis.

In this paper, we analyze the impact of channel estimation errors for both decode-and-forward (DF) and amplify-and-forward (AF) cooperative communication systems over Nakagami-m fading channels. Firstly, we derive the exact one-integral and the approximate expressions of the symbol error rate (SER) for DF and AF relay systems with different modulations. We also present expressions showing the limitations of SER under channel estimation errors. Secondly, in order to quantify the impact of channel estimation errors, the average signal-to-noise-ratio (SNR) gap ratio is investigated for the two types of cooperative communication systems. Numerical results confirm that our theoretical analysis for SER is very efficient and accurate. Comparison of the average SNR gap ratio shows that DF model is less susceptible to channel estimation errors than AF model.

Unmanned aerial vehicle (UAV) communication has drawn rising interest recently with the distinctive gains brought by its inherent mobility. In this paper, we investigate the throughput maximization problem in UAV-enabled uplink communication, where multiple ground nodes communicate with a UAV while a group of ground jammers send jamming signals to jam the communications between UAV and the ground nodes. In contrast to the previous works that only considering UAV's transmit power allocation and two-dimension (2D) trajectory design, the ground nodes' transmit power allocation and scheduling along with the UAV's three-dimensional (3D) trajectory design are jointly optimized. The formulated throughput maximization problem is a mixed-integer non-convex programme that hard to be solved in general. Thus, we propose an iterative algorithm to make the problem trackable by applying the block coordinate descent and successive convex optimization techniques. Simulation results show that our proposed algorithm outperforms the benchmark methods that improving the throughput of the system significantly.

In this paper, we identify the tradeoff between security and reliability in the amplify-and-forward (AF) distributed beamforming (DBF) cooperative network with K untrusted relays. In particular, we derive the closed-form expressions for the connection outage probability (COP), the secrecy outage probability (SOP), the tradeoff relationship, and the secrecy throughput. Analytical and simulation results demonstrate that increasing K leads to the enhancement of the reliability performance, but the degradation of the security performance. This tradeoff also means that there exists an optimal K maximizing the secrecy throughput.

Joint transmit and receive antenna selection (JTRAS) is proposed for the multiple-input multiple-output (MIMO) two-way relaying channel. A simple and closed-form lower bound on the outage probability of JTRAS is derived. Furthermore, asymptotic analysis reveals that JTRAS can attain the maximum achievable diversity order of the MIMO dual-hop relaying channel.

Presented is a new measuring and reconstruction framework of Compressed Sensing (CS), aiming at reducing the measurements required to ensure faithful reconstruction. A sparse vector is segmented into sparser vectors. These new ones are then randomly sensed. For recovery, we reconstruct these vectors individually and assemble them to obtain the original signal. We show that the proposed scheme, referred to as SegOMP, yields higher probability of exact recovery in theory. It is finished with much smaller number of measurements to achieve a same reconstruction quality when compared to the canonical greedy algorithms. Extensive experiments verify the validity of the SegOMP and demonstrate its potentials.

This letter studies secure transmission design with finite alphabet input for cooperative jamming network under individual power constraint. By adopting the zero-force scheme, where the jamming signal is fully laid in the null space of the relay-destination channel, the problem of enhancing the achievable secrecy rate is decomposed into two independent subproblems: relay weights design and power control. We reveal that the problem of relay weights design is identical to the problem of minimizing the maximal equivalent source-eavesdropper channel gain, which can be transformed into a semi-definite programming (SDP) problem and thus is tackled using interior point method. Besides, the problem of power control is solved with the fundamental relation between mutual information and minimum mean square error (MMSE). Numerical results show that the proposed scheme achieves significant performance gains compared to the conventional Gaussian design.

For amplify-and-forward (AF) relaying with imperfect channel estimation, we present the average symbol error rate (SER) and the diversity and multiplexing tradeoff (DMT) analysis for both opportunistic relaying (OPR) and all-participate relaying (APR) schemes. SER comparisons show that when the channel estimation quality order is no larger than 1, OPR will perform worse than APR in high SNR region. Moreover, small channel estimation quality orders will also lead to significant DMT loss.

In this letter, we investigate the physical layer security in multi-user multi-relay networks, where each relay is not merely a traditional helper, but at the same time, can become a potential eavesdropper. We first propose an efficient low-complexity user and relay selection scheme to significantly reduce the amount of channel estimation as well as the amount of potential links for comparison. For the proposed scheme, we derive the closed-form expression for the lower bound of ergodic secrecy rate (ESR) to evaluate the system secrecy performance. Simulation results are provided to verify the validity of our expressions and demonstrate how the ESR scales with the number of users and relays.

This paper studies the secrecy throughput performance of the three-node wireless-powered networks and proposes two secure transmission schemes, namely the half-duplex maximal ratio combining (HD&MRC) scheme and the full-duplex jamming scheme based on time switching simultaneous wireless information and power transfer (FDJ&TS-SWIPT). The closed-form expressions of the secrecy throughput are derived, and intuitive comparison of the two schemes is provided. It is illustrated that the HD&MRC scheme only applies to the low and medium signal-to-noise ratio (SNR) regime. On the contrary, the suitable SNR regime of the FDJ&TS-SWIPT is much wider. It is depicted that FDJ&TS-SWIPT combing with current passive self-interference cancellation (SIC) algorithm outperforms HD&MRC significantly, especially when a medium or high transmit SNR is provided. Numerical simulations are conducted for verifying the validity of the analysis.

This work investigates the physical layer security for three cooperative automatic-repeat-request (CARQ) protocols, including the decode-and-forward (DF) CARQ, opportunistic DF (ODF) CARQ, and the distributed space-time code (DSTC) CARQ. Assuming that there is no instantaneous channel state information (CSI) of legitimate users' channel and eavesdropper's channel at the transmitter, the connection outage performance and secrecy outage performance are derived to evaluate the reliability and security of each CARQ protocol. Then, we redefine the concept of the secrecy throughput to evaluate the overall efficiency of the system in terms of maintaining both reliable and secure transmission. Furthermore, through an asymptotic analysis in the high signal-to-noise ratio (SNR) regime, the direct relationship between reliability and security is established via the reliability-security tradeoff (RST). Numerical results verify the analysis and show the efficiency of the CARQ protocols in terms of the improvement on the secrecy throughput. More interestingly, increasing the transmit SNR and the maximum number of transmissions of the ARQ protocols may not achieve a security performance gain. In addition, the RST results underline the importance of determining how to balance the reliability vs. security, and show the superiority of ODF CARQ in terms of RST.