ABSTRACT The development of reconfigurable intelligent surface (RIS) makes direction‐of‐arrival (DOA) estimation possible for single‐antenna receivers. However, non‐ideal situations such as spectral aliasing occur when facing communication signals using orthogonal frequency division multiplexing modulation. This paper proposes a RIS‐based single‐channel DOA estimation method for communication signals. Specifically, by extending the time intervals to dynamically reduce the RIS state change rate, a real‐time DOA estimation is achieved while mitigating the impact of non‐ideal spectral shifts on communication. Then, based on the compressed sensing and mutual incoherence property, the method exploits the sparse property of the signal in space to reduce the estimation time while improving the estimation accuracy. Simulation results show an reduction in computation time for the proposed method compared to the traditional CVX tool. Additionally, the estimation accuracy is as low as . To verify the practicality and robustness, we develop a prototype system and conduct extensive experiments. The results are consistent with our theoretical analysis, and the method proposed in this paper can realize single‐path DOA estimation with an accuracy of less than within . More excitingly, the presented experimental platform achieves DOA estimation for two coherent paths.

Abstract Reconfigurable intelligent surface (RIS)‐assisted physical layer key generation plays an important role in the eavesdropping problem on a typical multi‐user scenario of wireless networks. Existing RIS‐assisted physical key generation technology mainly solved the security issues in the single‐antenna and multi‐user scenario, which is based on the idealistic assumption of a spatially independent channel model at the RIS. It limits the degrees of freedom and neglects the existence of channel spatial correlation, which would possibly degrade the sum key generation rate (SKGR). To solve the above problem, this paper proposes a secret key generation scheme for RIS‐assisted multiple‐input single‐output multi‐user system. This scheme establishes a spatial correlation channel model, which comprehensively considers the influence of spatial correlation among antennas of the base station (BS), multi‐user, and RIS elements on SKGR. Based on this, a key generation framework is designed to generate a more secure secret key with the maximum SKGR. Specifically, a closed‐form SKGR expression and an optimization problem formulation are obtained to obtain the joint optimal coefficient of the BS and RIS. Then, the difference convex‐successive convex approximation based alternating optimization algorithm is proposed to solve this optimization problem. The simulation results show that the proposed scheme has improved 10‐bit/channel use compared with the randomization scheme of BS precoding and RIS reflection coefficient. It also has an improvement of 12‐bit/channel use compared with the spatially independent scheme.

Abstract Satellite communications (SatCom) have been viewed as a promising technique to achieve ubiquitous global coverage in next‐generation wireless systems. This article investigates the secure energy efficient downlink transmission for SatCom where an intelligent transmissive surface‐aided transmitter is deployed at the satellite to perform energy efficient beamforming and an intelligent reflecting surface as well as a cooperative jammer are deployed on the ground to enhance the secure performance. The aim is to maximize the secure energy efficiency by jointly designing ITS beamforming, IRS phase shift, jammer precoding vector, and transmit power allocation. To develop a low‐complexity solution,first, an approximated concave lower bound of the non‐concave objective function is derived by utilizing Dinkelbach's method and a novel successive convex approximation technique. Then the reformulated problem is decoupled using alternating optimization algorithm and the subproblems are solved by adopting Riemannian manifold optimization, element‐wise block coordinate descent, Lagrange dual method and Karush–Kuhn–Tucker conditions. At last, simulation results demonstrate the effectiveness of the proposed scheme.

In this paper, we present a double‐intelligent reflecting surfaces (IRS)‐assisted multiuser secure system where the inter‐IRS channel is considered. In particular, we maximize the weighted sum secrecy rate of the system by jointly optimizing the beamforming vector for transmitted signal and artificial noise at the base station (BS) and the cooperative phase shifts of two IRSs, under the constraints of transmission power at the BS and the unit‐modulus phase shift of IRSs. To tackle the nonconvexity of the optimization problem, we first convert the objective function to its concave lower bound by utilizing a novel successive convex approximation technique, then solve the transformed problem iteratively by applying an alternating optimization method. The Lagrange dual method, Karush–Kuhn–Tucker conditions, and alternating direction method of multipliers are applied to develop a low‐complexity solution for each subproblem. Finally, simulation results are provided to verify the advantages of the cooperative double‐IRS scheme in comparison with the benchmark schemes.

Reconfigurable intelligent surface (RIS), which can manipulate the wireless environment, has recently been integrated into physical-layer key generation (PKG) systems to establish randomness symmetric keys in static environments. However, few studies have jointly considered the optimization and randomization of the RIS elements to simultaneously achieve a high key generation rate (KGR) and communication performance. This study proposes a RIS-assisted communication and security-integrated protocol for dual-function integration of communication enhancement and PKG in static environments. The protocol partitions RIS elements for beamforming and random beams for parallel execution, utilizing a sparsity adaptive matching pursuit-based channel estimation algorithm to obtain individual channel state information. Subsequently, an optimization problem is formulated for KGR maximization while satisfying quality of service (QoS) requirements. The non-convex optimization problem is addressed through monotonicity analysis and triangle inequality. We validate the efficacy of the proposed protocol by developing a 4.9 GHz RIS-assisted PKG prototype system, comprising modular hardware and flexible software. The field trials demonstrate a 30.81 bit/s KGR for static environments with an average received power increase of 10.6 dB, achieving effective simultaneous integration of communication and security.

Due to the limited coverage of reflecting-only reconfigurable intelligent surfaces (RIS), the existing RIS-assisted physical-layer key generation (PKG) scheme limits its overall performance in the full space. This paper proposes a novel simultaneously transmitting and reflecting (STAR)-RIS-assisted PKG protocol for multiple-input multiple-output (MIMO) systems, where the closed-form sum secret key rate is derived in the presence of full-space eavesdroppers. Two optimization problems are formulated to maximize the sum secret key rate by designing the transmit beamforming (TBF) and transmitting and reflecting coefficients (TRCs) for energy splitting (ES) with coupled phase-shift and mode switching (MS) mode. For ES mode with coupled phase-shift, a penalty-based alternating optimization (AO) algorithm is proposed to address its non-convexity. For MS mode, the semidefinite relaxation-successive convex approximation-based AO algorithm is utilized to achieve continuous solutions and then quantize to binary value for the MS mode. Simulation results demonstrate that the coupled phase-shift STAR-RIS incurs a slight KGR loss in comparison to the independent phase-shift STAR-RIS. Additionally, the ES mode outperforms the MS mode in terms of KGR performance. Finally, STAR-RIS can achieve a higher sum secret key rate than traditional reflecting-only RIS.

This paper investigates the simultaneously transmitting and reflecting reconfigurable surface (STAR-RIS) assisted physical layer key generation (PKG) for multiuser networks. We propose a novel STAR-RIS-assisted PKG protocol and formulate a sum secret key rate maximization problem by jointly optimizing the active and passive beamforming. To address the non-convex problem, a block coordinate descent (BCD) algorithm is developed, using both semidefinite relaxation (SDR) and successive convex approximation (SCA) methods to optimize active and passive precoding alternately. Simulation results demonstrate the key generation performance of the proposed algorithm outperforms schemes that STAR-RISs using the random configuration and conventional reflecting/transmitting-only RISs.

Abstract This paper explores the potential application of simultaneously transmitting and reflecting reconfigurable intelligent surface (STAR‐RIS) in improving the physical layer security (PLS) of millimetre wave (mmWave) non‐orthogonal multiple access (NOMA) uplink communications. In particular, the legitimate users on both sides of STAR‐RIS send confidential information simultaneously to the base station (BS) while keeping it secret from the eavesdroppers near the BS by exploiting the STAR‐RIS to proactively regulate the electromagnetic propagation environment. By jointly designing the transmit power, the active beamforming at the BS, and the reflecting/transmitting coefficients at the STAR‐RIS, the authors' goal is to maximize the minimum secrecy capacity subject to the successive interference cancellation decoding order constraints. Due to the non‐convexity of the formulated problem, an efficient algorithm is proposed by capitalizing on alternating optimization, a penalty‐based approach, successive convex approximation, and semi‐definite relaxation. Firstly, a two‐layer iterative algorithm based on the penalty for the joint beamforming optimization sub‐problem is proposed. Then, the non‐convex problem is transformed into a convex positive semi‐definite programming problem for the transmit power sub‐problem. Numerical simulation results reveal that the STAR‐RIS‐aided system has more tremendous advantages and effectiveness in improving the PLS of mmWave NOMA uplink communication compared with the benchmark schemes.

Abstract The reconfigurable intelligent surface (RIS) fundamentally changes the existing anti‐jamming paradigm by reconstructing the wireless propagation environment. However, the existing RIS‐based anti‐jamming work mainly considers narrow‐band frequency‐flat fading channels. As an extension of existing work, the use of RIS to enhance the anti‐jamming capability of broadband orthogonal frequency division multiplexing (OFDM) system in frequency‐selective fading channels is first studied. In the multipath frequency‐selective fading channels, the anti‐jamming design needs to satisfy the channel gains of all signal paths with different delays. To this end, the authors propose a joint design scheme of active precoding at the transmitter and passive precoding at the RIS to attenuate the jamming signal and enhance the legitimate signal, and formulate the joint design objective to maximize the average rate of all subcarriers. An alternating optimization algorithm is developed to address this non‐convex problem due to the complex coupling of active and passive precoding. In detail, the active and passive precoding are solved by the Cauchy–Schwarz inequality and power water‐filling method and the alternating direction method of multipliers method assisted by multidimensional complex quadratic transform, respectively. Simulation results demonstrate that the proposed method can significantly improve the anti‐jamming communication performance of the OFDM system compared with the scheme without RIS. In addition, the impact of the number of RIS elements and deployment location on system performance is revealed.

Abstract Confidentiality and authentication are two important security properties of wireless communication. There are currently two types of research in wireless communication security: one is based on cryptography, which can be too complicated for some wireless systems; the other is based on physical layer characteristics, which has some security problems and cannot work as well as the cryptography‐based method. In this paper, a lightweight encryption and message authentication framework for wireless communication is proposed. The proposed framework has lower complexity than the cryptography‐based method and works more securely and efficiently than the classical physical layer method. For the encryption, a physical layer offered chain key (PHYLOCK) structure is proposed to generate one‐time keys, which are then XOR‐ed with the plaintext to generate the ciphertext. A security analysis of PHYLOCK is performed and it is proved that it has better security features than the traditional physical layer key generation. For the message authentication, three types of PHYLOCK‐CRC‐based message authentication schemes are developed whose generator polynomial is determined by one‐time keys generated by PHYLOCK. PHYLOCK‐CRC‐based message authentication detects not only random errors introduced by noises but also malicious attacks. The error‐detecting and anti‐attack capabilities are analyzed mathematically. Compared to the standard CRC, PHYLOCK‐CRC‐based message authentication has a decline in error correction capability but is enhanced with cryptographic security features. Monte‐Carlo simulations are provided to evaluate the proposed scheme.

Physical layer key generation (PKG) technology leverages reciprocal channel randomness to generate shared secret keys. However, multipath fading at the receiver may degrade the correlation between legitimate uplink and downlink channels, resulting in a low key generation rate (KGR). In this paper, we propose a PKG scheme based on the pattern-reconfigurable antenna (PRA) to boost the secret key capacity. First, we propose a reconfigurable intelligent surface (RIS) based PRA architecture with the capability of flexible and reconfigurable antenna patterns. Then, we present the PRA-based PKG protocol to improve the KGR via mitigation of the effects of multipath fading. Specifically, a novel algorithm for estimation of the multipath channel parameters is proposed based on atomic norm minimization. Thereafter, a novel optimization method for the matching reception of multipath signals is formulated based on the improved binary particle swarm optimization (BPSO) algorithm. Finally, simulation results show that the proposed scheme can resist multipath fading and achieve a high KGR compared to existing schemes. Moreover, our findings indicate that the increased degree of freedom of the antenna patterns can significantly increase the secret key capacity.

Existing works on solving jamming signals within the receiving antenna's bandwidth are generally difficult to strike a balance between flexibility and effectiveness. To this end, we propose a joint space-frequency anti-jamming scheme. Considering the broadband response of the Reconfigurable Intelligent Surface (RIS), we innovatively exploit different spatial and frequency responses of the RIS to generate space-frequency filtering during the propagation of the jamming signal. We formulate a problem to design reflection coefficients of the RIS so the jamming signals will be attenuated, but the legitimate signal will be enhanced at the receiver. Then the problem is equiv-alently transformed into a quadratically constrained quadratic programming (QCQP) problem which can be efficiently solved. We also present a jamming suppression scheme when legitimate transmitter pilots are submerged. Simulation results show that the proposed joint space-frequency anti-jamming scheme consti-tutes an equivalent broadband band-stop filter to the jamming signal and has better resistance to strong jamming. Meanwhile, the anti-jamming ability will further increase with the number of RIS elements. As an equivalent space-frequency filter embedded in the wireless environment, the proposed scheme introduces a different filtering paradigm to collaborate with existing anti-jamming techniques effectively and reveal its potential in some military or civilian scenarios.

Abstract The secure communication scheme based on physical layer non‐reconciled keys receives extensive attention due to its high encryption rate. However, the mismatched secret bit sequences between the two users leads to higher BER and lower coding efficiency for this type of scheme. To solve this problem, this paper proposes an efficient and secure communication scheme for OFDM system with non‐reconciled keys. Initially, an adaptive coding method is designed to encode information blocks with different code rates to improve the overall efficiency. Then, on this basis, a sorting xor encryption algorithm is designed to reduce the bit error rate by sorting the channel estimation value and mapping them to corresponding sub‐channels. Theoretical analysis and simulation results indicate that this scheme can effectively reduce the bit error rate and improve the efficiency of information coding compared to the existing method.

The sixth-generation mobile communication (6G) networks will face more complex endogenous security problems, and it is urgent to propose new universal security theories and establish new practice norms to deal with the “unknown unknown” security threats in cyberspace. This paper first expounds the new paradigm of cyberspace endogenous security and introduces the vision of 6G cyberspace security. Then, it analyzes the security problems faced by the 6G core network, wireless access network, and emerging associated technologies in detail, as well as the corresponding security technology development status and the integrated development of endogenous security and traditional security. Furthermore, this paper describes the relevant security theories and technical concepts under the guidance of the new paradigm of endogenous security.

In this work, we investigate a delay-constrained covert communication system wherein a multi-antenna transmitter is considered for the first time. Under the assumption of Rayleigh fading and a warden existed, beamforming method is adopted to assist in delivering private message covertly. We derive the closed-form expression of the tight average covert probability, which emerges as the covertness metric. Furthermore, an optimization framework for maximal covert throughput incorporating blocklength and transmit power designs is established. In particular, we prove that adopting the maximum blocklength is optimal under the above framework. Our numerical results show the significant superiority of overall rate performance improvement through multi-antenna technology.

Abstract This paper studies multi‐antenna covert communication exploiting a public communication link over the wireless fading channel. In particular, a relatively practical covert communication scenario is considered for the first time, where a warden with radiometer may improve its detection accuracy by jointly detecting uplink covert pilot and downlink covert communication. To this end, a joint covert communication system, jointly considering uplink covert pilot, imperfect channel state information issue and downlink covert communication, is proposed and further studied. Specifically, the detection performance of warden and the covertness performance of system are comprehensively studied, respectively. Afterwards, an optimization problem for covert capacity is formulated to maximize overall performance. Then, with our analysis and simplification, an optimal power allocation algorithm is designed for covert capacity accordingly. Our examination shows a win‐win situation has been achieved in the proposed system, that is, covert communication would rarely affect the normal communication of public link and occupy its communication resources. Interestingly enough, we analytically find an invariance property of downlink covert communication that covertness performance is not impacted by noise levels or warden's position. Based on this extraordinary finding, we conclude that the downlink covert communication system can perfectly combat with a powerful warden adopting power trend test method, while the joint covert communication system may resist that through a pilot deception scheme.

Abstract This paper investigates a three‐node proactive eavesdropping system with the aid of intelligent reflecting surface (IRS), where a monitor tries to wiretap information and transmit jamming signals simultaneously to interfere with the suspicious link. The IRS is deployed around the suspicious users to reconstruct propagation channel. Meanwhile, with large low‐cost passive reflecting elements, it can provide more spatial degrees of freedom to moderate the link quality. In order to degrade exposure risk of eavesdropping behavior, the authors' objective is to minimize the jamming power by carefully designing jamming beamforming vectors and the phase shifts under the constraint of reliable intercepted information. The formulated problem is non‐trivial to solve due to the coupling variables and unit‐modulus constraints. Fortunately, by using alternating optimization and successive convex approximation techniques, the original problem is transformed into convex form and a sub‐optimal solution is achieved. Numerical results show that the proposed scheme can effectively reduce the jamming power and the number of the jamming antennas over benchmark schemes, which is quite suitable for covertly overhearing signal.

In this paper, secure transmission in a simultaneous wireless information and power transfer technology-enabled heterogeneous network with the aid of multiple IRSs is investigated. As a potential technology for 6G, intelligent reflecting surface (IRS) brings more spatial degrees of freedom to enhance physical layer security. Our goal is to maximize the secrecy rate by carefully designing the transmit beamforming vector, artificial noise vector, and reflecting coefficients under the constraint of quality-of-service. The formulated problem is hard to solve due to the nonconcave objective function as well as the coupling variables and unit-modulus constraints. Fortunately, by using alternating optimization, successive convex approximation, and sequential Rank-1 constraint relaxation approach, the original problem is transformed into convex form and a suboptimal solution is achieved. Numerical results show that the proposed scheme outperforms other existing benchmark schemes without IRS and can maintain promising security performance as the number of terminals increases with lower energy consumption.

Due to the channel estimation error, most of the physical layer secret key generation schemes need information reconciliation to correct error key bits, resulting in reduced efficiency. To solve the problem, this work proposes a novel secure communication scheme based on a equivalent interference channel. Different keys generated from imperfect channel state information are directly applied to signal scrambling and descrambling, which is equivalent to the process of a signal passing through an interference channel. Legitimate communication parties can reduce interference with the help of similar keys and channel coding without sending additional signals, while the eavesdropper channel is deteriorated due to the spatial decorrelation. For this kind of schemes, we first establish a discrete memoryless broadcast channel model to derive the expressions of bit error rate (BER), channel capacity, and security capacity for performance analysis. Simulation results verify the derivations that the proposed scheme achieves secure communication with a correlated eavesdropping channel and has a higher upper bound of transmission rate. Furthermore, we design a new metric to evaluate the efficiency and the result shows that the proposed scheme has superior performance on error reconciliation efficiency, despite its slight increase in BER.

With the ellipsoid‐bounded channel state information (CSI) errors, this study investigates the robust secrecy energy efficiency (SEE) optimisation in a wireless powered heterogeneous network. Specifically, the authors consider the network where multiple femtocell base stations (FBSs) are deployed under the coverage of one macrocell base station (MBS). Meanwhile, the MBS serves multiple macrocell users in the presence of a malicious multiple‐antenna eavesdropper (Eve) while each FBS serves a pair of information receiver (IR) and energy receiver (ER) with multiple antennas, where the ER attempts to wiretap the information of IR in the same femtocell. To promote the secrecy performance, artificial noise (AN) is aided into the downlink signal at the MBS and FBSs, and the problem of maximising SEE is formed in a cross‐tier multi‐cell AN‐aided transmit beamforming design. This problem is non‐convex while containing infinite constraints caused by CSI errors, which cannot be solved directly. In this regard, the authors resort to the successive convex approximation, semi‐definite relaxation techniques and Lagrange duality theory to acquire its solvable form. Moreover, to reduce the overhead of information exchange among coordinated BSs, they further propose a distributed approach based on alternative direction multiplier method. Finally, simulation results validate the effectiveness of the proposed design.

Here, the authors investigate robust secure transmission for wireless information and power transfer in heterogeneous networks (HeNets) under the deterministic and stochastic CSI errors, respectively, where one macrocell base station (MBS) and one femtocell base station (FBS) respectively serve to macrocell users (MUs) and femtocell users (FUs). Meanwhile, FUs acquire energy from the FBS and multiple eavesdroppers attempt to wiretap its downlink information. To secure the wireless information and power transfer, the authors propose an artificial noise (AN)‐aided transmission design. Under the deterministic CSI error, the authors jointly design the beamforming and AN vectors of the MBS and FBS to minimise the total transmit power, while satisfying the constraints on the signal‐to‐interference plus noise (SINR) requirement at each MU, energy harvesting (EH) and secrecy outage probability requirement at each FU. This formulated problem is non‐convex. Utilising S‐procedure and successive convex approximation technique, the authors successfully transfer it into a series of convex problems. Under the stochastic CSI error, the joint design problem is formulated with a range of outage probabilistic constraints. Further, the authors, respectively, resort to large deviation and Bernstein‐type inequalities, S‐procedure to convert it into solvable forms. Simulation results demonstrate the effectiveness of the authors’ proposed design.

Existing handover authentication schemes are implemented in the upper layer through cryptographic techniques with different protocols and parameters involved under different handover scenarios, introducing high latency and complexity especially in the next generation (5G) highly heterogeneous network (HetNet). The authors propose to introduce wireless link signatures decided by users' locations as handover authentication data to achieve unified and fast handover authentication at the physical layer in 5G software defined networking‐based HetNet. Specifically, the unique wireless channel characteristics between a user and the serving access point (AP) are extracted as the secure context information (SCI) and transferred to the target AP. The latter determines whether the user is the legitimate one who has already been authenticated according to the received SCI. They then analyse the authentication performance relating to multiple attributes and results demonstrate that the authentication strength can be adaptively adjusted. Furthermore, they find that optimum performance can be achieved by setting a proper decision threshold and derive the sub‐optimal performance by iterative search. Lastly, analysis and simulations on latency and overhead compared with existing ones are conducted and results prove the effectiveness of the proposed scheme.

Delay and security are both highly concerned in massive internet of things (IoT) which is a promising application scenario in 5G wireless communication system. In this study, the authors develop an integrated framework to study delay performance and secrecy performance in massive IoT. First, stochastic geometry and queuing theory are applied to model the spatially location of IoT devices and the temporal arrival of packets. To enhance the physical layer security of massive IoT with limited overhead increment at IoT devices, a low‐complexity noise injection scheme is applied. Then, the packet delay and packet secrecy outage probability are derived to characterise delay performance and secrecy performance. It is demonstrated that the IoT device intensity and power allocation coefficient arouse a tradeoff between the delay and security. Furthermore, optimal power allocation coefficient that maximises secrecy transmission rate can be derived, which can improve the delay‐security tradeoff. The analytical and simulation results show the effects of power allocation coefficient and IoT device intensity on the tradeoff between delay performance and secrecy performance.

This paper develops a tractable analysis framework to evaluate the reliability and security performance of cooperative non-orthogonal multiple access (co-NOMA) in cognitive networks, where both a primary base station (PBS) and a NOMA-strong primary user (PU) send confidential messages to multiple uniformly distributed PUs in the presence of randomly located external eavesdroppers. For constricting the interference to the PUs imposed by cognitive femto base stations (CFBSs), a mobile association scheme is introduced. Moreover, an eavesdropper-exclusion zone is introduced around the PBS for improving the secrecy performance of the primary networks. To characterize the security-reliability tradeoff of the considered network, we first derive the activation probability of CFBSs and the conditional probability density function associated with the distance between the relay user and other PUs. Then, the connection outage probability (COP) and the secrecy outage probability (SOP) of each PU with NOMA (co-NOMA) or non-cooperative NOMA (nco-NOMA) are separately derived to obtain the overall COP and SOP in the primary networks. Finally, the tradeoff between COP and SOP with co-NOMA (identified as transmission SOP) is investigated for simultaneously reflecting the security and reliability. Numerical results demonstrate the performance improvements of the proposed co-NOMA scheme in comparison to that of the nco-NOMA scheme in terms of different parameters. Furthermore, the security-reliability tradeoff performance of co-NOMA is shown.

This paper investigates the physical layer security in simultaneous wireless information and power transfer (SWIPT)-enabled cooperative non-orthogonal multiple access (NOMA) transmissions. Taking the malicious eavesdropper into account, we study on the problem of artificial noise (AN)-aided transceiver optimization. To guarantee the quality of service (QoS) at cell-edge users and promote the average performance of system, we consider the multi-cell beam-forming (MCBF) and formulate the problem of maximizing the secrecy spectral efficiency fairness (SSEF) among multiple coordinated cells. As the formulated problem is nonconvex and difficult to solve with existing methods, we apply the semi-definition relaxation (SDR) technique and propose an iterative algorithm based on successive convex approximation (SCA) for complexity reduction. Furthermore, we analyze the complexity of the proposed algorithm. Finally, simulations results demonstrate our analysis and illustrate the validity of AN-aided MCBF transmission scheme.

Recent researches show that millimeter wave (mmWave) communication offers the promise of orders of magnitude increases in the cellular network capacity. Due to the severe path loss, relay aided transmission has been regarded as an effective way to extend mmWave communication range. In this paper, we apply an opportunistic relay selection (ORS) scheme for range extension to mmWave networks and develop a framework to analyze the connection outage probability (COP) and secrecy outage probability (SOP) using stochastic geometry. We first introduce the ORS scheme where each base station transmits its data in first time slot and the best relay is selected by competition to forward the infirmation in second time slot. Then the COP, SOP and secrecy throughput in direct transmission and ORS transmission are derived, respectively. By comparing the reliability and security performance of the two transmission schemes, it is demonstrated that ORS scheme enhances the reliability of the communication, but unfortunately increases the risk that confidential information be intercepted by an eavesdropper. We also find the secrecy throughput of ORS scheme is higher than that of direct conventional transmission.

Focusing on the problem of information leakage in information reconciliation (IR), this paper proposes an IR method based on systematic secure polar code (SSPC), which can ensure the security of transmitted check bits. First, the upper and lower bounds of decoded bit error ratio are derived through Gaussian approximation. Then, the generic algorithm is utilized to design suitable SSPC for IR based on the initial quantified bit error ratios, key strength and IR outage probability (IROP). At last, the completely IR procedures are simulated to evaluate the performances of proposed IR method. Simulation results show that the proposed method not only satisfies the requirements of key strength and IROP threshold, but also achieves higher IR efficiency, compared with traditional low density parity check (LDPC) code based IR method.

In this paper, we consider the secure communication of the cellular downlink between the base station and the cellular user underlaying D2D communication. Base stations, cellular users, D2D transmitters and eavesdroppers are modeled as the independent homogeneous Poisson point processes (PPPs). We consider a worst case in which each base station has no channel state information (CSI) from D2D transmitters which are generally deployed in the cell edge. In order to guarantee the secure transmission for cellular links, each multi-antenna base station employs the artificial noise assisted transmission strategy to keep the confidential message from being intercepted by the malicious eavesdropper having the multi-user decedability. Firstly, we derive the secrecy outage probability for the typical cellular link in the interference-limited network in which the additive noise is neglected. Then, the connection outage probability for the typical D2D link in the hybrid network is derived and some comprehensive analysis are presented. Finally, Finally, simulation results are provided to validate the effectiveness of theoretical analysis.

The mutual interference induced by the hybrid links can bring the secrecy gain for device-to-device (D2D) communication underlaying cellular networks, where there have been few works on studying its impact on the secrecy performance of the accessed D2D pairs. In this paper, our aim is to mainly analyze the secrecy performance gain of the accessed D2D pair brought by the mutual interference.Firstly,an opportunistic D2D pairs selection scheme based on the wireless channel direction information (CDI) is proposed. The proposed scheme determines a set of candidate D2D pairs with the required interference limitation for the cellular user. Then, the D2D pair with best channel condition is scheduled to share the same channel with cellular users for its own transmission. Further, the analytical expressions of the secrecy outage probability are derived with presence of multiple D2D pairs and multiple eavesdroppers. Finally, the secrecy performance of the proposed scheme is demonstrated by simulations.

When extracting secret key from shared wireless channel between two legitimate moving terminals, its capacity is affected by the time difference of channel sampling, terminal's mobility, and additive noise. In order to quantitatively analyze their effects, a closed-form solution to physical layer secret key capacity in the time domain is derived over the uniform scattering environment. Afterwards, simulations in the uniform and non-uniform scattering environment are carried out to demonstrate its validity and applicability, respectively. Simula-tion results show that the derivation can be utilized to provide theoretical reference for physical layer secret key extraction between two moving terminals located among dense scatters.

Due to the dense random deployment of heterogeneous cellular networks (HetNets), the system is more seriously affected by channel estimation errors. However, there is a lack of effective secure transmission scheme in this scenario. In order to solve this problem, a transmit antenna selection strategy based on channel estimation accuracy is proposed. First, the stochastic geometric tool is used to derive the secrecy outage probability of K-tier dense HetNets. Then the influence of channel estimation accuracy on secure performance of the system is analyzed. Finally, the validity of the theoretical derivation is verified and the influence of some parameters on the security performance of the system is analyzed.

For preventing the leakage of confidential messages sent to a marcocell user in dense heterogeneous networks, a physical layer security scheme based on base station cooperation is proposed in the paper. To improve transmission rate of confidential messages and make the downlink signals of other legitimate users interfere with eavesdroppers, the beamforming vectors at a macrocell base station and femtocell base stations are jointly optimized. The problem of maximizing the secrecy rate is modeled under the limitations of quality of service(QoS) and base station power. Due to the intractability, this problem is recast into a convex SemiDefinite Program(SDP) problem using the SemiDefinite Relaxation(SDR) technique and the successive convex approximation(SCA) algorithm. Simulation results validate the efficacy and the security of the scheme.

When extracting physical layer security secret key with multiple wireless channel samples, its capacity is affected by the time difference of channel sounding, terminal's moving speed, sampling period, the number of samples, and additive noise. In order to quantitatively analyze their effects and determine the constrains on the optimal sampling period, a closed-form solution to the physical layer secret key capacity in the time domain is derived over the uniform scattering environment. Simulation results indicate that the results of this paper can be applied to both the uniform and non-uniform scattering environment. Furthermore, the feasibility to extract physical layer secret key from the commercial TD-LTE and the promising co-frequency co- time full duplex communication systems is verified.

In this paper, we investigate D2D underlaying cellular networks in which both the D2D links and the cellular downlink links have secrecy requirement. We aim to enhance the secrecy sum rate of D2D pairs(DUs) and cellular users(CUs)by sharing the downlink resources of cellular users and exploiting artificial noise. We achieve the design principle for the downlink signal and artificial noise, which provide guidance on secrecy sum rate maximization. Moreover, a pricing-based pairing and D2D power control algorithm is proposed to pair the DUs and CUs for maximizing system secrecy throughput. Finally, simulation results indicate that the secrecy sum rates of DUs and CUs are improved efficiently by injected artificial noise. The proposed pricing-based scheme obtains better performance of system secrecy throughput than random or graph-based algorithms.

In the wireless position techniques for cellular networks, the traditional geolocation algorithms have been researched because of the advantage low complexity, however the representative LLOP algorithm does not well performed in the cellular networks since it is constrained with the geometry relationship between mobile station and the base stations. For the low accuracy problem of LLOP algorithm, we have proposed a TOA-based geolocation algorithm utilizing convex combination. The method introduces convex combination theory, which the convex combination of a set of coarse position estimations can be used to generate position estimation with higher accuracy, and proposes a linearized procedure to calculate the convex combination coefficients. Simulation results verify that the proposed algorithm decreases the position error by 6.19%, 7.51% and 40.97% compared with LLS- MLE algorithm, LLOP-LS algorithm and LLOP algorithm respectively when the number of base stations is 5 and the measurement noise standard deviation is 50m.

This paper considers a MIMO communication system that includes a transmitter, a legitimate receiver and an eavesdropper. In such a scenario, the eavesdropper has the knowledge of the pilot and utilizes pilot contamination to reduce the secrecy rate. Firstly, we analyze the effects of malicious pilot contamination on channel estimation. The more the pilot contamination power is, the more the eavesdropping performance enhances, by deducing the secrecy rate and its asymptotic expression in the data transmission phase. Besides, the optimal power allocation scheme for a full-duplex eavesdropper to simultaneously transmit pilot contamination and noise jamming is further studied. Simulation results show that the average secrecy rate with pilot contamination is 0.899bits/s/Hz less than that with noise jamming when the jamming power is 10 mW.

Cooperative relaying is a promising technology which can improve the energy efficiency of cellular networks. However, the relays' static power consumption may cancel out the energy saved by the deployed relays. Energy harvesting (EH) technique is introduced for relay nodes in cellular networks in order to deploy flexibility and reduce the energy charge. Due to the EH property, relay nodes cannot maintain a stable energy flow and keep active with a certain probability, which would degrade the benefit from relay-aided cooperative transmission. In this paper, an analytical model is proposed to investigate the energy efficiency of cellular networks aided by EH relay nodes. Meanwhile, the closed-form expressions of coverage probabilities and mean achievable rates for different links are derived. Numerical results show that EH relays bring more improvement on energy efficiency compared with non-EH relayed transmission. The influence of the density and transmit power of stations is also given through numerical simulation.

Recently, wireless local area networks (WLANs) have become ubiquitous. In high density WLANs, interference resulting from neighbor cells is a challenging problem which would affect the network performance. To get higher throughput, it is important to improve spatial reuse of the channels. Since transmit power control (TPC) may cause asymmetric links unless carefully designed, we demonstrate that dynamic sensitive control (DSC) can be used to improve capacity in dense environment. In order to reduce the influence of inter-cell interference and achieve fairness, an adaptive DSC scheme is proposed to provide the edge users with higher clear channel assessment (CCA) threshold. The CCA adaptation strategy for access point (AP) is presented as well, and a stochastic geometry model is introduced in this paper. Coverage probability and average throughput derived based on the analytical model are used to measure the network performance. Furthermore, simulations show that the proposed DSC method can provide considerable performance improvement compared with the existing methods.

In the wireless Ad-hoc networks, the Relays which transmit message are selfish, they need to consume their energy and compute resources to transmit message. For the problems of the message transmission interrupted by Relay selfishness and the decrease of secrecy rates, we have proposed a Relay-selection method to ensure the security of the Ad-hoc network using game theory incentive mechanism. The method introduces virtual currency, which encourages and regulates the cooperation between different nodes, and proposes the incentives mechanism of twice quotation competition based on virtual currency measurement. According to the secrecy rate and quotation, source nodes will select one Relay which makes the maximum secrecy rate utility. Simulations show that the proposed method improves the average secrecy rate per user up by 20%~32% compared with the conventional Relay selection method.

Visible light communications (VLC) are gaining popularity and may provide an alternative means of communications in indoor environment, due to their great advantages in high transmission rate, high bandwidth, green healthy, flexible coverage, etc. However, the past works mainly focus on the elements design, physical and MAC layer, little attention has been paid to system planning and design for VLC networking. In this paper, we design the typical architecture of indoor VLC networks based on its technical characteristic; from a point view of the evolution and development of the wireless communication system, we propose some networking schemes for the indoor visible light networking, including multi-tier cell coverage, the separation of user plane and control plane, the distributed and client-server mode coexisted. Those networking policies will effectively accelerate the application and popularization of indoor VLC networks.

This study proposes an approach for achieving strong communication security based on explosive fountain code with coset pre‐coding, where both main and wire‐tap channels are memoryless binary erasure channels. Coset pre‐coding is used to prevent the eavesdroppers from intercepting the confidential information from the leaked bits. Further, an explosive fountain code is designed to ensure the reliability and low information leakage. By this way, the proposed approach can keep strong security and reliability when the erasure probability of the main channel is slightly lower than that of the wire‐tap channel. Extensive simulations are conducted to verify the correctness and effectiveness of the approach.

The existing sequential estimation algorithms repeatedly accumulate the previous erroneous information. Thus, their performance is usually poor in the low SNR region, especially when the sequence initial state is unknown. This paper presents a new method, called Innovation Net Accumulation-Sequential Acquisition (INASE) for sequential acquisition. By designing innovation net accumulating scheme, the useful information can be accumulated more effectively. The comparison between INASE and the existing acquisition algorithm shows that INASE provides better acquisition performance and can successfully acquire the PN sequence even in extremely bad communication environments.

A secure and effective handoff scheme is the key to guarantee seamless roaming of mobile terminals in all IP heterogeneous wireless networks. In the current work, Fast handoffs for mobile IPv6 (FMIPv6) can reduce the handoff latency, but the process of registration update badly affects the handoff efficiency, and it doesn't think of the necessary secure function when handoff across heterogeneous networks and different management domains. This paper proposes a FMIPv6-based concurrently executing handoff method-CE-FMIPv6, which integrates Wireless Shared Key Exchange (W-SKE) into FMIPv6 and substitutes previous access router (PAR) for mobile node to complete the registration update process. With the assistant of PAR, the mutual authentication, registration update and layer 2 handoff are executed simultaneously, and the handoff delay caused by registration update and authentication is improved evidently. This method also takes account of the fast re-authentication process to improve the handoff efficiency of micro-mobility. The theoretical analysis indicates that this method could reach a good compromise between security and handoff efficiency.

A location method aiming at suppressing non-line of sight (NLOS) errors using single observer is proposed, which is named by pseudo-target dynamic feasible region constraint (PTDFRC) method. The method needs less resources and cost than traditional multi-observer location methods. The scatters around the target are regarded as pseudo-target. Angle of arrival (AOA) and the changing rate of AOA of pseudo-target are measured to get the location of pseudo-target. Then the feasible region of real target is constructed according to the location of pseudo-target and the geometrical relationship between real target and pseudo-target. In the feasible region, the optimization methods are applied to estimate the location of real target and deal with the NLOS errors. PTDFRC method converts multi-path signals, usually regarded as harmful factors, to advantage factors. Optimized route of maneuvering observer is also calculated to improve the location accuracy and shorten the convergence time. As proved in simulation experiments, the proposed method can depress the location errors effectively and rapidly.

The paper presents the average bit error rate (BER) of a maximal ratio combining (MRC) two-dimensional (2D)-RAKE receiver in correlated frequency selective Nakagami fading environments in the presence of multiple co-channel interferences. A closed-form expression of the simple approximated probability density function for the signal-to-interference-plus-noise ratio (SINR) is derived for the receiver with multiple correlated antennas and multiple RAKE branches in arbitrary fading environments. The effects of spatial and temporal diversity order, angular spread, antenna spacing, average multi-path strength and fading severity on the performance of the MRC 2D-RAKE receivers are all illustrated.

The closed-form expressions of signal-to-interference-plus-noise ratio (SINR) and the outage probability are derived for a maximal ratio combining (MRC) two-dimensional (2D)-RAKE receiver with imperfect power control in a frequency-selective Nakagami fading channel. The impact of power control error (PCE) on the performance of the receiver is analyzed for various fading environments. Numerical results show that the performance of 2D-RAKE receivers degrades due to imperfect power control. But when PCE is not serious, increasing the number of antennae and temporal diversity order can compensate for the performance loss. The exact performance improvement due to space-time processing varies with PCE and the fading environment.

The smart antenna and spatial diversity-combining receiver are two of the most important spatial signal processing technologies. This paper studies the radio propagation characteristics of the transmission path, spatio-temporal channel model and channel characteristics in different environments. On the basis of those analyses, the authors analyzed the operating principle of the smart antenna and spatial diversity-combining technology, and especially showed the differences between these two technologies in several aspects.

A simplified and approximated probability density function (PDF) has been obtained for the signal-to-interference-plus-noise ratio (SINR) of the maximal ratio combining (MRC) 2D-RAKE receiver in a frequency-selective Nakagami multipath fading with arbitrary fading parameters, thus simplifying the analysis of bit error rate (BER) and outage probability in the presence of multi-path interferers. The numerical results indicate that the 2D-RAKE receiver could improve the system performance of WCDMA communication systems.