Cognitive Satellite Terrestrial Networks Research Articles

Green integrated cooperative spectrum sensing for cognitive satellite terrestrial networks

AbstractIn this paper, a two‐way relay‐aided cognitive satellite terrestrial network (TR‐CSTN) model is proposed, where primary users are located at the edge of the base station. In the TR‐CSTN, one of satellite terminal users (STUs) is selected by the fusion center as the TR to forward information between two edge primary users with power of the TR. Meanwhile, these edge primary users share the licensed frequency band with the selected TR to send information to the satellite. Then, given the limited spectrum utilization and energy efficiency (EE) of the communication system, the cooperative spectrum sensing is employed to realize green communication. Specifically, the fusion center threshold, energy detection threshold, sensing duration and number of STUs are jointly optimized to enhance EE. Furthermore, considering that the node's energy shortage results in a short network lifetime, absolute EE gets improved. In detail, a power allocation scheme named normalized power aided Lévy flight trajectory‐based whale optimization algorithm (NP‐LWOA) is provided, which fulfills effective energy compensation among STUs to prolong the network lifetime notably. Finally, numerical results confirm the theoretical analysis and show the effectiveness of the TR‐CSTN and the NP‐LWOA in efficiently achieving the concept of green communication compared with other methods.

Secure Energy Efficiency for mmWave-NOMA Cognitive Satellite Terrestrial Network

In this letter, we investigate secure energy efficiency (SEE) for millimeter-wave non-orthogonal multiple access (mmWave-NOMA) cognitive satellite terrestrial network (CSTN), where the primary satellite network coexists with the secondary terrestrial network in the same mmWave bands. In the terrestrial network, there are multiple legitimate receivers (LRs) and an eavesdropper (Eve). Based on this, we divide the LRs into multiple clusters and design the hybrid analog/digital precoding. The LRs belonging the same cluster are served by NOMA. Considering the spectrum sharing issues of the CSTN and imperfect channel state information of the Eve, a power allocation optimization problem is formulated to maximize the SEE. To solve the non-convex optimization problem, we transform the fractional SEE problem to a subtractive form. Moreover, the subtractive-form problem is transformed into a semidefinite program by Dinkelbach, successive convex approximation and S-procedure technologies. Finally, an iterative algorithm is proposed to solve the SEE problem. The simulation results are provided to verify the performance of the proposed schemes.

Rate-Splitting Multiple Access-Enabled Security Analysis in Cognitive Satellite Terrestrial Networks

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 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">rate splitting multiple access scheme</i> (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 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">beamforming</i> (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.

Secure Spectrum-Energy Efficiency Tradeoff Based on Stackelberg Game in a Two-Way Relay Cognitive Satellite Terrestrial Network

In this letter, we consider a two-way relay <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">cognitive satellite terrestrial network</i> (CSTN) in the presence of a friendly jammer and an <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">eavesdropper</i> (Eve). In this system, we investigate the tradeoff between the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">secure spectrum efficiency</i> (SSE) and the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">secure energy efficiency</i> (SEE). To be specific, firstly, two frames corresponding to the busy and idle working states of the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">primary users</i> (PUs) are designed to flexibly analyze the system performance. Secondly, the SSEs, SEEs, and utility functions for both the cognitive satellite network and the terrestrial primary network are deduced, respectively, considering the different working states of the PUs and the Eve. Finally, based on the Stackelberg Game model, the mathematically intractable problem on the spectrum-energy exchange is solved, thus we maximize the SSE and the SEE jointly. Numerical results are given to validate that there exists an SSE-SEE tradeoff. Also, we show that the proposed spectrum-energy exchange scheme based on the Stackelberg Game outperforms the fixed parameter allocation scheme remarkably.

Energy Efficient Power Control for Cognitive Multibeam-Satellite Terrestrial Networks With Poisson Distributed Users

With great potential to alleviate spectrum scarcity in the next generation wireless communication, cognitive satellite terrestrial networks (CSTNs) have attracted considerable attention recently. To realize efficient spectrum sharing between satellite and terrestrial networks, in this paper, we propose an energy efficient power control scheme for CSTNs, where a multibeam satellite network acts as the secondary system and the cellular network acts as the primary system. Especially, satellite users and primary base stations are spatially Poisson distributed and the channel state information (CSI) of satellite interference link is assumed to be outdated. We firstly analyze the statistical characteristic of the terrestrial aggregate interference with probabilistic stochastic geometry. On this basis, to guarantee reliable communications for both networks, we formulate the power control scheme as an energy efficiency maximization problem subjected to interference power constraints imposed by terrestrial communications and outage constraints of satellite communications. Further, by employing the Dinkelbach and Lagrange duality method, we solve the nonlinear concave optimization problem and derive the optimal solution of the transmit power. Finally, simulation results demonstrate the validity of the theoretical results, reveal the trade-off between the performance of two networks, present the impacts of aggregate interference on the performance of satellite networks, and show the performance superiority of considering outdated CSI compared with perfect CSI assumption in terms of interference violation probability.

Optimal Cooperative Transmission for Overlay Cognitive Satellite Terrestrial Networks

In this letter, we investigate an overlay cognitive satellite terrestrial network, where the secondary terrestrial network cooperates with the primary satellite network for spectrum access in a time splitting manner. To maximize the spectrum efficiency of such a cooperative cognitive network, we propose an optimal cooperative transmission scheme by optimizing the time splitting factors. Specifically, we firstly analyze the feasible range of time splitting factors to guarantee both transmission requirements of the satellite and terrestrial networks. On this basis, we decompose the non-concave optimization problem into several categories and employ the Charnes-Cooper transformation to determine the optimal time splitting factors.

Sum Secrecy Rate Maximization in NOMA-Based Cognitive Satellite-Terrestrial Network

In this letter, we present a joint beamforming design for non-orthogonal multiple access (NOMA)-based cognitive satellite-terrestrial network (CSTN), where satellite network applies orthogonal multiple access (OMA) technology and NOMA scheme is utilized by the terrestrial network. The scheme key is to maximize sum secrecy rate of satellite users under the imperfect channel state information, while meeting the rate requirements of terrestrial users and transmit power constraints of the CSTN. Since the formulated optimization problem is non convex and intractable, we convert the original non convex maximization problem to a corresponding tractable convex one by successive convex approximation (SCA) and semidefinite relaxation (SDR), and then propose an SCA-based iterative beamforming algorithm to get the secure beamforming vectors. Finally, numerical simulation results are provided to verify the effectiveness and superiority of the proposed joint beamforming design.

A Game-Theoretical Learning Approach for Spectrum Trading in Cognitive Satellite-Terrestrial Networks

This letter investigates the bandwidth allocation problem for discontinuous frequency bands in cognitive satellite-terrestrial networks (CSTNs). Different from existing studies, we take the realistic assumption that the available idle spectrum bands are disconnected. Most of the existing works focused on the continuous bandwidth allocation problem and proposed corresponding algorithms optimizing continuous variables, which cannot directly solve the bandwidth allocation problem for discontinuous frequency bands. Besides, we also take the individual bandwidth requirement, the priority of terrestrial cognitive users, and the limitation on the total available bandwidth into consideration. The bandwidth allocation for discontinuous frequency bands is formulated as a bandwidth auction game, which is proven to have at least one pure strategy Nash Equalization (NE) solution. Furthermore, an improved best response learning algorithm based on exploration and exploitation (BREE) is proposed to achieve satisfying performance. Finally, simulations are conducted to verify the convergence and superiority of the proposed BREE algorithm.

A PHY Layer Security of a Jamming-Based Underlay Cognitive Satellite-Terrestrial Network

In this work, we investigate the physical layer security of a jamming-based underlay cognitive satellite-terrestrial network consisting of a radio frequency link at the first hop and an optical feeder at the second hop. Particularly, one secondary user (SU) is transmitting data to an end-user optical ground station through the aid of a relay satellite, in the presence of an active eavesdropper at each hop. Moreover, another SU located in the first hop is acting as a friendly jammer and continuously broadcasting an artificial noise that cannot be decoded by the wiretapper so as to impinge positively on the system’s secrecy. Owing to the underlying strategy, the SUs are permanently adjusting their transmit powers in order to avoid causing harmful interference to primary users. The RF channels undergo shadowed-Rician and Rayleigh fading models, while the optical link is subject to Gamma-Gamma turbulence with pointing error. Closed-form and asymptotic expressions for the intercept probability (IP) are derived considering two different scenarios regardless of the channel’s conditions, namely (i) absence and (ii) presence of a friendly jammer. The effect of various key parameters on IP, e.g., sources’ transmit power, artificial noise, maximum tolerated interference power, and fading severity parameters are examined. Precisely, we aim to answer the following question: could a friendly jammer further enhance the security of such a system even in a low SNR regime? All the derived results are corroborated by Monte Carlo simulations and new insights into the considered system’s secrecy are gained.

Performance of NOMA-Enabled Cognitive Satellite-Terrestrial Networks With Non-Ideal System Limitations

Satellite-terrestrial networks (STNs) have received significant attention from research and industry due to their capability of providing a stable connection to rural and distant areas, where the allocation of terrestrial infrastructures is uneconomical or difficult. Moreover, the STNs are considered as a promising enabler of fifth-generation communication networks. However, expected massive connectivity in future communication networks will face issues associated with spectrum scarcity. In this regard, the integration of cognitive radio and non-orthogonal multiple access (NOMA) techniques into STNs is considered as a promising remedy. Thereafter, in this article, we investigate NOMA-assisted cognitive STN under practical system conditions, such as transceiver hardware impairments, channel state information mismatch, imperfect successive interference cancellation, and interference noises. Generalized coverage probability formulas for NOMA users in both primary and secondary networks are derived considering the impact of interference temperature constraint and its correctness is verified through Monte Carlo simulation. Furthermore, to achieve performance fairness among the users, power allocation factors based on coverage fairness for primary and secondary NOMA users are provided. Moreover, the numerical results demonstrate superior performance compared to the ones obtained from an orthogonal multiple access scheme and examine the imperfection's impact on the system performance in terms of coverage and throughput.

Correlated Equilibrium Based Distributed Power Control in Cognitive Satellite-Terrestrial Networks

In this letter, we investigate the distributed power control problem in downlink cognitive satellite-terrestrial networks (CSTNs) while considering the quality of service (QoS) requirements of the primary satellite links. Specifically, a game-theoretic approach is employed to analyze the distributed but mutually affected power control decision-making problem. With the perspective of resource efficiency enhancement and interference mitigation, a novel utility function based on the trade-off between transmission rate and mutual interference is properly designed for all players in the power control game. Then, the existence of correlated equilibrium (CE) of the proposed game is discussed, and the criteria of optimality for the CE solution is introduced. Moreover, we design a regret-matching based distributed adaptive learning algorithm to obtain the CE solution and demonstrate it through representative numerical simulations.

Secure and Energy Efficient Transmission for RSMA-Based Cognitive Satellite-Terrestrial Networks

Rate-splitting multiple access (RSMA) has recently received considerable attention due to its high efficiency in both spectral utilization and energy consumption. Inspired by this emerging technique, this letter presents a secure beamforming (BF) scheme for RSMA-based cognitive satellite terrestrial networks in the presence of multiple eavesdroppers. Assuming that the system operates in the millimeter wave band and only imperfect wiretap channel state information is available at the satellite and terrestrial base station, our objective is to maximize the secrecy-energy efficiency of the earth station (ES) while meeting the constraints on the ES secrecy rate, the cellular users’ rate requirements, and transmit power budgets of the satellite and base station. As the formulated optimization problem is mathematically intractable, by applying successive convex approximation and Taylor expansion methods, we propose a robust BF scheme to convert the nonconvex objective and constraints into convex ones, which can be iteratively solved. The effectiveness and superiority of the proposed scheme are confirmed through simulation results.

Cognitive Region Design for Overlay Cognitive Satellite Terrestrial Networks

In this letter, we investigate an overlay cognitive satellite terrestrial network (OCSTN), where the secondary terrestrial network assists the primary satellite communication in exchange for the opportunities of spectrum access. To achieve a win-win cooperation of the satellite and terrestrial networks in the OCSTN, we propose a cognitive region to determine the conditions that terrestrial nodes can work as effective relays to cooperate with the satellite network in a time-splitting spectrum sharing manner. Specifically, we first analyze the ergodic rates of the satellite and terrestrial networks. On this basis, we design a cognitive region seeking the feasible location set of the secondary relay and the corresponding range of time splitting ratios, which can improve the satellite communication performance while enabling the transmission of terrestrial network.

Robust Secure Beamforming for Wireless Powered Cognitive Satellite-Terrestrial Networks

This article addresses the security problem for wireless powered cognitive satellite-terrestrial network, where a multibeam satellite sub-network shares the portion of millimeter wave bands with multiple cellular networks, each consisting of a base station, several mobile users (MUs) and energy receivers (ERs). Considering that the ERs are potential eavesdroppers of the MUs, and only imperfect knowledge of the angles of departure for the wiretap channels is available, we aim at maximizing aggregated rate of the considered network while guaranteeing the signal-to-interference-plus-noise ratio requirements of the MUs, the energy harvesting thresholds and the secrecy constraints at ERs. Since the formulated optimization problem is mathematically intractable, we exploit a discretization method and the Taylor expansion method to transform the non-convex objective and constraints into convex ones, and then propose an iterative beamforming (BF) algorithm to solve the problem. Furthermore, we present a combined multibeam scheme to obtain suboptimal BF weight vectors with low computational burden. Finally, simulation results reveal that the proposed BF schemes can efficiently improve the aggregated rate with fast convergence compared to the benchmark schemes.

On the Performance of NOMA-Assisted Overlay Multiuser Cognitive Satellite-Terrestrial Networks

In this letter, we investigate the performance of an overlay cognitive satellite-terrestrial network comprising a primary satellite source with its multiple terrestrial receivers and a secondary transmitter-receiver pair on the ground. Herein, the primary satellite source employs a non-orthogonal multiple access (NOMA) scheme to simultaneously serve its all users, while the secondary transmitter assists the primary communication through cooperative relaying technique in exchange for spectrum access. For this overall set-up, we obtain the closed-form expressions for the outage probability of primary satellite network and secondary terrestrial network by adopting pertinent heterogeneous fading models. Further, we derive the asymptotic outage behaviour at high signal-to-noise-ratio (SNR) for the primary and secondary networks, and thereby calculate the achievable diversity orders. Our analytical findings are corroborated through various numerical and simulation results.

Secure Beamforming for Cognitive Satellite Terrestrial Networks With Unknown Eavesdroppers

This article proposes a beamforming (BF) scheme for a cognitive satellite terrestrial network, where the base station (BS) and a cooperative terminal (CT) are exploited as green interference resources to enhance the system security performance in the presence of unknown eavesdroppers. Different from the related works, we assume that only imperfect channel information of the mobile user (MU) and earth station (ES) is available. Specifically, we formulate an optimization problem with the objective to degrade the possible wiretap channels within the private signal beampattern region, while imposing constraints on the signal-to-interference-plus-noise ratio (SINR) at the MU, the interference level of the ES and the total transmit power budget of the BS and CT. To solve this mathematically intractable problem, we propose a joint artificial noise generation and cooperative jamming BF scheme to suppress the interception. Finally, the effectiveness and superiority of the proposed BF scheme are confirmed through computer simulations.

Secure Energy Efficiency Maximization in Cognitive Satellite-Terrestrial Networks

This article investigates the secure energy efficiency (EE) optimization problem in a cognitive satellite-terrestrial network with a capable eavesdropper. The objective is to maximize the secure EE for the primary satellite network while satisfying the allowable signal-to-interference-plus-noise ratio requirements of the secondary and primary users along within the transmit power limitation of both satellite and the terrestrial base station. Owing to the nonconvexity and intractability of the original optimization problem, a beamforming scheme and associated transformation algorithms are proposed by jointly applying the Taylor approximation, fraction programming, and alternating search to cope with the implementation difficulty. The key is to convert the original optimization problem into a simple convex framework and obtain the optimal solution step by step. Finally, numerical simulations are given to verify the feasibility and practicability of the proposed optimization algorithms.

Energy-Efficient Power Control for Cognitive Satellite-Terrestrial Networks With Outdated CSI

Taking account of the limited energy and large feedback delay in satellite communications, in this article, we propose an energy-efficient power control scheme for cognitive satellite-terrestrial networks with outdated channel state information (CSI), where satellite network reuses the spectrum resources of terrestrial networks. Specifically, to guarantee reliable communications for both networks, we first formulate the power control scheme as an energy efficiency (EE) maximization problem subjected to interference power constraints imposed by terrestrial communications and rate constraints of satellite communications. Moreover, we solve the nonlinear concave optimization problem and derive the average transmit power for theoretical performance evaluation. Simulation results reveal the impacts of various key parameters on satellite communications.

Energy-Efficient Cooperative Spectrum Sensing in Cognitive Satellite Terrestrial Networks

Having the ability to provide seamless coverage and alleviate the frequency scarcity, the cognitive satellite terrestrial network becomes a promising candidate for future communication networks. In the cognitive network, spectrum sensing plays an important role in detecting the channel state for opportunistic utilization, where cooperative spectrum sensing is employed to improve the sensing performance. Additionally, it is critical for battery-powered satellite mobile terminals to diminish energy consumption costs. In this regard, this paper proposes a novel sensing-based cognitive satellite terrestrial network (SCSTN), which integrates the cognitive satellite terrestrial network with the distributed cooperative spectrum sensing network. Specifically, we focus on energy-efficient cooperative sensing in the SCSTN, which maximizes the energy efficiency (EE) of the cognitive satellite network by a tradeoff between the average throughput and the average energy consumption. In the SCSTN, the energy detection threshold of the sensing node and the rule threshold of fusion affect the average throughput and the average energy consumption. Hence, the objective of this paper is to identify the energy detection threshold of the sensing node and the rule threshold of fusion to achieve the maximum EE. We first study the EE formulation of the rule threshold of fusion when the energy detection threshold of the sensing node is given, and transform the ratio-type objective function of EE into a parametric formulation. Subsequently, by exploring the relationship between the two formulations and making use of the monotonicity of the parametric formulation, an algorithm to obtain the optimal rule threshold of fusion for the original problem is developed. Furthermore, we study the optimal formulation of the energy sensing threshold of the sensing node and discuss the effect of the sensing duration and the number of distributed cooperative terminals on the EE. Lastly, the performance of the proposed method is evaluated through numerical simulation results.

Sensing-Based Dynamic Spectrum Sharing in Integrated Wireless Sensor and Cognitive Satellite Terrestrial Networks.

This paper presents a cognitive satellite communication based wireless sensor network, which combines the wireless sensor network and the cognitive satellite terrestrial network. To address the conflict between the continuously increasing demand and the spectrum scarcity in the space network, the cognitive satellite terrestrial network becomes a promising candidate for future hybrid wireless networks. With the higher transmit capacity demand in satellite networks, explicit concerns on efficient resource allocation in the cognitive network have gained more attention. In this background, we propose a sensing-based dynamic spectrum sharing scheme for the cognitive satellite user, which is able to maximize the ergodic capacity of the satellite user with the interference of the primary terrestrial user below an acceptable average level. Firstly, the cognitive satellite user monitors the channel allocated to the terrestrial user through the wireless sensor network; then, it adjusts the transmit power based on the sensing results. If a terrestrial user is busy, the satellite user can access the channel with constrained power to avoid deteriorating the communication quality of the terrestrial user. Otherwise, if the terrestrial user is idle, the satellite user allocates the transmit power based on its benefit to enhance the capacity. Since the sensing-based dynamic spectrum sharing optimization problem can be modified into a nonlinear fraction programming problem in perfect/imperfect sensing conditions, respectively, we solve them by the Lagrange duality method. Computer simulations have shown that, compared with the opportunistic spectrum access, the proposed method can increase the channel capacity more than for in a perfect sensing scenario. In an imperfect sensing scenario, dB and dB, the optimal sensing time achieving the highest ergodic capacity is about 2.34 ms when the frame duration is 10 ms.