• September 2021 Vol. 18 No. 9

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  • Chao Liu, Zhongshan Zhang
    2021, 18(9): 1-10.
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    The Unmanned Aerial Vehicle (UAV) technologies are envisioned to play an important role in the era of Air-Space-Ground integrated networks. In this paper, we investigate the connectivity of a Flying Ad hoc Network (FANET) in the presence of a ground-based terminal. In particular, the connected probability of the UAV-to-UAV (U2U) link as well as that of the UAV-to-Ground (U2G) link in a three dimensional (3D) space are analyzed. Furthermore, to mitigate the aggregate interference from UAV individuals, a priority based power control scheme is implemented for enhancing the connectivity of both U2U and U2G links. Numerical results illustrate the effectiveness of the proposed analysis.
  • Yitao Li, Zhongqiang Luo, Wuyang Zhou, Jinkang Zhu
    2021, 18(9): 11-23.
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    Satellite mobile system and space-air-ground integrated network have a prominent superiority in global coverage which plays a critical role in remote and non-land regions, as well as emergency communications. However, due to the gradual angle attenuations of the satellite antennas, it is difficult to achieve full frequency multiplex among different beams as terrestrial 5G network. Multi-color frequency reuse is widely adopted in both academic and industry. Beam hopping scheme has attracted the attention of researchers recently due to the allocation flexibility. In this paper, we focus on analyzing the performance benefits of beam hopping compared with multi-color frequency reuse scheme in non-uniform user and traffic distributions in satellite system. Aerial networks are also introduced to form a space-air-ground integrated network for coverage enhancement, and the capacity improvement is analyzed. Besides, additional improved techniques are provided to make comprehensive analysis and comparisons. Theoretical analysis and simulation results indicate that the beam hopping scheme has a prominent superiority in the system capacity compared with the traditional multi-color frequency reuse scheme in both satellite mobile system and future space-air-ground integrated network.
  • Shu Fu, Bibo Wu, Shaohua Wu, Fang Fang
    2021, 18(9): 24-36.
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    The six-generation (6G) wireless network is expected to satisfy the requirements of ubiquitous connectivity and intelligent endogenous. Terrestrial-satellite networks (TSN) enable seamless coverage for terrestrial users in a wide area, making it very promising in 6G. As data traffic in TSNs surges, the integrated management for caching, computing, and communication (3C) has attracted much research attention. In this paper, we investigate the multi-resource management in the uplink and downlink transmission of TSN, respectively. In particularly, we aim to guarantee both throughput fairness and data security in the uplink transmission of TSN. Considering the intermittent communication of the satellite, we introduce two kinds of relays, i.e., terrestrial relays (TRs) and aerial relays (ARs) to improve the system throughput performance in the downlink transmission of TSN. Finally, we study a specific case of TSN with the uplink and downlink transmission, and the corresponding simulation results validate the effectiveness of our proposed schemes.
  • Tao Ni, Xiaojin Ding, Yunfeng Wang, Jun Shen, Lifeng Jiang, Gengxin Zhang
    2021, 18(9): 37-47.
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    In this paper, we investigate a spectrum-sensing system in the presence of a satellite, where the satellite works as a sensing node. Considering the conventional energy detection method is sensitive to the noise uncertainty, thus, a temporal convolutional network (TCN) based spectrum-sensing method is designed to eliminate the effect of the noise uncertainty and improve the performance of spectrum sensing, relying on the offline training and the online detection stages. Specifically, in the offline training stage, spectrum data captured by the satellite is sent to the TCN deployed on the gateway for training purpose. Moreover, in the online detection stage, the well trained TCN is utilized to perform real-time spectrum sensing, which can upgrade spectrum-sensing performance by exploiting the temporal features. Additionally, simulation results demonstrate that the proposed method achieves a higher probability of detection than that of the conventional energy detection (ED), the convolutional neural network (CNN), and deep neural network (DNN). Furthermore, the proposed method outperforms the CNN and the DNN in terms of a lower computational complexity.
  • Chen Zhang, Xudong Zhao, Gengxin Zhang
    2021, 18(9): 48-61.
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    Beam hopping technology provides a foundation for the flexible allocation and efficient utilization of satellite resources, which is considered as a key technology for the next generation of high throughput satellite systems. To alleviate the contradiction between resource utilization and co-frequency interference in beam hopping technology, this paper firstly studies dynamic clustering to balance traffic between clusters and proposes cluster hopping pool optimization method to avoid inter-cluster interference. Then based on the optimization results, a novel joint beam hopping and precoding algorithm is provided to combine resource allocation and intra-cluster interference suppression, which can make efficient utilization of system resources and achieve reliable and near-optimal transmission capacity. The simulation results show that, compared with traditional methods, the proposed algorithms can dynamically adjust to balance demand traffic between clusters and meet the service requirements of each beam, also eliminate the co-channel interference to improve the performance of satellite network.
  • Fangjiong Chen, Zilong Jiang, Fei Ji, Hua Yu, Quansheng Guan, Feng Liu
    2021, 18(9): 62-70.
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    An important vision of next generation mobile system is to provide global internet access. The Space-Terrestrial Integrated Network(STIN) has been proposed and intensively studied to tackle this challenge. Due to the severe attenuation of radio signals in water, the STIN cannot be directly applied in underwater scenarios. In this paper we envision a framework of integrated radio-acoustic network arming at high-efficient data transmission in underwater scenarios, where acoustic signal is for underwater communication and radio signal is for surface and air communications. Since radio links have much higher data transmission rate and lower delay, in the integrated radio-acoustic network, the acoustic links easily become congested, at the same time the radio links are not fully utilized. We therefore propose that the integrated radio-acoustic network should be properly designed to minimize the hop count of acoustic links, as well as the signaling overhead in the acoustic subnetwork. We then present a novel network framework and the relative technologies to help moving the signaling overhead to the radio subnetwork.
  • Runze Dong, Buhong Wang, Kunrui Cao
    2021, 18(9): 71-87.
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    The high mobility of unmanned aerial vehicles (UAVs) could bring abundant degrees of freedom for the design of wireless communication systems, which results in that UAVs, especially UAV swarm, have attracted considerable attention. This paper considers a UAV Swarm enabled relaying communication system, where multiple UAV relays are organized via coordinated multiple points (CoMP) as a UAV swarm to enhance physical layer security of the system in the presence of an eavesdropper. In order to maximize achievable secrecy rate of downlink, we jointly optimize the beamforming vector of the virtual array shaped by the UAV swarm and bandwidth allocation on it for receiving and forwarding, and both amplify-and-forward (AF) and decode-and-forward (DF) protocols are considered on the UAV swarm. Due to the non-convexity of the joint optimization problem, we propose an alternating optimization (AO) algorithm to decompose it into two subproblems utilizing block coordinate descent technique, then each subproblem is solved by successive convex optimization method. Simulation results demonstrate that DF has competitive performance advantage compared with AF and the superiority of the proposed secure transmission strategy with optimal beamforming and bandwidth allocation compared with benchmark strategies.
  • Liang Jin, Xiaoyan Hu, Yangming Lou, Zhou Zhong, Xiaoli Sun, Huiming Wang, Jiangxing Wu
    2021, 18(9): 88-99.
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    The information security and functional safety are fundamental issues of wireless communications sytems. The endogenous security principle based on Dynamic Heterogeneous Redundancy provides a direction for the development of wireless communication security and safety technology. This paper introduces the concept of wireless endogenous security from the following four aspects. First, we sorts out the endogenous security problems faced by the current wireless communications system, and then analyzes the endogenous security and safety attributes of the wireless channel. After that, the endogenous security and safety structure of the wireless communications system is given, and finally the applications of the existing wireless communication endogenous security and safety functions are listed.
  • Chao Li, Ting Jiang, Sheng Wu
    2021, 18(9): 100-115.
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    Aiming at the problem of music noise introduced by classical spectral subtraction, a short-time modulation domain (STM) spectral subtraction method has been successfully applied for single-channel speech enhancement. However, due to the inaccurate voice activity detection (VAD), the residual music noise and enhanced performance still need to be further improved, especially in the low signal to noise ratio (SNR) scenarios. To address this issue, an improved frame iterative spectral subtraction in the STM domain (IMModSSub) is proposed. More specifically, with the inter-frame correlation, the noise subtraction is directly applied to handle the noisy signal for each frame in the STM domain. Then, the noisy signal is classified into speech or silence frames based on a predefined threshold of segmented SNR. With these classification results, a corresponding mask function is developed for noisy speech after noise subtraction. Finally, exploiting the increased sparsity of speech signal in the modulation domain, the orthogonal matching pursuit (OMP) technique is employed to the speech frames for improving the speech quality and intelligibility. The effectiveness of the proposed method is evaluated with three types of noise, including white noise, pink noise, and hfchannel noise. The obtained results show that the proposed method outperforms some established baselines at lower SNRs (-5 to +5 dB).
  • Rui Ma, Haowei Wu, Liubin Wang, Jinglan Ou, Lian Yan
    2021, 18(9): 116-129.
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    This work investigates the security issue of the energy-constrained untrusted relay network with imperfect channel reciprocity, where the relay without the built-in power supply can only scavenge energy from radio-frequency signals radiated by the source and destination. A hybrid power-splitting (PS)- and time-switching (TS)-based relaying (HPTR) protocol is presented to improve the degraded secrecy performance due to the incomplete self-interference cancellation at the destination. To evaluate the secrecy throughput (ST) of the studied system, the analytical expression of the secrecy outage probability under the delay-limited transmission mode and the closed-form lower bound of the ergodic secrecy capacity under delay-tolerant transmission mode are derived. Both linear and nonlinear models for the energy harvester at the relay are compared. The optimal PS and TS ratios are evaluated numerically. The theoretical derivations are validated by numerical results, revealing that the residual jamming has a negative effect on the secrecy performance of untrusted relay networks, which can be alleviated by the HPTR protocol. Besides, we compare the ST performance of the HPTR protocol with that of the PS and TS relaying schemes, and the results show that the HPTR protocol outperforms both PS and TS relaying protocols in terms of the ST.
  • Yitian Chen, Shaoshuai Gao, Guofang Tu, Hao Qiu
    2021, 18(9): 130-147.
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    Massive multiple-input multiple-output (MIMO), a technique that can greatly increase spectral efficiency (SE) of cellular networks, has attracted significant interests in recent years. One of the major limitations of massive MIMO systems is pilot contamination, which will deteriorate the SE. The superimposed pilot-based scheme has been proved to be a viable method for pilot contamination reduction. However, it cannot break through another limitation of massive MIMO, i.e., spatial correlation. In addition, it will also lead to interference between the pilot and user data since they are imposed together. In this paper, we try to tackle these two issues, which will be described as follows. Firstly, a column-wise asymptotically orthogonal matrix, named as pseudo-channel matrix, is developed by orthogonalization of received signal. To recover the information about the large-scale fading (LSF) coefficients, the pseudo-channel matrix is truncated according to the cardinality of adjacent users set (CAUS). By this means, spatial correlation can be mitigated effectively. Secondly, robust independent component analysis (RobustICA) is used to reduce the interference caused by user data, and as a result the system performance can be further improved. Numerical simulation results demonstrate the effectiveness of the proposed method.
  • Shifeng Ding, Zile Jiang, Sanjay K. Bose, Gangxiang Shen
    2021, 18(9): 148-166.
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    Network virtualization is important for elastic optical networks (EONs) because of more flexible service provisioning. To ensure guaranteed quality of service (QoS) for each virtual elastic optical network (VEON), clients usually request network resources from a network operator based on their bandwidth requirements predicted from historical traffic demands. However, this may not be efficient as the actual traffic demands of users always fluctuate. To tackle this, we propose a new VEON service provisioning scheme, called SATP, which consists of three stages, i.e., spectrum assignment (SA), spectrum trading (ST), and spectrum purchasing (SP). Unlike conventional once-for-all VEON service provisioning approaches, the SATP scheme first allocates spectrum resources to VEONs according to their predicted bandwidth requirements with a satisfaction ratio $\alpha$ ($0 < \alpha \leq 1$). Then, to minimize service degradation on VEONs which are short of assigned spectra for their peak traffic periods, the scheme allows VEONs to trade spectra with each other according to their actual bandwidth requirements. Finally, it allows VEON clients to purchase extra spectrum resources from a network operator if the spectrum resources are still insufficient. To optimize this entire process, we formulate the problem as a mixed integer linear programming (MILP) model and also develop efficient heuristic algorithms for each stage to handle large test scenarios. Simulations are conducted under different test conditions for both static and dynamic traffic demand scenarios. Results show that the proposed SATP scheme is efficient and can achieve significant performance improvement under both static and dynamic scenarios.
  • Wenfa Yan, Qin Shu, Peng Gao
    2021, 18(9): 167-174.
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    In this paper,we investigate and analyze the network security risks faced by 5G private industrial networks.Based on current network security architecture and 3GPP requirements and considering the actual application of 5G private industrial networks, a comparative analysis is used to plan and design a private network security construction scheme.The network security construction model, network organization, and key processes of 5G private industrial networks at the current stage are investigated. In addition, the key direction for the next stage of construction is discussed.
  • Ziyi Yang, Yu Zhang
    2021, 18(9): 175-191.
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    Reconfigurable intelligent surface (RIS) is a promising technology that utilizes massive low-cost elements to reflect incident signals to desired direction. In this paper, we consider a RIS-aided cell free multiple-input multiple-output (MIMO) network that composed of multiple access points (APs), multiple RISs, multiple information receivers (IRs), and multiple energy receivers (ERs). Under the maximum transmit power constraints of the APs and the minimum total energy harvesting power constraints of the ERs, we aim to maximize the weighted sum-rate (WSR) by jointly optimizing the beamforming matrices and the passive RIS reflection matrices. However, the formulated problem is nonconvex and very challenging to solve. Therefore, we propose an alternating optimization algorithm to obtain a suboptimal solution. Explicitly, the proposed algorithm decomposes the original optimization problem into three subproblems that can be efficiently solved. To overcome the nonconvexity of the subproblems, a successive convex approximation (SCA) based algorithm is proposed to tackle the energy harvesting constraints. Moreover, an alternating direction method of multipliers (ADMM) based algorithm is proposed to optimize the constant modulus constrained RIS reflecting elements. Finally, simulations are conducted to demonstrate the performance advantages of the proposed algorithms.
  • Yuan Luo, Long Cheng, Yu Liang, Jianming Fu, Guojun Peng
    2021, 18(9): 192-209.
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    Cyber-physical systems (CPS) have been widely deployed in critical infrastructures and are vulnerable to various attacks. Data integrity attacks manipulate sensor measurements and cause control systems to fail, which are one of the prominent threats to CPS. Anomaly detection methods are proposed to secure CPS. However, existing anomaly detection studies usually require expert knowledge (eg., system model-based) or are lack of interpretability (eg., deep learning-based). In this paper, we present DEEPNOISE, a deep learning-based anomaly detection method for CPS with interpretability. Specifically, we utilize the sensor and process noise to detect data integrity attacks. Such noise represents the intrinsic characteristics of physical devices and the production process in CPS. One key enabler is that we use a robust deep autoencoder to automatically extract the noise from measurement data. Further, an LSTM-based detector is designed to inspect the obtained noise and detect anomalies. Data integrity attacks change noise patterns and thus are identified as the root cause of anomalies by DEEPNOISE. Evaluated on the SWaT testbed, DEEPNOISE achieves higher accuracy and recall compared with state-of-the-art model-based and deep learning-based methods. On average, when detecting direct attacks, the precision is 95.47%, the recall is 96.58%, and F1 is 95.98%. When detecting stealthy attacks, precision, recall, and F1 scores are between 96% and 99.5%.
  • Zhonghong Ou, Wenjun Chai, Lifei Wang, Ruru Zhang, Jiawen He, Meina Song, Lifei Yuan, Shengjuan Zhang, Yanhui Wang, Huan Li, Xin Jia, Rujian Huang
    2021, 18(9): 210-220.
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    Leveraging deep learning-based techniques to classify diseases has attracted extensive research interest in recent years. Nevertheless, most of the current studies only consider single-modal medical images, and the number of ophthalmic diseases that can be classified is relatively small. Moreover, imbalanced data distribution of different ophthalmic diseases is not taken into consideration, which limits the application of deep learning techniques in realistic clinical scenes. In this paper, we propose a Multi-modal Multi-disease Long-tailed Classification Network (M2LC-Net) in response to the challenges mentioned above. M2LC-Net leverages ResNet18-CBAM to extract features from fundus images and Optical Coherence Tomography (OCT) images, respectively, and conduct feature fusion to classify 11 common ophthalmic diseases. Moreover, Class Activation Mapping (CAM) is employed to visualize each mode to improve interpretability of M2LC-Net. We conduct comprehensive experiments on realistic dataset collected from a Grade III Level A ophthalmology hospital in China, including 34,396 images of 11 disease labels. Experimental results demonstrate effectiveness of our proposed model M2LC-Net. Compared with the state-of-the-art, various performance metrics have been improved significantly. Specifically, Cohen's kappa coefficient $\kappa$ has been improved by 3.21%, which is a remarkable improvement.
  • Ce Sun, Zesong Fei, Bin Li, Xinyi Wang, Nan Li, Lijie Hu
    2021, 18(9): 221-235.
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    Non-orthogonal multiple access (NOMA) is deemed to have a superior spectral efficiency and polar codes have became the channel coding scheme for control channel of enhanced mobile broadband (eMBB) in the fifth generation (5G) communication systems. In this paper, NOMA combined with polar codes is used to achieve secure transmission. Both degraded wiretap channel and non-degraded wiretap channel are considered, where an eavesdropper intercepts the communication between base station (BS) and users. For the degraded wiretap channel scenario, a secure polar encoding scheme is proposed in NOMA systems with power allocation to achieve the maximum secrecy capacity. With regard to the non-degraded wiretap channel, a polar encoding scheme with multiple-input-single-output (MISO) system is proposed, where artificial noise is generated at BS to confuse the eavesdropper's channel via transmit beamforming. The security and the secure rate are employed respectively in order to measure the secrecy performance. We prove that the proposed schemes for each scenario can achieve the secure rate and can transmit the signal securely and reliably. The simulation results show that the eavesdropper hardly decoding the secure signal when the legitimate receiver can decode the signal with very low block error rate (BLER).
  • Dinesh Kumar, Rajiv Kumar, Neeru Sharma
    2021, 18(9): 236-248.
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    This paper presents a halfway signaling exchange shared path protection (HSE-SPP) on the backup route for a fast connection recovery strategy. In the proposed HSE-SPP, a pre-assigned intermediate node on the backup route is chosen for signaling exchange. When connection fails, source and destination nodes simultaneously generate backup connection setup messages to the pre-assigned intermediate node on the reserved backup route. At the intermediate node, signaling process occurs, and acknowledgment is generated for data transmission to the respective end nodes. Consequently, connection recovery time by applying HSE-SPP becomes very low. Simulations are performed for network parameters and results are verified with existing strategies. The average recovery time (RT), bandwidth blocking probability (BBP), bandwidth provisioning ratio (BPR), and resource overbuild (RO) ratio of HSE-SPP for ARPANET is 13.54ms, 0.18, 3.02, 0.55, and for dedicated path protection (DPP) are 13.20ms, 0.56, 6.30, 3.75 and for shared path protection (SPP) 22.19ms, 0.22, 3.23, 0.70 respectively. Similarly, average RT, BBP, BPR and RO of HSE-SPP for COST239 are 8.33ms, 0.04, 1.64, 0.26, and for DPP 4.23, 0.47, 3.50, 2.04, and for SPP 11.81, 0.08, 1.66, 0.27 respectively. Hence, results of the proposed strategy are better in terms of RT, BBP, BPR, and RO ratio.
  • Yang Liang, Zhigang Hu, Xinyu Zhang, Hui Xiao
    2021, 18(9): 249-264.
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    With the number of connected devices increasing rapidly, the access latency issue increases drastically in the edge cloud environment. Massive low time-constrained and data-intensive mobile applications require efficient replication strategies to decrease retrieval time. However, the determination of replicas is not reasonable in many previous works, which incurs high response delay. To this end, a correlation-aware replica prefetching (CRP) strategy based on the file correlation principle is proposed, which can prefetch the files with high access probability. The key is to determine and obtain the implicit high-value files effectively, which has a significant impact on the performance of CRP. To achieve the goal of accelerating the acquisition of implicit high-value files, an access rule management method based on consistent hashing is proposed, and then the storage and query mechanisms for access rules based on adjacency list storage structure are further presented. The theoretical analysis and simulation results corroborate that CRP shortens average response time over 4.8%, improves average hit ratio over 4.2%, reduces transmitting data amount over 8.3%, and maintains replication frequency at a reasonable level when compared to other schemes.