Table of Content

    20 December 2020 Volume 47 Issue 6
    Special Issue: Information Transmission and Access Technologies for B5G/6G
    Editorial:Introduction to the special issue on information transmission and access technologies for B5G/6G
    BAI Baoming,MA Xiao,CHEN Wen,ZHANG Zhaoyang
    Journal of Xidian University. 2020, 47(6):  1-4.  doi:10.19665/j.issn1001-2400.2020.06.001
    Abstract ( 81 )   HTML ( 21 )   PDF (737KB) ( 78 )   Save
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    Polar coded non-orthogonal multiple access to 6G wireless systems
    NIU Kai,XU Wenjun,ZHANG Ping
    Journal of Xidian University. 2020, 47(6):  5-12.  doi:10.19665/j.issn1001-2400.2020.06.002
    Abstract ( 100 )   HTML ( 9 )   PDF (1351KB) ( 29 )   Save
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    As the first type of channel codes which has achieved the channel capacity, polar codes are an important candidate for the 6G data transmission. A polar coded framework of the non-orthogonal multiple access (NOMA) to the 6G system is proposed. In this framework, the scheme for the polar coded coordinated NOMA is investigated to fulfill the requirement of high-capacity transmission of 6G systems. Furthermore, the scheme for the polar coded non-coordinated NOMA can achieve the ultra-high reliable access to the 6G internet scenario. All these schemes indicate that polar coded NOMA techniques can dramatically boost the performance of 6G wireless transmission and has a broad application prospect.

    Access strategy design based on one-coincidence sequence in random access
    TANG Xiaobo,LI Li,HAO Li,FAN Pingzhi
    Journal of Xidian University. 2020, 47(6):  13-20.  doi:10.19665/j.issn1001-2400.2020.06.003
    Abstract ( 52 )   HTML ( 4 )   PDF (815KB) ( 18 )   Save
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    In multi-stage preamble (MSPA) transmission based random access (RA), the base station may fail to combine every individually detected preamble to a legitimate MSPA selected by an active device. This phenomenon is called the preamble detection ambiguity of MSPA transmission based RA. In this paper, we propose a one-coincidence sequence aided MSPA construction method. The proposed method which effectively extends the RA resource pool and eliminates the MSPA detection ambiguity. Furthermore, a tag is further incorporated into our RA strategy to facilitate active MSPA detection. Simulation results show that compared with the traditional single-stage PA transmission based RA strategy, our tagged MSPA RA strategy achieves a better RA performancein terms of the probability of PA collision and access success probability.

    Additive Fourier transform encoding algorithm for binary quasi-cyclic codes
    LI Runzhou,HUANG Qin
    Journal of Xidian University. 2020, 47(6):  21-29.  doi:10.19665/j.issn1001-2400.2020.06.004
    Abstract ( 34 )   HTML ( 1 )   PDF (810KB) ( 12 )   Save
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    To improve the encoding efficiency of binary quasi-cyclic codes, this paper proposes a frequency domain encoding algorithm based on the additive Fourier transform. Based on the equivalence of multiplication of vectors and cyclic matrices and cyclic convolution, finite field Fourier transform is used to accelerate the cyclic convolution operation, thereby realizing fast encoding. The Lin-Chung-Han transform is selected as a tool with its convolution theorem explained. Based on the frequency domain encoding algorithm with the normal Fourier transform, it is proved that the Lin-Chung-Han transform can also be used in frequency domain encoding. To reduce the encoding complexity of binary quasi-cyclic codes, the conjugate constraint of finite field Fourier transform is used to propose the encoding algorithm for binary quasi-cyclic codes. The complexity of the given fast encoding algorithm is analyzed and compared with other algorithms. The algorithm proposed in this paper has a low complexity when the code length is long, and the transformation structure is symmetrical, which has a certain advantage in applications.

    Receiver design scheme in high speed train scenarios
    SHI Tao,HAN Xuefeng,CHEN Wen
    Journal of Xidian University. 2020, 47(6):  30-36.  doi:10.19665/j.issn1001-2400.2020.06.005
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    In order to better ensure the reliability of small user terminal communications in high-speed train scenarios, an anti-Doppler frequency offset receiver design scheme is proposed based on non-uniform array beamforming and no change to the existing system model. First, the channel model and signal model in the high-speed train scenario is established. According to the characteristics of the user equipment and the signal model, a non-uniform antenna array is designed to separate useful signals by beamforming, on the basis of which frequency offset processing, channel estimation and signal combination are performed. The channel estimation response which is windowed to smooth and reduce noise, and the combination method based on the array received signal power further improve the system performance. Simulation results show that the scheme is better than the traditional direct reception method in the high-speed train scenario and that it is an effective solution for the signal reception of small user equipment in high-speed train scenarios.

    Gaussian-approximated message passing algorithm for the SM-SCMA system
    PAN Zhipeng,LEI Jing,WEN Lei,TANG Chaojing
    Journal of Xidian University. 2020, 47(6):  37-44.  doi:10.19665/j.issn1001-2400.2020.06.006
    Abstract ( 32 )   HTML ( 1 )   PDF (1306KB) ( 10 )   Save
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    The SM-SCMA, an efficient combination of sparse code multiple access (SCMA) and spatial modulation (SM) techniques, is able to support high spectrum efficiency and massive user connections. Due to the high complexity of the traditional multiuser detection algorithm, in this paper, we propose a low complexity detection method, namely, Gaussian approximated message passing algorithm (GA-MPA). According to the central limit theorem, the GA-MPA approximates the sum of signals sent by the multiuser following the Gaussian distribution, and directly uses its mean and variance to calculate the message in the process of message passing, which avoids the exponential computation and effectively reduces the complexity. Theoretical analysis and simulation results show that the GA-MPA has a linear complexity and can achieve a BER performance similar to that of the traditional message passing algorithm at a certain number of receiving antennas.

    Algorithm for structured pilot sequence design and low complexity detection
    ZHOU Jiaxin,SHEN Bingsheng,ZHOU Zhengchun,FAN Pingzhi,LUO Zhe
    Journal of Xidian University. 2020, 47(6):  45-49.  doi:10.19665/j.issn1001-2400.2020.06.007
    Abstract ( 28 )   HTML ( 3 )   PDF (726KB) ( 8 )   Save
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    Massive random access is one of the three major application scenarios of 5G. In this scenario, pilot sequences supporting a large number of users need to be constructed, and low-complexity detection algorithms should be designed. In this paper, some deterministic low correlation sequence sets are used as the pilot sequence set. The low complexity detection algorithm is realized by using the cyclic structure of the pilot sequence set and the discretefast Fourier transform (FFT).Research shows that, compared with the traditional random pilot sequence, the pilot sequence proposed in this paper has the advantages of simple implementation and small storage space. Furthermore, the block fast Fourier transform can greatly reduce the matrix multiplication operation and accelerate the detection speed for active users. Simulation results imply that the deterministic pilot sequence set constructed in this paper performs better than the gaussian random sequence set of the same size.

    ZigZag-IRSA random access scheme in IoT-oriented satellite networks
    SU Jingrui,REN Guangliang,WANG Qiwei,XIN Jirong
    Journal of Xidian University. 2020, 47(6):  50-57.  doi:10.19665/j.issn1001-2400.2020.06.008
    Abstract ( 24 )   HTML ( 1 )   PDF (1792KB) ( 5 )   Save
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    The throughput performance of random access (RA) in internet of things (IoT)-oriented satellite networks deteriorates seriously under a high traffic load as collision loops radically increase. To further improve the throughput, a ZigZag decoding based segmented irregular slotted ALOHA (IRSA) RA protocol is proposed. In this protocol, we shorten the length of the packet by utilizing modulation and coding techniques and design segment-level based frame format; thus, the different packet mapping modes are formed in the same timeslot. At the receiver, after the packet-level successive interference cancellation, by considering replicas as retransmitted packets, collided segments of collision loops are cancelled by the segment-level ZigZag decoder and the whole packet can be recovered by combining the successfully decoded segments. The performance of the proposed scheme is analyzed through the density evolution analysis. Compared with traditional RA protocols, the proposed protocol optimized by degree distribution has significantly improved the packet loss rate and throughput, and especially the throughput is 270% better than that of the IRSA. The proposed protocol can effectively solve the collision problem under a high traffic load, so it can work effectively in the IoT-oriented satellite networks with massive IoT devices.

    Study on belief propagation list decoding of concatenated polar codes with high throughput
    ZHOU Shenyang,BAI Baoming,REN Zhaofeng,ZHU Min,LI Binghao,TANG Ruibo
    Journal of Xidian University. 2020, 47(6):  58-65.  doi:10.19665/j.issn1001-2400.2020.06.009
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    Aiming for the requirements of high throughput for future mobile communication, this paper studies the high throughput and high reliable Belief Propagation List (BPL) decoding algorithm for improving the error-correction performance of Polar codes. The Impact of different code construction methods for Polar codes on the performance of the BPL decoding algorithm, together with the decoding convergence, is first investigated. Then, the BPL algorithm is applied to the concatenated LDPC-Polar codes, where a majority-logic based criterion is proposed to replace the out-of-work minimum Euclidean distance path pruning criterion. This new method effectively improves the performance of parallel decoding algorithms for LDPC-Polar concatenated codes. Simulation results show that, for the Polar code of length N=1024 and code rate R=1/2, the proposed decoding algorithm has about 1~1.5 dB performance improvement at the block-error-rate of 10-3 compared with the conventional BP decoding of Polar and LDPC-Polar codes.

    Weighted sum codes-aided SCL decoding of polar codes
    ZHANG Meng,LI Zhuo,XING Lijuan
    Journal of Xidian University. 2020, 47(6):  66-71.  doi:10.19665/j.issn1001-2400.2020.06.010
    Abstract ( 28 )   HTML ( 0 )   PDF (666KB) ( 2 )   Save
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    To further reduce the latency of succession cancellation list (SCL) decoding algorithm for polar codes, a weighted sum codes-aided SCL decoding algorithm is proposed. A concatenated coding scheme is designed which uses weighted sum codes as outer codes and polar codes as inner codes. The check bits generated by weighted sum coding and all information bits are put into the polar encoder. The modified weighted sum codes-aided SCL decoder feeds the candidate sequences into the weighted sum detector and outputs the one which fulfills the detector with highest reliability. Weighted sum codes combine the error detection properties of cyclic redundancy check with efficient hardware implementation. Simulation results show that the proposed scheme provides almost the same performance as the widely-used CRC-aided successive cancellation list decoding and that it considerably reduces the check latency without performance loss.

    Method for designing CRC-Polar codes to improve minimum distances
    SONG Jiawei,ZHENG Huijuan,TONG Sheng
    Journal of Xidian University. 2020, 47(6):  72-77.  doi:10.19665/j.issn1001-2400.2020.06.011
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    In view of the excellent error correction performance of short concatenated CRC-Polar codes, the 5G standard has adopted concatenated CRC-Polar codes as the channel coding scheme for control channels in the eMBB scenario. This paper examines the optimal design of concatenated CRC-Polar codes, and aims to increase the minimum distance of concatenated CRC-Polar codes in order to improve their error correction performance at the high SNR region. To this end, this paper considers both the optimal design of the CRC code and the selection of information bit positions on the minimum distance behaviors of concatenated codes, and proposes a new design method for concatenated CRC-Polar codes. The proposed scheme can effectively reduce the number of codewords with a minimum Hamming weight, and even can increase the minimum distances of concatenated CRC-Polar codes for some code parameters. Simulation results verify the effectiveness of the proposed design method.

    Sliding window decoding of the spatially coupled LDPC code Over Rayleigh fading channels
    ZHANG Yamei,ZHOU Lin,CHEN Chen,CHEN Qiwang,HE Yucheng
    Journal of Xidian University. 2020, 47(6):  78-83.  doi:10.19665/j.issn1001-2400.2020.06.012
    Abstract ( 18 )   HTML ( 0 )   PDF (1141KB) ( 2 )   Save
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    A recent research hot spot, the sliding window decoding (SWD) of spatially coupled low density parity check (SC-LDPC) codes has the advantages of low decoding latency, low complexity, and small memory requirements. But at present, most of the current research work is focused on Gaussian channels. Over the Rayleigh fading channel, an improved approach to extending the size of the decoding window based on the channel state information (CSI) is proposed, and the CSI is obtained by using the received signal-to-noise ratio (SNR). During the decoding process, if the average received SNR of the current window is less than the preset threshold, the decoding window is extended and then the iteration is performed again. The above process is repeated until the average received SNR of the current window is larger than the preset threshold or the window size is extended to its maximum value, and finally decoding is performed based on the extended window. Simulation results show that the SWD of SC-LDPC codes has a better performance over Rayleigh fading channels, and the performance of the proposed algorithm is significantly better than that of the traditional SWD algorithm.

    Research on the reliability of LDPC convolutional codes in the underwater acoustic communication system
    CAI Zihao,MU Liwei,ZHAN Li,LIU Qiang
    Journal of Xidian University. 2020, 47(6):  84-90.  doi:10.19665/j.issn1001-2400.2020.06.013
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    In order to ensure the high reliability of signal transmission in the underwater acoustic channel, LDPC convolutional codes are used to study the improvement of the information reliability in the underwater acoustic channel in this paper. The gradient model combined with the multipath model is adopted to simulate the underwater acoustic channel, and the FBMC/OQAM underwater acoustic channel communication system is built according to the characteristics that FBMC can suppress inter symbol interference and OQAM can suppress adjacent carrier interference. The LDPC convolutional code is adopted as the channel encoding scheme for realizing the lossless transmission of multimedia audio and image signals in the underwater acoustic channel. The RC-LDPC convolutional code is also used to study the decoding performance of the FH underwater acoustic communication system. Simulation results show that LDPC convolutional codes have a good bit error rate (BER) performance in the underwater acoustic channel, achieve a low BER signal transmission, and can effectively overcome the multipath effect and improve channel utilization. Thus, the LDPC convolutional code can be selected as the channel coding scheme for underwater acoustic communication.

    Scheme for FBMC channel estimation with a variable amplitude of the auxiliary pilot
    ZHAO Qinghua,MA Tianming,WANG Xing
    Journal of Xidian University. 2020, 47(6):  91-98.  doi:10.19665/j.issn1001-2400.2020.06.014
    Abstract ( 18 )   HTML ( 1 )   PDF (1737KB) ( 5 )   Save
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    A Variable Amplitude Auxiliary Pilot (VAAP) channel estimation scheme for the FBMC (Filter Bank Multicarrier) is put forward, which adds the auxiliary items in the AP positions directly to the pilots and fills the known data into the AP positions to solve the problem of excessive power of the auxiliary items in the conventional AP method. Theoretical analysis and simulation results demonstrate that compared with the Code Auxiliary Pilot (CAP) method and Double Auxiliary Pilot (DAP) method, when applying a single AP, the presented scheme can achieve a higher spectrum efficiency and reduce the power of AP positions effectively with no influence of the BER (Bit Error Rate) and it is second only to the AP method in computational complexity. By adopting the dual tunable AP, our proposed scheme can further improve the performance of the estimation accuracy and BER.

    Method for node acceptance in broadband access networks
    QI Xiaoxin,ZHANG Bing,QIU Zhiliang
    Journal of Xidian University. 2020, 47(6):  99-105.  doi:10.19665/j.issn1001-2400.2020.06.015
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    In an HINOC (HIgh performance Network Over Coax) network, the node acceptance process takes a long time due to conflicts in the shared channel. To solve this problem, a dynamic method of node acceptance is proposed. The channel is divided into contention periods and training periods. Each contention period contains a variable number of uplink detection frame slots in which network nodes send acceptance requests. The node acceptance problem is formulated as a Markov decision process. The objective is to minimize the total time needed to complete the acceptance of all nodes. The optimal policy is obtained by the value iteration algorithm. According to the number of nodes remaining to be accepted in the current network, the number of uplink frame detection frame slots in each contention period and the number of slots that each node is allowed to select are determined. Simulation results show that, compared with the method with a fixed number of slots, the proposed method can significantly reduce the contention time for node acceptance and improve the channel utilization. The optimal policy can be calculated offline, which speeds up the node acceptance process with a lower online computing overhead.

    Receiver joint optimization algorithm for the coded transceiver spatial modulation
    WANG Leijun,CHEN Rongjun,ZHAO Huimin
    Journal of Xidian University. 2020, 47(6):  106-112.  doi:10.19665/j.issn1001-2400.2020.06.016
    Abstract ( 18 )   HTML ( 1 )   PDF (833KB) ( 6 )   Save
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    In order to make the trade-off between spectral efficiency and energy efficiency and the trade-off between bit error rate performance and computational complexity, a coded transceive spatial modulation system is designed. In addition, we propose a layered suboptimal joint optimization algorithm, which can reduce the complexity of both the detection and demapping algorithm. The candidate set of antennas and signals is used to reduce computational complexity with the parameters adjustable. We use the BMST channel coding scheme, which can be easily designed according to the spectral efficiency requirement and can predict the lower bound performance. The computational complexity is analyzed and the Monte Carlo simulation is performed, with the results showing that, at the bit error rate (BER) of 10-5, the candidate set L = 6, L' = 4, the system has about 0.5dB performance loss compared with the optimal algorithm. However, the computational complexity can be greatly reduced.

    Research on the slot length prediction algorithm for the helicopter rotor blade
    LI Shengfeng,WANG Zihao,CHEN Xiang,WANG Ling
    Journal of Xidian University. 2020, 47(6):  113-121.  doi:10.19665/j.issn1001-2400.2020.06.017
    Abstract ( 28 )   HTML ( 0 )   PDF (1783KB) ( 5 )   Save
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    Wideband satellite communication is one of the key components in the 6G space-ground integrated network, which provides high data rate channels for Helicopter broadband communications. However, in the process of helicopter satellite communication, the communication interruption caused by rotor occlusion seriously affects the system performance. In this paper, aiming at the complex rotor occlusion environment of the coaxial twin rotor helicopter, an algorithm based on the Kalman filter is proposed for predicting the duration of the helicopter satellite communication rotor blade gap. Based on the basic principle of the Kalman filter, this algorithm can predict the blade slot during burst transmission of the return link, and ensure effective signal transmission of the helicopter's airborne terminal under limited conditions. Simulation results show that the prediction algorithm presented in this paper is superior to the traditional algorithm in terms of prediction accuracy, and that it can also rapidly converge when the rotor speed changes, so as to realize accurate tracking and prediction for the change of the blade slot of the rotor blockage.

    Spectrum sharing management method for the small-area-blockchain based on district partition
    LI Jinze,WANG Zhonghao,LI Mengheng,QIN Tuanfa
    Journal of Xidian University. 2020, 47(6):  122-130.  doi:10.19665/j.issn1001-2400.2020.06.018
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    In view of the low capacity and vulnerability of the spectrum sharing system architecture in traditional RANs (Radio Access Networks), a method of the distributed spectrum sharing system based on the small area blockchain is proposed . To ensure the integrity and security of the user’s transaction data, the blockchain distributed ledger storage technology is used for storing the complete data of all nodes in the blockchain. The nodes are classified according to their functions, and the mobile end users act as light nodes which can reduce their energy consumption and cost. The spectrum resource providers are divided into different blockchains by the k-means clustering algorithm to reduce the delay caused by the consensus process. In this paper, the spectrum resource providers are used as consensus nodes, and the mobile end nodes are used as light nodes. Simulation results show that the method of the small area blockchain proposed in this paper increases the number of block confirmations, and the average time for all nodes to complete the confirmations in the system is 16 seconds, while the similar scheme studied in the related work shows that it would take 36 seconds to complete the minimum number of confirmations under the premise of ensuring the security of the system. The proposed method can both improve the security of the system and reduce the delay of the new block confirmation process.

    Multi-user computation offloading approach for mobile edge computing
    ZHANG Wenzhu,CAO Beibei,YU Jinghua
    Journal of Xidian University. 2020, 47(6):  131-138.  doi:10.19665/j.issn1001-2400.2020.06.019
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    Computation offloading technology in Mobile Edge Computing (MEC) offloads resource-intensive applications on mobile user devices to edge servers. It can solve the deficiencies of mobile devices in terms of computing power, storage capacity, and energy efficiency. Orienting to the LTE, a multi-user computation offloading approach for MEC environment is proposed, which can jointly optimize mobile users’ delay and MEC servers’ resource allocation balance. First, a mobile edge computing system model is designed, on the basis of which an objective function for jointly optimizing the average computation offloading delay and resource allocation balance is constructed. And then with the goal of minimizing the offloading delay of mobile users and allocating MEC server resources in a balanced manner, the optimal solution is solved, and the computation offloading is implemented reasonably. Simulation results show that the approach can effectively reduce the average offloading delay of multi-users, and balance the workload of MEC servers at the same time.

    Cloned piggybacking framework for distributed storage
    ZHANG Lu,SUN Rong,LIU Jingwei
    Journal of Xidian University. 2020, 47(6):  139-147.  doi:10.19665/j.issn1001-2400.2020.06.020
    Abstract ( 36 )   HTML ( 1 )   PDF (842KB) ( 7 )   Save
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    With the rapid development of 5G technology, distributed storage systems are popular with its features such as low cost, high availability, high throughput and massive storage capacity. Due to the frequent node failures, it is important to adopt data fault tolerance technology to ensure the reliability of data. In recent years, the piggybacking framework has received extensive attention for its excellent repair properties. In this paper, we propose a cloned piggybacking framework design to optimize average repair bandwidth and repair locality. Different from other piggybacking frameworks, the piggybacking and repairing methods are carried out on one set of nodes. Then the corresponding nodes in other groups are piggybacked in the same way. The trade-off between repair bandwidth and repair locality is established by the idea of “one parity node only piggybacks symbols from one substripe”. Compared with the existing piggybacking framework, the cloned piggybacking framework is simple in design and can further reduce the repair bandwidth of information nodes.

    Information and Communications Engineering & Cyberspace Security
    Residual attention mechanism for visual tracking
    CHENG Lei,WANG Yue,TIAN Chunna
    Journal of Xidian University. 2020, 47(6):  148-157.  doi:10.19665/j.issn1001-2400.2020.06.021
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    In recent years, with the development of training data and hardware, a large number of tracking algorithms based on deep learning have been proposed. Compared with the traditional tracking algorithm, tracking algorithms based on deep learning have a great developing potential. However, the traditional convolutional neural network structure cannot effectively perform its powerful feature learning and representation abilities in a tracking task. In this paper, an improved feature extraction network is proposed for video target tracking. Based on the traditional feature extraction network, an attention mechanism and a feature fusion strategy in the form of residual network are introduced. At the same time, a loss function based on the regional overlap rate is introduced in the training stage of the network model, which makes the algorithm produce a better positioning effect. Experimental results show that the improved algorithm can track the target accurately for a long time. Besides, the method has a generalization ability, which can be used for reference for other tracking algorithms based on deep learning.

    Simple proof the generalized Helberg codes being capable of correcting insertion/deletion errors
    MA Guochen,JIAO Xiaopeng,MU Jianjun,HAN Hui,GUO Junjun
    Journal of Xidian University. 2020, 47(6):  158-163.  doi:10.19665/j.issn1001-2400.2020.06.022
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    Since the existing proof method of the error correction capability for generalized Helberg codes is complicated, a simple proof that generalized Helberg codes are capable of correcting multiple insertion/deletion errors is proposed. By making a detailed analysis of the monotonicity of the inner product between the codeword and the weights for the generalized Helberg codes, the upper and lower bounds of the difference of the inner product between any two different codewords and weights are proved. By using the upper and lower bounds, the existing proof method for the error correction capability for generalized Helberg codes is simplified. The proposed simple proof is helpful in understanding generalized Helberg codes and making a further study.

    PHP code vulnerability mining technology based on theimproved ASTNN
    HU Jianwei,ZHAO Wei,CUI Yanpeng,CUI Junjie
    Journal of Xidian University. 2020, 47(6):  164-173.  doi:10.19665/j.issn1001-2400.2020.06.023
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    In order to solve the problems of low efficiency and high false positives of the traditional PHP vulnerability mining technology, a deep neural network mining method based on the ASTNN is proposed. At the same time, this method is also used to solve the problem of high false positives of the existing neural network model with the token sequence and software metrics as features. First, according to the characteristics of the PHP abstract syntax tree, the rules for dividing statement trees are defined. Second, according to the special structure of the PHP abstract syntax tree, improvements are made to the encoding layer of the traditional ASTNN deep neural network to better preserve the semantic information contained in the abstract syntax tree. Experimental results show that the PHP vulnerability mining method based on the improved ASTNN model has a higher accuracy and recall rate than the traditional method. The improved ASTNN deep neural network model is suitable for PHP vulnerability mining.