A new cyclic prefix(CP)-based nonoverlapping FBMC-QAM(CP-NO-FBMC-QAM)system with two prototype filters is proposed in this paper,which satisfies complex orthogonality conditions and good frequency energy confinement a...A new cyclic prefix(CP)-based nonoverlapping FBMC-QAM(CP-NO-FBMC-QAM)system with two prototype filters is proposed in this paper,which satisfies complex orthogonality conditions and good frequency energy confinement at the same time.We analyze its inter-carrier interference/inter-symbol interference(ICI/ISI)over multipath channels.Owing to the additional CP,the ISI of received symbols over multipath channels is eliminated in the proposed system,and the resulting improvement in the signal-to-interference ratio(SIR)performance is evaluated by theoretical analysis.Moreover,for the ICI caused by multipath propagation in received symbols,we develop a method that eliminates the ICI by frequency-domain channel estimation and equalization before the receiver filtering process.The proposed CP-NO-FBMC-QAM system and ICI cancellation method(ICICM)are validated by comparisons of implementation complexity,power spectral density(PSD),bit error rate(BER)and channel estimation performance with conventional CP-based orthogonal frequency division multiplexing(CP-OFDM)and FBMC-QAM systems.展开更多
Border Gateway Protocol(BGP)is a standard inter-domain routing protocol for the Internet that conveys network layer reachability information and establishes routes to different destinations.The BGP protocol exhibits s...Border Gateway Protocol(BGP)is a standard inter-domain routing protocol for the Internet that conveys network layer reachability information and establishes routes to different destinations.The BGP protocol exhibits security design defects,such as an unconditional trust mechanism and the default acceptance of BGP route announcements from peers by BGP neighboring nodes,easily triggering prefix hijacking,path forgery,route leakage,and other BGP security threats.Meanwhile,the traditional BGP security mechanism,relying on a public key infrastructure,faces issues like a single point of failure and a single point of trust.The decentralization,anti-tampering,and traceability advantages of blockchain offer new solution ideas for constructing secure and trusted inter-domain routing mechanisms.In this paper,we summarize the characteristics of BGP protocol in detail,sort out the BGP security threats and their causes.Additionally,we analyze the shortcomings of the traditional BGP security mechanism and comprehensively evaluate existing blockchain-based solutions to address the above problems and validate the reliability and effectiveness of blockchain-based BGP security methods in mitigating BGP security threats.Finally,we discuss the challenges posed by BGP security problems and outline prospects for future research.展开更多
In this paper,we exhibit a free monoid containing all prefix codes in connection with the sets of i-th powers of primitive words for all i≥2.This extends two results given by Shyr and Tsai in 1998 at the same time.
Prefixation is a dynamic method of word formation in Bengali. Sometimes prefixes become derivational to create new words, which differ in part-of-speech and meaning from the words with which these are attached. Thus, ...Prefixation is a dynamic method of word formation in Bengali. Sometimes prefixes become derivational to create new words, which differ in part-of-speech and meaning from the words with which these are attached. Thus, prefixation acquires an identity of a morphodynamic process in the language through which new words take birth, while old words change their forms, functions, and meanings to increase lexical stock of Bengali. With reference to a large lexical database of prefixed words obtained from the Bengali corpus （Dash, 2009）, this paper tries to explore the nature and type of morphosemantic processes that occur at the time of prefixation to highlight the patterns of change in forms and meaning of prefixed words. Also, it aims at laying a theoretical foundation about the nature of lexical generativity of prefixes used in formation of words. The application relevance of this study may be attested in descriptive linguistics, applied linguistics, and language technology, since analysis of forms and functions of prefixes supplies necessary information for developing text materials for Bengali language teaching, compiling dictionaries, designing systems for machine learning, and developing databases for machine translation. Indirectly, it ventilates into the nature of complexities embedded in linguistic generativity of the Bengali speakers展开更多
It is not surprising that non-native speakers of English frequently make morphological errors when they are speaking or writing in English. But it is interesting to find out that some native English speakers sometimes...It is not surprising that non-native speakers of English frequently make morphological errors when they are speaking or writing in English. But it is interesting to find out that some native English speakers sometimes use words in an ungrammatical or inappropriate way. This article analyses the usage of the word"uncorrect"and tries to show the background of this term by searching online and consulting to the dictionaries and also to analyze the word formation and usage of this term.展开更多
To enhance the bandwidth efficiency of the guard interval （GI） assisted wireless communication system, an attractive scheme is proposed, which combines the functions of pilots and the GI together, so that the pilot ...To enhance the bandwidth efficiency of the guard interval （GI） assisted wireless communication system, an attractive scheme is proposed, which combines the functions of pilots and the GI together, so that the pilot resource used for estimating channel state is saved. Based on the proposed different known guard intervals （DKGI）, the time-domain channel estimation can be simply applied on the receiver side. After channel estimation, the receiver can employ the cyclic convolution restoring （CCR） function to reconstruct the cyclical convolution relationship between the signal and the channel, by which the receiver can also achieve good performance through the conventional 1-tap frequency domain equalization （FDE）.展开更多
Conventional OFDM transmission system uses a fixed-length Cyclic Prefix to counteract Inter-Symbol Inter- ferences (ISI) caused by channel delay spreading under wireless mobile environment. This may cause considerabl...Conventional OFDM transmission system uses a fixed-length Cyclic Prefix to counteract Inter-Symbol Inter- ferences (ISI) caused by channel delay spreading under wireless mobile environment. This may cause considerable per- formance deterioration when the CP length is less than the channel RMS delay spread, or may decrease the system power and spectrum efficiency when it is much larger. A novel Orthogonal Frequency Division Multiplexing (OFDM) transmission scheme is proposed in this paper to adapt the CP length to the variation of channel delay spread. AOFDM-VCPL utilizes the preamble or pilot sub-carriers of each OFDM packet to estimate the channel RMS delay spread; and then uses a criterion to calculate the CP length , which finally affects the OFDM transmitter. As illustrated in the simulation section, by deploying this scheme in a typical wireless environment, the system can transmit at data rate 11.5 Mb/s higher than conventional non-adaptive system while gaining a 0.65 dB power saving at the same BER performance.展开更多
There exists an inherent difficulty in the original algorithm for the construction of Dwarf, which prevents it from constructing true Dwarfs. We explained when and why it introduces suffix redundancies into the Dwarf ...There exists an inherent difficulty in the original algorithm for the construction of Dwarf, which prevents it from constructing true Dwarfs. We explained when and why it introduces suffix redundancies into the Dwarf structure. To solve this problem, we proposed a completely new algorithm called PID. It bottom-up computes partitions of a fact table, and inserts them into the Dwarf structure. If a partition is an MSV partition, coalesce its sub-Dwarf; otherwise create necessary nodes and cells. Our performance study showed that PID is efficient. For further condensing of Dwarf, we proposed Condensed Dwarf, a more com- pressed structure, combining the strength of Dwarf and Condensed Cube. By eliminating unnecessary stores of “ALL” cells from the Dwarf structure, Condensed Dwarf could effectively reduce the size of Dwarf, especially for Dwarfs of the real world, which was illustrated by our experiments. Its query processing is still simple and, only two minor modifications to PID are required for the construction of Condensed Dwarf.展开更多
Orthogonal Frequency Division Multiplexing (OFDM) systems suffer from performance deterioration when the length of Cyclic Prefix (CP) is shorter than the Channel Impulse Response (CIR). The fundamental reason of this ...Orthogonal Frequency Division Multiplexing (OFDM) systems suffer from performance deterioration when the length of Cyclic Prefix (CP) is shorter than the Channel Impulse Response (CIR). The fundamental reason of this impairment is the InterCarrier Interference (ICI) and Inter- Symbol Interference (ISI) introduced by the excessive multipath delay. Specifically, Multiple Input Multiple Output (MIMO) beamforming is helpful in cancelling such interference since it can spatially suppress some of the multipath. In this paper, we propose an ICI eliminating beamforming scheme employing a per-tone processing approach, thus with moderate computational complexity. The ISI is removed by using a simple decision feedback equalizer, while the optimal steering and combining vectors are then derived to maximize the Signal to Interference plus Noise Ratio (SINR). This method not only achieves the beamforming benefit, but also significantly alleviates the ICI. Simulation results show that the proposed algorithm can effectively reduce the system Symbol Error Rate (SER), per- mitting good performance for multipath delay profiles that would break conventional links.展开更多
With the increasing maritime activities,a great demand of wide-area maritime digital data services is needed.Therefore,Narrowband Internet of Things(NB-IoT)that can provide wide coverage has been expected as an applic...With the increasing maritime activities,a great demand of wide-area maritime digital data services is needed.Therefore,Narrowband Internet of Things(NB-IoT)that can provide wide coverage has been expected as an application for maritime communication networks(MCNS).In this paper,we aim to enhance the spectral efficiency in NB-IoT by reducing the cyclic prefix(CP)overhead in random access signal without causing interference.The key point of the proposed scheme is the symbols transmitted for multiple times repeatedly in NB-IoT.Specifically,all CP are removed and multi-path fading effect is eliminated by using a repeated symbol to cover the disturbed symbol to construct a circular convolution structure of the channel with the same effect as adding CP.In addition,a single-tap equalization is still appropriate.To validate the effectiveness of the proposed scheme,simulation results are carried out with respect to the bit error ratio(BER).展开更多
文摘A new cyclic prefix(CP)-based nonoverlapping FBMC-QAM(CP-NO-FBMC-QAM)system with two prototype filters is proposed in this paper,which satisfies complex orthogonality conditions and good frequency energy confinement at the same time.We analyze its inter-carrier interference/inter-symbol interference(ICI/ISI)over multipath channels.Owing to the additional CP,the ISI of received symbols over multipath channels is eliminated in the proposed system,and the resulting improvement in the signal-to-interference ratio(SIR)performance is evaluated by theoretical analysis.Moreover,for the ICI caused by multipath propagation in received symbols,we develop a method that eliminates the ICI by frequency-domain channel estimation and equalization before the receiver filtering process.The proposed CP-NO-FBMC-QAM system and ICI cancellation method(ICICM)are validated by comparisons of implementation complexity,power spectral density(PSD),bit error rate(BER)and channel estimation performance with conventional CP-based orthogonal frequency division multiplexing(CP-OFDM)and FBMC-QAM systems.
基金the National Natural Science Foundation of China,GrantNumbers(62272007,62001007)the Natural Science Foundation of Beijing,GrantNumbers(4234083,4212018)The authors also acknowledge the support from King Khalid University for funding this research through the Large Group Project under Grant Number RGP.2/373/45.
文摘Border Gateway Protocol(BGP)is a standard inter-domain routing protocol for the Internet that conveys network layer reachability information and establishes routes to different destinations.The BGP protocol exhibits security design defects,such as an unconditional trust mechanism and the default acceptance of BGP route announcements from peers by BGP neighboring nodes,easily triggering prefix hijacking,path forgery,route leakage,and other BGP security threats.Meanwhile,the traditional BGP security mechanism,relying on a public key infrastructure,faces issues like a single point of failure and a single point of trust.The decentralization,anti-tampering,and traceability advantages of blockchain offer new solution ideas for constructing secure and trusted inter-domain routing mechanisms.In this paper,we summarize the characteristics of BGP protocol in detail,sort out the BGP security threats and their causes.Additionally,we analyze the shortcomings of the traditional BGP security mechanism and comprehensively evaluate existing blockchain-based solutions to address the above problems and validate the reliability and effectiveness of blockchain-based BGP security methods in mitigating BGP security threats.Finally,we discuss the challenges posed by BGP security problems and outline prospects for future research.
基金Supported by the National Natural Science Foundation of China(11861071).
文摘In this paper,we exhibit a free monoid containing all prefix codes in connection with the sets of i-th powers of primitive words for all i≥2.This extends two results given by Shyr and Tsai in 1998 at the same time.
文摘Prefixation is a dynamic method of word formation in Bengali. Sometimes prefixes become derivational to create new words, which differ in part-of-speech and meaning from the words with which these are attached. Thus, prefixation acquires an identity of a morphodynamic process in the language through which new words take birth, while old words change their forms, functions, and meanings to increase lexical stock of Bengali. With reference to a large lexical database of prefixed words obtained from the Bengali corpus （Dash, 2009）, this paper tries to explore the nature and type of morphosemantic processes that occur at the time of prefixation to highlight the patterns of change in forms and meaning of prefixed words. Also, it aims at laying a theoretical foundation about the nature of lexical generativity of prefixes used in formation of words. The application relevance of this study may be attested in descriptive linguistics, applied linguistics, and language technology, since analysis of forms and functions of prefixes supplies necessary information for developing text materials for Bengali language teaching, compiling dictionaries, designing systems for machine learning, and developing databases for machine translation. Indirectly, it ventilates into the nature of complexities embedded in linguistic generativity of the Bengali speakers
文摘Key Facts Synonyms：Gonadal vein thrombosis.Definition：Rare complication usually associated with ascending postpartum ovarian vein thrombophlebitis.Incidence：1%-2%following cesarean section complicated by endometritis;less than 0.2% following vaginal delivery.
文摘It is not surprising that non-native speakers of English frequently make morphological errors when they are speaking or writing in English. But it is interesting to find out that some native English speakers sometimes use words in an ungrammatical or inappropriate way. This article analyses the usage of the word"uncorrect"and tries to show the background of this term by searching online and consulting to the dictionaries and also to analyze the word formation and usage of this term.
基金The National High Technology Research and Deve-lopment Program of China (863Program)(No.2002AA123031).
文摘To enhance the bandwidth efficiency of the guard interval （GI） assisted wireless communication system, an attractive scheme is proposed, which combines the functions of pilots and the GI together, so that the pilot resource used for estimating channel state is saved. Based on the proposed different known guard intervals （DKGI）, the time-domain channel estimation can be simply applied on the receiver side. After channel estimation, the receiver can employ the cyclic convolution restoring （CCR） function to reconstruct the cyclical convolution relationship between the signal and the channel, by which the receiver can also achieve good performance through the conventional 1-tap frequency domain equalization （FDE）.
基金Project supported by the National Natural Science Foundation ofChina (No. 60002003) and the Hi-Tech Research and Develop-ment Program (863) of China (No. 2002AA123044)
文摘Conventional OFDM transmission system uses a fixed-length Cyclic Prefix to counteract Inter-Symbol Inter- ferences (ISI) caused by channel delay spreading under wireless mobile environment. This may cause considerable per- formance deterioration when the CP length is less than the channel RMS delay spread, or may decrease the system power and spectrum efficiency when it is much larger. A novel Orthogonal Frequency Division Multiplexing (OFDM) transmission scheme is proposed in this paper to adapt the CP length to the variation of channel delay spread. AOFDM-VCPL utilizes the preamble or pilot sub-carriers of each OFDM packet to estimate the channel RMS delay spread; and then uses a criterion to calculate the CP length , which finally affects the OFDM transmitter. As illustrated in the simulation section, by deploying this scheme in a typical wireless environment, the system can transmit at data rate 11.5 Mb/s higher than conventional non-adaptive system while gaining a 0.65 dB power saving at the same BER performance.
基金Project (No. 20030487032) supported by the Specialized Research Fund for the Doctoral Program of Higher Education, China
文摘There exists an inherent difficulty in the original algorithm for the construction of Dwarf, which prevents it from constructing true Dwarfs. We explained when and why it introduces suffix redundancies into the Dwarf structure. To solve this problem, we proposed a completely new algorithm called PID. It bottom-up computes partitions of a fact table, and inserts them into the Dwarf structure. If a partition is an MSV partition, coalesce its sub-Dwarf; otherwise create necessary nodes and cells. Our performance study showed that PID is efficient. For further condensing of Dwarf, we proposed Condensed Dwarf, a more com- pressed structure, combining the strength of Dwarf and Condensed Cube. By eliminating unnecessary stores of “ALL” cells from the Dwarf structure, Condensed Dwarf could effectively reduce the size of Dwarf, especially for Dwarfs of the real world, which was illustrated by our experiments. Its query processing is still simple and, only two minor modifications to PID are required for the construction of Condensed Dwarf.
基金Supported by the National Science Fund for Distinguished Young Scholars (No. 60725105)the National Basic Re-search Program of China (2009CB320404)+5 种基金the Program for Changjiang Scholars and Innovative Research Team in Universitythe National High Technology Research and Development Program of China (2007AA01Z288)the 111 Project (B08038)the National Natural Science Founda-tion of China (No. 60902032, 60902033, and 60702057)the Key Project of Chinese Ministry of Education (107103) the Program for State Key Laboratory of Integrated Service Networks (ISN02080001)
文摘Orthogonal Frequency Division Multiplexing (OFDM) systems suffer from performance deterioration when the length of Cyclic Prefix (CP) is shorter than the Channel Impulse Response (CIR). The fundamental reason of this impairment is the InterCarrier Interference (ICI) and Inter- Symbol Interference (ISI) introduced by the excessive multipath delay. Specifically, Multiple Input Multiple Output (MIMO) beamforming is helpful in cancelling such interference since it can spatially suppress some of the multipath. In this paper, we propose an ICI eliminating beamforming scheme employing a per-tone processing approach, thus with moderate computational complexity. The ISI is removed by using a simple decision feedback equalizer, while the optimal steering and combining vectors are then derived to maximize the Signal to Interference plus Noise Ratio (SINR). This method not only achieves the beamforming benefit, but also significantly alleviates the ICI. Simulation results show that the proposed algorithm can effectively reduce the system Symbol Error Rate (SER), per- mitting good performance for multipath delay profiles that would break conventional links.
文摘With the increasing maritime activities,a great demand of wide-area maritime digital data services is needed.Therefore,Narrowband Internet of Things(NB-IoT)that can provide wide coverage has been expected as an application for maritime communication networks(MCNS).In this paper,we aim to enhance the spectral efficiency in NB-IoT by reducing the cyclic prefix(CP)overhead in random access signal without causing interference.The key point of the proposed scheme is the symbols transmitted for multiple times repeatedly in NB-IoT.Specifically,all CP are removed and multi-path fading effect is eliminated by using a repeated symbol to cover the disturbed symbol to construct a circular convolution structure of the channel with the same effect as adding CP.In addition,a single-tap equalization is still appropriate.To validate the effectiveness of the proposed scheme,simulation results are carried out with respect to the bit error ratio(BER).
