Rapid growth in mobile computing and other wireless multimedia services isinspiring many research and development activities on high-speed wireless communication systems.Main challenges in this area include the develo...Rapid growth in mobile computing and other wireless multimedia services isinspiring many research and development activities on high-speed wireless communication systems.Main challenges in this area include the development of efficient coding and modulation signalprocessing techniques for improving the quality and spectral efficiency of wireless systems. Therecently emerged space-time coding and signal processing techniques for wireless communicationsystems employing multiple transmit and receive antennas offer a powerful paradigm for meeting thesechallenges. This paper provides an overview on the recent development in space-time coding andsignal processing techniques for multiple-input multiple-output (MIMO) communication systems. Wefirst review the information theoretic results on the capacities of wireless systems employingmultiple transmit and receive antennas. We then describe two representative categories of space-timesystems, namely, the BLAST system and the space-time block coding system, both of which have beenproposed for next-generation high-speed wireless system. Signal processing techniques for channelestimation and decoding in space-time systems are also discussed. Finally, some other coding andsignal processing techniques for wireless systems employing multiple transmit and receive antennasthat are currently under intensive research are also briefly touched upon.展开更多
Nonaromatic amino acids are generally believed to be nonemissive, owing to their lack of apparently remarkable conjugation within individual molecules. Here we report the intrinsic visible emission of nonaromatic amin...Nonaromatic amino acids are generally believed to be nonemissive, owing to their lack of apparently remarkable conjugation within individual molecules. Here we report the intrinsic visible emission of nonaromatic amino acids and poly(amino acids) in concentrated solutions and solid powders. This unique and widespread luminescent characteristic can be well rationalized by the clustering-triggered emission(CTE) mechanism, namely the clustering of nonconventional chromophores(i.e. amino, carbonyl,and hydroxyl) and subsequent electron cloud overlap with simultaneous conformation rigidification. Such CTE mechanism is further supported by the single crystal structure analysis, from which 3 D through space electronic communications are uncovered.Besides prompt fluorescence, room temperature phosphorescence(RTP) is also detected from the solids. Moreover, persistent RTP is observed in the powders of exampled poly(amino acids) of ε-poly-L-lysine(.-PLL) after ceasing UV irradiation. These results not only illustrate the feasibility of employing the building blocks of nonaromatic amino acids in the exploration of new luminescent biomolecules, but also provide significant implications for the emissions of peptides and proteins at aggregated or crystalline states. Meanwhile, they may also shed lights on further understanding of autofluorescence from biological systems.展开更多
Orthogonal time frequency space(OTFS)modulation has been widely considered for high-mobility scenarios.Satellite-to-ground communications have recently received much attention as a typical high-mobility scenario and f...Orthogonal time frequency space(OTFS)modulation has been widely considered for high-mobility scenarios.Satellite-to-ground communications have recently received much attention as a typical high-mobility scenario and face great challenges due to the high Doppler shift.To enable reliable communications and high spectral efficiency in satellite mobile communications,we evaluate OTFS modulation performance for geostationary Earth orbit and low Earth orbit satellite-to-ground channels at sub-6-GHz and millimeter-wave bands in both lineof-sight and non-line-of-sight cases.The minimum mean squared error with successive detection(MMSE-SD)is used to improve the bit error rate performance.The adaptability of OTFS and the signal detection technologies in satellite-to-ground channels are analyzed.Simulation results confirm the feasibility of applying OTFS modulation to satellite-to-ground communications with high mobility.Because full diversity in the delay-Doppler domain can be explored,different terminal movement velocities do not have a significant impact on the performance of OTFS modulation,and OTFS modulation can achieve better performance compared with classical orthogonal frequency division multiplexing in satellite-to-ground channels.It is found that MMSE-SD can improve the performance of OTFS modulation compared with an MMSE equalizer.展开更多
Space/air communications have been envisioned as an essential part of the next-generation mobile communication networks for providing highquality global connectivity. However, the inherent broadcasting nature of wirel...Space/air communications have been envisioned as an essential part of the next-generation mobile communication networks for providing highquality global connectivity. However, the inherent broadcasting nature of wireless propagation environment and the broad coverage pose severe threats to the protection of private data. Emerging covert communications provides a promising solution to achieve robust communication security. Aiming at facilitating the practical implementation of covert communications in space/air networks, we present a tutorial overview of its potentials, scenarios, and key technologies. Specifically, first, the commonly used covertness constraint model, covert performance metrics, and potential application scenarios are briefly introduced. Then, several efficient methods that introduce uncertainty into the covert system are thoroughly summarized, followed by several critical enabling technologies, including joint resource allocation and deployment/trajectory design, multi-antenna and beamforming techniques, reconfigurable intelligent surface(RIS), and artificial intelligence algorithms. Finally, we highlight some open issues for future investigation.展开更多
One of the major challenges arising in internet of military things(IoMT)is accommodating massive connectivity while providing guaranteed quality of service(QoS)in terms of ultra-high reliability.In this regard,this pa...One of the major challenges arising in internet of military things(IoMT)is accommodating massive connectivity while providing guaranteed quality of service(QoS)in terms of ultra-high reliability.In this regard,this paper presents a class of code-domain nonorthogonal multiple accesses(NOMAs)for uplink ultra reliable networking of massive IoMT based on tactical datalink such as Link-16 and joint tactical information distribution system(JTIDS).In the considered scenario,a satellite equipped with Nr antennas servers K devices including vehicles,drones,ships,sensors,handset radios,etc.Nonorthogonal coded modulation,a special form of multiple input multiple output(MIMO)-NOMA is proposed.The discussion starts with evaluating the output signal to interference-plus-noise(SINR)of receiver filter,leading to the unveiling of a closed-form expression for overloading systems as the number of users is significantly larger than the number of devices admitted such that massive connectivity is rendered.The expression allows for the development of simple yet successful interference suppression based on power allocation and phase shaping techniques that maximizes the sum rate since it is equivalent to fixed-point programming as can be proved.The proposed design is exemplified by nonlinear modulation schemes such as minimum shift keying(MSK)and Gaussian MSK(GMSK),two pivotal modulation formats in IoMT standards such as Link-16 and JITDS.Numerical results show that near capacity performance is offered.Fortunately,the performance is obtained using simple forward error corrections(FECs)of higher coding rate than existing schemes do,while the transmit power is reduced by 6 dB.The proposed design finds wide applications not only in IoMT but also in deep space communications,where ultra reliability and massive connectivity is a keen concern.展开更多
Free Space Optical （FSO） networks, also known as optical wireless networks, have emerged as viable candidates for broadband wireless communications in the near future. The range of the potential application of FSO n...Free Space Optical （FSO） networks, also known as optical wireless networks, have emerged as viable candidates for broadband wireless communications in the near future. The range of the potential application of FSO networks is extensive, from home to satellite. However, FSO networks have not been popularized because of insufficient availability and reliability. Researchers have focused on the problems in the physical layer in order to exploit the properties of wireless optical channels. However, recent technological developments with successful results make it practical to explore the advantages of the high bandwidth. Some researchers have begun to focus on the problems of network and upper layers in FSO networks. In this survey, we classify prospective global FSO networks into three subnetworks and give an account of them. We also present state-of- the-art research and discuss what kinds of challenges exist.展开更多
Delay/Disruption-Tolerant Networking(DTN) originated from research on Interplanetary Internet and still today space applications are the most important application field and research stimulus. This paper investigates ...Delay/Disruption-Tolerant Networking(DTN) originated from research on Interplanetary Internet and still today space applications are the most important application field and research stimulus. This paper investigates DTN communications between the Earth and the far side of the Moon, by means of a lunar orbiter acting as relay. After an introductory part, the paper presents a comprehensive analysis of the DTN performance that can be achieved on the identified communication scenario. The focus is on the evaluation of the stateof-the-art ability of Interplanetary Overlay Network(ION), the NASA DTN implementation of Bundle Protocol(BP) and Contact Graph Routing(CGR), to meet the many challenges of the space communication scenario investigated(and more generally of a future interplaynetary Internet): intermittent links, network partitioning, scarce bandwidth, long delays, dynamic routing, handling of high priority and emergency traffic, interoperability issues. A study of security threats and Bundle Security Protocol(BSP) countermeasures complete the work.The many results provided, confirm the essential role of DTN in future space communications.展开更多
In polarization-encoded free-space quantum communications, a transmitter on a satellite and a receiver in a ground station each have a respective polarization zero direction, by which they encode and decode every pola...In polarization-encoded free-space quantum communications, a transmitter on a satellite and a receiver in a ground station each have a respective polarization zero direction, by which they encode and decode every polariza-tion quantum bit required for a quantum com-munication protocol. In order to complete the protocol, the ground-based receiver needs to track and compensate for the polarization zero direction of the satellite-based transmitter. Ex- pressions satisfied by amplitudes of the s-polarization component and the p-polarization component are derived based on a two-mirror model, and a condition satisfied by the reflec- tion coefficients of the two mirrors is given. A polarization tracking principle is analyzed for satellite-to-ground quanaun communications, and quantum key encoding and decoding prin- ciples based on polarization tracking are given. A half-wave-plate-based dynamic polariza- tion-basis compensation scheme is proposed in this paper, and this scheme is proved to be suitable for satellite-to-ground and intersatellite quantum communications.展开更多
A new differential space-time code, called differential space-time block-diagonal code （DSTBDC）, is proposed for multiple-input multiple-output （MIMO） wireless communication systems. By exploiting the block-diagon...A new differential space-time code, called differential space-time block-diagonal code （DSTBDC）, is proposed for multiple-input multiple-output （MIMO） wireless communication systems. By exploiting the block-diagonal construction of DSTBDC, we can design a variety of high-performance DSTBDC, especially for the cases of large numbers of transmit antennas and high date rates. In flat fading channels, DSTBDC outperforms traditional differential space-time codes if the data rate is higher than 1 bps/Hz, especially when the number of transmit antennas is large. In frequency-selective fading channels, multiple-input multiple-output orthogonal frequency-division multiplexing （MIMO-OFDM） systems using DSTBDC have the powerful ability to achieve very high diversity gain in space, time, and frequency simultaneously. Due to the special orthogonal construction, DSTBDC has a simple decoding algorithm. In addition, DSTBDC can significantly save the cost of radio frequency circuits.展开更多
According to the requirements of the high-sensitivity acquisition of Direct Sequence Spread Spectrum(DSSS) signals under ultrahigh dynamic environments in space communications, a three-dimensional joint search of the ...According to the requirements of the high-sensitivity acquisition of Direct Sequence Spread Spectrum(DSSS) signals under ultrahigh dynamic environments in space communications, a three-dimensional joint search of the phase of Pseudo-Noise-code(PN-code),Doppler frequency and its rate-of-change is presented to achieve high sensitivity in sensing high-frequency dynamics. By eliminating the correlation peak loss caused by ultrahigh Doppler frequency and its rate-of-change offset,the proposed method improves the acquisition sensitivity by increasing the non-coherent accumulation time. The validity of the algorithm is proved by theoretical analysis and simulation results. It is shown that signals with a carrier- to-noise ratio as low as 39 dBHz can be captured with high performance when the Doppler frequency is up to ±1 MHz and its rate-of-change is up to ±200 kHz/s.展开更多
文摘Rapid growth in mobile computing and other wireless multimedia services isinspiring many research and development activities on high-speed wireless communication systems.Main challenges in this area include the development of efficient coding and modulation signalprocessing techniques for improving the quality and spectral efficiency of wireless systems. Therecently emerged space-time coding and signal processing techniques for wireless communicationsystems employing multiple transmit and receive antennas offer a powerful paradigm for meeting thesechallenges. This paper provides an overview on the recent development in space-time coding andsignal processing techniques for multiple-input multiple-output (MIMO) communication systems. Wefirst review the information theoretic results on the capacities of wireless systems employingmultiple transmit and receive antennas. We then describe two representative categories of space-timesystems, namely, the BLAST system and the space-time block coding system, both of which have beenproposed for next-generation high-speed wireless system. Signal processing techniques for channelestimation and decoding in space-time systems are also discussed. Finally, some other coding andsignal processing techniques for wireless systems employing multiple transmit and receive antennasthat are currently under intensive research are also briefly touched upon.
基金supported by the National Natural Science Foundation of China(51473092)the Shanghai Rising-Star Program(15QA1402500)
文摘Nonaromatic amino acids are generally believed to be nonemissive, owing to their lack of apparently remarkable conjugation within individual molecules. Here we report the intrinsic visible emission of nonaromatic amino acids and poly(amino acids) in concentrated solutions and solid powders. This unique and widespread luminescent characteristic can be well rationalized by the clustering-triggered emission(CTE) mechanism, namely the clustering of nonconventional chromophores(i.e. amino, carbonyl,and hydroxyl) and subsequent electron cloud overlap with simultaneous conformation rigidification. Such CTE mechanism is further supported by the single crystal structure analysis, from which 3 D through space electronic communications are uncovered.Besides prompt fluorescence, room temperature phosphorescence(RTP) is also detected from the solids. Moreover, persistent RTP is observed in the powders of exampled poly(amino acids) of ε-poly-L-lysine(.-PLL) after ceasing UV irradiation. These results not only illustrate the feasibility of employing the building blocks of nonaromatic amino acids in the exploration of new luminescent biomolecules, but also provide significant implications for the emissions of peptides and proteins at aggregated or crystalline states. Meanwhile, they may also shed lights on further understanding of autofluorescence from biological systems.
基金Project supported by the National Key R&D Program of China(No.2020YFB1806903)the National Natural Science Foundation of China(Nos.61922012,62001519,52042201,U1834210,and 61961130391)+2 种基金the State Key Laboratory of Rail Traffic Control and Safety,China(Nos.RCS2020ZT008,RCS2019ZZ007,and RCS2020ZT010)the Teaching Reform Project,China(No.134811522)the Fundamental Research Funds for the Central Universities,China(Nos.2020JBZD005 and I20JB0200030)。
文摘Orthogonal time frequency space(OTFS)modulation has been widely considered for high-mobility scenarios.Satellite-to-ground communications have recently received much attention as a typical high-mobility scenario and face great challenges due to the high Doppler shift.To enable reliable communications and high spectral efficiency in satellite mobile communications,we evaluate OTFS modulation performance for geostationary Earth orbit and low Earth orbit satellite-to-ground channels at sub-6-GHz and millimeter-wave bands in both lineof-sight and non-line-of-sight cases.The minimum mean squared error with successive detection(MMSE-SD)is used to improve the bit error rate performance.The adaptability of OTFS and the signal detection technologies in satellite-to-ground channels are analyzed.Simulation results confirm the feasibility of applying OTFS modulation to satellite-to-ground communications with high mobility.Because full diversity in the delay-Doppler domain can be explored,different terminal movement velocities do not have a significant impact on the performance of OTFS modulation,and OTFS modulation can achieve better performance compared with classical orthogonal frequency division multiplexing in satellite-to-ground channels.It is found that MMSE-SD can improve the performance of OTFS modulation compared with an MMSE equalizer.
基金supported in part by the National Natural Science Foundation of China(NSFC)under grant numbers U22A2007 and 62171010the Beijing Natural Science Foundation under grant number L212003.
文摘Space/air communications have been envisioned as an essential part of the next-generation mobile communication networks for providing highquality global connectivity. However, the inherent broadcasting nature of wireless propagation environment and the broad coverage pose severe threats to the protection of private data. Emerging covert communications provides a promising solution to achieve robust communication security. Aiming at facilitating the practical implementation of covert communications in space/air networks, we present a tutorial overview of its potentials, scenarios, and key technologies. Specifically, first, the commonly used covertness constraint model, covert performance metrics, and potential application scenarios are briefly introduced. Then, several efficient methods that introduce uncertainty into the covert system are thoroughly summarized, followed by several critical enabling technologies, including joint resource allocation and deployment/trajectory design, multi-antenna and beamforming techniques, reconfigurable intelligent surface(RIS), and artificial intelligence algorithms. Finally, we highlight some open issues for future investigation.
基金supported in part by the National Natural Science Foundation of China(Grant Nos.61601346 and 62377039)the Natural Science Basic Research Plan in Shaanxi Province of China(Grant No.2018JQ6044)+2 种基金the Ministry of Industry and Information Technology of the People's Republic of China(Grant No.2023-276-1-1)the Fundamental Research Funds for the Central Universities,Northwestern Polytechnical University(Grant No.31020180QD089)the Aeronautical Science Foundation of China(Grant Nos.20200043053004 and 20200043053005)。
文摘One of the major challenges arising in internet of military things(IoMT)is accommodating massive connectivity while providing guaranteed quality of service(QoS)in terms of ultra-high reliability.In this regard,this paper presents a class of code-domain nonorthogonal multiple accesses(NOMAs)for uplink ultra reliable networking of massive IoMT based on tactical datalink such as Link-16 and joint tactical information distribution system(JTIDS).In the considered scenario,a satellite equipped with Nr antennas servers K devices including vehicles,drones,ships,sensors,handset radios,etc.Nonorthogonal coded modulation,a special form of multiple input multiple output(MIMO)-NOMA is proposed.The discussion starts with evaluating the output signal to interference-plus-noise(SINR)of receiver filter,leading to the unveiling of a closed-form expression for overloading systems as the number of users is significantly larger than the number of devices admitted such that massive connectivity is rendered.The expression allows for the development of simple yet successful interference suppression based on power allocation and phase shaping techniques that maximizes the sum rate since it is equivalent to fixed-point programming as can be proved.The proposed design is exemplified by nonlinear modulation schemes such as minimum shift keying(MSK)and Gaussian MSK(GMSK),two pivotal modulation formats in IoMT standards such as Link-16 and JITDS.Numerical results show that near capacity performance is offered.Fortunately,the performance is obtained using simple forward error corrections(FECs)of higher coding rate than existing schemes do,while the transmit power is reduced by 6 dB.The proposed design finds wide applications not only in IoMT but also in deep space communications,where ultra reliability and massive connectivity is a keen concern.
基金This work is supported in part by the US National Science Foundation under Grants CNS-1320664, and by the Wireless Engineering Research and Education Center （WEREC） at Auburn University, Aubur, AL, USA.
文摘Free Space Optical （FSO） networks, also known as optical wireless networks, have emerged as viable candidates for broadband wireless communications in the near future. The range of the potential application of FSO networks is extensive, from home to satellite. However, FSO networks have not been popularized because of insufficient availability and reliability. Researchers have focused on the problems in the physical layer in order to exploit the properties of wireless optical channels. However, recent technological developments with successful results make it practical to explore the advantages of the high bandwidth. Some researchers have begun to focus on the problems of network and upper layers in FSO networks. In this survey, we classify prospective global FSO networks into three subnetworks and give an account of them. We also present state-of- the-art research and discuss what kinds of challenges exist.
文摘Delay/Disruption-Tolerant Networking(DTN) originated from research on Interplanetary Internet and still today space applications are the most important application field and research stimulus. This paper investigates DTN communications between the Earth and the far side of the Moon, by means of a lunar orbiter acting as relay. After an introductory part, the paper presents a comprehensive analysis of the DTN performance that can be achieved on the identified communication scenario. The focus is on the evaluation of the stateof-the-art ability of Interplanetary Overlay Network(ION), the NASA DTN implementation of Bundle Protocol(BP) and Contact Graph Routing(CGR), to meet the many challenges of the space communication scenario investigated(and more generally of a future interplaynetary Internet): intermittent links, network partitioning, scarce bandwidth, long delays, dynamic routing, handling of high priority and emergency traffic, interoperability issues. A study of security threats and Bundle Security Protocol(BSP) countermeasures complete the work.The many results provided, confirm the essential role of DTN in future space communications.
基金supported by the Scientific Research Fund of Heilongjiang Provincial Education Department of China under Grant No.12511119
文摘In polarization-encoded free-space quantum communications, a transmitter on a satellite and a receiver in a ground station each have a respective polarization zero direction, by which they encode and decode every polariza-tion quantum bit required for a quantum com-munication protocol. In order to complete the protocol, the ground-based receiver needs to track and compensate for the polarization zero direction of the satellite-based transmitter. Ex- pressions satisfied by amplitudes of the s-polarization component and the p-polarization component are derived based on a two-mirror model, and a condition satisfied by the reflec- tion coefficients of the two mirrors is given. A polarization tracking principle is analyzed for satellite-to-ground quanaun communications, and quantum key encoding and decoding prin- ciples based on polarization tracking are given. A half-wave-plate-based dynamic polariza- tion-basis compensation scheme is proposed in this paper, and this scheme is proved to be suitable for satellite-to-ground and intersatellite quantum communications.
基金Supported by the National 863 Program of China (Grant No. 2003AA12331004)
文摘A new differential space-time code, called differential space-time block-diagonal code （DSTBDC）, is proposed for multiple-input multiple-output （MIMO） wireless communication systems. By exploiting the block-diagonal construction of DSTBDC, we can design a variety of high-performance DSTBDC, especially for the cases of large numbers of transmit antennas and high date rates. In flat fading channels, DSTBDC outperforms traditional differential space-time codes if the data rate is higher than 1 bps/Hz, especially when the number of transmit antennas is large. In frequency-selective fading channels, multiple-input multiple-output orthogonal frequency-division multiplexing （MIMO-OFDM） systems using DSTBDC have the powerful ability to achieve very high diversity gain in space, time, and frequency simultaneously. Due to the special orthogonal construction, DSTBDC has a simple decoding algorithm. In addition, DSTBDC can significantly save the cost of radio frequency circuits.
基金supported by the Youth Science Fund,National Natural Science Foundation of China under Grant No.61102130
文摘According to the requirements of the high-sensitivity acquisition of Direct Sequence Spread Spectrum(DSSS) signals under ultrahigh dynamic environments in space communications, a three-dimensional joint search of the phase of Pseudo-Noise-code(PN-code),Doppler frequency and its rate-of-change is presented to achieve high sensitivity in sensing high-frequency dynamics. By eliminating the correlation peak loss caused by ultrahigh Doppler frequency and its rate-of-change offset,the proposed method improves the acquisition sensitivity by increasing the non-coherent accumulation time. The validity of the algorithm is proved by theoretical analysis and simulation results. It is shown that signals with a carrier- to-noise ratio as low as 39 dBHz can be captured with high performance when the Doppler frequency is up to ±1 MHz and its rate-of-change is up to ±200 kHz/s.
