Tajikistan represents a core region of the biodiversity hotspot in Central Asian mountains and has exceptional vascular plant diversity.However,the species diversity of the country faces urgent conservation challenges...Tajikistan represents a core region of the biodiversity hotspot in Central Asian mountains and has exceptional vascular plant diversity.However,the species diversity of the country faces urgent conservation challenges.There has been a lack of a comprehensive and multidimensional assessment to inform strategic conservation planning.Therefore,this study integrated 4 key biodiversity indices including species richness(SR),phylogenetic diversity(PD),threatened species richness(TSR),and endemic species richness(ESR)to map species diversity distribution patterns,identify conservation gaps,and elucidate their effects of climatic factors.This study revealed that species diversity shows a clear trend of decreasing from the western region to the eastern region of Tajikistan.The central–western mountains(specifically the Gissar-Darvasian and Zeravshanian regions)emerge as irreplaceable biodiversity hotspots.However,we found a severe spatial mismatch between these priority areas and the existing protected areas(PAs).Protection coverage for all hotspots was alarmingly low,ranging from 31.00%to 38.00%.Consequently,a critical 64.80%of integrated priority areas fall outside of the current PAs,representing a major conservation gap.This study identified precipitation seasonality and isothermality as the principal drivers,collectively explaining over 50.00%of the diversity variation and suggesting high vulnerability to hydrological shifts.Furthermore,we detected significant geographic sampling bias in the public biodiversity databases,with the most critical hotspot being systematically under-sampled.This study provides a robust scientific basis for conservation action,highlighting the urgent need to strategically expand PAs in the under-protected southwestern region and to mitigate critical sampling gaps through targeted data digitization and field surveys.These measures are indispensable for securing Tajikistan’s unique biodiversity and achieving the Kunming-Montreal Global Biodiversity Framework Target 3(“30×30 Protection”).展开更多
Several space-time coding based transmit diversity techniques for wideband code division multiple access (WCDMA) systems with four transmitter antennas are investigated. Performances of the rake receivers are analyzed...Several space-time coding based transmit diversity techniques for wideband code division multiple access (WCDMA) systems with four transmitter antennas are investigated. Performances of the rake receivers are analyzed and compared with those of the multi-antenna receive diversity techniques. Theoretical analysis shows that the multi-antenna transmit diversity techniques provide considerable performance gain at the mobile receiver in the wireless channel with less inherent multipath diversity, especially the G4 coding based scheme. Compared with the multi-antenna receive diversity techniques with the same diversity order, the transmit diversity techniques introduce much more multi-access plus multipath interference and require measures of interference suppression in the multi-user environments.展开更多
Space-time spreading (STS) and orthogonal transmit diversity (OTD) are towtransmit diversity schemes proposed by cdma2000 standard. In this paper, performance comparisonanalysis of the two transmits diversity schemes ...Space-time spreading (STS) and orthogonal transmit diversity (OTD) are towtransmit diversity schemes proposed by cdma2000 standard. In this paper, performance comparisonanalysis of the two transmits diversity schemes in multipath channel under multiuser situation arecarried out. Link level simulation in forward link cdma2000 is performed in IMT-2000 channel.Performance analysis and simulation results show that the performance improvement provided STS overOTD decreases as the increase of propagation path number and decrease of the user number.展开更多
Space time coding can provide high data rate and performance gain for wireless communication system. Performance comparison of space time trellis codes and space time transmit diversity is carried out under the sam...Space time coding can provide high data rate and performance gain for wireless communication system. Performance comparison of space time trellis codes and space time transmit diversity is carried out under the same bandwidth efficiency in this paper. We also propose some optimum low rate space time trellis codes in quasi static Rayleigh fading chan￣nel. Performance analysis and simulation show that the low rate space time trellis codes outperform space time transmit diversity at the same bandwidth efficiency, and are more suitable for the power limited wireless communication system which has no strict requirement on bandwidth efficiency.展开更多
Many common multimedia signal processing,including cropping,filtering,and perceptual coding,make watermark signal fading-like modification.A scheme that applies transmit diversity technique to improve robustness of di...Many common multimedia signal processing,including cropping,filtering,and perceptual coding,make watermark signal fading-like modification.A scheme that applies transmit diversity technique to improve robustness of digital watermarking is presented.First,the scheme decomposes the original image using wavelet pyramid algorithm and chooses the middle-frequency band for transmission channel that the watermark will be embedded into.Then the watermark is pseudo-randomly permuted.The scheme makes use of space-time coding and differential detection technique to embed and extract watermark.The extracting process has access to neither the original image nor channel state information.Experimental results demonstrate that the scheme improves the performance of robust watermarking.展开更多
The paper investigates closed-loop transmit diversity （CLTD） systems with antenna selection technique. The expected received signal-noise-ratio （RxSNR） of the proposed systems is analyzed and compared with CLTD sy...The paper investigates closed-loop transmit diversity （CLTD） systems with antenna selection technique. The expected received signal-noise-ratio （RxSNR） of the proposed systems is analyzed and compared with CLTD systems. An algorithm is proposed for determining the number of increased transmit antennas in terms of a reduced RF chains without performance degradation. Since a feedback channel is bandwidth-limited, we present a method of quantizing transmit-weight vectors. Simulation results demonstrate advantage of the proposed systems with full and quantized feedback information. Quantized feedback has less effect on the proposed systems than CLTD systems.展开更多
This paper deals with channel estimation for orthogonal frequency-division multiplexing (OFDM) systems with transmit diversity. Space time coded OFDM systems, which can provide transmit diversity, require perfect chan...This paper deals with channel estimation for orthogonal frequency-division multiplexing (OFDM) systems with transmit diversity. Space time coded OFDM systems, which can provide transmit diversity, require perfect channel estimation to improve communication quality. In actual OFDM systems, training sequences are usually used for channel estimation. The authors propose a training based channel estimation strategy suitable for space time coded OFDM systems. This novel strategy provides enhanced performance, high spectrum efficiency and relatively low computation complexity.展开更多
Transmit diversity has been recently proposed to reduce the effects of fading channels in various wireless applications. Orthogonal transmit diersity (OTD) is one of the standardized techniques in 3G systems. In this ...Transmit diversity has been recently proposed to reduce the effects of fading channels in various wireless applications. Orthogonal transmit diersity (OTD) is one of the standardized techniques in 3G systems. In this paper, we apply orthogonal transmit diversity technique to multicarrier CDMA systems. Andlysis and simulation results show that performance benefits can be achieved compared with conventioal MC-CDMA systems in multipath fading channels.展开更多
This paper investigates the transmission scheme of the orthogonal time frequency space(OTFS)system with multiple antennas.Previous works have studied the multi-antenna transmitter diversity scheme with the ideal pulse...This paper investigates the transmission scheme of the orthogonal time frequency space(OTFS)system with multiple antennas.Previous works have studied the multi-antenna transmitter diversity scheme with the ideal pulse shaping in OTFS systems assuming the wireless channels of two consecutive frames duration are invariant.However,the ideal pulse shaping can not be realized in practice and the channel varies rapidly in two consecutive frames in the high-speed mobility scenarios.To this end,we redesign the multi-antenna transmitter diversity scheme to ensure its practicability in the rectangular-pulsebased OTFS systems.At first,the information symbols of each antenna are divided into two half frames along the Doppler domain.Then,the guard symbols are carefully arranged to eliminate the interference between two half frames,and to ensure the equivalent channels of two half frames being identical.By considering the positions of the guard symbols,the transmission codeword is designed and a low complexity linear detection is proposed.Finally,simulation results validate that the bit error rate performance of the proposed scheme has the superiority over the existing works.展开更多
In this paper, a time-switched space-time （TSST） coded orthogonal frequency division nmltiplexing （OFDM） scheme against the time-varying channels is proposed. In the TSST-OFDM scheme, it is equipped with four tran...In this paper, a time-switched space-time （TSST） coded orthogonal frequency division nmltiplexing （OFDM） scheme against the time-varying channels is proposed. In the TSST-OFDM scheme, it is equipped with four transmit antennas, but only double of them are used for coding in every time slot. It is shown that the signal to inter-antenna interference ratio is a function of Doppler frequency in time-varying channels for a given space-time code. The analyses and simulations results validate that the proposed scheme not only gets time- switched diversity and lower decoding complexity, but also suffers less time-varying impairments. Hence, it ex- hibits better performance than quasi-orthogonal space-time coded scheme.展开更多
In this paper, the closed loop transmit diversity technology for the Wideband Code Division Multiple Access(WCDMA) systems is investigated in a multipath Rayleigh fading channel. The RAKE receiver model and the weighi...In this paper, the closed loop transmit diversity technology for the Wideband Code Division Multiple Access(WCDMA) systems is investigated in a multipath Rayleigh fading channel. The RAKE receiver model and the weighing vector algorithm are presented. The performance is theoretically analyzed in terms of the average maximal Signal-to-Noise Ratio(SNR) gain available over the Space-Time block coding based Transmit Diversity(STTD) technology. Theoretic analysis and simulation results show that the closed loop transmit diversity can provide a 3dB performance gain over the open loop scheme in a single path fading channel, while the performance gain decreases dramatically with the increasing inherent multipath diversity of the wireless channel.展开更多
In this paper, we introduce a novel merger of antenna arrays with scanning beam patterns, and Orthogonal Frequency Division Multiplexing (OFDM) systems. Controlled time varying phase shifts are applied to the antenna ...In this paper, we introduce a novel merger of antenna arrays with scanning beam patterns, and Orthogonal Frequency Division Multiplexing (OFDM) systems. Controlled time varying phase shifts are applied to the antenna array elements mounted at the base station with beam patterns directed toward the desired user. This creates a small beam pattern movement called Beam Pattern Scanning (BPS). In rich scattering environments BPS creates a time varying environment leading to time diversity exploitable at the receiver enhances its probability-of-error performance. Here, we apply OFDM signals to BPS antenna arrays, and we achieve: (1) directionality, which supports Space Division Multiple Access (SDMA);and (2) a time diversity gain, which leads to high performance. We discuss the structure of the base station antenna array and the OFDM receiver that exploits time diversity. We also introduce the merger of BPS and multi-carrier OFDM (MC-OFDM) systems. In MC-OFDM each bit is transmitted over all sub-carriers after serial to parallel conversion. BPS/ MC-OFDM receiver exploits both time diversity inherent in BPS, and frequency diversity inherent in MC-OFDM transmission technique. Simulation results show high Probability-of-error performance is achie- vable via BPS/OFDM and BPS/MC-OFDM schemes comparing to the traditional OFDM and MC-OFDM, respectively. Simulations also reveal that MC-OFDM system as well as its merger with BPS is capable of mitigating large Peak-to-Average Ratio (PAPR) problem in traditional OFDM system. In addition, performance simulations with coded OFDM (COFDM) and coded MC-OFDM (MC-COFDM) and their merger with BPS are studied.展开更多
The performance analysis, using outage capacity for a forward link cellular communications system is presented. The effects of correlated fading, the distribution of angle of arrivals, and the array configurations are...The performance analysis, using outage capacity for a forward link cellular communications system is presented. The effects of correlated fading, the distribution of angle of arrivals, and the array configurations are considered. The objective is to examine the effect of angle of arrival (AOA) energy distributions on two systems (transmit diversity and beamforming) with angle spread. We do so by comparing the performance of transmit diversity with a system that uses beamforming to point a relatively narrow beam at the mobile station. Analytical results show that the transmit diversity system using uniform linear arrays (ULA) and uniform circular arrays (UCA) with truncated Laplacian AOA, performs better even at smaller angle spreads as compared to other energy distributions. The ULA geometry is a preferable configuration for transmit diversity system as compared to UCA.展开更多
The next generation of High Throughput Satellite(HTS)will exploit Q/V band for the feeder link and Ka band for the user link.The exploitation of multiple gateways(GWs)is a transmit diversity measure to compensate seve...The next generation of High Throughput Satellite(HTS)will exploit Q/V band for the feeder link and Ka band for the user link.The exploitation of multiple gateways(GWs)is a transmit diversity measure to compensate severe rain attenuation of Q/V band feeder links.This paper introduces a new smart gateway diversity combination scheme that combinates N-active(K=2)and N+1 diversity method in detail from the working principle,gateway switching strategy,evaluation of system availability and implementation complexity.In addition,a feeder link outage event prediction algorithm featuring combination scheme is given detailly based on modified time-adaptive linear regression.Compared with the existing N+P scheme,the proposed scheme can provide higher system availability and more stable user’s experience under the condition of properly increasing the complexity of payload design.Compared with Nactive scheme that has been reported,it is much easier to implement in engineering and more cost-effective.As a result,the combination scheme is a realistic solution based on a trade-off between performance improvement and implementation complexity.展开更多
This study primarily aimed to investigate the prevalence of human papillomavirus(HPV)and other common pathogens of sexually transmitted infections(STIs)in spermatozoa of infertile men and their effects on semen parame...This study primarily aimed to investigate the prevalence of human papillomavirus(HPV)and other common pathogens of sexually transmitted infections(STIs)in spermatozoa of infertile men and their effects on semen parameters.These pathogens included Ureaplasma urealyticum,Ureaplasma parvum,Chlamydia trachomatis,Mycoplasma genitalium,herpes simplex virus 2,Neisseria gonorrhoeae,Enterococcus faecalis,Streptococcus agalactiae,Pseudomonas aeruginosa,and Staphylococcus aureus.A total of 1951 men of infertile couples were recruited between 23 March 2023,and 17 May 2023,at the Department of Reproductive Medicine of The First People’s Hospital of Yunnan Province(Kunming,China).Multiplex polymerase chain reaction and capillary electrophoresis were used for HPV genotyping.Polymerase chain reaction and electrophoresis were also used to detect the presence of other STIs.The overall prevalence of HPV infection was 12.4%.The top five prevalent HPV subtypes were types 56,52,43,16,and 53 among those tested positive for HPV.Other common infections with high prevalence rates were Ureaplasma urealyticum(28.3%),Ureaplasma parvum(20.4%),and Enterococcus faecalis(9.5%).The prevalence rates of HPV coinfection with Ureaplasma urealyticum,Ureaplasma parvum,Chlamydia trachomatis,Mycoplasma genitalium,herpes simplex virus 2,Neisseria gonorrhoeae,Enterococcus faecalis,Streptococcus agalactiae,and Staphylococcus aureus were 24.8%,25.4%,10.6%,6.4%,2.4%,7.9%,5.9%,0.9%,and 1.3%,respectively.The semen volume and total sperm count were greatly decreased by HPV infection alone.Coinfection with HPV and Ureaplasma urealyticum significantly reduced sperm motility and viability.Our study shows that coinfection with STIs is highly prevalent in the semen of infertile men and that coinfection with pathogens can seriously affect semen parameters,emphasizing the necessity of semen screening for STIs.展开更多
The relation between conflict and governance has been dominated by type of government rather than by system of government.With increasing conflict in countries with ethnic and religious diversity,the debate has gradua...The relation between conflict and governance has been dominated by type of government rather than by system of government.With increasing conflict in countries with ethnic and religious diversity,the debate has gradually shifted to understand better the link between conflict and system of government.There is a growing evidence that suggests federal system performs better than unitary system in managing diversity and reducing conflict.Decentralization is even seen to be more effective than federal system not only in managing diversity and reducing conflict but also in delivering public goods.This article provides an account of evolution of system of government in South Sudan.It finds a clear association of centralized unitary system with violent conflict and a relative peace during period of decentralized government or federal system.A decentralized federal system may be appropriate for South Sudan in managing diversity and mitigating conflict.Despite the popular demand by their citizens for a federal system to manage diversity and reduce violent conflict,the ruling elites in the post-independent South Sudan adopted instead an autocratic centralized unitary system that contributed among other factors to the persistent violent conflicts,erosion of social cohesion,and rising mistrust between state and citizens and between and among the communities of South Sudan.展开更多
Paeonia suffruticosa Andr.is an endemic shrub flower in China with 2n=10.This study used 228 cultivars from four populations,i.e.,Jiangnan,Japan,Northwest,and Zhongyuan,as materials to explore the genetic diversity le...Paeonia suffruticosa Andr.is an endemic shrub flower in China with 2n=10.This study used 228 cultivars from four populations,i.e.,Jiangnan,Japan,Northwest,and Zhongyuan,as materials to explore the genetic diversity levels among different populations of tree peony varieties.The results showed that 34 bands were amplified using five pairs of cp SSR primers,with an average of 6.8 bands per primer pair.The average number of different alleles(N_(a)),effective alleles(N_(e)),Shannon's information index(I),diversity(H),and polymorphic information content(PIC)were 3.600,2.053,0.708,0.433,and 0.388,respectively.The PIC value was between 0.250 and 0.500,indicating a moderate level of polymorphism for the five cp SSR primer pairs.The genetic diversity levels of peony cultivars varied among different populations,with the Northwest population showing relatively lower levels(I=0.590,H=0.289,and PIC=0.263).A total of 52 haplotypes were identified in the four examined populations,and the number of haplotypes per population ranged from 11 to 22.Forty-four private haplotypes were detected across populations,and the Northwest population exhibiting the highest count of private haplotypes with 17.The mean number of effective number of haplotypes(N_(eh)),haplotypic richness(R_(h)),and diversity(H)were 8.351,6.824,and 0.893,respectively.Analysis of molecular variance indicated that genetic variation within tree peony germplasm was greater than that between germplasm resources,and the main variation was found within individuals of peony germplasm.Cluster analysis,principal coordinate analysis,and genetic structure analysis classified tree peonies from different origins into two groups,indicating a certain degree of genetic differentiation among these four tree peony cultivation groups.This study provides a theoretical basis for the exploration,utilization,and conservation of peony germplasm resources,as well as for research on the breeding of excellent varieties.展开更多
Soil microbial communities are key factors in maintaining ecosystem multifunctionality(EMF).However,the distribution patterns of bacterial diversity and how the different bacterial taxa and their diversity dimensions ...Soil microbial communities are key factors in maintaining ecosystem multifunctionality(EMF).However,the distribution patterns of bacterial diversity and how the different bacterial taxa and their diversity dimensions affect EMF remain largely unknown.Here,we investigated variation in three measures of diversity(alpha diversity,community composition and network complexity)among rare,intermediate,and abundant taxa across a latitudinal gradient spanning five forest plots in Yunnan Province,China and examined their contributions on EMF.We aimed to characterize the diversity distributions of bacterial groups across latitudes and to assess the differences in the mechanisms underlying their contributions to EMF.We found that multifaceted diversity(i.e.,diversity assessed by the three different metrics)of rare,intermediate,and abundant bacteria generally decreased with increasing latitude.More importantly,we found that rare bacterial taxa tended to be more diverse,but they contributed less to EMF than intermediate or abundant bacteria.Among the three dimensions of diversity we assessed,only community composition significantly affected EMF across all locations,while alpha diversity had a negative effect,and network complexity showed no significant impact.Our study further emphasizes the importance of intermediate and abundant bacterial taxa as well as community composition to EMF and provides a theoretical basis for investigating the mechanisms by which belowground microorganisms drive EMF along a latitudinal gradient.展开更多
The Qinghai-Tibet Plateau(QTP)has three main grassland types:alpine meadow,alpine steppe,and alpine desert steppe.In this study,we asked how plant productivity and species diversity vary with altitude,longitude and la...The Qinghai-Tibet Plateau(QTP)has three main grassland types:alpine meadow,alpine steppe,and alpine desert steppe.In this study,we asked how plant productivity and species diversity vary with altitude,longitude and latitude in alpine grasslands of the QTP.We then identified the environmental factors that drive these observed patterns of plant productivity and species diversity.We found that although plant productivity and species diversity varied greatly across large-scale longitudinal and latitudinal gradients,these changes were strongest across the longitudinal gradient.This finding indicates that moisture rather than temperature has the greatest impact on plant productivity and species diversity of the alpine grasslands in the QTP.We also found that besides soil and climate factors,partial pressure of carbon dioxide(pCO_(2))also has significant effects on plant productivity,and barometric pressure and partial pressure of oxygen(pO_(2))also have significant effects on species diversity.Furthermore,the relationship between the biomass of grassland-dominant species and species diversity was affected by the spatial scale at which these factors were studied.Our study provides new insights into the interconnections between plant productivity and species diversity and the major factors that influence alpine grasslands.It also provides a scientific basis for the maintenance of plant diversity and ecosystem functions in hypoxic(low-oxygen)regions.展开更多
Preserving genetic diversity is crucial for the long-term survival of wild plant species,yet many remain at risk of genetic erosion due to small population sizes and habitat fragmentation.Here,we present a comparative...Preserving genetic diversity is crucial for the long-term survival of wild plant species,yet many remain at risk of genetic erosion due to small population sizes and habitat fragmentation.Here,we present a comparative genomic study of the critically endangered Oreocharis esquirolii(Gesneriaceae)and its widespread congener O.maximowiczii.We assembled and annotated chromosome-level reference genomes for both species and generated whole-genome resequencing data from 28 O.esquirolii and 79 O.maximowiczii individuals.Our analyses reveal substantially lower genetic diversity and higher inbreeding in O.esquirolii,despite its overall reduced mutational burden.Notably,O.esquirolii exhibits an elevated proportion of strongly deleterious mutations relative to O.maximowiczii,suggesting that limited opportunities for purging have allowed these variants to accumulate.These contrasting genomic profileslikely reflectdivergent demographic histories,with O.esquirolii having experienced severe bottlenecks and protracted population decline.Collectively,our findingshighlight the critically endangered status of O.esquirolii,characterized by diminished genetic diversity,pronounced inbreeding,and reduced ability to eliminate deleterious alleles.This study provides valuable genomic resources for the Gesneriaceae family and underscores the urgent need for targeted conservation measures,including habitat protection and ex situ preservation efforts,to mitigate the extinction risk facing O.esquirolii and potentially other threatened congeners.展开更多
基金the Chinese Academy of Sciences Research Center for Ecology and Environment of Central Asia(RCEECA),the construction and joint research for the China-Tajikistan“Belt and Road”Joint Laboratory on Biodiversity Conservation and Sustainable Use(2024YFE0214200)the Shanghai Cooperation Organization Partnership and International Technology Cooperation Plan of Science and Technology Projects(2023E01018,2025E01056)the Chinese Academy of Sciences President’s International Fellowship Initiative(PIFI)(2024VBC0006).
文摘Tajikistan represents a core region of the biodiversity hotspot in Central Asian mountains and has exceptional vascular plant diversity.However,the species diversity of the country faces urgent conservation challenges.There has been a lack of a comprehensive and multidimensional assessment to inform strategic conservation planning.Therefore,this study integrated 4 key biodiversity indices including species richness(SR),phylogenetic diversity(PD),threatened species richness(TSR),and endemic species richness(ESR)to map species diversity distribution patterns,identify conservation gaps,and elucidate their effects of climatic factors.This study revealed that species diversity shows a clear trend of decreasing from the western region to the eastern region of Tajikistan.The central–western mountains(specifically the Gissar-Darvasian and Zeravshanian regions)emerge as irreplaceable biodiversity hotspots.However,we found a severe spatial mismatch between these priority areas and the existing protected areas(PAs).Protection coverage for all hotspots was alarmingly low,ranging from 31.00%to 38.00%.Consequently,a critical 64.80%of integrated priority areas fall outside of the current PAs,representing a major conservation gap.This study identified precipitation seasonality and isothermality as the principal drivers,collectively explaining over 50.00%of the diversity variation and suggesting high vulnerability to hydrological shifts.Furthermore,we detected significant geographic sampling bias in the public biodiversity databases,with the most critical hotspot being systematically under-sampled.This study provides a robust scientific basis for conservation action,highlighting the urgent need to strategically expand PAs in the under-protected southwestern region and to mitigate critical sampling gaps through targeted data digitization and field surveys.These measures are indispensable for securing Tajikistan’s unique biodiversity and achieving the Kunming-Montreal Global Biodiversity Framework Target 3(“30×30 Protection”).
基金TheNationalNaturalScienceFoundationofChina (No .60 3 90 5 40 ) .
文摘Several space-time coding based transmit diversity techniques for wideband code division multiple access (WCDMA) systems with four transmitter antennas are investigated. Performances of the rake receivers are analyzed and compared with those of the multi-antenna receive diversity techniques. Theoretical analysis shows that the multi-antenna transmit diversity techniques provide considerable performance gain at the mobile receiver in the wireless channel with less inherent multipath diversity, especially the G4 coding based scheme. Compared with the multi-antenna receive diversity techniques with the same diversity order, the transmit diversity techniques introduce much more multi-access plus multipath interference and require measures of interference suppression in the multi-user environments.
文摘Space-time spreading (STS) and orthogonal transmit diversity (OTD) are towtransmit diversity schemes proposed by cdma2000 standard. In this paper, performance comparisonanalysis of the two transmits diversity schemes in multipath channel under multiuser situation arecarried out. Link level simulation in forward link cdma2000 is performed in IMT-2000 channel.Performance analysis and simulation results show that the performance improvement provided STS overOTD decreases as the increase of propagation path number and decrease of the user number.
文摘Space time coding can provide high data rate and performance gain for wireless communication system. Performance comparison of space time trellis codes and space time transmit diversity is carried out under the same bandwidth efficiency in this paper. We also propose some optimum low rate space time trellis codes in quasi static Rayleigh fading chan￣nel. Performance analysis and simulation show that the low rate space time trellis codes outperform space time transmit diversity at the same bandwidth efficiency, and are more suitable for the power limited wireless communication system which has no strict requirement on bandwidth efficiency.
基金supported by the National Natural Science Foundation of China(60072041).
文摘Many common multimedia signal processing,including cropping,filtering,and perceptual coding,make watermark signal fading-like modification.A scheme that applies transmit diversity technique to improve robustness of digital watermarking is presented.First,the scheme decomposes the original image using wavelet pyramid algorithm and chooses the middle-frequency band for transmission channel that the watermark will be embedded into.Then the watermark is pseudo-randomly permuted.The scheme makes use of space-time coding and differential detection technique to embed and extract watermark.The extracting process has access to neither the original image nor channel state information.Experimental results demonstrate that the scheme improves the performance of robust watermarking.
基金Project supported by the National Natural Science Foundation of China （Grant No.60472103）, the Shanghai Excellent Academic Leader Project （Grant No.05XP14027）, and the Shanghai Leading Academic Discipline Project （Grant No.T0102）.
文摘The paper investigates closed-loop transmit diversity （CLTD） systems with antenna selection technique. The expected received signal-noise-ratio （RxSNR） of the proposed systems is analyzed and compared with CLTD systems. An algorithm is proposed for determining the number of increased transmit antennas in terms of a reduced RF chains without performance degradation. Since a feedback channel is bandwidth-limited, we present a method of quantizing transmit-weight vectors. Simulation results demonstrate advantage of the proposed systems with full and quantized feedback information. Quantized feedback has less effect on the proposed systems than CLTD systems.
基金Project supported by the Hi-Tech Research and Development Pro-gram (863) of China (No. 2003AA123310) and the National Natural Science Foundation of China (No. 60332030)
文摘This paper deals with channel estimation for orthogonal frequency-division multiplexing (OFDM) systems with transmit diversity. Space time coded OFDM systems, which can provide transmit diversity, require perfect channel estimation to improve communication quality. In actual OFDM systems, training sequences are usually used for channel estimation. The authors propose a training based channel estimation strategy suitable for space time coded OFDM systems. This novel strategy provides enhanced performance, high spectrum efficiency and relatively low computation complexity.
文摘Transmit diversity has been recently proposed to reduce the effects of fading channels in various wireless applications. Orthogonal transmit diersity (OTD) is one of the standardized techniques in 3G systems. In this paper, we apply orthogonal transmit diversity technique to multicarrier CDMA systems. Andlysis and simulation results show that performance benefits can be achieved compared with conventioal MC-CDMA systems in multipath fading channels.
基金supported in part by the Fundamental Research Funds for the Central Universities under Grants 2020JBM081 and 2020JBZD005in part by the National Key R&D Program of China under Grant 2020YFB1806903in part by the National Natural Science Foundation under Grant U1834210。
文摘This paper investigates the transmission scheme of the orthogonal time frequency space(OTFS)system with multiple antennas.Previous works have studied the multi-antenna transmitter diversity scheme with the ideal pulse shaping in OTFS systems assuming the wireless channels of two consecutive frames duration are invariant.However,the ideal pulse shaping can not be realized in practice and the channel varies rapidly in two consecutive frames in the high-speed mobility scenarios.To this end,we redesign the multi-antenna transmitter diversity scheme to ensure its practicability in the rectangular-pulsebased OTFS systems.At first,the information symbols of each antenna are divided into two half frames along the Doppler domain.Then,the guard symbols are carefully arranged to eliminate the interference between two half frames,and to ensure the equivalent channels of two half frames being identical.By considering the positions of the guard symbols,the transmission codeword is designed and a low complexity linear detection is proposed.Finally,simulation results validate that the bit error rate performance of the proposed scheme has the superiority over the existing works.
基金Sponsored by the Science and Technology Project of Dalian,China (Grant No. 2011J21DW009)
文摘In this paper, a time-switched space-time （TSST） coded orthogonal frequency division nmltiplexing （OFDM） scheme against the time-varying channels is proposed. In the TSST-OFDM scheme, it is equipped with four transmit antennas, but only double of them are used for coding in every time slot. It is shown that the signal to inter-antenna interference ratio is a function of Doppler frequency in time-varying channels for a given space-time code. The analyses and simulations results validate that the proposed scheme not only gets time- switched diversity and lower decoding complexity, but also suffers less time-varying impairments. Hence, it ex- hibits better performance than quasi-orthogonal space-time coded scheme.
基金Supported by the National Natural Science Foundation of China (No. 60496311)
文摘In this paper, the closed loop transmit diversity technology for the Wideband Code Division Multiple Access(WCDMA) systems is investigated in a multipath Rayleigh fading channel. The RAKE receiver model and the weighing vector algorithm are presented. The performance is theoretically analyzed in terms of the average maximal Signal-to-Noise Ratio(SNR) gain available over the Space-Time block coding based Transmit Diversity(STTD) technology. Theoretic analysis and simulation results show that the closed loop transmit diversity can provide a 3dB performance gain over the open loop scheme in a single path fading channel, while the performance gain decreases dramatically with the increasing inherent multipath diversity of the wireless channel.
文摘In this paper, we introduce a novel merger of antenna arrays with scanning beam patterns, and Orthogonal Frequency Division Multiplexing (OFDM) systems. Controlled time varying phase shifts are applied to the antenna array elements mounted at the base station with beam patterns directed toward the desired user. This creates a small beam pattern movement called Beam Pattern Scanning (BPS). In rich scattering environments BPS creates a time varying environment leading to time diversity exploitable at the receiver enhances its probability-of-error performance. Here, we apply OFDM signals to BPS antenna arrays, and we achieve: (1) directionality, which supports Space Division Multiple Access (SDMA);and (2) a time diversity gain, which leads to high performance. We discuss the structure of the base station antenna array and the OFDM receiver that exploits time diversity. We also introduce the merger of BPS and multi-carrier OFDM (MC-OFDM) systems. In MC-OFDM each bit is transmitted over all sub-carriers after serial to parallel conversion. BPS/ MC-OFDM receiver exploits both time diversity inherent in BPS, and frequency diversity inherent in MC-OFDM transmission technique. Simulation results show high Probability-of-error performance is achie- vable via BPS/OFDM and BPS/MC-OFDM schemes comparing to the traditional OFDM and MC-OFDM, respectively. Simulations also reveal that MC-OFDM system as well as its merger with BPS is capable of mitigating large Peak-to-Average Ratio (PAPR) problem in traditional OFDM system. In addition, performance simulations with coded OFDM (COFDM) and coded MC-OFDM (MC-COFDM) and their merger with BPS are studied.
文摘The performance analysis, using outage capacity for a forward link cellular communications system is presented. The effects of correlated fading, the distribution of angle of arrivals, and the array configurations are considered. The objective is to examine the effect of angle of arrival (AOA) energy distributions on two systems (transmit diversity and beamforming) with angle spread. We do so by comparing the performance of transmit diversity with a system that uses beamforming to point a relatively narrow beam at the mobile station. Analytical results show that the transmit diversity system using uniform linear arrays (ULA) and uniform circular arrays (UCA) with truncated Laplacian AOA, performs better even at smaller angle spreads as compared to other energy distributions. The ULA geometry is a preferable configuration for transmit diversity system as compared to UCA.
基金supported by the Key Pre-Research Project for Civil Space Technology(No.B0106).
文摘The next generation of High Throughput Satellite(HTS)will exploit Q/V band for the feeder link and Ka band for the user link.The exploitation of multiple gateways(GWs)is a transmit diversity measure to compensate severe rain attenuation of Q/V band feeder links.This paper introduces a new smart gateway diversity combination scheme that combinates N-active(K=2)and N+1 diversity method in detail from the working principle,gateway switching strategy,evaluation of system availability and implementation complexity.In addition,a feeder link outage event prediction algorithm featuring combination scheme is given detailly based on modified time-adaptive linear regression.Compared with the existing N+P scheme,the proposed scheme can provide higher system availability and more stable user’s experience under the condition of properly increasing the complexity of payload design.Compared with Nactive scheme that has been reported,it is much easier to implement in engineering and more cost-effective.As a result,the combination scheme is a realistic solution based on a trade-off between performance improvement and implementation complexity.
基金supported by the Yunnan Provincial Key Laboratory of Clinical Virology(No.202002AG070062)the Key Projects of Yunnan Province Science and Technology Department(No.202302AA310044)the National Natural Science Foundation of China(No.82060664).
文摘This study primarily aimed to investigate the prevalence of human papillomavirus(HPV)and other common pathogens of sexually transmitted infections(STIs)in spermatozoa of infertile men and their effects on semen parameters.These pathogens included Ureaplasma urealyticum,Ureaplasma parvum,Chlamydia trachomatis,Mycoplasma genitalium,herpes simplex virus 2,Neisseria gonorrhoeae,Enterococcus faecalis,Streptococcus agalactiae,Pseudomonas aeruginosa,and Staphylococcus aureus.A total of 1951 men of infertile couples were recruited between 23 March 2023,and 17 May 2023,at the Department of Reproductive Medicine of The First People’s Hospital of Yunnan Province(Kunming,China).Multiplex polymerase chain reaction and capillary electrophoresis were used for HPV genotyping.Polymerase chain reaction and electrophoresis were also used to detect the presence of other STIs.The overall prevalence of HPV infection was 12.4%.The top five prevalent HPV subtypes were types 56,52,43,16,and 53 among those tested positive for HPV.Other common infections with high prevalence rates were Ureaplasma urealyticum(28.3%),Ureaplasma parvum(20.4%),and Enterococcus faecalis(9.5%).The prevalence rates of HPV coinfection with Ureaplasma urealyticum,Ureaplasma parvum,Chlamydia trachomatis,Mycoplasma genitalium,herpes simplex virus 2,Neisseria gonorrhoeae,Enterococcus faecalis,Streptococcus agalactiae,and Staphylococcus aureus were 24.8%,25.4%,10.6%,6.4%,2.4%,7.9%,5.9%,0.9%,and 1.3%,respectively.The semen volume and total sperm count were greatly decreased by HPV infection alone.Coinfection with HPV and Ureaplasma urealyticum significantly reduced sperm motility and viability.Our study shows that coinfection with STIs is highly prevalent in the semen of infertile men and that coinfection with pathogens can seriously affect semen parameters,emphasizing the necessity of semen screening for STIs.
文摘The relation between conflict and governance has been dominated by type of government rather than by system of government.With increasing conflict in countries with ethnic and religious diversity,the debate has gradually shifted to understand better the link between conflict and system of government.There is a growing evidence that suggests federal system performs better than unitary system in managing diversity and reducing conflict.Decentralization is even seen to be more effective than federal system not only in managing diversity and reducing conflict but also in delivering public goods.This article provides an account of evolution of system of government in South Sudan.It finds a clear association of centralized unitary system with violent conflict and a relative peace during period of decentralized government or federal system.A decentralized federal system may be appropriate for South Sudan in managing diversity and mitigating conflict.Despite the popular demand by their citizens for a federal system to manage diversity and reduce violent conflict,the ruling elites in the post-independent South Sudan adopted instead an autocratic centralized unitary system that contributed among other factors to the persistent violent conflicts,erosion of social cohesion,and rising mistrust between state and citizens and between and among the communities of South Sudan.
基金supported by Innovation Scientists and Technicians Troop Construction Projects of Henan Province(Grant No.212101510003)the Central Plains Scholar Workstation Project(Grant No.224400510002)+1 种基金the Youth Science Foundation of Henan Province(Grant No.202300410136)the Experimental Development Foundation of Henan University of Science and Technology(Grant No.SY2324004)。
文摘Paeonia suffruticosa Andr.is an endemic shrub flower in China with 2n=10.This study used 228 cultivars from four populations,i.e.,Jiangnan,Japan,Northwest,and Zhongyuan,as materials to explore the genetic diversity levels among different populations of tree peony varieties.The results showed that 34 bands were amplified using five pairs of cp SSR primers,with an average of 6.8 bands per primer pair.The average number of different alleles(N_(a)),effective alleles(N_(e)),Shannon's information index(I),diversity(H),and polymorphic information content(PIC)were 3.600,2.053,0.708,0.433,and 0.388,respectively.The PIC value was between 0.250 and 0.500,indicating a moderate level of polymorphism for the five cp SSR primer pairs.The genetic diversity levels of peony cultivars varied among different populations,with the Northwest population showing relatively lower levels(I=0.590,H=0.289,and PIC=0.263).A total of 52 haplotypes were identified in the four examined populations,and the number of haplotypes per population ranged from 11 to 22.Forty-four private haplotypes were detected across populations,and the Northwest population exhibiting the highest count of private haplotypes with 17.The mean number of effective number of haplotypes(N_(eh)),haplotypic richness(R_(h)),and diversity(H)were 8.351,6.824,and 0.893,respectively.Analysis of molecular variance indicated that genetic variation within tree peony germplasm was greater than that between germplasm resources,and the main variation was found within individuals of peony germplasm.Cluster analysis,principal coordinate analysis,and genetic structure analysis classified tree peonies from different origins into two groups,indicating a certain degree of genetic differentiation among these four tree peony cultivation groups.This study provides a theoretical basis for the exploration,utilization,and conservation of peony germplasm resources,as well as for research on the breeding of excellent varieties.
基金supported by the Fundamental Research Funds of Chinese Academy of Forestry(Nos.CAFYBB2022SY037,CAFYBB2021ZA002 and CAFYBB2022QC002)the Basic Research Foundation of Yunnan Province(Grant No.202201AT070264).
文摘Soil microbial communities are key factors in maintaining ecosystem multifunctionality(EMF).However,the distribution patterns of bacterial diversity and how the different bacterial taxa and their diversity dimensions affect EMF remain largely unknown.Here,we investigated variation in three measures of diversity(alpha diversity,community composition and network complexity)among rare,intermediate,and abundant taxa across a latitudinal gradient spanning five forest plots in Yunnan Province,China and examined their contributions on EMF.We aimed to characterize the diversity distributions of bacterial groups across latitudes and to assess the differences in the mechanisms underlying their contributions to EMF.We found that multifaceted diversity(i.e.,diversity assessed by the three different metrics)of rare,intermediate,and abundant bacteria generally decreased with increasing latitude.More importantly,we found that rare bacterial taxa tended to be more diverse,but they contributed less to EMF than intermediate or abundant bacteria.Among the three dimensions of diversity we assessed,only community composition significantly affected EMF across all locations,while alpha diversity had a negative effect,and network complexity showed no significant impact.Our study further emphasizes the importance of intermediate and abundant bacterial taxa as well as community composition to EMF and provides a theoretical basis for investigating the mechanisms by which belowground microorganisms drive EMF along a latitudinal gradient.
基金supported by the Second Tibetan Plateau Scientific Expedition and Research Program(STEP),Grant No.2019QZKK0606.
文摘The Qinghai-Tibet Plateau(QTP)has three main grassland types:alpine meadow,alpine steppe,and alpine desert steppe.In this study,we asked how plant productivity and species diversity vary with altitude,longitude and latitude in alpine grasslands of the QTP.We then identified the environmental factors that drive these observed patterns of plant productivity and species diversity.We found that although plant productivity and species diversity varied greatly across large-scale longitudinal and latitudinal gradients,these changes were strongest across the longitudinal gradient.This finding indicates that moisture rather than temperature has the greatest impact on plant productivity and species diversity of the alpine grasslands in the QTP.We also found that besides soil and climate factors,partial pressure of carbon dioxide(pCO_(2))also has significant effects on plant productivity,and barometric pressure and partial pressure of oxygen(pO_(2))also have significant effects on species diversity.Furthermore,the relationship between the biomass of grassland-dominant species and species diversity was affected by the spatial scale at which these factors were studied.Our study provides new insights into the interconnections between plant productivity and species diversity and the major factors that influence alpine grasslands.It also provides a scientific basis for the maintenance of plant diversity and ecosystem functions in hypoxic(low-oxygen)regions.
基金supported by National Key R&D Program of China(2024YFF1307400)Guangdong S&T Program(2022B1111230001).
文摘Preserving genetic diversity is crucial for the long-term survival of wild plant species,yet many remain at risk of genetic erosion due to small population sizes and habitat fragmentation.Here,we present a comparative genomic study of the critically endangered Oreocharis esquirolii(Gesneriaceae)and its widespread congener O.maximowiczii.We assembled and annotated chromosome-level reference genomes for both species and generated whole-genome resequencing data from 28 O.esquirolii and 79 O.maximowiczii individuals.Our analyses reveal substantially lower genetic diversity and higher inbreeding in O.esquirolii,despite its overall reduced mutational burden.Notably,O.esquirolii exhibits an elevated proportion of strongly deleterious mutations relative to O.maximowiczii,suggesting that limited opportunities for purging have allowed these variants to accumulate.These contrasting genomic profileslikely reflectdivergent demographic histories,with O.esquirolii having experienced severe bottlenecks and protracted population decline.Collectively,our findingshighlight the critically endangered status of O.esquirolii,characterized by diminished genetic diversity,pronounced inbreeding,and reduced ability to eliminate deleterious alleles.This study provides valuable genomic resources for the Gesneriaceae family and underscores the urgent need for targeted conservation measures,including habitat protection and ex situ preservation efforts,to mitigate the extinction risk facing O.esquirolii and potentially other threatened congeners.
