The coverage probability of both the cellular users and the Device-to-Device(D2D) users are analyzed. We assume that the cellular users are able to communication with the Base Station(BS) either by relying on the assi...The coverage probability of both the cellular users and the Device-to-Device(D2D) users are analyzed. We assume that the cellular users are able to communication with the Base Station(BS) either by relying on the assistance of Full-Duplex(FD) mode relays or via direct user-to-BS links with high-enough Signal-to-Interference-plus-Noise-Ratio(SINR). Note that the FD-mode devices are capable of simultaneously operating in two modes,i.e. the D2D mode and the cooperative relay mode,with the sum power consumption at these devices kept constant. The closedform expressions for coverage probability of both tier users are derived. After that,numerical analyses are provided,showing that the coverage probability of the both the cellular and the D2D users can be substantially influenced by a variety of parameters,including the power allocation factor of the relays,the density of users,and the self-interference imposed on the FD mode relays,etc. Furthermore,in the D2D enabled networks,it is shown that the FD relay aided transmission is beneficial to enhancing the coverage probability of the cellular users if the target SINR is lower than 5 d B.展开更多
Interference alignment （IA） is well understood to approach the capacity of interference channels, and believed to be crucial in cellular networks in which the ability to control and exploit interference is key. Howe...Interference alignment （IA） is well understood to approach the capacity of interference channels, and believed to be crucial in cellular networks in which the ability to control and exploit interference is key. However, the achievable performance of IA in cellular networks depends on the quality of channel state information （CSI） and how effective IA is in practical settings is not known. This paper studies the use of IA to mitigate inter-cell interference of cellular networks under imperfect CSI conditions. Our analysis is based on stochastic geometry where the structure of the base station （BS） locations is considered by a Poisson point process （PPP）. Our main contribution is the coverage probability of the network and simulation results confirm the accuracy.展开更多
The ultra-dense network is a promising technology to increase the network capacity in the forthcoming fifthgeneration(5G)mobile communication networks by deploying lots of low power Small Base Stations(SBSs)which over...The ultra-dense network is a promising technology to increase the network capacity in the forthcoming fifthgeneration(5G)mobile communication networks by deploying lots of low power Small Base Stations(SBSs)which overlap with Macro Base Stations(MBSs).The interference and energy consumption increase rapidly with the number of SBSs although each SBS transmits with small power.In this paper,we model a downlink heterogeneous ultra-dense network where a lot of SBSs are randomly deployed with MBSs based on the Poisson point process.We derive the coverage probability and its variance,and analyze the area spectral efficiency and energy efficiency of the network considering three Fractional Power Control(FPC)strategies.The numerical results and Monte Carlo simulation results show that power control can mitigate the interference and balance the performances of inner-user and edge-user equipments.Especially,a great improvement of energy efficiency is archived with a little loss of area spectral efficiency when FPC is adopted.Finally,we analyze the effect of base stations’(BSs’)sleeping on the performance of the network when it is partially loaded.展开更多
Backscatter communication(BC)is con-sidered a key technology in self-sustainable commu-nications,and the unmanned aerial vehicle(UAV)as a data collector can improve the efficiency of data col-lection.We consider a UAV...Backscatter communication(BC)is con-sidered a key technology in self-sustainable commu-nications,and the unmanned aerial vehicle(UAV)as a data collector can improve the efficiency of data col-lection.We consider a UAV-aided BC system,where the power beacons(PBs)are deployed as dedicated radio frequency(RF)sources to supply power for backscatter devices(BDs).After harvesting enough energy,the BDs transmit data to the UAV.We use stochastic geometry to model the large-scale BC sys-tem.Specifically,the PBs are modeled as a type II Mat´ern hard-core point process(MHCPP II)and the BDs are modeled as a homogeneous Poisson point process(HPPP).Firstly,the BDs’activation proba-bility and average coverage probability are derived.Then,to maximize the energy efficiency(EE),we opti-mize the RF power of the PBs under different PB den-sities.Furthermore,we compare the coverage proba-bility and EE performance of our system with a bench-mark scheme,in which the distribution of PBs is mod-eled as a HPPP.Simulation results show that the PBs modeled as MHCPP II has better performance,and we found that the higher the density of PBs,the smaller the RF power required,and the EE is also higher.展开更多
Purpose: To develop a new statistical index “percent CTV (clinical target vo-lume) coverage probability” (%CCP), defined as the probability that a specific percent (e.g., 95%) of the CTV can be reliably covered by t...Purpose: To develop a new statistical index “percent CTV (clinical target vo-lume) coverage probability” (%CCP), defined as the probability that a specific percent (e.g., 95%) of the CTV can be reliably covered by the prescription dose, for evaluating the coverage loss of brain (fractionated) stereotactic radiosurgery (SRS/fSRS) when the PTV (planning target volume) margin is zero. Methods: The random variable Q for CTV percent coverage was derived using a previously developed model for CTV random motion that follows a three-dimensional (3D) independent normal distribution with a zero mean and a standard deviation of 𝜎<sub>𝑆</sub>(for translation) or 𝜎<sub>𝛿</sub>(for rotation). Assuming both CTV and PTV are spherical with the same diameter d<sub>CTV</sub>, the cumulative distribution function of Q could be obtained analytically using the relation of sphere-sphere intersection. The %CCP was then derived as the reliability function of Q and was used to quantify the coverage loss for selected d<sub>CTV</sub>. Results: The 95%-95% clinical goal (95% of the times, at least 95% of the CTV is covered) is not achievable with d<sub>CTV</sub> mm. For common CTVs (d<sub>CTV</sub> mm) encountered in SRS/fSRS, only 60%-90% of the CTV could be reliably covered by the prescription dose 95% of the time. For 𝜎𝑆</sub></sub>=0.5mm and 𝜎𝛿</sub></sub> =0.4˚, the 95% CCP was the highest when the distance between the CTV and the isocenter 𝑑𝐼⇔𝑇</sub><sub></sub>=0 and gradually decreased with the increasing 𝑑<sub>𝐼⇔𝑇</sub></sub>. Conclusions: The %CCP was successfully derived for evaluating the CTV coverage loss for brain SRS/fSRS. When the PTV margin is zero, the 95%-95% clinical goal cannot be achieved for most targets (d<sub>CTV</sub> mm).展开更多
The Poisson point process(PPP) has been widely used in wireless network modeling and performance analysis due to the independence between its nodes. Therefore, it may not be a suitable model for many of the exclusive ...The Poisson point process(PPP) has been widely used in wireless network modeling and performance analysis due to the independence between its nodes. Therefore, it may not be a suitable model for many of the exclusive networks between the nodes. This paper analyzes the energy efficiency(EE) and optimizes the two-tier heterogeneous cellular networks(Het Nets). Considering the mutual exclusion between macro base stations(MBSs) distribution, the deployment of MBSs is modeled by the Matérn hard-core point process(MHCPP), and the deployment of pico base stations(PBSs) is modeled by the PPP. We adopt a simple approximation method to study the signal to interference ratio(SIR) distribution in two-tier MHCPP-PPP networks and then derive the coverage probabilities, the average data rates and the energy efficiency of Het Nets. Finally, an optimization algorithm is proposed to improve the EE of Het Nets by controlling the transmit power of PBSs. The simulation results show that the EE of a system can be effectively improved by selecting the appropriate transmit power for the PBSs. In addition, two-tier MHCPP-PPP Het Nets have higher energy efficiency than two-tier PPP-PPP Het Nets.展开更多
Motivated by the objective of pursuing revenue, improvement in coverage and reduction in energy cost for wireless communication networks have been of great significance for mobile operators. Therefore, heterogeneous c...Motivated by the objective of pursuing revenue, improvement in coverage and reduction in energy cost for wireless communication networks have been of great significance for mobile operators. Therefore, heterogeneous cellular networks(HCNs) and Coordinated Multipoint(Co MP) transmission are considered as promising solutions to enhance the performances of wireless communication systems. This paper analyzed the K-tier HCNs with a dynamic downlink Co MP scheme, in which the flexible clusters of cooperative stations are determined by a connecting threshold θ. Using stochastic geometry, the coverage probability(CP) and energy efficiency(EE) of a K-tier HCN operating under this scheme are derived, based on which the trade-off between CP and EE is discovered and discussed. Simulation results show the validity of our derivations. The proposed schememay significantly reduce energy consumption sacrificing a small amount of CP, and outperforms the fixed scheme as well. The CP-EE trade-off are also revealed, whichsuggests suitable trade-off points between CP and EE that will deliver the maximum economic profitability. Tendencies discovered in this paper may provide the operators with opportunities for further optimization in pursuit of economic profitability.展开更多
This study investigates physical layer security in downlink multipleinput multiple-output(MIMO) multi-hop heterogeneous cellular networks(MHCNs),in which communication between mobile users and base stations(BSs) is es...This study investigates physical layer security in downlink multipleinput multiple-output(MIMO) multi-hop heterogeneous cellular networks(MHCNs),in which communication between mobile users and base stations(BSs) is established by a single or multiple hops,to address the problem of insufficient security performance of MIMO heterogeneous cellular networks.First,two-dimensional homogeneous Poisson point processes(HPPPs) are utilized to model the locations of K-tier BSs in MIMO MHCNs and receivers,including those of legitimate users and eavesdroppers.Second,based on the channel gain distribution and the statistics property of HPPP,the achievable ergodic rates of the main and eavesdropper channels in direct and ad hoc links are derived,respectively.Third,the secrecy coverage probability and the achievable ergodic secrecy throughput of downlink MIMO MHCNs are explored,and their expressions are derived.Lastly,the correctness of the theoretical derivation is verified through Monte Carlo simulations.展开更多
In this paper, we consider the construction of the approximate profile-</span><span style="font-family:""> </span><span style="font-family:Verdana;">likelihood confiden...In this paper, we consider the construction of the approximate profile-</span><span style="font-family:""> </span><span style="font-family:Verdana;">likelihood confidence intervals for parameters of the 2-parameter Weibull distribution based on small type-2 censored samples. In previous research works, the traditional Wald method has been used to construct approximate confidence intervals for the 2-parameter Weibull distribution</span><span style="font-family:""> </span><span style="font-family:Verdana;">under type-2 censoring scheme. However, the Wald technique is based on normality assumption and thus may not produce accurate interval estimates for small samples. The profile-likelihood and Wald confidence intervals are constructed for the shape and scale parameters of the 2-parameter Weibull distribution based on simulated and real type-2 censored data, and are hence compared using confidence length and coverage probability.展开更多
This paper presents four methods of constructing the confidence interval for the proportion <i><span style="font-family:Verdana;">p</span></i><span style="font-family:;" ...This paper presents four methods of constructing the confidence interval for the proportion <i><span style="font-family:Verdana;">p</span></i><span style="font-family:;" "=""><span style="font-family:Verdana;"> of the binomial distribution. Evidence in the literature indicates the standard Wald confidence interval for the binomial proportion is inaccurate, especially for extreme values of </span><i><span style="font-family:Verdana;">p</span></i><span style="font-family:Verdana;">. Even for moderately large sample sizes, the coverage probabilities of the Wald confidence interval prove to be erratic for extreme values of </span><i><span style="font-family:Verdana;">p</span></i><span style="font-family:Verdana;">. Three alternative confidence intervals, namely, Wilson confidence interval, Clopper-Pearson interval, and likelihood interval</span></span><span style="font-family:Verdana;">,</span><span style="font-family:Verdana;"> are compared to the Wald confidence interval on the basis of coverage probability and expected length by means of simulation.</span>展开更多
Cloud computing.based heterogeneous networks(C.Het Nets) have been considered as promising network architecture of future wireless communication systems. However, its performance is constrained by the capability of fr...Cloud computing.based heterogeneous networks(C.Het Nets) have been considered as promising network architecture of future wireless communication systems. However, its performance is constrained by the capability of fronthaul. To study the performance limit of C.Het Nets, the coverage performance of the open access strategy in C.Het Nets is analyzed in this paper. In particular, the non.ideal condition of fronthaul in C.Het Nets is characterized by establishing a stochastic geometry.based model, and a tight lower bound on coverage probability is derived for downlink transmissions. Based on the derived results, the constraint of the fronthaul is given to ensure that open access strategy can achieve the best coverage performance. Finally, the simulation results are provided to verify the theoretical results and show the impact of fronthaul constrains.展开更多
Energy efficiency(EE) of cellular networks has attracted considerable attention recently. However, EE of relay-assisted cellular networks where the macro base stations(MBSs) are equipped with the multi-antenna has not...Energy efficiency(EE) of cellular networks has attracted considerable attention recently. However, EE of relay-assisted cellular networks where the macro base stations(MBSs) are equipped with the multi-antenna has not been thoroughly addressed. This paper considered the downlink transmission of multi-antenna relay-assisted cellular networks, meanwhile, a strategic sleep scheme was used in relay stations(RSs), which dynamically adjusted the RS working mode according to whether the number of users serviced by the relay exceeds a given threshold. A geometric model was built to derive the coverage probability and mean achievable rate from the MBSs to user(UE), the MBS to RS, the RS to UE links and analyze the system EE. It is shown that the energy efficiency of cellular network with strategic sleep RS is slightly higher than that of cellular network with non-sleeping strategy. Furthermore, the MBS equipped with multi-antenna has better impact on energy efficiency and spectral efficiency than the MBS with single antenna.展开更多
This article deals with correlating two variables that have values that fall below the known limit of detection (LOD) of the measuring device;these values are known as non-detects (NDs). We use simulation to compare s...This article deals with correlating two variables that have values that fall below the known limit of detection (LOD) of the measuring device;these values are known as non-detects (NDs). We use simulation to compare several methods for estimating the association between two such variables. The most commonly used method, simple substitution, consists of replacing each ND with some representative value such as LOD/2. Spearman’s correlation, in which all NDs are assumed to be tied at some value just smaller than the LOD, is also used. We evaluate each method under several scenarios, including small to moderate sample size, moderate to large censoring proportions, extr</span><span style="font-family:Verdana;">eme imbalance in censoring proportions, and non-bivariate nor</span><span style="font-family:Verdana;">mal (BVN) data. In this article, we focus on the coverage probability of 95% confidence intervals obtained using each method. Confidence intervals using a maximum likelihood approach based on the assumption of BVN data have acceptable performance under most scenarios, even with non-BVN data. Intervals based on Spearman’s coefficient also perform well under many conditions. The methods are illustrated using real data taken from the biomarker literature.展开更多
This article deals with the case of the failure-censored constant-stress partially accelerated life test （CSPALT） for highly reliable materials or products assuming the Pareto distribution of the second kind. The ma...This article deals with the case of the failure-censored constant-stress partially accelerated life test （CSPALT） for highly reliable materials or products assuming the Pareto distribution of the second kind. The maximum likelihood （ML） method is used to estimate the parameters of the CSPALT model. The performance of ML estimators is investigated via their mean square error. Also, the average confidence interval length （IL） and the associated co- verage probability （CP） are obtained. Moreover, optimum CSPALT plans that determine the optimal proportion of the test units al- located to each stress are developed. Such optimum test plans minimize the generalized asymptotic variance （GAV） of the ML estimators of the model parameters. For illustration, Monte Carlo simulation studies are given and a real life example is provided.展开更多
THE 19th National Congress of the Communist Party of China（CPC）attracted global attention with1,818 journalists from abroad to cover the event in Beijing on October 18-24,more coverage than for the18th CPC National ...THE 19th National Congress of the Communist Party of China（CPC）attracted global attention with1,818 journalists from abroad to cover the event in Beijing on October 18-24,more coverage than for the18th CPC National Congress.Most of them have been based in China or visited China on several occasions.They have witnessed the changes of Chinese people＇s life in the past five years.展开更多
Device-to-device(D2D)communication underlay cellular networks offers several benefits,including offloading cellular traffic and improving throughput.In this paper,a scheme is proposed for D2D communication underlay ce...Device-to-device(D2D)communication underlay cellular networks offers several benefits,including offloading cellular traffic and improving throughput.In this paper,a scheme is proposed for D2D communication underlay cellular networks,by taking resource allocation algorithm into account.Firstly,a scenario where cellular users(CUs)and D2D users(DUs)coexist is considered.To characterize the clustering feature of DUs,the locations of CUs and DUs are modeled as Poisson cluster processes(PCPs),and the locations of base stations(BSs)are modeled as a Poisson point process(PPP).Subsequently,a resource allocation algorithm is proposed to allocate resources for CUs to DUs in the cluster,which involves the optimization of matching between D2D user and cellular user.Finally,the coverage probability of the clustering network is analyzed.The simulation results indicate that the proposed scheme can effectively enhance system capacity and reveal the effects of various parameters on system performance.展开更多
Accurate estimation of disease prevalence is crucial for effective public health intervention and resource allocation.Generating data by individual testing methods is often impractical and expensive for large populati...Accurate estimation of disease prevalence is crucial for effective public health intervention and resource allocation.Generating data by individual testing methods is often impractical and expensive for large populations,particularly when disease prevalence is low.Pool testing involves combining samples from multiple individuals into a pool and performing a single test,and offers a costeffective and efficient alternative.In pool testing strategy with retesting,if a pool tests negative,it is classified as non-defective,whereas if it is positive,then a retest is needed.The retesting strategy mitigates the effects of initial test errors,thereby enhancing the accuracy of the estimation of the prevalence rate.Evidence in the literature indicates that the traditional Wald method has been used to construct approximate confidence intervals for the prevalence rate.However,this interval estimation method is based on the normality ap-proximation and hence may not be accurate when the true prevalence rate is close to zero.In this paper,we propose a Bayesian interval estimation ap-proach which is not affected by extreme values of the prevalence rate and al-lows for incorporating prior information about the prevalence rate.We as-sumed that the prior distribution for the unknown prevalence rate p is a Beta distribution with parameters α_(0) and β_(0) and based on pool testing outcomes for the n pools each of size k,100(1-α)% credible intervals were constructed from the resulting posterior distribution.Simulation studies were carried out to compare the efficiencies of the Bayesian and Wald interval estimation methods for various values of p.展开更多
Low-earth orbit(LEO)satellite networks ignite global wireless connectivity.However,signal outages and co-channel interference limit the coverage in traditional LEO satellite networks where a user is served by a single...Low-earth orbit(LEO)satellite networks ignite global wireless connectivity.However,signal outages and co-channel interference limit the coverage in traditional LEO satellite networks where a user is served by a single satellite.This paper explores the possibility of satellite cooperation in the downlink transmissions.Using tools from stochastic geometry,we model and analyze the downlink coverage of a typical user with satellite cooperation under Nakagami fading channels.Moreover,we derive the joint distance distribution of cooperative LEO satellites to the typical user.Our model incorporates fading channels,cooperation among several satellites,satellites'density and altitude,and co-channel interference.Extensive Monte Carlo simulations are performed to validate analytical results.Simulation and numerical results suggest that coverage with LEO satellites cooperation considerably exceeds coverage without cooperation.Moreover,there are optimal satellite density and satellite altitude that maximize the coverage probability,which gives valuable network design insights.展开更多
Caching popular content in the storage of small cells is deemed as an efficient way to decrease latency, offload backhaul and satisfy user＇s demands. In order to investigate the performance of cache-enabled small cel...Caching popular content in the storage of small cells is deemed as an efficient way to decrease latency, offload backhaul and satisfy user＇s demands. In order to investigate the performance of cache-enabled small cell networks, coverage probability is studied in both single-point transmission and cooperative multipoint（Co MP） transmission scenarios. Meanwhile, the caching distribution modeled as Zipf and uniform distribution are both considered. Assuming that small base stations（SBSs） are distributed as a homogeneous Poisson point process（HPPP）, the closed-form expressions of coverage probability are derived in different transmission cases. Simulation results show that Co MP transmission achieves a higher coverage probability than that of single-point transmission. Furthermore, Zipf distribution-based caching is more preferable than uniform distribution-based caching in terms of coverage probability.展开更多
Millimeter wave(mm-wave)communication is widely considered to be a promising technique for 5G(Fifth Generation)cellular systems.Owing to the high path loss of mm-wave channels,5G networks could employ a heterogeneous ...Millimeter wave(mm-wave)communication is widely considered to be a promising technique for 5G(Fifth Generation)cellular systems.Owing to the high path loss of mm-wave channels,5G networks could employ a heterogeneous structure that consists of an MBS(Macro Base Station)and numerous SBSs(Small Base Stations).In this paper,we analyze the coverage and rate performance of an mm-wave heterogeneous network.Using user beam selection,we derive analytical expressions for the coverage probabilities of the SBSs and MBS.Furthermore,the average achievable rate for a typical user is also investigated.It is shown that the analytical results closely follow those of the simulations with marginal differences.展开更多
基金supported by Key Project of the National Natural Science Foundation of China (Grant No.61431001)National Natural Science Foundation of China (Grant Nos.61501182,U1501253,61377024)+3 种基金Research Foundation of Education Department of Hunan Province (Grant No.15C0558)Startup Foundation for Doctors of Hunan University of Science and Technology (Grant No.E51539)Key Laboratory of Cognitive Radio and Information Processing,Ministry of Education (Guilin University of Electronic Technology)Foundation of Beijing Engineering and Technology Center for Convergence Networks and Ubiquitous Services
文摘The coverage probability of both the cellular users and the Device-to-Device(D2D) users are analyzed. We assume that the cellular users are able to communication with the Base Station(BS) either by relying on the assistance of Full-Duplex(FD) mode relays or via direct user-to-BS links with high-enough Signal-to-Interference-plus-Noise-Ratio(SINR). Note that the FD-mode devices are capable of simultaneously operating in two modes,i.e. the D2D mode and the cooperative relay mode,with the sum power consumption at these devices kept constant. The closedform expressions for coverage probability of both tier users are derived. After that,numerical analyses are provided,showing that the coverage probability of the both the cellular and the D2D users can be substantially influenced by a variety of parameters,including the power allocation factor of the relays,the density of users,and the self-interference imposed on the FD mode relays,etc. Furthermore,in the D2D enabled networks,it is shown that the FD relay aided transmission is beneficial to enhancing the coverage probability of the cellular users if the target SINR is lower than 5 d B.
文摘Interference alignment （IA） is well understood to approach the capacity of interference channels, and believed to be crucial in cellular networks in which the ability to control and exploit interference is key. However, the achievable performance of IA in cellular networks depends on the quality of channel state information （CSI） and how effective IA is in practical settings is not known. This paper studies the use of IA to mitigate inter-cell interference of cellular networks under imperfect CSI conditions. Our analysis is based on stochastic geometry where the structure of the base station （BS） locations is considered by a Poisson point process （PPP）. Our main contribution is the coverage probability of the network and simulation results confirm the accuracy.
基金the Major Program of the National Nature Science Foundation of China(Grant No.61831004).
文摘The ultra-dense network is a promising technology to increase the network capacity in the forthcoming fifthgeneration(5G)mobile communication networks by deploying lots of low power Small Base Stations(SBSs)which overlap with Macro Base Stations(MBSs).The interference and energy consumption increase rapidly with the number of SBSs although each SBS transmits with small power.In this paper,we model a downlink heterogeneous ultra-dense network where a lot of SBSs are randomly deployed with MBSs based on the Poisson point process.We derive the coverage probability and its variance,and analyze the area spectral efficiency and energy efficiency of the network considering three Fractional Power Control(FPC)strategies.The numerical results and Monte Carlo simulation results show that power control can mitigate the interference and balance the performances of inner-user and edge-user equipments.Especially,a great improvement of energy efficiency is archived with a little loss of area spectral efficiency when FPC is adopted.Finally,we analyze the effect of base stations’(BSs’)sleeping on the performance of the network when it is partially loaded.
文摘Backscatter communication(BC)is con-sidered a key technology in self-sustainable commu-nications,and the unmanned aerial vehicle(UAV)as a data collector can improve the efficiency of data col-lection.We consider a UAV-aided BC system,where the power beacons(PBs)are deployed as dedicated radio frequency(RF)sources to supply power for backscatter devices(BDs).After harvesting enough energy,the BDs transmit data to the UAV.We use stochastic geometry to model the large-scale BC sys-tem.Specifically,the PBs are modeled as a type II Mat´ern hard-core point process(MHCPP II)and the BDs are modeled as a homogeneous Poisson point process(HPPP).Firstly,the BDs’activation proba-bility and average coverage probability are derived.Then,to maximize the energy efficiency(EE),we opti-mize the RF power of the PBs under different PB den-sities.Furthermore,we compare the coverage proba-bility and EE performance of our system with a bench-mark scheme,in which the distribution of PBs is mod-eled as a HPPP.Simulation results show that the PBs modeled as MHCPP II has better performance,and we found that the higher the density of PBs,the smaller the RF power required,and the EE is also higher.
文摘Purpose: To develop a new statistical index “percent CTV (clinical target vo-lume) coverage probability” (%CCP), defined as the probability that a specific percent (e.g., 95%) of the CTV can be reliably covered by the prescription dose, for evaluating the coverage loss of brain (fractionated) stereotactic radiosurgery (SRS/fSRS) when the PTV (planning target volume) margin is zero. Methods: The random variable Q for CTV percent coverage was derived using a previously developed model for CTV random motion that follows a three-dimensional (3D) independent normal distribution with a zero mean and a standard deviation of 𝜎<sub>𝑆</sub>(for translation) or 𝜎<sub>𝛿</sub>(for rotation). Assuming both CTV and PTV are spherical with the same diameter d<sub>CTV</sub>, the cumulative distribution function of Q could be obtained analytically using the relation of sphere-sphere intersection. The %CCP was then derived as the reliability function of Q and was used to quantify the coverage loss for selected d<sub>CTV</sub>. Results: The 95%-95% clinical goal (95% of the times, at least 95% of the CTV is covered) is not achievable with d<sub>CTV</sub> mm. For common CTVs (d<sub>CTV</sub> mm) encountered in SRS/fSRS, only 60%-90% of the CTV could be reliably covered by the prescription dose 95% of the time. For 𝜎𝑆</sub></sub>=0.5mm and 𝜎𝛿</sub></sub> =0.4˚, the 95% CCP was the highest when the distance between the CTV and the isocenter 𝑑𝐼⇔𝑇</sub><sub></sub>=0 and gradually decreased with the increasing 𝑑<sub>𝐼⇔𝑇</sub></sub>. Conclusions: The %CCP was successfully derived for evaluating the CTV coverage loss for brain SRS/fSRS. When the PTV margin is zero, the 95%-95% clinical goal cannot be achieved for most targets (d<sub>CTV</sub> mm).
基金partly supported by the National Natural Science Foundation of China(Grant No.61871241,No.61701221)the Natural Science Foundation of Jiangsu Province(No.BK20160781)+1 种基金Nantong Science and Technology Project(No.JC2018127,No.JC2019117)the Research Innovation Project for College Graduates of Jiangsu Province(No.KYLX16_0662)。
文摘The Poisson point process(PPP) has been widely used in wireless network modeling and performance analysis due to the independence between its nodes. Therefore, it may not be a suitable model for many of the exclusive networks between the nodes. This paper analyzes the energy efficiency(EE) and optimizes the two-tier heterogeneous cellular networks(Het Nets). Considering the mutual exclusion between macro base stations(MBSs) distribution, the deployment of MBSs is modeled by the Matérn hard-core point process(MHCPP), and the deployment of pico base stations(PBSs) is modeled by the PPP. We adopt a simple approximation method to study the signal to interference ratio(SIR) distribution in two-tier MHCPP-PPP networks and then derive the coverage probabilities, the average data rates and the energy efficiency of Het Nets. Finally, an optimization algorithm is proposed to improve the EE of Het Nets by controlling the transmit power of PBSs. The simulation results show that the EE of a system can be effectively improved by selecting the appropriate transmit power for the PBSs. In addition, two-tier MHCPP-PPP Het Nets have higher energy efficiency than two-tier PPP-PPP Het Nets.
基金supported by the National Natural Science Foundation of China under Grant No.61231009the National High-tech Research and Development Program of China under Grant No.2014AA01A701the Program for New Century Excellent Talents in University of Ministry of Education of China under Grant No.NCET 12-0795
文摘Motivated by the objective of pursuing revenue, improvement in coverage and reduction in energy cost for wireless communication networks have been of great significance for mobile operators. Therefore, heterogeneous cellular networks(HCNs) and Coordinated Multipoint(Co MP) transmission are considered as promising solutions to enhance the performances of wireless communication systems. This paper analyzed the K-tier HCNs with a dynamic downlink Co MP scheme, in which the flexible clusters of cooperative stations are determined by a connecting threshold θ. Using stochastic geometry, the coverage probability(CP) and energy efficiency(EE) of a K-tier HCN operating under this scheme are derived, based on which the trade-off between CP and EE is discovered and discussed. Simulation results show the validity of our derivations. The proposed schememay significantly reduce energy consumption sacrificing a small amount of CP, and outperforms the fixed scheme as well. The CP-EE trade-off are also revealed, whichsuggests suitable trade-off points between CP and EE that will deliver the maximum economic profitability. Tendencies discovered in this paper may provide the operators with opportunities for further optimization in pursuit of economic profitability.
基金supported in part by National High-tech R&D Program(863 Program) under Grant No.2014AA01A701National Natural Science Foundation of China under Grant No.61379006,61401510,61521003Project funded by China Postdoctoral Science Foundation under Grant No.2016M592990
文摘This study investigates physical layer security in downlink multipleinput multiple-output(MIMO) multi-hop heterogeneous cellular networks(MHCNs),in which communication between mobile users and base stations(BSs) is established by a single or multiple hops,to address the problem of insufficient security performance of MIMO heterogeneous cellular networks.First,two-dimensional homogeneous Poisson point processes(HPPPs) are utilized to model the locations of K-tier BSs in MIMO MHCNs and receivers,including those of legitimate users and eavesdroppers.Second,based on the channel gain distribution and the statistics property of HPPP,the achievable ergodic rates of the main and eavesdropper channels in direct and ad hoc links are derived,respectively.Third,the secrecy coverage probability and the achievable ergodic secrecy throughput of downlink MIMO MHCNs are explored,and their expressions are derived.Lastly,the correctness of the theoretical derivation is verified through Monte Carlo simulations.
文摘In this paper, we consider the construction of the approximate profile-</span><span style="font-family:""> </span><span style="font-family:Verdana;">likelihood confidence intervals for parameters of the 2-parameter Weibull distribution based on small type-2 censored samples. In previous research works, the traditional Wald method has been used to construct approximate confidence intervals for the 2-parameter Weibull distribution</span><span style="font-family:""> </span><span style="font-family:Verdana;">under type-2 censoring scheme. However, the Wald technique is based on normality assumption and thus may not produce accurate interval estimates for small samples. The profile-likelihood and Wald confidence intervals are constructed for the shape and scale parameters of the 2-parameter Weibull distribution based on simulated and real type-2 censored data, and are hence compared using confidence length and coverage probability.
文摘This paper presents four methods of constructing the confidence interval for the proportion <i><span style="font-family:Verdana;">p</span></i><span style="font-family:;" "=""><span style="font-family:Verdana;"> of the binomial distribution. Evidence in the literature indicates the standard Wald confidence interval for the binomial proportion is inaccurate, especially for extreme values of </span><i><span style="font-family:Verdana;">p</span></i><span style="font-family:Verdana;">. Even for moderately large sample sizes, the coverage probabilities of the Wald confidence interval prove to be erratic for extreme values of </span><i><span style="font-family:Verdana;">p</span></i><span style="font-family:Verdana;">. Three alternative confidence intervals, namely, Wilson confidence interval, Clopper-Pearson interval, and likelihood interval</span></span><span style="font-family:Verdana;">,</span><span style="font-family:Verdana;"> are compared to the Wald confidence interval on the basis of coverage probability and expected length by means of simulation.</span>
基金supported in part by the National Natural Science Foundation of China (Grant 61501045)in part by State Major Science and Technology Special Projects (Grant 2016ZX03001017-004)
文摘Cloud computing.based heterogeneous networks(C.Het Nets) have been considered as promising network architecture of future wireless communication systems. However, its performance is constrained by the capability of fronthaul. To study the performance limit of C.Het Nets, the coverage performance of the open access strategy in C.Het Nets is analyzed in this paper. In particular, the non.ideal condition of fronthaul in C.Het Nets is characterized by establishing a stochastic geometry.based model, and a tight lower bound on coverage probability is derived for downlink transmissions. Based on the derived results, the constraint of the fronthaul is given to ensure that open access strategy can achieve the best coverage performance. Finally, the simulation results are provided to verify the theoretical results and show the impact of fronthaul constrains.
基金partly supported by the National Natural Science Foundation of China (Grant No. 61371112, No.61701221 )the Jiangsu Natural Science Foundation (No. BK20160781)+2 种基金Jiangsu Higher Education Institutions Natural Science Foundation (No. 16KJB510013, 16KJB510038)the Research Innovation Project for College Graduates of Jiangsu Province (No. KYLX16_0662)the Natural Science Foundation of Nantong University Xinglin College (No. 2016K116)
文摘Energy efficiency(EE) of cellular networks has attracted considerable attention recently. However, EE of relay-assisted cellular networks where the macro base stations(MBSs) are equipped with the multi-antenna has not been thoroughly addressed. This paper considered the downlink transmission of multi-antenna relay-assisted cellular networks, meanwhile, a strategic sleep scheme was used in relay stations(RSs), which dynamically adjusted the RS working mode according to whether the number of users serviced by the relay exceeds a given threshold. A geometric model was built to derive the coverage probability and mean achievable rate from the MBSs to user(UE), the MBS to RS, the RS to UE links and analyze the system EE. It is shown that the energy efficiency of cellular network with strategic sleep RS is slightly higher than that of cellular network with non-sleeping strategy. Furthermore, the MBS equipped with multi-antenna has better impact on energy efficiency and spectral efficiency than the MBS with single antenna.
文摘This article deals with correlating two variables that have values that fall below the known limit of detection (LOD) of the measuring device;these values are known as non-detects (NDs). We use simulation to compare several methods for estimating the association between two such variables. The most commonly used method, simple substitution, consists of replacing each ND with some representative value such as LOD/2. Spearman’s correlation, in which all NDs are assumed to be tied at some value just smaller than the LOD, is also used. We evaluate each method under several scenarios, including small to moderate sample size, moderate to large censoring proportions, extr</span><span style="font-family:Verdana;">eme imbalance in censoring proportions, and non-bivariate nor</span><span style="font-family:Verdana;">mal (BVN) data. In this article, we focus on the coverage probability of 95% confidence intervals obtained using each method. Confidence intervals using a maximum likelihood approach based on the assumption of BVN data have acceptable performance under most scenarios, even with non-BVN data. Intervals based on Spearman’s coefficient also perform well under many conditions. The methods are illustrated using real data taken from the biomarker literature.
基金supported by the King Saud University,Deanship of Scientific Research and College of Science Research Center
文摘This article deals with the case of the failure-censored constant-stress partially accelerated life test （CSPALT） for highly reliable materials or products assuming the Pareto distribution of the second kind. The maximum likelihood （ML） method is used to estimate the parameters of the CSPALT model. The performance of ML estimators is investigated via their mean square error. Also, the average confidence interval length （IL） and the associated co- verage probability （CP） are obtained. Moreover, optimum CSPALT plans that determine the optimal proportion of the test units al- located to each stress are developed. Such optimum test plans minimize the generalized asymptotic variance （GAV） of the ML estimators of the model parameters. For illustration, Monte Carlo simulation studies are given and a real life example is provided.
文摘THE 19th National Congress of the Communist Party of China（CPC）attracted global attention with1,818 journalists from abroad to cover the event in Beijing on October 18-24,more coverage than for the18th CPC National Congress.Most of them have been based in China or visited China on several occasions.They have witnessed the changes of Chinese people＇s life in the past five years.
文摘Device-to-device(D2D)communication underlay cellular networks offers several benefits,including offloading cellular traffic and improving throughput.In this paper,a scheme is proposed for D2D communication underlay cellular networks,by taking resource allocation algorithm into account.Firstly,a scenario where cellular users(CUs)and D2D users(DUs)coexist is considered.To characterize the clustering feature of DUs,the locations of CUs and DUs are modeled as Poisson cluster processes(PCPs),and the locations of base stations(BSs)are modeled as a Poisson point process(PPP).Subsequently,a resource allocation algorithm is proposed to allocate resources for CUs to DUs in the cluster,which involves the optimization of matching between D2D user and cellular user.Finally,the coverage probability of the clustering network is analyzed.The simulation results indicate that the proposed scheme can effectively enhance system capacity and reveal the effects of various parameters on system performance.
文摘Accurate estimation of disease prevalence is crucial for effective public health intervention and resource allocation.Generating data by individual testing methods is often impractical and expensive for large populations,particularly when disease prevalence is low.Pool testing involves combining samples from multiple individuals into a pool and performing a single test,and offers a costeffective and efficient alternative.In pool testing strategy with retesting,if a pool tests negative,it is classified as non-defective,whereas if it is positive,then a retest is needed.The retesting strategy mitigates the effects of initial test errors,thereby enhancing the accuracy of the estimation of the prevalence rate.Evidence in the literature indicates that the traditional Wald method has been used to construct approximate confidence intervals for the prevalence rate.However,this interval estimation method is based on the normality ap-proximation and hence may not be accurate when the true prevalence rate is close to zero.In this paper,we propose a Bayesian interval estimation ap-proach which is not affected by extreme values of the prevalence rate and al-lows for incorporating prior information about the prevalence rate.We as-sumed that the prior distribution for the unknown prevalence rate p is a Beta distribution with parameters α_(0) and β_(0) and based on pool testing outcomes for the n pools each of size k,100(1-α)% credible intervals were constructed from the resulting posterior distribution.Simulation studies were carried out to compare the efficiencies of the Bayesian and Wald interval estimation methods for various values of p.
文摘Low-earth orbit(LEO)satellite networks ignite global wireless connectivity.However,signal outages and co-channel interference limit the coverage in traditional LEO satellite networks where a user is served by a single satellite.This paper explores the possibility of satellite cooperation in the downlink transmissions.Using tools from stochastic geometry,we model and analyze the downlink coverage of a typical user with satellite cooperation under Nakagami fading channels.Moreover,we derive the joint distance distribution of cooperative LEO satellites to the typical user.Our model incorporates fading channels,cooperation among several satellites,satellites'density and altitude,and co-channel interference.Extensive Monte Carlo simulations are performed to validate analytical results.Simulation and numerical results suggest that coverage with LEO satellites cooperation considerably exceeds coverage without cooperation.Moreover,there are optimal satellite density and satellite altitude that maximize the coverage probability,which gives valuable network design insights.
基金supported by National Natural Science Foundation of China (61302081)the National Hi-Tech Research and Development Program of China (2014AA01A701)
文摘Caching popular content in the storage of small cells is deemed as an efficient way to decrease latency, offload backhaul and satisfy user＇s demands. In order to investigate the performance of cache-enabled small cell networks, coverage probability is studied in both single-point transmission and cooperative multipoint（Co MP） transmission scenarios. Meanwhile, the caching distribution modeled as Zipf and uniform distribution are both considered. Assuming that small base stations（SBSs） are distributed as a homogeneous Poisson point process（HPPP）, the closed-form expressions of coverage probability are derived in different transmission cases. Simulation results show that Co MP transmission achieves a higher coverage probability than that of single-point transmission. Furthermore, Zipf distribution-based caching is more preferable than uniform distribution-based caching in terms of coverage probability.
基金supported by the National Natural Science Foundation of China(Nos.61231011,61231013,and 61571025).
文摘Millimeter wave(mm-wave)communication is widely considered to be a promising technique for 5G(Fifth Generation)cellular systems.Owing to the high path loss of mm-wave channels,5G networks could employ a heterogeneous structure that consists of an MBS(Macro Base Station)and numerous SBSs(Small Base Stations).In this paper,we analyze the coverage and rate performance of an mm-wave heterogeneous network.Using user beam selection,we derive analytical expressions for the coverage probabilities of the SBSs and MBS.Furthermore,the average achievable rate for a typical user is also investigated.It is shown that the analytical results closely follow those of the simulations with marginal differences.
