Digital compass for multi-user beam access in mmWave cellular networks

Beamforming in stand-alone Millimeter-Wave(mmWave)communications results in prolonged access times and latencies due to the increased number of measurements required to determine the optimal beam directions at the Mobile Station(MS)and Base Station(BS),returning the highest received signal level.Therefore,dynamic and fast access schemes that meet the Third-Generation Partnership Project(3GPP)specifications are required here.Therefore,in this paper,a novel initial access scheme is proposed for multiple MS users by leveraging for the first time a digital compass in the access procedure.Namely,when a new MS joins the footprint of a BS,it probes the channel for beacon signaling about the BS direction,i.e.,broadcasted by a neighboring MS that completed beam association at previous time steps.Then,a digital compass is utilized to adjust the coordinates of the BS according to the location of the new MS.The proposed scheme is applied for a single and multi-user settings at various broadcasting approaches.This includes a single associated MS user that broadcasts information to a single incoming MS user,a single user that broadcasts signals to multiple incoming users,or all multiple associated users broadcast to multiple incoming users.Overall,the proposed schemes yield in notable efficiency in terms of the computational complexity,access times,power and energy consumption as compared to existing access schemes.Further,high success rates are achieved at the detriment of relatively higher cost.

Analysis and Simulation for Capacity of Time Division-Synchronous Code Division Multiple Access System

Capcity both in uplink and downlink of TD-SCDMA (time division-synchronous code division multiple access) system is studied in a multi-cell environment. The theoretical expressions of the mean of intercell interference in uplink and the mean of sum of power allocation in downlink are given, by which uplink and downlink capacity is analyzed. Furthermore, we give the simulation models for both uplink and downlink capacity. The results from theoretical analysis and simulation fit very well. In the end, the maximum number of users that TD-SCDMA system can serve for 12.2 k speech service is given.

Implementing Discretionary Access Control with Time Character in Linux and Performance Analysis

DAC （Discretionary Access Control Policy） is access control based on ownership relations between subject and object, the subject can discretionarily decide on that who, by what methods, can access his owns object. In this paper, the system time is looked as a basic secure element. The DAC_T （Discretionary Access Control Policy with Time Character） is presented and formalized. The DAC_T resolves that the subject can discretionarily decide that who, on when, can access his owns objects. And then the DAC_T is implemented on Linux based on GFAC （General Framework for Access Control）, and the algorithm is put forward. Finally, the performance analysis for the DAC T Linux is carried out. It is proved that the DAC T Linux not only can realize time constraints between subject and object but also can still be accepted by us though its performance have been decreased.

A 65-nm 1-Gb NOR floating-gate flash memory with less than 50-ns access time

This paper presents a 65-nm 1-Gb NOR-type floating-gate flash memory,in which the cell device and chip circuit are developed and optimized.In order to solve the speed problem of giga-level NOR flash in the deep submicron process,the models of long bit-line and word-line are first given,by which the capacitive and resistive loads could be estimated.Based on that,the read path and key modules are optimized to enhance the chip access property and reliability.With the measurement results,the flash memory cell presents good endurance and retention properties,and the macro is operated with 1-ls/byte program speed and less than 50-ns read time under 3.3 V supply.

Accessibility Comparison and Spatial Differentiation of Xi’an Scenic Spots with Different Modes Based on Baidu Real-time Travel

A study of the accessibility of a city’s scenic spots via different travel modes can contribute to optimization of tourism-related transportation while improving tourists’ travel-related satisfaction levels and advancing tourism. We systematically analyzed the accessibility of 56 scenic spots in Xi’an City, China, via car and public transport travel modes using the real-time travel function of the Baidu Maps API(Application Programming Interface) along with spatial analysis methods and the modal accessibility gap index of scenic spots. We obtained the following results. First, maximum and minimum travel times using public transport exceeded those using cars. Moreover, the accessibility of scenic spots via cars and public transport presented a circular spatial pattern of increasing travel time from the center to the periphery. Contrasting with travel by public transport, car travel showed a clear time-space compression effect. Second, accessibility of the scenic spots via cars and public transport showed some spatial heterogeneity, with no clear advantages of car accessibility in the central urban area. However, advantages of car accessibility were increasingly evident moving from the center to the periphery. Third, whereas the correlation of the modal accessibility gap index of scenic spots in Xi’an with global space was significantly positive, local spatial interdependence was only evident in some inner city areas and in marginal areas. Moreover, spatial heterogeneity was evident in two regions but was insignificant in other areas, indicating that the spatial interdependence of the modal accessibility gap index in most scenic spots was not apparent in terms of the overall effect of public transport routes, road networks, and the distribution of scenic spots. The improvement of public transport coverage in marginal areas and the optimization of public transport routes in central urban areas are essential tasks for improving travel using public transport in the future.

User-Based Discrete-Time Queuing Analysis for Opportunistic Spectrum Access in Cognitive Radio Networks

In cognitive radio networks, the spectrum utilization can be improved by cognitive users opportunistically using the idle channels licensed to the primary users. However, the new arrived cognitive users may not be able to use the channel immediately since the channel usage state is random. This will impose additional time delay for the cognitive users. Excessive waiting delay can make cognitive users miss the spectrum access chances. In this paper, a discrete-time Markov queuing model from a macro point of view is provided. Through the matrix-geometric solution theory, the average sojourn time for cognitive users in the steady state before accessing the spectrum is obtained. Given the tolerant delay of cognitive users, the macro-based throughput is derived and an access control mechanism is proposed. The numerical results show the effects of service completion probability on average sojourn time and throughput. It is confirmed that the throughput can be obviously improved by using the proposed access control mechanism. Finally, the performance evaluations based on users are compared to that based on data packets.

A passive optical network based on optical code division multiplexing and time division multiple access technology

A passive optical network （PON） scheme based on optical code division multiplexing （OCDM） for the downstream traffics is proposed and analyzed in detail. In the PON, the downstream traffics are broadcasted by OCDM technology to guarantee the security, while the upstream traffics pass through the same optical fiber by the common time division multiple access （TDMA） technology to decrease the cost. This schemes are denoted as OCDM/TDMA-PON, which can be applied to an optical access network （OAN） with full services on demand, such as Internet protocol, video on demand, tele-presence and high quality audio. The proposed OCDM/TDMA-PON scheme combines advantages of PON, TDMA, and OCDM technology. Simulation results indicate that the designed scheme improves the OAN performance, and enhances flexibility and scalability of the system.

Hybrid Deep Learning-Based Adaptive Multiple Access Schemes Underwater Wireless Networks

Achieving sound communication systems in Under Water Acoustic(UWA)environment remains challenging for researchers.The communication scheme is complex since these acoustic channels exhibit uneven characteristics such as long propagation delay and irregular Doppler shifts.The development of machine and deep learning algorithms has reduced the burden of achieving reli-able and good communication schemes in the underwater acoustic environment.This paper proposes a novel intelligent selection method between the different modulation schemes such as Code Division Multiple Access(CDMA),Time Divi-sion Multiple Access(TDMA),and Orthogonal Frequency Division Multiplexing(OFDM)techniques using the hybrid combination of the convolutional neural net-works(CNN)and ensemble single feedforward layers(SFL).The convolutional neural networks are used for channel feature extraction,and boosted ensembled feedforward layers are used for modulation selection based on the CNN outputs.The extensive experimentation is carried out and compared with other hybrid learning models and conventional methods.Simulation results demonstrate that the performance of the proposed hybrid learning model has achieved nearly 98%accuracy and a 30%increase in BER performance which outperformed the other learning models in achieving the communication schemes under dynamic underwater environments.

Role of Time-Domain Based Access Control Model

While Role-Based Access Control Model (RBAC) is being analyzed, the concept of Role of Time-domain Based Access Control Model (T-RBAC) is put forward. With time-domain added, both time-domain and authority control roles. The basic idea of T-RBAC is introduced and described formally, and the safely of this model is analyzed. The research shows that T-RBAC fulfills both rules of information security, which are principle of least privilege and separation of duties. With practical application of T-RBCA, it can handle most of the time-related or authority-related problems. What’s more, it also increases the security level, flexibility and dynamic adaptation of the system and has lower complexity than system only handled by authority. This model also can solve conflicts caused by authority.

考虑综合经济性的风光配电网储能优化配置

在配电网中配置储能系统可以有效缓解风光接入对配电网产生的影响,提升对风光的消纳能力、减少电压偏差等,而储能接入的位置和容量不同会对配电网产生不同的影响。首先分析储能建设过程中的主要费用,考虑基于分时电价下的网损成本和峰谷差收益,以年综合成本、配电网的日节点电压偏差和最小为目标,建立配电网储能选址定容模型,采用改进多目标遗传二代算法(improved multi-objective nondominated sorting genetic Ⅱ algorithm, INSGA-Ⅱ)对模型进行求解,利用改进理想点决策法(improved ideal point based decision, IIPBD)来选取最优配置方案,最后在IEEE-33节点模型中对方案进行验证。仿真结果表明:使用INSGA-Ⅱ算法进行求解时最终决策出的储能配置方案实现了成本最小,并且显著提升了电压的稳定性,验证了改进后算法的优良性和所提出的储能优化配置方案的有效性。

心临其境——“云旅游”中临场感对旅游意愿的影响研究

“云旅游”是一个受众广、效果佳的营销渠道,“心临其境”的临场感对旅游意愿具有重要的影响。基于S-O-R(Stimuli-Organism-Response,S-O-R)模型,引入临场感理论,探究临场感对旅游意愿的作用,并将感知收益作为中介变量,上网时长作为调节变量,研究临场感对旅游意愿的影响路径。文章依据375份调查问卷,采用结构方程模型进行实证研究,研究发现:临场感间接影响旅游意愿,社会临场感对旅游意愿的影响大于物理临场感;临场感对感知收益具有显著正向影响,感知收益在临场感对旅游意愿的影响中发挥完全中介作用;上网时长在临场感对旅游意愿的影响中发挥负向调节作用,即上网时长越长,临场感对旅游意愿的影响越弱。将临场感引入“云旅游”情景中,解释了“云旅游”过程中旅游意愿形成的具体过程,为旅游目的地设计“云旅游”产品提供理论依据与实践指导。

太阳同步轨道遥感卫星快速目标访问计算方法

目标访问计算是指根据遥感卫星轨道和待观测目标的位置,计算遥感卫星对目标观测的时刻和姿态,是遥感卫星任务管控领域的重要基础技术之一。高效的目标访问计算方法可大幅提升卫星任务管控的时效性,对后续大规模遥感星座任务管控具有重要意义。利用太阳同步轨道卫星交点地方时不变的特点,快速估算出卫星经过目标的较短时间窗口,对时间窗口内的星历进行逐点计算,获取卫星对目标进行访问的最佳时刻。试验结果证明,该方法可大幅提升目标访问时间的计算效率。

城市中心区轨道交通站点步行接驳路径特征及优化

轨道交通站点步行接驳路径特征研究,对提升轨道交通承担率具有重要意义。基于百度时空大数据API,运用空间分析法、情景模拟法、视觉语义分割法,以天津市营口道站点为例,构建城市中心区轨道交通站点步行接驳路径特征分析方法,挖掘步行接驳路径特征并揭示成因,提出针对性的优化对策。研究表明,目标站点步行接驳效率南部高于北部,具体表现在路段重复率分布均匀度南部大于北部,差异路径分布数量北部多于南部,超过3/4路径的非直线系数偏高;除站点周边区域外,接驳路径品质西北部优于东南部,具体表现在西北部视觉出行环境建设最优,区域整体设施服务水平良好。根据步行接驳路径特征,提出路网结构调整、道路断面优化、出入口调整、绿化品质提升的优化对策。

基于流量感知的无线接入网智能切片资源分配方法研究

为保障业务服务等级协议(Service Level Agreements, SLA)需求,使不同应用间差异化的服务质量需求同时得到良好满足,无线接入网(Radio Access Network, RAN)的动态网络资源配置十分关键。本文针对网络流量波动、网络状态快速变化的场景,提出一种结合时间序列预测和深度强化学习的智能化带宽分配策略,通过合理利用长短期记忆(Long Short-Term Memory, LSTM)网络和Dueling深度Q网络(Dueling Deep Q Network, Dueling DQN)以最大限度提高无线接入网切片的频谱效率和SLA满意度。通过使用LSTM网络对切片中数据流量进行预测,可以将深度强化学习算法的计算周期与实际切片配置周期有效解耦。同时为了在保障LSTM性能的同时降低其计算复杂度,以适应RAN中有限的计算资源,本文采用控制神经元连接比例的随机连接长短期记忆(Randomly Connected LSTM, RCLSTM)网络。此外,Dueling DQN与传统DQN相比,能够提高切片策略学习过程的Q值估计精度,以提升收敛速度。仿真结果表明:与原始DQN、优势Actor-Critic(Advantage Actor Critic, A2C)和硬切片方法相比,所提RCLSTM-Dueling DQN方案可以通过提前感知网络性能变化,有效降低网络环境波动对密集流量场景下无线切片资源管理的影响,在具有三种不同流量波动模式及服务质量需求的RAN切片场景中,可以获得收敛速度、频谱效率和切片SLA满意率的明显提升。同时,10%连接比例的RCLSTM网络能在保持极低性能损失的前提下,将原始LSTM的计算时间降低约11%。

一种可见光网络的入网与网络维护设计

为了简单有效地提升室内可见光网络有限带宽资源分配性能,设计了一种基于时分多址(TDMA)机制的入网与网络维护方法,详细描述了用户竞争入网流程和网络维护机制。通过设计具体的帧结构,分析了用户入网概率。实验结果表明:提入网与网络维护方法能够支持多个移动用户的灵活接入和资源动态分配,5个终端全部接入所需的总时间仅为25 ms,该方法工程实现简单,能有效提升资源利用率。

多基站无线非正交多址接入的平滑视频流传输算法

视频服务需求的快速增长对于视频流畅播放提出了巨大挑战,从用户体验角度分析,视频播放中的卡顿时间可能是最重要指标之一。随着5G网络技术的发展,非正交多址接入(NOMA)技术被重点关注,NOMA技术具有叠加编码和连续干扰消除2个特点,根据这2个特点实现数据的并行传输。利用NOMA技术的并行传输能力来提高基站为用户提供视频的实时性。在用户需求视频名称和视频分辨率给定的情况下,通过联合基站-用户配对方式和基站功率分配来降低视频播放时的卡顿时间。通过对问题进行建模,并提出1个两步启发式算法对问题进行求解,第1步为确定基站与用户的配对方式,第2步为分配基站的发射功率。实验结果表明,基于NOMA的传输调度方案与传统的传输调度方案相比,用户需求的平均卡顿时间有明显的下降,相对于在不采用NOMA机制时,在2-SIC接收机情况下,用户平均卡顿时间减少了55.56%。

含网关节点的高时隙复用率TDMA协议

针对网络收敛慢、拓扑表不完整时导致的信道冲突以及空闲时隙浪费问题,提出一种提高节点时隙利用率和网络可靠性的多跳时分多址接入协议。该协议提出3种新机制,使用时隙请求时期快速收敛机制,加快时隙请求时期的收敛;使用空闲时隙公平重用机制,消除中心节点调度时隙碰撞问题,提高空闲时隙利用率;使用一跳邻居多层次调度机制,降低数据重传的时延。仿真结果表明,在时隙请求时期收敛时间、数据传输平均时延及数据传输成功率方面,该协议较现有协议性能更优。

非正交多址光通信系统信道均衡的虚拟时反方法

室内非正交多址(non-orthogonal multiple access, NOMA)可见光通信系统(visible light communications, VLC)可实现高速率多用户通信,但多径效应会造成通信可靠性及用户公平性明显下降,为此,提出一种虚拟时间反转技术(virtual time reversal mirror, VTRM)对NOMA-VLC进行信道均衡,消除多径效应对通信过程的影响。分析了多用户场景下室内NOMA-VLC系统模型及其通信光链路的特性,依据光链路增益的稀疏特性采用稀疏度自适应匹配追踪(sparsity adaptive matching pursuit,SAMP)算法,估计NOMA-VLC系统的信道冲激响应(channel impulse response, CIR)。在此基础上,采用VTRM方法对NOMA-VLC进行信道均衡,通过VTRM的时空聚焦特性减少信道衰落影响,并重构接收信号,抑制多径效应。理论分析和实验结果表明:经论文算法均衡后的NOMAVLC系统,在满足前向纠错(forward error correction,FEC)误码率阈值的同时,用户1性能提高了4.4 dB,用户2性能提高了5.7 dB,两用户平均性能提高了5.05 dB,用户间性能差异由1.6 dB降为0.5 dB,为NOMA-VLC信道均衡提供了有效的解决方案。

宽带跳频TDMA辐射源网群的定位及网群划分方法

为了解决现有方法难以对宽带跳频时分多址(frequency hopping-time division multiple access,FH-TDMA)辐射源网群定位的问题,提出一种仅利用波达方向(direction of arrival,DOA)信息的多站定位及网群划分方法。首先通过模拟滤波对各站接收到的信号进行频段划分,通过基于多相滤波的数字信道化方法把信号输出到多个信道中;然后通过直接定位(direct position determination,DPD)算法计算得出各时隙辐射源的位置;最后先通过不同参数的基于密度的噪声应用空间聚类(density-based spatial clustering of applications with noise,DBSCAN)算法选择出最佳的辐射源定位结果,再根据提出的基于先验信息的改进K-means聚类算法进行网群划分。所提方法实现了采样率和信号处理速率的降低,且无需站间严格的时间同步。结果表明,所提方法有效估计出了辐射源的数量、位置,以及网群划分情况。

基于改进浮动单元的城市职住平衡时间尺度估计——以广州市为例

已有研究对城市职住平衡的测度往往存在可塑性面积单元问题,且忽略了交通网络在职住联系中的媒介作用。提出一种改进的浮动单元法,构建基于道路和城市轨道交通网络的数据集,以时间为职住分析尺度生成浮动单元,运用手机信令数据对职住平衡进行测度。以广州市为例,对就业中心和居住区的职住平衡时间尺度进行估计。研究发现:广州市中心城区职住平衡时间尺度分布呈圈层式空间特征,职住平衡时间尺度从一级就业中心向外围先减小再增大;城市轨道交通缩小了就业中心的职住平衡时间尺度;一级、二级(不处于一级就业中心的辐射范围内)和三级就业中心的职住平衡时间尺度分别为32~40 min、14~28 min和10~20 min,而居住组团的职住平衡时间尺度主要依附于就业中心且受到城市轨道交通的影响。最后,提出在合适的时间尺度下对职住空间结构进行评估和优化住房和就业等资源配置,并重视城市轨道交通对职住空间结构的影响。