LTE TDD系统随机接入过程研究

随机接入技术是移动通信系统中UE与网络建立连接,进行通信的首要步骤,设计一种快速有效的随机接入过程将对系统的性能具有重要的意义。首先对LTE系统随机接入技术的进展情况进行了介绍,然后重点介绍一种基于LCR TDD帧结构的随机接入过程,给出接入流程。最后对碰撞概率进行定量分析。     

卫星终端小区重选策略设计及优化

小区重选能够保证为卫星终端提供不间断的服务。为了能更节能、更高效地完成小区重选,分别对卫星终端正常模式及低功耗模式下的小区重选进行了设计。小区重选过程中,为了使终端在切换频点后能够正常接收信道数据,分别提出了频率校正信道（Frequency Correction Channel,FCCH）同步和帧及时隙同步两种方法,并在低功耗场景中对这两种同步方法进行优化。经过实测功耗数据,优化后的方法实现过程功耗更低、效率更高;经过JY5000软件仿真后,设计的小区重选方案满足协议一致性。     

一种解决TSP的改进遗传算法

旅行推销员问题TSP(Traveling Salesman Problem)问题是组合优化中的经典NP难题,一些典型的遗传算法(GA)在求解TSP问题时的性能并不理想.提出基于"最小邻域接入法"CBMC(Connecting Based on Minimum Circle)思想的改进的遗传算法,并在算法中增加一些控制策略,与其他算法相比,获得了更好的性能和收敛速度.通过用中国33个省会的TSP问题对提出算法进行实验验证,结果证明了改进后的算法在收敛速度和收敛到最优解的概率都优于其他遗传算法.     

自由接入信道中带优先级的二叉树分裂算法及其仿真

提出了一种带优先级的二叉树分裂算法,使得高优先级的分组能以更大的概率接入信道,且不会出现分组的拥塞现象。分析了算法中影响优先级分组划分及传输效率的因素。通过计算机仿真实验,在双优先级条件下,改变到达率、初始接入概率、优先级的比重和重发概率时,对阻塞式接入和自由式接入信道系统的时延和吞吐率进行了分析。结果表明,算法具有较好的有效性和可靠性。     

基于能量效率的认知无线网络联合优化算法

为提高认知无线网络能量有效性,提出一种基于能量效率的联合优化算法。在考虑主用户干扰容限的基础上构建了能量有效性模型,将优化目标分解为接入策略求解和功率优化问题,采用粒子群算法反复迭代,得到接入概率与功率分配的联合最优解。仿真结果表明,相对于不考虑功率优化或接入概率的传统优化方法,所提算法可使系统能量效率得到显著提升。     

FTTX和WLAN接入比较分析

随着城市的发展,城市城区内每年建设有大最的居民生活小区和中高档写字楼,采取何种技术方式有效地为该类区域的用户提供语音及宽带服务,一直是困扰运营商的难题之一。本文分场景对采用FTTX接入和WLAN接入时该类区域如何进行通信服务进行了较为详细的对比分析,并提出服务该类区域的优选技术方案。     

OFDMA系统中的多业务接入控制算法

提出一种针对分析正交频分多址接入(OFDMA)系统的改进多业务接入控制算法。OFDMA系统为用户提供一定数量的子载波进行传输,通过压缩原信道带宽或传输速率,降低原信道上的业务服务质量,从而提高小区内可使用的信道数量。仿真结果表明,与传统信道预留算法相比,该算法可提高信道资源利用率,降低目标小区的切换呼叫阻塞率和新呼叫阻塞率。     

基于TD-SCDMA系统的单基站定位算法

TD-SCDMA系统采用智能天线技术使基站(Node B)能够很方便地获得移动终端(UE)的到达角度估计,即AOA(Angle Of Arrival)。同时UE在建立上行同步和进行小区切换时,Node B可以通过UE提交的测量信息计算出Node B到UE的距离。在已知UE到Node B的距离和方向后,只需一个Node B就可以对UE进行定位。     

认知无线电中基于多址接入信道的多用户联合频谱感知算法

针对多用户联合感知场景问题,考虑次用户至决策中心之间有损信道的情况,提出了基于多址接入信道（MAC）的联合频谱感知算法。在系统结构和数学建模基础上,分析了传统MAC算法渐近性、中断概率等性能。在次用户平均发射功率约束下,以最大化检测概率为目标,对基于MAC算法中的发射增益进行优化;并考虑了一定服务质量情况下最小化次用户数目的问题。仿真结果表明,MAC算法能够保证良好的检测性能,以决策中心错误概率为例,提出的优化算法取得了指数级的性能提升。     

基子TD-SCDMA系统的单基站定位算法

TD-SCDMA系统采用智能天线技术使基站(Node B)能够很方便地获得移动终端(UE)的到达角度估计,即AOA(Angle Of Arrival).同时UE在建立上行同步和进行小区切换时,Node B可以通过UE提交的测量信息计算出Node B到UE的距离.在已知UE到Node B的距离和方向后,只需一个Node B就可以对UE进行定位.     

Efficient cooperative access class barring with load balancing and traffic adaptive radio resource management for M2M communications over LTE-A

We propose two efficient cooperative access class barring with load balancing (CACB-LB) and traffic adaptive radio resource management (TARRM) schemes for M2M communications over LTE-A. The proposed CACB-LB uses the percentage of the number of Machine-Type Communication (MTC) devices that can only access one eNB between two adjacent eNBs as a criterion to allocate those MTC devices that are located in the overlapped coverage area to each eNB. Note that an eNB is a base station of LTE-A. In this way, the proposed CACB-LB can achieve better load balancing among eNBs than CACB, which is the best available related work. The proposed CACB-LB also uses the ratio of the channel quality indication that an MTC device received from an eNB over the number of MTC devices that attach to the eNB as a criterion to adjust the estimated number of MTC devices that may access the eNB. As a result, the proposed CACB-LB can have a better set of barring rates of access class barring than CACB and can reduce random access delay experienced by an MTC device, which is also applicable to user equipment (UE). After an MTC device successfully accesses to an eNB, the eNB needs to allocate radio resources for the MTC device. In addition, the proposed TARRM allocates radio resources for an MTC device based on the random access rate of the MTC device and the amount of data uploaded and downloaded by the MTC device in a homogeneous MTC device network, and the priority of an MTC device in a heterogeneous MTC device network. Furthermore, we use the concept from cognitive radio networks such that if there are unused physical resource blocks (PRBs) of UEs, an eNB can schedule MTC devices to use these PRBs to enhance the throughput performance. Simulation results show that either in a homogeneous MTC device network or in a heterogeneous MTC device network, the proposed CACB-LB’s average access delay of UEs/MTC devices and average throughput from UEs/MTC devices are better than CACB’s. The proposed CACB-LB with TARRM’s average throughput from UEs/MTC devices is also higher than CACB’s. Therefore, the proposed CACB-LB with TARRM is feasible for M2M communications over LTE-A.     

Throughput-optimal resource allocation in LTE-Advanced with distributed antennas

Distributed antennas are envisaged for LTE-Advanced deployments in order to improve the coverage and increase the cell throughput. The latter in turn depends on how resources are allocated to the User Equipments (UEs) at the MAC layer. In this paper we discuss how to allocate resources to UEs so as to maximize the cell throughput, given that UEs may receive from several antennas simultaneously. We first show that the problem is both NP-hard and APX-hard, i.e. no polynomial-time algorithm exists that approximates the optimum within a constant factor. Hence, we propose and evaluate two polynomial-time heuristics whose complexity is feasible for practical purposes. Our simulative analysis shows that, in practical scenarios, the two heuristics are highly accurate.     

多用户接入与SLT编码的二维喷泉系统及性能分析

在物联网时代,多用户接入系统的设计将迎来巨大的挑战。本文在现有系统基础上提出了一种多用户接入与SLT编码结合的二维喷泉系统。在时间层上对各用户原始信息进行SLT编码,在用户层上各用户通过接入概率竞争传输,从而构成一种二维喷泉形式,该系统充分利用喷泉编码能有效提高信号抗干扰能力。对于采用SLT编码的每个用户,可以简单地使用置信传播译码算法进行译码。仿真结果表明,与已有多用户接入系统相比,本文提出的系统明显能实现更好的吞吐性能,且解决了已有系统译码算法在较高接入概率下性能急剧下降的问题,从而能给更多的用户进行信息传输的机会,在多用户数据传输中有很好的实用性。     

Rate limitations of unitary event analysis

Unitary event analysis is a new method for detecting episodes of synchronized neural activity (Riehle, Grün, Diesmann, & Aertsen, 1997). It detects time intervals that contain coincident firing at higher rates than would be expected if the neurons fired as independent inhomogeneous Poisson processes; all coincidences in such intervals are called unitary events (UEs). Changes in the frequency of UEs that are correlated with behavioral states may indicate synchronization of neural firing that mediates or represents the behavioral state. We show that UE analysis is subject to severe limitations due to the underlying discrete statistics of the number of coincident events. These limitations are particularly stringent for low (0-10 spikes/s) firing rates. Under these conditions, the frequency of UEs is a random variable with a large variation relative to its mean. The relative variation decreases with increasing firing rate, and we compute the lowest firing rate, at which the 95% confidence interval around the mean frequency of UEs excludes zero. This random variation in UE frequency makes interpretation of changes in UEs problematic for neurons with low firing rates. As a typical example, when analyzing 150 trials of an experiment using an averaging window 100 ms wide and a 5 ms coincidence window, firing rates should be greater than 7 spikes per second.     

一种性能优化的小文件存储访问策略的研究

在分布式文件系统中,小文件的管理一般存在访问性能较差和存储空间浪费较大等缺点.为了解决这些问题,提出了一种性能优化的小文件存储访问(SFSA)策略.SFSA将逻辑上连续的数据尽可能存储在物理磁盘的连续空间,使用Cache充当元数据服务器的角色并通过简化的文件信息节点提高Cache利用率,提高了小文件访问性能;写数据时聚合更新数据及其文件夹域中的相关数据为一次I/O请求写入,减少了文件碎片数量,提高了存储空间利用率;文件传输时利用局部性原理,提前发送批量的高访问率的小文件,降低了建立网络连接开销,提升了文件传输性能.理论分析和实验证明,SFSA的设计思想和方法能有效地优化小文件的存储访问性能.     

Opportunistic scheduling and incentive mechanism for OFDMA networks with D2D relaying

The device-to-device (D2D) relaying is considered one of promising technologies to improve the spectral efficiency and extend the coverage of the cellular system with low additional costs. In the system with D2D relaying, some of user equipments (UEs) can act as relay stations (RSs) that forward other UEs’ data from/to the base station (BS). Compared with the RS, the D2D relaying has several advantages such as low deployment costs and high flexibility. We study an opportunistic subchannel scheduling problem in the OFDMA cellular network with D2D relaying in this paper. We formulate a stochastic optimization problem to maximize the sum-rate of the system with D2D relaying while satisfying the minimum average data rate requirement for each UE, and then develop an opportunistic scheduling algorithm by solving it. Due to a high computational complexity of the optimal scheduling algorithm, we also propose a heuristic algorithm with a lower computational complexity. In addition, since UEs that participate in D2D relaying sacrifice their resources to relay other UEs’ data, we also study incentive mechanisms to compensate their sacrifices. Through simulation results, we show the performance of our algorithms and the effects of our incentive mechanisms.     

Characterization of database access pattern for analytic prediction of buffer hit probability

The analytic prediction of buffer hit probability, based on the characterization of database accesses from real reference traces, is extremely useful for workload management and system capacity planning. The knowledge can be helpful for proper allocation of buffer space to various database relations, as well as for the management of buffer space for a mixed transaction and query environment. Access characterization can also be used to predict the buffer invalidation effect in a multi-node environment which, in turn, can influence transaction routing strategies. However, it is a challenge to characterize the database access pattern of a real workload reference trace in a simple manner that can easily be used to compute buffer hit probability. In this article, we use a characterization method that distinguishes three types of access patterns from a trace: (1) locality within a transaction, (2) random accesses by transactions, and (3) sequential accesses by long queries. We then propose a concise way to characterize the access skew across randomly accessed pages by logically grouping the large number of data pages into a small number of partitions such that the frequency of accessing each page within a partition can be treated as equal. Based on this approach, we present a recursive binary partitioning algorithm that can infer the access skew characterization from the buffer hit probabilities for a subset of the buffer sizes. We validate the buffer hit predictions for single and multiple node systems using production database traces. We further show that the proposed approach can predict the buffer hit probability of a composite workload from those of its component files.     

基于用户身份标识的外设访问控制方法

针对现有设备访问控制方法控制粒度粗、控制方式单一的问题,提出一种基于用户身份标识的外设访问控制方法。该方法利用角色外设访问控制列表、用户组外设访问控制列表、用户外设访问控制列表实现了对外设的灵活、细粒度控制。结合Linux操作系统进行了结构设计和实现,通过设备特征数据库实现对各种外设的甄别,通过策略数据库实现对外设的角色、用户组和用户控制,通过访问仲裁实现对外设的灵活访问控制,并对所有操作进行审计。最后,通过功能测试验证了方法的有效性,分析了方法的特点。     

基于ADO.NET数据库系统的并发控制协议研究

在数据库系统中,数据访问技术从连接模型发展到断开连接模型.断开连接访问模型技术自身的优点为有别于传统严格一致的可串行化并发控制协议提供了必要性和可能性.通过剖析断开连接数据访问模型ADO.NET基础上,提出了一种基于时间戳验证的两阶段封锁多版本并发控制协议.该协议解决了在断开连接访问模型下网络数据库系统的并发访问异常,保证了数据的一致性,提高了系统的性能和并发度.最后在.NET框架和Microsoft SQL Server2000下实现该协议.     

A stochastic model for beaconless IEEE 802.15.4 MAC operation

IEEE 802.15.4 is a popular choice for MAC/PHY protocols in low power and low data rate wireless sensor networks. In this paper, we develop a stochastic model for the beaconless operation of IEEE 802.15.4 MAC protocol. Given the number of nodes competing for channel access and their packet generation rates, the model predicts the packet loss probability and the packet latency. The model can also account for the impact of hidden nodes in certain situations. We compared the model predictions with NS2 simulation results and found an excellent match between the two for a wide range of the packet generation rates and the number of competing nodes in the network.