基于请求的多信道多数据项广播调度算法*

通过改进多信道单数据项请求的数据广播调度算法中的两层调度策略,提出了信道分配+QEM的算法;实现了用多信道广播来广播多数据项的请求;通过减少数据访问冲突和信道跳转减少了访问时间。分析证明此方法是可行和有效的。     

多数据项请求的多信道并行广播调度算法

为减少数据广播中用户请求的平均访问时间、提高广播性能,提出了一种新的基于减少数据访问冲突和应用重复广播技术的广播调度算法。该算法有效减少了多信道并行广播中多数据项请求的访问冲突,对热点数据项采取重复广播技术,极大地减少了对热点数据项请求的访问时间。仿真实验结果表明,该算法有效地降低了平均访问时间,提高了数据广播性能,特别是在访问概率偏斜率较大时具有更好的性能。     

移动环境下多数据项请求的广播策略研究*

提出了一种移动环境下的多信道试探广播策略MCHM（multiple channel heuristic method）。该广播策略在多信道广播中采用高效的数据调度算法,在不重复广播的情况下,消除了多信道广播中多数据请求的访问冲突,大大减少了移动客户机的访问时间,提高了数据广播的性能。     

无线数据广播中变长数据项偏斜调度算法

针对数据广播中用户访问时间最小化的问题,提出一种变长数据项的偏斜广播调度脱机算法。该算法在数据广播的平方根规则基础上,确定每个数据项的广播频率和在信道上的平均实例间隔,以此为依据选择生成周期广播序列。实验结果表明,该算法获得的平均访问时间接近于理论最优值,平均误差率在6%左右。     

数据广播调度自适应信道划分与分配方法

随着移动网络的不断发展,移动终端设备的计算能力与日俱增,越来越多的用户倾向于通过移动网络获取信息资源,这使得实时按需数据广播面临新的挑战：（1）数据内容和规模的多样化;（2）用户请求的实时性与需求多样性使得热点数据增加,直接导致广播数据总量的剧增;（3）用户对服务质量和水平的要求越来越高.当前的研究成果主要集中在固定信道模型和算法上,一定程度上忽略了当前数据广播调度环境的变化.固定信道存在如下问题：（1）局限于特定的网络,缺乏通用性;（2）信道大小、个数不能随着网络环境的变化而自动调整,降低了广播效率.基于以上考虑,对实时按需数据广播调度的自适应信道划分和分配进行研究,提出一种自适应信道划分与分配方法OCSM （optimized channel split method）,其根据数据请求特征的不同,实时自适应地调整信道个数和大小,从而提高系统敏感性、鲁棒性以及广播效率.该方法包括：（1）广播数据均衡聚类算法WASC （weight average and size clusteralgorithm）,其挖掘数据特征,为信道划分提供依据;（2）数据项广播优先级评定算法R×W/SL,其实时评定数据项调度优先级;（3）信道划分与分配算法CSA （channel split algorithm）.实验包括两个方面：（1）确定不同数据项大小和请求截止期分布下的信道划分策略,并分析聚类算法中聚类距离K在不同情况下的最佳取值以及最佳信道划分;（2）验证自适应信道划分与分配策略的有效性,并通过对比实验验证在不同情况下OCSM的有效性.实验结果表明：OCSM优于其他调度算法,并具有较强的自适应.     

基于贪心策略的多信道数据广播调度算法

为减少多信道数据广播环境中的多信道平均延迟时间,提出一种基于贪心策略的多信道数据广播调度算法,将数据项合理地分配到各信道,最小化多信道数据项平均访问时间,在每个信道内采用近似最优的Log-time算法。实验结果表明,在不同的系统环境下,该算法都能够达到近似最优的性能。     

基于重复热点数据的CF广播结构改进算法*

针对现有广播结构构建中对数据访问概率倾斜度考虑不足的问题,在CF索引树的基础上提出了一种基于数据倾斜度的广播构建算法。该算法充分考虑热点数据的请求,根据数据在CF索引树中所处位置的不同,在一个广播周期内重复广播热点数据及其对应的索引节点,尽量减少移动用户的访问时间。最后通过实验验证了改进后广播结构的有效性。     

无线环境中的数据广播调度理论分析及算法研究

数据广播是无线环境中一种独特的数据发布方式。首先系统地归纳了周期广播、on-demand广播和混合广播3种广播方式的理论分析模型及其特点,然后针对单信道和多信道对各种广播方式的调度算法进行了分类、比较,并突出了理论模型对调度算法研究的指导价值。最后指出今后的研究方向。     

实时环境下一种混合广播调度策略

在实时的非对称通讯环境下,自适应混合广播策略能够根据数据的请求模式以及时间限制等特征来动态分配周期广播和按需广播的带宽比例.将这一策略推广到基于事务的多数据项广播调度中,同时引入"分布式广播"思想,以更精细的周期广播粒度来解决过长的周期广播与事务及数据的实时要求之间的矛盾,并且动态分配时间槽.实验结果表明:改进的调度策略更适合于实时环境下的数据广播,具有更低的事务失败率以及更小的上行信道负荷.     

无线城域网中MPEG视频传输的上行调度算法

针对现有无线城域网中MPEG视频传输的实时轮询服务算法的不足，提出了一种更为有效的媒体接入控制上行调度算法。该算法无需基站周期地提供带宽请求机会，而是在视频应用的连接建立以后，主动周期地分配固定带宽来传输视频数据的特定部分，剩余部分的带宽通过携带请求的方式获得，以此保证更好的服务质量。仿真中使用典型的视频测试源，结果表明，新算法在近似现有算法的信道利用率的情况下，具有更小的视频帧延迟和抖动。     

A tree-structured index allocation method with replication over multiple broadcast channels in wireless environments

Broadcast has often been used to disseminate frequently requested data efficiently to a large volume of mobile units over single or multiple channels. Since mobile units have limited battery power, the minimization of the access and tuning times for the broadcast data is an important problem. There have been many research efforts that focus on minimizing access and tuning times by providing indexes on the broadcast data. We have studied an efficient index allocation method for broadcast data with skewed access frequencies over multiple physical channels which cannot be coalesced into a single high bandwidth channel. Previously proposed index allocation techniques have one of two problems. The first problem is that they require equal size for both index and data. The second problem is that their performance degrades when the number of given physical channels is not enough. These two problems result in an increased average access time for the broadcast data. To cope with these problems, we propose a tree-structured index allocation method. Our method minimizes the average access time by broadcasting the hot data and their indices more frequently than the less hot data and their indexes over the dedicated index and data channels. We present an in-depth experimental and theoretical analysis of our method by comparing it with other similar techniques. Our performance analysis shows that it significantly decreases the average access and tuning times for the broadcast data over existing methods.     

Channel dynamic adjustment in data broadcast

Data broadcasting has become the preferred method to dispense data to a large number of mobile users. Current researches on on-demand data broadcast mainly propose algorithms based on a single broadcast channel or fixed multi-channel, i.e., fixed channel model. As a result of the dynamic diversity of data characteristics and client demands, the fixed channel model faces significant challenges in parallel broadcast diverse data. Further, the dynamic adjustment of the broadcast channel (dynamic channel model) based on client requests is favorable to service quality because it determines the number and sizes of channels that adapt to client demand in real-time. However, the dynamic channel model has not yet been thoroughly investigated for on-demand wireless data broadcasts. Accordingly, in this paper, a channel dynamic adjustment method (CDAM) is proposed. The innovations behind CDAM lie in three aspects. First, a data item priority evaluation and selection algorithm (S-RxW/SL) is proposed for evaluating the priority of data items and selecting the high priority data items to be considered in a broadcast cycle. Second, a weight and size average cluster algorithm (WSAC) is proposed for mining data item characteristics and clustering them. Third, based on the clustering results of WSAC, a channel splitting and data allocation algorithm (CSDA) is proposed for dynamically splitting the channel and allocating data items to the corresponding sub-channel. We compare the proposed method with some state-of-the-art scheduling methods through simulation. The theoretical findings and simulation results reveal that significantly better request loss rate (LR) can be obtained by using our method as compared to its alternatives.     

无线环境中不均匀广播算法研究

阿查里亚的多盘碟片算法实现了在一段广播时间内,将热门数据分发次数多于较冷门的数据,即不均匀广播,在降低用户等待时间方面提供了很好的表现。然而,移动设备必须不断地调整无线广播频道去检查数据,消耗了大量的能量。在广播的文件上使用索引技术,可以在无显著增加等待时间的前提下,大大降低移动设备的能量消耗。本文在多盘广播算法的基础上,提出一种倾斜索引(SI)的高效不均匀索引。这种算法根据用户的倾斜访问模式建立了一个索引树,在一个广播循环内,多次分发热门索引节点,少分发非热门索引节点。     

A Hybrid Index Technique for Power Efficient Data Broadcast

The intention of power conservative indexing techniques for wireless data broadcast is to reduce mobile client tune-in time while maintaining an acceptable data access time. In this paper, we investigate indexing techniques based on index trees and signatures for data disseminated on a broadcast channel. Moreover, a hybrid indexing method combining strengths of the signature and the index tree techniques is proposed. Different from previous studies, our research takes into consideration of two important data organization factors, namely, clustering and scheduling. Cost models for the three indexing methods are derived for various data organization accommodating these two factors. Based on our analytical comparisons, the signature and the hybrid indexing techniques are the best choices for power conservative indexing of various data organization on wireless broadcast channels.     

Effective Generation of Data Broadcast Schedules with Different Allocation Numbers for Multiple Wireless Channels

Existing methods of scheduling data items over multiple wireless broadcast channels focus on the assignment of a data item to a channel. However, data items are not allocated more than once per broadcast cycle to a single channel. Our scheme considers the numbers of copies of a data item that should be allocated in the context of the channel assignment problem and aims to reduce the average data access time by allocating a popular data item more than once per cycle to the channel to which it is assigned. The number of times that each data item is allocated reflects its access probability. Simulation results show that our scheme reduces the average expected delay, especially when there are few channels.