一种动态利用码资源的CDMA系统性能研究

本文提出了一种基于随机预约ALOHA访问方式,能支持话音和数据业务的动态使用码资源的码分多址访问协议。在该协议中,话音终端采用预约请求排队访问方式。数据终端采用时隙ALOHA方式传输数据分组。理论分析和计算机仿真结果表明,该协议能有效地提高系统码资源的利用率。在系统处于重负载情况下该协议能优先保证话音业务服务质量,而处于轻负载下系统码资源能为数据业务充分使用。     

基于序贯线性贝叶斯的RFID标签数量估计算法

为解决现有标签数量估计算法中估计精度与复杂度之间的矛盾,在分析比较现有算法的基础上,提出一种基于序贯线性贝叶斯的射频识别（RFID）标签数量估计算法。首先,基于线性贝叶斯理论,充分利用空闲、成功和碰撞时隙数量观测值及相关性,建立了标签数量估计问题的线性模型;然后,推导了标签数量估计值的闭式表达式,给出了表达式各阶统计量的序贯式求解方法;最后,对序贯式贝叶斯算法的计算复杂度进行了分析和对比。仿真结果表明,所提算法通过序贯贝叶斯方法提高了估计精度和识别效率,当观测时隙数为帧长一半时估计误差仅为4%。该算法以线性解析式形式更新标签数量估计值,避免了穷举搜索,与高精度的最大后验概率和马氏距离算法相比,计算复杂度由O（n²）和O（n）下降为O（1）。经理论分析和仿真验证,基于序贯线性贝叶斯的RFID标签数量估计算法兼具高精度和低复杂度的特性,能很好地满足硬件资源受限应用场景下对标签数量的估计需求。     

A stochastic control approach to Slotted-ALOHA random access protocol

ALOHA random access protocols are distributed protocols based on transmission probabilities, that is, each node decides upon packet transmissions according to a transmission probability value. In the literature, ALOHA protocols are analysed by giving necessary and sufficient conditions for the stability of the queues of the node buffers under a control vector (whose elements are the transmission probabilities assigned to the nodes), given an arrival rate vector (whose elements represent the rates of the packets arriving in the node buffers). The innovation of this work is that, given an arrival rate vector, it computes the optimal control vector by defining and solving a stochastic control problem aimed at maximising the overall transmission efficiency, while keeping a grade of fairness among the nodes. Furthermore, a more general case in which the arrival rate vector changes in time is considered. The increased efficiency of the proposed solution with respect to the standard ALOHA approach is evaluated by means of numerical simulations.