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21.
Rajamani Ganesh Kuriacose Joseph Newman D. Wilson Dipankar Raychaudhuri 《International Journal of Wireless Information Networks》1994,1(3):199-222
This paper presents a simulation-based study of cellular packet CDMA systems operating in an integrated voice/data traffic scenario. Spread-spectrum CDMA provides a suitable framework for resource-shared packet transport capable of combining isochronous (voice, ISDN) and bursty data services. In this work, a general network model for cellular packet CDMA with mixed voice/data traffic is described and used to evaluate the capacity/performance impact of several key system parameters. First, the effect of spreading factor (N) and forward error correction (FEC) rate are studied, confirming earlier work indicating a weak dependence onN and a well-defined optimum code rate in the range of 0.5–0.7 (with BCH coding). Next, the effect of propagation loss coefficient () on network capacity is investigated over a range of possible assumptions for, including both constant and distance-dependent models. The results show that system capacity depends strongly on, varying by as much as a factor of 2 over the range of parameters considered. For a given distance-dependent assumption, performance results are also obtained for different cell sizes in order to understand the overall spatial reuse efficiency achievable in different cellular and microcellular scenarios. This is followed by an investigation of traffic source model effects: first the capacity improvement from voice activity detection VAD) is presented, showing the expected 21 gains. Results for varying proportions of voice and data traffic intensities indicate that the operating efficiency does not change significantly as the proportion of bursty data relative to voice is varied. 相似文献
22.
湍流大气中光强闪烁对光通信链路的影响 总被引:4,自引:0,他引:4
给出了用大气传输通信设备进行传输距离 3.4 km外场试验光强闪烁对光通信链路影响的实验结果 ,并简要分析了光强闪烁对信号检测的影响和误码原因 相似文献
23.
A closed form expression for the bit error rate (BER) performance of frequency domaindifferential demodulation(FDDD) for orthogonal frequency division multiplexing system in flat fadingchannel is derived.The performance is evaluated by computer simulation and compared with the timedomain differential demodulation(TDDD).The results indicate that the performance of FDDD is betterthan that of TDDD,and the lower band of BER in the former is lower than that of the latter. 相似文献
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The age of information (AoI) metric was proposed to measure the freshness of messages obtained at the terminal node of a status updating system. In this paper, the AoI of a discrete time status updating system with probabilistic packet preemption is investigated by analyzing the steady state of a three-dimensional discrete stochastic process. We assume that the queue used in the system is , which represents that the system size is 2 and the packet in the buffer can be preempted by a fresher packet with probability . Instead of considering the system’s AoI separately, we use a three-dimensional state vector to simultaneously track the real-time changes of the AoI, the age of a packet in the server, and the age of a packet waiting in the buffer. We give the explicit expression of the system’s average AoI and show that the average AoI of the system without packet preemption is obtained by letting . When is set to 1, the mean of the AoI of the system with a queue is obtained as well. Combining the results we have obtained and comparing them with corresponding average continuous AoIs, we propose a possible relationship between the average discrete AoI with the queue and the average continuous AoI with the queue. For each of two extreme cases where and , we also determine the stationary distribution of AoI using the probability generation function (PGF) method. The relations between the average AoI and the packet preemption probability , as well as the AoI’s distribution curves in two extreme cases, are illustrated by numerical simulations. Notice that the probabilistic packet preemption may occur, for example, in an energy harvest (EH) node of a wireless sensor network, where the packet in the buffer can be replaced only when the node collects enough energy. In particular, to exhibit the usefulness of our idea and methods and highlight the merits of considering discrete time systems, in this paper, we provide detailed discussions showing how the results about continuous AoI are derived by analyzing the corresponding discrete time system and how the discrete age analysis is generalized to the system with multiple sources. In terms of packet service process, we also propose an idea to analyze the AoI of a system when the service time distribution is arbitrary. 相似文献
28.
宋宝亚 《信息技术与信息化》2007,32(4):97-99,102
软件测试是开发过程的重要环节。回归错误在开发过程中严重影响着开发的效率,其隐匿特性也使得测试比较困难。因此,本文提出一种非间断测试的模型,用于加强对回归错误的管理,节约不必要的无谓工作时间,提高软件开发的效率。这种模型对用户开发行为进行模拟和推测,在经过大量的数据训练后,寻找测试行为、错误发生等开发动作的捕获点,从而找到最佳的测试策略。在不影响开发人员工作的前提下,可对当前最新的代码进行测试,最大程度上避免回归错误长期隐藏在前期代码中,保持整个开发过程的稳步前进。 相似文献
29.
This paper proves the optimal estimations of a low-order spatial-temporal fully discrete method for the non-stationary Navier-Stokes Problem. In this paper, the semi-implicit scheme based on Euler method is adopted for time discretization, while the special finite volume scheme is adopted for space discretization. Specifically, the spatial discretization adopts the traditional triangle trial function pair, combined with macro element form to ensure local stability. The theoretical analysis results show that under certain conditions, the full discretization proposed here has the characteristics of local stability, and we can indeed obtain the optimal theoretic and numerical order error estimation of velocity and pressure. This helps to enrich the corresponding theoretical results. 相似文献
30.
对武汉地区1982~1994年有雨分维数与有雨概率之间的关系进行了初步的分析和研究,并给出了研究结果.为今后修改降雨衰减预报模型作准备. 相似文献