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991.
Dynamic Reservation Multiple Access (DRMA): A new multiple access scheme for Personal Communication System (PCS) 总被引:2,自引:0,他引:2
To improve the spectrum efficiency of integrated voice and data services in Personal Communication System (PCS), several reservation-type multiple access schemes, such as Packet Reservation Multiple Access (PRMA), Dynamic Time Division Multiple Access (D-TDMA), Resource Auction Multiple Access (RAMA), etc., have been proposed. PRMA uses the data packet itself to make a channel reservation, and is inefficient in that each unsuccessful reservation wastes one slot. However, it does not have a fixed reservation overhead and offers shorter access delay. On the other hand, fixed reservation overhead is unavoidable in both RAMA and D-TDMA. Compared to D-TDMA and PRMA, RAMA is superior in the sense that its slot assignment is independent of the traffic load. But its implementation is difficult. With these observations, a new reservation protocol, called Dynamic Reservation Multiple Access (DRMA), is proposed in this paper. With this new protocol, the success probability of channel access is greatly improved at the expense of slightly increased system complexity. It solves the problem of inefficiency in PRMA, but without introducing the fixed reservation overhead as in D-TDMA and RAMA. In addition, it is more suited to the dynamic behavior of the integrated traffic because there is no fixed boundary between voice and data slots (which is mandatory in D-TDMA and RAMA). Our numerical results indicate that its performance is superior to the existing reservation protocols, especially in the integrated traffic scenario. Moreover, the soft capacity feature is exhibited when the traffic load increases. 相似文献
992.
阐述了功率GaAsMESFET器件热阻测试中温敏参数VGSF和测试电流Im的选取,给出了1~5W器件典型温敏参数的温度测试系数M与测试电流Im的关系。讨论了测试延迟时间tmd对△VGSF测量值的影响和三种校正方法。 相似文献
993.
994.
A Metwali D Elliott AM Blum J Li M Sandor R Lynch N Noben-Trauth JV Weinstock 《Canadian Metallurgical Quarterly》1996,157(10):4546-4553
IL-4 plays an important role in polarizing inflammation toward a Th2 response. It remains uncertain, however, whether IL-4 also serves to prevent expression of Th1 inflammation. Therefore, using a genetically pure C57BL/6 IL-4-deficient mouse, we studied the role of IL-4 in regulating the production of IFN-gamma and Th1 inflammation in the granulomas of mice infected with Schistosoma mansoni. In contrast to normal animals, IL-4 mutant mice generated smaller liver granulomas that contained fewer eosinophils and no mast cells. Collagenase-dispersed granuloma cells were analyzed by flow cytometry and cultured in vitro to measure cytokine and Ig production. Compared with control granuloma cells, IL-4-/- cells secreted only small quantities of IL-5 and IL-10. Also, there was impaired expression of the IL-4-dependent molecules IgE and IgG1 as well as B cell surface class II and CD23. Yet the granulomas of IL-4 -/- animals produced little IFN-gamma, IgG2a, or other molecules associated with Th1 inflammation even after Ag or anti-CD3 stimulation. Splenocytes from IL-4 -/- animals stimulated with schistosome Ag also failed to produce a Th1 response. Our data show that most aspects of the Th2 response in murine schistosomiasis are highly dependent on IL-4 production. But in the absence of IL-4, neither the natural local granulomatous response to schistosome ova nor the systemic response to soluble egg Ag switches to the type 1 phenotype. Thus the production of IL-4 early in the inflammatory response is not the only factor preventing Th1 expression in inflammation. 相似文献
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998.
在简单介绍了ADSL技术的基础上,具体介绍了如何在EWSDU交换机中创速和设置ADSL用户功能和xDSL功能. 相似文献
999.
某尾矿库周围环境中污染物生态转移研究 总被引:4,自引:0,他引:4
对我国某尾矿库周围环境中放射性核素U、^226Ra、Th及非放污染物Mn^2 、Cd、Cr、Pb在农作物和水生生物等介质中的浓集情况进行了现场研究,给出了相应的污染物生态学转移系数Bv和Bp值。 相似文献
1000.
Duan Li Fucai Qian Peilin Fu 《Automatic Control, IEEE Transactions on》2002,47(12):2010-2020