通信工程英文論文(編輯修改稿)
2024-11-24 13:41 本頁面
【文章內(nèi)容簡介】 iateunderstanding of the effects of cochannel interference on the capacity andperformance is therefore required when deploying cellular systems, or when analyzingand designing system methodologies that mitigate the undesired effects ofcochannelinterference. These effects are strongly dependent on system aspects ofthemunication system, such as the number of users sharing the channel andtheirlocations. Other aspects, more related to the propagation channel, such aspath loss,shadow fading (or shadowing), and antenna radiation patterns are alsoimportant in thecontext of system performance, since these effects also vary withthe locations ofparticular users. In this chapter, we will discuss the application ofsystemlevelsimulation in the analysis of the performance of a cellular municationsystem under the effects of cochannel interference. We will analyze a simplemultipleusercellular system, including the antenna and propagation effects of atypical the simplicity of the example system considered in thischapter, the analysispresented can easily be extended to include other features ofa cellular system. 2 Cellular Radio System SystemLevel Description： Cellular systems provide wireless coverage over a geographic service area by dividingthe geographic area into segments called cells as shown in Figure 21. Theavailable frequency spectrum is also divided into a number of channels with a groupof channels assigned to each cell. Base stations located in each cell are equippedwith wireless modems that can municate with mobile users. Radio frequencychannels used in the transmission direction from the base station to the mobile arereferred to as forward channels, while channels used in the direction from the mobileto the base station are referred to as reverse channels. The forward and reversechannels together identify a duplex cellular frequency divisionduplex(FDD) is used, the forward and reverse channels are split in frequency. Alternatively,when time division duplex (TDD) is used, the forward and reverse channelsare on the same frequency, but use different time slots for transmission. Figure 21 Basic architecture of a cellular munications system Highcapacity cellular systems employ frequency reuse among cells. This requiresthat cochannel cells (cells sharing the same frequency) are sufficiently farapart from each other to mitigate cochannel interference. Channel reuse is implementedby covering the geographic service area with clusters of N cells, as shownin Figure 22, where N is known as the cluster size. Figure 22 Cell clustering:Depiction of a threecell reuse pattern The RF spectrum available for the geographic service area is assigned to each
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