通信工程專業(yè)英文翻譯--蜂窩無線通信系統(tǒng)的仿真-展示頁
2025-05-26 15:28本頁面
【正文】 s of cochannel interference. These effects are strongly dependent on system aspects of the munication system, such as the number of users sharing the channel and their locations. Other aspects, more related to the propagation channel, such as path loss, shadow fading (or shadowing), and antenna radiation patterns are also important in the context of system performance, since these effects also vary with the locations of particular users. In this chapter, we will discuss the application of systemlevel simulation in the analysis of the performance of a cellular munication system under the effects of cochannel interference. We will analyze a simple multipleuser cellular system, including the antenna and propagation effects of a typical system. Despite the simplicity of the example system considered in this chapter, the analysis presented can easily be extended to include other features of a cellular system. 2 Cellular Radio System SystemLevel Description： Cellular systems provide wireless coverage over a geographic service area by dividing the geographic area into segments called cells as shown in Figure . The available frequency spectrum is also divided into a number of channels with a group of channels assigned to each cell. Base stations located in each cell are equipped with wireless modems that can municate with mobile users. Radio frequency channels used in the transmission direction from the base station to the mobile are referred to as 4 forward channels, while channels used in the direction from the mobile to the base station are referred to as reverse channels. The forward and reverse channels together identify a duplex cellular channel. When frequency division duplex (FDD) is used, the forward and reverse channels are split in frequency. Alternatively, when time division duplex (TDD) is used, the forward and reverse channels are on the same frequency, but use different time slots for transmission. Highcapacity cellular systems employ frequency reuse among cells. This requires that cochannel cells (cells sharing the same frequency) are sufficiently far apart from each other to mitigate cochannel interference. Channel reuse is implemented by covering the geographic service area with clusters of N cells, as shown in Figure , where N is known as the cluster size. 5 The RF spectrum available for the geographic service area is assigned to each cluster, such that cells within a cluster do not share any channel . If M channels make up the entire spectrum available for the service area, and if the distribution of users is uniform over the service area, then each cell is assigned M/N channels. As the clusters are replicated over the service area, the reuse of channels leads to tiers of cochannel cells, and cochannel interference will result from the propagation of RF energy between cochannel base stations and mobile users. Cochannel interference in a cellular system occurs when, for example, a mobile simultaneously receives signals from the base station in its own cell, as well as from cochannel base stations in nearby cells from adjacent tiers. In this instance, one cochannel forward link (base station to mobile transmission) is the desired signal, and the other cochannel signals received by the mobile form the total cochannel interference at the receiver. The power level of the cochannel interference is closely related to the separation distances among cochannel cells. If we model the cells wi
畢業(yè)設(shè)計(jì)相關(guān)推薦
鄂ICP備17016276號-1