通信工程专业英文翻译--蜂窝无线通信系统的仿真(编辑修改稿)

通信工程专业英文翻译--蜂窝无线通信系统的仿真(编辑修改稿)内容摘要：

he 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 with a hexagonal shape, as in Figure , the minimum distance between the center of two cochannel cells, called the reuse distance ND , is RDN N3 （ ） where R is the maximum radius of the cell (the hexagon is inscribed within the radius). Therefore, we can immediately see from Figure that a small cluster size (small reuse distance ND ), leads to high interference among cochannel cells. The level of cochannel interference received within a given cell is also dependent on the number of active cochannel cells at any instant of time. As mentioned before, cochannel cells are grouped into tiers with respect to a particular cell of interest. The number of cochannel cells in a given tier depends on the tier order and the geometry adopted to represent the shape of a cell (., the coverage area of an individual base station). For the classic hexagonal shape, the closest cochannel cells are located in the first tier and there are six cochannel cells. The second tier consists of 12 cochannel cells, the third, 18, and so on. The total 6 cochannel interference is, therefore, the sum of the cochannel interference signals transmitted from all cochannel cells of all tiers. However, cochannel cells belonging to the first tier have a stronger influence on the total interference, since they are closer to the cell where the interference is measured. Cochannel interference is recognized as one of the major factors that limits the capacity and link quality of a wireles。