【導讀】在當今高度信息化的社會，信息和通信已成為現(xiàn)代社會的“命脈”。融合，已成為21世紀國際社會和世界經(jīng)濟發(fā)展的強大動力。為了適應時代的要。多媒體通信業(yè)務。一個數(shù)量級，可在物理層采用三項技術，即OFDM、UWB和空時調(diào)制編碼。OFDM已用于Mbit/s高比特率數(shù)字用戶線，6Mbit/s. OFDM應用于5GHz上提供54Mbit/s無線本地網(wǎng)IEEE. 為城域網(wǎng)IEEE標準。與單載頻調(diào)制制式。高速移動通信的另一要求是在寬噪聲帶寬下，所需解調(diào)信噪比應盡可能降低，從而增加覆蓋面積?？刹扇】顾ヂ涞目焖侔l(fā)射功率控制和導頻輔助快速跟蹤相干。率選擇性衰落的OFDMA技術，鏈路自適應技術，聯(lián)合編碼技術。系，容量可達Shannon的90%。MIMO技術主要包括空間復用和空間分集技術，在獨立信。收發(fā)雙方的空間分集是高容量無線通信系統(tǒng)采用技術之一。利用MIMO所構成的跨時域和空域的擴展信號還可以抵抗多徑干擾。而發(fā)射和接收端均采。準干擾信號到達方向。沖成型后可直接送至天線發(fā)射。蜂窩通信系統(tǒng)允許大量移動用戶無縫地、同時地利用有限的射

　　

【正文】 trol codes, equalizers, and other ponents that serve to mitigate the transient effects created by the channel. However, in order to determine the overall system performance of a large number of users spread over a wide geographic area, it is necessary to incorporate largescale effects such as the statistical behavior of interference and signal levels experienced by individual users over large distances, while ignoring the transient channel characteristics. One may think of linklevel simulation as being a vernier adjustment on the performance of a munication system, and the systemlevel simulation as being a coarse, yet important, approximation of the overall level of quality that any user could expect at any time. Cellular systems achieve high capacity (., serve a large number of users) by allowing the mobile stations to share, or reuse a munication channel in different regions of the geographic service area. Channel reuse leads to cochannel interference among users sharing the same channel, which is recognized as one of the major limiting factors of performance and capacity of a cellular system. An appropriate understanding of the effects of cochannel interference on the capacity and performance is therefore required when deploying cellular systems, or when analyzing and designing system methodologies that mitigate the undesired effects 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. Cellular radio system SystemLevel Description： Cellular systems provide wireless coverage over a geographic service area by dividing the geographic area into segments called cells. 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 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. 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 Figure32, the minimum distance between the center of two cochannel cells, called the reuse distance ND , is RDN N3? （ 31） 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 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.