通信工程專業(yè)英文翻譯--蜂窩無線通信系統(tǒng)的仿真-在線瀏覽
2025-07-30 15:28本頁面
【正文】 th 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 wireless munications system and plays an important role in the tradeoff between system capacity (largescale system issue) and link quality (smallscale issue). For example, one approach for achieving high capacity (large number of users), without increasing the bandwidth of the RF spectrum allocated to the system, is to reduce the channel reuse distance by reducing the cluster size N of a cellular system . However, reduction in the cluster sizeincreases cochannel interference, which degrades the link quality. The level of interference within a cellular system at any time is random and must be simulated by modeling both the RF propagation environment between cells and the position location of the mobile users. In addition, the traffic statistics of each user and the type of channel allocation scheme at the base stations determine the instantaneous interference level and the capacity of the system. The effects of cochannel interference can be estimated by the signaltointerference ratio (SIR) of the munication link, defined as the ratio of the power of the desired signal S, to the power of the total interference signal, I. Since both power levels S and I are random variables due to RF propagation effects, user mobility and traffic variation, the SIR is also a random variable. Consequently, the severity of the effects of cochannel interference on system performance is frequently analyzed in terms of the system outage probability, defined in this particular case as the probability that SIR is below a given threshold 0SIR . This is dxp]S IRP r[S IRP )x0S I R0 S I R0o u t p a g e （???? （ ） Where is the probability density function (pdf) of the SIR. Note the distinction between the definition of a link outage probability, that classifies an outage SIR(x)p 7 based on a particular bit error rate (BER) or Eb/N0 threshold for acceptable voice performance, and the system outage probability that considers a particular SIR threshold for acceptable m
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