the CellA cell is an area where a Mobile Station (MS) receives a signal strength that is high enough for setting up and maintaining a radio connection on a dedicated channel, that is, SDCCH or TCH. The size of a cell (or the size of the coverage area) is mainly determined by four parameters:
- The output power (BSTXPWR) at the antenna of the BTS: the Effective Radiated Power (ERP)
- The minimum received level at the MS (this is MSRXMIN for MS in “busy” mode)
- The minimum received level at the BTS (this is BSRXMIN)
- The Timing Advance (TA): the TA is a measure of the traveling time of the bursts between the MS and the BTS; the maximum value of TA in a cell is defined by the parameter MAXTA (MAXimum Timing Advance).
A second cell criterion is the existence of a BCCH. A cell must have exactly one BCCH because the BCCH carries essential information which must be known to the MS before call setup.
The previous example presented a cell of circular shape, an omni-cell. Generally, the shape of a cell depends on the antenna, connected to the cell. The antenna can also focus its power on a certain sector of a circle. This is called a sector-cell. It is up to the cell planner to select a suitable antenna. The cell shape can also depend on the geographic conditions. Each sector can have its own output power assigned. The BCCH frequencies must be different in all the sectors.小区 小区是移动台(MS)接受信号强度足够强到可以在专用通道SDCCH(独立专用控制信道)或TCH(业务信道)上建立和保持无线电联接的区域.小区或覆盖区域范围的大小主要由4个参数决定: 基站收发台天线的输出功率(BSTXPWP):有效辐射功率(ERP) 在移动站的最低接收水平(MSRXMIN,是MS的“忙”模式) 在基站的最低接收水平(BSRXMIN) 定时提前(TA):是一种在移动台和基站之间突发的传输时间的度量;小区中的定时提前的最大值取决于MAXTA(最大时间提前)参数。 第二个小区标准是广播控制信道的存在。小区必须应有一个广播控制信道,因为该控制信道携载着通话建立起来之前移动台必须的基本信息。
以上的例子介绍了一种圆形的小区,一种全方位小区。通常,小区的形状取决于与其相连的天线。天线也可以将其功率集中于被称为扇区小区的环的特定区域。要由小区规划者选择合适的天线。小区形状也可由地理条件决定。每一区域都有其分配的输出功率。广播控制信道的频率在所有的区域必须是不同的。
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