RSSI与距离d之间的关系

1. Path Loss Model, RSSI and RF Parameters A, n

      To determine the distance from the RSSI values, Chipcon applies a simple path loss model (free space path loss自由空间损耗) shown in ?gure 2.3 and equation (2.1). The location engine requires, in addition to the RSSI value two RF model

parameters, A and n which are discussed in this section.                                                           

                d1 = distance to the sender [m]
                d2 = distance to the sender [m]
                P1 = power at distance d1 [W]
                P2 = power at distance d2 [W]
                n = path loss coe?cient

One can write equation (2.1) in logarithmic notation, which is done in equation (2.2).

                  在CC2530和CC2430中，RSSI最一开始是用两位16进制数表示的

                 若在协议栈中取得的RSSI已考虑过偏移问题（大部分协议栈都处理过），

                  则只需将RSSI转换为10进制，再减去255，其单位就变换成了dbm

                  再用公式d=10^((ABS(RSSI(dbm))-A)/(10*n))进行计算，就得到大致距离了。

                 d = distance to the sender [m]
                 A = absolute value of power at one meter distance to the sender [dBm]
                 n = path loss coe?cient

  所以 测量测距离与已知RSSI、A、n 之间的关系如下所示

                 d=10^((ABS(RSSI)-A)/(10*n))

  其中RSSI与LQI之间的转换关系如下：

                 RSSI =  -(81-(LQI*91)/255)

  通过实验，A值的最佳范围为45—49，n值最佳范围为3.25—4.5，N在15---25。

 

如果对于静止或者低速的运动物理的时，可用平均值滤波来提高测量精度

 或者IIR滤波执行利递归解得平均值处理的，典型的a去0.75--0.95 ：  

 如果对于高速运动的物体可用卡曼滤波。