zigbee 定位

我一直都提醒  zigbee  RSSI定位不靠谱，但是既然非要这样，先mark一下简单的两点定位。 特别是在隧道里，还会有多径干扰， 模型也不是标准的。所以zigbee定位应该只适用实验室研究吧。要是想用，估计应该是多点定位吧。

原文： http://hxqhit.blog.163.com/blog/static/15357922200948112142918/ 

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).

                      

 

                 

                 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。