RSSI与距离d之间的关系(重点部分进行修改)
原文地址: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*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。