Wlan定位之三点定位分析：
本文完全是根据实际开发环境所写，我们这套系统由定位设备和定位服务器组成，之间通信采用私有协议，定位设备采用傲天的ap,定位服务器是我司IPS设备
*注释 ：以下定位设备称为sensor，定位服务器成为IPS,被定为目标称为DDev
sensor主要工作：采集数据，计算距离
IPS主要工作：管理探针，计算被定位设备坐标，定位页面图形展示。
用户态采集数据：sensor每100ms采集DDev 的Beacon 或者Probe
response帧等的信号强度，一共30组数据
计算距离：30组数据经过高斯滤波算法得到平均的RSSI,代入公式 rssi = -(10nlgd +A),其中n为环境因子，A为sensor距离DDev一米采集到的DDev的信号强度
源码如下：
/*算法实现函数*/
float rtlsCalcAverageRssi(char
*pstRssi, char n)
{
int k, l = 0;
char i , j, m, mm;
float perRssi;
float AverageRssi =
0;
float sigma = 0, mu = 0;
//calc mu
for(i = 0; i < n; i++)
{
perRssi = pstRssi[i];
mu += perRssi;
}
mu = mu/n;
//calc sigma
for(j = 0; j < n; j++)
{
perRssi = pstRssi[j] - mu;
perRssi = pow(perRssi, 2);
sigma += perRssi;
}
sigma = sigma/(n -1);
sigma = pow(sigma, 0.5);
_sensor_printf(g_sensordDebug, MSG_BASIC, "__Localtion
: mu = %f , sigma = %f__", mu, sigma);
float lowerLimit = 0.15*sigma + mu;//既有公式
//lowerLimit = (int)lowerLimit;
//printf("lowerLimit = %d\n", (int)lowerLimit);
float upperLimit = 3.09*sigma + mu;//既有公式
//upperLimit = (int)upperLimit;
//printf("upperLimit = %d\n", (int)upperLimit);
_sensor_printf(g_sensordDebug, MSG_BASIC, "__Localtion
: lowerLimit = %f , upperLimit = %f__", lowerLimit, upperLimit);
for(m = 0; m < n; m++)
{
mm = pstRssi[m];
if((mm
>= (int)lowerLimit)&&(mm
<= (int)upperLimit))
{
++l;
AverageRssi += mm;
//_sensor_printf(g_sensordDebug, MSG_BASIC,
"__Localtion : l = ", l);
}
}
if(l)
{
_sensor_printf(g_sensordDebug, MSG_BASIC, "__Localtion
: count = %d", l);
AverageRssi = AverageRssi/l;
return AverageRssi;
}
return mu;
}
/*发送距离给IPS*/
VOID sensorCalc(sensorLocalDev
*pstLocalDev)
{
struct list_head
*listAP;
struct list_head
*listn;
sensorLocalDev *psttmpLocalDev = NULL;
char i= 0;
UCHAR sample_rssi[130] = {0};
UCHAR sample_rssi_s[4] = {0};
_sensor_printf(g_sensordDebug, MSG_BASIC, "__sensor
start calc ......");
for(i = 0; i < SENSOR_SAMPLE_COUNT; i++)
{
snprintf(sample_rssi_s, 4, "%d ",
pstLocalDev->sampleRssi[i]);
strncat(sample_rssi, sample_rssi_s, 4);
}
_sensor_printf(g_sensordDebug, MSG_BASIC, "__Localtion
: sample_rssi = %s", sample_rssi);
float rssi =0;
rssi = rtlsCalcAverageRssi(pstLocalDev->sampleRssi,
SENSOR_SAMPLE_COUNT);
float distance;
if((g_sensorLocalpara.para_A)&&(g_sensorLocalpara.para_N))
{
distance = rtlsCalcDiance(rssi,
g_sensorLocalpara.para_A, g_sensorLocalpara.para_N);
}
else
distance =
rtlsCalcDiance(rssi, pstLocalDev->para_A, pstLocalDev->para_N);
_sensor_printf(g_sensordDebug, MSG_BASIC, "__Localtion
: rssi = %f , distance = %f__", rssi, distance);
//send to idp
sensorSendLocalinfo(distance, pstLocalDev);
return;
}
/*定时采集信号强度函数*/
VOID sensorSampleRssi(void
*eloop_ctx, void *timeout_ctx)
{
struct AP_info *ap_cur = NULL;
sensorLocalDev *pstLocalDev = (sensorLocalDev *)eloop_ctx;
ap_cur = G.ap_1st;
while( ap_cur != NULL )
{
if( (ap_cur->nb_pkt < 2) || !memcmp( ap_cur->bssid, BROADCAST,
WIDP_SENTOR_MAC_LEN ) ||(ap_cur->avg_power >= -1) ||
!memcmp( ap_cur->bssid, NULL_MAC,
WIDP_SENTOR_MAC_LEN ))
{
ap_cur = ap_cur->next;
continue;
}
if(!memcmp( ap_cur->bssid, pstLocalDev->LocalMacAddr,
WIDP_SENTOR_MAC_LEN ))
{
_sensor_printf(g_sensordDebug, MSG_BASIC,
"__LocalMacAddr is exist in the g_linktable__ !");
if(pstLocalDev->sampleCount >=
SENSOR_SAMPLE_COUNT)
{
pstLocalDev->sampleCount = 0;
sensorCalc(pstLocalDev);
//return;
}
else
{
_sensor_printf(g_sensordDebug,
MSG_BASIC, "__local power == %d", ap_cur->avg_power);
//if((ap_cur->avg_power <=
-20)&&(ap_cur->avg_power >= -80))
{
pstLocalDev->sampleRssi[pstLocalDev->sampleCount]
= ap_cur->avg_power;
pstLocalDev->sampleCount++;
}
}
break;
}
ap_cur = ap_cur->next;
}
eloop_register_timeout(0, 100*1000, sensorSampleRssi, pstLocalDev, NULL);
return;
}
计算被定位设备坐标：IPS负责计算DDev坐标，如果要计算精确的DDev坐标，需要三个sensor,IPS负责管理这些sensor,包括sensor坐标的设置，以及页面的动态显示，主要调用highcharts.js和highcharts-more.js插件并经过自己的修改完成的，有兴趣的哥们姐们可以研究一下这两个插件，我在这里不做分析。
刚才说到sensor会发送距离d给IPS，IPS会做进一步的处理,那究竟是什么处理呢，我们在这里详细说说.
/*对d的值进行啦一次高斯滤波算法*/
int
Gaussian_distribution(unsigned short *array, int n)
{
int k=0;
int i;
float perRssi;
int tmp;
int
Average = 0;
float sigma = 0, mu = 0;
//calc mu
for(i = 0; i < n; i++)
{
// printf("[%d]
%d \n",i, array[i]);
perRssi = (float)array[i];
mu += perRssi;
}
mu = mu/n;
//calc sigma
for(i = 0; i < n; i++)
{
perRssi = (float)array[i] -
mu;
perRssi = pow(perRssi, 2);
sigma += perRssi;
}
sigma = sigma/(n -1);
sigma = pow(sigma, 0.5);
int lowerLimit = 0.15*sigma + mu;//既有公式
// printf("lowerLimit
= %d\n", (int)lowerLimit);
int upperLimit = 3.09*sigma + mu;//既有公式
// printf("upperLimit
= %d\n", (int)upperLimit);
for(i = 0; i < n; i++)
{
tmp = array[i];
if((tmp >= lowerLimit)
&& (tmp <= upperLimit))
{
k++;
Average += tmp;
}
}
if( k > 0 )
{
Average = Average/k;
}
else
{
Average = mu;
}
return Average;
}
/*IPS 获取d函数*/
int widp_get_ap_location(struct
widp_cmd_msg_head *mhead)
{
struct list_head *pos;
int len = 0;
char buf[1024];
struct widp_cmd_msg_head *rcv_head =
(struct widp_cmd_msg_head*)buf;
char *msg = buf + sizeof(struct
widp_cmd_msg_head);
int id = mhead->area_id;
struct widp_location_ask_info *apinfo =
(struct widp_location_ask_info *)(mhead->msg);
struct widp_ap_location_node
*locaion_node;
int i;
float dis = 0;
/*get all location info*/
if(apinfo->num >= 0)
{
return
widp_get_ap_location_all(apinfo->num);
}
rcv_head->area_id = id;
rcv_head->cmd_type = WIDP_RCV_MSG;
pthread_mutex_lock(&widp_positioning_ap_list.lock);
list_for_each( pos,
&widp_positioning_ap_list.l)
{
locaion_node= list_entry(
pos, struct widp_ap_location_node, h);
if(MAC_IS_EQUAL(apinfo->bssid.mac,
locaion_node->ap_bssid.mac))
{
for(i=0 ; i <
WIDP_SENSOR_MAX; i++)
{
if(mac_zero(locaion_node->location[i].sensor.mac))
{
break;
}
if(locaion_node->location[i].dis[MAX_DISTANCE_NUM
- 1])
{
dis
= Gaussian_distribution(locaion_node->location[i].dis, MAX_DISTANCE_NUM);
}
else
if(locaion_node->location[i].index > 1)
{
dis
= Gaussian_distribution(locaion_node->location[i].dis,
locaion_node->location[i].index);
}
else
{
dis
= locaion_node->location[i].dis[0];
}
printf("Gaussian_distribution
dis %f\n", dis);
len +=
PRINTF_MAC_TO_STR(msg+len,locaion_node->location[i].sensor.mac);
if(locaion_node->location[i].name[0])
{
len
+= sprintf(msg+len, "|%s",locaion_node->location[i].name);
}
else
{
len
+= sprintf(msg+len, "|null");
}
len +=
sprintf(msg+len, "|(%d,%d)",
locaion_node->location[i].coordinate_x,
locaion_node->location[i].coordinate_y);
if(dis >
WIDP_AP_DISTANCE_MAX)
{
len
+= sprintf(msg+len, "|>100\n");
}
else
{
len
+= sprintf(msg+len, "|%d\n",(int)dis);
}
}
//memset(apn->location,
0 , WIDP_SENSOR_MAX* sizeof(struct location_info));
break;
}
}
pthread_mutex_unlock(&widp_positioning_ap_list.lock);
if(len == 0)
{
len += sprintf(msg+len,
"NO LOCATION INFO\n");
}
msg[len++] = 0;
rcv_head->msg_len = len;
len += sizeof(struct
widp_cmd_msg_head);
send_to_cmd_client(buf, len);
return 0;
}