Following the source of WiFi signal using rssi - arduino

Question

I have an arduino uno with wifi shield and I want it to be able to go to source of signal.
The rssi that I get is usually -80 dBm above -40 dBm I assume the robot has found the source.
So the robot goes straight and checks every 2 seconds the rssi if the new signal is worse than it was before it turns 90 degrees right and goes straight and keeps doing that until it finds the source.
Void loop() is the logic of the robot.
int angle = 90;
char ssid[]="AndroidAP";
bool sourceFound = false;
long rssi = -100;
long prevRssi = 0;
void setup() {
Serial.begin(9600);
updateRSSI();
servoLeft.attach(8);
servoRight.attach(9);
goStraight();
}
void loop() {
if(!sourceFound){
updateRSSI();
if(prevRssi>rssi){
turnRight();
goStraight();
delay(2500);
}
if(rssi>-41){
stayStill();
detachServos();
sourceFound = true;
Serial.print("Source found.");
Serial.println();
}
}
}
/*MOVEMENT CONTROLS*/
void turnLeft(){
servoLeft.writeMicroseconds(1300);
servoRight.writeMicroseconds(1300);
delay(angle*10.6);
}
void turnRight(){
servoLeft.writeMicroseconds(1700);
servoRight.writeMicroseconds(1700);
delay(angle*10.6);
}
void turnAround(){
if((double)rand() / (double)RAND_MAX==0){
turnLeft();
turnLeft();
}else{
turnRight();
turnRight();
}
}
void stayStill(){
servoLeft.writeMicroseconds(1500);
servoRight.writeMicroseconds(1500);
}
void goStraight(){
servoLeft.writeMicroseconds(1600);
servoRight.writeMicroseconds(1444 );
}
void detachServos(){
servoLeft.detach();
servoRight.detach();
}
/*MOVEMENT CONTROLS*/
/*WIFI SHIELD CONTROLS*/
void updateRSSI(){
prevRssi = rssi;
uint8_t available_networks = WiFi.scanNetworks();
for (uint8_t net = 0; net < available_networks; ++net)
{
if (strcmp(WiFi.SSID(net), ssid) == 0)
{
// ssidFound = true;
rssi = WiFi.RSSI(net);
if(rssi-prevRssi<-10){ //disregard the measurement and try again
rssi = prevRssi;
updateRSSI();
}
Serial.print("Old: ");
Serial.print(prevRssi);
Serial.print(" dBm ");
Serial.print("New: ");
Serial.print(rssi);
Serial.print(" dBm");
Serial.println();
break;
}
}
}
The problem is that the signal varies a lot which will cause robot sometimes to turn right even when it's pretty close to the source and always going right is not the most effective way of getting to router it is quite random. Is there an easier way or more efficient way to find and get to the source?

Answer 1

Basically your robot is doing the localization part of a common task called "wardriving" (sounds illegal but it's not). I was recently doing some research in pretty much exactly what you were doing although some papers found that essentially the signal strength of WiFi stations is to weak and inconsistent for use.
Dartmouth study (Page 14) This study found that using typical war driving methods they were only able to detect between 40 and 60 % of all WiFi nodes and on average was around 30-40m of error from the actual transmitter.
Another study (Page 4) Here you have a plot of 3 base stations being sampled for signal strength at a constant distance away. You will notice a bell curve which looks to have a standard deviation of at least 5 (sadly no table for the data). However that does pretty clearly show how noisy of a signal you should expect.
I'm not saying that your goal is impossible I am saying however you will need to do a lot of filtering and move very slowly (something my project could not do). Contrary to instincts WiFi signal strength is incredibly noisy making accurate wardriving difficult without an extremely large data set. Hope having these papers at least helps curve your expectations.