iphone - How to find out carrier signal strength programmatically

Question

Here is the code that I have used to find out carrier signal strength:

int getSignalStrength()
{
    void *libHandle = dlopen("/System/Library/Frameworks/CoreTelephony.framework/CoreTelephony", RTLD_LAZY);
    int (*CTGetSignalStrength)();
    CTGetSignalStrength = dlsym(libHandle, "CTGetSignalStrength");
    if( CTGetSignalStrength == NULL) NSLog(@"Could not find CTGetSignalStrength");
    int result = CTGetSignalStrength();
    dlclose(libHandle);
    return result;
}

It is giving me values between 60 to 100, but when I test the signal strength in device by calling to this *3001#12345#* number it showed me as -65. Below I have attached the screenshot. Is the value coming from getSignalStrength() accurate? Then why is it returning positive values always?

Answer 1

getSignalStrength() is showing negated dB attenuation, e.g. -(-60) == 60. The call in is displaying it more conventionally as a measurement less than zero. Yes, these kinds of variations are typical. Even in strictly controlled conditions you can get +/- 20 decibels. One way you can fix it is to take a series of measurements over time, say every second, and keep a running list of the last 10 or so measurements. Then report the mean or median or some other statistic. In my experience this cuts down the variation a lot. You can also do standard deviation to provide a measure of reliability.