How can I evaluate the GPS signal strength? (iPhone)

I need a way of categorising the strength of the GPS signal. So far I have come across the horizontalAccuracy property of CLLocation (Class Reference).

To be more specific I need to create something like the following; the issue I'm having is filling in the if statements.

if (someLocation.horizontalAccuracy ...)
{
    // No Signal
}
else if (someLocation.horizontalAccuracy ...)
{
    // Poor Signal
}
else if (someLocation.horizontalAccuracy ...)
{
    // Average Signal
}
else if (someLocation.horizontalAccuracy ...)
{
    // Good Signal
}
else
{
    // Excellent Signal
}

Please can someone assist me in this?