Android : i need to find mobile signal strength for current and changing status also.anybody help me

my coding is class myPhoneStateListener extends PhoneStateListener {

   @Override
    public void onSignalStrengthsChanged(SignalStrength signalStrength) {
        super.onSignalStrengthsChanged(signalStrength);
        SignalStrength = signalStrength.getGsmSignalStrength();
        SignalStrength = (2 * SignalStrength) - 113; // -> dBm   



        int internet = getConnectivityStatus(context);

       if( TYPE_WIFI == internet){

            txt3.setText("Wifi Network availability "+ SignalStrength + "%");

        }

       if( TYPE_MOBILE == internet){

            txt3.setText("Mobile Network availability "+ SignalStrength + "%");

        }   

        if (TYPE_NOT_CONNECTED == internet) {
            txt3.setText("No Network....");
        } 

    }

it only shows the current ststus of mobile signalstrength.i need the status of changing mobile network value