A GSM cellular telephone standard requires a minimum of 9 dB rejection of interfering signal levels of -23 dBm at 3 MHz from the carrier, -33 dBm at 1.6 MHz from the carrier, and -43 dBm at 0.6 MHz from the carrier, for a carrier level of -99 dBm. Determine the required local oscillator phase noise at 3 MHz carrier frequency offset.

Phase noise is given by the expression C (dBm)-S (dB) –I (dBm)-10log (B). Substituting the given values in the above expression, the oscillator phase noise is -138.