850 MHz & 900 MHz Co-Existence 850 MHz Out-Of-Band Emissions Problem

Network administrators and engineers around the globe acknowledge that 850 MHz and 900 MHz spectrums generate interference problems when deployed in the same geographic area. This interference occurs in two ways:

  • Receiver blocking and resultant intermodulation interference, caused by high power levels from the 850 MHz downlink (DL) transmit hitting the front end of the 900 MHz BTS receiver.
  • Out-of-band emissions from 850 MHz BTS entering the 900 MHz uplink (UL) band.

The interference caused by out-of-band emissions from an 850 MHz BTS can only be fixed by fitting a filter to the 850 MHz transmitter (Carrier-2 in this paper) to sufficiently reduce any out-of-band transmissions. Addressing the receiver blocking problem requires a filter in the 900 MHz site (Carrier-1 in this paper). This paper incorporates a link budget methodology to estimate the additional attenuation required to address the 850 MHz out-of-band emission issue.