Frequency coordination between CDMA and non-CDMA systems

Abstract

Mutual interference between non-CDMA (FM and TDMA) subscriber stations (SS) and CDMA base stations (BS), as well as interference between CDMA SS and non-CDMA BS are investigated. The noise figure is used as a measure of degradation of the receiver performance. It is shown that at a frequency offset of more than 870 kHz, the non-CDMA SS will not cause any degradation to the CDMA BS. Conversely, the CDMA BS will degrade the noise figure of the non-CDMA SS. It is also shown that a space separation (guard zone) of 144 dB path loss or more is sufficient in cases where the CDMA system shares the frequency band with the non-CDMA system. This can be achieved by having one tier of cells, operating at a different frequency, separating the two systems. The effect of a CDMA SS on an FM BS depends on the size of the CDMA BS. For large cells, the CDMA SS is required to transmit at full power with noticeable sidebands and will cause more degradation to the FM BS before the FM BS can degrade the CDMA SS noise figure. For medium size cells, the CDMA SS is not required to transmit at full power (hence, having much lower sidebands). In this case the FM BS will be able to tolerate the CDMA SS. Meanwhile, the CDMA SS will suffer degradation as it is moved closer to the FM BS. For small cells, the CDMA SS will transmit at much less than full power and will have no effect at all on the FM BS, even if moved very close to the FM BS.