Adjacent channel interference in UMTS networks

One of the purposes of receive filtering in a Universal Mobile Telecommunication System (UMTS) handset receiver is to attenuate out-of-channel interference to provide channel selectivity. A UMTS handset receiver using a receive filter adaptive on out-of-channel interfer- ence level can be more computationally efficient than a handset with a fixed receive filter provided that the hand- set operates in low out-of-channel interference conditions often enough. The UMTS Adjacent Channel Selectivity (ACS) test case requires the adaptive receive filter to pro- vide a worst case ACS of 33 dB. An adaptive receive filter is more computationally efficient than a fixed receive fil- ter when the required ACS is less than 23 dB, because the added complexity of measuring the out-of-channel interfer- ence is compensated for by the reduction in the required number of filter taps to achieve the ACS. Measurements of the out-of-channel interference show that currently the interference levels for which the maximum ACS of 33 dB is required are hardly ever reached in practice. For the currently measured interference levels an adaptive receive filter will be computationally more efficient than a fixed receive filter 97% of the time. However, the current out-of-channel interference mea- surements might be on the optimistic side, because the loads of the UMTS networks are low. When these loads in- crease in the future, the out-of-channel interference levels may increase and the advantage in computational efficiency of the adaptive receive filter will be reduced.