Adaptive receive filter structures for UMTS

Receive filtering in the Universal Mobile Telecommunication System (UMTS) handset has two functions. Performing Root- Raised Cosine (RRC) filtering to mitigate Inter Chip Interference (ICI) and providing selectivity in order to be able to operate in the presence of strong interference. This strong interference is however not always present in practice. Therefor it is attractive to make the selectivity adaptive on the measured amount of interference. This is possible with an adaptive digital receive filter structure found in literature, which reduces the number of used filter coefficients when less selectivity is required. This reduces the required number of operations per filtered sample. This structure however has the disadvantage that it increases ICI for low selectivity. This can be solved by using a modified adaptive digital receive filter structure which uses optimized sets of filter coefficients with different lengths for a range of selectivity requirements. The required number of operations per filtered sample still reduces when less selectivity is required, but the filter structure becomes more complex because it needs to store and load the sets of filter coefficients.