Searcher

"CDMA receivers typically employ a rake architecture to demodulate the received signal. In a rake architecture, a separate finger (a correlator receiver) is assigned to each detected multipath. The output of the fingers are then compensated for delay and phase and combined into one symbol. Correctly identifying the multipath profile at any given time is critical to the performance of the system. Using additional correct multipaths provides more signal energy to the rake receiver while combining invalid multipaths increases the noise level. Furthermore, the multipath profile changes in time due to dynamic nature of the wireless channel.

The multipath searcher in the base station is responsible for continuously monitoring the channel and determining the multipath profile. A microprocessor uses the profile data obtained by the searcher, to allocate the available rake fingers to the different multipaths.

The multipath searcher in the mobile is used to find frame synchronization and identify the group of the cell found, by correlating the Down-Link Common Pilot Channel (CPICH) data with a secondary synchronization code and identifying the maximum correlation value.

Features
Over-sampling factor: Two samples per chip
Uncertainty window: 128 chips (256 samples)
Number of users: One
Coherent correlation length: 15 slots (one radio frame)
Non-coherent correlation size: 15 slots (one radio frame)
Number of pilot bits per slot: Three to eight
Input data quantization: Variable"