Primary Searcher Using Golay Correlator in WCDMA

The main objective of 3G cellular systems is to provide higher data rate services with improved service quality and capacity compared to second generation systems. The currently standardized Universal Mobile Telecommunication system (UMTS) is based on Wideband Code Division Multiple Access (WCDMA) technology. This standard employs spreading codes to differentiate physical channels from the same base station and scrambling codes are used to differentiate base stations. During the cell search, the User Equipment (UE) searches for a cell and determines the downlink scrambling code and frame synchronization of that cell. The cell search is typically carried out in three steps: Slot synchronization, Frame synchronization and code-group identification, Scrambling-code identification.

The first step of the cell search procedure, the UE uses the Synchronous Channel's (SCH) primary synchronization code to acquire slot synchronization of a cell. The primary synchronization code (PSC) is constructed as a so-called generalized hierarchical Golay sequence. Detection is typically done with a single matched filter matched to the primary synchronization code which is common to all cells. The slot timing of the cell can be obtained by detecting peaks in the matched filter output. The PSC code has a length of 256 chips. The conventional matched filter requires at least 255 multiplier unit and addition units. This is a huge requirement. To overcome this, taking the structural advantages of PSC, a simpler form of matched filter called Golay Correlator is used. This brings down the processing requirements considerably.