Reduced complexity Primary and secondary synchronisation codes with good aperiodic correlation properties for the WCDMA system

1 Reduced complexity Primary and secondary synchronisation codes with good aperiodic correlation properties for the WCDMA system Texas Instruments, April 12 1999 Summary: The 3Gpp S1.13 on FDD [1], spreading and modulation uses the primary (PSC) and secondary synchronization code (SSC) words based upon a hierarchical sequence and length 256 Hadamard sequences respectively. The complexity of stage 1 of acquisition for the above codes is 30 complex adds per correlation output of the input data. Further, as has been brought to notice by Nortel [4] that the aperiodic cross correlation from the SSC’s to the PSC for the current sequences is significant. This could impact stage 1 of acquisition, depending upon the number of slots chosen for averaging during stage 1. In this proposal we consider alternative sequences for the PSC and the SSC based upon the Golay sequences and show that they have the following advantages: (1) The complexity of stage 1 of acquisition is reduced by half to 15 complex adds per correlation output. Further, a detailed comparison of the current and proposed PSC schemes based upon the number of adds and the number of memory read/write shows that the proposed scheme should give an estimated 40 % savings in power consumption of stage 1 of acquisition for the current scheme. Further, the aperiodic auto correlation properties of the proposed Golay PSC are better than the currently used Hierarchical PSC. (2) For both the one slot, eight slot averaging during stage 1, the SSC aperiodic cross correlation to PSC is much superior for the proposed sequences compared to the currently used PSC, SSC sequences and also the Nortel proposed SSC sequences. The expected improvement in the performance of stage 1 for proposed sequences over currently used sequences is between 0.9 to 2.6 dB depending upon the comma free code of the base station. (3) The complexity of stage 2 of acquisition is unchanged for the proposed SSC sequences. (4) The only required change in the WCDMA standard is a specification for different PSC and SSC codes. The basic structure of the synchronization channel (SCH) is unchanged; thus the overall change in the WCDMA standard is very small.