P-SCHsequences.doc

TSG RAN WG1 meeting #49 R1-072321 Kobe, Japan, May 7-11, 2007 Agenda Item: 7.2 SCH and Cell Search Source: Huawei Title: P-SCH sequences Document for: Discussion and decision Introduction At the previous meeting (RAN1#48bis) it was agreed that the primary synchronization (P-SCH) signals have non-repetitive structure, and are based on the Zadoff-Chu (ZC) sequences [1]. The P-SCH signals are OFDM signals with up to 72 active subcarriers, centred around the DC subcarrier [2]. The active subcarriers are modulated with the elements of a cell-specific P-SCH sequence du(n), n=0,…,71, of length L=72, selected from a set of three different ZC sequences with root indices u=u1, u2 and u3. The mapping of a P-SCH sequence du(n) to available subcarriers is illustrated in Fig.1. Fig.1. Mapping of a P-SCH sequence to subcarriers. In [3] it was proposed that du(n) are the ZC sequences of length 71, with root indices u=1, 5 and 70. The reason for choosing the length 71 was to maximise the utilization of available subcarriers for P-SCH signal, while in the same time minimize the pair-wise cross-correlations of corresponding P-SCH signals in time domain. With this proposal one available sub-carrier remains unused. In [4] it was proposed that du(n) are the ZC sequences of length 72, with no specified root indices u. It can be shown that the maximum crosscorrelations of the multiple P-SCH signals obtained from the different root indices of ZC sequences of length 72 are higher than if the length of ZC sequences is 71 or 73. It is worth mentioning that the P-SCH signals generated through mapping shown in Fig.1 are in time domain not equivalent to ZC sequences, because the ZC sequence in frequency domain is not mapped onto consecutive subcarriers (DC subcarrier is skipped). Because of that, the matched filters corresponding to such P-SCH signals cannot be implemented by using a very efficient matched filter structure available for any GCL sequence [5]. In this paper we sh