Method for carrier frequency offset fine estimation in TD-SCDMA system

• US 20060140257A1
• Filed: 12/09/2005
• Published: 06/29/2006
• Est. Priority Date: 12/24/2004
• Status: Active Grant

• Current Assignee: Spreadtrum Communications USA
• Original Assignee: Spreadtrum Communications USA
• Inventors: Liu, Jiwu
• Granted Patent: US 7,693,209 B2
• Time in Patent Office: Days
• US Class Current: 375/148
• CPC Class Codes: H04B 1/707 using direct sequence modulation
• CPC Class Codes: H04L 27/0014 Carrier regulation of chaotic carriers H04L27/001; for multicarrier receivers H04L27/2657

Abstract

A simple and efficient method is provided for frequency offset fine estimation. The method comprises: subtracting the QPSK modulation phase of a synchronization code from its received phase to generate the phase drift, and then computing the frequency offset based on the phase drift.

Claims

1. A method for frequency offset fine estimation in a TD-SCDMA system comprising:

subtract a QPSK modulation phase of a transmitted sequence from its operational phase to generate a phase drift;

determining the frequency offset based on the phase drift.

2. The method of claim 1, wherein said QPSK modulation phase is established by determining the QPSK modulation phase of a SYNC-DL sequence after a cell search process upon a mobile handset powering on.

3. The method of claim 1, wherein said QPSK modulation phase is established by detecting a P-CCPCH'"'"'s presence or not so as to inversely determine between two QPSK modulation sequences S1 or S2 of four consecutive SYNC-DL codes.

4. A method of frequency offset fine estimation comprising:

completing a cell search process and reading a BCH message;

determining a P-CCPCH position;

based upon the P-CCPCH position determining whether sequence S1 or S2 is present by if a P-CCPCH is present in a next superframe, sequence S1 is ascertained and if there is no such P-CCPCH is present in said next superframe, sequence S2 is ascertained;

determining a QPSK modulation of the SYNC-DL code based upon the sequence determined;

measuring the phase of the received SYNC-DL sequence;

substracting the QPSK modulation from an operational phase to determine a phase drift; and

deriving the frequency offset using the phase drift with the equation of Δ

φ

=Δ

f* T, where Δ

φ

is phase drift, Δ

f represents frequency offset and T denotes sequence duration.