# US 2006/0133526 A1 · Method for joint time synchronization and frequency offset estimation in OFDM system and apparatus of the same > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2006/0133526 A1 - Document ID: US20060133526A1 - Status: Published application - Kind: A1 - Application number: 11/286,874 - Filed: 2005-11-22 - Published: 2006-06-22 - Earliest claimed: 2004-11-25 - Assignees: Ntt Docomo, Inc. - Inventors: Zhongshan Zhang; Hidetoshi Kayama - Web page: https://patentgrep.com/patent/US20060133526A1 ## CPC - H04L 27/2613: {Structure of the reference signals} - H03M 13/27: using interleaving techniques - H04L 27/2657: {Carrier synchronisation} - H04L 27/2662: {Symbol synchronisation} - H04L: TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION (arrangements common to telegraphic and telephonic communication H04M) - H03M: CODING; DECODING; CODE CONVERSION IN GENERAL (using fluidic means F15C4/00; optical analogue/digital converters G02F7/00; coding, decoding or code conversion, specially adapted for particular applications, see the relevant subclasses, e.g. G01D, G01R, G06F, G06T, G09G, G10L, G11B, G11C, H04B, H04L, H04M, H04N; ciphering or deciphering for cryptography or other purposes involving the need for secrecy G09C) ## Abstract Embodiments of the present invention include a method for performing joint time synchronization and carrier frequency offset estimation in a wireless communication system, comprising steps of: on a transmitter: performing frequency domain spreading and interleaving on input data by using a predetermined spreading factor (SF) to generate a frequency domain training symbol; performing Inverse Discrete Fourier Transformation (IDFT) on the generated frequency domain training symbol to generate a first time domain training symbol; reversely copying the generated first time domain training symbol to a second time domain training symbol such that a complete training sequence is formed; and on a receiver: detecting an average power of received signals to judge the coming of a training sequence, and performing coarse frame synchronization; performing joint fine frame synchronization and carrier frequency offset estimation based on a received training sequence; and compensating for the carrier frequency offset based on the carrier frequency offset estimation result so as to eliminate the carrier frequency offset. In addition, embodiments of the present invention also include an apparatus for performing joint time synchronization and carrier frequency offset estimation and a method for generating a training sequence. ## Claims ### Claim 1 A method for performing joint time synchronization and carrier frequency offset estimation in a wireless communication system, comprising: on a transmitting side: performing frequency domain spreading and interleaving on input data by using a predetermined spreading factor (SF) to generate a frequency domain training symbol; performing Inverse Discrete Fourier Transformation (IDFT) on the generated frequency domain training symbol to generate a first time domain training symbol; reversely copying the generated first time domain training symbol to a second time domain training symbol such that a complete central-symmetric comb-shaped training sequence is formed; and on a receiving side: detecting an average power of received signals to judge the coming of the training sequence, and performing coarse frame synchronization; performing joint fine frame synchronization and carrier frequency offset estimation based on the received training sequence; and compensating for the carrier frequency offset based on the carrier frequency offset estimation result to eliminate the carrier frequency offset. ### Claim 2 (depends on 1) The method according to claim 1 further comprising encoding the input data stream and mapping the encoded data stream to a constellation. ### Claim 3 (depends on 1, 2) The method according to any of claims 1 or 2, further comprising serial/parallel converting the encoded data stream. ### Claim 4 (depends on 1) The method according to claim 1, further comprising mapping the interleaved frequency domain training symbol to each sub-carrier. ### Claim 5 (depends on 1) The method according to claim 1, further comprising reducing the Peak Average Power Ratio (PAPR) of the signals to be transmitted. ### Claim 6 (depends on 1) The method according to claim 1, wherein detecting the average power of received signals comprises detecting the power of a series of received samples and determining whether the detected power is larger than a predetermined threshold or not. ### Claim 7 (depends on 1) The method according to claim 1, further comprising estimating a total carrier frequency offset and compensating for the total carrier frequency offset. ### Claim 8 (depends on 7) The method according to claim 7, wherein estimating the total carrier frequency offset comprises performing both the carrier frequency offset acquisition and fine estimation on the carrier frequency offset after the acquisition, and then summing the estimation results. ### Claim 9 (depends on 1) The method according to claim 1, further comprising discriminating and detecting multi-path signals and collecting the detected multi-path signals in a case where multi-path signals exist. ### Claim 10 (depends on 7) The method according to claim 7, further comprising performing Discrete Fourier Transformation (DFT) on the signals whose carrier frequency offset has been compensated for. ### Claim 11 An apparatus for performing joint time synchronization and carrier frequency offset estimation in a wireless communication system, the apparatus comprising: a transmitter including: a variable spreading factor (SF) control unit to set a variable spreading factor; a frequency domain spreading and interleaving unit to spread and interleaving input data in frequency domain by using the spreading factor (SF) to generate a frequency domain training symbol; an Inverse Discrete Fourier Transformation unit to transform the frequency domain training symbol to generate a first time domain training symbol; a symbol reverse repetition unit to reverse copying the generated first time domain training symbol to a second time domain training symbol such that a central-symmetric comb-shaped training sequence is formed; a receiver including: a power detection and coarse frame synchronization unit to detect the power of received data and performing coarse frame synchronization on the received data when the training sequence is detected; a joint fine frame synchronization and carrier frequency offset estimation unit to perform joint fine frame synchronization and carrier frequency offset estimation on the received data based on the received training sequence. ### Claim 12 (depends on 11) The apparatus for performing joint time synchronization and carrier frequency offset estimation in a wireless communication system according to claim 11, wherein the transmitter further comprises a serial/parallel conversion unit to perform serial/parallel conversion complex points on a constellation. ### Claim 13 (depends on 11) The apparatus for performing joint time synchronization and carrier frequency offset estimation in a wireless communication system according to claim 11, wherein the transmitter further comprises a Peak Average Power Ratio (PAPR) reduction unit to reduce PAPR of the data. ### Claim 14 (depends on 11) The apparatus for performing joint time synchronization and carrier frequency offset estimation in a wireless communication system according to claim 11, wherein the power detection and coarse frame synchronization means comprises a power detection unit to detect the average power of a series of received signals to determine whether the detected power is larger than a predetermined threshold or not, and a coarse frame synchronization unit to perform coarse frame synchronization based on the detected signals. ### Claim 15 (depends on 11) The apparatus for performing joint time synchronization and carrier frequency offset estimation in a wireless communication system according to claim 11, wherein the joint fine frame synchronization and carrier frequency offset estimation unit comprises a fine frame synchronization and frequency offset acquisition unit to perform joint fine frame synchronization and carrier frequency offset estimation. ### Claim 16 (depends on 11) The apparatus for performing joint time synchronization and carrier frequency offset estimation in a wireless communication system according to claim 11 wherein the receiver further comprises a multi-path detection and discrimination unit to discriminate multi-path signals and detecting the power of the multi-path signals. ### Claim 17 (depends on 11) The apparatus for performing joint time synchronization and carrier frequency offset estimation in a wireless communication system according to claim 11, wherein the joint fine frame synchronization and carrier frequency offset estimation unit comprises a carrier frequency offset fine adjustment unit to estimate and correct the remaining carrier frequency offset after the carrier frequency offset acquisition. ### Claim 18 (depends on 11) The apparatus for performing joint time synchronization and carrier frequency offset estimation in a wireless communication system according to claim 11 wherein the receiver comprises a carrier frequency offset compensation unit to compensate for the carrier frequency offset based on the estimated carrier frequency offset. ### Claim 19 A method of generating a training sequence for joint time synchronization and carrier frequency offset estimation in a wireless communication system, comprising: generating a spreading factor (SF); spreading and interleaving selected complex points on a constellation to generate a frequency domain training symbol; performing Inverse Discrete Fourier Transformation (IDFT) on the generated frequency domain training symbol to obtain a first time domain training symbol; and reversely repeating the generated first time domain training symbol to a second time domain training symbol such that a central-symmetric comb-shaped training sequence is formed. ### Claim 20 (depends on 19) The method according to claim 19, wherein the spreading and interleaving step comprising repeating the selected complex points on the constellation for SF times (where SF is the n power of 2 and n is an integer) to form complete frequency domain training symbol. ### Claim 21 (depends on 19) The method according to claim 19, wherein there are SF-1 zero samples between any two adjacent non-zero samples with respect to the generated time domain training symbol.