# US 10,122,564 B2 · Wireless communication device and method therein for time synchronization in a wireless communication network

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- Number: US 10,122,564 B2
- Document ID: US10122564B2
- Status: Granted
- Kind: B2
- Application number: 15/543,884
- Filed: 2015-12-07
- Published: 2017-12-28
- Granted: 2018-11-06
- Earliest claimed: 2015-12-07
- Assignees: Telefonaktiebolaget LM Ericsson (publ)
- Applicants: Telefonaktiebolaget Lm Ericsson (Publ)
- Inventors: Hai Wang; Shaohua Li; Jianfeng Wang; Yanli Zheng
- Web page: https://patentgrep.com/patent/US10122564B2

## CPC

- H04L 27/266: {Fine or fractional frequency offset determination and synchronisation}
- H04L 25/0204: {of multiple channels}
- H04L 25/0212: {of impulse response}
- H04L 25/022: {of frequency response}
- H04L 27/2659: {Coarse or integer frequency offset determination and synchronisation}
- H04L 27/2663: {Coarse synchronisation, e.g. by correlation}
- H04L 27/2665: {Fine synchronisation, e.g. by positioning the FFT window}
- H04L 27/2695: {with channel estimation, e.g. determination of delay spread, derivative or peak tracking (channel estimation H04L25/0202)}
- H04L 27/2675: {Pilot or known symbols}
- H04L: TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION (arrangements common to telegraphic and telephonic communication H04M)

## Abstract

A wireless communication device and method therein for time synchronization in a wireless communication network are disclosed. The wireless communication device determines a first timing (tc) by performing a coarse time synchronization based on a synchronization signal received by the wireless communication device, wherein the received synchronization signal is sampled either in an original sampling rate or a reduced sampling rate. The wireless communication device determines a second timing (tf) by performing a fine time synchronization based on the determined first timing (tc) and the received synchronization signal.

## Claims

### Claim 1

A method performed in a wireless communication device for time synchronization in a wireless communication network, the method comprising:
determining a first timing, tc, by performing a coarse time synchronization based on a synchronization signal received by the wireless communication device, wherein the received synchronization signal is sampled either in an original sampling rate or a reduced sampling rate; and
determining a second timing, tf, by performing a fine time synchronization based on the determined first timing and the received synchronization signal, wherein
determining the first timing comprises:
selecting a number of timing offset, m, values with a granularity corresponding to or smaller than a length of the shortest cyclic-prefix supported by the synchronization signal;
obtaining channel estimates by performing channel estimations on the received synchronization signal for each selected timing offset value in frequency domain;
transforming the channel estimates in frequency domain to time domain;
calculating channel powers, Pm, for each selected timing offset value based on its channel estimates in time domain; and
determining the first timing based on the calculated channel powers.

### Claim 2 (depends on 1)

The method of claim 1, wherein the determining the second timing comprises:
selecting a number of timing error values, ε, with a granularity corresponding to one sample with the original sampling rate;
obtaining channel estimates by performing channel estimations on the received synchronization signal in frequency domain;
phase rotating the channel estimates based on each selected timing error value;
transforming the phase rotated channel estimates to time domain;
calculating channel powers, Pε, for each selected timing error value based on its phase rotated channel estimates in time domain; and
determining the second timing based on the calculated channel powers for each selected timing error value.

### Claim 3 (depends on 2)

The method according to claim 2, wherein the obtaining channel estimates when determining the second timing comprises:
shifting the received synchronization signal in time domain by the determined first timing adjusted by a timing advancement parameter, A, wherein the timing advancement parameter corresponds to a largest timing error, E;
transforming the shifted synchronization signal in time domain to frequency domain;
selecting frequency components of sub-carriers corresponding to a bandwidth of the synchronization signal; and
multiplying the selected frequency components with a conjugate of the synchronization signal in frequency domain to obtain the channel estimates.

### Claim 4 (depends on 2)

The method according to claim 2, wherein the calculating channel powers for each selected timing error value comprises:
calculating the channel power by combining the channel estimates at its origin position and at a number of its neighbors positions.

### Claim 5 (depends on 2)

The method according to claim 2, wherein the determining the second timing based on the calculated channel powers for each selected timing error value comprises:
determining a maximum timing error value, ε*M, by searching a maximum channel power in the calculated channel powers for each of the selected timing error values;
subtracting the maximum timing error value and the timing advancement parameter from the determined first timing to obtain the second timing.

### Claim 6 (depends on 1)

The method according to claim 1, wherein the obtaining channel estimates when determining the first timing further comprises:
shifting the received synchronization signal in time domain by the selected timing offset value;
transforming the shifted synchronization signal in time domain to frequency domain;
selecting frequency components of sub-carriers corresponding to a bandwidth of the synchronization signal; and
multiplying the selected frequency components with a conjugate of the synchronization signal in frequency domain to obtain the channel estimates for the selected timing offset value.

### Claim 7 (depends on 1)

The method according to claim 1, wherein the calculating channel powers when determining the first timing comprises:
searching a peak position in the channel estimates in time domain for the selected timing offset value; and
calculating the channel power for the selected timing offset value by combining its channel estimates at the peak position and at a number of positions neighbored to the peak position.

### Claim 8 (depends on 1)

The method according to claim 1, wherein the determining the first timing further comprises:
determining a maximum timing offset value, m*M, by searching a maximum channel power in the calculated channel powers for each of the selected timing offset values;
calculating a channel gravity position;
combining the maximum timing offset value with the channel gravity position to obtain the first timing.

### Claim 9

A wireless communication device for time synchronization in a wireless communication network, wherein the wireless communication device is configured to:
determine a first timing, tc, by being configured to perform a coarse time synchronization based on a synchronization signal received by the wireless communication device, wherein the received synchronization signal is sampled either in an original sampling rate or a reduced sampling rate; and
determine a second timing, tf, by being configured to perform a fine time synchronization based on the determined first timing and the received synchronization signal, wherein
the wireless communication device is configured to determine the first timing by performing steps comprising:
selecting a number of timing offset, m, values with a granularity corresponding to or smaller than a length of the shortest cyclic-prefix supported by the synchronization signal;
obtaining channel estimates by performing channel estimations on the received synchronization signal for each selected timing offset value in frequency domain;
transforming the channel estimates in frequency domain to time domain;
calculate channel powers, Pm, for each selected timing offset value based on its channel estimates in time domain; and
determining the first timing based on the calculated channel powers.

### Claim 10 (depends on 9)

The wireless communication device according to claim 9, wherein the wireless communication device is configured to determine the second timing by performing step comprising:
selecting a number of timing error values, ε, with a granularity corresponding to one sample with the original sampling rate;
obtaining channel estimates by performing channel estimations on the received synchronization signal in frequency domain;
phase rotating the channel estimates based on each selected timing error value;
transforming the phase rotated channel estimates to time domain;
calculating channel powers, Pε, for each selected timing error value based on its phase rotated channel estimates in time domain; and
determining the second timing based on the calculated channel powers for each selected timing error value.

### Claim 11 (depends on 10)

The wireless communication device according to claim 10, wherein the wireless communication device is configured to obtain channel estimates, when determining the second timing, by being configured to:
shift the received synchronization signal in time domain by the determined first timing adjusted by a timing advancement parameter, A, wherein the timing advancement parameter corresponds to a largest timing error, E;
transform the shifted synchronization signal in time domain to frequency domain;
select frequency components of sub-carriers corresponding to a bandwidth of the synchronization signal; and
multiply the selected frequency components with a conjugate of the synchronization signal in frequency domain to obtain the channel estimates.

### Claim 12 (depends on 10)

The wireless communication device according to claim 10, wherein the wireless communication device is configured to calculate channel powers, Pε, for each selected timing error value, ε, by being configured to:
calculate the channel power by combining the channel estimates at its origin position and at a number of its neighbors positions.

### Claim 13 (depends on 10)

The wireless communication device according to claim 10, wherein the wireless communication device is configured to determine the second timing based on the calculated channel powers for each selected timing error value, by being configured to:
determine a maximum timing error value, ε*M, by searching a maximum channel power in the calculated channel powers for each of the selected timing error values; and
subtract the maximum timing error value and the timing advancement parameter from the determined first timing to obtain the second timing.

### Claim 14 (depends on 9)

The wireless communication device according to claim 9, wherein the wireless communication device is further configured to obtain channel estimates, when determining the first timing, by being configured to:
shift the received synchronization signal in time domain by the selected timing offset value;
transform the shifted synchronization signal in time domain to frequency domain;
select frequency components of sub-carriers corresponding to a bandwidth of the synchronization signal; and
multiply the selected frequency components with a conjugate of the synchronization signal in frequency domain to obtain the channel estimates for the selected timing offset value.

### Claim 15 (depends on 9)

The wireless communication device according to claim 9, wherein the wireless communication device is configured to calculate channel powers, when determining the first timing, by being configured to:
search a peak position in the channel estimates in time domain for the selected timing offset value; and
calculate the channel power for the selected timing offset value by combining its channel estimates at the peak position and at a number of positions neighbored to the peak position.

### Claim 16 (depends on 9)

The wireless communication device according to claim 9, wherein the wireless communication device is configured to determine the first timing by being configured to:
determine a maximum timing offset value, m*M, by searching a maximum channel power in the calculated channel powers for each of the selected timing offset values;
calculate a channel gravity position; and
combine the maximum timing offset value with the channel gravity position to obtain the first timing.