Method of clock synchronization between transmitter and receiver

1 . A method of clock synchronization between a transmitter and a receiver, comprising:

sampling a first receiver timestamp and a second receiver timestamp of the receiver at a first time and a second time respectively;

sampling a first transmitter timestamp and a second transmitter timestamp of the transmitter at a third time and a fourth time respectively;

sampling a first timing synchronization function (TSF) receiver timestamp and a second TSF receiver timestamp by a Wi-Fi TSF at the first time and the second time respectively;

sampling a first TSF transmitter timestamp and a second TSF transmitter timestamp by the Wi-Fi TSF at the third time and the fourth time respectively;

generating an initial timestamp according to the first receiver timestamp and the first transmitter timestamp;

generating an initial TSF timestamp according to the first TSF receiver timestamp and the first TSF transmitter timestamp;

generating a target phase difference according to the initial timestamp, the initial TSF timestamp, the first receiver timestamp, the second receiver timestamp, the first TSF receiver timestamp, the second TSF receiver timestamp, the second TSF transmitter timestamp, and the second transmitter timestamp; and

performing a coarse tune at a receiver system clock periodically to compensate the target phase difference.

2 . The method of claim 1 , wherein generating the initial timestamp according to the first receiver timestamp and the first transmitter timestamp is subtracting the first transmitter timestamp from the first receiver timestamp to generate the initial timestamp.

3 . The method of claim 1 , wherein generating the initial TSF timestamp according to the first TSF receiver timestamp and the first TSF transmitter timestamp is subtracting the first TSF transmitter timestamp from the first TSF receiver timestamp to generate the initial timestamp.

4 . The method of claim 1 , wherein generating the target phase difference according to the initial timestamp, the initial TSF timestamp, the first receiver timestamp, the second receiver timestamp, the first TSF receiver timestamp, the second TSF receiver timestamp, the second TSF transmitter timestamp, and the second transmitter timestamp is:

Target

⁢

Phase

⁢

Difference

=

(

R

1

-

T

INI

)

+

(

R

2

-

R

1

)

*

T

⁢

S

⁢

F

T

⁢

2

-

(

T

⁢

S

⁢

F

R

⁢

1

-

T

⁢

S

⁢

F

INI

)

T

⁢

S

⁢

F

R

⁢

2

-

T

⁢

S

⁢

F

R

⁢

1

-

T

2

wherein:

R 1 is the first receiver timestamp;

R 2 is the second receiver timestamp;

T INI is the initial timestamp;

TSF T2 is the second TSF transmitter timestamp;

TSF R1 is the first TSF receiver timestamp;

TSF INI is the initial TSF timestamp;

TSF R2 is the second TSF receiver timestamp; and

T 2 is the second transmitter timestamp.

5 . The method of claim 4 wherein the coarse tune is performed according to a following equation:

Coarse

⁢

tune

=

Target

⁢

Phase

⁢

Difference

(

TS

⁢

F

T

⁢

2

-

TSF

T

⁢

1

)

*

Tf

×

TSFf

wherein:

TSF T1 is the first TSF transmitter timestamp;

Tf is a frequency of a system clock; and

TSFf is a frequency of a TSF clock.

6 . The method of claim 5 , wherein the frequency of the system clock is about 10 MHz, and the frequency of the TSF clock is about 1 MHz.

7 . The method of claim 4 , further comprising:

sampling an ith receiver timestamp and an (i−1)th receiver timestamp by a receiver system clock at an ith time and an (i−1)th time respectively;

sampling an ith transmitter timestamp and an (i−1)th transmitter timestamp by a transmitter system clock at a jth time and a (j−1)th time respectively;

sampling an ith TSF receiver timestamp and an (i−1)th TSF receiver timestamp by the Wi-Fi TSF at the ith time and the (i−1)th time respectively;

sampling an ith TSF transmitter timestamp and an (i−1)th TSF transmitter timestamp by the Wi-Fi TSF at the jth time and the (j−1)th time respectively;

generating a phase difference according to the initial timestamp, the initial TSF timestamp, the ith receiver timestamp, the (i−1)th receiver timestamp, the ith TSF transmitter timestamp, the ith TSF receiver timestamp, the (i−1)th TSF receiver timestamp and the ith transmitter timestamp;

generating first differences between the target phase difference and phase differences;

applying a loop filter to filter the first differences to an average difference; and

performing a fine tune at receiver system clock periodically to compensate the average difference;

wherein i and j are integers larger than 2.

8 . The method of claim 7 , wherein generating the phase difference according to the initial timestamp, the initial TSF timestamp, the ith receiver timestamp, the (i−1)th receiver timestamp, the ith TSF transmitter timestamp, the ith TSF receiver timestamp, the (i−1)th TSF receiver timestamp and the ith transmitter timestamp is:

Phase

⁢

Diff

=

(

R

i

-

1

-

T

INI

)

+

(

R

i

-

R

i

-

1

)

*

T

⁢

S

⁢

F

T

i

-

(

T

⁢

S

⁢

F

R

i

-

1

-

T

⁢

S

⁢

F

INI

)

T

⁢

S

⁢

F

R

i

-

T

⁢

S

⁢

F

R

i

-

1

-

T

i

wherein:

R i-1 is the (i−1)th receiver timestamp;

R i is the ith receiver timestamp;

TSF T i is the ith TSF transmitter timestamp;

TSF R i-1 is the (i−1)th TSF receiver timestamp;

TSF R i is the ith TSF receiver timestamp; and

T i is the ith transmitter timestamp.

9 . The method of claim 8 , wherein generating the first differences between the target phase difference and the phase differences comprises subtracting the target phase difference from the phase difference to generate a first difference.

10 . The method of claim 9 , wherein the fine tune is performed according to a following equation:

fine

⁢

tune

=

∑

i

=

j

j

+

n

-

1

⁢

f

⁢

d

i

(

T

⁢

S

⁢

F

T

i

-

T

⁢

S

⁢

F

T

i

-

1

)

×

Tf

×

n

×

TSFf

wherein:

fd i is an ith first difference;

TSF T i-1 is an (i−1)th TSF transmitter timestamp;

Tf is a frequency of a system clock;

TSFf is a frequency of a TSF clock; and

n is an integer greater than 0.

11 . The method of claim 10 , wherein the frequency of the system clock is about 10 MHz, and the frequency of the TSF clock is about 1 MHz.

12 . The method of claim 7 , further comprising discarding the ith transmitter timestamp and the ith TSF transmitter timestamp when a following condition is satisfied:

|

T

⁢

S

⁢

F

T

i

-

T

⁢

S

⁢

F

T

i

-

1

-

T

o

⁢

b

|

>

⁢

threshold

wherein:

TSF T i is the ith TSF transmitter timestamp;

TSF T i-1 is an (i−1)th TSF transmitter timestamp; and

T ob is a time duration for observing transmitter timestamps.

13 . The method of claim 1 , wherein receiver timestamps and transmitter timestamps are sampled at a frequency of 5 Hz.