Feed-forward carrier recovery system and method
View Patent ↗A method of feedforward phase recovery on a data stream is described. Phase estimation base points are calculated, at a phase detector, for each block of the received data stream. A current phase, at a phase interpolator, between two phase estimation base points. Data stream delays within the phase detector are matched with delays within the phase interpolator.
1. A method of feedforward phase recovery on a data stream, wherein the data stream includes data frames segmented into data blocks comprising:
calculating phase estimation base points, at a phase detector, for each block of the received data stream, comprising:
calculating one of: a number of sync symbols and a number of pilot symbols in each block;
processing each sync symbol or pilot symbol, at a matched filter; and
calculating a carrier phase offset, at the phase detector, over a block of sync symbols or pilot symbols.
setting a current phase, at a phase interpolator, between two phase estimation base points; and
matching data stream delays within the phase detector with delays within the phase interpolator, wherein the number of said data blocks is calculated by the equation
N
=
64800
M
*
1440
,
where M denotes the modulation factor, and the carrier phase offset is calculated by the equation
θ
(
n
)
=
arg
(
∑
N
z
(
nT
)
a
*
(
nT
)
)
,
where z(nT) denotes the matched filter output for each pilot or sync symbol and a(nT) denotes pre-known pilot or sync symbols at time nT.
2. A method of feedforward phase recovery on a data stream, comprising:
calculating phase estimation base points, at a phase detector, for each block of the received data stream;
setting a current phase, at a phase interpolator, between two phase estimation base points; and
matching data stream delays within the phase detector with delays within the phase interpolator, wherein calculating the two phase estimation base points is performed at a sawtooth device, and wherein the sawtooth device uses the equation θ″(i)=θ″(i−1)+SAW(θ′(i)−θ″(i−1)), where θ′(i−1),θ′(i) denotes the estimate of the phase offset in the (i−1)-th and the i-th blocks and where θ″(i−1),θ″(i) denotes the corresponding un-wrapping values, and
detecting and tracking out phase variations, at a post-processing block,
wherein detecting and tracking out phase variations is calculated using the equation: θ″(i)=θ″(i−1)+α·SAW(θ′(i)−θ′(i−1)) with α≦1.0.
3. The method of claim 2 , further comprising estimating the frequency of the output of said sawtooth device at a frequency estimation block.
4. An apparatus that performs feedforward phase recovery on a data stream, comprising:
a phase detector, that calculates phase estimation base points for each block of the received data stream;
a phase interpolator, that sets a current phase between two phase estimation base points;
a delay line, that matches data stream delays within the phase detector with delays within the phase interpolatorl; and
a matched filter that calculates one of: a number of sync symbols and a number of pilot symbols in each block and processes each sync symbol or pilot symbol,
wherein the phase detector calculates the two phase estimation base points over a block of sync symbols or pilot symbols, and wherein the number of said blocks is calculated by the equation
N
=
64800
M
*
1440
,
where M denotes the modulation factor, and the carrier phase offset is calculated by the equation
θ
(
n
)
=
arg
(
∑
N
z
(
nT
)
a
*
(
nT
)
)
,
where z(nT) denotes the matched filter output for each pilot or sync symbol and a(nT) denotes pre-known pilot or sync symbols at time nT.
5. An apparatus that performs feedforward phase recovery on a data stream, comprising:
a phase detector, that calculates phase estimation base points for each block of the received data stream;
a phase interpolator, that sets a current phase between two phase estimation base points;
a delay line, that matches data stream delays within the phase detector with delays within the phase interpolatorl;
a sawtooth device that calculates the two phase estimation base points, wherein the sawtooth device uses the equation θ″(i)=θ″(i−1)+SAW(θ′(i)−θ″(i−1)), where θ′(i−1), θ′(i) denotes the estimate of the phase offset in the (i−1)-th and the i-th blocks and where θ″(i−1), θ″(i) denotes the corresponding un-wrapping values; and
a post-processing block, that detects and tracks out phase variations from the output of the sawtooth device, wherein the post-processing block uses the equation:
θ″( i )=θ″( i− 1)+α·SAW(θ′( i )−θ′( i− 1)), with α≦1.0.
6. The apparatus of claim 5 , further comprising a frequency estimation block, that estimates the frequency of the output from the sawtooth device.
7. The method of claim 3 , wherein the convergence speed of the frequency estimation block is adjusted by a β parameter, wherein the value of said β depends on he delay between an outer frequency correction circuit fed by said frequency estimation block and said post processing block.
8. The method of claim 7 , wherein the values of α and β are switched from acquisition values to tracking values.
9. The method of claim 8 , wherein the values of α tracking values is smaller than the α acquisition value.
10. The method of claim 9 , wherein the values of β tracking values is smaller than the β acquisition value.
11. The method of claim 8 , wherein switching from acquisition to tracking values is based on a threshold detector.
12. The method of claim 11 , wherein said threshold detector is based on the value of the sawtooth output.
13. The method of claim 12 , wherein said threshold switching from acquisition to tracking value if the sawtooth output is below a certain value for a period of time.
14. The apparatus of claim 6 , wherein the convergence speed of the frequency estimation block is adjusted by β parameter, wherein the value of said β depends on the delay between an outer frequency correction circuit fed 1 by said frequency estimation block and said post processing block.
15. The apparatus of claim 14 , wherein the values of α and β are switched from acquisition values to tracking values.
16. The apparatus of claim 15 , wherein the α tracking values is smaller than the α acquisition value.
17. The apparatus of claim 15 , wherein the β tracking values is smaller than the β acquisition value.
18. The apparatus of claim 15 , further comprising a threshold detector for performing the switch from acquisition to tracking values.
19. The method of claim 18 , wherein said threshold detector performs the switch based on the value of the sawtooth output.
20. The method of claim 19 , wherein said threshold detector switches from acquisition to tracking value if the sawtooth output is below a certain value for a period of time.