Systems and methods for processing variable coding and modulation (VCM) based communication signals using feedforward carrier and timing recovery
Processing a digital bit stream and systems for implementing the methods are provided. The method includes dividing the digital bit stream into a plurality of data packets. In a first processing block performing a carrier recovery error calculation on a first portion of the plurality of data packets, comprising preforming a first phase locked loop (PLL) function on decimated data of the data packets and performing a carrier recovery operation on the first portion of the plurality of data packets. In a second processing block, in parallel with the processing of the first portion of the plurality of packets, performing the carrier recovery error calculation on a second portion of the plurality of data packets, comprising preforming the first PLL function on decimated data of the data packets and performing the carrier recovery operation on second portion of the plurality of data packets.
1 . A method for processing a digital bit stream, wherein the digital bit stream is a frame based digitized communication signal, the method comprising:
dividing, at one or more processors, the digital bit stream into a plurality of data packets;
detecting one or more frame markers in the plurality of data packets;
performing a timing recovery error calculation and a carrier recovery error calculation on the plurality of data packets, the timing recovery error calculation comprising preforming a first phase locked loop (PLL) function on the plurality of data packets;
performing, at a first processing block of the one or more processors, a timing recovery operation, based on the timing recovery error calculation, on a first portion of the plurality of data packets;
performing, at a second processing block of the one or more processors in parallel with the first processing block, the timing recovery operation, based on the timing recovery error calculation, on a second portion of the plurality of data packets;
combining the output of the first processing block and the output of the second processing block into combined blocks of time corrected symbols including the one or more frame markers;
executing a correlator process and a frequency tracking process to locate frame boundaries and track a carrier frequency; and
outputting frames of the time corrected symbols.
2 . The method of claim 1 , wherein executing the correlator process and the frequency tracking process comprises:
performing a frequency lock loop (FLL) function to compare a phase difference between two adjacent frame markers.
3 . The method of claim 2 wherein performing the FLL function to compare the phase difference between the two adjacent frame markers comprises calculating arctan(A*conj(B))/(2*pi)*FR to obtain a calculated value, where A is an in-phase and quadrature (IQ) value of a previous collapsed frame marker, B is an IQ value of a current collapsed frame marker and FR is an update rate of a frame marker.
4 . The method of claim 3 , further comprising:
dividing, at the one or more processors, the frames of the time corrected symbols into a plurality of time corrected symbols;
detecting one or more frame markers in the plurality of data packets; and
performing, at a third processing block of the one or more processors in parallel with the first and second processing blocks, a carrier recovery operation on the plurality of time corrected symbols.
5 . The method of claim 4 further comprising performing a second PLL function after the FLL function to further enhance tracking and provide an improved phase, Doppler and Doppler estimate for use in the carrier recovery error calculation.
6 . The method of claim 1 , wherein the one or more processors are one or more general-purpose central processing units (CPUs) and first one or more processing blocks comprise a first one or more CPU cores of the one or more general-purpose CPUs and second one or more processing blocks comprise a second one or more CPU cores of the one or more general-purpose CPUs.
7 . A method for processing a digital bit stream, wherein the digital bit stream is a frame based digitized communication signal, the method comprising:
dividing, at one or more processors, the digital bit stream into a plurality of data packets;
detecting one or more frame boundaries in the plurality of data packets;
performing a timing recovery error calculation on the plurality of data packets, the timing recovery error calculation comprising preforming a first phase locked loop (PLL) function on the plurality of data packets;
performing, at a first processing block of the one or more processors, a timing recovery operation on a first portion of the plurality of data packets, based on the timing recovery error calculation;
performing, at a second processing block of the one or more processors in parallel with the first processing block, the timing recovery operation on a second portion of the plurality of data packets, based on the timing recovery error calculation;
combining the output of the first processing block and the output of the second processing block into blocks of time corrected symbols; and
locating frame boundaries of the blocks of time corrected symbols by detecting a frame marker.
8 . The method of claim 7 , wherein locating the frame boundaries includes:
executing a correlator process and a frequency tracking process to locate the frame boundaries and track a carrier frequency; and
outputting frames of the time corrected symbols.
9 . The method of claim 8 , wherein executing the correlator process and the frequency tracking process comprises:
performing a frequency lock loop (FLL) function to compare a phase difference between two adjacent frame markers.
10 . The method of claim 7 , wherein the one or more processors are one or more general-purpose central processing units (CPUs) and first one or more processing blocks comprise a first one or more CPU cores of the one or more general-purpose CPUs and second one or more processing blocks comprise a second one or more CPU cores of the one or more general-purpose CPUs.
11 . A system for processing a digital bit stream representative of a frame based digitized communication signal, the system comprising:
a digitizer configured to convert a received analog signal into the digital bit stream; and
one or more processors communicatively coupled to the digitizer, the one or more processors including a first processing block and a second processing block and configured to
divide the digital bit stream into a plurality of data packets,
detect one or more frame boundaries in the plurality of data packets,
perform a timing recovery error calculation on the plurality of data packets, the timing recovery error calculation comprising preforming a first phase locked loop (PLL) function on the plurality of data packets,
wherein the first processing block is configured to perform a timing recovery operation on a first portion of the plurality of data packets, based on the timing recovery error calculation,
wherein the second processing block is coupled in parallel with the first processing block and configured to perform the timing recovery operation on a second portion of the plurality of data packets, based on the timing recovery error calculation,
the one or more processors further configured to
combine the output of the first processing block and the output of the second processing block into blocks of time corrected symbols, and
locate frame boundaries of the blocks of time corrected symbols by detecting a frame marker.