phaserec#

Phase and carrier offset estimation and correction

Functions for carrier offset and phase estimation and correction functions

qampy.phaserec.bps(E, Mtestangles, N, **kwargs)#

Perform a blind phase search after _[1]

Parameters:

  • E (SignalObject) – input signal

  • Mtestangles (int) – number of test angles to try

  • N (int) – block length to use for averaging

  • **kwargs – keyword arguments to be passed to the core function

Returns:

  • Eout (SignalObject) – signal with compensated phase

  • ph (array_like) – unwrapped angle from phase recovery

References

..[1] Timo Pfau et al, Hardware-Efficient Coherent Digital Receiver Concept With Feedforward Carrier Recovery for M-QAM Constellations, Journal of Lightwave Technology 27, pp 989-999 (2009)

qampy.phaserec.bps_twostage(E, Mtestangles, N, B=4, **kwargs)#

Perform a blind phase search phase recovery using two stages after _[1]

Parameters:

  • E (SignalObject) – input signal

  • Mtestangles (int) – number of initial test angles to try

  • symbols (array_like) – the symbols of the modulation format

  • N (int) – block length to use for averaging

  • B (int, optional) – number of second stage test angles

  • **kwargs – keyword arguments to be passed to the core function

Returns:

  • Eout (SignalObject) – phase compensated field

  • ph (array_like) – unwrapped angle from phase recovery

References

..[1] Qunbi Zhuge and Chen Chen and David V. Plant, Low Computation Complexity Two-Stage Feedforward Carrier Recovery Algorithm for M-QAM, Optical Fiber Communication Conference (OFC, 2011)

qampy.phaserec.comp_freq_offset(sig, freq_offset)#

Compensate for frequency offset in signal

Parameters:

  • sig (array_line) – signal array with N modes

  • freq_offset (array_like) – frequency offset to compensate for if 1D apply to all modes

Returns:

comp_signal – input signal with removed frequency offset

Return type:

array with N modes

qampy.phaserec.correct_pilot_const_phase(signal, phase_offsets)#

Corrects a constant phase offset between the decoded pilot symbols and the transmitted ones

Parameters:

  • signal (array_like) – received signal

  • phase_offsets (array_like) – constant phase offsets (1 per mode)

Returns:

signal_out – signal with corrected phases

Return type:

array_like

qampy.phaserec.find_freq_offset(sig, average_over_modes=False, fft_size=4096)#

Find the frequency offset by searching in the spectrum of the signal raised to 4. Doing so eliminates the modulation for QPSK but the method also works for higher order M-QAM.

Parameters:

  • sig (SignalObject) – signal array with N modes

  • average_over_modes (bool) – Using the field in all modes for estimation

  • fft_size (array) – Size of FFT used to estimate. Should be power of 2, otherwise the next higher power of 2 will be used.

Returns:

freq_offset – found frequency offset

Return type:

int

qampy.phaserec.find_pilot_const_phase(rec_pilots, ref_pilots)#

Finds a constant phase offset between the decoded pilot symbols and the transmitted ones

Parameters:

  • rec_pilots (array_like) – Complex received pilots (after FOE and alignment)

  • ref_pilots (array_like) – Corresponding transmitted pilot symbols (aligned!)

Returns:

phase_corr – array of constant phase offsets per mode

Return type:

array_like

qampy.phaserec.pilot_cpe(signal, N=3, pilot_rat=1, max_blocks=None, nframes=1, use_seq=False)#

Pilot based Carrier Phase Estimation

Parameters:

  • signal (PilotSignalObject) – the signal to perform phase estimation on

  • N (int (optional)) – length of the averaging filter for phase estimation

  • pilot_rat (int (optional)) – use every nth pilot

  • max_blocks (int (optional)) – maximum number of blocks to process

  • nframes (int (optional)) – how many frames to process, the output data will be truncated to min(signal.shape[-1], signal.frame_len*nframes)

  • use_seq (bool (optional)) – use the pilot sequence for CPE as well

Returns:

  • signal (PilotSignalObject) – phase compensated signal

  • trace (array_like) – phase trace

qampy.phaserec.viterbiviterbi(E, N)#

Viterbi-Viterbi blind phase recovery for an M-PSK signal

Parameters:

  • E (array_like) – the electric field of the signal

  • N (int) – block length of samples to average over

Returns:

Eout – Field with compensated phases

Return type:

array_like