def __init__(self, params):
"""
Initialize L2C tracking channel with L2C specific data.
Parameters
----------
params : dictionary
L2C tracking initialization parameters
"""
# Convert acquisition SNR to C/N0
cn0_0 = 10 * np.log10(params['acq'].snr)
cn0_0 += 10 * np.log10(defaults.L2C_CHANNEL_BANDWIDTH_HZ)
params['cn0_0'] = cn0_0
params['coherent_ms'] = 20
params['coherent_iter'] = 1
params['loop_filter_params'] = defaults.l2c_loop_filter_params
params['lock_detect_params'] = defaults.l2c_lock_detect_params_20ms
params['IF'] = params['samples'][gps_constants.L2C]['IF']
params['prn_code'] = L2CMCodes[params['acq'].prn]
params['code_freq_init'] = params['acq'].doppler * \
gps_constants.l2c_chip_rate / gps_constants.l2
params['chipping_rate'] = gps_constants.l2c_chip_rate
TrackingChannel.__init__(self, params)
self.cnav_msg = CNavMsg()
self.cnav_msg_decoder = CNavMsgDecoder()
class TrackingChannelL2C(TrackingChannel):
"""
L2C tracking channel.
"""
def __init__(self, params):
"""
Initialize L2C tracking channel with L2C specific data.
Parameters
----------
params : dictionary
L2C tracking initialization parameters
"""
# Convert acquisition SNR to C/N0
cn0_0 = 10 * np.log10(params['acq'].snr)
cn0_0 += 10 * np.log10(defaults.L2C_CHANNEL_BANDWIDTH_HZ)
params['cn0_0'] = cn0_0
params['coherent_ms'] = 20
params['coherent_iter'] = 1
params['loop_filter_params'] = defaults.l2c_loop_filter_params
params['lock_detect_params'] = defaults.l2c_lock_detect_params_20ms
params['IF'] = params['samples'][gps_constants.L2C]['IF']
params['prn_code'] = L2CMCodes[params['acq'].prn]
params['code_freq_init'] = params['acq'].doppler * \
gps_constants.l2c_chip_rate / gps_constants.l2
params['chipping_rate'] = gps_constants.l2c_chip_rate
TrackingChannel.__init__(self, params)
self.cnav_msg = CNavMsg()
self.cnav_msg_decoder = CNavMsgDecoder()
def is_pickleable(self):
"""
L2C tracking channel object is not pickleable due to complexity
of serializing cnav_msg_decoder Cython object.
out : bool
False - the L2C tracking object is not pickleable
"""
return False
def _short_n_long_preprocess(self):
if self.short_n_long:
# When simulating short and long cycles, short step resets EPL
# registers, and long one adds up to them
if self.short_step:
self.E = self.P = self.L = 0.j
# L2C CM code is only half of the PRN code length.
# The other half is CL code. Thus multiply by 2.
self.code_chips_to_integrate = \
int(2 * defaults.l2c_short_step_chips)
else:
# L2C CM code is only half of the PRN code length.
# The other half is CL code. Thus multiply by 2.
self.code_chips_to_integrate = \
2 * gps_constants.l2_cm_chips_per_code - \
self.code_chips_to_integrate + self.code_phase
code_chips_to_integrate = self.code_chips_to_integrate
else:
self.E = self.P = self.L = 0.j
code_chips_to_integrate = 2 * gps_constants.l2_cm_chips_per_code
return self.coherent_iter, code_chips_to_integrate
def _short_n_long_postprocess(self):
more_integration_needed = False
if self.short_n_long:
if self.short_step:
# In case of short step - go to next integration period
self.short_step = False
self.alias_detect.first(self.P.real, self.P.imag)
more_integration_needed = True
else:
# Next step is short cycle
self.short_step = True
return more_integration_needed
def _run_postprocess(self):
"""
Run L2C coherent integration postprocessing.
Runs navigation bit sync decoding operation.
"""
symbol = 0xFF if np.real(self.P) >= 0 else 0x00
res, delay = self.cnav_msg_decoder.decode(symbol, self.cnav_msg)
if res:
logger.debug("[PRN: %d (%s)] CNAV message decoded: "
"prn=%d msg_id=%d tow=%d alert=%d delay=%d" %
(self.prn + 1,
self.signal,
self.cnav_msg.getPrn(),
self.cnav_msg.getMsgId(),
self.cnav_msg.getTow(),
self.cnav_msg.getAlert(),
delay))
tow = self.cnav_msg.getTow() * 6000 + delay * 20
logger.debug("[PRN: %d (%s)] ToW %d" %
(self.prn + 1, self.signal, tow))
self.track_result.tow[self.i] = tow
else:
self.track_result.tow[self.i] = self.track_result.tow[self.i - 1] + \
self.coherent_ms
