apps/grgsm_trx: add baseband frequency shift feature
An ability to shift the baseband frequency would allow one to
run both base stations and (OsmocomBB-based) mobile stations on
any frequency (e.g. in 2.4 GHz WiFi band)!
This is achieved by adding a given frequency offset to the
result of "ARFCN -> RX/TX frequency" calculation.
Usage example:
grgsm_trx --freq-offset -500M
Both RX (Downlink) and TX (Uplink) frequencies will be shifted
by 500 MHz back, e.g. tuning request to ARFCN 105 would result
in tuning the radio to 456.0 MHz (instead of 956.0 MHz).
Related: OS#3520 (https://osmocom.org/versions/136)
Change-Id: I42e397e47402a87f4141ef31b25eff4c8c1267e2
diff --git a/python/trx/radio_if.py b/python/trx/radio_if.py
index d2afcf6..407e724 100644
--- a/python/trx/radio_if.py
+++ b/python/trx/radio_if.py
@@ -4,7 +4,7 @@
# GR-GSM based transceiver
# Follow graph implementation
#
-# (C) 2016-2017 by Vadim Yanitskiy <axilirator@gmail.com>
+# (C) 2016-2018 by Vadim Yanitskiy <axilirator@gmail.com>
# (C) 2017 by Piotr Krysik <ptrkrysik@gmail.com>
#
# All Rights Reserved
@@ -29,6 +29,7 @@
from math import pi
+from gnuradio import eng_notation
from gnuradio import digital
from gnuradio import blocks
from gnuradio import uhd
@@ -59,6 +60,7 @@
class radio_if(gr.top_block):
# PHY specific variables
+ freq_offset_hz = None
rx_freq = 935e6
tx_freq = 890e6
osr = 4
@@ -274,11 +276,21 @@
return self.ppm / 1.0e6 * 2 * pi * fc / self.sample_rate
def set_rx_freq(self, fc):
+ if self.freq_offset_hz is not None:
+ fc += self.freq_offset_hz
+ print("[#] Shifting RX freq. to %s (offset is %s)"
+ % (eng_notation.num_to_str(fc),
+ eng_notation.num_to_str(self.freq_offset_hz)))
self.phy_src.set_center_freq(fc, 0)
self.rotator_src.set_phase_inc(self.calc_phase_inc(fc))
self.rx_freq = fc
def set_tx_freq(self, fc):
+ if self.freq_offset_hz is not None:
+ fc += self.freq_offset_hz
+ print("[#] Shifting TX freq. to %s (offset is %s)"
+ % (eng_notation.num_to_str(fc),
+ eng_notation.num_to_str(self.freq_offset_hz)))
self.phy_sink.set_center_freq(fc, 0)
self.rotator_sink.set_phase_inc(-self.calc_phase_inc(fc))
self.tx_freq = fc