diff --git a/python/trx/radio_if.py b/python/trx/radio_if.py
index d8c0444..689f074 100644
--- a/python/trx/radio_if.py
+++ b/python/trx/radio_if.py
@@ -29,17 +29,66 @@
 
 from math import pi
 
+from gnuradio.filter import firdes
+from gnuradio import digital
 from gnuradio import blocks
+from gnuradio import uhd
 from gnuradio import gr
 
+
+# HACK: should be implemented in C++!
+import numpy as np
+
+class burst_type_filter(gr.sync_block):
+    def __init__(self, burst_types=[]):
+        gr.sync_block.__init__(
+            self,
+            name='Burst type filter',
+            in_sig=[],
+            out_sig=[]
+        )
+        self.burst_types = burst_types
+        self.message_port_register_in(pmt.intern("bursts_in"))
+        self.message_port_register_out(pmt.intern("bursts_out"))
+        self.set_msg_handler(pmt.intern("bursts_in"), self.filter)
+
+    def filter(self, msg):
+        burst_with_header = pmt.to_python(pmt.cdr(msg))
+        burst = burst_with_header[-148:]
+        header = np.ndarray.tolist(burst_with_header[0:-148])
+        burst_type = header[12]
+        if burst_type in self.burst_types:
+            self.message_port_pub(pmt.intern("bursts_out"), msg)
+
+class burst_to_fn_time(gr.basic_block):
+    def __init__(self):  # only default arguments here
+        gr.basic_block.__init__(
+            self,
+            name='Burst to fn_time',
+            in_sig=[],
+            out_sig=[]
+        )
+        self.message_port_register_in(pmt.intern("bursts_in"))
+        self.message_port_register_out(pmt.intern("fn_time_out"))
+        self.set_msg_handler(pmt.intern("bursts_in"), self.convert)
+
+    def convert(self, msg):
+        fn_time = pmt.dict_ref(pmt.car(msg),pmt.intern("fn_time"),pmt.PMT_NIL)
+        fn_time_msg = pmt.dict_add(pmt.make_dict(), pmt.intern("fn_time"), fn_time)
+        if pmt.to_python(fn_time) is not None:
+            self.message_port_pub(pmt.intern("fn_time_out"), fn_time_msg)
+
 class radio_if(gr.top_block):
 	# PHY specific variables
-	shiftoff = 400e3
-	fc = 941.6e6 # TODO: set ARFCN to 0?
+	rx_freq = 935e6
+	tx_freq = 890e6
 
 	# Application state flags
 	trx_started = False
-	fc_set = False
+
+	# GSM timings
+	delay_correction = 285.616e-6
+	ul_dl_shift = -(6.0/1625000*(156.25)*3)
 
 	def __init__(self, phy_args, phy_sample_rate,
 			phy_rx_gain, phy_tx_gain, phy_ppm,
@@ -53,83 +102,149 @@
 		self.tx_gain = phy_tx_gain
 
 		gr.top_block.__init__(self, "GR-GSM TRX")
-		shift_fc = self.fc - self.shiftoff
 
-		##################################################
-		# PHY Definition
-		##################################################
-		self.phy = osmosdr.source(args = "numchan=%d %s" % (1, phy_args))
+		# TRX Burst Interface
+		self.trx_burst_if = grgsm.trx_burst_if(
+			trx_remote_addr, str(trx_base_port))
 
-		self.phy.set_bandwidth(250e3 + abs(self.shiftoff), 0)
-		self.phy.set_center_freq(shift_fc, 0)
-		self.phy.set_sample_rate(phy_sample_rate)
-		self.phy.set_freq_corr(phy_ppm, 0)
-		self.phy.set_iq_balance_mode(2, 0)
-		self.phy.set_dc_offset_mode(2, 0)
-		self.phy.set_gain_mode(False, 0)
-		self.phy.set_gain(self.rx_gain, 0)
-		self.phy.set_if_gain(20, 0)
-		self.phy.set_bb_gain(20, 0)
-		self.phy.set_antenna(phy_rx_antenna, 0)
 
-		##################################################
-		# GR-GSM Magic
-		##################################################
-		self.blocks_rotator = blocks.rotator_cc(
-			-2 * pi * self.shiftoff / phy_sample_rate)
+		# RX path definition
+		self.phy_src = uhd.usrp_source(phy_args,
+			uhd.stream_args(cpu_format="fc32",
+				channels=range(1)))
+
+		self.phy_src.set_center_freq(self.rx_freq, 0)
+		self.phy_src.set_antenna(phy_rx_antenna, 0)
+		self.phy_src.set_samp_rate(phy_sample_rate)
+		self.phy_src.set_bandwidth(650e3, 0)
+		self.phy_src.set_gain(phy_rx_gain)
 
 		self.gsm_input = grgsm.gsm_input(
-			ppm = phy_ppm, osr = 4, fc = self.fc,
-			samp_rate_in = phy_sample_rate)
+			ppm = phy_ppm - int(phy_ppm), osr = 4,
+			fc = self.rx_freq, samp_rate_in = phy_sample_rate)
 
 		self.gsm_receiver = grgsm.receiver(4, ([0]), ([]))
 
 		self.gsm_clck_ctrl = grgsm.clock_offset_control(
-			shift_fc, phy_sample_rate, osr = 4)
+			self.rx_freq, phy_sample_rate, osr = 4)
 
-		self.gsm_ts_filter = grgsm.burst_timeslot_filter(0)
-		self.gsm_ts_filter.set_policy(grgsm.FILTER_POLICY_DROP_ALL)
+		self.ts_filter = grgsm.burst_timeslot_filter(0)
+		self.ts_filter.set_policy(grgsm.FILTER_POLICY_DROP_ALL)
 
-		self.gsm_trx_burst_if = grgsm.trx_burst_if(
-			trx_remote_addr, str(trx_base_port))
-
-		##################################################
 		# Connections
-		##################################################
-		self.connect((self.phy, 0), (self.blocks_rotator, 0))
-		self.connect((self.blocks_rotator, 0), (self.gsm_input, 0))
-		self.connect((self.gsm_input, 0), (self.gsm_receiver, 0))
+		self.connect(
+			(self.phy_src, 0),
+			(self.gsm_input, 0))
 
-		self.msg_connect((self.gsm_receiver, 'measurements'),
+		self.connect(
+			(self.gsm_input, 0),
+			(self.gsm_receiver, 0))
+
+		self.msg_connect(
+			(self.gsm_receiver, 'C0'),
+			(self.ts_filter, 'in'))
+
+		self.msg_connect(
+			(self.ts_filter, 'out'),
+			(self.trx_burst_if, 'bursts'))
+
+		self.msg_connect(
+			(self.gsm_receiver, 'measurements'),
 			(self.gsm_clck_ctrl, 'measurements'))
 
-		self.msg_connect((self.gsm_clck_ctrl, 'ctrl'),
+		self.msg_connect(
+			(self.gsm_clck_ctrl, 'ctrl'),
 			(self.gsm_input, 'ctrl_in'))
 
-		self.msg_connect((self.gsm_receiver, 'C0'),
-			(self.gsm_ts_filter, 'in'))
 
-		self.msg_connect((self.gsm_ts_filter, 'out'),
-			(self.gsm_trx_burst_if, 'bursts'))
+		# TX Path Definition
+		self.phy_sink = uhd.usrp_sink(phy_args,
+			uhd.stream_args(cpu_format="fc32",
+				channels=range(1)), "packet_len")
 
-	def check_available(self):
-		return self.fc_set
+		self.phy_sink.set_antenna(phy_tx_antenna, 0)
+		self.phy_sink.set_samp_rate(phy_sample_rate)
+		self.phy_sink.set_center_freq(self.tx_freq, 0)
+		self.phy_sink.set_gain(self.tx_gain)
+
+		self.tx_time_setter = grgsm.txtime_setter(
+			0xffffffff, 0, 0, 0, 0, 0,
+			self.delay_correction + self.ul_dl_shift)
+
+		self.tx_burst_proc = grgsm.preprocess_tx_burst()
+
+		self.pdu_to_tagged_stream = blocks.pdu_to_tagged_stream(
+			blocks.byte_t, 'packet_len')
+
+		self.gmsk_mod = grgsm.gsm_gmsk_mod(
+			BT = 4, pulse_duration = 4, sps = 4)
+
+		self.burst_shaper = digital.burst_shaper_cc(
+			(firdes.window(firdes.WIN_HANN, 16, 0)),
+			0, 20, False, "packet_len")
+
+		# Connections
+		self.msg_connect(
+			(self.trx_burst_if, 'bursts'),
+			(self.tx_time_setter, 'bursts_in'))
+
+		self.msg_connect(
+			(self.tx_time_setter, 'bursts_out'),
+			(self.tx_burst_proc, 'bursts_in'))
+
+		self.msg_connect(
+			(self.tx_burst_proc, 'bursts_out'),
+			(self.pdu_to_tagged_stream, 'pdus'))
+
+		self.connect(
+			(self.pdu_to_tagged_stream, 0),
+			(self.gmsk_mod, 0))
+
+		self.connect(
+			(self.gmsk_mod, 0),
+			(self.burst_shaper, 0))
+
+		self.connect(
+			(self.burst_shaper, 0),
+			(self.phy_sink, 0))
+
+
+		# RX & TX synchronization
+		self.bt_filter = burst_type_filter([3])
+		self.burst_to_fn_time = burst_to_fn_time()
+
+		# Connections
+		self.msg_connect(
+			(self.gsm_receiver, 'C0'),
+			(self.bt_filter, 'bursts_in'))
+
+		self.msg_connect(
+			(self.bt_filter, 'bursts_out'),
+			(self.burst_to_fn_time, 'bursts_in'))
+
+		self.msg_connect(
+			(self.burst_to_fn_time, 'fn_time_out'),
+			(self.tx_time_setter, 'fn_time'))
 
 	def shutdown(self):
 		print("[i] Shutdown Radio interface")
 		self.stop()
 		self.wait()
 
-	def set_fc(self, fc):
-		self.phy.set_center_freq(fc - self.shiftoff, 0)
+	def set_rx_freq(self, fc):
+		self.phy_src.set_center_freq(fc, 0)
+		self.gsm_clck_ctrl.set_fc(fc)
 		self.gsm_input.set_fc(fc)
-		self.fc_set = True
-		self.fc = fc
+		self.rx_freq = fc
+
+	def set_tx_freq(self, fc):
+		self.phy_sink.set_center_freq(fc, 0)
+		self.tx_freq = fc
 
 	def set_rx_gain(self, gain):
-		self.phy.set_gain(gain, 0)
+		self.phy_src.set_gain(gain, 0)
 		self.rx_gain = gain
 
 	def set_tx_gain(self, gain):
-		# TODO: TX chain not implemented yet
+		self.phy_sink.set_gain(gain, 0)
 		self.tx_gain = gain