Add phase correction for generation of 5G NR time domain signals

sionna/nr/carrier_config.py

@@ -145,6 +145,20 @@ def frame_number(self, value):
         assert value in range(0,1024), "frame_number must be in [0, 1023]"
         self._frame_number = value
 
+    #---carrier_frequency---#
+    @property
+    def carrier_frequency(self):
+        r"""
+        float: Carrier frequency :math:`f_0` in Hz
+        """
+        self._ifndef("carrier_frequency", 0.)
+        return self._carrier_frequency
+
+    @carrier_frequency.setter
+    def carrier_frequency(self, value):
+        assert value > 0, "carrier_frequency must be positive"
+        self._carrier_frequency = value
+
     #--------------------------#
     #---Read-only parameters---#
     #--------------------------#

sionna/nr/pusch_config.py

@@ -967,6 +967,19 @@ def tb_size(self):
 
         return tb_size
 
+    @property
+    def phase_correction_sequence(self):
+        r"""
+        np.ndarray[float], read-only: Vector of phase rotations (implicitly)
+            defined in Section 5.4 [3GPP38211]_.
+        """
+        symbol_durations = (self.carrier.cyclic_prefix_length +
+                            self.fft_size / self.sample_rate)
+        # Reference point is start of first symbol, so ignore first cyclic prefix
+        symbol_durations[0] = 0.
+        symbol_start_times = np.cumsum(symbol_durations)
+        return np.exp(1j*2*np.pi*self.carrier.carrier_frequency*symbol_start_times)
+
     #-------------------#
     #---Class methods---#
     #-------------------#
@@ -1170,7 +1183,8 @@ def check_pusch_configs(pusch_configs):
         "tb_size" : pc.tb_size,
         "dmrs_length" : pc.dmrs.length,
         "dmrs_additional_position" : pc.dmrs.additional_position,
-        "num_cdm_groups_without_data" : pc.dmrs.num_cdm_groups_without_data
+        "num_cdm_groups_without_data" : pc.dmrs.num_cdm_groups_without_data,
+        "phase_correction_sequence" : pc.phase_correction_sequence,
     }
     params["bandwidth"] = params["num_subcarriers"]*params["subcarrier_spacing"]
     params["cyclic_prefix_length"] = np.ceil(carrier.cyclic_prefix_length *

sionna/nr/pusch_receiver.py

@@ -162,6 +162,8 @@ def __init__(self,
                 l_min=self._l_min,
                 cyclic_prefix_length=pusch_transmitter._cyclic_prefix_length)
 
+            self._phase_correction_sequence = pusch_transmitter._phase_correction_sequence
+
         # Use or create default ChannelEstimator
         self._perfect_csi = False
         self._w = None
@@ -246,6 +248,8 @@ def call(self, inputs):
         # (Optional) OFDM Demodulation
         if self._input_domain=="time":
             y = self._ofdm_demodulator(y)
+            y *= tf.expand_dims(tf.cast(
+                self._phase_correction_sequence, y.dtype), -1)
 
         # Channel estimation
         if self._perfect_csi:

sionna/nr/pusch_transmitter.py

@@ -257,7 +257,9 @@ def call(self, inputs):
 
         # (Optionally) apply OFDM modulation
         if self._output_domain=="time":
-            x = self._ofdm_modulator(x_pre)
+            x = x_pre / tf.expand_dims(tf.cast(
+                self._phase_correction_sequence, x_pre.dtype), -1)
+            x = self._ofdm_modulator(x)
         else:
             x = x_pre
 

test/unit/nr/test_pusch_config.py

@@ -301,3 +301,33 @@ def test_cyclic_prefix_length(self):
         np.testing.assert_array_almost_equal(carrier_config.cyclic_prefix_length * 1e6, [0.81] + [0.29] * 13, decimal=2)
         carrier_config = CarrierConfig(subcarrier_spacing=240, slot_number=1)
         np.testing.assert_array_almost_equal(carrier_config.cyclic_prefix_length * 1e6, [0.29] * 14, decimal=2)
+
+
+class TestPUSCHConfig(unittest.TestCase):
+    """Tests for the PUSCHConfig class"""
+
+    def test_phase_correction_sequence(self):
+        """Generate carrier signal for upconversion and compare phase shift at
+        the start of each symbol with the generated phase correction sequence"""
+        for subcarrier_spacing in [15, 30, 60, 120, 240]:
+            pusch_config = PUSCHConfig(subcarrier_spacing=subcarrier_spacing,
+                                       sample_rate="standard")
+            for carrier_frequency in np.arange(1e9, 10e9, .5e9):
+                pusch_config.carrier.carrier_frequency = carrier_frequency
+
+                fft_size = pusch_config.fft_size
+                cp_lengths = np.round(pusch_config.carrier.cyclic_prefix_length *
+                                      pusch_config.sample_rate).astype(int)
+
+                sample_idx = np.arange(-cp_lengths[0], np.sum(cp_lengths[1:])
+                                       + fft_size * len(cp_lengths))
+                upconversion_vector = np.exp(2.j*np.pi*carrier_frequency*
+                                             sample_idx/pusch_config.sample_rate)
+
+                symbol_end_idx = np.cumsum(cp_lengths + fft_size)
+                phase_rotations = []
+                for idx in symbol_end_idx:
+                    phase_rotations.append(upconversion_vector[idx - fft_size])
+
+                np.testing.assert_array_almost_equal(phase_rotations,
+                                     pusch_config.phase_correction_sequence)