Instead of using the projected velocity and acceleration vectors,
calculate vel_sat_gnb and acc_sat_gnb so the delay is correct for
epoch_time, epoch_time + 5 seconds and epoch_time + 10 seconds.
Separate timing_advance (N_TA) from timing_advance_ntn (N_common_TA_adj + N_UE_TA_adj)
to keep N_TA when updating N_common_TA_adj + N_UE_TA_adj.
Fixes#981
Instead of trying to estimate N_UE_TA_adj with a second degree polynomial,
we introduce orbit propagation to calculate N_UE_TA_adj with higher accuracy.
When we receive the satellite ephemeris data consisting of the satellite position vector
and the satellite velocity vector, we calculate parameters for orbit propagation, assuming
a circular orbit in the plane created by the satellite position vector and the satellite
velocity vector. This is done in the function prepare_ue_sat_ta().
Every millisecond, we use these parameters together with the time since epoch to calculate
the satellite position on that orbit and from this the reound-trip-time between UE and the
satellite, what corresponds to N_UE_TA_adj. This is done in the function apply_ntn_timing_advance().
TS 38.331 clause 5.3.7.4 specifies to apply the configuration defined in 9.2.1 for SRB1 at UE side.
This implies that the gNB also has to apply sn_field_length = 12, but there are no implications on the other RLC parameters.
As wrong timer values break SRB1 e.g. for long RTT NTN scenarios, this commit switches to using the RLC timer values provided in the configuration file.
Currently we still set poll_pdu, poll_byte and max_retx_threshold to the values defined in 9.2.1, but this can be changed.
In the current implementation, if UE transmission is interrupted via nr_mac_interrupt_ue_transmission(),
UE_sched_ctrl.ta_frame is modified to be the previous frame avoiding TA scheduling in the measurement gap.
So the next scheduled TA is shifted to be in 99 frames. As there are other measurement gaps before that,
the scheduled TA is always shifted, but actually never reached, effectively disabling the MAC TA commands.
To fix this, UE_sched_ctrl.ta_frame is changed to not indicate the last TA command transmission, but the
next one. This allows to check in nr_mac_interrupt_ue_transmission() if the next TA command transmission
is within the measurement gap and if so shift it to just after that gap.
If the RLC indicates that there is no more data in the buffer, also the scheduler's
LCID_buffer_remain should be set to 0. Else the UE sends BSR indicating it has data
to be transmitted. The gNB would then unnecessarily schedule UL for this UE, which
would not be used, as there is no actual data to be transmitted.
If the DCI in PDCCH is not correctly received, no PDSCH would be decoded but counted as no error.
Also if the DCI was not correctly received, a TBS of 0 would be used in some computations and memory allocations.
Fix these not counting if there is no PDSCH decoding, and by using the known TBS instead of the one received from the DCI.
The acceleration magnitude on the orbital path can be calculated as:
t = 2 * pi * r / v
omega = 2 * pi / t = v / r
acceleration = omega² * r = v² / r
Where t is the orbital period, r is the orbital radius, v is the orbital velocity, omega is the angular velocity.
The acceleration direction is from the SAT position towards the earth center.
To calculate the acceleration towards the UE, this is projected on the direction from the SAT to the UE.
The boolean value v17_sib was not set to true when allocating si_schedulingInfo_v17 and schedulingInfo2_r17.
So multiple Rel-17 SIBs would lead to multiple allocations and only the last SIB being actually configured.
Fix this by removing the redundant v17_sib variable and directly check if the memory was already allocated.
Also move the definition and allocation of si_schedulingInfo_v17 closer to its actual usage.
Now that we reliably receive SIB19, we can set the ntn-UlSyncValidityDuration-r17 to a sane value
and thus make sure that the UE always has up-to-date SIB19 information.
This fixes a lifelock in nr_ue_get_sdu(), because select_logical_channels() would select
a suspended LCID for scheduling, but fill_mac_sdu() would not provide data for it.
The implementation is limited to epoch times that are not more than 5.12 seconds in the future (allowed are up to 10.24 seconds)
and ntn-UlSyncValidityDuration < 5.12 seconds (allowed are up to 90 seconds).
To fix this limitation, the hyper frame number HFN has to be introduced at the OAI UE!
Before, we only considered ta_Common_r17 and the SAT position from SIB19 to compute the initial timing advance value.
This is good enough if the satellite does not move too fast (e.g. GEO satellite).
Now we also consider ta_CommonDrift_r17 and the SAT velocity together with the epoch time from SIB19.
This improves the accuracy of the initial TA computation, esp. for LEO satellite scenarios.
During reestablishment the UE goes back to not synchronized state.
While the synchronizatin is running, we trash frames using the function readFrame().
And when we successfully synchronize, we skip samples to align with the start of the frame using syncInFrame().
In rfsimulator mode, both of these functions send dummy data using the function dummyWrite().
Unfortunately, the writeTimestamp provided to that function was always assuming a duration from RX to TX of NR_UE_CAPABILITY_SLOT_RX_TO_TX.
But in NTN mode, this value is changed when receiving SIB19.
Therefore we have to consider this changed value instead of the static one.
The DPDK driver may directly provide the internal HW mbuf in the dequeued structure.
So don't try to free the mbufs from that dequeued structure, but the ones we allocated.
esp. for LEO NTN scenarios the timing drifts during initial sync, which is mostly compensated with --ntn-initial-time-drift.
But there might be a residual time offset, and by extending the peak search window we make this more tolerant.
Thomas Schlichter