Receivers for non-terrestrial networks
Some wireless communications systems provide communications between user equipments (UEs) and non-terrestrial networks (NTNs). An NTN may include one or more NTN nodes (e.g., satellites). When communicating with low Earth orbit (LEO) satellites, a signal received by a UE may exhibit a time-varying carrier frequency shift or Doppler shift. Some examples of the techniques described herein may address the effects of NTN Doppler on front end processing. Some examples of the techniques described herein may use a Doppler-dependent droop compensation filter after Doppler compensation using a rotator. In some approaches, Doppler-independent droop compensation may be performed. For example, a droop compensation filter may be designed for wider bandwidth that addresses a Doppler shift. A filter for jammer rejection may be utilized based on the Doppler shift or based on an NTN or terrestrial network (TN) scenario.
1 . A user equipment (UE), comprising:
one or more memories storing processor-executable code; and
one or more processors coupled with the one or more memories and individually or collectively operable to execute the code to cause the UE to:
receive a first signal from a non-terrestrial network node, the first signal associated with a carrier frequency shift from relative motion between the UE and the non-terrestrial network node;
filter the first signal using a first filter for droop compensation with fixed filter coefficients or a second filter for droop compensation with filter coefficients based at least in part on the carrier frequency shift, the first filter having a bandwidth including a carrier bandwidth and a limited carrier frequency offset for filtering the first signal before signal rotation, the second filter having a bandwidth that is based at least in part on a carrier bandwidth and the carrier frequency shift for filtering the first signal after signal rotation; and
demodulate the first signal that is filtered using the first filter or the second filter.
2 . The UE of claim 1 , wherein the one or more processors are individually or collectively further operable to execute the code to cause the UE to:
compensate for the carrier frequency shift via a rotator, wherein the second filter is determined based at least in part on the carrier frequency shift compensated via the rotator.
3 . The UE of claim 2 , wherein the second filter is determined in response to the carrier frequency shift being within a frequency range or is determined in response to the carrier frequency shift differing by a threshold quantity from a previous carrier frequency shift.
4 . The UE of claim 1 , wherein the one or more processors are individually or collectively further operable to execute the code to cause the UE to:
receive a second signal from a terrestrial network node, the second signal at least partially overlapping in a frequency band with the first signal; and
filter the second signal using a third filter for droop compensation after signal rotation, the third filter having a bandwidth that is less than the bandwidth of the first filter.
5 . The UE of claim 1 , wherein the first signal is filtered using the first filter, and the one or more processors are individually or collectively further operable to execute the code to cause the UE to:
filter the first signal using a third filter for droop compensation after signal rotation and decimation, the third filter having fixed coefficients based at least in part on a frequency response of a decimator for performing the decimation.
6 . The UE of claim 5 , wherein filtering the first signal using the third filter comprises filtering the first signal in a frequency domain after a frequency domain transformation or comprises time domain filtering the first signal.
7 . The UE of claim 1 , wherein the first signal is received during an initial acquisition period before determining the carrier frequency shift, and the one or more processors are individually or collectively further operable to execute the code to cause the UE to:
receive a second signal from the non-terrestrial network node; and
compensate for the carrier frequency shift in the second signal using a local oscillator after the initial acquisition period based at least in part on determining the carrier frequency shift.
8 . The UE of claim 1 , wherein the one or more processors are individually or collectively further operable to execute the code to cause the UE to:
receive a second signal from the non-terrestrial network node, the second signal associated with a second carrier frequency shift;
detect a jamming signal from a terrestrial network node, wherein the second carrier frequency shift reduces a frequency domain spacing between the first signal and the jamming signal; and
filter the second signal using a third filter for suppressing the jamming signal, the third filter having a steeper frequency response than the first filter or the second filter between the second signal and the jamming signal for the reduced frequency domain spacing.
9 . The UE of claim 1 , wherein the one or more processors are individually or collectively further operable to execute the code to cause the UE to:
receive a second signal from the non-terrestrial network node, the second signal associated with a second carrier frequency shift;
detect a jamming signal from a terrestrial network node, wherein the second carrier frequency shift causes a reduced frequency domain spacing between the first signal and the jamming signal; and
filter the second signal using the first filter or the second filter, wherein the first filter or the second filter provides reduced jamming performance relative to a signal without the reduced frequency domain spacing.
10 . A method for wireless communications by a user equipment (UE), comprising:
receiving a first signal from a non-terrestrial network node, the first signal associated with a carrier frequency shift from relative motion between the UE and the non-terrestrial network node;
filtering the first signal using a first filter for droop compensation with fixed filter coefficients or a second filter for droop compensation with filter coefficients based at least in part on the carrier frequency shift, the first filter having a bandwidth including a carrier bandwidth and a limited carrier frequency offset for filtering the first signal before signal rotation, the second filter having a bandwidth that is based at least in part on a carrier bandwidth and the carrier frequency shift for filtering the first signal after signal rotation; and
demodulating the first signal that is filtered using the first filter or the second filter.
11 . The method of claim 10 , further comprising:
compensating for the carrier frequency shift via a rotator, wherein the second filter is determined based at least in part on the carrier frequency shift compensated via the rotator.
12 . The method of claim 11 , wherein the second filter is determined in response to the carrier frequency shift being within a frequency range or is determined in response to the carrier frequency shift differing by a threshold quantity from a previous carrier frequency shift.
13 . The method of claim 10 , further comprising:
receiving a second signal from a terrestrial network node, the second signal at least partially overlapping in a frequency band with the first signal; and
filtering the second signal using a third filter for droop compensation after signal rotation, the third filter having a bandwidth that is less than the bandwidth of the first filter.
14 . The method of claim 10 , wherein the first signal is filtered using the first filter, the method further comprising:
filtering the first signal using a third filter for droop compensation after signal rotation and decimation, the third filter having fixed coefficients based at least in part on a frequency response of a decimator for performing the decimation.
15 . The method of claim 14 , wherein filtering the first signal using the third filter comprises filtering the first signal in a frequency domain after a frequency domain transformation or comprises time domain filtering the first signal.
16 . The method of claim 10 , wherein the first signal is received during an initial acquisition period before determining the carrier frequency shift, and wherein filtering the first signal is performed using the first filter, the method further comprising:
receiving a second signal from the non-terrestrial network node; and
compensating for the carrier frequency shift in the second signal using a local oscillator after the initial acquisition period based at least in part on determining the carrier frequency shift.
17 . The method of claim 10 , further comprising:
receiving a second signal from the non-terrestrial network node, the second signal associated with a second carrier frequency shift;
detecting a jamming signal from a terrestrial network node, wherein the second carrier frequency shift reduces a frequency domain spacing between the first signal and the jamming signal; and
filtering the second signal using a third filter for suppressing the jamming signal, the third filter having a steeper frequency response than the first filter or the second filter between the second signal and the jamming signal for the reduced frequency domain spacing.
18 . The method of claim 10 , further comprising:
receiving a second signal from the non-terrestrial network node, the second signal associated with a second carrier frequency shift;
detecting a jamming signal from a terrestrial network node, wherein the second carrier frequency shift causes a reduced frequency domain spacing between the first signal and the jamming signal; and
filtering the second signal using the first filter or the second filter, wherein the first filter or the second filter provides reduced jamming performance relative to a signal without the reduced frequency domain spacing.
19 . A non-transitory computer-readable medium storing code for wireless communications, the code comprising instructions executable by one or more processors to:
receive a first signal from a non-terrestrial network node, the first signal associated with a carrier frequency shift from relative motion between a user equipment (UE) and the non-terrestrial network node;
filter the first signal using a first filter for droop compensation with fixed filter coefficients or a second filter for droop compensation with filter coefficients based at least in part on the carrier frequency shift, the first filter having a bandwidth including a carrier bandwidth and a limited carrier frequency offset for filtering the first signal before signal rotation, the second filter having a bandwidth that is based at least in part on a carrier bandwidth and the carrier frequency shift for filtering the first signal after signal rotation; and
demodulate the first signal that is filtered using the first filter or the second filter.
20 . The non-transitory computer-readable medium of claim 19 , wherein the instructions are further executable by the one or more processors to:
compensate for the carrier frequency shift via a rotator, wherein the second filter is determined based at least in part on the carrier frequency shift compensated via the rotator.