Enhanced secrecy for orthogonal time frequency space (OTFS) waveforms at the physical layer

1 . A method for wireless communications at a network entity, comprising:

transmitting control signaling indicating that a secure downlink message is scheduled for transmission to a user equipment (UE);

receiving, in response to the control signaling, a sounding reference signal for generating a channel estimate for a channel between the network entity and the UE, wherein the channel estimate is generated in accordance with a delay-Doppler domain channel estimation scheme;

encoding the secure downlink message in accordance with an orthogonal time frequency space precoding scheme based at least in part on the delay-Doppler domain channel estimation scheme;

adding interference to the encoded secure downlink message over a slot duration, the added interference being based at least in part on the channel estimate; and

transmitting, via the channel, the encoded secure downlink message that includes the added interference.

2 . The method of claim 1 , further comprising:

transmitting a channel state information reference signal;

receiving a feedback message based at least in part on the channel state information reference signal; and

determining one or more calibration coefficients based at least in part on the feedback message and the channel estimate, wherein encoding the secure downlink message is based at least in part on the one or more calibration coefficients.

3 . The method of claim 2 , wherein the one or more calibration coefficients are associated with a ratio of a first gain value to a second gain value, the first gain value comprising a product of a transmission channel gain at the network entity and a reception channel gain at the UE, and the second gain value comprising a product of a transmission channel gain at the UE and a reception channel gain at the network entity.

4 . The method of claim 1 , further comprising:

generating an uplink channel estimate based at least in part on the received sounding reference signal; and

generating the channel estimate for the channel based at least in part on the uplink channel estimate and a time domain duplexing configuration for communications between the network entity and the UE.

5 . The method of claim 1 , wherein the added interference is associated with a null space of a product of a first matrix and a second matrix, the first matrix being representative of the channel estimate and the second matrix corresponding to a cyclic prefix removal matrix.

6 . The method of claim 5 , wherein the added interference comprises a product of a vector and third matrix, and the third matrix spans the null space of the product of the first matrix and the second matrix.

7 . The method of claim 6 , wherein the vector comprises one or more values that are randomly-generated.

8 . The method of claim 6 , wherein the vector comprises one or more values that are preconfigured.

9 . The method of claim 1 , wherein the control signaling comprises radio resource control signaling.

10 . The method of claim 1 , wherein the control signaling comprises downlink control information.

11 . The method of claim 1 , wherein the control signaling comprises a medium access control (MAC) control element.

12 . The method of claim 1 , wherein the encoded secure downlink message includes control signaling, data signaling, a demodulation reference signal, or a combination thereof.

13 . A method for wireless communications at a user equipment (UE), comprising:

receiving control signaling indicating that a secure downlink message is scheduled for transmission from a network entity;

transmitting, in response to the control signaling, a sounding reference signal for generating a channel estimate for a channel between the network entity and the UE in accordance with a delay-Doppler domain channel estimation scheme;

receiving, via the channel, the secure downlink message that includes added interference over a slot duration, the added interference being based at least in part on the channel estimate, wherein the secure downlink message is encoded in accordance with an orthogonal time frequency space precoding scheme based at least in part on the delay-Doppler domain channel estimation scheme; and

decoding the secure downlink message in accordance with the orthogonal time frequency space precoding scheme.

14 . The method of claim 13 , further comprising:

receiving one or more channel state information reference signals;

generating a downlink channel estimate for the channel based at least in part on the received one or more channel state information reference signals; and

transmitting a feedback message indicating the downlink channel estimate for one or more calibration coefficients applied to the channel estimate.

15 . The method of claim 13 , further comprising:

receiving, with the secure downlink message, one or more channel state information reference signals; and

determining one or more calibration coefficients based at least in part on a downlink channel estimate generated using the one or more channel state information reference signals, wherein decoding the secure downlink message is based at least in part on the one or more calibration coefficients.

16 . The method of claim 15 , wherein the one or more calibration coefficients are associated with a ratio of a first gain value to a second gain value, the first gain value comprising a product of a transmission channel gain at the network entity and a reception channel gain at the UE, and the second gain value comprising a product of a transmission channel gain at the UE and a reception channel gain at the network entity.

17 . The method of claim 13 , wherein the added interference is associated with a null space of a product of a first matrix and a second matrix, the first matrix being representative of the channel estimate and the second matrix corresponding to a cyclic prefix removal matrix.

18 . The method of claim 17 , wherein the added interference comprises a product of a vector and third matrix, and the third matrix spans the null space of the product of the first matrix and the second matrix.

19 . The method of claim 18 , wherein the vector comprises one or more values that are randomly-generated.

20 . The method of claim 18 , wherein the vector comprises one or more values that are preconfigured.

21 . The method of claim 13 , wherein the control signaling comprises radio resource control signaling.

22 . The method of claim 13 , wherein the control signaling comprises downlink control information.

23 . The method of claim 13 , wherein the control signaling comprises a medium access control (MAC) control element.

24 . The method of claim 13 , wherein the secure downlink message includes control signaling, data signaling, a demodulation reference signal, or a combination thereof.

25 . An apparatus for wireless communications at a network entity, comprising:

one or more processors;

one or more memories coupled with the one or more processors; and

instructions stored in the one or more memories and executable by the one or more processors to cause the apparatus to:

transmit control signaling indicating that a secure downlink message is scheduled for transmission to a user equipment (UE);

receive, in response to the control signaling, a sounding reference signal for generating a channel estimate for a channel between the network entity and the UE, wherein the channel estimate is generated in accordance with a delay-Doppler domain channel estimation scheme;

encode the secure downlink message in accordance with an orthogonal time frequency space precoding scheme based at least in part on the delay-Doppler domain channel estimation scheme;

add interference to the encoded secure downlink message over a slot duration, the added interference being based at least in part on the channel estimate; and

transmit, via the channel, the encoded secure downlink message that includes the added interference.

26 . The apparatus of claim 25 , wherein the instructions are further executable by the one or more processors to cause the apparatus to:

transmit a channel state information reference signal;

receive a feedback message based at least in part on the channel state information reference signal; and

determine one or more calibration coefficients based at least in part on the feedback message and the channel estimate, wherein encoding the secure downlink message is based at least in part on the one or more calibration coefficients.

27 . The apparatus of claim 26 , wherein the one or more calibration coefficients are associated with a ratio of a first gain value to a second gain value, the first gain value comprising a product of a transmission channel gain at the network entity and a reception channel gain at the UE, and the second gain value comprising a product of a transmission channel gain at the UE and a reception channel gain at the network entity.

28 . An apparatus for wireless communications at a user equipment (UE), comprising:

one or more processors;

one or more memories coupled with the one or more processors; and

instructions stored in the one or more memories and executable by the one or more processors to cause the apparatus to:

receive control signaling indicating that a secure downlink message is scheduled for transmission from a network entity;

transmit, in response to the control signaling, a sounding reference signal for generating a channel estimate for a channel between the network entity and the UE in accordance with a delay-Doppler domain channel estimation scheme;

receive, via the channel, the secure downlink message that includes added interference over a slot duration, the added interference being based at least in part on the channel estimate, wherein the secure downlink message is encoded in accordance with an orthogonal time frequency space precoding scheme based at least in part on the delay-Doppler domain channel estimation scheme; and

decode the secure downlink message in accordance with the orthogonal time frequency space precoding scheme.

29 . The apparatus of claim 28 , wherein the instructions are further executable by the one or more processors to cause the apparatus to:

receive one or more channel state information reference signals;

generate a downlink channel estimate for the channel based at least in part on the received one or more channel state information reference signals; and

transmit a feedback message indicating the downlink channel estimate for one or more calibration coefficients applied to the channel estimate.