Channel estimation reference signals for pre-equalization
Methods, systems, and devices that support channel estimation reference signals for pre-equalization are described. In some examples, channel state information (CSI) for a link between a user equipment (UE) and another wireless device may be acquired by the UE based on samples of a downlink reference signal transmitted from the UE to the wireless device. Specifically, the wireless device (e.g., an extended reality (XR) device) may obtain samples of the downlink reference signal (e.g., a channel estimation reference signal) and report or indicate (e.g., transmit) the samples to the UE via an uplink transmission. For example, the reference signals may be sampled at the wireless device side, and CSI may be obtained using the samples signaled back to the UE by the wireless device. The UE may perform channel estimation based on the received samples, which may enable transmit pre-equalization of signals sent to the wireless device.
1 . A user equipment (UE) for wireless communication, 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:
transmit, to a wireless device, a resource allocation message indicating an allocation of a set of downlink resources for one or more downlink reference signals and an allocation of a set of uplink resources for a sample message;
transmit the one or more downlink reference signals to the wireless device via a sidelink communication link and the set of downlink resources in accordance with the resource allocation message;
receive, from the wireless device via the sidelink communication link and the set of uplink resources in accordance with the resource allocation message, the sample message indicating raw reference signal samples of the one or more downlink reference signals; and
transmit a data signal to the wireless device, wherein the data signal is pre-equalized using a downlink channel estimation that is based at least in part on a reconstruction of the raw reference signal samples.
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:
generate the downlink channel estimation from the reconstruction of the raw reference signal samples; and
perform pre-equalization on the data signal using the downlink channel estimation generated from the reconstruction of the raw reference signal samples.
3 . The UE of claim 2 , wherein:
the raw reference signal samples comprise quantized raw reference signal samples, and
the downlink channel estimation is generated based at least in part on the reconstruction of the quantized raw reference signal samples.
4 . The UE of claim 3 , wherein:
the quantized raw reference signal samples are quantized in accordance with one or more quantization schemes, and
the one or more quantization schemes comprise differential quantization, differential pulse coding modulation, Lloyd-Max quantization, time domain sample quantization, frequency domain sample quantization, or a combination thereof.
5 . 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:
transmit, to the wireless device, a quantization configuration message indicating one or more quantization schemes to be applied to the raw reference signal samples, wherein the raw reference signal samples indicated by the sample message are quantized in accordance with the one or more quantization schemes.
6 . 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:
transmit a second pre-equalized data signal via a downlink slot, wherein the one or more downlink reference signals are transmitted via the downlink slot without pre-equalization and without precoding.
7 . The UE of claim 6 , wherein:
transmitting the second pre-equalized data signal comprises transmitting the second pre-equalized data signal via one or more symbols of the downlink slot, and
the one or more downlink reference signals are transmitted via one symbol of the downlink slot.
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:
frequency-division multiplex ports of the one or more downlink reference signals on resource elements of a resource block to produce frequency-division multiplexed downlink reference signals, wherein the frequency-division multiplexed downlink reference signals are transmitted on the sidelink communication link via the resource elements of the resource block.
9 . The UE of claim 8 , wherein, to transmit the one or more downlink reference signals, the one or more processors are individually or collectively operable to execute the code to cause the UE to:
transmit the one or more downlink reference signals on the sidelink communication link using a plurality of ports mapped to the resource elements of the resource block with a frequency domain mapping having a density of at least six.
10 . The UE of claim 1 , wherein, to transmit the one or more downlink reference signals, the one or more processors are individually or collectively operable to execute the code to cause the UE to:
transmit the one or more downlink reference signals on an orthogonal frequency-division multiplexing symbol without data multiplexing.
11 . The UE of claim 1 , wherein the set of uplink resources for the sample message is within a threshold time interval after the set of downlink resources for the one or more downlink reference signals.
12 . 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:
transmit a second pre-equalized data signal via a first downlink slot, wherein the one or more downlink reference signals are transmitted via a latter portion of the first downlink slot, the raw reference signal samples are received via an uplink slot following the first downlink slot, and the data signal is transmitted via a second downlink slot after the uplink slot.
13 . The UE of claim 1 , wherein:
the one or more downlink reference signals comprise one or more demodulation reference signals or one or more channel state information reference signals.
14 . A wireless device for wireless communication, 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 wireless device to:
receive, from a user equipment (UE), a resource allocation message indicating an allocation of a set of downlink resources for one or more downlink reference signals and an allocation of a set of uplink resources for a sample message;
receive, from the UE, the one or more downlink reference signals via a sidelink communication link and the set of downlink resources in accordance with the resource allocation message;
transmit, to the UE via the sidelink communication link and the set of uplink resources in accordance with the resource allocation message, the sample message indicating raw reference signal samples of the one or more downlink reference signals; and
receive a data signal from the UE, wherein the data signal is pre-equalized in accordance with a downlink channel estimation that is based at least in part on a reconstruction of the raw reference signal samples.
15 . The wireless device of claim 14 , wherein the one or more processors are individually or collectively further operable to execute the code to cause the wireless device to:
quantize the raw reference signal samples in accordance with one or more quantization schemes, wherein the sample message comprises the quantized raw reference signal samples.
16 . The wireless device of claim 15 , wherein the one or more quantization schemes comprise differential quantization, differential pulse coding modulation, Lloyd-Max quantization, time domain sample quantization, frequency domain sample quantization, or a combination thereof.
17 . The wireless device of claim 15 , wherein the one or more processors are individually or collectively further operable to execute the code to cause the wireless device to:
receive, from the UE, a quantization configuration message indicating the one or more quantization schemes to be applied to the raw reference signal samples, wherein the raw reference signal samples are quantized in accordance with the one or more quantization schemes.
18 . The wireless device of claim 14 , wherein the one or more processors are individually or collectively further operable to execute the code to cause the wireless device to:
receive a second pre-equalized data signal via a downlink slot, wherein the one or more downlink reference signals are received via the downlink slot without pre-equalization and without precoding.
19 . The wireless device of claim 18 , wherein:
receiving the second pre-equalized data signal comprises receiving the second pre-equalized data signal via one or more symbols of the downlink slot, and
the one or more downlink reference signals are received via one symbol of the downlink slot.
20 . The wireless device of claim 14 , wherein receiving the one or more downlink reference signals comprises receiving frequency-division multiplexed downlink reference signals on the sidelink communication link via resource elements of a resource block.
21 . The wireless device of claim 20 , wherein, to receive the one or more downlink reference signals, the one or more processors are individually or collectively operable to execute the code to cause the wireless device to:
receive the one or more downlink reference signals on the sidelink communication link based at least in part on a plurality of ports mapped to the resource elements of the resource block with a frequency domain mapping having a density of at least six.
22 . The wireless device of claim 14 , wherein, to receive the one or more downlink reference signals, the one or more processors are individually or collectively operable to execute the code to cause the wireless device to:
receive the one or more downlink reference signals on an orthogonal frequency-division multiplexing symbol without data multiplexing.
23 . The wireless device of claim 14 , wherein the set of uplink resources for the sample message is within a threshold time interval after the set of downlink resources for the one or more downlink reference signals.
24 . The wireless device of claim 14 , wherein the one or more processors are individually or collectively further operable to execute the code to cause the wireless device to:
receive a second pre-equalized data signal via a first downlink slot, wherein the one or more downlink reference signals are received via a latter portion of the first downlink slot, the raw reference signal samples are transmitted via an uplink slot following the first downlink slot, and the data signal is received via a second downlink slot after the uplink slot.
25 . The wireless device of claim 14 , wherein the wireless device is an extended reality device and the data signal is indicative of video data.
26 . The wireless device of claim 14 , wherein:
the one or more downlink reference signals comprise one or more demodulation reference signals or one or more channel state information reference signals.
27 . A method for wireless communications at a user equipment (UE), comprising:
transmitting, to a wireless device, a resource allocation message indicating an allocation of a set of downlink resources for one or more downlink reference signals and an allocation of a set of uplink resources for a sample message;
transmitting the one or more downlink reference signals to the wireless device via a sidelink communication link and the set of downlink resources in accordance with the resource allocation message;
receiving, from the wireless device via the sidelink communication link and the set of uplink resources in accordance with the resource allocation message, the sample message indicating raw reference signal samples of the one or more downlink reference signals; and
transmitting a data signal to the wireless device, wherein the data signal is pre-equalized using a downlink channel estimation that is based at least in part on a reconstruction of the raw reference signal samples.
28 . A method for wireless communications at a wireless device, comprising:
receiving, from a user equipment (UE), a resource allocation message indicating an allocation of a set of downlink resources for one or more downlink reference signals and an allocation of a set of uplink resources for a sample message;
receiving, from the UE, the one or more downlink reference signals via a sidelink communication link and the set of downlink resources in accordance with the resource allocation message;
transmitting, to the UE via the sidelink communication link and the set of uplink resources in accordance with the resource allocation message, the sample message indicating raw reference signal samples of the one or more downlink reference signals; and
receiving a data signal from the UE, wherein the data signal is pre-equalized in accordance with a downlink channel estimation that is based at least in part on a reconstruction of the raw reference signal samples.