US-12621693-B2 - Event-based triggering of channel quality measures

US12621693B2US 12621693 B2US12621693 B2US 12621693B2US-12621693-B2

Abstract

There is provided mechanisms for event-based triggering of second channel quality measures. A method is performed by a network node. The method comprises obtaining a first measure of channel quality of a radio propagation channel extending between the network node and a user equipment from measurements on an uplink signal received from the user equipment. The method comprises triggering, when determining that the first measure of channel quality causes an event-based triggering condition to be fulfilled, transmission of a further uplink signal from the user equipment for the network node to obtain a second measure of the quality of the radio propagation channel. Determining that the first measure of channel quality causes the event-based triggering condition to be fulfilled involves making a comparison between the first measure of channel quality and a reference channel quality.

Inventors

Hamed FARHADI
Niklas Wernersson
Karl Werner

Assignees

TELEFONAKTIEBOLAGET LM ERICSSON (PUBL)

Dates

Publication Date: 20260505
Application Date: 20210305

Claims (19)

1 . A method for event-based triggering of second channel quality measures, the method being performed by a network node, the method comprising: obtaining a first measure of channel quality of a radio propagation channel extending between the network node and a user equipment from measurements on an uplink signal received from the user equipment; triggering, when determining that the first measure of channel quality causes an event-based triggering condition to be fulfilled, transmission of a further uplink signal from the user equipment for the network node to obtain a second measure of the channel quality of the radio propagation channel, wherein determining that the first measure of channel quality causes the event-based triggering condition to be fulfilled involves making a comparison between the first measure of channel quality and a reference channel quality; and updating beamforming vectors as a function of the second measure of the channel quality, wherein the beamforming vectors are to be applied during at least one of downlink transmission and uplink reception, wherein the beamforming vectors are updated based on an estimated covariance matrix of the second measure of the channel quality.
2 . The method according to claim 1 , wherein the method further comprises: storing the first measure of channel quality.
3 . The method according to claim 1 , wherein the first measure of channel quality is an incomplete representation of the radio propagation channel.
4 . The method according to claim 1 , wherein the reference channel quality is a previously obtained measure of channel quality of the radio propagation channel.
5 . The method according to claim 1 , wherein the reference channel quality is derived from a previously obtained complete representation of the radio propagation channel.
6 . The method according to claim 1 , wherein the reference channel quality is represented by a CSI value.
7 . The method according to claim 1 , wherein the event-based triggering condition is fulfilled when the first measure of channel quality differs more than a threshold value from the reference channel quality.
8 . The method according to claim 1 , wherein the event-based triggering condition is fulfilled when a timestamp of the first measure of channel quality differs more than a threshold value from a timestamp of the reference channel quality.
9 . The method according to claim 1 , wherein the comparison between the first measure of channel quality and the reference channel quality is any of: a power difference, a cross correlation, an inner product between the first measure of channel quality and the reference channel quality.
10 . The method according to claim 1 , wherein the comparison between the first measure of channel quality and the reference channel quality pertains to at least one of: channel quality accuracy, channel quality freshness, and channel quality rotation, wherein the channel quality accuracy is defined in terms of channel estimation error of channel estimation of the radio propagation channel, wherein the channel quality freshness is defined in terms of variation between the first measure of channel quality and a previously obtained measure of the channel quality, and wherein the channel quality rotation is defined in terms of channel subspace rotation between the first measure of channel quality and a previously obtained measure of the channel quality.
11 . The method according to claim 1 , wherein the reference channel quality is a combination of at least two previously obtained measures of channel quality of the radio propagation channel, and wherein at least one of the previously obtained measures of channel quality was obtained in a wider frequency interval, or using more ports at the network node, than the first measure of channel quality.
12 . The method according to claim 1 , wherein the first measure of channel quality pertains to any of: a channel estimate of less than the complete carrier bandwidth, second order statistics of the radio propagation channel as derived from a channel estimate of the radio propagation channel, a wideband channel estimate of less than all ports of the user equipment, a channel estimate constrained to a linear subspace and pertaining to what is measured on a second carrier different from a first carrier on which the first measure of channel quality was obtained, and a measure of decoding success of the uplink signal.
13 . The method according to claim 1 , wherein the first measure of channel quality is impacted by at least one further parameter, the at least one further parameter being any of: channel coherence time of the radio propagation channel, speed of the user equipment, available resources allocated for channel estimation at the network node.
14 . The method according to claim 1 , wherein a periodic transmission of a respective further uplink signal from the user equipment for the network node to obtain a respective second measure of the channel quality of the radio propagation channel is triggered, the periodicity and transmission power of which is dependent on the comparison between the first measure of channel quality and the reference channel quality.
15 . The method according to claim 1 , wherein the first measure of channel quality is obtained from measurements on the uplink signal any of: a DMRS related to a PUSCH transmission, a DMRS related to a PUCCH transmission, and a RACH preamble.
16 . The method according to claim 1 , wherein the uplink signal is obtained in a narrower frequency interval, or using fewer ports at the network node, than the further uplink signal.
17 . A network node for event-based triggering of second channel quality measures, the network node comprising processing circuitry, the processing circuitry being configured to cause the network node to: obtain a first measure of channel quality of a radio propagation channel extending between the network node and a user equipment from measurements on an uplink signal received from the user equipment; trigger, when determining that the first measure of channel quality causes an event-based triggering condition to be fulfilled, transmission of a further uplink signal from the user equipment for the network node to obtain a second measure of the channel quality of the radio propagation channel, wherein determining that the first measure of channel quality causes the event-based triggering condition to be fulfilled involves making a comparison between the first measure of channel quality and a reference channel quality; and update beamforming vectors as a function of the second measure of the channel quality, wherein the beamforming vectors are to be applied during at least one of downlink transmission and uplink reception, wherein the beamforming vectors are updated based on an estimated covariance matrix of the second measure of the channel quality.
18 . A network node for event-based triggering of second channel quality measures, the network node comprising: an obtain module configured to obtain a first measure of channel quality of a radio propagation channel extending between the network node and a user equipment from measurements on an uplink signal received from the user equipment; a trigger module configured to trigger, when determining that the first measure of channel quality causes an event-based triggering condition to be fulfilled, transmission of a further uplink signal from the user equipment for the network node to obtain a second measure of the channel quality of the radio propagation channel, wherein determining that the first measure of channel quality causes the event-based triggering condition to be fulfilled involves making a comparison between the first measure of channel quality and a reference channel quality; and an update module configured to update beamforming vectors as a function of the second measure of the channel quality, wherein the beamforming vectors are to be applied during at least one of downlink transmission and uplink reception, wherein the beamforming vectors are updated based on an estimated covariance matrix of the second measure of the channel quality.
19 . A computer program product for event-based triggering of second channel quality measures, comprising a non-transitory computer readable medium storing a computer program comprising computer code which, when run on processing circuitry of a network node, causes the network node to: obtain a first measure of channel quality of a radio propagation channel extending between the network node and a user equipment from measurements on an uplink signal received from the user equipment; trigger, when determining that the first measure of channel quality causes an event-based triggering condition to be fulfilled, transmission of a further uplink signal from the user equipment for the network node to obtain a second measure of the channel quality of the radio propagation channel, wherein determining that the first measure of channel quality causes the event-based triggering condition to be fulfilled involves making a comparison between the first measure of channel quality and a reference channel quality; and update beamforming vectors as a function of the second measure of the channel quality, wherein the beamforming vectors are to be applied during at least one of downlink transmission and uplink reception, wherein the beamforming vectors are updated based on an estimated covariance matrix of the second measure of the channel quality.

Description

CROSS REFERENCE TO RELATED APPLICATION(S) This application is a 35 U.S.C. § 371 National Stage of International Patent Application No. PCT/SE2021/050198, filed Mar. 5, 2021. TECHNICAL FIELD Embodiments presented herein relate to a method, a network node, a computer program, and a computer program product for event-based triggering of channel quality measures. BACKGROUND In communications networks, there may be a challenge to obtain good performance and capacity for a given communications protocol, its parameters and the physical environment in which the communications network is deployed. For example, for millimeter wave (mmWave) beamforming, hybrid multiple-antenna beamforming combining large-dimensional pre/postprocessing (in time domain) with lower dimensional digital processing (in frequency domain) can be used for reducing hardware costs and training overhead in multi-antenna systems operating at the mmWave frequency band. This leads to a need for lower number of radio frequency chains (and hence lower hardware cost) for processing of signals received over large antenna arrays. The accuracy of the beamforming at high frequency band relies on the quality of acquired channel state information (CSI). CSI comprises information regarding the propagation of the signal from transmitter to receiver and includes the combined effect of, for example, scattering, fading, and the decaying power with distance. In a communication system with possible one/multiple antenna(s) at transmitter and receiver, the CSI can represent the effective signal attenuation between each transmit and receive antenna pair, or a function of this. For example, in a system with M transmit antenna and N receive antennas, the received signal can be represented as follows: y⁡(t)=H⁡(t)⁢x⁡(t)+n⁡(t), where x(t) is an M×1 transmit vector, y(t) is an N×1 receive vector, n(t) is an N×1 received noise vector, and H(t) is an N×M matrix of channel gains at time instance t. The element in the i:th row and the j:th column of the matrix H(t) is denoted as hij and represents the signal attenuation from the j:th antenna of the transmitter to the i:th antenna of the receiver. The CSI can be represented as an estimation of H(t) or a function of it, e.g. the covariance of H (t), denoted as Q (t), or the quantized version of H(t) denoted as Ĥ(t). CSI can be acquired by either of codebook-based or reciprocity-based approaches as follows. Codebook-based CSI acquisition relies on Channel State Information Reference Signal (CSI-RS) sent in the downlink (i.e., from access network node towards user equipment). The user equipment receives the CSI-RS and use it to estimate the channel and report channel quality information back to the access network node. Certain information is extracted based on the estimated CSI at the user equipment (such as RI (rank indicator) to be used for selecting the number of layers for MIMO transmission, PMI (precoding matrix indicator) to be used for selecting the precoding matrix to be used at the transmitter to conduct beamforming, and CQI (channel quality feedback) that indicate the quality of the channel and can be used for link adaptation at the transmitter side. RI, PMI, and CQI are computed as functions of estimated CSI and are mapped to codewords in pre-designed codebooks for each of these quantities, and the indices of the appropriate codewords will be sent to the access network node. The CSI-RS might be configured specific to each user equipment, but multiple user equipment can also share the same CSI-RS. Reciprocity-based CSI acquisition relies on Sounding Reference Signals (SRSs) sent in the uplink i.e., from user equipment towards access network node). The SRS is transmitted by the user equipment to help the access network node obtain the CSI for each user equipment. The access network node exploits the underlying reciprocity of the radio propagation channel between the downlink and the uplink and extrapolates the CSI for the downlink from the received SRSs. The SRS is configured specific to each user equipment. Allocating more radio resources for CSI acquisition enables more accurate CSI to be obtained, but results in less radio resources being available for payload data to be communicated. Triggering CSI acquisition causes power consumption of the user equipment to increase. Further, using a fixed amount of radio resources allocated for CSI acquisition does not allow the CSI acquisition to adapt to changing radio propagation channel conditions and may lead to a level of CSI quality that is inefficient for the data communication. As a first example, for a stationary receiver (like for example in a fixed wireless access (FWA) network) the radio propagation channel conditions may be very stable channel, and triggering CSI acquisition too often may incur a high cost in radio resources, without improving the accuracy of the CSI. As a second example, for a fast-moving receiver the radio propagation channel conditions may change ve