WO2023206435A1

WO2023206435A1 - Srs transmission mechanism for positioning

Info

Publication number: WO2023206435A1
Application number: PCT/CN2022/090493
Authority: WO
Inventors: Pengli YANG; Chiao-Yao CHUANG; Jijian CHEN; Xuancheng Zhu; Xiao Liang
Original assignee: Mediatek Singapore Pte. Ltd.
Priority date: 2022-04-29
Filing date: 2022-04-29
Publication date: 2023-11-02

Abstract

This disclosure provides a new transmission mechanism of sounding reference signal (SRS) for positioning that can improve the uplink measurement accuracy of the RedCap UE. According to the provided higher layer parameters of uplink SRS configuration for positioning, the UE with limited transmission bandwidth could perform frequency hopping by transmitting the SRS with a different starting RB index in frequency domain in a different time instance via RF re-tuning. Thus, the system with base station is able to receive the SRS resource for positioning with a larger bandwidth by combining each of the small SRS bandwidth transmitted in different time instances, in this way, the measurement accuracy will be improved.

Description

SRS TRANSMISSION MECHANISM FOR POSITIONING

FIELD

This present disclosure relates generally to wireless communications, and more specifically, to techniques of positioning a user equipment (UE) with the limited transmission bandwidth.

BACKGROUND

A reduced capacity UE (RedCap UE) has the limited maximum bandwidth for downlink and uplink. In order to enable the system with base station to observe the sounding reference signal (SRS) for positioning with larger bandwidth transmission to improve the accuracy of uplink measurement, a new transmission mechanism of SRS for RedCap UE may be beneficial.

SUMMARY

The purpose of this disclosure is to propose an SRS transmission mechanism for positioning that can improve the uplink measurement accuracy of the UE with small transmission bandwidth.

In the first aspect of this disclosure, SRS for positioning should be configured to support SRS transmission outside active UL BWP is proposed. Based on this proposal, the UE receives the higher layer parameters for uplink SRS configuration, including the spatial information, frequency and time location information, and frequency hopping parameters of each SRS resource within and outside active UL BWP.

In the second aspect of this disclosure, to enable the system with base stations be able to observe the SRS resource for positioning with larger bandwidth, the UE with smaller bandwidth capability for transmission and reception may transmit the SRS by frequency hopping manner. The transmission of a SRS resource in a time instance may have different starting PRB index than another SRS resource in another time instance by RF re-tuning.

In the third aspect of this disclosure, the smaller-bandwidth SRS transmission with a different starting PRB index in frequency domain in a different time instance maybe overlapped partially in frequency domain.

In the fourth aspect of this disclosure, the UE performs SRS frequency hopping by intra-slot hopping, inter-slot hopping, or intra-slot hopping in conjunction with inter-slot hopping according to the number of OFDM symbols within a slot of each SRS resource transmission.

In the fifth aspect of this disclosure, two ways are proposed for UE to perform SRS frequency hopping by transmitting the SRS resource with a different starting PRB index in frequency domain in a different time instance. One is that UE supports more SRS resources, each of them is configured with a different starting PRB index (n _shift) to achieve frequency hopping. The other is that UE performs transmission bandwidth hopping by changing the starting PRB index of one SRS resource at different time instances based on the frequency hopping parameters.

In the sixth aspect of this disclosure, to make sense for the system with base station to combine multiple SRS transmissions, the SRS resources for positioning should be configured by the higher layer parameter with the same spatial domain transmission filter between associated SRS resources within or outside BWP, the resources may be associated to a same downlink RS or a SRS resource for the spatial relation measurement.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is an example for a UE with limited transmission bandwidth to perform transmission bandwidth hopping within and outside BWP in order to enable the system with base station to observe larger SRS bandwidth.

Fig. 2 is an example for a UE with limited transmission bandwidth to perform transmission bandwidth hopping with intra-slot hopping (as shown in Fig. 2 (a) ) , inter slot hopping (as shown in Fig. 2 (b) ) , and intra-slot hopping in conjunction with inter-slot hopping (as shown in Fig. 2 (c) ) .

Fig. 3 is an example of the UE performs SRS frequency hopping by transmitting multiple SRS resources each with a different starting PRB index under configuration of higher layer parameter n _shift.

Fig. 4 is an example of the UE performs hopping by transmitting an SRS resource at a different starting PRB index in a different time under configurations of frequency hopping parameters C _SRS, B _SRS .

DETAILED DESCRIPTION

NR supports the SRS transmission for positioning within the active UL BWP of the UE, this disclosure proposes that SRS for positioning should also be configured to support SRS transmission outside active UL BWP for RedCap UE.

The SRS resource is configured to measure at least one of the uplink relative time of arrival (RTOA) , angle of arrival (AOA) , uplink RSRP (reference signal receiving power) , and receiving and transmitting (Rx-Tx) time difference.

To enable the system that with base stations be able to observe the SRS resources for positioning with larger bandwidth, the UE with smaller bandwidth capability for transmission and reception may transmit the SRS by frequency hopping manner. The transmission of a SRS resource in a time instance may have different starting PRB index than another SRS resource in another time instance by RF re-tuning, as illustrated in Fig. 1. The large-bandwidth SRS is generally defined to be comparable to the channel bandwidth of a component carrier. The smaller-bandwidth SRS is generally defined to be comparable to the maximum transmission bandwidth of RedCap UEs, and the maximum transmission bandwidth of RedCap UEs is generally smaller than the channel bandwidth of a component carrier.

The transmission of SRS for positioning within the active UL BWP is still limited by the maximum transmission bandwidth of UE. To transmit outside the active UL BWP may also require the base station to avoid uplink data scheduling when the UE doesn't stay within the active UL BWP. This means, if the base station configures a UE for SRS transmission outside the corresponding active UL BWP in frequency hopping manner, the UE is not expected the uplink data scheduling during the hopping duration. If the uplink data scheduling and SRS transmission happen simultaneously, the UE is not expected to transmit SRS outside the active UL BWP. The base station may also configure/re-configure the UE whether to perform frequency hopping outside the active UL BWP or not.

The smaller-bandwidth SRS transmission with a different starting PRB index in frequency domain in a different time instance maybe overlapped partially in frequency domain, as shown in Fig. 1. In this way, the system with base station is able to observe the same RS within a frequency domain segment in different time instance in order to estimate the change of the transmitting phase due to RF re-tuning.

The base station may configure a SRS resource set for positioning for the purpose of frequency hopping outside the BWP. Each SRS resource within the resource set may have the associated starting PRB index as frequency domain position. The resources may be associated to a same downlink RS or a SRS resource for the spatial relation measurement.

According to the number of OFDM symbols within a slot of each SRS resource transmission, the UE can perform SRS frequency hopping by intra-slot hopping (as shown in Fig. 2 (a) ) , inter-slot hopping (as shown in Fig. 2 (b) ) , or intra-slot hopping in conjunction with inter-slot hopping (as shown in Fig. 2 (c) ) , the time interval between two SRS resource transmissions should be sufficient for UE to perform RF retuning.

When the SRS resource transmission with a small number of OFDM symbols within a slot and it is sufficient to complete hopping among all sub-bands within a slot, the SRS resource for positioning will perform bandwidth transmission with intra-slot hopping, as shown in Fig. 2 (a) .

When it is not sufficient for SRS hopping across all sub-bands within a slot, the SRS resource for positioning performs bandwidth transmission with inter-slot hopping or intra-slot hopping in conjunction with inter-slot hopping. Additionally, the OFDM symbols could be allocated in same location within each slot when inter-slot hopping is performed, as shown in Fig. 2 (b) .

The frequency-domain starting position

is defined by

Where

Based on this formula, the hopping of SRS transmission for positioning can be performed in two ways.

Two ways are proposed for UE to perform SRS frequency hopping by transmitting the SRS resource with a different starting PRB index in frequency domain in a different time instance. One is that UE supports more SRS resources to perform frequency hopping, each of them is configured with a different starting PRB index (n _shift) . The other is that UE performs hopping by retuning RF to change the starting PRB of one SRS resource at different time instances based on frequency hopping parameters.

When the UE performs SRS frequency hopping by transmitting multiple SRS resources, each with a different starting PRB index, the SRS resources for positioning should be configured by the higher layer parameter with the same spatial domain transmission filter between associated SRS resources within or outside BWP, as illustrated in Fig. 1 and Fig. 3.

When the UE performs SRS frequency hopping by transmission multiple SRS resources, the SRS resources for positioning within or outside BWP should be configured by the higher-layer parameter freqDomainShift n _shift, which can be used to determine the starting frequency position and to achieve overlapping between adjacent resources. The frequency-domain starting position is independent of the parameters in the second term of the formula (1) since freqDomainPosition n _RRC is not configured for SRS resource for positioning, n _RRC=0 and n _b=0. In this way, no frequency hopping parameters are configured and only n _shift is configured for each SRS resource to determine the frequency-domain starting PRB, as illustrated in Fig. 3.

As illustrated in Fig. 3, when the smaller-bandwidth SRS for positioning is transmitted, the starting PRB index for transmission in next time instance based on that in current time instance could be determined by

or

Where

denotes the RedCap UE transmission BW.

is the overlapping BW between two smaller-bandwidth SRS transmission in adjacent time instances. For example,

j is the SRS transmission number. n _{shift_0} is the first frequency position of the SRS transmission for hopping, could be determined by

n _{shift_0}=n _{shift_normal}

or

n _{shift_normal}is starting PRB index of the SRS resource for positioning of normal UE with large bandwidth,

denotes the transmission BW of normal UE.

The frequency hopping parameters C _SRS, B _SRS should be configured when the UE performs hopping by transmitting an SRS resource at different starting PRB indexes in different times. A UE should support a C _SRS configuration corresponding to a large bandwidth transmission. The small bandwidth of RedCap UE can be regarded as a sub-band. Add a configuration about B _SRS to set the appropriate sub-band bandwidth and the number of sub-bands, at the same time, partial overlapping in frequency domain could be implicitly configured by the value of C _SRS and B _SRS. In other words, as long as the sub-band bandwidth is smaller than the transmission bandwidth of RedCap UE, the partial overlapping in frequency domain could be realized. For example, the large bandwidth of normal UE is

the small bandwidth of RedCap UE

and the large bandwidth

is divided into N ₁=8 segments, each with m _SRS, ₁=34, as illustrated in Fig. 4. In addition, different number of RBs overlapped in frequency domain could correspond to different C _SRS configuration. The configuration n _shift for one SRS resource is fixed and will not change over time, so modify the second term in the formula (1) to change the starting PRB index is proposed. The starting PRB index should be changed with SRS transmission number n _SRS, so frequency domain sub-band index

can be modified to

Claims

A method of wireless communication of a user equipment (UE) , comprising:

receiving, from a serving base station of the UE, the higher layer parameters of sounding reference signal (SRS) configuration for positioning

transmitting, at a baseband of the UE, the SRS for positioning within the active UL BWP with first starting frequency position

re-adjusting, at the RF frequency of the UE, for the transmission of the SRS outside the active UL BWP with multiple starting frequency positions.
The method of claim 1, wherein the SRS configuration for positioning further comprises the spatial relation between the SRS resources across several transmissions within and outside the corresponding active UL BWP, the resources may be associated to a same downlink RS or a SRS resource for the spatial relation measurement.
The method of claim 1, wherein the SRS configuration for positioning further comprises the frequency hopping parameters.
The method of claim 1, wherein the SRS resource is associated to a SRS resource set for positioning which is configured by the base station for the purpose of frequency hopping outside the BWP.
The method of claim 1, wherein each SRS resource within a resource set is configured with the associated starting PRB index as frequency domain position, each starting PRB index associated to the transmission in a time instance.
The method of claim 1, wherein the SRS resources with different starting PRB indexes have overlapping in frequency domain for transmission.
The method of claim 1, wherein the SRS transmission outside the active UL BWP require the base station to avoid uplink data scheduling when the UE doesn't stay within the active UL BWP.
The method of claim 5, wherein the starting PRB index for SRS transmission in next time instance based on that in current time instance could be determined by

where
denotes the RedCap UE transmission BW.
is the overlapping BW between two smaller-bandwidth SRS transmission in adjacent time instances. For example,
i=0, 1, 2, ....; j is the SRS transmission number. n _{shift_0} is the first frequency position of the SRS transmission for hopping.
The method of claim 5, wherein the starting PRB index for transmission in next time instance based on that in current time instance could also be determined by

Where n _b denotes frequency domain sub-band index, n _SRS is the SRS transmission number.