Patent Application
20230388953
Disclosed are embodiments related to propagation delay compensation.
1. Current 3GPP Status
The 3GPP Rel-17 RAN work item “Enhanced Industrial Internet of Things (IoT) and ultra-reliable and low latency communication (URLLC) support for NR” has the following objective related with propagation delay compensation: “Enhancements for support of time synchronization: a. RAN impacts of SA2 work on uplink time synchronization for TSN, if any. [RAN2]; b. Propagation delay compensation enhancements (including mobility issues, if any). [RAN2, RAN1, RAN3, RAN4].”
RAN1 has agreed in RAN1#102e that
The reference cell for reference time delivery is the Primary Cell (PCell). The reference time information sent on Radio Resource Control (RRC) contains a field that indicates the reference System Frame Number (SFN) corresponding to the reference time information. It is possible to have unaligned SFN across carriers in a cell group, and thus a reference cell is needed and defined in RRC that “If referenceTimeInfo field is received in DLInformationTransfer message, this field indicates the SFN of PCell.” PSCell is not included as DLInformationTransfer is sent on SRB1/2 on the Master Cell Group (MCG) not on the Secondary Cell Group (SCG). Additionally, System Information Block 9 (SIB9) is only broadcasted on the PCell and this restriction aligns the RRC-dedicated and broadcast message for reference time delivery.
2. Multi-RTT Positioning Method
In the Multi-RTT positioning method, the UE position is estimated based on measurements performed at both, UE and TRPs. The measurements performed at the UE and TRPs are UE/gNB Rx−Tx time difference measurements (and optionally DL-PRS-RSRP and UL-SRS-RSRP) of DL-PRS and UL-SRS, which are used by an LMF to determine the RTTs.
In what below, we show an example of New Radio (NR) base station (gNB) measurement for positioning.
The reporting range of gNB Rx−Tx time difference, as defined in Clause 5.2.3 of TS 38.215, is defined from −985024Tc to +985024×Tc. The reporting resolution is uniform across the reporting range and is defined as T=Tc*2k where k is selected by gNB from the set {0, 1, 2, 3, 4, 5}.
LMF (Location Management Function) provides a recommended k value (k1). gNB selects parameter k (k2) and informs to the LMF.
The mapping of measured quantity for each reporting resolution (k) is defined in Table 13.2.1-1 to Table 13.2.1-6 of 3GPP TS 38.133 V16.4.0, which are shown below.
3. Report Mapping
The reporting range of UL SRS RSRP, as defined in clause 5.2.5 of 38.215, is defined from −156 dBm to −31 dBm with resolution 1 dB. The mapping of measured quantity is defined in Table 13.3.1-1 of TS 38.133 (which is shown below). The range in the signalling may be larger than the guaranteed accuracy range.
Certain challenges presently exist. For instance, although the principle of the propagation delay compensation method is the same as the Timing Advance (TA) for uplink timing alignment and Round-Trip-Time (RTT) for positioning, the signalling details to support those two approaches (i.e., TA and RTT) on the Access Stratum (AS) layer are missing.
Accordingly, in one aspect this disclosure provides a method performed by a UE. The method includes the UE receiving a message transmitted by a network node, the message comprising RTT based measurement information and at least one measurement reporting configuration. The UE also performs at least one of: i) transmitting to the network node a first time difference report in accordance with the measurement reporting configuration, wherein the first time difference report transmitted by the UE comprises a first time difference measurement result, or ii) receiving a second time difference report transmitted by the network node, wherein the second time difference report transmitted by the network node comprises a second time difference measurement result.
In another aspect there is provided a computer program comprising instructions which when executed by processing circuitry of a UE, causes the UE to perform the UE methods disclosed herein. In another aspect there is provided a carrier containing the computer program, wherein the carrier is one of an electronic signal, an optical signal, a radio signal, and a computer readable storage medium.
In another aspect there is provided a UE where the UE is configured to perform the UE methods disclosed herein. In some embodiments, the UE includes processing circuitry and a memory containing instructions executable by the processing circuitry, whereby the UE is configured to perform the UE methods disclosed herein.
In another aspect there is a method performed by a network node (e.g., a base station). The method includes the network node transmitting to a UE a message comprising RTT based measurement information and at least one measurement reporting configuration. The network node also performs at least one of: i) receiving a first time difference report transmitted by the UE in accordance with the measurement reporting configuration, wherein the first time difference report transmitted by the UE comprises a first time difference measurement result, or ii) transmitting to the UE a second time difference report, wherein the second time difference report transmitted by the network node comprises a second time difference measurement result.
In another aspect there is provided a computer program comprising instructions which when executed by processing circuitry of a network node, causes the network node to perform the network node methods disclosed herein. In another aspect there is provided a carrier containing the computer program, wherein the carrier is one of an electronic signal, an optical signal, a radio signal, and a computer readable storage medium.
In another aspect there is provided a network node where the network node is configured to perform the network node methods disclosed herein. In some embodiments, the network node includes processing circuitry and a memory containing instructions executable by the processing circuitry, whereby the network node is configured to perform the network node methods disclosed herein.
Advantages of the embodiments is that they enable a UE and/or network node to compensate for propagation delays.
The accompanying drawings, which are incorporated herein and form part of the specification, illustrate various embodiments.
The legacy multi-RTT positioning method makes use of the UE Rx−Tx time difference measurements and Downlink (DL) Positioning Reference Signal (PRS) Reference Signal Received Power (RSRP) of downlink signals received from multiple TRPs measured by the UE, and the measured gNB Rx−Tx time difference measurements and UL-SRS-RSRP at multiple TRPs of uplink signals transmitted from UE. The measurements are used to determine the RTT at the positioning server which are used to estimate the location of the UE.
The RTT based delay compensation is leveraged on the legacy multi-RTT positioning method illustrated in
Next, the gNB transmits a downlink frame j to the UE, and records transmission time as t2. Next, the UE receives downlink frame j and records the time of arrival of the first detected path as t4. The following calculations are performed in the UE and gNB, respectively: i) UERx-Txdiff=t4−t1; and ii) gNBRx-Tx diff=t3−t2. This quantity can be positive or negative depending on the whether gNB transmits the DL frame before or after receiving the UL frame. The propagation delay can be calculated as follows: RTT=(gNB Rx−Tx time difference)+(UE Rx−Tx time difference).
In one embodiment, gNB uses a message 202 (e.g., an RRC message) to configure UE 102 with information identifying the reference signals to be used for the RTT-based measurement and the measurement reporting configurations. After sending message 202, gNB may trigger the UE to perform the RTT-based measurements and transmit a report by transmitting to UE 102 a trigger message 204 (e.g., Downlink Control Information (DCI) or MAC Control Element (CE)). In the below example, the uplink reference signals are Sounding Reference Signals (SRS) and the downlink reference signals are Channel State Information Reference Signals (CSI-RS). Other reference signals can also be used.
The reporting can be periodic after receiving the RRC configuration message 202. The reporting can also be semi-periodic after receiving the RRC configuration message 202 in such a case a durationForSemiPeriodic is configured so that UE stops reporting after the configured time durationForSemiPeriodic. The durationForSemiPeriodic can also take a value of infinity. The reporting can also be aperiodic and triggered by Downlink Control Information (DCI).
UE can either send the reporting in an UL MAC CE or in an RRC message. As multiple reporting configurations are configured, gNB can configure UE on which one or multiple ones to be used through trigger message 204 (e.g., DCI or MAC CE signaling), which also serves as the triggering mechanism for the UE to start reporting. If only one is configured, then it is the default one to be used.
1. UE Reports UE Rx−Tx Time Difference to gNB
In this embodiment, UE reports UE Rx−Tx time difference to gNB on the Uu interface (see report 206).
In the reporting configurations, gNB can configure UE to send the average of a configurable number of consecutive measurements instead of each measurement. This is indicated by, for example, the parameter measAveragingFactor. The purpose of this is to reduce the uplink reporting overhead. A measAverageFactor of 5 allows UE to average 5 measurements and thus, reduce the overhead five-fold.
In another embodiment, gNB can configure UE to apply a layer-3 filtering of the measurements before reporting, for example with a moving average window with different weights. For example, gNB configure an index of length 10=[0.2, 0.4, 0.6, 0.8, 1, 1, 1, 1, 1, 1] where each value represents the weight of the measurement in the final reporting. At time t when reporting, the weight is 0.2 at t−10, the weight is 0.4 at t−9, the weight is 0.6 at t−8, etc. In another example, UE uses the formula to report the value of Fn=(1−α)*Fn-1+a*Mn and Mn is the measurement at time n and a is the weighting factor.
In another embodiment, UE is configured to report periodically every t, t+5, t+10, etc. in which the reporting periodicity is every 5 ms which is different and larger than the periodicity of the periodic occurrences of the reference signals.
Below is an example of an IE to configure RTT request:
In the above, network can configure one RTT-request with a pair of DL and UL references signals to use for RTT measurement. This is linked to one report configuration. The network can configure a list of multiple such requests. Multiple pairs of DL and UL reference signals can be linked to one report configuration and multiple report configurations can be linked to one pair of DL and UL reference signals.
For semi-periodic reporting type, the network can activate/de-active any one by using a MAC CE. For aperiodic reporting type, it is triggered by a pointer in the DCI field.
In the uplink reporting of UE Rx−Tx, UE can report the measurement in the RRC message. It is a list of measurements ordered by the time the measurements are taken, if timestamp is absent. Optionally, timeStamp can be added. The measurement element points to the specific RTT request ID which subsequently identify which pair of DL and UL signals have been used and the reporting configurations.
Note that the variable names above are exemplary, and other names can be used without changing the functionality of the signaling. For instance, release suffix can be attached to a parameter name, e.g., ‘dl-PRS-ID-r16’ or ‘dl-PRS-ID-r17’.
In another embodiment, the UE Rx-TX time difference can be reported in the UL MAC CE.
2. gNB Node Reports gNB Rx—Tx Time Difference to UE
In this reporting configuration, gNB sends the measurement results of gNB Rx−Tx time difference to UE (see report 208). While the reporting does not involve a location server, the same reporting mapping tables (for example, gNB Rx−Tx time difference measurement report mapping table, UL SRS RSRP report mapping) defined for positioning can be reused for time synchronization purpose between gNB and UE (for instance, propagation time estimation). The reporting IE is illustrated below:
In one embodiment, a different set of reporting mapping tables (for example, gNB Rx−Tx time difference measurement report mapping table, UL SRS RSRP report mapping) can be defined for time synchronization purpose between gNB and UE. In another embodiment, the gNB measurement results are sent to UE via MAC CE(s).
3. Dependencies of Achievable Time Synchronization Accuracy
The granularity of achievable RTT based time synchronization accuracy may depend on various parameters and configurations. In one example, the accuracy achievable is a function of the downlink subcarrier spacing (SCS) of the active Bandwidth Part (BWP), and/or uplink SCS of the active BWP. In another example, the granularity achievable of the RTT method depends on the k value (i.e., k=0 to 5) used to determine the gNB Rx−Tx time difference measurement report mapping.
In another example, a k value (i.e., k=0 to 5) is introduced to determine the UE Rx−Tx time difference measurement report mapping table. Then, the granularity achievable of the RTT method depends on the k value of the UE Rx−Tx time difference measurement report mapping.
In another example, the time synchronization accuracy is negotiated between gNB and UE using the k value defined for Rx−Tx time difference reporting. With possible value {0,1,2,3,4,5} for k, k=0 corresponds to finest granularity, and k=5 corresponds to coarsest granularity. The granularity level can be negotiated between UE and gNB.
For instance, the gNB can signal the desired granularity level k to UE. The UE can reply with the actually realized k to the gNB, which may or may not be equal to the desired k from gNB.
For instance, the UE can signal the desired granularity level k to gNB. This k value depending on the synchronization accuracy requirement at the application layer (e.g., part of the information in the time sensitive networking (TSN) configuration). The gNB can reply with the actually realized k to the UE, which may or may not be equal to the desired k from UE. In this approach, UE can request one or more than one k values and gNB can rely none of them can be supported.
In another approach, no negotiation is allowed. For instance, gNB selects one k value based on UE capability, the SCS of the current activated BWPs, and the available remaining reference signal resources in the cell and etc. In other words, this is a configuration from the gNB.
In some embodiments, the RTT based measurement information comprising information identifying reference signals to be used for one or more RTT-based measurements.
In some embodiments, the first time difference report comprises an Rx−Tx time difference calculated by the UE (i.e., a time difference between the time at which the UE performs a transmission to the base station (e.g., transmits a frame to the base station) and the time at which the UE receives a transmission from the base station (e.g., receives a frame transmitted by the base station)).
In some embodiments, the first time difference report comprises an average value representing the average of a number of Rx−Tx time differences calculated by the UE.
In some embodiments, the first time difference report comprises a filtered Rx−Tx time difference calculated by the UE.
In some embodiments, the UE generated the filtered Rx−Tx time difference using a moving average window.
In some embodiments, the RTT based measurement information comprises: an SRS resource identifier identifying an SRS resource configuration (e.g., a configuration that identifies a frequency band, a number of SRS ports, and a resource mapping); and a CSI-RS resource identifier identifying a CSI-RS resource configuration. In some embodiments, the RTT based measurement information comprises a reporting configuration identifier that identifies the measurement reporting configuration.
In some embodiments, the measurement reporting configuration comprises one or more of: report type information identifying a reporting type; reporting frequency information identifying a reporting frequency; a duration value; or a measurement averaging factor.
In some embodiment, process 300 further includes the UE, after receiving message 202, receiving a trigger message 204 for triggering the UE to start RTT-based measurements using the RTT based measurement information included in the message 202.
In some embodiment, process 400 further includes the base station 104, after transmitting message 202, transmitting to the UE a trigger message 204 for triggering the UE to start RTT-based measurements using the RTT based measurement information included in the message 202.
In some embodiments, the trigger message identifies a reporting configuration to be used by the UE for reporting the RTT-based measurements. In some embodiments, the trigger message is Downlink Control Information, DCI, or a MAC control element, CE.
While various embodiments are described herein, it should be understood that they have been presented by way of example only, and not limitation. Thus, the breadth and scope of this disclosure should not be limited by any of the above-described exemplary embodiments. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the disclosure unless otherwise indicated herein or otherwise clearly contradicted by context.
Additionally, while the processes described above and illustrated in the drawings are shown as a sequence of steps, this was done solely for the sake of illustration. Accordingly, it is contemplated that some steps may be added, some steps may be omitted, the order of the steps may be re-arranged, and some steps may be performed in parallel.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2021/077940 | 10/8/2021 | WO |
| Number | Date | Country | |
|---|---|---|---|
| 63092723 | Oct 2020 | US |
