GB2576045A

GB2576045A - Improvements in and relating to positioning reference signal multiplexing in a telecommunication system

Info

Publication number: GB2576045A
Application number: GB1812678.9A
Authority: GB
Inventors: Qi Yinan
Original assignee: Samsung Electronics Co Ltd
Current assignee: Samsung Electronics Co Ltd
Priority date: 2018-08-03
Filing date: 2018-08-03
Publication date: 2020-02-05
Also published as: GB201812678D0

Abstract

Disclosed is method of configuring a Positioning Reference Signal (PRS) in a Long Term Evolution (LTE) telecommunication system, comprising transmitting the positioning reference signal multiplexed with another signal. The other signals may be data or other reference signals, e.g. Channel State Information-Reference (CSI-RS), Demodulation Reference (DMRS), Phase Tracking Reference (PTRS) signals, or a Synchronization Signal Block (SSB). A guard band may be provided between the subcarrier(s) containing the PRS and those containing the other signals. A PRS may be punctured or shifted to a neighbouring Resource Element to avoid collision with other reference signals.

Description

Improvements in and relating to Positioning Reference Signal Multiplexing in a telecommunication system

The present invention relates to improvements in Location based Services (LBS) used in mobile telecommunication networks to provide location information of a particular User Equipment (UE).

Demand for mobile services is expanding quickly and one of the fastest growing segments is Location Based Services (LBS), primarily driven by two major requirements: emergency services and commercial applications. Emergency services desire to know the location of a UE in the event of, for instance, a vehicular accident. Commercial applications desire to know the location of a UE so that the user can be presented with relevant information or advertisements such as, for instance, restaurant deals in his vicinity.

In response to these needs, second and third generation networks (WCDMA, GSM, CDMA) have added support for several positioning technologies, which vary in their accuracy and Time to First Fix (TTFF) performance. 3GPP Release 9 for LTE defines support for various positioning technologies: Extended Cell ID (ECID), Assisted Global Navigation Satellite System (A-GNSS), Observed Time Difference Of Arrival (OTDOA) and LTE Positioning Protocol (LPP), a new positioning protocol. A new reference signal, i.e. positioning reference signal (PRS) has been defined in LTE, to support this new protocol.

Further in Release 11 of LTE, Uplink Observed Time Different of Arrival (UOTDA) has been adopted using Sounding Reference Signal (SRS) measurement. 3GPP Release 15 defines support for some (Radio Access Technology) RAT-independent positioning techniques, such as Real Time Kinematic (RTK) GNSS, to improve the accuracy of LTE positioning.

Embodiments of the present invention aim to address problems encountered in the prior art whether mentioned here or not.

According to the present invention there is provided an apparatus and method as set forth in the appended claims. Other features of the invention will be apparent from the dependent claims, and the description which follows.

Although a few preferred embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes and modifications might be made without departing from the scope ofthe invention, as defined in the appended claims.

For a better understanding of the invention, and to show how embodiments of the same may be carried into effect, reference will now be made, by way of example only, to the accompanying diagrammatic drawings in which:

Figure 1 shows PRS RBs multiplexing with data according to an embodiment ofthe invention;

Figure 2a shows PRS RBs multiplexing with DMRS/PTRS (with PRS puncturing according to an embodiment ofthe invention; and

Figure 2b shows PRS RBs multiplexing with DMRS/PTRS (with PRS shifted) according to an embodiment ofthe invention; and

Figure 3 shows Multiplexing of SSB and PRS according to an embodiment ofthe invention;

In the prior art LTE system, PRS is always transmitted alone, since it is a high priority signal and it is not possible to multiplex it. Embodiments ofthe present invention permit and facilitate multiplexing of PRS with data and/or other reference signals.

If multiple PRS antenna ports are configured to one UE, these antenna ports should be orthogonal to each other to reduce interference and ensure hearability. In this application, hearability describes the ability of a signal to be detected. PRS multiplexing with data (e.g., URLLC data) can be addressed at two levels:

1) RB level where some ofthe RBs are allocated to PRS; and

2) subcarrier level within a RB where PRS can be multiplexed with data within the RBs allocated to PRS.

Dealing with option 1) first, in order to improve the hearability ofthe UE, it is possible that no data will be transmitted with PRS to reduce interference. This can be managed by gNB scheduling. In such a case, cell-specific and UE-specific PRS configurations make little difference because their signalling overhead will be similar. The PRS RBs can be placed in the middle, on the edge or some predefined position in the entire bandwidth.

However, 5G needs to support URLLC data, which requires extremely low latency and therefore may impose some constraints on gNB scheduling. There are two different approaches: 1) reservation-based scheduling, where URLLC resources are reserved prior to the data scheduling; and 2) instant scheduling, where any ongoing data transmission is interrupted to initiate the URLLC packet. The following alternatives can be considered for reservation-based scheduling.

• 1: The resources for URLLC or the subframes/slots/mini slots containing these resources should be avoided when configuring PRS, e.g., PRS periodicity including starting point and duration. The information of URLLC resources should be conveyed to and known by positioning protocols, e.g., LPP.

• 2: The resources for URLLC or the subframes/slots/mini slots containing these resources are scheduled without considering PRS and they will be punctured or shifted to the next available subframes/slots/mini slot to ensure no data is transmitted in the subframes/slots/mini slots containing URLLC resources if PRS is configured.

In this application, reference is made to frames/subframes/slots/mini slots. These are all temporal divisions and represent different periods of time.

Alternative 1 above can be applied to the case there the priority level of URLLC data is higher than the positioning request. However, since the positioning request can be triggered by an emergency, it could potentially have a high level of priority. In such a case, Alternative 2 can be used. These two alternatives can be combined to handle positioning requests with different levels of priority.

For instant scheduling, the ongoing PRS transmission could be interrupted by a URLLC packet and the following solutions should be considered:

• 1: The ongoing PRS transmission is stopped in the subframes/slots/mini slots where URLLC packets are initiated and this is signaled to the UE by DCI;

• 2: The URLLC packets are punctured or initiated from the first subframes/slots/mini slots after the latest PRS transmission.

Alternative 1 above can be applied to the case there the priority level of URLLC data is higher than positioning request and Alternative 2 can be used otherwise.

Considering the wider bandwidth supported in NR, it would be a huge waste not to transmit any data in the subframes/slots/mini slots including PRS. In such a case, PRS can be configured in a sub-band and the rest of the parts can be used for data transmission. The following alternatives can be considered:

• 1: PRS RBs are around the middle with guard bands on the two sides as shown in Fig. 1(a). In such a case, the number of guard bands can be either pre-defined or configured by upper layers;

• 2: PRS RBs are on the two edges with guard bands as shown in Fig. 1 (b). In such a case, it can benefit from frequency diversity gain;

• 3: PRS RBs are on one edge as shown in Fig. 1 (c). In such a case, only one guard band is needed and capacity loss is reduced.

The above three alternatives can be combined and which to use can be configured by upper layers.

Note that in Figure 1, time is on the x axis and frequency is on the y axis, so that each of Figures 1(a), (b) and (c) independently represents a simultaneous transmission. The use of guard bands is to ensure proper separation (in frequency) of PRS and the simultaneously transmitted data.

In order to improve the hearability of the UE, PRS should not be multiplexed with data on RE level within one RB.

It is possible to multiplex PRS with other reference signals. DMRS and PTRS are only used for data demodulation purpose. If no data is transmitted when PRS is transmitted, there is no need to consider multiplexing of PRS and DMRS/PTRS. If data can be transmitted, the following alternatives may be considered:

• 1: PRS pattern is designed to avoid the symbols where DMRS could potentially be configured as shown in Fig. 2a. For additional DMRS and PTRS, PRS can be punctured. In this context, PRS is punctured where it would otherwise coincide with PTRS or DMRS;

• 2: DMRS/PTRS is punctured/shifted by one or multiple REs or symbols when colliding with PRS to ensure the reception of PRS;

• 3: PRS is shifted by one or multiple REs or symbols when colliding with DMRS/PTRS This is shown in Figure 2b where PRS which would otherwise be punctured (as in Figure 2a) is shifted to a neighbouring (or possibly other) RE so that the frequency of PRS transmission is maintained.

In Figures 2a and 2b,the x-axis represents OFDM symbol index (k=0-13) and the y axis represents sub-carrier (1=0-11). In Figures 2a and 2b, control information is usually included in the first 3 symbols (k=0-2) and so these are not available.

It is further possible to multiplex PRS with CSI-RS. CSI-RS is used to acquire channel state information (CSI) and CSI might be needed even when there is no data transmission. Two alternatives can be considered as follows.

• 1: CSI-RS is punctured/shifted by one or multiple REs or symbols when colliding with PRS;

• 2: PRS is punctured/shifted by one or multiple REs or symbols when colliding with CSI-RS.

For Alternative 1, the positioning request has higher priority level than CSI acquisition and otherwise for Alternative 2. CSI-RS puncture can also depend on the type of CSI-RS. For example, periodic CSI-RS can be punctured when colliding with PRS but for aperiodic CSI-RS, PRS will be punctured instead.

In LTE, both PSS/SSS/PBCH and PRS are configured around the center of the frequency so that PRS is not configured in the subframe with PSS/SSS/PBCH, which can be achieved by configuring the offset of the PRS subframes. However, in NR, PSS/SSS/PBCH is not necessarily located around the centre of the frequency. Therefore, PRS could be multiplexed with PSS/SSS/PBCH in the frequency domain as shown in Fig. 3 and the following alternatives are possible:

• 1: A pre-defined offset between PSS/SSS/PBCH and PRS;

• 2: An offset between PSS/SSS/PBCH and PRS which can be explicitly configured by upper layer, e.g., LPP/RRC;

• 3: The offset can be implicitly derived from cell-specific parameters, e.g., cell ID, and/or UE specific parameters, e.g., RNTI.

The offset has the effect that PRS and PSS/SSS/PBCH are transmitted simultaneously but one of the signals is shifted in frequency to avoid collision.

Once data or other reference signals are blanked/punctured, the power can be used to boost the power of PRS to improve hearability. If there is only one PRS antenna port, all the power can be allocated to this antenna port. However, if more than one antenna port is configured for PRS transmission, the power may be split between these antenna ports. The power boosting ratio can be defined as energy per resource element (EPRE) ratio to SSB and can be predefined, configured by an upper layer, or implicitly derived from blanked/punctured REs.

At least some of the example embodiments described herein may be constructed, partially or wholly, using dedicated special-purpose hardware. Terms such as ‘component’, ‘module’ or ‘unit’ used herein may include, but are not limited to, a hardware device, such as circuitry in the form of discrete or integrated components, a Field Programmable Gate Array (FPGA) or

Application Specific Integrated Circuit (ASIC), which performs certain tasks or provides the associated functionality. In some embodiments, the described elements may be configured to reside on a tangible, persistent, addressable storage medium and may be configured to execute on one or more processors. These functional elements may in some embodiments include, by way of example, components, such as software components, object-oriented software components, class components and task components, processes, functions, attributes, procedures, subroutines, segments of program code, drivers, firmware, microcode, circuitry, data, databases, data structures, tables, arrays, and variables. Although the example embodiments have been described with reference to the components, modules and units discussed herein, such functional elements may be combined into fewer elements or separated into additional elements. Various combinations of optional features have been described herein, and it will be appreciated that described features may be combined in any suitable combination. In particular, the features of any one example embodiment may be combined with features of any other embodiment, as appropriate, except where such combinations are mutually exclusive. Throughout this specification, the term “comprising” or “comprises” means including the component(s) specified but not to the exclusion of the presence of others.

Attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.

Each feature disclosed in this specification (including any accompanying claims, abstract and drawings) may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

The invention is not restricted to the details of the foregoing embodiment(s). The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

Claims

1. A method of configuring a positioning reference signal in a telecommunication system comprising transmitting the positioning reference signal multiplexed with another signal.

2. The method of claim 1 wherein transmitting the positioning reference signal multiplexed with another signal comprises the simultaneous transmission of the positioning reference signal on one or more subcarriers, different to the one or more subcarriers on which the other signal is transmitted.

3. The method of any preceding claim wherein a guard band is provided between the one or more subcarriers on which the positioning reference signal is transmitted and the one or more subcarriers on which the other signal is transmitted.

4. The method of any preceding claim wherein the other signal is one of data and a reference signal.

5. The method of claim 4 wherein the reference signal is one of DMRS and PTRS.

6. The method of claim 5 wherein the positioning reference signal is either punctured or shifted in the event of collision with CSI-RS, DMRS or PTRS.

7. The method of claim 6 wherein in the event of the positioning reference signal being shifted, it is shifted to a neighbouring resource element.

8. The method of claim 4 wherein the reference signal is SSB.

9. The method of claim 8 wherein an offset is introduced between the positioning reference signal and SSB.

10. The method of any preceding claim wherein configuration of PRS and the other signal is performed either by an upper layer or derived implicitly from cell or system parameters.

11. The method of any preceding claim wherein the positioning reference signal is power boosted to improve hearability.