WO2021086363A1

WO2021086363A1 - Ping-pong-based accurate positioning

Info

Publication number: WO2021086363A1
Application number: PCT/US2019/059054
Authority: WO
Inventors: Wolfgang Zirwas; Diomidis Michalopoulos; Mikko Saily
Original assignee: Nokia Technologies Oy; Nokia Of America Corporation
Priority date: 2019-10-31
Filing date: 2019-10-31
Publication date: 2021-05-06
Also published as: EP4052516A1

Abstract

In a first aspect of the present disclosure, a method includes receiving reference signals from at least one network node; sending at least one parameter relating to a measured channel impulse response back to the at least one network node; and repeating the receiving of reference signals and the sending of the at least one parameter relating to the measured channel impulse response M times for calculation of M single-trip intervals or N round-trip intervals, M and N being integers. In a second aspect of the present disclosure, a method includes transmitting reference signals to a network entity B from a network entity A, wherein network entity A and network entity B are each one of a network node and a user equipment; receiving a measured channel impulse response back from the network entity B after a first round-trip time interval; sending the channel impulse response back to the network entity B; receiving the channel impulse response back from the network entity B after a second round-trip time interval; repeating the preceding sending and receiving to record N round-trip time intervals, N being an integer; calculating a total time for the N round-trip intervals; and dividing the total time by N to obtain an estimate of a single round-trip time more accurate by a factor of 2N.

Description

PING-PONG-BASED ACCURATE POSITIONING

TECHNICAL FIELD

This disclosure relates to a 5G new radio (NR) mobile communication system and to options for accurate-to-extremely-accurate localization and positioning solutions in such a system, but it is not limited to such a system.

BACKGROUND

Accurate positioning with current solutions, such as observed timed difference of arrival (OTDOA), rely on accurately measuring the delay from a transmitting radio station to a receiving radio station. In 3 GPP, the current baseline approach uses the receiver (Rx) sample grid of the time-domain received signal. In the case of a 20-MHz LTE system with a sampling rate of 33 ns, the resulting time measurements have a lower limit for an ideal position estimation scheme of at least ± 5 m. This would exceed a ± 1 cm position resolution, which may be needed for future applications, by a factor of 500.

In Sven Fischer, “Observed Time Difference of Arrival (OTDOA) Positioning in 3GPP LTE”, Qualcomm Technologies, Inc., June 6, 2014, Fischer provided an overview of the OTDOA concept as it is being standardized for 3GPP LTE. In particular, Fischer gives the limits of OTDOA to a best-case location accuracy of 32 ns, which, again, is equivalent to about ± 5 m.

In addition, there are many other positioning proposals, such as those using machine learning (ML) on radio frequency (RF) fingerprinting, received power offset compensation, and direct estimation based on side-link communication to a multitude of sensor devices with known positions.

For example, several positioning proposals are made in the following references: Qualcomm Incorporated, “Combined Downlink and Uplink NR Positioning Procedures”, 3 GPP TSG-RAN WG2 Meeting #104, R2-1817899, Spokane, USA, 12 to 16 November 2018; Fernando Perez-Cruz, Chih-Kuang Lin, Howard Huang, “BLADE: A Universal, Blind Learning Algorithm for ToA Localization in NLOS Channels”, 2016 IEEE Globecom; and Andrea Conti, Matteo Guerra, Davide Dardari, Nicolo Decarli, and Moe Z. Win, “Network Experimentation for Cooperative Localization, IEEE Journal on Selected Areas in Communications, Vol. 30, No. 2, February 2012. The technique to be proposed below has the benefit of increasing accuracy without placing overly stringent requirements on the processing capabilities of a user equipment (UE).

It should be understood, in the discussion to follow, that the term “gNB” should be understood to mean “network node”. The term “gNB” is used to denote a network node in 5G. However, it should be understood that the present invention, as described below, is not limited to 5G, but may be applicable to future generations yet to be developed. As a consequence, “gNB” should be understood more broadly as a network node.

SUMMARY

In a first aspect of the present invention, a method comprises receiving reference signals from at least one network node; sending at least one parameter relating to a measured channel impulse response back to said at least one network node; and repeating said receiving of reference signals and said sending of said at least one parameter relating to the measured channel impulse response M times for calculation of M single-trip intervals or N round-trip intervals, M and N being integers.

In a second aspect of the present invention, an apparatus comprises at least one processor; and at least one memory including computer program code, the at least one memory and the computer program code being configured, with the at least one processor, to cause the apparatus to perform: receive reference signals from at least one network node; send at least one parameter relating to a measured channel impulse response back to said at least one network node; and repeat said receive of reference signals and said send of said at least one parameter relating to the measured channel impulse response M times for calculation of M single-trip intervals or N round-trip intervals, M and N being integers.

In a third aspect of the present invention, an apparatus comprises means for receiving reference signals from at least one network node; means for sending at least one parameter relating to a measured channel impulse response back to said at least one network node; and means for repeating said receiving of reference signals and said sending of said at least one parameter relating to the measured channel impulse response M times for calculation of M single-trip intervals or N round-trip intervals, M and N being integers. In a fourth aspect of the present invention, a computer program product comprises a non-transitory computer-readable storage medium bearing computer program code embodied therein for use with a computer, the computer program code comprising code for performing: receiving reference signals from at least one network node; sending at least one parameter relating to a measured channel impulse response back to said at least one network node; and repeating said receiving of reference signals and said sending of said at least one parameter relating to the measured channel impulse response M times for calculation of M single-trip intervals or N round-trip intervals, M and N being integers. In a fifth aspect of the present invention, a method comprises transmitting reference signals to a network entity B from a network entity A, wherein network entity A and network entity B are each one of a network node and a user equipment; receiving a measured channel impulse response back from the network entity B after a first round-trip time interval; sending the channel impulse response back to the network entity B; receiving the channel impulse response back from the network entity B after a second round-trip time interval; repeating the preceding sending and receiving to record N round- trip time intervals, N being an integer; calculating a total time for the N round-trip intervals; and dividing the total time by N to obtain an estimate of a single round-trip time more accurate by a factor of 2N. In a sixth aspect of the present invention, an apparatus comprises at least one processor; and at least one memory including computer program code, the at least one memory and the computer program code being configured, with the at least one processor, to cause the apparatus to perform: transmit reference signals to a network entity B from the apparatus, wherein the apparatus and the network entity B are each one of a network node and a user equipment; receive a measured channel impulse response back from the network entity B after a first round-trip time interval; send the channel impulse response back to the network entity B; receive the channel impulse response back from the network entity B after a second round-trip time interval; repeat the preceding send and receive to record N round-trip time intervals, N being an integer; calculate a total time for the N round-trip intervals; and divide the total time by N to obtain an estimate of a single round-trip time more accurate by a factor of 2N.

In a seventh aspect of the present invention, an apparatus comprises means for transmitting reference signals to a network entity B from the apparatus, wherein the apparatus and the network entity B are each one of a network node and a user equipment; means for receiving a measured channel impulse response back from the network entity B after a first round-trip time interval; means for sending the channel impulse response back to the network entity B; means for receiving the channel impulse response back from the network entity B after a second round-trip time interval; means for repeating the preceding sending and receiving to record N round-trip time intervals, N being an integer; means for calculating a total time for the N round-trip intervals; and means for dividing the total time by N to obtain an estimate of a single round-trip time more accurate by a factor of 2N.

In an eighth aspect of the present invention, a computer program product comprises a non-transitory computer-readable storage medium bearing computer program code embodied therein for use with a computer, the computer program code comprising code for performing: transmitting reference signals to a network entity B from a network entity A, wherein network entity A and network entity B are each one of a network node and a user equipment; receiving a measured channel impulse response back from the network entity B after a first round-trip time interval; sending the channel impulse response back to the network entity B; receiving the channel impulse response back from the network entity B after a second round-trip time interval; repeating the preceding sending and receiving to record N round-trip time intervals, N being an integer; calculating a total time for the N round-trip intervals; and dividing the total time by N to obtain an estimate of a single round-trip time more accurate by a factor of 2N.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other aspects of these teachings are made more evident in the following detailed description, when read in conjunction with the attached drawing figures.

Figure 1 shows a simplified block diagram of certain apparatus in which the subject matter of the present disclosure may be practiced.

Figures 2 and 3 show an example of New Radio (NR) architecture having the 5G core (5GC) and the NG-RAN. Figure 4 illustrates the simplest implementation of the proposed ping-pong concept for a line-of-sight (LOS) link with a single MPC and for a single gNB-UE link.

Figure 5 illustrates the main effects of the radio channel on the Tx- and Rx- signals and of the UE processing. Figure 6 illustrates the combined retransmission of received Dirac pulses from two gNBs.

Figure 7 illustrates the combined processing of multiple gNB signals to overcome UE baseband processing non-idealities, Figure 8 illustrates the proposed ping-pong time estimation over multiple steps including a time-alignment process.

Figure 9 presents a message-sequence chart for the present ping-pong positioning method.

Figure 10 is a flow chart illustrating a method performed in accordance with one aspect of the present disclosure.

Figure 11 is a flow chart illustrating a method performed in accordance with another aspect of the present disclosure.

DETAILED DESCRIPTION Figure 1 is a block diagram of one possible and non-limiting example in which the subject matter of the present disclosure may be practiced. A user equipment (UE) 110, radio access network (RAN) node 170, and network element(s) 190 are illustrated. In the example of Figure 1, the user equipment (UE) 110 is in wireless communication with a wireless network 100. A UE is a wireless device, typically mobile, that can access the wireless network. The UE 110 includes one or more processors 120, one or more memories 125, and one or more transceivers 130 interconnected through one or more buses 127. Each of the one or more transceivers 130 includes a receiver, Rx, 132 and a transmitter, Tx, 133. The one or more buses 127 may be address, data, or control buses, and may include any interconnection mechanism, such as a series of lines on a motherboard or integrated circuit, fiber optics or other optical communication equipment, and the like. The one or more transceivers 130 are connected to one or more antennas 128. The one or more memories 125 include computer program code 123. The UE 110 includes a module 140, comprising one of or both parts 140-1 and/or 140-2, which may be implemented in a number of ways. The module 140 may be implemented in hardware as module 140-1, such as being implemented as part of the one or more processors 120. The module 140-1 may be implemented also as an integrated circuit or through other hardware such as a programmable gate array. In another example, the module 140 may be implemented as module 140-2, which is implemented as computer program code 123 and is executed by the one or more processors 120. For instance, the one or more memories 125 and the computer program code 123 may be configured, with the one or more processors 120, to cause the user equipment 110 to perform one or more of the operations as described herein. The UE 110 communicates with RAN node 170 via a wireless link 111.

The RAN node 170 in this example is a base station that provides access by wireless devices, such as the UE 110, to the wireless network 100. The RAN node 170 may be, for example, a base station for 5G, also called New Radio (NR). In 5G, the RAN node 170 may be an NG-RAN node, which is defined as either a gNB or an ng- eNB. A gNB is a node providing NR user plane and control-plane protocol terminations toward the UE, and connected via the NG interface to a 5GC, such as, for example, the network element(s) 190. The ng-eNB is a node providing E-UTRA user plane and control plane protocol terminations towards the UE, and connected via the NG interface to the 5GC. The NG-RAN node may include multiple gNBs, which may also include a centralized unit (CU) (gNB-CU) 196 and distributed unit(s) (DUs) (gNB-DUs), of which DU 195 is shown. Note that the DU may include or be coupled to and control a radio unit (RU). The gNB-CU is a logical node hosting RRC, SDAP and PDCP protocols of the gNB or RRC and PDCP protocols of the en-gNB that controls the operation of one or more gNB-DUs. The gNB-CU terminates the FI interface connected with the gNB-DU. The FI interface is illustrated as reference 198, although reference 198 also illustrates a link between remote elements of the RAN node 170 and centralized elements of the RAN node 170, such as between the gNB-CU 196 and the gNB-DU 195. The gNB-DU is a logical node hosting RLC, MAC and PHY layers of the gNB or ng-eNB, and its operation is partly controlled by gNB-CU. One gNB-CU supports one or multiple cells. One cell is supported by only one gNB-DU. The gNB-DU terminates the FI interface 198 connected with the gNB-CU. Note that the DU 195 is considered to include the transceiver 160, for example, as part of a RU, but some examples of this may have the transceiver 160 as part of a separate RU, for example, under control of and connected to the DU 195. The RAN node 170 may also be an eNB (evolved NodeB) base station, for LTE (long term evolution), or any other suitable base station or node.

The RAN node 170 includes one or more processors 152, one or more memories 155, one or more network interfaces (N/W I/F(s)) 161, and one or more transceivers 160 interconnected through one or more buses 157. Each of the one or more transceivers 160 includes a receiver, Rx, 162 and a transmitter, Tx, 163. The one or more transceivers 160 are connected to one or more antennas 158. The one or more memories 155 include computer program code 153. The CU 196 may include the processor(s) 152, memories 155, and network interfaces 161. Note that the DU 195 may also contain its own memory/memories and processor(s), and/or other hardware, but these are not shown.

The RAN node 170 includes a module 150, comprising one of or both parts 150-1 and/or 150-2, which may be implemented in a number of ways. The module 150 may be implemented in hardware as module 150-1, such as being implemented as part of the one or more processors 152. The module 150-1 may be implemented also as an integrated circuit or through other hardware such as a programmable gate array. In another example, module 150 may be implemented as module 150-2, which is implemented as computer program code 153 executed by the one or more processors 152. For instance, the one or more memories 155 and the computer program code 153 are configured, with the one or more processors 152, to cause the RAN node 170 to perform one or more of the operations as described herein. Note that the functionality of the module 150 may be distributed, such as being distributed between the DU 195 and the CU 196, or be implemented solely in the DU 195.

The one or more network interfaces 161 communicate over a network such as via the links 176 and 131. Two or more gNBs 170 may communicate using, e.g., link 176. The link 176 may be wired or wireless or both and may implement, for example, an Xn interface for 5G, an X2 interface for LTE, or other suitable interface for other standards.

The one or more buses 157 may be address, data, or control buses, and may include any interconnection mechanism, such as a series of lines on a motherboard or integrated circuit, fiber optics or other optical communication equipment, wireless channels, and the like. For example, the one or more transceivers 160 may be implemented as a remote radio head (RRH) 195 for LTE or a distributed unit (DU) 195 for gNB implementation for 5G, with the other elements of the RAN node 170 possibly being physically in a different location from the RRH/DU, and the one or more buses 157 could be implemented in part as, for example, fiber optic cable or other suitable network connection to connect the other elements (e.g., a centralized unit (CU), gNB-CU) of the RAN node 170 to the RRH/DU 195. Reference 198 also indicates those suitable network link(s).

It is noted that description herein indicates that “cells” perform functions, but it should be clear that equipment which forms the cell will perform the functions. The cell makes up part of a base station. That is, there can be multiple cells per base station. For example, there could be three cells for a single carrier frequency and associated bandwidth, each cell covering one-third of a 360° area so that the single base station’s coverage area covers an approximate oval or circle. Furthermore, each cell can correspond to a single carrier and a base station may use multiple carriers. So if there are three 120° cells per carrier and two carriers, then the base station has a total of 6 cells.

The wireless network 100 may include a network element or elements 190 that may include core network functionality, and which provides connectivity via a link or links 181 with a further network, such as a telephone network and/or a data communications network (e.g., the Internet). Such core network functionality for 5G may include access and mobility management function(s) (AMF(S)) and/or user plane functions (UPF(s)) and/or session management function(s) (SMF(s)). Such core network functionality for LTE may include MME (Mobility Management Entity)/SGW (Serving Gateway) functionality. These are merely exemplary functions that may be supported by the network element(s) 190, and note that both 5G and LTE functions might be supported. The RAN node 170 is coupled via a link 131 to a network element 190. The link 131 may be implemented as, for example, an NG interface for 5G, or an SI interface for LTE, or other suitable interface for other standards. The network element 190 includes one or more processors 175, one or more memories 171, and one or more network interfaces (N/W I/F(s)) 180, interconnected through one or more buses 185. The one or more memories 171 include computer program code 173. The one or more memories 171 and the computer program code 173 are configured, with the one or more processors 175, to cause the network element 190 to perform one or more operations.

The wireless network 100 may implement network virtualization, which is the process of combining hardware and software network resources and network functionality into a single, software-based administrative entity, a virtual network. Network virtualization involves platform virtualization, often combined with resource virtualization. Network virtualization is categorized as either external, combining many networks, or parts of networks, into a virtual unit, or internal, providing network-like functionality to software containers on a single system. Note that the virtualized entities that result from the network virtualization are still implemented, at some level, using hardware such as processors 152 or 175 and memories 155 and 171, and also such virtualized entities create technical effects.

The computer-readable memories 125, 155, and 171 may be of any type suitable to the local technical environment and may be implemented using any suitable data storage technology, such as semiconductor-based memory devices, flash memory, magnetic memory devices and systems, optical memory devices and systems, fixed memory and removable memory. The computer-readable memories 125, 155, and 171 may be means for performing storage functions. The processors 120, 152, and 175 may be of any type suitable to the local technical environment, and may include one or more of general purpose computers, special purpose computers, microprocessors, digital signal processors (DSPs) and processors based on a multi-core processor architecture, as nonlimiting examples. The processors 120, 152, and 175 may be means for performing functions, such as controlling the UE 110, RAN node 170, and other functions as described herein.

In general, the various embodiments of the user equipment 110 can include, but are not limited to, cellular telephones such as smart phones, tablets, personal digital assistants (PDAs) having wireless communication capabilities, portable computers having wireless communication capabilities, image capture devices such as digital cameras having wireless communication capabilities, gaming devices having wireless communication capabilities, music storage and playback appliances having wireless communication capabilities, Internet appliances permitting wireless Internet access and browsing, tablets with wireless communication capabilities, as well as portable units or terminals that incorporate combinations of such functions. Figures 2 and 3 show an example of New Radio (NR) architecture having the 5G core (5GC) and the NG-RAN. The base stations gNB are coupled to the 5GC by the interface to Core NGs, and the gNBs are coupled to each other by the inter-base stations interface Xn.

Having thus introduced one suitable, but non-limiting, technical context for the practice of example embodiments, the example embodiments will now be described with greater specificity.

The main idea of the present disclosure is to realize multiple back-and- forth, or ping-pong, measurements for estimating multi-path component (MPC) delays of a time-domain channel impulse response (CIR) between one or more gNBs and a UE. By estimating the combined length of the MPC delay over multiple back- and-forth transmissions over N times, ideally, a limited measurement resolution of Dt, for example, can be reduced to Dt/2N. Here, Dt represents a deterministic limit for the measurement accuracy of the system setup without using any ping pong operation. Here it is taken to be an absolute delay value with respect to the MPC delay. The limited measurement accuracy may have one of a number of underlying causes, such as a delay offset between cooperating gNBs, a limited quantization of the time estimation in the UE, or, for example, the best possible resolution of the profiling delay estimation for the given SINR, and the profiling algorithm being used.

Figure 4 illustrates the simplest implementation for a line-of-sight (LOS) link with a single MPC and for a single gNB-UE link. It should be noted, then, for the positioning itself, three or more such delay measurements to suitably located gNBs have to be done in parallel: « At time instant ti (upper left-hand side), the gNB transmits a single Dirac pulse 402, represented for convenience by an upstanding arrow, to the UE, which receives the Dirac pulse at time t = ti + Dίi (right-hand side of the figure).

• Assuming an ideal UE, or ideal reflector, the received Dirac pulse is retransmitted from the UE without any additional delay, so that it will be received at the gNB at time t = ti + 2Ati (lower left-hand side of the figure).

• This process is repeated N times until the gNB performs the final delay estimation of the multiple reflections at time t_N = ti + N 2Ati. The accuracy of this measurement, however, depends on the capabilities of the gNB. For example, a classical LTE system would measure.tN with a TD = 32 ns accuracy and, accordingly, with a position accuracy of + 5 m. TD is, in this case, the sample timing of the time domain signal for a 20-MHz LTE system. As a radio signal traveling at the speed of light would cover about 9.6 meters in 32 ns, the position accuracy would be limited to be about one half of that, or ± 5 m.

• For estimating the delay Ati._est of the gNB-UE link, the gNB calculates time Ati._est = (t_N - ti) / 2N. That way, the measurement limitations of the gNB, for example, of Dt

= 32 ns, can be improved by a factor of 2N ideally to Dt/2N. For example, for N = 10 ping-pong retransmissions, the position accuracy can be improved from ± 5 m to about + 0.25 m, which is one twentieth of + 5 m.

The present disclosure is concerned with deterministic errors, such as those from delay offsets at the gNB and quantization errors of the measurement device. In the present “mirror” operation, deterministic errors can be reduced by a factor of 2N.

By doing a “mirror” operation instead of the same measurements multiple times, the delay of the MPC adds up delays, even if they are below the quantization estimation accuracy of the final measurement “device”. For that purpose, the UE is, in one embodiment, just receiving the signal from the gNB and retransmitting it in the next possible subframe without - or, more accurately, with minimum - processing. In particular, the mirror operation is without any delay estimation at the UE.

In this example, the measurement device quantization error is assumed to be 32 ns, which is equivalent to ± 5 m. This is the deterministic error. By multiple mirror operations, small deviations from the quantization raster add up to a large value, so that, after division by 2N, the final inaccuracy is reduced (ideally) by a factor of 2N.

In principle, and depending on the positioning method applied, there can be multiple factors affecting the accuracy of position estimation. Taking the example of the Observed Time Difference of Arrival (OTDOA) method, such factors include:

1. the accuracy of the measurements at the UE;

2. the relative geometric positions of the transmission points, such as gNBs;

3. the synchronization level of the transmission points, such as gNBs;

4. the precision of the knowledge of the location of transmission points at the location server; and

5. the multipath excess delay.

The present method can in fact reduce the uncertainty level of factors 1, 3, and 5 above. For further information on the effect of the estimation error factors on the overall accuracy of position estimation, section 8.7 (“Exemplary Error Budget”) of Sven Fischer, “Observed Time Difference of Arrival (OTDOA) Positioning in 3GPP LTE”, Qualcomm Technologies, Inc., June 6, 2014, noted above, provides a nice summary.

Taking the round trip time (RTT) method as another example, the benefit of the present method is that it tackles deterministic errors, such as constant bias errors on measurements, which cannot be averaged out by simple averaging.

An inventive step of the present disclosure, then, is to apply ping-pong retransmissions and to estimate the delay and/or path length for a gNB-UE link based on the length of the combined path over multiple retransmissions. Relevant, then, are the specific means for implementing the present invention in a mobile radio system, so that the best possible estimation quality may be achieved.

The main benefits of the proposed ping-pong delay estimation method are:

• The method allows an accurate path-length estimation having a relatively lower measurement resolution (Dt) with UEs and gNBs of limited capabilities to be made. With N ping-pong transmissions, the estimation accuracy can ideally be improved to a value of Dt/2N, that is, the measurement resolution would be improved (reduced) by a factor of 2N.

• In the example above, for Dt = 32 ns, the position accuracy would improve from ± 5 m to about ± 0.25 m. In combination with profiling, a specific solution for accurate parameter estimation of multi-path components, as disclosed in International Publication No. WO 2019/138156 Al, published July 18, 2019, and entitled “Profiled Channel Impulse Response for Accurate Multipath Parameter Estimation”, the teachings of which are incorporated herein by reference, Dt can be improved to values of 0.1 to 1 ns. In that case, and again assuming N = 10, positioning accuracy might be improved from ± 0.01 to 0.1 m to about + 0.001 to 0.01 m, that is, positioning accuracy will be close to the cm range, which may be needed for future applications.

• As will be discussed further below, specific implementation options will relax gNB synchronization requirements for OTDOA-like positioning methods. Now, some specific implementation approaches for minimizing the impact of UE- and gNB-specific imperfections, such as frequency offsets and varying processing delays, are proposed:

• Figure 5 is an extension of Figure 4 and includes the main effects of the radio channel on the Tx- and Rx- signals and the main effects of the UE processing: · The effect of the limited Tx-bandwidth (BW) modifies the ideal Dirac pulse 402, first shown in Figure 4, into a sine integral (SI) function of the form SI = sin(x)/x.

• Multiple reflections in the radio environment will generate a superposition of multiple multi-path components, instead of a single Dirac pulse.

• The UE will typically not be an ideal reflector, but will have to do an active retransmission of the Rx-signal together with some baseband processing. This baseband processing will add some delay and may add some jitter in case the internal UE clock has some time-varying frequency offsets.

Several options are available for minimizing the above-mentioned effects. A first approach is to maximize the bandwidth so that the SI functions become as narrow as possible, that is, more like Dirac pulses. Then, massive multiple-input multiple-output (MIMO) beamforming may be used to suppress a large part of the multi-path components, with the exception of the strongest one, by appropriately chosen beamformers. This assumes that the reflected multi-path components have typical angles of arrival (AoA), and that only the strongest multi-path component is received with high power at the center of the narrow beamformer. In more controlled settings, such as industrial plants and indoor shopping malls, one can ensure that there will always be good line-of-sight (LOS) connections from the gNBs to a UE device, so that multi-path reflections will be of quite low power. In addition, the following extensions are proposed:

• To combine this proposed baseline scheme with “CIR profiling”, as discussed in International Publication No. WO 2019/138156 Al, noted above, and illustrated by the bolder curves 502, 504 in Figure 5. CIR profiling permits multi-path component parameters, like delay, amplitude and phase, to be identified with high accuracy. Even for a relatively limited RF bandwidth of 20 MHz, for example, for a real-world outdoor non-line-of-sight (NLOS) channel, the multi-path component delays could be estimated with an accuracy of about 0.1 ns or, equivalently, 100 ps. See the finer SI curves 506, 508 in Figure 5.

• Therefore, according to one embodiment of the present invention, the multi-path component delay parameters are estimated from the received channel impulse response to identify the strongest or the intended multi-path component, which should be used for the delay measurement, and to generate a new artificial Tx signal, which contains only the relevant multi-path component. This can be achieved by a super-resolution technique, in which the multi-path component parameters are estimated for each multi-path component. Then, all multi-path components, with the exception of the strongest one, are subtracted from the combined channel impulse response. In that way, only the strongest multi-path component is maintained. The benefit of this proposal is that, despite a potentially rich scattering environment, each back-and-forth transmission always uses a clean Tx signal containing only the multi-path component of interest. Otherwise, the received multi-path components of the first transmission will be retransmitted from the UE over the rich scattering radio channel, so that the gNB will receive a channel impulse response with an exponentially increasing number of superposed multi-path components per retransmission.

• According to another embodiment of the present invention, the received channel impulse response is estimated, and a rising slope of the received channel impulse response above a threshold is identified, for example, to identify and differentiate the transmitted signal first autocorrelation value above the noise. The time value above the threshold represents the shortest path of the propagation environment and is used for delay measurement and to generate a new artificial Tx signal (with reference to the preceding paragraph). In other words, a simple thresholding for doing the delay estimation may be used instead of a more complex ‘profiling’ operation. The now quite simple estimated delay is used to generate an artificial

Tx-signal with one MPC using the estimated delay value. Note that such a simplified operation might work quite well in case there is only one strong MPC for all gNB-UE links.

• In cases of multiple ping-pong reflections, the low-delay estimation inaccuracies of about 100 ps will add up unfavorably for large number of reflections N even when a Gaussian normal distribution for the delay error function is assumed. Moreover, profiling is a relatively complex and time-consuming process, which may be beyond a UE’s capabilities. Therefore, in still another embodiment, the UEs may identify the peak of the profiled channel impulse response, which is close to the intended strongest multi-path component, as can be concluded from

Figure 5 by comparing the finer Si-function 506 and the bolder profiled CIR 502. For a line-of-sight scenario with a single multi-path component, the peak and the delay of the (single) strongest multi-path component will coincide, but, for non- line-of-sight scenarios, the present method will generate its own error due to the relative delay of the peak and of the relevant multi-path component. To address this issue, in this embodiment the UE stores the profiled CIR for each reflection process and reports the profiled CIR to the gNB, either directly or at the end of the entire ping-pong process. This enables the gNB to carry out the complex processing for the parameter estimation based on the profiled CIR offline after the ping-pong process has been completed. By identifying the delay between the peak of the profiled CIR and the relevant multi-path component, the gNB can apply relevant delay corrections for all of the active UE reflections, as well as for all of the gNB reflections. Many positioning use cases have only moderate latency requirements, so that there will be some time available for the corresponding offline processing for doing the profiling for multiple reflections.

Depending on the use case, it may also be sufficient just to retransmit with the delay of the peak of the profiled channel impulse response.

• Whether active reflection is based on the peak of the profiled CIR or on the estimated delay of the relevant multi-path component, the overall baseband processing for the active reflection has to be considered conventionally. For example, for a 20-MHz bandwidth, the UE will use a 33-ns sample-time grid, which is too coarse by far for present purposes. Therefore, it is proposed to calculate the artificial CIR with the estimated delay, for example, in the frequency domain by adding the appropriate phase slope representing the estimated delay of the MPC relative to the coarse tap delays.

• For the above embodiments, ideal and stable clock signals for the baseband processing have been assumed, so that each active retransmission of the received signal will have exactly the same delay between reception and retransmission. In reality, the effect of the variable frequency offsets and jitter of the baseband clock signals, especially with respect to the UE side, has to be considered. This will add some unknown delay variations to each active reflection; the delay variations will degrade the overall delay estimation. To address this issue, multiple signals from multiple gNBs may be processed simultaneously, as illustrated in Figure 6. Simultaneous processing means that the UE receives the CSI RSs - at the same time slot transmitted from two or more gNBs - simultaneously and processes the combined received signal together. This is in contrast to doing RTT measurements to different gNBs sequentially, which has an issue in case the parasitic effects will change over time. Assume, for example, a UE clock drift. By processing the signals from two or more gNBs simultaneously and by doing the very same baseband processing for the two or more signals, the two or more signals will undergo the same practical imperfections, such as varying baseband processing delays. For example, by adding a signal from a known reference gNB with an exactly known position, the delay variations over all ping-pong reflections may be estimated and an appropriate correction may be made. Alternatively, with three gNB positions, it may be possible to compensate mathematically for a common delay error for all gNBs without the use of a reference gNB. In Figure 6, the UE receives the transmit signals 602, 604 from gNBl and gNB2 simultaneously (two Diracs in ideal illustration) and retransmits (broadcasts) these simultaneously received Dirac signals 602, 604 after a certain baseband processing delay (not shown) back to gNBl and gNB2. The main issue for the “mirror” operation is then that the UE does not try to estimate the delays of the Diracs and to retransmit after a certain time (identified by a UE clock timer) the estimated delay values for both Diracs to the gNBs as it is done in prior art. Instead, the UE more or less retransmits as accurately as possible what has been received. As the UE now retransmits the Diracs from gNBl and gNB2 simultaneously, therefore gNBl has to delete the Dirac from gNB2 and vice versa as otherwise after multiple reflections the number of Diracs will increase exponentially making a proper evaluation challenging.

• Receiving, baseline processing and retransmitting two or more gNB signals raise another issue when the relative delays of the relevant multi-path components from two or more gNB-UE links are quite similar. In such a case, it will be difficult to distinguish the multi-path components from the different gNBs. To address this issue, in an additional embodiment, artificial delays may be added at the gNB side, so that the combined channel impulse response received at the UE will have a large delay separation between all of the gNBs. It should be noted that this artificial extra delay at the gNBs may be generated by determining phase slopes fitted to the channel transfer functions. As these applied phase slopes are known by the gNBs, the corresponding delays can be subtracted in the end for the estimation of the relative delays for all gNBs.

• Retransmission of a combined channel impulse response from two or multiple gNBs raises yet another issue. The gNBs will now receive the combined channel impulse response as being transmitted from the UE (see Figure 6). If the gNB retransmits this signal, it will lead to growing numbers of unintended multi-path components. For that reason, in another embodiment, the received part of the channel impulse response, which does not belong to the received gNB, is canceled. Such cancellation may be done quite easily due to the strong artificial delay separation between gNBs. Moreover, the gNB may store the received relative delay for both gNBs as this might be used for calibration of time synchronization errors between the transmitting gNBs, which, in any event, are expected to be connected over a powerful backhaul link. For specific embodiments, it may be assumed that the multiple transmission points (TRP) for the localization are served from a single central unit with one accurate local oscillator, so that the relative gNB timing may be more or less perfect.

• Figures 7 and 8 illustrate some aspects of a mirror operation in greater detail. In Figure 7, at time step II, a Dirac pulse 701 is transmitted at gNB 1 with a certain delay ti, and simultaneously a Dirac pulse 702 is transmitted at gNB 2 with delay ti + At_x, where At_x is an artificial extra delay to ensure good separability of the channel impulse responses of gNBl and gNB2. The UE simultaneously receives the Dirac pulses 701, 702 from gNB 1 and 2. The UE retransmits the combined CIR including the Dirac pulses 701, 702 received from gNBl and gNB2 at the next possible scheduling opportunity. This retransmission of the combined CIR may be seen as an active mirror operation as the relative delays between gNBl and gNB2 are maintained in the combined channel impulse response. At time step 12, gNB 1 and gNB2 receive the retransmitted combined channel impulse response with an extra delay T1 (for gNBl) and T2 (for gNB2), so that, for gNBl, Dirac pulse 701 has an extra delay of Dti. Dirac pulse 702 is also received, but is deleted from the channel impulse response, as indicated by the overlying “X”, so that it will not be retransmitted in a subsequent step. The deletion of Dirac pulse 702 at gNBl was the reason to add the artificial delay At_x, so that it would be separated from Dirac pulse 701.

Figure 8 mainly illustrates the same operation as that of Figure 7, but with a focus on how the delays add up and how the time alignment procedure affects the result.

For that purpose, it is assumed that, in time step II, the UE time-aligns to Dirac pulse 801 as being received from gNBl. This leads at the first retransmission to the relative delay Ati, at time step 12 and 13 and 2 Ati at time step 14. As the time alignment is done for Dirac pulse 801 from gNBl, Dirac pulse 802 from gNB2 has a certain fixed offset, but over the time instances the delay will add up by multiples of At2. Figure 8 illustrates the proposed ping-pong time estimation over multiple steps including a time-alignment process as being standardized for all current 3GPP systems. What can be observed is that the time alignment will synchronize the UE to the timing of the gNB so that the delay of the gNB-UE link will be set artificially to zero (or a small value). Nonetheless, the ping- pong measurements will then add up growing overall delays with the increasing number of retransmissions.

• In yet another embodiment, the above cancellation of the received part of the channel impulse response is executed at the Location Management Function (LMF), which is placed at the core network. In this case, the LMF obtains a replica of the received channel impulse responses corresponding to the multiple gNBs (two in the example of Figure 7). As a result, the LMF can filter only the relevant channel impulse response in each case, thereby obtaining multiple independent responses - in the example of Figure 7, two independent responses, one per gNB - from which only the relevant information per gNB is extracted. This embodiment corresponds to an implementation example aligned with the conventional positioning architecture where the estimation of the position of the UE is carried out at the LMF at the core network.

• In another embodiment, the above cancellation of the received part of the channel impulse is executed at the RAN. This implies that the gNBs aiming at canceling the non-relevant channel impulse response coordinate among themselves. Specifically, the gNBs communicate via the Xn interface such that a replica of the channel impulse response per gNB is available at the other participating gNB. The estimation of the location of the UE then takes place at the respective RAN network element responsible for positioning activities, known as the “local” LMF placed at the RAN. This embodiment represents an alternative implementation example to the previous one, involving the alternative positioning architecture where the location management functionality is executed at the RAN, targeting low latency positioning applications.

Figure 9 provides a simplified message-sequence chart for some possible embodiments for the proposed novel ping-pong positioning methods, and highlights a number of novel implementation and reporting steps. For a proper interaction of the gNBs and the UE, these steps have to be standardized and controlled by corresponding downlink control information (DCI) messages adapted to the method used.

In the message-sequence chart of Figure 9, messages made between UE 902 and gNBl 904 and gNB2 906 in accordance with various embodiments of the present invention are illustrated. With message 908, gNBl 904 transmits to UE 902 a CSI RS signal #1 or a specific PRS signal #1. Similarly, with message 910, gNB2 906 transmits to UE 902 a CSI RS signal #2 or a specific PRS signal #2.

After receiving messages 908, 910, the UE 902 may perform combined base band (BB) processing, as indicated in block 912, to identify the delay of the strongest multi-path component for messages 908, 910 from gNBl 904 and gNB2 906; to remove the weaker multi-path components of those messages; and to retransmit the strongest multi-path components of the messages 908, 910 from gNBl 904 and gNB2906 with a fixed delay relative to the delay of the strongest multi-path component received. UE 902 then transmits (multicasts) a combined channel impulse response to gNBl 904 and gNB2 906 in messages 914, 916, respectively. gNBl 904 removes weak multi-path components and multi-path components of gNB2 906 from message 914 in block 918. Similarly, gNB2 906 removes weak multi-path components and multi-path components of gNBl 904 from message 916 in block 920.

Subsequently, in message 922, gNBl 904 transmits a clean channel impulse response to UE 902, and, in message 924, gNB2 906 transmits a clean channel impulse response to UE 902. Then, in message 926, UE 902 reports to gNBl 904 a profiled channel impulse response. The entire process described above, starting with messages 908, 910, is repeated N times, where N is a number, such as ten (10). At the conclusion of the so- repeated process, gNBl 904 may estimate a combined delay over all retransmissions; may estimate a base-band processing delay for UE 902; may use profiling for fine tuning the estimated delay; and/or may divide the delay by N to obtain single path delay estimates, as indicated in block 928.

Some benefits and advantages of the present inventions are:

• Increased localization accuracy for more or less state-of-the-art UEs.

• Specialized methods to minimize any mobile-radio-related imperfections like: use profiling to identify MPCs and/or retransmit peak of profiled CIR and/or profiled CIR for each retransmission and/or process and retransmit combined CIR for two or more gNBs and/or add artificial delay per gNB, so that combined CIR has no unresolvable overlaps from multiple gNB channels.

• Especially the retransmission of a combined CIR for two or more gNBs is an essential part of an active mirror operation as the relative delays of the two or more multipath components from two to more gNBs is then stored in the combined CIR. Therefore, this combined CIR can then be retransmitted in some of the next subframes without any accuracy degradation. This is in contrast to conventional RTT measurements, where the delay estimation accuracy of the UE and the clock drifts add up to over-the- time increasing inaccuracies. · Support of highest positioning requirements in industry applications based on confined scenarios with optimized Tx- and Rx-devices.

Figure 10 is a flow chart illustrating a method performed in accordance with one aspect of the present disclosure. In block 1002, reference signals are received from at least one network node. In block 1004, at least one parameter relating to a measured channel impulse response is sent back to the at least one network node. “Channel impulse response” is quite general; the response may also be “channel transfer function” or some other CSI-related function. And, in block 1006, the receiving of reference signals and the sending of the at least one parameter relating to the measured channel impulse response is repeated M times for calculation of M single-trip intervals or N round-trip intervals, M and N being integers.

The parameter relating to a measured channel impulse response to the reference signals may be, for example, the amplitude, phase, delay, or AoA (angle of arrival) of the measured channel impulse response.

The sending and receiving may occur between two UEs, either using SideLink or without using SideLink. This may also apply to V2V (vehicle-to-vehicle). This is potentially independent timing without explicit control from a gNB.

Figure 11 is a flow chart illustrating a method performed in accordance with another aspect of the present disclosure. In block 1102, reference signals are transmitted to a network entity B from a network entity A, wherein network entity A and network entity B are each one of a network node and a user equipment. In block 1104, a measured channel impulse response is received back from the network entity B after a first round-trip time interval. In block 1106, the channel impulse response is sent back to the network entity B. In block 1108, the channel impulse response is received back from the network entity B after a second round-trip time interval. In block 1110, the preceding sending and receiving is repeated to record N round-trip time intervals, N being an integer. In block 1112, a total time for the N round-trip intervals is calculated. And, in block 1114, the total time is divided by N to obtain an estimate of a single round-trip time more accurate by a factor of 2N.

In general, the various exemplary embodiments may be implemented in hardware or special purpose circuits, software, logic or any combination thereof. For example, some aspects may be implemented in hardware, while other aspects may be implemented in firmware or software, which may be executed by a controller, microprocessor or other computing device, although the invention is not limited thereto.

While various aspects of the exemplary embodiments of this invention may be illustrated and described as block diagrams, flow charts, or using some other pictorial representation, it is well understood that these blocks, apparatus, systems, techniques or methods described herein may be implemented in, as non-limiting examples, hardware, software, firmware, special purpose circuits or logic, general purpose hardware or controller or other computing devices, or some combination thereof.

It should thus be appreciated that at least some aspects of the exemplary embodiments of the inventions may be practiced in various components, such as integrated circuit chips and modules, and that the exemplary embodiments of this invention may be realized in an apparatus that is embodied as an integrated circuit. The integrated circuit, or circuits, may comprise circuitry, as well as possibly firmware, for embodying at least one or more of a data processor or data processors, a digital signal processor or processors, baseband circuitry and radio frequency circuitry that are configurable so as to operate in accordance with the exemplary embodiments of this invention.

Various modifications and adaptations to the foregoing exemplary embodiments of this invention may become apparent to those skilled in the relevant arts in view of the foregoing description, when read in conjunction with the accompanying drawings. For example, while the exemplary embodiments have been described above in the context of advancements to the 5G NR system, it should be appreciated that the exemplary embodiments of this invention are not limited for use with only this one particular type of wireless communication system. The exemplary embodiments of the invention presented herein are explanatory and not exhaustive or otherwise limiting of the scope of the invention.

The following abbreviations have been used in the preceding discussion: AoA Angle-of-Arrival

BB Base Band

BVDM Building Vector Data Map

BW Bandwidth

CIR Channel Impulse Response

CSI Channel State Information

CTF Channel Transfer Function

CU Centralized Unit

DCI Downlink Control Information

DU Distributed Unit gHZ Gigahertz gNB gNodeB (next generation Node B) gNB-CU gNB Centralized Unit gNB -DU gNB Distributed Unit GoB Grid-of-Beam LMF Location Management Function LOS Line-of-Sight LTE Long Term Evolution MIMO Multiple-Input Multiple-Output ML Machine Learning MPC Multi-Path Component NLOS Non-Line-of-Sight NR New Radio (5G)

OTDOA Observed Time Difference of Arrival RAN Radio Access Node RF Radio Frequency RRC Radio Resource Control RRH Remote Radio Head RU Radio Unit Rx Receiver SI Sine Integral

SINR Signal to Interference and Noise Ratio Tx Transmitter UE User Equipment V2V Vehicle-to-Vehicle 3 GPP 3^rd Generation Partnership Project 5G 5^th Generation

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a”, “an”, and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising”, when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. The description of the present invention has been presented for purposes of illustration and description, but is not intended to be exhaustive or limited to the invention in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the invention. The embodiment was chosen and described in order to best explain the principles of the invention and the practical application, and to enable others of ordinary skill in the art to understand the invention for various embodiments with various modifications as are suited to the particular use contemplated.

Various modifications and adaptations may become apparent to those skilled in the relevant arts in view of the foregoing description, when read in conjunction with the accompanying drawings. However, any and all modifications of the teachings of this disclosure will still fall within the scope of the non-limiting embodiments of this invention.

Although described in the context of particular embodiments, it will be apparent to those skilled in the art that a number of modifications and various changes to these teachings may occur. Thus, while the invention has been particularly shown and described with respect to one or more embodiments thereof, it will be understood by those skilled in the art that certain modifications or changes may be made therein without departing from the scope of the invention as set forth above, or from the scope of the claims to follow.

Claims

WHAT IS CLAIMED IS:

1. A method comprising: receiving reference signals from at least one network node; sending at least one parameter relating to a measured channel impulse response back to said at least one network node; and repeating said receiving of reference signals and said sending of said at least one parameter relating to the measured channel impulse response M times for calculation of M single-trip intervals or N round-trip intervals, M and N being integers.

2. The method as claimed in claim 1, wherein the channel impulse response received from the at least one network node includes multi-path components, and wherein only the strongest of the multi-path components is sent back to the at least one network node.

3. The method as claimed in claim 1, wherein an artificial delay has been added to the channel impulse response sent from the at least one network node to distinguish the received channel impulse response from channel impulse responses of other network nodes.

4. The method as claimed in claim 1, wherein profiling is performed on the received channel impulse response, and the peak of the profiled channel impulse response is sent back to the at least one network node.

5. The method as claimed in claim 1, wherein profiling is performed on the received channel impulse response, and only the strongest multi path component of the profiled channel impulse response is sent back to the at least one network node.

6. The method as claimed in claim 1, further comprising subtracting, from the received channel impulse response, any channel impulse responses from other network nodes.

7. The method as claimed in claim 1, wherein profiling is performed on the received channel impulse response, the profiled channel impulse response is stored for each repeated step, and reported to the at least one network node.

8. The method as claimed in claim 7, wherein the profiled channel impulse response is reported after each repeated step.

9. The method as claimed in claim 7, wherein the profiled channel impulse response is reported at the end of all of the repeated steps.

10. An apparatus comprising: at least one processor; and at least one memory including computer program code, the at least one memory and the computer program code being configured, with the at least one processor, to cause the apparatus to perform: receive reference signals from at least one network node; send at least one parameter relating to a measured channel impulse response back to said at least one network node; and repeat said receive of reference signals and said send of said at least one parameter relating to the measured channel impulse response M times for calculation of M singletrip intervals or N round-trip intervals, M and N being integers.

11. The apparatus as claimed in claim 10, wherein the channel impulse response received from the at least one network node includes multi-path components, and wherein only the strongest of the multi-path components is sent back to the at least one network node.

12. The apparatus as claimed in claim 10, wherein an artificial delay has been added to the channel impulse response sent from the at least one network node to distinguish the received channel impulse response from channel impulse responses of other network nodes.

13. The apparatus as claimed in claim 10, wherein profiling is performed on the received channel impulse response, and the peak of the profiled channel impulse response is sent back to the at least one network node.

14. The apparatus as claimed in claim 10, wherein profiling is performed on the received channel impulse response, and only the strongest multi path component of the profiled channel impulse response is sent back to the at least one network node.

15. The apparatus as claimed in claim 10, wherein the at least one memory and the computer program code are further configured, with the at least one processor, to cause the apparatus to subtract, from the received channel impulse response, any channel impulse responses from other network nodes.

16. The apparatus as claimed in claim 10, wherein profiling is performed on the received channel impulse response, the profiled channel impulse response is stored for each repeated step, and reported to the at least one network node.

17. The apparatus as claimed in claim 16, wherein the profiled channel impulse response is reported after each repeated step.

18. The apparatus as claimed in claim 16, wherein the profiled channel impulse response is reported at the end of all of the repeated steps.

19. An apparatus comprising: means for receiving reference signals from at least one network node; means for sending at least one parameter relating to a measured channel impulse response back to said at least one network node; and means for repeating said receiving of reference signals and said sending of said at least one parameter relating to the measured channel impulse response M times for calculation of M single-trip intervals or N round-trip intervals, M and N being integers.

20. The apparatus as claimed in claim 19, wherein the channel impulse response received from the at least one network node includes multi-path components, and wherein only the strongest of the multi-path components is sent back to the at least one network node.

21. The apparatus as claimed in claim 19, wherein an artificial delay has been added to the channel impulse response sent from the at least one network node to distinguish the received channel impulse response from channel impulse responses of other network nodes.

22. The apparatus as claimed in claim 19, wherein profiling is performed on the received channel impulse response, and the peak of the profiled channel impulse response is sent back to the at least one network node.

23. The apparatus as claimed in claim 19, wherein profiling is performed on the received channel impulse response, and only the strongest multi path component of the profiled channel impulse response is sent back to the at least one network node.

24. The apparatus as claimed in claim 19, further comprising: means for subtracting, from the received channel impulse response, any channel impulse responses from other network nodes.

25. The apparatus as claimed in claim 19, wherein profiling is performed on the received channel impulse response, the profiled channel impulse response is stored for each repeated step, and reported to the at least one network node.

26. The apparatus as claimed in claim 25, wherein the profiled channel impulse response is reported after each repeated step.

27. The apparatus as claimed in claim 25, wherein the profiled channel impulse response is reported at the end of all of the repeated steps.

28. A computer program product comprising a non-transitory computer-readable storage medium bearing computer program code embodied therein for use with a computer, the computer program code comprising code for performing: receiving reference signals from at least one network node; sending at least one parameter relating to a measured channel impulse response back to said at least one network node; and repeating said receiving of reference signals and said sending of said at least one parameter relating to the measured channel impulse response M times for calculation of M single-trip intervals or N round-trip intervals, M and N being integers.

29. The computer program product as claimed in claim 28, wherein the channel impulse response received from the at least one network node includes multi-path components, and wherein only the strongest of the multi-path components is sent back to the at least one network node.

30. The computer program product as claimed in claim 28, wherein an artificial delay has been added to the channel impulse response sent from the at least one network node to distinguish the received channel impulse response from channel impulse responses of other network nodes.

31. The computer program product as claimed in claim 28, wherein profiling is performed on the received channel impulse response, and the peak of the profiled channel impulse response is sent back to the at least one network node.

32. The computer program product as claimed in claim 28, wherein profiling is performed on the received channel impulse response, and only the strongest multi path component of the profiled channel impulse response is sent back to the at least one network node.

33. The computer program product as claimed in claim 28, wherein the computer program code further comprises code for performing: subtracting, from the received channel impulse response, any channel impulse responses from other network nodes.

34. The computer program product as claimed in claim 28, wherein profiling is performed on the received channel impulse response, the profiled channel impulse response is stored for each repeated step, and reported to the at least one network node.

35. The computer program product as claimed in claim 34, wherein the profiled channel impulse response is reported after each repeated step.

36. The computer program product as claimed in claim 34, wherein the profiled channel impulse response is reported at the end of all of the repeated steps.

37. A method comprising: transmitting reference signals to a network entity B from a network entity A, wherein network entity A and network entity B are each one of a network node and a user equipment; receiving a measured channel impulse response back from the network entity B after a first round-trip time interval; sending the channel impulse response back to the network entity B; receiving the channel impulse response back from the network entity B after a second round-trip time interval; repeating the preceding sending and receiving to record N round-trip time intervals, N being an integer; calculating a total time for the N round-trip intervals; and dividing the total time by N to obtain an estimate of a single round-trip time more accurate by a factor of 2N.

38. The method as claimed in claim 37, wherein a modified reference signal time difference (RSTD) measurement is applied, where the time difference of the received reference signals corresponds to the difference after dividing the total time by N.

39. The method as claimed in claim 37, wherein the measured channel impulse response received back from the network entity B includes multi-path components, and wherein only the strongest of the multi-path components is sent back to the network entity B.

40. The method as claimed in claim 37, further comprising adding an artificial delay when performing the sending and receiving to distinguish the received measured channel impulse response from the channel impulse responses of other network entities received from the network entity B.

41. The method as claimed in claim 37, wherein profiling is performed on the received measured channel impulse response, and a single multipath component with the delay of the peak of the profiled channel impulse response is sent back to the network entity B.

42. The method as claimed in claim 37, wherein profiling is performed on the received measured channel impulse response, and only the strongest multi path component of the profiled channel impulse response is sent back to the network entity B.

43. The method as claimed in claim 37, further comprising subtracting, from the received measured channel impulse response, any channel impulse responses of other network entities received from the network entity B.

44. An apparatus comprising: at least one processor; and at least one memory including computer program code, the at least one memory and the computer program code being configured, with the at least one processor, to cause the apparatus to perform: transmit reference signals to a network entity B from the apparatus, wherein the apparatus and the network entity B are each one of a network node and a user equipment; receive a measured channel impulse response back from the network entity B after a first round-trip time interval; send the channel impulse response back to the network entity B; receive the channel impulse response back from the network entity B after a second round-trip time interval; repeat the preceding send and receive to record N round-trip time intervals, N being an integer; calculate a total time for the N round-trip intervals; and divide the total time by N to obtain an estimate of a single round-trip time more accurate by a factor of 2N.

45. The apparatus as claimed in claim 44, wherein a modified reference signal time difference (RSTD) measurement is applied, where the time difference of the received reference signals corresponds to the difference after dividing the total time by N.

46. The apparatus as claimed in claim 44, wherein the measured channel impulse response received back from the network entity B includes multi-path components, and wherein only the strongest of the multi-path components is sent back to the network entity B.

47. The apparatus as claimed in claim 44, wherein the at least one memory and the computer program code are further configured, with the at least one processor, to cause the apparatus to: add an artificial delay when performing the sending and receiving to distinguish the received measured channel impulse response from the channel impulse responses of other network entities received from the network entity B.

48. The apparatus as claimed in claim 44, wherein profiling is performed on the received measured channel impulse response, and a single multipath component with the delay of the peak of the profiled channel impulse response is sent back to the network entity B.

49. The apparatus as claimed in claim 44, wherein profiling is performed on the received measured channel impulse response, and only the strongest multi path component of the profiled channel impulse response is sent back to the network entity B.

50. The apparatus as claimed in claim 44, wherein the at least one memory and the computer program code are further configured, with the at least one processor, to cause the apparatus to: subtract, from the received measured channel impulse response, any channel impulse responses of other network entities received from the network entity B.

51. An apparatus comprising: means for transmitting reference signals to a network entity B from the apparatus, wherein the apparatus and the network entity B are each one of a network node and a user equipment; means for receiving a measured channel impulse response back from the network entity B after a first round-trip time interval; means for sending the channel impulse response back to the network entity B; means for receiving the channel impulse response back from the network entity B after a second round-trip time interval; means for repeating the preceding sending and receiving to record N round-trip time intervals, N being an integer; means for calculating a total time for the N round-trip intervals; and means for dividing the total time by N to obtain an estimate of a single round-trip time more accurate by a factor of 2N.

52. The apparatus as claimed in claim 51, wherein a modified reference signal time difference (RSTD) measurement is applied, where the time difference of the received reference signals corresponds to the difference after dividing the total time by N.

53. The apparatus as claimed in claim 51, wherein the measured channel impulse response received back from the network entity B includes multi-path components, and wherein only the strongest of the multi-path components is sent back to the network entity B.

54. The apparatus as claimed in claim 51, further comprising: means for adding an artificial delay when performing the sending and receiving to distinguish the received measured channel impulse response from the channel impulse responses of other network entities received from the network entity B.

55. The apparatus as claimed in claim 51, wherein profiling is performed on the received measured channel impulse response, and a single multipath component with the delay of the peak of the profiled channel impulse response is sent back to the network entity B.

56. The apparatus as claimed in claim 51, wherein profiling is performed on the received measured channel impulse response, and only the strongest multi path component of the profiled channel impulse response is sent back to the network entity B.

57. The apparatus as claimed in claim 51, further comprising: means for subtracting, from the received measured channel impulse response, any channel impulse responses of other network entities received from the network entity B.

58. A computer program product comprising a non-transitory computer-readable storage medium bearing computer program code embodied therein for use with a computer, the computer program code comprising code for performing: transmitting reference signals to a network entity B from a network entity A, wherein network entity A and network entity B are each one of a network node and a user equipment; receiving a measured channel impulse response back from the network entity B after a first round-trip time interval; sending the channel impulse response back to the network entity B; receiving the channel impulse response back from the network entity B after a second round-trip time interval; repeating the preceding sending and receiving to record N round-trip time intervals, N being an integer; calculating a total time for the N round-trip intervals; and dividing the total time by N to obtain an estimate of a single round-trip time more accurate by a factor of 2N.

59. The computer program product as claimed in claim 58, wherein a modified reference signal time difference (RSTD) measurement is applied, where the time difference of the received reference signals corresponds to the difference after dividing the total time by N.

60. The computer program product as claimed in claim 58, wherein the measured channel impulse response received back from the network entity B includes multi-path components, and wherein only the strongest of the multi-path components is sent back to the network entity B.

61. The computer program product as claimed in claim 58, wherein the computer program code further comprises code for performing: adding an artificial delay when performing the sending and receiving to distinguish the received measured channel impulse response from the channel impulse responses of other network entities received from the network entity B.

62. The computer program product as claimed in claim 58, wherein profiling is performed on the received measured channel impulse response, and a single multipath component with the delay of the peak of the profiled channel impulse response is sent back to the network entity B.

63. The computer program product as claimed in claim 58, wherein profiling is performed on the received measured channel impulse response, and only the strongest multi path component of the profiled channel impulse response is sent back to the network entity B.

64. The computer program product as claimed in claim 58, wherein the computer program code further comprises code for performing: subtracting, from the received measured channel impulse response, any channel impulse responses of other network entities received from the network entity B.