Patent Publication Number: US-2023156658-A1

Title: Position estimation

Description:
TECHNOLOGICAL FIELD 
     Embodiments of the present disclosure relate to position estimation. Some relate to position estimation of a terminal node using multipath information. 
     BACKGROUND 
     A wireless network comprises a plurality of network nodes including terminal nodes and access nodes. Communication between the terminal nodes and access nodes is wireless. 
     In some circumstances it may be desirable to improve accuracy in estimating positions of the terminal nodes. 
     BRIEF SUMMARY 
     According to various, but not necessarily all, embodiments there is provided examples as claimed in the appended claims. 
     According to various, but not necessarily all, embodiment there is provided 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 configured to, with the at least one processor, cause the apparatus to perform:   determining, for a terminal node, at least one time delay value for a plurality of access nodes;   determining at least one metric for the access nodes, the at least one metric indicative of probability of line of sight conditions between the terminal node and the access nodes;   determining, based, at least in part, on the at least one metric, a first set of line of sight time delay values having an associated probability of line of sight conditions above a threshold;   determining, based, at least in part, on the at least one metric, a second set of time delay values having an associated probability of line of sight conditions below the threshold;   determining a position estimate of the terminal node based, at least in part, on the first set of line of sight time delay values;   determining, based at least in part on the position estimate of the terminal node, at least one line of sight time delay value of the second set; and   determining a new estimate of the position of the terminal node based, at least in part, on the at least one determined line of sight time delay value of the second set.   

     In examples determining the at least one time delay value for a plurality of access nodes comprises determining a plurality of time delay values for one or more of the plurality of access nodes. 
     In examples the at least one metric is determined based, at least in part, on one or more power delay profile metrics determined based, at least in part, on the at least one time delay value for the plurality of access nodes. 
     In examples the one or more power delay profile metrics comprises one or more of: mean excess delay, root mean square delay spread, a list of time delay values that are less than a determined line of sight time delay value for an access node and within a predetermined amount from the highest or maximum received power for that access node, and the number of multipath components above a predetermined power. 
     In examples determining the at least one metric comprises determining the at least one metric based, at least in part, on historical line of sight information of at least one of the access nodes. 
     In examples determining a first set of line of sight time delay values having an associated probability of line of sight conditions above a threshold comprises comparing the at least one metric to at least one threshold value. 
     In examples determining a position estimate of the terminal node comprises using an observed time difference of arrival method based, at least in part, on the first set of line of sight time delay values. 
     In examples determining at least one line of sight time delay value of the second set comprises comparing distances from the access nodes represented by one or more time delay values of the second set with the position estimate of the terminal node. 
     In examples comparing distances from the access nodes represented by time delay values of the second set with the position estimate of the terminal node comprises determining a distance between the position estimate of the terminal node and a colinear point on a circle or hyperbola described by one or more of the time delay values of the second set. 
     In examples determining a new estimate of the position of the terminal node comprises updating the position estimate of the terminal node based, at least in part, on the at least one determined line of sight time delay value of the second set. 
     In examples the at least one memory and the computer program code are configured to, with the at least one processor, cause the apparatus to store, at least, the at least one metric for the plurality of access nodes and a position of the terminal node. 
     In examples the at least one memory and the computer program code are configured to, with the at least one processor, cause the apparatus to determine positions of the plurality of access nodes. 
     In examples determining, for a terminal node, at least one time delay value for a plurality of access nodes comprises receiving one or more signals from the plurality of access nodes. 
     In examples, determining, for a terminal node, at least one time delay value for a plurality of access nodes comprises receiving one or more signals from the terminal node. 
     In examples the terminal node is user equipment and the access nodes are gNBs. 
     According to various, but not necessarily all, embodiments there is provided user equipment comprising an apparatus as described herein. 
     According to various, but not necessarily all, embodiments, there is provided a server comprising an apparatus as described herein. 
     According to various, but not necessarily all, embodiments there is provided a method comprising:
     determining, for a terminal node, at least one time delay value for a plurality of access nodes;   determining at least one metric for the access nodes, the at least one metric indicative of probability of line of sight conditions between the terminal node and the access nodes;   determining, based, at least in part, on the at least one metric, a first set of line of sight time delay values having an associated probability of line of sight conditions above a threshold;   determining, based, at least in part, on the at least one metric, a second set of time delay values having an associated probability of line of sight conditions below the threshold;   determining a position estimate of the terminal node based, at least in part, on the first set of line of sight time delay values;   determining, based at least in part on the position estimate of the terminal node, at least one line of sight time delay value of the second set; and   determining a new estimate of the position of the terminal node based, at least in part, on the at least one determined line of sight time delay value of the second set.   

     According to various, but not necessarily all, embodiments there is provided an apparatus comprising means for performing:
     determining, for a terminal node, at least one time delay value for a plurality of access nodes;   determining at least one metric for the access nodes, the at least one metric indicative of probability of line of sight conditions between the terminal node and the access nodes;   determining, based, at least in part, on the at least one metric, a first set of line of sight time delay values having an associated probability of line of sight conditions above a threshold;   determining, based, at least in part, on the at least one metric, a second set of time delay values having an associated probability of line of sight conditions below the threshold;   determining a position estimate of the terminal node based, at least in part, on the first set of line of sight time delay values;   determining, based at least in part on the position estimate of the terminal node, at least one line of sight time delay value of the second set; and   determining a new estimate of the position of the terminal node based, at least in part, on the at least one determined line of sight time delay value of the second set.   

     According to various, but not necessarily all, embodiments there is provided a computer program comprising instructions for causing an apparatus to perform at least the following or for performing at least the following:
     determining, for a terminal node, at least one time delay value for a plurality of access nodes;   determining at least one metric for the access nodes, the at least one metric indicative of probability of line of sight conditions between the terminal node and the access nodes;   determining, based, at least in part, on the at least one metric, a first set of line of sight time delay values having an associated probability of line of sight conditions above a threshold;   determining, based, at least in part, on the at least one metric, a second set of time delay values having an associated probability of line of sight conditions below the threshold;   determining a position estimate of the terminal node based, at least in part, on the first set of line of sight time delay values;   determining, based at least in part on the position estimate of the terminal node, at least one line of sight time delay value of the second set; and   determining a new estimate of the position of the terminal node based, at least in part, on the at least one determined line of sight time delay value of the second set.   

     According to various, but not necessarily all, embodiments there is provided 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 configured to, with the at least one processor, cause the apparatus to perform:   transmitting at least one signal to a terminal node, the at least one signal comprising information indicative of a request for the terminal node to respond with, at least, one or more power delay profile metrics for access nodes contactable by the terminal node and at least one metric indicative of probability of line of sight conditions between the terminal node and the access nodes.   

     In examples the one or more power delay profile metrics comprises at least one of: mean excess delay, root mean square delay spread, a list of time delay values that are less than a determined line of sight time delay value for an access node and within a predetermined amount from the highest or maximum received power for that access node, and the number of multipath components above a predetermined power. 
     According to various, but not necessarily all, embodiments there is provided 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 configured to, with the at least one processor, cause the apparatus to perform:   transmitting, from a terminal node, at least one signal to a server, the at least one signal comprising information indicative of one or more power delay profile metrics for access nodes contactable by the terminal node and at least one metric indicative of probability of line of sight conditions between the terminal node and the access nodes.   

     In examples the one or more power delay profile metrics comprises at least one of: mean excess delay, root mean square delay spread, a list of time delay values that are less than a determined line of sight time delay value for an access node and within a predetermined amount from the highest or maximum received power for that access node, and the number of multipath components above a predetermined power. 
    
    
     
       BRIEF DESCRIPTION 
       Some examples will now be described with reference to the accompanying drawings in which: 
         FIG.  1    shows an example of the subject matter described herein; 
         FIG.  2    shows another example of the subject matter described herein; 
         FIG.  3    shows another example of the subject matter described herein; 
         FIG.  4    shows another example of the subject matter described herein; 
         FIG.  5    shows another example of the subject matter described herein; 
         FIG.  6    shows another example of the subject matter described herein; 
         FIG.  7    shows another example of the subject matter described herein; 
         FIG.  8 A  shows another example of the subject matter described herein; 
         FIG.  8 B  shows another example of the subject matter described herein. 
     
    
    
     DETAILED DESCRIPTION 
       FIG.  1    illustrates an example of a network  100  comprising a plurality of network nodes including terminal nodes  110 , access nodes  120  and one or more core nodes  129 . The terminal nodes  110  and access nodes  120  communicate with each other. The one or more core nodes  129  communicate with the access nodes  120 . 
     The one or more core nodes  129  may, in some examples, communicate with each other. The one or more access nodes  120  may, in some examples, communicate with each other. 
     The network  100  may be a cellular network comprising a plurality of cells  122  at least one served by an access node  120 . In this example, the interface between the terminal nodes  110  and an access node  120  defining a cell  122  is a wireless interface  124 . 
     The access node  120  is a cellular radio transceiver. The terminal nodes  110  are cellular radio transceivers. 
     In the example illustrated the cellular network  100  is a third generation Partnership Project (3GPP) network in which the terminal nodes  110  are user equipment (UE) and the access nodes  120  are base stations. 
     In some examples the network  100  is an Evolved Universal Terrestrial Radio Access network (E-UTRAN). The E-UTRAN consists of E-UTRAN NodeBs (eNBs)  120 , providing the E-UTRA user plane and control plane (RRC) protocol terminations towards the UE  110 . The eNBs  120  are interconnected with each other by means of an X2 interface  126 . The eNBs are also connected by means of the S1 interface  128  to the Mobility Management Entity (MME)  129 . 
     In some examples the network  100  is a Next Generation (or New Radio, NR) Radio Access network (NG-RAN). The NG-RAN consists of gNodeBs (gNBs)  120 , providing the user plane and control plane (RRC) protocol terminations towards the UE  110 . The gNBs  120  are interconnected with each other by means of an X2/Xn interface  126 . The gNBs are also connected by means of the N2 interface  128  to the Access and Mobility management Function (AMF). 
     In examples the network  100  comprises at least one server  112 . In the illustrated example the server  112  is a location server  112 . 
     In examples one or more of the terminal nodes  110  can communicate with the location server  112  and one or more signals  162 ,  163 , comprising information, (see, for example,  FIGS.  3  and  4   ) can be transmitted directly, or indirectly, between one or more of the terminal nodes  110  and the location server  112 . 
     In the illustrated example, the interface between a plurality of the terminal nodes  110  and the location server  112  is a wireless interface  124 , however any suitable interface can be used. 
     In examples, communications between the elements illustrated in  FIG.  1    can proceed via any number of intervening elements, including no intervening elements. 
       FIG.  2    illustrates an example of a method  200 . 
     In examples the method  200  can be performed at one or more of the elements in the network  100  of  FIG.  1   . For example, the method  200  can be performed at an access node  110 , such as a UE  164 , and/or a server  112 , such as a location server  112 . 
     One or more of the features discussed in relation to  FIG.  2    can be found in one or more of the other figures. 
     At block  202 , the method  200  comprises determining, for a terminal node  110 , at least one time delay value  138  for a plurality of access nodes  120 . 
     Any suitable method for determining, for a terminal node  110 , at least one time delay value  138  for a plurality of access nodes  120  can be used. 
     As used herein, the term “determining” (and grammatical variants thereof) can include, not least: calculating, computing, processing, deriving, investigating, looking up (for example, looking up in a table, a database or another data structure), ascertaining and the like. Also, “determining” can include receiving (for example, receiving information), accessing (for example, accessing data in a memory) and the like. Also, “determining” can include resolving, selecting, choosing, establishing, and the like. 
     As used herein, a time delay value  138  is intended to include any measurement, metric, value, parameter and/or quantity indicative of and/or representing and/or quantifying time taken for one or more signals to travel from an access node  120  to a terminal node  110 . In some examples, a time delay value  138  can be considered a delay. 
     Under line of sight conditions between an access node  120  and a terminal node  110 , a time delay value  138  can be used to determine a distance between the access node  120  and the terminal node  110 . 
     Under line of sight conditions between an access node  120  and a terminal node  110 , a time delay value  138  for line of sight conditions can be considered a line of sight time delay value  142  or time of arrival. 
     The at least one time delay value  138  for the plurality of access nodes  120  can have any suitable form. In examples the time delay values  138  can be in the form of absolute timings and/or relative timings. 
     For example, the at least one time delay value for the access nodes  120  can be in the form of a delay between transmission from the access nodes  120  and reception by the terminal node  110 . 
     In some examples the at least one time delay value  138  for the plurality of access nodes  120  can be in the form of a delay for a reference or anchor access node  120  and time differences relative to the reference or anchor access node  120  delay. 
     In examples the access nodes  120  transmit time synchronized positioning reference signals with constant power which are received by a terminal node  110 , via at least one path, and allow the terminal node  110  to determine or be caused or controlled to determine time delay value(s)  138  for received signals from the access nodes  120 . In some examples the terminal node  110  determines or is caused or controlled to determine reference signal time differences relative to a time delay value  138  of an anchor access node  120 . 
     In examples, any suitable method can be used to determine at least one time delay value  138  for received signals from the access nodes  120 . For example, channel impulse response or correlation-based methods can be used to determine time delay values  138  and associated power for signals received from the access nodes  120 . 
     In some examples, the determining at least one time delay value  138  for received signals from the access nodes  120  comprises cross-correlating the received signals with locally generated positioning reference signals and distinguishing N different channels, corresponding to N access nodes  120 . 
     Accordingly, in examples, determining, for a terminal node  110 , at least one time delay value  138  for a plurality of access nodes  120  comprises receiving one or more signals from the plurality of access nodes  120 . 
     In some examples determining the at least one time delay value  138  for a plurality of access nodes  120  comprises determining a plurality of time delay values  138  for one or more of the plurality of access nodes  120 . 
     In examples, determining a plurality of time delay values  138  for an access node  120  can be considered determining multipath time delay information for the access node  120 . 
     Signal(s), such as positioning reference signals, transmitted by an access node  120  can reach the terminal node  110  via multiple paths, including line of sight (LOS) and/or non line of sight (NLOS) paths. 
     In such examples, the terminal node  110  can determine a plurality of different time delay values  138  for an access node  120  as a result of the multipath arrival of the signals. 
     In examples, the method  200  comprises determining an LOS time delay value  142  for the access nodes  120  which could be considered as time of arrival for signals received from the access nodes and used in determining a position/location of the terminal node  110 . 
     In some examples determining an LOS time delay value  142  for an access node  120  comprises determining which of a plurality of time delay values  138  for the terminal node is or is to be considered the LOS time delay value  142 . 
     Determining the LOS time delay value from a plurality of time delay values  138  can be done in any suitable way, using any suitable method considering any suitable factor or factors. 
     For example, the LOS time delay value  142  can, at least initially, be considered to be the time delay value  138 , of a plurality of time delay values  138 , having the highest associated power. 
     However, in certain contexts power of LOS signals can be attenuated compared to NLOS signals resulting in an incorrect identification of the LOS time delay value  142  which can cause errors in determining a position/location of at terminal node  110 . 
     Accordingly, as used herein a line of sight (LOS) time delay value  142  can be considered to be the time delay value  138  having a high, and/or the highest confidence level and/or probability of being from line of sight conditions between an access node  120  and the terminal node  110 . 
     In some examples an LOS time delay value  142  can be considered to be the time delay value  138  currently considered to be the LOS time delay value  142  based on the available information and/or the factor(s) considered in determining the LOS time delay value  142 . 
     In examples determining, for a terminal node  110 , at least one time delay value  138  for a plurality of access nodes  120  comprises receiving one or more signals  162  from the terminal node  110 . 
     The one or more signals  162  can also comprise additional information for use in determining a position/location of the terminal node  110 . For example, the one or more signals  162  can comprise one or more time delay values  138  and one or more metrics and/or measurements. In some examples the one or more metrics and/or measurements can comprise one or more power delay profile metrics. See, for example, block  204 . 
     In examples, the one or more signals  162  are received at a location server  112 . See, for example,  FIG.  3     
     At block  204  the method  200  comprises determining at least one metric  140  for the access nodes  120 , the at least one metric  140  indicative of probability of line of sight conditions between the terminal node  110  and the access nodes  120 . 
     In examples, the at least one metric  140  can be considered to be indicative of a level of confidence of line of sight conditions between the terminal node  110  and the access nodes  120 . 
     In examples, the at least one metric  140  is or can be considered to be an estimate and/or determination and/or measurement of the probability or confidence that an LOS time delay value  142  for an access node  120  has been received under line of sight conditions. 
     Additionally, or alternatively, in examples, the at least one metric  140  is or can be considered to be an estimate and/or determination and/or measurement of the probability or confidence that an LOS time delay value  142  for an access node  120  has been correctly identified. 
     Any suitable method for determining the at least one metric  140  can be used. In examples, determining the at least one metric  140  comprises processing and/or analyzing multipath information. 
     In some examples the at least one metric  140  is determined based, at least in part, on one or more power delay profile metrics determined, based, at least in part, on the at least one time delay value  138  for the plurality of access nodes  120 . 
     A power delay profile (PDP) can be considered to represent the intensity or power of a signal received through a multipath channel as a function of time delay. 
     Accordingly, in examples, the power delay profile for the plurality of access nodes  120  can represent the intensity or power of the signals received as a function of the at least one time delay value  138  for the access nodes. See, for example,  FIG.  5   . 
     Any suitable power delay profile metric can be used. For example, the at least one power delay profile metric can be determined based, at least in part, on one or more of the energy in the channel, the spread of the time delay value(s)  138 , the power associated with the time delay value(s)  138 , the number of time delay values  138  and so on. 
     In some examples, the one or more power delay profile metrics comprises one or more of: mean excess delay, root mean square delay spread, a list of time delay values  138  that are less than a determined line of sight time delay value  142  for an access node  120  and within a predetermined amount from the highest or maximum received power for that access node  120 , and the number of multipath components above a predetermined power. 
     The mean excess delay (MED) can be considered to be the time delay during which the energy in the channel falls to a predetermined amount below the highest or maximum power. 
     In examples, any suitable predetermined amount below the highest or maximum power can be used. For example, a predetermined amount in the range 7.5 dB to 12.5 dB can be used. 
     In examples, the predetermined amount is substantially 10 dB and therefore, in such examples, the MED is the time delay during which the energy in the channel falls to 10 dB below the highest or maximum. 
     A small MED value is an indication of line of sight conditions. In examples, an MED value in the order of tens of nanoseconds is considered a small MED value. In some examples, an MED value in the range 10 to 100 nanoseconds can be considered a small MED value. In some examples, an MED value in the range 30 to 70 nanoseconds can be considered a small MED value. 
     The root mean square delay spread (RMS-DS) can be considered to be the square root of the second central moment of the power delay profile. 
     A small RMS-DS value is an indication of line of sight conditions. In examples, an RMS-DS value in the order of tens of nanoseconds is considered a small RMS-DS value. In some examples, an RMS-DS value in the range 10 to 100 nanoseconds can be considered a small RMS-DS value. In some examples, an RMS-DS value in the range 30 to 70 nanoseconds can be considered a small RMS-DS value. 
     With regard to the list of time delay values  138  that are less than a determined line of sight time delay value  142  for an access node  120  and within a predetermined amount from the highest or maximum received power for that access node  120 , any suitable predetermined amount can be used. In examples the list can be represented by Lc. 
     For example, a predetermined amount in the range 2 to 4 dB can be used. 
     In examples, the predetermined amount is substantially 3 dB and in such examples the list is of time delay values  138  that are less than a determined line of sight time delay value 42 for an access node  120  and within 3 dB from the highest or maximum received power for that access node  120 . 
     The list of time delay values  138  can be beneficial in removing the error introduced when the true LOS time delay value  142  is attenuated compared to a NLOS time delay value  138  and is not correctly identified as the LOS time delay value  142 . 
     With regard to the number of multipath components above a predetermined power, this can be considered ‘channel sparsity’. 
     In examples, any suitable predetermined power value can be used. For example, the number of multipath components of non-negligible power can be determined. In some examples, the noise floor can be used in determining channel sparsity and, in such examples, the number of multipath components above the noise floor is determined. 
     Channel sparsity can be beneficial in determining whether line of sight conditions are present. In examples, channel sparsity can be used in combination with one or more other power delay profile metrics in determining whether a channel is LOS or NLOS. 
     In examples, one or more power delay profile metrics can be used in any suitable way to determine the at least one metric  140 . 
     In examples, the at least one metric  140  can be a single metric, represented by P LOS  for example, defined as a step function based on at least one or more power delay profile metrics. In some examples, the metric  140 , P LOS , can be defined as a step function based on mean excess delay, root mean square delay spread and channel sparsity. 
     In some examples, P LOS  can be defined as a step function based on a comparison of MED, RMS-DS and channel sparsity against respective thresholds. 
     For example, P LOS  can be defined as: 
     
       
         
           
             
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      Where: η MED , η RMS  and η K  are threshold values for MED, RMS-DS and channel sparsity respectively. 
     In examples any suitable threshold values can be used. For example, η MED  can be in the range 250 ns to 750 ns, can be in the range 400 ns to 600 ns and/or can be in the range 450 ns to 550 ns. In some examples, η MED  can be or can be approximately 500 ns. 
     In some examples, η RMS  can be in the range 0.5 to 1.5 µs, can be in the range 0.75 to 1.25 µs, and/or can be in the range 0.9 to 1.1 µs. In some examples, η RMS  can be or can be approximately 1 µs. 
     In some examples, η K  can be in the range 5 to 15, can be in the range 7 to 13 and/or can be in the range 9 to 11. In some examples, η K  can be or can be approximately 10. 
     In some examples the at least one metric  140  can be determined as a LOS probability. For example, P LOS  can represent the probability of LOS conditions on channel and can be determined based, at least in part on one or more power delay profile metrics. 
     In some examples, one or more power delay profile metrics, for example one or more of MED, RMS-DS, Lc and channel sparsity, can be used as inputs to a machine learning module which is configured to output the at least one metric  140 . 
     Any suitable machine learning module can be used. For example, one or more artificial neural networks and/or support vector machines. 
     In examples, the machine learning module can be implemented by means of supervised learning, for example as an artificial neural network regressor, or classifier, or with algorithms from the reinforcement learning framework. 
     In examples, a neural network can implement several hidden layers, which can be characterized by various activation functions such a s ReLU, linear, tanh and so on. 
     In examples the machine learning module is trained on artificially generated channels, for example from ray tracing, and can be used once the false positive rate for LOS condition detection is minimized. 
     In examples, a neural network can be trained on a set of measurements collected in a controlled environment, for example with known LOS/NLOS conditions. 
     The loss function can be cross-entropy, hinge and so on. 
     In some examples, in a machine learning framework, a neural network with an output activation function such as softmax, sigmoid function, or similar can be used. 
     In some examples determining the at least one metric  140  comprises hypothesis testing. For example, one or more power delay profile metrics can be tested to determine whether they are drawn from distributions characterizing LOS or NLOS conditions. 
     In examples an optimization problem is formulated and Bayesian inference methods used, for example, to determine probabilities of the at least one metric  140 . 
     In examples determining the at least one metric  140  comprises determining the at least one metric  140 , based at least in part, on historical line of sight information of at least one of the access nodes  120 . 
     Any suitable method for determining the at least one metric  140 , based at least in part, on historical line of sight information of at least one of the access nodes  120  can be used. 
     In examples, the at least one metric  140  is determined based, at least in part, on previously determined or estimated channels substantially at and/or in the vicinity of and/or proximate and/or nearby a current position/location of the terminal node  110  and/or an area where the terminal node  110  is currently located. 
     For example, the at least one metric  140  can be determined based, at least in part, on previously determined values of the at least one metric  140  for the access nodes  120 . 
     In some examples, the at least one metric  140  is determined based, at least in part, on historical information of one or more other terminal nodes  110 . 
     For example, the at least one metric  140  can be determined based, at least in part, on previously determined values of the at least one metric  140  determined for at least one or more other terminal nodes  110  at and/or proximate and/or nearby a current position/location of the terminal node  110  for the access nodes  120  from which the terminal node  110  has received one or more signals. 
     In examples, previously determined values of the at least one metric  140  determined for at least one or more other terminal nodes  110  within substantially or approximately 10 m of a current position/location of the terminal node  110  can be used. 
     In examples, the current position/location of the terminal node  110  can be estimated based, at least in part, on information of the terminal node’s past position(s)/location(s) and an estimated velocity. In some examples this process can be referred to as dead reckoning. 
     Such an estimate of the position/location of a terminal node  110  can be used with historical information in the determination of the at least one metric  140 . 
     In examples, the at least one metric  140  for the access nodes  120  is stored or caused to be stored in at least one data structure, for example at least one table, which can be considered a tracking data structure or tracking table. 
     In some examples, one or more of the one or more power delay profile metrics for the access nodes are also stored in the at least one data structure. 
     For example, when the method  200  is performed at a terminal node  110 , the determined at least one metric  140  and, in some examples, the at least one power delay profile metrics for the access nodes are stored or caused to be stored in a tracking data structure, such as a tracking table, with an associated time stamp. 
     In examples, the information in the at least one tracking data structure can be considered to trace or track the channels from the access nodes  120 . 
     The tracking data structure can be implemented as a first-in first-out (FIFO) tracking data structure and/or tracking table. For example, the data structure can be implemented as a FIFO queue, with at most K entries, where the most recent K measurements are stored. 
     In examples, K can be fixed or variable. In some examples K can be proportional to the capabilities, such as speed, of the terminal node  110 . 
     Examples of a tracking data structure, in the form of a tracking table, for two access nodes  120  is shown in table 1. In the example of table 1, the access nodes  120  are gNBs. 
     Furthermore, in the example of table 1, the determined LOS time delay values  142  are indicated as ‘ToA’. 
     
       
         
          TABLE 1
           
               
               
               
               
               
               
               
             
               
                 gNB 1 
               
             
            
               
                 T2 
                 500 ns 
                 8 \mus 
                 1 \mus 
                 {40 ns} 
                 5 
                 0 
               
               
                 T1 
                 550 ns 
                 14 \mus 
                 1 \mus 
                 {10 ns} 
                 7 
                 0 
               
            
           
           
               
               
               
               
               
               
               
             
               
                 gNB 2 
               
             
            
               
                 T2 
                 900 ns 
                 7 \mus 
                 3 \mus 
                 {400, 700 ns} 
                 5 
                 0 
               
               
                 T1 
                 1500 ns 
                 8 \mus 
                 3 \mus 
                 {400, 800 ns} 
                 7 
                 0 
               
            
           
         
       
     
     In the example of table 1, the LOS time delay value  142 , or ToA, at least one metric, P LOS , and power delay profile metrics MED, RMS-DS, Lc and channel sparsity at two different timestamps have been stored. 
     In examples, at least a portion of the information determined at a timestamp is transmitted or caused to be transmitted from the terminal node  110  to a location server  112 . See for example,  FIG.  3   . 
     At block  206  the method  200  comprises determining, based, at least in part, on the at least one metric  140 , a first set  144  of line of sight time delay values  142  having an associated probability of line of sight conditions above a threshold. 
     In examples an associated probability can be or be considered an associated confidence and/or confidence level of line of sight conditions. 
     Any suitable method for determining, based, at least in part, on the at least one metric  140 , a first set  144  of line of sight time delay values  142  having an associated probability of line of sight conditions above a threshold can be used. 
     Determining a first set  144  of line of sight time delay values  142  having an associated probability of line of sight conditions above a threshold can be considered determining a first set  144  of time delay values  138  having an associated probability of line of sight conditions above a threshold. 
     In some examples, determining a first set  144  of line of sight time delay values  142  having an associated probability of line of sight conditions above a threshold comprises comparing the at least one metric  140  to at least one threshold value. 
     Comparing the at least one metric  140  to at least one threshold value can be done in any suitable way. For example, comparing the at least one metric  140  to the at least one threshold value can comprise determining if the at least one metric  140  is greater than, greater than or equal to, less than, or less than or equal to the at least one threshold value. 
     In examples, the at least one threshold value can be determined in any suitable way. For example, determining the at least one threshold value can comprise receiving the at least one threshold value. In examples, the at least one threshold value can be received at the terminal node  110  from the location server  112 . 
     Any suitable threshold(s) determined in any suitable way can be used. In examples where the at least one metric  140  is determined as a step function, see for example Eqn 1, the threshold can be 0.5. 
     In examples where the at least one metric is determined as a probability, the threshold can be in the range 40% to 60% and/or in the range 45 % to 55%. In some examples, the threshold can be or can be approximately 50%. 
     In some examples the threshold can be a predetermined value selected from one or more predetermined values. For example, the threshold can be retrieved from memory  134 . 
     In examples the threshold can be determined based, at least in part, on one or more factors. Any suitable factors can be used, for example, number of access nodes  120  available to the terminal node  110  and/or requested accuracy of position/location estimate and/or historical line of sight information and so on. 
     In the example of table 1, where the determination is greater than or equal to a threshold value of 0.5, neither gNB 1 or gNB 2 would be in the first set  144  as both gNBs have P LOS  values of 0, at both T1 and T2. 
     At block  208  the method comprises determining, based, at least in part, on the at least one metric  140 , a second set  146  of time delay values  138  having an associated probability of line of sight conditions below the threshold. 
     In some examples, determining a second set  146  of time delay values  138  having an associated probability of line of sight conditions below the threshold can be considered determining a second set  146  of line of sight time delay values  142  having an associated probability of line of sight conditions below the threshold. 
     Any suitable method for determining, based, at least in part, on the at least one metric  140 , a second set  146  of time delay values  138  having an associated probability of line of sight conditions below the threshold can be used. 
     In examples, determining the second set  146  of time delay values  138  comprises comparing the at least one metric  140  to the at least one threshold as described in relation to block  206 , but in the opposite sense. 
     For example, if determining the first set  144  comprises determining associated metric(s)  140  greater than or equal to the threshold, then determining the second set  146  would comprise determining metric(s)  140  less than the threshold and so on. 
     In some examples, determining the second set  146  of time delay values  138  comprises determining the time delay values  138  not in the first set  144 . 
     Accordingly, in some examples blocks  206  and  208  of method  200  can be combined into a single block or action comprising comparing the at least one metric  140  associated with the determined time delay values  138  for the access nodes  120  with the threshold. 
     In examples it can be considered that the time delay values  138  and/or the line of sight time delay values  142  for the access nodes  120  are grouped into the first set  144  having good or high probability or confidence of line of sight conditions and the second set  146  having bad or low probability or confidence of line of sight conditions. 
     At block  210  the method  200  comprises determining a position estimate  148  of the terminal node  110  based, at least in part, on the first set  144  of line of sight time delay values  142 . 
     In examples, determining a position estimate  148  can be considered determining a location estimate  148 . 
     Any suitable method for determining a position estimate  148  of the terminal node  110 , based, at least in part, on the first set  144  of line of sight time delay values  142  can be used. 
     In examples, determining a position estimate  148  of the terminal node  110  comprises using an observed time difference of arrival method, based, at least in part, on the first set of line of sight time delay values  142 . 
     At block  212  the method  200  comprises determining, based, at least in part, on the position estimate  148  of the terminal node  110 , at least one line of sight time delay value  142  of the second set  146 . 
     In some examples, the time delay values  138  of the second set  146  have determined line of sight time delay values  142 , but with low associated probability or confidence of line of sight conditions and/or correct identification of line of sight time delay value  142 . 
     Accordingly, in examples, determining at least one line of sight time delay value  142  of the second set  146  can be considered and/or comprise determining at least one updated or new line of sight time delay value  142  of the second set  146 . 
     In some examples, determining at least one light of sight time delay value  142  of the second set  146  can be considered and/or comprise confirming at least one line of sight time delay value  142  of the second set  146 . 
     Any suitable method for determining, based, at least in part, on the position estimate  148  of the terminal node  110 , at least one line of sight time delay value  142  of the second set  146  can be used. 
     In examples, determining at least one line of sight time delay value  142  of the second set  146  comprises comparing distances  152  from the access nodes  120  represented by one or more time delay values  138  of the second set  146  with the position estimate  148  of the terminal node  110 . See, for example,  FIGS.  6  and  7   . 
     The comparison can be made for one or more of the time delay values  138  of the second set  146 . In some examples, the comparison can be made for the time delay values  138  in list Lc. 
     Comparing distances  152  from the access nodes  120  represented by time delay values  138  of the second set  146  with the position estimate  148  can be done in any suitable way. 
     In some examples, comparing distances  152  from the access nodes  120  represented by time delay values  138  in the second set  146  with the position estimate  148  of the terminal node  110  comprises determining a distance  152  between the position estimate  148  of the terminal node  110  and a colinear point  154  on a circle  156  or hyperbola described by one or more of the time delay values  138  of the second set  146 . See for example,  FIG.  6   . 
     For example, a Euclidean or Manhattan distance  152  between the position estimate  148  of the terminal node  110  and a colinear point  154  on a circle  156  or hyperbola described by one or more of the time delay values  138  can be used. However, any suitable distance measurement or metric can be used. 
     In examples the line of sight time delay value  142  for an access node  120  of the second set  146  is determined as the time delay value  138  having the smallest determined distance  152  for that access node  120 . 
     In some examples the line of sight time delay value  142 , or time of arrival, can be defined as: 
     
       
         
           
             T 
             o 
             
               A 
               
                 S 
                 2 
               
             
             = 
             arg  
             
               
                 min 
               
               
                 T 
                 o 
                 A 
                 ∈ 
                 L 
                 c 
               
             
             
               
                 d 
                 
                   
                     A 
                     , 
                     B 
                     
                       
                         t 
                         1 
                       
                     
                   
                 
                 , 
                 d 
                 
                   
                     A 
                     , 
                     C 
                     
                       
                         t 
                         2 
                       
                     
                   
                 
               
             
           
         
       
     
      Where: d(A,B(t1)) is the distance between the position estimate  148  of the terminal node  110  (A) and the colinear point  154  on a circle  156  represented by t1 (B); and d(A,B(t2)) is the distance between the position estimate  148  of the terminal node  110  (A) and the colinear point  154  on a circle  156  represented by t2 (B). 
     In the example of eqn 2, two time delay values  138  (t1 and t2) are considered. However, any suitable number of time delay values  138  for an access node  120  can be considered. 
     At block  214  the method  200  comprises determining a new estimate of the position of the terminal node  110  based, at least in part, on the at least one determined line of sight time delay value  142  of the second set  146 . 
     Any suitable method for determining a new estimate of the position of the terminal node  110  based, at least in part, on the at least one determined line of sight time delay value  142  of the second set  146  can be used. 
     In some examples, determining a new estimate of the position of the terminal node  110  comprises updating the position estimate of the terminal node  110  based, at least in part, on the at least one determined line of sight time delay value  142  of the second set  146 . 
     Updating the position of the terminal node  110  based, at least in part, on the at least one determined line of sight time delay value  142  of the second set  146  can be done in any suitable way. 
     In some examples, updating the position estimate of the terminal node  110  comprises recalculating the position of the terminal node  110  using the line of sight time delay values  142  of the first set  144  and the line of sight time delay value(s)  142  of the second set  146  determined at block  212 . 
     For example, updating the position estimate of the terminal node  110  can comprise using an observed time difference of arrival method, based, at least in part, on the first set of line of sight time delay values  142  and the line of sight time delay value(s)  142  of the second set  146  determined at block  212 . 
     In some examples, updating the position estimate of the terminal node  110  comprises refining and/or altering and/or changing and/or amending and/or moving the position estimate of the terminal node  100  based, at least in part, on the line of sight time delay value(s)  142  of the second set  146  determined at block  212 . 
     For example, a second position estimate of the terminal node  110  can be determined based, at least in part, on the line of sight time delay value(s)  142  of the second set  146  determined at block  212  and the new estimate of the position of the terminal node  110  determined based, at least in part, on the position estimate and second position estimate. 
     In examples, determining a second position estimate of the terminal node  110  comprises using an observed time difference of arrival method, based, at least in part, on the line of sight time delay value(s)  142  of the second set  146  determined at block  212 . 
     In some examples, the new position of the terminal node  110  is defined as the midpoint of the segment defined by the position estimate  148  of the terminal node  110  and the second position estimate of the terminal node  110 . 
     A technical advantage provided by the method  200  is an improvement in accuracy in determination of a position/location of a terminal node  110 , such as user equipment (UE)  164 . 
     In examples, the technical benefit is provided by using an location estimate of the terminal, derived from line of sight time delay values  142  for access nodes  120  having high probability or confidence of line of sight conditions, to determine one or more line of sight time delay values  142  from multipath data for other access nodes  120  having, initially, lower probability or confidence of line of sight conditions. 
     This provides, for example, mitigation of errors in the position estimate of a terminal node  110  arising from incorrect identification of a NLOS time delay value  138  as the LOS time delay value  142  or time of arrival. 
     At block  216  the method  200  comprises causing storage of, at least, the at least one metric  140  for the plurality of access nodes  120  and a position of the terminal node  110 . 
     For example, the at least one metric  140  and the new estimate of the location of the terminal node  110 , determined at block  214 , can be stored in memory  134 . 
     In some examples, further information can also be stored. For example, one or more of the power delay profile metrics. 
     This provides technical advantages. For example, it provides for a terminal node  110 , such as a UE  164 , and/or a server  112 , such as a location server  112 , to maintain channel tracking information which can be used to improve future determinations of the at least one metric  140 . This therefore provides, for example, a more accurate and/or efficient position determination over time. See, for example, block  204 . 
     Additionally, or alternatively an LOS map can be built, for example by a location server  112  and provided to one or more serving access nodes  120  for resource allocation purposes, more dynamic MCS tuning and so on. 
     A technical advantage provided is also therefore efficient resource allocation in a network  100  for example. 
     In some examples, the method  200  comprises determining positions of the plurality of access nodes  120 . 
     Any suitable method for determining the positions of the plurality of access nodes  120  can be used. 
     For example, determining the positions of the plurality of access nodes  120  can comprise receiving the positions of the plurality of access nodes  120  and/or retrieving the positions of the plurality of access nodes  120  from memory  134 . 
     In examples, determining the positions of the plurality of access nodes  120  is performed as part of block  212 . 
     Consequently,  FIG.  2    illustrates a method comprising:
     determining, for a terminal node  110 , at least one time delay value  138  for a plurality of access nodes  120 ;   determining at least one metric  140  for the access nodes  120 , the at least one metric  140  indicative of probability of line of sight conditions between the terminal node  110  and the access nodes  120 ;   determining, based, at least in part, on the at least one metric  140 , a first set  144  of line of sight time delay values  142  having an associated probability of line of sight conditions above a threshold;   determining, based, at least in part, on the at least one metric  140 , a second set  146  of time delay values  138  having an associated probability of line of sight conditions below the threshold;   determining a position estimate  148  of the terminal node  110  based, at least in part, on the first set  144  of line of sight time delay values  142 ;   determining, based at least in part on the position estimate  148  of the terminal node  110 , at least one line of sight time delay value  142  of the second set  146 ; and determining a new estimate of the position of the terminal node  110  based, at least in part, on the at least one determined line of sight time delay value  142  of the second set  146 .   

       FIG.  3    illustrates an example of position estimation of a terminal node  110 . 
       FIG.  3    can also be considered to disclose a method  300 . 
     In the example of  FIG.  3    a plurality of apparatuses communicate across a network. In examples, any suitable form of communication in any suitable network setup can be used. For example, the network  100  of  FIG.  1    can be used. 
     In the illustrated example, a terminal node  110  is communicating with a server  112 . In the example of  FIG.  3    the terminal node  110  is user equipment (UE)  164  and the server is a location server  112 . 
     At block  302 , at least one signal  163  is transmitted from the location server  112  to the UE  164 . 
     As  FIG.  3    illustrates one or more actions of transmission of one or more signals between the location server  112  and the UE  164   FIG.  3    also illustrates the corresponding transmitting/causing transmitting feature. 
     Similarly, for any transmitting/causing transmitting feature  FIG.  3    also illustrates the corresponding receiving action. 
     For example, block  302  therefore also illustrates receiving at least one signal  163  from the location server  112 . 
     In the example of  FIG.  3   , the at least one signal  163  comprises information indicative of a request for the terminal node  110  to respond with, at least, one or more power delay profile metrics for access nodes  120  contactable by the terminal node and at least one metric  140  indicative of probability of line of sight conditions between the terminal node  110  and the access nodes  120 . 
     In examples, the at least one metric  140  and/or the one or more power delay profile metrics can be as described in relation to block  204  of  FIG.  2   . 
     Any suitable information indicative of a request for the terminal node  110  to respond with the information can be used. 
     For example, the at least one signal  163  can comprise one or more flags indicating which information the terminal node  110  should respond with. For example, the at least one signal can comprise one or more flags to indicate which, if any, of the power delay profile metrics the terminal node  110  should respond with. 
     Additionally, or alternatively the at least one signal  163  can comprise the power threshold for use in determining the list of time delay values Lc. See, for example, block  204  of  FIG.  2   . 
     Additionally, or alternatively the at least one signal  163  can comprise the threshold value for use in determining the first and second sets  144 ,  146  of time delay values  142 ,  138 . See, for example, blocks  206  and  208  of  FIG.  2   . 
     In examples, the one or more signals  163  comprises information indicative of a request for the terminal node  110  to respond with one or more time delay values  138  for the plurality of access nodes  120 . 
     Any suitable information indicative of the request can be used. 
     In response to receiving the at least one signal  163 , the terminal node  110 , which in the example of  FIG.  3    is a UE  164 , determines the requested information. 
     In the example of  FIG.  3    the UE  164  determines at least one time delay value  138  for the plurality of access nodes  120 . This can be as described in relation to block  202  of  FIG.  2    and is therefore is indicated as  202  in  FIG.  3   . 
     In the example of  FIG.  3    the UE  164  also determines the at least one metric  140  and requested power delay profile metrics for the plurality of access nodes  120 . This can be as described in relation to block  204  of  FIG.  2    and therefore is indicated as  204  in  FIG.  3   . 
     In the example of  FIG.  3    the UE also stores the at least one metric  140  for the plurality of access nodes  216 , for future use. This can be as described in relation to block  216  of  FIG.  2    and therefore is illustrated as  216  in  FIG.  3   . 
     At block  304  at least one signal  162  is transmitted from the terminal node  110  to the server  112  to provide the requested at least one metric  140  and one or more power delay profile metrics to the server  112 . 
     In the example of  FIG.  3    the one or more time delay values  138  are provided in the at least one signal  162 . 
       FIG.  3    therefore illustrates transmitting, from a terminal node, at least one signal  162  to a server  112 , the at least one signal  162  comprising information indicative of one or more power delay profile metrics for access nodes  120  contactable by the terminal node  110  and at least one metric  140  indicative of probability of line of sight conditions between the terminal node  110  and the access nodes  120 . 
     Any suitable information indicative of the power delay profile metrics and at least one metric  140  can be used. For example, the values determined for the metrics can be provided in the at least one signal  162 . 
     In examples, the most recent entry in the data structure illustrated in table 1 is provided in the at least one signal  162 . 
     In the example of  FIG.  3    the location server  112  then performs the method  200  of  FIG.  2    based, at least in part, on the information received from the terminal node  110  in the at least one signal  162  to determine a position/location estimate of the UE  164 . 
     Accordingly, in the example of  FIG.  3   , determining at least one time delay value  138  (block  202  of method  200 ) and determining at least one metric  140  (block  204  of method  200 ) comprises receiving one or more signals  162  from the terminal node  110 . 
     In examples, the location server  112  can refine and/or correct the at least one metric  140  received for the access nodes  120  using topology information and/or historical information, for example past metric(s)  140  reported by different terminal nodes  110  located in substantially the same area. 
     Although in the example of  FIG.  3    actions are performed at the terminal node  110  it is to be understood that the method  200  is performed at the server  112  based, at least in part, on information received from the terminal node  110 . 
     In examples, transmitting at least one signal can comprise transmitting at least one message. 
     In some examples the example of  FIG.  3    can comprise transmitting/receiving one or more additional signals (not illustrated) between the server  112  and the terminal node  110 . 
     For example, one or more additional signals can be transmitted between the server  112  and the terminal node  110  to determine the capabilities of the terminal node  110   and/or provide additional information, such as access node identifications and/or locations, to the terminal node  110 . 
     The method  300  illustrated in the example of  FIG.  3    can be considered UE assisted positioning. In this example the location server  112  determines the position estimate based, at least in part, on information provided by the UE  164 . 
     In other examples, the positioning can be UE based. See, for example,  FIG.  4   . 
       FIG.  4    illustrates an example of position estimation of a terminal node  110 . 
       FIG.  4    can also be considered to disclose a method  400 . 
     The example of  FIG.  4    is similar to the example illustrated in  FIG.  3    and also illustrates a terminal node  110  communicating with a server  112 . In the example of  FIG.  4    the terminal node  110  is user equipment (UE)  164  and the server  112  is a location server  112 . 
     At block  402 , at least one signal  163  is transmitted from the location server  112  to the UE  164 . In examples, the at least one signal  163  can be as described in relation to  FIG.  3   . 
     In some examples, the at least one signal  163  in  FIG.  4    can be different and comprises information indicative of a request for the terminal node  110  to respond with an estimate of the position/location of the terminal node  110 . In some examples the at least one signal  163  of  FIG.  4    can be considered an activation signal. 
     In response to receiving the at least one signal  163  the terminal node  110 , which in the illustrated example is a UE  164 , performs the method  200  of  FIG.  2    to determine a position/location estimate of the terminal node  110 . This is illustrated by the block labelled  200  in the example of  FIG.  4   . 
     Accordingly, in the example of  FIG.  4   , block  202  of method  200  comprises receiving one or more signals from the plurality of access nodes  120 . 
     At block  404 , at least one signal  162  is transmitted from the terminal node  110  to the server  112 . 
     In examples the at least one signal  162  can be as described in relation to  FIG.  3   . 
     In some examples, the at least one signal  162  in the example of  FIG.  4    is different and comprises the position/location estimate of the terminal node  110 . 
     In some examples the example of  FIG.  4    can comprise transmitting/receiving one or more additional signals (not illustrated) between the server  112  and the terminal node  110 . 
     For example, one or more additional signals can be transmitted between the server  112  and the terminal node  110  to determine the capabilities of the terminal node  110  and/or provide additional information, such as access node identifications and/or locations, to the terminal node  110 . 
     The method  400  illustrated in the example of  FIG.  4    can be considered UE based positioning. In this example the UE  164  determines the position estimate and provides it to the location server  112 . 
       FIG.  5    illustrates examples of power delay profiles for a plurality of access nodes  120 . 
     In the example of  FIG.  5    the power delay profiles are determined by a terminal node  110 , such as a UE  164 . 
     In  FIG.  5    power delay profiles for five access nodes  120  are shown. In the illustrated example the power delay profiles are labelled A to E. 
     The power delay profiles show a plurality of time delay values  138  for access nodes 120-A to E. In the illustrated example, the power delay profiles have been determined by cross-correlating received positioning reference signals with locally generated positioning reference signal sequences. 
     It can be seen in  FIG.  5    that power delay profiles A to D comprise a plurality of time delay values  138 . Power delay profiles A to D therefore comprise multipath information. 
     In the example of  FIG.  5   , line of sight time delay values  142  with an associated probability of line of sight conditions above a threshold have been determined for profiles B, D and E. The determination can be as described in relation to block  208  of  FIG.  2   . 
     Accordingly, in the example of  FIG.  5   , the line of sight time delay values  142  of profiles B, D and E are determined to be in the first set  144 . 
     However, the time delay values  138  of profiles A and C are determined to have an associated probability of line of sight conditions below the threshold and are therefore determined to be in the second set  146 . 
     In profile A of  FIG.  5    the threshold used in determination of list Lc is shown as dashed line  166  and the threshold used in determination of channel sparsity is shown as dot-dashed line  168 . See, for example, block  204  of  FIG.  2   . 
     In examples, a line of sight time delay value  142  can be determined for profiles A and C, however this is not marked in  FIG.  5    as it is determined that there is insufficient probability or confidence that the correct line of sight time delay value  142  for profiles A and C has been determined. 
     For example, the time delay values  138  having the highest power can initially be determined as the line of sight time delay values  142  for profiles A and C. This is the time delay value labelled ‘3’ for both profile A and profile C. 
     In the example of  FIG.  5    a position estimate  148  of the terminal node  110  is determined based, at least in part, on the line of sight time delay values  142  in the first set  144 . That is, the line of sight time delay values  142  of profiles B, D and E. This can be as described in relation to block  210  of  FIG.  2   . 
     As described in relation to  FIG.  2   , the position estimate  148  can be used to improve the determination of the line of sight time delay value  142  for profiles A and D. See, for example,  FIGS.  6  and  7   . 
       FIG.  6    illustrates an example scenario.  FIG.  6    illustrates an example of determining a line of sight time delay value  138  based, at least in part on the position estimate  148  of the terminal node  110 . 
     The example of  FIG.  6    corresponds to profile A of  FIG.  5   . 
     In the example of  FIG.  6   , circles are drawn illustrating circles described by the first and second time delay values  138 , labelled ‘1’ and ‘2’ in  FIG.  5   , and the positions of the respective access nodes  120 . 
     In the illustrated example, these can be considered the delays present in list Lc for profile A. 
     Also illustrated in  FIG.  6    is the position estimate  148  relative to the positions of the access nodes  120 . 
     In  FIG.  6   , distances  152  between the position estimate  148  and colinear points on the circles are also shown. 
     It can be seen that the distance  152  for the second time delay value  138  is less than the distance  152  for the first time delay value  138 . 
     Therefore, in this example, the second time delay value  138  of profile A is determined to be the line of sight time delay value  142 . 
     This is illustrated in the example of  FIG.  7    which shows the power delay profile labelled ‘A’ with the determined line of sight time delay value  142  indicated. 
     In examples a similar process could be followed for profile C of  FIG.  5   . 
     Accordingly, a new position estimate for the terminal node  110  can be determined based on the line of sight time delay values  142  for some or all profiles A to E, providing improved accuracy in the position estimate for the terminal node by use of multipath information. 
       FIG.  8 A  illustrates an example of an apparatus  130 , the apparatus may be a controller of an apparatus or device such as terminal node  110 , for example UE  164 , or server  112 , for example location server  112 . 
     Implementation of apparatus  130  may be as controller circuitry. The apparatus  130  may be implemented in hardware alone, have certain aspects in software including firmware alone or can be a combination of hardware and software (including firmware). 
     As illustrated in  FIG.  8 A  the apparatus  130  may be implemented using instructions that enable hardware functionality, for example, by using executable instructions of a computer program  136  in a general-purpose or special-purpose processor  132  that may be stored on a computer readable storage medium (disk, memory etc) to be executed by such a processor  132 . 
     The processor  132  is configured to read from and write to the memory  134 . The processor  132  may also comprise an output interface via which data and/or commands are output by the processor  132  and an input interface via which data and/or commands are input to the processor  132 . 
     The memory  134  stores a computer program  136  comprising computer program instructions (computer program code) that controls the operation of the apparatus  130  when loaded into the processor  132 . The computer program instructions, of the computer program  136 , provide the logic and routines that enables the apparatus to perform the methods illustrated in  FIGS.  2 ,  3  and or  4   . The processor  132  by reading the memory  134  is able to load and execute the computer program  136 . 
     The apparatus  130  therefore comprises:
     at least one processor  132 ; and   at least one memory  134  including computer program code the at least one memory  134  and the computer program code configured to, with the at least one processor  132 , cause the apparatus  130  at least to perform: determining, for a terminal node, at least one time delay value for a plurality of access nodes;   determining at least one metric for the access nodes, the at least one metric indicative of probability of line of sight conditions between the terminal node and the access nodes;   determining, based, at least in part, on the at least one metric, a first set of line of sight time delay values having an associated probability of line of sight conditions above a threshold;   determining, based, at least in part, on the at least one metric, a second set of time delay values having an associated probability of line of sight conditions below the threshold;   determining a position estimate of the terminal node based, at least in part, on the first set of line of sight time delay values;   determining, based at least in part on the position estimate of the terminal node, at least one line of sight time delay value of the second set; and determining a new estimate of the position of the terminal node based, at least in part, on the at least one determined line of sight time delay value of the second set.   

     As illustrated in  FIG.  8 A , the computer program  136  may arrive at the apparatus  130  via any suitable delivery mechanism  137 . The delivery mechanism  137  may be, for example, a machine readable medium, a computer-readable medium, a non-transitory computer-readable storage medium, a computer program product, a memory device, a record medium such as a Compact Disc Read-Only Memory (CD-ROM) or a Digital Versatile Disc (DVD) or a solid state memory, an article of manufacture that comprises or tangibly embodies the computer program  136 . The delivery mechanism may be a signal configured to reliably transfer the computer program  136 . The apparatus  130  may propagate or transmit the computer program  136  as a computer data signal. 
     Computer program instructions for causing an apparatus to perform at least the following or for performing at least the following:
     determining, for a terminal node, at least one time delay value for a plurality of access nodes;   determining at least one metric for the access nodes, the at least one metric indicative of probability of line of sight conditions between the terminal node and the access nodes;   determining, based, at least in part, on the at least one metric, a first set of line of sight time delay values having an associated probability of line of sight conditions above a threshold;   determining, based, at least in part, on the at least one metric, a second set of time delay values having an associated probability of line of sight conditions below the threshold;   determining a position estimate of the terminal node based, at least in part, on the first set of line of sight time delay values;   determining, based at least in part on the position estimate of the terminal node, at least one line of sight time delay value of the second set; and determining a new estimate of the position of the terminal node based, at least in part, on the at least one determined line of sight time delay value of the second set.   

     The computer program instructions may be comprised in a computer program, a non-transitory computer readable medium, a computer program product, a machine readable medium. In some but not necessarily all examples, the computer program instructions may be distributed over more than one computer program. 
     Although the memory  134  is illustrated as a single component/circuitry it may be implemented as one or more separate components/circuitry some or all of which may be integrated/removable and/or may provide permanent/semi-permanent/ dynamic/cached storage. 
     In examples the memory  134  comprises a random access memory  170  and a read only memory  172 . In examples the computer program  136  can be stored in the read only memory  172 . See, for example,  FIG.  8 B   
     In some examples the memory  134  can be split into random access memory  170  and read only memory  172 . 
     Although the processor  132  is illustrated as a single component/circuitry it may be implemented as one or more separate components/circuitry some or all of which may be integrated/removable. The processor  132  may be a single core or multi-core processor. 
     References to ‘computer-readable storage medium’, ‘computer program product’, ‘tangibly embodied computer program’ etc. or a ‘controller’, ‘computer’, ‘processor’ etc. should be understood to encompass not only computers having different architectures such as single /multi- processor architectures and sequential (Von Neumann)/parallel architectures but also specialized circuits such as field-programmable gate arrays (FPGA), application specific circuits (ASIC), signal processing devices and other processing circuitry. References to computer program, instructions, code etc. should be understood to encompass software for a programmable processor or firmware such as, for example, the programmable content of a hardware device whether instructions for a processor, or configuration settings for a fixed-function device, gate array or programmable logic device etc. 
     As used in this application, the term ‘circuitry’ may refer to one or more or all of the following:
     (a) hardware-only circuitry implementations (such as implementations in only analog and/or digital circuitry) and   (b) combinations of hardware circuits and software, such as (as applicable): 
   (i) a combination of analog and/or digital hardware circuit(s) with software/firmware and   (ii) any portions of hardware processor(s) with software (including digital signal processor(s)), software, and memory(ies) that work together to cause an apparatus, such as a mobile phone or server, to perform various functions and   
   (c) hardware circuit(s) and or processor(s), such as a microprocessor(s) or a portion of a microprocessor(s), that requires software (e.g. firmware) for operation, but the software may not be present when it is not needed for operation.   

     This definition of circuitry applies to all uses of this term in this application, including in any claims. As a further example, as used in this application, the term circuitry also covers an implementation of merely a hardware circuit or processor and its (or their) accompanying software and/or firmware. The term circuitry also covers, for example and if applicable to the particular claim element, a baseband integrated circuit for a mobile device or a similar integrated circuit in a server, a cellular network device, or other computing or network device. 
     The blocks illustrated in the  FIGS.  2 ,  3  and or  4    may represent steps in a method and/or sections of code in the computer program  136 . The illustration of a particular order to the blocks does not necessarily imply that there is a required or preferred order for the blocks and the order and arrangement of the block may be varied. Furthermore, it may be possible for some blocks to be omitted. For example, block  216  of  FIG.  2    may be omitted. 
     Where a structural feature has been described, it may be replaced by means for performing one or more of the functions of the structural feature whether that function or those functions are explicitly or implicitly described. 
     Thus, the apparatus can comprise means for:
     determining, for a terminal node, at least one time delay value for a plurality of access nodes;   determining at least one metric for the access nodes, the at least one metric indicative of probability of line of sight conditions between the terminal node and the access nodes;   determining, based, at least in part, on the at least one metric, a first set of line of sight time delay values having an associated probability of line of sight conditions above a threshold;   determining, based, at least in part, on the at least one metric, a second set of time delay values having an associated probability of line of sight conditions below the threshold;   determining a position estimate of the terminal node based, at least in part, on the first set of line of sight time delay values;   determining, based at least in part on the position estimate of the terminal node, at least one line of sight time delay value of the second set; and   determining a new estimate of the position of the terminal node based, at least in part, on the at least one determined line of sight time delay value of the second set.   

     The systems, apparatus, methods and computer programs may use machine learning which can include statistical learning. Machine learning is a field of computer science that gives computers the ability to learn without being explicitly programmed. 
     The computer learns from experience E with respect to some class of tasks T and performance measure P if its performance at tasks in T, as measured by P, improves with experience E. The computer can often learn from prior training data to make predictions on future data. Machine learning includes wholly or partially supervised learning and wholly or partially unsupervised learning. It may enable discrete outputs (for example classification, clustering) and continuous outputs (for example regression). Machine learning may for example be implemented using different approaches such as cost function minimization, artificial neural networks, support vector machines and Bayesian networks for example. Cost function minimization may, for example, be used in linear and polynomial regression and K-means clustering. Artificial neural networks, for example with one or more hidden layers, model complex relationship between input vectors and output vectors. Support vector machines may be used for supervised learning. A Bayesian network is a directed acyclic graph that represents the conditional independence of a number of random variables. 
     The above described examples find application as enabling components of: automotive systems; telecommunication systems; electronic systems including consumer electronic products; distributed computing systems; media systems for generating or rendering media content including audio, visual and audio visual content and mixed, mediated, virtual and/or augmented reality; personal systems including personal health systems or personal fitness systems; navigation systems; user interfaces also known as human machine interfaces; networks including cellular, non-cellular, and optical networks; ad-hoc networks; the internet; the internet of things; virtualized networks; and related software and services. 
     The term ‘comprise’ is used in this document with an inclusive not an exclusive meaning. That is any reference to X comprising Y indicates that X may comprise only one Y or may comprise more than one Y. If it is intended to use ‘comprise’ with an exclusive meaning then it will be made clear in the context by referring to “comprising only one...” or by using “consisting”. 
     In this description, reference has been made to various examples. The description of features or functions in relation to an example indicates that those features or functions are present in that example. The use of the term ‘example’ or ‘for example’ or ‘can’ or ‘may’ in the text denotes, whether explicitly stated or not, that such features or functions are present in at least the described example, whether described as an example or not, and that they can be, but are not necessarily, present in some of or all other examples. Thus ‘example’, ‘for example’, ‘can’ or ‘may’ refers to a particular instance in a class of examples. A property of the instance can be a property of only that instance or a property of the class or a property of a sub-class of the class that includes some but not all of the instances in the class. It is therefore implicitly disclosed that a feature described with reference to one example but not with reference to another example, can where possible be used in that other example as part of a working combination but does not necessarily have to be used in that other example. 
     Although examples have been described in the preceding paragraphs with reference to various examples, it should be appreciated that modifications to the examples given can be made without departing from the scope of the claims. 
     Features described in the preceding description may be used in combinations other than the combinations explicitly described above. 
     Although functions have been described with reference to certain features, those functions may be performable by other features whether described or not. 
     Although features have been described with reference to certain examples, those features may also be present in other examples whether described or not. 
     The term ‘a’ or ‘the’ is used in this document with an inclusive not an exclusive meaning. That is any reference to X comprising a/the Y indicates that X may comprise only one Y or may comprise more than one Y unless the context clearly indicates the contrary. If it is intended to use ‘a’ or ‘the’ with an exclusive meaning then it will be made clear in the context. In some circumstances the use of ‘at least one’ or ‘one or more’ may be used to emphasis an inclusive meaning but the absence of these terms should not be taken to infer any exclusive meaning. 
     The presence of a feature (or combination of features) in a claim is a reference to that feature or (combination of features) itself and also to features that achieve substantially the same technical effect (equivalent features). The equivalent features include, for example, features that are variants and achieve substantially the same result in substantially the same way. The equivalent features include, for example, features that perform substantially the same function, in substantially the same way to achieve substantially the same result. 
     In this description, reference has been made to various examples using adjectives or adjectival phrases to describe characteristics of the examples. Such a description of a characteristic in relation to an example indicates that the characteristic is present in some examples exactly as described and is present in other examples substantially as described. 
     Whilst endeavoring in the foregoing specification to draw attention to those features believed to be of importance it should be understood that the Applicant may seek protection via the claims in respect of any patentable feature or combination of features hereinbefore referred to and/or shown in the drawings whether or not emphasis has been placed thereon.