Patent Publication Number: US-2022236361-A1

Title: Observed Time Difference of Arrival (OTDOA) Positioning in Wireless Communication Networks

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. application Ser. No. 15/721,051, filed on Sep. 29, 2017, entitled “Observed Time Difference of Arrival (OTDOA) Positioning in Wireless Communication Networks”, which application is hereby incorporated herein by reference. 
    
    
     BACKGROUND 
     Wireless communication networks can employ various positioning techniques to determine a position of user equipment. For example, Observed Time Difference of Arrival (OTDOA) positioning is a downlink positioning technique specified in Long Term Evolution (LTE) standards developed by the 3rd Generation Partnership Project (3GPP). OTDOA positioning relies on a target device measuring a difference in the time of arrival of Positioning Reference Signals (PRSs) that the target device receives from neighboring base stations. 
     SUMMARY 
     According to one aspect of the present disclosure, there is provided a first method for Observed Time Difference of Arrival (OTDOA) positioning. The first method can include receiving from a serving cell of a first network assistance data for measuring a time difference of arrival of Positioning Reference Signals (PRSs) that can be received from a plurality of neighboring cells of a second network. The first method can further include receiving from the serving cell a gap pattern for decoding a Master Information Block (MIB) of a first neighboring cell of the plurality of neighboring cells, or a System Frame Number (SFN) offset of the first neighboring cell, and determining an SFN timing of the first neighboring cell based on the gap pattern for decoding the MIB of the first neighboring cell or the SFN offset of the first neighboring cell. In one example, the assistance data includes at least one of cell identity information of the plurality of neighboring cells, PRS configuration information of the plurality of neighboring cells, and SFN timing information of the plurality of neighboring cells each indicating an offset between a neighboring cell or a reference cell that is one of the plurality of neighboring cells. 
     Optionally, embodiments of the first method can further include transmitting a decoding request for a measurement gap for decoding the MIB of the first neighboring cell, the decoding request including an identity of the first neighboring cell without specifying a timing of the measurement gap. The gap pattern can include a measurement gap that matches a MIB transmission of the first neighboring cell. Optionally and alternatively, in any of the preceding aspects, the gap pattern can include a measurement gap having a time length longer than a MIB transmission period of the first neighboring cell. 
     Optionally, in any of the preceding aspects, the first method can further include determining timings of PRS positioning occasions of one or more of the plurality of neighboring cells based on the SFN timing of the first neighboring cell and the assistance data, and transmitting a measurement request for a set of measurement gaps for measuring the PRSs, the measurement request including timings of the set of measurement gaps that match the PRS positioning occasions of the one or more of the plurality of neighboring cells. The first method can further include transmitting measurements of the time difference of arrival of the PRSs obtained by measuring the PRSs during the set of measurement gaps. 
     According to another aspect of the disclosure, there is provided a second method for OTDOA positioning that can include transmitting by a serving cell of a first network to a User Equipment (UE) assistance data for measuring time difference of arrival of PRSs received from a plurality of neighboring cells of a second network at the UE, and transmitting by the serving cell a first gap pattern for decoding a MIB of a first neighboring cell of the plurality of neighboring cells, or an SFN offset of the first neighboring cell, in order to determine an SFN timing of the first neighboring cell at the UE. 
     Optionally, embodiments of the second method can further include receiving by the serving cell a decoding request for a measurement gap for decoding the MIB of the first neighboring cell, the decoding request including an identity of the first neighboring cell without specifying a timing of the measurement gap. Optionally, in any of the preceding aspects, the first gap pattern includes a measurement gap that matches a MIB transmission of the first neighboring cell. Optionally and alternatively, in any of the preceding aspects, the first gap pattern includes a measurement gap having a time length longer than a MIB transmission period of the first neighboring cell. 
     Optionally, in any of the preceding aspects, the second method can further include receiving by the serving cell a measurement request for a set of measurement gaps for measuring the PRSs, the measurement request including timings of the set of measurement gaps that match PRS positioning occasions of one or more of the plurality of neighboring cells, transmitting by the serving cell a second gap pattern including the requested set of measurement gaps in response to receiving the measurement request for the set of measurement gaps, and receiving by the serving cell measurements of the time difference of arrival of the PRSs from the UE. The SFN offset of the first neighboring cell is defined according to a modulus; for example, the SFN offset of the first neighboring cell may be defined modulo 1024. 
     According to a further aspect of the present disclosure, there is provided a UE for OTDOA positioning. The UE can include a memory storage comprising instructions, and one or more processor in communication with the memory. The one or more processors can execute the instructions to receive from a serving cell of a first network assistance data for measuring time difference of arrival of PRSs received from a plurality of neighboring cells of a second network, receive from the serving cell a gap pattern for decoding a MIB of a first neighboring cell of the plurality of neighboring cells, or an SFN offset of the first neighboring cell, and determine an SFN timing of the first neighboring cell based on the gap pattern for decoding the MIB of the first neighboring cell or the SFN offset of the first neighboring cell. 
     Optionally, in an embodiment of the UE, the one or more processor can execute the instructions to transmit a decoding request for a measurement gap for decoding the MIB of the first neighboring cell, the decoding request including an identity of the first neighboring cell without specifying a timing of the measurement gap. The gap pattern can include a measurement gap that matches a MIB transmission of the first neighboring cell. Optionally and alternatively, in any of the preceding aspects the gap pattern can include a measurement gap having a time length longer than a MIB transmission period of the first neighboring cell. 
     Optionally, in any of the preceding aspects, the one or more processor can execute the instructions to determine timings of PRS positioning occasions of one or more of the plurality of neighboring cells based on the SFN timing of the first neighboring cell and the assistance data, and transmit a measurement request for a set of measurement gaps for measuring the PRSs, the measurement request including timings of the set of measurement gaps that match the PRS positioning occasions of the one or more of the plurality of neighboring cells. In any of the preceding aspects, the one or more processor can execute the instructions to transmit measurements of the time difference of arrival of the PRSs obtained by measuring the PRSs during the set of measurement gaps. The first network can be an NR network, and the second network can be an LTE network. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Various embodiments of this disclosure that are proposed as examples will be described in detail with reference to the following figures, wherein like numerals reference like elements, and wherein: 
         FIG. 1  shows an exemplary communication network that includes a Long Term Evolution (LTE) network and a New Radio (NR) network; 
         FIG. 2  shows an exemplary Positioning Reference Signal (PRS) configuration according to an embodiment of the disclosure; 
         FIG. 3  shows an example Reference Signal Time Difference (RSTD) measurement process according to an embodiment of the disclosure; 
         FIG. 4  shows a flowchart of an exemplary Observed Time Difference of Arrival (OTDOA) positioning process according to an embodiment of the disclosure; 
         FIG. 5  shows a flowchart of another exemplary OTDOA positioning process according to an embodiment of the disclosure; 
         FIG. 6  shows an exemplary block diagram of user equipment (UE) according to an embodiment of the disclosure; and 
         FIG. 7  shows an exemplary block diagram of a base station according to an embodiment of the disclosure. 
     
    
    
     DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS 
     Aspects of this disclosure describe a system and method for Observed Time Difference of Arrival (OTDOA) positioning in wireless communication networks. More specifically, the disclosure describes techniques for obtaining a System Frame Number (SFN) of a neighboring cell during an OTDOA positioning process to determine a position of a target device. The neighboring cell can be associated with a first wireless network that is configured to support OTDOA positioning, while the target device can be associated with a second wireless network that does not support OTDOA positioning. 
     During the OTDOA positioning process, a location server can provide the target device with positioning assistance data via the second wireless network. The positioning assistance data can include identification of one or more neighboring cells that belong to the first wireless network and are adjacent to the target device. Further, the assistance data can include positioning reference signal (PRS) timings of each of the neighboring cells that are defined with respect to an SFN timing of the respective neighboring cell, while SFN timings of each neighboring cell can be specified with respect to a reference cell that is a member of the listed neighboring cells. Based on the techniques described herein, an SFN timing of one of the listed neighboring cells can be obtained, and accordingly the timings of the PRSs can be determined. Determining the SFN timing of the reference cell may comprise first determining the SFN timing of a neighboring cell different from the reference cell, followed by inferring, from the SFN timing of the neighboring cell, the SFN timing of the reference cell based on the assistance data. 
       FIG. 1  shows an exemplary communication network  100  that includes a Long Term Evolution (LTE) network  101  and a New Radio (NR) network  102 . The LTE network  101  and the NR network  102  coexist in the communication network  100 . In one example, the LTE network  101  can include an LTE core network  120  and a plurality of eNodeB base stations, such as eNodeB base stations  131 - 133 , that are connected to the LTE core network  120 . The NR network  102  can include an NR core network  150  and a plurality of gNB base stations, such as the gNB base station  160 . In addition, the communication network  100  includes a location server  110  that can be connected to the LTE core network  120  and the NR core network  150 . 
     According to this exemplary embodiment, the LTE network  101  can be a network compliant with 3rd Generation Partnership Project (3GPP) LTE standards, while the NR network  102  can be a network compliant with 3GPP NR standards. While the LTE network  101  and the NR network  102  are used as examples in  FIG. 1 , the present disclosure is not limited to a LTE network and a NR network. The techniques described herein can also be applicable to other types of wireless communication networks that may compliant to other communication standards and coexist with each other. 
     The location server  110  can be deployed as part of either the LTE core network  120  or the NR core network  150 , or can be dependent from the LTE core network  120  and the NR core network  150 . However, the location server  110  can be associated to both of the LTE core network  120  and the NR core network  150 . In one example, the location server  110  performs functions of an Evolved Serving Mobile Location Center (E-SMLC) as defined in LTE standards, and is deployed in the LTE core network  120 . In another example, the location server  110  performs location management functions (LMF) as defined in NR standards as well as functions of an E-SMLC, and is deployed in the NR core network  150 . 
     The eNodeB base stations  131 - 133  can be base stations implementing an eNodeB node specified in the 3GPP LTE standards, while the gNB base station  160  can be a base station implementing a gNB node specified in the 3GPP NR standards. Each base station  131 - 133  or  160  can transmit radio signals towards certain directions to cover a geographical area that is referred to as a cell. A cell can be assigned a cell identity by which it can be identified in the wireless communication network  100 . In  FIG. 1 , cells  141 - 143  are formed by the eNodeB base stations  131 - 133 , respectively, while a cell  161  is formed by the gNB base station  160 . Transmission or reception of signals from a base station can be said to be transmission or reception of the signals from a cell associated with the respective base station. 
     As shown in  FIG. 1 , the communication network can include user equipment (UE)  170 . The UE  170  can be any device capable of wirelessly communicating with the communication network  100 , such as a mobile phone, a laptop computer, a vehicle carried device, and the like. In the  FIG. 1  example, the UE  170  is able to operate on the LTE network  101 , as well as the NR network  102 . Accordingly, the UE  170  includes circuits configured to perform signal processing in accordance with the LTE standards and the NR standards. In one example, the NR network  102  and the LTE network  101  are configured to operate on different frequency bands. For example, the gNB base station  160  operates on millimeter wave bands while eNodeB base stations  131 - 133  operate on frequency bands with lower frequencies. Accordingly, the UE  170  can include a transceiver configured to operate on respective different frequencies. 
     In the  FIG. 1  example, the UE  170  is wirelessly connected to the gNB base station  160 . For example, the UE  170  can operate in a connected mode maintaining a radio resource control (RRC) connection between the UE  170  and the gNB base station  160 . Alternatively, the UE  170  can operate in an idle mode but monitoring signals transmitted from the gNB base station  160 . As shown in  FIG. 1 , the UE  170  is under the coverage of the cells  141 - 143  and  161 . As the UE  170  is connected to the gNB base station  160  and ready to be served by the gNB  160 , the cell  161  is referred to as a serving cell of the UE  170 , while the other cells  141 - 143  are referred to as neighboring cells of the UE  170 . Of course, there can be a plurality of neighboring cells that cover the UE  170 , but are not shown in  FIG. 1 . 
     In one example, the OTDOA positioning, a downlink positioning scheme, is used to locate the UE  170 . In OTDOA positioning, a target device measures PRSs from a plurality of cells that may include a serving cell and/or neighboring cells, and determines differences in time of arrival of PRSs between a reference cell and other cells. For example, the serving cell can be used as the reference cell which provides a time baseline for determining the differences in time of arrival of PRSs. This process is referred to as a Reference Signal Time Difference (RSTD) measurement process. The difference between a pair of cells can determine a hyperbola, and intersections of at least two hyperbolae can determine a position of the target device. Positions of base stations of the measured cells can be used for the determination. 
     In the  FIG. 1  example, the LTE network  101  is configured to support the OTDOA positioning, while the NR network  102  does not support the OTDOA positioning. To facilitate the RSTD measurement, the eNodeB base stations  131 - 133  of the LTE network  101  are configured to transmit PRSs periodically. Transmission of PRSs, referred to as positioning occasions, can be based on a PRS configuration. The PRS configuration specifies when PRS positioning occasions will take place with respect to an SFN of a respective base station transmitting the respective PRSs. 
     In addition, to facilitate the RSTD measurement, the location server  110  can be configured to provide assistance data to the UE  170 , receive RSTD measurements from the UE  170 , and accordingly calculate a location of the UE  170 . Specifically, in one example, the location server  110  can communicate with the eNodeB base stations  131 - 133 , for example, using LTE Positioning Protocol A (LPPa) specified in 3GPP standards. By exchanging of LPPa messages, the location server  110  can collect information from the eNodeB base stations  131 - 133 . For example, the collected information can include PRS configurations, SFN timing information, frame timing information, cell identifications, antenna coordinates corresponding to neighboring cells  141 - 143 . The location server  110  can further generate assistance data based on the collected data (or information from other sources), and provide the assistance data to the UE  170 . In one example, the assistance data is transmitted to the UE  170  using LTE Positioning Protocol (LPP) specified in 3GPP standards. The assistance data can include the PRS configurations, the SFN timing information, the frame timing information, and the cell identities of the neighboring cells  141 - 143 . 
     Assuming the UE  170  is connected to the eNodeB base station  131 , based on the assistance data, the UE  170  can typically determine timings of PRS positioning occasions of the neighboring cells  141 - 143 , and accordingly capture the PRS transmission during the PRS positioning occasions to perform RSTD measurement. For example, in the assistance data, the serving cell  141  can be used as a reference cell, and SFN timings and frame timings of other neighboring cells  142 - 143  can be specified with respect to this reference cell  141 . A frame timing can refer to one of time points when frames are sequentially transmitted. An SFN timing can refer to one of time points when frames having certain SFNs are transmitted. As an example, a frame timing offset of a neighboring cell with respect to the reference cell  141  can be provided in the assistance data, and the corresponding SFN timing information can be provided in a form of an SFN offset with respect to the SFN of the reference cell  141 . In an alternative example, frame boundaries of the serving cell  141  and the neighboring cells  142 - 14  can be synchronized, meaning frame timing offset equals zero. Accordingly, the assistance data may not include frame timing offset information, but includes SFN offset information. 
     As the UE  170  is assumed to be connected to the eNodeB base station  131 , the UE  170  knows SFN timings of its serving cell  141  (frame timings of the serving cell  141  and SFNs of each frame received from the serving cell). Accordingly, the UE  170  may be able to determine frame timings and SFN timings of the neighboring cells  142 - 143  based on the assistance data. 
     As described above, in the  FIG. 1  example the UE  170  is connected to the NR network  102  that does not support the OTDOA positioning, and therefore the above described OTDOA positioning cannot be readily performed to locate the UE  170 . Specifically, the gNB base station  160  may not transmit PRSs due to configuration. In addition, the location server  110  cannot collect information about the serving cell  161  of the UE  170 , and consequently does not include the serving cell  161  as one of the cells listed in assistance data for OTDOA measurement. However, the assistance data can still be transmitted to the UE  170  through the NR core network  150  and the gNB base station  160 , for example, by using the LPP messages. The transmission of the assistance data can be transparent for the gNB base station  160 . For example, the assistance data may be transmitted as signaling of a Non-Access Stratum (NAS) protocol. One of the neighboring cells  141 - 143  can be used as a reference cell in the assistance data, instead of a serving cell. 
     According to an aspect of the disclosure, under the above circumstances where the UE  170  is connected to a serving cell that is not included in positioning assistance data, the UE  170  can obtain an SFN timing of at least one of the neighboring cells included in the assistance data. The at least one of the neighboring cells can be a reference cell as specified in the assistance data, or can be a neighboring cell other than the reference cell. In one example, the UE  170  can read a MIB of a neighboring cell to obtain the SFN information. For example, the UE  170  can send a request to the serving cell  161  for a measurement gap, and can decode a MIB of one of the neighboring cells listed in the assistance data during the measurement gap. In another example, the gNB  160  can provide an SFN offset and a frame timing offset of a neighboring cell listed in the assistance data to the UE  170  as a response to a request from the UE  170 . As a result, a location of the UE  170  being connected to a network that does not support the OTDOA positioning can be determined. 
     In various examples, the SFN timing of a neighboring cell can be represented as a combination of a frame timing offset with respect to the serving cell  161  (or in other words, a frame timing difference between the neighboring cell and the serving cell  161 ) and an SFN of the neighboring cell. Accordingly, obtaining an SFN timing of the neighboring cell is equivalent to obtaining a frame timing offset and an SFN of the neighboring cell. While in  FIG. 1  example three neighboring cells  141 - 143  are listed as neighboring cells in the assistance data, number of neighboring cells listed in assistance data can be more than three, for example, 10, 20 or more than 20 in other examples. 
       FIG. 2  shows an exemplary PRS configuration  200  according to an embodiment of the disclosure. A sequence of sub-frames  201  starting at a first sub-frame of a frame with SFN=0 is shown in  FIG. 2 . PRS positioning occasions  210   a - 210   c  take place periodically among the sequence of sub-frames  201 . The PRS configuration  200  in the time domain can be defined by three parameters. A first parameter  210  is PRS positioning occasion that refers to a number of consecutive sub-frames that carry PRSs. For example, each of the PRS positioning occasions  210   a ,  210   b , or  210   c  can include 1, 2, 4, or 6 sub-frames. A second parameter  220  is PRS transmission period  220 . For example, a PRS transmission period can last for 160, 320, 640, or 1280 sub-frames. A third parameter is PRS sub-frame offset that refers to a number of sub-frames before the first PRS positioning occasion  210   a  since the beginning of the first frame with SFN=0. As shown, when SFN timings of the sequence of sub-frames are known, PRS positioning occasion timings can be determined based on the PRS configuration. 
       FIG. 3  shows an example RSTD measurement process  300  according to an embodiment of the disclosure. During the process  300 , an SFN of a neighboring cell is obtained by reading a MIB of the neighboring cell. In the  FIG. 3  example, the UE  170  is connected to the NR serving cell  161 , and the LTE neighboring cell  141  is used as a reference cell in the assistance data provided by the location server  110 . The process  300  can be performed to obtain an SFN of the neighboring cell  141  as well as frame timings of the neighboring cell  141 . 
     Three time lines  310 - 330  corresponding to the LTE neighboring cell  141 , the NR serving cell  161 , and the UE  170 , respectively, are shown in  FIG. 3 . The first timeline  310  includes a sequence of sub-frames  301 - 306  carrying MIBs. Each of the sub-frames  301 - 306  can be a first sub-frame of one of a sequence of consecutive frames transmitted from the neighboring cell  141 . Thus, the MIBs have a transmission period of one frame. Each MIB can carry SFN information, and decoding a MIB can obtain an SFN of a respective frame that carries the MIB. Each sub-frame  301 - 306  can also carry one or more synchronization sequences transmitted before the SFN information, such as primary synchronization signal (PSS) and secondary synchronization signal (SSS). The UE  170  can accordingly obtain the frame timings of the neighboring cell  141  by reading those synchronization sequences. In addition, the first time line  310  also shows a sequence of PRS positioning occasions  311 - 312 . PRSs of the PRS positioning occasions  311 - 312  are transmitted from the neighboring cell  141  according to a PRS configuration. 
     The second time line  320  includes multiple measurement gaps  321 - 323 . A measurement gap refers to a time period configured for performing an inter-frequency measurement. For example, a UE is connected to a serving cell operating on a first carrier frequency, and performs a measurement (such as RSTD measurement) of signals received from a neighboring cell operating on a second carrier frequency. The UE can send a request through an RRC connection to the serving cell for one or more measurement gaps. Optionally, in the request, timings and duration of the measurement gaps can be specified. As a response to the request, the serving cell can configure the measurement gaps for the UE and return a measurement gap pattern. For example, a measurement gap pattern can include one or more measurement gaps that each has a starting time and a time length. During the measurement gaps, no uplink or downlink data transmission is scheduled for the UE. The UE can switch from the serving cell frequency to the neighboring cell frequency to perform an inter-frequency measurement, and subsequently switch back to the serving cell. Duration of a measurement gap can include time for switching between different carrier frequencies, and time for performing the measurement. 
     In a first example, the serving cell  161  of the NR network  102  knows frame timings of the neighboring cell  141  of the LTE network  101 . For example, as part of a configuration of the NR network  102 , frame timings of the neighboring cell  141  are provided to the serving cell  161  in a form of frame timing offsets with respect to the serving cell  161 . Accordingly, when requesting a measurement gap for reading a MIB of the neighboring cell  141 , the UE  170  can specify a purpose of the measurement gap (to read MIB) but without specifying a particular time of the measurement gap. The serving cell  161  knows MIB timings (frame timings) of the neighboring cell  141 , and can accordingly schedule a measurement gap  321  that matches a transmission of a MIB, such as the sub-frame  302  in the  FIG. 3  example. In one example, the measurement gap  321  lasts for about 2 ms. In alternative examples, the measurement gap  321  can take other lengths. 
     In a second example, the serving cell  161  does not have knowledge of frame timings of the neighboring cell  141 . In this case, a longer measurement gap  323  than the measurement gap  321  can be configured. For example, the measurement gap  323  can have duration suitable for the UE  170  to decode a MIB of the neighboring cell  141  without knowing the frame timings. In one example, the measurement gap  323  has a time length longer than a frame. For example, frames on time line  310  have duration of 10 ms, and the measurement gap  323  is configured to be about 11 ms or longer than 11 ms. Under such configuration, at least one sub-frame carrying a MIB can be captured within the span of the measurement gap  323 . In alternative example, more than one measurement gap  321  or  323  can be configured. For example, when the neighboring cell is of low signal quality, decoding MIBs may be tried more than once. The timing of the more than one measurement gap may facilitate receiver behaviors such as combining of different transmission instances of the MIB, for instance, allowing the receiver to overcome bad radio conditions. 
     The measurement gap  322  can be configured for RSTD measurement. For example, after SFN and frame timing of the neighboring cell  141  are obtained, based on assistance data from the location server  110 , the UE  170  can determine timings of PRS positioning occasions of the neighboring cells  141 - 143 . Accordingly, the UE  170  can send a second gap request to the serving cell  161  specifying a gap pattern including one or more measurement gaps matching the PRS positioning occasions of the neighboring cells  141 - 143 . 
     In one example, the neighboring cells  141 - 143  operate on a same frequency, and frame timings of the neighboring cells  141 - 143  are synchronized. In addition, PRS configurations of the neighboring cells  141 - 143  are configured in a way that the PRS positioning occasions of the neighboring cells  141 - 143  are aligned in time (transmitted during a same sub-frame). In this case, one measurement gap  322  can be used to perform the RSTD measurement towards PRSs from the three neighboring cells  141 - 143 . In one example, a time length of the measurement gap  322  can be determined based on duration of the to-be-measured PRS positioning occasions in addition to time used for switching between different carrier frequencies. 
     In another example, PRS positioning occasions of the neighboring cells  141 - 143  can take place at different times, for example, due to PRS configurations or asynchronization among the neighboring cells  141 - 143 . Or, the neighboring cells  141 - 143  can operate on different carrier frequencies which may require RSTD measurement be performed separately on different carrier frequencies. Accordingly, multiple measure gaps can be configured for the RSTD measurement. 
     As shown, the process  300  includes multiple steps  341 - 344 . At step  341 , the UE  170  sends a first gap request (also referred to as a decoding request) for a first measurement gap in order to decode a MIB of the neighboring cell  141 . The first gap request may not include a timing of the measurement gap. As a response to the first gap request, the measurement gap  321  or  323  can be configured by the serving cell  161  depending on whether the serving cell  161  knows the frame timings of the neighboring cell  141 . At step  342 , the UE  170  decodes a MIB carried on the sub-frame  302  during the measurement gap  321 , or decodes a MIB carried on a sub-frame within the measurement gap  323 , to obtain the SFN. At the same time, based on synchronization sequences carried on a sub-frame, frame timings of the neighboring cell  141  can be obtained before decoding the MIB. For example, the UE  170  can first read the synchronization sequences in the sub-frame  302  to obtain a timing of the sub-frame  302 , and subsequently read the MIB of the sub-frame  302 . 
     At step  343 , the UE  170  sends a second gap request (also referred to as a measurement request) for a second measurement gap for RSTD measurement. Accordingly, assuming PRS positioning occasions of the neighboring cells  141 - 143  are time aligned and on a same carrier frequency, the measurement gap  322  can be scheduled that matches the timings of PRS positioning occasions of the neighboring cells  141 - 143 . At step  344 , PRSs from the neighboring cells  141 - 143  can be received and measured. Time differences of arrival of the PRSs can accordingly be obtained. In examples where assistance data includes more than three neighboring cells, the RSTD measurement may be performed only on a portion of all the listed neighboring cells. For example, the UE  170  may send a second gap request that includes measurement gaps matching PRS positioning occasions of a part of all listed neighboring cells. 
       FIG. 4  shows a flowchart of an exemplary OTDOA positioning process  400  according to an embodiment of the disclosure. With reference to  FIG. 1 , such process  400  can be performed in the wireless communication network  100  to locate the UE  170 . Messages corresponding to different steps of the process  400  are shown transmitted among the UE  170 , the gNB base station  160 , the eNodeB base stations  131 - 133 , and the location server  110 . Particularly, during the process  400 , the UE  170  requests a measurement gap from the serving cell  161  and reads a MIB of the neighboring cell  141  to obtain an SFN of the neighboring cell  141 . 
     At step  410 , assistance data and a request for RSTD measurements can be transmitted from the location server  110  to the UE  170  through the serving cell  161 . In one example, LPP messages are used for the transmission of the assistance data. The assistance data can include a list of neighboring cells, for example, the neighboring cells  141 - 143 . One of the neighboring cells  141 - 143  is used as a reference cell, for example, the neighboring cell  141 . The assistance data can also include SFN offsets and/or frame timing offsets of the neighboring cells  142 - 143  with respect to the reference cell  141 . The assistance data can further include PRS configurations of each neighboring cell  141 - 143 . The assistance data can include other information useful for RSTD measurement. 
     At step  412 , a first request for a measurement gap to read MIB can be transmitted from the UE  170  to the gNB base station  160 , for example, by sending an RRC message. The request may not specify when the measurement gap is supposed to take place because the UE  170  does not have knowledge of frame timings of the neighboring cells  141 - 143 . However, the request may specify the purpose to read a MIB, and include an identity of the reference cell  141 . It is noted that obtaining an SFN of any one of the neighboring cells listed in the assistance data is sufficient to determine SFN timings and PRS positioning occasion timings of each neighboring cells. Accordingly, the request may include an identity of any one of the neighboring cells  141 - 143  other than the reference cell  141  in order to carry out RSTD measurement. 
     At step  414 , a first gap pattern can be transmitted from the gNB base station  160  to the UE  170 , for example, by sending an RRC message. The first gap pattern can include configuration information of a measurement gap, such as duration and starting time of the measurement gap. In a first scenario, the gNB base station  160  can have knowledge of frame timings of the reference cell  141 . Accordingly, the gNB base station  160  can determine when the measurement gap for reading a MIB is to be scheduled. A measurement gap matching transmission of the MIB can be determined. In a second scenario, the gNB base station  160  may not know frame timings of the reference cell  141 . Accordingly, a measurement gap with a time length larger than a MIB transmission period can be configured. The resultant measurement gap provides sufficient time for the UE  170  to decode a MIB. 
     At step  416 , a MIB of the reference cell  141  can be read by the UE  170  during the measurement gap specified in the first gap pattern. The UE  170  decodes the MIB to obtain an SFN. At the same time, a frame timing of the reference cell  141  can be obtained according to synchronization sequences carried in a sub-frame carrying the MIB. Alternatively, frame timings of the reference cell  141  can be obtained by receiving a frame timing offset of the reference cell  141  from the gNB base station  160  when the gNB base station  160  knows the frame timings of the reference cell  141 . Based on the assistance data and the above obtained frame timing and SFN, the UE  170  can determine timings of PRS positioning occasions of the neighboring cells  141 - 143 . 
     At step  418 , a second request for measurement gaps for RSTD measurement can be transmitted from the UE  170  to the gNB base station  160 , for example, by sending an RRC message. The request may include timings of the measurement gaps that match PRS positioning occasion timings obtained at step  416 . When PRS positioning occasions of the neighboring cells  141 - 143  are aligned in time, one measurement gap can be requested for the RSTD measurement. Alternatively, when PRS positioning occasions of the neighboring cells  141 - 143  occur at different times or the neighboring cells  141 - 143  operate on different carrier frequencies, more than one measurement gaps may be requested. In addition, in some examples, duration of the measurement gaps can be specified according to duration of respective PRS positioning occasions. At step  420 , a second gap pattern can be transmitted from the gNB base station  160  to the UE  170  to inform the UE  170  that the requested measurement gaps have been scheduled. For example, an RRC message can be used for transmission of the second gap pattern. The gap pattern can be determined based on information carried in the second gap request. 
     At step  422 , PRSs from the multiple neighboring cells  141 - 143  can be received and measured at the UE  170  during the measurement gap (s) of the second gap pattern. At step  424 , RSTD measurements can be calculated based on measured times of arrivals of the PRSs from the neighboring cells  141 - 143 . For example, using the reference cell  141  as a time basis, time differences of arrival of PRSs between the reference cell  141  and other neighboring cells  142 - 143  can be determined. 
     At step  426 , the RSTD measurements can be transmitted from the UE  170  to the location server  110 , for example, by transmitting an LPP message. The location server  110  can accordingly estimate the position of the UE  170  based on the RSTD measurements. In alternative examples, the RSTD measurements may not be transmitted to the location server  110 . Instead, the UE  170  itself can use the RSTD measurements to determine a location of the UE  170  with base station location information included in the assistance data. 
       FIG. 5  shows a flowchart of another exemplary OTDOA positioning process  500  according to an embodiment of the disclosure. With reference to  FIG. 1 , such process  500  can be performed in the wireless communication network  100  to locate the UE  170 . Similarly, messages corresponding to different steps of the process  500  are shown transmitted among the UE  170 , the gNB base station  160 , the eNodeB base stations  131 - 133 , and the location server  110 . Different from the process  400 , during the process  500 , the UE  170  can request SFN timing information of a neighboring cell listed in the assistance data from the serving cell  161 . 
     The process  500  includes steps that are similar to that of the process  400 . For example, steps  510 ,  518 - 526  are similar to the steps of  410 ,  418 - 426 . However, steps  512 - 516  are different from the steps  412 - 416 . Description of steps  510 ,  518 - 526  is omitted while steps  512 - 516  are described below. 
     At step  512 , a request for SFN timing information of a neighboring cell  141 - 143  can be transmitted from the UE  170  to the serving cell  161 , for example, by sending an RRC message. For example, assistance data received at step  510  can include a list of neighboring cells, for example, the neighboring cells  141 - 143 , that are to be measured. The neighboring cell  141  can be used as a reference cell, and frame timing offsets and SFN offsets of other neighboring cells  141 - 143  can be specified in the assistance data with respect to the reference cell  141 . Accordingly, the request can include an identity of the reference cell  141 . 
     At step  514 , SFN timing information can be transmitted from the serving cell  161  to the UE  170  as a response to the request at step  512 . For example, the gNB base station  160  can have knowledge of SFN timings of the neighboring cells  141 - 143  due to configuration of the NR network  102 . In one example, the SFN timing information includes a frame timing offset and an SFN offset of the reference cell  141  with respect to frame timing and SFN of the serving cell  161 . In one example, the SFN timing information is carried in an RRC message specific to transmission of the SFN timing information. In another example, a neighboring cell list as on-demand system information can be transmitted to the UE  170 . SFN timings of the neighboring cells  141 - 143  can be included in entries of the neighboring cell list. 
     In one example, an SFN of the NR network  102  has a length that is longer than an SFN of the LTE network  101 . For example, an NR SFN may have a length of 12 bits while an LTE SFN may have a length of 10 bits. Accordingly, an SFN offset between the LTE SFN and the NR SFN can be defined modulo 1024 (with respect to a modulus of 1024). For example, an SFN offset between the LTE network  101  and the NR network  102  can be calculated using the following expression, 
       SFN offset=(LTE SFN−NR SFN)mod 1024,
 
     where LTE SFN and NR SFN correspond to SFNs of an NR LTE frame and an LTE frame under comparison. 
     At step  516 , gap timings needed for RSTD measurement are determined at the UE  170 . For example, based on the assistance data and the received SFN timing information of the reference cells  141 - 143 , timings of PRS positioning occasions of the neighboring cells  141 - 143  can be determined. Accordingly, timings of measurement gaps can be determined. Depending on whether the PRS positioning occasions of the neighboring cells  141 - 143  are aligned in time, or whether the neighboring cells  141 - 143  operates on different carrier frequencies, one or more measurement gaps can be scheduled. A request for a measurement gap including timings of at least one gap can subsequently be transmitted. 
       FIG. 6  shows an exemplary block diagram of a UE  600  according to an embodiment of the disclosure. The UE  600  can be configured to implement various embodiments of the disclosure described herein. The UE  600  can include a processor  610 , a memory  620 , and a radio frequency (RF) module  630  that are coupled together as shown in  FIG. 6 . In different examples, the UE  600  can be a mobile phone, a tablet computer, a desktop computer, a vehicle carried device, and the like. 
     The processor  610  can be configured to perform various functions of the UE  170  described above with reference to  FIGS. 1-5 . For example, the processor  610  can be configured to receive assistance data from a location server, and accordingly perform RSTD measurement and report RSTD measurements to the location server. Particularly, the processor  610  can be configured to request a measurement gap from a serving cell of the UE  600  and conduct a MIB decoding process to obtain SFN of a reference cell included in a list of neighboring cells in the assistance data. Alternatively, the processor  610  can be configured to request SFN timing information of the reference cell. Further, the processor  610  can be configured to subsequently determine PRS positioning occasions of the neighboring cells, and accordingly request a set of measurement gaps to perform the RSTD measurement towards the PRSs from the neighboring cells. 
     The UE  600  can operate on different types of wireless networks, such as an LTE network, a 5G NR network, and the like. Accordingly, the processor  610  can include signal processing circuitry to process received or to be transmitted data according to communication protocols corresponding to different types of wireless networks. Additionally, the processor  610  may execute program instructions, for example, stored in the memory  620 , to perform functions related with different communication protocols. The processor  610  can be implemented with suitable hardware, software, or a combination thereof. For example, the processor  610  can be implemented with application specific integrated circuits (ASIC), field programmable gate arrays (FPGA), and the like, that includes circuitry. The circuitry can be configured to perform various functions of the processor  610 . 
     In one example, the memory  620  can store program instructions that, when executed by the processor  610 , cause the processor  610  to perform various functions as described herein. For example, the memory  620  can store program instructions  621  for performing an OTDOA positioning process as described in this disclosure. In addition, the memory  620  can store data related with the OTDOA positioning process, such as positioning assistance data  622 , RSTD measurements  623 , and the like. The memory  620  can include a read only memory (ROM), a random access memory (RAM), a flash memory, a solid state memory, a hard disk drive, and the like. 
     The RF module  630  can be configured to receive a digital signal from the processor  610  and accordingly transmit a signal to a base station in a wireless communication network via an antenna  640 . In addition, the RF module  630  can be configured to receive a wireless signal from a base station and accordingly generate a digital signal which is provided to the processor  610 . The RF module  630  can include digital to analog/analog to digital converters (DAC/ADC), frequency down/up converters, filters, and amplifiers for reception and transmission operations. Particularly, the RF module  630  can include signal processing circuits to support the UE  170  to operate on different types of wireless communication networks, such as a LTE network, a 5G NR network, and the like. For example, the RF module  630  can include converter circuits, filter circuits, amplification circuits, and the like, for processing signals on different carrier frequencies. 
     The UE  600  can optionally include other components, such as input and output devices, additional CPU or signal processing circuitry, and the like. Accordingly, the UE  600  may be capable of performing other additional functions, such as executing application programs, and processing alternative communication protocols. 
       FIG. 7  shows an exemplary block diagram of a base station  700  according to an embodiment of the disclosure. The base station  700  can be configured to implement various embodiments of the disclosure described herein. Similarly, the base station  700  can include a processor  710 , a memory  720 , and a radio frequency (RF) module  730 . Those components are coupled together as shown in  FIG. 7 . In different examples, the base station can be an eNodeB in an LTE network, a gNB in an NR network, and the like. 
     The processor  710  can be configured to perform various functions of the gNB base station  160  described with reference to  FIGS. 1-5 . For example, the processor  710  can be configured to schedule a measurement gap for a UE to decode MIB of a reference cell to obtain SFN of the reference cell during an OTDOA positioning process. When the base station  700  is configured with frame timings of the reference cell, the measurement gap can be configured in a way that the measurement gap matches a MIB transmission of the reference cell. When the base station  700  does not know frame timings of the reference cell, a measurement gap having a time length longer than a MIB transmission period of the reference cell can be configured. Alternatively, the processor  710  can be configured to provide an SFN offset and frame timing offset to the UE as a response to a request from the UE. 
     The processor  710  can include signal processing circuits for signal processing according to various communication protocols, such as protocols specified in the 3GPP LTE or 5G NR standards. The processor  710  can also be configured to execute program instructions to carry out various functions according to the various communication protocols. The processor  710  can be implemented with hardware, software, or a combination thereof. For example, the processor  710  can be implemented with application specific integrated circuits (ASIC), field programmable gate arrays (FPGA), and the like, that includes circuitry. The circuitry can be configured to perform various functions of the processor  710 . 
     In one example, the memory  720  can store program instructions that, when executed by the processor  710 , cause the processor  710  to perform various functions described herein. For example, the memory  720  can store program instructions  721  for scheduling measurement gaps as described in this disclosure. In addition, the memory  720  can store data related with an OTDOA positioning process, such as neighboring cell frame timing offsets and/or SFN offsets  722  depending on configuration of the base station  700 . Similarly, the memory  720  can include a read only memory (ROM), a random access memory (RAM), a flash memory, a solid state memory, a hard disk drive, and the like. 
     The RF module  730  can have functions and structure similar to that of the RF module  630 . However, the RF module  730  can have functions and structures more suitable for performance of the base station  700 . For example, the RF module  730  can have a higher transmission power for coverage of a large serving area and multiple UE users, or support more downlink or uplink component carriers. The RF module  730  can receive or transmit wireless signals via an antenna  740 . 
     In the claims, the word “comprising” does not exclude other elements or steps, and the indefinite article “a” or “an” does not exclude a plurality. A single processor or other unit may fulfill the functions of several items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate, preclude or suggest that a combination of these measures cannot be used to advantage. A computer program may be stored or distributed on a suitable medium, such as an optical storage medium or a solid-state medium supplied together with, or as part of, other hardware, but may also be distributed in other forms, such as via the Internet or other wired or wireless telecommunication systems. 
     While aspects of the present disclosure have been described in conjunction with the specific embodiments thereof that are proposed as examples, alternatives, modifications, and variations to the examples may be made. Accordingly, embodiments as set forth herein are intended to be illustrative and not limiting. There are changes that may be made without departing from the scope of the claims set forth below.