HK1184010A - Methods and apparatus for supporting inter-frequency measurements - Google Patents

Description

Method and apparatus for supporting inter-frequency measurements

Technical Field

The present invention relates generally to inter-frequency measurements in wireless communication networks, and in particular to signaling support for such measurements in wireless network architectures using signal measurements from multiple cells for e.g. positioning services, location services and location based services.

Background

The Universal Mobile Telecommunications System (UMTS) is one of the third generation mobile communication technologies designed to take over GSM. The 3GPP Long Term Evolution (LTE) is an item in the third generation partnership project (3GPP) to improve the UMTS standard to meet future demands for improved services, such as higher data rates, increased efficiency and reduced costs. The Universal Terrestrial Radio Access Network (UTRAN) is the radio access network of UMTS, while the evolved UTRAN (E-UTRAN) is the radio access network of LTE systems. In E-UTRAN, a wireless device, such as User Equipment (UE)150a, is wirelessly connected to a Radio Base Station (RBS)110a, commonly referred to as evolved nodeb (enodeb), as shown in fig. 1 a. Each eNodeB 110a, 110b serves one or more areas, each referred to as a cell 120a, 120b, and is connected to a core network. In LTE, the enodebs 110a, 110b are connected to a Mobility Management Entity (MME) (not shown) in the core network. The positioning server 140 (also called location server) in the control plane architecture in fig. 1a is connected to the MME. The positioning server 140 is a physical or logical entity that manages positioning for a so-called target device, i.e., a wireless device being positioned. The location server is in a control plane architecture also referred to as an evolved serving mobile location center (E-SMLC). As shown in fig. 1a, the E-SMLC 140 may be a separate network node, but it may also be functionality integrated in some other network node. In the user plane architecture, positioning is part of a Secure User Plane Location (SUPL) location platform (SLP). The positioning server may be connected to the radio network node via a logical link while using one or more physical connections via other network nodes, e.g. MME. A Network Management (NM) or operations and maintenance (O & M) node 141 may be provided to perform various network management operations and activities in the network.

The possibility of identifying the geographic location of users in a network has enabled a number of commercial and non-commercial services such as navigation assistance, social networking, location-aware advertising, and emergency calls, among others. Different services may have different positioning accuracy requirements imposed by the application. In addition, in some countries there are some regulatory requirements on the positioning accuracy of basic emergency services, such as FCC E911 in the united states.

Three key network elements in the LTE positioning architecture are a location services (LCS) client, an LCS target, and an LCS server. The LCS server is a physical or logical entity that manages the positioning of the LCS target device by collecting measurements and other location information, assisting the terminal in making measurements when necessary, and estimating the LCS target location. An LCS client is a software and/or hardware entity interacting with an LCS server in order to obtain location information for one or more LCS targets, i.e. located entities. The LCS client may reside in the LCS target itself. The LCS client sends a request to the LCS server for location information, and the LCS server processes and services the received request and sends the positioning result and optionally the velocity estimate to the LCS client. The location request can originate from a terminal or a network.

Two positioning protocols operating via a radio network exist in LTE, namely the LTE Positioning Protocol (LPP) and the LPP annex (LPPa). LPP is a point-to-point protocol used between an LCS server and an LCS target device to locate the target device. LPP can be used in both the user and control planes and multiple LPP processes in series and/or parallel are allowed, thereby reducing latency. In the control plane, LPP uses the RRC protocol as transport.

LPPa is a protocol between eNodeB and LCS server primarily specified for control plane positioning procedures, but it can still assist user plane positioning by querying enodebs for information and eNodeB measurements. A Secure User Plane (SUPL) protocol is used as a transport for LPP in the user plane. LPP also has the possibility to pass LPP extension messages inside LPP messages, e.g. specifying the current Open Mobile Alliance (OMA) LPP extensions (LPPe) in order to allow e.g. operator or manufacturer specific assistance data or assistance data not available for LPP, or to support other location reporting formats or new positioning methods. LPPe may also be embedded in messages of other positioning protocols that are not necessarily LPP.

One advanced architecture currently being standardized in LTE is shown in fig. 2, where the LCS target is a terminal 200 and the LCS server is an E-SMLC 201 or SLP 202. In the figure, the control plane location protocol with E-SMLC as termination point is illustrated by arrows 203, 204 and 205 and the user plane location protocol is illustrated by arrows 206 and 207. The SLP 202 may comprise two components, a SUPL Positioning Center (SPC) and a SUPL Location Center (SLC), which may also reside in different nodes. In one exemplary implementation, the SPC has a proprietary interface with the E-SMLC 201 and a LIp interface with the SLC, and the SLC portion of the SLP communicates with a PDN gateway (P-GW) (not shown) and an external LCS client 208.

Additional positioning infrastructure elements may also be deployed to further enhance the performance of a particular positioning method. For example, deploying radio beacons is a cost-effective solution that can significantly improve positioning performance indoors and also outdoors by allowing more accurate positioning, e.g., using proximity location technology.

UE positioning is the process of determining UE coordinates in space. Once these coordinates are available, they may be mapped to a certain place or location. The mapping function and the delivery of location information on request are part of the location service required for basic emergency services. Services that further exploit or are based on location knowledge to provide some added value to customers are referred to as location-aware and location-based services. The possibility of identifying the geographic location of wireless devices in a network has enabled a number of commercial and non-commercial services, such as navigation assistance, social networking, location-aware advertising, and emergency calls. Different services may have different positioning accuracy requirements imposed by the application. Furthermore, there are requirements in some countries for the positioning accuracy of basic emergency services defined by regulatory bodies. An example of such a regulatory body is the federal communications commission that regulates the telecommunications field of the united states.

In many environments, wireless device location can be accurately estimated by using Global Positioning System (GPS) based positioning methods. Today, networks also often have the following possibilities: wireless devices are assisted to improve the device receiver sensitivity and GPS start-up performance as in, for example, assisted GPS (a-GPS) positioning methods. However, a GPS or a-GPS receiver may not necessarily be available in all wireless devices. Furthermore, GPS is known to often fail in indoor environments and urban canyons. Therefore, a supplementary terrestrial positioning method called observed time difference of arrival (OTDOA) has been standardized by 3 GPP. In addition to OTDOA, the LTE standard also specifies methods, procedures and signaling support for enhanced cell ID (E-CID) and assisted global navigation satellite system (a-GNSS) positioning. In the future, uplink time difference of arrival (UTDOA) may also be standardized for LTE.

OTDOA positioning

With OTDOA, a wireless device, such as a UE, measures the timing differences of downlink reference signals received from multiple different locations. For each measured neighbor cell, the UE measures a Reference Signal Time Difference (RSTD) which is a relative timing difference between the neighbor cell and a reference cell. As shown in fig. 3, the UE location estimate is then looked up as the intersection 430 of hyperbolas 440 corresponding to the measured RSTD. To find the two coordinates of the UE, at least three measurements from geographically dispersed RBSs 410a-c with good geometry are needed. To find this position, accurate knowledge of the transmitter position and the transmit timing offset is required. The position calculation may be performed, for example, by a positioning node such as E-SMLC or SLP in LTE or by the UE. The former approach corresponds to a UE-assisted positioning mode, while the latter approach corresponds to a UE-based positioning mode.

In UTRAN Frequency Division Duplex (FDD), SFN-SFN type 2 measurements (SFN stands for system frame number) performed by the UE are used for OTDOA positioning methods. The measurement is based on the relative timing difference between cell j and cell i of the primary common pilot channel (CPICH) from cell j and cell i. The SFN-SFN type 2 reported by the UE is used by the network to estimate the UE location.

Positioning reference signal

In order to enable positioning in LTE and to facilitate positioning measurements of a suitable quality and for a sufficient number of different locations, physical signals dedicated to positioning, such as Positioning Reference Signals (PRS), have been introduced in 3GPP and low interference positioning subframes have been specified. PRSs are transmitted from one antenna port R6 in a predefined pattern, as described in more detail below.

A frequency shift as a function of Physical Cell Identity (PCI) can be applied to the designated PRS patterns to generate orthogonal patterns and model for effective frequency reuse of six, which makes it possible to significantly reduce the interference of neighboring cells on the measured PRS and thus improve positioning measurements. Even though PRS have been specifically designed for positioning measurements and are generally characterized by better signal quality than other reference signals, the standard does not mandate the use of PRS. Other reference signals, such as cell-specific reference signals (CRS), may also be used for positioning measurements.

The PRS are transmitted in a predefined pattern and following one of the predefined PRS configurations. PRS are transmitted in predefined positioning subframes grouped by N _ PRS consecutive subframes, i.e. one positioning occasion, as shown in fig. 4. The positioning occasions occur periodically with a certain periodicity of N subframes corresponding to the time interval T _ prs between two positioning occasions. The normalized time interval T _ prs is 160 ms, 320 ms, 640 ms, and 1280 ms, and the number of consecutive subframes N _ prs is 1, 2, 4, and 6. Each predefined PRS configuration includes a PRS transmission bandwidth, N _ PRS, and T _ PRS.

OTDOA assistance information

Since PRS signals from multiple different locations need to be measured for OTDOA positioning, a UE receiver will often have to process PRS that are much weaker than those received from the UE's serving cell. Furthermore, without proper knowledge of when these measurement signals are expected to arrive and what the exact PRS patterns used are, the UE needs to search for signals in a large window, which can affect the time and accuracy of the measurements as well as the UE complexity. To facilitate UE measurements, assistance information, also referred to as assistance data, is transmitted to the UE, including, for example, reference cell information, a neighbor cell list containing the PCIs of neighbor cells, the number of consecutive downlink subframes N-PRS, PRS transmission bandwidth and frequency.

The assistance information is signaled from a positioning server, e.g., E-SMLC, in the control plane of the LTE system to the UE through LPP.

OTDOA inter-frequency measurements and measurement gaps

In LTE OTDOA, the UE measures a Reference Signal Time Difference (RSTD), which is defined in the standard as the relative timing difference between cell j and cell i, defined as T_SubframeRxj-T_SubframeRxiWherein: t is_SubframeRxjIs the time, T, at which the UE receives the start of a subframe from cell j_SubframeRxiIs the time the UE receives from cell i the corresponding start of the one subframe closest in time to the subframe received from cell j. The reference point for the observed subframe time difference will be the antenna connector of the UE. These measurements are specified for intra-frequency and inter-frequency and are made in the RRC _ CONNECTED state.

Inter-frequency measurements including RSTD are performed during periodic inter-frequency measurement gaps configured in such a way that each gap starts with an SFN and subframe that satisfy the following conditions:

SFN mod T = FLOOR(gapOffset/10)；

subframe = gapOffset mod 10;

where T = MGRP/10, where MGRP represents the "measurement gap repetition period" and mod is a modulo function. According to this standard, the E-UTRAN is required to provide a single measurement gap pattern with a constant gap duration for concurrent monitoring of all frequency layers and Radio Access Technologies (RATs). The UE is required to support two configurations according to the standard, where MGRP is 40 and 80 milliseconds (ms), each with a measurement gap length of 6 ms. In practice, due to the switching time, this leaves less than 6 but at least 5 complete subframes for measurement in each such measurement gap.

In LTE, measurement gaps are configured by the network, i.e. the eNodeB, to enable measurements on different LTE frequencies and/or different RATs, e.g. UTRA, GSM and CDMA 2000. The measurements are configured using Radio Resource Control (RRC) to signal the measurement configuration to the UE. The gap configuration is signaled to the UE as part of a measurement configuration. Only one gap pattern can be configured at a time. The same mode is used for all types of configured measurements, such as inter-frequency neighbor cell measurements, inter-frequency positioning measurements, inter-RAT neighbor cell measurements, inter-RAT positioning measurements, and the like.

In multi-carrier LTE, inter-frequency measurement gaps have so far been mainly intended for performing cell identification and mobility measurements, such as Reference Signal Receiver Power (RSRP) and Reference Signal Received Quality (RSRQ). These measurements require the UE to perform measurements on the synchronization signals, i.e., Primary Synchronization Signals (PSS) and Secondary Synchronization Signals (SSS), and cell-specific reference signals (CRS), in order to achieve inter-frequency handover and enhance system performance. The synchronization signal is transmitted in subframes 0 and 5 through 62 resource units in the center of the allocated bandwidth. The PSS is transmitted in the last OFDM symbol of the first slot of the subframe, and the SSS is transmitted in the second to last OFDM symbol of the first slot of the subframe. CRS symbols are transmitted per subframe and over the entire bandwidth in one of the standardized time-frequency patterns. Different cells can use 6 different frequency offsets and there are 504 different signals. With two Transmit (TX) antennas, the effective reuse of CRS is three.

As can be seen from the above, both synchronization signals and CRS are transmitted relatively often, but PSS and SSS are transmitted less frequently than CRS. This leaves enough freedom in deciding the exact timing of the measurement gaps so that the gaps can cover enough symbols with the signal of interest, i.e. PSS/SSS and/or CRS. For 6 ms measurement gaps, at most two SSS symbols and two PSS symbols are possible for very accurate timing, while capturing one SSS symbol and one PSS symbol is possible almost without any timing restrictions on these measurement gaps, since the minimum required effective measurement time is on average 5 ms.

In LTE OTDOA, the network, i.e. the eNodeB, is able to signal a list of cells operating on up to three frequency layers including the serving cell frequency. The 3GPP RAN4 requirements for RSTD inter-frequency measurements are defined for two frequency layers including the serving cell frequency. Furthermore, these measurement gaps will be defined such that they do not overlap with PRS occasions of the serving cell layer, which would otherwise increase the effective measurement time of the serving cell and inter-frequency cells. Since the measurement gaps for this UE are configured for RSTD measurements and also for mobility measurements, it has been agreed that a predefined "gap pattern # 0" specifying denser and frequent measurement gaps can be used only when inter-frequency RSTD measurements are configured. According to the predefined gap pattern #0, a measurement gap of 6 ms occurs every 40 ms.

As described above, the measurement gap to be applied by the UE is configured by the eNodeB through RRC. However, it is the positioning server, e.g. the E-SMLC, that knows whether the UE will perform positioning inter-frequency measurements, e.g. inter-frequency RSTD or inter-frequency E-CID, and the time to perform positioning inter-frequency measurements, and this information is communicated transparently to the UE via the eNodeB. Thus, to be on the safe side, the eNodeB may always configure UEs for the worst case, i.e. for the 40 ms measurement gaps according to gap pattern #0, even when these UEs only measure intra-frequency cells. This is a serious limitation on the network, as it reduces the amount of radio resources available for intra-frequency measurements, and it leads to an inefficient measurement procedure.

Disclosure of Invention

It is an object of the present invention to provide improved methods and arrangements for supporting configuration of a measurement gap pattern for user equipments requiring measurement gaps for performing inter-frequency measurements for positioning.

The above object is achieved by a method and an arrangement according to the independent claims.

A first embodiment provides a method in a radio network node of a wireless communication system, the method supporting configuration of a measurement gap pattern for user equipments requiring measurement gaps for performing inter-frequency measurements for positioning. The method comprises receiving an indication from the user equipment that the user equipment is to perform inter-frequency measurements for positioning and that the inter-frequency measurements require measurement gaps.

A second embodiment provides a radio network node of a wireless communication system. The radio network node is configured for signal interaction with a user equipment requiring a configuration of measurement gap patterns for performing inter-frequency measurements for positioning. The radio network node comprises a receiver configured to receive an indication from a user equipment that the user equipment is to perform an inter-frequency measurement for positioning and that the inter-frequency measurement requires a measurement gap.

A third embodiment provides a method in a user equipment of a wireless communication system of supporting configuration of a measurement gap pattern for inter-frequency measurements performed by the user equipment for positioning. The method includes receiving an indication of: requesting the user equipment to start inter-frequency measurements for positioning for which the user equipment requires measurement gaps. The method further comprises transmitting an indication to the radio network node that the user equipment is to perform inter-frequency measurements for positioning and that the inter-frequency measurements require measurement gaps.

A fourth embodiment provides a user equipment for use in a wireless communication system. The user equipment is configured for signal interaction with a radio network node. The user equipment comprises a receiver configured to receive an indication requesting the user equipment to start inter-frequency measurements for positioning for which the user equipment requires measurement gaps. The user equipment also comprises a transmitter configured to transmit an indication to the radio network node that the user equipment is to perform an inter-frequency measurement for positioning and that the UE requires a measurement gap for the inter-frequency measurement.

An advantage of some of the embodiments described herein is that by informing the radio network node that the UE is to perform inter-frequency measurements for positioning for which the UE requires measurement gaps, the radio network node is able to configure an appropriate measurement gap pattern for the UE. If the radio network node does not know when the UE will perform inter-frequency measurements for positioning for which the UE requires measurement gaps, the radio network node may be required to always configure the UE for measurement gap patterns in order to accommodate the inter-frequency measurements for positioning, even when the UE only makes measurements on intra-frequency cells. This is a serious limitation on the network, as it reduces the amount of radio resources available for intra-frequency measurements, and it leads to an inefficient measurement procedure.

Other advantages and features of embodiments of the present invention will become apparent from a reading of the following detailed description in conjunction with the drawings.

Drawings

Fig. 1 is a schematic block diagram of a cellular communication system in which embodiments described herein may be implemented.

Fig. 1a is a schematic block diagram of a wireless communication system including a location server in which embodiments described herein may be implemented.

Fig. 2 is a schematic block diagram illustrating an LTE system with positioning functionality.

Fig. 3 is a schematic block diagram illustrating positioning of a User Equipment (UE) by determining an intersection point of hyperbolas corresponding to a measured Reference Signal Time Difference (RSTD).

Fig. 4 is a schematic block diagram showing a measurement gap pattern.

Fig. 5 is a schematic block diagram illustrating a positioning reference signal pattern when one or two antennas are used for a Physical Broadcast Channel (PBCH).

Fig. 6 is a flow chart illustrating an exemplary embodiment of a method in a radio network node for supporting a configuration of a measurement gap pattern for a UE requiring measurement gaps for performing inter-frequency measurements.

Fig. 7 is a flow diagram illustrating an alternative exemplary embodiment of a method in a radio network node for supporting configuration of a measurement gap pattern for a UE requiring measurement gaps for performing inter-frequency measurements.

Fig. 8 is a flowchart illustrating an exemplary embodiment of a method in a UE for supporting configuration of a measurement gap pattern for the UE in order to perform inter-frequency measurements.

Fig. 9 is a flow diagram illustrating an alternative exemplary embodiment of a method in a UE for supporting configuration of a measurement gap pattern for the UE in order to perform inter-frequency measurements.

Fig. 10 is a flow diagram illustrating another alternative exemplary embodiment of a method in a UE for supporting configuration of a measurement gap pattern for the UE in order to perform inter-frequency measurements.

Fig. 11 is a schematic block diagram illustrating an exemplary embodiment of a UE and a radio network node.

Detailed Description

The term "UE" is used throughout this description as a non-limiting term, which denotes any wireless device or node such as a PDA, a laptop, a mobile station, a sensor, a fixed relay, a mobile relay, or even a small base station that locates when timing measurements for location are considered, i.e. LCS targets in general, etc. The UE may also be an advanced UE that is capable of advanced features such as carrier aggregation but may still require measurement gaps in order to perform measurements on at least some cells and at least a certain carrier frequency.

A cell is associated with a radio network node, wherein a radio network node in a general sense comprises any node capable of transmitting and/or receiving radio signals that may be used for positioning and/or measurements, such as an eNodeB, macro/micro/pico base station, home eNodeB, relay, beacon device or repeater. The radio network node may be a single RAT or a multi-RAT or multi-standard radio base station. Note that the downlink transmission and the uplink transmission need not be between the UE and the same radio network node.

The positioning server described in the different embodiments is a node with positioning functionality. For example, for LTE, it may be understood as a positioning platform in the user plane (e.g. SLP in LTE) or a positioning server in the control plane (e.g. E-SMLC in LTE). The SLP may also consist of SLC and SPC, as described above, where the SPC may also have a proprietary interface with the E-SMLC. In a test environment, at least the positioning server may be simulated or emulated by the test equipment.

The signaling described in the different embodiments is via a direct link or a logical link, e.g. via a higher layer protocol such as RRC and/or via one or more network nodes. For example, in LTE, in the case of signaling between E-SMLC and LCS clients, positioning results may be communicated via multiple nodes, at least via the MME and the gateway mobile location center GMLC.

The term "measurement gap indication" will be used herein to denote a message indicating the need for a measurement gap for a UE. The measurement gap indication may also contain additional information, such as information specifying the frequency to which the measurement relates. There may be a specific measurement gap indication, e.g. OTDOA, for a specific positioning method.

Inter-frequency measurements in the present invention will be understood in a general sense to include, for example, inter-frequency measurements, inter-band measurements or inter-RAT measurements, at least in some embodiments. Some non-limiting examples of inter-frequency positioning measurements are inter-frequency E-CID measurements such as UE Rx-Tx time difference, RSRP and RSRQ, and inter-frequency RSTD measurements for OTDOA positioning.

At least some embodiments described herein are not limited to LTE, but are applicable to any RAN, single RAT, or multi-RAT. Some other RAT examples are LTE-advanced, UMTS, GSM, cdma2000, WiMAX, and WiFi.

According to the current 3GPP standard, the eNodeB can use the following three different predefined measurement gap configurations for the UE to perform inter-frequency measurements and inter-RAT measurements. Inter-frequency measurement means that a carrier frequency different from a serving carrier frequency is measured. Both the serving carrier frequency and the inter-frequency carrier can belong to a Frequency Division Duplex (FDD) mode or a Time Division Duplex (TDD) mode or any combination thereof.

According to a first predefined measurement gap configuration, no measurement gap is configured. In this case, the UE can perform inter-frequency measurements and/or inter-RAT measurements without measurement gaps. This may be the case, for example, if the UE has multiple receivers that can be activated in parallel. One example is a multi-carrier capable UE, i.e. a UE capable of receiving data over more than one carrier.

According to a second predefined measurement configuration, measurement gap pattern #0 (also referred to as gap pattern 0) is configured. When the UE is configured with gap pattern #0 for performing positioning measurements, there is no degradation of UE inter-frequency/inter-RAT neighbor cell and positioning measurement performance. This is because, in this mode, the gaps are significantly dense and frequent, i.e., 6 ms gaps occur every 40 ms. This means that the mobility and positioning, e.g. OTDOA or E-CID measurement requirements specified in the standard will be met.

According to a third predefined measurement configuration, measurement gap pattern #1 (also referred to as gap pattern 1) is configured. According to the gap pattern #1, a gap of 6 ms occurs every 80 ms. There is a risk that: UE inter-frequency/inter-RAT neighbor cell and positioning measurement performance is degraded if this mode is used. This is due to the longer periodicity of the measurement gap occurrences compared to gap pattern # 0. The result may be, for example, a significantly longer measurement period of one or more of the above measurements in order to meet the corresponding target accuracy requirements.

It should also be noted that the inter-frequency measurement configuration includes not only the gap pattern but also, for example, a subframe gap offset, and may include other parameters such as SFN offset, frame offset, and the like.

To ensure expected performance, it is desirable to configure an appropriate measurement gap configuration at the UE when positioning measurements, e.g., OTDOA measurements such as RSTD, are to be performed by the UE during a measurement gap. In the above E-UTRA example, when requesting the UE to measure inter-frequency RSTD measurement for positioning, measurement gap pattern #0 should be configured. Further, in order to ensure desired performance, it is also desirable to: the measurement gap configurations are decided such that a sufficient amount of reference signals for positioning measurements in the measurement gaps fall into these measurement gaps. In E-UTRAN, these Positioning Reference Signals (PRS) are examples of reference signals.

The goal of configuring an appropriate measurement gap pattern can be achieved by ensuring that the radio network node configuring the measurement gaps knows the timing at which the UE has been requested to perform one or more positioning related measurements requiring measurement gaps and the occurrence of reference signals for positioning measurements in the gaps.

Examples of information that may be used to indicate the timing of the occurrence of the reference signal are timing offsets, such as the SFN offset, frame offset, subframe offset, or more specifically subframe gap offset, previously described.

Thus, the embodiments described in more detail below provide the radio network node with the necessary information about the positioning measurements to be made during the measurement gaps, in order to enable the radio network node to configure the appropriate measurement gap pattern for performing the positioning measurements.

In case the gaps for these positioning measurements are configured by the eNodeB, in order for the eNodeB to configure the appropriate measurement gaps, information related to the UE's measurements needs to be provided to or made available at the eNodeB.

As mentioned above, fig. 1a shows a positioning architecture. As shown in fig. 1a, there is an interface 163, e.g., X2, between two enodebs 110a and 110b, and an interface 164 between the eNodeB and a network management and/or operation and maintenance (O & M) block 141. It is assumed here that the positioning node or positioning server 140 is an E-SMLC server in E-UTRAN. The protocol used for messaging between the E-SMLC 140 and the eNodeB 110a is referred to as LPPa. The radio interface protocol between the E-SMLC 140 and the UEs 150a, 150b is referred to as LPP. Note that the links between different network entities may be physical links or logical links.

A path of a higher layer protocol is a logical link that may include one or more physical links.

Given an architecture such as that shown in FIG. 1a, an exemplary embodiment will be described. The exemplary embodiments relate to gap configuration based on explicit indication by the positioning server or UE, implicit indication by assistance data (by which the positioning server or UE forwards assistance data to the eNodeB), packet probing, predefined rules and autonomous detection. The solution according to all embodiments described herein is applicable when the UE is in a non-Discontinuous Reception (DRX) state or in a DRX state. These embodiments are described in more detail below.

According to one embodiment involving an explicit indication by the positioning server, the radio network node, e.g. an eNodeB in E-UTRAN, changes or configures the gap configuration for a particular UE, wherein the configuration is based on available information related to the positioning measurements, e.g. OTDOA RSTD inter-frequency measurements or E-CID inter-frequency measurements in E-UTRAN. This information can be cell-specific or specific for a group of UEs or for a specific UE, and it is provided by the positioning server to the eNodeB, e.g. by periodic or event-triggered updates, upon request or without request. The reception of such information may also be used to trigger a change of an existing gap configuration in case the existing configuration gap pattern is not suitable for the positioning measurements to be performed.

According to an exemplary embodiment, the location server, e.g., the E-SMLC, sends a cell-specific or UE-specific gap configuration handover indicator to the eNodeB. The gap configuration handover indicator instructs the eNodeB to use the appropriate gap configuration for the specified UE, a group of UEs, or all UEs in the cell for inter-frequency measurements. The gap configuration switch indicator may be, for example, "1" when inter-frequency measurements are to be used by a designated UE, a group of UEs, or all UEs in the cell that are performing inter-frequency measurements. In the event that the eNodeB has used a gap pattern for a particular UE that is not suitable for the positioning measurements to be performed (e.g., if the pattern is expected to degrade performance), the eNodeB switches the existing gap pattern for that UE to the appropriate gap pattern. The appropriate gap pattern is either predefined or explicitly indicated by the positioning server. The positioning server also provides information about the carrier frequency on which these positioning measurements, e.g. RSTDs, are to be performed by the UE in measurement gaps. Other information (e.g., timing information of whether cells on the carrier frequency are asynchronous or synchronous or reference signals, etc.) can also be provided by the positioning server to the eNodeB, which can use the other information to determine the most appropriate gap pattern for the measurements.

The eNodeB may optionally send an Acknowledgement (ACK) to the E-SMCL to acknowledge receipt of the indicator sent by the E-SMLC to the eNodeB. Thus, if the ACK is used, the E-SMLC receives the ACK.

Further, according to an exemplary embodiment, the eNodeB sends gap reconfiguration information (e.g., details of gap pattern, subframe gap offset, frame offset, SFN offset, etc.) to the UE by, for example, broadcasting/multicasting or unicasting via RRC signaling or UE specific messages, wherein the gap configuration contains all necessary and standardized information needed by the UE to configure measurement gaps. The eNodeB may also store the gap configuration for each UE. The information signaled to the UE can include at least a time or reference point from when the gap configuration will apply and/or such measurement gap configurations.

In a variation of the embodiment of explicit indication to the eNodeB, the eNodeB receives the information needed for gap reconfiguration from the Network Management (NM) and O & M node 141 instead of from the positioning server 140. In this case, information originating from positioning node 140 is also passed to NM and O & M node 141.

In another variation of the embodiment of explicit indication to the eNodeB, the eNodeB receives information from the UE needed for appropriate measurement gap configuration or reconfiguration. The UE is made aware that it will perform inter-frequency measurements for positioning when the positioning server requests such measurements from the UE. Accordingly, the UE may signal an explicit indication to indicate to the radio network node that it requires measurement gaps.

According to one embodiment involving an explicit indication, assistance data is forwarded to the eNodeB to inform the eNodeB that the UE will perform measurements for which it needs to configure measurement gaps. According to an alternative, the positioning server 140 signals assistance data or certain elements of assistance data for each UE or a group of UEs to the radio network node. In the E-UTRAN example shown in fig. 1a, this means that the E-SMLC 140 signals the assistance data, or a part thereof, to the eNodeB 110a or 110b over the LPPa protocol. The eNodeB 110a/b may also send an acknowledgement message to the E-SMLC in the same manner as described above for the exemplary embodiment with an explicit indication. According to an exemplary embodiment, the elements of assistance data signaled to the eNodeB will contain at least information related to the carrier frequency of the cell to be used for the positioning measurements. The radio network node (i.e. the eNodeB in this example) knows the serving carrier frequency f1 of the UE. In case the assistance data received by the radio network node contains more than one carrier frequency, e.g. f1 and f2, or if it contains one or more carrier frequencies f2 different from the serving carrier frequency, the radio network node can use this information to infer that the UE is requested to make inter-frequency measurements, e.g. inter-frequency RSTD measurements, for positioning. The measurements are performed by the UE in measurement gaps. Thus, the eNodeB may use this information to configure measurement gaps that are relevant for positioning measurements to be performed in these measurement gaps. In E-UTRAN, this means that the eNodeB can use the received assistance data or a part thereof and configure gap pattern 0 or modify existing gap pattern 1 to gap pattern 0, e.g. for all measurements to be performed in the measurement gaps. The configuration or modification of these measurement gaps can be performed in the same manner as described above. Accordingly, the radio network node may signal information to the UE in order to initiate the use of the appropriate gap pattern in the UE. The information signaled to the UE may for example comprise a determined measurement gap pattern, an indication or reference of a predefined measurement gap pattern and/or a time or reference point from when the measurement pattern to be configured shall be applied.

The assistance data is sent from the positioning server 140 to the UE 150a or 150b in order for the UE to perform positioning measurements, such as RSTD in case of OTDOA or signal strength/quality measurements of enhanced cell ID, etc. For example, in E-UTRAN, assistance data is sent to the UE via LPP protocol, and in 3GPP TS 36.355V 9.1.0(2010-03) "Evolved Universal Radio Access (E-UTRA); section 6.5.1.2 of LTE Positioning Protocol (LPP) (release 9) ". Since the LPP protocol is between the UE and the E-SMLC, the eNodeB does not receive assistance data when it is transmitted from the E-SMLC to the UE. As mentioned above, the idea of the above described embodiments is that the assistance data or a part of the assistance data sent to the UE is also forwarded by the positioning node to the radio network node, e.g. the eNodeB. In a variant of this embodiment, the assistance data or a part of the assistance data is forwarded by the UE to the radio network node. According to an example, the data elements sent to the eNodeB are UE-specific, sent over LPPa and are data elements in the following information element OTDOA-neighbor cell information list (OTDOA-neighbor cell information list) specified in section 6.5.1.2 of 3GPP TS 36.355 above:

“OTDOA-NeighbourCellInfoList。

the IE OTDOA-neighbourcelllnfolist is used by the location server to provide neighbour cell information for OTDOA assistance data. The OTDOA-neighbourcelllnfolist is classified according to the best measurement geometry estimated at the a priori position of the target device. That is, the target device is expected to provide measurements in increasing neighbor cell list order (to the extent that this information is available to the target device).

As can be seen from the above, this information element contains carrier frequency information, since "earfcn" is the frequency channel of the cell concerned. For example, if there is at least a carrier different from the serving carrier, the eNodeB can use this information to infer whether the UE is required to perform positioning measurements, e.g., RSTD measurements, in the measurement gap. Accordingly, the eNodeB can ensure that the relevant measurement gaps are configured to facilitate measurements in the gaps, e.g., inter-frequency RSTD measurements, etc. Similarly, assistance data or parts thereof, e.g. carrier frequency information, relating to other positioning methods than OTDOA, e.g. enhanced cell ID, can also be signaled to the eNodeB by the positioning server or by the UE.

An alternative exemplary embodiment, which will now be described, relates to packet probing. This embodiment is useful in case the eNodeB has no explicit or implicit information about the positioning measurements to be performed by the UE during the measurement gaps. Thus, all actions including the determination as to whether a particular UE performs inter-frequency measurements are performed by the radio network node or eNodeB configuring the measurement gap. If the radio network node configuring the measurement gap is an eNodeB, the eNodeB can probe for packets with LPP or similar messages sent by the positioning server to the UE. The probed message may include assistance information to be used by the UE for performing positioning measurements, such as inter-frequency carriers and the like. The message containing the assistance information is delivered transparently through the eNodeB. Thus, the eNodeB can probe for these messages. The assistance information obtained by probing enables the eNodeB to decide whether to configure a measurement gap pattern for performing inter-frequency positioning measurements. The measurement gap pattern may be, for example, a gap pattern predefined for positioning measurements, such as gap pattern # 0. For example, if the eNodeB detects assistance information on at least two cells present in assistance data operating on different frequencies, e.g., cell 1 and cell 2 operating on frequencies f1 and f2, respectively, by probing, the eNodeB can consider that a measurement gap is needed for positioning measurements. In addition, the eNodeB knows the serving carrier frequency f1, which means that the eNodeB can think that f2 is inter-frequency. Thus, the eNodeB will configure the measurement gap pattern, or in case the measurement gap pattern is already in operation, adjust the existing measurement gap pattern in order to ensure that a sufficient number of reference signals on carrier f2 fall within the measurement gaps of the configured or adjusted measurement gap pattern. The reference signal may be, for example, a PRS on f2, and the measurement gap pattern may be, for example, configured or adjusted such that at least one subframe containing the reference signal falls within the measurement gaps. The configuration of the measurement gap pattern in the UE can be performed in the same way as described above, irrespective of whether the radio network node knows, by probing or by another way such as an explicit or implicit indication from the positioning server or the UE, that the UE needs measurement gaps in order to perform inter-frequency measurements for positioning.

Another alternative embodiment relates to predefined rules in the UE. When assistance data is received by the UE, e.g. via LPP, and the UE is to make inter-frequency measurements or another type of measurement in the measurement gaps of carrier f1 and carrier f2, the UE itself reconfigures the measurement gap that is most relevant for the measurement to be performed. As described above, the carriers f1 and f2 can be given in the field 'earfcn' of the assistance data. The measurement gaps to be configured or reconfigured can be predefined in the standard. Accordingly, the UE can configure the measurement gap on its own following one or more predefined rules. For example, the following predefined rule sets can be used:

the above exemplary set of predefined rules indicates that the UE changes the current gap configuration to a predefined gap pattern configuration suitable for positioning measurements, e.g. inter-frequency measurements, to be made in the measurement gap.

In a variant of this embodiment, the UE can indicate to the eNodeB that "positioning is ongoing" and that it needs gap pattern 0, if a solution of predefined rules for the UE is used. When positioning is no longer desired, the UE can update the eNodeB again. This information "positioning in progress" can also be communicated over the X2 interface, for example, to a node associated with the new serving cell of the UE when the UE performs handover or to a neighboring node, in order to indicate the measurement gap pattern used in this cell for positioning measurements.

Yet another exemplary embodiment relates to autonomous detection in a network node. In case the RS or PRS used by the UE to perform positioning measurements are configured on more than one carrier frequency in the eNodeB, the eNodeB may then be configured to always use the most suitable gap pattern needed to perform positioning measurements, e.g. the eNodeB only configures gap pattern 0 for all measurements in E-UTRAN. The eNodeB considers measurements on at least one of these carrier frequencies to be made in the gaps. Second, the measurement gaps are configured to ensure that as many PRS subframes on different carriers as possible are located in the measurement gaps. This embodiment is useful in the case where the eNodeB has no other way to determine whether a positioning measurement is made in a measurement gap for a particular UE.

Another exemplary embodiment relates to the use of the X2 interface for exclusively exchanging information about cells on the frequency used for positioning. In LTE it is possible for enodebs to exchange information over the X2 interface. This information can be, for example, a list of all bandwidths on all carriers in the associated cell. According to this embodiment, in addition to the carrier information, the eNodeB also comprises information on whether the carrier is used for positioning measurements, e.g. whether the frequency f1 is used for PRS transmission and/or configuring positioning subframes or whether the UE performs positioning measurements on the CRS. In another embodiment, PRS transmission bandwidth is also exchanged via X2.

Yet another exemplary embodiment relates to applying a default measurement gap configuration. Examples of applicable default configurations are:

in a multi-RAT and/or multi-frequency system, when a site is co-located, the eNodeB can decide to use gap pattern 0 when different cells of the site operate on different frequencies/RATs.

Slot pattern 0 is always used as default slot configuration in eNodeB when the network provides location services.

When transmitting PRS, slot pattern 0 is used as default configuration in eNodeB.

The configuration of gap pattern 0 is triggered by a positioning request.

The gap configuration, e.g. gap pattern, of the eNodeB can be decided and configured by another node (e.g. NM and/O & M node 141, Self Organizing Network (SON) node, macro eNoeB, etc.).

The default gap configuration is used by the eNodeB when configuring the UE for inter-frequency measurements. In one embodiment, the eNodeB reconfigures the UE to the new default gap configuration in case of one of the events listed above, and the default configuration changes.

The above-described embodiments have a number of advantages over previous methods and apparatus, including, for example, addressing the problem of incomplete support for inter-frequency measurements.

Some of the above embodiments relate to the UE indicating a need for a measurement gap to the radio network node. Such an indication may be signaled to the radio network node by RRC signaling. One advantage of the UE sending the indication instead of the positioning server sending the indication is that this embodiment is applicable to user plane positioning as well as control plane positioning. It is not certain that: the location server knows whether the UE actually requires measurement gaps, since the location server may not have full knowledge of the UE capabilities. Accordingly, an advantage of having the UE itself indicate its need for measurement gaps is that it reduces the risk of configuring measurement gaps in case the UE does not require measurement gaps.

Fig. 6 is a flow chart of a method in a radio network node for supporting configuration of a measurement gap pattern for a UE requiring measurement gaps for performing inter-frequency measurements. The method comprises receiving an indication from the UE that the UE is to perform inter-frequency measurements for positioning and that the inter-frequency measurements require measurement gaps in step 71. The inter-frequency measurements may be, for example, reference signal time difference, RSTD, measurements. The received indication may include an indication of a measurement gap pattern required by the UE to perform the inter-frequency measurements. Such an indication may be an indication of the need to configure a predefined measurement gap pattern, e.g. gap pattern #0 specifying gaps of 6 ms occurring every 40 ms.

Fig. 7 is a flow diagram illustrating an alternative embodiment of a configuration in a radio network node for supporting a measurement gap pattern for UEs requiring measurement gaps for performing inter-frequency measurements. The step 71 in which the radio network node receives an indication from the user equipment that the UE is to perform inter-frequency measurements for positioning and that the inter-frequency measurements require measurement gaps is the same as described above in connection with fig. 6. The method in fig. 7 further comprises a step 73, in which the radio network node determines a measurement gap pattern for performing inter-frequency measurements based on the received indication. Another step 74 comprises signaling information to the UE to initiate use of the determined measurement gap pattern in the UE. The information signaled to the UE may for example comprise a time or reference point from when the determined gap pattern will be applied and/or the determined measurement gap pattern. The information signaled to the UE may specify, for example, a gap offset and/or a mode activation time to apply.

According to further variants of the embodiments shown in fig. 6 and 7, the radio network node may store information related to the determined measurement gap pattern of the associated UE. Thus, the radio network node may store information relating to different measurement gap patterns configured for different UEs. In another variant, the radio network node receives an indication from the UE that the user equipment is to stop inter-frequency measurements. Thus, the radio network node is informed that the UE no longer needs a measurement gap pattern for performing inter-frequency measurements.

Fig. 8 is a flowchart illustrating a method in a UE for supporting configuration of a measurement gap pattern for inter-frequency measurements performed by the UE. The method comprises receiving an indication of a request for a user equipment to start inter-frequency measurements for positioning for which the user equipment requires measurement gaps in step 101. An indication may be received from a location server, such as E-SMCL or SLP, requesting the UE to start inter-frequency measurements. In step 102, the UE transmits an indication to the radio network node that the UE is to perform inter-frequency measurements for positioning and that the inter-frequency measurements require measurement gaps. If the UE has the capability to perform inter-frequency measurements without measurement gaps, it should not indicate to the radio network node that it requires measurement gaps for performing inter-frequency measurements. The indication transmitted to the radio network node may comprise an indication of a measurement gap pattern required by the user equipment for performing inter-frequency measurements. In one variant of the illustrated embodiment, the UE further transmits an additional indication to the radio network node indicating that the user equipment will stop inter-frequency measurements. The indication may be applicable to one or more predefined positioning methods, e.g. OTDOA and/or E-CID.

As mentioned above, there are embodiments in which the radio network node configures the measurement gap pattern to be applied by the UE and other embodiments in which the UE itself configures the measurement gap pattern based on predefined rules in the UE. Fig. 9 and 10 are flow diagrams illustrating embodiments according to these different alternatives.

Fig. 9 illustrates a method in which the UE itself configures a measurement gap pattern to be used for inter-frequency positioning measurements. The method comprises the same steps 101 and 102 as described above in connection with fig. 8. In addition, the method further comprises step 103, wherein the UE determines a measurement gap pattern to be used for performing inter-frequency measurements. Step 103 is initiated in response to receiving an indication that the UE is requested to perform inter-frequency measurements. The UE determines a measurement gap pattern based on a predefined set of rules. In step 104, the determined measurement gap pattern is configured in the UE.

Fig. 10 shows a method wherein a UE receives information about a determined measurement gap configuration from a radio network node. The method comprises the same steps 101 and 102 as described above in connection with fig. 8. Furthermore, the method comprises a step 105, wherein the UE receives information from the radio network node indicating the determined measurement gap pattern to be used for performing inter-frequency measurements. In step 106, the UE uses the determined measurement gap pattern.

In a variant, the method shown in fig. 9 and 10 further comprises the following steps: wherein the UE determines that it requires measurement gaps to perform inter-frequency measurements for positioning based on the capability of the UE. If the UE is capable of performing inter-frequency measurements for positioning, the UE should of course not send any indication to the radio network node that it requires measurement gaps for performing inter-frequency measurements for positioning.

Fig. 11 is a schematic block diagram illustrating exemplary embodiments of a radio network node 81 and a UE 91, respectively, which may be configured to perform the methods illustrated in fig. 6-10.

The radio network node 81 comprises a receiver 82, a processor 83, a transmitter 84 and at least one antenna 89 and a memory 88. The receiver 82 may be configured to receive an indication 85 indicating that the UE is to perform inter-frequency measurements for which the UE requires measurement gaps. The processor 83 may be configured to determine a measurement gap pattern based on the indication 85, and the transmitter 84 may be configured to transmit information 86 to the UE in order to initiate use of the determined measurement gap pattern. The memory 88 may store information related to the determined measurement gap pattern for different UEs.

The UE 91 comprises a receiver 92, a processor 93, a transmitter 94 and at least one antenna 95. The receiver 92 is configured to receive an indication 87, e.g. from a positioning server, the indication 87 indicating that the UE is requested to perform inter-frequency measurements. The transmitter 94 is configured to transmit the indication 85 to the radio network node 81. The processor 93 may be configured to determine the measurement gap pattern to apply according to a predefined set of rules.

The functional blocks shown in fig. 11 can be combined and rearranged in various equivalent ways, and many of the functions can be performed by one or more appropriately programmed digital signal processors and other known electronic circuits, such as discrete logic gates interconnected to perform a dedicated function or application-specific integrated circuits. Furthermore, the connections between the functional blocks shown in fig. 11 and the information provided or exchanged by these functional blocks can be changed in various ways in order to enable the radio network node and the UE, respectively, to implement the above-described methods and other methods involved in the operation of the radio network node or the UE of the wireless communication system.

Aspects of embodiments presented herein are described in terms of sequences of actions that can be performed by, for example, elements of a programmable computer system. Examples of UEs include, for example, mobile telephones, pagers, headsets, laptop computers and other mobile terminals, and the like. Furthermore, some embodiments described herein can also be considered to be embodied entirely within any form of computer-readable storage medium having stored therein an appropriate set of instructions for use by or in connection with an instruction-execution system, apparatus, or device, such as a computer-based system, processor-containing system, or other system that can fetch instructions from a medium and execute the instructions. As used herein, a "computer-readable medium" can be any means that can contain, store, or transport the program for use by or in connection with the instruction execution system, apparatus, or device. The computer readable medium can be, for example, but not limited to, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device. More specific examples (a non-exhaustive list) of the computer-readable medium include an electrical connection having one or more wires, a portable computer diskette, a Random Access Memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or flash memory), and an optical fiber. Thus, there are numerous different embodiments in many different forms, not all of which are described above, which fall within the scope of the appended claims. For each of the aspects, any such form may be referred to as "logic configured to" perform a described action, "or alternatively as" logic that "performs a described action.

The several embodiments described above use the LTE case as an exemplary application case. The LTE standard specification can be seen as an evolution of the current Wideband Code Division Multiple Access (WCDMA) specification. LTE systems use Orthogonal Frequency Division Multiplexing (OFDM) as a multiple access technique (called OFDMA) in the Downlink (DL) from the system nodes to the User Equipment (UE). The LTE system has a channel bandwidth ranging from about 1.4 MHz to 20 MHz and supports a throughput of over 100 megabits per second (Mb/s) on the maximum bandwidth channel. One type of physical channel defined for the LTE downlink is the Physical Downlink Shared Channel (PDSCH), which conveys information from higher layers in the LTE protocol stack and to which one or more specific transport channels are mapped. The control information is transmitted through a Physical Uplink Control Channel (PUCCH) and through a Physical Downlink Control Channel (PDCCH). LTE channels are described in 3GPP Technical Specification (TS)36.211 v9.1.0 "physical channels and modulation" (release 9) (12 months 2009) and other specifications.

IMT-advanced communication systems use the Internet Protocol (IP) multimedia subsystem (IMS) of LTE, HSPA or other communication systems for IMS Multimedia Telephony (IMT). In an advanced IMT system, which may be referred to as a "fourth generation" (4G) mobile communication system, bandwidths of 100 MHz and more are considered. The 3GPP releases LTE, HSPA, WCDMA and IMT specifications as well as specifications that standardize other kinds of cellular wireless communication systems.

In an OFDMA communication system, the data stream to be transmitted is divided among a plurality of narrowband subcarriers transmitted in parallel. In general, a resource block dedicated to a particular UE is a particular number of particular subcarriers used in a particular time period. Different groups of subcarriers can be used for different users at different times. Because each subcarrier is narrowband, each carrier is subject primarily to flat fading, which makes it easier for the UE to demodulate each subcarrier. OFDMA communication systems are described in documents such as U.S. patent application publication No. us 2008/0031368 a1 to b.lindoff et al.

Fig. 1 illustrates a typical cellular communication system 10. Radio Network Controllers (RNCs) 12, 14 control various radio network functions including, for example, radio access bearer establishment, diversity handover, and the like. In general, each RNC directs calls to and from UEs, such as Mobile Stations (MSs), mobile phones, or other remote terminals, via the appropriate Base Station (BS), which communicate with each other through DL channels (or forward channels) and uplink (UL, or reverse) channels. In FIG. 1, RNC 12 is shown coupled to BSs 16, 18, 20, and RNC 14 is shown coupled to BSs 22, 24, 26. Each BS, or eNodeB as a BS in an LTE system, serves a geographical area that is divided into one or more cells. In fig. 1, BS 26 is shown with five antenna sectors S1-S5, which can be said to constitute a cell of BS 26, however, the sectors or other areas served by signals from the BS can also be referred to as cells. In addition, a BS may also transmit signals to a UE using more than one antenna.

These BSs are typically coupled to their corresponding RNCs by dedicated telephone lines, fiber optic links, microwave links, etc. The RNCs 12, 14 are connected to external networks, such as the Public Switched Telephone Network (PSTN), the internet, etc., through one or more core network nodes, such as a mobile switching center (not shown) and/or a packet radio service node (not shown).

It will be appreciated that the arrangement of functionality shown in fig. 1 can be modified in LTE and other communication systems. For example, the functionality of the RNCs 12, 14 can be transferred to the enodebs 22, 24, 26, and other functionality can be transferred to other nodes in the network. It will also be appreciated that a base station can use multiple transmit antennas to transmit information into a cell/sector/region, and that those different transmit antennas can transmit different respective pilot signals.

The use of multiple antennas plays an important role in modern wireless communication systems, such as LTE systems, in order to achieve improved system performance, including capacity and coverage, and service provisioning. Obtaining Channel State Information (CSI) at the transmitter or receiver is important for proper implementation of multi-antenna techniques. In general, channel characteristics such as impulse response are estimated by transmitting and receiving one or more predefined training sequences, which can also be referred to as reference signals. For example, to estimate the channel characteristics of the DL, the BS transmits reference signals to the UEs, which estimate the DL channel using the received versions of the known reference signals. These UEs can then use the estimated channel matrix for coherent demodulation of the received DL signal and derive the potential beamforming gain, spatial diversity gain, and spatial multiplexing gain available with multiple antennas. In addition, these reference signals can be used to make channel quality measurements to support link adaptation.

In the case of OFDM transmission, a straightforward design of the reference signal is to transmit known reference symbols in an OFDM frequency and time grid. Cell-specific reference signals and symbols are described in clauses 6.10 and 6.11 of 3GPP TS 36.211 V9.0.0 "Evolved Universal Radio Access (E-UTRA), Physical Channels and Modulation (release 9)" (12 months 2009). Up to four cell-specific reference signals are specified corresponding to up to four transmit antennas of the eNodeB. Such reference signals are used by the eNodeB for codebook-based multi-stream spatial multiplexing transmission. The codebook is a predefined limited set of several precoding matrices with different ranks. In codebook-based precoding, the UE estimates channel matrices based on cell-specific reference signals, performs an exhaustive search of all precoding matrices, and reports a preferred Precoding Matrix Indicator (PMI) to the eNodeB according to a certain criterion, thereby maximizing system throughput and the like. The PMI determined by the UE can be ignored by the eNodeB.

3GPP TS 36.211 also defines UE-specific reference signals on antenna port 5 transmitted only on the resource block to which the corresponding Physical Downlink Shared Channel (PDSCH) is mapped. The UE-specific reference signal supports non-codebook based single-stream beamforming transmission. In non-codebook based precoding, the precoding weight matrix applied to the UE-specific reference symbols and data symbols is not from the codebook set, but is directly computed by the eNodeB according to various criteria, e.g., the weight matrix can be computed based on eigen-decomposition or based on direction of arrival. In Time Division Duplex (TDD) systems, non-codebook based beamforming/precoding can further reduce uplink feedback and improve beamforming gain due to channel reciprocity.

The DL of LTE systems can use both codebook-based precoding and non-codebook based beamforming/precoding for up to four transmit antennas. The transmit mode switching between codebook-based multi-stream spatial multiplexing transmission and non-codebook-based single-stream beamforming transmission is semi-statically configured via higher layer signaling.

Some communication systems currently specified by 3GPP (such as LTE-advanced) can employ more than four transmit antennas in order to achieve more aggressive performance goals. For example, from a precoder and reference signal perspective, a system with an eNodeB with eight transmit antennas requires an extension of current LTE codebook-based precoding.

PRSs are transmitted from one antenna port (R6) in a predefined pattern, as for example in 3GPP TS 36.211 V9.0.0 "Evolved universesClause 6.10.4 of al terrestial Radio Access (E-UTRA), Physical Channels and Modulation (Release 9) "(12 months 2009). One of the currently agreed upon PRS patterns is shown in FIG. 5, which corresponds to the left side of diagram 6.10.4.2-1 of 3GPP TS 36.211, containing R₆The squares of (a) indicate PRS resource elements in a block of 12 subcarriers over 14 OFDM symbols (i.e., a 1-ms subframe with a normal cyclic prefix).

A set of frequency shifts can be applied to the predefined PRS patterns in order to obtain a set of orthogonal patterns that can be used in neighboring cells to reduce interference to the PRS and thus improve positioning measurements. An effective frequency reuse of six can be modeled in this manner. The frequency shift is defined as a function of the physical cell id (pci) and is expressed as follows:

。

wherein v is_shiftIs the frequency shift, mod () is the modulo function, and PCI is the physical cell ID. PRSs can also be transmitted with zero power or in the case of muting (muted).

To improve the audibility of PRS, i.e. to enable detection of PRS from multiple sites and with suitable quality, positioning subframes have been designed as low interference subframes, i.e. it has also been agreed that data transmission is generally not allowed in positioning subframes. Thus, the PRS of the synchronization network ideally suffer only from PRS interference from other cells with the same PRS pattern index, i.e., the same vertical offset (v _ shift), and not from data transmission interference.

In partially aligned asynchronous networks, PRSs can still suffer from transmission over data channels, control channels and any physical signal interference when positioning subframes collide with normal subframes, but this interference is reduced by partial alignment, i.e., by aligning the start of positioning subframes in multiple cells within half of a subframe with respect to some time base. PRS is performed over a plurality of consecutive subframes (N_PRS) I.e. a predefined positioning subframe grouped by one positioning occasion, which occurs periodically with a certain periodicity of the N subframes, i.e. the time interval between two positioning occasions. The currently agreed periods N are 160, 320, 640 and 1280 ms, and consecutive sub-frames N_PRSCan be 1, 2, 4 or 6 as described in 3GPP TS 36.211 referenced above.

As mentioned above, methods and apparatus according to the above embodiments include, but are not limited to, one or more of the following: signaling to support gap configuration, methods for gap configuration and using the X2 interface for exchanging information about the frequency used for positioning measurements.

Furthermore, the above embodiments can also be incorporated in user plane and/or control plane positioning solutions (although the latter is currently considered more general), in addition to OTDOA and E-CID, as well as other positioning methods and hybrids thereof. It will be understood that the present description is provided in terms of an eNodeB as a radio network node, but the invention can be implemented in other types of radio network nodes, e.g. pico BSs, home nodebs, etc.

Claims (42)

1. A method in a radio network node (81) of a wireless communication system, of supporting configuration of a measurement gap pattern for a user equipment (91) requiring measurement gaps for performing inter-frequency measurements for positioning, the method comprising:

receiving (71) from the user equipment an indication (85) of: the user equipment (91) will perform inter-frequency measurements for positioning, which inter-frequency measurements require measurement gaps.

2. The method of claim 1, wherein the inter-frequency measurements are reference signal time difference, RSTD, measurements.

3. The method according to claim 1 or 2, wherein the received indication (85) comprises an indication of a measurement gap pattern required by the user equipment (91) for performing the inter-frequency measurements.

4. The method according to any of claims 1-3, wherein the received indication comprises information on timing of occurrence of a reference signal to be used for the inter-frequency measurements.

5. The method of claim 4, wherein the received indication comprises offset information that can be used to configure the measurement gap pattern such that a sufficient amount of reference signals to be used for the inter-frequency measurements fall in measurement gaps of the measurement gap pattern.

6. The method of claim 3, wherein the indication of a measurement gap pattern is an indication of a need to configure a predefined measurement gap pattern.

7. The method of claim 6, wherein the predefined measurement gap pattern specifies a 6 ms gap occurring every 40 ms.

8. The method of any of claims 1-7, further comprising: determining (73) a measurement gap pattern for performing the inter-frequency measurement based on the received indication (85).

9. The method of claim 8, further comprising: signaling information (86) to the user equipment (91) to initiate use of the determined measurement gap pattern in the user equipment (91).

10. The method of claim 9, wherein the information (86) signaled to the user equipment comprises:

a time or reference point from when the determined gap pattern will be applied, and/or

The determined measurement gap pattern.

11. The method of any of claims 8-10, further comprising: storing the determined measurement gap pattern associated with the user equipment.

12. The method of any of claims 1-11, further comprising: receiving an indication from the user equipment that the user equipment (91) is to stop the inter-frequency measurements.

13. A radio network node (81) of a wireless communication system, wherein the radio network node is configured for signal interaction with a user equipment (91) requiring configuration of a measurement gap pattern for performing inter-frequency measurements, wherein the radio network node comprises a receiver (82), the receiver (82) is configured to receive from the user equipment an indication (85) of: the user equipment (91) will perform inter-frequency measurements for positioning, which inter-frequency measurements require measurement gaps.

14. The radio network node (81) according to claim 13, wherein the inter-frequency measurements are reference signal time difference, RSTD, measurements.

15. The radio network node (81) according to claim 13 or 14, wherein the indication (85) comprises an indication of a measurement gap pattern required by the user equipment (91) for performing the inter-frequency measurements.

16. The radio network node (81) according to any of claims 13-15, wherein the indication (85) comprises information about the timing of the occurrence of a reference signal to be used for the inter-frequency measurements.

17. The radio network node (81) according to claim 16, wherein the indication (85) comprises offset information which can be used to configure the measurement gap pattern such that a sufficient amount of reference signals to be used for the inter-frequency measurements fall in measurement gaps of the measurement gap pattern.

18. The radio network node (81) according to claim 15, wherein the indication of a measurement gap pattern is an indication of a predefined measurement gap pattern.

19. The radio network node (81) according to claim 18, wherein the predefined measurement gap pattern specifies a 6 ms gap occurring every 40 ms.

20. The radio network node (81) according to any of claims 13-19, further comprising a processor (83), the processor (83) being configured to determine a measurement gap pattern for performing the inter-frequency measurements based on the received indication.

21. The radio network node (81) according to claim 20, further comprising a transmitter (84), the transmitter (84) being configured to signal information (86) to the user equipment in order to initiate the use of the determined measurement gap pattern in the user equipment (91).

22. The radio network node (81) according to claim 21, wherein the transmitter (84) is configured to include in the information signalled to the user equipment (91):

a time or reference point from when the determined gap pattern will be applied, and/or

The determined measurement gap pattern.

23. The radio network node (81) according to any of claims 20-22, further comprising a memory (88), the memory (88) being configured to store the determined measurement gap pattern associated with the user equipment (91).

24. The radio network node (81) according to any of claims 13-23, wherein the receiver (82) is further configured to receive an indication from the user equipment (91) that the user equipment (91) will stop the inter-frequency measurements.

25. A method in a user equipment (91) of a wireless communication system, of supporting configuration of a measurement gap pattern for inter-frequency measurements performed by the user equipment (91), the method comprising:

receiving (101) an indication (87) requesting the user equipment to start inter-frequency measurements for positioning; and

transmitting (102), to the radio network node (81), an indication (85) about: the user equipment (91) will perform inter-frequency measurements for positioning, which inter-frequency measurements require measurement gaps.

26. The method of claim 25, wherein the inter-frequency measurements are reference signal time difference, RSTD, measurements.

27. The method of claim 25 or 26, wherein the method further comprises the steps of: determining, based on a capability of the user equipment (91), that the user equipment (91) requires a measurement gap for performing the inter-frequency measurement for positioning.

28. The method of any of claims 25-27, further comprising

Determining (103), in response to the received indication, a measurement gap pattern to be configured for performing the inter-frequency measurement based on a predefined set of rules,

configuring (104) the determined measurement gap pattern in the user equipment (91).

29. The method of any of claims 25-27, further comprising: receiving (105), from the radio network node (81), information (86) indicating the determined measurement gap pattern to be configured for performing the inter-frequency measurements;

configuring (106) the determined measurement gap pattern in the user equipment.

30. The method according to any of claims 25-29, wherein the transmitted indication (85) comprises an indication of a measurement gap pattern required by the user equipment for performing the inter-frequency measurements.

31. The method according to any of claims 25-30, wherein the transmitted indication (85) comprises information relating to timing of occurrence of a reference signal to be used for the inter-frequency measurements.

32. The method of claim 31, wherein the transmitted indication (85) comprises offset information which can be used to configure the measurement gap pattern such that a sufficient amount of reference signals to be used for the inter-frequency measurements fall in measurement gaps of the measurement gap pattern.

33. The method of any of claims 25-32, further comprising: transmitting an additional indication to the radio network node (81) indicating that the user equipment (91) will stop the inter-frequency measurements.

34. A user equipment (91) for use in a wireless communication system, wherein the user equipment (91) is configured for signal interaction with a radio network node (81), the user equipment (91) comprising:

a receiver (92) configured to receive an indication (87) of: requesting the user equipment to start inter-frequency measurements for positioning, for which the user equipment requires measurement gaps,

a transmitter (94) configured to transmit, to the radio network node (81), an indication (85) about: the user equipment (91) will perform inter-frequency measurements for positioning, which inter-frequency measurements require measurement gaps.

35. The user equipment (91) according to claim 34, wherein the inter-frequency measurements are reference signal time difference, RSTD, measurements.

36. The user equipment (91) according to claim 34 or 35, wherein the user is configured to determine, based on the capabilities of the user equipment (91), that the user equipment (91) requires a measurement gap for performing the inter-frequency measurements for positioning.

37. The user equipment (91) according to any of claims 34-36, further comprising a processor (93), the processor (93) being configured to:

determining a measurement gap pattern to be configured for performing the inter-frequency measurement in response to the received indication (87) and based on a predefined set of rules, an

Configuring the determined measurement gap pattern in the user equipment.

38. The user equipment (91) according to any of claims 34-36, wherein the receiver (92) is further configured to receive information from the radio network node (81) indicating the determined measurement gap pattern to be configured for performing the inter-frequency measurements, and wherein the user equipment (91) further comprises a processor (93), the processor (93) being configured to configure the determined measurement gap pattern in the user equipment (91).

39. The user equipment (91) according to any of claims 34-38, wherein the transmitter is configured to include in the indication (85) that the transmitter is configured to transmit an indication of a measurement gap pattern required by the user equipment for performing the inter-frequency measurements.

40. The user equipment (91) according to any of claims 34-39, wherein the transmitter is configured to include information relating to timing of occurrence of reference signals to be used for the inter-frequency measurements in the indication (85) that the transmitter is configured to transmit.

41. The user equipment (91) according to claim 40, wherein the transmitter is configured to include offset information in the indication (85) that the transmitter is configured to transmit, the offset information being usable to configure the measurement gap pattern such that a sufficient amount of reference signals to be used for the inter-frequency measurements fall in measurement gaps of the measurement gap pattern.

42. The user equipment (91) according to any of claims 34-41, wherein the transmitter is further configured to transmit an additional indication to the radio network node (81) indicating that the user equipment (91) will stop the inter-frequency measurements.