WO2010107356A1

WO2010107356A1 - An arrangement and a method in a communication network node, an arrangement and a method in a user equipment in a radio communications system

Info

Publication number: WO2010107356A1
Application number: PCT/SE2009/051065
Authority: WO
Inventors: Dirk Gerstenberger; Daniel Larsson
Original assignee: Telefonaktiebolaget Lm Ericsson (Publ)
Priority date: 2009-03-17
Filing date: 2009-09-24
Publication date: 2010-09-23

Abstract

The present invention relates to a communication network node (11, 12) in a radio communications system (100). The communication network node (11, 12) is configured to transmit a positioning subframe to a user equipment (13) within a cell (10) served by the communication network node. The positioning subframe comprises a positioning reference signal (PRS) pattern, which PRS pattern is define based on a cell identifier of the cell, and the positioning subframe with the positioning reference signal pattern is transmitted on a reference signal radio channel to the user equipment (13).

Description

AN ARRANGEMENT AND A METHOD IN A COMMUNICATION NETWORK NODE, AN ARRANGEMENT AND A METHOD IN A USER EQUIPMENT IN A RADIO COMMUNICATIONS SYSTEM

TECHNICAL FIELD

The invention relates to an arrangement and a method in a communication network node, an arrangement and a method in a user equipment in a radio Communications system. In particular, the invention relates to transmit a positioning subframe to the user equipment within a cell of the radio communications system.

BACKGROUND

In radio today's communications system, a function that is increasingly used is the positioning of a user equipment (UE). This enables a number of different services, for example, location services, to be provided to cellular subscribers. Positioning methods specified for WCDMA are described below. These methods are generally applicable also in wireless communications systems using other radio access technologies, such as the Long-Term Evolution (LTE), also known as the Evolved Universal Terrestrial Radio Access Network (E-UTRAN).

The third generation cellular systems can be equipped with a number of different positioning methods, thereby enabling location services to the cellular subscribers. The methods that are available comprise

Cell identity (Cell-ID) positioning. Enhanced cell identity (Ecell-ID) positioning • Assisted GPS (A-GPS) positioning

Observed time difference of arrival - with idle periods in the downlink (OTDOA-

IPDL) positioning

Uplink time difference of arrival (UTDOA) positioning

These positioning methods are briefly described as follows:

Cell-ID positioning determines the cell to which the user equipment (UE) is connected. The position of the user is hence determined with cell granularity. Typically the radio network controller (RNC) of the radio access network (RAN) determines a 3-15 corner polygon that determines the geographical extension of the cell. The corners of this polygon are given as latitude, longitude coordinate pairs in the WGS84 geographical reference system. The cell-ID method is the backbone of all cellular positioning system since it is always available when the user equipment can be connected to the system.

Ecell-ID positioning augments the Cell-ID positioning with auxiliary information that narrows down the area that is determined by the cell polygon. The most useful method in the wideband code division multiple access (WCDMA) system is the round trip time (RTT) measurement. This RTT measurement determines the travel time from the radio base station (RBS) to the user equipment and back. Using the speed of light, the distance from the known position of the RBS to the user equipment can be calculated, which determines a circular strip around the RBS where the user equipment is located. The thickness of the strip is determined by the measurement uncertainty. The Ecell-ID method is obtained by noticing that the user equipment is located both in the cell and in the circular strip - hence the user equipment is located in the intersection of these two geographical regions.

A-GPS positioning is an enhancement of the US military global positioning system (GPS). GPS reference receivers attached to e.g. a cellular communication system, collect assistance data that, when transmitted to GPS receivers in user equipments connected to the cellular communication system, enhances the performance of the GPS user equipment receivers. Typically, A-GPS accuracy can become as good as ten meters also without differential operation. The accuracy becomes worse in dense urban areas and indoors, where the sensitivity is often not high enough for detection of the very weak signals from the GPS satellites. Advantages of A-GPS includes a high accuracy, the method easily meets the North-American emergency positioning E-91 1 requirements of 50 meters for 67% of all positionings and 150 meters for 95% of all positionings. A drawback is the limited indoor coverage, which is a result of the low ranging signal strengths that are obtained at ground level.

OTDOA-IPDL positioning is similar to A-GPS in that it relies on time difference of arrival measurements. However, the OTDOA-IPDL method uses in WCDMA user equipment measurements of Common Pilot Channel (CPICH) signals transmitted from several RBSs. The measurement results are signaled to the RNC, where a hyperbolic trilateration method is used for calculation of the position of the user equipment. In order to enhance the hearability of the RBSs in the user equipment, there is a possibility to use idle periods in the downlink (IPDL), to attenuate the transmissions from the RBS to which the user equipment is connected. This reduces the interference and hence enhances the hearability of other RBSs. A possible advantage with OTDOA-IPDL is that it theoretically provides a better indoor coverage than A-GPS.

UTDOA positioning is another method. It is similar to A-GPS in that it relies on time difference of arrival measurements. However, the UTDOA method uses RBS or separate location measurement unit (LMU) measurements of signals transmitted from the positioned user equipment. The transmitted signal is detected in a number of RBSs or LMUs, after which the measured results are signaled to a positioning node where the position of the user equipment is determined by a trilateration method. In order to be able to detect the time of arrival from measurements of opportunity from the user equipment, a reference signal first needs to be created in a master-LMU or master RBS. This is done by decoding of the signal, followed by reconstruction of the chip stream that then forms the reference signal. An advantage of UTDOA positioning is that it provides a better indoor coverage than does A-GPS. Outdoor accuracy is normally inferior to A-GPS though.

An issue with terrestrial time difference of arrival methods, that is, OTDOA-IPDL and UTDOA, is the receiver sensitivity when positioning is considered. Theoretically, the methods can provide a 3-D position from four time of arrival - measurements, that is, equivalent to three time difference of arrival pseudo measurements. However, radio propagation conditions are far less beneficial than for A-GPS, since OTDOA-IPDL and UTDOA ranging signals propagate along the surface of the Earth, whereas A-GPS signals propagate from above. The terrestrial positioning methods therefore suffer more from non- line-of-sight (LOS) propagation and multipath propagation. This results in outlier measurements, whose suppression requires the availability of excess detections i.e. detections from significantly more than the minimum number of RBSs. In practice, to achieve a useful positioning accuracy, at least 6-8 RBSs need to be detected in the user equipment in case OTDOA-IPDL positioning is used. For UTDOA positioning at least 6-8 RBSs need to detect the user equipment transmissions in order to obtain useful position estimates in practical environments.

The consequence of the above is that more remote RBSs need to be detected in OTDOA-IPDL or detect the user equipment in UTDOA. This means that lower signal strengths need to be detected with high probability. Calculations typically show that signals need to be detected down to about -40 dB C/l. Further, the pre-detection step needs to enhance the signal to about 1 1-13 dB C/l in order to achieve a sufficiently low false alarm rate. In essence, the processing gain for positioning purposes in any Code Division Multiple Access (CDMA) system needs to be 50-55 dB for terrestrial positioning to be useful. This is significantly more than what is needed for other services, which means that positioning sensitivity requirements need to be assessed at the definition phase of the air-interface.

A problem with these positioning methods is that A-GPS positioning is a high precision technology with one main drawback - the poor indoor positioning availability. Furthermore, the OTDPA-IPDL and UTDOA positioning have the technical potential to provide better indoor coverage than A-GPS and to deliver good precision. However, the presently available detection sensitivities are not sufficient to provide a good enough accuracy.

SUMMARY

An object of embodiments herein is to disclose a mechanism that improves the positioning accuracy of a user equipment in a cell.

In order to achieve the object a method in a communication network node is provided. The communication network node is comprised in a radio communications system. The method is for transmitting a positioning subframe to a user equipment within a cell served by the communication network node. The positioning subframe supports positioning of the user equipment and comprises a positioning reference signal pattern. The communication network node defines the positioning reference signal pattern in the positioning subframe based on a cell identifier of the cell, and transmits the positioning subframe according to the positioning reference signal pattern on a reference signal radio channel to the user equipment. The communication network node may be represented by a radio base station or a network node, such as a positioning node.

In order to perform the method an arrangement in the communication network node is provided. The arrangement comprises a defining unit arranged to define the positioning reference signal pattern in the positioning subframe based on the cell identifier of the cell. The arrangement further comprises a transmitting unit arranged to transmit the positioning subframe with the positioning reference signal pattern on the reference signal radio channel to the user equipment. Hence, the positioning accuracy, by increasing the hearabiiity for the user equipment, for various multiple access schemes, is improved.

According to a second aspect, the object is achieved by providing a method in a user equipment. The method is for determining a time indication related to an arrival of a positioning subframe at the user equipment transmitted from the communication network node. The user equipment receives a cell identifier from the communication network node and calculates a positioning reference signal pattern based on the cell identifier. The user equipment further detects a positioning subframe comprising the calculated positioning reference signal pattern, and determines the time indication of the detected positioning subframe.

In order to perform the method an arrangement in the user equipment is provided. The arrangement comprises a receiving unit arranged to receive the cell identifier from the communication network node. The arrangement further comprises a calculating unit arranged to calculate the positioning reference signal pattern based on the cell identifier. Furthermore, the arrangement comprises a detecting unit arranged to detect a positioning subframe comprising the calculated positioning reference signal pattern from the communication network node. The arrangement also comprises a determining unit arranged to determine the time indication of the detected positioning subframe.

It should here be understood that the time indication may then be used to position the user equipment in the user equipment, a radio base station, or a positioning node.

The invention enables an automatic method for defining how PRS pattern should be defined for positioning subframes. This method would, automatically, select the PRS pattern on the basis of cell identifier and, in some embodiments also time, which would decrease the complexity of deploying positioning in for example, LTE network and increase the hearabiiity for the user equipments. Hence, the positioning accuracy is improved.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments will now be described in more detail in relation to the enclosed drawings, in which: Figure 1 shows an overview of a radio communications system,

Figure 2 shows a schematic overview of positioning subframes,

Figure 3 shows a schematic combined method and signalling scheme in radio communications system, Figure 4 shows a schematic combined method and signalling scheme in a radio communications system,

Figure 5 shows a flow chart of a method in a communication network node in a radio communications system,

Figure 6 shows a flowchart of a method in a communication network node in a radio communications system,

Figure 7 shows a schematic overview of a communication network node in a radio communications system,

Figure 8 shows a schematic overview of a communication network node in radio communications system, Figure 9 shows a flowchart of a method in a user equipment in a radio communications system,

Figure 10 shows a flowchart of a method in a user equipment in a radio communications system, and

Figure 11 shows a schematic overview of a user equipment in a radio communications system.

DETAILED DESCRIPTION

Fig. 1 shows an overview of a radio communications system 100 in which present solution is suitably applied. As shown, the radio communications system 100 is a cellular system and comprises a number of cells; one is shown as a cell 10 in Fig 1. For each cell in the radio communications system 100, there is a controlling node, generically referred to as a "radio base station", RBS, which is shown as 11 in Fig 1. In the radio communications system 100 the RBS 11 is connected to a network node 12, such as a positioning node in the core network. The radio base station 1 1 and the network node 12 are herein also referred to as communication network nodes. Each cell may comprise a number of user terminals, with the generic name "UE", User Equipment, one is shown as a user equipment 13 in Fig 1. One role of the radio base station 1 1 is that all traffic to and from the user equipment 13 in the cell 10 are routed via the radio base station 1 1. The base station 1 1 serves the user equipment 13 in the cell 10 of the base station 11. The present solution is applicable in WCDMA systems, LTE systems as well as to other systems, wherein the 5 radio base station 11 may be denoted as NodeB or eNodeB.

In some embodiments the radio communications system 100 uses OTDOA for positioning. For LTE, Downlink OTDOA is one candidate for positioning the user equipment 13 using user equipment measurements on measurement signals, e.g.

10 reference signals and/or synchronization signals from radio base stations. In the illustrated example, two second radio base stations 14,15 are comprised in the radio communications system 100 and the radio base stations 11 ,14,15 transmit positioning subframes. The user equipment 13 performs measurements in designated positioning subframes. The measurements on cells with weak received signals at the user equipment

15 13 are improved by designating low interference subframes in some of the positioning subframes.

The user equipment 13 determines time differences of arrival of the positioning subframe of the different radio base stations 14,15 relative the arrival of the positioning

20 subframe from radio base station 11. From the time differences of arrival, knowing the positions and transmission times, a first distance 16 from the first radio base station to the user equipment and a second and third distance 17,18 from the second and third radio base station 14, 15 to the user equipment 13 may be determined. The distances may then be used in the user equipment 13, radio base station 11 or the network node 12 5 to determine the position coordinates of the user equipment 13.

In a radio communications system, to support positioning based on OTDOA, all cells typically have simultaneous designated positioning subframes. To increase hearability for the user equipment 13 when measuring on the measurement signals of 0 cells in the neighborhood of the serving cell 10 that are not necessarily strictly adjacent cells, a positioning subframe may contain a specific Reference Signal (RS) pattern intended for positioning. The RS pattern may be denoted as Positioning Reference Signal (PRS) pattern or RS reuse pattern. In practice a positioning subframe may, for example, be a subframe which has no data scheduled in it, which has no data scheduled in a part or parts of it, or which has less than the maximum possible amount of data scheduled in it, or in a part or parts of it. Furthermore, a positioning subframe may have specific RS pattern in part or parts of the subframe that is intended to be used for positioning. The specific RS pattern has a reuse factor, so that different cells have different pattern. The reuse pattern may either be in frequency or time or both.

Embodiments herein focus on a technique wherein the PRS pattern shall be based on a cell identifier and also in some embodiments a timing varying component increasing the hearability for the user equipment 13 improving the accuracy of the positioning of the user equipment 13. Hence, the positioning accuracy, for various multiple access schemes, is improved. In particular orthogonal frequency division multiple (OFDM) access schemes are discussed as well as a multiple access method with combined variable bandwidth, time division access with scrambling codes added. The invention is however not limited to these access methods - other combinations are likely to occur in the future

Fig. 2 shows a combined method and signalling scheme in the radio communications system 100 showing embodiments of the present solution. The steps do not have to be taken in the order stated below, but may be taken in any suitable order.

Step 201

This is an optional step. The network node 12, such as a positioning node, transmits a cell identifier of the cell 10 of the radio base station 11 and possibly other configuration parameters to the radio base station 1 1. The network node 12 may be represented by an Operation Support System (OSS) node.

Step 202 The radio base station 11 transmits the cell identifier and other configuration parameters to the user equipment 13. The cell identifier may be broadcasted from the radio base station 11 with other system information such as a System Frame Number (SFN), subframe number, slot number and/or the like. This may also be broadcasted transparently through the radio base station 11 from the network node 12, such as an evolved Serving Mobile Location Center (eSMLC) that provides a centralized serving location calculation platform for the evolved UTRAN in LTE

Step 203 This is an optional step The network node 12 may comprise a function to disclose position of the user equipment 13 or be connected to an emergency centre that needs to know the position of the user equipment 13 The network node 12 may then request a positioning of the user equipment 13 from the radio base station 11

Step 204

The radio base station 11 defines a PRS pattern of a positioning subframe to be used to position the user equipment 13 The PRS pattern is defined based on the cell identifier The radio base station 1 1 automatically determines the PRS pattern to be used in a positioning frame based on at least the cell identifier The PRS pattern may automatically be defined by the cell identifier, a SFN, a subframe number, and/or the like The term "positioning subframe" refers to a subframe intended for positioning purposes That is, signalling reference signals to be used for positioning

It should be understood that the radio base station 11 may have different PRS patterns to different served cells but may also use the same PRS pattern for cells served by the same radio base station, for example, all cells in a three sector site

This step may also be performed by the network node 12

Step 205

The user equipment 13 defines or generates the PRS pattern of a positing subframe using the cell identifier The way of defining the user equipment is preset in the user equipment, transmitted during configuration, and/or the like The user equipment 13 then knows the PRS pattern to detect in the positioning subframe, by, for example, using the cell identifier in a function that automatically defines the PRS pattern of that cell It should, however, be understood that the radio base station 11 may transmit the PRS pattern as such to the user equipment 13

Step 206

The radio base station 1 1 transmits the positioning subframe with the PRS pattern on a pilot radio channel to the user equipment 13 The radio base station 11 may broadcast the positioning subframe periodically within the cell The positioning frame may be transmitted in a configured manner, for example, once every second and/or the like The time of transmission may be recorded, stored and/or determined at the radio base station 11 This step may also be performed by the network node 12

Step 207

The user equipment 13 receives the positioning frame and detects the positioning subframe based on the PRS pattern The user equipment then determines a time indication of the arrival of the positioning subframe The user equipment may further receive positioning subframes from different, synchronized or not synchronized, radio base stations The user equipment 13 may then determine time differences of arrival of the different positioning subframes from the different radio base stations and records and stores the time differences of arrival

Step 208 This is an optional step The user equipment 13 transmits the time differences of arrival of the positioning subframes to the radio base station 11

The radio base station 11 may determine position of the user equipment 13 based on the time differences of arrival of the positioning subframes if the radio base station 11 has information of locations as well as transmission times of the different radio base stations However, in the illustrated embodiment the radio base station 10 continues to step 209

Step 209 This is an optional step The radio base station 11 transmits the time differences of arrival to the network node 12 The network node 12 may be represented by an OSS node or a positioning node

Step 210 This is an optional step The network node 12 calculates the position of the user equipment 13 from the received time differences of arrival in conjunction with known positions and transmission times of the radio base stations 11 ,14,15 This may be performed as a multilateration calculation, tπlateration or the like It should be understood that this step may also be performed in the user equipment 13 and/or the radio base station if the positions and transmission times of the radio base stations are known in these devices

Step 211

5 This is an optional step The position may be transmitted to the radio base station

11 and/or the user equipment 13 The position may be used in many different ways and applications The user equipment 13 may be informed of the position to be used in a positioning application in the user equipment 13, the radio base station 11 may be informed of the position to be used in a positioning application in the radio base station 10 11 The network node 12, being represented as an OSS or a positioning node, may transmit the position to a central emergency server for determining position of a user equipment 13 if the user is in distress, and/or the like

It should be noted that the network node 12 or the radio base station 11 may 15 determine which cell identifiers that are relevant to the user equipment 13 For example, the network node 12 determines a number of cell identifiers that are in a range of the cell of the radio base station 11 So if cell identifiers of neighbouring cells of a cell of the radio base station are transmitted to the user equipment 13, the user equipment 13 knows which positioning subframes to look out for Thereby the operation of positioning the user 0 equipment 13 may be efficiently performed

Fig. 3 is a combined signalling scheme and flowchart depicting embodiments of a method for determining a position of the user equipment 13 in the user equipment 13 The 5 steps do not have to be taken in the order stated below, but may be taken in any suitable order

In step 311 , a first radio base station 1111 transmits a cell identifier of a first cell served by the first radio base station 1 1 11 on a broadcast channel 0

In step 312, a second radio base station 1112 transmits a cell identifier of a second cell served by the second radio base station 1 1 12 on a broadcast channel

In step 313, a third radio base station 1113 transmits a cell identifier of a third cell 5 served by the third radio base station 1 1 13 on a broadcast channel In step 32, the user equipment 13 defines a PRS pattern for each cell

In step 331, the first radio base station 1111 transmits a positioning subframe carrying a PRS pattern of the first cell over a carrier such as a pilot channel

In step 332, the second radio base station 1112 transmits a positioning subframe carrying a PRS pattern of the second cell over a carrier

In step 333, the third radio base station 1113 transmits a positioning subframe carrying a PRS pattern of the third cell over a carrier

In step 34, the user equipment 13 determines a time value, a time of arrival, and specific in the illustrated embodiment the time differences of arrival with respect to a signal received from the radio base station 1 111 serving the user equipment These time values may be transmitted to a central entity for determining position of the user equipment 13 The central entity may be represented by a radio base station, an OSS node, or and eSLMC Thus, the user equipment 13 receives the positioning subframes and performs time measurements on these The user equipment 13 may also, based on these measurements, knowing the positions and transmission times of the radio base stations, determine its own position

An example of the PRS pattern is shown in Fig 4, which corresponds to one Physical Resource Block (PRB) for LTE DL for one TX antenna, where f is the subcamer numbering and I is the OFDM symbol number The PRS pattern is only defined in frequency for this case and it has six possible PRS pattern, however in Fig 4 only two of the six PRS patterns are shown In a first subframe 41 reference signals, the diagonally striped symbols, are allocated according to a first positioning reference pattern In a second subframe 42 reference signals are allocated according to a second positioning reference pattern With this pattern only 6 unique PRS pattern may be constructed

The reuse factor is limited to finite number of possible PRS pattern The user equipment 13 has to measure up to five or six different cells in its neighborhood to acquire accurate position for OTDOA based positioning Configuring each cell in the network separately to use a specific PRS pattern for the RS is a complex task Hence, an automatic method would be preferred that also minimizes the need for extra signaling overhead

Embodiments herein focus on a technique for determining which PRS pattern is used in a specific cell The PRS pattern is based on a cell identifier and also in some embodiments a timing varying component as stated above

The PRS pattern to be used is defined by a cell identifier A cell identifier constitutes a particular cell in the wireless communications system Examples of cell identifiers are the physical layer cell-id (PCI), EUTRAN Cell Global identity (E-CGI) or the cell-id in conjunction or not with a cell-specific parameter A further step may be to inform the user equipment 13 about the cell identifier for all the cells it should measure on during the positioning subframe For a LTE system, this involves signaling of control information from the network node 12, such as an eSLMC

The physical-layer cell-identity group N^ is typically the same for all cells with the same carrier frequency in a three-sector site In a three-sector site deployment the embodiment would imply that all the cells at the same base station 11 and with the same carrier frequency follow the PRS pattern This would hence minimize the disturbance from the closest site when the user equipment 13 is measuring on cells at other sites, i e in the neighborhood For handling other cell deployment scenarios where distinct cells in the neighborhood may have the same physical-layer cell-identity group e g in cases where distributed radio heads are used that are controlled by the same base station or in cases where time dispersion becomes too large, a cell-specific configurable parameter could be utilized

In some embodiments, a time varying function for changing the PRS pattern in time, may be based on System Frame Number (SFN) n_f , subframe number and/or slot number A further step is for the user equipment 13 to be able to determine which PRS pattern is used in a network that is not SFN synchronized, where the user equipment 13 will have to be signaled either one or multiple SFN offsets between serving cell and the measured cells or the complete SFN timing of the measured cells For an LTE system positioning is based on the node 12 in the core network called eSLMC that signals control information directly to the user equipment 13, transparently through the radio base station 11. Another possibility would be that the user equipment 13 blindly detects which PRS pattern is used.

One example on how the PRS pattern may be calculated could be implemented as outlined below. Other ways to implement this could also be possible implementations of the solution.

f{Nff,n_f )= {N%^ll +n_f )modn_n reuse factor where N₁^ is the cell identifier, n_reuse f_actor is the number of PRS pattern factors that are available and

J defines the specific reuse pattern to use in the specific cell in during a specific SFN.

f(N$ , n, , n_→cmκ ) = HT w,c(i + [k, - n_f + k₂ - n_sιώfnme J) mod n_{reme jaam} ,

where the pseudo-random sequence c(i) is defined by a length-31 Gold sequence, 7V is a parameter, Ic_x and Ic₂ are constants, ⁿ _subfr_ame '^s *^ne subframe number, W₁ are weights, [xj denotes the largest number not greater than x and f (N⁰^n_n n_uώframe) define the specific reuse pattern to use in the specific cell during a specific subframe within a specific SFN.

An exemplary set of values of the parameters is N = 9 , k_x = 10 , k₂ = 1 , W₁ = 2' .

The pseudo-random sequence generator shall be initialized with c_init = N_iD .

The solution enables an automatic method for defining how PRS pattern should be defined for positioning subframes. This method would automatically select the PRS pattern on the bases of cell identifier and also, in some embodiments, time which would decrease the complexity of deploying positioning LTE network and increase the hearability for the user equipments.

A general case is when a collision between PRS in measurement subframes should be avoided, which is especially relevant in case of a synchronized network. To avoid collision, the PRS pattern can be reused in the frequency domain. From a network deployment complexity point of view however, it is preferable to define a simple reuse scheme, e.g. derived from to the cell identifier. It would further simplify the cell planning if the PRS pattern in a cell would vary in time.

In Fig. 5, a general embodiment of a method in a communication network node 11 ,12, exemplary denoted in the illustrated embodiment of Fig. 5 as radio base station 11 but may also be the network node 12, for transmitting a positioning subframe to a user equipment 13 within a cell served by the communication network node 11 , 12 is shown. The steps do not have to be taken in the order stated below, but may be taken in any suitable order. As mentioned above, the communication network node 11 ,12 is comprised in the radio communications system 100. Furthermore, the positioning subframe supports positioning of the user equipment 13 and comprises a positioning reference signal pattern.

In step 51 , the radio base station 11 defines the positioning reference signal pattern in the positioning subframe based on a cell identifier of the cell. The cell identifier may comprise the PCI.

In step 52, the radio base station 11 transmits the positioning subframe according to the positioning reference signal pattern on a reference signal radio channel to the user equipment 13.

This method would automatically select the positioning reference signal pattern on the bases of cell identifier, which would decrease the complexity of deploying positioning network and increase the hearability for the user equipments within the cell of the radio base station.

The method steps in the communication network node for transmitting data transmissions to a user equipment in a first cell according to some further embodiments will now be described with reference to a flowchart depicted in Fig. 6. The steps do not have to be taken in the order stated below, but may be taken in any suitable order. The communication network node is illustrated as the radio base station 11 but may also be represented by a core network node such as a eSLMC, a controller node, and/or any node within a communications system used for positioning

In optional step 61, the radio base station 11 transmits data comprising the CeII- ID, subframe number, and/or configuration parameter such as a time offset within the cell to the user equipment over a control channel The control channel may comprise a broadcast channel and the cell identifier may be represented by a PCI of the cell, the cell- id in conjunction or not with a cell-specific parameter and/or the like This is for informing the user equipment of the positioning reference signal pattern of which the user equipment should perform signal measurements Thus, the user equipment may determine the RS reuse pattern defined by a function comprising the received data The received data comprising cell identifier and, in some embodiments, SFN, configuration parameter and/or the like,

The radio base station 11 may receive a request to position the user equipment

The request may be received from an OSS node, a/the user equipment, another communication device, an application within the radio base station 11 and/or the like The position may be determined on demand

In step 62, the radio base station 11 defines the positioning reference signal pattern in the positioning subframe based on a cell identifier of the cell The cell identifier may comprise the PCI Step 62 of Fig 6 corresponds to the step 51 in Fig 5

The defining of the positioning reference signal pattern may also be based on a time varying function, which time varying function changes the positioning reference signal pattern in time based on a time parameter This would further increase the number of positioning reference signal patterns Furthermore, the time varying function may use a SFN, subframe number and/or slot number as the time parameter

The positioning reference signal pattern may be automatically selected according to a function of cell identifier and a factor of the number of reusable positioning reference signal pattern that are available

In step 63, the radio base station 11 transmits the positioning subframe according to the positioning reference signal pattern on a reference signal radio channel to the user equipment Step 63 of Fig 6 corresponds to the step 52 in Fig 5 The reference signal radio channel may comprise reference signals in an LTE system or pilot signals in a WCDMA system.

Positioning subframes may be sent on demand from a user equipment when the user equipment wants to be positioned. However, in some embodiments, the positioning subframes may be configured to be continuously transmitted and when a user equipment want to be positioned the user equipment uses the positioning subframes. Thereby, a complicated coordination of base stations may be avoided that may be needed to support "on demand" embodiments.

In optional step 64, the radio base station 11 receives a response message with a time indication related to the positioning subframe from the user equipment 13. Such a time indication may comprise time difference of arrival indication of the positioning subframe, arrival time indication or transmission time and/or the like.

In optional step 65, wherein the time indication comprises time differences of arrival of positioning subframes of two different cells related to the positioning subframe of the cell, the radio base station 11 receives at least two positional bits of data from at least one radio base station 14,15 or a network node 12, which at least two positional bits of data each indicates position of different radio base stations 14,15 serving the different cells. The bits of data may also comprise transmission times of the positioning subframes of the different cells.

In optional step 66, the radio base station 11 positions the user equipment 13 to position coordinates based on the time differences of arrival, the position of the radio base station 11 and the received at least two positional bits of data. This may be performed by multilateration, trilateration or the like.

In order to position the user equipment 13 a plurality of distances of the user equipment 13 to other communication devices may be analysed and compared, this may be performed in the radio base station 11 , an OSS node, a positioning node and/or the like. The position may be determined, such as a differential distance value to the user equipment 13 based on time differences of arrival of the positioning subframes.

In alternate step 67, the radio base station 11 transmits over a network interface the time indication, for example, the time differences of arrival, to a communication network node. The communication network node may then determine position of the user equipment 13 The radio base station 11 may also transmit over the network interface the position coordinates to a communication network node

A positioning system using the PRS pattern may comprise an OTDPA-IPDL system

The Cell identifiers may be defined in the network during configuration and hence the positioning reference signal pattern may be defined automatically in the network during configuration through the function

It should here be understood that the radio base station 11 or an OSS node may have knowledge of surrounding cells/radio base stations and may determine based on, for example, what cell the user equipment 13 is presently located in, relevant cells that may be used to determine the position of the user equipment 13

Another example of a method in the communication network node 11 ,12 such as a positioning node such as eSLMC, an OSS node for positioning a user equipment or the radio base station is here described

The communication network node 1 1 ,12 may determine a number of relevant, to be able to position the user equipment 13, cells of surrounding communication devices The communication network node 1 1 ,12 may then transmit the cell identifier of these relevant cells to the user equipment 13 The user equipment 13 may then perform measurements during the positioning subframe for the positioning reference signal pattern of these relevant cells Hence, the user equipment 13 may based on the cell identifier calculate/determine the positioning reference signal pattern of that cell The user equipment 13 may then perform measurements, for example, time of arrival, of positioning subframes of the relevant cells

Furthermore, the communication network node 11 ,12 transmits positioning subframes comprising the positioning reference signal pattern based on the cell identifier of the cell controlled or served by the communication network node 11 , 12

The communication network node 1 1 ,12 may also receive time measurements of positional subframe, time differences of arrival, from the user equipment 13 of at least one, some or all relevant cells Based on the received time measurements, the communication network node 11 ,12 may determine a position of the user equipment 13 In order to perform the methods an arrangement 700 in the communication network node 11 ,12 is provided. In Fig. 7, the communication network node 11 ,12 comprising the arrangement 700 is shown. The arrangement 700 is configured to transmit the positioning subframe to a user equipment 13 within the cell 10 served by the communication network node 11 ,12. The communication network node 11 ,12 is illustrated as the radio base station 11.

The radio base station 11 comprises a defining unit 701 arranged to define the positioning reference signal pattern in the positioning subframe based on a cell identifier of the cell. The radio base station 11 further comprises a transmitting unit TX 703 arranged to transmit the positioning subframe with the positioning reference signal pattern on reference signal radio channel to the user equipment.

In some embodiments, the reference signal radio channel comprises a reference signals in LTE or pilot signals in WCDMA.

The positioning reference signal pattern may further be based on a time varying function, which time varying function changes the positioning reference signal pattern in time based on a time parameter. The time parameter may comprise a system frame number, subframe number and/or slot number.

Furthermore, the transmitting unit TX 703 may further be arranged to transmit data comprising the cell identifier, subframe number, and/or configuration parameter within the cell 10 to the user equipment 13 over a control channel.

The arrangement 700 may further comprise a receiving unit RX 705 configured to receive, from the user equipment 13, a response comprising a time indication related to the positioning subframe. The time indication may comprise time differences of arrival between different positioning subframes of different cells in relation to the time of arrival of the positioning subframe of the cell.

The arrangement 700 may comprise a network interface NI 708 arranged to transmit the time indication, for example, the time differences of arrival, to a communication network node. The communication network node may then determine position. The network interface 708 may also be arranged to receive at least two positional bits of data from at least one radio base station 14,15 or a network node 12 The two positional bits of data each indicates position of different radio base stations 14,15 serving the different cells and transmission times of the different positioning subframes

The arrangement 700 may further comprise a positioning unit 709 arranged to position the user equipment 13 to a position based on the time differences of arrival, the communication node position, the positions of the different radio base stations and transmission times

Furthermore, the arrangement 700 may comprise a memory unit 710 arranged to store data such as positions, pattern calculations, time indications, applications to perform the methods and/or the like The memory unit 710 may comprise a single memory or a plurality of memories, external and/or internal

In Fig. 8, a schematic block diagram of an arrangement 800 in the communication network node 11 ,12 is shown In the illustrated example, the communication network node 12 comprises a positioning node, such as a eSLMC

The positioning node 12 comprises a defining unit 801 arranged to define the positioning reference signal pattern in the positioning subframe based on a cell identifier of the cell 10 The radio base station 12 further comprises a network interface unit (Nl) 803 arranged to transmit the positioning subframe with the positioning reference signal pattern on reference signal radio channel to the user equipment 13 via the radio base station 11 ,1111

The NI 803 may further be configured to receive, from the user equipment 13 via the radio base station 11 , 11 11 , a response comprising a time indication related to the positioning subframe The time indication may comprise time differences of arrival between different positioning subframes of different cells

The arrangement 800 may further comprise a positioning unit 805 arranged to position the user equipment 13 to a position based on the time differences of arrival, positions and transmission times of radio base stations It should be understood that the radio base stations may or may not be synchronised

Furthermore, the arrangement 800 may comprise a memory unit 807 arranged to store data such as positions, pattern calculations, time indications, applications to perform the methods and/or the like The memory unit 807 may comprise a single memory or a plurality of memories, external and/or internal

Fig. 9 is a schematic block diagram depicting a general embodiment of a method in the user equipment 13 The method is for determining a time indication related to an arrival of a positioning subframe at the user equipment 13 transmitted from a communication network node 11 ,12 The positioning subframe supports positioning of the user equipment 13 The steps do not have to be taken in the order stated below, but may be taken in any suitable order

Step 91

The user equipment 13 receives a cell identifier from the communication network node

Step 92

The user equipment 13 calculates a positioning reference signal pattern based on the cell identifier

Step 93 The user equipment 13 detects a positioning subframe comprising the calculated positioning reference signal pattern

Step 94

The user equipment 13 determines the time indication related to the arrival of the detected positioning subframe

The method steps in the user equipment for determining the time indication related to the arrival of the detected positioning subframe according to some further embodiments will now be described with reference to a flowchart depicted in Fig. 10. The steps do not have to be taken in the order stated below, but may be taken in any suitable order.

Step 101 The user equipment 13 receives a cell identifier from the communication network node. Step 101 of Fig. 10 corresponds to step 91 in Fig. 9.

Step 102

The user equipment 13 calculates a positioning reference signal pattern based on the cell identifier. Step 102 of Fig. 10 corresponds to step 92 in Fig. 9.

Step 103

The user equipment 13 detects a positioning subframe comprising the calculated positioning reference signal pattern. Step 103 of Fig. 10 corresponds to step 93 in Fig. 9.

Step 104

The user equipment 13 determines the time indication related to the arrival of the detected positioning subframe. Step 104 of Fig. 10 corresponds to step 94 in Fig. 9. In some embodiments, the user equipment may also receive an indication of time offset of the transmission from the communication network node 11 ,12, and wherein the step of determining time indication of arrival takes the indication into account.

Furthermore, the user equipment 13 may comprise receiving different positioning subframes from different communication network nodes (14,15), and the step of determining 104 the time indication comprises to determine time differences of arrival of the different positioning subframes compared to arrival of the detected positioning subframe.

Step 105 This is an optional step.

Thus, the user equipment 13 may transmit the time differences of arrival to the communication network node.

Step 106 This is an optional step. The user equipment 13 may calculate the position the user equipment 13 based on the determined time indication of the positioning subframes from the same or a different communication network node 11 ,12,14,15

In order to perform the method an arrangement 1100 in the user equipment 13 is provided Fig.11 is a schematic block diagram of the arrangement 1100 in the user equipment 13 The arrangement 1100 comprises a receiving unit 111 arranged to receive a cell identifier from the communication network node 11 ,12 The arrangement 1 100 further comprises a calculating unit 112 arranged to calculate a positioning reference signal pattern based on the cell identifier

Additionally, the arrangement 1100 comprises a detecting unit 113 arranged to detect a positioning subframe comprising the calculated positioning reference signal pattern from the communication network node 11 ,12 Furthermore, the arrangement 1100 comprises a determining unit 114 arranged to determine the time indication of the detected positioning subframe

Furthermore, the user equipment 13 may comprise a transmitting unit 115 arranged to transmit time indication to the communication network node For example, transmitting the time indication comprising the time differences of arrival of different positioning subframes of different radio base stations

In addition, the arrangement 1100 may further comprise a memory unit 116 arranged to store data such as positions, pattern calculations, time indications, applications to perform the methods and/or the like The memory unit 119 may comprise a single memory or a plurality of memories, external and/or internal

In the drawings and specification, there have been disclosed exemplary embodiments of the invention However, many variations and modifications can be made to these embodiments without substantially departing from the principles of the present invention Accordingly, although specific terms are employed, they are used in a generic and descriptive sense only and not for purposes of limitation, the scope of the invention being defined by the following claims

Claims

1 A method in a communication network node (11 ,12) for transmitting a positioning subframe to a user equipment (13) within a cell (10) served by the communication network node (11 ,12), which communication network node (11 ,12) is comprised in a radio communications system (100), wherein the positioning subframe supports positioning of the user equipment (13) and comprises a positioning reference signal pattern, the method being characterised in comprising

- defining (51 ,62) the positioning reference signal pattern in the positioning subframe based on a cell identifier of the cell (10), and - transmitting (52,63) the positioning subframe according to the positioning reference signal pattern on a reference signal radio channel to the user equipment (13)

2 A method according to claim 1 , wherein the defining step (51 ,62) of the positioning reference signal pattern further is based on a time varying function, which time varying function changes the positioning reference signal pattern in time based on a time parameter

3 A method according to claim 2, wherein the time parameter comprises one or more of a system frame number, subframe number and/or slot number

4 A method according to any of the claims 1-3, further comprising

- transmitting (61) data comprising the cell identifier, subframe number, and/or configuration parameter within the cell (10) to the user equipment (13) over a control channel

5 A method according to any of the claims 1 -4, wherein the reference signal radio channel comprises reference signals in a Long Term Evolution system or pilot signals in a Wideband Code Division Multiple Access system

6 A method according to any of the claims 1-5, further comprising

- receiving (64), from the user equipment (13), a response message comprising a time indication related to the positioning subframe 7 A method according to claim 6, wherein the time indication comprises time differences of arrival of positioning subframes of two different cells related to the positioning subframe of the cell, further comprising

- receiving (65) at least two positional bits of data from at least one radio base station (14,15) or a network node (12), which at least two positional data each indicates position of different radio base stations (14,15) serving the different cells and transmission times of the positioning subframes of two different cells,

- positioning (66) the user equipment (13) to position coordinates based on the time differences of arrival, position of the communication network node

(1 1) and the received at least two positional bits of data

8 A method according to any of the claims 6-7, further comprising

- transmitting (67) over a network interface the position coordinates or the time indication to one radio base station (14,15) or a network node (12)

9 An arrangement (700,800) in a communication network node (11 ,12) in a radio communications system (100), the arrangement (700,800) is configured to transmit a positioning subframe to a user equipment (13) within a cell (10) served by the communication network node (11 ,12), wherein the positioning subframe comprises a positioning reference signal pattern, characterized in that the arrangement (700,800) comprises a defining unit (701 ,801) arranged to define the positioning reference signal pattern in the positioning subframe based on a cell identifier of the cell, and a transmitting unit (703,803) arranged to transmit the positioning subframe with the positioning reference signal pattern on a reference signal radio channel to the user equipment (13)

10 A method in a user equipment (13) for determining a time indication related to an arrival of a positioning subframe at the user equipment (13) transmitted from a communication network node (11 ,12), which positioning subframe supports positioning of the user equipment (13) comprising

- receiving (91 ,101) a cell identifier from the communication network node, characterised in that the method comprising - calculating (92, 102) a positioning reference signal pattern based on the cell identifier,

- detecting (93,103) a positioning subframe comprising the calculated positioning reference signal pattern, and - determining (94,104) the time indication of the detected positioning subframe

11 A method according to claim 10, further comprising

- receiving different positioning subframes from different communication network nodes (14,15), and the step of determining the time indication comprises to determine time differences of arrival of the different positioning subframes compared to arrival of the detected positioning subframe

12 A method according to claim 11 , further comprising

- transmitting (105) the time differences of arrival to the communication network node

13 A method according to any of the claims 11-12, wherein the step of receiving (91 ,101) further comprising receiving an indication of time offset of the transmission from the communication network node (11 ,12), and wherein the step of determining (94,104) of the time indication takes the received indication of time offset into account

14 A method in a user equipment (13) for positioning the user equipment (13) wherein the method comprises any of the steps of claims 11-13, further comprising

- positioning (106) the user equipment (13) based on the determined time differences of arrival of the positioning subframes from the same or a different communication network node (1 1 , 12, 14,15)

15 An arrangement (1100) in a user equipment (13) for determining a time indication related to an arrival of a positioning subframe at the user equipment (13) from a communication network node (11 ,12), comprising - a receiving unit (111) arranged to receive a cell identifier from the communication network node (11 ,12), wherein the method is characterized in comprising

- a calculating unit (1 12) arranged to calculate a positioning reference signal pattern based on the cell identifier,

- a detecting unit (113) arranged to detect a positioning subframe comprising the calculated positioning reference signal pattern from the communication network node (11 ,12), and

- a determining unit (114) arranged to determine the time indication of the detected positioning subframe.