WO2015176782A1

WO2015176782A1 - Secondary cell measurement adaptation

Info

Publication number: WO2015176782A1
Application number: PCT/EP2014/068559
Authority: WO
Inventors: Joakim Axmon; Dandan HAO
Original assignee: Telefonaktiebolaget L M Ericsson (Publ)
Priority date: 2014-05-19
Filing date: 2014-09-02
Publication date: 2015-11-26

Abstract

A method is disclosed of a wireless communication device adapted to operate in association with a cellular communication system using carrier aggregation. The method comprises acquiring a speed of the wireless communication device, acquiring a cell size of a secondary cell of the carrier aggregation, and selecting a cell measurement rate associated with the secondary cell based on the cell size and the speed. Corresponding computer program product, arrangement and wireless communication device are also disclosed. Furthermore, a server comprising a database is also disclosed. The server is adapted to store, in the database, information pertaining to a secondary cell for carrier aggregation used by a cellular communication system, and share at least part of the information with a wireless communication device adapted to operate in association with the cellular communication system in response to receiving a request from the wireless communication device. The information pertaining to the secondary cell is indicative of a cell size of the secondary cell and is for selecting, at the wireless communication device, a cell measurement rate associated with the secondary cell based on said cell size and a speed of the wireless communication device. Corresponding use of the server is also disclosed.

Description

SECONDARY CELL MEASUREMENT ADAPTATION

Technical Field

The present invention relates generally to the field of carrier aggregation (CA) and secondary cell (SCell) measurements. More particularly, it relates to adaptation of secondary cell measurements.

Background

Carrier aggregation has been introduced in the E-UTRAN standard (Evolved UMTS - Universal Mobile Telecommunication Standard - Terrestrial Radio Access Network). One possible benefit with carrier aggregation is that higher bit rates may be achieved (e.g. the 1000 Mbit/s requirement for 4G - 4^th generation mobile

telecommunication standard). Another possible benefit with carrier aggregation is that aggregation of scattered spectrum portions may enhance performance and user experience (e.g. applicable for operators with scattered spectrum allocations).

A wireless communication device (e.g. a user equipment - UE, also referred to herein as a device for short) operating in a carrier aggregation scenario is typically connected to a serving cell (primary cell - PCell) using the primary component carrier (PCC), where mobility is catered for. If the device configured for carrier aggregation uses services that require high throughput, the network may activate one or more additional serving cells (secondary cells - SCells) using respective secondary component carrier(s) (SCC). The SCell activation may typically take place before or after the SCell has been detected by the device.

Two types of aggregation scenarios are considered for E-UTRAN, Release 10: - Intra-band contiguous aggregation, and

Inter-band aggregation.

In E-UTRAN, Release 11, one more type of carrier aggregation is added:

Intra-band non-contiguous aggregation.

For intra-band contiguous aggregation, the PCell and SCell(s) are contiguous in frequency. Due to various requirements of the standard, intra-band contiguous aggregation is typically implemented by co-located PCell and SCell(s) (i.e. PCell and SCell(s) operated by the same site).

For intra-band non-contiguous aggregation, the PCell and SCell(s) are not necessarily contiguous in frequency and the PCell and SCell(s) need not necessarily be co-located.

For inter-band carrier aggregation, the PCell and SCell(s) are from different frequency bands, and the PCell and SCell(s) need not necessarily be co-located.

A situation when the PCell and SCell(s) are co-located is termed intra-node carrier aggregation, and a situation when the PCell and SCell(s) are not co-located is termed inter-node carrier aggregation.

Examples of some foreseen deployment scenarios are shown in Figure 1 (see also 3 GPP TS 36.300 rev 11.5.0 Annex J). Solid lines illustrate PCell on a carrier frequency Fl and dashed lines illustrate SCell on a carrier frequency F2.

Part (a) of Figure 1 illustrates a co-located overlaid intra-band scenario, a scenario with fully overlapping coverage of PCell and SCell. Three base station sites 101a, 102a, 103 a are illustrated, each providing three PCells (as illustrated by 121 :1a, 121 :2a, 121 :3a for the site 101a) and three SCells (as illustrated by 131 : 1a, 131 :2a, 131 :3a for the site 101a). Since the different carrier frequencies of PCell and SCell are in the same frequency band, the path losses experienced in PCell and SCell respectively are comparable and, hence, the coverage area of PCell and SCell are similar.

Part (b) of Figure 1 illustrates a co-located overlaid inter-band scenario. Three base station sites 101b, 102b, 103b are illustrated, each providing three PCells (as illustrated by 121 :1b, 121 :2b, 121 :3b for the site 101b) and three SCells (as illustrated by 131 : 1b, 131 :2b, 131 :3b for the site 101b). Since the different carrier frequencies of PCell and SCell are not in the same frequency band, the difference between path losses experienced in PCell and SCell respectively is large and, hence, the coverage area of PCell and SCell are different.

Part (c) of Figure 1 illustrates a co-located, partially overlaid, inter-band scenario. Three base station sites 101c, 102c, 103c are illustrated, each providing three PCells (as illustrated by 121 :1c, 121 :2c, 121 :3c for the site 101c) and three SCells (as illustrated by 131 :1c, 131 :2c, 131:3c for the site 101c). The coverage area of PCell and SCell are different.

Part (d) of Figure 1 illustrates a non-co-located inter-band scenario. Three base station sites lOld, 102d, 103d are illustrated, each providing three PCells (as illustrated by 121 : Id, 121 :2d, 121 :3d for the site lOld). Further, there are remote radio heads (e.g. 111 : 1 d, 111 :2d) each providing a PCell (as illustrated by 131 : 1 d for 111 : 1 d and by 131 :2d for 111 :2d) to provide improved throughput at hotspots. The coverage area of PCell and SCell are different.

Part (e) of Figure 1 illustrates a co-located overlaid inter-band scenario with repeaters. Similarly to part (b), three base station sites lOle, 102e, 103e are illustrated, each providing three PCells (as illustrated by 121 :1c, 121 :2c, 121 :3c for the site 101c) and three SCells (as illustrated by 131 : 1 c, 131 :2c, 131 :3c for the site 101c), wherein the coverage area of PCell and SCell are different. Further, there are repeaters (e.g. 111 :2d) each providing a PCell (as illustrated by 141 :2d for 111 :2d) to provide improved throughput at hotspots.

Figure 2 illustrate an example of a future deployment scenario. In this scenario, a network node 210 serves three cells 211, 212, 213 on carrier frequency Fl and three cells 214, 215, 216 on another carrier frequency F2, another network node 220 serves three cells 221, 222, 223 on carrier frequency Fl and three cells 224, 225, 226 on carrier frequency F2, and a third network node 230 serves a cell 231 on a third carrier F3 as illustrated in part (a) of Figure 2. Part (b) shows that a device 200 aggregating different carriers from different network nodes when it is in coverage of cells 211 , 221 , 224, 231.

It may be assumed that, in some future deployment scenarios, virtually every suitable spectrum will be used in order to meet the targets for 5G (5^th generation mobile telecommunication standard) and onwards. It may also be assumed that, in some future deployment scenarios, there will be a mix of cells with different coverage area (e.g. macro, micro, pico and femto cells) and a mix of intra-node and inter-node aggregation. Even mobile base stations may be assumed to exist in some future deployment scenarios.

Figure 3 illustrate an example future deployment scenario with carrier aggregation using 5 downlink carriers. Part (a) illustrates two layers 310 with macro cells (typical radius: > 2000 m) using respective different carriers, a layer 320 with micro/pico cells (typical radius: 200-2000 m and 10-200 m, respectively) using a third carrier, a layer 330 with pico cells using a fourth carrier and a layer 340 with femto cells (typical radius: > 0-10 m) using a fifth carrier. Part (b) illustrates the complexity of the deployment landscape that a device 300 may experience in this scenario.

It will typically be cumbersome for a wireless communication device (e.g. the device 300 of Figure 3) to manage performing measurements for all - potential and/or actual - secondary cells in complex scenarios with various carriers and various cell sizes. An increase in efforts spent on measurements will typically impact hardware cost and/or power consumption of the device. For example, if the device is mobile it will frequently go in and out of coverage of small cells, leading to high measurement efforts but short, if any, utilization of the cells.

US 2013/0084849 Al discloses a mobility enhancement in a heterogeneous network environment where detecting and measuring of small neighbor cells may be omitted if a user equipment which sends the measurement reports is classified as fast moving. Such a solution would indeed decrease efforts spent on measurements.

However, considerable effort may still be spent on measurements (i.e. the efforts would not be decreased to a desired degree) and/or the benefits of having a heterogeneous network deployment may not be utilized to its full extent (i.e. excluding a large number of cells from consideration by not performing any measurements relating to them).

Therefore, there is a need for alternative and improved secondary cell measurement approaches.

Summary

It should be emphasized that the term "comprises/comprising" when used in this specification is taken to specify the presence of stated features, integers, steps, or components, but does not preclude the presence or addition of one or more other features, integers, steps, components, or groups thereof.

The references herein to E-UTRAN and related parameters and notations are meant as to provide illustrative, non-limiting examples. It should be noted that embodiments may be equally applicable for secondary cell measurements in other carrier aggregation scenarios.

It is an object of some embodiments to obviate at least some of the above disadvantages and to provide methods and arrangements for alternative and improved secondary cell measurements.

According to a first aspect, this is achieved by a method of a wireless communication device adapted to operate in association with a cellular communication system using carrier aggregation.

The method comprises acquiring a speed of the wireless communication device, acquiring a cell size of a secondary cell of the carrier aggregation, and selecting a cell measurement rate associated with the secondary cell based on the cell size and the speed.

The secondary cell may be a cell already acting as secondary cell (e.g. a serving secondary cell) or may be a potential secondary cell.

The selected cell measurement rate may, for example, be applied for one or more of cell search and other cell measurements such as, e.g., received power.

Acquiring the speed may comprise determining the speed by the wireless communication device. For example, the speed may be estimated based on speed related measurements made by the wireless communication device or by the cellular communication network. In some embodiments, a speed mode used by a mobility manager may be used as the acquired speed. Alternatively or additionally, acquiring the speed may comprise receiving an indication of the speed from the cellular

communication network.

Acquiring the cell size may comprise determining the cell size by the wireless communication device. For example, the cell size may be estimated based on cell size related measurements made by the wireless communication device or by the cellular communication network. In some embodiments, a previously stored cell size indication may be used as the acquired cell size. Alternatively or additionally, acquiring the cell size may comprise receiving an indication of the cell size from the cellular

communication network or a server (e.g. a cloud-based server). Selecting the cell measurement rate associated with the secondary cell based on the cell size and the speed may, in some embodiments, comprise using the acquired cell size to determine a typical cell size for the corresponding carrier, possibly applicable in a certain geographical area (e.g. a tracking area or location area of the cellular communication system). The typical cell size may, for example, be an average, maximum or minimum cell size acquired for the carrier. When a typical cell size has been determined for a carrier, the cell measurement rate may be selected based on the speed for a cell using that carrier.

Selecting the cell measurement rate associated with the secondary cell based on the cell size and the speed may, for example, comprise selecting a lower cell measurement rate for large cells than for small cells. Alternatively or additionally, selecting the cell measurement rate associated with the secondary cell based on the cell size and the speed may, for example, comprise selecting a lower cell measurement rate for low speeds than for high speeds.

According to some embodiments, the cell measurement rate may be selected from a set of cell measurement rate values comprising a first cell measurement rate value and a second measurement rate value. Then, the first cell measurement rate value may be selected for a first speed and a first cell size and the second cell measurement rate value may be selected for a second speed and a second cell size, wherein the first cell measurement rate value is higher than the second cell measurement rate value if the first speed is higher than the second speed or if the first size is smaller than the second size. In some of these embodiments, the first and second cell size may be equal or the first and second speed may be equal.

In some embodiments, one or more speed thresholds are defined as functions of the cell size and the cell measurement rate is selected based on how the speed relates to the one or more speed thresholds.

Selecting the cell measurement rate may, in some embodiments, comprise determining whether the speed exceeds a speed threshold, wherein the speed threshold is based on the cell size, and selecting the first cell measurement rate value if the speed exceeds the speed threshold. In some embodiments, the method may further comprise classifying the speed is into one of a plurality of speed categories and classifying the cell size of the secondary cell into one of a plurality of cell size categories, wherein the cell measurement rate is selected based on the speed classification and the cell size classification.

The plurality of speed categories may, for example, comprise a stationary category, a low speed category, a medium speed category and a high speed category.

The plurality of cell size categories may, for example, comprise a macro category, a micro category, a pico category and a femto category.

Selecting the cell measurement rate may, for example, comprise:

- if the speed is classified into the stationary category, using a third cell measurement rate value for the macro category, the micro category and the pico category and using the second cell measurement rate value for the femto category, wherein the second cell measurement rate value is higher than the third cell measurement rate value,

- if the speed is classified into the low speed category, using the second cell measurement rate value for the macro category, the micro category and the pico category and using the first cell measurement rate value for the femto category,

- if the speed is classified into the medium speed category, using the second cell measurement rate value for the macro category and the micro category, using the first cell measurement rate value for the pico category and performing no cell measurements for the femto category, and

- if the speed is classified into the high speed category, using the first cell measurement rate value for the macro category and the micro category and performing no cell measurements for the pico category and the femto category.

In some embodiments, the method may further comprise determining if the speed category according to the speed classification is different compared to a speed category of a prior speed classification, and updating a speed information used by the wireless communication device for the selection of the cell measurement rate if it is determined that the speed category is different. In some embodiments, the method may further comprise determining if the cell size category according to the cell size classification is different compared to a cell size category of a prior cell size classification, and updating a cell size information used by the wireless communication device for the selection of the cell measurement rate if it is determined that the cell size category is different.

The wireless communication device may, according to some embodiments, comprise a measurement manager adapted to select the cell measurement rate based on speed information and cell size information.

According to some embodiments, the method may further comprise estimating a distance from a network node providing the secondary cell to the wireless

communication device, and (if the estimated distance is larger than a distance threshold) increasing the cell measurement rate for the secondary cell.

If acquiring the cell size of the secondary cell comprises estimating the cell size, the method may further comprise uploading an indication of the estimated cell size to a server for storing according to some embodiments.

The indication may, for example, comprise at least one of a carrier

classification of a carrier associated with the secondary cell and a geographical area associated with a validity of the indication.

A second aspect is a computer program product comprising a computer readable medium, having thereon a computer program comprising program instructions. The computer program is adapted to cause execution of the method according to the first aspect when the computer program is loaded into and run by a data-processing unit of the wireless communication device.

In some embodiments, the computer readable medium may be a non-transitory computer readable medium.

According to a third aspect an arrangement is provided for a wireless communication device adapted to operate in association with a cellular communication system using carrier aggregation.

The arrangement comprises a speed acquiring unit adapted to acquire a speed of a wireless communication device, a cell size acquiring unit adapted to acquire a cell size of a secondary cell of the carrier aggregation, and a selection unit adapted to select a cell measurement rate associated with the secondary cell based on the cell size and the speed.

The speed acquiring unit may, in some embodiments, comprise at least one of a speed measurement unit adapted to perform measurements related to the speed of the wireless communication device, a speed estimator adapted to estimate the speed of the wireless communication device, and a receiver adapted to receive an indication of the speed of the wireless communication device from the cellular communication system.

The speed acquiring unit may, in some embodiments, comprise at least one of a cell size measurement unit adapted to perform measurements related to the cell size of the secondary cell, a cell size estimator adapted to estimate the cell size of the secondary cell, a receiver adapted to receive an indication of the cell size of the secondary cell from the cellular communication system, and a data storage unit adapted to store one or more previously acquired cell sizes.

In some embodiments, the third aspect may additionally have features identical with or corresponding to any of the various features as explained above for the first aspect.

A fourth aspect is a processor adapted to execute (or cause execution of) the method according to the first aspect.

A fifth aspect is a wireless communication device comprising the arrangement of the third aspect or the processor of the fourth aspect.

In a sixth aspect, a server comprising a database is provided.

The server is adapted to store (in the database) information pertaining to a secondary cell for carrier aggregation used by a cellular communication system, and share at least part of the information with a wireless communication device adapted to operate in association with the cellular communication system in response to receiving a request from the wireless communication device.

The information pertaining to the secondary cell is indicative of a cell size of the secondary cell and is for selecting (at the wireless communication device) a cell measurement rate associated with the secondary cell based on said cell size and a speed of the wireless communication device. The server according to the sixth aspect may be a cloud-based server, e.g. a server logically located on the Internet.

A seventh aspect is use of the server according to the sixth aspect by receiving a measurement report from the wireless communication device indicating at least one of a cell size classification, a carrier classification and a geographical location, and updating the information pertaining to the secondary cell in the database based on the measurement report.

The use may, according to some embodiments, further comprise receiving the request from the wireless communication device, and transmitting the information pertaining to the secondary cell to the wireless communication device.

An advantage of some embodiments is that the effort spent by a wireless communication device on secondary cell measurements may be flexibly adjusted.

For example, the secondary cell measurement effort may be adjusted such that secondary cell measurements are performed are performed at a (cell size dependent) rate to maximize usefulness of the measurement data.

Brief Description of the Drawings

Further objects, features and advantages will appear from the following detailed description of embodiments, with reference being made to the accompanying drawings, in which:

Fig. 1 is a schematic drawing illustrating some example carrier aggregation network deployments where some embodiments may be applicable;

Fig. 2 is a schematic drawing illustrating an example carrier aggregation network deployment where some embodiments may be applicable;

Fig. 3 is a schematic drawing illustrating an example carrier aggregation network deployment where some embodiments may be applicable;

Fig. 4 is a flow chart illustrating example method steps according to some embodiments;

Fig. 5 is a flow chart illustrating example method steps according to some embodiments; Fig. 6 is a flow chart illustrating example method steps according to some embodiments;

Fig. 7 is a flow chart illustrating example method steps according to some embodiments;

Fig. 8 is a flow chart illustrating example method steps according to some embodiments;

Fig. 9 is a flow chart illustrating example method steps according to some embodiments;

Fig. 10 is a flow chart illustrating example method steps according to some embodiments;

Fig. 11 is a flow chart illustrating example method steps according to some embodiments;

Fig. 12 is a schematic block diagram illustrating an example arrangement according to some embodiments; and

Fig. 13 is a schematic drawing illustrating an example computer program product according to some embodiments.

Detailed Description

In the following, embodiments will be described where secondary cell measurements in a wireless communication device are adapted based on cell size and the speed of the device. More particularly, a rate at which the cell measurements are conducted is adapted.

In a typical embodiment, the device takes into account the current mobility scenario and the characteristics of cells (e.g. an average cell size, a minimum cell size or a maximum cell size within a geographical area) on different carriers when it selects how often to perform cell measurements for the relevant carrier frequencies.

For example, ultra-dense layers with very small cells may be monitored up to a particular speed, above that speed the device only tracks small size, medium size and macro size cells, and at even higher speed the device only tracks medium size and macro size cells. Approaches according to various embodiments allow the device to spend available resources more wisely than if it would apply legacy measurement and cell search rates.

Figure 4 illustrates an example method according to some embodiments. The example method of Figure 4 may, for example, be performed by a wireless

communication device (e.g. a UE) adapted to operate in association with a cellular communication system using carrier aggregation when the device is configured for carrier aggregation mode as illustrated by step 400.

The method comprises acquiring a speed of the wireless communication device in step 410 and acquiring a cell size of a secondary cell in step 420. In step 430, a cell measurement rate associated with the secondary cell is selected based on the cell size and the speed.

Acquiring the device speed in step 410 may for example comprise estimating it by the device and/or receiving an indication estimated by the network (e.g. based on handover rate or similar).

Estimation of the device speed may be performed using any suitable known or future method. For example, the speed may be estimated based on one or more of geographical (e.g. GPS - Global Positioning System) information, Doppler frequency, cell drift (typically with compensation for clock drift), handover rate (typically limited to macro and possibly micro cells), timing advance change rate. Any suitable combination of the above approaches may be used (e.g. choosing a maximum speed, average speed, or a speed indicated by a majority of the approaches).

Acquiring the cell size in step 420 may for example comprise estimating a hypothetical cell radius.

In an example embodiment of cell radius estimation, the UE gets information regarding the carrier frequency and transmission power (Ρχχ) used for SCell via the PDSCH-Config IE (Physical Downlink Shared CHarmel Configuration Information Element) which is part of the RRCConnectionReconfiguration message sent by the eNB (evolved NodeB) to the UE when configuring the SCell. The UE can use this information to calculate an approximate cell radius (which allows it to classify the SCell as macro, micro, pico or femto). Assuming line-of-sight, the attenuation of electromagnetic waves can be modeled by Friis transmission formula,

which states that the fraction of the transmitted power (Ρτχ) received at the UE (PRX), is proportional to the square of the ratio between wavelength (λ) and the distance (r) from the base station antenna. The distance r may be used as an approximation of the cell radius, at least if the formula is applied near the cell border.

Typically, the base station transmission antenna gain factor G_TX is already taken into account in the broadcasted system information regarding P_TX, and can be assumed to equal 1 in the expression above. The UE receiver antenna gain factor G_RX is known by the UE.

In some embodiments, the UE may use some fixed power level PRX (e.g. - 90dBm/15kHz) as reference when calculating the hypothetical cell radius. Then, the fact that the cell radius may be decreased due to interference from densely packed neighbor cells is not taken into account.

In multipath propagation scenarios without a dominating line-of-sight comp timistic and empirical results yield that

more accurately models the attenuation and may be used to estimate the cell radius.

Figure 5 illustrates an example method for selecting the cell measurement rate. The example method of Figure 5 may, for example, be performed as part of step 430 of Figure 4.

The method starts in step 500 with setting a speed threshold based on cell size (e.g. the cell size acquired in step 420 of Figure 4). Then, in step 501, the speed of the device (e.g. the speed acquired in step 410 of Figure 4) is compared with the speed threshold. If the speed exceeds the speed threshold (YES-path out from step 501) a first measurement rate is selected in step 502. If the speed does not exceed the speed threshold (NO-path out from step 501) a second measurement rate is selected in step 503. Typically, it may be beneficial if the first measurement rate is higher than the second measurement rate. In some embodiments, several speed thresholds may be applied to enable selection among more than two measurement rates.

Furthermore, a variation of the method presented in Figure 5 comprises setting cell size threshold based on the speed of the device, and comparing the acquired cell size to the cell size threshold for measurement rate selection.

In some embodiments, the speed may be classified into one of a plurality of speed categories and/or the cell size of the secondary cell may be classified into one of a plurality of cell size categories before performing the cell measurement rate selection based on the classification(s). For example, the threshold(s) described in connection with Figure 5 may define intervals of the various categories. In a typical example, the speed categories may be stationary (e.g. speed = 0 m/s), low speed (e.g. 0 m/s < speed < 2 m/s), medium speed (e.g. 2 m/s < speed < 20 m/s) and a high speed (e.g. 20 m/s < speed) and the cell size categories maybe macro, micro, pico, femto, etc. Other categories are, of course, possible.

Selection of the cell measurement rate based on categories may be performed in any suitable way and the following provides one illustrative example:

- for stationary devices, a low (lower than nominal) measurement rate may be applied for macro, micro and pico cells while a medium (nominal) measurement rate may be applied for femto cells,

- for low speed devices, the medium measurement rate may be applied for macro, micro and pico cells while a high (higher than nominal) measurement rate may be applied for femto cells,

- for medium speed devices, the medium measurement rate may be applied for macro and micro cells, while the high measurement rate may be applied for pico cells, and femto cells are not measured at all, and

- for high speed devices, the high measurement rate may be applied for macro and micro cells, while pico and femto cells are not measured at all.

Figures 6 and 7 illustrate two example methods applicable in connection with classification of speed and cell size, respectively. The methods of Figures 6 and 7 may be used alone or in combination. Furthermore, one or more of the methods of Figure 6 and 7 may be combined with the any of the methods described in connection with Figures 4 and 5.

The example method of Figure 6 may, for example, be performed by a wireless communication device adapted to operate in association with a cellular communication system using carrier aggregation when the device is configured for carrier aggregation mode as illustrated by step 6200 (compare with step 400 of Figure 4).

The method comprises acquiring a speed of the wireless communication device in step 6205 (compare with step 410 of Figure 4).

In step 6210, the acquired speed is classified into a speed category (e.g. as elaborated on above). It is determined whether or not the speed category of step 6210 differs from a previous speed category in step 6215. The previous speed category may, for example, comprise the speed information currently held by a measurement manager of the wireless communication device and used to select the cell measurement rate.

If the speed category has changed (YES-path out from step 6215) the speed information used to select the cell measurement rate is updated in step 6220 and the method returns to step 6205 until a new speed is acquired. If the speed category has not changed (NO-path out from step 6215) the method returns directly to step 6205.

The example method of Figure 7 may, for example, be performed by a wireless communication device adapted to operate in association with a cellular communication system using carrier aggregation when the device is configured for carrier aggregation mode as illustrated by step 7200 (compare with step 400 of Figure 4).

The method comprises acquiring a cell size of the wireless communication device in step 7205 (compare with step 410 of Figure 4).

In step 7210, the acquired cell size is classified into a cell size category (e.g. as elaborated on above). It is determined whether or not the cell size category of step 7210 differs from a previous cell size category in step 7215. The previous cell size category may, for example, comprise the cell size information currently held by a measurement manager of the wireless communication device and used to select the cell measurement rate.

If the cell size category has changed (YES-path out from step 7215) the cell size information used to select the cell measurement rate is updated in step 7220 and the method returns to step 7205 until a new cell size is acquired. If the cell size category has not changed (NO-path out from step 7215) the method returns directly to step 7205.

Figure 8 illustrates an example method applicable in connection with classification of cell size. The method of Figure 8 illustrates one example of how the acquired cell size may be used to classify the corresponding carrier information, which may then be used directly to select the measurement rate. The method of Figure 8 may be combined with the any of the methods described in connection with Figures 4, 5, 6 and 7.

The example method of Figure 8 may, for example, be performed by a wireless communication device adapted to operate in association with a cellular communication system using carrier aggregation when the device is configured for carrier aggregation mode as illustrated by step 8100 (compare with step 400 of Figure 4).

When a new SCell configuration is received for the cellular communication network (YES-path out from step 8105), it is checked in step 8110 whether or not a database comprises SCell information for the downlink (DL) carrier - or for the particular cell - indicated in the SCell configuration.

The SCell configuration may, for example, be received via a SCellToAddMod element in an RRCConnectionReconfiguration message in accordance with 3 GPP technical specification (TS) 36.331 V12.1.0, section 6.2.

The database may, for example, be comprised in the wireless communication device itself or in a server.

The SCell information for a downlink carrier may comprise cell size information in relation to the downlink carrier. Fore example, the SCell information for a downlink carrier may indicate one or more of a dominant cell size, a maximum cell size, a minimum cell size and an average cell size among cells using that downlink carrier in a particular geographical area (e.g. a tracking area or a location area).

If the database comprises SCell information for the downlink carrier - or for the particular cell - (YES-path out from step 8115) no further classification is needed and the method returns to step 8105 until a further SCell configuration is received. In some examples, the SCell information may be considered to be comprised in the database if the database has such information that is considered valid (e.g. based on sufficient statistics and/or time stamp indicating not older than a timeout limit).

If the database does not comprise SCell information for the downlink carrier - or for the particular cell - (NO-path out from step 8115) classification is needed and the method continues to step 8120 where the downlink carrier frequency (e.g. element dl- CarrierFreq of SCellToAddMod element) and the reference signal power (e.g.

referenceSignalPower of SCellToAddMod element) is extracted from the SCell configuration received in step 8105.

A hypothetical cell radius is calculated as a measure of cell size in step 8125 using a transmission formula (e.g. Frii's formula) as elaborated in above (compare with step 420 of Figure 4), and the cell is classified (e.g. to one of the categories macro, micro, pico, and femto or any other suitable collection of classes, e.g. large, medium, and small) based on the hypothetical cell radius in step 8130 (compare with step 7210 of Figure 7).

Information regarding the cell and the classification is then stored in the database according to step 8135, and a classification of the carrier is then made or updated (in step 8140) based in the cell radius/classification of SCell(s) in the location.

For example, if there is a mixed cell size deployment, the wireless

communication device may earlier have found a micro cell and classified the carrier accordingly but now finds out that there also are also pico cells on the carrier. Then, it may consider changing the classification of the carrier from a micro cell layer to a pico cell layer.

The information regarding the cell and the classification may, for example, comprise one or more of:

- cell identity (e.g. EARFCN - E-UTRA Absolute Radio Frequency

Channel Number - and PCI - Physical Cell Identity) of the SCell,

- cell identity (e.g. EARFCN and PCI) of neighboring cells (may be used for fingerprinting),

- RSRP - Reference Signal Received Power - for neighboring cells, - time stamp,

- carrier, - cell radius,

- location (e.g. GPS - Global Positioning System - coordinates, a

geographical area that the cell belongs to).

It is determined whether or not the carrier classification of step 8140 differs from a previous carrier classification in step 8145. The previous carrier classification may, for example, comprise the carrier classification information currently held by a measurement manager of the wireless communication device and used to select the cell measurement rate.

If the carrier classification has changed (YES-path out from step 8145) the carrier classification information used to select the cell measurement rate is updated in step 8150 and the method returns to step 8105 until a further SCell configuration is received. If the carrier classification has not changed (NO-path out from step 8145) the method returns directly to step 8105.

Figure 9 illustrates an example method applicable in connection with classification of cell size and storing of SCell (or carrier) classification in a server (e.g. a cloud-based server). The method of Figure 9 may be combined with the any of the methods described in connection with Figures 4, 5, 6, 7 and 8.

The example method of Figure 9 may, for example, be performed by a wireless communication device adapted to operate in association with a cellular communication system using carrier aggregation when the device is configured for operation in carrier aggregation (CA) mode (compare with step 400 of Figure 4) and configured to report SCell classification to a server as illustrated by step 9500.

If a new classification of a SCell is acquired (YES-path out from step 9505, compare with steps 7201, 8130) information regarding the cell and the classification is stored in step 9510 in a repository (e.g. a transmission buffer) for reporting. The information regarding the cell and the classification may, for example, be as described above in connection with step 8135 of Figure 8.

When a reporting criterion is fulfilled (YES-path out from step 9 15) the SCell information stored in the repository (possibly from several classifications according to step 9505) is uploaded to the server using any suitable method as illustrated by step 9520, and the reporting repository is flushed. The reporting criterion may, for example, be a time-based criterion (report at certain time intervals) and/or an amount-based criterion (report if a certain number of cells are classified).

Alternatively or additionally, the wireless communication device only reports (and possibly only classifies) SCells that are previously unknown (e.g. not having any associated valid cell size information in the server).

Alternatively or additionally, the wireless communication device only reports SCells where the associated cell size information in the server differs from the classification by the wireless communication device.

Thus, the wireless communication device may store historical information regarding cell sizes (for particular cells or in relation to different carriers) in a database for future use.

For example, it may be determined that a complete layer is a femto cell layer and/or pico cell layer and this information may be used whenever that carrier is used by a SCell, e.g. to proactively modify the cell measurement rate. In one example, the wireless communication device, if noticing that a layer comprises, say, both pico and femto cells, continues to monitor the layer when the speed is medium even if the presently configured SCell is a femto cell.

A time stamp may be attached to the stored information to allow it to become obsolete and be refreshed after some period of time (e.g. hours or days).

Alternatively or additionally, the wireless communication device may share (historical) information regarding cell sizes and/or characteristics of a layer with a proprietary server (e.g. cloud-based) comprising a database. This allows the information to be used by other wireless communication devices also. For example, when a wireless communication device enters a geographical area (e.g. a tracking or location area) it may acquire the cell size (or carrier) information from the server and does not necessarily have to determine the cell size itself.

In some examples, the information in the database (of the server or the device) may be further based on fingerprinting, allowing the information to be tailored to different geographical areas. In this context, fingerprinting is typically a way to identify the secondary cell more precisely. For example, there may be several cells (spread out geographically) having the same EARFCN and PCI. Since their respective location is the separating factor in such a scenario, there might be separate databases for but for different geographical areas (and/or the geographical area may be one parameter of database entries). Neighboring cell parameters may also assist in differentiating between cells with the same EARFCN and PCI.

The server may also be adapted to further process the information provided by one or more devices. For example, the server may weigh together or combine information from several devices before storing in the database.

In some examples, the server may be adapted to configure the devices to provide the information (i.e. request the information from the devices).

A wireless communication device may be configured to not base the cell measurement rate selection on its own findings regarding cell size, but only on verified cell size information provided by the server.

Figure 10 illustrates an example method applicable in connection with storing of SCell (or carrier) classification in a server. The method of Figure 10 may be combined with the any of the methods described in connection with Figures 4, 5, 6, 7, 8 and 9.

The example method of Figure 10 may, for example, be performed by a wireless communication device adapted to operate in association with a cellular communication system using carrier aggregation when the device is configured for operation in carrier aggregation (CA) mode (compare with step 400 of Figure 4) as illustrated by step 1000.

When a cell switch (handover or reselection) occurs (YES -path out from step 1005) and the new cell belongs to a new geographical area (YES-path out from step 1010), the wireless communication device downloads SCell and/or carrier classification for the area from the server as illustrated in step 1015.

The downloaded information may, for example, comprise information regarding the cell and the classification as described above in connection with step 8135 of Figure 8. For example, the downloaded information may comprise one or more of:

- EARFCN and cell size classification valid for a whole geographical area, - EARFCN and sets of cell size classification related to various location information within the geographical area (in a mixed but geographically separated deployment),

- EARFCNs and list of PCIs including cell classification,

- EARFCNs and list sets of PCIs, cell location information, and cell

classifications.

Figure 11 illustrates an example method where a measurement manager of a wireless communication device adapts the cell measurement rate to changed conditions regarding device speed, carrier classification (or cell size) and activation status on each secondary component carrier. The method of Figure 11 may be combined with the any of the methods described in connection with Figures 4, 5, 6, 7, 8, 9 and 10.

The example method of Figure 11 may, for example, be performed by a wireless communication device adapted to operate in association with a cellular communication system using carrier aggregation when the device is configured for operation in carrier aggregation (CA) mode (compare with step 400 of Figure 4) as illustrated by step 1100.

When a new measurement configuration is detected (e.g. a SCell is added or removed, YES-path out from step 1105), the measurement manager updates the set of measured component carriers accordingly in step 1125 and continues to step 1130.

If the measurement configuration is un-changed (NO-path out from step 1105) but either of a new speed class (YES-path out from step 1110, compare with step 6220), a new carrier class (YES-path out from step 1115, compare with step 7220), and a changed activation status (YES-path out from step 1120) is detected the method also continues to step 1130 where a measurement rate is selected (compare with step 430) for the monitored carriers based on speed, characteristics (e.g. cell size) of the monitored carriers and activation status of the various SCells (i.e. if a cell is used as SCell or not).

The measurement manager may, for example, determine:

- Total resources to be used (hardware accelerator utilization, digital signal processor utilization, receiver utilizations, memory and memory transfer utilization, power consumption). - Distribution of total resources to be used over the carriers to be measured (measurement rate, cell search rate).

In an illustrative example, considering a nominal cell search and measurement rate of one measurement occasion every 40-60 ms, a UE may measure a carrier with an active SCell where the carrier comprises femto cells more often, e.g. every 20-30 ms when the UE is in low speed mode since radio conditions are expected to change rapidly due to the small cell radius. Potentially, this dense measurement approach will be at the expense of measuring a carrier with an active SCell where the carrier comprises macro cells more sparsely, e.g. every 60-80 ms. On the other hand, when the UE is at medium or high speed it may completely skip measurements on carriers with configured SCells where the carrier comprises femto cells since coverage of femto cells will be left so fast that they cannot be used for communication anyway. It shall be understood that the rates above are only examples.

In addition to the example methods described above, the device (e.g. a measurement manager of the device) may further estimate a distance from a network node providing the secondary cell to the device, and (if the estimated distance is larger than a distance threshold, i.e. if the device is close to a cell border) increasing the cell measurement rate for the secondary cell (or the corresponding carrier). The estimate may be based on RSRP (Reference Signal Received Power) and the signaled reference signal transmission power for a configured SCell as explained above. Alternatively, a threshold on RSRP may be used directly to determine when the device is close to a cell border.

In addition to the example methods described above, the device (e.g. a measurement manager of the device) may further use and estimated SINR - Signal-to- Interference-and-Noise Ratio - (or RSRQ - Reference Signal Received Quality) to determine if the SCell signal quality is deteriorating to a level where the cell risks being too interfered to be used. For example, if the SINR (or RSRQ) falls below a threshold, the cell measurement rate for the secondary cell (or the corresponding carrier) may be increased.

Figure 12 illustrates an example arrangement 1200 according to some embodiments. The arrangement 1200 may, for example, be comprised in a wireless communication device adapted to operate in association with a cellular communication system using carrier aggregation. Furthermore, the arrangement 1200 may be adapted to perform one or more of the methods as described above in connection to Figures 4-11. Details of the possible functionality of the various elements of the example arrangement 1200 will be apparent for the skilled person from the description of the methods of Figures 4-11 and will not be elaborated on further.

Generally, an arrangement adapted to perform one or more of the methods as described above in connection to Figures 4-11 may comprise a speed acquiring unit adapted to acquire a speed of a wireless communication device, a cell size acquiring unit adapted to acquire a cell size of a secondary cell of the carrier aggregation, and a selection unit adapted to select a cell measurement rate associated with the secondary cell based on the cell size and the speed.

The particular arrangement 1200 comprises a transceiver (RX/TX) 1201, a speed estimator (SE) 1203, a cell size estimator (CSE) 1204, a measurement unit (MEAS) 1202, a selection unit (SEL) 1205 and a data storage unit (STR) 1206.

In some embodiments, the transceiver 1201 may be adapted to receive an indication of the speed of the wireless communication device, for example, as estimated by the cellular communication system. In such embodiments, the transceiver may be seen as a speed acquiring unit and the speed estimator 1203 may be optional.

Alternatively or additionally, the speed estimator 1203 may be adapted to estimate the speed of the wireless communication device according to any suitable known or future method. The speed estimator may be adapted to estimate the speed based on measurements related to the speed of the wireless communication device performed by the measurement unit 1202 when acting as a speed measurement unit. In such embodiments, the speed estimator (possibly in combination with the measurement unit) may be seen as a speed acquiring unit.

In some embodiments, the transceiver 1201 may be adapted to receive an indication of the cell size of the secondary cell, for example, as indicated in a database of a server. In such embodiments, the transceiver may be seen as a cell size acquiring unit and the cell size estimator 1204 and/or the data storage unit 1206 may be optional. Alternatively or additionally, the cell size estimator 1204 may be adapted to estimate the cell size of the secondary cell according to any suitable known or future method, for example as elaborated on above. The cell size estimator may be adapted to estimate the cell size based on measurements related to the cell size of the secondary cell performed by the measurement unit 1202 when acting as a cell size measurement unit. The cell size estimation may be stored in the data storage unit 1206 in some embodiments and/or uploaded to a database of a server (by way of the transceiver being adapted to transmit a report indicative of the cell size estimation). Thus, the cell size estimator (possibly in combination with the measurement unit and/or the data storage unit) may be seen as a cell size acquiring unit. In some embodiments, the cell size estimation is not performed if the data storage unit (or the server) already has a valid cell size indication for the secondary cell.

The selection unit 1205 is adapted to select the cell measurement rate associated with the secondary cell based on the cell size and the speed acquired by the cell size acquiring unit and the speed acquiring unit, respectively. The selection unit 1205 may, for example, be a measurement manager.

Generally, when reference is made to cells size (estimation, indication, acquiring, etc.) herein, this is meant to include embodiments where a carrier is classified based on the cell sizes of cells on that carrier as elaborated on above.

The described embodiments and their equivalents may be realized in software or hardware or a combination thereof. They may be performed by general-purpose circuits associated with or integral to a communication device, such as digital signal processors (DSP), central processing units (CPU), co-processor units, field- programmable gate arrays (FPGA) or other programmable hardware, or by specialized circuits such as for example application-specific integrated circuits (ASIC). All such forms are contemplated to be within the scope of this disclosure.

Embodiments may appear within an electronic apparatus (such as a wireless communication device) comprising circuitry/logic or performing methods according to any of the embodiments. The electronic apparatus may, for example, be a portable or handheld mobile radio communication equipment, a mobile radio terminal, a mobile telephone, a communicator, an electronic organizer, a smartphone, a computer, a notebook, or a mobile gaming device.

According to some embodiments, a computer program product comprises a computer readable medium such as, for example, a diskette, a USB-stick, a plug-in card, an embedded drive or a CD-ROM (such as the CD-ROM 1300 illustrated in Figure 13). The computer readable medium may have stored thereon a computer program comprising program instructions. The computer program may be loadable into a data- processing unit (PROC) 1302, which may, for example, be comprised in a mobile terminal 1301. When loaded into the data-processing unit, the computer program may be stored in a memory (MEM) 1303 associated with or integral to the data-processing unit. According to some embodiments, the computer program may, when loaded into and run by the data-processing unit, cause the data-processing unit to execute method steps according to, for example, the methods shown in any of the Figures 4-11.

Reference has been made herein to various embodiments. However, a person skilled in the art would recognize numerous variations to the described embodiments that would still fall within the scope of the claims. For example, the method

embodiments described herein describes example methods through method steps being performed in a certain order. However, it is recognized that these sequences of events may take place in another order without departing from the scope of the claims.

Furthermore, some method steps may be performed in parallel even though they have been described as being performed in sequence.

In the same manner, it should be noted that in the description of embodiments, the partition of functional blocks into particular units is by no means limiting.

Contrarily, these partitions are merely examples. Functional blocks described herein as one unit may be split into two or more units. In the same manner, functional blocks that are described herein as being implemented as two or more units may be implemented as a single unit without departing from the scope of the claims.

Hence, it should be understood that the details of the described embodiments are merely for illustrative purpose and by no means limiting. Instead, all variations that fall within the range of the claims are intended to be embraced therein.

Claims

1. A method of a wireless communication device adapted to operate in association with a cellular communication system using carrier aggregation, the method comprising:

- acquiring (410, 6205) a speed of the wireless communication device;

- acquiring (420, 7205) a cell size of a secondary cell of the carrier

aggregation; and

- selecting (430, 500, 501 , 502, 503, 1130) a cell measurement rate associated with the secondary cell based on the cell size and the speed.

2. The method according to claim 1, wherein the cell measurement rate is selected from a set of cell measurement rate values comprising a first cell measurement rate value and a second measurement rate value, wherein the first cell measurement rate value is selected for a first speed and a first cell size and the second cell measurement rate value is selected for a second speed and a second cell size, and wherein the first cell measurement rate value is higher than the second cell measurement rate value if the first speed is higher than the second speed or if the first size is smaller than the second size.

3. The method according to claim 2, wherein selecting the cell measurement rate comprises:

- determining (501) whether the speed exceeds a speed threshold, wherein the speed threshold is based on the cell size; and

- selecting (502) the first cell measurement rate value if the speed exceeds the speed threshold.

4. The method according to any of claims 2 to 3 further comprising:

- classifying (6210) the speed is into one of a plurality of speed categories;

- classifying (7210) the cell size of the secondary cell into one of a plurality of cell size categories; and wherein the cell measurement rate is selected based on the speed classification and the cell size classification.

5. The method according to claim 4 wherein the plurality of speed categories comprises a stationary category, a low speed category, a medium speed category and a high speed category, wherein the plurality of cell size categories comprises a macro category, a micro category, a pico category and a femto category, and wherein selecting the cell measurement rate comprises:

- if the speed is classified into the stationary category, using a third cell measurement rate value for the macro category, the micro category and the pico category and using the second cell measurement rate value for the femto category, wherein the second cell measurement rate value is higher than the third cell measurement rate value;

- if the speed is classified into the low speed category, using the second cell measurement rate value for the macro category, the micro category and the pico category and using the first cell measurement rate value for the femto category;

- if the speed is classified into the medium speed category, using the second cell measurement rate value for the macro category and the micro category, using the first cell measurement rate value for the pico category and performing no cell measurements for the femto category; and

6. The method according to any of claims 4 to 5, further comprising:

- determining (6215) if the speed category according to the speed classification is different compared to a speed category of a prior speed classification; and

- updating (6220) a speed information used by the wireless communication device for the selection of the cell measurement rate if it is determined that the speed category is different.

7. The method of any of claims 4 to 6, further comprising:

- determining (7215) if the cell size category according to the cell size classification is different compared to a cell size category of a prior cell size classification; and

- updating (7220) a cell size information used by the wireless communication device for the selection of the cell measurement rate if it is determined that the cell size category is different.

8. The method according to any of claims 1 to 7, further comprising:

- estimating a distance from a network node providing the secondary cell to the wireless communication device; and

- if the estimated distance is larger than a distance threshold, increasing the cell measurement rate for the secondary cell.

9. The method according to any of the preceding claims wherein acquiring the cell size of the secondary cell comprises estimating the cell size, the method further comprising uploading (9520) an indication of the estimated cell size to a server for storing.

10. The method according to claim 9 wherein the indication comprises at least one of a carrier classification of a carrier associated with the secondary cell and a geographical area associated with a validity of the indication.

11. A computer program product comprising a computer readable medium, having thereon a computer program comprising program instructions, the computer program adapted to cause execution of the method according to any of claims 1 through 10 when the computer program is loaded into and run by a data-processing unit of the wireless communication device.

12. An arrangement for a wireless communication device adapted to operate in association with a cellular communication system using carrier aggregation, the arrangement comprising:

- a speed acquiring unit (1201, 1202, 1203) adapted to acquire a speed of a wireless communication device;

- a cell size acquiring unit (1201, 1202, 1204, 1206) adapted to acquire a cell size of a secondary cell of the carrier aggregation; and

- a selection unit (1205) adapted to select a cell measurement rate associated with the secondary cell based on the cell size and the speed.

13. The arrangement according to claim 12 wherein the speed acquiring unit comprises at least one of:

- a speed measurement unit (1202) adapted to perform measurements related to the speed of the wireless communication device;

- a speed estimator (1203) adapted to estimate the speed of the wireless communication device; and

- a receiver (1201) adapted to receive an indication of the speed of the wireless communication device from the cellular communication system.

14. The arrangement according to any of claims 12 through 13 wherein the speed acquiring unit comprises at least one of:

- a cell size measurement unit (1202) adapted to perform measurements related to the cell size of the secondary cell;

- a cell size estimator (1204) adapted to estimate the cell size of the secondary cell;

- a receiver (1201) adapted to receive an indication of the cell size of the secondary cell from the cellular communication system; and

- a data storage unit (1206) adapted to store one or more previously acquired cell sizes.

15. A wireless communication device comprising the arrangement of any of claims 12 through 14.

16. A server comprising a database, the server adapted to:

store, in the database, information pertaining to a secondary cell for carrier aggregation used by a cellular communication system; and

share at least part of the information with a wireless communication device adapted to operate in association with the cellular communication system in response to receiving a request from the wireless communication device,

wherein the information pertaining to the secondary cell is indicative of a cell size of the secondary cell and is for selecting, at the wireless communication device, a cell measurement rate associated with the secondary cell based on said cell size and a speed of the wireless communication device.

17. Use of the server according to claim 16, comprising:

- receiving a measurement report from the wireless communication device indicating at least one of a cell size classification, a carrier classification and a geographical location; and

- updating the information pertaining to the secondary cell in the database based on the measurement report.

18. The use according to claim 17 further comprising:

- receiving the request from the wireless communication device; and

- transmitting the information pertaining to the secondary cell to the wireless communication device.