TECHNICAL FIELD

[ 001 ] This disclosure relates to systems, methods and computer program products for use in determining when a wireless communication device (WCD) (also referred to herein as user equipment, UE) is in the proximity of a base station (such as a low power base station) (e.g., in the proximity of a cell serviced by the base station).

BACKGROUND

[ 002 ] In a cellular network it is often the case that there exist areas with high traffic, e.g., high concentration of WCDs. In those areas it would be desirable to deploy additional capacity to ensure user satisfaction. The added capacity could be in the form of an additional macro base station. In order to concentrate the capacity boost on a smaller area, the added capacity could also be in the form of a base station with lower output power (i.e., "low power base stations" or "small base stations") that covers a smaller area than a macro base station.

[ 003 ] There will also often be areas with bad coverage where there is a need for coverage extension. One way to provide for coverage extension is to deploy a low power base station to concentrate the coverage boost in a small area.

[ 004 ] One argument for choosing base stations with lower output power in the above cases is that the impact on the macro network can be minimized, e.g. it is a smaller area where the macro network may experience interference. Currently there is a strong drive in the industry in the direction towards the use of low power base stations.

[ 005 ] FIG. 1 illustrates a heterogeneous wireless network 100 comprising a macro base station 102 (a.k.a., "macro cell"), which provides a wide coverage area. FIG. 1 also shows low power base stations 103, 104, 105 that are deployed to provide small area capacity/coverage. In this example, the following low power base stations are illustrated: a pico base station 103, a relay 104, and home base stations 105 (a.k.a., femto cells or Home (e)NBs (H(e)NBs. Although FIG. 1 shows a cluster 106 of femto cells 105, single cell deployments may also exist. As further shown in FIG. 1, a WCD 101 (a.k.a., UE 101) may communication wirelessly with any of the illustrated base stations 102-105.

[ 006 ] The lower power base stations (a.k.a., low power nodes) can be deployed using the same frequency as the macro base station (known as intra- frequency deployment) or on a different frequency (known as inter-frequency deployment). Thus, a low power base station that is located within a macro cell and that uses the same frequency as the macro cell is referred to as an intra-frequency low power base station. Similarly, a low power base station that is located within a macro cell and that uses a different frequency than the macro cell is referred to as an inter- frequency low power base station. The different cells may use different radio access technologies (RATs).

[ 007 ] WCD Measurements

[ 008 ] WCDs can be configured to report measurements, mainly for the sake of supporting mobility. As specified in 3GPP TS 36.331, the E-UTRAN provides the measurement configuration applicable for a WCD in RRC CON ECTED through dedicated signaling, i.e. using the RRC Connection Reconfiguration message. The following measurement configurations can be signaled to the WCD:

[ 009 ] (1) Measurement objects: These define on what the WCD should perform the measurements - such as a carrier frequency. The measurement object may also include a list of cells to be considered (white-list or black-list) as well as associated parameters, e.g. frequency- or cell-specific offsets.

[ 0010 ] (2) Reporting configurations: These include the periodic or event- triggered criteria which cause the WCD to send a measurement report, as well as the details of what information the WCD is expected to report (e.g. the quantities, such as Received Signal Code Power (RSCP) for UMTS or Reference Signal Received Power (RSRP) for LTE, and the number of cells).

[ 0011 ] (3) Measurement identities: These identify a measurement and define the applicable measurement object and reporting configuration. Each measurement identity links one measurement object with one reporting configuration. By configuring multiple measurement identities it is possible to link more than one measurement object to the same reporting configuration, as well as to link more than one reporting configuration to the same measurement object. The measurement identity is used as a reference number in the measurement report.

[ 0012 ] (4) Quantity configurations: The quantity configuration defines the filtering to be used on each measurement. One quantity configuration is configured per RAT type, and one filter can be configured per measurement quantity.

[ 0013 ] (5) Measurement gaps: Measurement gaps define time periods when no uplink or downlink transmissions will be scheduled, so that the WCD may perform the measurements (e.g. inter-frequency measurements where the WCD has only one Tx/Rx unit and supports only one frequency at a time). The measurement gaps are common for all gap-assisted measurements

[ 0014 ] The E-UTRAN configures only a single measurement object for a given frequency, but more than one measurement identity may use the same measurement object. The identifiers used for the measurement object and reporting configuration are unique across all measurement types. It is possible to configure the quantity which triggers the report (RSCP or RSRP) for each reporting configuration.

[ 0015 ] In LTE, significant measurements are the Reference Signal Received Power (RSRP) and Reference Signal Received Quality (RSRQ). RSRP is a cell specific measure of signal strength and it is mainly used for ranking different cells for handover and cell reselection purposes, and it is calculated as the linear average of the power of the Resource Elements (REs) which carry cell-specific Reference Signals (RSs). The RSRQ, on the other hand, also takes the interference into consideration by taking the total received wideband power into account as well.

[ 0016 ] One of the measurement configuration parameters that WCDs receive from their serving base station (e.g., base stations in an LTE network - evolved Node Bs ("eNBs")) is the S-measure, which tells the WCD when to start measuring neighboring cells. If the measured RSRP of the serving cell falls below the S- measure, indicating the signal of the serving cell is not that strong anymore, the WCD starts measuring the signal strength of RSs from the neighboring cells. The S-measure is an optional parameter and different S-measure values can be specified for initiating intra-frequency, inter-frequency and inter-RAT measurements. [ 0017 ] Once the WCD is enabled for measuring, it can report any of the following: (a) the serving cell; (b) listed cells (i.e. cells indicated as part of the measurement object); and (c) detected cells on a listed frequency (i.e. cells which are not listed cells but are detected by the WCD).

[ 0018 ] There are several measurement configuration parameters that specify the triggering of measurement reports from the WCD. The following event-triggered criteria are specified for intra-RAT measurement reporting in LTE:

Event Al : Primary serving cell (PCell) becomes better than absolute threshold.

Event A2: PCell becomes worse than absolute threshold.

Event A3 : Neighbor cell becomes better than an offset relative to the PCell.

Event A4: Neighbor cell becomes better than absolute threshold.

Event A5: PCell becomes worse than one absolute threshold and neighbor cell becomes better than another absolute threshold.

Event A6: Neighbor cell becomes better than an offset relative to a secondary cell (SCell).

[ 0019 ] For inter-RAT mobility, the following event-triggered reporting criteria are specified: Event Bl : Neighbor cell becomes better than absolute threshold; Event B2: Serving cell becomes worse than one absolute threshold and neighbor cell becomes better than another absolute threshold.

[ 0020 ] A significant measurement report triggering event related to handover is A3, and its usage is illustrated in FIG. 2. The triggering conditions for event A3 can be formulated as: N > S + HOM (1), where N and S are the signal strengths of the neighbor and serving cells, respectively, and HOM is the handover margin. HOM is the difference between the radio quality of the serving cell and the radio quality needed before attempting a handover. The radio quality is measured either using RSRP or RSRQ (see 36.133 for further explanation).

[ 0021 ] The WCD triggers the intra-frequency handover procedure by sending event A3 report to the eNB. This event occurs when the WCD measures that the target cell is better than the serving cell with a margin "HOM". The WCD is configured over RRC when entering a cell and the HOM is calculated from the following configurable parameters: HOM = Ofs + Ocs + Off - Ofn - Ocn + Hys, where: Ofs is the frequency specific offset of the serving cell; Ocs is the cell specific offset (CIO) of the serving cell; Off is the a3-Offset; Ofn is the frequency specific offset of the neighbor cell; Ocn is the CIO of the neighbor cell; Hys is the hysteresis.

[ 0022 ] If the condition in (1) is satisfied and it remains valid for a certain duration known as Time To Trigger (TTT), the WCD sends a measurement report to the serving e B (in FIG. 2, event A3 is satisfied at point A and measurement report is sent at point B in time). When the serving eNB gets the measurement report, it can initiate a handover towards the neighbor.

[ 0023 ] In addition to event-triggered reporting, the WCD may be configured to perform periodic measurement reporting. In this case, the same parameters may be configured as for event-triggered reporting, except that the WCD starts reporting immediately rather than only after the occurrence of an event.

[ 002 ] Proximity Detection

[ 0025 ] The use of proximity indication was introduced in Release 9 to facilitate the inbound mobility of WCDs from macros to Closed Subscriber Group (CSG) or hybrid H(e)NBs (see 3 GPP TS 36.300 "E-UTRAN Overall Description: stage 2"). A WCD can use autonomous search function (ASF) to determine when it is within a CSG or hybrid cell whose CSG ID is in the WCD's CSG whitelist, and it may send the serving eNB a proximity indication report. The proximity indication may be used as follows:

[ 0026 ] (1) If a measurement configuration is not present for the concerned frequency /RAT, the source eNB may configure the WCD to perform measurements and reporting for the concerned frequency/RAT; and

[ 0027 ] (2) The source eNB may determine whether to perform other actions related to handover to HNB/HeNBs based on having received a proximity indication (for example, the source eNB may not configure the WCD to acquire system information of the HNB/HeNB unless it has received a proximity indication).

[ 0028 ] How the ASF is performed is left to WCD implementation, but a straightforward implementation could be location based if the WCD supports that functionality. For example, the WCD can store its coordinates when it connects to the H(e) B cell for the first time (or even in IDLE mode, when the user manually selects the cell for camping), and whenever its current location is close to the stored location, the WCD can send a proximity indication to the serving e B, notifying it that it is within range of a H(e) B cell. If the WCD does not have the capability to determine its location, then the fingerprinting of the H(e) B cell ("the target cell") could be made based on some kind of signal strength map of the neighboring macro e Bs (e.g., neighboring cells) when the WCD first connects to the H(e)NB cell.

[ 0029 ] Using proximity detection can be advantageous both in inter- frequency and intra-frequency deployment scenarios. In the case of inter-frequency deployment, the WCDs will be enabled to measure on the carrier frequency of the H(e) B cells only when they are in the vicinity of a He B cell that they have access to. When an eNB receives the proximity indication, it can enable the WCD to start performing measurements on the H(e)NB's carrier frequency.

[ 0030 ] Proximity Detection of Inter-Frequency Low Power Nodes

[ 0031 ] If a low power node is an open access node (e.g., a pico node or an open access H(e)NBs) and the cells are deployed in intra-frequency fashion, there will be minimal performance penalty on the WCD like in the case of CSG cells because the WCD can be handed over to them if the signal quality from these cells qualifies the handover requirements (i.e. the measurements will not be in vain, which would have been the case if the WCD was measuring on a CSG cell that it has no access to).

[ 0032 ] If the open access low power node is deployed in an inter-frequency layer, WCDs can be enabled with inter-frequency measurement configurations in order to discover such offloading targets. However, inter-frequency cell search usually requires the use of measurement gaps.

[ 0033 ] Two measurement gap configurations can be used, whereby the WCD can have a 6ms gap every 40 or 80ms. This can drain the WCD battery and reduce the resources available for data communication (by up to 15% for the measurement gap with 40ms periodicity). The impacts will be even more if the WCD has to monitor several frequencies. Thus, proper proximity detection and reporting of inter-frequency low power nodes, regardless of the fact that they are open or closed to the WCD, may be important. [ 0034 ] eNB Measurements

[ 0035 ] Some measurements may also require the eNB to measure the signals transmitted by the WCD in the uplink. One measurement performed by the eNB in LTE is the estimation of Timing Advance (TA). For LTE, uplink orthogonally is required to avoid intra-cell interference and as such it is advantageous to have all the uplink signals time-aligned when they are received at the eNB. Thus, eNBs try to compensate for the propagation delay differences of their WCDs (due to their differing distances from the eNB), by instructing them to apply different timing advances, and the WCDs will apply the configured timing advance when they are transmitting. The TA can first be estimated during the initial random access procedure when the WCD establishes a connection with the eNB (either due to handover or going from idle to connected mode). TA updates are then performed throughout the duration the WCD is connected to the eNB, as the propagation delay might change, for example due to the movement of the WCD, the change of the environment due to movement of other objects in a dense urban setting, etc. For these updates, the eNBs may measure received uplink signals such as Sounding Reference Signals (SRS), Channel Quality Indicator (CQI), ACKs and NACKs in response to downlink data reception, or the uplink data transmission. The details of uplink timing measurements at the eNB are not standardized and left to implementation.

[ 0036 ] eNBs that have multiple antenna elements could also use their diversity to measure the Angle of Arrival (AoA) of the uplink signals that they receive from their WCDs. The AoA and TA can be used to estimate the relative coordinates of the WCDs within the cell.

[ 0037 ] Automatic Neighbor Relations

[ 0038 ] The PCI is an essential configuration parameter of a radio cell. PCIs are grouped into 168 unique physical layer cell identity groups, each group containing 3 unique identities. Thus, there are only 504 different PCIs altogether. Limiting the number of PCIs makes the initial PCI detection by the WCD during cell search easier, but the limited number of PCIs inevitably leads to the reuse of the same PCI values in different cells. Therefore, a PCI might not uniquely identify a neighbor cell, and each cell additionally broadcasts, as a part of the system information (SI), a globally unique cell identifier (CGI/ECGI). [ 0039 ] When a new node (e B or He B) is brought into the field, a PCI needs to be selected for each of its supported cells, avoiding collision with respective neighboring cells. The use of identical PCI by two cells in close proximity results in interference conditions that might hinder the identification and use of any of them. Otherwise if both cells have a common neighbor, handover measurements that are based on PCI will become ambiguous thus leading to confusing measurement reports or even to the handing over of a WCD to the wrong cell, which can cause Radio Link Failure (RLF).

[ 00 0 ] The PCI assignment shall fulfill the following two conditions: (I) Collision-free: The PCI is unique in the area that the cell covers; (II) Confusion-free: a cell shall not have more than one neighboring cell with identical PCI.

[ 00 1 ] Using an identical PCI for two cells creates collision, which can only be solved by restarting at least one of the cells and reassigning PCIs upon restart, causing service interruption. PCI confusion, on the other hand, can be resolved by instructing the WCDs to read the CGI of the concerned neighbor cell. However, this might require the WCDs to stop transmitting/receiving from their serving node during the idle period that is required to read the neighbor's system information, which can be in the range of 250 ms. Therefore, putting a PCI in use which causes either collision or confusion is highly undesirable.

[ 0042 ] Traditionally, a proper PCI is derived from radio network planning and is part of the initial configuration of the node. The network planning tool calculates the possible PCIs for the new cell(s) based on estimated neighbor relations of the new cells, as estimated by cell coverage area predictions. However, prediction errors, due to imperfections in map and building data, and to inaccuracies in propagation models, have forced operators to resort to drive/walk tests to ensure proper knowledge of the coverage region and identify all relevant neighbors and handover regions. Even the accuracy of that is questionable as some factors such as seasonal changes (the falling of leaves or snow melting) can alter the propagation conditions. Also, the inaccuracy of cell coverage and neighbor relation assessment increases with time as the live network and its surroundings evolve over time.

[ 0043 ] LTE has a support for a feature known as WCD A R (User Equipment Automatic Neighbor Relations), which allows WCDs to decode and report the CGI/ECGI information of neighbor cells (in addition to the CSG cell ID in the case of He Bs) to the serving cell upon request. e Bs maintain a neighbor relation table ( RT) for each of their cells. Apart from the PCI to CGI/ECGI mapping, each neighbor relation contains other relevant information such as the possibility of X2 connectivity.

[ 0044 ] The CGIs/ECGIs of the neighbor cells are the ones that are used when signaling to the neighbor e B via the MME, since the MME routes the messages based on eNB identity which is a part of CGI/ECGI. If the policy is to establish X2 for neighbor relations and if X2 is not already available, then the CGI/ECGI can be used to retrieve the target node's IP address, which is used for X2 setup. When the X2 interface is established, the neighboring eNBs can share information about their served cells including PCIs and CGIs/ECGIs. It is also possible to share such information via the Operation and Maintenance (OAM or O&M) system.

[ 0045 ] Energy saving via adaptive cell activation/deactivation

[ 004 6 ] There is a growing interest in making more energy efficient wireless networks, mainly due to two reasons: (I) reduce operating expenditures (OPEX) (nearly half of a network service provider's annual OPEX is for energy costs); and (II) environmental considerations (even though the telecommunications industry is attributed to only 2% of the global C0 ₂ emissions, it is expected to grow and reach up to 4% by 2020). As such, there is an increasing pressure to improve the network efficiency, driven by both financial and environmental (political) factors.

[ 0047 ] In wireless networks, more than 80% of the energy is consumed by the network infrastructure, of which more than 70% at the base station sites. The main reason for this is that base stations are energy inefficient (in the order of 6%, which means a base station site that is transmitting at 120W needs input power in the order of 2 KW). Even under low load conditions, the energy consumption is almost 75% of the maximum. Considering this and the fact that traffic patterns vary quite a lot within a given day, the relation of power consumption with load suggests that an efficient way to save energy during hours of low traffic is to deactivate a number of the base stations or, for a number of base stations that serve multiple cells, one or more cells serviced by the base station. Results have shown that over a 24-h period, deactivating base stations, or individual cells, can result in energy savings of around 30%. [ 00 8 ] 3GPP has addressed this need for energy saving by enabling the X2 interface between base stations to communicate the activation and deactivation of cells. Specifically, these two procedures are concerned with energy saving:

[ 004 9 ] (I) Deactivation/(re)activation notification: eNBs can use the eNB CONFIGURATION UPDATE message to communicate to their peers the activation state of their cells. When an eNB decides to deactivate a cell(s) for energy saving reasons, it can send an eNB CONFIGURATION UPDATE message to its peers, where it includes the information about the deactivated cell(s) in the Served Cells To Modify Information Element and set the Deactivation Indication IE for that cell(s). Similarly, when the eNB later on decides to re-activate the cell(s), it will send the configuration update, but this time without the Deactivation Indication set.

[ 0050 ] (II) Activation request: A neighbor eNB might need the services of a cell(s) belonging to a neighboring eNB for normal handover as well load balancing. As such, if an eNB notices that such a cell(s) is/are deactivated, it can request the eNB that hosts this/these cell(s) to re-activate the cell(s) by using the CELL ACTIVATION REQWCDST message.

SUMMARY

[ 0051 ] As mentioned above, proximity reporting is currently standardized only for CSG H(e)NB cell. A proposal has been made for a network based/assisted fingerprinting mechanism that can be used to in the detection or reporting of inter- frequency low power nodes (be they CSG H(e)NBs, open/hybrid H(e)NBs, picos, WLAN, etc.). See International Patent Application No. PCT/SE2012/050833, filed on July 13, 2012.

[ 0052 ] With network based/assisted fingerprinting, the low power nodes make fingerprints of themselves (for example, considering the top n cells that they or their WCDs can detect) and macro eNBs also fingerprint their neighboring low power nodes in a similar manner. The fingerprints made by the macro eNBs and the low power nodes are then combined/consolidated to make a more accurate fingerprint. Note that in this document, the term "small cells" is used interchangeably for the cells of low power nodes. Once the fingerprints are made by the network, they can be used, for example, in network based proximity detection and in network assisted proximity detection.

[ 0053 ] Identified Drawbacks:

[ 0054 ] With the network based/assisted fingerprinting mechanism described herein, it is possible to have a more accurate and reliable fingerprinting and proximity detection than WCD autonomous proximity detection. Certain Release 8 WCDs that do not support proximity reporting can also benefit from the network based/assisted fingerprinting mechanism described herein. However, in some cases there are potential drawbacks to certain network based fingerprinting solutions, for example:

[ 0055 ] (l) in some embodiments where the WCD performs proximity detection, fingerprints are transmitted towards the WCD— this may require standardization changes and it can lead to high overhead signaling where a large amount of fingerprint information is transmitted (e.g., absolute or relative signal level thresholds of many intra-frequency cells might be transmitted in some embodiments);

[ 0056 ] (2) if the fingerprints are not communicated to the WCD (i.e. no proximity indication required from the WCD), the network, in some embodiments, receives a measurement report from the WCD and attempts to match it with a fingerprint. Thus, offloading opportunities can be missed if the network doesn't receive up to date intra-frequency measurement reports from its WCDs; and

[ 0057 ] (3) as discussed above, lightly loaded cells may be temporarily deactivated to save energy; hence, Fingerprints that were based on such cells that may be deactivated intermittently could make the fingerprints for the small cells unreliable.

[ 0058 ] Additionally, a WCD often has a limited number of CSG or hybrid He Bs to which it has membership (e.g., CSG cells deployed at home, at the office, regular coffee shop, etc). Making the WCD perform ASF for these cells can be desirable, but, in the case of picos or open HeNBs, there can be quite a lot of cells (hundreds, for example, in certain cases of dense deployment) that are relevant to the WCD. In some cases it can be quite demanding for the WCD, both from processing power and memory point of view, to make accurate fingerprints (location based, neighbor signal strength based, etc.) for all these cells and try to match them continuously. [ 0059 ] In this disclosure, we describe embodiments to address some or all of these drawbacks. For example, describe herein are optimizations of network based fingerprinting and proximity detection mechanisms for reducing the overhead of required intra-frequency measurements and/or amount of fingerprint information to be communicated to the WCD.

[ 0060 ] In some embodiments, the amount of required intra-frequency measurements is reduced by considering factors such as the deployment density of the inter-frequency small cells, the load of the serving macro cell, the data activity of a particular WCD, etc.

[ 0061 ] In some embodiments, the amount of fingerprint information communicated towards the WCD is reduced by including only basic information such as cell IDs of neighbour cells that the WCD is expected to hear when in the vicinity of the inter-frequency small cell. The WCD can then include the intra-frequency measurement report in the proximity indication report, and network can verify if the proximity detection was accurate enough by comparing the included measurement report with the detailed fingerprint that it has.

[ 0062 ] Also described herein are mechanisms to make network-based and/or network-assisted fingerprinting function well even in scenarios where some cells can be activated on or off intermittently. For example, mechanisms are disclosed where relevant WCDs may be informed, e.g. by a macro e B, when cells that are parts of relevant fingerprints are activated or deactivated. Such updates may be communicated when needed or proactively in the form of predefined activity/inactivity schedules. The eNB may in turn be informed of activity/inactivity from neighbouring eNBs across the X2 interface. If predefined activity/inactivity schedules are used, these may be acquired through explicit signalling across the X2 interface, from the O&M system or by automatic learning through observations.

[ 0063 ] Accordingly, in one aspect there is provided a method for proximity detection in a wireless network comprising a network node. The method comprises the network node storing a set of cell identifiers, the set of cell identifiers being logically linked with a target cell. The method also comprises the network node determining that a cell identified by one of the cell identifiers included in the set has changed state. The method further comprises the network node creating a new fingerprint for the target cell that is different than an initial fingerprint for the target cell that was created prior to the creation of the new fingerprint in response to determining that a cell identified by one of the cell identifiers included in the set has changed state.

[ 0064 ] The step of determining that the cell has changed state may consist of determining that the cell has been deactivated. The step of creating the new

fingerprint may comprise removing the cell identifier from the initial fingerprint for the target cell. The step of determining that the cell has changed state may consist of determining that the cell has been reactivated. The step of creating the new fingerprint may comprise adding the cell identifier to the initial fingerprint for the target cell.

[ 0065 ] In some embodiments, the method further comprises the network node transmitting to a wireless communication device, WCD, the initial fingerprint for the target cell prior to determining that a cell identified by one of the cell identifiers included in the set has changed state. In such an embodiment, the initial fingerprint may include a set of entries, and the method further comprises the network node transmitting to the WCD information indicating the entries included in the initial fingerprint that the WCD should not use in determining its proximity with the target cell.

[ 0066 ] In some embodiments, the method further comprises the network node transmitting with the initial fingerprint a schedule indicating one or more time periods during which a cell identified by a cell identifier included in the initial fingerprint will be in a deactivated state.

[ 0067 ] In some embodiments, the method further comprises the network node, in response to determining that a cell identified by one of the cell identifiers included in the set has changed state, transmitting the new fingerprint to the WCD.

[ 0068 ] In some embodiments, the method further comprises the network node, in response to determining that a cell identified by one of the cell identifiers included in the set has changed state, transmitting to the WCD the cell identifier and either (i) an instruction to add the cell identifier to the initial fingerprint or (ii) an instruction to remove the cell identifier from the initial fingerprint.

[ 0069 ] In some embodiments, the method further comprises the network node, prior to determining that a cell identified by one of the cell identifiers included in the set has changed state, transmitting to a wireless communication device, WCD, i) a plurality of initial fingerprints for the target cell and ii) a time schedule indicating, for each of the plurality of initial fingerprints, a time period during which the initial fingerprint is an active initial fingerprint.

[ 0070 ] In some embodiments, the method further comprises: the network node, prior to determining that a cell identified by one of the cell identifiers included in the set has changed state, determining whether the target cell is a closed subscriber group, CSG, cell; the network node, in response to determining that the target cell is a closed CSG cell, determining whether a WCD that it is serving has a whitelist that includes the target cell; and the network node, in response to determining that the WCD has a whitelist that includes the target cell, transmitting to the WCD the initial fingerprint for the target cell. In such embodiments, the WCD may be configured to use the initial fingerprint to determine whether the WCD is within the target cell.

[ 0071 ] In another aspect, there is provided an apparatus for use in a wireless network. The apparatus adapted to store a set of cell identifiers, the set of cell identifiers being logically linked with a target cell. The apparatus is also adapted to determine that a cell identified by one of the cell identifiers included in the set has changed state. The apparatus is further adapted to create a new fingerprint for the target cell that is different than an initial fingerprint for the target cell that was created prior to the creation of the new fingerprint in response to determining that a cell identified by one of the cell identifiers included in the set has changed state.

[ 0072 ] In another aspect there is provided an apparatus that comprises means for storing a set of cell identifiers, the set of cell identifiers being logically linked with a target cell. The apparatus also comprises means for determining that a cell identified by one of the cell identifiers included in the set has changed state. The apparatus further comprises means for creating a new fingerprint for the target cell that is different than an initial fingerprint for the target cell that was created prior to the creation of the new fingerprint in response to determining that a cell identified by one of the cell identifiers included in the set has changed state.

[ 0073 ] In another aspect a method for proximity detection in a wireless network comprising a wireless communication device, WCD, is provided. The method comprises the WCD receiving from a network node an initial fingerprint, wherein the initial fingerprint comprises a first set of cell identifiers, the first set of cell identifiers being logically linked with a target cell. The method further comprises the WCD receiving from a network node a new fingerprint. The new fingerprint comprises a second set of cell identifiers. The second set of cell identifiers is logically linked with said target cell. The second set of cell identifiers is not the same as the first set of cell identifiers such that a particular cell identifier is either a) included in the second set of cell identifiers and not included in the first set of cell identifiers or b) included in the first set of cell identifiers and not included in the second set of cell identifiers, and the cell identified by the particular cell identifier is a cell that has changed state after the point in time at which the network node transmitted the initial fingerprint.

[ 0074 ] In another aspect a wireless communication device, WCD, apparatus for use in a wireless network is provided. The WCD apparatus is adapted to receive from a network node an initial fingerprint, wherein the initial fingerprint comprises a first set of cell identifiers, the first set of cell identifiers being logically linked with a target cell. The WCD apparatus is further adapted to receive from a network node a new fingerprint. The new fingerprint comprises a second set of cell identifiers. The second set of cell identifiers is logically linked with said target cell. The second set of cell identifiers is not the same as the first set of cell identifiers such that a particular cell identifier is either a) included in the second set of cell identifiers and not included in the first set of cell identifiers or b) included in the first set of cell identifiers and not included in the second set of cell identifiers. The cell identified by the particular cell identifier is a cell that has changed state after the point in time at which the network node transmitted the initial fingerprint.

[ 0075 ] In another aspect, a computer program is provided. The computer program comprises instructions which, when executed on at least one processor, cause the at least one processor to carry out a method described above. The computer program may be a component of a computer program product.

[ 0076 ] The above and other aspects and embodiments are described in further detail below.

BRIEF DESCRIPTION OF THE DRAWINGS

[ 0077 ] FIG. 1 illustrates an example heterogeneous network.

[ 0078 ] FIG. 2 is a plot of signal strength over time to illustrate triggering conditions. [ 0079 ] FIG. 3 is an exemplary message flow diagram.

[ 0080 ] FIG. 4 is another exemplary message flow diagram.

[ 0081 ] FIG. 5 is a message flow diagram according to some embodiments

[ 0082 ] FIG. 6 illustrates a process according to some embodiments.

[ 0083 ] FIG. 7 is a diagram of a network node according to some

embodiments.

[ 0084 ] FIG. 8 illustrates a process according to some embodiments.

[ 0085 ] FIG. 9 illustrates a process according to some embodiments.

[ 0086 ] FIG. 10 illustrates a process according to some embodiments.

[ 0087 ] FIG. 11 illustrates a process according to some embodiments.

[ 0088 ] FIG. 12 illustrates a process according to some embodiments.

[ 0089 ] FIG. 13 illustrates a process according to some embodiments.

[ 0090 ] FIG. 14 is a diagram of a WCD according to some embdiments.

[ 0091 ] FIG. 15 illustrates a process according to some embodiments.

DETAILED DESCRIPTION

[ 0092 ] For the sake of brevity, various aspects and embodiments of this disclosure are illustrated in an environment where the WCDs are being served by macro cells, and measuring only on the macro frequency and getting into the vicinity of an inter-frequency small cell. However, the aspects and embodiments are equally applicable to the case of inter-frequency macro neighbor cells and also for the case where the WCD was being served by the inter-frequency small cell and approaching the edges of the coverage area of the small cell (as in some cases, for the sake of reducing the battery consumption, it might be beneficial to disable measuring on the macro frequency after the WCD has been offloaded to the inter-frequency small cell). Also, even though an LTE network may be described as the radio access technology (RAT) both in the macro and small cell layers in the discussions, the described mechanisms are equally applicable to other RATs such as UMTS, HSPA, WiMAx, etc. Even non cellular RATs such as WLAN can be assumed to be the inter- frequency small cells (in such cases enabling/disabling of inter-frequency measurement reporting may consist of (or comprise) enabling or disabling of the WLAN radio or modifying the modification of the scanning periodicity for WLAN networks.

[ 0093 ] FIG. 3 illustrates a procedure of network based proximity detection. The WCD 101 is configured for intra-frequency measurement reporting. That is, for example, base station 102 sends to WCD 101 a configuration message 301 that specifies a reporting condition. The WCD 101 sends to base station 102 a

measurement report 302 (e.g., an intra-frequency measurement report) when the reporting condition is met. The network (e.g., base station or other network node) compares these intra-frequency reports with the fingerprint that it has for its inter- frequency small cell neighbors. As used herein a cell is a neighbor to another cell if the cells share a coverage area, either completely or partially. If there is a match, the base station 102 sends to WCD 101 a measurement reconfiguration message 303 enabling WCD 101 for inter-frequency measurements. The WCD 101 will then send an inter-frequency measurement report 304 when it detects an inter-frequency cell (e.g., base station 103), and this might lead to the WCD 101 being handed over to the inter-frequency small cell 103.

[ 0094 ] FIG. 4 illustrates a procedure of network assisted proximity detection. The e B 102 configures the WCD 101 with measurement configurations that includes the fingerprint(s) of the inter-frequency small cell neighbors of the serving cell of the WCD 101 and also enables it for proximity reporting. That is, for example, eNB 102 transmits to WCD 101 a message 401 including the measurement configurations. The WCD keeps comparing its measurements with the fingerprint(s) and sends out a proximity indication 402 when there is a match. The eNB can then configure the WCDs for inter-frequency measurements. That is, the eNB 102 can transmit to the WCD 101 a reconfiguration message 403. The WCD will be able to send inter-frequency measurement reports 404 when it detects such cell(s), and this might lead to the WCD being handed over to an inter-frequency small cell.

[ 0095 ] Intra-Frequency Reporting Optimization:

[ 0096 ] In some embodiments, a network node (e.g., a macro eNB) configures a WCD that it is serving with periodic intra-frequency measurement reports, and the periodicity (i.e. the duration between measurement reports) or frequency is determined based on the density of the inter-frequency small power base stations (e.g., small power cells) in the neighborhood of the macro base station. For example, if the density is very high, more frequent measurement reporting can be configured. A way to evaluate whether the periodicity of measurements is frequent enough is for the e B to analyze the WCD History Information sent via handover signaling when the WCD accesses any of the cells served by the eNB. If the WCD History information does not show expected handover to small cells in the neighborhood, then a higher frequency of measurements should be used. Alternatively, if the small cells are deployed for coverage extension, another way to evaluate whether the periodicity is sufficiently high is to analyze the number of failures during handover procedures reported via RLF Reports as part of the Mobility Robustness Optimization function described in TS 36.300. The eNB may configure the WCD by transmitting to the WCD measurement configuration information, which may be included in a configuration message. The configuration message may be (or may be a part of) a reconfiguration message (e.g., an RRC Connection Reconfiguration message).

[ 0097 ] In some embodiments, the load of the serving cell is considered in setting the periodicity of intra-frequency measurement reports. For example, if the load of the serving cell is high (e.g., exceeds a predetermined threshold), the network node can configure the WCD to perform more frequent intra-frequency measurement reporting so that more offloading opportunities can be found (i.e. chances of a WCD sending a measurement report when in the vicinity of an inter-frequency small cell increases).

[ 0098 ] However, having more frequent measurement reports can further exacerbate the load situation in the cell, especially if the UL load was the problem. Thus, in some embodiments, the WCD's data activity may be considered as well. This way, the network node can configure only the WCDs that are contributing the most towards the cell load (UL and/or DL) to perform periodic intra-frequency

measurement reporting, or it can configure all WCDs with intra-frequency

measurement reporting, but scale how frequent the reporting should be based on the WCD's traffic activity. For example, WCDs receiving or/and transmitting the most data can be configured to perform more frequent intra-frequency measurement reporting. This will increase the probability of these WCDs being offloaded towards the inter-frequency cells, and as the WCDs are already having lots of data

transmission, the percentage overhead of the intra-frequency measurement reports will not be that much.

[ 0099 ] In some embodiments, the network node can send a onetime configuration message to a certain WCD or a group of WCDs. For example, when the network node notices that the load of one of its cells is increasing, it can send this request to some of the WCDs that are contributing the most towards this load and compare their reports with the fingerprint of inter-frequency small cells that it has to see if any of them are in the vicinity of the small cells. This option can be used with or without periodic reporting (i.e. if periodic reporting was already enabled for the WCD, then this message takes precedence and WCD reports back immediately, but still maintains the periodic reporting). This embodiment can be realized by

configuring the trigger type periodic and the report amount equal to 1 of the measurement report triggering configuration in LTE, or it can be enabled by using a choice of threshold values in the already standardized events to guarantee a message reception. For example, event Al can be used (primary serving cell becomes better than absolute threshold), if the threshold is set to a very low value.

[ 00100 ] In some embodiments, a detailed one time configuration is given to the WCD that contains a mapping of the periodicity of the reporting with the WCD's data activity. The mapping may be in the form of rules, such as: if data activity in UL < threshold low, then disable periodic reporting; if threshold low <=data activity in UL <threshold_medium, then report with medium reporting periodicity; if

threshold medium <=data activity in UL <threshold_high, then report with very short reporting periodicity, etc. In some embodiments, instead of configuring the periodicity, one time measurement reports can be pre-configured to specify when the WCD sends out the one time measurement reports. For example, the WCD could be specified to send one time measurement report every time the data activity in UL passes a certain threshold. A filtering time could also be specified for the WCD to average the data activity within certain duration in order to prevent changing the behavior just because a short data spike occurs.

[ 00101 ] In some embodiments, the network node configures the WCD with periodic intra-frequency measurement reports and the periodicity is determined based on the load of the inter-frequency small cell neighbors. For example, if the network node finds out that most of the inter-frequency small cell neighbors are loaded, it can decrease the intra-frequency reporting frequency of its WCDs, as the offloading chances towards the small cell neighbors can be limited. The network node could be aware of the load conditions of the inter-frequency small cell neighbors via existing X2 based load exchange mechanisms.

[ 00102 ] In some embodiments, the network node configures its WCDs with periodic intra-frequency measurement reports and the periodicity is determined based on the activity state of the inter-frequency small cell neighbors. This is relevant for cases where the small cell neighbors could be sometimes switched (e.g. energy saving considerations). For example, if the network node finds out that most of the small cell neighbors are inactive, it can configure its WCDs to send less frequent intra- frequency measurement reports.

[ 00103 ] In some embodiments, the network node configures its WCDs with periodic intra-frequency measurement reports and the periodicity is determined based on the mobility state of the WCD. This can be applied, for example, in a way similar to the scaling of cell reselection parameters in LTE. The WCD can be given a scaling factor that it uses to adjust the periodicity based on its estimated mobility state (which can be based, for example, on the number of cell reselections within certain duration, or more accurate information such as GPS is available). Alternatively, the mobility state of the WCD may be known at the network but not the WCD (e.g. Doppler estimation at the network node), and the WCD's reporting period is increased or decreased when significant changes in the WCD speed are detected.

[ 00104 ] In embodiments described herein, the network node may configure a WCD with respect to measurement reporting by sending to the WCD measurement configuration information, which information, as described herein may be selected using information identifying a network condition of the wireless network, such as, for example, information identifying one or more of: network data activity, a network configuration, a network load, and a network state. The information identifying a network configuration may comprise information identifying the density of network devices (e.g., inter-frequency low power base stations) near the serving base station that serves the WCD. The information identifying the network load may comprise information identifying a load on the serving base station (e.g., the load the base station experiences with respect to the cell serving the WCD). The information identifying the network data activity may comprise information identifying a data activity of the WCD, such as, for example, identifying an upload or download data activity of the WCD.

[ 00105 ] Fingerprint Optimization:

[ 00106 ] FIG. 5 is a message flow diagram illustrating an embodiment of a fingerprint optimization aspect of this disclosure. In the embodiment shown, eNB 102 sends to WCD 101 a reconfiguration message 501, which may include a simplified fingerprint, which is also referred to as a "coarse fingerprint". The WCD 101 then performs proximity detection using one or more of its own fingerprints (e.g., a fingerprint that WCD created or a coarse fingerprint provided to the WCD) and when WCD 101 determines based on a particular fingerprint associated with a cell that it is within the proximity of the cell, WCD 101 sends to eNB 102 a proximity indication identifying the cell and an intra-frequency measurement report (see message 502). In response to receiving message the proximity indication and the intra-frequency measurement report, eNB 102 determines, based at least in part on the intra-frequency measurement report, whether the proximity indication is valid. If it is not valid, then eNB 102 may send to WCD 101 a spurious detection indication (see message 503) (e.g., a negative acknowledgement (NACK)) signifying the WCD's fingerprint for the cell is not accurate enough, otherwise eNB 102 send to WCD 101 a reconfiguration message 504 to instruct the WCD 101 to perform inter-frequency measurements and transmit a measurement report 505 reporting the inter-frequency measurements.

[00107] FIG. 6 is flow chart illustrating a fingerprint optimization process according to some embodiments. The process includes the following steps:

[ 00108 ] Step 612: The network (i.e., a node of the network) makes fingerprint of an inter-frequency cell.

[00109] Step 614: The network (e.g, eNB 102) communicates a simplified fingerprint to WCD 101 (optional) (e.g., the eNB 102 sends reconfiguration message 501 to the WCD). [00110] Step 622: The WCD makes fingerprint of an inter-frequency cell via ASF (optional).

[00111] Step 624 : The WCD detects proximity to inter-frequency cell via matching with own fingerprint.

[00112] Step 626 : The WCD sends to the network an enhanced proximity indication report that includes the measurement report (e.g., the WCD sends message 502)

[00113] Step 628 : The network compares the intra-frequency measurement report with its own fingerprint

[0011 ] Step 630: The network determines whether the intra-frequency measurement report is in agreement with its own fingerprint. If it is, the process proceeds to step 632, otherwise it proceeds to step 634.

[00115] Step 632: The network reconfigures the WCD for inter-frequency measurements (e.g, e B 102 send to the WCD message 504)

[00116] Step 634: Network send the spurious detection indication 503 (e.g., a NACK) to the WCD signifying the WCD's fingerprint is not accurate enough.

[00117 ] Step 636: WCD uses the received information (e.g., either the message 503 or message 504) to adapt own fingerprint.

[00118] As described above, in some embodiments, a network node (e.g., a macro base station) sends a reconfiguration message 501 that configures a WCD (e.g., a WCD being served by the network node) for proximity reporting of inter-frequency small cells. That is, for example, the network node requests the WCD to send to the network node a proximity message when the WCD determines that it is near an inter- frequency low power base station, wherein the proximity message includes information indicating that the WCD is within the vicinity of an inter-frequency low- power base station.

[00119] The reconfiguration message 501 may comprise a set of one or more coarse fingerprints, where each coarse fingerprint is associated with a different base station (e.g., each coarse fingerprint may be associated with a cell served by the base station, which could be an inter-frequency low power base station), as opposed to a set of detailed fingerprints, such as those specified in PCT/SE2012/050833, mentioned above. A coarse fingerprint may include only basic information (e.g., a set of cell IDs that the WCD is expected to detect when the WCD is in the vicinity of the cell with which the fingerprint is associated), rather than detailed information such as relative or absolute signal strength values. In this way, the amount of fingerprint data to be communicated to the WCD can be reduced significantly, especially in cases where there are several inter-frequency low power base stations neighboring the network node.

[ 00120 ] In some embodiments, the WCD is configured with a coarse fingerprint in the form of set of cell identifiers (CIs) (e.g., physical cell IDs (PCIs), cell identifiers of other RAT, etc.), and the WCD is requested to send a measurement report or proximity indication in response to detecting the transmission of each of the CIs as the proximity step. In some embodiments, the WCD is requested to send a measurement report in response to detecting the transmission of each of the CIs within a time window. In some embodiments, the WCD stores a threshold value, and the WCD is requested to trigger a measurement report in response to detecting the transmission of at least N of the PCIs. N may be an absolute value or a fraction value.

[00121 ] In some embodiments, the WCD stores several sets of PCIs, each associated with a set identifier. When a measurement report has been triggered, a set identifier is included in the report together with the measurements. Each set may also be associated either with a time window, or a common time window. Each set may also be associated either with a threshold or fraction value, or a common threshold or fraction value to be used to trigger a report when a subset of the physical cell IDs in the configured set has been detected.

[ 00122 ] In some embodiments, also the txRxTimeDifference (representing how much earlier the WCD starts transmitting an uplink frame compared to when the WCD receives the start of a downlink frame) can be used in the report triggering condition. For example, a report is triggered if other criterions are met, and one of the following criterions are met: (1) txRxTimeDifference is equal to a configured value; (2) txRxTimeDifference is greater than (or greater than or equal to) a configured threshold; (3) txRxTimeDifference is less than (or less than or equal to) a configured threshold; and (4) txRxTimeDifference is greater than (or greater than or equal to) a configured first threshold, and is less than (or less than or equal to) a configured second threshold.

[ 00123 ] If the coarse fingerprint is not included in the configuration message 501, the WCD can be instructed to use some ASF mechanism to make the proximity detection. In some embodiments, when the WCD has detected proximity due to a match of either the coarse fingerprint provided in the measurement configuration or a fingerprint that it has generated itself using ASF, the WCD sends a proximity indication report back towards the network node, along with the measurement report that resulted in the matching of the fingerprint. For instance, as discussed above, the WCD sends back toward the network node a proximity indication identifying the cell and an intra-frequency measurement report (see e.g., message 502).

[ 00124 ] In some embodiments, when the network node gets a proximity indication report that contains a measurement report, it compares the measurement report with a detailed fingerprint that it has to validate whether the WCD's proximity detection is accurate. In response to determining that the proximity detection is accurate (i.e. the WCD measurement report matches the detailed fingerprint), the network node configures the WCD to perform inter-frequency measurements. That is, the network node transmits to the WCD a reconfiguration message 504.

[ 00125 ] In some embodiments, in response to determining that the proximity detection that was reported by the WCD is incorrect, the network node sends to the WCD a spurious detection indication indicating that the proximity detection was spurious (see e.g., message 503). This message may be a new RRC message. This message could also be a simple flag (e.g. negative acknowledgement, NACK) signifying that the proximity detection performed by the WCD was not accurate, or the message may contain additional information, such as: the signal level range of the cells that should have been heard (or should not have been heard); the cells with signals level lower (higher) than expected; the RATs that should have been monitored; etc. In some embodiments, the network node doesn't send any indication of spurious detection towards the WCD, and if the WCD has not received any measurement reconfiguration within a certain duration after the sending of the proximity detection, the WCD assumes that the proximity detection that it has performed was not accurate. [00126] In some embodiments, the WCD, in response to determining that the proximity detection that it has performed was not accurate (either via a reception of an explicit spurious detection indication from the network node or implicitly when it has not received a measurement reconfiguration after a certain duration after the sending out of the proximity indication report), the WCD updates its fingerprint (either the coarse fingerprint it received from the network node originally or the one that it generated via ASF). In case fingerprint information was provided by the network node to the WCD in a spurious detection message, the WCD may use the fingerprint information to update its fingerprint.

[ 00127 ] In some embodiments, the WCD may not have any fingerprint to begin with (neither a coarse fingerprint received from a network node nor a fingerprint generated via ASF). In such a situation, the WCD, in response to receiving from a network node a request to perform inter-frequency measurements, which request was triggered by an intra-frequency measurement report transmitted by the WCD, the WCD uses the measurement report to create a fingerprint. In some embodiments, the WCD fingerprint created using the measurement report is a coarse fingerprint (e.g., a fingerprint that merely includes a set of one or more PCIs).

[ 00128 ] Handling Intermittent Cells

[00129] Many types of cells may benefit from proximity detection, in particular proximity detection based on fingerprints. Typically, low power cells (e.g., pico cells, femto cells) that are overlaid by macro cells and that are deployed for coverage extension (e.g. indoor) and/or capacity boosts, are associated with a fingerprint. A general term for a cell that is associated with a fingerprint that may be used herein is "target cell" and the eNB or He B/HNB or access point, etc. serving it may be denoted "target base station" or "target eNB".

[ 00130 ] In some embodiments, a macro eNB stores a fingerprint for each of its neighboring cells, which fingerprint includes a set of cell identifiers. The eNB, in response to determining that a cell identified by a cell identifier included in one of the stored fingerprints changes state from active to inactive, the eNB creates a new fingerprint accordingly (e.g., by removing the cell id from the fingerprint). Likewise, the eNB, in response to determining that a cell identified by a cell identifier that the eNB removed from a particular fingerprint changes state from inactive to active, the eNB creates a new fingerprint accordingly (e.g., by adding the cell id back to the particular fingerprint). In some embodiments, the same holds true for WCDs. That is, a WCD, in response to determining that a cell identified by a cell identifier included in a fingerprint stored by the WCD changes state from active to inactive, the WCD creates a new fingerprint accordingly; and the WCD, in response to determining that a cell identified by a cell identifier that was removed from a fingerprint stored by the WCD changes state from inactive to active, the WCD creates a new fingerprint accordingly.

[ 00131 ] The eNB may determine such state changes from messages received from other base stations. For example, the activation/deactivation may be

communicated to the eNB via the X2 eNB CONFIGURATION UPDATE, as discussed. An alternative to communicating activity/inactivity via the X2 interface may be that the concerned eNB(s) (e.g. a neighboring eNB serving an overlaying macro cell) is informed by the O&M system, e.g. by an OSS. Yet another way may be that an eNB learns the activity/inactivity of neighboring cells by monitoring their activity states (through own measurements or aided by measurements performed by WCDs). As a simple example, consider the case where the original fingerprint for a target cell was something like "signal level of cell A > level A and signal level of cell B > level B and signal level of cell C > level C". If the eNB determines that cell B has become inactive, the fingerprint is changed to "signal level of cell A > level A and signal level of cell C > level C". Similarly, if later on A becomes inactive and B is re-activated, the fingerprint will change to "signal level of cell B > level B and signal level of cell C > level C" and so on.

[ 00132 ] If network based proximity detection is employed (e.g., fingerprint matching is performed in the eNB as illustrated in FIG. 3), the eNB keeps the updated fingerprint to itself. However, the case of network assisted proximity detection where the fingerprint matching is performed in the WCD (see FIG. 4) is different.

[ 00133 ] With network assisted proximity detection, the eNB communicates the new fingerprint to the relevant WCDs. In this case the relevant WCDs could be new WCDs that are being handed over to the eNB, WCDs going from RRC IDLE to RRC CONNECTED state (i.e. establishing an RRC connection) in a cell served by the eNB (e.g. a cell overlaying the target cell) and also WCDs that are already being served by the e B. If the fingerprint is associated with a closed subscriber group (CSG) cell and the eNB can get the CSG whitelist of the WCDs from a core network node, then the eNB will inform only the WCDs that have the CSG cell in their whitelist. Otherwise if the fingerprint is not associated with a CSG cell, then the eNB may inform all the WCDs that it is currently serving, as well as all WCDs that are being handed over to it.

[ 00134 ] Instead of communicating an entire new fingerprint for a target cell to a WCD, the eNB can inform the WCD of only the cells that should be excluded from or added to a fingerprint maintained by the WCD for the target cell. In the above example where a fingerprint for a target cell includes an identifier for cell B and cell B becomes inactive, the eNB could simply inform the WCD to remove cell B from the fingerprint (e.g., deactivate the entry in the fingerprint pertaining to cell B by, for example, ignoring the information regarding cell B when attempting matching the fingerprint). Suitable means for communicating such updates to the concerned WCDs could be an RRC message, e.g. a new RRC message or in the measConfig IE in the RRCConnectionReconfiguration message (or in the RRCConnectionSetup message for WCDs establishing an RRC connection).

[00135 ] When a WCD doesn't hear a cell, it can be due to the cell's deactivation or it can be because the WCD is outside the coverage area of the cell. As such, the information about the deactivation of the cell is important to the WCD. Likewise, information about activation of a cell that is included in a fingerprint is important to the WCD, so that the WCD knows that if it does not hear the cell, it means that the fingerprint does not match the current location. (In some cases information about activation of a cell may be redundant, e.g., when the WCD is located in the coverage area of a cell that was previously indicated as inactive and the WCD starts hearing this cell when it is activated, it will know for sure the cell has become active again.) Thus, when a WCD becomes aware that a cell that has been previously communicated as inactive has again become active, it will activate the entries corresponding to that cell in the fingerprints that it has.

[ 00136 ] When an entry pertaining to a cell is removed from a fingerprint due to the cell becoming inactive, the accuracy of the fingerprint may be reduced. One possible way to counteract this reduction in accuracy is that when the original fingerprint is made, we may gather more information than is needed. For example, consider a case where the signal levels from four cells are used for fingerprinting. When making the original fingerprinting, we gather information from more than four cells, say, 7 cells. The fingerprint with entries only from the four most relevant cells will be communicated to the WCDs. If one of the cells in the top 4 becomes inactive, then an entry from the bottom 3 of the fingerprint list is "upgraded" to be used by the WCD. The eNB then communicates the upgraded entry to the WCD when informing the WCD of the inactivation of the concerned cell in the top 4. A possible alternative is that all seven cells are included in the fingerprint that is originally communicated to the WCD, but with indications of which of the cells in the fingerprint that should be used, i.e. the top 4. With this alternative, inactivation of a cell in the top 4 causes the eNB to indicate the concerned cell as not to be used in the fingerprint matching and to change the corresponding indication of a cell being upgraded so that this cell will be used in the fingerprint matching.

[ 00137 ] Intermittently sleeping cells can be included in the fingerprints, with or without an indication of their intermittent nature, and the list of intermittently sleeping neighbor cells can be included in the system information. The list could contain all intermittently sleeping cells that are included in any of the fingerprints the

neighboring inter-frequency small cells and each cell in the list should be associated with an indication of its present status (sleeping or awake). Changes of this list in the system information should not necessarily trigger paging of WCDs to indicate system information change.

[ 00138 ] In some embodiments, weighting of matching of each part of a fingerprint could be employed, e.g. if a certain cell X should have signal strength within a certain range, then the degree of matching the criterion depends on how far from the middle of the range the signal strength is (e.g. 1 in the middle and 0 at the edges of the range). With this principle, the degree of matching for each criterion could be multiplied by a weight reflecting the importance of the criterion in relation to other criteria in the fingerprint. For instance, intermittent cells could be assigned lower weights. When determining whether a fingerprint match is detected, a sum of the product of weight and degree of match for each criterion could be calculated and should exceed a certain threshold value in order to indicate a matching fingerprint. [ 00139 ] In certain cases, it might be known in advance when a cell is scheduled to be deactivated. For example, an operator can schedule some cells to be turned off between specific times as the load is expected to be very low during those times. In that case, a time schedule of the activity nature of the cells can be included as part of the fingerprint, and WCDs will check the time of day as well as the activity schedule of the cells in their fingerprints to decide which ones to consider or not. That way, e Bs do not have to update fingerprints on demand when a cell becomes

active/inactive. The activity/inactivity schedule of a cell may be communicated to neighboring eNBs (e.g. from an eNB serving a small cell to an eNB serving an overlaying macro cell) via new extensions of X2AP, e.g. as new parameters of the eNB CONFIGURATION UPDATE message. In addition, protocol extensions, preferably RRC protocol extensions, would be needed to communicate such schedules to the WCD, e.g. new parameters to be communicated together with the fingerprint information. An alternative to communicating activity/inactivity schedules via the X2 interface may be that the concerned eNB(s) (e.g. a neighboring eNB serving an overlaying macro cell) is informed by the O&M system, e.g. by an OSS. Yet another way may be that an eNB learns the activity/inactivity schedules of neighboring cells by monitoring their activity states (through own measurements or aided by

measurements performed by WCDs.

[001 0] It could also be envisioned that different fingerprints for different times of the day can be utilized. That way, there may be a set of fingerprints for one particular target cell, where each said fingerprint is relevant for only a certain time period during the day. The time periods may e.g. be chosen to match

activity/inactivity schedules of concerned cells (wherein the activity/inactivity schedules may be acquired in any of the ways described above

[001 1] In some embodiments, a way to deal with the intermittent nature of cells in a fingerprint is that the eNB responsible for the fingerprint defines the fingerprint using logical expressions, such as conditional expressions. For example, the following kind of conditional definition could be used:

IF cell A, B and C but not D can be heard THEN use fingerprint X

ELSE IF cell A, B and D, but not C can be heard THEN use fingerprint Y [ 00142 ] More advanced logic could also be used in the fingerprint definition, e.g. mixing conditional expressions with sequential matching attempts with different fingerprint variants.

[001 3] In some embodiments, a cell that is deactivated may be a target cell (i.e., a network node may store a fingerprint for the cell, which may be a small cell). In the case of network based proximity detection, the fingerprint matching for inactive cells can be suspended. In the case of network assisted proximity detection where the fingerprints are communicated to the WCD, the WCD can be informed about a fingerprint for a target cell that has gone inactive so that the WCD will not try to match that fingerprint when performing proximity detection. Similarly, when the cell becomes active, the fingerprint becomes enabled again. By doing so, unnecessary processing due to fingerprint matching for cells that are inactive can be prevented. This is especially beneficial for the case of network assisted proximity detection, as the WCD's processing capability is more of a limitation than that of the e B.

[00144] Exemplary Apparatuses

[ 00145 ] FIG. 7 illustrates a block diagram of an apparatus (e.g., a network node, such as a base station), according to some embodiments, for proximity detection. As shown in FIG. 7, the network node may include: a data processing system 702, which may include one or more data processing apparatuses (e.g., a blade network node, a network node computer, etc.) each having one or more processors (e.g., a microprocessor) and/or one or more circuits, such as an application specific integrated circuit (ASIC), Field-programmable gate arrays (FPGAs), etc.; a transceiver 705, coupled to an antenna 722, for receiving and transmitting messages; a data storage system 706, which may include one or more computer-readable data storage mediums, such as non-transitory data storage apparatuses (e.g., hard drive, flash memory, optical disk, etc.) and/or volatile storage apparatuses (e.g., random access memory (RAM)). Data storage system 706 may store a set of one or more fingerprints 790. The data processing system 702, transceiver 705 and data storage system 706 need not be co-located.

[00146] In embodiments where data processing system 702 includes a processor (e.g., a microprocessor), a computer program product may be provided, which computer program product includes: computer readable program code 743 (e.g., instructions), which implements a computer program, stored on a computer readable medium 742 of data storage system 706, such as, but not limited, to magnetic media (e.g., a hard disk), optical media (e.g., a DVD), memory devices (e.g., random access memory), etc. In some embodiments, computer readable program code 743 is configured such that, when executed by data processing system 702, code 743 causes the processing system 702 to perform steps described herein (e.g., steps shown in any of the figures).

[ 001 7 ] In some embodiments, the network node may be configured to perform steps described above without the need for code 743. For example, data processing system 702 may consist merely of specialized hardware, such as one or more application-specific integrated circuits (ASICs). Hence, the features of the present invention described above may be implemented in hardware and/or software. For example, in some embodiments, the functional components of network node described above may be implemented by data processing system 702 executing program code 743, by data processing system 702 operating independent of any computer program code 743, or by any suitable combination of hardware and/or software.

[ 001 8 ] FIG. 14 illustrates a block diagram of a WCD, according to some embodiments. As shown in FIG. 14, the WCD may include: a data processing unit 1404, which may include one or more data processing apparatuses each having one or more processors (e.g., a microprocessor) and/or one or more circuits, such as an application specific integrated circuit (ASIC), Field-programmable gate arrays (FPGAs), etc.; a transceiver 1403 for receiving and transmitting messages via the antenna system 1401; a data storage system or memory 1402, which may include one or more computer-readable data storage mediums, such as non-transitory data storage apparatuses (e.g., hard drive, flash memory, optical disk, etc.) and/or volatile storage apparatuses (e.g., random access memory (RAM)). Data storage system 1402 may store a set of one or more coarse fingerprints and optionally configuration

information. The data processing unit 1404, transceiver 1403 and data storage system 1402 need not be co-located. The transceiver 1403 may be configured to detect physical cell IDs or similar in other radio access technologies based on signals received via the antenna system 1401, and transfer detected cell IDs to the data processing unit 1404. The data processing unit 1404 may further compare the detected cell IDs to the coarse fingerprint, optionally considering the configuration information as described in some of the embodiments. At a positive detection, the data processing unit 1404 may prepare a proximity indication, that is sent to the serving base station from the transceiver 1403 via the antenna system 1401.

[001 9] Advantages

[ 00150 ] At least some of the below advantages are realized by embodiments described in this disclosure:

[00151] (1) The amount of required intra-frequency measurement reporting for the sake of inter-frequency small cell detection is reduced;

[00152] (2) The amount of required signaling for communicating the fingerprints to the WCDs is reduced;

[00153 ] (3) Even WCDs without fingerprinting support can benefit; and

[00154 ] (4) WCDs can use mechanisms described to fine tune the fingerprints they have acquired via ASF.

[ 00155 ] (5) Efficient use fingerprints in proximity detection in the presence of intermittently active/inactive cells - - this is very beneficial, since energy efficiency is increasingly high on operators' agendas, and rightly so because of its importance for network operation costs and environmental concerns.

[00156] Aspects and Embodiments

[00157] 1. First Aspect

[ 00158 ] In a first aspect, there is provided a method for proximity detection in a wireless network wherein a wireless communication device (WCD) is in

communication with a network node (e.g., a base station). This method is shown in FIG. 8. In some embodiments, the method comprises: (1) obtaining information identifying (e.g., indicating) a network condition of the wireless network (step 802); (2) selecting measurement configuration information for configuring the WCD with respect to measurement reporting using the obtained information identifying a network condition of the wireless network (step 804); and (3) transmitting the selected measurement configuration information towards the WCD (step 806). [00159] In some embodiments, the measurement configuration information specifies a reporting frequency (i.e., the frequency with which the WCD should transmit measurement reports - - such as intra-frequency measurement reports). For example, the configuration information may specify that the WCD should transmit a measurement report every 100ms; and the frequency is selected based on the information identifying the network condition. In some embodiments, the WCD may adjust the specified reporting frequency based on its mobility state. For example, measurement configuration information may specify not only a reporting frequency but also a mobility scale factor that the WCD uses to adjust the reporting frequency. In embodiments where the WCD does not have information regarding its mobility state, but the network node does have such information, then the network node may select the reporting frequency based on the WCD's mobility state.

[00160 ] In some embodiments, the information identifying the network condition comprises (or consists of) information identifying one or more of: network data activity, a network configuration, a network load, and a network state.

[00161] In some embodiments, the information identifying the network condition comprises information identifying a network configuration. In some embodiments, the information identifying network configuration comprises information identifying the density of active base stations neighboring the network node (e.g., the density of the cells neighboring the serving cell). In some

embodiments, said base stations consist of inter-frequency low power base stations. In some embodiments, the step of selecting measurement configuration information comprises selecting first measurement configuration information in response to determining that the identified density is greater than a threshold and selecting second measurement configuration information in response to determining that the identified density is less than the threshold. In such embodiments, the first measurement configuration information specifies a first reporting frequency (e.g., 1 report every 100ms) and the second measurement configuration information specifies a second reporting frequency that is less than the first reporting frequency (e.g., 1 report every 200ms).

[00162] In some embodiments, the information identifying the network condition comprises information identifying a load on the wireless network. In some embodiments, the information identifying a load on the wireless network comprises information identifying a load on the network node. In some embodiments, the step of selecting measurement configuration information comprises selecting first measurement configuration information in response to determining that the identified load is greater than a threshold and selecting second measurement configuration information in response to determining that the identified load is less than the threshold. In such embodiments, the first measurement configuration information specifies a first reporting frequency and the second measurement configuration information specifies a second reporting frequency that is less than the first reporting frequency.

[00163] In some embodiments, the information identifying the network condition comprises information identifying a load on the network node and information indicating the degree to which the WCD is contributing to the load. It is possible that the network node (e.g., a macro base station) serves several cells, in which case the information identifying the load may be information that identifies i) the total load from all cells served by the network node or ii) the load from a set of one or more cells served by the node). In this embodiment, the step of selecting measurement configuration information may comprise selecting first measurement configuration information in response to determining that (i) the identified load is greater than a first threshold and (ii) the indicated degree is greater than a second threshold; and selecting second measurement configuration information in response to determining that (i) the identified load is less than the first threshold and (ii) the indicated degree is less than the second threshold. In such embodiments, the first measurement configuration information may specify a first reporting frequency and the second measurement configuration information may specify a second reporting frequency that is less than the first reporting frequency.

[00164] In some embodiments, the information identifying the network condition comprises information identifying a load on the network node and information indicating the degree to which the WCD is contributing to the load. In such embodiments, the step of selecting measurement configuration information may comprise selecting measurement configuration information that requests the WCD to transmit a one-time measurement report when the identified load and indicated degree exceed a first and second threshold, respectively.

[00165] In some embodiments, the information identifying the network condition comprises information identifying (e.g., indicating) a load on a set of base stations neighboring the network node. In some embodiments, the step of selecting measurement configuration information comprises selecting first measurement configuration information in response to determining that the identified load is greater than a threshold and selecting second measurement configuration information in response to determining that the identified load is less than the threshold. In such embodiments, the first measurement configuration information specifies a first reporting frequency and the second measurement configuration information specifies a second reporting frequency that is greater than the first reporting frequency.

[00166] 2. Second Aspect

[00167 ] In a second aspect, there is provided a network node for use in a wireless network. In some embodiments, the network node is configured to: (1) obtain information identifying (e.g., indicating) a network condition of the wireless network; (2) select measurement configuration information for configuring the WCD with respect to measurement reporting using the obtained information identifying a network condition of the wireless network; and (3) transmit the selected measurement configuration information towards the WCD.

[00168] 3. Third Aspect

[00169] In a third aspect, there is provided a method for proximity detection in a wireless network wherein a wireless communication device (WCD) is in

communication with a network node (e.g., a base station). This method is illustrated in FIG. 10. In some embodiments, this method comprises: (1) the network node obtaining a measurement reporting rule (step 1002); and (2) transmitting the measurement reporting rule towards the WCD (step 1004), wherein the rule (i) instructs the WCD to disable periodic measurement reporting when the WCD's data transmission activity falls below a first threshold, (ii) instructs the WCD to provide a measurement report at least once every si seconds when the WCD's data transmission activity exceeds the first threshold, and (iii) instructs the WCD to provide a measurement report at least once every s2 seconds when the WCD's data transmission activity exceeds a second threshold, wherein s2 < si and the second threshold is greater than the first threshold.

[00170] 4. Fourth Aspect

[00171] In a fourth aspect there is provided another method for proximity detection in a wireless network wherein a wireless communication device (WCD) is in communication with a network node (e.g., a base station). This method is illustrated in FIG. 11. In some embodiments, this method comprises: (1) obtaining a coarse fingerprint associated with a base station (step 1 102); and (2) transmitting to the WCD the coarse fingerprint and configuration information instructing the WCD to use the coarse fingerprint in performing proximity detection (step 1 104). The coarse fingerprint may consists of a set of one or more cell identifiers (CIs). The WCD may be configured such that it transmits a proximity indication to the network node in response to detecting all of the one or more CIs. In other embodiments, the WCD is configured to transmit the proximity indicating in response to detecting at least N of the CIs, where N is an absolute value or percentage value.

[ 00172 ] The method may further include: (3) receiving from the WCD a proximity indication indicating that the WCD is in the vicinity of the base station, wherein the WCD transmitted the proximity indication in response to determining, based on intra-frequency measurement information and the coarse fingerprint, that it is in the vicinity of the base station; (4) receiving from the WCD said measurement information that the WCD used to determine that it is in the vicinity of the base station; (5) using the measurement information and a detailed fingerprint associated with the base station to determine whether the proximity indication is accurate.

[00173] 5. Fifth Aspect

[0017 ] In a fifth aspect there is provided another method for proximity detection in a wireless network wherein a wireless communication device (WCD) is in communication with a network node (e.g., a base station). This method is illustrated in FIG. 12. In some embodiments, this method comprises: (1) the network node receiving from the WCD a proximity indication indicating that the WCD is in the vicinity of a base station (step 1202), wherein the WCD transmitted the proximity indication in response to determining, based on intra-frequency measurement information, that it is in the vicinity of the base station; (2) the network node receiving from the WCD said measurement information that the WCD used to determine that it is in the vicinity of the base station (step 1204); and (3) the network node using the measurement information and a detailed fingerprint associated with the base station to determine whether the proximity indication is accurate (step 1206).

[00175] 6. Sixth Aspect

[00176] In a sixth aspect, there is provided another method for proximity detection in a wireless network comprising a network node (e.g., a base station). This method is illustrated in the flow chart shown in FIG. 13. In some embodiments, this method comprises: (1) the network node storing a set of cell identifiers, the set of cell identifies being logically linked with a target cell (e.g., associated with a base station that serves the target cell or associated with a cell identifier that identifies the target cell) (step 1302); (2) the network node determining that a cell identified by one of the cell identifiers included in the set has changed state (step 1304); and (3) in response to determining that a cell identified by one of the cell identifiers included in the set has changed state, the network node creating a new fingerprint for the target cell that is different than an initial fingerprint for the target cell that was created prior to the creation of the new fingerprint (step 1306).

[00177] In some embodiments, the step of determining that the cell has changed state consists of determining that the cell has been deactivated, and the step of creating the new fingerprint comprise removing the cell identifier from the initial fingerprint for the target cell. In some embodiments, the step of creating the new fingerprint further comprises adding to the initial fingerprint a cell identifier included in the set of cell identifiers.

[00178] In some embodiments, the step of determining that the cell has changed state consists of determining that the cell has been reactivated, and the step of creating the new fingerprint comprise adding the cell identifier to the initial fingerprint for the target cell. In some embodiments, the step of creating the new fingerprint further comprises removing a cell identifier from the initial fingerprint. [ 00179 ] In some embodiments, the method further comprises: (4) the network node, prior to performing step (2), transmitting to a wireless communication device (WCD) the initial fingerprint for the target cell, wherein the WCD is configured to use at least part of the initial fingerprint to determine whether the WCD is within the target cell.

[ 00180 ] In some embodiments, the method further comprises: (5) the network node transmitting with the initial fingerprint a schedule indicating one or time periods during which a cell identified by a cell identifier included in the initial fingerprint will be in the deactivated state.

[ 00181 ] In some embodiments, the method further comprises: (4) the network node, prior to performing step (2), transmitting to a wireless communication device (WCD) (i) a plurality of initial fingerprints for the target cell and (ii) a time schedule indicating, for each of the plurality of initial fingerprints, a time period during which the initial fingerprint is an active initial fingerprint and a time period during which the initial fingerprint is an inactive initial fingerprint.

[ 00182 ] In some embodiments, the initial fingerprint includes a set of entries, and the method further comprises (5) the network node transmitting to the WCD information indicating the entries included in the initial fingerprint that the WCD should not use in determining its proximity with the target cell.

[ 00183 ] In some embodiments, the method further comprises: (5) the network node, in response to determining that a cell identified by one of the cell identifiers included in the set has changed state, transmitting the new fingerprint to the WCD, whereby, in response to receiving the new fingerprint, the WCD will use the new fingerprint rather than the initial fingerprint to determine whether the WCD is within the target cell.

[ 00184 ] In some embodiments, the method further comprises: (5) the network node, in response to determining that a cell identified by one of the cell identifiers included in the set has changed state, transmitting to the WCD the cell identifier and either (i) an instruction to add the cell identifier to the initial fingerprint or (ii) an instruction to remove the cell identifier from the initial fingerprint. [ 00185 ] In some embodiments, the method further comprises: (4) the network node, prior to performing step (2), determining whether the target cell is a closed subscriber group (CSG) cell; (5) the network node, in response to determining that the target cell is a closed subscriber group (CSG) cell, determining whether a wireless communication device (WCD) that it is serving has a whitelist that includes the target cell; and (6) the network node, in response to determining that the WCD has a whitelist that includes the target cell, transmitting to the WCD an initial fingerprint for the target cell, wherein the WCD is configured to use the initial fingerprint to determine whether the WCD is within the target cell.

[ 00186 ] In some embodiments, the step of determining that a cell identified by one of the cell identifiers (CIs) has changed state is performed by the network node. In some embodiments, the method comprises measuring, with the network node, information relating to the state of the cell. In some embodiments, the method comprises receiving, with the network node, information regarding the state of the cell. In some embodiments the method comprises receiving, with the network node, measurements relating to the state of the cell from one or more WCDs. One or more of the steps herein relating to receiving information can include receiving information via an X2 interface, via the operation and maintenance (O&M) system, and/or via an operation support system (OSS).

[ 00187 ] 7. Seventh Aspect

[ 00188 ] In a seventh aspect, there is provided another method for proximity detection. This method is illustrated in the flow chart shown in FIG. 9. In some embodiments, this method comprises: (1) obtaining i) information identifying the density of active base stations (e.g., active base station cells) neighboring a network node and/or ii) information indicating a load on the network node (e.g., information indicating the load on a serving cell) and a degree to which a WCD is contributing to the load (step 902); a (2) selecting step (904) in which measurement configuration information is selected; and (3) transmitting the selected measurement configuration information towards the WCD (step 906). In some embodiments, selecting step 904 comprises one or more of: i) selecting measurement configuration information based on the information identifying the density of active base stations neighboring the network node (step 904a); and ii) selecting measurement configuration information based on the information identifying the load on the network node and the degree to which the WCD is contributing to the load (step 904b).

[00189] 8. Eighth Aspect

[00190] In an eighth aspect, there is provided another method for proximity detection in a wireless network comprising a network node (e.g., a base station). This method is illustrated in the flow chart shown in FIG. 15 and is performed by a WCD. In some embodiments, this method comprises: (1) the WCD receiving a coarse fingerprint (and optional configuration information) (step 1502); (2) the WCD uses at least the coarse fingerprint (and possible the optional configuration information) to perform proximity detection (step 1504); and (3) the WCD triggering a proximity indication to a serving base station conditioned on a positive proximity detection (step 1506). For example, in step 1506, the WCD send to the serving base station message 502 discussed above.

[00191] 9. Ninth Aspect

[00192] In a Ninth aspect, there is provided a network node, and, in some embodiments, this network node is configured to perform a method described herein.

[00193] Conclusion

[00194 ] While various aspects and embodiments of the present disclosure have been described above, it should be understood that they have been presented by way of example only, and not limitation. Thus, the breadth and scope of the present disclosure should not be limited by any of the above-described exemplary

embodiments. Moreover, any combination of the elements described in this disclosure in all possible variations thereof is encompassed by the disclosure unless otherwise indicated herein or otherwise clearly contradicted by context.

[00195] Additionally, while the processes described herein and illustrated in the drawings are shown as a sequence of steps, this was done solely for the sake of illustration. Accordingly, it is contemplated that some steps may be added, some steps may be omitted, the order of the steps may be re-arranged, and some steps may be performed in parallel.