WO2018099548A1

WO2018099548A1 - Measurement event triggering

Info

Publication number: WO2018099548A1
Application number: PCT/EP2016/079231
Authority: WO
Inventors: Bernhard Wegmann; Ingo Viering; Andreas Lobinger; Henrik MARTIKAINEN
Original assignee: Nokia Technologies Oy
Priority date: 2016-11-30
Filing date: 2016-11-30
Publication date: 2018-06-07

Abstract

There is provided a method comprising: performing, by a terminal device, measurements to obtain a received signal strength value in a first cell providing a cellular communication service to the terminal device, and a received signal strength value in each of a plurality of second cells, the first cell and each of the plurality of second cells operating on same carrier frequency; and initiating a triggering of a measurement event report if the measured received signal strength value of at least a predetermined number of second cells among the plurality of second cells is at least as strong as the measured received signal strength value of the first cell subtracted by an offset parameter.

Description

DESCRIPTION TITLE

MEASUREMENT EVENT TRIGGERING TECHNICAL FIELD

The invention relates to communications.

BACKGROUND

In cellular communication networks, different measurement events may be recognized which may relate to changing serving cell or cells of a terminal device. As the complexity of cellular communication networks is increasing, there may be a need to introduce additional measurement events to enhance operation of said networks.

BRIEF DESCRIPTION

According to an aspect, there is provided the subject matter of the independent claims. Some embodiments are defined in the dependent claims.

One or more examples of implementations are set forth in more detail in the accompanying drawings and the description below. Other features will be apparent from the description and drawings, and from the claims.

BRIEF DESCRIPTION OF DRAWINGS

In the following some embodiments will be described with reference to the attached drawings, in which

Figures 1 and 2 illustrate examples of cellular communication systems to which embodiments of the invention may be applied;

Figures 3 and 4 illustrate flow diagrams according to some embodiments;

Figures 5A and 5B illustrate signal diagrams according to some embodiments; Figure 5C illustrates a control message according to an embodiment;

Figures 6A to 6C illustrate some embodiments;

Figure 7 illustrates an embodiments; and

Figures 8 and 9 illustrate block diagrams of apparatuses according to some embodiments. DETAILED DESCRIPTION OF SOME EMBODIMENTS

The following embodiments are exemplifying. Although the specification may refer to "an", "one", or "some" embodiment(s) in several locations of the text, this does not necessarily mean that each reference is made to the same embodiment(s), or that a particular feature only applies to a single embodiment. Single features of different embodiments may also be combined to provide other embodiments.

Embodiments described may be implemented in a radio system, such as in at least one of the following: Worldwide Interoperability for Micro-wave Access (WiMAX), Global System for Mobile communications (GSM, 2G), GSM EDGE radio access Network (GERAN), General Packet Radio Service (GRPS), Universal Mobile Telecommunication System (UMTS, 3G) based on basic wideband-code division multiple access (W-CDMA), high-speed packet access (HSPA), Long Term Evolution (LTE), and/or LTE-Advanced.

The embodiments are not, however, restricted to the system given as an example but a person skilled in the art may apply the solution to other communication systems provided with necessary properties. Another example of a suitable communications system is the 5G concept. 5G is likely to use multiple input - multiple output (MIMO) techniques (including MIMO antennas), many more base stations or nodes than the LTE (a so-called small cell concept), including macro sites operating in co-operation with smaller stations and perhaps also employing a variety of radio technologies for better coverage and enhanced data rates. 5G will likely be comprised of more than one radio access technology (RAT), each optimized for certain use cases and/or spectrum. 5G mobile communications will have a wider range of use cases and related applications including video streaming, augmented reality, different ways of data sharing and various forms of machine type applications, including vehicular safety, different sensors and real-time control. 5G is expected to have multiple radio interfaces, namely below 6GHz, cmWave and mmWave, and also it may be integrated with existing legacy radio access technologies, such as the LTE. Integration with the LTE may be implemented, at least in the early phase, as a system, where macro coverage is provided by the LTE and 5G radio interface access comes from small cells by aggregation to the LTE. In other words, 5G is planned to support both inter-RAT operability (such as LTE-5G) and inter-RI operability (inter-radio interface operability, such as below 6GHz - cmWave, below 6GHz - cmWave - mmWave). One of the concepts considered to be used in 5G networks is network slicing in which multiple independent and dedicated virtual sub-networks (network instances) may be created within the same infrastructure to run services that have different requirements on latency, reliability, throughput and mobility. It should be appreciated that future networks will most probably utilize network functions virtualization (NFV) which is a network architecture concept that proposes virtualizing network node functions into "building blocks" or entities that may be operationally connected or linked together to provide services. A virtualized network function (VNF) may comprise one or more virtual machines running computer program codes using standard or general type servers instead of customized hardware. Cloud computing or cloud data storage may also be utilized. In radio communications this may mean node operations to be carried out, at least partly, in a server, host or node operationally coupled to a remote radio head. It is also possible that node operations will be distributed among a plurality of servers, nodes or hosts. It should also be understood that the distribution of labor between core network operations and base station operations may differ from that of the LTE. Some of the functions of the LTE may even be non-existent in the 5G system. Some other technology advancements probably to be used are Software- Defined Networking (SDN), Big Data, and all-IP, which may change the way networks are being constructed and managed.

Figure 1 illustrates example of a radio system (also referred to as a cellular communication system or cellular system) to which embodiments of the invention may be applied. Radio communication networks or wireless communication networks, such as the Wireless Local Area Network (WLAN) (sometimes referred to as WiFi), the Long Term Evolution (LTE), the LTE-Advanced (LTE-A) of the 3^rd Generation Partnership Project (3GPP), or the predicted future 5G solutions, are typically composed of at least one network element, such as a network element 102, providing at least one cell 104. In the example of Figure 1 , cells 104, 1 14, 124 may be shown. The cell 1 14 may be provided by a network element 1 12, and the cell 124 may be provided by a network element 122, for example. The cell 104 may be provided by the network element 102. It is, however, possible that a network element of the radio system may provide more than one cell. Thus, for example, the network element 102 may provide the cell 104, the cell 1 14, and/or the cell 124. In general, the system may comprise one or more network elements (similar to those described with reference to Figure 1 ), wherein each network element provides one or more cells providing service to one or more terminal devices in the cells.

Each cell of the radio communication network may be, e.g., a macro cell, a micro cell, a femto, or a pico-cell, for example, meaning that there may be one or more of each of the described cells. Each network element of the radio communication network, such as the network elements 102, 112, 122, may be an evolved Node B (eNB) as in the LTE and LTE- A, a radio network controller (RNC) as in the UMTS, a base station controller (BSC) as in the GSM/GERAN, Access Point (AP), or any other apparatus capable of controlling radio communication and managing radio resources within a cell or cells. That is, there may be one or more of each of the described apparatuses or entities. To give couple of examples, the network element 102 may be an eNB, for example. The network element 1 12 may also be an eNB. For example, network element 102 may provide a macro cell and the network element 1 12 may provide a small cell. However, these are only examples and thus, as explained above, the system may be configured in many different ways. For 5G solutions, the implementation may be similar to LTE-A, as described above. However, there may be some differences also as the specifications of 5G develop in the future. In the case of multiple eNBs in the communication network, the eNBs may be connected to each other with an X2 interface 190 as specified in the LTE. Example of this may be shown in Figure 1 , wherein the network element 1 12 may be shown to be connected to the network element 102 via the X2 interface 190. Other communication methods between the network elements may also be possible. For example, the network elements 102, 1 12, 122 may be configured to communicate with each other via wireless or wired connection. At least some of the network elements 102, 1 12, 122 may be further connected via an S1 interface to an evolved packet core, more specifically to a mobility management entity (MME) and to a system architecture evolution gateway (SAE-GW). So in general, the network elements of Figure 1 may be communicatively connected (wireless and/or wired) to each other using one or more circuitries. The X2 interface 190 is one example of how to realize such communication.

The radio system may support Dual Connectivity (DC). This may be enabled by the network element 102 and a second network element (e.g. local area access nodes(s) 112, 122), for example. Naturally, in order to use DC, the at least one terminal device 1 10, 120, 130, 140 may also need to support DC. The DC may be a radio system feature, wherein the at least one terminal device 1 10, 120, 130, 140 may simultaneously receive from and/or may simultaneously transmit to at least two network points. Similarly, the radio system of Figure 1 may support Multiple- In put and Multiple-Output (MIMO). Thus, the network elements and/or the terminal devices of the radio system may comprise more than one antenna for data transfer. For example, the network element 102 may be a primary network element (e.g. Primary eNB) providing a Primary Cell (PCell) and at least one of the local area access nodes 1 12, 122 may be a secondary network element (e.g. Secondary eNB) and/or a primary secondary network element (e.g. Primary Secondary eNB) providing a Secondary Cell (SCell) and/or Primary Secondary Cell (PSCell).

It may be possible that the radio system shown in Figure 1 supports Licensed- Assisted Access (LAA) which relates to using unlicensed radio band(s) for data transfer. For example, the network element 102 and/or the second network element may provide one or more unlicensed cells in order to increase data transfer capability on the radio system. For example, the network element 102 may allocate radio resources of the one or more unlicensed cell for the at least one terminal device 1 10, 120, 130, 140 through Carrier Aggregation (CA), thus increasing the data transfer between the at least one terminal device 110, 120, 130, 140 and the network element(s).

In some examples, the radio system of Figure 1 comprises one or more WLAN or WiFi Access Points (APs) providing cellular connectivity to terminal device(s) together with the at least one network element 102 of a cellular network. The cells 1 14, 124 may, in some instances, be referred to as sub-cells or local area cells, for example. The network elements 1 12, 122 may be referred to as sub-network elements or local area access nodes, for example. The cell 104 may be referred to as a macro cell, for example. The network element 102 may be referred to as a macro network element, for example. In an embodiment, the local area access nodes 1 12, 122 are network elements similar to the network element 102. Thus, for example, the local area access node 1 12 may be an eNB or a macro eNB.

The cells 104, 1 14, 124 may provide service for at least one terminal device 1 10, 120, 130, 140, wherein the at least one terminal device 1 10, 120, 130, 140 may be located within or comprised in at least one of the cells 104, 1 14, 124. The at least one terminal device 1 10, 120, 130, 140 may communicate with the network elements 102, 1 12, 122 using communication link(s), which may be understood as communication link(s) for end-to-end communication, wherein source device transmits data to the destination device. It needs to be understood that the cells 104, 1 14, 124 may provide service for a certain area, and thus the at least one terminal device 1 10, 120, 130, 140 may need to be within said area in order to be able to use said service (horizontally and/or vertically). For example, a third terminal device 130 may be able to use service provided by the cells 104, 1 14, 124. On the other hand, fourth terminal device 140 may be able to use only service of the cell 104, for example.

The cells 104, 1 14, 124 may be at least partially overlapping with each other.

Thus, the at least one terminal device 1 10, 120, 130, 140 may be enable to use service of more than one cell at a time. For example, the sub-cells 1 14, 124 may be small cells that are associated with the macro cell 104. This may mean that the network element 102 (e.g. macro network element 102) may at least partially control the network elements 1 12, 122 (e.g. local area access nodes). For example, the macro network element 102 may cause the local area access nodes 1 12, 122 to transmit data to the at least one terminal device 1 10, 120, 130, 140. It may also be possible to receive data, by the network element 102, from the at least one terminal device 1 10, 120, 130, 140 via the network elements 1 12, 122. To further explain the scenario, the cells 1 14, 124 may be at least partially within the cell 104. Even further, the radio system of Figure 1 may comprise more than three cells. For example, there may be one or more macro cells and one or more small cells, wherein the cells are provided by one or more radio access points or network elements.

In an embodiment, the at least one terminal device 1 10, 120, 130, 140 is able to communicate with other similar devices via the network element 102 and/or the local area access nodes 1 12, 122. For example, a first terminal device 1 10 may transmit data via the network element 102 to a third terminal device 130. The other devices may be within the cell 104 and/or may be within other cells provided by other network elements. The at least one terminal device 1 10, 120, 130, 140 may be stationary or on the move.

The at least one terminal device 1 10, 120, 130, 140 may comprise mobile phones, smart phones, tablet computers, laptops and other devices used for user communication with the radio communication network. These devices may provide further functionality compared to the MTC schema, such as communication link for voice, video and/or data transfer. However, it needs to be understood that the at least one terminal device 1 10, 120, 130, 140 may also comprise Machine Type Communication (MTC) capable devices, such as sensor devices, e.g. providing position, acceleration and/or temperature information to name a few examples.

So in general, the radio system of Figure 1 may support Heterogeneous Network (HetNet) deployment, for example. HetNet may be generalized as a network or networks that support connectivity using various technologies (e.g. various Radio Access Technologies (RATs)) and/or use of various different types of network elements (e.g. eNB(s) and WLAN AP(s)) or cells (e.g. macro and small cells). So for example, cellular connectivity for a terminal device (sometimes referred to also as User Equipment (UE)) may be provided utilizing one or more macro cells and one or more small cells. In general, the cells may be understood as cells provided by a radio access point(s) of the radio system of Figure 1 . Macro cells may have a larger coverage compared with the small cells. That is, in general, the macro cells are provided with a higher power than the small cells. Both may utilize unlicensed and/or licensed radio bands, but in some deployments, the small cells are configured to increase communication capability of the radio system by introducing unlicensed radio bands (e.g. WLAN AP deployment for cellular communication purposes). So one example of small cell may be a cell provided by a WLAN AP and another example may be a small eNB. Small eNB may be similar as a macro eNB, but it may be configured to provide the cell with smaller coverage, for example (e.g. less transmit power).

Handovers (HO) in cellular communication systems enable a terminal device to change serving cell or cells, i.e. change the cell that provides the communication service to the terminal device. Handovers may be triggered by measurement events reported by a terminal device when certain measurement criteria are fulfilled. Inter-frequency and inter- RAT handovers, respectively, are typically triggered by measurement reporting events which are sent when a dual-threshold criterion is fulfilled, i.e. when the signal strength of the serving cell falls below a first threshold and the signal of a measured neighboring cell operating on another frequency and/or on another RAT (it needs to be noted that different RATs may also operate on different frequencies) is better than a second threshold. Such dual threshold events are, for instance in LTE the measurement A5 for inter-frequency measurements and the event B2 for inter-RAT measurements. Inter-frequency and inter- RAT handovers may be referred to as inter-layer handovers which means that frequency and/or RAT is changed in the handover event.

Intra-frequency handover may refer to a situation in which the terminal device may change to an adjacent cell as a target cell which is getting stronger. Such may happen, for example, when the user of the terminal device moves and thus some cells may become weaker compared with some other cells. The identical signal quantities may be compared and a relative measurement criterion (e.g. A3 in LTE) may be most useful for intra-frequency handover. However, for inter-RAT the measured signals of different cells may not be one- to-one comparable and may also not interfere with each other either. It needs to be noted that RATs may comprise, for example, 2G, 3G, LTE, LTE-A, 5G and/or WLAN. Thus, for example, inter-RAT HO may refer to change from LTE-A cell to 5G cell, or vice versa. As the LTE-A and 5G may operate on different carrier frequencies, the cells may not interfere with each other. Therefore, dual threshold events are used for inter-RAT cell change (e.g. B2 in LTE or 3A in UMTS). For inter-frequency cell changes the relative criterion A3 principally could be used, however the dual threshold event A5 is more natural since there is no interference between source and target, i.e. there is no need to change a cell if a neighbor cell has stronger signal strength. Other criteria such as load or cell size might be more relevant then differences in the signal strength.

In HetNet deployment, so-called traffic hot spot areas, such as squares in cities, may additionally be covered by small cells operating on different frequency or on different RAT. This may increase the performance off the radio system in areas having more terminal devices. For instance, the 5G roll out may start with small cell deployment with LTE being used for Macro coverage (i.e. macro cell(s)). In that case, the terminal devices leaving the small cell 5G coverage may need to be handed over to LTE Macro layer without losing connection. Unfortunately, deploying increasing number of small cells (or some other cells) in some particular hot spots could lead to a problem that inter-RAT handovers are not properly triggered, which may be caused by a terminal device experiencing very low Signal to Interference-plus-Noise Ratio (SINR) and Radio Link Failures (RLF). This may happen even though the terminal device measures sufficiently good signal strength (i.e. signal strength > first threshold) to trigger handover, and even though there is no better cell on the same frequency layer.

Such problem may occur, for instance, for small deployments when a plurality of small base stations and/or small cells are situated in a restricted area. When the terminal leaves this restricted area, the signal strengths of said restricted area may become more and more similar. Example of this may be seen in Figure 2 illustrating an area 200 (e.g. square) and three small cells 1 14A-E. A terminal device 1 10 at a South-West corner of the area 200 may receive almost equally good signal strength in five small cells 1 14A-E (e.g. from five different nodes providing the cells 1 14A-E). Thus, the measured or experienced SINR by the terminal device 100 in Figure 2 may be indicated as follows: SINR= x/4x=1/4= -6 decibels (dB), wherein x denotes signal strength in a cell amongst the cells 1 14A-E. In fact, one may even argue that even other small cells which are not directly located on the square have similar signal strength as well which brings the SINR even further down. Basically, interference may increase when further cells and/or nodes providing the cells are deployed in the area 200. It needs to be noted that the cells 1 14A-E may differ in shape and/or size. For example, one or more of the cells may be associated with a higher transmission power than the others. For example, one or more of the cells may be achieved using directional antenna(s) and thus the shape of the cell may be different from substantially circular (e.g. cell 1 14D). Further, according to an embodiment, the cells 1 14A- E are situated at least partially within a macro cell of the radio system. For example, the network element 102 may provide the macro cell, wherein the network element 102 is further configured to control the macro cell and at least some of the small cells 1 14A-E (e.g. dual connectivity or carrier aggregation, but not necessarily limited to these examples).

Since for intra-frequency handover, i.e. handover between neighboring/adjacent cells, an offset (e.g. A3-offset in LTE) of 3dB is assumed, the received signal can be up to 3dB weaker than all 4 neighbors without triggering an intra-frequency handover. That is, the offset enables the handover only when a target cell has 3dB better signal strength than in the current cell. Hence, taking the 3dB offset into account: SINR = (x/2)/4x=1/8= -9dB, which means that the situation of Figure 2 worsens even below -8dB and thus may result in RLFs. And still, no handover event may have been triggered.

A terminal device experiencing an RLF is out-of-sync, i.e. not in RRCJDLE either and for achieving connection re-establishment, cell selection may be required. In case of RLF, the cell selection is typically using stored information of carrier frequencies to be looked for and optionally also information on cell parameters, from previously received measurement control information elements or from previously detected cells. However, the cell selection criterion S may only be fulfilled when both received signal strength (RSRP) and signal quality (RSRQ) are fulfilling their criteria. Since RSRQ criterion (good mapping to SINR for low SINR range) may not be fulfilled, the terminal device may reconnect to another RAT. In the example of Figure 2, the terminal device 1 10 may reconnect to macro cell (e.g. cell 102 provided by the network element 102). The terminal device may escape from such interference hole (i.e. terminal device is getting out-of-sync even though coverage from signal strength perspective is still rather good), if an inter-layer handover is triggered. But there is a following dilemma: on one side, since the signal strength is good, the B2 (or A5) measurement event with signal strength based reporting criteria (e.g. referred to as B2_RxLev) will not be triggered and the terminal device runs into said interference hole. On the other side, if one increases the first threshold in order to escape to the other layer before running into the interference hole, the whole small cell coverage will dramatically shrank. On network load perspective, this is not a desired situation as the small cells should be used as long as possible to reduce load on the macro cell layer.

Alternatively, a B2 measurement event could also be configured with signal quality (RSRQ) based thresholds, e.g. B2_Qual based inter-RAT handover. However, RSRQ measurements (may be some other quality measurement depending on the employed RAT) from the terminal devices may be inaccurate. RSRQ seems to be able to provide only a rather coarse view of the real channel quality (i.e. SINR). This may lead to a trade-off between exploiting the small cell coverage (stay in the small cell as long as possible) and leaving the small cell early enough to avoid RLFs. Looking at the large cloud of measurements (also due to the fact that the RSRQ flattens out towards larger SINRs), the RSRQ based first threshold may need to be configured extremely conservatively which may shrink the coverage or serving area of the small cells. More precisely, in order to reliably avoid SINRs below -8dB (leading to RLFs) first threshold (quality measurement quantity RSRQ) should be around -15dB to be on the safe side, which could also trigger terminal devices with SINRs up +6dB, which are definitely wanted to be kept in the small cells for offloading.

Therefore, there is provided a new measurement event report to be used, for example, for inter-layer handovers. By utilizing the proposed solution, for example the situation of Figure 2 may be enhanced such that the handover may be enabled to be performed timely and also enable the terminal device to utilize services from one or more small cells without performing the handover too early.

Figure 3 illustrates a flow diagram according to an embodiment. Referring to Figure 3, a terminal device may perform measurements to obtain a received signal strength value in a first cell providing a cellular communication service to the terminal device and a received signal strength value in each of a plurality of second cells (block 310); and initiate a triggering of a measurement event report if the measured received signal strength value of at least a predetermined number of second cells among the plurality of second cells is at least as strong as the measured received signal strength value of the first cell subtracted by an offset parameter (block 320). The first cell and each of the plurality of second cells, according to an embodiment, operate on same carrier frequency. Thus, the second cells may cause intra-frequency interference to the terminal device 110 served by the first cell, and therefore the described measurements and measurement event may be beneficial to be performed.

In an embodiment, the terminal device performing the steps of Figure 3 is the terminal device 1 10, 120, 130 or 140. In an embodiment, said terminal device comprises t e terminal device 1 10, 120, 130 or 140, or is comprised in the terminal device 1 10, 120, 130 or 140. For example, said method steps may be performed by a circuity or circuitries causing a respective terminal device to carry the steps of Figure 3 or any one of the embodiments described hereinafter that are performed by a terminal device.

Figure 4 illustrates a flow diagram according to an embodiment. Referring to

Figure 4, a network element of a cellular communication network may transmit at least one control message to a terminal device, wherein the at least one control message configures the terminal device to perform measurements to obtain a received signal strength value in a first cell providing a cellular communication service to the terminal device and a received signal strength value in each of a plurality of second cells (block 410); and receiving, by the network element, a message from the terminal device, wherein the message indicates that the measured, by the terminal device, received signal strength value of at least a predetermined number of second cells among the plurality of second cells is at least as strong as the measured, by the terminal device, received signal strength value of the first cell subtracted by an offset parameter (block 420). The first cell and each of the plurality of second cells may operate on the same carrier frequency. Thus, the network element may configure the terminal device to perform intra-frequency measurements on the frequency of the serving cell (e.g. in this case the first cell). Frequency as described may need to be understood as a broad definition comprising radio band or radio bands on which the serving cell operates (i.e. radio band(s) on which the first cell and the second cells operate). Such definition is clear to a skilled person.

In an embodiment, the network element performing the steps of Figure 4 is the network element 102, 1 12 or 122. In an embodiment, said network element comprises the network element 102, 1 12 or 122, or is comprised in the network element 102, 1 12 or 122. For example, said method steps may be performed by a circuity or circuitries causing a respective network element to carry the steps of Figure 4 or any one of the embodiments described hereinafter performed by the network element, such as eNB, radio node, base station, or similar apparatus comprised in radio system.

Let us now look closer on some examples and/or embodiments of the described solution. In the examples and embodiments reference is made to network element 102 and terminal device 1 10. However, the examples and embodiments are not necessarily limited to these specific apparatuses. Thus, for example, examples and embodiments may be applicable to network elements 1 12, 122, terminal devices 120, 130, 140, and also to other network elements and terminal devices that are not explicitly indicated.

Figures 5A to 5B illustrate signal diagrams according to some embodiments.

Referring first to Figure 5A, the network element 102 may transmit at least one control message to the terminal device 1 10 (block 502). This transmission may be similar or equivalent to transmission of block 410. The at least control message may be unicasted, multicasted and/or broadcasted, for example. Thus, for example, the same message(s) may be transmitted to one or more terminal devices in a cell or cells. For example, the network element 102 may provide the cell 104, wherein the network element 102 may transmit the at least one control message to one or more terminal devices in said cell 104. Said cell 104 may be a different cell than the described first and second cells, for example. However, in some cases the cell 104 may be one of the first and second cells. For example, said cell may be the first cell.

The terminal device 1 10 may receive the control message(s) transmitted by the network element 102. The received at least one control message may configured and/or cause the terminal device to perform measurements to obtain a received signal strength value in a first cell providing a cellular communication service to the terminal device 1 10 and a received signal strength value in each of a plurality of second cells (block 506). So basically, the network element 102 may configure the terminal device 1 10 and/or some other terminal devices to perform the described measurements. The configuring may also comprise indicating the steps, parameters, and/or actions that are to be performed by the terminal device 1 10 based on the measurements. So in general, it may be stated that the at least one control message may be used to configure the terminal device 1 10 with the measurement event report which is described later in more detail.

In block 508, the terminal device 1 10 may initiate triggering of the measurement event report if the condition described with respect to block 320 is true. To perform such determination, the terminal device 110 may need to acquire, a received signal strength value of the first cell and a received signal strength value of each of the second cells. If said condition is true, the terminal device 1 10 may proceed on initiating triggering the event. According to an embodiment, this means that the terminal device 1 10 transmits said measurement event report. Thus, the triggered measurement event may comprise or trigger the terminal device 1 10 to transmit one or more messages or reports to the network element 102 or to some other network element. Said one or more messages may indicate, to the network element 102, that the measurement event has been or is triggered. In general, said one or more messages may be described as measurement event report (e.g. A7 measurement event report in case of LTE). That is, if the condition of block 320 is true (meaning that the terminal device 1 10 measured at least the predetermined number of second cells having at least as strong received signal strength value than the first cell received signal strength value subtracted by the offset parameter), the measurement event may be triggered. According to an embodiment, this means that the measurement event report is triggered and thus the report will be sent to the network element 102 provided that the trigger condition remains fulfilled within a time interval (e.g. for a certain time period there are at least the predetermined number of cells that are at least as strong as or stronger than the serving cell). For example, a timer may be started when the measurement event is triggered and the report is sent once the timer expires.

According to an embodiment, the first cell is not necessarily the serving cell. That is, for example, one of the second cells may be the serving cell. In such case the first cell may be the cell having the strongest measured received signal strength value among the measured cells. Thus, the network element 102 may simply configure the terminal device 1 10 to perform intra-frequency measurements, and the terminal device 110 then may perform the measurements as described, and trigger the measurement event if the condition of block 320 is true (but the strongest cell denoted as the first cell in this case). However, in some instances the strongest measured cell not being the serving cell may lead to a handover via some other measurement event. That is, the network may initiate handover if the strongest cell is not the serving cell on that carrier frequency.

Referring to Figure 5B, the network element 102 is configured, according to an embodiment, to determine one or more parameters associated with the measurements event (block 500). Said one or more parameters may comprise an offset parameter and/or said predetermined number. The network element 102 may indicate the offset parameter and/or said predetermined number using the at least one control message (block 502) to the terminal device 1 10. Thus, the terminal device 1 10 may receive the offset parameter and/or the said predetermined number from the network element 102.

However, in an embodiment, the at least one control message explicitly indicates the offset parameter and/or said predetermined number. In an embodiment, the at least one control message comprises the offset parameter and/or said predetermined number.

Further, the determination of the one or more parameters by the network element in block 500, may comprise communicating with one or more network elements of the cellular communication network. For example, if the network element 102 is a pico network element providing a small cell, the network element 102 may communicate with a macro network element providing a macro cell, wherein the communication comprises acquiring, by the network element 102, the one or more parameters form the macro network element. However, in some embodiments, the network element 102 is the macro network element, and thus the control message(s) may be transmitted directly to the terminal device or via some other network element co-operating and/or controlled by the network element 102. So as explained above giving a few examples, the terminal device 1 10 may be configured with the one or more parameters, such as the offset parameter and/or the predetermined number. It needs to be noted once again that the predetermined number refers to number of second cells (e.g. minimum number of critical cells), as described above. According to an embodiment, the communication of the control message denotes Radio Resource Control (RRC) signaling. That is, the measurement event may be configured to the terminal device via RRC signaling. So, the network element 102 may configured the terminal device 1 10 to perform the measurements via RRC signaling.

According to an embodiment, the RRC signaling is used to indicate the offset parameter and/or said predetermined number to the terminal device 110. According to an embodiment, the offset parameter and said predetermined number are comprised in or indicated by the same control message (e.g. RRC message). However, they may also be transmitted in separate messages. One example is shown in an embodiment of Figure 5C illustrating the offset parameter 522 and the number of cells 524 (e.g. the predetermined number or defining the predetermined number) in the same control message 520. The control message 520 may be an RRC control message. The number of cells may indicate the minimum number of cells required to fulfill the described criterion to trigger the measurement event. According to an embodiment, the condition of block 320 requires that there are more than the predetermined number of second cells having at least as strong or stronger received signal strength value than received signal strength value of the first cell subtracted by the offset parameter.

According to an embodiment, the control message 520 indicates or provides one or more other measurement events (e.g. block 526 of Figure 5C). For example, the one or more other measurements events define leaving conditions for the terminal device (discussed below in more detail). The control message 520 may thus, in general, be configured to define one or more leaving conditions for the terminal device 1 10. According to an embodiment, the control message indicates one or more other measurement events defining one or more conditions to the terminal device 1 10 that prevent the triggering of the measurement event report.

Referring to Figure 5B, the blocks 506 and 508 may be similar to what was explained with reference to Figure 5A. However, according to an embodiment, the network element 102 initiates and/or performs, based at least partly on the received message from the terminal device 1 10 (block 508), handover of the terminal device 1 10 from the first cell to another cell. In an embodiment, the first cell is a small cell and said another cell is a macro cell. The handover may be performed according to specifications of the RAT(s) utilized. In an embodiment, the handover is inter-layer handover. For example, frequency area used may be different by the target cell (i.e. said another cell) than frequency area used by the first cell. For example, first cell may be a cell of a first RAT (e.g. 5G) and the target cell may be a cell of a second RAT (e.g. LTE-A). The handover may require communication between the terminal device 1 10 and the network element 102. Also, communication may be required between the network element 102 and some other network element may be required. For example in some embodiments, the terminal device 1 10 may transmit the measurement event report (block 508) to a small network element. The pico network element may forward the report to a macro network element. Additionally or instead, the pico network element may determine, based on the report that the handover should be initiated. In such case, the pico network element may indicate this to a target network element (e.g. network element providing the macro cell). Hence, the terminal device 1 10 may be handed over from the small cell (e.g. micro cell) to a macro cell of the communication network. Thus, the intra-frequency measurements may lead to a handover to a different frequency carrier. Thus, the terminal device 100 may advantageously escape the intra-frequency interference that may happen, for example, in an area that is densely populated by small cells (e.g. situation of Figure 2).

Let us then refer again to Figure 2 regarding some embodiments. According to an embodiment, each of the plurality of second cells 1 14B-E is a neighboring cell of the first cell 1 14A. The first cell, as described with respect to Figure 3, may refer to a cell that provides or is currently providing cellular communication service to the terminal device 1 10. According to an embodiment, the first cell 1 14A and the second cells 1 14B-E are small cells of a cellular communication network. The small cells may be realized by pico radio nodes, femto radio nodes, and/or relay radio nodes, for example. E.g. one cell is provided by one network element, such as the radio nodes described above. For example, the network elements 1 12, 122 may provide such cells.

According to an embodiment, the first cell and the second cell are densely deployed cells of a cellular communication network operating on the same frequency carrier (e.g. situation of Figure 2). Moreover, said cells may at least partly be situated within another cell, such as a macro cell (e.g. cell 104).

In an embodiment, the handover is performed from the first cell 1 14A (e.g. a small cell) to the cell 104 (e.g. macro cell of the communication network). As described also above, in an embodiment, the first cell 1 14A and the second cells 1 14B-E are at least partially within the cell 104 (e.g. the target cell of the handover). It needs to be understood that although only 4 second cells 1 14B-E are illustrated, there may be less or more than 4 second cells. For example, there may be more than four second cells (e.g. cells that cause interference to the terminal device 1 10). In an embodiment, the second cells 1 14B-E are cells operating on the same frequency area (i.e. same radio band(s)) and/or RAT as the first cell 1 14A.

Figures 6A to 6C illustrate some embodiments. Referring to Figures 6A to 6C, a received signal strength values of the first cell 1 14A and the second cells 1 14B-E may be indicated. Reference sign 600A may indicate the received signal strength value of the first cell 1 14A measured by the terminal device 1 10. Reference signs 600B-600E (or simply 600B-E) may indicate t e received signal strength values of the second cells 1 14B-1 14E (or simply 1 14B-E measured by the terminal device 1 10 (i.e. 600B received signal strength value of second cell 1 14B, 600C received signal strength value of second cell 1 14C, and so on for each indicated signal strength value). Again it needs to be noted that there may be plurality of received signal strength values of second cells. Number of values may depend on the number of measured second cells (e.g. 10 second cells, 10 values and also 1 value for first cell).

Referring to Figure 6A, the offset parameter (e.g. the offset parameter 522 comprised in the control message 520) may be substantially zero. This consequently means that the received signal strength values of the second cells 600B-E may need to be substantially the same as or stronger than the measured received signal strength value (eventually manipulated by an offset value) of the first cell 600A to initiate the triggering of the measurement event. In the example of Figure 6A, the received signal strength values 600B, 600C, 600E may be substantially the same as received signal strength value 600A and the received signal strength value 600D may be stronger than the received signal strength value 600A. It needs to be noted that, in general, the offset parameter may indicate or denote a value that is subtracted from the received signal strength value 600A. In the case of Figure 6A, the offset parameter may substantially be OdB and thus a lower limit 602 may be substantially the same as the received signal strength value of the first cell 600A. It is further noted that in such case the offset parameter may not be needed to be configured to the terminal device 100 at all. However, use of the offset parameter may enable the described event to be more configurable.

Referring to Figure 6B, the offset parameter (e.g. offset parameter 522) may be a positive value. Thus, the subtraction of the received signal strength of the first cell 600A by the offset parameter may reduce the limit 602. Limit 602 may denote the lower limit for triggering the measurement event. I.e. if the received signal strengths of at least the predetermined number of second cells 600B-C is at least as strong as the lower limit 602, the measurement event may be triggered.

In an embodiment, the offset parameter is a negative value. Hence, the limit 602 may actually be increased. So, the offset parameter may be used in many different ways to configure the limit 602.

According to an embodiment, the offset parameter allows some additional flexibility with respect to the lower bound of a value range or a tolerance.. An upper limit (e.g. 604 shown in Figure 6C) may typically result from another measurement event (e.g. A3 in LTE) which is triggered when the measured signal strength of at least one of second cells is a certain dedicated margin ( e.g. A3-offset) stronger than the received signal strength value of the serving cell. Even if the proposed measurement event has been triggered but not yet reported, another measurement event triggering a handover may pre-empt the trigger event, i.e. the upper limit can also be interpreted as leaving condition for the proposed measurement event. Other measurement events which can pre-empt the proposed trigger event can be indicated, for instance, by the control message 520. In an embodiment, the terminal device 1 10 prevents the triggering of the measurement event report if received signal strength value of at least one second cell among the plurality of second cells 600B-E is at least as strong as a predetermined signal strength value. In one example, the measurement event may be initiated when the criterion of block 320 is true. However, this may trigger a timer as described in more detail below. If before the timer expires (i.e. a predetermined time has passed) the at least one second cell is at least as strong as the predetermined signal strength (e.g. threshold of another measurement event), the initiated measurement event may be canceled. I.e. the measurement event may be prevented to be reported.

In an embodiment, the control message transmitted, by the network element 102 to the terminal device 1 10, indicates the pre-empting condition. Thus, the network element 102 may configure the terminal device with said pre-empting condition. This may mean that the triggering of the measurement event may be pre-empted if at least one of the measured cells fulfills a condition of another measurement event (e.g. A3, A5, or B2 events in case of LTE). So, in this case, even though the condition of block 320 would be true, the measurement event is not triggered and consequently the report is not sent if the configured pre-empting condition is also fulfilled. The pre-empting condition may be fulfilled, for example, if at least one of the measured cells has a received signal strength value that is above a threshold associated with at least one of the indicated pre-empting measurement events. That is, the network element 102 may potentially indicate more than one pre- empting conditions (e.g. more than one other measurement event) that prevent the triggering and reporting of the measurement event if at least one of the pre-empting conditions is fulfilled. For example, the control message may simply indicate one or more measurement events (e.g. A3, A5, and/or B2) which should be regarded as pre-empting conditions.

In an embodiment, said predetermined signal strength is defined by a threshold of another measurement event triggering a handover (e.g. A3 threshold). This may be beneficial as if the received signal strength value 600B-E is greater than the upper limit 604 (e.g. A3 threshold), the terminal device 1 10 may trigger a different (e.g. A3) measurement event report, eventually leading to a handover. However, this does not necessarily resolve the problem as indicated above as the handover is not inter-layer handover. So same problems could still occur even if, for example, the small cell would be changed. According to an embodiment, the terminal device 1 10 prevents the initiating the triggering of the measurement event report if criterion of another measurement event is fulfilled. For example in LTE, other measurement events may be A3, A5 and B2 which are typically used for radio triggered handovers. A3 for intra-frequency, A5 for inter-frequency and B2 for inter-RAT HO. Thus, if conditions for some other measurement event are fulfilled, the described measurement event may be prevented or stopped. In one example, said another measurement event may define the upper limit 604 by a threshold of said another measurement event. Thus, in Figure 6C, the received signal strength 600D of one of the second cells may trigger said another measurement event and thus the described measurement event may be prevented, for example.

The terminal device 110 may measure the received signal strength values 600A-600E. The received signal strength values may denote received signal strength indicator (RSSI) or RSRP, for example. However, there are many different ways to measure experienced signal strength in a cell, and in principal any of these measurements may be utilized. According to an embodiment, the received signal strength values of first cell and second cells are determined and/or measured using same or similar measurement and same or similar indicator. This may mean that if the first received signal strength value 600A is indicated as RSSI, the second received signal strength values 600B-E are indicated as RSSI also. For example, the received signal strength value may be indicated as decibels.

As a further example, in Figure 6B the measurement event may be triggered if said predetermined number is 4 or less as the received signal strength values 600B- E are above or at the lower limit 602 defined by the offset parameter 522 and the received signal strength value 600A.

Figure 7 illustrates a flow diagram according to some embodiments. Referring to Figure 7, the initiating the triggering of the measurement event report (i.e. block 320 if the condition is true) comprises activating a timer (block 710), and further comprises transmitting the measurement event report in response to the timer being active for at least a predetermined time (block 720). Thus, when the terminal device 110 determines that there are at least the predetermined number (e.g. 4) of second cells 1 14B-E causing interference (i.e. measured second received signal strength values 1 14B-E above or at the limit 602) to the terminal device 1 10, the terminal device 1 10 may activate the timer. Activating may mean that the timer is set to run (e.g. started or continued). The timer may be a countdown timer, for example. Thus, when the timer expires, the terminal device 1 10 is reporting the triggered measurement event. This may mean that the terminal device 1 10 informs the network element 102 or some other network element about said event using one or more report messages. In an embodiment, the terminal device 1 10 is configured to release the triggering condition in response to determining that the received signal strength value 600B-E of less than said predetermined number (e.g. parameter 524) of second cells among the plurality of second cells 1 14B-1 14C is as strong as the received signal strength value of the first cell (block 712). Said predetermined number may be the predetermined number described, for example, with respect to block 320. In an embodiment, said predetermined number is the predetermined number described, for example, with respect to block 320 deducted by a hysteresis parameter (the hysteresis parameter being, for example, 0, 1 or 2). In an embodiment, the terminal device 1 10 obtains the hysteresis parameter from the network element 102. E.g. if said predetermined number is four, four or more relevant cells activate the timer, less than four (i.e. 3 or less) relevant cells the triggering condition is released as well as the timer. There may be alternative ways to indicate these conditions to the terminal device 1 10. Along with leaving or releasing the triggering condition the timer is released or stopped. Releasing the triggering condition may mean that the measurement event report is not transmitted as the condition of block 320 is no longer valid or another condition (e.g. another measurement event condition indicated with the control message 520) pre-empts the triggering condition. The triggering condition may denote the condition of block 320.

To put it in other words, when the condition of block 320 is true the terminal device 1 10 may enter into a state associated with the triggering the measurement event. This may be indicated as entering condition. When the terminal device enters said state, the timer may be activated (i.e. time to trigger starts to run). Once the timer expires, the measurement event will be reported. Thus, for example, the measurement event report may be transmitted to the network element 102. However, if the condition described with respect to leaving the triggering condition is fulfilled during the time that the timer is running (i.e. is active), the terminal device 110 may leave said state. This may be indicated as leaving condition. This may further mean that the timer is also released. Once the terminal device 1 10 has left said state, the whole measurement event may be reset, e.g. meaning that the terminal device 1 10 may resume normal operation state. The terminal device 1 10 may then, for example, again enter said state if the condition of block 320 is once again fulfilled. For example, the entering condition may mean that the triggering of the measurement event report is initiated. However, the reporting of the event may happen once the timer expires, if it expires. I.e. expiring may be prevented by the leaving condition. Further, the leaving condition may also be fulfilled if a criterion or criteria of some other measurement event is fulfilled. For example, the criteria of A3 event is fulfilled, the leaving condition may be fulfilled.

According to an embodiment, the terminal device releases the triggering of the proposed measurement event in response to determining that another measurement criterion is fulfilled among a group of measurement events triggering an intra-frequency handover, inter-frequency handover and/or inter-Radio Access Technology, RAT, handover. That is, if criteria or criterion for another measurement event is fulfilled, the timer may be stopped and the triggering conditioned dissolved.

The blocks 710 and 712 may be indicated also as formulas. That is, entering condition to initiating triggering of the measurements event report (i.e. activating the timer) can be indicated as:

|{n|Mn > Ms - Off}\≥ number _c ells, and

leaving condition (i.e. deactivating the timer) can be indicated as:

\{n\Mn > Ms - Off}\≤ number _cells - Hys, wherein

Ms is the measurement result of the serving cell (i.e. 600A of the first cell 104A), not taking into account any offsets,

Mn is the measurement result of the neighboring cell (i.e. 600B-E of the second cells 104B-E, not taking into account any offsets,

Hys is the hysteresis parameter,

Off is the offset parameter for this event,

number_cells indicates the predetermined number, and

n indicates the current second cell number. I.e. if there are 6 second cells measured, n will run from 1 to 6 (i.e. 1 , 2, 3, 4, 5, and 6), wherein n will indicate the current second cell number.

Mn and Ms may be expressed in dBm in case of RSRP.

Off may be expressed in dB, Hys and number_cells may be dimensionless numbers.

So basically what is performed here is that each second cell received signal strength value is compared with first cell received signal strength value. If there are more than number_cells number of second cells with measurement result within the range 602, the timer may be activated (or in some cases this will automatically lead to transmitting the measurement report without any timers). If there are less than number_cells - Hys (e.g. Hys= 0 or 1 ) number of second cells with measurement result within the range 602, the timer may be stopped and the triggering conditioned dissolved.

In other words, the equations may count all neighbors n whose measurement Mn is stronger than offset Off below the serving cell. This cell count is compared with the parameter number_cells.

For instance, the entry condition could start a "time to trigger" (TTT) timer (e.g. timer). The measurement report may be triggered when the TTT timer expires. The TTT timer is stopped and released when the leaving condition is fulfilled or is true. One parameter setting could be Off = xdB, number_cells=y and Hys=z. Once (at least) y cells (e.g. second cells 104B-E) are counted with signal strengths larger than xdB below the serving cell (e.g. first cell 104A), the entry condition may be fulfilled. For example, the measurement report may be sent after TTT. Leaving condition may be fulfilled if the number of cells larger than xdB below the serving cell falls below or is equal to y-z.

Figures 8 to 9 provide apparatuses 800, 900 comprising a control circuitry (CTRL) 810, 910, such as at least one processor, and at least one memory 830, 930 including a computer program code (software) 832, 932, wherein the at least one memory and the computer program code (software) 832, 932, are configured, with the at least one processor, to cause the respective apparatus 800, 900 to carry out any one of the embodiments of Figures 1 to 7, or operations thereof.

Referring to Figures 8 to 9, the memory 830, 930, may be implemented using any suitable data storage technology, such as semiconductor based memory devices, flash memory, magnetic memory devices and systems, optical memory devices and systems, fixed memory and removable memory. The memory 830, 930 may comprise a database 834, 934 for storing data. In some embodiments, the apparatus is connected to one or more external memories (e.g. one or more databases). Thus, data may additionally or alternatively be stored outside the apparatus.

The apparatuses 800, 900 may further comprise radio interface (TRX) 820, 920 comprising hardware and/or software for realizing communication connectivity according to one or more communication protocols. The TRX may provide the apparatus with communication capabilities to access the radio access network, for example. The TRX may comprise standard well-known components such as an amplifier, filter, frequency-converter, (de)modulator, and encoder/decoder circuitries and one or more antennas. For example, the TRX may enable communication between the terminal device 1 10 and the network element 102. So, in general, the TRX may provide communication capabilities to the respective apparatus, such that said respective apparatus may communicate with other apparatuses of the communication network. For example, the TRX may provide access to the X2 interface 190 for the network element 102, for example.

The apparatuses 800, 900 may comprise user interface 840, 940 comprising, for example, at least one keypad, a microphone, a touch display, a display, a speaker, etc. The user interface 840, 940 may be used to control the respective apparatus by a user of the apparatus 800, 900. For example, a network element may be configured using the user interface comprised in said network element. Naturally, a terminal device may comprise a user interface.

In an embodiment, the apparatus 800 may be or be comprised in a terminal device, such as a mobile phone, MTC device, or cellular phone, for example. The apparatus 800 may be t e terminal device 1 10, for example. In an embodiment, the apparatus 800 is comprised in the terminal device 1 10 or in some other terminal device. Further, the apparatus 800 may be or be comprised in the terminal device performing the steps of Figure 3, for example.

Referring to Figure 8 according to an embodiment, the control circuitry 810 comprises a measurement circuitry 812 configured to perform measurements to obtain a received signal strength value in a first cell providing a cellular communication service to the terminal device and a received signal strength value in each of a plurality of second cells; and a measurement event circuitry 814 configured to initiate a triggering of a measurement event report if the measured received signal strength value of at least a predetermined number of second cells among the plurality of second cells is at least as strong as the measured received signal strength value of the first cell subtracted by an offset parameter. The first and second cells may operate on the same carrier frequency.

In an embodiment, the apparatus 900 may be or be comprised in a base station (also called a base transceiver station, a radio access point, a Node B, a radio network controller, or an evolved Node B, for example). The apparatus 900 may be the network element 102 or be comprised in the network element 102, for example. Further, the apparatus 900 may be the network element performing the steps of Figure 4.

Referring to Figure 9 according to an embodiment, the control circuitry 910 comprises a message transmitting circuitry 914 configured to transmit at least one control message to a terminal device, wherein the at least one control message configures the terminal device to perform measurements to obtain a received signal strength value in a first cell providing a cellular communication service to the terminal device and a received signal strength value in each of a plurality of second cells, the first cell and each of the plurality of second cells operating on same carrier frequency; and a message receiving circuitry 916 configured to receive a message from the terminal device, wherein the message indicates that the measured, by the terminal device, received signal strength value of at least a predetermined number of second cells among the plurality of second cells is at least as strong as the measured, by the terminal device, received signal strength value of the first cell subtracted by an offset parameter.

According to an embodiment, the control circuitry 910 further comprises a parameter obtaining circuitry 912 configured to determine said predetermined number and said offset parameter, and wherein the at least one control message, transmitted by the message transmitting circuitry 914, indicates said predetermined number and said offset parameter to the terminal device.

In an embodiment of Figure 9, at least some of the functionalities of the apparatus 900 (e.g. the network element 102) may be shared between two physically separate devices, forming one operational entity. Therefore, the apparatus may be considered to depict the operational entity comprising one or more physically separate devices for executing at least some of the above-described processes. Thus, the apparatus of Figure 9, utilizing such a shared architecture, may comprise a remote control unit (RCU), such as a host computer or a server computer, operatively coupled (e.g. via a wireless or wired network) to a remote radio head (RRH) located at a base station site. In an embodiment, at least some of the described processes of the network element (e.g. network element 102) may be performed by the RCU. In an embodiment, the execution of at least some of the described processes may be shared among the RRH and the RCU. In such a context, the RCU may comprise the components illustrated in Figure 9, and the radio interface 920 may provide the RCU with the connection to the RRH. The RRH may then comprise radio frequency signal processing circuitries and antennas, for example.

In an embodiment, the RCU may generate a virtual network through which the RCU communicates with the RRH. In general, virtual networking may involve a process of combining hardware and software network resources and network functionality into a single, software-based administrative entity, a virtual network. Network virtualization may involve platform virtualization, often combined with resource virtualization. Network virtualization may be categorized as external virtual networking which combines many networks, or parts of networks, into the server computer or the host computer (i.e. to the RCU). External network virtualization is targeted to optimized network sharing. Another category is internal virtual networking which provides network-like functionality to the software containers on a single system. Virtual networking may also be used for testing the terminal device.

In an embodiment, the virtual network may provide flexible distribution of operations between the RRH and the RCU. In practice, any digital signal processing task may be performed in either the RRH or the RCU and the boundary where the responsibility is shifted between the RRH and the RCU may be selected according to implementation.

As was also described above, virtualization of network functions (e.g. Virtual Network Functions (VNFs)) may even further advance in the future. Thus, at least some of the described functions of the communication network (e.g. network element 102 performed functions) may be performed as virtual functions. Basically, this means that virtual functions are performed using one or more virtual machines running on one or more physical entities (e.g. servers, memories, databases, networks). Thus, in general, actions performed by the network element (e.g. network element 102) may be performed by physical and/or virtual entities.

As used in this application, the term 'circuitry' refers to all of the following: (a) hardware-only circuit implementations, such as implementations in only analog and/or digital circuitry, and (b) combinations of circuits and soft-ware (and/or firmware), such as (as applicable): (i) a combination of processor(s) or (ii) portions of processor(s)/software including digital signal processor(s), software, and memory(ies) that work together to cause an apparatus to perform various functions, and (c) circuits, such as a microprocessor(s) or a portion of a microprocessor(s), that require software or firmware for operation, even if the software or firmware is not physically present. This definition of 'circuitry' applies to all uses of this term in this application. As a further example, as used in this application, the term 'circuitry' would also cover an implementation of merely a processor (or multiple processors) or a portion of a processor and its (or their) accompanying software and/or firmware. The term 'circuitry' would also cover, for example and if applicable to the particular element, a baseband integrated circuit or applications processor integrated circuit for a mobile phone or a similar integrated circuit in a server, a cellular network device, or another network device.

In an embodiment, at least some of the processes described in connection with Figures 1 to 7 may be carried out by an apparatus comprising corresponding means for carrying out at least some of the described processes. Some example means for carrying out the processes may include at least one of the following: detector, processor (including dual-core and multiple-core processors), digital signal processor, controller, receiver, transmitter, encoder, decoder, memory, RAM, ROM, software, firmware, display, user interface, display circuitry, user interface circuitry, user interface software, display software, circuit, antenna, antenna circuitry, and circuitry. In an embodiment, the at least one processor, the memory, and the computer program code form processing means or comprises one or more computer program code portions for carrying out one or more operations according to any one of the embodiments of Figures 2 to 7 or operations thereof.

According to yet another embodiment, the apparatus carrying out the embodiments comprises a circuitry including at least one processor and at least one memory including computer program code. When activated, the circuitry causes the apparatus to perform at least some of the functionalities according to any one of the embodiments of Figures 1 to 7, or operations thereof.

The techniques and methods described herein may be implemented by various means. For example, these techniques may be implemented in hardware (one or more devices), firmware (one or more devices), software (one or more modules), or combinations thereof. For a hardware implementation, the apparatus(es) of embodiments may be implemented within one or more application-specific integrated circuits (ASICs), digital signal processors (DSPs), digital signal processing devices (DSPDs), programmable logic devices (PLDs), field programmable gate arrays (FPGAs), processors, controllers, microcontrollers, microprocessors, other electronic units designed to perform the functions described herein, or a combination thereof. For firmware or software, the implementation can be carried out through modules of at least one chip set (e.g. procedures, functions, and so on) that perform the functions described herein. The software codes may be stored in a memory unit and executed by processors. The memory unit may be implemented within the processor or externally to the processor. In the latter case, it can be communicatively coupled to the processor via various means, as is known in the art. Additionally, the components of the systems described herein may be rearranged and/or complemented by additional components in order to facilitate the achievements of the various aspects, etc., described with regard thereto, and they are not limited to the precise configurations set forth in the given figures, as will be appreciated by one skilled in the art.

Embodiments as described may also be carried out in the form of a computer process defined by a computer program or portions thereof. Embodiments of the methods described in connection with Figures 1 to 7 may be carried out by executing at least one portion of a computer program comprising corresponding instructions. The computer program may be in source code form, object code form, or in some intermediate form, and it may be stored in some sort of carrier, which may be any entity or device capable of carrying the program. For example, the computer program may be stored on a computer program distribution medium readable by a computer or a processor. The computer program medium may be, for example but not limited to, a record medium, computer memory, read-only memory, electrical carrier signal, telecommunications signal, and software distribution package, for example. The computer program medium may be a non- transitory medium, for example. Coding of software for carrying out the embodiments as shown and described is well within the scope of a person of ordinary skill in the art. In an embodiment, a computer-readable medium comprises said computer program.

Even though the invention has been described above with reference to an example according to the accompanying drawings, it is clear that the invention is not restricted thereto but can be modified in several ways within the scope of the appended claims. Therefore, all words and expressions should be interpreted broadly and they are intended to illustrate, not to restrict, the embodiment. It will be obvious to a person skilled in the art that, as technology advances, the inventive concept can be implemented in various ways. Further, it is clear to a person skilled in the art that the described embodiments may, but are not required to, be combined with other embodiments in various ways.

Claims

1 . A method comprising:

performing, by a terminal device, measurements to obtain a received signal strength value in a first cell providing a cellular communication service to the terminal device, and a received signal strength value in each of a plurality of second cells, the first cell and each of the plurality of second cells operating on same carrier frequency; and initiating a triggering of a measurement event report if the measured received signal strength value of at least a predetermined number of second cells among the plurality of second cells is at least as strong as the measured received signal strength value of the first cell subtracted by an offset parameter.

2. The method of claim 1 , further comprising:

receiving, by a terminal device, a control message from a network element, the control message indicating the offset parameter.

3. The method of any preceding claim, further comprising:

receiving, by a terminal device, a control message from a network element, the control message indicating said predetermined number.

4. The method of any preceding claim, wherein the offset parameter and said predetermined number are indicated by same control message received from a network element.

5. The method of any preceding claim, further comprising:

preventing the triggering of the measurement event report if criterion of another measurement event is fulfilled.

6. The method of claim 5, wherein the control message received from the network element further provides other measurement events being able to prevent the triggering of the measurement event report

7. The method of the preceding claim 4 to 6, wherein the information about the preventing measurement events is provided with the same control message that indicates said offset parameter and said predetermined number.

8. The method of any preceding claim, wherein each of the plurality of second cells is a neighboring cell of the first cell.

9. The method of any preceding claim, wherein the first cell and the second cell are densely deployed cells of a cellular communication network operating on the same frequency carrier.

10. The method of any preceding claim, wherein the first cell and the second cells are small cells realized by pico radio nodes, femto radio nodes, or relay radio nodes.

1 1 . The method of any preceding claim, wherein initiating the triggering of the measurement event report comprises activating a timer and transmitting the measurement event report in response to the timer being active for a predetermined time.

12. The method of claim 1 1 , further comprising:

releasing the triggering condition and stopping the timer in response to determining that the measured received signal strength value of less than the predetermined number of second cells among the plurality of second cells is at least as strong as the received signal strength value of the first cell.

13. The method of claim 1 1 , further comprising:

releasing the triggering condition and stopping the timer in response to determining that another measurement event criterion is fulfilled among a group of measurement events triggering an intra-frequency handover, inter-frequency handover and/or inter-Radio Access Technology, RAT, handover.

14. The method of any preceding claim 1 1 to 13, wherein the timer is a time-to- trigger timer, and wherein the measurement event report is transmitted in response to the time-to-trigger timer expiring.

15. A method comprising:

transmitting, by a network element of a cellular communication network, at least one control message to a terminal device, wherein the at least one control message configures the terminal device to perform measurements to obtain a received signal strength value in a first cell providing a cellular communication service to the terminal device and a received signal strength value in each of a plurality of second cells, the first cell and each of the plurality of second cells operating on same carrier frequency; and receiving, by t e network element, a message from the terminal device, wherein the message indicates that the measured, by the terminal device, received signal strength value of at least a predetermined number of second cells among the plurality of second cells is at least as strong as the measured, by the terminal device, received signal strength value of the first cell subtracted by an offset parameter.

16. The method of claim 15, wherein the at least one control message indicates said predetermined number.

17. The method of claim 15 or 16, wherein the at least one control message indicates said offset parameter.

18. The method of any preceding claim 15 to 17, further comprising: performing, based at least partly on the received message from the terminal device, handover of the terminal device from the first cell to another cell.

19. The method of claim 18, wherein the first cell and the second cell are small cells of a cellular communication network, and wherein said another cell is a macro cell.

20. An apparatus comprising:

at least one processor; and

at least one memory including a computer program code, wherein the at least one memory and the computer program code are configured, with the at least one processor, to cause a terminal device to perform operations comprising:

performing measurements to obtain a received signal strength value in a first cell providing a cellular communication service to the terminal device, and a received signal strength value in each of a plurality of second cells, the first cell and each of the plurality of second cells operating on same carrier frequency; and

initiating a triggering of a measurement event report if the measured received signal strength value of at least a predetermined number of second cells among the plurality of second cells is at least as strong as the measured received signal strength value of the first cell subtracted by an offset parameter.

21 . The apparatus of claim 20, wherein the at least one memory and the computer program code are configured, with the at least one processor, to cause the terminal device further to perform operations comprising: receiving a control message from a network element, the control message indicating the offset parameter.

22. The apparatus of any preceding claim 20 to 21 , wherein the at least one memory and the computer program code are configured, with the at least one processor, to cause the terminal device further to perform operations comprising:

receiving a control message from a network element, the control message indicating said predetermined number.

23. The apparatus of any preceding claim 20 to 22, wherein the offset parameter and said predetermined number are indicated by same control message received from a network element.

24. The apparatus of any preceding claim 20 to 23, wherein the at least one memory and the computer program code are configured, with the at least one processor, to cause the terminal device further to perform operations comprising:

25. The apparatus of claim 24, wherein the control message received from the network element further provides other measurement events being able to prevent the triggering of the measurement event report.

26. The apparatus of claim 23 to 25, wherein the information about the preventing measurement events is provided with the same control message that indicates said offset parameter and said predetermined number.

27. The apparatus of any preceding claim 20 to 26, wherein each of the plurality of second cells is a neighboring cell of the first cell.

28. The apparatus of any preceding claim 20 to 27, wherein the first cell and the second cell are densely deployed cells of a cellular communication network operating on the same frequency carrier.

29. The apparatus of any preceding claim 20 to 28, wherein the first cell and the second cells are small cells realized by pico radio nodes, femto radio nodes, or relay radio nodes.

30. The apparatus of any preceding claim 20 to 29, wherein initiating the triggering of the measurement event report comprises activating a timer and transmitting the measurement event report in response to the timer being active for a predetermined time.

31 . The apparatus of claim 30, wherein the at least one memory and the computer program code are configured, with the at least one processor, to cause the terminal device further to perform operations comprising:

32. The apparatus of claim 30, wherein the at least one memory and the computer program code are configured, with the at least one processor, to cause the terminal device further to perform operations comprising:

33. The apparatus of any preceding claim 30 to 32, wherein the timer is a time- to-trigger timer, and wherein the measurement event report is transmitted in response to the time-to-trigger timer expiring.

34. An apparatus comprising:

at least one processor; and

at least one memory including a computer program code, wherein the at least one memory and the computer program code are configured, with the at least one processor, to cause a network element of a cellular communication network to perform operations comprising:

transmitting, at least one control message to a terminal device, wherein the at least one control message configures the terminal device to perform measurements to obtain a received signal strength value in a first cell providing a cellular communication service to the terminal device and a received signal strength value in each of a plurality of second cells, t e first cell and each of the plurality of second cells operating on same carrier frequency; and

receiving a message from the terminal device, wherein the message indicates that the measured, by the terminal device, received signal strength value of at least a predetermined number of second cells among the plurality of second cells is at least as strong as the measured, by the terminal device, received signal strength value of the first cell subtracted by an offset parameter.

35. The apparatus of claim 34, wherein the at least one control message indicates said predetermined number.

36. The apparatus of claim 34 or 35, wherein the at least one control message indicates said offset parameter.

37. The apparatus of any preceding claim 34 to 36, wherein the at least one memory and the computer program code are configured, with the at least one processor, to cause the network element further to perform operations comprising:

performing, based at least partly on the received message from the terminal device, handover of the terminal device from the first cell to another cell.

38. The apparatus of claim 37, wherein the first cell and the second cell are small cells of a cellular communication network, and wherein said another cell is a macro cell.

39. A computer program product embodied on a distribution medium readable by a computer and comprising program instructions which, when loaded into an apparatus, execute the method according to any of claims 1 to 19.

40. A computer program product comprising program instructions which, when loaded into an apparatus, execute the method according to any of claims 1 to 19.

41 . An apparatus comprising means for performing the method according to any of claims 1 to 19.