WO2012110075A1

WO2012110075A1 - Base station wake-up control

Info

Publication number: WO2012110075A1
Application number: PCT/EP2011/052120
Authority: WO
Inventors: Juergen Michel; Dirk Rose; Krzysztof Kordybach
Original assignee: Nokia Siemens Networks Oy
Priority date: 2011-02-14
Filing date: 2011-02-14
Publication date: 2012-08-23
Also published as: EP2676468A1

Abstract

There are provided measures for a base station wake-up control, more specifically a base station wake-up control in a heterogeneous network environment. Such measures exemplarily comprise a retrieval of an average uplink interference level at a base station, a pathloss level between the base station and a neighboring base station and a wake-up threshold interference level of the neighboring base station, an evaluation of a wake-up condition of the base station based on the retrieved average uplink interference level, pathloss level and wake-up threshold interference level, and a switch of the base station from an inactive state in which a transmitter is switched off to an active state in which the transmitter is switched on, when the wake-up condition is evaluated to be satisfied.

Description

DESCRIPTION

Title Base station wake-up control Field of the invention

The present invention relates to a base station wake-up con- trol. More specifically, the present invention relates to a base station wake-up control in a heterogeneous network envi^¬ ronment .

Background of the invention

The present specification basically relates to energy/ power saving in communication networks.

Low power consumption is to be considered an important per- formance indicator for communication networks and the users of a cellular phone. Today, the power consumption of a user equipment (UE) is typically described in terms of battery life time and, more specifically, talk time and standby time. On the network side, the power consumption is mainly de- scribed by the power consumption of access nodes (such as base stations) , and is typically measured for different con^¬ figuration and load assumptions. In principle the access node power consumption for zero load over the air interface could be seen then as standby time power leakage of the access sys- tern. In future, it is expected that energy related measures are playing a more and more important role in the design and configuration of a competitive future radio access network.

Therefore, and to support energy efficient radio access net- works, 3GPP (Third Generation Partnership Project) has intro^¬ duced higher layer procedures for base station switch-off or switch-on (wake-up) . The procedures in general can be distin^¬ guished to be controlled autonomously at the base station or centrally e.g. via an OAM (Operation Administration and Maintenance) entity, and some of such procedures measure the up^¬ link (UL) interference to decide when to switch the base sta^¬ tion on and/or off.

In the development of cellular systems in general, and access networks in particular, heterogeneous network environments, also referred to as multi-layer cellular network systems, comprising a combination of macro or overlay cells and micro or underlay cells (also referred to as pico cells or femto cells) are proposed as one concept. Thereby, the macro cells (having high transmit power) typically provide for a large geographical coverage, while the micro cells (having low transmit power) typically provide for additional capacity of low geographical coverage in areas with a high user deploy^¬ ment. In the context of LTE or LTE-Advanced (LTE: Long Term Evolution) , the macro cells are typically deployed by base stations denoted as eNBs, while micro cells are typically de^¬ ployed by capacity transmission nodes such as home base sta- tions denoted as HeNBs, pico base stations, relay nodes, or the like. Such heterogeneous network environment may, thus, be considered to be composed at least of two network layers, i.e. an underlay (micro cell) layer and an overlay (macro cell) layer.

A specific example of a heterogeneous network environment is a relay-enhanced cellular system. In relaying, a terminal or user equipment (UE) is not directly connected with an access node such as a radio base station (e.g. denoted as eNodeB or eNB) of a radio access network (RAN) , but via a relay node (RN) which is connected to the access node.

The two network layers of a heterogeneous network environ^¬ ment, i.e. the base stations and/or cells of the two network layers, may be implemented by the same or different radio ac^¬ cess technologies. For example, a heterogeneous network envi- ronment may be composed of a GSM-based macro cell layer and a LTE-based micro cell layer.

Multi-layer or heterogeneous (e.g. LTE-based) networks might be deployed using co-channel deployment, dedicate carrier de^¬ ployment, or a combination of those. In co-channel deploy^¬ ment, both the macro and micro base stations are using the same carrier frequency. In dedicate carrier deployment, macro and micro base stations are using different carrier frequen- cies.

In the context of heterogeneous network environments, to re^¬ duce the network power consumption in heterogeneous networks without harming the system performance, the above-outlined energy/power saving procedures are specifically directed to switch off the capacity transmission nodes such as home base stations, pico base stations, relay nodes, or the like, espe^¬ cially during off peak network times. For this purpose, efforts for energy/power saving in evolved access systems such as E-UTRAN (Evolved Universal Terrestrial Radio Access Network) have been started and are still ongo^¬ ing. Among others, the following solutions are for example discussed in this regard, which are specifically relevant for the heterogeneous co-channel case:

- Transmission node (such as eNB or the like) switch- off: An autonomous switch-off decision can be done by indi^¬ vidual nodes e.g. based on load thresholds. Before a node is switched off, the neighbor nodes are informed after the deci^¬ sion is made.

- Transmission node (such as eNB or the like) switch-on: A switch-on (wake-up) should be performed upon request by a neighbor transmission node or is done by individual decision of switched off node. In case of switch on by neighbor re^¬ quest, the requesting node is informed about the outcome of the request, and all other neighbors are informed in case of the switch-on.

As mentioned above, most of the energy/power saving proce- dures in this regard are based on a threshold level at the relevant base station (e.g. mico cell).

However, in the context of heterogeneous networks, such pro^¬ cedures are not completely reliable. That is, switch-off and switch-on decisions could be made wrongly or at an inappro^¬ priate time, i.e. too early or too late.

Namely, the problem of those procedures in the context of heterogeneous networks basically resides in that the inter- ference threshold controlled wake-up of micro cells results in a too late cell wake-up for micro cells, which are close to a (co-channel) macro (wide area) cell, and a too early cell wake-up for micro cells, which are near the cell border of a (co-channel) macro (wide area) cell. This is mainly due to the UL power control in LTE and the fact that UEs at the cell border of a macro (wide area) cell are transmitting with a power close to their maximum power, while on the other hand UEs that are closer to a macro (wide area) base station transmit with less power. Accordingly, the expected interfer- ence of a UE residing near a remotely located base station is higher than that of a UE residing near a base station which is closer to or equals the macro base station.

Further, in case of a high load problem at a macro base sta- tion, the currently discussed energy/power saving procedures would result in waking up all micro nodes/cells and, in case no load is to be served by an individual now active micro node/cell, this particular micro node/cell is switched off again .

A solution in view thereof could reside in specifying for each individual micro cell in the coverage range of a macro cell an individual wake-up threshold. Yet, such solution would be cumbersome and inefficient in terms of required sig^¬ naling load and management/control efforts.

In view thereof, there do not exist any reliable and effi- cient mechanisms for properly and correctly handling base station wake-up control, specifically but not exclusively in a heterogeneous network environment. Accordingly, such mecha^¬ nisms are needed. Summary of embodiments of the invention

Embodiments of the present invention aim at addressing at least some of the above-mentioned issues and/or problems and drawbacks .

Embodiments of the present invention are made to provide for mechanisms for properly and correctly handling base station wake-up control, specifically but not exclusively in a het^¬ erogeneous network environment.

This object may for example be achieved by the subject-matter defined in the attached claims.

According to an exemplary first aspect of the present inven- tion, there is provided a method comprising retrieving an average uplink interference level at a base station, a pathloss level between the base station and a neighboring base station, and a wake-up threshold interference level of the neighboring base station, evaluating a wake-up condition of the base station based on the retrieved average uplink inter^¬ ference level, pathloss level and wake-up threshold interfer^¬ ence level, and switching the base station from an inactive state in which a transmitter is switched off to an active state in which the transmitter is switched on, when the wake- up condition is evaluated to be satisfied.

According to further developments or modifications thereof, one or more of the following applies: - the evaluating further comprises calculating a wake-up threshold value by weighting the retrieved wake-up threshold interference level by the retrieved pathloss level, and com^¬ paring the calculated wake-up threshold value with the re- trieved average uplink interference level, wherein the wake- up condition is evaluated to be satisfied when the retrieved average uplink interference level exceeds the calculated wake-up threshold value,

- the method is operable at or by the base station,

- in case of the method being operable at or by the base station :

- the retrieving comprises measuring the uplink interference level, measuring and/or estimating the pathloss level, and receiving the wake-up threshold interference level from a management entity or the neighboring base station,

- the method further comprises receiving a wake-up re^¬ quest from the neighboring base station, wherein the wake-up request triggers the evaluation of the wake-up condition,

- the method further comprises receiving multiple wake-up threshold interference levels of multiple neighboring base stations from a management entity or the multiple neighboring base stations, respectively, and selecting the neighboring base station, from which the wake-up request is received, as a reference neighboring base station for evaluating the wake- up condition using the pathloss level between the base sta^¬ tion and said reference neighboring base station and the wake-up threshold interference level of said reference neighboring base station,

- the method further comprises reporting the switching from the inactive state to the active state to any neighbor^¬ ing base station,

- the method is operable at or by the neighboring base sta^¬ tion,

- in case of the method being operable at or by the neighboring base station:

- the retrieving comprises receiving a measurement of the uplink interference level from the base station, receiving a measurement and/or estimation of the pathloss level from the base station, and locally fetching or receiving, from a management entity, the wake-up threshold interference level,

- an interference level is an interference-to-thermal noise interference level,

- the average uplink interference level at the base station is retrieved in a frequency band of the neighboring base sta^¬ tion,

- the base station and/or the neighboring base station comprises an access node in a heterogeneous network environment comprising at least a macro cell layer and a micro cell layer,

- the base station comprises a pico node or a relay node in a micro cell layer of a heterogeneous network environment,

- the neighboring base station comprises a macro node in a macro cell layer of a heterogeneous network environment, and/or

- the base station and/or the neighboring base station comprises an access node in accordance with an LTE or LTE- Advanced radio access system.

According to an exemplary second aspect of the present inven^¬ tion, there is provided an apparatus comprising an interface configured to communicate with another apparatus, and a proc^¬ essor configured to retrieve an average uplink interference level at a base station, a pathloss level between the base station and a neighboring base station and a wake-up threshold interference level of the neighboring base station, evaluate a wake-up condition of the base station based on the retrieved average uplink interference level, pathloss level and wake-up threshold interference level, and switch the base station from an inactive state in which a transmitter is switched off to an active state in which the transmitter is switched on, when the wake-up condition is evaluated to be satisfied .

According to further developments or modifications thereof, one or more of the following applies: ... - the processor, for evaluating, is further configured to calculate a wake-up threshold value by weighting the re^¬ trieved wake-up threshold interference level by the retrieved pathloss level, and compare the calculated wake-up threshold value with the retrieved average uplink interference level, wherein the processor is configured to evaluate the wake-up condition to be satisfied when the retrieved average uplink interference level exceeds the calculated wake-up threshold value,

- the apparatus is operable as or at the base station,

- in case of the apparatus being operable as or at the base station:

- the processor, for retrieving, is configured to measure the uplink interference level, measure and/or estimate the pathloss level, and receive, via the interface, the wake-up threshold interference level from a management entity or the neighboring base station,

- the interface is further configured to receive a wake- up request from the neighboring base station, and the proces^¬ sor is further configured to be triggered for the evaluation of the wake-up condition by the wake-up request,

- the interface is further configured to receive multiple wake-up threshold interference levels of multiple neighboring base stations from a management entity or the multiple neighboring base stations, respectively, and the processor is further configured to select the neighboring base station, from which the wake-up request is received, as a reference neighboring base station for evaluating the wake-up condition using the pathloss level between the base station and said reference neighboring base station and the wake-up threshold interference level of said reference neighboring base sta^¬ tion,

- the processor and/or the interface is further config- ured to report the switching from the inactive state to the active state to any neighboring base station,

- the apparatus is operable as or at the neighboring base station, - in case of the apparatus being operable as or at the neighboring base station:

- the processor, for retrieving, is configured to receive, via the interface, a measurement of the uplink inter- ference level from the base station, receive, via the inter^¬ face, a measurement and/or estimation of the pathloss level from the base station, and locally fetch or receive, from a management entity via the interface, the wake-up threshold interference level,

- the processor is configured to retrieve an interference- to-thermal noise interference level as an interference level,

- the processor is configured to retrieve the average up^¬ link interference level at the base station in a frequency band of the neighboring base station,

- the apparatus and/or the base station and/or the

neighboring base station comprises an access node in a het^¬ erogeneous network environment comprising at least a macro cell layer and a micro cell layer,

- the apparatus and/or the base station comprises a pico node or a relay node in a micro cell layer of a heterogeneous network environment,

- the apparatus and/or the neighboring base station comprises a macro node in a macro cell layer of a heterogeneous network environment, and/or

- the apparatus and/or the base station and/or the

neighboring base station comprises an access node in accordance with an LTE or LTE-Advanced radio access system.

According to an exemplary third aspect of the present inven- tion, there is provided a computer program product including a program comprising software code portions being arranged, when run on a processor of an apparatus (such as e.g. accord^¬ ing to the above second aspect and/or developments or modifi^¬ cations thereof) , to perform the method according to the above first aspect and/or developments or modifications thereof . According to further developments or modifications thereof, the computer program product may comprise a computer-readable medium on which the software code portions are stored, and/or wherein the program is directly loadable into an internal memory of the processor.

By way of exemplary embodiments of the present invention, there are provided mechanisms for properly and correctly han^¬ dling base station wake-up control, specifically but not ex- clusively in a heterogeneous network environment.

Brief description of the drawings

In the following, the present invention will be described in greater detail by way of non-limiting examples with reference to the accompanying drawings, in which

Figure 1 shows a schematic diagram of a deployment scenario of a heterogeneous network environment, for which exemplary embodiments of the present invention are applicable,

Figure 2 shows a schematic diagram of a typical deployment scenario of a relay-enhanced cellular system, for which exemplary embodiments of the present invention are applicable,

Figure 3 shows a schematic diagram of an exemplary deployment scenario of a heterogeneous network environment and the in^¬ terference situation therein, for which exemplary embodiments of the present invention are applicable,

Figure 4 shows a schematic diagram of another exemplary de^¬ ployment scenario of a heterogeneous network environment and the interference situation therein, Figure 5 shows a flowchart of an exemplary method according to exemplary embodiments of the present invention, Figure 6 shows a schematic diagram of still another exemplary deployment scenario of a heterogeneous network environment and the interference situation therein, for which exemplary embodiments of the present invention are applicable,

Figure 7 shows a signaling diagram of an exemplary procedure according to exemplary embodiments of the present invention, and Figure 8 shows a block diagram illustrating exemplary devices according to embodiments of the present invention.

Detailed description of embodiments of the present invention The present invention is described herein with reference to particular non-limiting examples and to what are presently considered to be conceivable embodiments of the present in^¬ vention. A person skilled in the art will appreciate that the invention is by no means limited to these examples, and may be more broadly applied.

The present invention and its embodiments are mainly de^¬ scribed in relation to 3GPP specifications being used as non- limiting examples for certain exemplary network configura- tions and deployments. In particular, an LTE (E-UTRAN) radio access network and corresponding standards (LTE releases 8, 9 and LTE-Advanced release 10 and beyond) are used as a non- limiting example for the applicability of thus described ex^¬ emplary embodiments. As such, the description of exemplary embodiments given herein specifically refers to terminology which is directly related thereto. Such terminology is only used in the context of the presented non-limiting examples, and does naturally not limit the invention in any way.

Rather, any other network configuration or system deployment, etc. may also be utilized as long as compliant with the fea^¬ tures described herein. Generally, embodiments of the present invention may be appli^¬ cable for/in any kind of modern and future communication network including any conceivable mobile/wireless communication networks according to 3GPP (Third Generation Partnership Pro- ject) or IETF (Internet Engineering Task Force) specifica^¬ tions .

In particular, embodiments of the present invention may be specifically applicable in any heterogeneous network environ- ment such as for example in any relay-enhanced (cellular) ac^¬ cess system.

Hereinafter, various embodiments and implementations of the present invention and its aspects or embodiments are de- scribed using several alternatives. It is generally noted that, according to certain needs and constraints, all of the described alternatives may be provided alone or in any con^¬ ceivable combination (also including combinations of individ^¬ ual features of the various alternatives) .

According to exemplary embodiments of the present invention, in general terms, there are provided mechanisms, measures and means for properly and correctly handling base station wake- up control, specifically but not exclusively in a heterogene- ous network environment.

In the following, for the sake of intelligibility, LTE (Long- Term Evolution according to 3GPP terminology) or LTE-Advanced is taken as a non-limiting example for a radio access network of cellular type being applicable in the context of the pre^¬ sent invention and its embodiments. However, it is to be noted that any kind of radio access network of cellular type, such as GSM, GPRS, HSPA, UMTS and/or WiMAX, may likewise be applicable, as long as it exhibits comparable features and characteristics as described hereinafter. Figure 1 shows a schematic diagram of a deployment scenario of a heterogeneous network environment comprising a combina^¬ tion of macro cells and micro cells, for which exemplary em^¬ bodiments of the present invention are applicable. In Figure 1, macro cells are illustrated by hexagonal blocks, while mi^¬ cro cells are illustrated by rectangular blocks. In the dashed circle, an enlarged view of a micro cell including a micro cell base station and a user equipment is illustrated. Figure 2 shows a schematic diagram of a typical deployment scenario of a relay-enhanced cellular system, such as e.g. a LTE or LTE-Advanced RAN with radio-relayed extensions, for which exemplary embodiments of the present invention are ap^¬ plicable. As shown in Figure 2, UEs at disadvantaged posi- tions such as a cell edge and/or high shadowing areas are connected to a macro base station which could for example be a so-called donor base station (DeNB) via a respective relay node RN. Generally, any one of the relay nodes may be sta^¬ tionary/fixed or mobile. Such relay nodes are specific exam- pies of micro cells or micro base stations.

The solutions according to exemplary embodiments of the pre^¬ sent invention are based on the subsequently described situa^¬ tions, relations and considerations found by the present in- ventors .

Figure 3 shows a schematic diagram of an exemplary deployment scenario of a heterogeneous network environment and the in^¬ terference situation therein, for which exemplary embodiments of the present invention are applicable.

In Figure 3, there is assumed a heterogeneous network with co-channel deployment. Within the network two UEs (UE1 and UE2) are transmitting to the macro cell, as illustrated by the solid line arrows, respectively. Due to these transmis^¬ sions, interference is produced by those UEs at the pico and relay cell (s) , as illustrated by the dotted/dashed line ar^¬ rows, respectively.

Due to power control, such as the standardized LTE power con- trol as mentioned beforehand, the UE transmit power of UE1 is higher than the UE transmit power of UE2 which is more closely located to the macro cell. From this, in general for a macro cell with equal or quasi equal user distribution, the average measured UL (uplink) interference at a micro cell (i.e. a pico or relay node) is found to depend strongly on the pathloss between the micro base station and the macro base station, namely on geometry, distance and/or location of the micro cell relative to the macro cell. Figure 4 shows a schematic diagram of another exemplary de^¬ ployment scenario of a heterogeneous network environment and the interference situation therein.

In Figure 4, there is shown a setup (e.g. a simulation setup) in which micro cells 1 to 3 are located within the coverage range of a macro cell. The user distribution of micro cells 2 and 3 is comparable (from user activity and user density per^¬ spective) , whereas the user distribution of micro cell 1 is higher compared to that of micro cells 2 and 3. As the macro node or base station is indicated by the black dot on the left hand side of the left diagram of Figure 4, the deploy^¬ ment scenario is set up such that micro cell 1 is located nearest to the macro cell, and micro cells 2 and 3 are lo^¬ cated in a nearly equal distance to the macro cell. The left graph in Figure 4 shows the measured (or simulated) average interference (IoT: interference-over-thermal noise) at the three micro nodes of micro cells 1, 2 and 3. As ex^¬ plained above and due to the UL power control, the left graph in Figure 4 shows an about 8 dB higher IoT at micro cell 3 and an about 10 dB higher IoT at micro cell 2 compared to mi^¬ cro cell 1, even if the micro cell 1 is to serve the highest amount of users, for example. Hence, micro cell 2 would be woken up first, i.e. prior to micro cells 1 and 3, although more users would have to be served in micro cell 1 and wak- ing-up micro cell 1 would thus be more beneficial from the point of view of network performance.

In a case of a non-individual UL interference threshold set^¬ ting (e.g. all micro cells have the same interference thresh^¬ old for wake-up) , the measured average interference (for ex- ample, in the above-outlined case according to Figure 4) leads to a too late cell wake-up for micro cells, which are close to a (co-channel) macro cell, and a too early cell wake-up for micro cells, which are near the cell border of a (co-channel) macro cell, thus being farther away (locally and/or physically) .

Accordingly, the situation according to Figure 4 would require a cell-individual UL interference threshold setting for cell wake-up in the individual micro cells so as to avoid that micro cell 1 is switching on too late and/or micro cell 3 is switching on too early.

According to exemplary embodiments of the present invention, there are provided measures for establishing such cell- individual UL interference threshold settings for cell wake- up in the micro cells.

According to exemplary embodiments of the present invention, there is enabled an autonomous setting of interference threshold values at individual micro cells, without requiring a cumbersome and/or inefficient central control thereof. In this regard, exemplary embodiments of the present invention propose to use a single interference threshold value for (all) micro nodes of a single macro cell, and to do an autonomous correction of the macro cell-specific single in- terference threshold value at the micro cell itself, respec^¬ tively.

The right graph in Figure 4 shows the measured (or simulated) average interference weighted by the pathloss level (IoT^*: interference-over-thermal noise weighted by the pathloss level) at the three micro nodes of micro cells 1, 2 and 3. As can be seen, the micro cell 1 now results in the highest IoT weighted by the pathloss level due to the high amount of us- ers located in micro cell 1. Hence, according to exemplary embodiments of the present invention, micro cell 1 will be woken up first, i.e. prior to micro cells 2 and 3, and this is beneficial from the point of view of network performance, since micro cell 1 has to serve the most users.

Referring to the description of Figure 4 above, IoT* is used as a measure for a wake-up threshold value instead of IoT ac^¬ cording to exemplary embodiments of the present invention. Accordingly, according to exemplary embodiments of the present invention, such cell-individual UL interference thresh^¬ old settings for cell wake-up in the micro cells may be es^¬ tablished in an efficient manner in terms of required signal^¬ ing load and management/control efforts. Namely, the proposed measures according to exemplary embodiments of the present invention have the advantage that only a single threshold value is needed from a central/network point of view while individualization is accomplished at the micro cell layer, instead of having the need to signal and fine-tune a wake-up interference threshold for each individual micro cell from a central management entity such as from SON (self optimizing network) or OAM perspective. Stated in other words, according to exemplary embodiments of the present invention, the need may be avoided to specify for each individual micro cell in the coverage range of a macro cell an individual wake up threshold . Accordingly, exemplary embodiments of the present invention are effective for enhancing/improving energy/ power saving procedures, in particular a base station (micro cell) wake-up control, on an interference threshold basis.

In the following, exemplary embodiments of the present invention are described with reference to methods, procedures and functions, as well as with reference to structural arrange- ments and configurations.

Figure 5 shows a flowchart of an exemplary method according to exemplary embodiments of the present invention. The exem^¬ plary method according to Figure 5 may be regarded as an en- hanced base station wake-up control for waking up a base sta^¬ tion (such as, for example, a micro cell in a heterogeneous network environment) .

The exemplary method according to Figure 5 may, for example, be performed by or at a base station to be woken up (such as, for example, a micro cell in a heterogeneous network environ^¬ ment) according to Figure 8 and/or a base station neighboring (and/or even controlling) the base station to be woken up (such as, for example, a macro cell in a heterogeneous net- work environment) according to Figure 8.

As shown in Figure 5, a method according to exemplary embodi^¬ ments of the present invention may comprise an operation of retrieving required parameters and values (S51), an operation of evaluating a wake-up condition of the base station to be woken up based on the parameters and values retrieved in the above retrieval operation (S52), and an operation of switching the base station to be woken up from an inactive state in which a transmitter is switched off to an active state in which the transmitter is switched on, when the wake-up condi^¬ tion is evaluated to be satisfied (S53) . -

The above-mentioned retrieval operation may comprise measur^¬ ing, storing and restoring of indicators and/or receiving indications (e.g. measurements and/or estimations) of an aver^¬ age uplink interference level (UL IoT level) (in the fre- quency band of the neighboring base station) at the base sta^¬ tion to be woken up, a pathloss level between the base sta^¬ tion to be woken up and the neighboring base station, and a wake-up threshold interference level (IoT wake-up threshold) of the neighboring base station.

According to exemplary embodiments of the present invention, a pathloss level is used as a measure for geometry, distance and/or location between neighboring base stations, e.g. of a micro cell relative to a macro cell. Yet, the present inven- tion and its embodiments is not restricted thereto, and any conceivable parameters representing a corresponding measure may be equally utilized.

In case the method is performed at the base station to be woken up (e.g. a micro cell), the average uplink interference level (UL IoT level) at the base station may be measured (in the frequency band of the neighboring base station) , the pathloss level between the base station and the neighboring base station (e.g. a macro cell) may be measured or restored from a stored measurement and/or estimation, and the wake-up threshold interference level (IoT wake-up threshold) of the neighboring base station may be received from that neighboring base station or a management entity (e.g. a SON or OAM entity) or may be restored from a value received from that neighboring base station or management entity before.

In case the method is performed at the neighboring base sta^¬ tion (e.g. a macro cell), a measurement of the average uplink interference level (UL IoT level) (in the frequency band of the neighboring base station) at the base station to be woken up (e.g. a micro cell) may be received from this base sta^¬ tion, a measurement and/or estimation of the pathloss level between the base station to be woken up and the neighboring base station may be received from this base station, and the wake-up threshold interference level (IoT wake-up threshold) of the neighboring base station may be locally fetched at this neighboring base station or received from a management entity (e.g. a SON or OAM entity) .

The evaluation operation (S52) in the method according to exemplary embodiments of the present invention may comprise an operation of calculating a wake-up threshold value, and an operation of comparing the calculated wake-up threshold value with the retrieved average uplink interference level. Then, the wake-up condition may be evaluated to be satisfied when the retrieved average uplink interference level exceeds the calculated wake-up threshold value. The calculation of the wake-up threshold value (IoT*) may preferably involve the re^¬ trieved average uplink interference level (UL IoT level) at the base station to be woken up and the retrieved pathloss level between the base station to be woken up and the

neighboring base station such that the resulting interference threshold is not only depending on the average uplink interference level but is weighted by the pathloss level. Stated in other words, the wake-up threshold value may preferably represent a measure of interference-over-thermal noise weighted by the pathloss level. For example, the wake-up threshold value may be calculated by weighting the retrieved wake-up threshold interference level by the retrieved path- loss level, e.g. by adding the retrieved pathloss level and wake-up threshold interference level (when assuming the dB/logarithmic domain) or, respectively, multiplying the re- trieved pathloss level and wake-up threshold interference level (when assuming the linear domain) .

Although not shown in Figure 5, a method according to exemplary embodiments of the present invention may further com- prise an operation of triggering the evaluation of the wake- up condition in the evaluation operation (S52) . Such triggering operation may comprise an operation of receiving a wake- up request from the neighboring base station in case the method is performed at the base station to be woken up (e.g. a micro cell), and/or an operation of (internally) initiating a wake-up request at the neighboring base station in case the method is performed at the neighboring base station (e.g. a macro cell) .

Although not shown in Figure 5, a method according to exemplary embodiments of the present invention may further com^¬ prise an operation of reporting the switching from the inac- tive state to the active state to any neighboring base sta^¬ tion. Such reporting operation may comprise an operation of broadcasting a corresponding state change information of the base station in case the method is performed at the base sta^¬ tion to be woken up (e.g. a micro cell), and/or an operation of instructing the base station to be woken up to switch on in case the method is performed at the neighboring base sta^¬ tion (e.g. a macro cell) .

Figure 6 shows a schematic diagram of an exemplary deployment scenario of a heterogeneous network environment and the in^¬ terference situation therein, for which exemplary embodiments of the present invention are applicable.

In the exemplary deployment according to Figure 6, a hetero- geneous network with omni-directional micro cells and three- sector macro cells is assumed. The macro cells are denoted by numbers 01, 02, 03, 06, 08, 09 and 11 which may be equivalent to a PCI (physical cell identifier) numbering used in a part of a wide area (macro layer) network. The micro cells are denoted by letters A, B, C, D, E, F, and G. Further, X2 con^¬ nections between micro cells and wide area (macro) cells are represented by chain dotted lines. Generally, as can also be seen in Figure 6, a micro cell can have multiple X2 connec^¬ tions to different macro cells, dependent on the cell over- laps and handover regions.

In the present example underlying the subsequent description, micro cell A is specifically considered, which has X2 connec- tions or virtual X2 connections (X2 connections which are fully or partly emulated via an SI interface) to macro cells 06, 08 and 01. Figure 7 shows a signaling diagram of an exemplary procedure according to exemplary embodiments of the present invention, which is based on the exemplary deployment scenario according to Figure 6. In Figure 7, the base stations of each relevant macro/micro cell are denoted as NB standing for (e)NodeB, i.e. a 3GPP/LTE base station.

The thus depicted procedure relates to a base station wake-up control according to exemplary embodiments of the present in^¬ vention, wherein micro cell A is to be switched on upon an initiation by macro cell 06 via the respective X2 connection.

Initially, cell A, i.e. the base station thereof, is informed about, and thus retrieves, the IoT threshold (wake-up thresh^¬ old interference level) of its macro cell neighbors and their PCI values. Apart from the individual neighbors, this infor^¬ mation may also be provided by one or more management enti^¬ ties (e.g. a SON or OAM entity) .

Then, cell A, i.e. the base station thereof, measures, and thus retrieves, the pathloss level (PL) to each of its macro cell neighbors (e.g. by using the PCI information to identify and distinguish the downlink signals like the primary synchronization signal, the secondary synchronization signal and the broadcast control channels of the neighbors which can be used for the PL measurement), i.e. the macro cells from which IoT thresholds have been received.

Next, in case cell A is in an inactive state (in which its transmitter is switched off, thus saving energy/power) , a switch-on (wake-up) can be triggered by cell 06 in that a corresponding request is transmitted from cell 06 to cell A. Thereupon, cell A, i.e. the base station thereof, is trig^¬ gered to measure, and thus retrieve, its received (average) UL IoT value (average uplink interference level) in the fre^¬ quency band of the macro cell neighbor, and to evaluate the wake-up condition accordingly. Alternatively, cell A, i.e. the base station thereof, may continuously or periodically measure its received (average) UL IoT value (average uplink interference level) in the frequency band of the macro cell neighbor, and be triggered to evaluate the wake-up condition upon the corresponding request. The evaluation of the wake-up condition may be such that it is evaluated to be satisfied, if IoT_measured > IoT_th,_n + PL_macr0- pico is true, as outlined above as a non-limiting example for the wake-up condition. Generally, for such evaluation, the macro cell neighbor, from which the wake-up request has been received, is selected as a reference macro cell neighbor. That is, in the present case, the IoT threshold (wake-up threshold interference level) of cell 06, i.e. IoT_th, 6, and the corresponding pathloss level, i.e. PL₀6-A,is utilized. In case the wake-up condition is evaluated to be satisfied, cell A, i.e. the base station thereof, is woken up, i.e.

switched in an active state in which the base station' s transmitter is switched on. Otherwise, the cell, i.e. the base station thereof, remains in the inactive state.

In view of the above, exemplary embodiments of the present invention may provide for one or more of the following func^¬ tions and/or operations. As mentioned above, the apparatus or base station, which is configured to decide on wake-up of a relevant base station, may be located at or be the base station itself (e.g. a micro cell) or may be located at or be a neighboring base station (e.g. a macro cell) . The basic difference in the various cases resides in the different kind of retrieval of corre^¬ sponding information (i.e. measurement/estimation or local retrieval vs. receipt of a corresponding (report of) a meas^¬ urement/estimation or respective information). Hereinafter, there is assumed the exemplary and non-limiting case that a micro cell in a heterogeneous network environment is to be woken up, and the wake-up procedure/control is per- formed locally at this micro cell.

The micro cell, e.g. a pico or relay cell, may receive, e.g. from respective macro (wide area) cells or a management (SON or OAM) entity, a single or multiple macro cell-specific IoT wake-up thresholds (IoT_th, n ) of neighbor cells (n = 1 .. N, wherein n is the number of the neighbor cell) , preferably to^¬ gether with the corresponding PCIs (physical cell IDs) of the neighbor cells so as to enable a linkage between n and PCI, respectively. The signaling of the IoT wake-up thresholds and PCIs may done via the X2 or the SI interface.

If multiple IoT wake-up thresholds (IoT_th, n ) are received, the micro cell may select the IoT wake-up threshold related to the neighbor cell which is initiating a wake-up or switch-on request, i.e. cell 6 according to Figure 7.

The micro cell may be triggered to evaluate a wake-up or switch-on condition via signaling from a neighbor macro cell or a management (Son or OAM) entity via the X2 or SI signal- ing (i.e. a wake-up or switch-on request)

Then, the micro cell may measure the average received uplink I o T ( = I o Traeasureci ) and the pathloss level to the macro cell which initiated the wake-up or switch-on request.

After that, the wake—up or switch-on condition may be evalu^¬ ated and, if the condition is satisfied, the inactive micro cell is woken up. The wake—up or switch-on condition is based on an appropriate threshold value factoring in the IoT wake- up threshold and the pathloss level with respect to the rele^¬ vant macro cell neighbor. In an exemplary and non-limiting example, the wake-up or switch-on condition according to exemplary embodiments may be defined as follows: IoT_measureci > Io th_/n PL_macr0-pi_c0 , wherein

IoT_th,n represents a cell-specific IoT wake-up threshold of cell n in decibel. Here, n is the cell which initiated the wake-up or switch-on request,

PL_macro-_Pico represents the pathloss level between micro cell and the macro cell n in decibel (measured by the inactive mi- cro cell) , and

IoTraeasureci represents the measured average IoT in the fre^¬ quency band of the macro cell in decibel (measured by the in^¬ active micro cell) .

In view of the above example, the wake-up threshold value in the dB/logarithmic domain according to exemplary embodiments of the present invention may for example be: IoT* — Io th/n PLmacro-pico ·

Equivalently, in the linear domain, the above-mentioned the wake-up or switch-on condition according to exemplary embodiments may be defined as follows:

IoT_measureci > Io th_/n " PLmacro-pico_*

In view of the above example, the wake-up threshold value in the linear domain according to exemplary embodiments of the present invention may for example be:

IoT* = IoTth/n " PLmacro-pico* Generally speaking, exemplary embodiments of the present in^¬ vention provide for an advanced base station wake-up control. Such advanced base station wake-up control is effective to keep the number of active access nodes (for example, but not exclusively, in heterogeneous network environments) low and, thus, to achieve an improved and reduced network power con^¬ sumption, especially during idle periods and off peak network hours. Further, such advanced base station wake-up control is effective to avoid a wrong and/or wrongly timed (i.e. too early or too late) reactivation of base stations in an inac^¬ tive state. Specifically, it may be avoided that micro cells are woken up even if there are no UEs which could be served by the newly activated micro cell. That is, according to exemplary embodiments of the present invention, the previously described problem may be overcome, according to which a UE far away from an overlay cell but close to a underlay cell may cause such high interferences that this underlay cell is woken up wrongly or that many UEs close to both the overlay cell and to an underlay cell may not cause enough interference to wake this cell up, although it would be needed.

According to exemplary embodiments of the present invention, base stations being switched off are transferred into a power efficient inactive mode, in which above-mentioned retrieval, evaluation and switch operations are operable, and in which the base station may be triggered by a neighboring base sta^¬ tion or a management entity (e.g. via the X2, SI or the Itf interface) to evaluate the wake-up condition and/or measure the average uplink interference level.

According to exemplary embodiments of the present invention, the average uplink interference measurement information may be beneficially used together with a pathloss-dependent part of a wake-up threshold value so as to distinguish if an inac^¬ tive micro cell should switch on its radio part (i.e. RF (ra^¬ dio frequency) transmitter or transceiver) again or not. According to exemplary embodiments of the present invention, different and individually adjusted wake-up thresholds for different cells are applicable without forcing a very complex management like setting or adjusting these threshold values all individually.

According to exemplary embodiments of the present invention, inefficient activations of nodes may be avoided (i.e. the ac- curacy of detecting a correct node to be switched on is im^¬ proved) , the energy efficiency in the network is improved, and the needed signaling overhead is reduced.

Generally, while the IoT (i.e. the interference level normal- ized by the thermal noise) is mainly used as a measure for an interference level, the present invention and its embodiments is not restricted thereto. Rather, any conceivable interfer^¬ ence measure may be equally utilized. The above-described procedures and functions may be imple^¬ mented by respective functional elements, processors, or the like, as described below.

While in the foregoing exemplary embodiments of the present invention are described mainly with reference to methods, procedures and functions, corresponding exemplary embodiments of the present invention also cover respective apparatuses, network nodes and systems, including both software and/or hardware thereof.

Respective exemplary embodiments of the present invention are described below referring to Figure 8, while for the sake of brevity reference is made to the detailed description of re^¬ spective corresponding methods and operations according to Figures 5 and 7 as well as the underlying system architec^¬ tures according to Figures 1 to 4 and 6. In Figure 8 below, the solid line blocks are basically con^¬ figured to perform respective operations as described above. The entirety of solid line blocks are basically configured to perform the methods and operations as described above, re- spectively. With respect to Figure 8, it is to be noted that the individual blocks are meant to illustrate respective functional blocks implementing a respective function, process or procedure, respectively. Such functional blocks are imple^¬ mentation-independent, i.e. may be implemented by means of any kind of hardware or software, respectively. The arrows and lines interconnecting individual blocks are meant to il^¬ lustrate an operational coupling there-between, which may be a physical and/or logical coupling, which on the one hand is implementation-independent (e.g. wired or wireless) and on the other hand may also comprise an arbitrary number of in^¬ termediary functional entities not shown. The direction of arrow is meant to illustrate the direction in which certain operations are performed and/or the direction in which certain data is transferred.

Further, in Figure 8, only those functional blocks are illus^¬ trated, which relate to any one of the above-described meth^¬ ods, procedures and functions. A skilled person will acknowl^¬ edge the presence of any other conventional functional blocks required for an operation of respective structural arrange^¬ ments, such as e.g. a power supply, a central processing unit, respective memories or the like. Among others, memories are provided for storing programs or program instructions for controlling the individual functional entities to operate as described herein.

Figure 8 shows a block diagram illustrating exemplary devices according to embodiments of the present invention. As men^¬ tioned above, it is noted that the illustration of (elec- tronic) devices according to Figure 8 is simplified.

In view of the above, the thus described apparatuses 10, and 20 are suitable for use in practicing the exemplary embodi- ments of the present invention, as described herein. The thus described apparatus 10 on the left hand side may represent a (part of a) neighboring base station (such as e.g. a macro cell node) , as described above, and may be configured to per- form a procedure and/or exhibit a functionality as described in conjunction with any one of Figures 5 and 7. The thus de^¬ scribed apparatus 20 on the right hand side may represent a (part of a) base station (such as e.g. a micro cell node), as described above, and may be configured to perform a procedure and/or exhibit a functionality as described in conjunction with any one of Figures 5 and 7.

As shown in Fig. 8, according to embodiments of the present invention a neighboring apparatus 10 comprises a processor 11, a memory 12, an interface 13, and a (RF) transceiver 14 which are connected by a bus 15 or the like. An apparatus 20 comprises a processor 21, a memory 22, an interface 23, and a (RF) transceiver 24 which are connected by a bus 25 or the like. The neighboring apparatus 10 may be connected with a user equipment through a link or connection 16, the apparatus 20 may be connected with a user equipment through a link or connection 26, and the neighboring apparatus 10 and the appa^¬ ratus 20 may be connected with each other through a link or connection 30 which may exemplarily comprise a X2 interface.

The memories 12 and 22 may store respective programs assumed to include program instructions that, when executed by the associated processors 11 and 21, enable the electronic device to operate in accordance with the exemplary embodiments of the present invention. The processors 11 and 21 may also in^¬ clude a modem to facilitate communication over the (hardwire or wireless) links 16, 26 and 30 via the interfaces 13 and 23. The interfaces 13 and 23 may further include a suitable transceiver coupled to one or more antennas or communication means for (hardwire or wireless) communications with the linked or connected device (s), respectively. The interfaces 13 and 23 are configured to communicate with another appara^¬ tus, i.e. the interface thereof. In general terms, the respective devices (and/or parts thereof) may represent means for performing respective opera^¬ tions and/or exhibiting respective functionalities, and/or the respective devices (and/or parts thereof) may have func^¬ tions for performing respective operations and/or exhibiting respective functionalities.

According to exemplary embodiments of the present invention, the processor 11 and/or 21 is configured to retrieve an aver^¬ age uplink interference level at a base station, a pathloss level between the base station and a neighboring base station and a wake-up threshold interference level of the neighboring base station, to evaluate a wake-up condition of the base station based on the retrieved average uplink interference level, pathloss level and wake-up threshold interference level, and to switch the base station from an inactive state in which a transmitter is switched off to an active state in which the transmitter is switched on, when the wake-up condi- tion is evaluated to be satisfied.

Further, the processor 11 and/or 21 may be configured to calculate a wake-up threshold value by weighting the retrieved wake-up threshold interference level by the retrieved path- loss level, e.g. by adding the retrieved pathloss level and wake-up threshold interference level in the dB/logarithmic domain or multiplying the retrieved pathloss level and wake- up threshold interference level in the linear domain, and to compare the calculated wake-up threshold value with the re- trieved average uplink interference level. Then, the proces^¬ sor 11 and/or 21 may be further configured to evaluate the wake-up condition to be satisfied when the retrieved average uplink interference level exceeds the calculated wake-up threshold value.

Still further, the processor 11 and/or the interface 13 and/or the processor 11 and/or the interface 13 may be con- figured to report/instruct the switching from the inactive state to the active state to any neighbor.

According to exemplary embodiments of the present invention, the apparatus 20 may be configured to perform the methods and operations according to Figures 5 and 7.

In such case, the processor 21, for retrieving, may be configured to measure the uplink interference level, measure and/or estimate the pathloss level, and receive, via the in^¬ terface 23, the wake-up threshold interference level from a management entity or the neighboring base station.

Further, in such case, the interface 23 may be configured to receive a wake-up request from the neighboring base station, and the processor 21may be configured to be triggered for the evaluation of the wake-up condition by the wake-up request. Still further, the interface 23 may be further configured to receive multiple wake-up threshold interference levels of multiple neighboring base stations from a management entity or the multiple neighboring base stations, respectively, and the processor 21 may be further configured to select the neighboring base station, from which the wake-up request is received, as a reference neighboring base station for evalu- ating the wake-up condition using the pathloss level between the base station and said reference neighboring base station and the wake-up threshold interference level of said refer^¬ ence neighboring base station. According to exemplary embodiments of the present invention, the neighboring apparatus 10 may be configured to perform the methods and operations according to Figures 5 and 7.

In such case, the processor 11, for retrieving, may be con- figured to receive, via the interface 13, a measurement of the uplink interference level from the base station, receive, via the interface 13, a measurement and/or estimation of the pathloss level from the base station, and locally fetch or receive, from a management entity via the interface, the wake-up threshold interference level.

In general, exemplary embodiments of the present invention may be implemented by computer software stored in the memo^¬ ries 12 and 22 and executable by the processors 11 and 21, or by hardware, or by a combination of software and/or firmware and hardware in any or all of the devices shown. According to exemplarily embodiments of the present inven^¬ tion, referring to the wording used above, the base station and/or the neighboring base station may comprise an access node (or transmission node) in a heterogeneous network environment comprising at least a macro cell layer and a micro cell layer, and/or the base station may comprise a micro node (e.g. a pico node or a relay node) in a micro cell layer of a heterogeneous network environment, and/or the neighboring base station may comprise a macro node in a macro cell layer of a heterogeneous network environment, and/or the base sta- tion and/or the neighboring base station may comprise an access node (or transmission node) in accordance with an LTE or LTE-Advanced radio access system.

According to exemplarily embodiments of the present inven- tion, a system may comprise any conceivable combination of the thus depicted apparatuses and other network elements, which are configured to cooperate as described above.

In general, it is to be noted that respective functional blocks or elements according to above-described aspects can be implemented by any known means, either in hardware and/or software, respectively, if it is only adapted to perform the described functions of the respective parts. The mentioned method steps can be realized in individual functional blocks or by individual devices, or one or more of the method steps can be realized in a single functional block or by a single device . Generally, any method step is suitable to be implemented as software or by hardware without changing the idea of the pre^¬ sent invention. Such software may be software code independ^¬ ent and can be specified using any known or future developed programming language, such as e.g. Java, C++, C, and Assem^¬ bler, as long as the functionality defined by the method steps is preserved. Such hardware may be hardware type inde^¬ pendent and can be implemented using any known or future de^¬ veloped hardware technology or any hybrids of these, such as MOS (Metal Oxide Semiconductor), CMOS (Complementary MOS) ,

BiMOS (Bipolar MOS), BiCMOS (Bipolar CMOS), ECL (Emitter Coupled Logic), TTL (Transistor-Transistor Logic), etc., using for example ASIC (Application Specific IC (Integrated Cir^¬ cuit) ) components, FPGA (Field-programmable Gate Arrays) com- ponents, CPLD (Complex Programmable Logic Device) components or DSP (Digital Signal Processor) components. An apparatus may be represented by a semiconductor chip, a chipset, or a (hardware) module comprising such chip or chipset; this, how^¬ ever, does not exclude the possibility that a functionality of an apparatus or module, instead of being hardware imple^¬ mented, be implemented as software in a (software) module such as a computer program or a computer program product comprising executable software code portions for execution/being run on a processor. A device may be regarded as an apparatus or as an assembly of more than one apparatus, whether func^¬ tionally in cooperation with each other or functionally independently of each other but in a same device housing, for ex^¬ ample . Devices and means can be implemented as individual devices, but this does not exclude that they are implemented in a dis^¬ tributed fashion throughout the system, as long as the func^¬ tionality of the device is preserved. Such and similar prin^¬ ciples are to be considered as known to a skilled person.

Software in the sense of the present description comprises software code as such comprising code means or portions or a computer program or a computer program product for performing the respective functions, as well as software (or a computer program or a computer program product) embodied on a tangible medium such as a computer-readable (storage) medium having stored thereon a respective data structure or code

means/portions or embodied in a signal or in a chip, poten^¬ tially during processing thereof.

The present invention also covers any conceivable combination of method steps and operations described above, and any con- ceivable combination of nodes, apparatuses, modules or ele^¬ ments described above, as long as the above-described con^¬ cepts of methodology and structural arrangement are applica^¬ ble . In view of the above, there are provided measures for a base station wake-up control, more specifically a base station wake-up control in a heterogeneous network environment. Such measures exemplarily comprise a retrieval of an average up^¬ link interference level at a base station, a pathloss level between the base station and a neighboring base station and a wake-up threshold interference level of the neighboring base station, an evaluation of a wake-up condition of the base station based on the retrieved average uplink interference level, pathloss level and wake-up threshold interference level, and a switch of the base station from an inactive state in which a transmitter is switched off to an active state in which the transmitter is switched on, when the wake- up condition is evaluated to be satisfied. The measures proposed according to exemplary embodiments of the present invention may be applied for any kind of network environment, particularly in any kind of heterogeneous net^¬ work environment, such as for example for those in accordance with 3GPP RA 2 /RA 3 standards and/or 3GPP LTE standards of release 10/11/12/... (LTE-Advanced and its evolutions).

Even though the invention is described above with reference to the examples according to the accompanying drawings, it is to be understood that the invention is not restricted

thereto. Rather, it is apparent to those skilled in the art that the present invention can be modified in many ways with^¬ out departing from the scope of the inventive idea as dis- closed herein.

Claims

1. A method comprising

retrieving an average uplink interference level at a base station, a pathloss level between the base station and a neighboring base station, and a wake-up threshold interference level of the neighboring base station,

evaluating a wake-up condition of the base station based on the retrieved average uplink interference level, pathloss level and wake-up threshold interference level, and

switching the base station from an inactive state in which a transmitter is switched off to an active state in which the transmitter is switched on, when the wake-up condi^¬ tion is evaluated to be satisfied.

2. The method according to claim 1, wherein the evaluating further comprises

calculating a wake-up threshold value by weighting the retrieved wake-up threshold interference level by the re- trieved pathloss level, and

comparing the calculated wake-up threshold value with the retrieved average uplink interference level,

wherein the wake-up condition is evaluated to be satis^¬ fied when the retrieved average uplink interference level ex- ceeds the calculated wake-up threshold value.

3. The method according to claim 1 or 2, wherein

the method is operable at or by the base station, the retrieving comprises measuring the uplink interfer- ence level, measuring and/or estimating the pathloss level, and receiving the wake-up threshold interference level from a management entity or the neighboring base station.

4. The method according to claim 3, further comprising

receiving a wake-up request from the neighboring base station,

wherein the wake-up request triggers the evaluation of the wake-up condition.

5. The method according to claim 4, further comprising receiving multiple wake-up threshold interference levels of multiple neighboring base stations from a management en^¬ tity or the multiple neighboring base stations, respectively, and

selecting the neighboring base station, from which the wake-up request is received, as a reference neighboring base station for evaluating the wake-up condition using the path- loss level between the base station and said reference neighboring base station and the wake-up threshold interference level of said reference neighboring base station.

6. The method according to any one of claims 3 to 5, further comprising

reporting the switching from the inactive state to the active state to any neighboring base station.

7. The method according to claim 1 or 2, wherein

the method is operable at or by the neighboring base station,

the retrieving comprises receiving a measurement of the uplink interference level from the base station, receiving a measurement and/or estimation of the pathloss level from the base station, and locally fetching or receiving, from a management entity, the wake-up threshold interference level.

8. The method according to any one of claims 1 to 7, wherein an interference level is an interference-to-thermal noise interference level, and/or

the average uplink interference level at the base sta^¬ tion is retrieved in a frequency band of the neighboring base station .

9. The method according to any one of claims 1 to 8, wherein the base station and/or the neighboring base station comprises an access node in a heterogeneous network environ- ment comprising at least a macro cell layer and a micro cell layer, and/or

the base station comprises a pico node or a relay node in a micro cell layer of a heterogeneous network environment, and/or

the neighboring base station comprises a macro node in a macro cell layer of a heterogeneous network environment, and/or

the base station and/or the neighboring base station comprises an access node in accordance with an LTE or LTE- Advanced radio access system.

10. An apparatus comprising

an interface configured to communicate with another ap- paratus, and

a processor configured to

retrieve an average uplink interference level at a base station, a pathloss level between the base station and a neighboring base station and a wake-up threshold interference level of the neighboring base station,

evaluate a wake-up condition of the base station based on the retrieved average uplink interference level, pathloss level and wake-up threshold interference level, and

switch the base station from an inactive state in which a transmitter is switched off to an active state in which the transmitter is switched on, when the wake-up condition is evaluated to be satisfied.

11. The apparatus according to claim 10, wherein the proces- sor, for evaluating, is further configured to

calculate a wake-up threshold value by weighting the re^¬ trieved wake-up threshold interference level by the retrieved pathloss level, and

compare the calculated wake-up threshold value with the retrieved average uplink interference level,

wherein the processor is configured to evaluate the wake-up condition to be satisfied when the retrieved average uplink interference level exceeds the calculated wake-up threshold value.

12. The apparatus according to claim 10 or 11, wherein

the apparatus is operable as or at the base station, the processor, for retrieving, is configured to measure the uplink interference level, measure and/or estimate the pathloss level, and receive, via the interface, the wake-up threshold interference level from a management entity or the neighboring base station.

13. The apparatus according to claim 12, wherein

the interface is further configured to receive a wake-up request from the neighboring base station, and

the processor is further configured to be triggered for the evaluation of the wake-up condition by the wake-up re^¬ quest .

14. The apparatus according to claim 13, wherein

the interface is further configured to receive multiple wake-up threshold interference levels of multiple neighboring base stations from a management entity or the multiple neighboring base stations, respectively, and

the processor is further configured to select the neighboring base station, from which the wake-up request is received, as a reference neighboring base station for evalu^¬ ating the wake-up condition using the pathloss level between the base station and said reference neighboring base station and the wake-up threshold interference level of said refer- ence neighboring base station.

15. The apparatus according to any one of claims 12 to 14, wherein the processor and/or the interface is further configured to

report the switching from the inactive state to the ac^¬ tive state to any neighboring base station.

16. The apparatus according to claim 10 or 11, wherein the apparatus is operable as or at the neighboring base station,

the processor, for retrieving, is configured to receive, via the interface, a measurement of the uplink interference level from the base station, receive, via the interface, a measurement and/or estimation of the pathloss level from the base station, and locally fetch or receive, from a management entity via the interface, the wake-up threshold interference level.

17. The apparatus according to any one of claims 10 to 16, wherein

the processor is configured to retrieve an interference- to-thermal noise interference level as an interference level, and/or

the processor is configured to retrieve the average up^¬ link interference level at the base station in a frequency band of the neighboring base station.

18. The apparatus according to any one of claims 10 to 17, wherein

the apparatus and/or the base station and/or the

neighboring base station comprises an access node in a het- erogeneous network environment comprising at least a macro cell layer and a micro cell layer, and/or

the apparatus and/or the base station comprises a pico node or a relay node in a micro cell layer of a heterogeneous network environment, and/or

the apparatus and/or the neighboring base station comprises a macro node in a macro cell layer of a heterogeneous network environment, and/or

the apparatus and/or the base station and/or the

neighboring base station comprises an access node in accor- dance with an LTE or LTE-Advanced radio access system.

19. A computer program product including a program comprising software code portions being arranged, when run on a proces^¬ sor of an apparatus, to perform the method according to any one of claims 1 to 9.

20. The computer program product according to claim 19, wherein the computer program product comprises a computer- readable medium on which the software code portions are stored, and/or wherein the program is directly loadable into an internal memory of the processor.