Methods and devices for saving network energy in a wireless communication system, taking into account distances between base stations

Abstract

The present disclosure relates to methods and devices for saving energy on a radio network access side of a wireless communication system.

Description

Technical area

[0001] The present disclosure relates to wireless communication systems and, more particularly, to methods and apparatus for saving energy on a radio access network side of the wireless communication system, also known as Network Energy Saving (NES). background

[0002] To limit energy consumption in Long Term Evolution (LTE), 5G or New Radio (NR) wireless communication systems, 3GPP (Third Partnership Project) is introducing NES features to reduce energy consumption on the Radio Access Network (RAN) side of the wireless communication system.

[0003] In some cases, the RAN may, for example, comprise a macro base station (BS) and a plurality of small BSs. "Macro" and "small" refer to the macro BS having a wider coverage area than the respective coverage areas of the small BSs. Essentially, the coverage area of ​​a BS, also known as the radio coverage area, corresponds to the geographical area within which user equipment (UEs) can be served by the BS in question.

[0004] In the case where the small BSs and their respective coverage areas are located within the macro BS's coverage area, the macro BS can then transmit some control messages on behalf of the small BSs. For example, in a 3GPP wireless communication system, the control messages that can be transmitted by the macro BS (sometimes referred to as an "anchor cell") for the small BSs (sometimes referred to as "non-anchor cells") can include system information block (SIB) messages, synchronization signal / physical channel block (SSB) messages, and paging messages.

[0005] Thus, these control messages transmitted by the macro-BSs do not need to be transmitted by the small-BSs, which allows for the reduction of the small-BSs' power consumption. However, there is a need to optimize NES functions to further improve power consumption. Brief description

[0006] The present disclosure aims to improve the situation. In particular, the present disclosure aims to address at least some of the limitations of the prior art discussed above. In particular, the present disclosure aims to propose a solution for optimizing NES functions in a wireless communication system.

[0007] To this end, the present disclosure proposes that a macro BS of the wireless communication system responsible for transmitting control messages for small BSs in its coverage area may, in some scenarios (i.e., when predetermined conditions are verified), decide to request that one or more of the small BSs in its coverage area resume transmitting all or part of these control messages previously transmitted by the macro BS to UEs in the respective coverage areas of these one or more small BSs.

[0008] According to a first aspect, the present disclosure relates to a method for transmitting control messages in a wireless communication system, wherein the wireless communication system comprises a macro base station (BS) and a plurality of small BSs located in a coverage area of ​​the macro BS, wherein the macro BS transmits control messages for the plurality of small BSs to user equipment (UEs) in respective coverage areas of the plurality of small BSs, the method being implemented by the macro BS and comprising: - selecting at least one small BS from the plurality of small BSs based on respective distances between the plurality of small BSs and the macro BS, - instructing the at least one selected small BS to resume transmitting all or part of the control messages previously transmitted by the macro BS to UEs in the coverage area of ​​that at least one selected small BS.

[0009] In some embodiments, the method according to the first aspect may further comprise one or more of the following optional features, contemplated either alone or in any technically possible combination.

[0010] In some embodiments of the method according to the first aspect, the at least one selected small BS includes the small BS that is furthest from or closest to the macro BS.

[0011] In some embodiments, the method according to the first aspect comprises receiving local utilization reports from the plurality of small BSs, wherein a local utilization report from a small BS is representative of a local utilization of that small BS due to the UEs in its coverage area, and wherein selecting at least one small BS from the plurality of small BSs is further based on the received local utilization reports,

[0012] In some embodiments of the method according to the first aspect, the local utilization message transmitted by a small BS is representative of the number of UEs located in the coverage area of ​​that small BS, and the at least one selected small BS includes the small BS that is the furthest from or closest to the macro BS having a number of UEs in its coverage area greater than a threshold.

[0013] In some embodiments, the method according to the first aspect comprises receiving distance reports from the plurality of small BSs, wherein a distance report from a small BS is representative of a distance between that small BS and the macro BS.

[0014] In some embodiments, the method according to the first aspect comprises receiving successive distance reports from a same small BS that is not stationary.

[0015] In some embodiments, the method according to the first aspect comprises: - receiving mobility status messages from the plurality of small BSs, wherein a mobility status message of a small BS is representative of whether the small BS is stationary or non-stationary, - Request that small BSs that are not stationary according to the received mobility status messages transmit distance reports in a recurring manner, preferably periodically.

[0016] In some embodiments of the method according to the first aspect, the macro BS configures respective transmission periods of distance messages by the plurality of small BSs based on the received mobility status messages.

[0017] According to a second aspect, the present disclosure relates to a method for transmitting control messages in a wireless communication system, wherein the wireless communication system comprises a macro base station (BS) and a plurality of small BSs located in a coverage area of ​​the macro BS, wherein the macro BS for the plurality of small BSs transmits control messages to user equipment (UEs) in respective coverage areas of the plurality of small BSs, wherein the method is implemented by a small BS of the plurality of small BSs and comprises: - Receiving, from the macro BS, an instruction to resume transmitting all or part of the control messages previously transmitted by the macro BS to UEs in the coverage area of ​​the small BS, - Transmitting all or part of the control messages previously transmitted by the macro BS to UEs in the coverage area of ​​the small BS.

[0018] In some embodiments, the method according to the second aspect may further comprise one or more of the following optional features, contemplated either alone or in any technically possible combination.

[0019] In some embodiments, the method according to the first aspect comprises transmitting, by the small BS, a distance message to the macro BS, wherein the distance message from a small BS is representative of a distance between that small BS and the macro BS.

[0020] In some embodiments of the method according to the second aspect, wherein the small BS is not stationary, this small BS transmits distance messages in a recurring manner, preferably periodically.

[0021] In some embodiments of the method according to the second aspect, the small BS transmits distance messages periodically with a transmission period determined by the macro BS.

[0022] In some embodiments, the method according to the second aspect comprises: - transmitting a local load message to the macro BS, where the local load message is representative of a local load of the small BS due to the UEs in its coverage area, and / or - Transmitting a mobility status message to the macro BS, the mobility status message being representative of whether the small BS is stationary or non-stationary.

[0023] In some embodiments of the method according to the second aspect, the control messages transmitted by the macro BS for the plurality of small BSs include system information block (SIB) messages, synchronization signal / physical broadcast channel block (SSB) messages, and paging messages, and transmitting all or part of the control messages by a small BS corresponds to transmitting at least one of the SIB messages, the SSB messages, and the paging messages.

[0024] According to a third aspect, the present disclosure relates to a computer program product comprising instructions that, when executed by at least one processor, configure the at least one processor to perform a method for transmitting control messages according to any of the embodiments of the present disclosure. The computer program product may use any programming language and may be in the form of source code, object code, or any form intermediate between source code and object code, such as in a partially compiled form, or in any other desired form.

[0025] According to a fourth aspect, the present disclosure relates to a (non-transitory) computer-readable storage medium comprising instructions that, when executed by at least one processor, configure the at least one processor to perform a method for transmitting control messages according to any of the embodiments of the present disclosure.

[0026] According to a fifth aspect, the present disclosure relates to a base station comprising at least one memory and at least one processor configured to perform one or more methods for transmitting control messages according to any of the embodiments of the present disclosure.

[0027] According to a sixth aspect, the present disclosure relates to a wireless communication system comprising a macro BS according to any of the embodiments of the present disclosure and a plurality of smaller BSs according to any of the embodiments of the present disclosure, wherein the plurality of small BSs are located in a coverage area of ​​the macro BS. Short description of the drawings

[0028] The invention will be better understood upon reading the following description, given as an example and in no way limiting, with reference to the figures, which show: - Fig. 1: a schematic diagram of an example of a wireless communication system comprising a macro BS and a plurality of small BSs, - Fig. 2 and Fig. 3: Flowcharts illustrating examples of methods for transmitting control messages implemented by a macro BS and a small BS, respectively, - Fig. 4 and Fig. 5: Flowcharts illustrating other examples of methods for transmitting control messages implemented by a small BS and a macro BS, respectively, - Fig. 6 and Fig. 7: Flowcharts illustrating other examples of methods for transmitting control messages implemented by a macro BS and a small BS, respectively, - Fig. 8 and Fig. 9: Flowcharts illustrating other examples of methods for transmitting control messages implemented by a macro BS and a small BS, respectively, - Fig. 10: a schematic representation of an example of a base station suitable for implementing one or more methods for transmitting control messages.

[0029] In these figures, reference numerals that are identical from one figure to another indicate identical or similar elements. For clarity, the elements shown are not to scale unless expressly stated otherwise. Detailed description

[0030] The detailed description below with reference to the figures is intended to be a description of various configurations and is not intended to represent the only configurations in which the presently described concepts may be practiced. The detailed description includes specific details for the purpose of providing a thorough understanding of the various concepts. However, it will be apparent to those skilled in the art that these concepts may be practiced without these specific details. For example, while this disclosure may use 3GPP terminology, e.g., from 5G NR, to explain embodiments herein, this should not be seen as limiting the scope of the present disclosure.

[0031] In general, all terms used herein should be interpreted according to their usual meaning in the relevant technical field, unless another meaning is clearly indicated and / or clear from the context in which it is used. All references to an element, facility, component, means, step, etc. should be openly construed as referring to at least one instance of the element, facility, component, means, step, etc., unless expressly stated otherwise.Likewise, the order of steps of any methods disclosed herein, particularly in the figures, is provided for illustrative purposes only and does not imply any limitation on the present disclosure, which may be applied with the same steps performed in a different order and / or with all or part of the steps performed in parallel or together, unless a step is expressly described as following or preceding a step and / or where it is implicit that a step must follow or precede another step. Likewise, steps depicted in a figure that are surrounded by a dashed line are to be considered optional for the embodiment depicted in that figure.Any feature of any of the embodiments disclosed herein may be applied to any other embodiment whenever appropriate. Likewise, any advantage of any of the embodiments may be applied to any other embodiment, and vice versa. Other objects, features, and advantages of the included embodiments will become apparent from the following description.

[0032] Fig. Figure 1 schematically illustrates an example of a wireless communication system, which may be, for example, a 5G NR wireless communication system. In particular, Fig. Figure 1 depicts a RAN of the wireless communication system, used to exchange data with UEs (not shown in the figures) via radio signals. The RAN can, for example, send data to the UEs (DL - downlink), such as data received from a core network (CN - core network, not shown in the figures). The RAN can also receive data from the UEs (UL - uplink), and this data can be forwarded to the CN.

[0033] As through Fig. As illustrated in Figure 1, the RAN comprises multiple base stations (BSs). Each of these BSs may be referred to as an NB, eNodeB (or eNB), gNodeB (or gNB), an access point, or the like, depending on the one or more wireless standards implemented.

[0034] Each UE may be a mobile phone, a wireless modem, a wireless communication device, a handheld device, a laptop computer, or the like. Each UE may also be an IoT (Internet of Things) device, such as a wireless camera, a smart sensor or smart meter, a vehicle, a Global Positioning System device, or any other device configured to communicate with a RAN of a wireless communication system.

[0035] In Fig. 1, a BS referred to as macro-BS 100 provides a wider coverage area 101 (also known as a cell) than other BSs referred to as small BSs 110. The small BSs 110 and their respective coverage areas 111 are located within the coverage area 101 of the macro BS 100. For example, the smaller coverage areas 111 of the small BSs 110 may be due to the small BSs 110 using lower transmission powers than the macro BS 100 and / or higher frequency carriers than the macro BS 100.

[0036] As discussed above, the wireless communication system implements NES functions to reduce the power consumption of some of the BSs. Since the coverage areas 111 of the small BSs 110 are included in the coverage area 101 of the macro BS 100, which implies that any UE located within the coverage area 111 of a small BS 110 can receive radio signals from both that small BS 110 and the macro BS 100, the macro BS 100 is specifically configured to transmit control messages on behalf of the small BSs 110 to the UEs located within the respective coverage areas 111 of the small BSs 110. This reduces the power consumption of the small BSs 110 because the power required to transmit these control messages is saved by these small BSs 110.

[0037] It is noted that other small BSs may also be present in the coverage area of ​​the macro BS 100, for which the macro BS 100 is not responsible for transmitting control messages. Such small BSs located in the coverage area 101 of the macro BS 100, for which the macro BS 100 is not responsible for transmitting control messages, are outside the scope of the present disclosure, which concerns small BSs 110 that rely on the macro BS 100 to transmit control messages to UEs in their respective coverage areas 111.

[0038] In some examples, the control messages transmitted by the macro BS 100 on behalf of the small BSs may be of different types. For example, in a 3GPP wireless communication system, the control messages may be at least one of the following (as indicated by Fig. 1 in a non-limiting way) include: - System Information Block (SIB) messages, - Synchronization Signal / PBCH Block (SSB - Synchronization Signal) messages (where PBCH stands for Physical Broadcast Channel), - Paging messages.

[0039] These control message types are considered familiar to those skilled in the art. For 3GPP wireless communication systems beyond LTE, definitions for these control message types can be found, for example, in the TS 38.300 V17.5.0 specification.

[0040] In some embodiments, the macro BS 100 transmits all SIB messages, SSB messages, and paging messages on behalf of the small BSs 110 in its coverage, thereby saving power at those small BSs 110.

[0041] As introduced above, the present disclosure proposes that the macro BS 100, which is responsible for transmitting control messages for the small BSs 110 in its coverage area 101, may decide, in some scenarios, to request that one or more of these small BSs 110 at least temporarily resume transmitting all or part of these control messages previously transmitted by the macro BS 100 to UEs in the respective coverage areas 111 of these one or more small BSs 110. Such arrangements make it possible to achieve a compromise between saving power at the small BSs 110 and saving power at the macro BS 100.

[0042] The authors now describe various examples of embodiments in which the macro BS 100 may at least temporarily stop transmitting the control messages on behalf of one or more small BSs 110 in its coverage area 101, which take responsibility for transmitting their own control messages that are no longer transmitted by the macro BS 100. Examples that consider a global congestion criterion

[0043] Fig. 2 illustrates a diagram showing steps of an exemplary embodiment of a method 20 for transmitting control messages implemented by a macro OS 100. Fig. 3 illustrates a diagram showing corresponding steps of an exemplary embodiment of a method 30 for transmitting control messages implemented by a small BS 110.

[0044] First, it is assumed that the macro BS 100 transmits control messages on behalf of the small BSs 110 in its coverage area 101. These control messages include, for example, SIB, SSB, and paging messages.

[0045] As through Fig. 2, the method 20 for transmitting control messages comprises a step S20 of evaluating whether a global load of the macro BS 100 due to the UEs and / or the plurality of small BSs 110 in the coverage area 101 of the macro BS verifies a predetermined global congestion criterion.

[0046] By “global,” the authors mean at the level of the macro-BS 100 for the entire coverage area 101 of this macro-BS 100. By “local,” when used below, the authors mean at the level of a small BS 110 for the corresponding coverage area 111 of this small BS 110.

[0047] The global load of the macro BS 100 can be any parameter representative of the amount of data that the macro BS 100 must handle due to the UEs in its coverage area 101 and / or due to the small BSs 110 in its coverage area 101. Essentially, the evaluation step S20 aims at detecting situations in which transmitting control messages on behalf of the small BS 110 may become difficult and / or inefficient for the macro BS 100.

[0048] For example, the global utilization may correspond to the number of small BSs 110 in its coverage area on behalf of which it is currently transmitting or is to transmit control messages. In such a case, the global congestion criterion for the macro BS 100 may be considered verified when this number of small BSs 110 in its coverage area becomes greater than a predetermined first threshold (for example, the first threshold may be equal to 7, and the global congestion criterion is verified when the number of small BSs 110 is equal to or greater than 8). According to another non-limiting example, the global utilization of the macro BS 100 may correspond to the number of UEs in its coverage area or the number of UEs in the respective coverage areas 111 of the small BS 110 on behalf of which the macro BS 100 is currently transmitting or is to transmit control messages.In such a case, the global congestion criterion for the macro BS 100 may be considered verified when this number of UEs becomes greater than a predetermined second threshold.

[0049] As through Fig. 2, if the global overload criterion is not verified (reference symbol S20b in Fig. 2), the macro-BS 100 then continues to transmit the control messages, and the evaluation step S20 can be performed recurrently.

[0050] If the global overload criterion is verified (reference S20a in Fig. 2), then the method 20 for transmitting control messages comprises a step S21, whereby the macro BS 100 instructs at least one small BS 110 to begin transmitting all or part of the control messages previously transmitted by the macro BS 100 to UEs in the coverage area of ​​this at least one small BS 110. For this purpose, the macro BS 100 transmits a corresponding message to the at least one small BS 110, for example, via an X2 interface.

[0051] This at least one small BS 110 may assume responsibility for transmitting all or only a portion of the control messages previously transmitted by the macro BS 100. Thus, if the macro BS 100 previously transmitted the SIB, SSB, and paging messages, this at least one small BS 110 may only need to transmit one of the SIB, SSB, and paging messages, or any combination thereof. Non-limiting examples of how the macro BS 100 may indicate to a small BS 110 which control messages it will assume responsibility for are discussed below. In some examples that maximize power savings at the macro BS 100, the at least one small BS 110 assumes responsibility for transmitting all or all of the control messages previously transmitted by the macro BS 100, i.e., all SIB / SSB / paging messages in the non-limiting example contemplated herein.The macro BS 100 can then, on behalf of this at least one small BS 110, stop transmitting the control messages for which this at least one small BS 110 has assumed responsibility, thereby saving energy.

[0052] The at least one small BS 110 that instructs the macro BS 100 to resume transmitting all or part of the control messages it has previously transmitted may, for example, be randomly selected from the plurality of small BSs 110 in the coverage area 101 of the macro BS 100.

[0053] In other examples, and as in the non-limiting example of Fig. 2, the at least one small BS 110 may be selected based on one or more parameters. In the Fig. 2, the instruction step S21 comprises a step S22 of receiving local utilization reports from the plurality of small BSs 110 in their coverage area 101.

[0054] It is noted that in some cases, the receiving step S22 may be performed independently of the result of the evaluation step S20, e.g., when the small BSs 110 are configured to transmit local load messages recurrently without being prompted to do so. In other examples that enable saving energy at the small BSs 110, the transmission of the local messages by the small BSs 110 is triggered by the fact that the global congestion criterion is verified. In such a case, the macro BS 100 may request (in Fig. 2 not shown) that the plurality of small BSs 110 begin transmitting local utilization reports received by the macro BS 100 during step S22.

[0055] As discussed above, by “local” the authors mean at the level of a small BS 110 for the corresponding coverage area 111 of that small BS 110.

[0056] The local load of a small BS 110 may be any parameter representative of the amount of data that the small BS 110 must handle due to the UEs in its coverage area 111. According to one example, the local load of a small BS 110 may correspond to the number of UEs in its coverage area 111 that the small BS 110 serves. According to another non-limiting example, the local load of a small BS 110 may correspond to the total traffic volume in that small BS 110.

[0057] In the non-limiting example of Fig. 2, the instruction step S21 also includes a step S23 of selecting at least one small BS 110 from the plurality of small BSs 110 based on the received local utilization reports. For example, the macro BS 100 may select the small BS 110 that reported the largest local utilization or a small BS 110 that reports a local utilization above a predetermined threshold. For example, if the local utilization of a small BS 110 corresponds to the number of UEs in its coverage area, the macro BS 100 may select the small BSs 110 that have the largest number of UEs in their coverage area or any small BS 110 that has a number of UEs in its coverage area 111 above a predetermined threshold, etc.

[0058] Selecting one or more small BSs that report the largest local loads may allow increasing energy savings at the macro BS 100. However, other selection strategies may also be considered in the present disclosure.

[0059] It is noted that the selection step S23 may also consider other parameters for selecting at least one small BS 110. For example, and as discussed below, during the selection step S23, the macro BS 100 may also consider the respective distances between the small BSs 110 and the macro BS 100, the respective mobility statuses of the small BSs 110, etc.

[0060] As through Fig. 2, the macro BS 100 instructs (step S24) each selected small BS 110 to begin transmitting all or part of the control messages previously transmitted by the macro BS 100 to UEs in their respective coverage areas 111, as discussed above.

[0061] In some examples, the macro BS 100 may request that the small BSs 110 recurrently transmit local utilization reports. Thus, the macro BS 100 receives consecutive local reports from the small BSs 110, allowing the macro BS 100 to repeat the selection step S23 to verify whether the at least one selected small BS 110 needs to be replaced by another small BS 110. Indeed, the number of UEs in the coverage areas 111 of the small BSs 110 may evolve over time, so that, for example, the small BS 110 among the plurality of small BSs 110 reporting the greatest local utilization may also change over time. Thus, in some cases, if the small BS 110 reporting the greatest changes in local utilization changes, the macro BS 100 may, for example: - instruct the previously selected small BS 110 to stop transmitting the control messages for which it has assumed responsibility, the transmission of which the macro BS 100 will resume, - instruct the newly selected small BS 110 to start transmitting all or part of the control messages previously transmitted by the macro BS 100 to UEs in its coverage area 111 (those control messages that the macro BS 100 may stop transmitting).

[0062] For example, the small BSs 110 may be instructed to periodically transmit local utilization messages. The transmission period used to periodically transmit local utilization messages may be predefined and / or may vary between one small BS 110 and another. In some examples, the respective transmission periods for the small BSs 110 may be set by the macro BS 100. In such a case, the macro BS 100 may set the same transmission period for all small BSs 110, or it may set different transmission periods for different small BSs 110. In some examples, the macro BS 100 may adjust the different transmission periods based on the received local utilization messages.For example, small BSs 110 reporting severe local loads may be configured with longer transmission periods than small BSs 110 reporting low local loads. Alternatively, or in combination, and as discussed below, the macro BS 100 may adjust the different transmission periods based on the respective distances between the small BSs 110 and the macro BS 100, the respective mobility statuses of the small BSs 110, etc.

[0063] As discussed above, Fig. 3 is a diagram showing corresponding steps of an exemplary embodiment of a method 30 for transmitting control messages that can be implemented by a small BS 110 when the macro BS 100 implements the method 20 for transmitting control messages that can be implemented by Fig. 2 is implemented.

[0064] As through Fig. 3, the method 30 for transmitting control messages includes a step S30 of receiving an instruction (transmitted by the macro BS 100 during step S21) to resume transmitting all or part of the control messages previously transmitted by the macro BS to UEs in the coverage area of ​​the small BS 110. In response to receiving such an instruction from the macro BS 100, the small BS 110 resumes transmitting the control messages for which it has assumed responsibility and which were previously transmitted by the macro BS 100 to UEs in the coverage area 111 of the small BS 110 during a step S31.

[0065] In some embodiments and as Fig. 3, the method 30 for transmitting control messages may include a step S32 of transmitting a local utilization report to the macro-BS 100 prior to receiving the instruction to begin transmitting all or part of the control messages. As discussed above, the transmitting step S32 may, in some cases, be performed in response to receiving a corresponding request to do so from the macro-BS 100 (in Fig. 3 not shown). As discussed above, the small BS 110 may transmit local utilization messages recurringly or, preferably, periodically, with a transmission period that may be determined by the macro BS 100.

[0066] It is noted that the macro-BS 100 may return to transmitting the control messages to all small BSs 110 in its coverage area, e.g., when the global load of the macro-BS 100 is reduced to an acceptable level. Thus, the macro-BS 100 may also perform a step (not shown in the figures) of evaluating whether the global load verifies a predetermined global normal load criterion (e.g., when the number of small BSs 110 becomes lower than a predetermined threshold, preferably equal to or lower than the threshold considered for the global congestion criterion). If the global normal load criterion is verified, i.e.,When the global utilization is reduced to an acceptable level, the macro BS 100 may resume transmitting the control messages for all small BSs 110 and may instruct the small BSs 110 that have transmitted all or part of the control messages to stop doing so. Examples that take into account a local congestion criterion

[0067] Fig. 4 illustrates a diagram showing steps of an exemplary embodiment of a method 40 for transmitting control messages implemented by a small BS 110. Fig. 5 illustrates a diagram showing corresponding steps of an exemplary embodiment of a method 50 for transmitting control messages implemented by a macro OS 100.

[0068] First, it is assumed that the macro BS 100 transmits control messages on behalf of the small BSs 110 in its coverage area 101. These control messages include, for example, SIB, SSB, and paging messages.

[0069] As through Fig. 4, the method 40 for transmitting control messages comprises a step S40 of evaluating whether a local load of the small BS 110 due to the UEs in its coverage area 111 verifies a predetermined local congestion criterion.

[0070] As discussed above, by “local” the authors mean at the level of the small BS 110 for the corresponding coverage area 111 of that small BS 110.

[0071] The local load of the small BS 110 can be any parameter representative of the amount of data that the small BS 110 must handle due to the UEs in its coverage area 111. Essentially, the evaluation step S40 aims to detect situations in which the contribution of the local load of the small BS 110 to the global load of the macro BS 100 transmitting control messages for the considered small BS 110 becomes significant.

[0072] For example, the local load of the small BS 110 may correspond to the number of UEs in its coverage area 111 (for which the macro BS 100 is currently transmitting or is intended to transmit control messages). In such a case, the local congestion criterion for the small BS 110 may be considered verified when this number of UEs in its coverage area 111 becomes greater than a predetermined first threshold. Such a first threshold may, for example, be predefined or set by the macro BS 100, etc. According to another non-limiting example, the local load of a small BS 110 may correspond to the total traffic volume in this small BS 110, in which case the local congestion criterion for the small BS 110 may be considered verified when this total traffic volume becomes too severe (e.g., greater than a predetermined threshold).

[0073] As through Fig. 4, if the local overload criterion is not verified (reference S40b in Fig. 4), the small BS 110 then executes the evaluation step S40 again later.

[0074] If the local overload criterion is verified (reference S40a in Fig. 4), then the method 40 for transmitting control messages comprises a step S41, whereby the small BS 110 informs the macro BS 100 that the local congestion criterion is verified by transmitting a corresponding message to the macro BS 100, for example via an X2 interface.

[0075] Once the macro BS 100 has been informed that the local congestion criterion for the small BS 110 is verified, it may decide to request that this small BS 110 begin transmitting all or part of the control messages for UEs in the coverage area 111 of this small BS 110. In such a case, the method 40 for transmitting control messages comprises a step S42 of receiving, by the small BS 110 and from the macro BS 100, an instruction to begin transmitting all or part of the control messages previously transmitted by the macro BS 100 to UEs in its coverage area. The method 40 for transmitting control messages then comprises a step S43, whereby the small BS 110 begins transmitting these control messages to UEs in its coverage area 111.As discussed above, the small BS 110 may assume responsibility for transmitting all or only a portion of the control messages previously transmitted by the macro BS 100. Thus, if the macro BS 100 previously transmitted the SIB, SSB, and paging messages, that small BS 110 may only need to transmit one of the SIB, SSB, and paging messages, or any combination thereof. Non-limiting examples of how the macro BS 100 may indicate to a small BS 110 which control messages it will assume responsibility for are discussed below. In some examples that maximize power savings at the macro BS 100, the small BS 110 assumes responsibility for transmitting all or all of the control messages previously transmitted by the macro BS 100—that is, all of the SIB / SSB / paging messages in the non-limiting example contemplated herein.The macro BS 100 can then, on behalf of this small BS 110, stop transmitting the control messages for which this small BS 110 has assumed responsibility.

[0076] Fig. 4 also illustrates a non-limiting example of how the macro BS can resume transmitting control messages for the small BS 110 under consideration. In principle, in this example, the macro BS 100 can resume transmitting control messages once the local load of the small BS 110 is reduced to an acceptable level. However, other examples are possible. For example, the macro BS 100 can resume transmitting control messages for the small BS 110 under consideration after a predetermined timer has expired, after a predetermined number of control messages have been transmitted by the small BS 110, etc.

[0077] In the non-limiting example of Fig. 4, the method 40 for transmitting control messages comprises, after the small BS 110 has started transmitting control messages, a step S44 of evaluating whether the local utilization of the small BS due to the UEs in its coverage area 111 verifies a predetermined local normal utilization criterion. Essentially, the evaluation step S44 aims to detect situations in which the contribution of the local utilization of the small BS 110 to the global utilization of the macro BS 100 returns to an acceptable level, thereby allowing the macro BS 100 to resume transmitting control messages on behalf of the small BS 110 under consideration.

[0078] For example, if the local utilization of the small BS 110 corresponds to the number of UEs in its coverage area 111, then the local normal utilization criterion is verified, for example, when the number of UEs in the coverage area of ​​the small BS 110 becomes lower than a predetermined second threshold. This second threshold may be equal to the first threshold introduced above for the local congestion criterion. In preferred examples, this second threshold is lower than the first threshold of the local congestion criterion to avoid constantly alternating between local congestion and local normal utilization when the number of UEs fluctuates around the first threshold. Such a second threshold may, for example, be predefined or set by the macro BS 100, etc.

[0079] As through Fig. 4, if the local normal load criterion is not verified (reference symbol S44b in Fig. 4), the small BS 110 will then continue to transmit the control messages for which it has assumed responsibility.

[0080] If the local normal load criterion is verified (reference S44a in Fig. 4), then the method 40 for transmitting control messages comprises a step S45, whereby the small BS 110 informs the macro BS 100 that the local normal load criterion is verified by transmitting a corresponding message to the macro BS 100, for example via the X2 interface.

[0081] Once the macro BS 100 has been informed that the local normal utilization criterion for the small BS 110 has been verified, it may decide to request that this small BS 110 cease transmitting the control messages for UEs in its coverage area. In such a case, the method 40 for transmitting control messages comprises a step S46 of receiving, by the small BS 110 and from the macro BS 100, an instruction to cease transmitting the control messages. The method 40 for transmitting control messages then comprises a step S47, whereby the small BS 110 interrupts the transmission of the control messages for which it had previously assumed responsibility, the transmission of which the macro BS 100 resumes on behalf of this small BS 110.

[0082] As discussed above, Fig. 5 is a diagram showing corresponding steps of an exemplary embodiment of a method 50 for transmitting control messages that may be implemented by the macro BS 100 when a small BS 110 implements the method 40 for transmitting control messages implemented by

[0083] Fig. 4 is implemented.

[0084] As through Fig. 5, the method 50 for transmitting control messages comprises a step S50 of receiving, from a small BS 110, an indication that a local load of this small BS 110 due to the UEs of its coverage area 111 verifies a local congestion criterion.

[0085] Based on this indication received from the small BS 110, the macro BS 100 may decide to stop transmitting all or part of the control messages on behalf of this small BS 110. In this case, the method 50 for transmitting control messages comprises a step S51 of instructing the small BS 110 from which an indication was received to resume transmitting all or part of the control messages previously transmitted by the macro BS 100 to UEs in its coverage area. The macro BS 100 may then stop transmitting the corresponding control messages that the small BS 110 has started transmitting or is about to transmit.

[0086] In some examples, the macro BS 100 may decide to automatically instruct a small BS 110, for which the local congestion criterion is verified, to begin transmitting its own control messages. However, in other examples, the macro BS 100 may consider other parameters to decide whether the small BS 110 should begin transmitting all or part of its control messages. In the non-limiting example of Fig. 5, the method 50 for transmitting control messages comprises a step S52 of evaluating, by the macro-BS 100, whether a global load verifies a predetermined global congestion criterion. If the global congestion criterion is verified (reference symbol S52a in Fig. 5), then the macro BS 100 instructs the small BS 110 to start transmitting all or part of its control messages. If the global congestion criterion is again not verified (reference symbol S52b in Fig. 5), then the macro BS 100 continues to transmit the control messages on behalf of the small BS 110. Everything said above with regard to the global overload criterion (and the global normal load criterion) applies similarly to the examples described by Fig. 4 and Fig. 5 are illustrated.

[0087] As discussed above, in some examples, the small BS 110 may also transmit an indication that a local normal utilization criterion is verified. In such cases, as illustrated by the example of Fig. 5, the method 50 for transmitting control messages may comprise a step S53 of receiving an indication that the local load of the small BS 110 verifies a local normal load criterion, and a further step S54 of instructing the small BS 110 to stop transmitting all or part of the control messages for which it had previously assumed responsibility (the control messages which the macro BS 100 then resumes transmitting). Examples that take into account the selection of tax message types

[0088] Fig. 6 illustrates a diagram showing steps of an exemplary embodiment of a method 60 for transmitting control messages implemented by a macro OS 100. Fig. 7 illustrates a diagram showing corresponding steps of an exemplary embodiment of a method 70 for transmitting control messages implemented by a small BS 110.

[0089] First, it is assumed that the macro BS 100 transmits control messages on behalf of the small BSs 110 in its coverage area 101.

[0090] As through Fig. 6, the method 60 for transmitting control messages comprises a step S60 of selecting a small BS 110 from the plurality of small BSs for which the macro BS 100 transmits control messages. For example, the macro BS 100 may randomly select a small BS 110 from the plurality of small BSs 110 in the coverage area 101 of the macro BS 100. In other examples, the small BS 110 may be selected based on one or more parameters. For example, during the selection step S60, the macro BS 100 may use local utilization reports received from the small BSs 110, as discussed hereinabove. Other examples of parameters that may be considered during the selection step S60 alternatively or in combination therewith include, for example, B. the respective distances between the small BSs 110 and the macro BS 100, the respective mobility statuses of the small BSs 110, etc.

[0091] In the example of Fig. 6, the method 60 for transmitting control messages also includes a step S61 of selecting control message types from the various control message types that the macro BS 100 is currently transmitting for the selected small BS 110 to be transmitted by this selected small BS 110.

[0092] For example, the different possible control message types may correspond to i) SIB control messages, ii) SSB control messages, and iii) paging control messages. Thus, the macro BS 100 may select any one of these control message types or any combination thereof. For example, the macro BS 100 may select a single control message type, e.g., paging control messages. The macro BS 100 may also select two control message types, e.g., both SIB and SSB control messages. The macro BS 100 may also decide to select all different control message types, i.e., all SIB / SSB / paging control messages.

[0093] The selection of control message types may use any suitable selection strategy. For example, the number of different control message types selected may depend on the desired amount of power savings (i.e., the macro OS 100 may increase the number of different control message types selected to increase power savings).

[0094] In the example of Fig. 6, the method 60 for transmitting control messages includes a step S62 of transmitting, to the selected small BS 110, an indication of the selected control message types previously transmitted by the macro BS 100, which the selected small BS 110 is to initiate transmission to the UEs in its coverage area 111. This indication is transmitted, for example, to the selected small BS 110 via an X2 interface.

[0095] The selected small BS 110 then assumes responsibility for transmitting all control message types mentioned in the indication received from the macro BS 100, which were previously transmitted by the macro BS 100. The macro BS 100 can then, on behalf of this selected small BS 110, stop transmitting the control message types for which the selected small BS 110 has assumed responsibility. For SIB, SSB, and paging control message types, for example, if the indication transmitted to the selected small BS 110 only mentions the SIB control message type, the macro BS 100 continues to transmit SSB and paging messages. If the indication transmitted to the selected small BS 110 mentions all SIB / SSB / paging control message types, the macro BS 100 can stop transmitting control messages on behalf of the selected small BS 110.

[0096] It is noted that the indication transmitted to the selected small BS 110 may directly indicate the control message types that the selected small BS 110 should begin transmitting, or indirectly by indicating the control message types that the macro BS 100 will continue transmitting. In the latter case, the selected small BS 110 will begin transmitting the control message types not explicitly mentioned in the received indication. In the following, the authors consider, in a non-limiting manner, the case where the indication explicitly mentions the control message types that the selected small BS 110 should begin transmitting.

[0097] In some examples, the indication of the control message types to be transmitted may be provided as a bit vector. The bit vector may, for example, comprise one bit per control message. In the example considered here for SIB, SSB, and paging control message types, it is therefore possible to use three bits. With three bits and three different control message types, it is therefore possible to specify any single control message type and any combination thereof (and even no control message type at all, e.g., if the selected small BS 110 is to stop transmitting control messages). It is also possible to use more bits or even fewer bits.For example, for SIB, SSB, and paging control message types, it is possible to use only two bits, either specifying which individual control message type from the SIB, SSB, and paging control message types should be transmitted by the small BS, or specifying that the small BS should transmit all SIB, SSB, and paging control message types. For example, it is possible to use a 2-bit vector as follows: - a bit vector set to '00' means that the selected small BS 110 should start transmitting SSB messages, - a bit vector set to '01' means that the selected small BS 110 should start transmitting SIB messages, - a bit vector set to '10' means that the selected small BS 110 should start transmitting paging messages, - a bit vector set to '11' means that the selected small BS 110 should start transmitting all SIB / SSB / paging messages.

[0098] In some examples, the macro BS 100 may decide to automatically select a small BS 110 to receive the transmission. However, in other examples, the macro BS 100 may consider other parameters to decide whether a small BS 110 should be selected to receive the transmission of all or part of its control messages. As previously referred to Fig. 4 and Fig. 5, the selection step S60 may be performed in response to receiving, from a small BS 110, an indication that a local congestion criterion is verified.

[0099] In the non-limiting example of Fig. 6, the selection step S60 is performed in response to verifying a global congestion criterion, and the method 60 for transmitting control messages comprises a step S63 of evaluating whether a global load of the macro-BS 100 verifies a predetermined global congestion criterion. If the global congestion criterion is verified (reference symbol S63a in Fig. 6), then the selection steps S60 and S61 are executed by the macro-BS 100. If the global overload criterion is again not verified (reference symbol S63b in Fig. 6), then the selection steps S60 and S61 are not executed. Everything stated above with regard to the global overload criterion (and the global normal load criterion) applies similarly to the examples described by Fig. 6 and Fig. 7 are illustrated.

[0100] As discussed above, Fig. 7 is a diagram showing corresponding steps of an exemplary embodiment of a method 70 for transmitting control messages that can be implemented by a small BS 110 when the macro BS 100 implements the method 60 for transmitting control messages that can be implemented by Fig. 6 is implemented.

[0101] As through Fig. 7, the method 70 for transmitting control messages includes a step S70 of receiving, from the macro BS 100, an indication (e.g., as a bit vector) about which control message types, from, e.g., the SIB, SSB, and paging control message types previously transmitted by the macro BS 100, the small BS 110 should initiate transmission to UEs in its coverage area 111. In response to receiving such an indication from the macro BS 100, the small BS 110 initiates transmission of the control message types indicated by the macro BS 100 to UEs in its coverage area 111 during step S71.

[0102] Examples that take into account a distance and / or a mobility status

[0103] Fig. 8 illustrates a diagram showing steps of an exemplary embodiment of a method 80 for transmitting control messages implemented by a macro OS 100. Fig. 9 illustrates a diagram showing corresponding steps of an exemplary embodiment of a method 90 for transmitting control messages implemented by a small BS 110.

[0104] First, it is assumed that the macro BS 100 transmits control messages on behalf of the small BSs 110 in its coverage area 101. These control messages include, for example, SIB, SSB, and paging messages. Fig. 8 and Fig. The examples shown in Figure 9 focus on how the macro BS 100 can select a small BS 110 to start transmitting control messages.

[0105] As through Fig. 8, the method 80 for transmitting control messages comprises a step S80 of selecting at least one small BS 110 from the plurality of small BSs 110 to start transmitting all or part of the control messages previously transmitted by the macro BS 100. In the Fig. In the example illustrated in Figure 8, the selection is based on respective distances between the plurality of small BSs 110 and the macro BS 100.

[0106] In fact, the distance to the macro BS 100 is a parameter that may be of interest in the context of NES functions.

[0107] For example, if the macro BS 100 uses the same transmission power to transmit control messages for all small BSs 110, then this transmission power may be unnecessarily high for a small BS 110 located near the macro BS 100. In such a case, it may be more efficient to select the small BS 110 closest to the macro BS 100, since the control messages can be transmitted with a lower transmission power when transmitted by the nearest small BS 110 than if they were transmitted by the macro BS 100, or to select small BSs 110 that have distances smaller than a predetermined threshold (i.e., that are located near the macro BS 100).

[0108] According to another example, when adapting the transmission power to the receiving UEs, the macro BS 100 will use a higher transmission power for UEs in the coverage area 111 of a small BS 110 located far from the macro BS 100 than for UEs in the coverage area 111 of a small BS 110 located close to the macro BS 100. In such a case, it may be more efficient to select the small BS 110 that is farthest away from the macro BS 100, since in such a case the control messages can be transmitted with a lower transmission power when transmitted by the farthest small BS 110 than if they were transmitted by the macro BS 100, or to select the small BSs 110 that have distances greater than a predetermined threshold (i.e., that are far away from the macro BS 100).

[0109] The distances between the small BSs 110 and the macro BS 100 may be determined using any suitable method. In some examples, the distances may be determined by the macro BS 100 without relying on specific data received by the small BS 110. For example, the received power of radio signals received by the small BSs 110 may be used to sort the small BSs 110 from nearest (highest received power) to farthest (lowest received power). In some examples, however, the macro BS 100 may use specific data received from the small BSs 110 to sort the small BSs 110 from nearest to farthest. This is the case in the non-limiting example illustrated by Fig. 8, in which the small BSs 110 transmit distance reports that are received by the macro BS 100 during step S82. Essentially, a distance report from a small BS 110 is representative of a distance between that small BS 110 and the macro BS 100 and corresponds to any information that enables the macro BS 100 to sort the small BSs 110 according to their distances to the macro BS 100. For example, the distance report from a small BS 110 may directly contain an estimate of the distance between that small BS 110 and the macro BS 100, as estimated by the small BS 110. According to other non-limiting examples, the distance report from a small BS 110 may contain any information that enables the macro BS 100 to estimate the distance to that small BS 110.Such a distance message may, for example, contain an estimated position of the small BS 110 (for example, provided by a GPS module of the small BS 110), which the macro BS 100 may compare with its own estimated position (for example, provided by a GPS module of the macro BS 100) to estimate the distance to this small BS 110.

[0110] The distances received in the distance messages or derived from information contained in the received distance messages are then used during the selection step S80 to select the at least one small BS 110 that is to start transmitting its own control messages.

[0111] It is noted that for a small BS 110 that is stationary (i.e., non-mobile) with respect to the macro BS 100, it is sufficient for the macro BS 100 to receive a single distance message, since the distance between a stationary small BS 110 and the macro BS 100 is not expected to vary over time. However, if a small BS 110 is non-stationary (i.e., mobile) with respect to the macro BS 100, then in some examples, such a non-stationary small BS 110 may transmit successive distance messages to the macro BS 100 in a recurring manner to inform the macro BS 100 how the distance to this non-stationary small BS 110 varies over time. Such recurring distance messages can be transmitted more frequently by a small BS 110 that moves quickly relative to the macro BS 100 than by a small BS 110 that moves slowly in this regard.In some examples, the selecting step S80 may be performed each time it is determined that the sorting of the small BSs 110 according to their distances from the macro BS 100 may have changed.

[0112] In some examples, the small BSs 110 may decide for themselves whether they should transmit distance messages recurringly. In other examples, the macro BS 100 may decide which small BSs 110 should transmit recurring distance messages. This is the case in the non-limiting example of Fig. 8, in which the method 80 for transmitting control messages comprises: a step S83 of receiving, by the macro BS 100, mobility status messages from the plurality of small BSs and a step S84 of instructing small BSs 110 that are not stationary according to the received mobility status messages to transmit distance messages in a recurring manner, preferably periodically.

[0113] Essentially, a mobility status message of a small BS 110 is representative of whether the small BS is stationary (i.e., non-mobile) or non-stationary (i.e., mobile) relative to the macro BS 100. In simple terms, the mobility status message may consist of two possible states, i.e., stationary or non-stationary. In other examples, the mobility status message for a non-stationary small BS 110 may provide an indication of the movement speed of the small BS 110, e.g., fast-moving or slow-moving. In the latter case, the macro BS 100 may further adjust the respective transmission periods of distance messages by the non-stationary small BS 110. For example, the macro BS 100 may configure a fast-moving small BS 110 with a shorter transmission period (i.e., more frequent transmissions) than a slower-moving BS 110.

[0114] As through Fig. 8, the method 80 for transmitting control messages includes a step S81, whereby the macro BS 100 instructs the at least one selected small BS 110 to begin transmitting all or part of the control messages previously transmitted by the macro BS 100 to UEs in the coverage area of ​​this at least one small BS 110. For this purpose, the macro BS 100 transmits a corresponding message to the at least one selected small BS 110, for example, via an X2 interface. As discussed above, this at least one selected small BS 110 may assume responsibility for transmitting all or only part of the control messages previously transmitted by the macro BS 100.The macro BS 100 can then, on behalf of this at least one small BS 110, stop transmitting the control messages for which this at least one selected small BS 110 has assumed responsibility, thereby saving energy.

[0115] In some examples, the selection step S80 may only consider the respective distances between the small BSs 110 and the macro BS 100.

[0116] However, the selection step S80 may also consider other parameters for selecting at least one small BS 110. For example, during the selection step S80, the macro BS 100 may also consider the respective local loads of the small BSs 110 in addition to the respective distances between the small BSs 110 and the macro BS 100. This is the case in the non-limiting example illustrated by Fig. 8, in which the method 80 for transmitting control messages comprises a step S85 of receiving local utilization reports from the plurality of small BSs 110 used during the selection step S80 in addition to the respective distances between the small BSs 110 and the macro BS 100.

[0117] Everything that has been said above with regard to local utilization applies similarly to the examples that are Fig. 8 and Fig. 9. For example, the local utilization of a small BS 110 may correspond to the number of UEs in the coverage area 111 of that small BS 110. In such a case, the macro BS 100 may, for example, select at least the small BS 110 furthest from the macro BS (or the closest, as discussed above) that has a number of UEs in its coverage area greater than a predetermined threshold. Of course, it is also possible to consider other selection strategies during the selection step S80.

[0118] As discussed above, Fig. 9 is a diagram showing corresponding steps of an exemplary embodiment of a method 90 for transmitting control messages that can be implemented by a small BS 110 when the macro BS 100 implements the method 80 for transmitting control messages implemented by Fig. 8 is implemented.

[0119] As through Fig. 9, the method 90 for transmitting control messages includes a step S90 of receiving an instruction (transmitted by the macro BS 100 during step S81) to resume transmitting all or part of the control messages previously transmitted by the macro BS 100 to UEs in the coverage area of ​​the small BS 110. In response to receiving such an instruction from the macro BS 100, the small BS 110 resumes transmitting the control messages for which it has assumed responsibility and which were previously transmitted by the macro BS 100 to UEs in the coverage area 111 of the small BS 110 during a step S91.

[0120] In some embodiments, and as in the non-limiting example of Fig. 9, the method 90 for transmitting control messages may include a step S92 of transmitting a distance message to the macro BS 100 before receiving the instruction to begin transmitting all or part of the control messages. As discussed above, the small BS 110 may transmit a single distance message (e.g., if it is stationary) or consecutive distance messages (e.g., if it is not stationary). In the latter case, a small BS 110 may transmit the distance messages periodically with a transmission period determined by the macro BS 100.

[0121] In some embodiments, and as in the example of Fig. 9, the method 90 for transmitting control messages may include: - a step S95 of transmitting a local load message to the macro BS 100 (which may be transmitted recurrently to inform the macro BS 100 how the local load of the small BS 110 varies over time), and / or - a step S93 of transmitting a mobility status message to the macro BS 100 (which may be transmitted recurrently to inform the macro BS 100 how the mobility status of the small BS 110 varies over time), which in some examples may be accompanied by a step S94 of receiving instructions regarding distance messages (e.g., recurrent or not, transmission period, etc.).

[0122] Fig. Figure 10 schematically illustrates an architecture example for a BS 120, whose architecture can be used either for a macro BS 100 or a small BS 110, or for both. Thus, the architecture of the BS 120 in Fig. 10 is suitable for implementing any method for transmitting control messages discussed in the present disclosure.

[0123] As through Fig. 10, the OS 120 includes one or more processors 121 (which may belong to the same computer or to different computers) and one or more memories 122 (which may belong to the same computer or to different computers). The one or more processors 121 may include, for example, a central processing unit (CPU), a digital signal processor (DSP), a field-programmable gate array (FPGA), an application-specific integrated circuit (ASIC), etc. The one or more memories 122 may include any type of computer-readable volatile and non-volatile memory (magnetic hard disk, solid-state memory, optical disk, electronic memory, etc.).The one or more memories may store a computer program product 123 in the form of a set of program-encoded instructions to be executed by the one or more processors to implement all or a portion of the steps of a method for transmitting control messages according to any of the embodiments disclosed herein.

[0124] As through Fig. As illustrated in Figure 10, the BS 120 also includes a wireless communication unit 124 configured to exchange data with UEs using radio signals. The wireless communication unit 124 may be, for example, a 3G, 4G, 5G, NR, WiFi, WiMAX, etc., transceiver, or the like.

[0125] As through Fig.As illustrated in Figure 10, the BS 120 also includes a network communication unit 125 configured to exchange data with other base stations of the RAN. The network communication unit 125 is used to exchange data between a macro BS 100 and a small BS 110, for example, via the X2 interface. The network communication unit 125 can also be used to exchange data with a CN. The network communication unit 125 can support one or more suitable communication protocols that are hardwired (including fiber optic) and / or wireless.

Claims

[1] A method (80) for transmitting control messages in a wireless communication system, the wireless communication system comprising a macro base station (BS) and a plurality of small BSs located in a coverage area of ​​the macro BS, the macro BS (100) transmitting control messages for the plurality of small BSs to user equipment (UEs) in respective coverage areas of the plurality of small BSs (110), the method being implemented by the macro BS and comprising: - selecting (S80) at least one small BS from the plurality of small BSs based on respective distances between the plurality of small BSs and the macro BS, - instructing (S81) the at least one selected small BS to start transmitting all or part of the control messages previously transmitted by the macro BS to UEs in the coverage area of ​​said at least one selected small BS. [2] The method (80) of claim 1, wherein the at least one selected small BS includes the small BS that is farthest from or closest to the macro BS. [3] The method of claim 1, comprising receiving (S85) local utilization reports from the plurality of small BSs, wherein a local utilization report from a small BS is representative of a local utilization of that small BS due to the UEs in its coverage area, and wherein selecting (S80) at least one small BS from the plurality of small BSs is further based on the received local utilization reports. [4] The method (80) of claim 3, wherein the local utilization message transmitted by a small BS is representative of the number of UEs located in the coverage area of ​​that small BS, and wherein the at least one selected small BS includes the small BS that is the furthest from or closest to the macro BS having a number of UEs in its coverage area greater than a threshold. [5] The method (80) of any preceding claim, comprising receiving (S82) distance reports from the plurality of small BSs, wherein a distance report from a small BS is representative of a distance between that small BS and the macro BS. [6] The method (80) of claim 5, comprising receiving successive distance reports from a same small BS that is not stationary. [7] Method (80) according to one of claims 5 to 6, comprising: - receiving (S83) mobility status messages from the plurality of small BSs, wherein a mobility status message of a small BS is representative of whether the small BS is stationary or non-stationary, - Requesting (S84) that small BSs that are not stationary according to the received mobility status messages transmit distance reports in a recurring manner, preferably periodically. [8] The method (80) of claim 7, wherein the macro BS configures respective transmission periods of distance messages by the plurality of small BSs based on the received mobility status messages. [9] A method (90) for transmitting control messages in a wireless communication system, the wireless communication system comprising a macro base station (BS) and a plurality of small BSs located in a coverage area of ​​the macro BS, the macro BS (100) transmitting control messages for the plurality of small BSs to user equipment (UEs) in respective coverage areas of the plurality of small BSs (110), the method being implemented by a small BS of the plurality of small BSs and comprising: - receiving (S90), from the macro BS, an instruction to start transmitting all or part of the control messages previously transmitted by the macro BS to UEs in the coverage area of ​​the small BS, - transmitting (S91) all or part of the control messages previously transmitted by the macro BS to UEs in the coverage area of ​​the small BS. [10] The method (90) of claim 9, comprising transmitting (S92), by the small BS, a distance message to the macro BS, wherein the distance message from a small BS is representative of a distance between that small BS and the macro BS. [11] The method (90) of claim 10, wherein, while the small BS is not stationary, said small BS transmits distance messages in a recurring manner, preferably periodically. [12] The method (90) of claim 11, wherein the small BS transmits distance messages periodically with a transmission period determined by the macro BS. [13] Method (90) according to one of claims 9 to 12, comprising: - transmitting (S95) a local load message to the macro BS, the local load message being representative of a local load of the small BS due to the UEs in its coverage area, and / or - transmitting (S93) a mobility status message to the macro BS, wherein the mobility status message is representative of whether the small BS is stationary or non-stationary. [14] The method (90) of any preceding claim, wherein the control messages transmitted by the macro BS for the plurality of small BSs include system information block (SIB) messages, synchronization signal / physical broadcast channel block (SSB) messages, and paging messages, and transmitting all or part of the control messages by a small BS corresponds to transmitting at least one of the SIB messages, the SSB messages, and the paging messages. [15] A computer program product comprising instructions that, when executed by at least one processor, configure the at least one processor to perform a method (80) according to any one of claims 1 to 8 and / or a method (90) according to any one of claims 9 to 14. [16] A computer-readable storage medium comprising instructions that, when executed by at least one processor, configure the at least one processor to perform a method (80) according to any one of claims 1 to 8 and / or a method (90) according to any one of claims 9 to 14. [17] Base station (BS - base station) (120), comprising at least one memory (122) and at least one processor (121) configured to carry out a method (80) according to one of claims 1 to 8 and / or a method (90) according to one of claims 9 to 14. [18] A wireless communication system comprising a macro base station (BS) and a plurality of small BSs located in a coverage area of ​​the macro BS, wherein the macro BS (100) transmits control messages for the plurality of small BSs to user equipment (UEs) in respective coverage areas of the plurality of small BSs (110), wherein: - the macro-OS comprises at least one memory and at least one processor configured to perform a method (80) according to any one of claims 1 to 8, - each small BS comprises at least one memory and at least one processor configured to perform a method (90) according to any one of claims 9 to 14.

Images