TECHNICAL FIELD

The present disclosure relates to a method, performed in a network node, of controlling energy consumption in a wireless backhaul link between a backhaul client of a low power radio base station, RBS, and a backhaul hub of the wireless network.

BACKGROUND

3GPP Long Term Evolution, LTE, is the fourth-generation mobile communication technologies standard developed within the 3rd Generation Partnership Project, 3GPP, to improve the Universal Mobile Telecommunication System, UMTS, standard to cope with future requirements in terms of improved services such as higher data rates, improved efficiency, and lowered costs. In a typical cellular radio system, wireless terminals also known as mobile stations and/or user equipment units, UEs, communicate via a radio access network, RAN, to one or more core networks. The Universal Terrestrial Radio Access Network, UTRAN, is the radio access network of a UMTS and Evolved UTRAN, E- UTRAN, is the radio access network of an LTE system. In an UTRAN and an E-UTRAN, a User Equipment, UE, is wirelessly connected to a Radio Base Station, RBS, commonly referred to as a NodeB, NB, in UMTS, and as an evolved NodeB, eNB or eNodeB, in LTE. An RBS is a general term for a radio network node capable of transmitting radio signals to a UE and receiving signals transmitted by a UE. There are numerous solutions addressing increasing demands of capacity and coverage in a mobile wireless network. One technique is a heterogeneous network deployment, wherein low power radio base stations provide enhanced coverage in a macro cell defined by a high power base station. In the following, the term Pico radio base station, Pico RBS, will be used to denominate a low power radio base station. The term macro RBS will be used to denominate a high power radio base station. A heterogeneous network deployment is, for example, found in urban areas where macro RBS are located to provide radio coverage in large areas, e.g. on a roof top, while Pico RBS are situated to provide local coverage near crowded areas, e.g. on building walls or lamp posts. In the heterogeneous deployment situation, there is usually a large number of Pico RBS deployed within the coverage area of one macro RBS.

The Pico RBS is usually configured to provide one or more combinations of radio access technologies over the radio access link, e.g. 3GPP LTE, 3GPP HSPA, 3GPP GSM or IEEE 802. llx, also known as Wi-Fi. Each Pico RBS is connected to the wireless network by means of a backhaul link. In the present disclosure, the backhaul link is a wireless backhaul link set up between the Pico RBS and a backhaul hub in the wireless network. The macro RBS is set up to function as a backhaul hub. The wireless backhaul link can either be implemented using microwave radio communication between the Pico RBS and the macro RBS. It is also common to implement the wireless backhaul link using a 3GPP radio access technology, e.g. 3GPP LTE. For such situations, the backhaul link is typically implemented by using a wireless device; also known as user equipment, UE, embedded into the Pico RBS. The wireless backhaul link is set up as an always on circuit switched backhaul. On the hub side of the backhaul link, the receiving macro RBS handles the connection as wireless connection to a connected user equipment, UE. Typically more than one Pico RBS will have a backhaul link to the same backhaul hub, i.e. to a macro RBS. Radio resource management functions are used in the backhaul hub to handle scheduling and prioritization of traffic on the backhaul links to Pico RBSs.

Heterogeneous network deployments are used to meet high traffic demands. However, the traffic over a Pico RBS varies very much at different periods of time. The traffic over a Pico RBS can for example be very high during rush hour, when people are moving back and forth to their respective work places and much lower during weekends or at night time. In order to address such traffic scenarios, different activity levels of the pico RBS are foreseen wherein the pico RBS is in an active mode when traffic load is high or in a dormant mode when there is no traffic.

However, the present solutions are not optimized for the disclosed traffic scenarios. For example, the power consumption in a wireless backhaul of a Pico RBS is considerable regardless of the current traffic demand in the Pico RBS. Therefore, there is a need for a solution to control backhaul energy consumption in a Pico RBS having a wireless backhaul link to a backhaul hub. SUMMARY

It is an object of the present disclosure to provide embodiments solving the problem of controlling energy consumption in a Pico RBS having a wireless backhaul.

The inventors have realized that one problem for wireless backhauls is that the backhaul link is maintained in an active mode having high energy consumption regardless of a current activity level or mode of the Pico RBS, e.g. when a dormant mode has been initiated in the pico RBS.

The proposed solution enables reduced energy consumption for a wireless backhaul link from a low power radio base station, RBS, to a backhaul hub by detecting periods when an activity level of the low power RBS is low.

This is achieved by a method performed in a network node, a network node configured to perform the method and a computer-readable storage medium including a computer program run in the network node.

The disclosure presents a method embodiment, performed in a network node, of controlling energy consumption in a wireless backhaul link between a backhaul client of a low power radio base station, RBS, and a backhaul hub of the wireless network. The method comprises estimating a wireless backhaul link traffic demand for the low power RBS. A backhaul power mode is selected from two or more backhaul power modes for the wireless backhaul link of the low power RBS based on the determined wireless backhaul link traffic demand in the low power RBS. The selected backhaul power mode is activated for the wireless backhaul link.

The disclosure enables reduced energy consumption of the backhaul link by use of backhaul power modes adapted to traffic load in the area of the low power radio base station. According to an aspect of the disclosure, the method is performed in the backhaul client of the low power radio base station, RBS or in the backhaul hub of the wireless network.

According to an aspect of the disclosure, the two or more backhaul power modes include an active backhaul power mode and an energy-saving backhaul power mode. Accordingly, the disclosure enables alignment of backhaul power modes with activity levels configured for the low power radio base station. Consequently, the disclosure provides for an active backhaul power mode corresponding to an active mode of the low power RBS and an energy-saving backhaul power mode applicable when a dormant state is activated for the low power RBS.

According to an aspect of the disclosure, the estimating of the wireless backhaul link traffic demand of the low power RBS comprises performing packet of one or more messages sent on the wireless backhaul link.

Packet inspection of messages sent to/from the low power RBS on the wireless backhaul link provides a reliable source of information relating to the wireless backhaul link traffic demand.

According to another aspect of the disclosure, the packet inspection is performed in a signaling proxy in the backhaul client of the low power RBS and/or in a signaling proxy in the backhaul hub of the wireless network. According to a further aspect of the disclosure, the method includes receiving in the backhaul client information on a wireless backhaul link traffic demand estimated in the signaling proxy in the backhaul hub to the backhaul client or receiving in the backhaul hub information on a wireless backhaul link traffic demand estimated in the signaling proxy in the backhaul client and estimating the wireless backhaul traffic demand based on the received information.

According to an aspect of the disclosure, the wireless backhaul link is operative in the active backhaul power mode prior to the step of selecting backhaul power mode and wherein the energy-saving backhaul power mode is selected during the step of selecting backhaul power mode. Consequently, the disclosure enables transition from an active state for the wireless backhaul link to an energy-saving state, thereby enabling power consumption reductions also in the wireless backhaul link. According to an aspect of the disclosure, activating of the selected energy-saving backhaul power mode includes activating an energy-saving mode in the backhaul client.

According to an aspect of the disclosure, the energy-saving backhaul mode is selected when the estimated wireless backhaul link traffic demand is below a predetermined link- specific threshold.

According to an aspect of the disclosure, the method further includes the step of activating the energy-saving backhaul power mode at the expiry of a predetermined time period following the step of selecting the energy-saving backhaul power mode.

According to an aspect of the disclosure, the method further includes the step of counting messages transmitted from the low power RBS on the wireless backhaul link and activating the energy-saving backhaul power mode when a predetermined number of messages has been transmitted following the step of selecting the energy-saving backhaul power mode.

The delays introduced from awaiting expiry of a time period or a specified message count provide mechanisms solutions to ensure that the messaging has been concluded prior to entering the dormant mode and that neighboring low power RBSs are made aware of the upcoming energy-saving mode.

According to an aspect of the disclosure, the wireless backhaul link is configured to allow keep-alive signaling when operative in the second backhaul power mode and wherein the signaling proxy of the backhaul client receives the keep-alive signaling, generates and transmits a response to the keep alive signaling.

Some protocols provide for keep-alive signaling on the signaling links between the low power RBS and network level entities. Configuring a signaling proxy of the backhaul client to reply to such keep-alive signaling on behalf of the low power RBS, prevents triggering of a signaling link failure based on keep-alive supervision.

According to an aspect of the disclosure, the method further includes the step of estimating a traffic demand for a plurality of wireless backhaul links to a backhaul hub of a wireless network and activating an energy-saving mode for the backhaul hub when the estimated traffic demand for the plurality of wireless backhaul links is below a predetermined hub-specific threshold.

Activating of an energy-saving mode for the backhaul hub provides the advantage of enabling further energy reductions with regard to the wireless backhaul structure. According to an aspect of the disclosure, the wireless link is operative in the energy- saving backhaul power mode at the step of selecting backhaul power mode, and wherein the active backhaul power mode is selected during the step of selecting backhaul power mode.

Thus, the disclosed method is applicable both when activating an energy saving mode for a backhaul link and when reactivating the wireless backhaul link.

According to an aspect of the disclosure, the first backhaul power mode is selected when the determining of the wireless backhaul link traffic demand comprises receiving an indication in the backhaul client of an increased wireless backhaul link traffic demand in the low power RBS. According to an aspect of the disclosure, the indication of an increased wireless backhaul link traffic demand is received in a signal from the backhaul hub.

According to an aspect of the disclosure, the indication of an increased wireless backhaul link traffic demand is received from the low power RBS.

The disclosure also relates to a network node embodiment for controlling energy consumption in a wireless backhaul link from a backhaul client of a low power RBS to a backhaul hub of the wireless network. The low power RBS comprises a processor, a communication interface and a memory. The memory contains instructions executable by the processor, where the low power RBS is operative to estimate a wireless backhaul link traffic demand for the low power RBS, select a backhaul power mode from two or more backhaul power modes for the wireless backhaul link of the low power RBS based on the determined wireless backhaul link traffic demand in the low power RBS, and activate the selected backhaul power mode for the wireless backhaul link. The disclosure further relates to an embodiment of a computer-readable storage medium, having stored thereon a computer program which when run in a network node, causes the network node to perform the disclosed method of controlling energy consumption in a wireless backhaul link. The network node and the computer-readable storage medium each display advantages corresponding to the advantages already described in relation to the disclosure of the method in a network node.

BRIEF DESCRIPTION OF THE DRAWINGS

Further objects, features and advantages of the present disclosure will appear from the following detailed description, wherein some aspects of the disclosure will be described in more detail with reference to the accompanying drawings, in which:

Figure 1 a. shows the basic LTE architecture; b. discloses a cellular structure with low power radio base stations ; Figure 2 a. is a schematic illustration of a dense urban heterogeneous deployment scenario including small cells; b. is a schematic illustration of a wireless backhaul set up; c. schematically illustrates network architecture including a wireless backhaul link;

Figure 3 is a flowchart schematically illustrating embodiments of method steps performed in a network node;

Figure 4 a. is a signaling diagram illustrating an example of network or low power radio base station initiated activation of an energy-saving backhaul power mode; b. is a signaling diagram illustrating an example of network or backhaul hub/client initiated re-activation of an active backhaul power mode;

Figure 5 is a block diagram schematically illustrating a network node embodiment.

DETAILED DESCRIPTION The general object or idea of embodiments of the present disclosure is to address at least one or some of the disadvantages with the prior art solutions described above as well as below. The various steps described below in connection with the figures should be primarily understood in a logical sense, while each step may involve the communication of one or more specific messages depending on the implementation and protocols used. Embodiments of the present disclosure relate, in general, to the field controlling backhaul energy consumption. In particular, the disclosure relates to embodiments for enabling reduced energy consumption for a wireless backhaul link from a low power radio base station, RBS, to a backhaul hub when an activity level of the low power RBS is low.

Figure la schematically illustrates a basic LTE, Long Term Evolution, network architecture, including radio base stations, RBS, arranged for communicating with wireless devices over a wireless communication interface. The plurality of RBSs, here shown as eNBs, is connected to MME/S-GW entities via SI interfaces. The eNBs are connected to each other via X2 interfaces.

Figure lb exemplifies a network deployment wherein very large capacity and performance is sought by deploying small cells 210 defined by the coverage areas of low power radio base stations 21, RBSs, for example Micro RBS and Pico RBS; in the following denominated Pico RBSs. A macro radio base station 20, e.g. eNB, provides coverage in a large cell 200 including a number of small cells 210. The Pico RBSs 21 are typically geographically oriented to densely populated areas with many users in the vicinity of a Pico RBS. A wireless device 10, e.g. a mobile/cellular phone or any other type of user equipment, is using a Radio Access Network, RAN, service to access the mobile network services. The Pico RBS provides one or a combination of several radio access technologies over the radio access link, e.g. 3GPP LTE, 3GPP HSPA, 3GPP GSM or IEEE 802. llx, also known as Wi-Fi. The Pico RBS needs to backhaul the RAN traffic to the mobile network, and uses a wireless backhaul link for this. Figure 2a provides a schematic illustration of a dense urban heterogeneous deployment scenario including small cells wherein macro and Pico radio base stations are connected via backhaul radio links. The macro radio base stations are generally located above rooftops, while the Pico radio base stations often are located on building walls and lamp posts. A user equipment, UE, also known as a wireless device, a mobile phone or a cellular phone, is illustrated as using radio access network, RAN, service to access the mobile network services over a RAN link. The Pico RBS provides one or a combination of several radio access technologies over the radio access link, e.g. 3GPP LTE, 3GPP HSPA, 3GPP GSM or IEEE 802.11x (Wi-Fi). The Pico RBS needs to backhaul the RAN traffic to the mobile network, and uses a wireless backhaul link for this.

Figure 2b illustrates an example of a state of the art wireless backhaul technology, e.g. the wireless backhaul technology used by the Pico RBSs illustrated in Figure 2a. A wireless backhaul link is implemented by means of two terminals, Terminal A and Terminal B, on either side of this link. A backhaul hub is illustrated at a termination point of a fixed link to the mobile network. The backhaul hub is configured to forward traffic terminated on Terminal B to the mobile backhaul network via the illustrated fixed link, e.g. a fixed link over copper or fiber media. The backhaul link between Terminal A and Terminal B is a wireless backhaul link possible to realize with various wireless technologies, wherein the most common alternatives at present are LTE and microwave. When the wireless backhaul link between Terminal A and Terminal B is implemented using LTE backhauling, the Terminal A will typically be implemented using a UE that is embedded into the Pico RBS. The UE will in the following be referred to as a backhaul client. On the hub side, the receiving terminal B will act as a radio base station. The receiving Terminal B will in the following be referred to as a backhaul hub. LTE backhauling can be carried either over normal IMT-bands, e.g. on 2.4 GHz, in which case we are using 3GPP standard LTE in-bands or out-of-band relaying, or by running LTE baseband on higher radio frequencies, such as 28 GHz. The wireless backhaul links are typically managed by LTE core control mechanisms. For example, the LTE Mobility Management Entity, MME, will provide session control of the LTE links, while the Home Subscription Service, HSS, will be needed to store security and Quality of Service, QoS, characteristics of the links individual UEs embedded in the Pico RBSs. Moreover, typically more than one Pico RBS will connect to the same backhaul hub. In those cases, each Pico RBS are equipped with its own backhaul client. The backhaul hub, is as any other radio base station, capable of radio resource management, such as scheduling and prioritization of the traffic to and from the different backhaul clients. The Pico RBSs are deployed to meet high traffic demands. However, depending on location of a Pico RBS the traffic could be low at some times while extremely high at other times, e.g. during rush hour. Thus, a number of different activity levels have been foreseen and configured for use in a Pico RBS, e.g. an active mode when traffic load is high or a dormant mode when there is no traffic. Figure 2c illustrates an example of architecture for a backhaul link. A backhaul client 211 communicates backhaul messages between a Pico RBS 21 and a backhaul hub 201, e.g. of a macro RBS 20. According to an aspect of the disclosure, the backhaul client 211 and the backhaul hub 201 includes signaling proxies 212, 202. The function and role of these signaling proxies will be further discussed below. The backhaul hub 201 includes a backhaul link to the MME/HSS of the wireless network. When one or more user equipments 10 are connected to the Pico RBS 21 and receives/transmits data to the Pico RBS, the wireless backhaul link serves as a backhaul connection to the MME/HSS. However, when an energy saving mode is activated in the Pico RBS, thereby significantly reducing the traffic demand of the Pico RBS on the backhaul link, a corresponding power control should also be exercised for the backhaul link.

Figure 3 discloses a flowchart schematically illustrating embodiments of method steps performed in a network node of controlling energy consumption in a wireless backhaul link between a backhaul client of a low power radio base station, RBS, and a backhaul hub of the wireless network. The method of controlling energy consumption in the wireless backhaul link is either performed in the backhaul client of the low power RBS, in the backhaul hub of the wireless network or in any other network entity or collaborating group of entities capable of controlling the backhaul client and/or backhaul hub.

In a first step S31, the method comprises determining a wireless backhaul link traffic demand for the low power RBS, also described as Pico RBS. In the following description, the situation where the Pico RBS is in an active state is considered as well as the situation where the Pico RBS is in a dormant state. The need to uphold a wireless backhaul link between the backhaul hub and the backhaul client of the Pico RBS is correlated to the present or predicted traffic load in the Pico RBS. According to an aspect of the disclosure, the estimation of a wireless backhaul link traffic demand for the Pico RBS is performed by packet inspection S311 of one or more messages sent on the wireless backhaul link, e.g. in a signaling proxy in the backhaul client of the Pico RBS and/or in a signaling proxy in the backhaul hub of the wireless network. A signaling proxy is arranged to intercept signaling messages which otherwise would be sent directly between two peer entities. This interception typically implies some kind of modification of the messages and/or replying on one of the peer's behalf to the other peer. An example of signaling proxy is a SIP proxy, which handles SIP (Session Initiation Protocol) signaling. A web proxy may also be seen as an example of a signaling proxy. Traffic demand could also be estimated based on information received in the backhaul client on the interface to the Pico RBS, e.g. information that the Pico RBS is about to enter a dormant state due to a low traffic load. Similarly, the traffic demand could be estimated based on information received in the backhaul client from the backhaul hub or vice versa, e.g. information that the backhaul hub has received from radio base stations that have neighbor relations to the Pico RBS. The receiving of information also includes receiving in the backhaul client information on an estimation performed in the signaling proxy in the backhaul hub or receiving in the backhaul hub information on the wireless backhaul link traffic demand estimated in the signaling proxy in the backhaul client.

In a next step S32, a backhaul power mode is selected from two or more backhaul power modes for the wireless backhaul link of the low power RBS based on the determined wireless backhaul link traffic demand in the low power RBS. As mentioned above, the disclosure considers the situation where the Pico RBS is in an active state as well as the situation where the Pico RBS is in a dormant state. When a Pico RBS is configured to operate in any of these two states, analogous modes are considered for the wireless backhaul link, i.e. said two or more backhaul power modes comprises an active backhaul power mode and an energy-saving backhaul power mode. For a Pico RBS configured to operate in further states than those mentioned above, further backhaul power modes are also within the scope of the disclosure. In a third step S33; the selected backhaul power mode is activated for the wireless backhaul link. For the situation where an energy-saving mode has been selected the activating includes activating an energy-saving mode in the backhaul client, i.e. to disconnect the wireless connection from the backhaul client to the backhaul hub. As previously mentioned, the wireless backhaul link is implemented using microwave radio communication between the Pico RBS and the macro RBS or using a 3GPP radio access technology, e.g. 3GPP LTE. For the latter situation, the backhaul link is typically implemented by using a wireless device; also known as user equipment, UE, embedded into the Pico RBS. The wireless backhaul link is set up as a wireless connection to a receiving radio base station, e.g. a macro RBS, representing the hub side of the backhaul link. On the hub side of the backhaul link, the receiving macro RBS handles the connection as an ordinary wireless connection to a connected user equipment, UE. When activating an energy-saving mode for the 3GPP implementation, the wireless connection to the receiving macro RBS is disconnected. Disconnection is either initiated from the backhaul client in the Pico RBS or from the backhaul hub, i.e. from the network side of the wireless connection.

The signaling diagrams of Figures 4a exemplifies signaling performed when activating an energy-saving mode of the wireless backhaul link. Figure 4a illustrates disconnection of the wireless connection initiated from the network. Figure 4a also illustrates disconnection initiated from the picoRBS. Optional signals are illustrated with dashed lines in dependence on where the disconnection was initiated. Signaling proxies are illustrated in the backhaul hub and backhaul client. These signaling proxies intercept signaling to/from the corresponding backhaul entity; thereby receiving and transmitting messages to/from the backhaul hub and backhaul client. In the following description of performed signaling, the signaling proxies will not be explicitly mentioned when discussing signaling between the backhaul hub and the backhaul client.

When the disconnection is initiated by the network, a signal Si41a Activate dormant state of Pico, typically received in the signaling proxy of the backhaul hub. The signal is sent from an O&M system or as alternative from a neighboring RBS, e.g. a macro RBS, in the wireless network. The backhaul hub forwards the signal Si41b Activate dormant state of Pico unchanged or in an amended form to a signaling proxy of the backhaul client providing the backhaul for the Pico RBS. The backhaul client forwards the signal Si41c Activate dormant state of Pico unchanged or in amended form to the Pico RBS. The Pico RBS provides a response signal Si42a Dormant state initiated. When the Pico RBS uses LTE on the access link, the message 'eNB Configuration Update', as defined in 3GPP TS36.323, is an option for providing the Si42a Dormant state initiated response. In the situation where the disconnection of the backhaul client is initiated from the Pico RBS, the Pico RBS sends S42a Dormant state initiated to initiate disconnection of the backhaul. When the LTE Pico RBS enters dormant mode, it includes an information element IE Deactivation Indication set to 'deactivated' in the message. The intercepting signaling proxy forwards the signal Si42b Dormant state initiated to the network, typically to radio base stations controlling neighboring cells, e.g. a macro RBS in a the case of a heterogeneous network. The signal Si42b is forwarded in an unchanged or amended form by the intercepting signaling proxy. The receiving radio base stations, here represented as the network, each respond with a signal Si43 Acknowledgement, e.g. in the form of an eNB Configuration Update Acknowledge. A timer or counter in the signaling proxy is arranged to uphold enable acknowledgements from neighboring nodes of the network, e.g. by keeping track of the messages received from the network or allowing a timer setting sufficient for concluding the messaging from the network. Upon expiry of the counter or timer, the signaling proxy sends a message Si44 Activate energy-saving backhaul power mode to the client. The client activates the energy-saving backhaul power mode and responds with the acknowledgement signal Si45 Energy saving backhaul power mode activated, i.e. an RRC Connection Release for LTE, to the receiving backhaul hub. For the alternative situation wherein the disconnection is initiated from the Pico RBS, a timer or counter is arranged in the backhaul client. When the counter or timer expires, the backhaul clients signals Si44 Activate energy-saving backhaul power mode to the backhaul hub. The hub responds with an acknowledgement Si45 Energy-saving backhaul power mode activated.

The signaling diagrams of Figures 4b exemplifies signaling performed when re-activating the wireless backhaul link, i.e. when an active mode of the wireless backhaul is selected. Figure 4b illustrates activation of the wireless connection initiated from the network as well as activation performed from the backhaul hub. Optional signals are illustrated with dashed lines in dependence on where the disconnection was initiated. For the situation where an active mode has been selected, the activating implies reestablishing a wireless connection between the backhaul client and the backhaul hub, e.g. implemented as a wireless connection between a UE and a radio base station. Reestablishment is then performed in accordance with normal procedures for setting up a wireless connection between a radio base station and user equipment. As will be disclosed in the following, the re-establishment of the wireless connection is either initiated from the backhaul client in the Pico RBS or from the backhaul hub, i.e. from the network side of the wireless connection. For the situation where the network initiates reactivation of the backhaul, a signal Si46 Activate active state of Pico/Cell activation request is sent to the backhaul hub from the network. The backhaul hub informs the backhaul client of the need to set up the backhaul through the signal Si47 Initiate active backhaul mode, e.g. a paging signal when considering an LTE backhaul. The backhaul client confirms receipt in an acknowledgement signal Si48 Acknowledge active mode, e.g. in an RRC connection establishment. Following the acknowledgement/RRC connection establishment, the backhaul hub signals a cell activation request Si49 Activate active state of Pico to the Pico RBS over the backhaul client. When the backhaul hub or backhaul client reactivates the backhaul radio link, activation of the radio link is initiated by the signal Si47 Initiated active backhaul mode. When activation is initiated in the backhaul client, the acknowledgement Si48 Acknowledge active mode is sent from the backhaul hub to the backhaul client. The client then transmits a cell activation request to the Pico RBS in the signal Si49b Activate active state of Pico.

Activating an energy-saving backhaul power mode

The following section addresses the specific situation when the wireless backhaul link is operative in the active backhaul power mode at a starting point, prior to the step of selecting backhaul power mode, and wherein the energy-saving mode is selected during the step of selecting backhaul power mode. When the traffic load in the radio access interface is low, i.e. few or no user equipment connections to the Pico RBS, the Pico RBS enters into a low energy. When the Pico RBS is about to enter into the a low energy/dormant state, the Pico RBS sends an "eNB configuration update" message over the backhaul link, the "eNB configuration update" message containing an information element "Deactivation Indication". The message is sent over the backhaul link to one or more neighboring Pico RBSs and/or a macro RBS serving a cell covering the area of the cell served by the Pico RBS. According to an aspect of the disclosure, the wireless backhaul link traffic demand is estimated by signal inspection by the signaling proxy in the backhaul client and/or in the backhaul hub. When the signal inspection reveals that an "eNB configuration update" including the information element, IE, "Deactivation Indication" has been sent from a Pico RBS, it is concluded that this reflects a low wireless backhaul link traffic demand for the Pico RBS. According to another aspect of the disclosure, a traffic demand may also be estimated by detecting in a signaling proxy that little or no uplink or downlink data is transmitted to/from the client. The detecting could either be performed in the signaling proxy of the backhaul hub or the signaling proxy of the backhaul client. The estimating of a traffic demand based on uplink or downlink data detection should be initiated after the Pico RBS have entered the dormant state, e.g. by using appropriate settings of a timer that is started when data is detected. According to another aspect of the disclosure, the traffic demand is estimated based on explicit signaling from the Pico RBS, e.g. an explicit signal from the Pico RBS to the client that orders the client to activate an energy-saving backhaul power mode. In the situation where several Pico RBSs are using the same client, the client activates the energy-saving backhaul power mode only when all Pico RBSs have entered dormant states. As an alternative the energy-saving backhaul power mode is activated only when the most prioritized Pico RBSs have entered dormant mode, given that each Pico RBS is associated with a priority. According to a further alternative, the energy-saving backhaul power mode is determined when the traffic goes below a predetermined link-specific threshold value used as reference for estimating a low traffic demand.

In step S32 of selecting a backhaul power mode, the energy-saving backhaul power mode is selected when the estimated wireless backhaul link traffic demand is below a predetermined link-specific threshold. The Pico RBS about to enter into the low energy/dormant state typically transmits a plurality of messages informing the other radio base stations of the upcoming dormant state. Thus, there is a need to maintain the wireless backhaul link until the Pico RBS has had the opportunity to inform the other radio base stations, e.g. neighboring Pico RBSs and a macro RBS. In order to accommodate the need for transmitting messages on the wireless backhaul link prior to activating a dormant state, activating of the selected low-energy backhaul power mode is delayed. According to an aspect of the disclosure, the energy-saving backhaul power mode is activated at the expiry of a predetermined time period following the step of selecting the energy-saving backhaul mode. When the backhaul client or backhaul hub detects the first "eNB configuration Update" message containing the IE "Deactivation Indication" during packet inspection performed by a signaling proxy, a timer is started. When the timer expires, the energy-saving mode for the wireless backhaul link is activated. According to another aspect of the disclosure a counter is used whereby the signaling proxy in the client or hub keeps track of how many other RBSs the particular Pico RBS will inform. The messages transmitted from the low power RBS on the wireless backhaul link are counted and the selected energy-saving backhaul power mode is activated when a predetermined number of messages has been transmitted following the step of selecting the energy-saving backhaul power mode. A counter is initialized to the number of other RBSs that the Pico RBS will inform. For each "eNB Configuration Update" message, containing the IE "Deactivation Indication", it decreases the counter by 1. When the counter reaches zero, the low-energy backhaul power mode is activated.

On the signaling links between the Pico RBS and e.g. the MME SI-CP, the SI Control Plane of the SI, there is a keep-alive signaling in the Stream Control Transmission Protocol, SCTP. The interval between those keep-alive messages is typically in the order of seconds. This means that keep-alive messages may trigger client wake up, especially if the client sleeps for several seconds. There could also be other messages on the application layer, e.g. SI AP, which are not important enough to wake up the client.

According to an aspect of the disclosure, the wireless backhaul link is configured to allow keep-alive signaling when operative in the energy-saving backhaul power mode and wherein the signaling proxy of the backhaul client receives the keep-alive signaling, generates and transmits a response to the keep-alive signaling. In the backhaul client and backhaul hub, the signaling proxies reply to the keep-alive messages on the behalf of the Pico RBS and e.g. MME, respectively, in order to prevent keep-alive supervision trigger of a signaling link failure. IPSec is configured in those proxies with the appropriate keys, in case IPSec is used for the signaling links. For other messages, e.g. payload over SCTP, the data is forwarded to the upper layer proxy if such a proxy exists. This upper layer proxy terminates unimportant messages, e.g. certain Sl-AP messages, and triggers wake up of the backhaul client when the messages are important. The messages are then forwarded.

When a hub has only one remaining backhaul client and a low-energy backhaul power mode is activated, it is possible to activate a low-energy mode of the backhaul hub as well. The same applies when there are only a few clients alive in the network or backhaul traffic is low so that there is no need to keep all hubs alive. A low-energy mode can then be activated for one or more of the backhaul hubs. The remaining backhaul hubs still operating in an active mode are requested to handle the remaining clients. According to an aspect of the disclosure, following a step of estimating traffic demand for a plurality of wireless backhaul links to a backhaul hub of a wireless network, an energy-saving mode is activated for the backhaul hub when the estimated traffic demand for the plurality of wireless backhaul links is below a predetermined hub-specific threshold.

Activating an active backhaul power mode

The following section addresses the specific situation when the wireless backhaul link is operative in the energy-saving backhaul power mode at a starting point, prior to the step of selecting backhaul power mode, and wherein the active backhaul power mode is selected during the step of selecting backhaul power mode.

The wireless backhaul link should be put into operation when there is downlink user data or an important signaling message to be transmitted from the backhaul hub or when there is corresponding uplink data. Such messages or data reflect an increased wireless backhaul link traffic demand. According to an aspect of the disclosure, an indication of the increased wireless backhaul link traffic demand is received in a signal from the backhaul hub or from the low power RBS.

Assuming the case when the backhaul hub receives an indication of a need to activate the wireless backhaul link, e.g. in a request from the Pico RBS, the backhaul hub initiates the wake-up of the backhaul client. The backhaul hub then sends a sync or paging signal to wake up the backhaul client. For example, a new preamble, i.e. a bit sequence not used for any other purpose than to trigger the backhaul client to wake up, is sent from the hub. Looking at the opposite case when there is uplink user data or an important signaling message to be transmitted from the Pico RBS, the backhaul clients is either activated by the Pico RBS or by the backhaul hub by order of the Pico RBS. The Pico RBS activates the backhaul client over the interface between the Pico RBS and the backhaul client. Existing techniques such as wake-on-LAN are used. Once the backhaul client has been activated, it initiates a connection setup to the backhaul hub as previously disclosed. The activation of the backhaul client, and thereby the wireless backhaul link, is also performed from the backhaul hub based on an order from the Pico RBS. Since the Pico RBS cannot use the wireless backhaul link to contact the backhaul hub, it uses an alternative connection to send the activation request, e.g. using the cellular macro network, based on LTE or another radio access technology.

Figure 5 is a block diagram schematically illustrating an example embodiment of a network node for performing the method steps embodiments. Figure 5 illustrates a network node, e.g. an eNB, a Pico RBS or core network node configured to perform the method steps.

The network node 50 comprises a processor 51 or a processing circuitry that may be constituted by any suitable Central Processing Unit, CPU, microcontroller, Digital Signal Processor, DSP, etc. capable of executing computer program code. The computer program may be stored in a memory, MEM 53. The memory 53 can be any combination of a Random Access Memory, RAM, and a Read Only Memory, ROM. The memory 53 may also comprise persistent storage, which, for example, can be any single one or combination of magnetic memory, optical memory, or solid state memory or even remotely mounted memory. The network node 50 further comprises a communication interface 52 configured communication with wireless devices in the network. According to one aspect the disclosure further relates to a computer-readable storage medium, having stored thereon the above mentioned computer program which when run in a network node, causes the node to perform the disclosed method embodiments. When the above mentioned computer program is run in the processor of the network node 50, it causes the node to estimate a wireless backhaul link traffic demand for the low power RBS; to select a backhaul power mode from two or more backhaul power modes for the wireless backhaul link of the low power RBS based on the determined wireless backhaul link traffic demand in the low power RBS; and to activate the selected backhaul power mode for the wireless backhaul link.

The disclosure also relates to a computer-readable storage medium, having stored there on a computer program which when run in a network node, causes the network node to perform the disclosed method.

According to a further aspect of the disclosure, processor 51 further comprises one or several of: a traffic demand estimation module 511 configured to estimate a wireless backhaul link traffic demand for the low power RBS; a selection module 512 configured to select a backhaul power mode from two or more backhaul power modes for the wireless backhaul link of the low power RBS based on the determined wireless backhaul link traffic demand in the low power RBS; and an activation module 513 arranged to activate the selected backhaul power mode for the wireless backhaul link.

The determination module 511, the selection module 512 and radio link configuration module 513 are implemented in hardware or in software or in a combination thereof. The modules 511, 512, 513 are according to one aspect implemented as a computer program stored in a memory 53 which run on the processing circuitry 51.