WO2014036710A1

WO2014036710A1 - Method and apparatus of energy saving in radio access networks

Info

Publication number: WO2014036710A1
Application number: PCT/CN2012/081091
Authority: WO
Inventors: Wei Hong; Tero Heikki Matti Henttonen; Haiming Wang; Lili Zhang
Original assignee: Broadcom Corporation
Priority date: 2012-09-06
Filing date: 2012-09-06
Publication date: 2014-03-13

Abstract

The present invention relates generally to energy saving in Radio Access Networks (RANs). Traditionally, a base station or an eNB (envolved Node B) has two modes: a normal mode and a sleep mode. When the base station is in the sleep mode, it does not transmit or receive anything until it is woken up, i.e. its mode is changed to the normal mode. Especially transmitting consumes power in the base station. The present invention suggests that a cell should initiate the change of the working mode, because it is the first to detect substantial changes in amounts of traffic. Thus, the cell measures the traffic and detects whether the measured amount of traffic is below a predetermined threshold. If it is, the cell requests a permission to enter an energy saving mode and, after the possible grant, the cell enters the energy saving mode. The sleep mode and a discontinuous transmissing (DTX) mode are known energy saving modes. In addition to them, the cell may enter an energy saving mode which is termed a "low-activity" mode. The low- activity mode provides at least one sleep period during which the base station of the cell omits transmitting and receiving. When a sleep period lasts at most several radio frames the base station can still serve user equipments located in the cell area.

Description

METHOD AND APPARATUS OF ENERGY SAVING IN RADIO ACCESS NETWORKS

TECHNICAL FIELD

[0001] The present application relates generally reducing energy consumption in radio access networks (RANs). Universal Mobile Telecommunication System (UMTS), Universal Terrestrial Radio Access Network (UTRAN), a Long Term Evolution (LTE) network called Evolved UTRAN (EUTRAN), and an LTE advanced network are some examples of RANs.

BACKGROUND

[0002] Energy consumption in cellular networks has rapidly moved from an area of low priority to a focus area of the whole telecommunication community. When analysing the energy consumption of RANs it becomes clear that in order to reduce the total energy usage it is important to concentrate the efforts on the most abundant network nodes namely the base stations (BS). The two most important drives for improved energy efficiency for mobile- networks operation are: a number of operators experiencing increased electricity costs for network operation; and an increased awareness in the society of how energy use relates to greenhouse gas emissions and global warming. Consequently, in a newly started research initiative called EARTH, (Energy Aware Radio and neTwork tecHnologies) industiy and academia have joined forces in addressing energy consumption in mobile systems.

[0003] FIGURE 1 shows Legacy cells and E-UTRAN cells as decribed in 3 GPP (third generation partnership project) document TS 36.927. E-UTRAN cells C, D, E, F, and G 101-105 are covered by Legacy cells A 106 and B 107 of which A 106 could be a UMTS cell and B 107 could represent some other radio access technology (RAT). Besides different kinds of cells FIG. 1 also illustates co-operation between RATs, which is termed "Inter-RAT". Each Legacy cell provides basic coverage of the services in the area, while E-UTRAN cells boost the capacity. E- UTRAN cells are deployed for capacity enhancement at some hot spots.

[0004] E-UTRAN cells 101-105 can also be termed "small cells". For example, to E- UTRAN cells, micro cells, pico cells, femto cells, hotspot cells, and phantom cells, are small cells. Legacy cells can be alternatively termed "macro cells" or "coverage cells" due to theirs large coverage areas. [0005] FIGURE 2 shows a macro cell and phantom cells. A coverage area of macro cell 201 comprises coverage areas of phantom cells 202-206. Macro cell 201 may use, for example, a frequency band at 2 GHz and phantom cells 202-206 may use, for example, a frequency band at 3.5 GHz. The phantom cells satisfy escalating data rate requirements. With shorter coverage ranges of tens or few hundreds of meters, the higher frequency band (3.5 GHz) is suited for high data rates.

[0006] Traditionally, a base station or an eNB (envolved Node B) has two modes: a normal mode and a sleep mode. When the base station is in the sleep mode, it does not send or receive anything until it is woken up, i.e. its mode is changed to the normal mode. Recently, it has been noticed that use of small cells significantly increases energy consumption of a RAN. While a BS of each small cell itself consumes a low amount of power, a wide scale deployment involving tens or hundreds of thousands of small cells result in that the total network energy consumption may soar to high. The above-mentioned TS 36.927 provides solutions to reduce the total network energy consumption. The solutions concern a cell, whose BS is currently in the sleep mode. This cell is termed a "dormant hotspot cell". A coverage cell is assumpted to detect high load after which it wakes up, i.e. activates, dormant hotspot cells. A first solution, labeled with A, means basically "do nothing".

[0007] The second solution, solution B, comprises OAM predefined 'low-load periods' policy, where OAM refers to operation, administration, and maintenance. When the coverage cell detects high load, it uses a proprietary algorithm to decide which dormant hotspot cells should be activated. The algorithm relies on pre-defined 'low-load periods' for each neighbour hotspot cell.

[0008] Solution C, ΊοΤ measurement', uses Interference over Thermal (IoT) measurements. When the coverage cell detects high load, it requests some dormant hotspot cells to switch on their listening capability, i.e. the coverage cell activas those hotspot cell(s).

[0009] Solution D is 'UEs measurement' , wherein UE refers to a mobile phone or some other type of user equipment. When the coverage cell detects high load, it requests dormant hotspot cells to transmit a pilot signal for a short time interval that is termed 'probing interval'. During the probing interval, UEs currently located on the coverage cell perform Reference Signal (RS) measurements from cells and send the measurement results to the coverage cell. Then, based on the measurement results, the coverage cell determines which cells must be active and which can be in the dormant mode.

[0010] Solution E is 'Positioning information'. When the coverage cell detects high load, it uses information concerning UE locations, hotspot cell locations, and cell radii/transmit powers to decide which hotspot cells should be active. An "active mode" is usually used as a synonym of the normal mode. In addition, a hotspot cell may use a timer so that after expiracy of this timer the hotspot cell determines its elves whether it should stay in the active mode.

Otherwise, it enters the dormant mode.

[0011] TS 36.927 further disclose in section 5.1.2.1 an OAM-based solution for an E- UTRAN cell entering the dormant mode. The E-UTRAN cell enters the dormant mode in response to an OAM decision that is made based on statistical information obtained from coverage and E-UTRAN cells. The OAM decision can be pre-configured or signalled to the EUTRAN cell. When E-UTRAN cell enters or leaves the dormant mode, its neighbour cells should be informed either via OAM or signalling.

SUMMARY

[0012] The present present application represents a method for energy saving in a radio access network comprising a first cell and a second cell located within a geographical area of the first cell. The first cell is, for example, a macro cell and the second cell is, for example, a pico cell. Altematilvely, the first cell is, for example, a pico cell and the second cell is, for example, a femto cell. In addition to these, there are a number of other examples in which the second cell locates on the geographical area of the first cell.

[0013] In one aspect, the present invention provides a method for energy saving in a radio access network comprising a first cell and a second cell located within a geographical area of the first cell, the method comprising the following to be performed in the second cell:

detecting that an amount of traffic in a base station of the second cell is below a predetermined threshold; obtaining from the first cell a permission to enter the base station into an energy saving mode; and entering the energy saving mode.

In one embodiment of the method, the energy saving mode is one of the following modes: a sleep mode in which transmitting is disabled, a discontinuos transmission (DTX) mode that omits scheduling user equipments. In one embodiment of the method, the energy saving mode is a low-activity mode, the low-activity mode providing at least one sleep period during which the base station omits at least transmitting and receiving.

In one embodiment of the method, the low-activity mode further provides at least one operating period during which the base station operates as in an active mode.

In one embodiment of the method, the method further comprises: offloading at least a part of the traffic to the first cell or a neighbor cell.

In one embodiment of the method, the obtaining comprises requesting from the first cell the permission to enter the energy saving mode.

In one embodiment of the method, the requesting comprises sending to the first cell at least one of the following messages: a resource status request message, a mobility change request message.

In one embodiment of the method, the requesting causes the second cell to send a load information message.

In one embodiment of the method, the method further comprises: informing a neighbor cell about the entering the energy saving mode.

In one embodiment of the method, the informing causes the second cell to send a setup request message to the neighbor cell.

In one embodiment of the method, the method further comprises: notifying a user equipment about the energy saving mode of the second cell.

In one embodiment of the method, wherein the notifying further comprises at least one of the following periods: a sleep period, an operating period, wherein the sleep period has a starting time and length and the operating period has a starting time and length.

In one embodiment of the method, the notifying causes the the second cell to send a system information block to the user equipment.

[0014] In one aspect, the present invention provides a method for energy saving in a radio access network comprising a first cell and a second cell located within a geographical area of the first cell, the method comprising the following to be performed in the first cell: obtaining from the second cell a message indicating that traffic in a base station of the second cell is under a predetennined threshold; granting a peraiission for the second cell to enter the base station into an energy saving mode. In one embodiment of the method, the energy saving mode is one of the following modes: a sleep mode in which transmitting is disabled, a discontinuos transmission (DTX) mode that omits scheduling user equipments.

In one embodiment of the method, the energy saving mode is a low-activity mode, the low-activity mode providing at least one sleep period during which the base station omits transmitting and receiving.

In one embodiment of the method, the method further comprises: handling traffic that is offloaded from the second cell.

In one embodiment of the method, the message is one of the following messages: a resource status request message, a mobility change request message, a load information message.

In one embodiment of the method, the granting comprises setting at least one of the following periods: a sleep period, an operating period, wherein at least the sleep period has a starting time and length and the operating period has a starting time and length. In one embodiment of the method, the method further comprises: granting a permission for a third cell to enter the energy saving mode, wherein the granting is performed so that an operating period of the third cell is non-overlapping with the operating period granted to the second cell.

[0015] In one aspect, the present invention provides a method for energy saving in a radio access network comprising a first cell and a second cell located within a geographical area of the first cell, wherein a user equipment is served by a base station that forms the second cell, the method comprising the following to be performed in the user equipment: obtaining information notifying the user equipment about an energy saving mode of the second cell, the base station having in the energy saving mode at least one sleep period; and scheduling a task so that the task is to be performed outside of the at least one sleep period, wherein the task is one of the following: communicating with the base station, measuring a pilot signal of the base station, performing a handover.

In one embodiment of the method, the information causes the user equipment to measure a pilot signal of at least one other base station. In one embodiment of the method, the handover is targeted to one of the following cells: the first cell, a neighbor cell of the second cell.

In one embodiment of the method, wherein at least part of the information is obtained with a system information block.

In one embodiment of the method, the radio access network uses at least one of the following techniques: orthogonal frequency-division multiple access (OFDMA), requency division multiple access (FDMA), code division multiple access (CDMA). In one embodiment of the method, the energy saving mode provides at least one operating period and the task is to be performed within the at least one operating period.

[0016] In one aspect, the present invention provides a method for energy saving in a radio access network comprising a cell formed by a base station, the method comprising the following: entering the cell in an energy saving mode providing at least one sleep period during which the base station of the cell omits transmitting and receiving.

In one embodiment of the method, the energy saving mode further provides at least one operating period.

In one embodiment of the method, during the operating period, the base station operates as in an active mode.

In one embodiment of the method, the base station omits transmitting a pilot signal when in the energy saving mode.

In one embodiment of the method, the radio access network further comprises a neighbor cell for the cell and wherein, during the operating period, the base station serves a geographical area of the cell and at least partly a geographical area of the neighbor cell. In one embodiment of the method, the radio access network further comprises an entity granting a permission to enter the energy saving mode.

[0017] In one aspect, the present invention provides an apparatus comprising: at least one processor; and at least one memory including computer program code, the at least one memory and the computer program code airanged to, with the at least one processor, cause the apparatus to perform at least the following: detecting that an amount of traffic in a base station is below a predetermined threshold, wherein a radio access network comprises a first cell and a second cell, the second cell is located within a geographical area of the first cell, and the base station forms the second cell; obtaining from the first cell a permission to enter the base station into an energy saving mode; and entering the energy saving mode.

In one embodiment of the apparatus, the energy saving mode is one of the following modes: a sleep mode in which transmitting is disabled, a discontinues transmission (DTX) mode that omits scheduling user equipments.

In one embodiment of the apparatus, the energy saving mode is a low-activity mode, the low-activity mode providing at least one sleep period during which the base station omits at least transmitting and receiving.

In one embodiment of the apparatus, the low-activity mode further provides at least one operating period during which the base station operates as in an active mode.

In one embodiment of the apparatus, the apparatus performs: offloading at least a part of the traffic to the first cell or a neighbor cell.

In one embodiment of the apparatus, the obtaining comprises requesting from the first cell the permission to enter the energy saving mode.

In one embodiment of the apparatus, the requesting comprises sending to the first cell at least one of the following messages: a resource status request message, a mobility change request message.

In one embodiment of the apparatus, the requesting comprises sending a load information message to the first cell.

In one embodiment of the apparatus, the apparatus performs: informing a neighbor cell about the entering the energy saving mode.

In one embodiment of the apparatus, the informing comprises sending a setup request message to the neighbor cell.

In one embodiment of the apparatus, the apparatus performs: notifying a user equipment about the energy saving mode of the second cell.

In one embodiment of the apparatus, the notifying comprises sending a system

information block to the user equipment.

In one embodiment of the apparatus, the apparatus is used in at least one of the following systems: a long term evolution (LTE) system, a LTE-A system.

In one embodiment of the apparatus, the apparatus is one of the following apparatuses: a base station, an eNB, an eNodeB. [0018] In one aspect, the present invention provides an apparatus comprising: at least one processor; and at least one memory including computer program code, the at least one memory and the computer program code arranged to, with the at least one processor, cause the apparatus to perform at least the following: obtaining from a second cell a message indicating that traffic in a base station of the second cell is under a predetermined threshold, wherein a radio access network comprises a first cell and the second cell and wherein the second cell is located within a geographical area of the first cell; granting a permission for the second cell to enter the base station into an energy saving mode.

In one embodiment of the apparatus, the energy saving mode is one of the following modes: a sleep mode in which transmitting is disabled, a discontinuos transmission (DTX) mode that omits scheduling user equipments.

In one embodiment of the apparatus, the energy saving mode is a low- activity mode, the low-activity mode providing at least one sleep period during which the base station omits transmitting and receiving.

In one embodiment of the apparatus, the apparatus performs: handling traffic that is offloaded from the second cell.

In one embodiment of the apparatus, the message is one of the following messages: a resource status request message, a mobility change request message, a load information message.

In one embodiment of the apparatus, the apparatus is one of the following apparatuses: a base station, an eNB, an eNodeB.

[0019] In one aspect, the present invention provides an apparatus comprising: at least one processor; and at least one memory including computer program code, the at least one memory and the computer program code arranged to, with the at least one processor, cause the apparatus to perform at least the following: obtaining information notifying a user equipment about an energy saving mode of a second cell, wherein a radio access network comprises a first cell and the second cell that is located within a geographical area of the first cell, the user equipment is served by a base station that forms the second cell, and the base station has in the energy saving mode at least one sleep period; and scheduling a task so that the task is to be performed outside of the at least one sleep period, wherein the task is one of the following: communicating with the base station, measuring a pilot signal of the base station, performing a handover.

In one embodiment of the apparatus, the information causes the user equipment to measure a pilot signal of at least one other base station.

In one embodiment of the apparatus, the handover is targeted to one of the following cells: the first cell, a neighbor cell of the second cell.

In one embodiment of the apparatus, the notifying comprises sending at least part of the information in a system information block.

In one embodiment of the apparatus, the radio access network uses at least one of the following techniques: orthogonal frequency-division multiple access (OFDMA), frequency division multiple access (FDMA), code division multiple access (CDMA). In one embodiment of the apparatus, the energy saving mode provides at least one operating period and the task is to be performed within the at least one operating period. In one embodiment of the apparatus, the apparatus is used in at least one of the following systems: a long term evolution (LTE) system, a LTE-A system.

[0020] In one aspect, the present invention provides an apparatus comprising: at least one processor; and at least one memory including computer program code, the at least one memory and the computer program code arranged to, with the at least one processor, cause the apparatus to perform at least the following: entering a cell into an energy saving mode providing at least one sleep period during which a base station of the cell omits transmitting and receiving, wherein a radio access network comprises the cell formed by the base station.

In one embodiment of the apparatus, the energy saving mode further provides at least one operating period.

In one embodiment of the apparatus, during the operating period, the base station operates as in an active mode. In one embodiment of the apparatus, the base station omits transmitting a pilot signal when in the energy saving mode.

In one embodiment of the apparatus, the radio access network further comprises a neighbor cell for the cell and wherein, during the operating period, the base station serves a geographical area of the cell and at least partly a geographical area of the neighbor cell.

In one embodiment of the apparatus, the radio access network further comprises an entity granting a permission to enter the energy saving mode.

BRIEF DESCRIPTION OF THE DRAWINGS

[0021] For a more complete understanding of examples and embodiments of the present invention, reference is now made to the following descriptions taken in connection with the accompanying drawings in which:

FIGURE 1 shows an example of Legacy cells and E-UTRA cells;

FIGURE 2 shows an example of a macro cell and phantom cells;

FIGURE 3 shows an embodiment of a method for energy saving;

FIGURE 4 shows options of the method for energy saving;

FIGURE 5A shows the first embodiment for requesting a working mode change;

FIGURE 5B shows the second embodiment for requesting a working mode change;

FIGURE 5C shows the third embodiment for requesting a working mode change;

FIGURE 6 shows the fourth embodiment for requesting a working mode change;

FIGURE 7 shows an example of informing neighbor cells;

FIGURE 8 shows an example of notifying user equipments;

FIGURE 9 shows an embodiment of an apparatus for energy saving.

FIGURE 10 shows an embodiment of a method for energy saving.

DETAILED DESCRIPTON OF THE INVENTION

[0022] For energy saving reasons it is sometimes better to use a macro cell instead of number of small cells. If there is low traffic, the small cells can sleep. When a small cell detects a low level of traffic, it aims to enter an energy saving mode, such as a sleep mode. The sleep mode basically corresponds to the dormant mode mentioned in the background of the application, because the small cell does not transmit anything in the sleep mode. The periods during which the small cell transmits and/or receives are relative short. The small cell sleeps between those periods and thus saves energy.

[0023] Generally speaking, offloading means that a cell moves at least a part of its traffic to another cell. Offloading is perfomed because it saves energy of the ceil. The energy saving is possible when the offloaded traffic can be handled, instead of two base stations, in one base station. The small cell offloads its traffic before entering the sleep mode because in the sleep mode it cannot serve either UEs or any other entities. When the energy saving mode is other than the sleep mode, the small cell may offload its traffic before entering the energy saving mode. Alternatively, the small cell offloads its traffic after entering the energy saving mode. If the small cell does not have any traffic, offloading is not needed.

[0024] Each small cell is the first to detect that its traffic is at low level. It would take longer that some other cell eventually detects the low traffic of the small cell. The small cell has some predetermined threshold for traffic. The small cell measures the traffic and detects whether the measured amount of traffic is below the predetermined threshold. In one embodiment the small cell measures the traffic as amount of served UEs. Alternatively, in another embodiment, the small cell measures the traffic as amount of downlink (DL)/uplink (UL) traffic. The DL traffic is known by the small cell directly and the small cell can determine the UL traffic on the basis of buffer status reports (BSR) which it reveives from UEs.

[0025] After the detection of low traffic the small cell requests from the macro cell a permission to leave the active mode. One fact at, this point of time, is that the small cell has minor traffic. Another fact is that the macro cell is a kind backup resource having enough capacity to handle the traffic of the small cell. Therefore, the small cell can probably offload its traffic and enter the energy saving mode. The traffic can be offloaded to the macro cell or a neighbor cell of the macro cell.

[0026] Offloading requires communication between the small cell and UEs .This communication may be based on RRC protocol layer that provides functions such as

broadcasting system information (SI) in a RAN. The system information is grouped together into a master information block (MIB) and various system information blocks (SIBs). MIB is transferred regularly (every 40 ms) on a broadcast channel of the RAN. A UE acquires MIB to decode a shared channel. MIB contains a downlink system bandwith, a physical HARQ (hybrid adaptive repeat and request) indicator channel, and a frame number. SIB1 is the first system information block to be transferred after transferring MIB. SIB1 contains cell-access-related information, information for cell selection, a frequency band indicator, etc. In addition, SIB1 contains SI- window length and a system information value tag. SIB 1 is transmitted in a system information block message and the other SIBs are transmitted in SI messages. Each SI message is transmitted periodically so that different SI messages do not overlap in time. In addition to SIB 1, the prior art comprises other SIBs for various puiposes.

[0027J FIGURE 3 shows the method for energy saving in a radio access network comprising a first cell and a second cell located within a geographical area of the first cell. The method comprises the following to be performed in the second cell: detecting 301 that an amount of traffic in a base station of the second cell is below a predetermined threshold; obtaining 302 from the first cell a permission to enter the base station into an energy saving mode; and entering 303 the energy saving mode. FIG. 3 shows a positive case, i.e. the case when the second cell obtains the permission. In a negative case the first cell does not grant the permission.

[0028] The energy saving mode may be a known mode such as a sleep mode in which transmitting is continuously disabled until the mode is changed. Usually, the sleep mode also means that receiving is disabled. There may be different implementations in different networks.

[0029] Another known energy saving mode is a discontinuos transmission (DTX) mode. The DTX mode used in a base station differs from the discontinuous transmission used in user equipments. The DTX mode does not comprise a sleep period or an operating period. When the base station is in the DXT mode, it stops scheduling UEs in order to save power. The base station, however, still transmits on a broadcast control channel (BCH) and/or cell-specific reference signal (CRS).

[0030] Alternatively, the energy saving mode can be a "low-activity mode". In one embodiment, the low-activity mode comprises at least one sleep period and at least one operating period. In one embodiment, the base station does not transmit or receive during the sleep period. The low activity mode allows the base station to sleep between the operating periods. When the sleep period is so short, e.g. several radio frames, the base station can still serve, during operating periods, those UEs which it is currently serving. Thus, it is not necessary to handover the UEs. In one embodiment, the base station operates in the working mode exactly as in the active mode. The low activity mode is not limited to this kind of RAN, but can be used by many types of access nodes (e.g. a base station, Node B or Evolved Node B), in many types of RANs for energy saving. The low-activity mode is discussed in detail with FIG. 10.

[0031] Generally speaking, u-ansmitting consumes the most of power in the base station. Especially a power amplifier consumes the power during each transmission. Therefore, especially such tasks which are not essential and which involve transmitting should be omitted, at the first cell, for energy saving reasons. Sometimes one base station is able to perform tasks of two or even more base stations. Thus, omitting tasks does not necessarily mean that the tasks are not performed at all. It may be possible to limit use of at least one transmitter of the base station. It may also be possible limit use of at least one receiver of the base station. A

transmitting/receiving limitation may concern only the data channels of the RAN. In addition, the transmitting/receiving limitation may concern the control channels of the RAN. In one embodiment, the base station listens to at least one control channel of the RAN and thus the base station can be contacted and its working mode can be changed. In one embodiment, the energy saving mode is a "swithed off minimizing the power consumption. In that mode the base station is switched off, but can be remotely swiched on.

[0032] FIGURE 4 shows options of the method for energy saving in accordance with some embodiments of the invention. The method described in FIG. 3 is usable as such, because the working mode of the second cell is changable by the method. The options provide certain additional features that can be utilized in various implementations of the method. A first option relates to the obtaining 302, a second option is offloading 401 of traffic, a third option is infonning 402 at least one neighbor cell of the second cell, and a fourth option is notifying 403 at least one user equipment served by the second cell, wherein the informing 402 and the notifying 403 may concern at least the working mode of the second cell.

[0033] As decribed in FIG. 3, the second cell detects when the measured amount of traffic is below the predetermined threshold. In one embodiment the measurement results are used for requesting 404 the permission from the first cell. In more detail, the second cell sends such traffic measurement results, which indicate low traffic, to the first cell and thus the second cell indicates its wish/desire for entering an energy saving mode. In some embodiments the second cell has no means for specifying to which energy saving mode it wants move. For example, when the first cell receives the traffic measurement results indicating low traffic that input (the traffic measurement results) does not as such disclose to which energy saving mode the second cell wants move. It is, however, possible to define a "default energy saving mode". The default energy saving mode is, for example, the low-activity mode. Then the permission granted by the first cell means that the second cell is allowed to move to the low-activity mode.

[0034] There are also embodiments in which the second cell has means for specifying a desired energy saving mode. Then the requesting 404 is performed by a message that is defined or modified for that purpose. For example, if an information element (IE) can carry a working mode value, such as "low-activity", from the second cell to the first cell, then the second cell can specify to which working mode it wants to move. Other possible values of the IE are, for example, "sleep" and "normal". When the second cell is specified, for example, that it wants to move to the low-activity mode, the first cell either grants the permission or not. The requesting 404 can be performed by sending a resource status request message and/or a mobility change request message to the first cell as illustrated in FIGs. 5A, 5B, and 5C. Alternatively, the requesting 404 can be performed by sending a load information message to the first cell as illustrated in FIG. 6.

[0035] The second option of the method is the offloading 401 of traffic. The method of

FIG. 3 is intended for such RAN in which a second cell locates within a geographical area of the first cell. In other words, the geographical area of the second cell locates inside the geographical area of the first cell. In one embodiment the traffic is offloaded from the second cell to the first cell. As can be seen in FIG. 1 and in FIG. 2, small cells may or may not overlap each other. When the macro cell covers the small cells, the macro can serve a UE when the UE leaves the small cell. Thus, the traffic can be offloaded to the first cell. If the small cells overlap, they can perform a handover on their cell border, i.e. the offloading traffic is possible on the cell border. The document TS 36.927 desccribes a scenario in which a small cell (an E-UTRAN cell) may enlarge, which creates possibilities to offload traffic to neighbor cell(s). The enlarging cell is termed a compensation cell because it compensates an "energy saving cell" when the energy saving cell moves to the dormant mode. In this scenario a cell enlarges on the geographical area of its neighbor cell and serves UEs on that area. In one embodiment of the method the second cell offloads the traffic to a neighbor cell. This offloading 401 to the neighbor cell requires that the first cell overlaps the neighbor cell or the neighbor cell is able to enlarge on the area of the second cell. The offloading 401 may concern the all UEs of the second cell or a part of them. [0036] The third option of the method is informing 402 neighbor cell(s) of the second cell so that the neighbor cell(s) can take into account the current working mode of the second cell.

[0037] The fourth option of the method is notifying 403 user equipment(s) of the second cell so the user equipment(s) can take into account the current working mode of the second cell.

[0038] FIGURE 5A shows the first embodiment for the requesting 404 a permission to enter an energy saving mode. This embodiment relates to the obtaining 301 the permission from the first cell. The second cell sends a resource status request message 501 to the first cell and receives a resource status update message 502 sent from the first cell. In one embodiment, the second cell may decide whether to send energy saving request to the first cell by the available resources of the first cell as indicated by the first call e.g. in the resource status update message. In some embodiments, the second cell set a timer before it sends the resource status request message 501. If the timer expires, the second cell intepretes that the permission is not granted. In some embodiments, a specific message is used for notifying that the permission is not granted. In some embodiments, the first cell sends to the second cell such message which includes either a "permission granted" or "not granted" notification.

[0039] FIGURE 5B shows the second embodiment for the requesting 404 the permission. It starts in the same way as the first embodiment, i.e. the second cell send a resource status request message 501 to the first cell and receives a resource status update message 502 sent from the first cell. Then the second cell sends a mobility change request message 503 with a cause value to the first cell. The second cell can specify by the cause value to which working mode or energy saving mode it wants to move. When the first cell acknowledges 504, e.g. with a mobility change acknowledge message, the mobility change request message 503, the second cell intepretes that the permission is granted. The cause value is, for example, "Energy Saving in Serving Ceil" and it is placed, for example, into the following information element (IE):

[0040] FIGURE 5C shows the third embodiment for the requesting 404 the permission. The second cell sends the mobility change request message 503 with the cause value to the first cell and when the first cell acknowledges 504 the mobility change request message 503, the second cell intepretes that the permission is granted.

[0041] As in the first embodiment (FIG. 5A), a timer can be utilized in the second or the third embodiment (FIGs. 5B and 5C). If the timer expires, the second cell interpretes that the first cell is not going to acknowledge the mobility change request message 503, i.e. the permission is not granted.

[0042] FIGURE 6 shows the fourth embodiment for the requesting 404 the permission.

The second cell sends a load information message 601 to the first cell and receives from the first cell a load information message 602 with an active interval and resource information. The second cell intepretes the message 602 as the permission to enter the energy saving mode. A timer can be utilized also in this embodiment.

[0043] FIGURE 7 shows example of informing neighbor cell(s) and it illustrates the option of the informing 402. In this example the second cell sets up interface (e.g. X2 interface) in order to inform a neighbor cell about its current working mode. At first, the second cell sends a setup request message 701 with specific information, such as "Served Cell Information" with the working mode "low-active", to the neighbor cell. The Served Cell Information is carried in an IE containing cell configuration information of a cell that the neighbor cell may need. Then the neighbor cell replies with a setup response message 702. The setup response message includes specific information, such as "Served Cell Information" with a current working mode. If the current working mode of the neighbor cell is "normal", the "Served Cell Information" will include "normal". When the second cell receives the setup request message 702 from the neighbor cell, it determines that the neighbor cell is now informed about the new working mode of the second cell. When the second cell is in the low-active mode and the mode includes sleep periods, the second cell does not necessarily take new UEs to be served. In other words, the low- activity mode may effect to handovers.

[0044] In addition to handovers, there are other reasons why neighbor cell(s) are informed about a working mode change. One reason is that the second cell and its neighbor cell can also be simultaneously in the low-activity mode. Then, in one embodiment, the second cell has a sleep period in the same time when the neighbor cell has its operating period, and correspondingly, the second cell has an operating period in the same time when the neighbor cell has its sleep period. Therefore, the second cell and the neighbor cell don't sleep in the same time, meaning that the UEs on theirs geographical area should not be without network services. In addition, the described embodiment enables that the second cell and first cell don't transmit in the same time, because theirs operating periods are not overlapping. A positive consequence is that the second cell and first cell don't interfer each other. As well-know, transmitting may cause radio interferences in neighbor cells. Therefore, in some embodiments, small cells, and generally cells, inform each other to coordinate theirs operating periods and to avoid radio interferences. For example, an update message (e.g. ENB configuration update message) can be used for infonning small cells about the new working mode and/or operating periods and/or sleep periods. In some embodiments, if the small cells have a macro cell, the working mode change

information can be sent from the macro cell.

[0045] FIGURE 8 shows an example of notifying user equipments) and it illustrates the option of the notifying 403. In this example the second cell has obtained the permission move to a new working mode, e.g. to the low-activity mode. Then the second cell notifies the UEs served by it about the current working mode. In one embodiment the UEs are informed with SIB 14. The low-activity mode can be disclosed, for example, as a new "low-active" value in SIB 14:

-- ASN1 START

SystemInfonnationBlockT pel4-rl2 ::= SEQUENCE {

workingMode-rl2 ENUMERATED {normal, low-active, sleep, sparel },

}

- ASN1STOP The first cell pages a UE to receive SIB 14. Then the first cell notifies with SIB 14 the UE about the current working mode. SIB 14 further comprises an operation interval, usable resources, serving power, etc. Alternatively, SIB2 can be modified correspondingly as SIB 14 by adding a new value ("low-active") into it. Then the first cell pages the UE to receive SIB2. in SIB2 the small cell notifies the UE about PRACH (physical random access channel) resources. Those resources are usable for communication between the base station and the UE. After receiving SIB 14 or SIB2, the UE starts to measure in the second cell. The measuments may concern, for example, reference symbol received power (RSRP). The first cell may decide to handover the UE based on the measurement report of the UE. The handover from the second cell to the first cell may be possible because the second cell locates inside the first cell. The handover may also possible to some neighbor cell of the second cell. Nevertheless, the offloading 401 of traffic is performed one UE handover at a time. The offloading 401 can be performed before the entering 303 the energy saving mode or after the entering 303.

[0046] FIGURE 9 shows an embodiment of an apparatus 901 for energy saving. The apparatus 901 comprises at least one processor and at least one memory including computer program code. The at least one memory and the computer program code arranged to, with the at least one processor, cause the apparatus to perform the following. The apparatus 901 is intended for energy saving in a radio access network comprising at least a first cell 902 and the second cell 903 located within a geographical area of the first cell 902. The apparatus can be incorporated into the second cell 903 though it is shown as a sapareted device in FIG. 9. The apparatus 901 detects that an amount of traffic in a base station 904 of a second cell 903 is below a predetermined threshold. Then the apparatus 901 obtains from the first cell 902 a permission to enter the base station 904 into an energy saving mode. After that, the apparatus 901 enters the base station 904 into the energy saving mode.

[0047] The notifying 403 can also be described from a point of view of a UE, such as a

UE 906. The UE 906 is served by the base station 904 of the second cell 903 and the UE 906 uses the following method. At first, it obtains information notifying the UE 906 about an energy saving mode of the second cell 903. The base station 904 has at least one sleep period in the energy saving mode. Then the UE 906 schedules a task so that the task is to be performed outside of the at least one sleep period. This task is a) communicating with the base station, b) measuring a pilot signal of the base station, or c) performing a handover. The energy saving mode fUrther provides at least one operating period. The UE 905 should perform the task within the at least one operating period. Otherwise the task fails, because the base station 904 is sleeping. When using orthogonal frequency-division multiple access (OFDMA), requency division multiple access (FDMA), or code division multiple access (CDMA), a same operating period is usable for the UE 906 and at at least one other UE. In one embodiment, the information obtained by the UE 906 causes the UE 906 to measure of a pilot signal of at least one other base station, for example, a pilot signal of a base station 907 or a pilot signal of a base station 908. Then, on the basis pilot signal measurements, the UE 906 may perform a handover to the first cell 902 or the neighbor cell 905. In one embodiment, the user equipment makes a decision about the handover. Thus, the UE 906 may stay in the second cell 903.

[0048] FIGURE 10 shows an embodiment of a method for energy saving. The method is usable in a radio access network that comprises at least one cell. The method comprises the following: entering a cell in an energy saving mode providing at least one sleep period during which a base station of the cell omits transmitting and receiving. In one embodiment of the method of FIG. 10 the energy saving mode is the low-activity mode. There exist various embodiments and some of them can be simultaneously utilized.

[0049] In embodiment #1, an ending time of the energy saving mode is preset.

[0050] In embodiment #2, there is no ending time but the energy saving mode ends when the mode is changed to another mode (embodiment #1 cannot be used simultaneously with embodiment #2).

[0051] In embodiment #3, the base station has a number of sleep periods and operating periods when it is in the energy saving mode.

[0052] In embodiment #4, the energy saving mode further provides an operating period within which the base station operates as in an active mode.

[0053] In embodiment #5, the base station omits tranmitting a pilot signal within the energy saving mode (in the active mode the base station omits nothing, thus embodiment #4 cannot be used simultaneously with embodiment #5). When using embodiment #5 the cell does take new user equipments to be served.

[0054] In embodiment #6, the base station serves, during the operating period, a geographical area of the cell and a geographical area of the neighbor cell. In one embodiment, the cell and the neighbor cell are cells of a heterogeneous network. For example, the cell is the second cell and the neighbor cell is the cell 905 in FIG. 9. In another embodiment, the cell and the neighbor cell are cells of a homogeneous network.

[0055] In embodiment #7, the radio access network further comprises an entity granting a permission to enter the energy saving mode. The entity is e.g. the first cell 902.

[0056] The following embodiments can be at least utilized with the method of FIG. 3 and the method of FIG. 10. In one embodiment, the length of a time period between each sleep period is a constant. In one embodiment, the length of the time period between each sleep period is the length of an operating period. In one embodiment, the length of the operating period is known when the length of the sleep period is known. In one embodiment, the length of the sleep period is known when the length of the operating period is known. In one embodiment, the length of a sleep period is a constant and the length of an operating period is a constant. For example, the lengtli of the sleep period could be four radio frames and the length of the operating period could be six radio frames. In this example, the sleep period recurs regularly, and correspondingly, the operation period recurs regularly. In one embodiment, the at least one the following varies: the length of a sleep period or a length of an operating period.

[0057] In one embodiment, the entity coordinates operation of cells, for example, the cells 903, 905. The entity considers which is currently the best energy saving mode for a certain cell. The best mode could be at first e.g. the low-activity mode. Then the base station of cell enters the low-activity mode and eventually it has served all its UEs. After that the cell can request from the entity a permission to enter the sleep mode. After the grant, the cell sleeps. The entity can move the cell again to the low-activity mode when there is more traffic. Alternatively, the entity can move the cell to the active mode, if the traffic suddenly increases.

[0058] The next example embodiments relates to homogeneous networks. Generally speaking, a cell needs a permission to enter the low-activity mode. The cell could have a "general permission" meaning that the base station of the cell is allowed to sleep intermittently, if the cell performs its duties during the operating periods related to the low-activity mode. In more detail, the base station should schedule its UEs so that it can have sleep periods. The scheduling comprises the notifying 403 that can be performed, as described in the above, e.g. with SIB 14. When an amount of traffic is low, the sleep periods are long. When the traffic increases, the base station shortens its sleep periods. Correspondingly, when there is a lot of traffic, the base station changes its working mode to the active mode. It should be, however, noticed that if a sleep period is relatively long, there is also a relatively long period during which the base station omits sending a pilot signal (assuming that the base station does not transmit anything when it is sleeping). There may be an upper limit for the maximum length of the sleep period. In one embodiment, the entity sets the length of a sleep period. In one embodiment, the cell sets the length of a sleep period. In one embodiment, the entity is allowed to change the length of a sleep period.

[0059] The present invention may be implemented in software, hardware, application logic or a combination of software, hardware and application logic. The hardware may be, for example, a chip, a modem, or some other apparatus which includes or is coupled to at least memory and at least one processor. The application logic, software or instruction set is maintained on any one of various conventional computer-readable media. In the context of this document, a "computer-readable medium" may be any media or means that contain, store, communicate, propagate or transport the instructions for use by or in connection with an instruction execution system, apparatus, or device, such as a computer. A computer-readable medium may comprise a computer-readable storage medium that may be any media or means that contain or store the instructions for use by or in connection with an instruction execution system, apparatus, or device, such as a computer.

[0060] When not otherwise mentioned, "one embodiment" in the above refers to "one embodiment of the present invention". The exemplary embodiments can store information relating to various processes described herein. This information can be stored in one or more memories, such as a hard disk, optical disk, magneto-optical disk, RAM, and the like.

[0061] All or a portion of the exemplary embodiments can be conveniently

implemented using one or more general puipose processors, microprocessors, digital signal processors, micro-controllers, and the like, programmed according to the teachings of the exemplary embodiments of the present invention, as will be appreciated by those skilled in the computer and/or software art(s). Appropriate software can be readily prepared by programmers of ordinaiy skill based on the teachings of the exemplary embodiments, as will be appreciated by those skilled in the software art. In addition, the exemplary embodiments can be implemented by the preparation of application-specific integrated circuits or by interconnecting an appropriate network of conventional component circuits, as will be appreciated by those skilled in the electrical art(s). Thus, the exemplary embodiments are not limited to any specific combination of hardware and/or software.

[0062] Stored on any one or on a combination of computer readable media, the exemplary embodiments of the present invention can include software for controlling the components of the exemplary embodiments, for driving the components of the exemplary embodiments, for enabling the components of the exemplary embodiments to interact with a human user, and the like. Such software can include, but is not limited to, device drivers, firmware, operating systems, development tools, applications software, and the like. Such computer readable media further can include the computer program of an embodiment of the present invention for performing all or a portion (if processing is distributed) of the processing performed in implementing the present invention. Computer code devices of the exemplary embodiments of the present invention can include any suitable interpretable or executable code mechanism, including but not limited to scripts, interpretable programs, dynamic link libraries (DLLs), Java classes and applets, complete executable programs, Common Object Request Broker Architecture (CORBA) objects, and the like.

[0063] While the present invention has been described in connection with a number of exemplary embodiments, and implementations, the present invention is not so limited, but rather covers various modifications, and equivalent arrangements, which fall within the purview of prospective claims.

Claims

WHAT IS CLAIMED IS:

A method for energy saving in a radio access network comprising a first cell and a second cell located within a geographical area of the first cell, the method comprising the following to be performed in the second cell:

The method according to claim 1, wherein the energy saving mode is one of the following modes: a sleep mode in which transmitting is disabled, a discontinues transmission (DTX) mode that omits scheduling user equipments.

The method according to claim 1, wherein the energy saving mode is a low-activity mode, the low-activity mode providing at least one sleep period during which the base station omits at least transmitting and receiving.

The method according to claim 3, wherein the low-activity mode further provides at least one operating period during which the base station operates as in an active mode.

The method according to claim 1, wherein the method further comprises:

offloading at least a part of the traffic to the first cell or a neighbor cell.

The method according to claim 1, wherein the obtaining comprises requesting from the first cell the permission to enter the energy saving mode.

The method according to claim 6, wherein the requesting causes the second cell to send at least one of the following messages: a resource status request message, a mobility change request message.

The method according to claim 6, wherein the requesting causes the second cell to send a load information message to the first cell.

The method according to claim 1, wherein the method further comprises:

informing a neighbor cell about the entering the energy saving mode.

The method according to claim 9, wherein the informing causes the second cell to send a setup request message or an update message to the neighbor cell.

The method according to claim 1, wherein the method further comprises: notifying a user equipment about the energy saving mode of the second cell.

12. The method according to claim 11, wherein the notifying further comprises at least one of the following periods: a sleep period, an operating period, wherein the sleep period has a starting time and length and the operating period has a starting time and length.

13. The method according to claim 11, wherein the notifying causes sending a system information block to the user equipment.

14. A method for energy saving in a radio access network comprising a first cell and a second cell located within a geographical area of the first cell, the method comprising the following to be performed in the first cell:

obtaining from the second cell a message indicating that traffic in a base station of the second cell is under a predetermined threshold; granting a permission for the second cell to enter the base station into an energy saving mode.

15. The method according to claim 14, wherein the energy saving mode is one of the following modes: a sleep mode in which transmitting is disabled, a discontinues transmission (DTX) mode that omits scheduling user equipments.

16. The method according to claim 14, wherein the energy saving mode is a low- activity mode, the low-activity mode providing at least one sleep period during which the base station omits transmitting and receiving.

17. The method according to claim 16, wherein the low-activity mode further provides at least one operating period during which the base station operates as in an active mode.

18. The method according to claim 14, wherein the method further comprises:

handling traffic that is offloaded from the second cell.

19. The method according to claim 14, wherein the message is one of the following messages: a resource status request message, a mobility change request message, a load information message.

20. The method according to claim 14, wherein the granting comprises setting at least one of the following periods: the sleep period, an operating period, wherein at least the sleep period has a starting time and length and the operating period has a starting time and length. 21. The method according to claim 20, wherein the method further comprises:

granting a permission for a third cell to enter the energy saving mode, wherein the granting is performed so that an operating period of the third cell is non- overlapping with the operating period granted to the second cell.

22. A method for energy saving in a radio access network comprising a first cell and a second cell located within a geographical area of the first cell, wherein a user equipment is served by a base station that forms the second cell, the method comprising the following to be performed in the user equipment:

obtaining information notifying the user equipment about an energy saving mode of the second cell, the base station having in the energy saving mode at least one sleep period; and scheduling a task so that the task is to be performed outside of the at least one sleep period, wherein the task is one of the following: communicating with the base station, measuring a pilot signal of the base station, performing a handover.

23. The method according to claim 22, wherein the information causes the user

equipment to measure a pilot signal of at least one other base station.

24. The method according to claim 22, wherein the handover is targeted to one of the following cells: the first cell, a neighbor cell of the second cell.

25. The method according to claim 22, wherein at least part of the information is

obtained with a system information block.

26. The method according to claim 22, wherein the radio access network uses at least one of the following techniques: orthogonal frequency-division multiple access (OFDMA), requency division multiple access (FDMA), code division multiple access (CDMA).

27. The method according to claim 22, wherein the energy saving mode provides at least one operating period and the task is to be performed within the at least one operating period.

28. A method for energy saving in a radio access network comprising a cell formed by a base station, the method comprising the following:

entering the cell in an energy saving mode providing at least one sleep period during which the base station of the cell omits transmitting and receiving. 29. The method according to claim 28, wherein the energy saving mode further provides at least one operating period.

30. The method according to claim 28, wherein during the operating period the base station operates as in an active mode.

31. The method according to claim 28, wherein the base station omits transmitting a pilot signal when in the energy saving mode.

32. The method according to claim 28, wherein the radio access network further

comprises a neighbor cell for the cell and wherein, during the operating period, the base station serves a geographical area of the cell and at least partly a geographical area of the neighbor cell.

33. The method according to claim 28, wherein the radio access network further

comprises an entity granting a permission to enter the energy saving mode.

34. An apparatus comprising:

at least one processor; and at least one memory including computer program code, the at least one memory and the computer program code arranged to, with the at least one processor, cause the apparatus to perform at least the following:

detecting that an amount of traffic in a base station is below a predetermined threshold, wherein a radio access network comprises a first cell and a second cell, the second cell is located within a geographical area of the first cell, and the base station forms the second cell; obtaining from the first cell a pennission to enter the base station into an energy saving mode; and entering the energy saving mode.

35. The apparatus according to claim 34, wherein the energy saving mode is one of the following modes: a sleep mode in which transmitting is disabled, a discontinuos transmission (DTX) mode that omits scheduling user equipments.

36. The apparatus according to claim 34, wherein the energy saving mode is a low- activity mode, the low-activity mode providing at least one sleep period during which the base station omits at least transmitting and receiving.

37. The apparatus according to claim 34, wherein the low-activity mode further

provides at least one operating period during which the base station operates as in an active mode.

38. The apparatus according to claim 34, wherein the apparatus performs: offloading at least a part of the traffic to the first cell or a neighbor cell.

39. The apparatus according to claim 34, wherein the obtaining comprises requesting f om the first cell the permission to enter the energy saving mode.

40. The apparatus according to claim 39, wherein the requesting comprises sending to the first cell at least one of the following messages: a resource status request message, a mobility change request message.

41. The apparatus according to claim 39, wherein the requesting comprises sending a load information message to the first cell.

42. The apparatus according to claim 34, wherein the apparatus performs:

informing a neighbor cell about the entering the energy saving mode.

43. The apparatus according to claim 42, wherein the informing comprises sending a setup request message to the neighbor cell.

44. The apparatus according to claim 34, wherein the apparatus performs:

notifying a user equipment about the energy saving mode of the second cell.

45. The apparatus according to claim 44, wherein the notifying comprises sending a system information block to the user equipment.

46. The apparatus according to claim 34, wherein the apparatus is used in at least one of the following systems: a long term evolution (LTE) system, a LTE-A system.

47. The apparatus according to claim 34, wherein the apparatus is one of the following apparatuses: a base station, an eNB, an eNodeB.

48. An apparatus comprising:

obtaining from a second cell a message indicating that traffic in a base station of the second cell is under a predetermined threshold, wherein a radio access network comprises a first cell and the second cell and wherein the second cell is located within a geographical area of the first cell; granting a permission for the second cell to enter the base station into an energy saving mode. 49. The apparatus according to claim 48, wherein the energy saving mode is one of the following modes: a sleep mode in which transmitting is disabled, a discontinuos transmission (DTX) mode that omits scheduling user equipments.

50. The apparatus according to claim 48, wherein the energy saving mode is a low- activity mode, the low-activity mode providing at least one sleep period during which the base station omits transmitting and receiving.

51. The apparatus according to claim 50, wherein the low-activity mode further

52. The apparatus according to claim 48, wherein the apparatus performs:

handling traffic that is offloaded from the second cell.

53. The apparatus according to claim 48, wherein the message is one of the following messages: a resource status request message, a mobility change request message, a load information message.

54. The apparatus according to claim 48, wherein the apparatus is used in at least one of the following systems: a long term evolution (LTE) system, a LTE-A system.

55. The apparatus according to claim 48, wherein the apparatus is one of the following apparatuses: a base station, an eNB, an eNodeB.

56. An apparatus comprising:

obtaining information notifying a user equipment about an energy saving mode of a second cell, wherein a radio access network comprises a first cell and the second cell that is located within a geographical area of the first cell, the user equipment is served by a base station that forms the second cell, and the base station has in the energy saving mode at least one sleep period; and scheduling a task so that the task is to be performed outside of the at least one sleep period, wherein the task is one of the following: communicating with the base station, measuring a pilot signal of the base station, performing a handover. 57. The apparatus according to claim 56, wherein the information causes the user equipment to measure a pilot signal of at least one other base station.

58. The apparatus according to claim 56, wherein the handover is targeted to one of the following cells: the first cell, a neighbor cell of the second cell.

59. The apparatus according to claim 56, wherein the notifying comprises sending at least part of the information in a system information block.

60. The apparatus according to claim 56, wherein the radio access network uses at least one of the following techniques: orthogonal frequency-division multiple access (OFDMA), frequency division multiple access (FDMA), code division multiple access (CDMA).

61. The apparatus according to claim 56, wherein the energy saving mode provides at least one operating period and the task is to be performed within the at least one operating period.

62. The apparatus according to claim 56, wherein the apparatus is used in at least one of the following systems: a long term evolution (LTE) system, a LTE-A system.

63. The apparatus according to claim 48, wherein the apparatus is one of the following apparatuses: a base station, an eNB, an eNodeB.

64. An apparatus comprising:

entering a cell into an energy saving mode providing at least one sleep period during which a base station of the cell omits transmitting and receiving, wherein a radio access network comprises the cell formed by the base station.

65. The apparatus according to claim 64, wherein the energy saving mode further provides at least one operating period.

66. The apparatus according to claim 65, wherein during the operating period the base station operates as in an active mode.

67. The apparatus according to claim 64, wherein the base station omits transmitting a pilot signal when in the energy saving mode. 68. The apparatus according to claim 64, wherein the radio access network further comprises a neighbor cell for the cell and wherein, during the operating period, the base station serves a geographical area of the cell and at least partly a geographical area of the neighbor cell.

69. The apparatus according to claim 64, wherein the radio access network further comprises an entity granting a permission to enter the energy saving mode.

70. An apparatus comprising:

detecting means for detecting that an amount of traffic in a base station is below a predetennined threshold, wherein a radio access network comprises a first cell and a second cell, the second cell is located within a geographical area of the first cell, and the base station forms the second cell; obtaining means for obtaining from the first cell a permission to enter the base station into an energy saving mode; and entering means for entering the energy saving mode.

71. The apparatus according to claim 70, wherein the energy saving mode is one of the following modes: a sleep mode in which transmitting is disabled, a discontinuos transmission (DTX) mode that omits scheduling user equipments.

72. The apparatus according to claim 70, wherein the energy saving mode is a low- activity mode, the low-activity mode providing at least one sleep period during which the base station omits at least transmitting and receiving.

73. The apparatus according to claim 72, wherein the low-activity mode further

74. The apparatus according to claim 70, wherein the apparatus further comprise: offloading means for offloading at least a part of the traffic to the first cell or a neighbor cell.

75. The apparatus according to claim 70, wherein the obtaining comprises requesting from the first cell the permission to enter the energy saving mode.

76. The apparatus according to claim 75, wherein the requesting comprises sending to the first cell at least one of the following messages: a resource status request message, a mobility change request message. 77. The apparatus according to claim 75, wherein the requesting comprises sending a load information message to the first cell.

78. The apparatus according to claim 70, wherein the apparatus further comprises: informing means for infonning a neighbor cell about the entering the energy saving mode.

79. The apparatus according to claim 78, wherein the informing comprises sending a setup request message to the neighbor cell.

80. The apparatus according to claim 70, wherein the apparatus further comprises: notifying means for notifying a user equipment about the energy saving mode of the second cell.

81. The apparatus according to claim 70, wherein the notifying comprises sending a system information block to the user equipment.

82. An apparatus comprising:

obtaining means for obtaining from a second cell a message indicating that traffic in a base station of the second cell is under a predetermined threshold, wherein a radio access network comprises a first cell and the second cell and wherein the second cell is located within a geographical area of the first cell; granting means for granting the first cell a permission to enter the base station into an energy saving mode.

83. The apparatus according to claim 82, wherein the energy saving mode is one of the following modes: a sleep mode in which transmitting is disabled, a discontinuos transmission (DTX) mode that omits scheduling user equipments.

84. The apparatus according to claim 82, wherein the energy saving mode is a low- activity mode, the low-activity mode providing at least one sleep period during which the base station omits transmitting and receiving.

85. The apparatus according to claim 82, wherein the low-activity mode further

86. The apparatus according to claim 82, wherein the apparatus further comprises: handling means for handling traffic that is offloaded from the second cell. 87. The apparatus according to claim 82, wherein the message is one of the following messages: a resource status request message, a mobility change request message, a load information message.

88. An apparatus comprising:

obtaining means for obtaining information notifying a user equipment about an energy saving mode of a second cell, wherein a radio access network comprises a first cell and the second cell that is located within a geographical area of the first cell, the user equipment is served by a base station that forms the second cell, and the base station has in the energy saving mode at least one sleep period; and scheduling means for scheduling a task so that the task is to be performed outside of the at least one sleep period, wherein the task is one of the following:

communicating with the base station, measuring a pilot signal of the base station, performing a handover.

89. The apparatus according to claim 88, wherein the information causes the user

equipment to measure a pilot signal of at least one other base station.

90. The apparatus according to claim 88, wherein the handover is targeted to one of the following cells: the first cell, a neighbor cell of the second cell.

91. The apparatus according to claim 88, wherein the notifying comprises sending at least part of the information in a system information block.

92. The apparatus according to claim 88, wherein the radio access network uses at least one of the following techniques: orthogonal frequency-division multiple access (OFDMA), frequency division multiple access (FDMA), code division multiple access (CDMA).

93. The apparatus according to claim 88, wherein the energy saving mode provides at least one operating period and the task is to be performed within the at least one operating period.

94. An apparatus comprising:

entering means for entering a cell in an energy saving mode providing at least one sleep period during which a base station of the cell omits transmitting and receiving, wherein a radio access network comprises the cell formed by the base station. 95. The apparatus according to claim 94, wherein the energy saving mode further provides at least one operating period.

96. The apparatus according to claim 95, wherein during the operating period the base station operates as in an active mode.

97. The apparatus according to claim 94, wherein the base station omits transmitting a pilot signal when in the energy saving mode.

98. The apparatus according to claim 94, wherein the radio access network further comprises a neighbor cell for the cell and wherein, during the operating period, the base station serves a geographical area of the cell and at least partly a geographical area of the neighbor cell.

99. The apparatus according to claim 94, wherein the radio access network further comprises an entity granting a permission to enter the energy saving mode.