WO2014154254A1

WO2014154254A1 - Method and apparatus

Info

Publication number: WO2014154254A1
Application number: PCT/EP2013/056424
Authority: WO
Inventors: Beatriz SORET-ALVAREZ; Troels Emil Kolding; Klaus Ingemann Pedersen
Original assignee: Nokia Solutions And Networks Oy
Priority date: 2013-03-26
Filing date: 2013-03-26
Publication date: 2014-10-02

Abstract

A method comprises using scheduling information for user equipment in a larger cell and scheduling information for user equipment in at least one smaller cell to determine if at least one cell is to be in a lower power mode, said at least one smaller cell at least partially overlapping said larger cell and is smaller than said larger cell.

Description

METHOD AND APPARATUS

This disclosure relates to methods and apparatus and in particular but not exclusively to methods and apparatus for use where there are at least partially overlapping cells.

A communication system can be seen as a facility that enables communication sessions between two or more nodes such as fixed or mobile devices, machine-type terminals, access nodes such as base stations, servers and so on. A communication system and compatible communicating entities typically operate in accordance with a given standard or specification which sets out what the various entities associated with the system are permitted to do and how that should be achieved. For example, the standards, specifications and related protocols can define the manner how devices shall communicate, how various aspects of communications shall be implemented and how devices for use in the system shall be configured.

A user can access the communication system by means of an appropriate communication device. A communication device of a user is often referred to as user equipment (UE) or terminal. A communication device is provided with an appropriate signal receiving and transmitting arrangement for enabling communications with other parties. Typically a device such as a user equipment is used for enabling receiving and transmission of communications such as speech and content data.

Communications can be carried on wireless carriers. Examples of wireless systems include public land mobile networks (PLMN) such as cellular networks, satellite based communication systems and different wireless local networks, for example wireless local area networks (WLAN). In wireless systems a communication device provides a transceiver station that can communicate with another communication device such as e.g. a base station of an access network and/or another user equipment. The two directions of communications between a base station and communication devices of users have been conventionally referred to as downlink and uplink. Downlink (DL) can be understood as the direction from the base

l station to the communication device and uplink (UL) the direction from the communication device to the base station.

Some systems may have a number of small-cells overlying larger or macro- cells.

According to a first aspect, there is provided a method comprising: using scheduling information for user equipment in a larger cell and scheduling information for user equipment in at least one smaller cell to determine if at least one cell is to be in a lower power mode, said at least one smaller cell at least partially overlapping said larger cell and being smaller than said larger cell.

The method may further comprise using said scheduling information to determine if said larger cell is to be in a lower power mode.

The scheduling information may comprise averaged scheduling information for a plurality of user equipment.

The averaged scheduling information for said at least one smaller cell may be determined from an average of an average for a plurality of smaller cells.

The scheduling information may comprise a scheduling metric.

The method may further comprise determining a scheduling metric using throughput supported for each user equipment and an average delivered throughput to said user equipment.

The method may further comprise determining a scheduling metric using a proportional fair method.

The using may comprise comparing at least one of said scheduling information for said larger cell and said scheduling information for said at least one smaller cell with respective scheduling information from at least one previous time interval.

The using may comprise using the scheduling information for a current time information and scheduling information for at least one previous time interval to determine if there is a change in said scheduling information.

The lower power mode may comprise a mute mode. The larger cell may have at least one sub frame which can be used either as a normal sub frame or a lower power sub frame.

The larger cell may comprise a macro cell.

The at least one smaller cell may be provided by at least one of a remote radio head, pico cell and femto cell.

According to a second aspect, there is provided 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 configured to, with the at least one processor, cause the apparatus at least to: use scheduling information for user equipment in a larger cell and scheduling information for user equipment in at least one smaller cell to determine if at least one cell is to be in a lower power mode, said at least one smaller cell at least partially overlapping said larger cell and being smaller than said larger cell

The apparatus may be an access point of the larger cell. The apparatus may be a base station.

The at least one memory and the computer program code may be further configured to use said scheduling information to determine if said larger cell is to be in a lower power mode.

The at least one memory and the computer program code may be further configured to determine averaged scheduling information for said at least one smaller cell from an average of an average for a plurality of smaller cells.

The scheduling information may comprise a scheduling metric.

The at least one memory and the computer program code may be further configured to determine a scheduling metric using throughput supported for each user equipment and an average delivered throughput to said user equipment.

The at least one memory and the computer program code may be further configured to determine a scheduling metric using a proportional fair method. The at least one memory and the computer program code may be further configured to compare at least one of said scheduling information for said larger cell and said scheduling information for said at least one smaller cell with respective scheduling information from at least one previous time interval.

The at least one memory and the computer program code may be further configured to use said scheduling information for a current time information and scheduling information for at least one previous time interval to determine if there is a change in said scheduling information.

The lower power mode may comprise a mute mode.

The larger cell may have at least one sub frame which can be used either as a normal sub frame or a lower power sub frame.

The larger cell may comprise a macro cell.

The at least one smaller cell is provided by at least one of a remote radio head, pico cell and femto cell.

According to another aspect, there is provided apparatus comprising: means for using scheduling information for user equipment in a larger cell and scheduling information for user equipment in at least one smaller cell to determine if at least one cell is to be in a lower power mode, said at least one smaller cell at least partially overlapping said larger cell and being smaller than said larger cell.

The using means may be for using said scheduling information to determine if said larger cell is to be in a lower power mode.

The apparatus may comprise determining means for determining the averaged scheduling information for said at least one smaller cell from an average of an average for a plurality of smaller cells.

The scheduling information may comprise a scheduling metric.

The apparatus may comprise means for determining a scheduling metric using throughput supported for each user equipment and an average delivered throughput to said user equipment. The apparatus may comprise means for determining a scheduling metric using a proportional fair method.

The apparatus may comprise means for comparing at least one of said scheduling information for said larger cell and said scheduling information for said at least one smaller cell with respective scheduling information from at least one previous time interval.

The using means may be for using the scheduling information for a current time information and scheduling information for at least one previous time interval to determine if there is a change in said scheduling information.

The lower power mode may comprise a mute mode.

The larger cell may comprise a macro cell.

Some embodiments will now be described with reference to the accompanying figures in which:

Figure 1 shows a schematic diagram of a communication system comprising a base station and a plurality of communication devices;

Figure 2 shows a schematic diagram of a mobile communication device according to some embodiments;

Figure 3 shows a schematic diagram of a control apparatus according to some embodiments;

Figure 4 shows a method flow of an embodiment;

Figure 5 shows a frame structure usable in some embodiments; and

Figure 6 shows a schematic diagram of a scheduling apparatus.

In the following certain exemplifying embodiments are explained with reference to a wireless or mobile communication system serving mobile communication devices. Before explaining in detail the exemplifying embodiments, certain general principles of a wireless communication system and mobile communication devices are briefly explained with reference to Figures 1 to 3 to assist in understanding the technology underlying the described examples.

In a wireless communication system mobile communication devices or user equipment (UE) 102, 103, 105 are provided wireless access via at least one base station or similar wireless transmitting and/or receiving node or point. In the Figure 1 an example of two overlapping access systems or radio service areas of a cellular system 100 and 1 10 provided by base stations 106 and 107 and three smaller radio service areas 1 15, 1 17 and 1 19 provided by remote radio heads 1 1 6, 1 18 and 120 are shown. Each mobile communication device and base station/RRH may have one or more radio channels open at the same time and may send signals to and/or receive signals from more than one source. It is noted that the radio service area borders or edges are schematically shown for illustration purposes only in Figure 1 . It shall also be understood that the sizes and shapes of radio service areas may vary considerably from the shapes of Figure 1 . A base station site can provide one or more cells. A base station can also provide a plurality of sectors, for example three radio sectors, each sector providing a cell or a subarea of a cell. All sectors within a cell may be served by the same base station.

Base stations are typically controlled by at least one appropriate controller apparatus so as to enable operation thereof and management of mobile communication devices in communication with the base stations. In Figure 1 control apparatus 108 and 109 is shown to control the respective macro level base stations 106 and 107. The control apparatus of a base station can be interconnected with other control entities. The control apparatus is typically provided with memory capacity and at least one data processor. The control apparatus and functions may be distributed between a plurality of control units. In some systems, the control apparatus may additionally or alternatively be provided in a radio network controller.

In Figure 1 base stations 106 and 107 are shown as connected to a wider communications network 1 1 3 via gateway 1 1 2. A further gateway function may be provided to connect to another network. The remote radio heads 1 16, 1 18 and 1 20 are connected to a respective macro cell. Thus RRH 120 is connected to macro cell base station 106 and RRHs 1 18 and 1 16 are connected to macro cell base station 109. The RRHs are located in the respective macro cell provided by the macro cell base station to which they are connected.

A possible mobile communication device will now be described in more detail with reference to Figure 2 showing a schematic, partially sectioned view of a communication device 102. Such a communication device is often referred to as user equipment (UE) or terminal. An appropriate mobile communication device may be provided by any device capable of sending and receiving radio signals. Non- limiting examples include a mobile station (MS) or mobile device such as a mobile phone or what is known as a 'smart phone', a computer provided with a wireless interface card or other wireless interface facility, personal data assistant (PDA) provided with wireless communication capabilities, or any combinations of these or the like. A mobile communication device may provide, for example, communication of data for carrying communications such as voice, electronic mail (email), text message, multimedia and so on. Users may thus be offered and provided numerous services via their communication devices. Non-limiting examples of these services include two-way or multi-way calls, data communication or multimedia services or simply an access to a data communications network system, such as the Internet. Users may also be provided broadcast or multicast data. Non-limiting examples of the content include downloads, television and radio programs, videos, advertisements, various alerts and other information.

The mobile device 102 may receive signals over an air interface 207 via appropriate apparatus for receiving and may transmit signals via appropriate apparatus for transmitting radio signals. In Figure 2 transceiver apparatus is designated schematically by block 206. The transceiver apparatus 206 may be provided for example by means of a radio part and associated antenna arrangement. The antenna arrangement may be arranged internally or externally to the mobile device. A wireless communication device can be provided with a Multiple Input / Multiple Output (MIMO) antenna system. MIMO arrangements as such are known. Ml MO systems use multiple antennas at the transmitter and receiver along with advanced digital signal processing to improve link quality and capacity. Although not shown in Figures 1 and 2, multiple antennas can be provided, for example at base stations and mobile stations, and the transceiver apparatus 206 of Figure 2 can provide a plurality of antenna ports. More data can be received and/or sent where there are more antenna elements. A station may comprise an array of multiple antennas. Signalling and muting patterns can be associated with TX antenna numbers or port numbers of MIMO arrangements.

A mobile device is typically provided with at least one data processing entity 201 , at least one memory 202 and other possible components 203 for use in software and hardware aided execution of tasks it is designed to perform, including control of access to and communications with access systems and other communication devices. The data processing, storage and other relevant control apparatus can be provided on an appropriate circuit board and/or in chipsets. This feature is denoted by reference 204. The user may control the operation of the mobile device by means of a suitable user interface such as key pad 205, voice commands, touch sensitive screen or pad, combinations thereof or the like. A display 208, a speaker and a microphone can be also provided. Furthermore, a mobile communication device may comprise appropriate connectors (either wired or wireless) to other devices and/or for connecting external accessories, for example hands-free equipment, thereto.

Figure 3 shows an example of a control apparatus for a communication system, for example to be coupled to and/or for controlling a station of an access system, such as a base station. In some embodiments, base stations comprise a separate control apparatus. In other embodiments, the control apparatus can be another network element such as a radio network controller. In some embodiments, each base station may have such a control apparatus as well as a control apparatus being provided in a radio network controller. The control apparatus 109 can be arranged to provide control on communications in the service area of the system. The control apparatus 109 comprises at least one memory 301 , at least one data processing unit 302, 303 and an input/output interface 304. Via the interface the control apparatus can be coupled to a receiver and a transmitter of the base station. For example the control apparatus 109 can be configured to execute an appropriate software code to provide the control functions.

The communication devices 102, 103, 105 may access the communication system based on various access techniques, such as code division multiple access (CDMA), or wideband CDMA (WCDMA). Other non-limiting examples comprise time division multiple access (TDMA), frequency division multiple access (FDMA) and various schemes thereof such as the interleaved frequency division multiple access (IFDMA), single carrier frequency division multiple access (SC-FDMA) and orthogonal frequency division multiple access (OFDMA), space division multiple access (SDMA) and so on.

An example of wireless communication systems are architectures standardized by the 3rd Generation Partnership Project (3GPP). A latest 3GPP based development is often referred to as the long-term evolution (LTE) of the Universal Mobile Telecommunications System (UMTS) radio-access technology. The various development stages of the 3GPP LTE specifications are referred to as releases. More recent developments of the LTE are often referred to as LTE Advanced (LTE-A). The LTE employs a mobile architecture known as the Evolved Universal Terrestrial Radio Access Network (E-UTRAN). Base stations of such systems are known as evolved or enhanced Node Bs (eNBs) and may provide E- UTRAN features such as user plane Radio Link Control/Medium Access Control/Physical layer protocol (RLC/MAC/PHY) and control plane Radio Resource Control (RRC) protocol terminations towards the communication devices. Other examples of radio access system include those provided by base stations of systems that are based on technologies such as wireless local area network (WLAN) and/or WiMax (Worldwide Interoperability for Microwave Access). Some embodiments may be used with LTE (or LTE-Advanced) co-channel deployment of macro eNBs and low power eNBs in the form of RRHs. Alternatively or additionally embodiments may be used with smaller cells such as pico or femto cells and/or other relay stations. The smaller cells and/or relay stations may be in communication with a macro eNB. One example of is a co-channel LTE HetNet scenario. This may arise where more than one transmitter is using the same channel or frequency. Some embodiments may address the problem of joint multi-cell packet scheduling for the downlink of such a system, while still maintaining fairness among all users.

Co-channel scenarios may suffer from interference problems in the downlink. A small cell connected UE may receive a relatively high interference from one or more macro cells. This problem may be an issue if a so-called range extension (RE) for the small cells is used to shift more traffic load from the macro-cells to the small- cells. The RE may be provided by one or more RRHs.

Enhanced inter-cell interference coordination (elCIC) has been proposed which use partial muting of some sub frames at the macro-cell layer. This may reduce the interference generated by the macro-cells towards a small cell connected UEs. elCIC has been designed for a macro cell with one or more pico cells scenario. This proposal assumes that the eNBs of the macro and pico cells are inter- connected via the X2 interface. The muting patterns may only be slowly adjusted and independent fast packet scheduling may be conducted in each cell.

However, consider the arrangement shown in Figure 1 where macro cells and remote radio heads (RRHs) are used. Each macro cell may host one or more of relatively low power cells, namely the RRHs. The RRHs may be connected to a macro-eNB via a relatively high-capacity, relatively low-latency fiber(s) (or similar performing wireless transport solution). All the baseband processing for the macro cell and RRHs may be in the macro-eNB. The set of a macro eNB and the or all RRHs in its coverage area is called a cluster.

This implementation enables the use of a joint multi-cell packet scheduler in each macro-eNB, which jointly schedules all user equipment in the cluster. In some embodiments each user equipment may be associated to only a single cell at a time (macro cell or small cell (RRH)), based on existing LTE cell selection / handover procedures. However in some embodiments, a user equipment may be associated with more than one cell at a time.

Using a joint scheduler for both macro and small cells, may allow relatively fast decisions every scheduling interval on which user equipment are scheduled per cell, and alternatively or additionally if the macro cell uses muting or not. The fast decision making on whether to use muting or normal transmission from the macro cell per scheduling interval may enable faster and more intelligent resource sharing between macro and small cells in the form of RRHs.

The joint multi-cell packet scheduling problem addressed by some embodiments may be how to decide for every scheduling interval if the macro cell shall be muted, or use a normal transmission. If the macro cell is using normal transmission, this means that macro-users can be scheduled. Otherwise if the macro cell is muted, no macro-users are schedulable to the macro cell. The small cell user equipment are scheduled in each of their small cells, but such decisions may depend on whether the user equipment are subject to macro-interference, or not. As the joint scheduler is provided in the macro-eNB for both the macro and small-cells, it is known for each scheduling interval if a macro cell is using muting or normal transmission.

Some known packet scheduler designs for a single-cell operation may be based on maximizing a certain objective. This may be done independently per cell, and therefore only helps to control fairness within each cell and not necessarily between user equipment in different cells. Based on the objective, a scheduling metric is derived, and the user equipment with the highest scheduling metric is scheduled within each cell on each resource set, e.g. PRBs (physical resource block) in LTE terminology. As an example, the proportional fair (PF) scheduler is based on an objective function to maximize the sum of logarithmic throughputs for all users per cell. This objective function results in a simple scheduling metric which equals the currently supported throughput per UE, divided by the average delivered throughput to the user equipment in the past. Extensions to the proportional fair metric are known so that the metric is scaled by a factor which reflects to which extent some absolute QoS (quality of service) target is fulfilled by given user equipment.

In some embodiments, the approach considers one or both aspects in terms of optimizing total capacity with "access probability fairness" and/or "service QoS fairness". Regardless of the approach, all user equipment in the same cell will converge to having approximately the same scheduling metric. The scheduling metric for a user equipment may have the property of decreasing if the user equipment is scheduled, giving an indication of the obtained scheduling opportunities.

In some embodiments, it may be assumed that the network is optimized when all user equipment in the network (regardless of whether the user equipment are connected to a macro cell or a RRH cell) have the same average scheduling metric (or better than a minimum value with a certain outage). It should be appreciated that in some embodiments between different small cells within the same macro cell area, it may not be possible to ensure simultaneous convergence for all user equipment as the number of user equipment per small RRH cell may be different.

In some embodiments, a user equipment may only be connected to a single- cell at a time, and/or may only report channel quality or the like for the serving cell of that user equipment.

Figure 4 shows an example of a scheduling framework which may be carried out in accordance with some embodiments. In some embodiments, user equipment may be scheduled based on a scheduling metric associated with the user equipment. For example user equipment with a higher scheduling metric may be scheduled first. A value of a scheduling metric associated with a user equipment may correspond to how recently that user equipment was scheduled. The scheduling metrics of the user equipment may correspond to how fairly scheduling is taking place. For example, a group of user equipment with lower scheduling metrics indicates that the user equipment in the group are being scheduled regularly whereas a group of user equipment with higher scheduling metrics may indicate that the user equipment are not being scheduled often enough.

In the example of figure 1 , a macro cell may interfere with the scheduling and transmissions in a smaller cell associated with the macro cell, for example an RRH. This may result in the user equipment associated with the macro cell having lower scheduling metrics than user equipment offloaded to the smaller cell. In the embodiments of figure 4, a period for which a macro cell is muted is adjusted which may cause the scheduling metrics of user equipment associated with the macro cell and the smaller cell to be adjusted. For example increasing the mute period may decrease the scheduling metrics associated with user equipment served by the smaller cell as interference caused by the macro cell is decreased.

An example of a basic scheduling framework is shown in Figure 4 is used and may be summarized as follows:

In step S1 , for each scheduling interval, the average scheduling metric for all macro-user cell user equipment and the average scheduling metric for all small-cell user equipment is calculated. An average scheduling metric may be calculated for each small cell or across all small cells associated with a given macro cell. In some embodiments, the scheduling metric may be determined less frequently than each scheduling interval.

In step S2, the calculated average scheduling metric is compared with one or more previous scheduling metrics.

In step S3, a determination is made as to whether the macro cell average scheduling metric is increasing. The muting ratio for the or a next scheduling interval is increased or decreased depending on the improvement / degradation of the average scheduling metric of small-cell-users and macro-users, compared to the previous scheduling interval.

If the macro cell average is increasing, then the next step is step S4. If the average scheduling metric of small-cell-user equipment is decreasing and the average scheduling of macro-users is increasing, then the muting ratio is decreased and the user equipment in the macro and small cells are scheduled according to their scheduling metric.

If the macro cell average is not increasing, then the next step is step S5 where it is determined if the macro cell average is decreasing.

If the average scheduling metric of small-cell-users is growing and the average scheduling of macro-users is decreasing, then the next step is step S6. In this step, the muting ratio is increased and the user equipment in the macro and small cells are scheduled according to their scheduling metric

If the macro cell average is not increasing or decreasing, the next step is step S7 in which the muting ratio is maintained at its current value and the users in the macro and small cells are scheduled according to their scheduling metric.

In the flow shown in Figure 4, the macro cell averaging scheduling metric is considered. In alternative embodiments, the smaller cell average scheduling metric may alternatively be taken into account. In some embodiments, both the macro cell average scheduling metric and the smaller cell averaging scheduling metric may both be taken into account. In generally, if the average scheduling metric of the macro cell is generally increasing with respect to the smaller cell average scheduling metric, then the muting ratio may be decreased. If the small cell average scheduling metric is generally increasing with respect to the macro cell average scheduling metric, then the muting ratio may be increased. If the ratios stay generally the same, then the current muting ratio may be retained. Of course more complex decisions may be made in alternative embodiments.

In the arrangement shown in Figure 4, steps S2 and S3 may be combined.

It should be appreciated that in alternative embodiments, a decision may be made as to whether the macro cell average scheduling metric is decreasing.

It should be appreciated that in some embodiments, steps S2, S3 and S5 may effectively be combined in one step with steps S4, S6 and S7 being respective outputs.

It should be appreciated that alternative embodiments may use different methods. The scheduling metric is any suitable metric for example a metric which is based on the proportional fair principle. One example is the currently supported throughput per UE, divided by the average delivered throughput to the user equipment in the past. Any other variation based on proportional fair can be applied. The previously mentioned examples of metric may be used.

In some embodiments, if an average scheduling metric is larger for the small- cell-layer as compared to the macro-layer, then small-cell-users are preferably scheduled with good quality.

By using muting at the macro cell level, no macro-users are scheduled, and small-cell users are scheduled with good quality due to no macro cell interference.

This implies that the scheduling metric for the macro-user equipment is increased, while the scheduling metric is decreasing for the small-cell users.

This may bring the system closer to the desired equilibrium where all user equipment have approximately the same scheduling metric, and therefore a desired multi-cell fairness.

Reference is made to figure 6 which shows a schematic diagram of a scheduling apparatus. The scheduling apparatus comprises a function for determining the scheduling metrics 10. This function 10 may receive one or more inputs of information which allows the respective metrics, as described above, to be determined. The determined metrics are provided to a memory 12 or any other suitable data storage function. The determined metrics are also provided to a comparing function 14. The comparing function 14 is arranged to compare the current determined scheduling metrics with one or more previous scheduling metrics, which may be obtained from memory. The comparing function 14 outputs information which is used by a decision function 16. The decision function 16 provides a controlling output to a muting ratio controller 1 8 which controls whether the muting ratio of the macro cell is increased, decreased or is maintained. The decision function also provides an output to a scheduler 20 which is configured to control the scheduling for the user equipment both in the macro cell and one or more smaller cells. The scheduling apparatus may be provided in the controller and/or the macro base station. The scheduling apparatus may be provided by one or more memory and one or more data processors. The one or more memories may contain computer code which when provide the functions as described.

In some embodiments, three types of macro sub frames may be defined:

1 . Normal sub frames: normal data transmission at the macro eNB

2. Mandatory Almost Blank Sub frames (ABS): PDSCH Physical Downlink Shared Channel and PDCCH Physical Downlink Control Channel are not transmitted at the macro eNB

3. Optional almost blank sub frames: can be either used as ABS or as normal sub frames

The number of optional, mandatory and normal sub frames per frame may be fixed and optionally may be the same over time. In Figure 5 an example of a frame configuration is shown. When the macro eNB is mute, macro UEs cannot be scheduled. At the same time, UEs connected to the RRHs experience a much lower interference from the macro eNB. On the other hand, during normal sub frames, macro UEs are normally scheduled and small cell users (especially those in the range extended area) may suffer from severe macro interference. In Figure 5 a V" means that there the interference is acceptable and a "x" means that the interference is relatively high.

In some embodiments, the decision on whether to use muting or not may be limited to the optional sub frames. The introduction of a minimum number of mandatory ABS and normal sub frames ensures that small cell UEs can be configured to perform RRH cell measurements at the proper sub frame. Small cell UE CSI measurements are made for separately for both mandatory ABS and normal sub frames. In some embodiments no CSI measurements are made for optional ABS. The macro UE CSI measurements may be made during normal sub frames.

During the optional sub frames, the CSI measure is applied depending on whether the sub frame is going to be used as ABS sub frame or a or normal sub frame. One example of an implementation of the fair joint scheduler such as discussed in relation to Figure 4 is shown in pseudo code below: while (new _ frameQ)

if(PF_RRH (n) < PF_RRH (n - 1)) & &(PF_macro (n) > PF_macro (n - 1)) ABS(n) = ABS(n - \) + \;

elseif (PF_macro(n) > PF_macro(n - \))

ABS(n) = ABS(n - \) - \;

else

ABS(n) =ABS(n - \);

end;

update PF_macro ;

update PF_RRH ;

end;

where

- PFmacro(n) is the average of the PF metrics of macro users at time n

- PF_RRH(n) is the average of the PF metrics of small cell users at time n

- ABS(n) is the muting ratio at time n

Some embodiments of how to obtain PF_macro and PF_RRH will now be described. The scheduling metric may be any objective function based on the proportional fair principle. For example the function may be defined as a currently supported throughput per UE r_k (n), divided by the average delivered throughput to the user in the past R_k. In some embodiments, the past Rk of the previous TTI is used. In other embodiments an average Rk over a time window is used, with that average being updated. The average may for example be updated every TTI. The window may be of any suitable size, for example of the order of 0.4s. This is by way of example only and the window may be larger or smaller than this size.

PF_k(n) = ^ (1)

In some alternative embodiments, in a QoS-focused system a metric may be defined that adds a term capturing an extent to which a QoS target is fulfilled. The QoS target may comprise one or more parameters such as a guaranteed bit rate, the delay, or the like. This way the QoS between the macro layer and the smaller cell layer may be balanced to a higher degree. For example, with the next metric users could be discarded or given a lower scheduling priority if a user has had twice the guaranteed throughput (R_gbr in the past):

PF_k(n) = ^- (R_k < 2R_gbr) (2)

Kk

Regardless of the scheduling metric used, the combined metric for the small cell layer may be obtained in some embodiments as described below. The scheduling metric for the small cell user equipment (PF_RRH) may be calculated as a simple average value. In cases with two or more small cells in the cluster, the metric of all small cells may be combined to a single value that can be compared with the macro user metric.

In one embodiment, one scheduling metric may be defined by a ratio of instantaneous throughput for the user equipment versus the average scheduled throughput to the user equipment in the past. In some embodiments, all the all small cell user equipment may be averaged. This provides a relatively aggressive muting of the macro cell layer to ensure that more small cell user equipment get scheduler metric values as close to the macro cell user equipment as possible.

In other embodiments, an average of the metric is obtained for each small cell and then these average values are in turn averaged to provide an average across the small cells. This may result in a less aggressive approach for macro cell muting.

It should be appreciated that any suitable method may be used to determine such an average to arrive at a single representative metric for the small cell layer.

Some embodiments may take into account outage constraints.

In some embodiments, a lower power mode may be provided for the macro cell base station. The mute mode may be one example of such a lower power mode. The lower power mode may be achieved by one or more of reducing the number of signals transmitted, reducing the number of different frequencies used, changing the power with which signals are transmitted, switching off one or more components, putting one or more components into a lower power mode such as a standby mode and reducing the amount of time for which the base station is in an active mode. One example of a lower power mode may be a sleep, dormant or mute mode.

The "macro-cell" may alternatively be any cell which is larger than the one or more smaller cells which at least partially overlap the larger cell.

Some embodiments have been described in relation to smaller cells provided by RRHs. Alternatively or additionally some embodiments may be used with smaller cells such as pico and/or femto cells or the like. With smaller cells such as pico and/or femto cells these cells may be arranged to send the required information to the larger or macro cell. The required information may be sent periodically. The macro cell would then operate in the same way as previously described. It will be appreciated that some embodiments may be applicable to systems in which the macro cell has knowledge of and/or control over the scheduling of a smaller cell.

In some embodiments the macro-cell may carry out all the baseband processing for a smaller cell, for example a RRH. In other embodiments a macro-cell may carry out processing on behalf of a smaller cell to varying degrees.

Some embodiments have been described as provided a lower power mode for a macro base station. It should be appreciated that alternatively or additionally, some embodiments may be used to control smaller cells such as RRHs, pico or femto cells to have lower power modes such as previously described.

In some embodiments the mute period may be adjusted in order to equalise the scheduling metrics of user equipment associated with the macro-cell and user equipment associated with the smaller cell. It will be appreciated that in some embodiments the scheduling metrics may be adjusted to be above or below a threshold and need not be equalised.

It is noted that whilst embodiments have been described in relation to LTE, similar principles may be applied to any other communication system or to further developments with LTE. Therefore, although certain embodiments are described above by way of example with reference to certain exemplifying architectures for wireless networks, technologies and standards, embodiments may be applied to any other suitable forms of communication systems than those illustrated and described herein.

The required data processing apparatus and functions of a base station apparatus, a communication device and any other appropriate apparatus may be provided by means of one or more data processors. The described functions at each end may be provided by separate processors or by an integrated processor. The data processors may be of any type suitable to the local technical environment, and may include one or more of general purpose computers, special purpose computers, microprocessors, digital signal processors (DSPs), application specific integrated circuits (ASIC), gate level circuits and processors based on multi core processor architecture, as non-limiting examples. The data processing may be distributed across several data processing modules. A data processor may be provided by means of, for example, at least one chip. Appropriate memory capacity can also be provided in the relevant devices. The memory or memories may be of any type suitable to the local technical environment and may be implemented using any suitable data storage technology, such as semiconductor based memory devices, magnetic memory devices and systems, optical memory devices and systems, fixed memory and removable memory.

In general, the various embodiments may be implemented in hardware or special purpose circuits, software, logic or any combination thereof. Some aspects of the invention may be implemented in hardware, while other aspects may be implemented in firmware or software which may be executed by a controller, microprocessor or other computing device, although the invention is not limited thereto. While various aspects of the invention may be illustrated and described as block diagrams, flow charts, or using some other pictorial representation, it is well understood that these blocks, apparatus, systems, techniques or methods described herein may be implemented in, as non-limiting examples, hardware, software, firmware, special purpose circuits or logic, general purpose hardware or controller or other computing devices, or some combination thereof. The software may be stored on such physical media as memory chips, or memory blocks implemented within the processor, magnetic media such as hard disk or floppy disks, and optical media such as for example DVD and the data variants thereof, CD.

The foregoing description has provided by way of exemplary and non-limiting examples a full and informative description of the exemplary embodiment of this invention. However, various modifications and adaptations may become apparent to those skilled in the relevant arts in view of the foregoing description, when read in conjunction with the accompanying drawings and the appended claims. However, all such and similar modifications of the teachings of this invention will still fall within the scope of this invention as defined in the appended claims. Indeed there is a further embodiment comprising a combination of one or more of any of the other embodiments previously discussed.

Claims

1 . A method comprising:

using scheduling information for user equipment in a larger cell and scheduling information for user equipment in at least one smaller cell to determine if at least one cell is to be in a lower power mode, said at least one smaller cell at least partially overlapping said larger cell and is smaller than said larger cell.

2. A method as claimed in claim 1 , comprising using said scheduling information to determine if said larger cell is to be in a lower power mode.

3. A method as claimed in any preceding claim, wherein said scheduling information comprises averaged scheduling information for a plurality of user equipment.

4. A method as claimed in claim, wherein said averaged scheduling information for said at least one smaller cell is determined from an average of an average for a plurality of smaller cells.

5. A method as claimed in any preceding claim, wherein said scheduling information comprises a scheduling metric.

6. A method as claimed in claim, comprising determining a scheduling metric using throughput supported for each user equipment and an average delivered throughput to said user equipment.

7. A method as claimed in claim, comprising determining a scheduling metric using a proportional fair method.

8. A method as claimed in any preceding claim, wherein said using comprises comparing at least one of said scheduling information for said larger cell and said scheduling information for said at least one smaller cell with respective scheduling information from at least one previous time interval.

9. A method as claimed in claim, wherein said using comprises using said scheduling information for a current time information and scheduling information for at least one previous time interval to determine if there is a change in said scheduling information.

10. A method as claimed in any preceding claim, wherein said lower power mode comprises a mute mode.

1 1 . A method as claimed in any preceding claim, wherein said larger cell has at least one sub frame which can be used either as a normal sub frame or a lower power sub frame.

12. A method as claimed in any preceding claim, wherein said larger cell comprises a macro cell.

13. A method as claimed in any preceding claim, wherein said at least one smaller cell is provided by at least one of a remote radio head, pico cell and femto cell.

14. 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 configured to, with the at least one processor, cause the apparatus at least to:

Use scheduling information for user equipment in a larger cell and scheduling information for user equipment in at least one smaller cell to determine if at least one cell is to be in a lower power mode, said at least one smaller cell at least partially overlapping said larger cell and is smaller than said larger cell

15. An apparatus of claim 14 wherein the apparatus is an access point of the larger cell.

16. An apparatus of any of claims 14 and 15 wherein the apparatus is a base station.

17. A system comprising a base station, said base station comprising an apparatus as claimed in any of claims 14 and 15.