WO2012034597A1

WO2012034597A1 - Apparatus and method for communication

Info

Publication number: WO2012034597A1
Application number: PCT/EP2010/063671
Authority: WO
Inventors: Klaus Ingemann Pedersen; Stanislaw Strzyz
Original assignee: Nokia Siemens Networks Oy
Priority date: 2010-09-17
Filing date: 2010-09-17
Publication date: 2012-03-22

Abstract

Apparatus and method for communication are provided. In the method, the downlink signal quality of terminals served by a first node is monitored (502). On the basis of the monitoring, a message is sent (504) to a second node serving a cell overlaying the cell of the first node, the message requesting the second node to adjust the usage of transmission resources utilised by the second node.

Description

Apparatus and method for communication

Field

The exemplary and non-limiting embodiments of the invention relate generally to wireless communication networks. Background

The following description of background art may include insights, discoveries, understandings or disclosures, or associations together with disclosures not known to the relevant art prior to the present invention but provided by the invention. Some of such contributions of the invention may be specifically pointed out below, whereas other such contributions of the invention will be apparent from their context .

Wireless communication systems are constantly under develop- ment . Developing systems provide a cost-effective support of high data rates and efficient resource utilization. One com^¬ munication system under development is the 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE) Release 8. An improved version of the Long Term Evolution radio ac- cess system is called LTE-Advanced (LTE-A) . The LTE is de^¬ signed to support various services, such as high-speed data, multimedia unicast and multimedia broadcast services.

Typically, in a geographical area of a radio communication system there is provided a plurality of different kinds of radio cells as well as a plurality of radio cells. A radio system may be implemented as a multilayer network including several kinds of cells, such as macro-, micro- and picocells. Radio cells may be macro cells (or umbrella cells) which are large cells, usually having a diameter of up to tens of kilo- metres, or smaller cells such as micro, femto or pico cells. The smaller cells may be located within the coverage area of a larger macro cell. Typically, small cells are used to in^¬ crease the capacity of the system in areas where the traffic density is high. The co-operation of different kind of cells must be planned carefully so that the capacity and quality of service of the system may be maximised. Summary

The following presents a simplified summary of the invention in order to provide a basic understanding of some aspects of the invention. This summary is not an extensive overview of the invention. It is not intended to identify key/critical elements of the invention or to delineate the scope of the invention. Its sole purpose is to present some concepts of the invention in a simplified form as a prelude to a more de^¬ tailed description that is presented later.

According to an aspect of the present invention, there is provided an apparatus comprising: at least one processor and at least one memory including a 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: monitor the downlink signal quality of terminals served by a first node; send on the basis of the monitoring a mes^¬ sage to a second node serving a cell overlaying the cell of the first node, the message requesting the second node to ad^¬ just the usage of transmission resources utilised by the sec- ond node.

According to another aspect of the present invention, there is provided a method comprising: monitoring the downlink signal quality of terminals served by a first node; sending on the basis of the monitoring a message to a second node serv- ing a cell overlaying the cell of the first node, the message requesting the second node to adjust the usage of transmis^¬ sion resources utilised by the second node.

According to an aspect of the present invention, there is provided an apparatus comprising: at least one processor and at least one memory including a 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: receive a message from a first node serving a cell lo^¬ cated within an overlaying cell served by a second node, the message comprising a request to adjust the usage of transmis^¬ sion resources utilised by a second node, determine the need to adjust the usage of transmission resources, and adjust the usage of transmission resources if needed. According to another aspect of the invention, there is provided a method comprising: receiving a message from a first node serving a cell located within an overlaying cell served by a second node, the message comprising a request to adjust the usage of transmission resources utilised by a second node, determining the need to adjust the usage of transmis^¬ sion resources, and adjusting the usage of transmission re^¬ sources if needed.

According to another aspect of the present invention, there is provided a computer program embodied on a distribution medium, comprising program instructions which, when loaded into an electronic apparatus, control the apparatus to: monitor the downlink signal quality of terminals served by a first node; send on the basis of the monitoring a message to a sec- ond node serving a cell overlaying the cell of the first node, the message requesting the second node to adjust the usage of transmission resources utilised by the second node. According to another aspect of the present invention, there is provided a computer program embodied on a distribution me- dium, comprising program instructions which, when loaded into an electronic apparatus, control the apparatus to: receive a message from a first node serving a cell located within an overlaying cell served by a second node, the message compris^¬ ing a request to adjust the usage of transmission resources utilised by a second node, determine the need to adjust the usage of transmission resources, and adjust the usage of transmission resources if needed.

According to another aspect of the present invention, there is provided an apparatus comprising: means for monitoring the downlink signal quality of terminals served by a first node; means for sending on the basis of the monitoring a message to a second node serving a cell overlaying the cell of the first node, the message requesting the second node to adjust the usage of transmission resources utilised by the second node. According to another aspect of the present invention, there is provided an apparatus comprising: means for receiving a message from a first node serving a cell located within an overlaying cell served by a second node, the message compris- ing a request to adjust the usage of transmission resources utilised by a second node, means for determining the need to adjust the usage of transmission resources, and means for ad^¬ justing the usage of transmission resources if needed. List of drawings

Embodiments of the present invention are described below, by way of example only, with reference to the accompanying draw^¬ ings, in which

Figure 1A shows a simplified block diagram illustrating an exemplary system architecture;

Figure IB illustrates an example of an apparatus according to embodiments of the invention;

Figure 2 illustrates a range extension technique;

Figure 3 illustrates an example of enhanced inter-cell inter- ference coordination;

Figure 4 is a flow chart illustrating an embodiment;

Figures 5A, 5B and 6 are flow charts illustrating further embodiments .

Description of some embodiments

Exemplary embodiments of the present invention will now be described more fully hereinafter with reference to the accom^¬ panying drawings, in which some, but not all embodiments of the invention are shown. Indeed, the invention may be embod^¬ ied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements. Although the specification may refer to "an", "one", or "some" embodiment ( s ) in several lo^¬ cations, this does not necessarily mean that each such reference is to the same embodiment ( s ) , or that the feature only applies to a single embodiment. Single features of different embodiments may also be combined to provide other embodi^¬ ments .

Embodiments of present invention are applicable to any net^¬ work element, node, base station, server, corresponding component, and/or to any communication system or any combination of different communication systems that support required functionalities. The communication system may be a wireless communication system or a communication system utilizing both fixed networks and wireless networks. The protocols used and the specifications of communication systems, servers and user terminals, especially in wireless communication, develop rap^¬ idly. Such development may require extra changes to an em^¬ bodiment. Therefore, all words and expressions should be in^¬ terpreted broadly and are intended to illustrate, not to re- strict, the embodiment.

With reference to Figure 1A, let us examine an example of a radio system to which embodiments of the invention can be ap^¬ plied. In this example, the radio system is based on LTE net^¬ work elements. However, the invention described in these ex- amples is not limited to the LTE radio systems but can also be implemented in other radio systems.

A general architecture of a communication system is illus^¬ trated in Figure 1A. Figure 1A is a simplified system archi^¬ tecture only showing some elements and functional entities, all being logical units whose implementation may differ from what is shown. The connections shown in Figure 1A are logical connections; the actual physical connections may be differ^¬ ent. It is apparent to a person skilled in the art that the systems also comprise other functions and structures. It should be appreciated that the functions, structures, ele^¬ ments, and protocols used in or for group communication are irrelevant to the actual invention. Therefore, they need not be discussed in more detail here.

The exemplary radio system of Figure 1A comprises a service core of an operator including the following elements: an MME (Mobility Management Entity) 108 and an SAE GW (SAE Gateway) 104.

Base stations that may also be called eNBs (Enhanced node Bs) 100, 102 of the radio system may host the functions for Radio Resource Management: Radio Bearer Control, Radio Admission

Control, Connection Mobility Control, Dynamic Resource Allo^¬ cation (scheduling) . The MME 108 is responsible for distrib^¬ uting paging messages to the eNBs 100, 102. The eNBs are con- nected to the SAE GW with an S1_U interface and to MME with an S1_MME interface. The eNBs may communicate with each other using an X2 interface.

Figure 1A shows user equipment 110 connected to the eNodeB 100 and user equipment 114 connected to the eNodeB 102. The user equipment refers to a portable computing device. Such computing devices include wireless mobile communication de^¬ vices operating with or without a subscriber identification module (SIM) , including, but not limited to, the following types of devices: mobile phone, smartphone, personal digital assistant (PDA), handset, laptop computer.

Figure 1A only illustrates a simplified example. In practice, the network may include more base stations and more cells may be formed by the base stations. The networks of two or more operators may overlap, the sizes and form of the cells may vary from what is depicted in Figure 1A, etc.

It should be appreciated that the communication system may also comprise other core network elements besides SAE GW 104 and MME 108. Direct communication between different eNodeBs over an air interface is also possible by implementing a re^¬ lay node concept, wherein a relay node may be considered as a special eNodeB having wireless backhauls or, for instance, X2 and SI interfaces relayed over the air interface by another eNodeB. The communication system is also able to communicate with other networks, such as a public switched telephone net^¬ work .

The embodiments are not, however, restricted to the network given above as an example, but a person skilled in the art may apply the solution to other communication networks pro- vided with the necessary properties. For example, the connec^¬ tions between different network elements may be realized with Internet Protocol (IP) connections.

Figure IB illustrates examples of an apparatus according to an embodiment of the invention. Figure IB shows a base sta- tion or eNodeB 118. The structure of eNodeBs 100 and 102 is similar to the illustrated node. The eNodeB 118 comprises a controller 120 operationally connected to a memory 122 and a transceiver 124. The controller 120 controls the operation of the base station. The memory 122 is configured to store soft^¬ ware and data. The transceiver 124 is configured to set up and maintain a wireless connection to user equipment within the service area of the base station. The transceiver 124 is operationally connected to an antenna arrangement 126. The antenna arrangement may comprise a set of antennas. The num^¬ ber of antennas may be two to four, for example. The number of antennas is not limited to any particular number.

The base station may be operationally connected to other net- work elements of the communication system. The network element may be an MME (Mobility Management Entity) , an SAE GW (SAE Gateway) , a radio network controller (RNC) , another base station, a gateway, or a server, for example. The base sta^¬ tion may be connected to more than one network element. The base station 100 may comprise an interface 128 configured to set up and maintain connections with the network elements. The connections with other network elements may be realized with wireless or wired connections.

As mentioned, a radio communication system may utilise a plu- rality of different kinds of radio cells. Due to the increase in the amount of traffic in communication systems, the commu^¬ nication systems must be able to offer high capacity and quality of service. A multi-layer radio access network (RAN) is a promising technology. A typical multi-layer network com- prises a set of macro-cells, also called "umbrella" cells served by eNodeBs, and one or more smaller cells under this "umbrella". The lower-layer cells may be called micro, femto or pico cells. Each lower-layer cell is served by an eNodeB. The network may simultaneously be not only a multi-layer sys- tern, but also a multi-vendor system.

In Figure 1A, the eNodeBs may be serving either an overlaying umbrella or macro cell or a lower-layer pico cell. Let us as^¬ sume for the sake of simplicity that the eNodeB 100 is an up^¬ per-layer node serving a macro cell and the eNodeB 102 is a lower-layer node serving a pico cell.

As known, the user equipment and nodes of a multi-layer net^¬ work may experience interference originating from a transmit^¬ ter operating on different layer if same transmission re- sources are utilised on both layers. Thus, some co-operation and planning is required in the use of resources in a multi^¬ layer network.

To increase the performance of a lower-layer cell, a so- called range extension (RE) technique has been proposed. Fig^¬ ure 2 illustrates the range extension technique. Figure 2 shows the eNodeB 100 serving an overlaying macro cell 200 and the eNodeB 102 serving a pico cell. The nodes are utilising the same transmission resources. Without the use of range ex- tension and traditional Reference Signal Received Power

(RSRP) based serving cell selection the eNodeB 102 serves a cell with an area denoted with 202. Thus, user equipment stay connected to the eNodeB 102 while the RSRP_Pi_Co > RSRP MACRO and in the area 202 this condition applies.

The goal of range extension is to extend the serving area of a pico node and reduce load on a macro cell. If range exten^¬ sion is utilized, user equipment stay connected to the eNodeB 102 while the RSRP_Pi_C0 + OFFSET > RSRP MACRO and in the area 204 this condition applies, OFFSET is a predefined parameter. In the area 200 served by the eNodeB 100, RSRP MACRO > RSRP_Pi_C0 +

OFFSET .

The value of OFFSET may be selected individually for each cell. It is known that co-channel deployment of macro and pico nodes works efficiently if aggressive pico node range extension is not applied. By applying large pico node RE off^¬ sets, the coverage area of the pico nodes is increased. How^¬ ever, when the pico node RE offset starts to be larger than approximately 3 dB, user equipment camped on a pico cell will start to suffer from too high interference from the macro- eNodeBs . The latter problem can actual be so critical that it results in dropped calls.

Thus, in order to facilitate configurations with large pico node RE offsets, time-domain (TDM) enhanced inter-cell inter^¬ ference coordination (elCIC) is applied between macro-eNBs and pico nodes. Figure 3 illustrates this method. Figure 3 show sub-frames 300 used by an eNodeB serving an overlaying cell and sub-frames 302 used by an eNodeB serving a pico cell within the overlaying cell. The sub-fames with normal trans- mission are hatched and almost blank sub-frames are without hatches .

In elCIC, a macro-eNodeB starts to mute (i.e. using so-called almost blank sub-frames) some of its sub-frames. During the muted sub-frames, the pico eNodeB is able to schedule users that would otherwise experience too high interference from the macro layer. However, muting sub-frames at the macro- eNodeB will of course also mean lower macro-cell capacity. Thus, the muting pattern at the macro cells needs to be care- fully optimized in order to achieve real gain from TDM elCIC in a multilayer system.

In Figure 3, the eNodeB serving the overlaying cell has muted sub-frames 304. The eNodeB serving the pico cell may schedule the user equipment which suffers most from interference originating from the overlaying cell to those sub-frames 304. Typically, large RE offsets are applied for these connec^¬ tions. The eNodeB may schedule the users without large RE offsets to the sub frames 306, 308 where the eNodeB serving the overlaying cell is also active.

To enable effective use of TDM elCIC, reliable communication between the eNodeBs serving different layer cells is re^¬ quired .

Figure 4 is a flow chart illustrating an embodiment. In this example, let us assume that eNodeB 102 is serving a pico cell and eNodeB 100 is serving a cell overlaying the cell of the eNodeB102. The process starts at step 400.

In step 402, the eNodeB 102 serving a pico cell measures a parameter related to the signal strength of signals received from nodes serving cells overlaying the cell of the eNodeB 102 and utilising the same channel resources as the eNodeB 102. The eNodeB may use network listen mode (NLM) , when it measures on the downlink received signals from co-channel de^¬ ployed macro-eNBs.

In step 404, the eNodeB 102 is configured to identify the co- channel deployed macro-node corresponding to the strongest received signal strength. The node having the strongest re^¬ ceived signal is designated as a node with which further sig^¬ nalling is executed. In step 406, the eNodeB 102 is configured to determine the nodes having a received signal strength within a given window relative to the strongest signal. The size of the window may be a network configuration parameter.

In step 408, the eNodeB 102 is configured to send the desig^¬ nated node a message comprising at least the identification of the eNodeB 102, the strongest measured signal strength and information on the nodes, if any, having a signal strength within a given window relative to the strongest signal. In an embodiment, the message is sent using the X2 interface.

The process ends in 410.

When the eNodeBs serving pico cells perform the above de^¬ scribed "pico node registration", each eNodeB serving a macro-cell knows exactly which pico nodes are inside the macro-cell coverage area. Knowledge of the path-loss from the eNodeB serving a macro cell to each pico node gives informa^¬ tion on the amount of macro-cell interference generated at each pico cell.

Figure 5A is a flow chart illustrating an embodiment. In this example, let us assume that eNodeB 102 is serving a pico cell and eNodeB 100 is serving a cell overlaying the cell of the eNodeB102. Range extension and TDM elCIC are utilized to in^¬ crease system capacity and quality of service experienced by the users. The process starts at step 500.

In step 502, the eNodeB 102 serving a pico cell is configured to monitor the downlink signal quality of terminals served by the node. The quality may be monitored via received Channel Quality Indicator (CQI) reports or delivered throughput to the users, for example.

In step 504, the eNodeB 102 serving a pico cell is configured to send on the basis of the monitoring a message to a second node serving a cell overlaying the cell of the eNodeB 102, the message requesting the second node to adjust the usage of transmission resources utilised by the second node. In an em- bodiment, the second node is the node designated during the registration process described in connection with Figure 4. In an embodiment, the message is sent using the X2 interface. The process ends in 506. Figure 5B is a flow chart illustrating another embodiment. As above, the eNodeB 102 is serving a pico cell and eNodeB 100 is serving a cell overlaying the cell of the eNodeB102. Range extension and TDM elCIC are utilized to increase system ca- pacity and quality of service experienced by the users. The process starts at step 510.

In step 512, the eNodeB 102 serving a pico cell is configured to monitor the downlink signal quality of terminals served by the node. The quality may be monitored via received Channel Quality Indicator (CQI) reports or delivered throughput to the users, for example.

In step 514, the eNodeB 102 is configured to compare the measured the signal quality to a given threshold. If the measured quality is too low for the pico-users, the eNodeB can not serve all pico-users according to their needs. The quality may be low due to interference from overlaying cell using the same transmission resources, especially for termi^¬ nals utilising large RE offset values. In such a case, the eNodeB 102 may send in step 516 the node serving the overlay- ing cell a message requesting the node to mute at least some of transmission resources utilised by the node. In an embodi^¬ ment, the node serving the overlaying cell is the node desig^¬ nated during the registration process described in connection with Figure 4. Let us assume in this example that the node is eNodeB 100. In an embodiment, the message is sent using the X2 interface.

For example, the eNodeB 102 may request the eNodeB 100 to in^¬ crease the number of muted sub frames in the eNodeB 100 downlink transmission.

If the eNodeB 102 determined in step 514 that the users ex^¬ perience good conditions, the eNodeB 102 may send in step 518 an X2 message to the node serving the overlaying cell indi^¬ cating that the number of muted sub-frames may be decreased. In step 520, the eNodeB 102 is configured to receive a mes- sage from the node serving the overlaying cell. The message may comprise information on the adjusting of the usage of the transmission resources of the second node. In an embodiment, the eNodeB 100 is configured to send the message to all nodes serving pico cells within the areas of the overlaying cell served by the eNodeB 100. Due to the registration process de^¬ scribed above, the eNodeB 100 is aware of pico cells within its area. The nodes serving pico cells may utilize the infor- mation when determining on the optimal scheduling of users in the pico cells. The users with large RE offset values may be scheduled to the sub-frames which are muted by the eNodeB 100.

The process ends in 522.

Figure 6 is a flow chart illustrating an embodiment. As above, eNodeB 102 is serving a pico cell and eNodeB 100 is serving a cell overlaying the cell of the eNodeB 102. Range extension and TDM elCIC are utilized to increase system ca^¬ pacity and quality of service experienced by the users. The process starts at step 600.

In step 602, the eNodeB 100 receives a message from a node serving a cell located within an overlaying cell served by the eNodeB 100, such as the eNodeB 102. The message comprises at least the identification of the node and the signal strength of the downlink transmission of the eNodeB 100 measured by the first node. In addition, the message may comprise information on the nodes, if any, having a signal strength within a given window relative to the strongest signal. In an embodiment, the message is received using the X2 interface. The eNodeB 100 may store the information related to the mes^¬ sage. In this way, the node serving overlaying cell is aware of pico nodes within its area utilising the same transmission resources as the eNodeB 100.

In step 604, the eNodeB 100 receives a message from a node serving a cell located within an overlaying cell served by the eNodeB 100, the message comprising a request to adjust the usage of transmission resources utilised by the eNodeB 100.

In step 606, the eNodeB 100 is configured to deter- mine the need to adjust the usage of transmission resources and adjust the usage of transmission resources if needed. In an embodiment, the adjusting of the transmission resources is realized by increasing or decreasing the number of muted sub frames in the eNodeB 100 downlink transmission.

In step 608, the eNodeB 100 may send a message to the nodes serving a cell located within an overlaying cell served by the eNodeB 100. The message may comprise information on the adjusting of the usage of the transmission resources of the second node. For example, the muted sub-frames are iden^¬ tified in the message. If the eNodeB determined not to adjust the number of sub-frames, the message may comprise a negative acknowledgement (NACK) .

In an embodiment, the eNodeB 100 is configured to send a message in step 610 to neighbouring nodes serving overlaying macro cells. The message may comprise information on the adjusting of the usage of the transmission resources of the eNodeB 100. This information may be used by a neighbouring node serving a macro cell to reschedule cell- edge users and forward users to pico-cells if the node serv^¬ ing the macro cell is inside a given window relative to the strongest signal (step 408 of Figure 4) . In an embodiment, the message may comprise a request for a node serving a macro cell to mute given sub-frames. The receiving node decides if it can follow the request. The receiving node may reply with and an acknowledgement (ACK) or a negative acknowledgement (NACK) message depending on whether it follows the request or not.

The process ends in 612.

If a node serving a macro cell receives an interference re^¬ port from a pico node requesting for the node serving a macro cell to increase the number of muted sub-frames, the node serving the macro cell is configured to estimate if this is possible while still being able to serve its existing users. If the latter is possible, the node serving the macro cell is configured to mute more sub-frames, and inform all the pico nodes inside its coverage area about the change using an X2 message. Similarly, if an interference report from a pico node requesting for the node serving a macro cell to decrease the number of muted sub-frames is received, the node may use the information to potentially reconfigure the muting pattern to use less number of muted sub-frames.

If several interference reports from pico nodes are received, requesting the node serving a macro cell to increase the num- ber of muted sub-frames, the node serving the macro cell may not always be able to meet the request. If the request is coming from a pico node that have almost equal exposure from multiple macro-cells (known on the basis of the procedure de^¬ scribed in connection with Figure 4), the node serving the macro cell may send the request (s) to those macro-cells, ask^¬ ing them to also mute more sub-frames.

The above steps may be performed at least in part by control^¬ lers of eNodeBs . The steps may be performed at least in part by other network elements of participating systems. The steps and related functions described in the attached figures are in no absolute chronological order, and some of the steps may be performed simultaneously or in an order differing from the given one. Other functions can also be executed between the steps or within the steps and other signalling messages sent between the illustrated messages. Some of the steps can also be left out or replaced with a corresponding step. The sig^¬ nalling messages are only exemplary and may even comprise several separate messages for transmitting the same informa^¬ tion. In addition, the messages may also contain other infor- mation.

The apparatuses or controllers able to perform the above- described steps may be implemented as an electronic digital computer, which may comprise a working memory (RAM) , a central processing unit (CPU), and a system clock. The CPU may comprise a set of registers, an arithmetic logic unit, and a controller. The controller is controlled by a sequence of program instructions transferred to the CPU from the RAM. The controller may contain a number of microinstructions for ba^¬ sic operations. The implementation of microinstructions may vary depending on the CPU design. The program instructions may be coded by a programming language, which may be a high- level programming language, such as C, Java, etc., or a low- level programming language, such as a machine language, or an assembler. The electronic digital computer may also have an operating system, which may provide system services to a computer program written with the program instructions.

An embodiment provides a computer program embodied on a dis- tribution medium, comprising program instructions which, when loaded into an electronic apparatus, are configured to con^¬ trol the apparatus to execute the embodiments described above .

The computer program may be in source code form, object code form, or in some intermediate form, and it may be stored in some sort of carrier, which may be any entity or device capa^¬ ble of carrying the program. Such carriers include a record medium, computer memory, read-only memory and a software distribution package, for example. Depending on the processing power needed, the computer program may be executed in a sin^¬ gle electronic digital computer or it may be distributed amongst a number of computers.

The apparatus may also be implemented as one or more inte^¬ grated circuits, such as application-specific integrated cir- cuits ASIC. Other hardware embodiments are also feasible, such as a circuit built of separate logic components. A hy^¬ brid of these different implementations is also feasible. When selecting the method of implementation, a person skilled in the art will consider the requirements set for the size and power consumption of the apparatus, the necessary proc^¬ essing capacity, production costs, and production volumes, for example.

It will be obvious to a person skilled in the art that, as technology advances, the inventive concept can be implemented in various ways. The invention and its embodiments are not limited to the examples described above but may vary within the scope of the claims.

Claims

1. An apparatus comprising:

at least one processor and at least one memory including a computer program code, the at least one memory and the com- puter program code configured to, with the at least one proc^¬ essor, cause the apparatus at least to:

monitor the downlink signal quality of terminals served by a first node;

send on the basis of the monitoring a message to a second node serving a cell overlaying the cell of the first node, the message requesting the second node to adjust the usage of transmission resources utilised by the second node.

2. The apparatus of claim 1, the apparatus being configured to send a message requesting the second node to mute at least some of transmission resources utilised by the second node if the signal quality is below a given threshold.

3. The apparatus of claim 1, the apparatus being configured to send a message requesting the second node to activate the use of at least some of transmission resources utilised by the second node if the signal quality is above a given threshold .

4. The apparatus of any preceding claim, wherein the apparatus is configured to receive from the second node a request to perform monitoring of the signal quality.

5. The apparatus of any preceding claim, wherein the appara- tus is configured to

measure a parameter related to the signal strength of signals received from nodes serving cells overlaying the cell of the first node and utilising same channel resources,

determine the node having the strongest received signal and select the node having the strongest received signal as the second node, and

determine the nodes having a signal strength within a given window relative to the strongest signal.

6. The apparatus of claim 5, wherein the apparatus is further configured to

send the second node a message comprising at least the iden^¬ tification of the first node, the strongest measured signal strength and information on the nodes having a signal

strength within a given window relative to the strongest sig^¬ nal .

7. The apparatus of any preceding claim, wherein the appara- tus is configured to receive a message from the second node, message comprising information on the adjusting of the usage of the transmission resources of the second node.

8. The apparatus of claim 7, wherein the apparatus is config- ured to evaluate the scheduling of terminals served by the first node on the basis of the received message.

9. An apparatus comprising:

at least one processor and at least one memory including a computer program code, the at least one memory and the com^¬ puter program code configured to, with the at least one proc^¬ essor, cause the apparatus at least to:

receive a message from a first node serving a cell located within an overlaying cell served by a second node, the mes- sage comprising a request to adjust the usage of transmission resources utilised by a second node,

determine the need to adjust the usage of transmission re^¬ sources, and

adjust the usage of transmission resources if needed.

10. The apparatus of claim 9, wherein the adjusting of the transmission resources is realized by increasing or decreas^¬ ing the number of muted sub frames in the second node downlink transmission.

11. The apparatus of claim 9, wherein the apparatus is con^¬ figured to send a message to the nodes serving a cell located within an overlaying cell served by a second node, message comprising information on the adjusting of the usage of the transmission resources of the second node.

12. The apparatus of claim 9, wherein the apparatus is con^¬ figured to send a message to neighbouring nodes serving an overlaying cell, the message comprising information on the adjusting of the usage of the transmission resources of the second node.

13. The apparatus of claim 9, wherein the apparatus is con^¬ figured to

receive a message from a first node serving a cell located within an overlaying cell served by a second node, the mes- sage comprising at least the identification of the first node and the signal strength of the downlink transmission of the second node measured by the first node.

14. A method comprising:

monitoring the downlink signal quality of terminals served by a first node;

sending on the basis of the monitoring a message to a second node serving a cell overlaying the cell of the first node, the message requesting the second node to adjust the usage of transmission resources utilised by the second node.

15. The method of claim 14, further comprising:

sending a message requesting the second node to mute at least some of transmission resources utilised by the second node if the signal quality is below a given threshold.

16. The method of claim 14, further comprising:

sending a message requesting the second node to activate the use of at least some of transmission resources utilised by the second node if the signal quality is above a given threshold .

17. The method of claim 16, further comprising: receiving from the second node a request to perform monitoring of the signal quality.

18. The method of any of the claims 14 to 17, further com- prising:

measuring a parameter related to the signal strength of a signal received from a node serving a cell overlaying the cell of the first node,

determining the node having the strongest received signal, determining the nodes having a signal strength within a given window relative to the strongest signal, and

selecting the node having the strongest received signal as the second node.

19. The method of claim 18, further comprising

sending the second node a message comprising at least the identification of the first node, the strongest measured sig^¬ nal strength and information on the nodes having a signal strength within a given window relative to the strongest sig- nal.

20. The method of any of the claims 14 to 19, further com^¬ prising :

receiving a message from the second node, message comprising information on the adjusting of the usage of the transmission resources of the second node.

21. The method of claim 20, further comprising: evaluating the scheduling of terminals served by the first node on the basis of the received message.

22. A method comprising:

receiving a message from a first node serving a cell located within an overlaying cell served by a second node, the mes- sage comprising a request to adjust the usage of transmission resources utilised by a second node,

determining the need to adjust the usage of transmission re^¬ sources, and adjusting the usage of transmission resources if needed.

23. The method of claim 22, wherein the adjusting of the transmission resources is realized by increasing or decreas- ing the number of muted sub frames in the second node downlink transmission.

24. The method of claim 22, further comprising:

sending a message to the nodes serving a cell located within an overlaying cell served by a second node, message comprising information on the adjusting of the usage of the transmission resources of the second node.

25. The method of claim 22, further comprising:

sending a message to neighbouring nodes serving an overlaying cell, the message comprising information on the adjusting of the usage of the transmission resources of the second node.

26. The method of claim 22, further comprising:

receiving a message from a first node serving a cell located within an overlaying cell served by a second node, the mes^¬ sage comprising at least the identification of the first node and the signal strength of the downlink transmission of the second node measured by the first node.

27. A computer program embodied on a distribution medium, comprising program instructions which, when loaded into an electronic apparatus, control the apparatus to:

monitor the downlink signal quality of terminals served by a first node;

28. A computer program embodied on a distribution medium, comprising program instructions which, when loaded into an electronic apparatus, control the apparatus to:

receive a message from a first node serving a cell located within an overlaying cell served by a second node, the mes^¬ sage comprising a request to adjust the usage of transmission resources utilised by a second node,

determine the need to adjust the usage of transmission re^¬ sources, and

adjust the usage of transmission resources if needed.

29. An apparatus comprising:

means for monitoring the downlink signal quality of terminals served by a first node;

means for sending on the basis of the monitoring a message to a second node serving a cell overlaying the cell of the first node, the message requesting the second node to adjust the usage of transmission resources utilised by the second node.

30. An apparatus comprising:

means for receiving a message from a first node serving a cell located within an overlaying cell served by a second node, the message comprising a request to adjust the usage of transmission resources utilised by a second node,

means for determining the need to adjust the usage of trans^¬ mission resources, and

means for adjusting the usage of transmission resources if needed .