WO2013037422A1

WO2013037422A1 - Communications in radio service areas

Info

Publication number: WO2013037422A1
Application number: PCT/EP2011/066147
Authority: WO
Inventors: Frank Frederiksen; Troels Emil Kolding
Original assignee: Nokia Siemens Networks Oy
Priority date: 2011-09-16
Filing date: 2011-09-16
Publication date: 2013-03-21

Abstract

Embodiment and apparatuses are provided for wireless communications when service areas of a first node and a second node overlap, !n a method a channel is provided by the second node during a period when the first node is configured to be muted. The channel of the second node is protected from interference by an active channel of the first node by shifting timing of at least one of the nodes, in accordance with a further aspect timing of a device for communications during at least the period when the first node is configured to be muted is adjusted to accommodate the shifted timing of at least one of the nodes.

Description

Communications in radio service areas

This disclosure relates to communications in a wireless communication system comprising a plurality of radio service areas where there can be inaccuracies in time synchronisation or even no time synchronisation between nodes of the different radio service areas.

A wireless communication system enables communication sessions between two or more entities such as fixed or mobile communication devices, machine-type terminals, base stations, and/or other nodes with wireless capabilities. In a wireless communication system at least a part of the communication between at least two stations occurs over a wireless link. 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 communication devices can access the communication system and how various aspects of communication shall be implemented between communicating devices.

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 communication device is used for enabling receiving and transmission of communications such as speech and data. 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 system and/or another user equipment. The communication device may access a carrier provided by a station, for example a base station, and transmit and/or receive communications on the carrier.

Examples of wireless systems include public land mobile networks (PL N) such as cellular networks, satellite based communication systems and different wireless local networks, for example wireless local area networks (WLAN). A wireless system can be divided into cells, and hence these are often referred to as cellular systems. A cell is provided by a base station. Regardless of the shape, size and access technology of the cell providing access for a user such area can be called radio service area or access area. Neighbouring radio service areas typically overlap, and thus a communication device in an area can often listen to more than one base station. This means that the other base stations can cause interference to communications with a serving base station.

A more specific example of communication systems attempting to satisfy the increased demands for capacity is an architecture standardized by the 3rd Generation Partnership Project (3GPP). This system is often referred to as the long-term evolution (LTE) of the Universal Mobile Telecommunications System (UMTS) radio-access technology. A further development of the LTE is often referred to as LTE-Advanced. The various development stages of the 3GPP LTE specifications are referred to as releases.

Base stations can comprise network nodes proving wide area coverage. In LTE-Advanced such a node is referred to as a macro eNode B, or simply eNB. For example, an eNB can provide coverage for an entire cell or similar radio service area. Network nodes can also provide smaller service areas. Examples of such local radio service area network nodes include femto nodes such as Home eNBs (HeNB) or pico nodes such as pico eNodeBs (pico-eNB). The smaller radio service areas can be located wholly or partially within a larger radio service area. A local service area may also be located within, and thus listen to, more than one larger radio service area. The nodes of the smaller radio service areas such as the femto nodes may be configured to support local offload. The local nodes can also, for example, be configured to extend the range of a ceil. In some instances a combination of wide area network nodes and small area network nodes can be deployed using the same frequency carriers (e.g. co- channel deployment). The local nodes may support user equipment(s) belonging to a closed subscriber group (CSG) or an open subscriber group (OSG).

Interference coordination between different radio service areas can be provided to address the possible interference. The coordination can be used to maintain performance, or at least ensure functioning, of users connected to the maero-eNB. For example, an aspect of LTE-Advanced is that time domain multiplexed (TDM) enhanced inter-cell interference coordination (elCIC) can be applied to network nodes to reduce interference between the network nodes. In some scenarios elCIC can be used for co-channel deployment of macro-eNBs and CSG HeNBs and/or co-channel deployment of macro-eNBs and pico-eNBs.

A so-called muting pattern may be used for the coordination. A muting pattern can be used in association with different nodes in a network, for example to enforce muting in nodes such as macro, pico and femto nodes. The muting patterns are typically configured to provide time periods where one or more ceils will not transmit, or the transmission are kept in their minimum so as to ensure interference free periods for the transmissions in another ceil or ceils. Optimal configuration and/or coordination of the muting patterns can be a challenging task, in particular when macro-eNB and GSG-Home-eNBs are deployed on same frequency carriers.

Particular examples in this context are scenarios with co-channel deployment of macro-eNBs and CSG Home-eNBs (HeNBs), and co-channel deployment of macro-eNBs and pico-eNBs using extensive range extension. The muting pattern enforced at the HeNBs for the former case, and at macro nodes for the latter case, needs to be accurately configured in order to achieve attractive benefits of time domain multiplexed (TDM) eiCIC. The main motivation for introducing this principle is to maintain the performance (or at least ensure functioning) of users connected to the macro-eNB (or pico nodes in case of extensive range extension).

The time periods made available by muting patterns can be relatively short. This can be particularly the case for periods reserved for control channels. There may be only a loose synchronisation between the different radio service areas, the synchronisation may be inaccurate for other reasons, or it may be that the overlapping radio service areas are not synchronised at all. This can mean that at least a part of the muted period is lost as an active subframe of an interfering ceil can extend on the time period when the victim cell should be transmitting a channel. It is not always easy or even practical to provide strict synchronization between the cells, for example for the reasons of complexity and/or cost. This may be especially the case when low-cost nodes are deployed.

Solutions that have been proposed for the synchronization include use of Global Positioning System (GPS), use of network listen mode (NLM) also in microcells and picocells, and use of a timing that is distributed over packet/backhaul transport link. However, GPS and other satellite based positioning systems in general have limitations in indoor hotspot solutions and requires additional hardware including an external antenna. Network listen mode may not be specified for all cells in an area and also requires additional hardware. The transport based synchronization methods can have a limited accuracy. An exchange of packets can be used to calculate the difference in time and frequency between two clocks. However, the overall precision of an Ethernet-based mobile backhaul is dependant on many factors and different topologies, equipment and traffic management introduce different amounts of latency and synchronisation jitter. Servicing delays can impact the accuracy of the timestamp which, in turn, can reduce the precision of the clock adjustment calculations. Synchronisation between clocks can also drift when the frequency offset between the master and the slave is being corrected. Additionally network equipment such as switches, routers, and gateways can all introduce latency and wandering errors. These are some of the reasons why the current solutions are not able to reach acceptable accuracy levels for ail applications, for example accuracy levels for less than 1 -2ps synchronization accuracy that would be required by schemes such as the e!CIC. Network operators may also desire to push down cost. This can mean utilizing e.g. statistical multiplexing and overbooking for better hardware re-use. Such designs can introduce some jitter which may be hard to control, in particular if the 1-2 microsecond accuracy level is desired.

It is noted that the above discussed issues are not limited to any particular communication environment, but may occur in any appropriate communication system comprising a plurality of radio service areas where muting of data transmissions may be provided.

Embodiments of the invention aim to address one or several of the above issues.

In accordance with an embodiment there is provided a method for wireless communications when service areas of a first node and of a second node overlap, the method comprising providing a channel by the second node during a period when the first node is configured to be muted, and protecting the channel of the second node from interference by an active channel of the first node by shifting timing of at least one of the nodes.

In accordance with another embodiment there is provided a method for wireless communications by a device in an area covered by a first node and a second node, the method comprising adjusting timing of the device for communications during at least a period when the first node is configured to be muted to accommodate shifted timing of at least one of the nodes, wherein the shifted timing of at least one of the nodes is for protection of a channel with the second node from interference by an active channel of the first node, and communicating on the channel when the first node is muted.

In accordance with another embodiment there is provided an apparatus for controlling wireless communications in an area where service areas of a first node and of a second node overlap and the second node provides a channel during a period when the first node is configured to be muted, the apparatus comprising at least one processor, and at least one memory including computer program code, wherein the at least one memory and the computer program code are configured, with the at least one processor, to protect the channel of the second node from interference by an active channel of the first node by causing shifting of timing of at least one of the nodes.

In accordance with yet another embodiment there is provided an apparatus for controlling wireless communications in an area covered by a first node and a second node, the apparatus comprising at least one processor, and at least one memory including computer program code, wherein the at least one memory and the computer program code are configured, with the at least one processor, to adjust timing of a device during at least a period when the first node is configured to be muted to accommodate shifted timing of at least one of the nodes, wherein the shifted timing is for protection of a channel with the second node from interference by an active channel of the first node.

In accordance wit ha more detailed embodiment method the protected channel comprises a control channel. The control channel may comprise a physical downlink control channel. The active channel may comprise a physical downlink shared channel. The shifting may be limited to a transmission time interval. The shifting may comprise shifting a channel to be within a period of muting of the first node.

The timing of the second node and/or the first node may be shifted. The time shifting of the at least one of the node may be configured by means of an X2 interface, pre-configuration, an estimate based on a general timing estimate, or a central network entity. One of the nodes may estimate timing of the other node and adjust timing of transmission of at least one muted subframe accordingly. Relative time difference between the first and second nodes may be determined. The shift can be determined accordingly, information about allowed maximum allowed shift may be communicated.

The channel may comprise at least one OFDM symbol. Time domain multiplexing (TDM) enhanced inter-cell interference coordination (e!CIC) may be applied to the nodes.

A node for a communication system, a communication device and/or a communication system comprising the apparatus may be provided.

The first node may comprises a macro base station and the second node may comprise a femto base station or a pico base station or vice versa.

A computer program comprising program code means adapted to perform the method may also be provided.

Various other aspects and further embodiments are also described in the following detailed description and in the attached claims.

The invention will now be described in further detail, by way of example only, with reference to the following examples and accompanying drawings, in which:

Figure 1 shows a schematic diagram of a network according to some embodiments;

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 representation of downlink transmission in sub-frames according to some embodiments; Figure 5 shows a flow diagram illustrating a method according to some embodiments; and

Figure 8 shows an exemplifying scenario in accordance with an embodiment.

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, access systems thereof, mobile communication devices and muting are briefly explained with reference to Figures 1 to 4 to assist in understanding the technology underlying the described examples.

A mobile communication device or user equipment 102, 103, 104, 105 is typically provided wireless access via at least one base station or similar wireless transmitter and/or receiver node of an access system. In figure 1 two neighbouring and overlapping access systems or radio service areas of a first type 100 and 1 10 and three local or smaller radio service areas of a second type 1 15, 1 17 and 1 19 are shown. The radio service areas are provided by base stations 106, 107, 1 16, 1 18 and 120.

The communication devices 102, 103, 104, 105 can access the communication system based on various access techniques, such as code division multiple access (CDMA), or wideband CDMA (WCDMA), 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.

It is noted that instead of the shown number of access systems, any number of access systems can be provided in a communication system. An access system can be provided by a cell of a cellular system or another system providing radio service area for a communication device. 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 ceil can be served by the same base station. Thus a base station can provide one or more radio service areas. Each mobile communication device and base station 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 cell borders or edges are schematically shown for illustration purposes only in Figure 1. it shall be understood that the sizes and shapes of radio service areas may vary considerably from the shapes of Figure 1.

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 base stations 106 and 107. The control apparatus of the smaller service areas is not shown for clarity. 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.

A non-limiting example of the recent developments in communication system architectures is the long-term evolution (LTE) of the Universal Mobile Telecommunications System (UMTS) that is being standardized by the 3rd Generation Partnership Project (3GPP). As explained above, further development of the LTE is referred to as LTE-Advanced. Non-limiting examples of appropriate LTE access nodes are a base station of a cellular system, for example what is known as NodeB (NB) in the vocabulary of the 3GPP specifications. 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). ENBs can 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 Controi (RRC) protocol terminations towards the user 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). Figure 1 depicts two wide radio service area base stations 106 and 107, which can be macro-eNBs. A macro-eNB can transmit and receive data over the entire coverage of the eel! it provides. Figure 1 also shows three smaller or local radio service areas than can be provided by Home eNBs 1 16, 1 18 and 120. A home-eNB (HeNB) can provide local offload of capacity to mobile communication devices. A HeNB can provide services to only mobile communication devices which are members of a closed subscriber group (CSG). Alternatively a HeNB can provide services to any mobile communication devices which are within the local area of the HeNB. The coverage of these base stations may generally be smaller than the coverage of wide area base stations. The coverage provided by the local nodes 1 16, 1 18 and 120 can overlap with the coverage provided by one or more of the macro-eNBs 106 and 107. The local radio service areas can also overlap with each other. Thus signals transmitted in a service area of a node can interfere with communications in service area of another node.

In Figure 1 the base stations 106 and 107 can be connected to a wider communications network 1 13 via gateway 1 12. A gateway function may be provided to connect to another network. The local base stations 1 16, 1 18 and 120 can also be connected to the network 1 13 by a separate gateway function. For example, the HeNB 1 16 and 1 18 can be connected via a HeNB gateway 1 1 1. The base stations 106, 107, 1 16, 1 18 and 120 can also be connected to each other by a communication link for sending and receiving data, this being shown by the dashed lines. The communication link can be any suitable means for sending and receiving data between the base stations. This feature is denoted by the dashed lines between the base stations. In certain embodiments the communication link can be an X2 link.

The mobile communication devices will now be described in more detail in reference to Figure 2. Figure 2 shows a schematic, partially sectioned view of a communication device 102 that a user can use for communication. 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) such as a mobile phone or what is known as a 'smart phone', a portable 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. User 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 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. Functionalities thereof in relation to timing in accordance with certain embodiments will be described in more detail below. 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. A wireless communication device can be provided with a Multiple Input / Multiple Output (MIMO) antenna system. MIMO arrangements as such are known. MIMO 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 208 of Figure 2 can provide a plurality of antenna ports. More data can be received and/or sent where there are more antennae elements. A station may comprise an array of multiple antennae. Signalling and muting patterns can be associated with Tx antenna numbers or port numbers of MIMO arrangements.

Figure 3 shows an example of a control apparatus 109 for a communication system, for example to be coupled to and/or for controlling a station of an access system. In some embodiments the base stations comprise a separate control apparatus, in other embodiments the control apparatus can be another network element. The control apparatus 109 can be arranged to provide control on communications in the service area of the system. The control apparatus 109 can be configured to provide control functions in association with timing and generation and communication of transmission patterns and other related information and muting signals by means of the data processing facility in accordance with certain embodiments described below. For this purpose 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. The control apparatus 109 can be configured to execute an appropriate software code to provide the control functions.

It shall be appreciated that similar components can be provided in a control apparatus provided elsewhere in the system for configuring muting patterns and/or controlling coordination of muting the service areas. For example, a central control apparatus 1 14 can provide at least a part of the coordination functions, an example of will be described later.

In accordance with an embodiment downlink transmissions in sub-frames on the same frequency carrier from a macro-eNB 107 and an HeNB 1 18 of Figure 1 are coordinated base on time domain multiplexed (TDM) enhanced inier-cel! interference coordination (e!CIC) between network nodes to reduce interference, in some scenarios elCIC can be used for co-channei deployment of macro-eNBs and CSG HeNBs and / or co-channel deployment of macro-eNBs and pico-eNBs. In such scenario it can be difficult and/or expensive to establish strict time synchronization between network nodes. Certain examples to address this are described below in association with networks with co-channel deployment of macro-eNBs (hereafter also called as eNBs) and other network nodes, for example pico nodes, open subscriber group (OSG) HeNBs or dosed subscriber group (CSG) HeNBs.

An example for a basic setup where loose time synchronisation may occur is illustrated in Figure 4 depicting use of downlink sub-frames at two network layers as a conceptual illustration. More particularly, in Figure 4 eNB 107 is active in all sub-frames while the HeNBs are only transmitting in a sub-set 401 of the sub-frames. The remaining sub-frames 402 are muted, and more particularly almost blank subframes. In this context, the term "almost blank" is intended to refer to cases where very little or nearly no transmission takes place from the HeNB. Thus the eNB is transmitting as "normal", and not suffering any performance penalty. This is so since the eNB shall typically ensure full cell coverage, while the CSG HeNB can be installed to introduce local offload. Macro-UEs that are not allowed to connect the CSG HeNB and are close to HeNB 1 18 can be scheduled during the time-periods with almost blank sub- frames from the HeNBs to avoid being exposed to overly high interference. At the same time other macro-UEs away from the CSG HeNB can also be scheduled in other sub-frames. A reason why this can be allowed is that their interference conditions are not necessarily impacted by the CSG HeNB. For the TDM eiCIC, it can in general be assumed that the macro-eNB 107 knows in which sub-frames the CSG HeNBs are muted. Also, the macro-eNB can signal, or otherwise indicate, to its users which sub-frames are almost blanked from HeNB-side. In TDM eiCIC the macro-eNBs are aware in which sub-frames no data is transmitted by the HeNBs. Similarly macro-eNB can signal or indicate to user equipments enabled to communicate with the macro-eNB within the coverage of the macro-eNB, which sub-frames comprise no data transmitted by the HeNBs. In this way macro-eNB enabled user equipments know during which sub-frames to receive from the macro-eNB. During the first time period 401 when the data in the sub-frames is normally transmitted on both the macro-eNB layer and the HeNB layer, HeNB enabled user equipment (UE) can be scheduled to receive data in sub-frames from the HeNB layer. Alternatively or additionally, when some macro-eNB enabled UEs do not experience excessive interference from HeNB these can be scheduled to receive data from the macro-eNB during the sub-frames when the HeNB is not muted. During the second time period 402 wherein the HeNB 1 18 is muted during some sub-frames, macro-eNB enabled UEs are scheduled to receive data transmitted from the macro-eNB 107. The macro-eNB enabled UEs may not be allowed to connect to a nearby HeNB 108, for example when the HeNB is configured for communication devices of only a closed subscriber group (CSG). This means that by scheduling the macro-eNB enabled UE to receive data during a sub-frame in which the HeNB is muted, the UEs are not exposed to high interference from the HeNB.

The other case of interference between eNBs and pico eNBs is opposite, where the macro eNB needs to mute some subframes to allow for pico nodes with large range extension (and thereby poor signal to interference plus noise ratio or SINR conditions) to maintain basic performance. It is important for the system performance, though, that the pico nodes know the TDM muting pattern from the macro eNBs.

Strict synchronization at the nodes can be a challenging task, and this may be especially the case when low-cost nodes are deployed, for example in indoor environments. In accordance with the herein described embodiments relaxed synchronization requirements are enabled for LTE frequency division duplex (FDD). The relaxation is provided to ensure that e.g. timing over a packet can work effectively. Support can be provided e.g. for the elCIC where synchronization requirements are in the 10-30 microsecond range.

In accordance with an embodiment for cases and scenarios where TDM elCIC is applied in connection to network deployments where it is difficult to obtain strict time synchronization, the aggressor node can be configured to operate in a time-shifting mode. The time-shifting mode can be arranged to provide special protection of the control channels of the victim ceil. The level of protection may be determined based on indicative values of the level of synchronization that is possible to obtain for each aggressor/victim node configuration in the network.

An embodiment will now be discussed with reference to the flowchart of Figure 5 showing a method for wireless communications by a communications device within service areas of a first node and a second node in a system where muting is coordinated. The first node may provide at 10 a radio service area of a first type, for example a macro service area 100 or 1 10 of Figure 1 and the second node may provide a radio service area of a second type, for example any of the femto cells 1 15, 1 18, 1 19 of Figure 1. The second node provides at 12 a channel during a period when the first node is configured to be muted. To protect the channel of the second node from interference by an active channel of the first node timing of at least one of the nodes is shifted at 14. The timing of the communication device can be adapted accordingly such that the communication on the channel can take place at 16 during a period when there is improved certainty that the second node is indeed muted.

In accordance with an embodiment the timing is shifted no more than one transmission time interval (TTI). For example, considering that in LTE frame timing is 10 ms and each transmission time interval (TTI) is 1 ms, the shifting can be limited to be less than 1 ms. Q: This can be advantageous for example in TDM eiCIC related solutions where patterns of 1 ms resolution are defined. Thus a limitation to 1 ms can be advantageously used in certain TDM eiCIC related embodiments and other similar environments to provide shifting that matches the used muting patterns.

The shifting can delay the timing of a node. However, in certain occasions the timing of a node may be brought forward to improve the certainty of a channel being received properly. It is also possible that the timing of both nodes is slightly changed. In this case the shifting may result one of the nodes being delays and the other being brought forward.

The adaptation of timing at the communication device to follow the shifted timing of at last one of the nodes can be provided based on timing instructions from a commanding node. For example, in LTE a node a user equipment is connected to can dictate the timing to be used. The timing can originally be derived from synchronization sequences (primary and secondary synchronization sequences; PSS/SSS). When a user equipment connects to a cell, it searches for the PSS and SSS to obtain timing and physical cell ID, In case networks are not time aligned, the user equipment can also change the system timing when performing a handover. So in case for example a HeNB changes the timing to provide better protection of a PDCCH, this shifted timing can be applied at the HeNB, and ail user equipments connected to this HeNB then follow this timing.

It is also possible that a communication device is associated with more than one active access node at a time. For example, a communication device within the area of a first node and a second node may be in communication with both of the nodes. Control apparatus in the communication device can be adapted to be able to observe and cause reporting of a determined relative time difference between the two nodes to the victim node. The victim node may then adjust its timing accordingly to better protect a particular channel. This approach may require changes to relevant standard specifications and/or to the communication device in view of how measurement are performed and reported.

A possibility is to have the victim node to implement a network listen mode where the victim node will do measurements in view of the timing relations for the aggressor node and adapt the timing according to the expected timing relations on the backhaul. This kind of operation can be applied for example to a macro- pico case and a macro-HeNB case. In the latter example a HeNB can monitor the timing of the macro and adapt itself to this timing by means of time shifting. In general, in interference scenario between a macro cell and another ceil, typically a minor cell, it is preferred to let the macro level node be the dominating node.

Figure 6 illustrates schematically an example where uncertainty in synchronisation between an aggressor ceil and a victim cell is addressed by shifting the relative timing between the cells. Although it would be desirable to have constant timing the timing relationship may not be known, or is not known accurately enough to remove the uncertainty. There can be a time shift or inaccuracy (denoted as "jitter" 61 in Figure 6) that is something that cannot be easily determined. A rough estimate of the "jitter" 61 / uncertainty period can be provided through either a network listen mode or network time protocols on the backhaul wired network. In Figure 6 the aggressor cell is shown to transmit a norma! or active subframe 60 followed by an almost blank subframe 62. A period of uncertainty or time jitter 61 is shown between the subframes 60 and 62. This can mean that transmission in the active subframe extends on the beginning of the muted subframe 62. In the victim cell the first two symbols 64 of each subframe 66, for example OFDM symbols, are reserved for a control channel, for example physical downlink control channel (PDCCH). if nothing is done, period 61 would mean that the first symbol of the control channel can potentially suffer from interference from active subframe 60 of the aggressor ceil. Figure 6 illustrates how this can be handled in association with a muted subframe 62 by introducing a shift of timing of victim ceil reception of the control channel. For the purposes of illustration, the shift has been set to one symbol to ensure that no interference appears on the victim cell control channel.

A penalty resulting from this kind of operation is that the data channel area (PDSCH) of the victim cell can potentially be interfered by the aggressor ceil. The last symbol 67 of the data channel, for example physical downlink data channel (PDSCH) of the victim ceil will see a full symbol of interference from the next active subframe 63 of the aggressor cell. However, as the relative fraction of data symbols being interfered is much less than the relative fraction of control symbols, the penalty of this approach is less severe and can usually be tolerated.

An embodiment relating to macro-pico cell case with loose time synchronization at a pico node is described next. This case may be experienced for example when pico nodes are used for creating local coverage, typically indoor coverage. In such cases it can be difficult and hence expensive to create strict time synchronization, especially on an accuracy level that is less than of the order of 1-2 micro-seconds. It can nevertheless be assumed that a level of synchronization is obtainable that is within the range of 1-2 orthogonal frequency division multiplexing (OFDM) symbols. This would mean accuracy in the level that is of less than 150 microseconds, corresponding to two OFDM symbols. There can be serious consequences for the victim ceil if the aggressor cell is time-wise off such that the victim cell's control channel (e.g. PDCCH) is heavily interfered by data transmission on the aggressor cell's shared channel (e.g. PDSCH). To protect the control channel the timing of the victim cell may be arranged such thai it can be ensured that the aggressor eel! cannot disturb the reception of control channels belonging to the victim cell.

The arrangement can be such that if the victim node is a pico node the macro network does not adjust its timing to accommodate the smaller cell's operation. A reason for this is that there may be multiple pico nodes within the coverage area of a single macro node. Hence, the macro node shall provide the reference point when defining timing. This can be so regardless whether the macro node is the aggressor or the victim cell.

The configuration of a pico node for operating in accordance with shifted frame timing may be provided, for example, by means of X2 configuration from the macro node. Specific X2 interface messages may be introduced.

Communication over X2 may for example include negotiations such as a pico node "asking" a macro node if it would be beneficial to shift timing to provide extra control channel protection. As a part of the negotiations the macro node can send a message indicating "yes/no". The macro node may also communicate information about the amount of shifting that would be allowed. This may be beneficial as shifting can impact the SINR variability over the received data packets.

An option is to pre-configure the pico node. The pre-configuration may be provided during manufacture or installation of the node, or later, for example based on specifications in a relevant standard. The pre-configuration may be based on estimation from a genera! timing estimation. For example, a node such as a pico or macro level node can obtain timing information by simply listening for the PSS and SSS from the macro node by means of network listen mode.

According to a possibility autonomous configuration is provided. This solution is based on use of network listen mode to adjust transmission timing instants at a node to "fit" into the macro operation with respect to timing.

According to a possibility the node is configured from a centra! network control entity. For example, an Operations, Administration, and Maintenance (OAM) server may be configured for providing the centralised control. A standardized signalling interface may be provided if there is a central element for controlling the amount of allowed misalignment to cope with timing uncertainty. Another exemplifying embodiment relates to macro-femto interference control case with loose or no time synchronization at a femto node. A co-channel deployed femto node such as a CSG HeNB can create coverage holes for macro connected user equipments that are not a part of the CSG. TDM eiCIC can be applied to avoid, or at least mitigate, the coverage hole creation. In this case the femto node can apply network listen mode (NLM) where the femto node disrupts its transmission on pre-defined timings and attempts to assess the macro network timing and adjust its own timing accordingly. When the femto node has obtained its timing estimate with a certain accuracy level it can introduce a transmit timing offset such that the ABS starts before the macro node would be transmitting its control channel, !n this way it can be ensured that the control channel of the macro node is protected for the entire coverage area of the femto node, and the risk of experiencing a coverage hole for macro node connected user equipments can be minimized or at least mitigated.

The embodiments of this invention may be implemented by computer software executable by a data processor apparatus, or by hardware, or by a combination of software and hardware. The required data processing apparatus and functions of a network control apparatus, a communication device and any node or element may be provided by means of one or more data processors. The described functions 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 muiti 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. An appropriately adapted computer program code product or products may be used for implementing the embodiments, when loaded or otherwise provided on an appropriate data processing apparatus, for example for causing determinations of appropriate time adjustment, operation of timers and communications of information between the various nodes. The program code product for providing the operation may be stored on, provided and embodied by means of an appropriate carrier medium. An appropriate computer program can be embodied on a computer readable record medium. A possibility is to download the program code product via a data network. In general, the various embodiments may be implemented in hardware or special purpose circuits, software, logic or any combination thereof. Embodiments of the inventions may thus be practiced in various components such as integrated circuit modules. The design of integrated circuits is by and large a highly automated process. Complex and powerful software tools are available for converting a logic level design into a semiconductor circuit design ready to be etched and formed on a semiconductor substrate.

It is noted that whilst embodiments have been described in relation to certain architectures, similar principles can be applied to other communication systems where carrier aggregation is provided and the issue of timing may arise. For example, this may be the case in application where no fixed access nodes are provided but a communication system is provided at least partially by means of a plurality of user equipment, for example in adhoc networks. Also, the above principles can also be used in networks where relay nodes are employed for relaying transmissions. Therefore, although certain embodiments were 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. It is also noted that different combinations of different embodiments are possible. It is also noted herein that while the above describes exemplifying embodiments of the invention, there are several variations and modifications which may be made to the disclosed solution without departing from the spirit and scope of the present invention.

Claims

1. A method for wireless communications when service areas of a first node and of a second node overlap, the method comprising:

providing a channel by the second node during a period when the first node is configured to be muted, and

protecting the channel of the second node from interference by an active channel of the first node by shifting timing of at least one of the nodes,

2. A method for wireless communications by a device in an area covered by a first node and a second node, the method comprising:

adjusting timing of the device for communications during at least a period when the first node is configured to be muted to accommodate shifted timing of at least one of the nodes, wherein the shifted timing of at least one of the nodes is for protection of a channel with the second node from interference by an active channel of the first node, and

communicating on the channel when the first node is muted.

3. A method according to claim 1 or 2, wherein the protected channel comprises a control channel.

4. A method according to claim 2, wherein the control channel comprises a physical downlink control channel.

5. A method in according to any preceding claim, wherein the active channel comprises a physical downlink shared channel.

6. A method in according to any preceding claim, wherein the shifting of the timing is limited to one transmission time interval at most.

7. A method in according to any preceding claim, wherein the shifting comprising shifting the channel to be within the period when the first node is muted.

8. A meihod according to any of the preceding claims, wherein the timing of the second node is shifted.

9. A method according to any of the preceding claims, wherein the timing of the first node is shifted.

10. A method according to any of the preceding claims, wherein the first node comprises a macro base station and the second node comprises a femto base station or a pico base station or vice versa.

1 1. A method according to any of the preceding claims, comprising configuring the time shifting of the at least one of the node by means of X2 interface, pre-configuration, an estimate based on a general timing estimate, or a central network entity.

12. A method according to any of the preceding claims, wherein one of the nodes estimates timing of the other node and adjusts timing of transmission of at least one muted subframe accordingly.

13. A method according to any of the preceding claims, comprising determining relative time difference between the first and second nodes and determining the shift in timing based thereon.

14. A method according to any of the preceding claims, comprising communicating information about maximum allowed shift.

15. A method according to any of the preceding claims, wherein the channel comprises at least one OFDM symbol.

16. A method according to any preceding claim, comprising applying time domain multiplexing (TDM) enhanced inter-ceil interference coordination (elCIC) to the nodes.

17, An apparatus for controlling wireless communications in an area where service areas of a first node and of a second node overlap and the second node provides a channel during a period when the first node is configured to be muted, the apparatus comprising at least one processor, and at least one memory including computer program code, wherein the at least one memory and the computer program code are configured, with the at least one processor, to protect the channel of the second node from interference by an active channel of the first node by causing shifting of timing of at least one of the nodes.

18. An apparatus for controlling wireless communications in an area covered by a first node and a second node, the apparatus comprising at least one processor, and at least one memory including computer program code, wherein the at least one memory and the computer program code are configured, with the at least one processor, to adjust timing of a device during at least a period when the first node is configured to be muted to accommodate shifted timing of at least one of the nodes, wherein the shifted timing is for protection of a channel with the second node from interference by an active channel of the first node.

19. An apparatus according to claim 17 or 18, wherein the protected channel comprises a control channel.

20. An apparatus according to any of claims 17 to 19, wherein the control channel comprises a physical downlink control channel and/or the active channel comprises a physical downlink shared channel.

21. An apparatus according to any of claims 17 to 20, wherein the apparatus is configured to shift the timing one transmission time interval at most.

22. An apparatus according to any of claims 17 to 21 , configure to shift the channel to be within the period when the first node is muted.

23. An apparatus according to any of claims 17 to 22, configured to cause shifting of timing of the second node.

24, An apparatus according to any of claims 17 to 23, configured to cause shifting of timing of the first node,

25, An apparatus according to any of claims 17 to 24, wherein the first node comprises a macro base station and the second node comprises a femto base station or a pico base station or vice versa.

26, An apparatus according to any of claims 17 to 25, configured to estimate timing of at least one of the nodes and adjust timing of transmission of at least one muted subframe accordingly.

27. An apparatus according to any of claims 17 to 26, configured to determine relative time difference between the first and second nodes and determine the shift in timing accordingly.

28, An apparatus according to any of claims 17 to 27, configured to apply the time shifting in connection with time domain multiplexing (TDM) enhanced inter- ceil interference coordination (e!CIC).

29. A node for a communication system, comprising the apparatus of claim 17 or any of the preceding claims dependent on claim 17.

30. A communication device, comprising the apparatus of claim 18 or any of the preceding claims dependent on claim 18.

31 , A communication system, comprising the apparatus of any of claims 17 to 28.

32. A computer program comprising code means adapted to perform the steps of any of claims 1 to 16 when the program is run on a processor.