WO2013071471A1

WO2013071471A1 - Muting in wireless communications

Info

Publication number: WO2013071471A1
Application number: PCT/CN2011/082147
Authority: WO
Inventors: Deshan Miao; Jingxiu Liu
Original assignee: Nokia Siemens Networks Oy
Priority date: 2011-11-14
Filing date: 2011-11-14
Publication date: 2013-05-23

Abstract

Methods and apparatuses for wireless communications are disclosed. Information associated with at least one subframe that is defined as a muted subframe is provided for indicating a power ratio of data and reference symbols in the at least one subframe for transmission of physical channel data in the at least one subframe. The information is transmitted to at least one recipient device. The received information associated with the at least one subframe that is defined as a muted subframe can then be used by the recipient device in demodulating physical channel data received in the at least one subframe.

Description

MUTING IN WIRELESS COMMUNICATIONS

This disclosure relates to muting in wireless communications.

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 nodes 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 and coordinated between communicating nodes.

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. 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 (PLMN) such as cellular networks, satellite based communication systems and different wireless local networks, for example wireless local area networks (WLAN). A base station can provide one or more wireless service areas known as cells. 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. Service areas can overlap, and thus a communication device in an area can often listen to more than one base station. Therefore communication by a station can cause interference to communications by another station.

A 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 such a node can be 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), pico nodes such as pico eNodeBs (pico-eNB) and remote radio heads. The nodes of the smaller radio service areas may be configured to support local offload. The local nodes can also, for example, be configured to extend the range of a cell. 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. 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). Coordinated multipoint (CoMP) transmissions have also been proposed. Interference caused by the different stations affects wireless system performance. A way to address interference is to transmit at least some of the transmission elements with reduced or minimal energy so that reduced power and/or other interfering activity is caused by the transmission thereof. An example of such transmission elements are subframes that are muted. An example of muted subframes is an almost blank subframe (ABS). Almost blank subframes are subframes that are transmitted with reduced transmit power, or subframes with no transmission power, and/or reduced activity on at least one physical channel. Interference coordination where interference between different radio service areas is coordinated may also be provided. 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 cells will not transmit, or the transmissions are kept in their minimum so as to ensure interference free periods for the transmissions in another cell or cells.

A detailed example is an aspect of the recent LTE releases providing time domain multiplexed (TDM) enhanced inter-cell interference coordination (elCIC) that can be applied to network nodes to reduce interference between the network nodes. In TDM-based enhanced inter-cell interference cancellation an almost blank subframe (ABS) can be used to control interference caused e.g. by a macro cell to a pico cell. In a typical almost blank subframe only (ABS) Common Reference Symbol (CRS) or Channel State Information (CS!) Reference Symbol (RS) is transmitted whilst the physical downlink shared channel (PDSCH) can be muted.

Therefore, in time division multiplexed (TDM) communications PDSCH is typically not permitted in a muted subframe. Such a limitation can have an impact on downlink (DL) capacity. To ease such a limitation it has been proposed that it should be possible to allow PDSCH transmission for a user who would not require the full power also in muted sub-frames. This could be so for example for users who are close to the base station / in the cell center, and therefore do not require the normal transmission power. However, the inventors have found that transmissions on shared physical resources during muted subframes can involve unresolved issues in view of, for example, certain reference symbols. A reference signal may be needed for channel estimation to obtain channel state information for the demodulation. For example, systems based on use of common reference symbols (CRS) can be problematic, in particular because demodulation at the receiver requires information about the power ratio of data to common reference symbols. To illustrate this issue further, an example is described with reference to LTE release 10 parameters p_A and p_B that are used to define physical downlink shared channel (PDSCH) energy per resource element (EPRE) to the cell-specific reference symbol (RS) EPRE. In this context parameter p_A corresponds to the orthogonal frequency division multiplexed (OFDM) symbol without CRS, and p_B corresponds to the OFDM symbol with CRS. Parameters p_A and p_B are configured in a higher protocol layer in accordance with indication by an eNB. In certain demodulation schemes the recipient device requires information about the relationship between power of the reference signal and the PDSCH so that it can determine power thresholds for modulation. However, if the PDSCH transmission is provided in an almost blank subframe, the power control indicator of a normal subframe cannot be used for this. If PDSCH in some transmission time intervals (TTIs) has lower transmission power and the recipient device does not have the power information, the device cannot provide demodulation because the threshold would be different from a normal PDSCH.

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 transmissions can 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, the method comprising providing information associated with at least one subframe that is defined as a muted subframe for indicating a power ratio of data and reference symbols in the at least one subframe for transmission of physical channel data in the at least one subframe, and transmitting the information to at least one recipient device.

In accordance with an embodiment there is provided a method for wireless communications, the method comprising receiving information associated with at least one subframe that is defined as a muted subframe, the information indicating a power ratio of data and reference symbols in the at least one subframe, and demodulating physical channel data received in the at least one subframe based on the information.

In accordance with an embodiment there is provided an 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 provide information associated with at least one subframe that is defined as a muted subframe for indicating a power ratio of data and reference symbols in the at least one subframe for transmission of physical channel data in the at least one subframe, and cause transmission of the information to at least one recipient device.

In accordance with an embodiment there is provided a method An 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 process information associated with at least one subframe that is defined as a muted subframe, the information indicating a power ratio of data and reference symbols in the at least one subframe, and demodulate physical channel data received in the at least one subframe based on the information.

In accordance with a more detailed embodiment the information relates to the power of the physical channel data. The information may also provide an indication whether it relates to at least one muted subframe or at least one non-muted subframe.

The reference symbol may comprise a common reference symbol.

The information may be communicated in association with channel state information. The information may be communicated in a measurement set, for example a channel state information measurement set. Similar channel state information measurement sets may be provided to macro and pico level communication devices. The at least one muted subframe may comprise at least one almost blank subframe.

The low power transmission may be applied to said physical channel data. The physical channel data may be transmitted on a physical downlink shared channel. The physical channel data may be transmitted in the at least one muted subframe by a macro base station.

A physical channel data transmitted in the at least one muted subframe can be demodulated based on the indicator.

Data transmitted on a physical channel may comprise at least one OFDM symbol. Time domain multiplexing (TDM) enhanced inter-cell interference coordination (elCIC) may be applied to the communications.

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

The apparatus may comprise a macro base station, a femto base station and/or a pico base station.

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; and Figure 5 shows a flow diagram illustrating a method according to some embodiments.

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 mobile user equipment 103 or 104 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 four access systems or radio service areas 100, 1 10, 1 17 and 1 19 of different types are shown. The radio service areas are provided by respective base stations 106, 107, 118 and 120. It is noted that instead of the shown number of access systems, any number of access systems can be provided in a communication system. A base station site can provide one or more cells. A base station can also provide a plurality of sectors, for example three radio sectors, each sector providing a cell or a subarea of a cell. All sectors within a cell 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 also noted that the service area 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 1 17 and 1 19 is not shown for clarity. The control apparatus of a base station can be interconnected with other control entities. 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). Non-limiting examples of appropriate LTE access nodes are a macro level 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 Control (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 cell it provides. Figure 1 also shows two smaller or local radio service areas than can be provided by femto or pico station 118 and 120. A service area may also be provided by a remote radio head (RRH) of a macro base station. The smaller station can provide local offload of capacity to the mobile communication devices. Alternatively stations 118 and/or 120 can provide services to any mobile communication devices which are within the local service area thereof. 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 118 and 120 can be within or at least partially 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 113 via gateway 112. A gateway function may be provided to connect to another network. The local base stations 118 and 120 can also be connected to the network 113 by a separate gateway function. For example, station 1 18 can be connected via a gateway 1 11 . The base stations 106, 107, 1 18 and 120 can also be connected to each other by a communication [ink 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. 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 200 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 200 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 muting and associated signalling 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 206 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 300 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 300 can be arranged to provide control on communications in the service area of the system. The control apparatus 300 can be configured to provide control functions in association with generation and communication of muting patterns and other related information and for the actual muting of subframes as well as decision in view of whether to follow the muting pattern by means of the data processing facility in accordance with certain embodiments described below. For this purpose the control apparatus 300 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 300 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 114 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 from a macro-eNB and a pico node can be coordinated base on time domain multiplexed (TDM) enhanced inter-cell interference coordination (elCIC) between nodes to reduce interference. An example for a basic setup where muting of subframes is applied to transmission by a node, for example a macro node is illustrated in Figure 4 depicting use of downlink sub-frames at a network layer as a conceptual illustration. The interference between at least one eNB and pico eNB is controlled such that the macro eNB transmits in subframes 5401 and mutes subframes 402 to allow for pico nodes to maintain performance. The muted subframes can comprise almost blank subframes (ABS). In this context, the term "almost blank" is intended to refer to cases where very little or nearly no transmission takes place. Almost blank subframe can be used for control of interference in a system comprising different cells. A typical almost blank subframe (ABS) only carries information such as Common Reference Symbol (CRS) or Channel State Information (CSI) Reference Symbol (RS) whilst the physical downlink shared channel (PDSCH) is muted. Therefore, in current time division multiplexed (TDM) communications in PDSCH may not be permitted in a muted subframe. Other muting scenarios are also possible, for example where a macro eNB is active in all sub-frames while smaller area nodes are only transmitting in a sub-set 401 of the sub-frames. The remaining sub-frames 402 of the smaller area nodes are muted. Thus the eNB can be transmitting as "normal" to ensure full cell coverage, while the femto and/or pico nodes can introduce local offload in accordance with a muting pattern. Macro enaled communication devices, or macro-UEs, can be scheduled to transmit during the time-periods with almost blank sub-frames from the smaller area node(s) to avoid being exposed to overly high interference.

If e.g. a user equipment (UE) in a pico cell can transmit data signal in an ABS subframe with lower power this can be seen as a time division multiplexed (TDM) solution where different cells may occupy different subframes to reduce interference when performing data transmission. In TDM-elCIC based systems the common reference signal power can be constant across time domain in different TTIs. Thus, when TDM-elCIC is enabled and in the absence of almost blank subframes the PDSCH has a normal power which is defined by parameters p_A and p_B and the power of the common reference signal. In almost blank subframes the PDSCH of relevant devices are provided with zero transmission power, i.e. these subframes are of lower power or muted. Thus the term low power shall be understood to mean a power level that is between zero and normal power of a physical channel. More generally, low power transmission can be understood to refer to any data signal transmission in muted subframes such as ABS subframes.

For the TDM elCIC, it can in general be assumed that the macro-eNB knows in which sub-frames are muted. In order for the system to perform adequately the pico nodes needs to know the TDM muting pattern. Information of this is typically provided by the macro eNBs. Also, the macro-eNB can signal, or otherwise indicate, to users which sub-frames are muted. In this way macro-eNB enabled user equipments know during which sub-frames to receive and wherefrom.

To demodulate a PDSCH, the recipient devices utilizes reference signal to do channel estimation so as to achieve channel state information, and then based on estimated channel information performs the actual demodulation. If modulation schemes such as 16QAM/64QAM and higher order modulation are used, the recipient device needs to know the relationship between transmitted power reference signal (which is used to estimate channel) and the PDSCH to be able to determine power thresholds for the modulation in the constellation. The device needs to determine the threshold to be able to judge the circle of the constellation the current sample belongs to. Such a threshold can be calculated based on the power of the reference signal and the power ratio between the reference signal and PDSCH.

The following describes certain exemplifying embodiments where a physical channel can have lower transmission power in some TTIs resource elements and where the recipient device is not readily provided with information of the lowered power. The embodiments may be used to provide the recipient device with the power information for demodulation so that it can determine the threshold or thresholds also for power levels that are different from the norma! power or powers used for the physical channel or channels.

An embodiment will now be discussed with reference to the flowchart of Figure 5 showing a method for wireless communications to at least one communication device in a plurality service areas where coordinated muting is applied at 50 to transmissions by at least one station in accordance with a defined muting pattern. In the method a physical channel is transmitted at 52 in at least one subframe that is defined to be a muted subframe for at least one recipient device. The at least one device is determined as suitable for a low power transmission, and thus the transmission of the physical channel takes place in at least one muted TTI despite the predefined muting or low power state thereof.

A subframe indicator associated with the at least one muted subframe can be transmitted at 51 by the station to provide information of a power ratio between data and reference symbols for the physical channel. The required signalling may be provided for example by means of the radio recourse control or by means of any other appropriate medium. The information is provided before the data transmission, or at the latest at the same time with the transmission of a muted subframe. Decision whether to enable transmission of data in muted subframes and the selection of appropriate subframes for this can be made e.g. by the control apparatus of a serving macro base station, or another appropriate network entity. The subframe indicator can be used to indicate whether the information comprises power ratio information for at least one muted subframe or power ratio information for at least one non-muted subframe.

At 53 at least one communication device receives the information associated with the at least one muted subframe and thus an indication of the power ratio between data and reference symbols for the physical channel. At 54 the physical channel is received in said at least one subframe that was defined in the muting pattern as being a muted subframe. The device can then use at 55 the received power information associated with the at least one muted subframe in demodulating the physical channel.

The power ratio for the low energy or power transmissions may be determined, for example based on experience and/or predefined values. For example, an eNB can determine a specific ratio based on feedback from communication devices regarding received downlink signal strength and neighbouring cell interference levels. The determination can be such that the possible interference by the low power transmissions in muted subframes does not cause unacceptable levels of interference to transmissions in neighbouring cells.

In accordance with an embodiment, a specific power control indicator for power ratio of data to common reference symbol (CRS) is provided to support low power transmission of physical downlink shared channel (PDSCH) in muted subframes. For example, a new field can be defined for this in RRC signaling of a measurement set. A measurement set may relate to one or more subframes. A flag bit may be used to differentiate a power indicator for a normal sub-frame from a power indicator for a muted sub-frame. For example, a flag bit '1 ' can be used to indicate an ABS sub-frame a and flag bit '0' can be used to indicate a normal subframe. The meaning of the indicator bit could be defined the other way around.

The indication can be associated with a channel state information (CSI) measurement set. For example, in LTE Release 10, two different CSI subframe measurement sets are defined, one for a normal subframe and another for an ABS subframe. Hence this power indicator can be indicated to the recipient device jointly with a CSI measurement subset indication, either simultaneously or separately. There are various possibilities to provide the power indicator for ABS subframe or subframes with low power PDSCH transmission. In accordance with a possibility independent signalling of ABS related parameters p_{A ABS} and p_{B ABS} are specified and signalled via radio resource control (RRC) signalling. These parameters can be used to define physical downlink shared channel (PDSCH) energy per resource element (EPRE) for the ABS. In this example p_{A ABS} corresponds to the orthogonal frequency division multiplexed (OFDM) symbol without CRS, and p_B ^ corresponds to the OFDM symbol with CRS. These parameters can be configured in a higher protocol layer in accordance with indication by an eNB. p_{A ABS} and p_{B ABS} parameters can be defined as device specific. According to the relevant ABS pattern, either p_A I p_B or p_{A ABS} I

P_{B ABS} ^can t^nen be used for CRS based detection and demodulation.

According to a possibility an offset between p_A and p_{A ABS} and/or an offset between p_B and p_{B ABS} is specified and signalled via the RRC. The recipient device can then determine the power based on the offset. Parameters p_A and P_{A ABS} ^{can nave tne} same definition except for the applicable subframe or measurement set. Parameter p_A can be applicable for a normal subframe and devices with normal power transmission in ABS. Parameter p_{A ABS} is only applicable for devices with lower power transmission in ABS. It is noted that it is not necessary to apply the low power transmission in muted subframes to all communication devices in an area. For example, the above principles may be applied to transmissions to only those communication devices that are close enough to a relevant macro eNB and/or devices that are determined to cause a relatively low interference to pico user equipment. Appropriate threshold for the distances and/or interference levels can be defined beforehand.

It can be defined that the subframe which can be used as low-power PDSCH transmission shall be in a CSI measurement set that corresponds to the relevant ABS subframe. In this embodiment some of the ABS transmission timing intervals (TTI) may become excluded from use for lower-power PDSCH transmission. It may not be specified which user equipment (UE) should be configured with one CS! measurement set and which UEs should be configured with two CS1 measurement sets. Currently a typical way of using CSI measurement sets for Macro-Pico scenario is that only pico enabled UEs (incl. macro UEs in bias region which are also connected to Pico) need a two CSI measurement set configuration and macro UEs only need one CSI measurement set. However, if the above described lower-power PDSCH transmission mode is used, macro UEs can experience different data transmission power in different TTls. Such TTI pattern should correspond to the CSI measurement set of pico UEs. To inform the macro UEs about the ABS patterns the similar two CSI measurement sets can also be configured to macro UEs as are configured to pico UEs.

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 multi core processor architecture, as non limiting examples. The data processing may be distributed across several data processing modules. A data processor may be provided by means of, for example, at least one chip. Appropriate memory capacity can also be provided in the relevant devices. The memory or memories may be of any type suitable to the local technical environment and may be implemented using any suitable data storage technology, such as semiconductor based memory devices, magnetic memory devices and systems, optical memory devices and systems, fixed memory and removable memory.

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 when low power transmissions in muted subframes is appropriate and control of the transmissions and related signalling and operations of 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 at least some of the access nodes are not fixedly located 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

What is Claimed

1. A method for wireless communications, the method comprising:

providing information associated with at least one subframe that is defined as a muted subframe for indicating a power ratio of data and reference symbols in the at least one subframe for transmission of physical channel data in the at least one subframe, and transmitting the information to at least one recipient device.

2. A method for wireless communications, the method comprising:

receiving information associated with at least one subframe that is defined as a muted subframe, the information indicating a power ratio of data and reference symbols in the at least one subframe, and demodulating physical channel data received in the at least one subframe based on the information.

3. A method according to claim 1 or 2, comprising providing information relating to the power of the physical channel data.

4. A method in according to any preceding claim, comprising providing information whether the information relates to at least one muted subframe or at least one non-muted subframe.

5. A method in according to claim 4, comprising communication of a bit indicative of either at least one muted subframe or at least one a non-muted subframe.

6. A method in according to any preceding claim, wherein the reference symbol comprises a common reference symbol.

7. A method in according to any preceding claim, wherein the information is communicated in association with channel state information.

8. A method in according to any preceding claim, wherein the at least one muted subframe comprises at least one almost blank subframe.

9. A method in according to any preceding claim, comprising low power transmission of said physical channel data.

10. A method according to any of the preceding claims, wherein the physical channel data is transmitted on a physical downlink shared channel.

11. A method according to any of the preceding claims, wherein the physical channel data is transmitted in the at least one muted subframe by a macro base station.

12. A method in according to any preceding claim, wherein the information is included in a channel state information measurement set.

13. A method in according to any preceding claim, comprising configuring similar channel state information measurement sets to macro and pico level communication devices.

14. A method according to any of the preceding claims, wherein the physical channel data is transmitted in at least one OFDM symbol.

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

16. A method according to any of the preceding claims, comprising demodulating physical channel data transmitted in the at Ieast one muted subframe based on the indicator.

17. An apparatus comprising at Ieast one processor, and at Ieast one memory including computer program code, wherein the at ieast one memory and the computer program code are configured, with the at Ieast one processor, to

provide information associated with at Ieast one subframe that is defined as a muted subframe for indicating a power ratio of data and reference symbols in the at least one subframe for transmission of physical channel data in the at Ieast one subframe, and cause transmission of the information to at Ieast one recipient device.

18. An apparatus comprising at Ieast one processor, and at Ieast one memory including computer program code, wherein the at Ieast one memory and the computer program code are configured, with the at Ieast one processor, to

process information associated with at Ieast one subframe that is defined as a muted subframe, the information indicating a power ratio of data and reference symbols in the at Ieast one subframe, and demodulate physical channel data received in the at Ieast one subframe based on the information.

19. An apparatus according to claim 17 or 18, wherein the information comprises an indication of the power of the physical channel data.

20. An apparatus according to any of claims 17 to 19, wherein the information indicates whether it relates to at least one muted subframe or at least one non-muted subframe.

21. An apparatus according to any of claims 17 to 20, wherein the reference symbol comprises a common reference symbol.

22. An apparatus according to any of claims 17 to 21 , configured to communicate the information in association with channel state information.

23. An apparatus according to any of claims 17 to 22, configured to communicate the information in a measurement set.

24. An apparatus according to any of claims 17 to 23, wherein the at least one muted subframe comprises at least one almost blank subframe.

25. An apparatus according to any of claims 17 to 24, configured to provide low power transmission of said physical channel data.

26. An apparatus according to any of claims 17 to 25, configured to control operation in relation to transmission of the physical channel data in at least one muted subframe on a physical downlink shared channel.

27. An apparatus according to any of claims 17 to 26, configured to include the information in or obtain the information from a channel state information measurement set.

28. An apparatus according to any of claims 17 to 27, configured to cause configuration of similar channel state information measurement sets to macro and pico level communication devices.

29. An apparatus according to any of claims 17 to 28, configured to operate in accordance with time domain multiplexing (TDM) enhanced inter-cell interference coordination (elCIC).

30. An apparatus according to any of claims 17 to 29, configured to cause demodulation of the physical channel data in the at least one muted subframe based on the information.

31 . A node for a communication system comprising the apparatus as claimed in any of claims 17 to 29.

32. A node as claimed in claim 30 comprising a macro base station or a mobile user equipment.

33. A communication system comprising an apparatus according to any of claims 17 to 29.

34. 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.