Signaling in TDD communication

There is provided a method, comprising: applying, by a first node operating under a time division duplex communication scheme, a frame structure comprising an extended transmission part, wherein the extended transmission part at least partially overlaps in time domain with a reception part of a frame structure applied by at least one second node operating at least partially under the same transmission/reception pattern as the first node; and causing specific signaling to the at least one second node in the extended transmission part.

This application is a national stage entry of PCT Application No. PCT/EP2012/068400, filed on Sept. 19, 2012 entitled “SIGNALING IN TDD COMMUNICATION”, which is hereby incorporated by reference in its entirety.

FIELD

The invention relates generally to mobile communication networks. More particularly, the invention relates to cross-node signaling performed in a time division duplex (TDD) communication scheme.

BACKGROUND

Time division duplex (TDD) is one possible communication scenario between two nodes, such as a base station (BS, eNB) and a user terminal (UT, UE). As a half-duplex technology, while one node transmits, the connected node receives, and vice versa.

BRIEF DESCRIPTION OF THE INVENTION

According to an aspect of the invention, there are provided methods.

According to an aspect of the invention, there are provided apparatuses.

According to an aspect of the invention, there is provided a computer program product.

According to an aspect of the invention, there is provided a computer-readable distribution medium carrying the above-mentioned computer program product.

According to an aspect of the invention, there is provided an apparatus comprising processing means configured to cause the apparatus to perform any of the embodiments as described in the appended claims.

According to an aspect of the invention, there is provided an apparatus comprising a processing system configured to cause the apparatus to perform any of the embodiments as described in the appended claims.

According to an aspect of the invention, there is provided an apparatus comprising means for performing any of the embodiments as described in the appended claims.

In an embodiment, a first node operating under a time division duplex communication scheme, applies a frame structure comprising an extended transmission part, wherein the extended transmission part at least partially overlaps in time domain with a reception part of a frame structure applied by at least one second node operating at least partially under the same transmission/reception pattern as the first node, and cause specific signaling to the at least one second node in the extended transmission part.

In an embodiment, a second node operating under a time division duplex communication scheme applies a frame structure comprising an extended reception part, wherein the extended reception part at least partially overlaps in time domain with a transmission part of a frame structure applied by at least one first node operating at least partially under the same transmission/reception pattern as the second node, and causes reception of a specific signaling from the at least one first node in the extended reception part.

In an embodiment, the overlapping transmission part of the frame structure applied by the at least one first node is a default transmission part or an extended transmission part.

In an embodiment, the second node may apply the frame structure comprising the extended reception part according to a predefined frequency for certain frames, and apply a default TDD frame structure for other frames.

In an embodiment, the second node may provide information of the frame structure applied by the second node to the first node, wherein the information indicates at least one of the following: a length of the frame, transmission-reception switching points in time domain, the number of RX parts, the number of TX parts, length of a guard period, whether or not the frame structure comprises the extended RX part, length of the default/extended RX part, number of the one or more extended RX parts.

In an embodiment, the second node may provide information indicating the frame structure to be applied to the first node.

In an embodiment, the extended reception part is located in the frame structure adjacent to a guard period, thus facilitating switching between transmission and reception.

Some embodiments of the invention are defined in the dependent claims.

DESCRIPTION OF EMBODIMENTS

A duplex communication system is a point-to-point system composed of two connected nodes or devices that can communicate with one another in both directions. One specific type of duplex communication is a half-duplex system which provides communication in both directions, but only one direction at a time (not simultaneously, as in full duplex). For two-way data-links, the time allocations for communication in such a half-duplex system may be strictly predefined and controlled. For example, a time division duplex (TDD) is a type of half duplex communication scheme in which the uplink (UL) is separated from the downlink (DL) by the allocation of different time slots in the same frequency band. In other words, UE and eNB are not allowed to transmit and receive at the same time.

Let us, as a non-limiting scenario, consider in the following a framed half-duplex TDD based wireless backhaul relay network with a multi-hop communication topology optimized for a local area. However, the use of wired backhaul (e.g. a dedicated fiber) is not excluded. Unlike wide area cellular systems, the local area systems may utilize a local-access-only frequency band including classical operator deployment and shared spectrum use, the license-exempt spectrum or white spaces to take advantage of the additional available bandwidth. As a further possible advantage, the local area system may offer an efficient device-to-device (D2D) operation mode to establish ad-hoc networks. D2D operation is not discussed here in detail as the possibility to apply such D2D communication between two nodes in a wireless communication network is well-known to a person skilled in the art.

FIG. 1, shows an example scenario of such a framed TDD based wireless backhaul relay network with a multi-hop communication topology. The functionality depicted inFIG. 1can be called also as self-backhauling. As shown, there is at least one master node that is connected to a wired link (i.e. access point (AP)100in this example case) and other nodes connected to this master node via the wireless backhaul links (i.e. AP102with single hop and AP104with multi-hop). Let us for the sake of simplicity assume that these nodes are access points (APs). However, the “slave” APs102and104may be fixed relays (inband) or even mobile devices functioning as APs. UEs (mobile devices)106may then be connected to at least one of the APs100to104in the system. In the example embodiment ofFIG. 1, the UE106is connected to the AP102as shown with a dashed line between them.

As further shown inFIG. 1, in the TDD system with half-duplex technology, the network nodes communicating with each other via the wireless links must have “opposite” frame structures, i.e. the neighboring connected devices/nodes are sending (TX) and receiving (RX) in turns. For example, when the AP100is transmitting, the neighboring AP102is receiving, and vice versa. Similarly, when the AP102is transmitting, the neighboring nodes (AP100, AP104and UE106) are receiving. The presence of such strict TX/RX switching times may be very important so that each of the nodes100to106are reliably able to listen and to receive data from the neighboring node(s) in turns.

However, the strict switching times may cause problems. Let us consider for example a transmission of a reference signal (RS) in such a half-duplex TDD system with multi-hop topology. The reference signal may be used in the downlink by broadcasting the RS so that the UEs in the proximity may hear the RS and derive the best available eNB/AP to connect to. Thus, in order to provide sufficient support for mobility, each AP100to104in the system may broadcast somewhere during its TX time a certain reference signal that may be heard and measured by the UEs106in the system. Such RS information is then used to make decisions when to switch the serving AP100,102or104from the current one to one with better channel conditions, for example. The problem in the scenario as presented inFIG. 1is now that according to the TDD frame structure model ofFIG. 1, the UE106is able to hear only the RSs which are sent during the UE106is in the “RX” mode, i.e. when it is listening the channel. Consequently, for example, the UE106inFIG. 1is not able to hear the RSs sent by the AP100or the AP104because they are sent during a time when the UE106is not in the “RX” mode. However, the reception of such RS signal measurements may be important because they are used not only for the initial access but also for handover scenarios. For example, LTE handover is based on the UE106measuring neighboring cells and reporting the measurement results to its home cell.

The same problem is valid also for UL direction. For example, there may be similar reference signal transmissions in the UL direction (e.g. the UE106sends the RS so that the APs100to104may listen and measure the UL RS). This type of RS is called as sounding reference signal in LTE terminology. Likewise, the problem described above is also valid in device-to-device (D2D) scenarios, where network nodes having the same TX/RX pattern are not able to hear one another. This problem may be a restricting factor, for example, in a D2D resource allocation signaling based on radio resource reservation requests and acknowledgements.

In order to at least partially solve the above mentioned problem, it is proposed to modify the existing TDD frame structure and include a support for inter-node (a.k.a. cross-node) reference and control signaling among the network nodes following the same Tx/Rx pattern so that the signals may be listened by all UEs106in the network from all the APs100to104in the network substantially at the same time. The cross-node signals may then be used for example in determining the path loss and/or the need for communication among the neighboring nodes having the same TX/RX pattern in use (e.g. between UE106and AP104inFIG. 1).

Therefore, it is proposed, as shown inFIGS. 2A and 3, that a first node, let us say the AP100as a non-limiting example, operating under the TDD communication scheme, applies, in step300, a frame structure comprising an extended transmission (TX) part200(marked with vertical lines). The extended TX part200may be adjacent to the default TX part (marked with TX in Figures). The thick black lines in the Figures represent a TX/RX or RX/TX switch via a guard period (which is not explicitly shown inFIG. 2A). From the figures it may be detected that the extended TX part200may at least partially overlap in time domain with a reception (RX) part of a frame structure applied by at least one second node operating at least partially under the same TX/RX pattern as the first node100. The overlapping RX part may be the default RX part or an extended RX part202(as illustrated later). The at least one second node may be, for example, the UE106, as assumed inFIGS. 2A to 2D.

Thus, even though the UE106applies at least partially the same default TX/RX pattern as the AP100, the first node (AP100) may advantageously transmit information (as shown with a dotted arrow inFIG. 2A) also to the UE106during the time period204because the UE106has a RX part valid at those time periods. It may be noted that the frame structures of the UE106and the AP100need not follow the same TX/RX pattern throughout the whole frame. However, the frame structure applied by the UE106may follow the same TX/RX pattern as the AP100with respect to the parts of the frames where the specific signaling is to be transmitted to the UE106. It may be that only certain parts of the frame, such as the protected parts of the frames, follow the same TX/RX pattern and this is the place where the specific signaling may need to be communicated. The rest of the frame may or may not follow the same TX/RX pattern. In step302, the first node (e.g. the AP100) may cause specific signaling to the at least one second node (e.g. the UE106) in the extended TX part200.

In the prior art, transmission of data directly to another node having the same TDD TX/RX pattern would not be possible because the switch from the TX to the RX (and vice versa) is strictly synchronized and controlled in the TDD communication scheme. This means that the switch from TX to RX occurs simultaneously (via the guard pattern) at the two TDD nodes (AP100and UE106) having the same TX/RX pattern. Therefore, there is no common data communication time window between the AP100and the UE106, as shown inFIGS. 2A to 2Dabove the dashed line.

It may further be seen fromFIG. 1, for example, that the UE106is connected to the AP102(as shown with the dashed line). In other words, the UE106may not have a direct TDD communication connection established with the AP100. Also, as the multi-hop scenario may require that neighboring nodes have opposite TX/RX patterns, this may mean that the AP100and the UE106may apply originally the same default TX/RX pattern in their TDD communication because they are two hops away from each other. An alternative or an additional solution may be to extend the default RX part of the second node106, as illustrated inFIGS. 2B and 4. In other words, the second node106operating under the TDD communication scheme may, in step400, apply a frame structure comprising an extended RX part202(marked with horizontal lines). The extended RX part202may be adjacent to a default RX part (marked with RX in Figures). The extended RX part202at least partially overlaps in time domain with the TX part of a frame structure applied by at least one first node (such as the AP100and/or AP104) operating at least partially under the same TX/RX pattern as the UE106. The overlapping TX part may be the default TX part or the extended TX part200. Then, in step402, the second node106may receive a specific signaling from the first node in the extended RX part202, as shown with a dotted arrow inFIG. 2Bduring the time period206.

Further, as shown inFIG. 2C, both the extended TX part200and the extended RX part202may be used for the communication of data from the first node100to the second node106. This embodiment allows for a longer time period208for the communication of the specific signaling to the second node106, as shown with dotted arrows inFIG. 2C. This embodiment may be advantageous for example in transmitting several types of data (such as the RS, control signaling, synchronization signaling, etc.) to the second node106as the time window may be longer than in the embodiments ofFIGS. 2A and 2B.

In an embodiment, a possible location for the specific signaling (such as the broadcast of RS) is in relation of either one or both of TX-RX and RX-TX switching points of a frame in order to minimize the guard period (GP) overhead. Thus, at least one of an extended TX part200and an extended RX part202is located/placed in the frame next to the GP in order to facilitate switching between TX and RX phases. It should be noted that in case the first node is for example an access point or a base station and the second node is a user terminal, the switch point from TX to RX may also be referred to as the switching point from DL to UL, and vice versa. Thus, the proposed solution may comprise a predetermined DL and/or UL specific signal positions in the TDD frame. In this manner, the embodiments take into account the properties of the framed access of the TDD communication scheme and the applied frame structure.

However, as may have been noted,FIGS. 2A to 2Cdo not, for simplicity reasons, depict the guard periods (GPs) between the TX/RX parts. However for the sake of completeness,FIG. 2Dshows such GPs with blocks having diagonal lines. For example, it needs to be taken care that attached eNBs/APs do not send to each other on the backhaul links during the GP period of either one of the eNBs/APs. This may be guaranteed by including the GP as a part of cross-node specific signaling structure.

FromFIG. 2Dit may be further detected that the extended RX part202of the frame structure applied by the UE106may in an embodiment at least partially overlap in time domain with the extended TX part200of the frame structure applied by the AP100, and vice versa. Thus, the specific signaling represented with a dotted arrow inFIG. 2Dmay be performed during the overlap of the extended RX part202and the extended TX part200(e.g. during the time window210). In case the extended TX part200had been longer, the specific signaling could be performed alternatively without applying any extended RX part202. Alternatively, in case the extended RX part202had been selected to be longer, the specific signaling could be performed without applying any extended TX part200.

Compared to the default TDD frame structure of two network devices following the same TX/RX pattern as shown above the horizontal dashed line inFIGS. 2A to 2D, a common signaling position is advantageously arranged to the frame structures by extending the TX part of the node sending the signaling (such as the AP100in this example) and/or extending the RX part of a node receiving the signaling (such as the UE106in this example).

The extended TX/RX position may be introduced at the end/beginning of either the default TX or the default RX period, depending on the phase of Tx/Rx cycle the given node operates. This may advantageously cause the TX part and the RX part (either the default TX/RX part or the extended TX/RX part200/202) to overlap and thus form a field or time window which may be used for the specific signaling between these network nodes following the same TX/RX patterns. As a result, the specific signaling location is in relation of DL-UL or UL-DL (or both) switching point(s) of the TDD frame. In an embodiment, the extended TX and/or RX part(s) locate in the protected part of the flexible TDD frame in order for it not to restrict the TX/RX flexibility of the frame. Thus, the embodiments do not exclude the possibility to maintain the UL-DL ratio flexibility of the underlying TDD frame structure.

In an embodiment, the frequency of the specific signaling (such as how many signaling positions there is in a frame and the frequency of frames containing such signaling position) may be predefined/configured on a network level. As a consequence, the nodes100and106may apply the frame structure comprising the extended TX/RX part200/202according to a predefined frequency for certain frames and apply the default TDD frame structure for the other frames. In this manner, the embodiments may be dynamically reconfigured by the network according to prevailing needs. This is shown inFIG. 5where four consecutive frames are shown from the point of view of the AP100, however, similar representation could be performed from the point of view of the UE106with extended RX parts being present (in case of DL signaling). In the first frame502, there is one extended TX part500A applied for transmission of data to the second node(s). In the second frame504, there are two extended TX parts500B and500C applied. In the third frame506, there are no extended TX parts but the default TX and RX parts are applied for the default TDD frame506. In the fourth frame508, there is one extended TX part500D applied.

As can be seen fromFIG. 5, the position of the extended TX/RX part may be altered from frame to frame. This information may be acquired from the network or acquired otherwise. The frequency of applying the frame structure comprising the one or more extended TX/RX parts may be configured by the network so that the extended TX/RX part will be applied regularly. Alternatively the network may dynamically command the nodes to apply the frame structure with the extended TX/RX part when needed. Also there may be one or more extended TX/RX parts200/202in the frame. It should be noted thatFIG. 5depicts only an example non-limiting TDD communication scheme.

In an embodiment, the specific signaling position is common for the whole network (including all the cells of the specific network). An example related to this embodiment is presented inFIGS. 6A and 6B. Let us further assume that the specific signaling comprises the broadcast of the RS in the downlink as a non-limiting example. In this network-specific case, it is required that at some point all the eNBs/APs100to104in the network are in the TX mode and all the UEs106to108in the network are in the RX mode independently of the TX/RX patterns of the underlying TDD frame structure. Thus, in an embodiment, the first node100,102, or104may cause specific signaling in the extended TX part600A,600B,600C, respectively, to a plurality of second nodes106to108each associated with a certain network604. This may be possible as the extended TX parts600A,600B,600C at least partially overlap in time domain with the RX part of the frame structures applied by the plurality of second nodes106to108, as shown inFIG. 6B. It should be noted that the overlapping RX part may be either the default RX part or the extended RX part602A,602B (as is the case inFIG. 6). In other words, even though the example ofFIG. 6applies both the extended TX and RX parts, only one of them may be sufficient, as illustrated with reference toFIGS. 2A and 2B. As a result, all UEs106to108in the network604may be able to hear the RS signals shown with dotted arrows inFIG. 6Bfrom the different eNB/APs100to104substantially at the same time. It may further be noted that for example the AP102may send the RS signal to the UE106also during the default TX part. However, a simultaneous transmission from all network nodes to all UEs in the network may provide improved reliability for the decision to perform a handover.

The node100to108may be understood to be associated with the certain network604when the node belongs to the infrastructure of the network604or the node is connected to one of the nodes of the network604. A single network604may naturally comprise a plurality of cells. AlthoughFIG. 6depicts the downlink scenario for transmitting the RS, similar approach may be used for the network-specific UL reference signaling (e.g. the sounding signaling) or UL resource requests. For such a case it may be required that at some point all the eNBs/APs100to104in the network are in the RX mode while all the UEs106to108in the network are in the TX mode.

In addition to the RS signal position common for the whole network as described with reference toFIGS. 6A and 6B, cell-specific, UE-specific, or UE group-specific signaling positions may be determined in the TDD frames on top of the original/default frame structure. Accordingly, in an embodiment, the first node (such as the node100) may cause specific signaling in the extended Tx part to at least one of the following: a plurality of second nodes each associated with a certain cell (i.e. cell-specific signaling), a specific second node (i.e. a node-specific signaling), a specific group of second nodes, wherein the extended Tx part at least partially overlaps in time domain with the RX part of the frame structures applied by the corresponding at least one second node (e.g. the UE106) receiving the signaling. Similar approach may be taken from the point of views of the UE106, in which case the extended Rx part of the UE106at least partially overlaps with the TX part of at least one of the following: a plurality of first nodes each associated with a certain cell, a specific first node a specific group of first nodes.

An example of such case is presented inFIGS. 7A and 7B. In this embodiment, the TX part706in the serving cell102may comprise a gap704B related to the neighboring cell(s). I.e. during the gap704B, the neighboring APs100,104may transmit the signals to the UE106served by the cell102, as shown with the dotted arrows inFIGS. 7A and 7B. Further, the cell/UE-specific signaling is in this embodiment located in the extended TX parts700A,700C and in the default TX part706of the corresponding frame structure. I.e. the AP102need not necessarily apply any extended TX part for transmitting the specific signaling. This may be because the UE108, to which the AP102is configured to transmit the specific signals, may apply the extended RX part702B. Alternatively, the AP102could use an extended TX part to transmit the RS to the UE108during the default RX part708of the frame structure applied by the UE108. The frame structure of the AP104also comprises a704C gap in order to allow the AP102to transmit the specific signaling to the UE108served by the AP104.

The UE106,108, for which the specific signaling (such as the RS) is targeted to, may extend their RX part as shown with reference numerals702A and702B. As the UE106,108is in the RX mode, the UE106,108may not send anything during this time to the serving AP102,104, respectively, as illustrated with the dotted blocks704B,704C. This “non-used part of a frame with the attached UE” may be advantageously used by the corresponding AP102,104to perform other functions, such as radio resource management. Although the UE-specific signaling may suffer from cross-link interference, it should be noted that if there were other UEs (connected to the APs100to104) that are not configured to listen to the RS signals from their neighboring APs, their frame structures or interaction with the serving AP would not be affected by the RS fields targeted to other UEs. This embodiment may allow more dynamic and flexible configuration of specific signaling as not each node of the network is set as the target.

As said, the position and frequency of the signaling may be configured in a cell- or a UE-specific manner. For example, the cell/UE-specific signaling position and frequency may be known by the UE106, the AP102connected to the UE106and the APs100,104sending the UE specific RS.

An embodiment provides coordination of the specific signaling (RS, control signals, synchronization signals, etc.) position between neighboring cells. This coordination may indicate for example the position/timing of the specific signaling and resources used to transmit/receive the signaling. In one embodiment, the first node (such as the AP100) may acquire information of the frame structure applied by the at least one second node (such as another AP102,014and/or the UEs1606,108). The information may indicate at least one of the following: a length of the frame, transmission-reception switching point(s) in time domain, the number of RX parts, the number of TX parts, length of a guard period, whether or not the frame structure comprises the extended RX part, length of the default/extended RX part, number of the extended RX parts. The first node100may thereafter determine the frame structure to be applied on the basis of the information. The first node100may receive such information via an X2 signaling, via the backhauls links, for example. Similarly, the second node may acquire such information of the frame structure applied by the first node and then the second node may derive the to-be-applied frame structure. One decision the first node or the second node may make on the basis of the acquired information is that is any extended TX part or any extended RX part needed in the frame or not. For example, if the other node already applies an extended TX part, the second node may not need to use a frame structure with an extended RX part.

In another embodiment, the first node100may receive information indicating the frame structure to be applied from a network or from at least one second node102to108. This embodiment provides low complexity as the first node100need not determine the frame structure itself but acquires it directly from the network or from another node. The eNBs may apply, for example, the X2 interface for exchanging such information, the relays may use the wireless backhaul channels, and the UE may receive the data via control signaling, broadcast of data or via an initial attach process, for example.

It should be noted that although some of the embodiments are described by referring to the half-duplex TDD based wireless backhaul relay network with the multi-hop communication topology (as depicted inFIGS. 1, 6A and 7A), the proposed solution is similarly applicable also for UL signaling wherein the first node may be a user terminal and the second node may be a base station. This is illustrated inFIG. 8with an example where in addition to DL signaling there is also an UL signaling field in a frame. Otherwise the underlying scenario may be the same as inFIG. 6B. In this example, all APs100to104in the network may listen to UL sounding signals or UL resource requests (or any other UL signaling such) from all of the UEs106,108substantially simultaneously independently of the underlying TX/RX TDD pattern of the APs100to104. The transmitted UL signals are shown with the dashed arrows inFIG. 8. As is the case with DL specific signaling, the UL signaling frequency and position may be configured. In addition, the position and frequency of the extended RX/TX parts of the UL related signaling may alternatively be determined to be cell-, node group or node-specific.

Also in an embodiment, D2D/mesh communication scenarios may advantageously apply the proposed scheme. In such D2D case, the first node and the second node are both user terminals, for example. Such D2D use case may advantageously guarantee that all UEs that are part of the D2D network are able to communicate with each other. The communication may include capability to receive discovery/resource request signals from all UEs without complicated allocation of Tx/Rx patterns.

In yet another embodiment, the first node and the second node may both be relay stations, access point or base stations, for example. In general, each node may comprise, be, or be comprised in a base station, a relay station, an access point or a user terminal.

Similarly, although the reference signals are used in some examples for describing the invention, the embodiments may as well be applied for a signaling of any information, such as control signals. In other words, the signaling may be extended to cover also or additionally other information. Let us look at this option more closely.

In an embodiment, the specific signaling comprises a number of hops and/or quality of the links indicating the estimated latency in a multi-hop wireless backhaul from the serving eNB/AP102,104to the master eNB/AP100. Therefore, the specific signaling may be used by the UE106,108for determining the route with best channel conditions and smallest latency when considering not only the link between UE and serving eNB/AP (such as the link from the AP102to the UE106) but also the rest of the backhaul links (shown with dashed lines inFIGS. 1, 6A and 7A) in a multi-hop wireless backhaul scenario.

In an embodiment, the specific signaling comprises information whether or not the eNB/AP100to104may be connected by any UE106,108and/or whether or not there are some restrictions, such as specific subscriber and/or UE groups (for example different operators).

In an embodiment, the specific signaling comprises other information about the capability of eNB/AP100to104and the related backhaul link to serve the UE106,108.

In an embodiment, the specific signaling comprises synchronization signals, such as a primary and/or secondary synchronization signals (PSS/SSS). The synchronization signals may allow initiating a UE-originated cell change (e.g. a hand-over).

In an embodiment, the specific signaling comprises system information (including e.g. information on the available random access resources). The specific signaling may carry also system information corresponding to the neighboring cell.

In an embodiment, the specific signaling comprises a radio resource allocation signaling, reservation requests and acknowledgements, such as a ready-to-send (RTS) and/or a clear-to-send (CTS) type of resource allocation signaling.

In an embodiment, the specific signaling may comprise a reference signal sequence used for the channel estimation of the link between the UE and the eNB/AP sending or receiving the RS/sounding signal. The reference signal may thus be a DL reference signal or an UL reference signal (e.g. a sounding signal). The RS signals may advantageously be used by the UEs for measurements with respect to both the serving cell and neighboring cell(s) substantially simultaneously.

In an embodiment, the specific signaling comprises device-to-device signaling between two D2D capable devices.

In an embodiment, the specific signaling may comprise transmission of inter-cell orthogonal signals. This may advantageously reduce the total signaling overhead. For example, in case the specific signaling relates to the DL reference signals broadcasted from the APs100to104, the design of the reference signal may advantageously be so that the same signal may be used in measurements related to both own and the neighboring cells. Thus, in an embodiment, the reference signal is an inter-cell orthogonal reference signal. The reference signal may carry information indicating the channel quality information of the channel between the transmitting AP and the receiving UE. The use of such inter-cell RS may maintain the total RS overhead at a reasonable level. In another embodiment, the reference signal is a node-specific reference signal targeted for a specific node (such as UE) only which may allow for more flexibility in the design of the network.

FIGS. 9 and 10provide apparatuses900and1000comprising a control circuitry (CTRL)902,1002, such as at least one processor, and at least one memory904,1004including a computer program code (PROG), wherein the at least one memory and the computer program code (PROG), are configured, with the at least one processor, to cause the respective apparatus900,1000to carry out any one of the embodiments described. It should be noted thatFIGS. 9 and 10show only the elements and functional entities required for understanding a processing systems of the apparatuses. Other components have been omitted for reasons of simplicity. It is apparent to a person skilled in the art that the apparatuses may also comprise other functions and structures.

Each of the apparatuses900,1000may, as said, comprise a control circuitry902,1002, respectively, e.g. a chip, a processor, a micro controller, or a combination of such circuitries causing the respective apparatus to perform any of the embodiments of the invention. Each control circuitry may be implemented with a separate digital signal processor provided with suitable software embedded on a computer readable medium, or with a separate logic circuit, such as an application specific integrated circuit (ASIC). Each of the control circuitries may comprise an interface, such as computer port, for providing communication capabilities. The respective memory904,1004may store software (PROG) executable by the corresponding at least one control circuitry

The apparatuses900,1000may further comprise radio interface components (TRX)906,1006providing the apparatus with radio communication capabilities with the radio access network. The radio interface components may comprise standard well-known components such as amplifier, filter, frequency-converter, (de)modulator, and encoder/decoder circuitries and one or more antennas.

The apparatuses900,1000may also comprise user interfaces908,1008comprising, for example, at least one keypad, a microphone, a touch display, a display, a speaker, etc. Each user interface may be used to control the respective apparatus by the user.

As said, the apparatuses900,1000may comprise the memories904,1004connected to the respective control circuitry902,1002. However, memory may also be integrated to the respective control circuitry and, thus, no memory may be required. The memory may be implemented using any suitable data storage technology, such as semiconductor based memory devices, flash memory, magnetic memory devices and systems, optical memory devices and systems, fixed memory and removable memory.

In an embodiment, the apparatus900,1000may comprise the terminal device of a cellular communication system, e.g. a computer (PC), a laptop, a tabloid computer, a cellular phone, a communicator, a smart phone, a palm computer, or any other communication apparatus. Alternatively, the apparatus900,1000is comprised in such a terminal device. Further, the apparatus900,1000may be or comprise a module (to be attached to the apparatus) providing connectivity, such as a plug-in unit, an “USB dongle”, or any other kind of unit. The unit may be installed either inside the apparatus or attached to the apparatus with a connector or even wirelessly. In an embodiment, the apparatus900,1000may be, comprise or be comprised in an AP, such as a wireless local area network access point or a pico area network access point. In an embodiment, the apparatus900,1000may be, comprise or be comprised in a base station or a relay station.

In an embodiment, the apparatus900may be the first node, i.e. the node transmitting the specific signaling (such as the AP100, as used in the description of some of the embodiments). The control circuitry902may comprise a TDD frame determination circuitry910for acquiring knowledge of the TDD frame which is to be applied. The circuitry910may determine, for example, whether the frame is to comprise an extended TX period or not. A transmission circuitry912may be for transmitting the specific signaling to the target second node(s) during the extended TX part, for example.

In an embodiment, the apparatus1000may be the second node, i.e. the node receiving the specific signaling (such as the UE106, as used in the description of some of the embodiments). The control circuitry1002may comprise a TDD frame determination circuitry1010for acquiring knowledge of the TDD frame which is to be applied. The circuitry1010may determine, for example, whether the frame is to comprise the extended RX period or not. The circuitry1002may also comprise a reception circuitry1012for receiving the specific signaling during the extended RX part from the first node(s), for example.

Embodiments as described may also be carried out in the form of a computer process defined by a computer program. The computer program may be in source code form, object code form, or in some intermediate form, and it may be stored in some sort of carrier, which may be any entity or device capable of carrying the program. For example, the computer program may be stored on a computer program distribution medium readable by a computer or a processor. The computer program medium may be, for example but not limited to, a record medium, computer memory, read-only memory, electrical carrier signal, telecommunications signal, and software distribution package, for example.