WO2015012753A1

WO2015012753A1 - Signaling of demodulation pilots in a shared radio cell

Info

Publication number: WO2015012753A1
Application number: PCT/SE2014/050109
Authority: WO
Inventors: Sairamesh Nammi; Yi-Pin Eric Wang
Original assignee: Telefonaktiebolaget L M Ericsson (Publ)
Priority date: 2013-07-23
Filing date: 2014-01-28
Publication date: 2015-01-29

Abstract

The present disclosure concerns radio communication. More particularly, the present disclosure inter alia introduces methods for transmitting and/or receiving information about demodulation pilots (e.g., D-CPICHs).According to one embodiment, a radio network node operates in a combined radio cell. The radio network node configures(110) a number of different demodulation pilots (D-CPICHs) to form a set of multiple demodulation pilot configurations. The radio network node also transmits (120), to auser equipment, a radio signal comprising information about demodulation pilots(D-CPICHs), wherein the radio signal comprises information about theset of multiple demodulation pilot configurations. To be published with fig. 9.

Description

SIGNALING OF DEMODULATION PILOTS IN A SHARED RADIO CELL

TECHNICAL FIELD

Embodiments of the technology presented herein generally relate to radio communication. More particularly, the embodiments presented herein generally relate to shared radio cell deployments (a.k.a. combined radio cell deployments or soft radio cell deployments). More specifically, the embodiments presented herein concern methods and means (e.g. radio network nodes and user equipments (UEs) for signaling information about demodulation pilots.

BACKGROUND

This section is intended to provide a background to the various embodiments of the technology that are described in this disclosure. Therefore, unless otherwise indicated herein, what is described in this section should not be interpreted to be prior art by its mere inclusion in this section.

Radio communication networks are widely deployed to provide various communication services such as telephony, video, data, messaging, broadcasts, and so on. Such radio communication networks support communications for multiple UEs by sharing the available network resources. One example of such a network is the Universal Mobile Telecommunications System (UMTS), a third generation (3G) technology standardized by the 3rd Generation Partnership Project (3GPP). UMTS includes a definition for a Radio Access Network (RAN), referred to as UMTS Terrestrial Radio Access Network (UTRAN). The UMTS, which is the successor to Global System for Mobile Communications (GSM) technologies, supports various air interface standards, such as Wideband-Code Division Multiple Access (W-CDMA), Time Division-Code Division Multiple Access (TD-CDMA), and Time Division-Synchronous Code Division Multiple Access (TD-SCDMA). The UMTS also supports enhanced 3G data communications protocols, such as High Speed Packet Access (HSPA), which provides higher data transfer speeds and capacity to associated UMTS networks. As the demand for mobile broadband access continues to increase, research and development continue to advance the UMTS technologies not only to meet the growing demand for mobile broadband access, but to advance and enhance the user experience with mobile communications. For example, third-generation UMTS based on W-CDMA has been deployed in many places of the world. To ensure that this system remains competitive in the future, 3GPP began a project to define the long-term evolution of UMTS cellular technology. The specifications related to this effort are formally known as Evolved UMTS Terrestrial Radio Access (E-UTRA) and Evolved UMTS Terrestrial Radio Access Network (E-UTRAN), but are more commonly referred to by the name Long Term Evolution (LTE). More detailed descriptions of radio communication networks and systems can be found in literature, such as in Technical Specifications published by, e.g., the 3GPP.

Classical versus Shared Radio Cell Deployments

In the following, the term point is used to mean a point having transmission and/or reception capabilities. As used herein, this term may interchangeably be referred to as "transmission point", "reception point", "transmission/reception point" or "node". To this end, it should also be appreciated that the term point may include devices such as radio network nodes (e.g. NodeB (NB), evolved NodeB (eNB), a Radio Network Controller (RNC), etc)) and radio units (e.g. Remote Radio Units (RRUs)). As is known among persons skilled in the art, radio network nodes generally differ from RRUs in that the radio network nodes have comparatively more controlling functionality. For example, radio network nodes typically include scheduler functionality, etc., whereas RRUs typically don't. Therefore, RRUs are typically consuming comparatively less computational power than radio network nodes. Sometimes, radio network nodes may be referred to as high power points or high power nodes (HPN) whereas RRUs may be referred to as low power points or low power nodes (LPN). In some cell deployments, LPNs are referred to as pico points and HPNs are referred to as macro points. Thus, macro points are points having comparatively higher power than the pico points. The classical way of deploying a network is to let different transmission/reception points form separate cells. That is, the signals transmitted from or received at a point is associated with a cell-id (e.g. a Physical Cell Identity (PCI)) that is different from the cell-id employed for other nearby points. Conventionally, each point transmits its own unique signals for broadcast (e.g., PBCH (Physical Broadcast Channel)) and sync channels (e.g., PSS (primary synchronization signal), SSS (secondary synchronization signal)). Furthermore, in WCDMA/HSPA systems, different NBs use different primary scrambling codes. The classical way of utilizing one cell-id per point is depicted in Figure 1 for a heterogeneous deployment where a number of LPNs are placed within the coverage area of a HPN. Note that similar principles also apply to classical macro-cellular deployments where all points have similar output power and perhaps are placed in a more regular fashion compared with the case of a heterogeneous deployment.

A recent alternative to the classical cell deployment is to instead let all the UEs within the geographical area outlined by the coverage of the HPN be served with signals associated with the same cell-id (e.g. the same Physical Cell Identity (PCI)) and/or the same primary scrambling code. In other words, from a UE perspective, the received signals appear coming from a single cell. This is schematically illustrated in Figure 2. Note that only one HPN 10 is shown, other HPNs would typically use different cell-id:s and/or different primary scrambling codes (corresponding to different cells) unless they are co-located at the same site. In the latter case of several co-located HPNs, the same cell-id may be shared across the co-located HPNs and those LPNs that correspond to the union of the coverage areas of the macro points. Sync channels, BCH (Broadcast Channels) and control channels may all be transmitted from the HPN (or simultaneously from both HPNs and LPNs) while data may be transmitted to a UE also from one LPN, e.g. by spatially reusing the resources allocated to shared data channels (e.g. a Physical Downlink Shared Channel (PDSCH)). In figure 2, the HPN may be a radio network node such as a eNB or a RNC to name a few examples. The LPNs may be radio units such as those commonly referred to as Remote Radio Units (RRUs).

The single cell-id approach, or shared radio cell deployment (aka combined radio cell deployment or soft radio cell deployment) can be geared towards situations in which there is fast backhaul communication between the points associated to the same cell. A typical case would be a radio network node serving one or more sectors on a macro level as well as having fast fiber connections to remote radio units (RRUs) playing the role of the other points sharing the same cell-id. Those RRUs could represent LPNs with one or more antennas each. Another example is when all the points have a similar power class with no single point having more significance than the others. The radio network node would then handle the signals from all RRUs in a similar manner. An advantage of the shared cell approach compared with the classical approach is that the typically involved handover procedure between cells only needs to be invoked on a macro basis. Generally, there is also greater flexibility in coordination and scheduling among the points which means the network can avoid relying on the inflexible concept of semi- statically configured "low interference" subframes as in e.g. 3GPP Release 10 (Rel-10). A shared cell approach may also allow decoupling of the downlink (DL) with the uplink (UL) so that for example path loss based reception point selection can be performed in UL while not creating a severe interference problem for the DL, where the UE may be served by a transmission point different from the point used in the UL reception. Downlink Transmission Modes in Shared Cell Deployment

There exist different transmission modes in a shared radio cell deployment. The different transmission modes can be divided into:

• Single Frequency Network (SFN): In this mode, all nodes transmit the same pilot channel. Also, data and control information are transmitted from all nodes. In this mode, only one UE can be served from all the nodes at any time. Hence, this mode can be said to be useful for coverage improvements. Furthermore, this mode generally works for legacy UEs. As used in this disclosure the expression "legacy UE" is used to mean a UE that supports 3GPP Rel-5, Rel-6, Rel-7, Rel-8, Rel-9, Rel-10, and/or Rel-1 1. That is, the expression "legacy UE" refers to pre-release 12

UEs. Figure 3 shows a pictorial view of the SFN mode. As can be seen in the example of Fig. 3, all nodes (i.e. Macro Node, LPN-1 , LPN-2, and LPN-3) utilize the same P-CPICH (Primary Common Pilot Channel). Also, all nodes utilize the same HS-SCCH (High Speed Shared Control Channel). Moreover, all nodes utilize the same HS-PDSCH (High Speed Physical Downlink Shared Channel).

• Node selection with Spatial Re-use (SR): In this mode, even though all nodes transmit the same pilot channel, data and control information transmitted from one node is different from the data and control information transmitted from other nodes. For example, a node may be serving a specific UE, while at the same time different data and control information may be sent to a different UE from a different node. Hence, the radio resources can be spatially reused. This mode thus allows for load balancing gains and, accordingly, the capacity of the shared radio cell can be increased. Figure 5 shows a pictorial view of the Spatial Re-use mode in a shared cell deployment.

In a shared radio cell deployment it is generally the radio network node (sometimes referred to as "the central controller") that takes responsibility for collecting operational information, operational data and/or operational statistics from various measurements that are made throughout the shared radio cell. Typically, but not necessarily, the decision of which LPN node (e.g. RRU) that should transmit to a specific UE is made by the radio network node based on the collected operational information, operational data and/or operational statistics. The operational information, operational data and/or operational statistics may be collected (e.g. obtained, acquired, or received) from the various LPNs. Additionally, or alternatively, this operational information, operational data and/or operational statistics may be collected from the UEs that are present in the shared radio cell.

Spatial Re-use in a Shared Radio Cell Deployment

Currently, the 3GPP is studying different pilot design options. Figure 5 illustrates a signaling diagram of example messages when employing spatial reuse in a shared radio cell deployment. Assume that a shared radio cell deployment comprises four nodes (or transmission points) serving multiple UEs. It should be appreciated that the same procedure is applicable also in scenarios where the nodes are less than or more than four.

All the nodes (i.e. Node-1 , Node-2, Node-3, Node-4) transmit the same pilot signal P- CPICH (Primary Common Pilot Channel) for channel sounding. From the P-CPICH signal, the UE can estimate the channel and feed back the channel quality information (CQI). The CQI information is sent in HS-DPCCH (High Speed-Dedicated Physical Control Channel). The same HS-DPCCH signal is received by all nodes. Once the central processing unit (e.g., the radio network node (such as a RNC or eNB)) has decided which one of the nodes (i.e. Node-1 , Node-2, Node-3 or Node-4) will transmit to the UE, this assigned node will transmit a demodulation pilot (D-CPICH) (sometimes called dedicated pilot) for the scheduled UE to estimate the channel for data demodulation. Hence the central processing unit informs the respective node to transmit to the scheduled UE in its coverage area. The assigned node transmits the downlink control channel (HS-SCCH, High Speed Shared Control Channel) and the downlink traffic channel (HS-PDSCH, High- Speed Physical Downlink Shared Channel) to its respective scheduled UE. Similarly the central processing unit informs the other nodes to transmit to the other scheduled UEs which are close to these nodes based on, e.g., the reliability factors. Thus, multiple nodes could be assigned to transmit simultaneously, each serving a different UE.

The inventors have realized that the introduction of spatial re-use in shared radio cell deployments may cause one or several challenges. For example, for spatial re-use to work properly, a UE may need to be able to unambiguously estimate the channel associated with the link from its assigned serving radio unit (e.g. RRU). Generally, the conventional P- CPICH cannot serve this purpose, as this P-CPICH is transmitted by all radio units (see e.g. Fig. 5) within a shared radio cell.

SUMMARY

It is in view of the above considerations and others that the various embodiments disclosed herein have been made. In one of its aspects, the technology presented herein therefore concerns a method for transmitting information about demodulation pilots (D-CPICHs) to a UE. The method is performed by, or otherwise implemented in, a radio network node. The radio network node may be a Radio Network Controller (RNC). Alternatively, the radio network node may be a NodeB (NB). In an alternative embodiment, the radio network node is an evolved NodeB (eNB).

More particularly, in one of its aspects, the technology presented herein concerns a method performed by a radio network node, which operates in a combined radio cell. A number of different demodulation pilots are configured to form a set of multiple demodulation pilot configurations. Also, a radio signal comprising information about demodulation pilots is transmitted to a UE. This radio signal comprises information about the set of multiple demodulation pilot configurations. For example, the radio signal may comprise one or more data field(s) including, or otherwise indicating, the information about the set of multiple demodulation pilot configurations.

In one embodiment, a set of available demodulation pilots is identified. Also, one or more demodulation pilots of the thus identified set of demodulation pilots is/are assigned to the UE. Furthermore, information about the assigned one or more demodulation pilots is transmitted to the UE along with said information about demodulation pilots. For example, the earlier-mentioned radio signal may comprise one or more data field(s) including, or otherwise indicating, the additional information about the assigned one or more demodulation pilots. In some embodiments, the radio signal comprises a Radio Resource Control (RRC) message. If so, the RRC message may comprise said information about the demodulation pilots.

In another of its aspects, the technology presented herein concerns a corresponding method for receiving information about demodulation pilots (D-CPICHs). The method is performed by, or otherwise implemented in, a UE. More particularly, a method performed by a UE operating in a combined radio cell is provided. The method comprises receiving, from a radio network node, a radio signal comprising information about demodulation pilots. This radio signal comprises information about one or more demodulation pilot configurations. For example, the radio signal may comprise one or more data field(s) including, or otherwise indicating, the information about the one or more demodulation pilot configurations. For example, the method may additionally comprise receiving information about one or more assigned demodulation pilots along with said information about demodulation pilots. For example, the earlier- mentioned radio signal may comprise one or more data field(s) including, or otherwise indicating, the additional information about the assigned one or more demodulation pilots. In one embodiment, the method also comprises estimating, in each Transmission Time Interval (TTI), a channel from each of said one or more assigned demodulation pilots.

In some embodiments, the radio signal comprises a Radio Resource Control (RRC) message. If so, the RRC message may comprise said information about the demodulation pilots.

In yet another aspect there is provided a radio network node configured to operate in a combined radio cell. The radio network node comprises a processor and a memory, wherein the memory stores computer program code which, when run in the processor, causes the radio network node to configure a number of different demodulation pilots to form a set of multiple demodulation pilot configurations. The radio network node also comprises a transmitter configured to transmit, to a UE, a radio signal comprising information about demodulation pilots, wherein the radio signal comprises information about a set of multiple demodulation pilot configurations. For example, the radio signal may comprise one or more data field(s) including, or otherwise indicating, the information about the set of multiple demodulation pilot configurations.

In one embodiment, the memory stores computer program code which, when run in the processor, causes the radio network node to identify a set of available demodulation pilots; and assign one or more demodulation pilots of said identified set of demodulation pilots to the UE. Also, the transmitter may be configured to transmit information about the assigned one or more demodulation pilots along with said information about demodulation pilots. For example, the earlier-mentioned radio signal may comprise one or more data field(s) including, or otherwise indicating, the additional information about the assigned one or more demodulation pilots.

In one embodiment, radio network node is a Radio Network Controller. Alternatively, the radio network node is a NodeB. In another embodiment, the radio network node may be an evolved NodeB. In still another aspect, there is provided a UE operating in a combined radio cell. The UE comprises a receiver configured to receive, from a radio network node, a radio signal comprising information about demodulation pilots, wherein the radio signal comprises information about one or more demodulation pilot configurations. For example, the radio signal may comprise one or more data field(s) including, or otherwise indicating, the information about the one or more demodulation pilot configurations. The receiver may also be configured to receive information about one or more assigned demodulation pilots along with said information about demodulation pilots. For example, the earlier-mentioned radio signal may comprise one or more data field(s) including, or otherwise indicating, the additional information about the assigned one or more demodulation pilots.

In one embodiment, the UE comprises a processor and a memory storing computer program code which, when run in the processor, causes the UE to estimate, in each TTI, a channel from each of said one or more assigned demodulation pilots. In some embodiments, the radio signal comprises a Radio Resource Control (RRC) message. If so, the RRC message may comprise said information about the demodulation pilots.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects, features and advantages will be apparent and elucidated from the following description of various embodiments, reference being made to the accompanying drawings, in which:

Fig. 1 shows an example of a heterogeneous radio network utilizing a classical cell deployment;

Fig. 2 shows an example of a radio network utilizing a shared cell deployment;

Fig. 3 shows a pictorial view of SFN in a shared radio cell deployment;

Fig. 4 shows a pictorial view of Spatial Re-use in a shared radio cell deployment; Fig. 5 is a message sequence chart showing messages between nodes and a UE for spatial reuse in a shared radio cell deployment;

Fig. 6 shows an example of spatial reuse in a shared radio cell deployment; Fig. 7 is a message sequence chart showing messages between nodes and a UE for spatial reuse in a shared radio cell deployment;

Fig. 8 shows another example of spatial reuse in a shared radio cell deployment; Figs. 9-11 show example methods according to various embodiments of the technology described throughout this disclosure; and Fig. 12 shows an example implementation of a radio network node; and Fig. 13 shows an example implementation of a user equipment; and

Fig. 14 is a message sequence chart showing messages between nodes and a UE for spatial reuse in a shared radio cell deployment with a proposed option 2.

DETAILED DESCRIPTION

The technology will now be described more fully with reference to the accompanying drawings, in which certain embodiments are shown. The technology may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided by way of example so that this disclosure will be thorough and complete, and will fully convey the scope of the technology to those persons skilled in the art. Like reference numbers refer to like elements or method steps throughout the description.

As used in this disclosure, the term "user equipment (UE)" is used to mean any device, which can be used by a user to communicate. Also, the term UE may be referred to as a mobile terminal, a terminal, a user terminal (UT), a wireless terminal, a wireless communication device, a wireless transmit/receive unit (WTRU), a mobile phone, a cell phone, etc. Yet further, the term UE includes MTC devices, which do not necessarily involve human interaction. In this regard, it should also be appreciated that the term "user equipment (UE)" as used herein may apply the definition as specified on page 33 of 3GPP TR 21.905 V.12.0.0 (2013-06).

As described earlier, the introduction of spatial re-use in shared radio cell deployments may cause one or several challenges. For example, for spatial re-use to work properly, a UE may need to be able to unambiguously estimate the channel associated with the link from its assigned serving radio unit (e.g. RRU). Generally, the conventional P-CPICH cannot serve this purpose, as this P-CPICH is transmitted by all radio units (see e.g. Fig. 5) within a shared radio cell^'.

To address this issue, the demodulation pilots D-CPICH could be introduced. One example of configuring D-CPICH is to configure it as node specific as is schematically illustrated in Figures 6 and 7, respectively. As can be seen in Figure 6, the UE is located in the coverage area of the radio sector served by RRU3 (also denoted 20-3). Thus, RRU3 will be assigned by the radio network node 10 to serve said UE. In this case, D-CPICH3 will be used by the UE as the reference for demodulating HS-PDSCH. It should be appreciated that it is conceivable that the D-CPICH could be shared by two RRUs (or potentially more RRUs). This would allow multiple RRUs to collaborate in transmitting to a UE in question. An advantage of this would e.g. be that this would support the possibility of beam forming using transmit antennas from multiple RRUs. This latter scenario is schematically illustrated in Figure 8. However, regardless of how D-CPICH is configured at the various RRUs in a shared radio cell deployment, the information about which D-CPICH to use as a reference should be transmitted to the UE in question.

In the following, different proposed methods of signaling demodulation pilots (e.g., D- CPICHs) and information about those in a shared/combined radio cell deployment will be described.

Option 1

In a shared radio cell, it is sometimes desirable that the spatial-reuse principle can be applied to the shared control channel HS-SCCH. This way the same OVSF code (i.e. Orthogonal Variable Spreading Factor code) may be reused by different radio units (e.g. LPNs) within a shared radio cell. As a consequence, more OVSF codes may be preserved for the use of the shared control channels as well as the data channels. One potential challenge arising when applying code spatial reuse for HS-SCCH is that for decoding HS- SCCH, the UE may need to be able to unambiguously estimate the channel. As described earlier, this implies that P-CPICH cannot be used as a reference for HS-SCCH reception. In one of its aspects and with reference to figs. 9-1 1 , a radio network node (e.g. a RNC or a NB or a eNB) transmits 120, to a UE, a radio signal comprising information about demodulation pilots (D-CPICHs). For example, the radio signal may comprise one or more data field(s) including, or otherwise indicating, the information about the demodulation pilots (D-CPICH).

According to one embodiment, the radio network node is configured to configure 110 a number N of different demodulation pilots (e.g., D-CPICHO, D-CPICH1 , D-CPICH2, ... , D- CPICHn). For example, the radio network node may identify 111 a set of available demodulation pilots (e.g., D-CPICHO, D-CPICH1 , D-CPICH2, D-CPICH3, D-CPICH4); and assign 112 one or more demodulation pilots (D-CPICH(s)) of said identified set of demodulation pilots (e.g., D-CPICH3) to the UE. Furthermore, the radio network node may transmit 120 (to the UE) information about the assigned one or more demodulation pilots (e.g., D-CPICH3) along with said information about demodulation pilots. For example, the radio network node may transmit 120 (to the UE) information about the assigned one or more demodulation pilots (e.g., D-CPICH3) along with said information about demodulation pilots in a radio signal. This radio signal may comprise one or more data fields which include(s) or otherwise indicate(s) the information about the assigned one or more demodulation pilots (e.g., D-CPICH3). The UE receives 210, from a radio network node, the radio signal comprising information about the demodulation pilots (D-CPICHs). Again, the radio signal may comprise one or more data field(s) including, or otherwise indicating, the information about the

demodulation pilots (D-CPICH). The received radio signal may thus comprise information about one or more demodulation pilot (D-CPICH) configurations. For example, the UE may receiving 210 information about one or more assigned demodulation pilots (e.g., D-

CPICH3) (i.e. which demodulation pilot(s) that the radio network node has assigned to the UE in question). Furthermore, the UE estimates 220 (e.g., in each Transmission Time Interval (TTI)) a channel from each of said one or more assigned demodulation pilots (e.g., D-CPICH3). As will be understood, the UE thus monitors the pool (or, set) of demodulation pilots assigned by radio network node. Hence, in each TTI, the UE can estimate the channel from each (assigned) demodulation pilot. With this channel estimate, the UE then tries to decode the set of HS-SCCHs assigned and checks the CRC (Cyclic Redundancy Check) of HS-SCCH. If the CRC check is a pass (i.e. approval), then it uses the channel estimate(s) for decoding the data on HS-PDSCH. According this option, the network informs the UE about a set of N D-CPICH

configurations. One of these D-CPICHs may be used as a reference for the demodulation of the HS-SCCH and/or HS-PDSCH channels intended for the UE. It should be

appreciated that the UE may be informed about the set of N D-CPICH configurations directly from the radio network node (e.g. RNC, NB, or eNB) or via the radio units (e.g. the RRUs) (see e.g. Fig. 2 or Fig. 6)

Higher Layer procedures: According to option 1 , the radio network node may assign a set of D-CPICHs for a UE e.g. using a RRC connection set up message (RRC is an abbreviation for Radio Resource Control). Such a RRC message may for example comprise information about the D-CPICH configurations such as the number of

demodulation pilots assigned (N), channelization codes of these demodulation pilots, pilot symbol values, and the power offsets and/or exact powers of these pilots. The radio network node (or the scheduler thereof) may dynamically use this pool (or set) of demodulation pilots. For instance, there might be instances where more than one demodulation pilot can be transmitted from a single RRU. Hence if two UEs are scheduled from same RRU at the same time, two demodulation pilots may be transmitted from that RRU. In another case, if a UE is served by two RRUs at the same time, the two RRUs may need to transmit the same demodulation pilot. Since the UE is generally asked, or requested, to monitor a complete set of D-CPICH within a shared radio cell, there is generally no need to send any further update when the UE moves within a shared radio cell.

Possible Complexity Reduction using HS-SCCH Orders: In one embodiment, the radio network node (or the scheduler thereof) may inform only a subset of demodulation pilots a UE can search. In other words, the radio network node (or the scheduler thereof) may inform the UE about a subset of demodulation pilots that the UE in question may search. However, in such embodiment, as the UE moves within a shared radio cell, the subset of demodulation pilots that a UE would need to monitor generally has to be updated. For example, consider that the UE is near RRU3 (see fig. 6) and is currently monitoring only D- CPICHO and D-CPICH3. When the UE moves closer to RRU2, the network may need to signal to the UE to ask (or request) the UE to monitor D-CPICHO and D-CPICH2. It is therefore proposed that this information is sent dynamically using a HS-SCCH order for a specific UE. Furthermore, such an update may be handled by the radio network node (or a scheduler thereof). Hence the UE can search only the subset of D-CPICHs as indicated by the HS-SCCH order. In this way, the complexity at the UE may be reduced further.

Dynamic Configuration of Number of Demodulation Pilots: In one embodiment, the radio network node may configure the number (N) of demodulation pilots dynamically. For example, when the traffic load is very low in the shared radio cell, the value of N can be reconfigured. The adjustment of N can be done either autonomously by the radio network node itself or it may adjust the value based on recommendation from the any of the RRUs controlled by the radio network node. This may allow for reducing the UE complexity for decoding.

Fig. 12 illustrates a radio network node 10 which is configured to perform the method described with reference to figs. 9-10. The radio network node 10 may e.g. be a RNC, NB, or eNB. The radio network node 10 comprises means 12, 13 adapted to configure a number of different demodulation pilots to form a set of multiple demodulation pilot configurations. Also, the radio network node 10 comprises means 11 adapted to transmit, to a UE 20 (see fig. 13), a radio signal comprising information about demodulation pilots, wherein the radio signal comprises information about the set of multiple demodulation pilot configurations. In some embodiments, means 12, 13 adapted to identify a set of available demodulation pilots are provided. Also, means 12, 13 adapted to assigning one or more demodulation pilots of said identified set of demodulation pilots to the UE are provided. Yet further, the radio network node may comprise means 11 adapted to transmit information about the assigned one or more demodulation pilots along with said information about demodulation pilots. In one example implementation, the radio network node comprises a processor 12 and a memory 13, wherein the memory stores computer program code which, when run in the processor 12, causes the radio network node 10 to configure a number of different demodulation pilots to form a set of multiple demodulation pilot configurations. The radio network node 10 may also comprise a transmitter 11 configured to transmit, to a UE, a radio signal comprising information about demodulation pilots, wherein the radio signal comprises information about a set of multiple demodulation pilot configurations. For example, the radio signal may comprise one or more data field(s) including, or otherwise indicating, the information about the set of multiple demodulation pilot configurations. In one embodiment, the memory 13 stores computer program code which, when run in the processor 12, causes the radio network node 10 to identify a set of available demodulation pilots and assign one or more demodulation pilots of said identified set of demodulation pilots to the UE. Also, the transmitter 11 may be configured to transmit information about the assigned one or more demodulation pilots along with said information about demodulation pilots. For example, the earlier-mentioned radio signal may comprise one or more data field(s) including, or otherwise indicating, the additional information about the assigned one or more demodulation pilots.

Fig. 13 illustrates a UE 20 which is configured to perform the method described with reference to fig. 1 1 . The UE 20 comprises means 21 adapted to receive, from a radio network node 10 (see fig. 12), a radio signal comprising information about demodulation pilots, wherein the radio signal comprises information about one or more demodulation pilot configurations. Also, the UE 20 may comprise means 21 adapted to receive information about one or more assigned demodulation pilots along with said information about demodulation pilots. Yet, further, the UE 20 may additionally comprise means 22, 23 adapted to estimate in each TTI, a channel from each of said one or more assigned demodulation pilots.

In one example implementation, the UE 20 comprises a receiver 21 configured to receive, from a radio network node 10, a radio signal comprising information about demodulation pilots, wherein the radio signal comprises information about one or more demodulation pilot configurations. For example, the radio signal may comprise one or more data field(s) including, or otherwise indicating, the information about the one or more demodulation pilot configurations. The receiver 21 may also be configured to receive information about one or more assigned demodulation pilots along with said information about demodulation pilots. For example, the earlier-mentioned radio signal may comprise one or more data field(s) including, or otherwise indicating, the additional information about the assigned one or more demodulation pilots. In one embodiment, the UE 20 also comprises a processor 22 and a memory 23 storing computer program code which, when run in the processor 22, causes the UE 20 to estimate, in each TTI, a channel from each of said one or more assigned demodulation pilots.

Option 2

With reference to Figure 14, another option is schematically illustrated. According to this option, instead of transmitting an individual HS-SCCH from a single RRU (e.g., Node-1 , Node-2, Node-3 and Node-4), multiple RRUs may transmit HS-SCCH for the intended UE. Thus, instead of using the spatial-reuse mode to transmit HS-SCCH, the single frequency network (SFN) mode may be used. Hence the UE may demodulate HS-SCCH from P- CPICH only. For decoding the data, the HS-SCCH will explicitly inform the D-CPICH index number or configuration.

It can be observed form figure 14 that the HS-SCCH is transmitted from all RRUs. Hence, the UE may decode the HS-SCCH without any explicit signaling of demodulation pilots. Note that conventionally HS-SCCH comprises information about modulation, number of codes, transport blocks, HARQ (Hybrid automatic repeat request) related information. It is proposed that, in addition to these, HS-SCCH should also include information about D- CPICH. For example, it could indicate the index of the demodulation pilot. For example if four D-CPICHs are allocated through the shared radio cell, only two bits are generally needed inform about the D-CPICH index. A non-exhaustive list of advantages of one or more aspects of the disclosed subject matter include:

Provide spatial reuse gain. In turn, the overall capacity and performance may be improved.

- Minimization or at least reduction in UE complexity for searching HS-SCCH. In turn, batter power may be saved.

In the detailed description hereinabove, for purposes of explanation and not limitation, specific details are set forth in order to provide a thorough understanding of various embodiments described in this disclosure. In some instances, detailed descriptions of well- known devices, components, circuits, and methods have been omitted so as not to obscure the description of the embodiments disclosed herein with unnecessary detail. All statements herein reciting principles, aspects, and embodiments disclosed herein, as well as specific examples thereof, are intended to encompass both structural and functional equivalents thereof. Additionally, it is intended that such equivalents include both currently known equivalents as well as equivalents developed in the future, i.e., any elements developed that perform the same function, regardless of structure. Thus, for example, it will be appreciated that block diagrams herein can represent conceptual views of illustrative circuitry or other functional units embodying the principles of the embodiments. Similarly, it will be appreciated that any flow charts and the like represent various processes which may be substantially represented in computer readable medium and so executed by a computer or processor, whether or not such computer or processor is explicitly shown. The functions of the various elements including functional blocks, may be provided through the use of hardware such as circuit hardware and/or hardware capable of executing software in the form of coded instructions stored on computer readable medium. Thus, such functions and illustrated functional blocks are to be understood as being either hardware-implemented and/or computer-implemented, and thus machine-implemented. In terms of hardware implementation, the functional blocks may include or encompass, without limitation, digital signal processor (DSP) hardware, reduced instruction set processor, hardware (e.g., digital or analog) circuitry including but not limited to application specific integrated circuit(s) [ASIC], and/or field programmable gate array(s) (FPGA(s)), and (where appropriate) state machines capable of performing such functions. In terms of computer implementation, a computer is generally understood to comprise one or more processors or one or more controllers. When provided by a computer or processor or controller, the functions may be provided by a single dedicated computer or processor or controller, by a single shared computer or processor or controller, or by a plurality of individual computers or processors or controllers, some of which may be shared or distributed. Moreover, use of the term "processor" or "controller" shall also be construed to refer to other hardware capable of performing such functions and/or executing software, such as the example hardware recited above.

Selected example embodiments

The technology disclosed herein thus encompasses without limitation the following example embodiments: Embodiment M1 : A method (100) performed by a radio network node, the method comprising: transmitting (120), to a user equipment, a radio signal comprising information about demodulation pilots (D-CPICHs).

Embodiment M2: The method (100) according to embodiment M1 , comprising: configuring (1 10) a number of different demodulation pilots (e.g., D-CPICH0, D-CPICH1 , D- CPICH2,... , D-CPICHn).

Embodiment M3: The method (100) according to embodiment M1 or M2, wherein the above-mentioned radio signal comprising information about demodulation pilots (D- CPICHs) comprises information about a set of multiple (e.g. N number) demodulation pilot configurations.

Embodiment M4: The method (100) according to any of the embodiments M1-M3, comprising: identifying (11 1) a set of available demodulation pilots (D-CPICHs); assigning (1 12) one or more demodulation pilots of said identified set of demodulation pilots (e.g., D- CPICH3) to the UE; and transmitting (120) information about the assigned one or more demodulation pilots (e.g., D-CPICH3) along with said information about demodulation pilots.

Embodiment M5: A method (200) performed by a user equipment (UE), the method comprising: receiving (210), from a radio network node, a radio signal comprising information about demodulation pilots (D-CPICHs).

Embodiment M6: The method (200) according to embodiment M5, wherein the radio signal comprising information about demodulation pilots (D-CPICHs) comprises information about one or more demodulation pilot (D-CPICH) configurations.

Embodiment M7: The method (200) according to embodiment M5 or M6, comprising: receiving (210) information about one or more assigned demodulation pilots (e.g., D- CPICH3) along with said information about demodulation pilots.

Embodiment M8: The method (200) according to embodiment M7, further comprising: estimating (220) (e.g., in each Transmission Time Interval (TTI)) a channel from each of said one or more assigned demodulation pilots (e.g., D-CPICH3). Embodiment N1 : A radio network node (10), comprising: a transmitter (1 1) configured to transmit, to a user equipment, a radio signal comprising information about demodulation pilots (D-CPICHs).

Embodiment N2: The radio network (10) node according to embodiment N1 , comprising a processor (12) and a memory (13), wherein the memory (13) stores computer program code which, when run in the processor (12), causes the radio network node (10) to configure a number of different demodulation pilots (e.g., D-CPICH0, D-CPICH1 , D- CPICH2,... , D-CPICHn). Embodiment N3: The radio network node (10) according to embodiment N1 or N2, wherein the above-mentioned radio signal comprising information about demodulation pilots (D- CPICHs) comprises information about a set of multiple (e.g. N number) demodulation pilot configurations.

Embodiment N4: The radio network node (10) according to any of the embodiments N1 - N3, wherein the memory (13) stores computer program code which, when run in the processor (12), causes the radio network node (10) to identify a set of available demodulation pilots (D-CPICHs); and assign one or more demodulation pilots of said identified set of demodulation pilots (e.g., D-CPICH3) to the UE; wherein the transmitter (1 1) is further configured to transmit information about the assigned one or more demodulation pilots (e.g., D-CPICH3) along with said information about demodulation pilots.

Embodiment N5: The radio network node (10) according to any of the embodiments N1- N4, wherein the radio network node (10) is a RNC, a NB or a eNB.

Embodiment U1 : A user equipment (UE) (20), comprising a receiver (21) configured to receive, from a radio network node, a radio signal comprising information about demodulation pilots (D-CPICHs). Embodiment U2: The UE (20) according to embodiment U1 , wherein the radio signal comprising information about demodulation pilots (D-CPICHs) comprises information about one or more demodulation pilot (D-CPICH) configurations.

Embodiment U3: The UE (20) according to embodiment U1 or U2, wherein the receiver (21) is configured to receive information about one or more assigned demodulation pilots (e.g., D-CPICH3) along with said information about demodulation pilots.

Embodiment U4: The UE (20) according to embodiment U3, comprising a processor (22) and a memory (23) storing computer program code which, when run in the processor (22), causes the UE (20) to estimate (e.g., in each Transmission Time Interval (TTI)) a channel from each of said one or more assigned demodulation pilots (e.g., D-CPICH3). Modifications and other variants of the described embodiments will come to mind to one skilled in the art having benefit of the teachings presented in the foregoing description and associated drawings. Therefore, it is to be understood that the embodiments are not limited to the specific example embodiments disclosed and that modifications and other variants are intended to be included within the scope of this disclosure. Although specific terms may be employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.

Claims

1. A method (100) performed by a radio network node operating in a combined radio cell, the method comprising:

configuring (1 10) a number of different demodulation pilots to form a set of multiple demodulation pilot configurations; and

transmitting (120), to a user equipment, a radio signal comprising information about demodulation pilots, wherein the radio signal comprises information about the set of multiple demodulation pilot configurations.

2. The method (100) according to claim 1 , comprising: identifying (1 1 1) a set of available demodulation pilots; assigning (1 12) one or more demodulation pilots of said identified set of demodulation pilots to the UE; and transmitting (120) information about the assigned one or more demodulation pilots along with said information about demodulation pilots.

3. The method (100) according to claim 1 or 2, wherein the radio signal comprises a Radio Resource Control, RRC, message and wherein the RRC message comprises said information about the demodulation pilots.

4. A method (200) performed by a user equipment (UE) operating in a combined radio cell, the method comprising: receiving (210), from a radio network node, a radio signal comprising information about demodulation pilots, wherein the radio signal comprises information about one or more demodulation pilot configurations.

5. The method (200) according to claim 4, comprising: receiving (210) information about one or more assigned demodulation pilots along with said information about demodulation pilots.

6. The method (200) according to claim 5, further comprising: estimating (220), in each Transmission Time Interval, a channel from each of said one or more assigned demodulation pilots.

7. The method (200) according to any of the claims 4-6, wherein the radio signal comprises a Radio Resource Control, RRC, message and wherein the RRC message comprises said information about the demodulation pilots.

8. A radio network node (10) configured to operate in a combined radio cell, the radio network node (10) comprising: a processor (12) and a memory (13), wherein the memory (13) stores computer program code which, when run in the processor (12), causes the radio network node (10) to configure a number of different demodulation pilots to form a set of multiple demodulation pilot configurations; and a transmitter (1 1) configured to transmit, to a user equipment, a radio signal comprising information about demodulation pilots, wherein the radio signal comprises information about a set of multiple demodulation pilot configurations.

9. The radio network node (10) according to claim 8, wherein the memory (13) stores computer program code which, when run in the processor (12), causes the radio network node (10) to identify a set of available demodulation pilots; and assign one or more demodulation pilots of said identified set of demodulation pilots to the UE; wherein the transmitter (1 1) is further configured to transmit information about the assigned one or more demodulation pilots along with said information about demodulation pilots.

10. The radio network node (10) according to claim 8 or 9, wherein the radio signal comprises a Radio Resource Control, RRC, message and wherein the RRC message comprises said information about the demodulation pilots.

1 1 . The radio network node (10) according to claim 8, 9 or 10, wherein the radio network node (10) is a Radio Network Controller, a NodeB or an evolved NodeB.

12. A user equipment (UE) (20) configured to operate in a combined radio cell, the UE (20) comprising a receiver (21) configured to receive, from a radio network node, a radio signal comprising information about demodulation pilots, wherein the radio signal comprises information about one or more demodulation pilot configurations.

13. The UE (20) according to claim 12, wherein the receiver (21) is configured to

receive information about one or more assigned demodulation pilots along with said information about demodulation pilots.

14. The UE (20) according to claim 13, comprising a processor (22) and a memory (23) storing computer program code which, when run in the processor (22), causes the UE (20) to estimate, in each Transmission Time Interval, a channel from each of said one or more assigned demodulation pilots.

15. The UE (20) according to any of the claims 12-14, wherein the radio signal

comprises a Radio Resource Control, RRC, message and wherein the RRC message comprises said information about the demodulation pilots.