HK1237152A1 - Network node and method in a wireless telecommunications network - Google Patents

Description

Network node and method in a wireless telecommunications network

Technical Field

Embodiments herein relate to a network node and a method therein. In particular, a method and a network node for managing transmission of cell reference signals are disclosed.

Background

Communication devices, such as User Equipment (UE), are enabled for wireless communication in a cellular communication network or a wireless communication system, sometimes also referred to as a cellular radio system or a cellular network. The communication may be performed, for example, between two UEs, between a UE and a normal telephone, and/or between a UE and a server, via a Radio Access Network (RAN) and possibly one or more core networks comprised within the cellular communication network.

A UE may also be referred to as a wireless terminal, mobile terminal and/or mobile station, mobile phone, cellular phone, laptop computer, tablet computer, or surfboard with wireless capability, to name just a few other examples. A UE in this context may be, for example, a portable, pocketed, handheld, computer-included, or vehicle-mounted mobile device enabled to communicate voice and/or data with another entity, such as another wireless terminal or a server, via the RAN.

The cellular communication network covers a geographical area which is divided into cell areas, wherein each cell area is served by a network node. A cell is a geographical area where a network node provides radio coverage.

The network node may further control several transmission points, e.g. with radio units (RRUs). Thus, a cell may comprise one or more network nodes, each controlling one or more transmission/reception points. A transmission point, also referred to as a transmission point/reception point, is an entity that transmits and/or receives radio signals. The entity has a position in space, e.g. an antenna. A network node is an entity that controls one or more transmission points. Depending on the technology and terminology used, the network node may for example be a base station such as a Radio Base Station (RBS), eNB, eNodeB, NodeB, B node or Base Transceiver Station (BTS). The base stations may have different categories, such as e.g. macro eNodeB, home eNodeB or pico base station, based on transmission power and thus also cell size.

Furthermore, each network node may support one or several communication technologies. The network node communicates over a radio frequency operated air interface with UEs within range of the network node. In the context of the present disclosure, the expression Downlink (DL) is used for the transmission path from the base station to the mobile station. The expression Uplink (UL) is used for the transmission path in the opposite direction, i.e. from the UE to the base station.

In third generation partnership project (3GPP) Long Term Evolution (LTE), a base station, which may be referred to as an eNodeB or even an eNB, may be directly connected to one or more core networks. In LTE, the cellular communication network is also referred to as evolved universal terrestrial radio access network (E-UTRAN).

The E-UTRAN cell is defined by certain signals broadcast from the eNB. These signals contain information about the cells that can be used by the UE to connect to the network through the cells. The signals include reference and synchronization signals used by the UE to find frame timing and physical cell identity and system information including parameters related to the entire cell.

Therefore, a UE that needs to connect to the network must first detect a suitable cell, as defined in 3GPP TS 36.304 v11.5.0. The UE may be in an IDLE state, also referred to as IDLE (IDLE) or radio resource control IDLE (RRC _ IDLE); or in a CONNECTED state, also referred to as CONNECTED (CONNECTED) or radio resource control CONNECTED (RRC _ CONNECTED). When a UE is in RRC _ IDLE, it monitors a paging channel, which is part of a logical level Paging Control Channel (PCCH), a transport channel level Paging Channel (PCH), and a Physical Downlink Shared Channel (PDSCH)) of a physical channel level. In doing so, the UE typically also performs a number of radio measurements, such as Reference Signal Received Power (RSRP), Reference Symbol Received Quality (RSRQ), or Received Signal Strength Indicator (RSSI), that the UE uses to evaluate the best cell. This is performed by measuring the received reference signal and/or the portion of the frequency spectrum comprising the reference signal transmitted by the cell. This may also be referred to as "listening" to the appropriate cell.

A suitable cell is typically a cell with an RSRQ or RSRP above a certain level. The cell with the highest RSRP or RSRQ may be referred to as the best cell or the most suitable cell. Listening for a suitable cell may include searching for a reference signal transmitted from a network node in an Orthogonal Frequency Division Multiplexing (OFDM) subframe. When the most suitable cell is found, the UE performs random access according to system information for the cell. This is done in order to transmit a Radio Resource Control (RRC) connection establishment request to the network node. Assuming that the random access procedure is successful and the network node receives the request, the network node will respond with an RRC connection setup message, which acknowledges the UE's request and informs it to enter an RRC _ CONNECTED state, or an RRC connection reject, which informs that the UE may not be able to connect to the cell. In the RRC _ CONNECTED state, parameters required for communication between the network node and the UE are known to both entities, and data transfer between the two entities is enabled.

When the UE is in RRC _ CONNECTED state, the UE continues to measure RSRP as an input to the CONNECTED mode mobility decision, such as for example deciding when to perform a handover from one cell to another. These measurements are typically performed in the full bandwidth of the subframe (which may also be referred to as the full spectrum).

RSRP is a measure of the signal strength of LTE cells that helps the UE rank different cells according to their signal strength as input for handover and cell reselection decisions. RSRP is the average of the power of all resource elements carrying cell-specific reference signals (CRS) over the entire bandwidth. Therefore, RSRP is only measured in OFDM symbols carrying CRS.

The RRC protocol handles control plane signaling at the network layer (also referred to as layer 3) between the UE and the network node, which may also be referred to as a UTRAN or E-UTRAN node. At any one time, only one RRC connection can be opened between the UE and the network node.

The network layer may further include:

the connection set-up and release functions are,

the broadcast of the system information is then transmitted,

radio bearer establishment/reconfiguration and release,

the RRC connection mobility procedure is used to control the RRC connection mobility procedure,

the notification and release of the page is carried out,

outer loop power control.

To support UE connectivity to a cell (which may also be referred to as an access cell), System Information Blocks (SIBs) are transmitted in control channels such as, for example, Broadcast Control Channel (BCCH) logical channels in the downlink, which may be mapped to PDSCH physical channels. In LTE, a number of different SIBs are defined, which are characterized by the information they carry. For example, the SIB1 carries cell access related parameters such as information about the operator of the cell, restrictions on what users may access the cell, and allocation of subframes to uplink/downlink. The SIB1 also carries information about the scheduling of other SIBs.

To reduce power consumption of the UE, Discontinuous Reception (DRX) may be implemented. The basic mechanism in DRX is a configurable DRX cycle in the UE, which may also be referred to as DRX mode. With the DRX cycle configured, the UE monitors control signaling only during the on duration (onDuration) interval of the DRX cycle. The onDuration interval may be one or more subframes, which may be referred to as one or more active subframes. In the remaining subframes of the DRX cycle, the UE may turn off its receiver, which may also be referred to as UE sleep, or as an off duration (off duration) interval of the DRX cycle. This allows a significant reduction in power consumption, i.e. the longer the DRX cycle and the shorter the onDuration interval, the lower the power consumption will be. In some cases, it may be possible to be scheduled again in the near future if the UE is already scheduled and active for receiving or transmitting data in one subframe. Waiting according to the DRX cycle until the next active subframe may result in additional delay in transmission. Thus, to reduce latency, the UE may remain active for some configurable time after being scheduled, which may also be referred to as an active time or an inactivity timer (DRX-inactivity timer) defined in 3GPP ts36.321ch 3.1. The duration of the active time is set by an inactivity timer, which is the following duration in the downlink subframe: the duration the UE waits from the last successful decoding of the Physical Downlink Control Channel (PDCCH) to before the UE shuts down and reenters the oftdd ration. The UE may restart the inactivity timer after a single successful decoding of the PDCCH for transmission. The time it takes for the UE to re-enter the oftdd ration after the last transmission may also be referred to as the inactivity time.

To facilitate handover to other cells, each network node may store cell identities of cells supported by other network nodes in an address database in order to know how to contact network nodes of potential target cells for handover. Each network node serving a cell typically stores in a database the cells with which it has a neighbour relation, i.e. to which cells in the area the UE often performs handover. The neighbor relation of a cell is hereinafter referred to as a "neighbor relation list" of the cell.

CRS are UE-known symbols inserted in Resource Elements (REs) of a subframe of an OFDM time and frequency grid and broadcast by a network node. Each RE has a spreading in the frequency domain corresponding to an OFDM subcarrier and a spreading in the time domain corresponding to an OFDM symbol interval.

The UE uses CRS for downlink channel estimation. The channel estimation is used for demodulation of downlink data when the UE is in an RRC _ CONNECTED state and is receiving user data and when the UE is in an RRC _ IDLE state and is reading system information. Due to the latter use case, the network node cannot know whether the UE wants to access the network before the UE performs random access, and thus even a cell of a UE without any RRC connected state must transmit the CRS therefrom. The downlink CRS is inserted into the first and third last OFDM symbols of each slot of the frequency domain interval having six subcarriers. A slot is a period of the OFDM time and frequency grid, typically 0.5 milliseconds long. Therefore, a problem with the known technique is that cells without any UE in RRC connected state still consume power due to CRS broadcast.

In case the network node uses several antennas for transmission and each antenna represents a cell, each antenna has to transmit a unique reference signal in order for the UE to connect to that particular cell. When one antenna transmits, the other antenna must be muted (silent) in order not to interfere with the first antenna reference signal. To reduce interference of reference signals between cells, the position of the CRS is typically shifted in frequency between cells. The CRS may be shifted between 0-5 subcarriers, each subcarrier corresponding to a frequency shift of 15kHz for LTE. The frequency shift may be derived from a physical cell identity (cell ID) signaled to the UE by selection of an appropriate Primary Synchronization Channel (PSCH) and Secondary Synchronization Channel (SSCH).

While this reduces interference of reference symbols (e.g., CRS symbols) between cells, there is a problem in that the reference symbols of one cell may interfere with PDSCH and PDCCH symbols of neighboring cells.

Thus, even if a cell does not have any UE in RRC _ CONNECTED state, interference may affect UE DL throughput in neighboring cells. Especially when the UE is at and/or near the border between cells.

Reducing the power of the CRS may alleviate this problem. However, in order to access a cell, the UE must be able to hear the CRS of the cell, i.e., the UE must be able to identify and receive the CRS transmitted from the cell. Therefore, reducing the power of the CRS also reduces the cell size, since more distant UEs will no longer hear the CRS transmitted by the cell. Further, when the signal-to-interference ratio (SINR) on the CRS decreases, the quality of the channel estimation used for demodulation decreases. Therefore, reducing the power of the CRS results in degradation of cell-edge performance. This degradation will be further exacerbated when the load in the network increases, especially if data is transmitted at higher power than the CRS, which is often the case when the impact of CRS interference will be reduced, resulting in reduced performance of the wireless communication network.

Disclosure of Invention

It is therefore an object of embodiments herein to enhance performance in a wireless communication network.

According to a first aspect of embodiments herein, the object is achieved by a method performed by a network node for managing transmission of cell reference signals, CRS.

The network node operates one or more cells. The network node identifies whether the cell is actively serving the set of UEs. The network node transmits CRS over the first bandwidth in one or more CRS subframes transmitted during the paging occasion and/or in one or more CRS subframes in which system information is transmitted when the cell is not actively serving any UE. The network node also transmits CRS over the second bandwidth in one or more CRS subframes not transmitted during the paging occasion and/or in one or more CRS subframes other than the subframe in which the system information is transmitted. The second bandwidth is reduced relative to the first bandwidth. When a cell is actively serving a set of UEs configured for discontinuous reception, DRX, the network node transmits CRS over the first bandwidth in one or more CRS subframes transmitted in the cell, and/or in one or more CRS subframes in which system information is transmitted, and/or in one or more CRS subframes in which downlink, DL, data is transmitted, during an onDuration interval of the DRX mode. The network node also transmits CRS over the second bandwidth in CRS subframes not transmitted in the cell during the onDuration interval of DRX and/or in one or more CRS subframes other than CRS subframes in which system information is transmitted and/or in one or more CRS subframes other than CRS subframes in which downlink DL data is transmitted. The second bandwidth is reduced relative to the first bandwidth.

According to a second aspect of embodiments herein, the object is achieved by a network node configured to manage transmission of cell reference signals, CRSs. The network node operates one or more cells. The network node is configured to identify whether a cell is actively serving a set of UEs. When the cell is not actively serving any UE, the network node is configured to transmit CRS on the first bandwidth in one or more CRS subframes transmitted during the paging occasion and/or in CRS subframes in which system information is transmitted. The network node is further configured to transmit CRS over the second bandwidth in one or more CRS subframes not transmitted during the paging occasion and/or in CRS subframes other than CRS subframes in which system information is transmitted. The second bandwidth is reduced relative to the first bandwidth. When the cell is actively serving a set of UEs configured for discontinuous reception, DRX, the network node is further configured to transmit CRS over the first bandwidth in one or more CRS subframes transmitted in the cell during an onDuration interval of the DRX pattern, and/or in CRS subframes in which system information is transmitted, and/or in CRS subframes in which downlink, DL, is transmitted data. The network node is further configured to transmit CRS over the second bandwidth in CRS subframes transmitted in the cell not during the onDuration interval of the DRX pattern and/or in CRS subframes other than CRS subframes in which system information is transmitted and/or in CRS subframes other than CRS subframes in which downlink DL data is transmitted. The second bandwidth is reduced relative to the first bandwidth.

By applying a bandwidth reduction pattern on CRSs transmitted in all subframes except subframes including subframes transmitted during or related to onDuration in a cell or subframes in which system information such as SIBs is transmitted or subframes related to subframes in which system information such as SIBs is transmitted, power consumption and interference from a cell can be reduced, thereby enhancing performance of a neighboring cell transmitting data. In other words, the reduced bandwidth mode is applied during the phase when no data transmission occurs and the UE turns off its receiver and enters the low power mode.

By applying the reduced bandwidth mode to the CRS in a cell that is not serving any UE in RRC connected mode, power consumption and interference from empty cells may be reduced, thereby enhancing the performance of cells with UEs in RRC connected mode.

Drawings

Embodiments herein are described in more detail with reference to the accompanying drawings, in which:

fig. 1 is a schematic block diagram illustrating an embodiment of a wireless communication network.

Fig. 2 is a schematic block diagram illustrating an embodiment of an OFDM subframe.

Fig. 3 is a flow chart depicting a first embodiment of a method in a network node.

Fig. 4 is a flow chart depicting a second embodiment of a method in a network node.

Fig. 5 is a schematic block diagram illustrating an embodiment of a network node.

Fig. 6a is a scheduling diagram illustrating a first embodiment of the method herein.

Fig. 6b is a scheduling diagram illustrating a first embodiment of the method herein.

Fig. 7 is a schematic block diagram illustrating an embodiment of a core network node.

Detailed Description

Term(s) for

The following general terms are used in the examples and are set forth below:

the radio network node: in some embodiments, the non-limiting term radio network node is more general and it refers to any type of network node serving a UE and/or connected to other network nodes or network elements or any radio node from which a UE receives signals. Examples of radio network nodes are node BS, Base Stations (BSs), multi-standard radio (MSR) radio nodes such as MSR BSs, eNode BS, network controllers, Radio Network Controllers (RNCs), base station controllers, relays, donor node control relays, Base Transceiver Stations (BTSs), Access Points (APs), transmission points, transmission nodes, RRUs, RRHs, nodes in a Distributed Antenna System (DAS), etc.

A network node: in some embodiments, the more general term "network node" is used, which may correspond to any type of radio network node or any network node in communication with at least a radio network node. Examples of network nodes are any of the above radio network nodes, core network nodes (e.g. Mobile Switching Centers (MSC), Mobility Management Entities (MME), etc.), operation and maintenance (O & M) centers, Operation Support Systems (OSS), self-organizing networks (SON), positioning nodes (e.g. evolved serving mobile positioning centers (E-SMLC), Main Data Telegrams (MDT), etc.

The user equipment: in some embodiments, the non-limiting term User Equipment (UE) is used, which refers to any type of wireless device communicating with a radio network node in a cellular or mobile communication system. Examples of UEs are target devices, device-to-device UEs, machine type UEs or UEs with machine-to-machine communication capabilities, PDAs, ipads, tablets, mobile terminals, smart phones, notebook computer embedded devices (LEEs), laptop computer installed devices (LMEs), USB security appliances, etc.

Embodiments herein are also applicable to a multipoint carrier aggregation system.

Note that although terminology from 3GPP LTE has been used in this disclosure to exemplify embodiments herein, this should not be seen as limiting the scope of embodiments herein to only the above-described systems. Other wireless systems, including WCDMA, WiMax, UMB and GSM, may also benefit from the ideas covered by this disclosure.

It is also noted that terms such as eNodeB and UE should be considered non-limiting, in particular not implying a certain hierarchical relationship between the two; in general, an "eNodeB" can be considered as device 1 and a "UE" as device 2, and the two devices communicate with each other over certain radio channels. Here we also focus on wireless transmission in the downlink, but the embodiments herein are equally applicable to the uplink.

In this section, embodiments herein will be illustrated in more detail by a number of exemplary embodiments. It should be noted that these embodiments are not mutually exclusive. Components of one embodiment may be assumed to be present in another embodiment by default, and it will be apparent to those skilled in the art how these components may be used in other exemplary embodiments.

Fig. 1 depicts an example of a wireless communication network 100 according to a first scenario in which embodiments herein may be implemented. The wireless communication network 100 is a wireless communication network such as LTE, E-UTRAN, WCDMA, GSM network, any 3GPP cellular network, Wimax or any cellular network or system.

The wireless communication network 100 comprises a plurality of network nodes, two of which (a first network node 110 and a second network node 111) are depicted in fig. 1. The first network node 110 and the second network node 111 are network nodes, each of which may be a transmission point such as a radio base station, e.g. an eNB, an eNodeB, or a home node B, a home eNode B, or any other network node capable of serving a wireless terminal such as a user equipment or a machine type communication device in a wireless communication network. The first network node 110 and the second network node 111 each serve a plurality of cells 130, 131, 132.

The wireless communication network 100 includes a set of UEs 121, which may include one or more UEs 120. First network node 110 and second network node 111 may each be a transmission point for UE 120. The UE120 is within radio range of the first network node 110 and the second network node 111, which means that it can hear signals from the first network node 110 and the second network node 111. There may also be one or more UEs 120 in each cell, and one or more of the UEs 120 may also be referred to as a UE set 121.

The UEs 120 in the set of UEs 121 may be, for example, wireless terminals, wireless devices, mobile wireless terminals or wireless terminals, mobile phones, computers such as laptops with wireless capability, Personal Digital Assistants (PDAs) or tablets (sometimes referred to as surfboards), or any other radio network element capable of communicating over a radio link in a wireless communication network. Note that the term wireless terminal as used in this document also covers other wireless devices such as machine-to-machine (M2M) devices.

Fig. 2 shows an exemplary downlink OFDM time and frequency grid, which may also be referred to as an OFDM subframe. Each subframe includes two slots. Each slot includes a plurality of Resource Elements (REs) 201 extending in both the time domain (x-axis) and the frequency domain (z-axis). The extension of each RE 201 in the frequency domain may be referred to as a subcarrier, and the extension in the time domain may be referred to as an OFDM symbol. In the time domain, LTE downlink transmissions are organized into 10ms radio frames, where each radio frame includes ten equally sized subframes. Furthermore, resource allocation in LTE can be generally described in terms of Physical Resource Blocks (PRBs) that include multiple REs. A resource block corresponds to one slot in the time domain and 12 consecutive subcarriers in the frequency domain.

The downlink and uplink transmissions are dynamically scheduled, i.e. in each subframe the first network node 110 transmits control information on to or from which UE120 data is transmitted and on which resource blocks. The control information may include system information, paging messages, and/or random access response messages. Control information for a given UE120 may be transmitted using one or more PDCCHs. Control information of the PDCCH is transmitted in a control region of each subframe. Fig. 2 shows an exemplary size of a conventional control region for three OFDM symbols allocated for control signaling (e.g., PDCCH). However, the size of the control region may be dynamically adjusted according to the current traffic situation. In the example shown in the figure, only the first OFDM symbol of the three possible OFDM symbols is used for control signaling. In general, the control region may include multiple PDCCHs carrying control information to multiple UEs 120 simultaneously. REs for control signaling are represented by wavy lines and REs for CRS are represented by diagonal lines.

UE120 uses CRS for downlink channel estimation. The channel estimates are used to determine demodulation of downlink data when UE120 is in an RRC connected state and when UE120 is in an RRC idle state and is reading system information. The downlink CRS may be inserted into the first and third last OFDM symbols of each slot of a frequency domain interval having six subcarriers. RSRP is a measure of the signal strength of the LTE cell that helps UE120 rank between different cells as input for handover and cell reselection decisions. RSRP is the average of the power of all resource elements carrying cell-specific reference signals (CRS) over the entire bandwidth. It is only measured in OFDM symbols carrying CRS.

The subframe also comprises data symbols for transmitting user data between the first network node 110 and the UE 120. The data symbols are located in an area following the control area, also referred to as data area.

A first example of an embodiment of a method in a network node 110 for managing transmission of Cell Reference Signals (CRS) will now be described with reference to the flowchart depicted in fig. 3. The network node 110 operates one or more cells 130, 131, 132, which may or may not serve the set of UEs 121.

The method may include the following acts, which may be performed in any suitable order. The dashed lines of the blocks in fig. 3 indicate that this operation is not mandatory.

Action 301

The network node 110 identifies whether a cell of the one or more cells 130, 131, 132 is actively serving the set of UEs 121. A cell that is actively serving the set of UEs 121 may also be referred to as a cell with a set of connected UEs, and a cell that is not actively serving the set of connected UEs 121 may be referred to as a null cell. This action 301 may be performed by an identification module 404 within a network node, such as network node 110. This action corresponds to action 401 described below.

When the network node 110 has identified a cell that is not actively serving the set of UEs 121, the network node performs actions 302 and 303 described below. Although acts 302 and 303 are depicted as following each other, the acts may be performed simultaneously.

Act 302

When the network node 110 has identified a cell that is not actively serving the set of UEs 121, the network node 110 transmits CRS over the first bandwidth in one or more CRS subframes transmitted during the paging occasion and/or in one or more CRS subframes transmitting system information.

Act 303

When the network node 110 has identified a cell that is not actively serving the set of UEs 121, the network node 110 also transmits CRS over the second bandwidth in one or more CRS subframes that are not transmitted during the paging occasion and/or in one or more CRS subframes other than the subframe in which the system information is transmitted. The second bandwidth is reduced relative to the first bandwidth.

In another embodiment herein, the paging occasion may be transmitted in one CRS subframe of each radio frame with paging only in cells not serving the set of UEs 121. Thus, the number of CRS subframes that must be transmitted at the first bandwidth is reduced, which allows the network node 110 to reduce the bandwidth in a higher number of CRS subframes.

When the network node has identified a cell that is actively serving a set of UEs (121), which set of UEs (121) is configured for discontinuous reception, DRX, the network node 110 performs the actions 304 and 305 described below. While acts 304 and 305 are depicted as following each other, the acts may be performed concurrently.

Act 304

When the network node has identified a cell that is actively serving a set of UEs (121), which set of UEs (121) is configured for discontinuous reception, the network node 110 transmits CRS subframes over the first bandwidth in one or more CRS subframes transmitted in the cell, and/or in one or more CRS subframes transmitting system information, and/or in one or more CRS subframes transmitting downlink DL data, during an onDuration interval of the DRX mode.

In other embodiments, the network node 110 may also transmit CRS over the first bandwidth in CRS subframes transmitted immediately before or after CRS subframes transmitted during the paging occasion and/or in CRS subframes transmitted during the onDuration and/or in CRS subframes transmitting DL data.

Act 305

When the network node has identified a cell that is actively serving a set of UEs (121), which set of UEs (121) is configured for discontinuous reception, the network node 110 also transmits CRS over the second bandwidth in CRS subframes that are not transmitted in the cell during an onDuration interval of DRX, and/or in one or more CRS subframes other than CRS subframes in which system information is transmitted, and/or in one or more CRS subframes other than CRS subframes in which DL data is transmitted. The second bandwidth is reduced relative to the first bandwidth. This action 305 corresponds to action 402 described below, so the embodiments described for action 402 may also be applied to this action 305.

Act 306

Network node 110 may also send a message including a DRX command to set of UEs 121 when network node 110 has identified a cell that is actively serving the set of UEs. The DRX command indicates a DRX mode for the set of UEs 121, which may also be referred to as a DRX cycle. The indicated DRX mode is the DRX mode that the set of UEs 121 will use. For the UEs 120 included in the set of UEs 121, the ondurations of the DRX patterns are aligned such that the UEs 120 have overlapping onDuration intervals. By aligning the onDuration intervals of the UEs 120, the UEs can be grouped, i.e., the UEs will have overlapping ondurations. This has the advantage that the occasions when the CRS is transmitted in the first bandwidth mode may be reduced and the number of subframes in which the CRS is transmitted over the second bandwidth is increased. This will further improve the performance of the cell.

This action 306 corresponds to action 403 described below, so the embodiment described for action 403 may also be applied to this action 306.

UEs may be grouped together by sending a message to all connected UEs in a cell including a command indicating the onDuration of the DRX mode, i.e., the UEs are configured to have overlapping ondurations. By doing so, the performance of the cell may be further improved, as occasions when the CRS has to be transmitted at full bandwidth may be minimized, as each UE performs radio measurements such as RSRP, RSRQ, or RSSI within the same time interval.

Another example of an embodiment of a method in a network node 110 for managing transmission of cell reference signals, CRSs, will now be described with reference to the flowchart shown in fig. 4. The network node 110 operates one or more cells and is configured to transmit the CRS in a first bandwidth mode during operation. This involves normal operation. The first bandwidth mode may also be referred to as a normal bandwidth mode for when at least one cell of the network node 110 is serving at least one UE120 in RRC connected mode and the at least one UE120 is scheduled to receive data. In normal bandwidth mode, CRS is transmitted over the entire available bandwidth of the DL Radio Frame (RF), i.e. CRS is transmitted in all Physical Resource Blocks (PRBs) of the cell.

The method may include the following acts, which may be performed in any suitable order. The dashed lines of the boxes in fig. 4 indicate that this operation is not mandatory.

Act 401

Network node 110 identifies cells serving a set of UEs 121 (which may also be referred to as a set of connected UEs). The set of UEs 121 is configured for Discontinuous Reception (DRX). The set of UEs 121 may include one or more UEs 120. The set of UEs 121 is not scheduled by the network node for receiving a transmission sent in one of the network node's cells from the network node. This may mean that the network node has not yet scheduled the set of UEs 121 for reception of transmissions sent from the network node 110 in the cell, or that a certain time (T) has elapsed since the set of UEs 121 were scheduled for transmission in the UL or DL. The time T may be a time set in the DRX inactivity timer. This action 401 may be performed by an identification module 404 within a network node, such as network node 110.

Act 402

When the network node 110 has identified a first cell serving a set of UEs 121 (which set of UEs 121 is not scheduled by the network node 110), the network node 110 applies a second bandwidth pattern (also referred to as a reduced CRS bandwidth pattern) to CRS in subframes that are not transmitted in the cell during onDuration of DRX or in subframes in which system information is sent. In another embodiment, the reduced CRS bandwidth pattern may also be applied to CRSs transmitted in subframes not transmitted for onDuration or related to subframes transmitting system information, which may be, for example, subframes immediately before or after onDuration or subframes transmitting system information. In the second bandwidth mode, the bandwidth is reduced relative to the first bandwidth mode. The system information may be, for example, a System Information Block (SIB). This reduced bandwidth mode may also be referred to as a low bandwidth mode. The low bandwidth mode means that the network node 110 does not transmit CRS in all PRBs of a subframe of the cell. By reducing the bandwidth of the CRS, i.e., transmitting the CRS only over a portion of the available bandwidth of the DL radio frame, the overall interference of the CRS from the cells 130 is reduced. Reducing interference from cell 130 increases throughput in neighboring cell 131 and increases RRC connected and scheduled UE 120.

Studies have shown that mobility measurements (also referred to as cell evaluations or best cell evaluations, such as RSRP) may be negatively affected when the CRS bandwidth is reduced. This may lead to the UE making an erroneous decision on which cell it should camp. Only a limited portion of the bandwidth is considered when UE120 performs mobility measurements on neighbor cells. This limited portion of the bandwidth may be, for example, the center six PRBs of the subframe. However, when the UE makes measurements on the cell in which it is camped (which may also be referred to as its own cell), the entire bandwidth is taken into account. If the bandwidth used to transmit the CRS in a cell is reduced, the CRS will be transmitted in only a portion of the bandwidth (e.g., the six PRBs in the center). However, RSRP is calculated as the average power of all REs carrying CRS over the entire bandwidth. Since the power of the CRS transmitted in, for example, the central six PRBs, is averaged over the entire bandwidth, not just over the reduced bandwidth, the RSRP of the own cell may appear lower than that of the neighboring cells. This may result in the UE connecting to a neighboring cell (which may also be referred to as performing a handover) that appears better and actually worse. This may result in the UE starting to perform multiple handovers back and forth between cells, which may also be referred to as a ping-pong effect, since a neighboring cell that evaluates only on the central six PRBs will always look better.

To prevent the reduced bandwidth mode from negatively affecting (such as destroying) mobility measurements (such as cell evaluations or best cell evaluations), the subframes transmitted during the onDuration of DRX or the subframes in which system information is sent are transmitted first, which may also be referred to as normal bandwidth mode.

In another embodiment, the CRS may also be transmitted in subframes around the subframe transmitted during onDuration in normal bandwidth mode. In one embodiment, the normal bandwidth mode may be applied to a number of subframes before or after the subframe transmitted during the onDuration. The number of subframes transmitted in the normal bandwidth mode may be up to twenty-five subframes, including subframes transmitted during onDuration. The onDuration may be located over two subframes. In another embodiment, the normal bandwidth mode may be applied on four subframes before onDuration and seven subframes after onDuration, such that the normal bandwidth mode is applied on a total of thirteen subframes. By transmitting the CRS in a normal bandwidth mode in subframes located around the onDuration, it can be ensured that legacy UEs, which do not perform measurements as accurately as modern UEs, are able to measure the CRS to perform channel estimation, even if the measurements are not performed accurately during the onDuration. Depending on the accuracy of the measurements performed by the UE, the number of subframes in which the CRS is transmitted in the normal bandwidth mode may be reduced. In another embodiment, the normal bandwidth mode may be applied, for example, to a subframe preceding a subframe transmitted during onDuration or a subframe transmitting system information. Thus, it can be ensured that the CRS is transmitted over the entire bandwidth (i.e. in normal bandwidth mode) when the UE performs measurements during onDuration. This embodiment is depicted in fig. 6.

In yet another embodiment, the CRS may also be transmitted in normal bandwidth mode during times of inactivity of the UE.

Having a long DRX cycle (i.e. a long time between ondurations of DRX) may further be beneficial as it enables the network node 110 to apply the reduced bandwidth mode over a larger number of subframes. In one embodiment herein, the DRX cycle (which may also be referred to as a period of the DRX mode) may be in a range of 20ms to 320 ms. In another embodiment herein, the DRX cycle may be in a range of 20ms to 80 ms. In yet another embodiment, the DRX cycle may be 40ms long. Studies have shown that this is the preferred period for a UE to typically read RSRP in order to assess the channel conditions in the cell to which it is connected.

Act 402 may be performed by a bandwidth adjustment module within a network node, such as network node 110.

Act 403

In another embodiment herein, the network node 110 may send a message to the set of UEs 121, the message comprising a Discontinuous Reception (DRX) command. The command indicates a DRX cycle in which the onDuration (which may also be referred to as the onDuration interval) of the DRX mode is aligned for the UEs included in the set of UEs 121. Thus, the UEs may be grouped, i.e. the UEs will have overlapping ondurations. This has the advantage that the occasions when CRS is transmitted in the first bandwidth mode can be reduced. This will further improve the performance of the cell.

In yet another embodiment herein, the onDuration of the DRX mode may be aligned with the transmission of one or more subframes that include system information, such as System Information Blocks (SIBs). In another embodiment herein, the onDuration is aligned with SIB 1. Since the SIB1 includes parameters related to cell access and information about the scheduling of other SIBs, SIB1 will be transmitted even if the remaining SIBs are not transmitted. Since the subframes transmitted in the first bandwidth mode can be further reduced, aligning the onDuration of the set of UEs 121 with the transmission of the SIB1 thus further improves the performance of the cell. Aligning the onDuration with the SIB1 further reduces losses, since SIB1 is transmitted with the full CRS bandwidth anyway. SIB1 may be transmitted at a 20ms periodicity in subframe 5, which may also be referred to as SFN mod 2 ═ 0. With forced DRX, the UE can be triggered (which may also be referred to as being activated, commanded, forced, or spoofed) to always evaluate the state of the current cell when CRS is transmitted in full bandwidth mode and to reduce bandwidth when connected UEs are sleeping. The trigger may be sent in a DRX command of the onDuration in which the DRX cycle is set. DRX mode may be applied to UE120 in order to trigger the evaluation of RSRP and other measurements of slots in case the network node has transmitted CRS over the entire bandwidth (i.e. in normal bandwidth mode).

In another embodiment, the network node 110 may force the UE to enter DRX sleep by sending a 3GPP DRX command MacControlElement, such as defined in, for example, 3GPP TS36.321 v11.5.0 Ch 6.1.3.3 and referred to as a DRX command MAC control element. The MacControl element may include an indication to stop the DRX inactivity timer and/or the onDuration timer.

In other embodiments herein, the alignment of DRX mode ondurations and/or the application of reduced CRS bandwidth may be deactivated when the number of connected UEs in a cell exceeds a certain threshold.

Act 403 may be performed by a sending module within a network node, such as network node 110. The transmitting module may also be comprised in a radio circuit within a network node, such as the network node.

In one embodiment herein, the reduced CRS bandwidth pattern is applied to CRSs transmitted in any subframe other than the subframe in which network node 110 transmits system information, paging, or random access response messages, or the subframe in which network node 110 assumes that UE120 performs measurements. By applying the CRS bandwidth reduction pattern in all subframes except the above subframes, the interference of the CRS is reduced while allowing UEs 120 in neighboring cells 131, 132 to hear the CRS from the empty cell 130. This is necessary in order for the UE120 to obtain information about the modulation of the signal in order to be able to demodulate the downlink control channel of the cell. In this embodiment, network node 110 may transmit the CRS over the entire bandwidth in a subframe in which network node 110 transmits system information such as SIBs, paging or random access response messages, or assumes that UE120 performs measurements.

In another embodiment herein, the network node 110 transmits the CRS in PRBs used for transmission of data or control information only in subframes in which the network node 110 transmits system information, paging or random access response messages, or assumes that the UE performs measurements.

The network node 110 may also transmit CRS in REs adjacent to REs mapped to the common search space of PDCCH. Therefore, CRS is only transmitted in regions where the UE is looking for PDCCH. Accordingly, the number of subframes in which the CRS may be transmitted over the second bandwidth is increased, which further improves the performance of the wireless communication network.

The CRS bandwidth may be further adapted to multiple levels. For LTE, the bandwidth in the cell 130 may vary, for example, on a level between 1.4Mhz and 20 Mhz. However, other bandwidths are possible depending on the technology used.

In another embodiment, a hysteresis function may be applied when changing CRS bandwidth levels, thereby avoiding unnecessary switching between bandwidth modes when cell 130 switches from the first bandwidth mode to the second bandwidth mode.

In yet another embodiment herein, for voice over IP (VoIP) or other "continuously on" type services, the UE may move to the lowest band with the best coverage, while the CRS may be muted on the higher band. Moving voice over LTE users to the lowest frequency band may be beneficial because these users are very active and need coverage. This facilitates carrier aggregation.

In another embodiment herein, some UEs may be configured with Channel Quality Indicator (CQI) on the Physical Uplink Control Channel (PUCCH) that may be aligned with DRX onDuration, while some UEs are not configured with CQI on PUCCH. Thus, the onDuration periods can be stacked more closely. Intelligent selection of UEs given PUCCH CQI may be achieved, for example, by looking at the path loss so as not to reduce the coverage of the system. A UE with high path loss may be configured with CQI on PUCCH, while others will not.

In another embodiment herein, dynamic reconfiguration of paging frames and paging occasions may be performed. Thereby reducing CRS transmission performed in the normal bandwidth mode while maintaining sufficient paging capacity.

In yet another embodiment, coordination on X2 may be performed between interfering cells. Thus, the interfering cells may inform each other which subframes (which may also be referred to as blank subframes) to transmit in the reduced bandwidth mode and which subframes (which may also be referred to as non-blank subframes) to transmit in the normal bandwidth mode. This may enable different network nodes to have different outer loop adjustment values for blank subframes versus non-blank subframes, which may improve the results of link adaptation.

In other embodiments herein, DL data may be transmitted to each UE in connected mode with a certain periodicity. This has been shown to increase the stability of measurements made by the UE (such as RSRP, RSRQ, or RSSI). The DL data may be transmitted during a period corresponding to the time of the onDuration of the UE. Tests have shown that the preferred period of DL data is about 2 seconds, i.e. DL data is sent to the DL about every 2 seconds. The DL data transmitted periodically may be arbitrary DL data. In one embodiment, the Timing Advance Command (TAC) is sent as periodic DL data. The CRS is transmitted in full bandwidth mode during transmission of DL data, providing the CRS to the UE during DL transmission and subsequent inactive time (also referred to as DRX-Inactivity time).

In other embodiments herein, the CRS may also be transmitted over the first bandwidth or full bandwidth mode during UL transmissions (e.g., subframes in which UL data is transmitted).

In other embodiments herein, the periodic DL data transmissions may be aligned between connected UEs. Since each DL transmission starts an inactivity timer as defined in 3GPP TS36.321 v.9.6.0, CRS will be transmitted to each UE in full bandwidth mode for the duration of the inactivity period. By aligning the periodic DL data transmission between connected UEs, the number of subframes in which full spectrum CRS needs to be transmitted is reduced. This improves the gain when many users are connected by ensuring that the full bandwidth CRS transmitted during the DRX-Inactivity timer of each UE coincide in time and thus maximize the number of subframes in which CRS can be muted. Thereby the performance of the cell can be further improved.

In other embodiments herein, a connected UE may release and force entry into idle mode after an inactivity timer in the network node monitoring UE activity has elapsed (i.e., when the UE has been inactive for a period of time). In embodiments herein, the inactivity timer may be variable. The inactivity timer may be changed based on the number of connected UEs in the cell. When the method for reducing CRS bandwidth for connected UEs is active, it is beneficial for the method described herein to have as few connected UEs as possible. Thus, a threshold for connected UEs in a cell may be defined. The duration of the inactivity timer for the connected UEs is reduced when the total number of connected UEs is below the threshold compared to the duration of the inactivity timer when the total number of connected UEs in the cell exceeds the threshold. Thus, when the method for managing the transmission of CRS is active, the connected UEs are released more quickly, which reduces the number of connected users to a minimum. The reduced inactivity timer may be, for example, approximately 4 seconds as compared to a normal inactivity timer of approximately 10 seconds.

In other embodiments herein, parameters of the methods described herein, such as DRX inactivity timer length, DRX onDuration period and length (which may also be referred to as onDuration interval), and/or TAC/DL data transmission period may be adapted (which may also be referred to as being tailored or tailored) according to different types of UEs. The International Mobile Equipment Identity (IMEI) and/or IMEI software version (IMEISV) of the UE may be sent from the core network to the network node and may be used as an identifier to distinguish between different UE types, e.g. different brands. In another embodiment, the core network node may identify the brand/type of the UE based on the IMEI or IMEISV and may send the brand of the UE to the network node. The network node may then adapt parameters of the method based on the received UE type. In another embodiment, the UE and the network node may establish a proprietary protocol that may be used to identify the UE type/brand, e.g., on the MAC, RLC, PDCP or RRC level. Based on the identity of the UE, the UE may request the network node to adapt the above parameters in a way that is advantageous for each UE type. The UE type may be identified by comparing the IMEI and/or IMEISV of the UE with a database comprising IMEI: s and/or IMEISV: s for different UE types. Depending on the method of identifying the UE, the database may be stored in the network node or the core network node.

In other embodiments herein, the parameters of the functions may be adapted based on the speed of movement of the UE. The indication shows that the UE may need more or less CRS: s to be transmitted in the DL depending on the speed of the UE. The velocity of the UE may be determined by a doppler estimation performed in the uplink by a network node (such as e.g. an eNodeB) and may be used as input to modify parameters of the methods herein, such as DRX inactivity timer length, DRX onDuration period and length, and/or TAC/DL data transmission period. These parameters may be adapted such that a larger doppler (i.e. a higher UE velocity) will give the UE more occasions to read CRS, whereas a low doppler estimate (i.e. a low velocity of the UE) will trigger the opposite.

According to a second aspect of embodiments herein, when identifying a second cell, which may also be referred to as serving a UE in IDLE mode, which is not actively serving any UE, the network node applies a reduced CRS bandwidth pattern on CRSs transmitted in the second cell. In the reduced bandwidth mode, the bandwidth is reduced relative to the first bandwidth mode.

In another embodiment, when the network node identifies that the cell is serving idle mode only UEs, the paging frequency may be reduced while the subframes of the paging occasions are transmitted with full CRS bandwidth. In some other embodiments herein, some surrounding subframes (e.g., one previous or one subsequent subframe) may also be transmitted with full CRS bandwidth. To minimize the number of subframes transmitted with full CRS bandwidth, there may be only one paging occasion in each radio frame with paging. The paging occasion may be in subframe 9. Subframes 9 and 0 may be transmitted with full bandwidth only in those radio frames that carry paging, thereby improving idle mode mobility. Furthermore, all subframes including SIBs may be transmitted with full CRS bandwidth in order to allow UEs to hear them. Subframes subsequent or prior to subframe 9 may also be transmitted with full bandwidth.

To perform the method acts for managing transmission of CRS described above with respect to fig. 4, network node 110 may include the following arrangement shown in fig. 5. As described above, the network node 110 operates one or more cells and is typically configured to transmit CRS in a first bandwidth mode.

Network node 110 includes radio circuitry 401 to communicate with UE120, communication circuitry 402 to communicate with other network nodes, and processing module 403. The communication module 402 may be, for example, an X2 interface.

The network node 110 is configured, e.g. by means of the identification module 404, to identify whether the cell 130, 131, 132 is actively serving the set of UEs 121, which may also be referred to as a set of connected UEs. The set of UEs 121 may not be scheduled by the network node 110 for receiving transmissions from the cell. The network node 110 is further configured to, or comprises, a bandwidth adjustment module 405 configured to, when the first cell is identified as actively serving the set of UEs 121, apply a reduced CRS bandwidth pattern of CRS in the first cell 130 relative to the first bandwidth pattern.

Network node 110 may also be configured, e.g., by means of bandwidth adjustment module 405, to apply a reduced CRS bandwidth pattern to CRSs transmitted in any subframe other than subframes in which network node 110 transmits system information, paging or random access response messages, or where UE120 is assumed to perform measurements, such as subframes transmitted during the onDuration of UE 120. In this embodiment, the network node 110 may be further configured, e.g. by means of the bandwidth adjustment module 405, to transmit the CRS over the entire bandwidth of a subframe in which the network node 110 transmits system information, a paging or random access response message or in a subframe in which it is assumed that the UE120 performs measurements, such as a subframe transmitted during the onDuration of the UE 120.

In another embodiment herein, network node 110 may be further configured, e.g., by means of bandwidth adjustment module 405, to apply a reduced CRS bandwidth pattern to CRSs transmitted in any subframe other than the first OFDM symbol of a subframe in which network node 110 transmits system information, a paging or random access response message, or in which UE120 is assumed to perform measurements, such as a subframe transmitted during the onDuration of UE 120. In this embodiment, the network node 110 may be further configured, e.g. by means of the bandwidth adjustment module 405, to transmit the CRS over the entire bandwidth in the first OFDM symbol of a subframe in which the network node 110 transmits system information, a paging or random access response message, or in which it is assumed that the UE120 performs measurements, such as a subframe transmitted during the onDuration of the UE 120.

Network node 110 may also be configured, e.g. by means of bandwidth adjustment module 405, to transmit CRS only in PRBs used for transmission in subframes in which network node 110 transmits system information, paging or random access response messages, or in which UE120 is assumed to perform measurements, such as subframes transmitted during the onDuration of UE 120.

In embodiments herein, the network node 110 may be further configured, e.g. by means of the bandwidth adjustment module 405, to transmit the CRS only in REs neighboring REs of the REs mapped to the common search space of the PDCCH. The common search space includes REs used by network node 110 to transmit control information common to all UEs 120.

The network node 110 may be further configured, e.g. by means of the transmitting module 408, to transmit a message, which may comprise a Discontinuous Reception (DRX) command, to all connected UEs in the cell. The DRX command may indicate a DRX mode of the connected UEs, wherein onDuration of the DRX mode may be aligned between UEs 120. The onDuration may also be aligned with the transmission of one or more subframes including System Information Blocks (SIBs). The network node may be further configured to apply a second CRS bandwidth pattern to CRSs in subframes not transmitted in the cell during the onDuration. In the second bandwidth mode, the bandwidth is reduced relative to the first bandwidth mode.

The sending module 408 may be comprised in the radio circuit 401 within the network node 110.

To reduce unnecessary switching between bandwidth modes, the network node 110 may also be configured, or may comprise, a bandwidth adjustment unit 405 further configured to reduce and/or increase the CRS bandwidth using a hysteresis function. By using the hysteresis function, the network node 110 may not switch bandwidth modes immediately when the number of connected UEs 120 changes, but will remain in one bandwidth mode for a period of time after the change of bandwidth mode in the cell has occurred.

In other embodiments herein, the network node 110 may be further configured, e.g. by means of the bandwidth adjustment module 405, to transmit DL data to each UE in connected mode with a certain periodicity. Thus, increased stability of measurements performed by the UE (such as RSRP, RSRQ, or RSSI) may be provided. The DL data may be transmitted during a period corresponding to the onDuration time of the UE. Tests have shown that the preferred period of DL data is about 2 seconds, i.e. DL data is sent to the UE about every 2 seconds. The DL data transmitted periodically may be arbitrary DL data. In one embodiment, the Timing Advance Command (TAC) is sent as periodic DL data. The CRS is transmitted in full bandwidth mode during transmission of DL data, providing the CRS to the UE during DL transmission and subsequent inactive times (also referred to as DRX-Inactivity times).

In other embodiments herein, the network node 110 may be further configured, e.g. by means of the bandwidth adjustment module 405, to align the periodic DL data transmission between the connected UEs. Since each DL transmission starts the DRX inactivity timer as defined in 3gpp ts36.321 v.9.6.0, CRS will be sent to each UE in full bandwidth mode for the duration of the inactivity period. By aligning the periodic DL data transmission between connected UEs, the number of subframes of full-spectrum CRS that need to be transmitted is reduced. This improves the gain when many users are connected by ensuring that the full bandwidth CRS transmitted during each UE DRX-Inactivity timer coincides in time and thus maximizes the number of subframes in which CRS can be muted. Thereby the performance of the cell can be further improved.

In other embodiments herein, the network node 110 may be configured, e.g. by means of the bandwidth adjustment module 405, to further be configured to start an inactivity timer that releases the connected UE and forces the UE to enter idle mode after a certain time of inactivity. The inactivity timer may be variable. When the method for reducing CRS bandwidth for connected UEs is active, it is beneficial for the method described herein to have as few connected UEs as possible. Thus, a threshold for connected UEs in a cell may be defined. The duration of the inactivity timer for the connected UEs is reduced when the total number of connected UEs is below the threshold, compared to the duration of the inactivity timer when the total number of connected UEs in the cell exceeds the threshold. Thus, when the method for managing the transmission of CRS is active, the connected UEs are released more quickly, which reduces the number of connected users to a minimum. The reduced inactivity timer may be, for example, approximately 4 seconds as compared to a normal inactivity timer of approximately 10 seconds.

In other embodiments herein, the network node 110 may be configured, e.g. by means of the bandwidth adjustment module 405, to further be configured to adapt or tailor parameters of the methods described herein, such as DRX inactivity timer length, DRX onDuration periodicity and length, and/or TAC/DL data transmission period, according to different types of UEs. The network node 110 may also be configured, e.g. by means of the identification module 404, to identify/distinguish different UE types based on the IMEI of the UE which may be received by the network node 110 from the core network node.

The network node 110 may be further configured, e.g. by means of the bandwidth adjustment module 405, to adapt parameters of the method in accordance with the received brand/type of the UE identified by the core network node based on the IMEI of the UE. The network node 110 may be further configured, e.g. by means of the bandwidth adjustment module 405, that a proprietary protocol for identifying the UE type may be established at e.g. the Medium Access Control (MAC), Radio Link Control (RLC), Packet Data Convergence Protocol (PDCP) or RRC level. Based on the identity of the UE, the network node 110 may be further configured, e.g. by means of the bandwidth adjustment module 405, to adapt the above parameters in a beneficial way for each UE type.

In other embodiments herein, the network node 110 may be further configured to adapt parameters of the method based on the moving speed of the UE, e.g. by means of the bandwidth adjustment module 405. The indication shows that the UE may need more or less CRS to be transmitted in the DL depending on the speed of the UE. The network node 110 may be further configured to determine the velocity of the UE by performing doppler estimation in the UL, e.g. by means of the bandwidth adjustment module 405. The network node 110 may also be configured, e.g. by means of the bandwidth adjustment module 405, to modify parameters of the methods herein, such as DRX inactivity timer length, DRX onDuration period and length, and/or data transmission period of TAC/DL, based on the doppler estimation. The parameters may be adapted such that a larger doppler (i.e., a higher velocity of UE 120) will give UE120 more opportunities to read CRS, whereas a low doppler estimate (i.e., a low velocity of UE 120) will trigger the opposite.

In other embodiments, the network node 110 may be further configured, e.g. by means of the receiving module 407, to receive the IMEI of the UE120 or the identified UE120 type from the core network node 140. The receiving module may be included in the communication circuit 402.

The embodiments herein for managing CRS transmission may be implemented by one or more processors (such as processing module 403 in network node 110 depicted in fig. 5) in conjunction with computer program code for performing the functions and acts of the embodiments herein. The program code mentioned above may also be provided as a computer program product, for example in the form of a data carrier carrying computer program code for performing the embodiments herein when being loaded into the network node 110. One such carrier may be in the form of a CD ROM disc. However, other data carriers, such as memory sticks, are also feasible. The computer program code may also be provided on a server and downloaded to the network node 110 and/or the core network node as pure program code.

The network node 110 may also include a memory 406 that includes one or more memory units. The memory 406 is arranged for storing the acquired information, measurements, data, configurations, schedules and applications for performing the methods herein when executed in the network node 110.

Fig. 6a and 6b disclose scheduling diagrams for DRX and bandwidth mode according to two embodiments of the above method. In order to prevent the reduced bandwidth mode from negatively affecting (such as corrupting) mobility measurements such as cell evaluations or best cell evaluations, subframes transmitted during ondurations of the DRX mode or subframes in which system information is sent are transmitted in a first bandwidth mode (which may also be referred to as full bandwidth mode).

Fig. 6a discloses an embodiment of the method, wherein CRS is transmitted over full bandwidth on a total of thirteen subframes arranged around the subframes of the onDuration. Four of the thirteen subframes precede two subframes for each onDuration and seven of these subframes follow each onDuration. The reduced bandwidth mode is applied to the remaining subframes of the radio frame. Tests have shown that some legacy UEs may not perform measurements as accurately as other UEs, and may start measurements shortly before or after onDuration. By transmitting the CRS in the normal bandwidth mode in a number of subframes located around the onDuration, it can be ensured that such less accurate UEs are able to measure the CRS in order to perform channel estimation, even if the measurements are not performed exactly during the onDuration.

Fig. 6b shows another embodiment of a method in which the number of subframes in which CRS is transmitted over full bandwidth has been reduced. In the present embodiment, the normal bandwidth mode is applied only to one subframe preceding a subframe transmitted during onDuration or a subframe transmitting system information. Accordingly, the number of subframes in which the CRS may be transmitted with a reduced bandwidth is increased, which further improves the performance of the network. This embodiment may be used when the UE120 connected to the cell provides high accuracy measurements.

The network node 110 may adapt the number of subframes in which CRS is transmitted over the full bandwidth based on the type of UE120 connected to the cell. The type of the UE120 may be identified based on an identifier such as the IMEI or the brand/type of the UE 120.

Some method acts for managing transmission of CRS described above with respect to fig. 3 may be performed by the core network node 140. The core network node 140 may comprise the following arrangement depicted in fig. 7. The core network node 140 may comprise a communication circuit 601 and a processing module 602 for communicating with other network nodes. The communication circuit 601 may be, for example, an X2 interface.

The core network node 140 may be configured, e.g. by means of the identification module 603, to identify/distinguish different UE brands/types based on the IMEI of the UE. The identification module 603 may be comprised in the processing unit 602.

The core network node 140 may be further configured, for example by means of the sending module 604, to send an indication of the brand/type to the network node. The indication may be the IMEI of the UE or the brand/type of UE identified by the core network node 140. The sending module 604 may be included in the communication circuit 601.

The embodiments herein for managing CRS transmission may be implemented by one or more processors (such as processing module 602 in a core network node shown in fig. 7) in conjunction with computer program code for performing the functions and acts of the embodiments herein. The program code mentioned above may also be provided as a computer program product, for example in the form of a data carrier carrying computer program code for performing the embodiments herein when loaded into a core network node. One such carrier may be in the form of a CD ROM disc. However, other data carriers, such as memory sticks, are also feasible. The computer program code may also be provided on a server and downloaded to the network node 110 and/or the core network node as pure program code.

The network node 110 may also include a memory 406 that includes one or more memory units. The memory 406 is arranged for storing the obtained information, measurements, data, configurations, schedules and applications for performing the methods herein when executed in the network node 110.

The core network node may also comprise a memory 605 comprising one or more memory units. The memory 605 is arranged for storing the obtained information, measurements, data, configurations, scheduling and applications for performing the methods herein when executed in a core network node.

Those skilled in the art will also appreciate that the above-described identification modules 404, 603 and bandwidth adjustment module 405 may refer to a combination of analog and digital circuitry, and/or one or more processors configured with software and/or firmware, for example, stored in memory 406, 660, executed by one or more processors, such as processing units 403, 602, as described above. One or more of these processors, as well as other digital hardware, may be included in a single Application Specific Integrated Circuit (ASIC), or several processors and various digital hardware may be distributed in several separate components, whether packaged separately or assembled into a system on a chip (SoC).

When the word "comprising" or "comprises" is used, it should be interpreted as non-limiting, i.e. to mean "consisting of at least.

When the word "set" is used herein, it should be interpreted to mean "one or more".

The embodiments herein are not limited to the preferred embodiments described above. Various alternatives, modifications, and equivalents may be used. Accordingly, the above-described embodiments should not be taken as limiting the scope of the invention, which is defined by the appended claims.

Claims (25)

1. A method performed by a network node (110) for managing transmission of one or more cell-specific reference signal, CRS, subframes, wherein the network node (110) operates one or more cells (130, 131, 132), the method comprising:

identifying (301) whether a cell of the one or more cells is actively serving a set of user equipments, UEs (121);

when the cell is not actively serving a set of UEs (121),

transmitting (302) CRS over a first bandwidth in one or more CRS subframes transmitted during a paging occasion and/or in one or more CRS subframes in which system information is transmitted,

transmitting (303) CRS over a second bandwidth in one or more CRS subframes not transmitted during a paging occasion and/or in one or more CRS subframes other than a subframe in which system information is transmitted, the second bandwidth being reduced relative to the first bandwidth;

when the cell is actively serving a set of UEs (121), the set of UEs (121) is configured for discontinuous reception, DRX,

transmitting (304) CRS over the first bandwidth in one or more CRS subframes transmitted in the cell during an on-duration interval of the DRX pattern, and/or in the one or more CRS subframes in which system information is transmitted, and/or in one or more CRS subframes in which downlink DL data is transmitted,

transmitting (305) CRS over the second bandwidth in CRS subframes not transmitted in the cell during the on-duration interval of the DRX, and/or in the one or more CRS subframes other than CRS subframes in which system information is transmitted, and/or in the one or more CRS subframes other than CRS subframes in which downlink DL data is transmitted, the second bandwidth being reduced relative to the first bandwidth.

2. The method of claim 1, wherein when the cell is actively serving a set of UEs (121), the method further comprises:

sending (306) a message to the set of UEs (121) comprising a DRX command, the DRX command indicating the DRX pattern for the set of UEs (121), wherein the on-durations of the DRX pattern are aligned for UEs (120) comprised in the set of UEs (121) such that the UEs (120) have overlapping on-duration intervals.

3. The method of claim 1 or 2, wherein CRS is also transmitted on the first bandwidth in CRS subframes transmitted immediately before or after the CRS subframes transmitted during a paging occasion and/or the CRS subframes in which system information is transmitted and/or the CRS subframes during an on duration interval and/or CRS subframes in which DL data is transmitted.

4. The method according to any of the preceding claims, wherein the paging occasion is only sent in one CRS subframe of each radio frame with paging in the cell not serving a set of UEs (121).

5. The method according to any of the preceding claims, wherein the on-duration intervals of the DRX pattern are aligned with transmission of one or more CRS subframes comprising system information.

6. The method of claim 5, wherein the on duration of the DRX mode is aligned with transmission of a System information Block 1SIB 1.

7. The method according to any of the preceding claims, wherein the DRX pattern has a period in the range of 20ms to 320 ms.

8. The method according to any of the preceding claims, wherein CRS is further transmitted with a first bandwidth in one or more CRS subframes before and/or after the CRS subframes transmitted during the on-duration interval of the DRX pattern or the subframe in which system information is transmitted.

9. The method according to any of the preceding claims, wherein the alignment of the DRX pattern of the UE (120) is deactivated when a threshold per cell connected UE (120) is exceeded.

10. The method according to any of the preceding claims, wherein DL data is sent from the network node to the set of UEs (121) with one periodicity.

11. The method according to any of the preceding claims, wherein the DRX-mode inactivity timer is variable such that a UE (120) connected to the cell has a shorter inactivity timer when the number of connected UEs (120) is below a threshold compared to a UE (120) connected to the cell when the number of connected UEs (120) in the cell exceeds the threshold.

12. The method according to one of the preceding claims, wherein the length of the active timer of the DRX pattern, and/or the period of the on-duration interval of the DRX pattern, and/or the period of the DL data is adaptable to different types of UEs (120) based on a UE identifier.

13. The method of claim 12, wherein the identifier is an International Mobile Equipment Identity (IMEI).

14. The method according to any of the preceding claims, wherein the second bandwidth is reduced to a bandwidth of six central physical resource blocks, PRBs.

15. A network node (110) for managing transmission of cell reference signals, CRS, wherein the network node (110) is configured to operate one or more cells, the network node (110) being configured to:

identifying whether a cell is actively serving a set of UEs (121);

when the cell is not actively serving a set of UEs (121),

transmitting CRS on a first bandwidth in one or more CRS subframes transmitted during a paging occasion and/or on CRS subframes in which system information is transmitted,

transmitting CRS on a second bandwidth in one or more CRS subframes not transmitted during a paging occasion and/or in CRS subframes other than CRS subframes in which system information is transmitted, the second bandwidth being reduced relative to the first bandwidth;

when the cell is actively serving a set of UEs (120), the set of UEs (120) is configured for discontinuous reception, DRX,

transmitting CRS over the first bandwidth in one or more CRS subframes transmitted in the cell, and/or in CRS subframes in which system information is transmitted, and/or in CRS subframes in which downlink DL data is transmitted during an on-duration interval of DRX pattern,

transmitting CRS on the second bandwidth in CRS subframes not transmitted in the cell during on-duration intervals of the DRX pattern, and/or in CRS subframes other than CRS subframes in which system information is transmitted, and/or on CRS subframes other than CRS subframes in which downlink DL data is transmitted, the second bandwidth being reduced relative to the first bandwidth.

16. The network node (110) according to claim 15, wherein the network node (110) is further configured to:

sending a message to the set of UEs (121) comprising a DRX command, the command indicating the DRX pattern for the set of UEs (121), and wherein the on-duration intervals of the DRX pattern are aligned for UEs (120) comprised in the set of UEs (121) such that the UEs (120) have overlapping on-duration intervals.

17. The network node (110) according to claim 15 or 16, wherein the network node (110) is further configured to: transmitting CRS on the first bandwidth in CRS subframes immediately before or after the CRS subframes transmitted during paging occasions and/or the CRS subframes in which system information is transmitted and/or the CRS subframes during on-duration intervals and/or CRS subframes in which downlink DL data is transmitted.

18. The network node (110) according to any of the preceding claims 15 or 17, wherein the network node (110) is further configured to: in a cell not serving a set of UEs (121), a page is sent in only one CRS subframe of each radio frame with a page.

19. The network node (110) according to any one of claims 15-18, wherein the network node (110) is further configured to: the first bandwidth pattern is also applied to one or more subframes before and/or after the subframe or subframes in which system information is transmitted during the on-duration interval of the DRX pattern.

20. The network node (110) according to any of claims 15-19, wherein the network node (110) is further configured to: deactivating the alignment of the DRX pattern of a connected UE (120) per cell when a threshold of the UE (120) is exceeded.

21. The network node (110) according to any of claims 15-20, wherein the network node is further configured to: transmitting DL data to the UE (120) with one periodicity.

22. The network node (110) according to any of the preceding claims 15-21, wherein the network node (110) is further configured to: sending a message comprising a DRX pattern with a variable inactivity timer such that a UE (120) connected to the cell has a shorter inactivity timer when the number of connected UEs (120) in the cell is below a threshold compared to a UE (120) connected to the cell when the number of connected UEs (120) in the cell exceeds the threshold.

23. The network node (110) according to any of the preceding claims 15-22, wherein the network node (110) is further configured to: adapting a length of the activity timer of the DRX pattern, and/or a period of the on-duration interval of the DRX pattern, and/or the period of the DL data, to different types of UEs (120) based on a UE identifier.

24. The network node (110) according to claim 23, wherein the identifier is an International Mobile Equipment Identity (IMEI).

25. The network node (110) according to any of the preceding claims 15-25, wherein the network node (110) is further configured to: reducing the second bandwidth to a bandwidth of six central physical resource blocks, PRBs.