WO2014148964A1

WO2014148964A1 - User equipment, network node and methods therein for reducing transmission of channel state information

Info

Publication number: WO2014148964A1
Application number: PCT/SE2013/051096
Authority: WO
Inventors: Sairamesh Nammi; Cagatay KONUSKAN
Original assignee: Telefonaktiebolaget L M Ericsson (Publ)
Priority date: 2013-03-19
Filing date: 2013-09-19
Publication date: 2014-09-25

Abstract

The exemplary embodiments relate to a method for use in a user equipment (UE); a UE (10) for reducing transmission of feedback of channel quality of channel state; a method for use in a network node; and a network node (12, 13) for initiating reduction of transmission of feedback of channel quality or channel state from the UE 10..The method performed in the UE comprises: obtaining information regarding whether the UE (10) shall mute transmissions and reducing transmission by muting the feedback in accordance with the obtained information. The method performed by the network node (12, 13) includes transmitting said information to the UE 10 and receiving from the UE the feedback regarding channel quality or channel state in unmuted transmissions.

Description

USER EQUIPMENT, NETWORK NODE AND METHODS THEREIN FOR REDUCING TRANSMISSION OF CHANNEL STATE INFORMATION

TECHNICAL FIELD

Embodiments herein relate to a user equipment, a network node and methods therein. In particular, embodiments herein relate to reducing transmission of channel state information from the user equipment to the network node.

BACKGROUND

In a typical radio communications network, wireless terminals, also known as mobile stations and/or user equipments (UEs), communicate via a Radio Access Network (RAN) to one or more core networks. The RAN covers a geographical area which is divided into cell areas, with each cell area being served by a base station, e.g., a radio base station (RBS), which in some networks may also be called, for example, a "NodeB" or "eNodeB". A cell is a geographical area where radio coverage is provided by the radio base station at a base station site or an antenna site in case the antenna and the radio base station are not collocated. Each cell is identified by an identity within the local radio area, which is broadcast in the cell. Another identity identifying the cell uniquely in the whole mobile network is also broadcasted in the cell. The base stations communicate over the radio interface operating on radio frequencies with the user equipments within range of the base stations. The user equipment is communicating with the radio base station over the radio interface in Uplink (UL) transmissions and the radio base station is communicating with the user equipment in Downlink (DL) transmissions. In some versions of the RAN, several base stations may be connected, e.g., by landlines or microwave, to a controller node, such as a radio network controller (RNC) or a base station controller (BSC), which supervises and coordinates various activities of the plural base stations connected thereto. The RNCs are typically connected to one or more core networks. A Universal Mobile Telecommunications System (UMTS) is a third generation mobile communication system, which evolved from the second generation (2G) Global System for Mobile Communications (GSM). The UMTS Terrestrial Radio Access Network (UTRAN) is essentially a RAN using Wideband Code Division Multiple Access (WCDMA) and/or High Speed Packet Access (HSPA) for user equipments. In a forum known as the Third Generation Partnership Project (3GPP), telecommunications suppliers propose and agree upon standards for e.g. third generation networks and further generations, and investigate enhanced data rate and radio capacity. High-Speed

Downlink Packet Access (HSDPA) is an enhanced communications protocol which allows networks based on UMTS to have higher data transfer speeds and capacity.

Specifications for the Evolved Packet System (EPS) have been completed within the 3GPP and this work continues in the coming 3GPP releases. The EPS comprises the Evolved Universal Terrestrial Radio Access Network (E-UTRAN), also known as the Long Term Evolution (LTE) radio access, and the Evolved Packet Core (EPC), also known as System Architecture Evolution (SAE) core network. E-UTRAN/LTE is a variant of a 3GPP radio access technology wherein the radio base stations are directly connected to the EPC core network rather than to RNCs. In general, in E-UTRAN/LTE the functions of a RNC are distributed between the radio base stations, e.g., eNodeBs in LTE, and the core network. As such, the RAN of an EPS has an essentially "flat" architecture comprising radio base stations without reporting to RNCs.

A Channel-Quality Indicator (CQI) is the key indicator for HSDPA DL channel quality and its frequent reporting is essential to maintain a good DL efficiency. The CQI is signaled from UE to NodeB on one or several uplink High Speed - Dedicated Physical Control Channel (HS-DPCCH) physical channels, together with other channel state information, depending on configured downlink transmission mode.

In UL HSPA all user equipments are transmitting using same spreading codes and user equipments are separated by non-orthogonal scrambling codes. This results in that uplink HSPA transmissions need to share an interference-limited resource. Reducing the interference in uplink frequencies is thereby critical to ensure high Signal to Interference Ratio (SIR) levels on uplink transmission channel and maintaining a stable system operation.

The HS-DPCCH transmissions from all UEs contribute to increase the interference level, Rise -over -Thermal (RoT), in UL. However there are scenarios where the HS- DPCCH transmissions could be reduced for lowering the RoT and enabling higher system throughput capacity or increased coverage. Overview of Channel Quality Reporting and Node B Procedures in HSDPA Figure 1 shows the messages exchanged between Node-B and the UE during typical data call set up. From the Common Pilot Channel (CPICH), UE estimates the channel and computes the channel quality information and precoding channel indicator. This information along with Hybrid Automatic Repeat Request (HARQ)

Acknowledgements or non-acknowledgements (ACK or NAK) is reported to Node-B using HS-DPCCH. The periodicity of HS-DPPCH is one subframe (2msec). The structure of HS-DPCCH for a single carrier is shown in Figure 2 when the UE is configured in non Multiple Input Multiple Output (MIMO) mode.

Figure 3 shows HS-DPCCH structure when the UE is configured in MIMO mode with 2 Transmit antennas, the CQI is computed as follows: when 2 transport blocks are preferred by the UE

when 1 transport block is preferred by the UE

where CQI is the channel quality per individual layer.

It can be observed from the above figure that if the CQI is less than 31 , the Rank information is 1 , otherwise Rank information is 2. Precoding Channel Index (PCI) is the precoding information bits selected in the subset of the codebook corresponding to the rank information.

Once the Node-B receives this information, it allocates the required channelization codes, modulation and coding, precoding channel index to the UE after scheduling. This information is conveyed to the UE by high speed shared control channel (HS-SCCH). Once the UE detects the HS-SCCH, downlink transmission starts through data traffic channel using Physical Downlink Shared Channel (HS-PDSCH).

For a 4 branch MIMO, the UE has to inform through feedback channel:

• HARQ ACK information- Same structure that of MIMO mode

· CQI per codeword- Since 2 codewords are defined in the standard, we need two codewords (8 bits)

• Rank Indicator (Rl)- Indicates the number of layers UE is preferring ( 2bits)

• PCI- Precoding Control Index in the Rank Index (4 bits) As shown in Figure 4, UE conveys information about the preferred number of streams, CQI and PCI corresponding to that preferred number of streams. For Type A reporting the 8 information bits are used to describe the CQI information for both the code words, 2 bits are used to convey the rank information and 4 bits are used to describe the PCI information. The resulting composite CQI/RI/PCI report is encoded with a

convolutional code then rate matched to make 40 encoded bits.

In a wireless communication system employing Adaptive Modulation and Coding (AMC) in downlink, Channel Quality Information (CQI) or channel state information from the UE is needed to schedule the users for downlink transmissions. Configuring the reporting period may be problematic. For example, if the reporting period is very small i.e. frequent, the quality of the CQI is very good i.e. the base station is keeping track of the channel. The drawback with frequent reporting is that it requires of higher signaling from UE. This may cause a reduced system throughput for uplink, i.e. uplink capacity. On the other hand if one fixes the reporting period to a high value, due to outdated CQI, downlink throughput is reduced dramatically for some channels.

SUMMARY

An object of embodiments herein is to provide efficient methods to signal channel state information or channel quality information from the user equipment to a network node in a radio communications network.

According to an aspect of embodiments herein the object is achieved by providing a method in a performed in a user equipment (UE) for reducing transmission of feedback of channel quality to a network node, the method comprising: obtaining information regarding whether the UE shall mute transmission regarding feedback indicating channel quality or channel state for at least one subframe, or at least one period, or at least one interval; and that being the case, reducing transmission regarding said feedback by muting transmission of the feedback for the at least one subframe, or the at least one period, or the at least one interval in accordance with the obtained information.

According to another aspect of embodiments herein the object is achieved by providing a method in a network node for initiating reduction of transmission of feedback of channel quality or channel state from a UE the method comprising: transmitting information to the UE informing that the UE shall mute transmission regarding feedback indicating channel quality or channel state for at least one subframe, or at least one period, or at least one interval; and receiving from the UE said feedback regarding channel quality or channel state, in unmuted transmissions According to an aspect of embodiments herein the object is achieved by providing a UE for reducing transmission of feedback of channel quality or channel state to a network node, the UE comprising a processing circuit configured to: obtain information regarding whether the UE shall mute transmission regarding feedback indicating channel quality or channel state for at least one subframe, or at least one period, or at least one interval; and that being the case, the processing circuit is further configured to reduce transmission regarding said feedback by muting transmission of the feedback for the at least one subframe, or the at least one period, or the at least one interval in accordance with the obtained information. According to an aspect of embodiments herein the object is achieved by providing a A network node for initiating reduction of transmission of feedback of channel quality or channel state from a UE the network node comprising: a transmitting circuit configured to transmit information to the UE informing that the UE shall mute transmission regarding feedback indicating channel quality or channel state for at least one subframe, or at least one period, or at least one interval; and a processing circuit configured to receive from the UE said feedback regarding channel quality or channel state, in unmuted transmissions.

Hence, embodiments herein propose methods and apparatuses to reduce channel state information reporting at both network node e.g. a Node B or a radio network controller (RNC) or at the UE. There is also proposed how the information can be conveyed to the UE or how the network node can identify when the UE implements Channel State Information (CSI) reduction.

An advantage with embodiments herein is to reduce battery consumption at the UE.

Another advantage with embodiments herein is to increase data rate since more power may be allocated for data channels. BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments will now be described in more detail in relation to the enclosed drawings, in which:

Figure 1 shows messages exchanged between Node-B and UE during a data call setup;

Figure 2 shows conventional HS-DPCCH structure when the UE is configured in non MIMO mode;

Figure 3 shows conventional HS-DPCCH structure when the UE is configured in

MIMO mode;

Figure 4 is an illustration of the HS-DPCCH slot format when the UE is configured in

MIMO mode with four transmits antennas;

Figure 5 shows a schematic overview depicting a radio communications network;

Figure 6 depicts a method performed in a UE for reducing transmission of feedback in accordance with embodiments herein;

Figure 7 shows a message sequence chart for conveying information via RRC;

Figure 8 shows a message sequence chart for conveying information via HS-SCCH orders;

Figure 9 shows a CSI reduction technique where both ACK and CQI are DTXed in accordance with an exemplary embodiment;

Figure 10 shows a CSI reduction technique where only CQI is DTXed in accordance with an exemplary embodiment;

Figure 1 1 depicts a method performed in a network node for initiating reduction of transmission of feedback from/by a UE in accordance with embodiments herein;

Figure 12 shows a method of determining whether to implement CSI reduction or not in accordance with an embodiment;

Figure 13 shows a method of determining whether to implement CSI reduction or not in accordance with an embodiment;

Figure 14 shows a method in a user equipment according to an exemplary

embodiment;

Figure 15 shows a method in a network node according to an exemplary embodiment Figure 16 shows a block diagram depicting a user equipment according to

embodiments herein.

Figure 17 shows a block diagram depicting a network node according to

embodiments herein. DETAILED DESCRIPTION

Fig. 5 is a schematic overview depicting a radio communications network 1. The radio communications network 1 comprises one or more Radio Access Networks (RANs) and one or more Core Networks (CNs). The radio communications network 1 may use a number of different technologies, such as Long Term Evolution (LTE), LTE-Advanced, Wideband Code Division Multiple Access (WCDMA), Global System for Mobile communications/Enhanced Data rate for GSM Evolution (GSM/EDGE), Worldwide Interoperability for Microwave Access (WMax), or Ultra Mobile Broadband (UMB), just to mention a few possible implementations. The illustrated examples herein are exemplified in a HSPA network.

In the radio communications network 1 , a user equipment (UE) 10, also known as a mobile station and/or a wireless terminal, communicates via a RAN to one or more core CNs. It should be understood by the skilled in the art that UE is a non-limiting term which means any wireless terminal, Machine Type Communication (MTC) device or node e.g. Personal Digital Assistant (PDA), laptop, mobile, sensor, relay, mobile tablets or even a small base station communicating within respective cell.

The radio communications network 1 covers a geographical area which is divided into cell areas, e.g. a cell 11 being served by a radio base station 12. The radio base station 12 may also be referred to as a first radio base station. The radio base station 12 may be referred to as e.g. a Node B, an evolved Node B (eNB, eNode B), a base transceiver station, Access Point Base Station, base station router, or any other network unit capable of communicating with a user equipment within the cell served by the radio base station depending e.g. on the radio access technology and terminology used. The radio base station 12 may serve one or more cells, such as the cell 1 1. A radio base station may also be viewed as a radio network node since it belongs to the RAN.

A cell is a geographical area where radio coverage is provided by the radio base station equipment at a base station site. The cell definition may also incorporate frequency bands and radio access technology used for transmissions, which means that two different cells may cover the same geographical area but using different frequency bands. Each cell is identified by an identity a so-called cell identity within the local radio area, which is broadcasted in the cell. Another identity identifying the cell 11 uniquely in the whole radio communications network 1 is also broadcasted in the cell 1 1. The radio base station 12 communicates over the air or radio interface operating on radio frequencies with the UE 10 within the range of the radio base station 12. The UE 10 transmits data over the radio interface to the radio base station 12 in Uplink (UL) transmissions and the radio base station 12 transmits data over an air or radio interface to the user equipment 10 in Downlink (DL) transmissions. In some versions of the radio communications network 1 , several base stations are typically connected, e.g. by landlines or microwave, to a Radio Network Controller 13 or a BSC, which supervises and coordinates various activities of the plural base stations connected thereto. The RNCs are typically connected to one or more CNs.

According to embodiments herein the user equipment 10 does not transmit CSI or feedback of channel quality, for e.g. HSDPA transmissions, back to the radio base station 12 over a certain time interval, subframes, or part of subframes, or period. This way of muting the transmissions is called Discontinuous transmission, DTX. Recall figure 2 showing the CSI field being 1 sub-frame long or 2 ms. As shown the CSI includes the CQI i.e. the channel quality indicator or channel quality information and the CSI also include the HARQ-ACK. Hence, the CQI corresponds to the feedback of channel quality that is transmitted with the CSI in e.g. the HS-DPCCH in the uplink from the UE to the radio base station. So when the CSI reduction is applied by the UE i.e. reduction of transmission of the feedback of channel quality CQI of the CSI, the UE is configured to mute transmission of the feedback of channel quality CQI of the CSI. This may be done by discontinuously transmitting the CQI of the CSI. It should be mentioned that the CSI may include other information such as the precoding index PCI and/or the rank indicator RI.An intention and an advantage of the proposed CSI reduction schemes is to reduce the signaling overhead of a control channel such as the HS-DPCCH. Another advantage is that power consumption at the UE can be saved. This is because less signaling overhead is required by e.g. muting or DTX:ing the CQI of the CSI. This power can instead be used for other data traffic or voice channels thereby improving the user experience. Moreover, with less frequent transmission of CSI or the CQI of the CSI, the interference to the other uplink users is minimized. Figure 6 illustrates the main steps performed by a UE for reducing transmission of feedback of channel quality to a network node or a base station or a RNC, in accordance with embodiments herein. As shown, the method comprises:

601 : obtaining information regarding whether the UE shall mute transmission regarding feedback indicating channel quality or channel state for at least one subframe, or at least one period, or at least one interval; and that being the case, 602: reducing transmission regarding said feedback by muting transmission of the feedback for the at least one subframe, or the at least one period, or the at least one interval in accordance with the obtained information.

According to an exemplary embodiment, in the obtaining step 601 , the method comprises obtaining, by the UE, said information in a radio resource control (RRC) message from the network node (base station). The information comprising a status of a a CSI reduction bit and a number of transmit time intervals (TTIs) the UE has to perform CSI reduction or CSI reporting. As an example, Figure 7 discloses this above described embodiments. As shown, information is conveyed from the Network or network node, exemplified her as the RNC 13, to the user equipment 10. Note that a base station or Node B 12 may also convey said information. In the example of figure 7 the conveying is done via RRC signalling from the RNC 13. The network or RNC 13 is shown conveying the information about the CSI reduction via RRC re-configuration. The message sequence chart is as shown Figure 7.

Action 701. The RNC 13 initially transmits a RRC message indicating no reduction.

Action 702. The UE 10 transmits a RRC response acknowledging the reception of the RRC message.

Action 703. The radio base station or Node B 12 transmits a Primary Common

Pilot Channel (P-CPICH) to the UE 10.

Action 704. The UE 10 determines CSI based on the P-CPICH and sends feedback to the radio base station 12 in reports indicating CSI.

Action 705: The decision to do or perform RRC re-configuration may be performed or done via a decision from the Node B 12. The decision may be taken based on speed of the UE 10, location of UE 10 and/or data available as disclosed below. The RNC 13 then transmits an RRC re-configuration message. The RRC re-configuration message may comprise:

- a. Status of CSI reduction bit - either on or off;

- b. How many TTIs it the UE 10 to do CSI reduction or normal CSI reporting.

Action 706. The UE 10 acknowledges the RRC re-configuration message by sending a RRC response. The UE 10 then uses the RRC re-configuration mesage when muting feedback e.g. CQI of the CSI over certain subframes, periods, intervals as indicated in the RRC-reconfiguration message i.e. in accordance with the information obtained from the RRC re-configuration message. According to an exemplary embodiment, the step 602 of reducing transmission comprises muting by the UE which is performed by e.g. DTX:ing, of the feedback in accordance with the obtained information as explained earlier.

According to an exemplary embodiment, the information may be obtained from the network node in a high speed shared control channel (HS-SCCH) order instead of using the RRC message. The feedback regarding channel quality or channel which is not muted is transmitted by the UE to the network node in a high speed dedicated physical control channel (HS-DPCCH) i.e. in unmuted transmissions.

Referring to Figure 8 there is shown an exemplary embodiment where the information is conveyed in a HS-SCCH order. The message sequence chart includes.:

Action 801. The radio base station or network node or Node B 12 transmits a P- CPICH to the UE 10.

Action 802. The UE 10 determines CSI based on the P-CPICH and sends feedback to the radio base station 12 in reports indicating CSI e.g. in HS-DPCCH.

Action 803. The radio base station 12 conveys information in HS-SCCH order regarding feedback set up to the user equipment 10. By set up is meant information regarding whether the UE shall mute transmission of the feedback or not. Thus, the radio base station 12 on its own can convey the information about CSI-reduction via HS-SCCH orders. The HS-SCCH order can convey the information as

- a. Switching on of CSI-Reduction or Switching off of CSI-Reduction, where the exact duration is signaled via RRC.

- b. On/Off status and also the duration of the CSI-reduction.

Action 804. The UE 10 transmits feedback according to the HS-SCCH order, that is muting some subframes, intervals, or certain data back to the radio base station 12, which subframes, intervals, or data are indicated in the HS-SCCH order.

According to yet another exemplary embodiment, obtaining the information regarding whether the UE shall mute transmission regarding feedback indicating channel quality or channel state may be performed internally with the UE i.e. the decision is performed within the UE to perform CSI reduction for at least one subframe, or at least one period, or at least one interval. This has the advantage that the UE has better knowledge on whether to save power and the UE does not need to receive a high level signaling or order from the network node which leads to less signaling from the network node. The decision to perform CSI reduction may be based on the speed of the UE or based on a signal to interference and noise ratio (SINR) or based on activity timer when there is no data to receive from the network node. This is further explained below.

Below some examples are presented to better understand the exemplary embodiments herein. Below are proposed two CSI reduction schemes. Let's assume that the CSI reporting period is 2msec as configured by RRC message. It should be mentioned that without CSI reporting reduction, the UE needs to report HARQ, CQI of a CSI for each subframe as explained earlier.

Figure 9 shows the proposed scheme or method where the HS-DPCCH is DTXed in certain subframes. In an embodiment as explained in Figs 7-8 or below, the exact DTX period may be configurable by Node B or RNC. In another embodiment, the user equipment may DTX for certain duration on its own i.e. the decision is taken internally. As shown in Figure 9, certain sub frames 81 , 82 e.g. both ACK and CQI, are DTXed. Figure 10 shows another scheme in which a HS-DPCCH transmission is performed and where only certain data 91 , 92, e.g. CQI, is DTXed, but HARQ- ACK is transmitted whenever necessary.

According to yet another embodiment herein, there is provided a method in a network node, Node B or RNC, for initiating reduction of transmission of feedback of channel quality or channel state from a UE.

The main steps of the method performed by the network node are depicted in Figure 11. The method comprises:

1 101 : transmitting information to the UE informing that the UE shall mute transmission regarding feedback indicating channel quality or channel state for at least one subframe, or at least one period, or at least one interval; and

1 102: receiving from the UE said feedback regarding channel quality or channel state, in unmuted transmissions.

As explained earlier, the information may be transmitted by the network node to the UE in a RRC message. The information comprising a status of a CSI reduction bit and a number of TTIs the UE has to perform CSI reduction or CSI reporting. Also explained earlier that the information may be transmitted from the network node to the UE in a HS-SCCH order and wherein said feedback indicating channel quality comprises a CQI.

According to an embodiment, the method performed by the network node further comprises measuring the speed of the UE and comparing the measured speed with a speed threshold and if the UE speed is less than the speed threshold, transmitting said information informing that the UE shall mute transmission regarding feedback indicating channel quality or channel state for at least one subframe, or at least one period, or at least one interval.

In another embodiment, the method performed by the network node comprises determining whether the UE is at cell edge and that being the case, transmitting said information informing that the UE shall mute transmission regarding feedback indicating channel quality or channel state for at least one subframe, or at least one period, or at least one interval.

Figure 12 illustrates the embodiments described above to initiate CSI

reduction. The triggering of CSI reduction may be done by either radio base station or

RNC (or also the UE as explained before).

In this section it is described how the radio base station may trigger the CSI reduction. Note that a combination of these methods may be used to initiate CSI reduction.

Scenario 1 : Based on Speed as illustrated in Figure 12:

Since the channel changes slowly in general for slow speed channels, sending frequently CQI reports is unnecessary. However, it should be mentioned that HARQ-ACK is needed when the data is transmitted from downlink i.e. from the network node to the UE. Hence by using this approach of scenario 1 CSI reduction technique as shown in

Figure 12 may be implemented. There are many techniques to find the speed of the channel, for example from uplink channel estimates.

The actions to implement the algorithm performed by the network node as shown in Figure 12 include:

' Action 1201 : Assuming a new cycle starts and the UE is ready for downlink scheduling. Set the speed flag = 0.

Action 1202: Measure the UE speed from uplink channel estimates.

Action 1203: Compute the speed. Let S_Th be speed threshold as set by the radio base station. This threshold may be a design parameter. Action 1204: Set the speed flag to off if the UE speed is less than S_Th. Else is S_Th = on;

Action 1205: If the UE speed flag is off (means low speed), then use CSI reduction technique as explained earlier. Go to Action 1006 else Go to Action 1007.

Action 1206 Send the signal as described above in e.g. figures 7-8 to inform the user equipment 10 about the CSI reduction.

Action 1207: Cycle Stops, End. This is the action taken when the UE speed flag is on. Scenario 1 : Based on available data in the network node:

The main idea behind this method or scenario is the following: Assume that for a number of applications (let say b applications), such as file downloading where the UE is scheduled in bursts. In that case, continuous transmission of CSI causes resource wastage. Therefore based on the available data for the specific UE the network node may initiate the CSI reduction technique. When no data is scheduled for the UE, CSI reduction of Figure 7 may be used e.g. by completely DTXing the HARQ-ACK and CQI.

Referring to Figure 13 there is illustrated the embodiments described above to initiate CSI reduction based on the location of the UE

The main idea behind this approach is that if the UE is at cell edge or at low Signal to Interference plus Noise Ratio (SINR) then the UE is power limited and either the UE requires a robust modulation and coding scheme, for example Quadrature Phase Shift Keying (QPSK) with low code rate, or there is no data to schedule to that specific UE. In that scenario CSI reduction in accordance with the examples of Figures 8 and 9 may be used.

An example of the actions to implement the algorithm is disclosed in Figure 13, and the actions are as follows:

Action 1301 : Assuming a new cycle starts, the network node checks whether the UE is at cell edge?

Action 1302: If the UE is at cell edge, then use CSI reduction(s) techniques as explained earlier else go to Action 1304.

Action 1303: Send the signal as outlined above in e.g. figures 7-8 to inform the UE about the CSI reduction i.e. using RRC message or HS-SCCH order from the network node. Action 1304: Cycle Stops. According to an embodiment, a decision on whether the UE is at cell edge or not may be taken based on e.g. a first option neighbour list or based on a second option.. Note that, the embodiments herein work for any algorithm other than these Options.

Option 1 : Based on Neighbour list

If the neighbour list of network node or base station or the RNC is greater than some predetermined number, one may conclude that the corresponding UE is at the cell edge. Option 2: Based on Uplink measurements

From the uplink measurements, for example UE pilot signal, the network node may conclude or decide that the UE is at cell edge or not based on the signal strength or the pilot signal.

As explained earlier, the UE may decide on its own whether to have CSI reduction or not. This is referred to below as UE autonomous CSI reduction.

UE autonomous CSI reduction:

In this embodiment the UE may decide to have CSI reduction for certain TTIs. For example the UE may decide based on speed, or based on SINR or based on activity timer when there is no data to receive. The UE may communicate to the radio base station or network node about the CSI reduction status or/and the duration of CSI reduction.

In another embodiment, the UE may autonomously perform CSI reduction without informing the radio base station or network node. Figure 14 discloses a flow chart depicting a exemplary method in the UE for transmitting feedback of channel quality or channel state to a network node, such as the radio base station or the RNC, in the radio communications network.

Action 1401. The UE obtains information regarding whether the UE should mute transmission regarding feedback indicating channel quality or channel state for a certain subframe, period, or certain feedback. This information may also be defined as information about DTX for feedback, or as information indicating muted feedback. In other words the UE obtains information indicating a muting of feedback for a subframe, TTI, or a feedback type. The information may be obtained by deciding within the UE based on speed, or based on SINR or based on activity timer when there is no data to receive, as explained before. The information may additionally or alternatively be obtained by receiving the information or data from the network node indicating reduced CSI feedback.

Action 1402. The UE transmits feedback based on the obtained information. Thus, the UE mutes certain feedback based on the obtained information.

Figure 15 discloses a flow chart depicting an exemplary method in the network node, e.g. radio base station or RNC, for configuring or transmitting information about feedback of channel quality or channel state from the UE in a radio communications network.

Action 1501. The network node may determine, or obtain indication regarding muting of feedback indicating channel quality or channel state for a certain subframe, period, or certain feedback. E.g. the network node may determine based on UE speed, UE location and/or data available for the UE, a muting pattern such as ACK and/or CQI are DTXed.

Action 1502. The network node transmits the information regarding the muting of the feedback to the UE thereby configuring the feedback transmission of the UE.

Figure 16 is a block diagram depicting a UE 10 in accordance with exemplary embodiments herein. The user equipment 10 comprises an obtaining circuit 1601 , which may comprise a processing circuit to obtain the information regarding the muting of the feedback transmissions. The user equipment 10 further comprises a feedback circuit 1602 configured to transmit feedback of the channel quality according to the obtained information, i.e. muting some subframes, or for a certain feedback such as feedback indicating ACK and/or CQI are DTXe.

The embodiments herein for configuring the UE 10 for feedback transmission may be implemented through one or more processors, such as a processing circuit 1603 in the UE 10. The processing circuit 1603 is thus configured to obtain information regarding whether the UE 10 shall mute transmission regarding feedback indicating channel quality or channel state for at least one subframe, or at least one period, or at least one interval; and that being the case, the processing circuit 1603 is further configured to reduce transmission regarding said feedback by muting transmission of the feedback for the at least one subframe, or the at least one period, or the at least one interval in accordance with the obtained information.

As previously described, the information is obtained in a RRC message from the network node, the information comprising a status of a channel state information, CSI, reduction bit and a number of transmit time intervals said UE 10 has to perform CSI reduction or CSI reporting. The processing circuit 1603 is further configured to mute transmission of the feedback by discontinuously transmitting, DTX, of the feedback in accordance with the obtained information.

According to another embodiment, the information is obtained in a HS-SCCH order and wherein said feedback indicating channel quality or channel state comprises a channel quality indicator, CQI. The feedback circuit 1601 is configured to transmit via an antenna (not shown), in a HS-DPCCH, said feedback regarding channel quality or channel state, to the network node, in unmuted transmissions.

Further the processing circuit 1603 is configured to obtain said information by deciding within the UE 10 to perform CSI reduction for at least one subframe, or at least one period, or at least one interval. The processing circuit 1603 is configured to decide to perform CSI reduction based on speed of the UE 10 or based on a signal to interference and noise ratio (SINR) or based on activity timer when there is no data to receive.

It should be mentioned that the processing circuit 1603 together with a computer program code may be used to perform the functions and/or method steps of the embodiments herein. The program code mentioned above may also be provided as a computer program product, for instance in the form of a data carrier carrying computer program code for performing embodiments herein when being loaded into the UE 10. One such carrier may be in the form of a CD ROM disc. It is however feasible with other data carriers such as a memory stick. The computer program code may furthermore be provided as pure program code on a server and downloaded to the UE 10.

The UE 10 may further comprise a memory 1604 for storing CSI, muting patterns, UE, speed, data available, SINR, UE location, application to perform the method when being executed and/or similar.

Referring to Figure 17 there is shown a network node 12, 13 to in accordance with embodiments herein. The network node 12, 13 comprises a determining circuit 1705 configured to determine the time period, the certain feedback information that UE10 is to mute feedback transmissions. The network node 12, 13 further comprises a transmitting circuit 1706 configured to transmit the information regarding the muting of the feedback transmissions.

The embodiments herein for configuring the UE 10 for feedback transmission may be implemented through one or more processors, such as a processing circuit 1707 in the network node 12, 13 depicted in Fig. 17, together with computer program code for performing the functions and/or method steps of the embodiments herein. The program code mentioned above may also be provided as a computer program product, for instance in the form of a data carrier carrying computer program code for performing embodiments herein when being loaded into the network node. One such carrier may be in the form of a CD ROM disc. It is however feasible with other data carriers such as a memory stick. The computer program code may furthermore be provided as pure program code on a server and downloaded to the network node12, 13.

Hence, the network node 12, 13 for initiating reduction of transmission of feedback of channel quality or channel state comprises, as shown a transmitting circuit 1706 configured to transmit information to the UE 10 informing that the UE 10 shall mute transmission regarding feedback indicating channel quality or channel state for at least one subframe, or at least one period, or at least one interval; and the network node 12, 13 may further comprise a processing circuit 1707, which may be part of the processing circuit 1707 configured to receive from the UE 10 said feedback regarding channel quality or channel state, in unmuted transmissions.

The transmitting circuit 1706 is configured to transmit said information in RRC message, the information comprising a status of a channel state information, CSI, reduction bit and a number of transmit time intervals said UE 10 has to perform CSI reduction or CSI reporting. The transmitting circuit 1606 may further be configured to transmit said information in a HS-SCCH order and wherein said feedback indicating channel quality or channel state comprises a CQI.

The network node 12, 13 may further be configured to measure the speed of the UE and to compare said speed with a speed threshold and if the UE speed is less than the speed threshold, the transmitting circuit 1606 is configured to transmit said information informing that the UE 10 shall mute transmission regarding feedback indicating channel quality or channel state for at least one subframe, or at least one period, or at least one interval. The network node 12, 13 may further be configured to determine whether the UE 10 is at cell edge and that being the case, the transmitting circuit 1606 is configured to transmit said information informing that the UE 10 shall mute transmission regarding feedback indicating channel quality or channel state for at least one subframe, or at least one period, or at least one interval.

As shown, the network node 12, 13 may further comprise a memory 1708 for storing CSI, muting patterns, UE speed, data available for the user equipment 10, SINR, UE location, application to perform the method when being executed and/or similar. Those skilled in the art will also appreciate that the various "circuits" described may refer to a combination of analog and digital circuits, and/or one or more processors configured with software and/or firmware (e.g., stored in memory) that, when executed by the one or more processors, perform as described above. One or more of these processors, as well as the other digital hardware, may be included in a single Application- Specific Integrated Circuit (ASIC), or several processors and various digital hardware may be distributed among several separate components, whether individually packaged or assembled into a System-on-a-Chip (SoC).

Throughout this disclosure, the word "comprise" or "comprising" has been used in a non-limiting sense, i.e. meaning "consist at least of". Although specific terms may be employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation. In particular, it should be noted that although terminology from 3GPP LTE of HSPA has been used in this disclosure to exemplify the invention, this should not be seen as limiting the scope of the invention to only the aforementioned system. Other wireless systems, including LTE-A (or LTE-Advanced), UMTS, WiMax, and wireless LAN, may also benefit from exploiting the ideas covered within this disclosure. The present embodiments may be realized in many ways. For example, one embodiment includes a computer program in the form of instructions stored in the UE as explained above. The instructions executable by the UE and stored on a computer- readable medium perform the method as previously described and as described in the pending claims relating to the UE.

In another example, one embodiment includes a computer program in the form of instructions stored in the network node as explained above. The instructions executable by the network node and stored on a computer-readable medium perform the method as previously described and as described in the pending claims relating the network node.

Abbreviations

MIMO - Multiple input multiple output

Tx Transmitter

HSDPA High Speed Downlink Packet Access HARQ Hybrid automatic repeat request

CRC Cyclic redundancy check

NAK non-acknowledgement

ACK acknowledgement

CC Chase combining

UE User Equipment

CQI - Channel quality information

MMSE Minimum Mean Square Error

TTI Transmit Time Interval

PCI Precoding control index

Claims

A method performed in a user equipment, UE, (10) for reducing

transmission of feedback of channel quality to a network node (12, 13), the method comprising:

- obtaining (601) information regarding whether the UE (10) shall mute transmission regarding feedback indicating channel quality or channel state for at least one subframe, or at least one period, or at least one interval; and that being the case,

- reducing (602) transmission regarding said feedback by muting transmission of the feedback for the at least one subframe, or the at least one period, or the at least one interval in accordance with the obtained information.

The method according to claim 1 wherein obtaining (601) comprises obtaining said information in a radio resource control, RRC, message from the network node (12, 13), the information comprising a status of a channel state information, CSI, reduction bit and a number of transmit time intervals said UE (10) has to perform CSI reduction or CSI reporting.

The method according to claim 1 or claim 2 wherein reducing (602) by muting comprises discontinuously transmitting, DTX, of the feedback in accordance with the obtained information.

The method according to anyone of claims 1-3 wherein obtaining (601) comprises obtaining said information, from the network node (12, 13) in a high speed shared control channel, HS-SCCH order and wherein said feedback indicating channel quality or channel state comprises a channel quality indicator, CQI.

The method according to anyone of claims 1-4 further comprising transmitting, in a high speed dedicated physical control channel, HS- DPCCH, said feedback regarding channel quality or channel state, to the network node (12, 13), in unmuted transmissions.

The method according to claim 1 wherein obtaining (601) comprises obtaining said information by deciding within the UE (10) to perform CSI reduction for at least one subframe, or at least one period, or at least one interval.

The method according to claim 6 wherein deciding comprises deciding to perform CSI reduction based on speed of the UE (10) or based on a signal to interference and noise ratio, SINR, or based on activity timer when there is no data to receive.

A method performed in a network node (12, 13) for initiating reduction of transmission of feedback of channel quality or channel state from a user equipment, UE, (10) the method comprising:

- transmitting (1101) information to the UE (10) informing that the UE (10) shall mute transmission regarding feedback indicating channel quality or channel state for at least one subframe, or at least one period, or at least one interval; and

- receiving (1102) from the UE (10) said feedback regarding channel quality or channel state, in unmuted transmissions.

The method according to claim 8 wherein transmitting (1 101) comprises transmitting said information in a radio resource control, RRC, message, the information comprising a status of a channel state information, CSI, reduction bit and a number of transmit time intervals said UE (19) has to perform CSI reduction or CSI reporting.

10. The method according to claim 8 wherein transmitting (1 101) comprises, transmitting said information in a high speed shared control channel, HS- SCCH order and wherein said feedback indicating channel quality comprises a channel quality indicator, CQI.

1 1. The method according to anyone of claims 8-10 further comprising,

measuring the speed of the UE (10) and comparing said speed with a speed threshold and if the UE speed is less than the speed threshold, transmitting (1101) said information informing that the UE (10) shall mute transmission regarding feedback indicating channel quality or channel state for at least one subframe, or at least one period, or at least one interval.

12. The method according to anyone of claims 8-10 further comprising,

determining whether the UE (10) is at cell edge and that being the case, transmitting said information informing that the UE (10) shall mute transmission regarding feedback indicating channel quality or channel state for at least one subframe, or at least one period, or at least one interval.

13. A user equipment, UE, (10) for reducing transmission of feedback of

channel quality or channel state to a network node (12, 13), the UE (10) comprising a processing circuit (1603) configured to:

- obtain information regarding whether the UE (10) shall mute transmission regarding feedback indicating channel quality or channel state for at least one subframe, or at least one period, or at least one interval; and that being the case, the processing circuit (1603) is further configured to

- reduce transmission regarding said feedback by muting transmission of the feedback for the at least one subframe, or the at least one period, or the at least one interval in accordance with the obtained information.

14. The UE (10) according to claim 13 wherein the information is obtained in a radio resource control, RRC, message from the network node (12, 13), the information comprising a status of a channel state information, CSI, reduction bit and a number of transmit time intervals said UE (10) has to perform CSI reduction or CSI reporting.

15. The UE (10) according to claim 13 or claim 14 wherein the processing circuit (1603) is configured to mute transmission of the feedback by discontinuously transmitting, DTX, of the feedback in accordance with the obtained information.

16. The UE (10) according to anyone of claims 13-15 wherein the information is obtained in a high speed shared control channel, HS-SCCH order and wherein said feedback indicating channel quality or channel state comprises a channel quality indicator, CQI.

17. The UE (10) according to anyone of claims 13-16 comprises a feedback circuit (1602) configured to transmit, in a high speed dedicated physical control channel, HS-DPCCH, said feedback regarding channel quality or channel state, to the network node, in unmuted transmissions.

18. The UE (10) according to claim 13 wherein the processing circuit (1603) is configured to obtain said information by deciding within the UE (10) to perform CSI reduction for at least one subframe, or at least one period, or at least one interval.

19. The UE (10) according to claim 18 wherein the processing circuit (1603) is configured to decide to perform CSI reduction based on speed of the UE (10) or based on a signal to interference and noise ratio (SINR) or based on activity timer when there is no data to receive.

20. A network node (12, 13) for initiating reduction of transmission of feedback of channel quality or channel state from a user equipment, UE, (10) the network node (12, 13) comprising:

- a transmitting circuit (1706) configured to transmit information to the UE (10) informing that the UE (10) shall mute transmission regarding feedback indicating channel quality or channel state for at least one subframe, or at least one period, or at least one interval; and

- a processing circuit (1707) configured to receive from the UE (10) said feedback regarding channel quality or channel state, in unmuted transmissions.

21. The network node (12, 13) according to claim 20 wherein the transmitting circuit (1707) is configured to transmit said information in a radio resource control, RRC, message, the information comprising a status of a channel state information, CSI, reduction bit and a number of transmit time intervals said UE (10) has to perform CSI reduction or CSI reporting.

22. The network node (12, 13) according to claim 20 wherein the transmitting circuit (1706) is configured to transmit said information in a high speed shared control channel, HS-SCCH order and wherein said feedback indicating channel quality or channel state comprises a channel quality indicator, CQI.

23. The network node (12, 13) according to anyone of claims 20-22 is further configured to measure the speed of the UE (12, 13) and to compare said speed with a speed threshold and if the UE speed is less than the speed threshold, the transmitting circuit (1706) is configured to transmit said information informing that the UE (10) shall mute transmission regarding feedback indicating channel quality or channel state for at least one subframe, or at least one period, or at least one interval.

24. The network node (12, 13) according to anyone of claims 20-23 is further configured to determine whether the UE (10) is at cell edge and that being the case, the transmitting circuit (1706) is configured to transmit said information informing that the UE (10) shall mute transmission regarding feedback indicating channel quality or channel state for at least one subframe, or at least one period, or at least one interval.

25. A Computer program, comprising computer readable code means, which when run in a processing unit comprised in a user equipment (10) according to claims 13-19 causes the UE (10) to perform the

corresponding method according to claims 1-7.

26. A Computer program product comprising a computer program

according to claim 25.

27. A Computer program, comprising computer readable code means, which when run in a processing unit comprised in a network node (12, 13) according to claims 20-24 causes the network node (12, 13) to perform the corresponding method according to claims 8-12.

28. A Computer program product comprising a computer program

according to claim 27.