HK1232035B - Method and arrangement for reporting channel state information in a telecommunication system - Google Patents

Description

Method and apparatus for reporting channel state information in a telecommunications system

Technical Field

The embodiments herein relate to methods and apparatus in user equipment and methods and apparatus in base stations, and more particularly, to reporting channel state information.

Background Art

A communication device, such as a mobile station, is also referred to as, for example, a mobile terminal, a wireless terminal, and/or a user equipment (UE). A mobile station is enabled to communicate wirelessly within a cellular communication network or wireless communication system (sometimes also referred to as a cellular radio system). For example, communication can occur between two mobile stations, between a mobile station and a conventional phone, and/or between a mobile station and a server via the Radio Access Network (RAN) and possibly one or more core networks included within the cellular communication network.

A mobile station may also be referred to as user equipment, a terminal, a mobile phone, a cellular phone, or a laptop computer with wireless capabilities, to mention only a few additional examples. A mobile station in this context may be, for example, a portable, pocket-storable, handheld, computer-containing, or vehicle-mounted mobile device that enables communication of voice and/or data with another entity (such as another mobile station or a server) via a radio access network.

A cellular communication network covers a geographical area divided into cell areas, each of which is served by a base station, such as a radio base station (RBS), which may sometimes be referred to as, for example, an eNB, eNodeB, NodeB, B-node, or BTS (base transceiver station), depending on the technology and terminology used. Base stations may belong to different categories, such as macro eNodeB, home eNodeB, or pico base station, based on their transmission power and, consequently, cell size. A cell is a geographical area provided with radio coverage by a base station at a base station site. One base station located at a base station site may serve one or several cells. In addition, each base station may support one or several communication technologies. A base station communicates with mobile stations within range of the base station via an air interface operating on radio frequencies.

In some radio access networks, several base stations may be connected to a radio network controller, such as a Radio Network Controller (RNC) in Universal Mobile Telecommunications System (UMTS), and/or to each other, for example, via landlines or microwave.

In 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE), base stations, which may be referred to as eNodeBs or even eNBs, may be directly connected to one or more core networks.

UMTS is a third-generation mobile communications system, an evolution of GSM. It aims to provide improved mobile communications services based on Wideband Code Division Multiple Access (WCDMA) access technology. The UMTS Terrestrial Radio Access Network (UTRAN) is essentially a radio access network that uses Wideband Code Division Multiple Access for mobile stations. 3GPP has begun further evolving the radio access network technologies based on UTRAN and GSM. This evolution of UTRAN is generally referred to as Evolved UTRAN (E-UTRAN) or LTE.

In the context of this disclosure, the expression downlink (DL) is used for the transmission path from a base station to a mobile station. The expression uplink (UL) is used for the transmission path in the opposite direction, ie from a mobile station to a base station.

Improved support for heterogeneous network operation is part of the ongoing enhancements to the LTE specifications for 3GPP LTE Release 10. In a heterogeneous network, a mix of cells of different sizes and overlapping coverage areas are deployed. One example of such a deployment is a picocell deployed within the coverage area of a macrocell. A picocell is a small cell base station that typically covers a small area. As such, the small cell base station transmits at low power. Consequently, the small cell base station can be referred to as a low-power node. Other examples of low-power nodes in a heterogeneous network are femtocells and repeaters. As will be discussed below, the large difference in output power (e.g., 46 dBm in a macrocell and less than 30 dBm in a picocell) results in different interference scenarios than would be seen in a network where all base stations have the same output power.

The goal of deploying low-power nodes (such as pico base stations) within the macro coverage area is to improve system capacity through cell splitting gain and to provide users with a wide-area experience of very high-speed data access across the entire network. Heterogeneous deployments are particularly effective in covering traffic hotspots, i.e., small geographic areas with high user density, such as those served by pico cells, and they represent an alternative deployment to denser macro networks.

FIG1 illustrates an example of a macro and pico cell deployment in a heterogeneous network 100 comprising a macro cell 110 and three pico cells 120. The most basic approach to operating a heterogeneous network is to apply frequency separation between the different layers in heterogeneous network 100 in FIG1 , namely, between macro cell 110 and pico cell 120. Frequency separation between the different layers is achieved by allowing the different layers to operate on different, non-overlapping carrier frequencies. In this way, any interference between the layers of the cell is avoided. In the absence of macrocell interference towards pico cell 120 in FIG1 , cell splitting gains are achieved when the pico cells can use all resources simultaneously. A disadvantage of operating the layers on different carrier frequencies is that it can lead to inefficient resource utilization. For example, in the case of low activity in pico cell 120, it may be more efficient to use all carrier frequencies in macro cell 110 and then essentially turn off pico cell 120. However, carrier frequency splitting across layers is typically performed statically.

Another related way of operating heterogeneous networks is to share radio resources on the same carrier frequency by coordinating transmissions across macro and pico cells. This type of coordination is called inter-cell interference coordination (ICIC), where certain radio resources are allocated for macro cells during a certain time period, while the remaining resources can be accessed by pico cells without interference from the macro cells. Depending on the traffic scenarios across the layers, this resource splitting can change over time to adapt to different traffic needs. Compared to the carrier frequency splitting mentioned above, this way of sharing radio resources across layers can be done more or less dynamically, depending on the implementation of the interfaces between the nodes in the heterogeneous network. In LTE, the X2 interface has been specified for exchanging different types of information between base station nodes. An example of such an information exchange is that a base station can inform other base stations that it will reduce its transmit power on certain resources.

Time synchronization between base station nodes is required to ensure that cross-layer ICIC will work effectively in heterogeneous networks. This is particularly important for time-domain based ICIC schemes that share resources in time on the same carrier.

LTE uses Orthogonal Frequency Division Multiplexing (OFDM) in the downlink and Discrete Fourier Transform Extended OFDM (DFT Extended OFDM) in the uplink. In OFDM transmission, a set of modulation symbols is transmitted via narrowband and orthogonal subcarriers, where the number of subcarriers defines the transmission bandwidth of the OFDM signal. In DFT Extended OFDM, the set of modulation symbols is first precoded before generating the OFDM signal, where the purpose of precoding is to provide power characteristics of the OFDM signal suitable for transmitting to power-limited terminals. The basic LTE physical resources can thus be viewed as a time-frequency grid as shown in Figure 2, where each resource element corresponds to a subcarrier during one OFDM symbol interval. Part of the OFDM symbol interval is a cyclic prefix introduced to mitigate inter-symbol interference. LTE supports two cyclic prefix lengths, generally referred to as normal and extended cyclic prefix.

In the time domain, LTE downlink transmissions are organized into 10ms radio frames, each consisting of ten 1ms equally sized subframes. A subframe is divided into two slots, each 0.5ms in duration. Each slot consists of 6 or 7 OFDM symbols, depending on the selected cyclic prefix length.

Resource allocation in LTE is described in terms of resource blocks, where a resource block corresponds to one time slot in the time domain and 12 consecutive 15 kHz subcarriers in the frequency domain. Two temporally consecutive resource blocks represent a resource block pair and correspond to the time interval for which scheduling operations are performed.

Transmissions in LTE are dynamically scheduled in each subframe, with the base station transmitting assignments and/or grants to certain user equipment via the Physical Downlink Control Channel (PDCCH). The PDCCH is transmitted in the first OFDM symbol in each subframe and spans the entire system bandwidth. A user equipment that has decoded the downlink control information carried by the PDCCH knows which resource elements in the subframe contain data for that user equipment. In LTE, data is carried by the Physical Downlink Shared Channel (PDSCH).

Demodulation of the transmitted data requires radio channel estimation using transmitted reference symbols (i.e., symbols known to the receiver). In LTE, cell-specific reference symbols are transmitted in all downlink subframes and, in addition to assisting with downlink channel estimation, are also used for mobility measurements performed by user equipment. LTE also supports user equipment-specific reference symbols that assist with channel estimation for demodulation purposes only.

The length of the control region is conveyed in the Physical Control Format Indicator Channel (PCFICH), which can vary based on the subframe. The PCFICH is transmitted within the control region at a location known to the user equipment. After the user equipment has decoded the PCFICH, it thus knows the size of the control region and which OFDM symbol the data transmission begins.

A Physical Hybrid ARQ Indicator Channel is also transmitted in the control region. This channel carries the acknowledgement/negative acknowledgement (ACK/NACK) response to the user equipment to inform the base station whether the uplink data transmission in the previous subframe was successfully decoded.

Before an LTE user equipment can communicate with an LTE network, it must first find and acquire synchronization with a cell within the network, i.e., perform a cell search. It must then receive and decode the system information required to communicate with and operate properly within the cell, and finally access the cell through a so-called random access procedure.

Figure 3 illustrates uplink and downlink coverage in a mixed cell scenario. To support mobility, a user device (UE) needs to continuously search, synchronize, and estimate the reception quality of its serving/camped cell and neighboring cells. The reception quality of neighboring cells is then evaluated relative to that of the current cell to determine whether handover should be performed for a UE in connected mode or cell reselection for a UE in idle mode. The process of changing cells depends on which of two radio resource control (RRC) states the UE is in: connected or idle. In idle mode, mobility is controlled by the UE, known as cell reselection, while in connected mode, mobility is controlled by the network, known as handover. For UEs in connected mode, the network makes handover decisions based on measurement reports provided by the UE. Examples of such reports are Reference Signal Received Power (RSRP) and Reference Signal Received Quality (RSRQ). Depending on how these measurements, which may be supplemented by a configurable offset, are used, the UE can connect to the cell with the strongest received power, the cell with the best path gain, or a combination of the two. These do not result in the same selected cell, as base stations in different cell types have different output powers. This is sometimes referred to as link imbalance. For example, the output power of a pico base station or repeater is approximately 30 dBm or less, while a macro base station can have an output power of 46 dBm. Consequently, even near a pico cell, the downlink signal strength from a macro cell can be greater than that of the pico cell. From a downlink perspective, cell selection based on downlink received power is preferable, while from an uplink perspective, cell selection based on path loss is preferable. Figure 3 illustrates the cell selection method.

Therefore, in the above scenario, from a system perspective, it may be better to connect to the pico cell even if the macro downlink is much stronger than the pico cell downlink. However, when the user equipment 300 operates in the area of the UL boundary and the DL boundary (i.e., the link imbalance region 310 depicted in Figure 3), cross-layer ICIC may be required.

The base station may request a user equipment in connected mode to perform channel state information (CSI) reporting, such as reporting an appropriate rank indicator (RI), one or more precoding matrix indices (PMIs), and a channel quality indicator (CQI). The CQI report reflects the instantaneous radio quality observed by the user equipment in a certain downlink subframe, while the RI and PMI reports provide the network with user equipment recommendations for parameter settings for multiple-input multiple-output (MIMO) transmissions. Other types of CSI are also contemplated, including explicit channel feedback and interference covariance feedback.

Summary of the Invention

The purpose of the embodiments herein is to improve the CSI reporting mechanism.

According to a first aspect of the embodiments herein, the objective is achieved by a method for reporting channel state information (CSI) in a user equipment. The user equipment is connected to a base station in a cellular communication network. The user equipment receives a grant from the base station in subframe n for CSI reporting. Next, the user equipment determines the subframe type of subframe n+p. The user equipment then reports the CSI to the base station. The CSI reflects the channel conditions in the subframe type of subframe n+p. p is a variable value.

According to a second aspect of the embodiments herein, the object is achieved by a method for obtaining CSI from a user equipment in a base station, the base station being included in a cellular communication network 400. The base station provides a grant in subframe n to be used for CSI reporting to the user equipment. Next, the base station receives CSI from the user equipment reflecting channel conditions in a subframe type of subframe n+p, where p is a variable value.

According to a third aspect of the embodiments herein, the object is achieved by an apparatus in a user equipment (UE) adapted to communicate with a base station in a cellular communication network. The UE is capable of reporting CSI to the base station. The apparatus comprises: processing circuitry configured to receive a grant in subframe n from the base station for CSI reporting; and to determine a subframe type for subframe n+p. The processing circuitry is further configured to report CSI reflecting channel conditions in the subframe type for subframe n+p to the base station. p is a variable value.

According to a fourth aspect of the embodiments herein, the object is achieved by an apparatus in a base station for obtaining CSI from a user equipment. The base station is included in a cellular communication network. The apparatus includes processing circuitry configured to provide a grant in subframe n to the user equipment for CSI reporting, and to receive CSI from the user equipment reflecting channel conditions in a subframe type of subframe n+p. p is a variable value.

Since the user equipment can determine the subframe type of subframe n+p based on the grant received in subframe n and can report CSI reflecting the channel conditions in the subframe type of subframe n+p, there is no need to extend the CSI reporting grant with additional bits to report radio conditions in subframes of different types, resulting in an improved mechanism for CSI reporting with less overhead.

BRIEF DESCRIPTION OF THE DRAWINGS

Examples of embodiments of the present invention are described in more detail with reference to the accompanying drawings, in which:

FIG1 is a schematic block diagram illustrating the prior art.

FIG2 is a schematic block diagram illustrating the prior art.

FIG3 is a schematic block diagram illustrating the prior art.

FIG4 is a schematic block diagram illustrating an embodiment of a cellular communication network.

Fig. 5 is a schematic block diagram illustrating embodiments in a cellular communication network.

Fig. 6 is a schematic block diagram illustrating embodiments in a cellular communication network.

FIG7 is a flow chart illustrating an embodiment of a method in a user equipment.

FIG8 is a schematic block diagram illustrating embodiments of an apparatus in a user equipment.

FIG9 is a flow chart illustrating an embodiment of a method in a base station.

FIG10 is a schematic block diagram illustrating embodiments of an apparatus in a base station.

DETAILED DESCRIPTION

In the following description, specific details, such as specific architectures, interfaces, and techniques, are set forth for purposes of illustration and not limitation, in order to provide a comprehensive understanding of the present invention. However, those skilled in the art will appreciate that the present invention may be implemented in other embodiments that depart from these specific details. In other instances, detailed descriptions of well-known devices, circuits, and methods are omitted so as not to obscure the understanding of the description of the present invention with unnecessary detail.

FIG4 illustrates a cellular communication network 400 in which embodiments herein may be implemented. Cellular communication network 400 is a cellular communication network such as an LTE, WCDMA, GSM network, any other 3GPP cellular network, or any other cellular network or system. Cellular communication network 400 may be a heterogeneous network comprising cells served by respective base stations having significant differences in output power. An example of such a heterogeneous network is a picocell deployed within the coverage area of a macrocell. A picocell is a small cellular base station that typically covers a small area. A picocell typically covers a much smaller geographic area than a macrocell.

Cellular communication network 400 includes base station 410. Base station 410 can be a low-power base station, such as, for example, a pico base station (also known as a pico eNB), a femto eNB, a repeater, or any other low-power base station capable of serving user equipment in a cellular communication system. The transmit power of a low-power base station is typically in the range of 10 dB to 25 dB lower than the transmit power of a macro base station. When the low-power base station is exemplified as a pico base station, base station 410 can also be denoted as a PeNB. Base station 410 is a radio base station that serves cell 415. Cell 415 can be, for example, a microcell, a picocell, or any other low-power cell, such as, for example, a femtocell.

The user equipment 420 is located within the cell 415. The user equipment 420 is configured to communicate within the cellular communication network 400 via the base station 410 over a radio link 405 when the user equipment 420 is present in the cell 415 served by the base station 410.

In the example of FIG4 , cellular communication network 400 also includes a cell adjacent to cell 415, and therefore referred to as neighbor cell 425. Neighbor cell 425 is served by macro base station 430. In this example, neighbor cell 425 is served by macro base station 430, and its coverage area is larger than that of cell 415 served by low-power base station 410. In this example, cell 415 is deployed within the coverage area of neighbor cell 425. Macro base station 425 may also be referred to as an MeNB.

CSI Report

An example of providing cross-layer ICIC is shown in Figure 5. In this case, neighbor cell 425 is interfering with cell 415, i.e., downlink interference towards cell 415. Macro base station 430 can avoid scheduling user equipment (not shown) it serves in certain subframes 501, implying that neither PDCCH nor PDSCH appears in those subframes. In this way, it is possible to generate low-interference subframes that can be used to protect user equipment 420 when user equipment 420 operates in a link imbalance region. In LTE, an interface called the X2 interface is used to interconnect base stations, and inter-cell messages are sent via the X2 application protocol (X2-AP). Macro base station 430 can indicate to base station 410 via the backhaul interface X2 in which frames the macro base station 430 will avoid scheduling user equipment. Messages carried by X2-AP are typically represented by a bitmap indicating the frames in which the macro base station 430 intends to avoid scheduling user equipment. Base station 410 will then take this information into account when scheduling user equipment such as user equipment 420 when operating within the link imbalance region (i.e., within cell 415 but outside the DL boundary). This can be done so that these user equipment are scheduled in subframes that are aligned (i.e., associated) with low-interference subframes at the macro layer (i.e., in interference-protected subframes). However, user equipment can be scheduled in all subframes (i.e., in protected and unprotected subframes) when operating within the DL boundary.

When user equipment 420 is operating in connected mode, base station 410 may request it to perform channel state information (CSI) measurements. When scheduling user equipment 420 in the downlink, base station 410 can use the feedback of the reported CSI to make decisions about a transmission scheme and the appropriate user equipment bit rate for transmission. In LTE, both periodic, i.e., recurring at regular intervals, and aperiodic, i.e., non-regular, CSI reporting are supported. With periodic CSI reporting, user equipment 420 may report CSI measurements based on a configured periodicity, such as on the Physical Uplink Control Channel (PUCCH), while with aperiodic reporting, CSI feedback may be transmitted at pre-specified times on the Physical Uplink Shared Channel (PUSCH) after receiving a CSI grant from the base station. According to embodiments herein, base station 410 may request CSI that reflects downlink radio conditions in a specific subframe using aperiodic CSI reporting.

To obtain accurate CSI measurements, user equipment 420 typically averages interference measurements across many subframes. The general principle is that the measurements will reflect the radio conditions in the subframes in which user equipment 420 is intended to be scheduled. When user equipment 420 is served by cell 415 and operating in a link imbalance region, it preferably only performs measurements in subframes aligned with low-interference subframes (i.e., protection subframes). Therefore, if high-interference subframes are also included in the CSI measurement, the CSI report will not reflect the radio conditions in the subframes in which it is intended to be scheduled, resulting in degraded system operation. Figure 6 illustrates base station 410 serving user equipment 420 in a first scenario, when the user equipment is within a DL boundary 610. In this scenario, user equipment 420 is referred to as 420-1. Figure 6 also illustrates base station 410 serving user equipment 420 in a second scenario, when the user equipment is outside of DL boundary 610. In this scenario, user equipment 420 is referred to as 420-2. The macro base station 430, which is a neighbor of the base station 410, operates with guard subframes in order to reduce interference towards user equipment operating in the link imbalance region (ie, within the cell 415 but outside the DL boundary 610).

That is, in this case, the user equipment 420 - 1 located in the cell 415 is in the vicinity of the base station 410 , ie, within the DL boundary 610 , and thus can be scheduled in all subframes.

User equipment 420-2 located at the edge of cell 415 (i.e., outside DL boundary 610) faces high interference from neighboring macro base station 430. In this case, user equipment 420-2 located at the edge of cell 415 is preferably scheduled in DL only in guard subframes (i.e., in subframes with low macro interference).

User equipment operating in link-imbalanced cells (e.g., pico cells) can be scheduled in all subframes or only in subframes aligned with or associated with low-interference subframes (i.e., protected subframes), depending on their location within the cell. For the base station to make good scheduling decisions, CSI measurements for both protected and unprotected subframes are required. The base station controls the subframe in which grants are sent and can then request CSI reports reflecting channel conditions in either protected or unprotected subframes.

Some embodiments herein provide procedures for differentiating measurements for aperiodic CSI reporting based on the type of subframe in which the user equipment 420 receives the corresponding measurement grant. If there are two types of defined subframes (e.g., subframe types "A" and "B") for CSI measurement purposes, the following procedure may be applied, for example.

If the user equipment 420 receives a CSI reporting grant in a downlink subframe corresponding to type "A", the CSI report will only be based on measurements that reflect the radio conditions in subframes of type "A".

If user equipment 420 receives a CSI reporting grant in a downlink subframe corresponding to type "B", the CSI report will be based on measurements reflecting the radio conditions in the subframe of type "B" or in a complementary subframe set of the subframe of type "A".

Subframe type "A" may correspond to protected subframes, while subframe type "B" may correspond to unprotected subframes. The above principle can be extended to more than two subframe types. A generalization of this concept includes that the subframe in which the CSI reporting grant appears may determine the subframe type in which the measurement of the associated CSI report will reflect the channel conditions.

Alternatively, the CSI itself, instead of the measurement, may reflect the channel conditions of a certain type of subframe. For example, the CQI/CSI reference resources may be constrained to a specific type of subframe based on the CSI reporting grant timing.

In the following text, the embodiments herein will be described first from the perspective of the user equipment 420 and second from the perspective of the base station 410 .

An embodiment of a method for reporting CSI in a user equipment 420 will now be described with reference to the flowchart depicted in Figure 7. As mentioned above, the user equipment 420 is connected to a base station 410 in a cellular communication network 400. The method includes the following actions, which may also be performed in another appropriate order than described below.

Action 701

In some embodiments, the subframe type of subframe n+p is one of two or more subframe types. The two or more subframe types are associated with corresponding sets of different subframes. The subframe sets contain subframes of the same subframe type. In these embodiments, user equipment 420 may receive a message from base station 410. The message indicates the subframe set.

In some embodiments, the set of subframes includes a subset of guard subframes that align with low interference generated by neighbor cells.

For example, a user equipment 420 served by a base station 410 may receive a message regarding a restricted subframe set to be considered for CSI measurement. This message may, for example, be broadcast from the base station 410 or sent specifically to the user equipment 420. Typically, the message corresponds to a higher-layer message, such as an RRC message. The restricted subframe set may, for example, represent all protected subframes, i.e., subframes aligned with low-interference subframes generated by neighboring cells, or correspond to a subset of protected subframes. The cellular communication network 400 may also broadcast or send, via the base station 410, a dedicated higher-layer message to the user equipment 420, including an additional higher-layer message indicating a restricted subframe set for complementary CSI measurement purposes. An example of a complementary subframe set to the signaled restricted subframe set is an unprotected subframe. The set of restricted subframes signaled by the cellular communication network 400 for certain CSI measurement purposes may, for example, be represented by a bitmap per set, where a bit may, for example, represent a subframe within a radio frame, or a subframe within several radio frames. The set of restricted subframes may have a start and end time and may repeat periodically until the cellular communication network 400 reconfigures the set of restricted subframes.

Action 702

The user equipment 420 receives a grant in subframe n from the base station 410 to be used for CSI reporting.

For example, the base station 410 may have sent a grant to the user equipment 420 in subframe n to request that the user equipment 420 send an aperiodic CSI report in subframe n+k.

Action 703

The user equipment 420 determines the subframe type of subframe n+p.

For example, the user equipment 420 receives and detects a CSI reporting grant in subframe n.

If subframe n+p corresponds to a subframe of type "A", the user equipment 420 will report CSI reflecting the radio conditions in the subframes indicated by the cellular communication network 400, eg via higher layer signalling, as being associated with subframes of type "A".

If subframe n likely corresponds to a subframe of type "B" via a known timing relationship, the user equipment 420 will report CSI reflecting the radio conditions in subframes indicated by the cellular communication network 400 as associated with subframes of type "B", for example via higher layer signalling.

This can be generalized to more than two subframe types. With each subframe type (A, B, C, ...), there may be an associated set of subframes. The CSI report in these embodiments will reflect the radio conditions in the subframes belonging to the associated set of subframes.

Action 704

The user equipment 420 reports CSI reflecting the channel condition in a subframe type of subframe n+p to the base station 410, where p is a variable value.

In some embodiments, p is a variable value known to both the cellular communication network 400 and the user equipment 420 .

In some embodiments, the subframe type of subframe n+p is one of two or more subframe types. The two or more subframe types are associated with corresponding sets of different subframes. In these embodiments, the act of reporting CSI may reflect the radio conditions in the subframes belonging to the subframe set associated with the subframe type of subframe n+p. In some embodiments, the value p is equal to zero, but as mentioned above, other values or functions known to both the cellular communication network 400 and the user equipment 420 are possible. For example, the value of p may be implicitly determined based on subframe n following some predetermined rules. When p is equal to zero, the subframe type of the subframe in which the user equipment 420 receives the grant determines the subframe type in which the channel conditions should be reflected in the CSI report.

This action of reporting CSI can be aperiodic or periodic.

In some embodiments, the set of subframes includes a subset of guard subframes that align with low interference generated by neighbor cells.

With the embodiments herein, there is no need to extend the CSI reporting grant with additional bits to report radio conditions in different types of subframes. The same basic CSI signaling mechanism used in LTE Release 8 can be reused, with additional implicit principles on how to perform measurements for CSI feedback in heterogeneous network operation with respect to link imbalance regions.

In some embodiments, the subframe type of subframe n+p is represented by a first subframe type corresponding to a protected subframe. The first subframe type is associated with a subframe set including protected subframes aligned with low interference generated by neighboring cells. In some embodiments, the subframe type of subframe n+p may be represented by a second subframe type corresponding to an unprotected subframe, the second subframe type being associated with a subframe set including unprotected subframes, which are subframes that are not part of protected subframes aligned with low interference generated by neighboring cells.

For example, the base station 410 sends a grant to the user equipment 420 in subframe n to request that the user equipment 420 send an aperiodic CSI report in subframe n+k. The user equipment 420 receives and detects the CSI report grant in subframe n. k is a non-negative integer, and p represents any integer, negative value, positive value, including zero.

If subframe n+p corresponds to a protected subframe, the user equipment 420 shall report CSI based on measurements reflecting the channel conditions in subframes that have been indicated as protected subframes by the cellular communication network 400, eg via higher layer signalling (ie the first set of subframes).

If subframe n+p corresponds to an unprotected subframe, the user equipment 420 shall report CSI reflecting the channel conditions in subframes that are not part of the restricted first set of subframes that have been indicated by the cellular communication network 400, e.g. via higher layer signalling, as protected subframes (i.e. the second set of subframes).

The user equipment 420 does not need to know whether the first set of subframes refers to protected subframes or unprotected subframes. The user equipment 420 reports the channel condition linked to the first set or the second set depending on which set the grant belongs to.

The value p is equal to zero in a specific embodiment, but other values or functions known to both the cellular communication network 400 and the user equipment 420 are also contemplated. The subframe in which the CSI reporting grant occurs may determine the subframe type in which the measurements of the associated CSI report will reflect the channel conditions.

In some other embodiments, the subframe type of subframe n+p is represented by a first subframe type corresponding to a protected subframe. The first subframe type is associated with a subframe set indicated as protected in the message from base station 410. In some embodiments, the subframe type of subframe n+p may be represented by a second subframe type corresponding to an unprotected subframe, the second subframe type being associated with a subframe set indicated as complementary in the message from base station 410.

For example, the base station 410 may send a grant to the user equipment 420 in subframe n to request that the user equipment 420 send an aperiodic CSI report in subframe n+k. The user equipment 420 receives and detects the CSI reporting grant in subframe n.

If subframe n+p corresponds to a protected subframe, the user equipment 420 shall report CSI based on measurements reflecting the channel conditions in a subframe that has been indicated as a protected subframe by the cellular communication network 400, eg via higher layer signalling.

If subframe n+p corresponds to an unprotected subframe, the user equipment 420 shall report CSI reflecting the channel conditions in the subframes in the set of complementary subframes that have been indicated as complementary subframes by the cellular communication network 400 via higher layer signalling.

If the base station 410 has sent a grant in subframe n corresponding to the unprotected subframe n+p and has not yet received a CSI report in subframe n+k, the base station 410 may expect or conclude that the user equipment 420 requested to send a CSI report in subframe n+k is in a link imbalance region and cannot detect the PDCCH in the unprotected subframe. The base station 410 may then send a CSI report grant to the user equipment 420 in the protected subframe.

To perform the method actions described above in the user equipment 420, the user equipment 420 comprises the following apparatus 800 depicted in Figure 8. As mentioned above, the user equipment 420 is adapted to communicate with the base station 410 in the cellular communication network 400. The user equipment 420 is also capable of reporting channel state information to the base station 410.

The apparatus 800 comprises a processing circuit 805 configured to receive a grant in a subframe n to be used for CSI reporting from a base station. For this function, the processing circuit 805 may comprise a receiving unit 810 .

The apparatus 800 comprises a processing circuit 805 configured to determine the subframe type of subframe n+p. For this function, the processing circuit 805 may comprise a determining unit 820.

In some embodiments, the subframe type of subframe n+p may be represented by a first subframe type corresponding to a protected subframe. The first subframe type is associated with a subframe set that includes protected subframes aligned with low interference generated by neighboring cells. In some embodiments, the subframe type of subframe n+p may be represented by a second subframe type corresponding to an unprotected subframe. The second subframe type is associated with a subframe set that includes unprotected subframes. Unprotected subframes are subframes that are not part of protected subframes aligned with low interference generated by neighboring cells.

In some embodiments, the subframe type of subframe n+p is represented by a first subframe type corresponding to a protected subframe. The first subframe type is associated with a subframe set indicated as protected in the message from base station 410. In some embodiments, the subframe type of subframe n+p may be represented by a second subframe type corresponding to an unprotected subframe. The second subframe type is associated with a subframe set indicated as complementary in the message from base station 410.

Processing circuit 805 is further configured to report CSI reflecting the channel conditions in the subframe type of subframe n+p to base station 410, where p is a variable value. In some embodiments, p is a variable value known to both the cellular communication network 400 and user equipment 420. To facilitate this functionality, processing circuit 805 may include reporting unit 830. The value p may be, for example, zero, although other values or functions known to both the cellular communication network 400 and user equipment 420 are possible. When p is zero, the subframe type of the subframe in which user equipment 420 receives the grant determines the subframe type in which the channel conditions should be reflected in the CSI report.

In some embodiments, the processing circuit 805 , such as, for example, the reporting unit 830 , is further configured to report the CSI aperiodically.

In some embodiments, the subframe type of subframe n+p is one of two or more subframe types, the two or more subframe types being associated with respective sets of different subframes. In these embodiments, the processing circuit 805, such as, for example, the reporting unit 830, may be further configured to report CSI reflecting channel conditions in subframes belonging to the set of subframes associated with the subframe type of subframe n+p.

In some embodiments, the processing circuit 805 , such as, for example, the receiving unit 810 , is further configured to receive a message from the base station 410 , the message indicating the subframe set.

In some embodiments, the set of subframes includes a subset of guard subframes that align with low interference generated by neighbor cells.

According to some embodiments, the apparatus 800 in the user equipment 420 includes a processing unit 840, for example, having a DSP (digital signal processor) and encoding and decoding modules. The processing unit 840 can be a single unit or multiple units that perform the different steps of the process described herein. The apparatus 800 also includes an input unit and an output unit. The input unit and the output unit can be arranged as a unit or separate units in the hardware of the apparatus 800 in the user equipment 420.

Furthermore, the apparatus 800 may include at least one computer program product in the form of a non-volatile memory 850 (e.g., an EEPROM, a flash memory, and a disk drive). The computer program product comprises a computer program comprising code means which, when executed on the processing unit 840, causes the apparatus 800 in the user equipment to perform the steps of the previously described process.

Thus, in the described exemplary embodiment, the code means in the computer program of the apparatus 800 in the user equipment includes, in the form of computer program code structured in computer program modules, means for receiving a grant in subframe n to be used for CSI reporting, in a specific embodiment, means for obtaining a value p, means for determining a subframe type of subframe n+p, and means for reporting CSI reflecting the channel conditions in the subframe type of subframe n+p.

Thus, in the described exemplary embodiment, the code means in the computer program of the apparatus 1000 in the base station include, in the form of computer program code structured in computer program modules, means for providing the user equipment 420 with a grant in subframe n to be used for CSI reporting, means for obtaining a value p in a specific embodiment, and means for receiving CSI from the user equipment reflecting the channel conditions in a subframe type of subframe n+p.

The present invention may, of course, be carried out in other ways than those specifically set forth herein without departing from essential characteristics of the invention.The present embodiments are to be considered in all respects as illustrative and not restrictive.

An embodiment of a method in a base station 410 for obtaining CSI from a user equipment 420 will now be described with reference to the flowchart depicted in Figure 9. As mentioned above, the base station 410 is included in the cellular communication network 400.

In some embodiments, base station 410 is represented by a low-power node serving a first cell, such as cell 415. In this case, cell 415 is represented by the first cell. The first cell is included in neighbor cell 425, represented by a macro cell, which is served by a macro base station. In this case, the neighbor base station is represented by a macro base station. In this case, neighbor base station 425 is represented by a macro base station. The first cell and the macro cell share radio resources on the same carrier frequency.

In some embodiments, base station 410 is represented by a pico base station serving a pico cell. In this case, cell 415 is represented by a pico cell. The pico cell is included in a neighbor cell 425, represented by a macro cell, served by a macro base station. In this case, neighbor base station 425 is represented by a macro base station. The pico cell and the macro cell share radio resources on the same carrier frequency.

The method comprises the following actions, which may also be performed in another suitable order than described below.

Action 901

The base station 410 provides the user equipment 420 with a grant in subframe n to be used for CSI reporting.

Action 902

Base station 410 receives CSI from user equipment 420 that reflects channel conditions in a subframe type of subframe n+p, where p is a variable value. In some embodiments, p is a variable value known to both the network and user equipment 420. The value p may be, for example, zero, but other values or functions known to both cellular communication network 400 and user equipment 420 are possible. When p is zero, the subframe type of the subframe in which user equipment 420 receives the grant determines the subframe type in which the channel conditions should be reflected in the CSI report.

The subframe type of subframe n+p is one of two or more subframe types. The two or more subframe types are associated with respective sets of different subframes. The CSI received from user equipment 420 reflects channel conditions in subframes belonging to the subframe set associated with the subframe type of subframe n+p.

Action 903

The base station 410 may send a message to the user equipment 420, the message indicating the subframe set.

In some embodiments, the subframe type of subframe n+p is represented by a first subframe type corresponding to a protected subframe. The first subframe type is associated with a subframe set that includes protected subframes aligned with low interference generated by neighboring cells. In some embodiments, the subframe type of subframe n+p is represented by a second subframe type corresponding to an unprotected subframe. The second subframe type is associated with a subframe set that includes unprotected subframes. An unprotected subframe is a subframe that is not part of a protected subframe aligned with low interference generated by a neighboring cell.

In some other embodiments, the subframe type of subframe n+p is represented by a first subframe type corresponding to a protected subframe, the first subframe type being associated with a subframe set indicated as protected in the message to the user equipment 420. In some embodiments, the subframe type of subframe n+p may be represented by a second subframe type corresponding to an unprotected subframe, the second subframe type being associated with a subframe set indicated as complementary in the message to the user equipment 420.

The subframe set may include a subset of guard subframes that align with low interference generated by neighbor cells.

In order to perform the above-described method actions for obtaining CSI from user equipment 420 in base station 410, base station 410 includes apparatus 1000 depicted in Figure 10. Base station 410 is capable of obtaining CSI from user equipment 420. Base station 410 is included in a cellular communication network.

In some embodiments, base station 410 is represented by a low-power node serving a first cell, such as cell 415. In this case, cell 415 is represented by the first cell. The first cell is included in neighbor cell 425, represented by a macro cell, which is served by a macro base station. In this case, the neighbor base station is represented by a macro base station. In this case, neighbor base station 425 is represented by a macro base station. The first cell and the macro cell share radio resources on the same carrier frequency.

In some embodiments, base station 410 is represented by a pico base station serving a pico cell. In this case, cell 415 is represented by a pico cell. The pico cell is included in a neighbor cell 425, represented by a macro cell, served by a macro base station. In this case, neighbor base station 425 is represented by a macro base station. The pico cell and the macro cell share radio resources on the same carrier frequency.

The apparatus 1000 in the base station 410 comprises a processing circuit 1005 configured to provide a grant in subframe n to be used for CSI reporting to the user equipment 420. For this function, the processing circuit 1005 may comprise a providing unit 1010.

Processing circuit 1005 is further configured to receive CSI from user equipment 420 that reflects channel conditions in a subframe type of subframe n+p, where p is a variable value. In some embodiments, p is a variable value known to both the network and user equipment 420. For this functionality, processing circuit 1005 may include receiving unit 1020. The value p may be equal to zero, but as mentioned above, other values or functions known to both cellular communication network 400 and user equipment 420 are possible. When p is equal to zero, the subframe type of the subframe in which user equipment 420 receives the grant determines the subframe type in which the channel conditions should be reflected in the CSI report.

According to some embodiments, the subframe type of subframe n+p is one of two or more subframe types. The two or more subframe types are associated with respective sets of different subframes. In these embodiments, the processing circuit 1005, such as, for example, the receiving unit 1020, may be further configured to receive, from the user equipment 420, CSI reflecting channel conditions in subframes belonging to the subframe set associated with the subframe type of subframe n+p.

The subframe set includes a subset of guard subframes that are aligned with low interference generated by neighbor cells.

In some embodiments, the processing circuit 1005 may be further configured to send a message indicating the subframe set to the user equipment 420. For this function, the processing circuit 1005 may include a sending unit 1030.

In some embodiments, the subframe type of subframe n+p is represented by a first subframe type corresponding to a protected subframe, and the first subframe type is associated with a subframe set including protected subframes aligned with low interference generated by neighboring cells. In some embodiments, the subframe type of subframe n+p may be represented by a second subframe type corresponding to an unprotected subframe. The second subframe type is associated with a subframe set including unprotected subframes. Unprotected subframes are subframes that are not part of protected subframes aligned with low interference generated by neighboring cells.

In some other embodiments, the subframe type of subframe n+p is represented by a first subframe type corresponding to a protected subframe, the first subframe type being associated with a subframe set indicated as protected in the message to the user equipment 420. In some embodiments, the subframe type of subframe n+p may be represented by a second subframe type corresponding to an unprotected subframe, the second subframe type being associated with a subframe set indicated as complementary in the message to the user equipment 420.

According to some embodiments, the apparatus 1000 in the base station 410 includes a processing unit 1040, for example, having a DSP (digital signal processor) and encoding and decoding modules. The processing unit 1040 can be a single unit or multiple units that perform the different steps of the process described herein. The apparatus also includes an input unit and an output unit. The input unit and the output unit can be arranged as a single unit or separate units in the hardware of the apparatus in the user equipment 420.

Furthermore, the apparatus 1000 may include at least one computer program product in the form of a non-volatile memory 1050 (e.g., an EEPROM, a flash memory, and a disk drive). The computer program product comprises a computer program comprising code means that, when executed on the processing unit 1040, causes the apparatus in the base station 410 to perform the steps of the previously described process.

Thus, in the described exemplary embodiment, the code means in the computer program of the apparatus 1000 in the base station 410 include, in the form of computer program code structured in computer program modules, means for providing a grant in subframe n to be used for CSI reporting to the user equipment 420, in a specific embodiment, means for obtaining a value p, and means for receiving CSI reflecting the channel conditions in a subframe type of subframe n+p from the user equipment.

The present invention may, of course, be carried out in other ways than those specifically set forth herein without departing from essential characteristics of the invention.The present embodiments are to be considered in all respects as illustrative and not restrictive.

When the word "comprising" is used, it is to be interpreted in a non-limiting sense, ie meaning "including at least".

The embodiments herein are not limited to the preferred embodiments described above. Various alternatives, modifications, and equivalents may be used. Therefore, the above embodiments should not be considered to limit the scope of the present invention, which is defined by the appended claims.

Claims (46)

1. A method for reporting Channel State Information (CSI) in a user equipment (420), the user equipment (420) being connected to a base station (410) in a cellular communication network (400), the method comprising: Receive (720) a license in subframe n to be used for CSI reporting from the base station (410); Determine the subframe type of subframe n+p (703); and Report (704) to the base station (410) the CSI of the channel conditions in the subframe type of subframe n+p, where p is a variable value. 2. The method according to claim 1, wherein the value p is equal to zero. 3. The method of claim 1, wherein the CSI is obtained by averaging interference measurements over a plurality of subframes. 4. The method according to any one of claims 1-3, wherein the subframe type of subframe n+p is one of two or more subframe types associated with corresponding sets of different subframes, and wherein the CSI reported (704) reflects the channel conditions in the subframes belonging to the set of subframes associated with the subframe type of subframe n+p. 5. The method according to claim 4, further comprising: Receive a (701) message from the base station, the message indicating the set of subframes. 6. The method according to any one of claims 1-3, wherein the subframe type is represented by a first subframe type corresponding to a guard subframe, the first subframe type being associated with a set of subframes including guard subframes aligned with low interference generated by neighboring cells. 7. The method according to any one of claims 1-3, wherein the subframe type is represented by a second subframe type corresponding to an unprotected subframe, the second subframe type being associated with a set of subframes including unprotected subframes, the unprotected subframes being subframes that are not part of protected subframes that are aligned with low interference generated by neighboring cells. 8. The method of claim 5, wherein the subframe type is represented by a first subframe type corresponding to a protected subframe, the first subframe type being associated with a set of subframes indicated as protected in a message from the base station (410). 9. The method of claim 5, wherein the subframe type is represented by a second subframe type corresponding to an unprotected subframe, the second subframe type being associated with a set of subframes indicated as complementary in a message from the base station (410). 10. The method of claim 4, wherein the set of subframes comprises a subset of guard subframes aligned with low interference generated by neighboring cells. 11. The method according to any one of claims 1-3, wherein the CSI report (704) is non-periodic. 12. A method for obtaining channel state information (CSI) from a user equipment (420) in a base station (410), the base station (10) being included in a cellular communication network (400), the method comprising: Provide the user equipment (420) (901) with permission in subframe n to be used for CSI reporting; and The user equipment (420) receives (902) a CSI reflecting the channel conditions in the subframe type of subframe n+p, where p is a variable value. 13. The method of claim 12, wherein the value p is equal to zero. 14. The method of claim 12, wherein the CSI is obtained by averaging interference measurements over a plurality of subframes. 15. The method according to any one of claims 12-14, wherein the subframe type of subframe n+p is one of two or more subframe types associated with corresponding sets of different subframes, and wherein the CSI received (902) from the user equipment (420) reflects the channel conditions in the subframes belonging to the set of subframes associated with the subframe type of subframe n+p. 16. The method of claim 15, further comprising: A message (903) is sent to the user equipment (420), the message indicating the subframe set. 17. The method of any one of claims 12-14, wherein the subframe type is represented by a first subframe type corresponding to a guard subframe, the first subframe type being associated with a set of subframes including guard subframes aligned with low interference generated by neighboring cells. 18. The method of any one of claims 12-14, wherein the subframe type is represented by a second subframe type corresponding to an unprotected subframe, the second subframe type being associated with a set of subframes including unprotected subframes, the unprotected subframes being subframes that are not part of protected subframes aligned with low interference generated by neighboring cells. 19. The method of claim 16, wherein the subframe type is represented by a first subframe type corresponding to a protected subframe, the first subframe type being associated with a set of subframes indicated as protected in a message to the user equipment (420). 20. The method of claim 16, wherein the subframe type is represented by a second subframe type corresponding to an unprotected subframe, the second subframe type being associated with a set of subframes indicated as complementary in a message to the user equipment (420). 21. The method of claim 15, wherein the set of subframes includes a subset of guard subframes aligned with low interference generated by neighboring cells. 22. The method according to any one of claims 12-14, wherein the base station (410) is represented by a low-power node serving a first cell, the first cell being included in a neighboring cell represented by a macro cell served by a macro base station, and the first cell and the macro cell sharing radio resources on the same carrier frequency. 23. The method according to any one of claims 12-14, wherein the base station (410) is represented by a pico base station serving a pico cell, the pico cell being included in a neighboring cell represented by a macro cell served by a macro base station, and the pico cell and the macro cell sharing radio resources on the same carrier frequency. 24. An apparatus (800) for a user equipment (420) suitable for communicating with a base station (410) in a cellular communication network (400), the user equipment (420) being capable of reporting channel state information to the base station (410), the apparatus (800) comprising a processing circuit (805) configured to perform the following operations: Receive permission from the base station (410) in subframe n to be used for CSI reporting; Determine the subframe type of subframe n+p; and The base station (410) reports the CSI reflecting the channel conditions in the subframe type of subframe n+p, where p is a variable value. 25. The apparatus of claim 24, wherein the value p is equal to zero. 26. The apparatus of claim 24, wherein the CSI is obtained by averaging interference measurements over a plurality of subframes. 27. The apparatus (800) according to any one of claims 24-26, wherein the subframe type of subframe n+p is one of two or more subframe types associated with corresponding sets of different subframes, and wherein the processing circuitry (805) is further configured to report CSI reflecting the channel conditions in subframes belonging to the set of subframes associated with the subframe type of subframe n+p. 28. The apparatus (800) of claim 27, wherein the processing circuit (805) is further configured to receive a message from the base station (410) indicating the subframe set. 29. The apparatus (800) according to any one of claims 24-26, wherein the subframe type is represented by a first subframe type corresponding to a guard subframe, the first subframe type being associated with a set of subframes including guard subframes aligned with low interference generated by neighboring cells. 30. The apparatus (800) according to any one of claims 24-26, wherein the subframe type is represented by a second subframe type corresponding to an unprotected subframe, the second subframe type being associated with a set of subframes including unprotected subframes, the unprotected subframes being subframes that are not part of protected subframes that are aligned with low interference generated by neighboring cells. 31. The apparatus (800) of claim 28, wherein the subframe type is represented by a first subframe type corresponding to a protected subframe, the first subframe type being associated with a set of subframes indicated as protected in a message from the base station (410). 32. The apparatus (800) of claim 28, wherein the subframe type is represented by a second subframe type corresponding to an unprotected subframe, the second subframe type being associated with a set of subframes indicated as complementary in a message from the base station (410). 33. The apparatus (800) of claim 27, wherein the set of subframes includes a subset of guard subframes aligned with low interference generated by neighboring cells. 34. The apparatus (800) according to any one of claims 24-26, wherein the processing circuit (805) is further configured to report CSI non-periodically. 35. An apparatus (1000) capable of obtaining Channel State Information (CSI) from a User Equipment (420) in a base station (410), the base station being included in a cellular communication network, the apparatus comprising processing circuitry (1010) configured to perform the following operations: Provide the user equipment (420) with permission in subframe n to be used for CSI reporting; and The user equipment (420) receives a CSI reflecting the channel conditions in the subframe type n+p, where p is a variable value. 36. The apparatus of claim 35, wherein the value p is equal to zero. 37. The apparatus of claim 35, wherein the CSI is obtained by averaging interference measurements over a plurality of subframes. 38. The apparatus (1000) of claim 35, wherein the subframe type of subframe n+p is one of two or more subframe types associated with corresponding sets of different subframes, and wherein the processing circuit (1005) is further configured to receive from the user equipment (420) a CSI reflecting channel conditions in subframes belonging to the set of subframes associated with the subframe type of subframe n+p. 39. The apparatus (1000) of claim 38, wherein the processing circuit (1005) is further configured to send a message to the user equipment (420) indicating the subframe set. 40. The apparatus (1000) according to any one of claims 35-38, wherein the subframe type is represented by a first subframe type corresponding to a guard subframe, the first subframe type being associated with a set of subframes including guard subframes aligned with low interference generated by neighboring cells. 41. The apparatus (1000) according to any one of claims 35-38, wherein the subframe type is represented by a second subframe type corresponding to an unprotected subframe, the second subframe type being associated with a set of subframes including unprotected subframes, the unprotected subframes being subframes that are not part of protected subframes that are aligned with low interference generated by neighboring cells. 42. The apparatus (1000) of claim 39, wherein the subframe type is represented by a first subframe type corresponding to a protected subframe, the first subframe type being associated with a set of subframes indicated as protected in a message to the user equipment (420). 43. The apparatus (1000) of claim 39, wherein the subframe type is represented by a second subframe type corresponding to an unprotected subframe, the second subframe type being associated with a set of subframes indicated as complementary in a message to the user equipment (420). 44. The apparatus (1000) of claim 38, wherein the set of subframes includes a subset of guard subframes aligned with low interference generated by neighboring cells. 45. The apparatus (1000) according to any one of claims 35-38, wherein the base station (410) is represented by a low-power node serving a first cell, the first cell being included in a neighboring cell represented by a macro cell served by the macro base station (410), and the first cell and the macro cell sharing radio resources on the same carrier frequency. 46. The apparatus (1000) according to any one of claims 35-38, wherein the base station (410) is represented by a pico base station serving a pico cell, the pico cell being included in a neighboring cell represented by a macro cell served by the macro base station (410), and the pico cell and the macro cell sharing radio resources on the same carrier frequency.