BACKGROUND:

Field:

[0001] Advanced receivers in 3rd generation partnership project (3GPP) long term evolution advanced (LTE-A) user equipment (UE) may be configured for interference limited operation. Signaling of reference symbol interference characteristics for advanced user equipment receivers may assist this configuration for interference limited operation. Interference suppression can lead to higher user throughput and therefore higher system capacity and better quality of service.

Description of the Related Art:

[0002] In an interference limited network, the throughput of each user may be limited by the amount of interference received from other transmissions within the cell or from neighboring cells. A multiantenna receiver may have, in principle, the capability to suppress part of the interference based on the spatial characteristics of the interference.

[0003] To enable interference suppression, however, the receiver may need to acquire information on the interference structure. Conventionally, a user equipment may form a linear minimum mean square error receiver based on estimates utilizing the available signals. However, there are limits on available information at the user equipment side.

SUMMARY:

[0004] In certain embodiments a method includes providing a user equipment with information about an expected interference situation on resource elements available for estimation of interference related parameters for data decoding. The resource elements may either carry reference signals such as cell specific reference signals (CRS), demodulation reference signals (DM-RS), channel state information reference signals (CSI-RS) and/or also zero power resource elements such as zero power CSI-RS. The user equipment is configured to apply the information to improve performance of a receiver of the user equipment.

[0005] A method, according to certain embodiments, includes receiving information about an expected interference situation on resource elements carrying reference signals or zero power resource elements. The method also includes applying the information to improve performance of a receiver in a user equipment.

[0006] An apparatus, in certain embodiments, includes at least one memory including computer program code and at least one processor. The at least one memory and computer program code are configured to, with the at least one processor, cause the apparatus at least to provide a user equipment with information about an expected interference situation on resource elements carrying reference signals or zero power resource elements. The user equipment is configured to apply the information to improve performance of a receiver of the user equipment.

[0007] According to certain embodiments, an apparatus includes at least one memory including computer program code and at least one processor. The at least one memory and computer program code are configured to, with the at least one processor, cause the apparatus at least to process information received about an expected interference situation on resource elements carrying reference signals or zero power resource elements. The at least one memory and computer program code are further configured to, with the at least one processor, cause the apparatus at least to apply the information to improve performance of a receiver in a user equipment.

[0008] An apparatus includes, in certain embodiments, generating means for generating information about an expected interference situation on resource elements carrying reference signals or zero power resource elements. The apparatus also includes providing means for providing the information to a user equipment. The user equipment is configured to apply the information to improve performance of a receiver of the user equipment.

[0009] An apparatus, according to certain embodiments, includes receiving means for receiving information about an expected interference situation on resource elements carrying reference signals or zero power resource elements. The apparatus also includes applying means for applying the information to improve performance of a receiver in a user equipment.

[0010] A non-transitory computer readable medium, according to certain embodiments, encodes a computer program that, when executed in hardware, performs a process. The process includes providing a user equipment with information about an expected interference situation on resource elements carrying reference signals or zero power resource elements. The user equipment is configured to apply the information to improve performance of a receiver of the user equipment.

[0011] In certain embodiments, a non-transitory computer readable medium encodes a computer program that, when executed in hardware, performs a process. The process includes receiving information about an expected interference situation on resource elements carrying reference signals or zero power resource elements. The process also includes applying the information to improve performance of a receiver in a user equipment.

[0012] In certain embodiments, a method includes providing a user equipment with information about an expected interference situation on resource elements used for estimation of interference related parameters. The information is configured to be applied by the user equipment to improve performance of a receiver of the user equipment.

[0013] A method, according to certain embodiments, includes receiving information about an expected interference situation on resource elements used for estimation of interference related parameters. The method also includes applying the information to improve performance of a receiver in a user equipment.

[0014] An apparatus includes, in certain embodiments, at least one memory including computer program code and at least one processor. The at least one memory and computer program code are configured to, with the at least one processor, cause the apparatus at least to provide a user equipment with information about an expected interference situation on resource elements used for estimation of interference related parameters. The information is configured to be applied by the user equipment to improve performance of a receiver of the user equipment.

[0015] According to certain embodiments, an apparatus includes at least one memory including computer program code and at least one processor. The at least one memory and computer program code are configured to, with the at least one processor, cause the apparatus at least to process received information about an expected interference situation on resource elements used for estimation of interference related parameters. The at least one memory and computer program code are also configured to, with the at least one processor, cause the apparatus at least to apply the information to improve performance of a receiver in a user equipment.

[0016] An apparatus, in certain embodiments, includes generating means for generating information about an expected interference situation on resource elements used for estimation of interference related parameters. The apparatus also includes providing means for providing a user equipment with the information about the expected interference situation on resource elements used for estimation of interferences parameters. The information is configured to be applied by the user equipment to improve performance of a receiver of the user equipment.

[0017] In certain embodiments, an apparatus includes receiving means for receiving information about an expected interference situation on resource elements used for estimation of interference related parameters. The apparatus also includes applying means for applying the information to improve performance of a receiver in a user equipment.

[0018] A non-transitory computer readable medium encoding a computer program that, when executed in hardware, performs a process, in certain embodiments. The process includes providing a user equipment with information about an expected interference situation on resource elements used for estimation of interference related parameters. The information is configured to be applied by the user equipment to improve performance of a receiver of the user equipment.

[0019] According to certain embodiments, a non-transitory computer readable medium encoding a computer program that, when executed in hardware, performs a process. The process includes receiving information about an expected interference situation on resource elements used for estimation of interference related parameters. The process also includes applying the information to improve performance of a receiver in a user equipment.

BRIEF DESCRIPTION OF THE DRAWINGS:

[0020] For proper understanding of the invention, reference should be made to the accompanying drawings, wherein:

[0021] Figure 1 illustrates a system in which base station is in an heterogeneous deployment according to certain embodiments.

[0022] Figure 2 illustrates a method according to certain embodiments.

[0023] Figure 3 illustrates a system according to certain embodiments. [0024] Figure 4 illustrates a method according to certain embodiments of the present invention.

[0025] Figure 5 illustrates a method according to certain embodiments of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S):

[0026] Figure 1 illustrates a system in which base station, such as an evolved Node B (eNodeB or eNB), is in an heterogeneous deployment, according to certain embodiments. As shown in Figure 1, a serving eNodeB 110 can have several low power remote radio heads (RRH) 120 distributed over a cell area 115. In a possible deployment the remote radio heads would share the same cell identifier (also known as cell identity number or cell-ID) with the macro-cell eNodeB 110.

[0027] In an example embodiment, the received signal y at the user equipment (UE) 130 can be expressed as

y ⁼ H _s P _s ^x s +∑ H _s P _c x _c +∑ H _k P _k x _k +∑ H _m P _m x _m + n, Equation ( 1 )

c k m

[0028] where H denotes the MEVIO channel gain, P denotes the combination of a precoder matrix and a transmit amplitude, x denotes a transmitted symbol, and n is the additional noise at the receiver. Furthermore, the subscript s denotes the intended signal, c denotes the co- scheduled signals (MU-MIMO transmissions from the same transmit point to other UEs 130), k denotes interfering signals from transmit points that share the same cell-ID as the serving transmit point, and m denotes the interfering signals from transmit points that have a different cell-ID as the serving eNodeB 110, such as those associated with one or more other eNodeB 140 (only one is shown). To simplify notation, the equivalent channel can be designated as H = HP .

[0029] In an example embodiment, an interference suppressing linear receiver matrix W for x _s given the received signal y is the LMMSE receiver can be expressed as

W H _S H? +∑H _c H ₊ ∑/¾H ₊ ∑H _ffl H ₊ p H s '

Equation (2)

[0030] where p _n is the noise power, / is the identity matrix, and () denotes the conjugate transpose operator. In order to calculate the receiver matrix W, the receiver may need to estimate the various quantities given in equations 1 and 2. The interference covariance matrices can be denoted as R _c = H _C H" , and other interfering signal subscripts can be c

similarly denoted.

[0031] In another example embodiment, instead of the LMMSE receiver, the user equipment may implement other receiver algorithms that possibly take other interference related parameters or statistics into account besides the interference covariance matrix or estimate thereof.

[0032] In an example embodiment, more than one reference signals can be used for channel estimation in, for example, 3rd generation partnership project (3GPP) long term evolution advanced (LTE-A), for the purpose of channel estimation for physical data shared channel (PDSCH) data demodulation. These reference signals can include cell-specific reference signals (CRS) and demodulation reference signals (DM-RS). The user equipment 130 may know the transmitted CRS and DM-RS symbols and positions in the time-frequency domain, that is the corresponding resource elements (RE) that include these symbols. Thus, the user equipment 130 can use the reference signals (from CRS and/or DM-RS) in estimation of interference related parameters such as the interference covariance matrix.

[0033] In addition to the cell-specific reference signals and demodulation reference signals, also other resource elements that are not used for PDSCH transmission within the allocated PDSCH region may be used for estimation of interference related parameters, at the user equipment. The channel state indication reference signal (CSI-RS) is one such signal. Also zero power resource elements may be included in the transmission in the form of for example zero power CSI-RS configuration. CSI-RS and zero power CSI-RS may occur at specific times and therefore may be used at those times.

[0034] In the remainder of the discussed embodiments the focus of the teachings is on reference signals that are present in each resource block carrying PDSCH such as CRS and DM-RS. Nevertheless the teachings are also in the same way applicable to any other reference signals such as CSI-RS and/or zero power resource elements such as zero power CSI-RS. [0035] In certain embodiments, the user equipment 130 estimates the channel H _s for the user equipment's own data transmission utilizing the reference signals, and then forms interference samples from the resource elements carrying reference symbols as

= { ^H s ^p s - H _s V _{re/ s} P _c x _{c ref} +∑ H _k P _k x _k +∑ H _m P _m x _mM + n _ref ,

J k m Equation

(3)

[0036] where the subscript ref refers to resource elements that carry reference signals. It is noted that also zero power reference symbols, ¾ _re = 0, may be included in such estimation by taking z _re f = y. An estimated linear minimum mean square error (LMMSE) receiver could be then formed as Equation (4)

[0037] The performance of the estimated LMMSE receiver in equation (4) can depend on the quality of the channel estimate H _s and the quality of the interference covariance matrix estimate. In principle, increasing the number of samples N _re f supporting the interference covariance matrix estimate provides better accuracy. The amount of resource elements available for interference covariance matrix estimation in each physical resource block (PRB), however, is limited, which may limit actual performance.

[0038] The CRS and possible CSI-RS symbols may not be precoded and are independent of the physical downlink shared channel transmission, while the DM-RS symbols may be precoded with the same precoder as the corresponding physical downlink shared channel symbols. However, even though the effective channel, including the effect of the precoder in the transmitter into the channel estimate, estimated from each of those reference signals is different in general, both reference signals can be used to form estimates of interference samples as, for example, in equation (3). [0039] Another difference between the CRS and DM-RS reference signals is that CRS can be cell-specific, meaning that the CRS from transmission (TX) points that share the same cell-ID may be the same and therefore may collide and combine at the receiver. Thus, in such cases the interference related statistics estimates that are obtained from the CRS resource elements will not include interference from intra-cell sources, including multiuser multiple input - multiple output (MU-MIMO) transmissions and potentially independent PDSCH transmissions from geographically separated transmission points with same cell-ID. Furthermore, as CRS is not precoded using the same precoding matrix as is used for the PDSCH transmission, if the CRS of an interfering cell collides with the own CRS, the statistics of the interference samples would not match that of the physical downlink shared channel of the interfering cell. This mismatch could affect receiver performance.

[0040] On the other hand, DM-RS resource elements may have all the interference sources present. Moreover, as noted above, the DM-RS resource elements may be precoded in the same way as the corresponding physical downlink shared channel.

[0041] Nevertheless, the density of DM-RS might be lower compared to the CRS density. Therefore, in scenarios with dominant intercell interference it may consider also other reference signals such as CRS, CSI-RS, and/or zero power reference symbols for purposes of estimation of interference related parameters to improve the reliability of the estimates by having more independent N _re f samples available.

[0042] In the scenario shown in Figure 1, two classes of UEs 130 can be identified. One class, illustrated by the right hand UE 130, may receive dominant interference from a transmission point (eNodeB or RRH) within a same cell (same cell-ID interference), for example, from remote radio heads 120 or serving eNodeB 1 10. The other class, illustrated by the left hand UE 130, receives dominant interference from another cell (different cell-ID interference), such as from other eNodeB 140. Depending on which group the UE 130 belongs to, it may or may not be helpful to utilize the CRS based interference samples in the estimation of interference related parameters.

[0043] Therefore, certain embodiments of the present invention provide a way to take also other reference signals besides DM-RS, such as CRS, CSI-RS, and/or zero power resource elements, into use in estimation of interference related parameters. [0044] According to certain embodiments, an eNodeB can inform a user equipment about the expected interference situation on resource elements carrying reference signals. This information can be applied in the user equipment for improving the receiver performance. The information may also be signaled indirectly from the eNodeB by recommending weights to be used by the user equipment when combining the interference estimates of interference related parameters obtained from different reference signals, such as CRS and DM-RS. Thus, certain embodiments employ a combining method of estimates of interference related parameters based on different reference signals, such as DM-RS, CRS, CSI-RS, and zero power resource elements such as zero power CSI-RS based estimates of interference related parameters to provide an advantageous receiver implementation.

[0045] Figure 2 illustrates a method according to certain embodiments. As shown in Figure 2, at 210 an eNodeB can estimate relative power of intercell interference and intracell interference with respect to one another. Thus, the eNodeB can estimate the expected balance between intra-cell and inter-cell interference for the user equipment.

[0046] The estimate can be based on a combination of information. The estimate can, at 211, be based on a relative location of the user equipment. For example, the estimate can be based on information regarding the user equipment's proximity to remote radio heads in the serving cell as well as the relative position of the remote radio head within the cell. A user equipment that is connected to a remote radio head close to a cell edge may be more likely to observe strong inter-cell interference than a user equipment connected to a remote radio head that is toward the middle of the cell.

[0047] The estimate can also, at 213, be based on user equipment measurements that are fed back to the eNodeB. The measurements can include, for example, reference signal received quality (RSRQ), channel quality indicator (CQI)/ precoder matrix indicator (PMI), and/or per transmission point CQI.

[0048] The estimate can further be based, at 215, on eNodeB measurements. For example, measurements on the possible uplink (UL) sounding channels can be used to form the estimate.

[0049] The estimate can additionally, at 217, be based on scheduling decisions that may affect the quality and quantity of the intra-cell interference. For example, the decisions related to multiuser precoder selection, dynamic point selection, dynamic point blanking, coordinated scheduling, joint transmission, and the like.

[0050] Also, at 219, the estimate can be based on reference symbol configurations in the serving and interfering cells. For example, the estimate can take into account frequency shift of the CRS pattern, the timing of the CSI-RS pattern in the serving and interfering cells, and/or the location of the zero-power resource elements in the physical resource block.

[0051] Then, at 220, the eNodeB can form a message (for example, reference signal interference characteristic) and signal the message semi-statically or dynamically to the user equipment (UE) on, for example, a downlink (DL) control channel.

[0052] Finally, at 230, based on the signaled information, the user equipment can implement a suitable estimator of interference related parameters such as the interference covariance matrix, that takes into account the presence of various interference sources on the various reference signals.

[0053] Γη an example embodiment the signaled information may be the proportion of inter- cell and intra-cell interference expected to be present on the physical downlink shared channel (PDSCH) or just simply if the expected inter-cell or intra-cell interference is dominant.

[0054] Γη another example embodiment the signaled information may be recommended weights to be used in estimation of interference related parameters. These weights could indicate how to combine the estimates of interference related parameters that are based on different reference signals such as CRS and DM-RS. For example, for the specific case of combining interference covariance matrix estimates based on CRS and DM-RS, the weights can be used in the following way: c = int,recom +

ref,CRS

[0055] Similar weighting could be applied also for other reference signals as CSI-RS, as well as zero power resource elements such as zero power CSI-RS, as well as for other interference related parameters besides the interference covariance matrix.

[0056] The signaled information may be suitably quantized to a limited number of bits in order to achieve a desirable tradeoff between signaling overhead and receiver performance. Thus, certain embodiments may be able to provide user equipment receiver performance that is adaptive to a wide variety of scenarios. For example, in certain embodiments w may be either 0 or 1/2 , meaning a simple implementation for either averaging over all S or then only DM-RS.

[0057] Figure 3 illustrates a system according to certain embodiments. In an example embodiment, a system may include three devices, user equipment (UE) 130, eNodeB 110, and remote radio head 120 (additional devices, such as additional remote radio heads may also be present in the system). Each of the devices 130, 110, and 120 may be equipped with at least one processor (respectively 334, 314, and 324), at least one memory (respectively 335, 315, and 325) (including computer program instructions or code), a transceiver (respectively 336, 316, and 326), and an antenna (respectively 337, 317, and 327). There is no requirement that each of these devices be so equipped. For example, the eNodeB 110 may be equipped for wired communication with a core network (not shown) and with the remote radio head 120.

[0058] The transceiver (respectively 336, 316, and 326) can be a transmitter, a receiver, both a transmitter and a receiver, or a unit that is configured both for transmission and reception. The transceiver (respectively 336, 316, and 326) can be coupled to corresponding one or more antenna(s) (respectively 337, 317, and 327), which may include a directional antenna.

[0059] The at least one processor (respectively 334, 314, and 324) can be variously embodied by any computational or data processing device, such as a central processing unit (CPU) or application specific integrated circuit (ASIC). The at least one processor (respectively 334, 314, and 324) can be implemented as one or a plurality of controllers.

[0060] The at least one memory (respectively 335, 315, and 325) can be any suitable storage device, such as a non-transitory computer-readable medium. For example, a hard disk drive (HDD) or random access memory (RAM) can be used in the at least one memory (respectively 335, 315, and 325). The at least one memory (respectively 335, 315, and 325) can be on a same chip as the corresponding at least one processor (respectively 334, 314, and 324), or may be separate from the corresponding at least one processor (respectively 334, 314, and 324).

[0061] The computer program instructions may be any suitable form of computer program code. For example, the computer program instructions may be a compiled or interpreted computer program.

[0062] The at least one memory (respectively 335, 315, and 325) and computer program instructions can be configured to, with the at least one processor (respectively 334, 314, and 324), cause a hardware apparatus (for example, user equipment 130, eNodeB 110, or remote radio head 120) to perform a process, such as any of the processes described herein (see, for example, Figures 2, 4, and 5).

[0063] Thus, in certain embodiments, a non-transitory computer-readable medium can be encoded with computer instructions that, when executed in hardware perform a process, such as one of the processes described herein. Alternatively, certain embodiments of the present invention may be performed entirely in hardware.

[0064] The devices of the system may also include additional components. For example, each of user equipment 130, eNodeB 110, and remote radio head 120 can include a user interface that is operable connected to the processor (respectively 334, 314, and 324) and memory (respectively 335, 315, and 325). That user interface can include a display, such as a liquid crystal display (LCD) or organic electroluminescent display (OELD), as well as speakers or audio outputs. Tactile outputs, such as a haptic feedback system, can also be included. The user interface may have a touch screen to receive user input. User input can also be provided by a keypad, keyboard, microphone, joystick, mouse, trackball, or other input device. Of course, there is no requirement that the devices include a user interface. For example, the eNodeB 110 and remote radio head 120 may be embodied as rack-mounted computers. In certain embodiments, the remote radio head 120 may serve as a peripheral device of the eNodeB 110, and thus may not necessarily have all the components illustrated in Figure 3.

[0065] As described herein, when it is mentioned that the eNodeB 120 sends a message to the user equipment 130, it should be understood that the message may be sent via a remote radio head 130. [0066] Figure 4 illustrates a method according to certain embodiments of the present invention. The method of Figure 4 may be performed by an eNodeB in cooperation with a user equipment (such as described above with reference to Figure 3). As shown in Figure 4, at 405, an eNodeB may estimate interference contributions for a particular user equipment, as described above with reference to Figure 2.

[0067] Then, at 410, the eNodeB may provide these interference expectations to the user equipment. The interference expectations can be provided in various ways. For example, at 420, as an example of providing these interference expectations, the eNodeB can recommend weights for how various estimates of interference related parameters such as the interference covariance matrix are combined by the user equipment. This recommendation can be merely advisory or it can be mandatory for the user equipment. Alternatively, at 420, the eNodeB can indicate the portion/share of the expected intra-cell and inter-cell interference, which may be as well a simple indication if either intra-cell or inter-cell interference is expected to dominate.

[0068] The eNodeB can also provide various reference signals such as cell-specific reference signals (CRS), demodulation reference signals (DM-RS), and/or channel state information reference signals (CSI-RS) to the user equipment. Moreover the eNodeB can also provide information on the configuration of zero power resource elements such as zero power CSI-RS to the user equipment. These signals can be supplied at the same time as the other information regarding interference expectations, or at a different time. The user equipment may be configured to apply, at 440, these expectations and other information to its own receiver.

[0069] Figure 5 illustrates a method according to certain embodiments. The method shown in Figure 5 may be performed by a user equipment in cooperation with an eNodeB (such as described above with reference to Figure 3).

[0070] As shown in Figure 5, the method can include, at 510, receiving information about an expected interference situation on resource elements carrying reference signals. The information can take various forms. For example, receiving the information can include, at 515, receiving recommended weights to be used when combining estimates of interference related parameters such as the interference covariance matrix estimates obtained from different reference signals. At 517, the method can include receiving resource elements carrying both a cell-specific reference signal and a demodulation reference signal.

[0071] The method can also include, at 520, applying the information to improve receiver decoding performance in a user equipment. The method can further include, at 530, feeding back measurements to an eNodeB, wherein the information about the expected interference situation is received from the eNodeB.

[0072] One having ordinary skill in the art will readily understand that the invention as discussed above may be practiced with steps in a different order, and/or with hardware elements in configurations which are different than those which are disclosed. Therefore, although the invention has been described based upon these preferred embodiments, it would be apparent to those of skill in the art that certain modifications, variations, and alternative constructions would be apparent, while remaining within the spirit and scope of the invention. In order to determine the metes and bounds of the invention, therefore, reference should be made to the appended claims.