COMPLEXITY REDUCTION FOR OPEN RADIO ACCESS NETWORK RADIO UNIT UPLINK RECEIVER FIELD: [0001] Some example embodiments may generally relate to communications including mobile or wireless telecommunication systems, such as Long Term Evolution (LTE) or fifth generation (5G) radio access technology or new radio (NR) access technology, or other communications systems. For example, certain example embodiments may generally relate to systems and/or methods for providing complexity reduction for an open radio access network (O- RAN) radio unit uplink receiver. While certain embodiments may be directly applicable to O-RAN alliance technical specifications and to an O-RAN uplink RU, O-RAN DU, and fronthaul therebetween, certain embodiments may also be applicable to various other use cases and other specifications. BACKGROUND: [0002] Examples of mobile or wireless telecommunication systems may include the Universal Mobile Telecommunications System (UMTS) Terrestrial Radio Access Network (UTRAN), Long Term Evolution (LTE) Evolved UTRAN (E-UTRAN), LTE-Advanced (LTE-A), MulteFire, LTE-A Pro, and/or fifth generation (5G) radio access technology or new radio (NR) access technology. 5G wireless systems refer to the next generation (NG) of radio systems and network architecture. A 5G system is mostly built on a 5G new radio (NR), but a 5G (or NG) network can also build on the E-UTRA radio. It is estimated that NR provides bitrates on the order of 10-20 Gbit/s or higher, and can support at least service categories such as enhanced mobile broadband (eMBB) and ultra-reliable low-latency-communication (URLLC) as well as massive machine type communication (mMTC). NR is expected to deliver extreme broadband and ultra-robust, low latency connectivity and massive networking to support the Internet of Things (IoT). With IoT and machine-to-machine (M2M) communication becoming more widespread, there will be a growing need for networks that meet the needs of lower power, low data rate, and long battery life. The next generation radio access network (NG-RAN) represents the RAN for 5G, which can provide both NR and LTE (and LTE-Advanced) radio accesses. It is noted that, in 5G, the nodes that can provide radio access functionality to a user equipment (i.e., similar to the Node B, NB, in UTRAN or the evolved NB, eNB, in LTE) may be named next-generation NB (gNB) when built on NR radio and may be named next- generation eNB (NG-eNB) when built on E-UTRA radio. SUMMARY: [0003] An embodiment may be directed to an apparatus that may include at least one processor and at least one memory comprising computer program code. The at least one memory and computer program code can be configured, with the at least one processor, to cause the apparatus at least to process an uplink signal from a user equipment by performing a first digital reception beamforming on the uplink signal. The at least one memory and computer program code can further be configured, with the at least one processor, to cause the apparatus at least to provide the processed uplink signal with additional information to a device supporting the apparatus. The additional information can be configured to enable a second digital reception beamforming on the processed uplink signal in the device. [0004] An embodiment may be directed to an apparatus that may include at least one processor and at least one memory comprising computer program code. The at least one memory and computer program code can be configured, with the at least one processor, to cause the apparatus at least to receive from a device supporting the apparatus, a processed uplink signal of an uplink signal transmitted from a user equipment, together with additional information regarding the uplink signal, wherein the processed uplink signal is obtained by performing a first digital reception beamforming on the uplink signal in the device. The at least one memory and computer program code can be configured, with the at least one processor, to cause the apparatus at least to perform a second digital beamforming on the processed uplink signal based on the additional information. The at least one memory and computer program code can be configured, with the at least one processor, to cause the apparatus at least to perform equalization on an output signal provided from the second digital beamforming. [0005] An embodiment may be directed to a method that can include processing an uplink signal from a user equipment by performing a first digital reception beamforming on the uplink signal. The method can further include providing, by the first device, the processed uplink signal with additional information to a second device supporting the first device. The additional information can be configured to enable a second digital reception beamforming on the processed uplink signal in the second device. [0006] An embodiment may be directed to a method that can include receiving, by a first device and from a second device supporting the first device, a processed uplink signal of an uplink signal transmitted from a user equipment, together with additional information regarding the uplink signal, wherein the processed uplink signal is obtained by performing a first digital reception beamforming on the uplink signal in the second device. The method can also include performing, by the first device, a second digital beamforming on the processed uplink signal based on the additional information. The method can further include performing, by the first device, equalization on an output signal provided from the second digital beamforming. [0007] An embodiment may be directed to an apparatus that can include means for processing an uplink signal from a user equipment by performing a first digital reception beamforming on the uplink signal. The apparatus can further include means for providing the processed uplink signal with additional information to a device supporting the apparatus. The additional information can be configured to enable a second digital reception beamforming on the processed uplink signal in the device. [0008] An embodiment may be directed to an apparatus that can include means for receiving from a device supporting the apparatus, a processed uplink signal of an uplink signal transmitted from a user equipment, together with additional information regarding the uplink signal, wherein the processed uplink signal is obtained by performing a first digital reception beamforming on the uplink signal in the device. The apparatus can also include means for performing a second digital beamforming on the processed uplink signal based on the additional information. The apparatus can further include means for performing equalization on an output signal provided from the second digital beamforming. BRIEF DESCRIPTION OF THE DRAWINGS: [0009] For proper understanding of example embodiments, reference should be made to the accompanying drawings, wherein: [0010] FIG.1 illustrates two split architecture cases; [0011] FIG.2 illustrates a split architecture according to certain embodiments; [0012] FIG. 3 illustrates a signal flow chart of a first method according to certain embodiments; [0013] FIG. 4 illustrates a signal flow chart of a second method according to certain embodiments; [0014] FIG. 5 illustrates a signal flow chart of a third method according to certain embodiments; [0015] FIG. 6 illustrates an example flow diagram of a method, according to an embodiment; [0016] FIG. 7 illustrates another example flow diagram of a method, according to an embodiment; [0017] FIG.8 illustrates an example block diagram of a system, according to an embodiment; [0018] FIG. 9A illustrates an example of signal and data flow in a system, according to an embodiments; and [0019] FIG.9B illustrates another example of signal and data flow in a system, according to an embodiments. DETAILED DESCRIPTION: [0020] It will be readily understood that the components of certain example embodiments, as generally described and illustrated in the figures herein, may be arranged and designed in a wide variety of different configurations. Thus, the following detailed description of some example embodiments of systems, methods, apparatuses, and computer program products for providing complexity reduction for an open radio access network radio unit uplink receiver, is not intended to limit the scope of certain embodiments but is representative of selected example embodiments. [0021] The features, structures, or characteristics of example embodiments described throughout this specification may be combined in any suitable manner in one or more example embodiments. For example, the usage of the phrases “certain embodiments,” “some embodiments,” or other similar language, throughout this specification refers to the fact that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment. Thus, appearances of the phrases “in certain embodiments,” “in some embodiments,” “in other embodiments,” or other similar language, throughout this specification do not necessarily all refer to the same group of embodiments, and the described features, structures, or characteristics may be combined in any suitable manner in one or more example embodiments. [0022] Certain embodiments may have various aspects and features. These aspects and features may be applied alone or in any desired combination with one another. Other features, procedures, and elements may also be applied in combination with some or all of the aspects and features disclosed herein. [0023] Additionally, if desired, the different functions or procedures discussed below may be performed in a different order and/or concurrently with each other. Furthermore, if desired, one or more of the described functions or procedures may be optional or may be combined. As such, the following description should be considered as illustrative of the principles and teachings of certain example embodiments, and not in limitation thereof. [0024] Open Radio Access Network (O-RAN), an industry alliance, has adopted a lower layer functional split between O-RAN Radio Unit (O-RU) and the O-RAN Distributed Unit (O-DU), known as 7-2X. See, for example, O-RAN Fronthaul Control, User and Synchronization Plane Specification 7.0 - July 2021 (O-RAN.WG4.CUS.0-v07.00). Various split strategies, including 7-2 and 7-3 may be applicable to uplink (UL) communication. Certain embodiments provide processes and signaling schemes between the O-RU and the O-DU, linking the O-DU with the O-RU for the uplink scenario, with a functional Split-7-2x based architecture which may achieve, or approximate, the performance and bandwidth requirements of a 7-3 architecture. [0025] FIG. 1 illustrates two split architecture cases. In the 7-2 split case, labeled 7-2x split in FIG.1, the channel estimation block is in the distributed unit (DU) side. In the 7-3 split case, labeled 7-3 split in FIG. 1, the channel estimation block is in the radio unit (RU) side. These split strategies can be used for the uplink case in an O-RAN radio access network (RAN). [0026] An open interface for the 7-2 architecture split point may enable one vendor to manufacture the RU while another vendor manufactures the DU. [0027] According to the 7-2 architecture split, uplink receive beamforming is performed in the RU, while receive channel estimation and other receive processing is performed in the DU. Thus, the beamformed in-phase and quadrature (I&Q) output samples flow over the fronthaul from the RU to the DU for the usual receiver processing. [0028] As shown in FIG.1, in the 7-2 architecture split the O-DU can include IQ decompression, channel estimation, digital Rx beamforming and equalization, and decoding. The O-RU, on the other hand, can include analog beamforming and IQ compression. Compression is provided as one way in which an original form or original version of a signal may be transformed into a different form or different version of the signal. For example, in addition to or instead of compression, the different form or version may be a linearly transformed and/or mapped version or form. Other processing to generate a form or version is also permitted. [0029] In contrast to the 7-2 architecture split, the 7-3 architecture split assumes the receive beamforming, receive channel estimation, and further receiver processing are all in the RU, and that I&Q data for the equalized layers is sent down the fronthaul to the DU for decoding. More particularly, in the 7-3 split, the O-RU can include not only analog beamforming and IQ compression, as in the 7-2 split, but also channel estimation and digital beamforming and equalization. In the 7-3 split, the O-DU may include IQ decompression and decoding, as in the 7-2 split, while omitting channel estimation and digital receive beamforming and equalization. [0030] FIG. 1 illustrates data flow in an uplink direction, with uplink signals for a device, such as next generation Node B (gNB) or the like, coming from a remote device over the air and incident on one or more antenna or antenna array, not shown. The uplink signal comes first to the O-RU, then goes over a fronthaul link to the O-DU, from which the signal can go to a processor or the like, which is not shown. The data-carrying capacity of the fronthaul link may be a constraining factor to be considered when deploying massive MIMO (Multiple Input Multiple Output) with any type of fronthaul interface, whether open or closed.

[0031] There may be various ways to model a communication system, of which the following is one example. For example, K co-scheduled desired user signals can be denoted by with their channel matrix denoted by outer-cell (inter-cell) interfering user signals S _i ∈ with their interfering channel matrix denoted by Equation (1) can denote the input-output signal relation as follows:

[0032] y = Hs _d + Gs _i + n Equation (1)

[0033]In Equation (1), and denotes complex white Gaussian noise with where Cov denotes covariance matrix of the noise vector n. In mMIMO systems, it can be safely assumed that M > K, due to fact that most often the number of antenna/receive elements (M) in a mMIMO system are much larger than the number the users (K) that the gNB is trying to receive signals from. For example, M can be 64 or 256 or 1024, while K is 8 or 4.

[0034] Furthermore, x = Gs _i + n can denote the interference-plus-noise signal. Moreover, can be the Hermitian symmetric covariance matrix of the interference-plus-noise signal x.

[0035] Assuming a linear receiver, the received signal after processing reception filter can be described by where the general implementation form of the whitening type interference rejecting combiner - minimum mean square error (IRC-MMSE) linear filter or equalizer can be given by Equation (2):

[0036]

[0037] The channel and covariance matrices given in Equation (2) may need to be estimated, as they are not known in advance. [0038] In order to implement the IRC-MMSE Linear equalizer when only intra-cell co-scheduled users’ channel matrix can be estimated, in order to compute the sample based Covariance matrix averaging can be performed over DMRS pilot symbols allocated within a resource block (RB) by Equation (3): [0039] [0040] where the number of resource elements occupied by RS (e.g., DMRS) pilots can be given by N _RE . [0041] IRC-MMSE linear filter implementation when both intra-cell and intercell users’ channel matrices ( and respectively) can be accomplished by first calculating the covariance matrix estimate directly by Equation (4): [0042] Equation (4) [0043] Equation (2) can be considered the main IRC-MMSE equalization equation of this model, and certain embodiments can be viewed as relates to the details of which parts of Equation (2) are to be implemented in which part of the UL receiver, whether in the RU or in the DU. [0044] In the case of 7-2x split, as shown for example in FIG.1, unless beam based processing is used, the fronthaul overhead may scale by the number of receiving antennas. This may lead to a relatively large fronthaul bandwidth overhead. Thus, depending on the fronthaul capacity, it might not be possible to fully utilize the highest number of multi-user pairing processes. In case of 7-3 split, all processing for the uplink channel estimation and equalization may be done inside of the RU, so this split may allow full port IRC-MMSE type processing at RU. However, the processing burden of O-RU is relatively higher than the case of 7-2x. [0045] Certain embodiments split uplink receiver signal processing computations between the RU and DU. The split of uplink receiver signal processing computations between the RU and DU may reduce the computational complexity of the RU side and the fronthaul overhead, or fronthaul bandwidth (BW), by spatial dimension reduction at the RU. With partial filtering/digital beamforming done in RU, fronthaul overhead can be scaled down to the number of scheduled users K×1, proportional to the number of data layers. Part of the processing burden of RU can be transferred to DU. [0046] Certain embodiments provide an effective method to distribute the reception filtering process between RU and DU. Certain embodiments can make the distribution considering interference channels and/or interference signals depending on coordination level. [0047] FIG.2 illustrates a split architecture according to certain embodiments. By splitting the UL receiver signal processing computations between the RU and DU, certain embodiments may reduce [0048] the computational complexity of the RU, and reduce the fronthaul BW by spatial dimension reduction at the RU, while keeping the receiver performance at the same or comparable level to that of 7-3 split architecture. [0049] FIG. 9A illustrates an example of signal and data flow in a system, according to an embodiments. As shown in FIG.9A, there can be dimensional reduction in a system according to certain embodiments. For example, an RU may receive an M -dimensional received signal vector, from, for example, a plurality of antennas or an antenna array. The RU may then provide K - dimensional processed data to the DU. The DU can provide control information to the RU. While the widths of the arrows are not to a precise scale, the width of the arrows is indicative of the reduction in the amount of data being provided. M may be much greater than K. For example, M may be 64, 256, or 1024, while K may be 8, 4, 2, or 1. Thus, certain embodiments may provide a reduction in the dimension of the data provided to the DU. [0050] FIG.9B illustrates another example of signal and data flow in a system, according to an embodiments. As shown in FIG.9B, there can be dimensional reduction in a system according to certain embodiments. For example, N RUs may each receive a corresponding M _i -dimensional received signal vector, M ₁ to M _N , from, for example, a plurality of antennas or an antenna array corresponding to each RU. Each RU may then provide K _i -dimensional processed data to the DU. The DU can provide control information to each RU. As in FIG.9A, while the widths of the arrows are not to a precise scale, the width of the arrows is indicative of the reduction in the amount of data being provided. M _i may be much greater than K _i . For example, M _i may be 64, 256, or 1024 while K _i may be 8, 4, 2, or 1. Thus, certain embodiments may provide a reduction in the dimension of the data provided to the DU. [0051] As shown in FIG. 2, in certain embodiments both of the RU and the DU have a signal processing unit. In a digital receiver beamforming split, the channel estimation may be performed in the O-RU, as in the 7-3 split. However, digital receiver beamforming may be split between the RU and the DU. A first digital receiver beamforming may be performed in the RU for spatial dimension complexity reduction. Then, a second digital receiver beamforming and equalization may be performed in the DU. The fronthaul interface may accommodate in the uplink direction, received signals and information for DU beamforming (BF)). In the reverse direction, control signals may propagate from the DU back to the RU BF. [0052] Certain embodiments may employ different strategies depending on whether or not to estimate the interference channel itself. There may be at least three methods that can implement certain embodiments. For convenience and ease of reference only, and not by way of limitation, priority, or preference, these may be described as the first, second, and third method. [0053] A first method may operate on the assumption that there is no co- ordination between DUs. Thus, each DU and/or RU may have no prior information on inter-cell interfering UEs. In this case, outer-cell interference signals and white noise can be treated together as a colored disturbance signal. In this approach, explicit estimation of the interference channel matrix G in Equation (1), for outer cell interfering users may not be possible. In certain embodiments, a single DU can control multiple RUs. Such a DU may or may not supply coordination information, such as information on interference, to the RUs that the DU may be controlling. In the first method, there may be an assumption that where the DU controls multiple RUs, the DU does not provide information on interference between/among RUs. [0054] The second method may operate on the assumption that there is co- ordination between DUs, so each DU and/or RU may be able to obtain prior scheduling and/or reference signal configuration information on inter-cell interfering UEs. In this case, outer-cell interference signals and white noise can be separately treated since the RU can estimate them separately. Thus certain embodiments can explicitly estimate the interference channel matrix G in equation (1), for outer cell interfering users. [0055] The third method may be similar to the second method, in that the third method may also operate on the assumption that there is co-ordination between DUs, so each DU and/or RU may be able to obtain prior scheduling and/or reference signal configuration information on inter-cell interfering UEs. Thus, outer-cell interference signals can be separately estimated by RU. One difference between the third method and the second method may be that while the second may provide or achieve exact IRC-MMSE equalization with the channel and covariance matrix estimates, the third method may provide an approximation to that equalization by using singular value decomposition and only retaining a certain number of dominant singular vectors. [0056] FIG. 3 illustrates a signal flow chart of a first method according to certain embodiments. As mentioned above, in the first method there may be an assumption that there is no co-ordination between DUs or between RUs controlled by a single DU. Thus, each DU and/or RU may have no prior information on inter-cell interfering UEs. In this case, outer-cell interference signals and white noise can be treated together as a colored disturbance signal. Certain embodiments may not explicitly estimate the interference channel matrix G , as shown in Equation (1), for outer cell interfering users. A simplified notation can be used. For example, the channel ( H, G) and covariance (R _x ) matrices can be written directly without using the circumflex sign, “^”, indicating that the estimated matrices are being used. [0057] At an initial stage, one or more UE whose transmitted data is desired labeled as 0-a may arrive at a gNB as physical uplink shared channel (PUSCH) demodulation reference signal (DMRS). Also, one or more interfering UE may transmit data labeled as 0-b that may also arrive at the gNB. Moreover, the DU may provide an indication of options labeled as 0-c. At 1, channel estimation ( H ) and interference covariance matrix ( R _x ) calculation can be performed based on the received PUSCH-DMRS. At 0-c, the DU can indicate to the RU one option of multiple possible options. These options may relate to which data is to be provided from the RU to the DU for signal processing. The options may be indicated in various ways from DU, such as by two bits in a control message. [0058] In one option (identified in FIG.3 as option #1 for reference only), the DU can indicate that the RU is to report/send D ₁ , H, _y1 to the DU. D ₁ = J ^H R _x ^{- 1} can be the receiving filter of the RU, and R _x = E{xx ^H } = GG ^H + N ₀ I The RU can compute the RU filter by estimating the desired channel and the interference signals. The effective received signals after applying the RU receiving filter can be denoted by y ₁ = D ₁ y, where y ₁ ∈ ℂ ^K×1 . The DU may request the RU to send desired channel information, for example, only if there is variation of the estimated channel over a certain threshold. The threshold may be provided by the DU to the RU. [0059] According to another option (identified in FIG. 3 as option #2 for reference only), the DU can indicate for the RU to report/send D ₂ , y ₁ to the DU. The DU may request RU to send them together. That is, whenever RU sends y ₁ to the DU, the RU may almost always need to send D ₂ , because the covariance of interference and noise may need to be updated for every slot. can denote the receiving filter of the DU side. In this option, the RU can calculate and determines the receiving filter of the DU. [0060] According to a further option, (identified in FIG. 3 as option #3 for reference only), the DU can indicate for the RU to report/send to the DU. The DU may be able to indicate different update rate or update periodicity, which can also be referred to as a reporting periodicity, between H and + as the desired channel information may not be necessarily updated for every slot, while interference plus noise covariance matrix may need to be updated every slot to guarantee performance. [0061] At 1 in FIG.3, the RU can perform estimation of the desired channels using sounding reference signals (SRS) and/or UL demodulation reference signals (DMRS). [0062] At 2 in FIG. 3, the RU can calculate the RU filter, for example the 1 ^st part of the whole MMSE IRC filter, and, at 3, can perform receiving signal processing. The RU can, at 4, send/report the signal information depending on the indicated option#1/#2/#3 by the DU. In option #1, the RU can send D ₁ , H, y ₁ to the DU. In option #2, the RU can send D ₂ , y ₁ to the DU. In option #3, the RU can send H to the DU. For example, the RU can send H with a periodicity of P1 indicated by DU and the RU can send with a periodicity of P2 indicated by DU. [0063] At 5 and 6 in FIG.3, there can be DU processing. In cases of option #1 and option #3, the DU can, at 5, first calculate the DU receiving filter by using the provided information such that and the DU can, at 6, process the received signal by using this filter, for example, z = D ₂ y ₁ . In case of option #2, the DU can use the provided receiving filter and can, at 6, process the received signal by using this filter, for example, z = D ₂ y ₁ . [0064] FIG. 4 illustrates a signal flow chart of a second method according to certain embodiments. As mentioned above, in the second method there may be an assumption that there is co-ordination between DUs, so each DU and/or RU may be able to obtain prior scheduling and/or reference signal configuration information on inter-cell interfering UEs. In the case of a single DU with multiple RUs, the second method may be applied with the assumption that the DU is providing coordination across the RUs served by the DU, such that the RUs can participate in inter-cell interference estimations. In this case, outer-cell interference signals and white noise can be separately treated, because the RU can estimate them separately. Thus certain embodiments can explicitly estimate the interference channel matrix G in equation (1), for outer cell interfering users. In this method, the receiving filter of RU can be denoted by D ₁ and the receiving filter of DU can be denoted by D ₂ , but should be understood to be different than the similarly denoted filters in the first method. [0065] At an initial stage, the flow of FIG.4 may be the same as that of 0-a, 0-b, 0-c, and 1 of FIG. 3. For example, desired and interfering UEs may transmit data to the access node, for example, the gNB, and channel estimation and interference covariance matrix calculation may be performed. [0066] At 0-c, the DU can indicate a specific option to the RU for receiving signal processing. As with the options in FIG. 3, the options in FIG. 4 are labeled option #1, option #2, and option #3 for reference only, and not by way of priority, sequence, or preference. [0067] According to option 1, the DU may indicate for the RU to report/send D ₁ , H, y ₁ to the DU. D ₁ = H ^H (GG ^H + N ₀ I ^{) -1} can be the receiving filter of the RU. The RU can compute the RU filter by estimating the desired channel and the interference channels. This filter may be the first filter of Meanwhile, y ₁ = D ₁ y can be the effective received signals after applying the RU receiving filter. The DU may request the RU to send desired channel information only if there is variation of the estimated channel over a certain threshold. The threshold value may be provided by the DU. [0068] According to option #2, the DU can indicate for the RU to report/send D ₂ , y ₁ to the DU. In this case, D ₂ = (H ^. (GG ^H + N ₀ I ^)-1 H + I) ^-1 can be the receiving filter of the DU side. In this option, the RU can calculate and determine the receiving filter of the DU. [0069] According to option #3, the DU can indicate for the RU to report/send H,G, N ₀ , y ₁ to the DU. The DU may be able to indicate different update rate or update periodicity between H and G considering the overhead and estimated/predicted channel variation. The consideration of overhead and estimated/predicted channel variation may be performed by the DU or may be configured to the DU by the manufacturer, or the like. As another example, the DU may request RU to send desired channel information ( H) and interference channel information (G) only if there is variation of the estimated channel over a certain threshold. The threshold value may be provided by the DU. [0070] At 1, as in FIG.3 so also in FIG. 4, the RU can perform estimates of the desired and interference channels using SRS and/or UL DMRS. Then, at 2, the RU can calculate the RU filter, which can be the 1 ^st part of the whole MMSE IRC filter, and can perform receiving signal processing. The RU can, at, 4, send/report the signal information depending on the indicated option#1/#2/#3 by the DU. In option #1, the RU can send D ₁ , H, y ₁ to the DU. In option #2, the RU can send D ₂ , y ₁ to the DU. In option #3, the RU can send H,G, N ₀ , y ₁ to the DU. For example, sending H with a periodicity of P1 can be indicated by DU. For example, the periodicity of P1 can be associated with SRS transmission periodicity of the desired users. As another example, sending G with a periodicity of P2 can be indicated by DU. For example, the periodicity of P2 can be associated with SRS transmission periodicity of the interference users. Additionally, as a further example, there may event-triggered transmission of H and/or G. For example, the RU can update H and/or G when the RU detects variation over a threshold. The threshold value may be provided by the DU. [0071] At 5 and 6 in FIG.4, there can be a DU processing phase. In the cases of option #1 and option #3, the DU can, at 5, calculate the DU receiving filter by using the provided information such that and the DU can, at 6, process the received signal by using this filter, for example, z = D ₂ y ₁ . In the case of option #2, the DU can use the provided receiving filter and can, at 6, process the received signal by using this filter, for example, z = D ₂ y ₁ . [0072] For ease of reference, the whole receiving filter information in certain embodiments may be expressed as follows: [0073] [0074] Thus, the whole receiving filter can be viewed as a combination of the first receiving filter, D ₁ and the second receiving filter, D ₂ . The first receiving filter may be in the RU, while the second receiving filter may be in the DU. [0075] FIG. 5 illustrates a signal flow chart of a third method according to certain embodiments. As mentioned above, in the second method there may be an assumption that there is co-ordination between DUs or by a DU among a set of RUs controlled by the DU, so each DU and/or RU may be able to obtain prior scheduling and/or reference signal configuration information on inter-cell interfering UEs. Thus, outer-cell interference signals can be separately estimated by the RU. [0076] At an initial stage, the flow of FIG.5 may be the same as that of 0-a, 0-b, 0-c, and 1 of FIGs. 3 and 4. For example, desired and interfering UEs may transmit data to the access node, for example, the gNB, and channel estimation and interference covariance matrix calculation may be performed. [0077] At 0-c, the DU can indicate a specific option to the RU for receiving signal processing. In this example, two options are denoted option #1 and option #2 for reference only. In option #1, the DU can indicate that the RU is to report/send D ₁ , H, y ₁ to the DU. y ₁ = D ₁ y can be the effective received signals after applying the RU receiving filter. D ₁ can be the receiving filter of the RU. The first receiving filter, D ₁ and the second receiving filter, D ₂ of the example of FIG.5 may be different from those of FIGS.3 and 4. [0078] In this method, design can be different depending on the number of antennas, desired users and interfering users. In a first case, where M can be the number of antennas, K can be the desired users, and can be the dimension of interference signals. In this case, vectors can be obtained based on singular value decomposition, in order to remove M − K dominant interference signals for a total of interference signals, where [0079] In a second case, In this case, at first for a total of interference signals, M − K dominant interference signal vectors can be selected based on the received signal power, for example g ₁ , g ₂ , …, g _M-K can be chosen. Then, a matrix can be constructed: Accordingly, it can be determined that this can imply that the receiving antennas, as a spatial resource, may be enough to fully handle the desired signal and interference signal by spatial separation. Thus, it possible to use simple zero- forcing or MMSE filtering in this case, hence there may not be a need to provide further details for this case. [0080] According to option #2, the DU can indicate that the RU is to report/send D ₂ , y ₁ to the DU. D ₂ = ((D ₁ H) ^H D ₁ H) ⁶⁷ (D ₁ H) ^H can be the receiving filter of the DU side. In this option, the RU can calculate and determines the receiving filter of the DU. This example is based on the pseudo inverse, but MMSE filter is also available. [0081] At 1, as in FIGs. 3 and 4, so also in FIG. 5, the RU can estimate the desired and interference channels using SRS and/or UL DMRS. [0082] At 2, the RU can calculate the RU filter, for example the 1 ^st part of the whole MMSE IRC filter, and, at 3, can perform receiving signal processing. The RU can, at 4, send/report the signal information depending on the indicated option#1/#2 by the DU. For option #1, the RU can send D ₁ H, y ₁ to the DU. For option #2, the RU sends D ₂ , y ₁ to the DU. [0083] At 5, the DU can calculate the reception filter such that D ₂ = ((D ₁ H) ^H D ₁ H ^)-1 (D ₁ H) ^. and can process the provided signal vector y ₁ using the filter, for example, 0 = D ₂ y ₁ . [0084] The order of the processes shown in FIGs.3, 4, and 5 can be changed, and/or two or more steps can be merged into a single step. [0085] FIG. 6 illustrates an example flow diagram of a method for providing complexity reduction for an open radio access network radio unit uplink receiver, according to certain embodiments. [0086] As shown in FIG.6, a method can include procedures performed by a radio unit. The procedures performed by the radio unit in FIG. 6 can be performed in combination with the procedures performed by the distributed unit in FIG.7, or separately from one another. [0087] As shown in FIG. 6, a method can include, at 610, performing, by a first device, channel estimation on uplink signals from a plurality of user equipment. The first device may be a radio unit. [0088] The method may also include, at, 620, performing, by the first device, a first digital reception beamforming on an uplink signal of a user equipment of the plurality of user equipment. This may be the first digital beamforming illustrated in FIG.2 and described above. [0089] The method may also include, at 630, providing, by the first device, a form or version of the uplink signal with additional information to a second device supporting the first device. The second device can be remote from the first device. The form or version may be a compressed form and/or linearly transformed/mapped form. The compressed form may be due to IQ compression or the like. The second device can be a distributed unit. The additional information may be configured to enable a second digital reception beamforming on the uplink signal in the second device. [0090] The method can also include, at 640, receiving, by the first device, control information from the second device. The method can further include, at 650, controlling or otherwise determining, by the first device, the first digital reception beamforming based on the control information from the second device. [0091] The method can also include, at 660, receiving, by the first device from the second device, a reporting configuration. The additional information can be provided to the second device in accordance with the reporting configuration. [0092] The reporting configuration can include at least one threshold for reporting. For example, as mentioned above, the threshold may be a threshold variation. The reporting configuration can also include an indication of the selection of a specific option, such as option #1, option #2, or option #3 in the examples described above. [0093] The reporting configuration can include an indication that values of at least two different parameters are to be provided together. For example, the configuration may indicate that if a value of a first parameter is provided then a value of a second parameter should also be provided. [0094] The reporting configuration can include an indication of update periodicity or reporting periodicity of at least one value of the additional information. Moreover, the reporting configuration can include two or more different update periodicities or reporting periodicities. Thus, one parameter value may be updated more frequently than another. [0095] The method can include, at 670, calculating, by the first device, a receiving filter of the second device. The additional information provided to the second device can include the receiving filter of the second device. [0096] It is noted that FIG. 6 is provided as one example embodiment of a method or process. However, certain embodiments are not limited to this example, and further examples are possible as discussed elsewhere herein. [0097] FIG.7 illustrates an example flow diagram of a method for complexity reduction for an open radio access network radio unit uplink receiver, according to certain embodiments. The procedures performed by the DU in FIG. 7 can be performed in combination with the procedures performed by the RU in FIG.6, or separately from one another. [0098] As shown in FIG. 7, a method can start at 705. The method can include, at 710, receiving, by a first device, a version of an uplink signal on which channel estimation has been performed, together with additional information regarding the uplink signal based on a first digital beamforming performed on a second device remote from the first device. This may be the same additional information and compressed or otherwise modified UL signal provided at 630 in FIG.6. In the discussion of FIG.7, the first device may be the distributed unit and the second device may be the radio unit. [0099] The method can also include, at 720 performing, by the first device, a second digital beamforming on the uplink signal based on the additional information. The method can further include, at 730, performing, by the first device, equalization on the uplink signal. [0100] The method can further include, at 740, providing, by the first device, control information to the second device to control or otherwise determine the first digital beamforming. This may be the same control information received at 640 in FIG.6. [0101] As shown in FIG. 7, the method can include, at 750, sending, by the first device to the second device, a reporting configuration. This may be the same reporting configuration received at 640 in FIG. 6. The additional information can be provided to the first device in accordance with the reporting configuration. [0102] The reporting configuration can include at least one threshold for reporting, as mentioned above. The reporting configuration can include an indication that values of at least two different parameters are to be provided together, as also mentioned above. Moreover, as further mentioned above, the reporting configuration can include an indication of update periodicity of at least one value of the additional information. For example, the reporting configuration can include multiple different update periodicities or reporting periodicities. The additional information can include a receiving filter of the first device. [0103] It is noted that FIG. 7 is provided as one example embodiment of a method or process. However, certain embodiments are not limited to this example, and further examples are possible as discussed elsewhere herein. [0104] FIG.8 illustrates an example of a system that includes an apparatus 10 according to an embodiment. In an embodiment, apparatus 10 may be a node, host, or server in a communications network or serving such a network. For example, apparatus 10 may be a network node, satellite, base station, a Node B, an evolved Node B (eNB), 5G Node B or access point, next generation Node B (NG-NB or gNB), TRP, HAPS, integrated access and backhaul (IAB) node, and/or a WLAN access point, associated with a radio access network, such as a LTE network, 5G or NR. In some example embodiments, apparatus 10 may be gNB or other similar radio node, for instance. [0105] It should be understood that, in some example embodiments, apparatus 10 may comprise an edge cloud server as a distributed computing system where the server and the radio node may be stand-alone apparatuses communicating with each other via a radio path or via a wired connection, or they may be co-located in an entity communicating within the entity via a wired connection. For instance, in certain example embodiments where apparatus 10 represents a gNB, it may be configured in a central unit (CU) and distributed unit (DU) architecture that divides the gNB functionality. In such an architecture, the CU may be a logical node that includes gNB functions such as transfer of user data, mobility control, radio access network sharing, positioning, and/or session management, etc. The CU may control the operation of DU(s) over a front-haul interface. The DU may be a logical node that includes a subset of the gNB functions, depending on the functional split option. Additionally, the DU may be provided with one or more RU, as described above. It should be noted that one of ordinary skill in the art would understand that apparatus 10 may include components or features not shown in FIG.8. [0106] As illustrated in the example of FIG. 8, apparatus 10 may include a processor 12 for processing information and executing instructions or operations. Processor 12 may be any type of general or specific purpose processor. In fact, processor 12 may include one or more of general-purpose computers, special purpose computers, microprocessors, digital signal processors (DSPs), field-programmable gate arrays (FPGAs), application- specific integrated circuits (ASICs), and processors based on a multi-core processor architecture, or any other processing means, as examples. While a single processor 12 is shown in FIG. 8, multiple processors may be utilized according to other embodiments. For example, it should be understood that, in certain embodiments, apparatus 10 may include two or more processors that may form a multiprocessor system (e.g., in this case processor 12 may represent a multiprocessor) that may support multiprocessing. In certain embodiments, the multiprocessor system may be tightly coupled or loosely coupled (e.g., to form a computer cluster). [0107] Processor 12 may perform functions associated with the operation of apparatus 10, which may include, for example, precoding of antenna gain/phase parameters, encoding and decoding of individual bits forming a communication message, formatting of information, and overall control of the apparatus 10, including processes related to management of communication or communication resources. [0108] Apparatus 10 may further include or be coupled to a memory 14 (internal or external), which may be coupled to processor 12, for storing information and instructions that may be executed by processor 12. Memory 14 may be one or more memories and of any type suitable to the local application environment, and may be implemented using any suitable volatile or nonvolatile data storage technology such as a semiconductor-based memory device, a magnetic memory device and system, an optical memory device and system, fixed memory, and/or removable memory. For example, memory 14 can be comprised of any combination of random access memory (RAM), read only memory (ROM), static storage such as a magnetic or optical disk, hard disk drive (HDD), or any other type of non-transitory machine or computer readable media, or other appropriate storing means. The instructions stored in memory 14 may include program instructions or computer program code that, when executed by processor 12, enable the apparatus 10 to perform tasks as described herein. [0109] In an embodiment, apparatus 10 may further include or be coupled to (internal or external) a drive or port that is configured to accept and read an external computer readable storage medium, such as an optical disc, USB drive, flash drive, or any other storage medium. For example, the external computer readable storage medium may store a computer program or software for execution by processor 12 and/or apparatus 10. [0110] In some embodiments, apparatus 10 may also include or be coupled to one or more antennas 15 for transmitting and receiving signals and/or data to and from apparatus 10. Apparatus 10 may further include or be coupled to a transceiver 18 configured to transmit and receive information. The transceiver 18 may include, for example, a plurality of radio interfaces that may be coupled to the antenna(s) 15, or may include any other appropriate transceiving means. The radio interfaces may correspond to a plurality of radio access technologies including one or more of global system for mobile communications (GSM), narrow band Internet of Things (NB-IoT), LTE, 5G, WLAN, Bluetooth (BT), Bluetooth Low Energy (BT-LE), near-field communication (NFC), radio frequency identifier (RFID), ultrawideband (UWB), MulteFire, and the like. The radio interface may include components, such as filters, converters (for example, digital-to-analog converters and the like), mappers, a Fast Fourier Transform (FFT) module, and the like, to generate symbols for a transmission via one or more downlinks and to receive symbols (via an uplink, for example). [0111] As such, transceiver 18 may be configured to modulate information on to a carrier waveform for transmission by the antenna(s) 15 and demodulate information received via the antenna(s) 15 for further processing by other elements of apparatus 10. In other embodiments, transceiver 18 may be capable of transmitting and receiving signals or data directly. Additionally or alternatively, in some embodiments, apparatus 10 may include an input and/or output device (I/O device), or an input/output means. [0112] In an embodiment, memory 14 may store software modules that provide functionality when executed by processor 12. The modules may include, for example, an operating system that provides operating system functionality for apparatus 10. The memory may also store one or more functional modules, such as an application or program, to provide additional functionality for apparatus 10. The components of apparatus 10 may be implemented in hardware, or as any suitable combination of hardware and software. [0113] According to some embodiments, processor 12 and memory 14 may be included in or may form a part of processing circuitry/means or control circuitry/means. In addition, in some embodiments, transceiver 18 may be included in or may form a part of transceiver circuitry/means. [0114] As used herein, the term “circuitry” may refer to hardware-only circuitry implementations (e.g., analog and/or digital circuitry), combinations of hardware circuits and software, combinations of analog and/or digital hardware circuits with software/firmware, any portions of hardware processor(s) with software (including digital signal processors) that work together to cause an apparatus (e.g., apparatus 10) to perform various functions, and/or hardware circuit(s) and/or processor(s), or portions thereof, that use software for operation but where the software may not be present when it is not needed for operation. As a further example, as used herein, the term “circuitry” may also cover an implementation of merely a hardware circuit or processor (or multiple processors), or portion of a hardware circuit or processor, and its accompanying software and/or firmware. The term circuitry may also cover, for example, a baseband integrated circuit in a server, cellular network node or device, or other computing or network device. [0115] As introduced above, in certain embodiments, apparatus 10 may be or may be a part of a network element or RAN node, such as a base station, access point, Node B, eNB, gNB, TRP, HAPS, IAB node, relay node, WLAN access point, satellite, or the like. In one example embodiment, apparatus 10 may be a gNB or other radio node, or may be a CU and/or DU of a gNB. According to certain embodiments, apparatus 10 may be controlled by memory 14 and processor 12 to perform the functions associated with any of the embodiments described herein. For example, in some embodiments, apparatus 10 may be configured to perform one or more of the processes depicted in any of the flow charts or signaling diagrams described herein, such as those illustrated in FIGs. 3-7, or any other method described herein. In some embodiments, as discussed herein, apparatus 10 may be configured to perform a procedure relating to complexity reduction for an open radio access network radio unit uplink receiver, for example. [0116] FIG. 8 further illustrates that the example system can include an apparatus 20 according to another embodiment. In an embodiment, apparatus 20 may be a node or element in a communications network or associated with such a network, such as a UE, communication node, mobile equipment (ME), mobile station, mobile device, stationary device, IoT device, or other device. As described herein, a UE may alternatively be referred to as, for example, a mobile station, mobile equipment, mobile unit, mobile device, user device, subscriber station, wireless terminal, tablet, smart phone, IoT device, sensor or NB-IoT device, a watch or other wearable, a head-mounted display (HMD), a vehicle, a drone, a medical device and applications thereof (e.g., remote surgery), an industrial device and applications thereof (e.g., a robot and/or other wireless devices operating in an industrial and/or an automated processing chain context), a consumer electronics device, a device operating on commercial and/or industrial wireless networks, or the like. As one example, apparatus 20 may be implemented in, for instance, a wireless handheld device, a wireless plug-in accessory, or the like. [0117] In some example embodiments, apparatus 20 may include one or more processors, one or more computer-readable storage medium (for example, memory, storage, or the like), one or more radio access components (for example, a modem, a transceiver, or the like), and/or a user interface. In some embodiments, apparatus 20 may be configured to operate using one or more radio access technologies, such as GSM, LTE, LTE-A, NR, 5G, WLAN, WiFi, NB-IoT, Bluetooth, NFC, MulteFire, and/or any other radio access technologies. It should be noted that one of ordinary skill in the art would understand that apparatus 20 may include components or features not shown in FIG.8. [0118] As illustrated in the example of FIG.8, apparatus 20 may include or be coupled to a processor 22 for processing information and executing instructions or operations. Processor 22 may be any type of general or specific purpose processor. In fact, processor 22 may include one or more of general- purpose computers, special purpose computers, microprocessors, digital signal processors (DSPs), field-programmable gate arrays (FPGAs), application-specific integrated circuits (ASICs), and processors based on a multi-core processor architecture, as examples. While a single processor 22 is shown in FIG. 8, multiple processors may be utilized according to other embodiments. For example, it should be understood that, in certain embodiments, apparatus 20 may include two or more processors that may form a multiprocessor system (e.g., in this case processor 22 may represent a multiprocessor) that may support multiprocessing. In certain embodiments, the multiprocessor system may be tightly coupled or loosely coupled (e.g., to form a computer cluster). [0119] Processor 22 may perform functions associated with the operation of apparatus 20 including, as some examples, precoding of antenna gain/phase parameters, encoding and decoding of individual bits forming a communication message, formatting of information, and overall control of the apparatus 20, including processes related to management of communication resources. [0120] Apparatus 20 may further include or be coupled to a memory 24 (internal or external), which may be coupled to processor 22, for storing information and instructions that may be executed by processor 22. Memory 24 may be one or more memories and of any type suitable to the local application environment, and may be implemented using any suitable volatile or nonvolatile data storage technology such as a semiconductor-based memory device, a magnetic memory device and system, an optical memory device and system, fixed memory, and/or removable memory. For example, memory 24 can be comprised of any combination of random access memory (RAM), read only memory (ROM), static storage such as a magnetic or optical disk, hard disk drive (HDD), or any other type of non-transitory machine or computer readable media. The instructions stored in memory 24 may include program instructions or computer program code that, when executed by processor 22, enable the apparatus 20 to perform tasks as described herein. [0121] In an embodiment, apparatus 20 may further include or be coupled to (internal or external) a drive or port that is configured to accept and read an external computer readable storage medium, such as an optical disc, USB drive, flash drive, or any other storage medium. For example, the external computer readable storage medium may store a computer program or software for execution by processor 22 and/or apparatus 20. [0122] In some embodiments, apparatus 20 may also include or be coupled to one or more antennas 25 for receiving a downlink signal and for transmitting via an uplink from apparatus 20. Apparatus 20 may further include a transceiver 28 configured to transmit and receive information. The transceiver 28 may also include a radio interface (e.g., a modem) coupled to the antenna 25. The radio interface may correspond to a plurality of radio access technologies including one or more of GSM, LTE, LTE-A, 5G, NR, WLAN, NB-IoT, Bluetooth, BT-LE, NFC, RFID, UWB, and the like. The radio interface may include other components, such as filters, converters (for example, digital-to-analog converters and the like), symbol demappers, signal shaping components, an Inverse Fast Fourier Transform (IFFT) module, and the like, to process symbols, such as OFDMA symbols, carried by a downlink or an uplink. [0123] For instance, transceiver 28 may be configured to modulate information on to a carrier waveform for transmission by the antenna(s) 25 and demodulate information received via the antenna(s) 25 for further processing by other elements of apparatus 20. In other embodiments, transceiver 28 may be capable of transmitting and receiving signals or data directly. Additionally or alternatively, in some embodiments, apparatus 20 may include an input and/or output device (I/O device). In certain embodiments, apparatus 20 may further include a user interface, such as a graphical user interface or touchscreen. [0124] In an embodiment, memory 24 stores software modules that provide functionality when executed by processor 22. The modules may include, for example, an operating system that provides operating system functionality for apparatus 20. The memory may also store one or more functional modules, such as an application or program, to provide additional functionality for apparatus 20. The components of apparatus 20 may be implemented in hardware, or as any suitable combination of hardware and software. According to an example embodiment, apparatus 20 may optionally be configured to communicate with apparatus 10 via a wireless or wired communications link 70 according to any radio access technology, such as NR. [0125] According to some embodiments, processor 22 and memory 24 may be included in or may form a part of processing circuitry or control circuitry. In addition, in some embodiments, transceiver 28 may be included in or may form a part of transceiving circuitry. [0126] As discussed above, according to some embodiments, apparatus 20 may be a UE, SL UE, relay UE, mobile device, mobile station, ME, IoT device and/or NB-IoT device, or the like, for example. According to certain embodiments, apparatus 20 may be controlled by memory 24 and processor 22 to perform the functions associated with any of the embodiments described herein, such as one or more of the operations illustrated in, or described with respect to, FIGs. 3-7, or any other method described herein. For example, in an embodiment, apparatus 20 may be controlled to perform a process relating to providing support for complexity reduction for an open radio access network radio unit uplink receiver, as described in detail elsewhere herein. [0127] In some embodiments, an apparatus (e.g., apparatus 10 and/or apparatus 20) may include means for performing a method, a process, or any of the variants discussed herein. Examples of the means may include one or more processors, memory, controllers, transmitters, receivers, and/or computer program code for causing the performance of any of the operations discussed herein. [0128] In view of the foregoing, certain example embodiments provide several technological improvements, enhancements, and/or advantages over existing technological processes and constitute an improvement at least to the technological field of wireless network control and/or management. Certain embodiments may have various benefits and/or advantages. For example, certain embodiments may provide complexity reduction while providing comparable performance to more complex arrangements. Moreover, certain embodiments may achieve low fronthaul bandwidth overhead. [0129] In some example embodiments, the functionality of any of the methods, processes, signaling diagrams, algorithms or flow charts described herein may be implemented by software and/or computer program code or portions of code stored in memory or other computer readable or tangible media, and may be executed by a processor. [0130] In some example embodiments, an apparatus may include or be associated with at least one software application, module, unit or entity configured as arithmetic operation(s), or as a program or portions of programs (including an added or updated software routine), which may be executed by at least one operation processor or controller. Programs, also called program products or computer programs, including software routines, applets and macros, may be stored in any apparatus-readable data storage medium and may include program instructions to perform particular tasks. A computer program product may include one or more computer-executable components which, when the program is run, are configured to carry out some example embodiments. The one or more computer-executable components may be at least one software code or portions of code. Modifications and configurations needed for implementing the functionality of an example embodiment may be performed as routine(s), which may be implemented as added or updated software routine(s). In one example, software routine(s) may be downloaded into the apparatus. [0131] As an example, software or computer program code or portions of code may be in source code form, object code form, or in some intermediate form, and may be stored in some sort of carrier, distribution medium, or computer readable medium, which may be any entity or device capable of carrying the program. Such carriers may include a record medium, computer memory, read-only memory, photoelectrical and/or electrical carrier signal, telecommunications signal, and/or software distribution package, for example. Depending on the processing power needed, the computer program may be executed in a single electronic digital computer or it may be distributed amongst a number of computers. The computer readable medium or computer readable storage medium may be a non-transitory medium. [0132] In other example embodiments, the functionality of example embodiments may be performed by hardware or circuitry included in an apparatus, for example through the use of an application specific integrated circuit (ASIC), a programmable gate array (PGA), a field programmable gate array (FPGA), or any other combination of hardware and software. In yet another example embodiment, the functionality of example embodiments may be implemented as a signal, such as a non-tangible means, that can be carried by an electromagnetic signal downloaded from the Internet or other network. [0133] According to an example embodiment, an apparatus, such as a node, device, or a corresponding component, may be configured as circuitry, a computer or a microprocessor, such as single-chip computer element, or as a chipset, which may include at least a memory for providing storage capacity used for arithmetic operation(s) and/or an operation processor for executing the arithmetic operation(s). [0134] Example embodiments described herein may apply to both singular and plural implementations, regardless of whether singular or plural language is used in connection with describing certain embodiments. For example, an embodiment that describes operations of a single network node may also apply to example embodiments that include multiple instances of the network node, and vice versa. [0135] One having ordinary skill in the art will readily understand that the example embodiments as discussed above may be practiced with procedures in a different order, and/or with hardware elements in configurations which are different than those which are disclosed. Therefore, although some embodiments have been described based upon these example 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 example embodiments. [0136] List of Abbreviations [0137] O-RAN Open RAN [0138] gNB 5G Base Station [0139] NR New Radio (5G) [0140] RS Reference Signal [0141] RSRP Reference Signal Received Power [0142] Rx Receive/ Receiver [0143] Tx Transmit/ Transmitter [0144] SRS Sounding Reference Signal [0145] DMRS Demodulation Reference Signals [0146] DL Downlink [0147] UL Uplink [0148] PUSCH Physical Uplink Shared CHannel [0149] MMSE Minimum Mean Square Error