Patent Publication Number: US-10771120-B2

Title: Base station front end preprocessing

Description:
RELATED APPLICATION 
     This application claims priority under 35 U.S.C. § 119 from PCT application no. PCT/CN2015/077533, filed Apr. 27, 2015. 
     FIELD 
     Embodiments of the present disclosure generally relate to the field of wireless communication, and more particularly, to methods and apparatuses for preprocessing in a base station of a multiple-input multiple-output (MIMO) wireless system. 
     BACKGROUND 
     Massive MIMO wireless systems, such as embodiments of fifth generation (5G) wireless systems, may include very large or massive numbers of antenna elements or antennas (e.g., at least twenty). Such systems can provide better performance and capacity gain over MIMO systems such as fourth generation Long Term Evolution (4G LTE), which may include 2 or 4 antennas. However, issues may arise in the operation of base stations in massive MIMO wireless systems. The base stations may include one or more baseband units (BBUs) and one or more remote radio units (RRUs, sometimes referred to as a base station front end). Issues in the operation of such base stations may relate to complexity of precoder calculation and large matrix manipulation within one or more BBUs, and bandwidth requirements between BBUs and RRUs. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments will be readily understood by the following detailed description in conjunction with the accompanying drawings. To facilitate this description, like reference numerals designate like structural elements. Embodiments are illustrated by way of example and not by way of limitation in the figures of the accompanying drawings. 
         FIG. 1  is a diagram of an example operating environment in which systems and/or methods described herein may be implemented in accordance with some embodiments. 
         FIG. 2  is a diagram illustrating an embodiment of an evolved Node B (eNB) with BBU in communication with RRU via an interconnection link. 
         FIG. 3  is a flowchart describing operations of an eNB in accordance with some embodiments. 
         FIG. 4  is a flowchart describing operations of an eNB in accordance with other embodiments. 
         FIG. 5  is a graph illustrating simulation of throughput versus signal-to-interference-plus-noise ratio (SINR) of uplink for example multi-user MIMO receivers. 
         FIG. 6  is a graph illustrating another simulation of throughput versus signal-to-interference-plus-noise ratio (SINR) of uplink for example multi-user MIMO receivers. 
         FIG. 7  is a graph illustrating cell-average spectral efficiency (SE) gain for example embodiments of MIMO systems. 
         FIG. 8  illustrates electronic device circuitry that may be included in or associated with an eNB. 
         FIG. 9  illustrates, for one embodiment, example components of an electronic device that may implement, be incorporated into, or otherwise be a part of a UE, an eNB, or some other suitable electronic device. 
     
    
    
     DETAILED DESCRIPTION 
     Various aspects of the illustrative embodiments will be described using terms commonly employed by those skilled in the art to convey the substance of their work to others skilled in the art. However, it will be apparent to those skilled in the art that alternate embodiments may be practiced with only some of the described aspects. For purposes of explanation, specific numbers, materials, and configurations are set forth in order to provide a thorough understanding of the illustrative embodiments. However, it will be apparent to one skilled in the art that alternate embodiments may be practiced without the specific details. In other instances, well-known features are omitted or simplified in order not to obscure the illustrative embodiments. 
     Further, various operations will be described as multiple discrete operations, in turn, in a manner that is most helpful in understanding the illustrative embodiments; however, the order of description should not be construed as to imply that these operations are necessarily order dependent. In particular, these operations need not be performed in the order of presentation. 
     The phrase “in some embodiments” is used repeatedly. The phrase generally does not refer to the same embodiments; however, it may. The terms “comprising,” “having,” and “including” are synonymous, unless the context dictates otherwise. The phrases “A or B,” “A/B,” and “A and/or B” mean (A), (B), or (A and B). 
     In some base station designs, an antenna with a radio frequency (RF) unit may be integrated in an RRU, which may be installed on top of a tower, and the in-phase/quadrature (I/Q) antenna data may be sampled and transported by fiber to a BBU, which is normally installed somewhere on the ground near the tower for easy maintenance and upgrade. In 20 megahertz (MHz) LTE 4 antenna system, I/Q data rate may be about four gigabits per second (Gbps). But for 5G system with 128 antenna system, each with 100 MHz of bandwidth, the corresponding data rate could be about 629 Gbps. The huge amount of input/output (I/O) data may be associated with an ultra-high-cost fiber connection. 
     Another option may be to integrate RRU and BBU functions together on top of the tower. However, this may result in a “fat” antenna that may face a critical issue of maintenance and upgrade, and present dangerous conditions for operators that would have to climb up the tower to repair and upgrade the BBU. 
     Another option to reduce I/O burden is to use analog beamforming, by which a digital spatial stream is limited to a small number (for example, eight for LTE). Analog beamforming technology may then be used to spot several beams to construct virtual sectors, similar to cell split by massive antenna. However, this kind of approach may suffer performance loss of massive antenna system, which can enjoy Zero-forcing like matrix algorithm to separate large number of users by spatial fading channel. 
     The embodiments of the present disclosure may provide techniques and systems that accommodate the large I/O data rate while keeping the benefits and gains of full digital massive MIMO operation. 
     In particular, illustrative embodiments of the present disclosure include, but are not limited to, methods, systems, computer-readable media, and apparatuses that may provide preprocessing within a front end of a base station or an evolved NodeB (eNB) of a MIMO wireless system, such as a massive MIMO wireless system. In embodiments, the preprocessing may be performed within one or more RRUs and may include application of a user equipment (UE)-specific spatial filter, such as in connection with a downlink (DL) user equipment (UE)-specific precoder. Such preprocessing may reduce complexity of precoder calculation and large matrix manipulation within one or more BBUs, and bandwidth requirements between BBUs and RRUs. 
       FIG. 1  is a diagram of an example operating environment in which systems and/or methods described herein may be implemented. As illustrated, the operating environment may include a MIMO system. In some embodiments, the MIMO system may include a very large number of antennas (for example, over 20 antennas and possibly up to hundreds of antennas) and may be referred to as a massive MIMO system. The MIMO system may include a baseband processing pool  110  of one or more BBUs  112  (e.g. BBUs  112 A- 112 C) that may communicate over a transport network  120  of one or more electrical or optical fiber cables  122  (e.g., optical fiber cables  122 A- 122 D) with a remote radio pool  130  of one or more RRUs  132  (e.g. RRUs  132 A- 132 I) that each may service a large number of antennas  136  (e.g., twenty or more). 
     BBUs  112  of baseband processing pool  110 , optical fiber cables  122  of transport network  120 , and RRUs  132  of remote radio pool  130  together may operate as a base station of a wireless wide area or cellular network, such as an evolved NodeB (eNB)  140 , which is in radio communication with multiple user equipments (UEs)  134  (e.g., UEs  134 A- 134 J). In embodiments, the radio communication may employ 5G wireless standards and/or protocols. It will be appreciated that the numbers of BBUs  112 , RRUs  132  and UEs  134  shown are merely illustrative and that in embodiments different numbers could be employed. In embodiments, the BBUs  112  of baseband processing pool  110  may be located together or centralized. The BBUs  112  may be coupled to load balancer and switches  118 A and  118 B via electrical or optical cabling  126 . The RRUs  132  may be separated from the BBUs  112  and, in embodiments, may be located with or adjacent to antennas  136 . In some embodiments, the BBUs  112  may be located at a base of a tower while the RRUs  132  may be located on top of the tower with or adjacent to the antennas  136 . 
       FIG. 2  is a diagram illustrating an embodiment of eNB  140  with BBU  112  in communication with RRU  132  via an interconnection link  202 . Interconnection link  202  may include, for example, any or all of load balancer and switches  118 , cabling  126 , and/or transport network  120 , as shown in  FIG. 1 . For downlink, BBU  112  may provide compressed downlink (DL) multiple-user (MU) streams  210  over interconnection link  202  to RRU  132  for downlink to multiple UEs  134 . RRU  132  may include a decompression unit  212  to decompress multiple-user streams  210  to provide a physical downlink control channel (PDCCH)  214  and a physical downlink shared channel (PDSCH)  216 . PDCCH  214  may pass to a wideband precoder  218 , and PDSCH  216  may pass to a UE-specific precoder  220 . 
     Wideband precoder  218  may apply to PDCCH  214  a wideband precoding so as to generate a wideband beam by which UEs  134  within a coverage area can receive the PDCCH correctly. UE-specific precoder  220  may apply to PDSCH  216  a UE-specific precoding that is specific to the UE  134  to which the PDSCH  216  is to be transmitted and may correspond to and compensate for characteristics of the channel between RRU  132  and the specific UE  134 . A framing unit  222  may receive the wideband-precoded PDCCH and the UE-specific-precoded PDSCH and may join them in a signal subframe structure that may pass to an inverse fast Fourier transform unit  224  and then to multiple antennas  230  of an antenna array  232  for downlink to UEs  134 . 
     For uplink, RRU  132  may include a fast Fourier transform and automatic gain control  240  that receives uplink signals from antennas  230  and provides Fourier transformed and gain-controlled uplink signals to a resource block (RB) selection unit  242 . RB selection unit  242  may provide a sounding reference signal (SRS)  244 , a physical uplink shared channel (PUSCH)  246 , and a physical uplink control channel (PUCCH)/physical random access channel (PRACH)  248 . The PUCCH/PRACH  248  may pass to the BBU  112  via interconnection link  202  as part of uplink multi-user detection  250 . The PUSCH  246  may pass through a UE-specific spatial pre-filtering unit  252 , which may include and apply a conjugate of the channel of a specific UE  134  to provide a compressed PUSCH  254  to BBU  112  via interconnection link  202 , as another part of the uplink multiple-user detection  250 . The SRS  244  may pass to the BBU  112  via interconnection link  202  as another part of the uplink multiple-user detection  250 , or may pass to an SRS unit  245 . SRS unit  245  may determine from SRS  244  a conjugate of the channel of a specific UE  134  as an estimated spatial filter precoder matrix, which may be delivered to and applied by a spatial pre-filtering unit  252 . BBU  112  may determine the conjugate channel of a specific UE  134  from SRS  244 , if SRS  244  is passed to BBU  112 . 
     Downlink multiple-user streams  210  transmitted from BBU  112  to RRU  132  may include spatial data streams (e.g., PDCCH  214  and PDSCH  216 ) that are destined for UEs  134 , as well as one or more precoding matrices via a connection  253  to be applied by either or both of wideband precoder  218  and UE-specific precoder  220 . Beamforming may include wideband precoder  218  and UE-specific precoder  220  multiplying corresponding precoding matrices and data streams PDCCH  214  and PDSCH  216 , respectively. In such embodiments, the data rate between BBU  112  and RRU  132  may be proportional to the number of data streams, rather than the number of antennas  230 . 
     Uplink data received from antennas  230  may be pre-filtered by UE-specific spatial prefiltering unit  252 , such that the antenna data may be converted to spatial stream data with a data rate that is proportional to the number of uplink multiple user streams. The conjugate of a channel of a specific UE  134  may be determined from SRS  244  as an estimated spatial filter precoder matrix, which may be determined in RRU  132  by SRS unit  245  or, in some embodiments, in BBU  112 . The estimated spatial pre-filter for each UE  134  may be used to construct a downlink precoder matrix for use in UE-specific precoder  220 . 
     Embodiments may provide one or more preprocessing operations within RRU  132 , rather than within BBU  112 . The one or more preprocessing operations may include or be provided by any or all of UE-specific precoder  220  on downlink and UE-specific spatial pre-filtering unit  252  and SRS unit  245  on uplink. Such preprocessing at RRU  132  may greatly reduce bandwidth requirements (e.g., I/O) of interconnection link  202  between BBU  112  and RRU  132  and can maintain performance gains of a massive MIMO wireless system. With such preprocessing at RRU  132 , for example, bandwidth requirements of interconnection link  202  between BBU  112  and RRU  132  may be proportional to the number of spatial streams Ns. In contrast, without such pre-processing by RRU  132 , bandwidth requirements may be proportional to the number of antenna Na. Normally in a massive MIMO system, Na may be much larger than Ns. 
       FIG. 3  is a flowchart  300  describing operations of an eNB in accordance with some embodiments. 
     At  302 , the RRU of an eNB may receive the SRS of a specific UE. In embodiments, RRU  132  may receive the SRS of a specific UE  134 . 
     At  304 , a conjugate of the channel between the eNB and the specific UE may be determined from the SRS of the specific UE. In embodiments, SRS unit  245  of RRU  132  may determine from an uplinked SRS  244  a conjugate of the channel of a specific UE  134 . 
     At  306 , the conjugate of the channel between the eNB and the specific UE may be applied as a UE-specific spatial prefilter. In embodiments, a conjugate of the channel of a specific UE  134  may be delivered to and applied by a spatial pre-filtering unit  252  as an estimated spatial filter precoder matrix. 
     At  308 , the UE-specific spatial prefilter may be provided as a UE-specific precoder. In embodiments, RRU  132  may include UE-specific precoder  220 , which may provide precoding that may correspond to and compensate for characteristics of the channel between RRU  132  and the specific UE  134 . 
     At  310 , the RRU of the eNB may receive from the BBU a PDSCH for downlink to the specific UE. In embodiments, BBU  112  and RRU  132  may be positioned apart from each other and RRU  132  may receive a PDSCH from BBU  112  over an interconnection link  202 . 
     At  312 , the UE-specific precoder may be applied to the PDSCH for downlink to the specific UE. In embodiments, UE-specific precoder  220  may apply the UE-specific precoding to PDSCH  216 . 
     At  314 , a beam may be formed for downlink to the specific UE. In embodiments, beams may be formed at multiple antennas  230  of a massive MIMO system, which may have 20 or more antennas  230  in an antenna array  232 . 
       FIG. 4  is a flowchart  400  describing operations of an eNB in accordance with other embodiments. 
     At  402 , downlink (DL) user equipment (UE)-specific precoding may be applied in RRU circuitry to control radio communication related to massive MIMO communication. In embodiments the massive MIMO communication may include at least twenty antennas and the UE-specific precoding may be applied in connection with DL beamforming. 
     At  404 , UE-specific spatial filtering may be applied in RRU circuitry to uplink signals received from a specific UE. In embodiments, UE-specific spatial filtering may be applied to a PUSCH to provide a compressed PUSCH. 
     In embodiments, aspects of uplink processing may be described in the following manner. An eNB  140  may include NR-number of receive antennas  230  and may serve K-number of UEs  134  concurrently. Channel frequency response on an ith subcarrier between UEk and a receive antenna Rxn may be denoted as H n,k,i , and the transmit symbol of UEk may be denoted as xk. After cyclic prefix (CP) removal and a fast Fourier transform (FFT), a frequency domain receive signal at the antenna Rxn may be represented as to: 
                     Y     n   ,   i       =         ∑     k   =   0       K   -   1       ⁢       H     n   ,   k   ,   i       ⁢     x     k   ,   i           +     w     n   ,   i                 (   1   )               
where w n,i  is Gaussian noise. For simplification, the subscript i may be omitted. Then the receive signal may then be simplified to:
 
                     Y   n     =         ∑     k   =   0       K   -   1       ⁢       H     n   ,   k       ⁢     x   k         +       w   n     .               (   2   )               
Adopting minimum mean square error (MMSE) equalization, the post-filtering W at the receiver may be represented as:
 
                         W   =       ⁢         H   H     ⁡     (       HH   H     +       σ   w   2     ⁢   I       )         -   1                   =       ⁢         (         H   H     ⁢   H     +       σ   w   2     ⁢   I       )       -   1       ⁢     H   H                     (   3   )               
where H=[H 0 H 1  . . . H k−1 ], H k =[H 0,k  . . . H n,k  . . . H N     R     −1,k ] T  and σ 2  is a variance of noise. After equalization, detected symbols may be represented as:
 
                           x   ^     =       ⁢   WY               =       ⁢         (         H   H     ⁢   H     +       σ   n   2     ⁢   I       )       -   1       ⁢     H   H     ⁢   Y                   (   4   )               
where {circumflex over (x)}=[{circumflex over (x)} 0  . . . {circumflex over (x)} k  . . . {circumflex over (x)} K-1 ] T  contains detected symbols of all UEs  134 , and Y=[Y 0  . . . Y N     R     −1 ] T  may be obtained by stacking all receive signals of all antennas  230 . The above detection may be separated into two steps to provide:
 
step1 :  Y =H   H   Y   (5)
 
step2 : {circumflex over (x)} =( H   H   H+σ   n   2   I ) −1     Y     (6)
 
     In step 1, the receive signal Y may be multiplied by a pre-filtering matrix, which may be a conjugation of the channel between the eNB  140  and a specific UE  134 . The N R ×1 receive signal Y may then be transformed into the K×1 vector  Y , which may be sent from RRU  132  to BBU  112  for demodulation in step 2. Transmit symbols may be detected in step 2 by interference cancellation among multiple UEs  134 . This equalization, which may include the operating first step at or in RRU  132  may significantly reduce interconnection bandwidth requirements between BBU  112  and RRU  132  without loss of performance. 
     The SRS  244  may be transmitted from a UE  134  for channel quality measurement, which can be utilized to calculate the UE-specific pre-filtering matrices. When several UEs  134  send their respective SRSs concurrently, a UE-specific cyclic phase shift may be applied to distinguish them. Thus, in embodiments, channel estimation for a specific UE  134  may be applied at the RRU  132  based on SRS  244 , and the UE-specific pre-filtering may be calculated by conjugating the estimated channel. In embodiments, the channel estimation may be based on or employ a discrete cosine transform (DCT), a discrete Fourier transform (DFT), and/or Wienner-filtering. 
     Following such pre-filtering, the received signal for BBU  112  on a specific subcarrier may be a K×1 vector,  Y =[ Y   0  . . .  Y   k  . . .  Y   k−1 ] T ,
         where       

                   Y   _     k     =         ∑       k   ′     =   0       K   -   1       ⁢       H   k   H     ⁢     H     k   ′       ⁢     x     k   ′           +       w   _     k         ,         
and
 
 w   k  is the combined noise. Rewritten in matrix form, the signal may be represented as
 
   Y = H x+ w     (7)
 
where  H  is the combined channel information.
 
     
       
         
           
             
               
                 
                   
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     In embodiments, BBU  112 , rather than RRU  132 , may estimate channel information of a specific UE  134  based on a receive signal  Y  and a demodulation reference signal (DMRS). Based on the estimated combined channel information, the interference among different UEs can be eliminated and the transmitted symbols may be detected according to equation (9).
 
 {circumflex over (x)} =(   H +σ     w     2   I ) −1     Y     (9)
 
The transmit bits may be obtained by decoding and descrambling on {circumflex over (x)}.
 
     A link level simulation may be used to evaluate performance impact of described embodiments on uplink for a multi-user MIMO receiver. The simulation may employ channel parameters based on 3GPP Technical Report (TR) 36.873, version 12.1.0, dated Mar. 26, 2015, and simulation parameters based on 3GPP TR 36.104, version 12.7.0, dated Mar. 28, 2015. 
       FIG. 5  is a graph illustrating throughput in megabits per second (Mbps) versus signal-to-interference-plus-noise ratio (SINR) in dB from a link level simulation of uplink for an example multi-user MIMO receiver for legacy MMSE, legacy equalization with maximal ratio combining (MRC), and embodiments of two-step equalization, such as two-step MMSE as described and two-step MRC. The graph of  FIG. 5  may be based on a simulation with modulation and coding scheme (MCS) index of 6, 64 receiving antennas, 2 users/scheduling, and an SRS period of 10 mS. 
     The graph of  FIG. 5  shows, for example, that two-step MMSE may have less than 0.5 dB performance loss at package error ratio (PER) of 0.1 These results reflect pre-filtering that is based upon UE-specific channel information, which may be estimated at RRU  132  based on SRSs  244 , rather than DMRSs. Inaccuracy may be delivered to the compressed PUSCH, and may degrade some performance. However, in embodiments with massive MIMO uplinks, a large receiver diversity gain may improve uplink performance much more than downlink transmit diversity. As a result, slight uplink level loss will not be an issue with regard to overall system performance. For example, the graph of  FIG. 5  shows working SINR could be as low as −10 dB in uplink. 
       FIG. 6  is a graph illustrating throughput in Mbps versus SINR in dB from a link level simulation of uplink for an example multi-user MIMO receiver for legacy MMSE and two-step MMSE, as described, based on MCS index of 28, 64 receiving antennas, 2 users/scheduling, and an SRS period of 10 ms. The graph of  FIG. 6  shows that at higher SINR, estimation error will decrease so that performance of two-step MMSE, as described may achieve performance similar to that of legacy MMSE. 
     Embodiments described herein may be used in and/or support a full-digital beamforming in a MIMO system, which may be distinct from analog beamforming in a 3D MIMO system and/or a 3D MIMO system with compensation.  FIG. 7  is a graph illustrating cell-average spectral efficiency (SE) gain, as percentages, for example embodiments of 3D-MIMO, 3D-MIMO with (Comp)ensation, and full-digital MIMO. The graph of  FIG. 7  shows that full-digital MIMO may provide cell-average SE gain of about 170%, in comparison to cell-average SE gains of less than or about equal to 20% for 3D-MIMO and 3D-MIMO with Comp, respectively, indicating the increased information or data rate over a given bandwidth that may be provided by full-digital MIMO. 
       FIG. 8  illustrates electronic device circuitry  800  that may be included in or associated with an eNB. In embodiments, the electronic device circuitry  800  may include radio transmit circuitry  802  and receive circuitry  804  coupled to control circuitry  806 . The control circuitry  806  may include RRU circuitry  808  and/or BBU circuitry  810 , as shown, while in other embodiments the RRU circuitry  808  and/or BBU circuitry  810  may be separate from the control circuitry  806 . In embodiments, the transmit circuitry  802  and/or receive circuitry  804  may be elements or modules of transceiver circuitry, as shown. The electronic device circuitry  800  may be coupled with one or more plurality of antenna elements of one or more antennas  812 . The electronic device circuitry  800  and/or the components of the electronic device circuitry  800  may be configured to perform operations similar to those described elsewhere in this disclosure. 
     In embodiments where the electronic device circuitry is an eNB or is part of or otherwise incorporated into an eNB that is configured to perform massive MIMO operations, the RRU circuitry  808  may be to perform one or more radio related processes related to the massive MIMO operations. The BBU circuitry  810  may be to perform one or more baseband related processes or operations, which may include baseband demodulation related to the massive MIMO operations and/or forming or processing of user data streams. 
     As used herein, the term “circuitry” may refer to, be part of, or include an Application Specific Integrated Circuit (ASIC), an electronic circuit, a processor (shared, dedicated, or group), and/or memory (shared, dedicated, or group) that execute one or more software or firmware programs, a combinational logic circuit, and/or other suitable hardware components that provide the described functionality. In some embodiments, the circuitry may be implemented in, or functions associated with the circuitry may be implemented by, one or more software or firmware modules. In some embodiments, circuitry may include logic, at least partially operable in hardware. 
     Embodiments described herein may be implemented into a system using any suitably configured hardware and/or software.  FIG. 9  illustrates, for one embodiment, example components of an electronic device  900 . In embodiments, the electronic device  900  may be, implement, be incorporated into, or otherwise be a part of a UE, an eNB, or some other suitable electronic device. In some embodiments, the electronic device  900  may include application circuitry  902 , baseband circuitry  904 , radio frequency (RF) circuitry  906 , front-end module (FEM) circuitry  908  and one or more antennas  910 , coupled together at least as shown. In embodiments, baseband circuitry  904  or portions of it may be included in or operate in connection with BBU  112 , and RF circuitry  906  or portions of it may be included in or operate in connection with RRU  132 . 
     The application circuitry  902  may include one or more application processors. For example, the application circuitry  902  may include circuitry such as, but not limited to, one or more single-core or multi-core processors. The processor(s) may include any combination of general-purpose processors and dedicated processors (e.g., graphics processors, application processors, etc.). The processors may be coupled with and/or may include memory/storage and may be configured to execute instructions stored in the memory/storage to enable various applications and/or operating systems to run on the system. 
     The baseband circuitry  904  may include circuitry such as, but not limited to, one or more single-core or multi-core processors. The baseband circuitry  904  may include one or more baseband processors and/or control logic to process baseband signals received from a receive signal path of the RF circuitry  906  and to generate baseband signals for a transmit signal path of the RF circuitry  906 . Baseband processing circuity  904  may interface with the application circuitry  902  for generation and processing of the baseband signals and for controlling operations of the RF circuitry  906 . For example, in some embodiments, the baseband circuitry  904  may include a second generation (2G) cellular baseband processor  904   a , third generation (3G) cellular baseband processor  904   b , fourth generation (4G) cellular baseband processor  904   c , and/or other cellular baseband processor(s)  904   d  for other existing generations, generations in development or to be developed in the future (e.g., fifth generation (5G), 6G, etc.). In embodiments, the electronic device  900  may implement, be incorporated into, or otherwise be a part of a UE that may include a WLAN (e.g., Wi-Fi) baseband processor or circuitry  904   e . The baseband circuitry  904  (e.g., one or more of cellular baseband processors  904   a - d  and, in embodiments, a WLAN baseband processor  904   e ) may handle various radio control functions that enable communication with one or more radio networks via the RF circuitry  906 . The radio control functions may include, but are not limited to, signal modulation/demodulation, encoding/decoding, radio frequency shifting, etc. In some embodiments, modulation/demodulation circuitry of the baseband circuitry  904  may include Fast-Fourier Transform (FFT), precoding, and/or constellation mapping/demapping functionality. In some embodiments, encoding/decoding circuitry of the baseband circuitry  904  may include convolution, tail-biting convolution, turbo, Viterbi, and/or Low Density Parity Check (LDPC) encoder/decoder functionality. Embodiments of modulation/demodulation and encoder/decoder functionality are not limited to these examples and may include other suitable functionality in other embodiments. 
     In some embodiments, the baseband circuitry  904  may include elements of a protocol stack such as, for example, elements of an evolved universal terrestrial radio access network (EUTRAN) protocol including, for example, physical (PHY), media access control (MAC), radio link control (RLC), packet data convergence protocol (PDCP), and/or radio resource control (RRC) elements. A central processing unit (CPU)  904   f  of the baseband circuitry  904  may be configured to run elements of the protocol stack for signaling of the PHY, MAC, RLC, PDCP and/or RRC layers. In some embodiments, the baseband circuitry  904  may include one or more audio digital signal processor(s) (DSP)  904   g . The audio DSP(s)  904   g  may be include elements for compression/decompression and echo cancellation and may include other suitable processing elements in other embodiments. 
     The baseband circuitry  904  may further include memory/storage  904   h . The memory/storage  904   h  may be used to load and store data and/or instructions for operations performed by the processors of the baseband circuitry  904 . Memory/storage for one embodiment may include any combination of suitable volatile memory and/or non-volatile memory. The memory/storage  904   h  may include any combination of various levels of memory/storage including, but not limited to, read-only memory (ROM) having embedded software instructions (e.g., firmware), random access memory (e.g., dynamic random access memory (DRAM)), cache, buffers, etc. The memory/storage  904   h  may be shared among the various processors or dedicated to particular processors. 
     Components of the baseband circuitry  904  may be suitably combined in a single chip, a single chipset, or disposed on a same circuit board in some embodiments. In some embodiments, some or all of the constituent components of the baseband circuitry  904  and the application circuitry  902  may be implemented together such as, for example, on a system on a chip (SOC). 
     In some embodiments, the baseband circuitry  904  may provide for communication compatible with one or more radio technologies. For example, in some embodiments, the baseband circuitry  904  may support communication with an evolved universal terrestrial radio access network (EUTRAN) and/or other wireless metropolitan area networks (WMAN), a wireless local area network (WLAN), a wireless personal area network (WPAN). Embodiments in which the baseband circuitry  904  is configured to support radio communications of more than one wireless protocol may be referred to as multi-mode baseband circuitry. 
     RF circuitry  906  may enable communication with wireless networks using modulated electromagnetic radiation through a non-solid medium. In various embodiments, the RF circuitry  906  may include switches, filters, amplifiers, etc. to facilitate the communication with the wireless network. RF circuitry  906  may include a receive signal path which may include circuitry to down-convert RF signals received from the FEM circuitry  908  and provide baseband signals to the baseband circuitry  904 . RF circuitry  906  may also include a transmit signal path which may include circuitry to up-convert baseband signals provided by the baseband circuitry  904  and provide RF output signals to the FEM circuitry  908  for transmission. 
     In some embodiments, the RF circuitry  906  may include a receive signal path and a transmit signal path. The receive signal path of the RF circuitry  906  may include mixer circuitry  906   a , amplifier circuitry  906   b  and filter circuitry  906   c . The transmit signal path of the RF circuitry  906  may include filter circuitry  906   c  and mixer circuitry  906   a . RF circuitry  906  may also include synthesizer circuitry  906   d  for synthesizing a frequency for use by the mixer circuitry  906   a  of the receive signal path and the transmit signal path. In some embodiments, the mixer circuitry  906   a  of the receive signal path may be configured to down-convert RF signals received from the FEM circuitry  908  based on the synthesized frequency provided by synthesizer circuitry  906   d . The amplifier circuitry  906   b  may be configured to amplify the down-converted signals and the filter circuitry  906   c  may be a low-pass filter (LPF) or band-pass filter (BPF) configured to remove unwanted signals from the down-converted signals to generate output baseband signals. Output baseband signals may be provided to the baseband circuitry  904  for further processing. In some embodiments, the output baseband signals may be zero-frequency baseband signals, although this is not a requirement. In some embodiments, mixer circuitry  906   a  of the receive signal path may comprise passive mixers, although the scope of the embodiments is not limited in this respect. 
     In some embodiments, the mixer circuitry  906   a  of the transmit signal path may be configured to up-convert input baseband signals based on the synthesized frequency provided by the synthesizer circuitry  906   d  to generate RF output signals for the FEM circuitry  908 . The baseband signals may be provided by the baseband circuitry  904  and may be filtered by filter circuitry  906   c . The filter circuitry  906   c  may include a low-pass filter (LPF), although the scope of the embodiments is not limited in this respect. 
     In some embodiments, the mixer circuitry  906   a  of the receive signal path and the mixer circuitry  906   a  of the transmit signal path may include two or more mixers and may be arranged for quadrature downconversion and/or upconversion respectively. In some embodiments, the mixer circuitry  906   a  of the receive signal path and the mixer circuitry  906   a  of the transmit signal path may include two or more mixers and may be arranged for image rejection (e.g., Hartley image rejection). In some embodiments, the mixer circuitry  906   a  of the receive signal path and the mixer circuitry  906   a  of the transmit signal path may be arranged for direct downconversion and/or direct upconversion, respectively. In some embodiments, the mixer circuitry  906   a  of the receive signal path and the mixer circuitry  906   a  of the transmit signal path may be configured for super-heterodyne operation. 
     In some embodiments, the output baseband signals and the input baseband signals may be analog baseband signals, although the scope of the embodiments is not limited in this respect. In some alternate embodiments, the output baseband signals and the input baseband signals may be digital baseband signals. In these alternate embodiments, the RF circuitry  906  may include analog-to-digital converter (ADC) and digital-to-analog converter (DAC) circuitry and the baseband circuitry  904  may include a digital baseband interface to communicate with the RF circuitry  906 . 
     In some dual-mode embodiments, a separate radio IC circuitry may be provided for processing signals for each spectrum, although the scope of the embodiments is not limited in this respect. 
     In some embodiments, the synthesizer circuitry  906   d  may be a fractional-N synthesizer or a fractional N/N+1 synthesizer, although the scope of the embodiments is not limited in this respect as other types of frequency synthesizers may be suitable. For example, synthesizer circuitry  906   d  may be a delta-sigma synthesizer, a frequency multiplier, or a synthesizer comprising a phase-locked loop with a frequency divider. 
     The synthesizer circuitry  906   d  may be configured to synthesize an output frequency for use by the mixer circuitry  906   a  of the RF circuitry  906  based on a frequency input and a divider control input. In some embodiments, the synthesizer circuitry  906   d  may be a fractional N/N+1 synthesizer. 
     In some embodiments, frequency input may be provided by a voltage controlled oscillator (VCO), although that is not a requirement. Divider control input may be provided by either the baseband circuitry  904  or the applications processor  902  depending on the desired output frequency. In some embodiments, a divider control input (e.g., N) may be determined from a look-up table based on a channel indicated by the applications processor  902 . 
     Synthesizer circuitry  906   d  of the RF circuitry  906  may include a divider, a delay-locked loop (DLL), a multiplexer and a phase accumulator. In some embodiments, the divider may be a dual modulus divider (DMD) and the phase accumulator may be a digital phase accumulator (DPA). In some embodiments, the DMD may be configured to divide the input signal by either N or N+1 (e.g., based on a carry out) to provide a fractional division ratio. In some example embodiments, the DLL may include a set of cascaded, tunable, delay elements, a phase detector, a charge pump and a D-type flip-flop. In these embodiments, the delay elements may be configured to break a VCO period up into Nd equal packets of phase, where Nd is the number of delay elements in the delay line. In this way, the DLL provides negative feedback to help ensure that the total delay through the delay line is one VCO cycle. 
     In some embodiments, synthesizer circuitry  906   d  may be configured to generate a carrier frequency as the output frequency, while in other embodiments, the output frequency may be a multiple of the carrier frequency (e.g., twice the carrier frequency, four times the carrier frequency) and used in conjunction with quadrature generator and divider circuitry to generate multiple signals at the carrier frequency with multiple different phases with respect to each other. In some embodiments, the output frequency may be a LO frequency (fLO). In some embodiments, the RF circuitry  906  may include an IQ/polar converter. 
     FEM circuitry  908  may include a receive signal path which may include circuitry configured to operate on RF signals received from one or more antennas  910 , amplify the received signals and provide the amplified versions of the received signals to the RF circuitry  906  for further processing. FEM circuitry  908  may also include a transmit signal path which may include circuitry configured to amplify signals for transmission provided by the RF circuitry  906  for transmission by one or more of the one or more antennas  910 . 
     In some embodiments, the FEM circuitry  908  may include a TX/RX switch to switch between transmit mode and receive mode operation. The FEM circuitry  908  may include a receive signal path and a transmit signal path. The receive signal path of the FEM circuitry  908  may include a low-noise amplifier (LNA) to amplify received RF signals and provide the amplified received RF signals as an output (e.g., to the RF circuitry  906 ). The transmit signal path of the FEM circuitry  908  may include a power amplifier (PA) to amplify input RF signals (e.g., provided by RF circuitry  906 ), and one or more filters to generate RF signals for subsequent transmission (e.g., by one or more of the one or more antennas  910 . 
     In some embodiments, the electronic device  900  may include additional elements such as, for example, memory/storage, display, camera, sensor, and/or input/output (I/O) interface. 
     In some embodiments, the electronic device  900  may be configured to perform one or more methods, processes, and/or techniques, or one or more portions thereof, as described herein. 
     Some non-limiting examples are provided below. 
     Example 1 may include an evolved NodeB (eNB), comprising remote radio unit (RRU) circuitry to control radio communication related to multiple-input multiple-output (MIMO) operation, including application of a user equipment (UE)-specific spatial filter; and baseband unit (BBU) circuitry coupled with the RRU circuitry to control baseband operation related to the MIMO operation. 
     Example 2 may include the eNB of example 1, or any other example herein, wherein the RRU circuitry may include a downlink (DL) user equipment (UE)-specific precoder to facilitate DL beamforming by the eNB. 
     Example 3 may include the eNB of example 2, or any other example herein, wherein operation of the DL UE-specific precoder may include application of a UE-specific conjugate channel. 
     Example 4 may include the eNB of example 2, or any other example herein, wherein the BBU circuitry is further to determine a UE-specific conjugate channel related to the UE-specific spatial filter and to transmit the UE-specific conjugate channel to the RRU circuitry. 
     Example 5 may include the eNB of any of examples 1-4, or any other example herein, wherein the RRU circuitry is further to apply the UE-specific spatial filter to an uplink (UL) data channel. 
     Example 6 may include the eNB of example 5, or any other example herein, wherein the UL data channel may include a physical uplink shared channel (PUSCH). 
     Example 7 may include the eNB of any of examples 1-6, or any other example herein, wherein the RRU circuitry is further to receive a UL sounding reference signal (SRS) and estimate the UE-specific spatial filter based on the SRS. 
     Example 8 may include the eNB of example 7, or any other example herein, wherein the estimate of the UE-specific spatial filter may include a conjugate channel of the UE. 
     Example 9 may include the eNB of any of examples 1-6, or any other example herein, wherein the eNB is to implement a MIMO wireless system having at least twenty antennas. 
     Example 10 may include or more computer-readable media having instructions stored thereon, wherein the instructions, in response to execution by a device, cause the device to: apply downlink (DL) user equipment (UE)-specific precoding in remote radio unit (RRU) circuitry to control radio communication in DL beamforming related to a multiple input, multiple output (MIMO) system having at least twenty antennas; and apply UE-specific spatial filtering in the RRU circuitry to uplink signals received from a specific UE. 
     Example 11 may include the one or more computer-readable media of example 10, or any other example herein, wherein the DL UE-specific precoding may include application of the UE-specific spatial filtering. 
     Example 12 may include the one or more computer-readable media of examples 10 or 11, or any other example herein, and may further include instructions to: receive a UL sounding reference signal (SRS); and estimate the UE-specific spatial filter based on the SRS. 
     Example 13 may include the one or more computer-readable media of example 12, or any other example herein, wherein the estimate of the UE-specific spatial filter may include a conjugate channel of the UE. 
     Example 14 may include remote radio unit (RRU) circuitry, comprising: a decompression unit to receive and decompress multiple user streams from a baseband unit; a downlink (DL) user equipment (UE)-specific precoder to compensate for characteristics of a channel between the RRU and a specific UE; and an uplink (UL) UE-specific spatial filter for a physical uplink shared channel (PUSCH). 
     Example 15 may include the circuitry of example 14, or any other example herein, wherein the DL UE-specific precoder includes application of the UE-specific spatial filter in connection with DL beamforming. 
     Example 16 may include the circuitry of either of examples 14 or 15, or any other example herein, and may further include a sounding reference signal (SRS) unit to receive a UL SRS and estimate the UE-specific spatial filter based on the SRS. 
     Example 17 may include the circuitry of example 16, or any other example herein, wherein the estimate of the UE-specific spatial filter includes a conjugate channel of the UE. 
     Example 18 may include the circuitry of any of examples 14-17, or any other example herein, wherein the circuitry is to control radio communication related to a massive multiple-input multiple-output (MIMO) system with at least twenty antennas. 
     Example 19 may include the circuitry of any of examples 14-17, or any other example herein, wherein the DL UE-specific precoder further is to receive the UE-specific spatial filter from a baseband unit. 
     Example 20 may include an evolved NodeB (eNB) to perform massive multiple-input multiple-output (MIMO) operation, the eNB comprising: remote radio unit (RRU) circuitry to perform one or more radio related processes related to the massive MIMO operation, wherein the one or more radio related processes include a downlink (DL) user equipment (UE)-specific precoding process; and baseband unit (BBU) circuitry coupled with the RRU circuitry, the BBU circuitry to perform baseband demodulation related to the massive MIMO operation. 
     Example 21 may include the eNB of example 20, or any other example herein, wherein the DL UE-specific precoding process is related to DL beamforming by the eNB. 
     Example 22 may include the eNB of example 20, or any other example herein, wherein the BBU circuitry is further to determine a UE-specific conjugate channel related to the DL UE-specific precoding process and transmit the UE-specific conjugate channel to the RRU circuitry. 
     Example 23 may include the eNB of any of examples 20-22, or any other example herein, wherein the RRU circuitry is further to perform a spatial pre-filtering function. 
     Example 24 may include the eNB of example 23, or any other example herein, wherein the spatial pre-filtering function is to compress data in an uplink (UL) data channel. 
     Example 25 may include a method, comprising: applying downlink (DL) user equipment (UE)-specific precoding in remote radio unit (RRU) circuitry to control radio communication in DL beamforming related to a multiple input, multiple output (MIMO) system having at least twenty antennas; and applying UE-specific spatial filtering in the RRU circuitry to uplink signals received from a specific UE. 
     Example 26 may include the method of example 25, or any other example herein, wherein the DL UE-specific precoding includes application of the UE-specific spatial filtering. 
     Example 27 may include the method of either of examples 25 or 26, or any other example herein, and may further include receiving a UL sounding reference signal (SRS); and estimating the UE-specific spatial filter based on the SRS. 
     Example 28 may include the method of example 27, or any other example herein, wherein estimating the UE-specific spatial filter includes determining a conjugate channel of the UE. 
     Example 29 may include an apparatus, comprising: means to control radio communication related to multiple-input multiple-output (MIMO) operation, including application of a user equipment (UE)-specific spatial filter; and means to control baseband operation related to the MIMO operation. 
     Example 30 may include the apparatus of example 29, or any other example herein, further including a downlink (DL) user equipment (UE)-specific precoder to facilitate DL beamforming by the apparatus. 
     Example 31 may include the apparatus of example 30, or any other example herein, further including means to determine a UE-specific conjugate channel related to the UE-specific spatial filter. 
     Example 32 may include the apparatus of any of examples 29-31, or any other example herein, wherein application of the user equipment (UE)-specific spatial filter includes applying the UE-specific spatial filter to an uplink (UL) data channel. 
     Example 33 may include the apparatus of example 32, or any other example herein, wherein the UL data channel includes a physical uplink shared channel (PUSCH). 
     Example 34 may include the apparatus of any of examples 29-33, or any other example herein, further including: means to receive a UL sounding reference signal (SRS) and to estimate the UE-specific spatial filter based on the SRS. 
     Example 35 may include the apparatus of example 34, or any other example herein, wherein the estimate of the UE-specific spatial filter includes a conjugate channel of the UE. 
     Example 36 may include the apparatus of any of examples 29-33, or any other example herein, wherein the apparatus is to implement a MIMO wireless system having at least twenty antennas. 
     Example 37 may include a method, comprising: applying downlink (DL) user equipment (UE)-specific precoding to control radio communication in DL beamforming related to a multiple input, multiple output (MIMO) system having at least twenty antennas; and applying UE-specific spatial filtering to uplink signals received from a specific UE. 
     Example 38 may include the method of example 37, or any other example herein, wherein the DL UE-specific precoding includes application of the UE-specific spatial filtering. 
     Example 39 may include the method of either of examples 37 or 38, or any other example herein, further including: receiving a UL sounding reference signal (SRS); and estimating the UE-specific spatial filter based on the SRS. 
     Example 40 may include the method of example 39, or any other example herein, wherein the estimate of the UE-specific spatial filter includes a conjugate channel of the UE. 
     Example 41 may include an apparatus, comprising: means to perform one or more radio related processes related to the massive MIMO operation, wherein the one or more radio related processes include a downlink (DL) user equipment (UE)-specific precoding process; and means to perform baseband demodulation related to the massive MIMO operation. 
     Example 42 may include the apparatus of example 41, or any other example herein, wherein the DL UE-specific precoding process is related to DL beamforming by the eNB. 
     Example 43 may include the apparatus of example 41, or any other example herein, further including means to determine a UE-specific conjugate channel related to the DL UE-specific precoding process. 
     Example 44 may include the apparatus of any of examples 41-43, or any other example herein, further including means to perform a spatial pre-filtering function. 
     Example 45 may include the apparatus of example, wherein the spatial pre-filtering function is to compress data in an uplink (UL) data channel. 
     Example 46 may include one or more computer-readable media having instructions stored thereon, wherein the instructions, in response to execution by a device, cause the device to: apply downlink (DL) user equipment (UE)-specific precoding to control radio communication in DL beamforming related to a multiple input, multiple output (MIMO) system having at least twenty antennas; and apply UE-specific spatial filtering to uplink signals received from a specific UE. 
     Example 47 may include the one or more computer-readable media of example 46, or any other example herein, wherein the DL UE-specific precoding includes application of the UE-specific spatial filtering. 
     Example 47 may include the one or more computer-readable media of either of examples 46 or 47, or any other example herein, further including instruction to: receive a UL sounding reference signal (SRS); and estimate the UE-specific spatial filter based on the SRS. 
     Example 49 may include the one or more computer-readable media of example 48, or any other example herein, wherein the estimate of the UE-specific spatial filter includes a conjugate channel of the UE. 
     The description herein of illustrated implementations, including what is described in the Abstract, is not intended to be exhaustive or to limit the present disclosure to the precise forms disclosed. While specific implementations and examples are described herein for illustrative purposes, various equivalent modifications are possible within the scope of the disclosure, as those skilled in the relevant art will recognize. These modifications may be made to the disclosure in light of the above detailed description.