Patent Publication Number: US-11025399-B2

Title: Interference suppression

Description:
BACKGROUND 
     Field 
     Various communication systems may benefit from improved reduction of cross link interference. For example, certain embodiments may benefit from cross link interference suppression. 
     Description of the Related Art 
     5th generation (5G) mobile communication networks support both frequency division duplexing (FDD) and time division duplexing (TDD) modes, with TDD providing improved availability of unpaired spectrum for new radio (NR) deployments. In addition, TDD may be a critical component to support features in massive multi-antenna communications over 5G NR, for example, massive multi-input multi-output (MIMO), beamforming, and adaptive antenna systems due to channel reciprocity. 
     SUMMARY 
     In accordance with some embodiments, a method may include receiving, by a first network entity, at least one downlink precoder map from a second network entity over at least one interface. The method may further include estimating, by the first network entity, at least one basis of at least one common spatial sub-space associated with at least one identified CLI source. The method may further include, for each reception associated with the first network entity, spatially projecting, by the first network entity, at least one interference rejection combining (IRC) estimated interference covariance matrix into at least one orthogonal projector sub-space. 
     In accordance with some embodiments, an apparatus may include means for receiving at least one downlink precoder map from a network entity over at least one interface. The apparatus may further include means for estimating at least one basis of at least one common spatial sub-space associated with at least one identified CLI sources. The apparatus may further include means, for each reception associated with the apparatus, spatially projecting at least one interference rejection combining (IRC) estimated interference covariance matrix into at least one orthogonal projector sub-space. 
     In accordance with some embodiments, an apparatus may include at least one processor and at least one memory including computer program code. The at least one memory and the computer program code may be configured to, with the at least one processor, cause the apparatus to at least receive at least one downlink precoder map from a network entity over at least one interface. The at least one memory and the computer program code may be further configured to, with the at least one processor, cause the apparatus to at least estimate at least one basis of at least one common spatial sub-space associated with at least one identified CLI sources. The at least one memory and the computer program code may be further configured to, with the at least one processor, cause the apparatus to at least, for each reception associated with the apparatus, spatially projecting at least one interference rejection combining (IRC) estimated interference covariance matrix into at least one orthogonal projector sub-space. 
     In accordance with some embodiments, a non-transitory computer readable medium may be encoded with instructions that may, when executed in hardware, perform a method. The method may receive at least one downlink precoder map from a network entity over at least one interface. The method may further estimate at least one basis of at least one common spatial sub-space associated with at least one identified CLI sources. The method may further, for each associated reception, spatially projecting at least one interference rejection combining (IRC) estimated interference covariance matrix into at least one orthogonal projector sub-space. 
     In accordance with some embodiments, a computer program product may perform a method. The method may receive at least one downlink precoder map from a network entity over at least one interface. The method may further estimate at least one basis of at least one common spatial sub-space associated with at least one identified CLI sources. The method may further, for each associated reception, spatially projecting at least one interference rejection combining (IRC) estimated interference covariance matrix into at least one orthogonal projector sub-space. 
     In accordance with some embodiments, an apparatus may include circuitry configured to receive at least one downlink precoder map from a network entity over at least one interface. The circuitry may further estimate at least one basis of at least one common spatial sub-space associated with at least one identified CLI sources. The circuitry may further, for each associated reception, spatially project at least one interference rejection combining (IRC) estimated interference covariance matrix into at least one orthogonal projector sub-space. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For proper understanding of the invention, reference should be made to the accompanying drawings, wherein: 
         FIG. 1  illustrates an example of DL-to-UL CLI occurrences in dynamic TDD according to certain embodiments. 
         FIG. 2  illustrates an example of URLLC outage latency of static and dynamic TDD according to certain embodiments. 
         FIG. 3  illustrates an example of buffered traffic ratios of dynamic TDD according to certain embodiments. 
         FIG. 4  illustrates an example of a signal flow diagram according to certain embodiments. 
         FIG. 5  illustrates an example of a method according to certain embodiments. 
         FIG. 6  illustrates an example of BS-BS CLI suppression and precoder map feedback according to certain embodiments. 
         FIG. 7  illustrates an example of three-step BS-BS CLI suppression according to certain embodiments. 
         FIG. 8  illustrates an example of a RFC book and hybrid frame design for TTI=7 OFDM symbols according to certain embodiments. 
         FIG. 9  illustrates an example of simulation parameters according to certain embodiments. 
         FIG. 10  illustrates an example of a timing diagram of signaling under a CU/DU structure according to certain embodiments. 
         FIGS. 11( a ) and 11( b )  illustrate an example of UL and DL URLLC outage latency performance according to certain embodiments. 
         FIG. 12  illustrates a table of URLLC outage latency at 10 −5  probability according to certain embodiments. 
         FIG. 13  illustrates an example of carrier-to-interference ratio performances in dB according to certain embodiments. 
         FIG. 14  illustrates an example of throughput per packet performance in Mbps according to certain embodiments. 
         FIG. 15  illustrates an example of buffered traffic ratio performance according to certain embodiments. 
         FIG. 16  illustrates an example of a system according to certain embodiments. 
         FIG. 17  illustrates an architecture according to certain embodiments. 
         FIG. 18  illustrates another architecture according to certain embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     Among other requirements, 5G NR should support a large number of applications with varying quality of service (QoS) requirements, causing a wide variety of asymmetric downlink (DL) and uplink (UL) traffic demands. TDD operation mode is a key factor in achieving this since the radio frame configuration (RFC) of each base station (BS) may be changed over time to adapt to instantaneous traffic demands. For example, each BS may independently change its DL-to-UL slots/symbols ratio within a radio frame based upon its traffic ratio. However, such an operation may introduce an additional type of inter-cell cross-link interference (CLI), such as UL-to-DL or DL-to-UL. This may include CLI between user equipment (UE-UE) and/or between base stations (BS-BS). Furthermore, ultra-reliable and low latency communications (URLLC) is a major component of 5G NR, providing an outage latency of one or several milliseconds with an outage probability of 10 −5 . Such URLLC latency and reliability are extremely challenging to achieve with dynamic TDD due to the UL/DL switching time and CLI. While UL/DL switching time may be minimized with the mini-slot transmissions of the 5G NR, CLI remains an open challenge. 
     In macro deployments, CLI is a critical issue, requiring mitigation on a pre-receiver or post-receiver basis. For example, due to the power imbalance between the DL and UL transmissions in macro setups, DL-heavy BSs may interfere with the transmissions of the adjacent UL-heavy BSs, leading to a significantly degraded UL performance. Thus, CLI, particularly BS-BS CLI, is considered a major hindrance for performance of 5G dynamic TDD macro systems. Coordination schemes among BSs have been developed to counteract the CLI; however, these frequently are only effective over certain CLI ranges, and otherwise fail to mitigate CLI. In addition, these coordination schemes may require extensive CLI user measurements, highly complex implementation, and/or significant signaling overhead. 
     Some techniques have been suggested for coordinating schemes of fully dynamic TDD systems. For example, one technique configures periodicity and numerology, such as subcarrier spacing and cyclic prefix length. A list may contain multiple entities of information indicating that slots within a periodicity are configured, as well as a UL region indication being configured for each slot, such as all DL, all UL, a number of DL symbols, and/or a number of UL symbols in a slot. 
     Another example includes a DL-to-UL CLI cancellation method using full packet exchange. The DL-heavy BSs signals adjacent UL-heavy BSs with DL data payloads, precoding information, timing information, modulation and coding information, and scheduling decisions. These UL-heavy BSs may cancel the DL-to-UL CLI, improving UL and DL capacity, but with significant control signalling overhead over the X n  interface. 
     Other techniques propose an X n -based coordination scheme to avoid the UE-UE CLI occurrence by pre-cancelling the more critical BS-BS CLI on a best-effort basis. This may lead to a significantly enhanced capacity and latency performance, but only within a limited BS-BS CLI bound, such as under a DL-heavy traffic assumption. Thus, with strong BS-BS CLI, the URLLC latency and capacity performance may exponentially degrade due to the excessive UL retransmissions. 
     Some proposals may relate to a network-based UL-DL coordination scheme. Here, base stations may be associated with a common RFC across the entire cluster, such as static TDD. When a base station demands an RFC change, it may signal all base stations within the cluster by an RFC change request. If all base stations agree, then the request is accepted, and all base stations may switch to the updated RFC, which may still be in a static TDD mode. If at least one base station rejects such a request, the requesting base station only changes to the desired RFC, and all base stations in the cluster may periodically start to monitor the CLI measurements. If the detected CLI levels exceed a predefined threshold, all base stations fall back to static TDD with the common RFC. Thus, CLI levels should be limited at all times. However, with a significantly reduced RFC flexibility, large signalling overhead across an X n  interface occurs, as well as the need for periodic CLI user measurements over the radio control channels. 
     Additional proposals may relate to a hybrid TDD coordination scheme, where BSs dynamically switch among static and dynamic TDD modes based on the detected CLI level. If the CLI level passes a threshold, all BSs switch back to the same static TDD RFC. Thus, the CLI is always minimized, but with extremely limited RFC flexibility in addition to the requirement of high quality CLI user measurements. 
     Some techniques may include coordinated cell muting and rate allocation between all BSs in a cluster to eliminate the major CLI aggressor BSs/PRBs, but at the expense of capacity regions. For example, some BSs may be muted over several subframes, requiring a significant amount of control overhead to globally publicise the BS individual scheduling decisions across the cluster. 
     Finally, a coordinated aligned reverse frame structure has been proposed where BSs are grouped in pairs. Each BS may select an RFC which needs to be fully reversed to the other BS in this pair, biasing the dynamic TDD system to more DL-to-UL CLI occurrences than the UL-to-DL ones. A coordinated DL-to-UL CLI cancellation may then be adopted at all BSs using advanced non-linear receivers and sophisticated coordination. However, the requirement of the fully-reversed frame structures of each two adjacent BSs may set a critical restriction on the TDD RFC flexibility, for example, two adjacent BSs may not originally select exactly the same RFC but with reverse order. 
     With a standard dynamic TDD system model over 5G NR, each BS may independently select its RFC based on its current traffic demands. A RFC may be composed from 10 subframes, with each having a 1-ms duration. Each RFC may be divided into two equally-sized half-frames of five subframes, each with half-frame-0 consisting of subframes 0-4 and half-frame-1 consisting of subframes 5-9. A subframe consists of 14 OFDM symbols for cases with a normal cyclic prefix, while it equals only 12 OFDM symbols for the case with extended cyclic prefixes and subcarrier spacing of 60 kHz. The number of slots per subframe/radio frame may depend on the subcarrier spacing. For 15 kHz subcarrier spacing, there may be one slot per subframe; for 30 kHz, there may be two slots per subframe; for 60 kHz, there are four slots per subframe, and so forth. A large number of possible slot formats may be defined in 3GPP TS 38.213, where “D” indicates downlink symbol, “U” indicates uplink symbol, and “F” is flexible. Hence, “F” could refer to muting or be used for downlink or uplink transmission. As an example, slot format 0 and 1 may correspond to downlink-only and uplink-only slots, respectively. Slot format 36 may contain first three downlink transmission symbols, followed by “F” (which could be set to mute for guard period), and ten uplink transmission symbols. As per 3GPP TS 38.213, the gNB may dynamically inform the UEs of the used slot format. 
     The flexible frame structure of 5G NR may allow for both short and long transmission time intervals (TTIs). Thus, it is applicable to both enhanced mobile broadband (eMBB) and ultra-reliable low-latency communication (URLLC) QoS classes. eMBB is facilitated by allowing both mini-slot transmission of, for example, 2- or 4-symbols to/from particular users, and full slot transmissions, or TTIs of aggregated slots. 
     If base stations do not use exactly the same RFC, adjacent base stations may experience different transmission directions over several symbols/slots, causing potentially severe CLI, as shown by the example in  FIG. 1 . Accordingly, the lower-power UL transmissions may be severely degraded due to the strong CLI resulting from adjacent larger-power DL transmissions. As a result, the achievable UL capacity may exhibit a significant loss, leading to more buffered UL traffic in those victim BSs. Hence, these base stations may be dictated by new and buffered UL traffic leading to a limited DL capacity and highly degraded overall spectral efficiency as a consequence. 
       FIG. 2  illustrates the complementary cumulative density function (CCDF) of the URLLC one-way latency, under the static and fully dynamic (non-coordinated) TDD setups, for a DL:UL offered traffic ratio as 2:1 (DL-heavy) and total of 4 Mbps/cell of offered load. At the 10 −5  URLLC outage probability, the static TDD setup provides improved URLLC latency compared with the dynamic TDD case, i.e., 16.2 ms compared to 105.4 ms with the dynamic TDD. This may be due to critical DL-to-UL, i.e., BS-BS, CLI that is significantly degrading the adjacent UL decoding ability, by higher-power DL interfering transmissions. Accordingly, the transmitted UL traffic may be accumulated in the scheduling buffers for further retransmissions. As a result, the system may be dictated by the new and buffered UL traffic, resulting in suboptimal UL and DL latency and capacity performance. 
     To further highlight such UL buffering problem,  FIG. 3  presents the average buffering queue ratio, which denotes the ratio of the DL buffered traffic to the total UL and DL buffered traffic 
               (     DL     DL   +   UL       )     ,         
for the fully dynamic TDD setup under two conditions: a) non-coordinated with no CLI suppression, and b) coordinated with theoretically perfect CLI suppression, i.e., CLI=0. For the non-coordinated case, the queue ratio is fairly small, such as at the 50 th  percentile, it is 0.248, which denotes that the average amount of buffered UL traffic is 3× times the buffered DL traffic, despite the fact that the offered DL traffic is 2× times the offered UL traffic. This is because the UL traffic almost get successfully decoded after several retransmissions due to the strong BS-BS CLI. Such behaviour is vanished when the CLI is theoretically assumed to be perfectly cancelled, i.e., CLI-free.
 
     Certain embodiments described herein may have various benefits and/or advantages to overcome the disadvantages described above by enabling coordination between base stations to manage CLI. For example, certain embodiments may provide a near-optimal TDD coordination scheme to suppress critical BS-BS CLI, leading to a significantly improved UL capacity and latency performance. As a result, a reduction of 143.0% in URLLC outage latency and 139.3% per-packet throughout gain as compared to non-coordinated TDD deployment. Furthermore, a consistent and reliable CLI suppression ability may be provided regardless of the amount of the offered load and the DL-to-UL traffic ratio, respectively, without requiring periodic CLI user measurements. 
     Certain embodiments may result in improved reliable BS-BS CLI suppression ability independently from an offered load level and DL. Some embodiments may also provide robust and reliable capacity performance in both UL and DL directions regardless of the offered traffic loads in both directions and potential CLI levels. Furthermore, various embodiments require low coordination complexity with limited signalling overhead over the Xn/F1 interface without periodic user CLI measurements, leading to improvements in computer-related technology. 
       FIG. 4  illustrates a signaling diagram according to some embodiments. In step  401 , NE  420 , which may be similar to NE  1610  in  FIG. 16 , may transmit at least one downlink precoder map to NE  430 , which may also be similar to NE  1610  in  FIG. 16 . A downlink precoder map may at least one wide-band or sub-band precoder index configured to be adopted by at least one scheduled downlink user during at least one upcoming mini-slot/slot transmission. At least one user-specific precoding matric index (PMIs) may be relayed between at least one base stations. In addition, NE  420  and/or NE  430  may be in communication with UE  440 , which may be similar to UE  1620  in  FIG. 16 . NE  420  and/or NE  430  may be associated with at least one BS-BS CLI symbol/slot within at least one current RFC and/or may be adjacent base stations. Additionally, NE  420  may be in a DL mode and/or NE  430  may be in an uplink mode. The at least one DL precoder map may be transmitted over at least one X n  interface. In some embodiments, the at least one DL precoder map may comprise at least one vector of bits configured to indicate at least one selected sub-band/wideband pre-coding matrix index (PMI) associated with at least one schedule DL user over the associated slot. The at least one selected sub-band/wideband PMI may be configured to be used by at least one scheduled user during a next DL symbol of the DL base stations, as illustrated in  FIG. 6( a ) . 
     In some embodiments, NE  420  may be similar to a centralized unit (CU) and/or NE  430  may be similar to a distributed unit (DU). Thus, NE  420  may transmit the at least one downlink precoder map to NE  430  over at least one X n -C interface configured to coordinate at least one X n AP procedure, as defined in 3GPP TS 38.423, herein incorporated in its entirety, and/or an NG interface towards at least one 5G core network (5GC). 
     In some embodiments, the 5G NR architecture may be configured to allow C-RAN implementation associated with at least one CU and/or at least one DU. The CU-DU configuration may be associated with at least one E1 interface between at least one control plane and at least one user plane in the CU, as described in 3GPP TS 38.460 and/or TS 38.463. Additionally or alternatively, the CU-DU configuration may be associated with at least one F1 interface between at least one CU and at least one DU, as described in 3GPP TS 38.470 and/or TS 38.473, herein incorporated in their entirety. 
     In some embodiments, where NE  430  is, or is similar to, UE  440 , NE  430  may directly communicate with at least one other user equipment, such as UE  1620  in  FIG. 16 , and/or with assistance from a network. For example, NE  430  may act as a relay UE, serving as a UL BS for at least one adjacent UE. In certain embodiments, the at least one adjacent UE may be affected by adjacent DL transmissions from neighboring base stations, as illustrated in  FIG. 6( b ) . Thus, downlink precoder signaling may be performed over at least one radio interface from NE  420  to NE  430 . 
     In various embodiments, the at least one CU may be configured to serve as a master and/or the at least one DU may be configured to serve as a slave, as illustrated in  FIG. 10 . The at least one downlink precoder map may be transmitted according to at least one F1 control plane signaling path, such as F1-C. In response, the at least one CU may determine at least one RFC associated with the at least one DU, and transmit the at least one determined RCC to the at least one DU. The CU may be configured to identify at least one slot/symbol associated with DU-DU CLI. 
     For each instance of DU-DU CLI, the CU may transmit at least one request to at least one interfering DU to report at least one used precoder map. In response, the CU may forward the at least one reported used precoder map to at least one interfered DU. The at least one interfered DU may, according to the received at least one used precoder map, adjust at least one parameter to reduce DU-DU CLI interference. 
     In some embodiments, the CU may coordinate with at least one DU to perform at least one DU-DU radio channel measurement associated with low-offered traffic and/or conditions exceeding at least one interference threshold associated with at least one channel estimation task. 
     In step  403 , in response to receiving the at least one DL precoder map, NE  430  may identify at least one BS-BS CLI source associated with CLI exceeding at least one predefined CLI source threshold. The at least one identified BS-BS CLI source may be scaled by at least one channel between at least one DL and at least one UL NE. In some embodiments, the at least one channel may be estimated according to at least one periodicity, which may be associated with at least one static property exceeding at least one predefined static property threshold. 
     In step  405 , NE  430  may sort the at least one identified BS-BS CLI source in an order, such as descending order or ascending order, according to the CLI associated with each BS-BS CLI source. In some embodiments, NE  430  may consider only the M r −1 BS-BS CLI sources, where M r  is a number of UE antennas. 
     In step  407 , NE  430  may estimate at least one basis of at least one common spatial sub-space associated with at least one, or all, identified N t −1 BS-BS CLI sources. For example, NE  430  may perform the estimation according to: 
               β   k     =     {                   J   1     ,     k   =   1                     J   k     -       ∑     j   =   1       k   -   1       ⁢           ⁢       proj     β   j       ⁡     (     J   k     )           ,     2   ≥   k   ≤       N   t     -   1               ⁢     
     ⁢       proj     β   k       ⁡     (     J   k     )         =       (         J   k     ·     β   k                β   k          2       )     ⁢     β   k         ,             
where β k  is the basis vector of the k th  BS-BS CLI source J k =Q k v k , where Q k  is the wireless channel between NE  420  and NE  430 ; and v k  is the precoder of the DL user transmitting on the corresponding sub-band.
 
     In step  409 , NE  430  may estimate at least one orthogonal projector span to the basis of the strongest BS-BS CLI interference according to:
 
 A =[β 1 ,β 2 , . . . ,β k ] T  
 
 A   ⊥   =A ( A   ⊥   A ) −1   A   T ,
 
where A and A ⊥  denote the BS-BS CLI sub-space and its orthogonal projector span, as illustrated in  FIG. 7 .
 
     In step  411 , for each reception associated with NE  430 , NE  430  may spatially project at least one interference rejection combining (IRC) estimated interference covariance matrix into at least one orthogonal projector sub-space, according to: 
                   w   ~       (       :     ,   i     )       =       (         w     (       :     ,   i     )       ·     A     (       :     .   i     )     ⊥                A     (       :     .   i     )     ⊥          2       )     ·     A     (       :     .   i     )     ⊥         ,         
where W and {hacek over (W)} are the IRC estimated interference covariance matrix and the corresponding covariance matrix projected over the estimated projector sub-space, respectively.
 
     In step  413 , NE  430  may calculate at least one standard IRC decoding matrix u according to the at least one IRC estimated interference covariance matrix, according to:
 
 u =( Hv ( hv ) H   +{tilde over (w)} ) −1   Hv,  
 
where H is the intended wireless channel, and v is the intended precoder of the respective user.
 
       FIG. 5  illustrates an example of a method performed by a NE, such as NE  1610  illustrated in  FIG. 16 , according to certain embodiments. In step  501 , the NE may receive at least one downlink precoder map from a neighbor NE, which may also be similar to NE  1610  in  FIG. 16 . The NE and/or the neighbor NE may be associated with at least one BS-BS CLI symbol/slot within at least one current RFC and/or may be adjacent base stations. Additionally, the NE may be in a DL mode and/or the neighbor NE may be in an uplink mode. The at least one DL precoder map may be transmitted over at least one X n  interface. In some embodiments, the at least one DL precoder map may comprise at least one vector of bits configured to indicate at least one selected sub-band/wideband pre-coding matrix index (PMI) associated with at least one schedule DL user over the associated slot. The at least one selected sub-band/wideband PMI may be configured to be used by at least one scheduled user during a next DL symbol of the DL base stations, as illustrated in  FIG. 6( a ) . 
     In some embodiments, the NE may be similar to a centralized unit (CU) and/or the neighbor NE may be similar to a distributed unit (DU). Thus, the NE may transmit the at least one downlink precoder map to the neighbor NE over at least one X n -C interface configured to coordinate at least one X n AP procedure, as defined in 3GPP TS 38.423, herein incorporated in its entirety, and/or an NG interface towards at least one 5G core network (5GC). The 5G NR architecture may be configured to allow C-RAN implementation associated with at least one CU and/or at least one DU. The CU-DU configuration may be associated with at least one E1 interface between at least one control plane and at least one user plane in the CU, as described in 3GPP TS 38.460 and/or TS 38.463, herein incorporated in their entirety. Additionally or alternatively, the CU-DU configuration may be associated with at least one F1 interface between at least one CU and at least one DU, as described in 3GPP TS 38.470 and/or TS 38.473, herein incorporated in their entirety. 
     In some embodiments, where the NE is, or is similar to, a UE, such as UE  1620  in  FIG. 16 , the NE may directly communicate with other UE, such as UE  1620  in  FIG. 16 , or with assistance from a network. For example, the NE may act as a relay UE, serving as a UL BS for at least one adjacent UE. In certain embodiments, the at least one adjacent UE may be affected by adjacent DL transmissions from neighboring base stations, as illustrated in  FIG. 6( b ) . Thus, downlink precoder signaling may be performed over at least one radio interface from the neighbor NE to the NE. 
     In various embodiments, the at least one CU may be configured to serve as a master and/or the at least one DU may be configured to serve as a slave, as illustrated in  FIG. 10 . The at least one downlink precoder map may be transmitted according to at least one F1 control plane signaling path, such as F1-C. In response, the at least one CU may determine at least one RFC associated with the at least one DU, and transmit the at least one determined RCC to the at least one DU. The CU may be configured to identify at least one slot/symbol associated with DU-DU CLI. 
     For each instance of DU-DU CLI, the CU may transmit at least one request to at least one interfering DU to report at least one used precoder map. In response, the CU may forward the at least one reported used precoder map to at least one interfered DU. The at least one interfered DU may, according to the received at least one used precoder map, adjust at least one parameter to reduce DU-DU CLI interference. 
     In some embodiments, the CU may coordinate with at least one DU to perform at least one DU-DU radio channel measurement associated with low-offered traffic and/or conditions exceeding at least one interference threshold associated with at least one channel estimation task. 
     In step  503 , in response to receiving the at least one DL precoder map, the NE may identify at least one BS-BS CLI source associated with CLI exceeding at least one predefined CLI source threshold. The at least one identified BS-BS CLI source may be scaled by at least one channel between at least one DL and at least one UL NE. In some embodiments, the at least one channel may be estimated according to at least one periodicity, which may be associated with at least one static property exceeding at least one predefined static property threshold. 
     In step  505 , the NE may sort the at least one identified BS-BS CLI source in an order, such as descending order or ascending order, according to the CLI associated with each BS-BS CLI source. In some embodiments, the NE may consider only the M r −1 BS-BS CLI sources, where M r  is a number of UE antennas. 
     In step  507 , the NE may estimate at least one basis of at least one common spatial sub-space associated with at least one, or all, identified N t −1 BS-BS CLI sources. For example, the NE may perform the estimation according to: 
     
       
         
           
             
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     where β k  is the basis vector of the k th  BS-BS CLI source J k Q k v k , where Q k  is the wireless channel between the NE and the neighbour NE, and v k  is the precoder of the DL user transmitting on the corresponding sub-band. 
     In step  509 , the NE may estimate at least one orthogonal projector span to the basis of the strongest BS-BS CLI interference according to:
 
 A =[β 1 ,β 2 , . . . ,β k ] T  
 
 A   ⊥   =A ( A   ⊥   A ) −1   A   T ,
 
where A and A ⊥  denote the BS-BS CLI sub-space and its orthogonal projector span, as illustrated in  FIG. 7 .
 
     In step  511 , for each reception associated with the NE, the NE may spatially project at least one interference rejection combining (IRC) estimated interference covariance matrix into at least one orthogonal projector sub-space, according to: 
                   w   ~       (       :     ,   i     )       =       (         w     (       :     ,   i     )       ·     A     (       :     .   i     )     ⊥                A     (       :     .   i     )     ⊥          2       )     ·     A     (       :     .   i     )     ⊥         ,         
where W and {hacek over (W)} are the IRC estimated interference covariance matrix and the corresponding covariance matrix projected over the estimated projector sub-space, respectively.
 
     In step  513 , the NE may calculate at least one standard IRC decoding matrix u according to the at least one IRC estimated interference covariance matrix, according to:
 
 u =( Hv ( Hv ) H   +{tilde over (w)} ) −   Hv,  
 
where H is the intended wireless channel, and v is the intended precoder of the respective user.
 
     Some embodiments described herein may be associated with particular signaling overhead. For example, in a system with 10 MHz bandwidth, 50 physical resource blocks (PRBs), sub-band feedback, each of 8 PRBs, and 4-bit PMI feedback based on the 4-antenna port transmissions may be associated with 3 BS-BS CLI slots. The overall signalling overhead of the DL precoder map associated with each radio frame duration, such as 10 ms, may be determined as: 
               Xn   ⁢     -     ⁢   interface   ⁢           ⁢   signalling   ⁢           ⁢   overhead     =       3   ×     (       (     50   8     )     ×     (         log   2     ⁡     (     50   8     )       +   4     )       )       =     124   ⁢           ⁢   bits   ⁢           ⁢   per   ⁢           ⁢   each   ⁢           ⁢   10   ⁢           ⁢   ms   ⁢           ⁢       (       i   .   e   .     ,     radio   ⁢           ⁢   frame   ⁢           ⁢   duration       )     .               
Such signalling may not be required between every DL and UL BS pair since some DL NEs may not contribute severe BS-BS CLI to adjacent UL BSs due to a weak channel in between, which may be due to a large distance, obstruction, advanced beamforming, etc., and may lead to a further reduction in signalling overhead.
 
     As discussed above, various embodiments described herein may provide certain advantages using at least one parameter shown in the table of  FIG. 9 . For example, within each cell, there may be K average number of active users. URLLC traffic may be characterized by at least one FTP3 traffic model, a finite Z-bit packet size per user, and/or a Poisson point arrival process λ. Thus, the aggregate offered DL and UL loads per cell in bits/sec may be given as K×λ {DL,UL} ×Z. The system bandwidth may be 10 MHz with 8 antennas at the BS and 2 antennas at the user equipment. Various coordination schemes described herein may be tested over various offered traffic loads of DL-heavy traffic ratio, which may correspond with strong DL-to-UL CLI. 
       FIGS. 11( a ) and 11( b )  depict the complementary cumulative distribution function (CCDF) of the UL and DL URLLC latency in ms for different offered load levels with DL:UL=2:1 in various embodiments, with an optimal CLI-free case. Various embodiments may provide an optimal CLI-free over all outage probabilities including the URLLC outage probability at 10 −5 . At such an outage probability, various embodiments may offer only +4 ms than the optimal CLI-free case for an extreme offered load of 7 Mbps, but with a significantly lower coordination overhead and only over the Xn-interface. 
       FIG. 12  provides the full numerical results of the URLLC latency at 10 −5  outage probability according to various embodiments described herein. Specifically, the NC and H-RFC schemes may suffer from extreme outage latency degradation due to the strong BS-BS CLI. Various embodiments may cause the UL packets to reach the maximum number of allowable retransmissions before being dropped, which may result in a significant loss of URLLC reliability. Various embodiments may provide an optimal CLI-free case with a consistent URLLC latency due to the absolute absence of the BS-BS and UE-UE CLI. However, certain embodiments may provide a similar outage latency performance as the optimal CLI-free case but with reduced signalling overhead space. As a result, various embodiments provide support for more offered loads to reach the same outage latency, such as from 4 Mbps to 7 Mbps. 
       FIG. 13  presents the empirical CDF (ECDF) of the carrier-to-interference ratio (CIR) in dB. Various embodiments may provide an increase of 3.5 dB in the CIR compared with NC and H-RFC, approaching the optimal CLI-free case due to the efficient BS-BS CLI suppression.  FIG. 14  similarly illustrates an average throughput per packets in Mbps, where certain embodiments may provide an average of 3× fold throughput per URLLC packet, compared to H-RFC and NC. 
       FIG. 15  illustrates a queue traffic ratio, as described above. As shown in  FIG. 14 , certain embodiments may provide a queue ratio where roughly twice the DL traffic may be buffered in comparison to UL traffic, wherein the offered DL traffic may be twice the UL traffic. As a result, UL traffic may be successfully and quickly decoded without being buffered for several retransmission attempts. Various embodiments may also provide an optimal CLI-free case. 
       FIG. 16  illustrates an example of a system according to certain embodiments. In one embodiment, a system may include multiple devices, such as, for example, network entity  1610  and/or user equipment  1620 . 
     Network entity  1610  may be one or more of: a base station, such as an evolved node B (eNB) or 5G or New Radio node B (gNB), a serving gateway, a server, and/or any other access node or combination thereof Network entity  1610  may also be a UE  1620  or be similar to UE  1620 . 
     User equipment  1620  may include one or more of a mobile device, such as a mobile phone, smart phone, personal digital assistant (PDA), tablet, or portable media player, digital camera, pocket video camera, video game console, navigation unit, such as a global positioning system (GPS) device, desktop or laptop computer, single-location device, such as a sensor or smart meter, or any combination thereof. 
     In addition, in some embodiments, functionality of the network entity  1610  and/or UE  1620  may be implemented by other network nodes, such as a wireless relay node. For example, functionalities of NE  1610  may be performed by a mobile termination (MT) component of the IAB node. Furthermore, network entity  1610  and/or user equipment  1620  may be one or more of a citizens broadband radio service device (CBSD). 
     One or more of these devices may include at least one processor, respectively indicated as  1611  and  1621 . Processors  1611  and  1621  may be embodied by any computational or data processing device, such as a central processing unit (CPU), application specific integrated circuit (ASIC), or comparable device. The processors may be implemented as a single controller, or a plurality of controllers or processors. 
     At least one memory may be provided in one or more of devices indicated at  1612  and  1622 . The memory may be fixed or removable. The memory may include computer program instructions or computer code contained therein. Memories  1612  and  1622  may independently be any suitable storage device, such as a non-transitory computer-readable medium. A hard disk drive (HDD), random access memory (RAM), flash memory, or other suitable memory may be used. The memories may be combined on a single integrated circuit as the processor, or may be separate from the one or more processors. Furthermore, the computer program instructions stored in the memory and which may be processed by the processors may be any suitable form of computer program code, for example, a compiled or interpreted computer program written in any suitable programming language. Memory may be removable or non-removable. 
     Processors  1611  and  1621  and memories  1612  and  1622  or a subset thereof, may be configured to provide means corresponding to the various blocks of  FIGS. 1-15 . Although not shown, the devices may also include positioning hardware, such as GPS or micro electrical mechanical system (MEMS) hardware, which may be used to determine a location of the device. Other sensors are also permitted and may be included to determine location, elevation, orientation, and so forth, such as barometers, compasses, and the like. 
     As shown in  FIG. 16 , transceivers  1613  and  1623  may be provided, and one or more devices may also include at least one antenna, respectively illustrated as  1614  and  1624 . The device may have many antennas, such as an array of antennas configured for multiple input multiple output (MIMO) communications, or multiple antennas for multiple radio access technologies. Other configurations of these devices, for example, may be provided. Transceivers  1613  and  1623  may be a transmitter, a receiver, or both a transmitter and a receiver, or a unit or device that may be configured both for transmission and reception. 
     The memory and the computer program instructions may be configured, with the processor for the particular device, to cause a hardware apparatus such as user equipment to perform any of the processes described below (see, for example,  FIGS. 1-15 ). Therefore, in certain embodiments, a non-transitory computer-readable medium may be encoded with computer instructions that, when executed in hardware, perform a process such as one of the processes described herein. Alternatively, certain embodiments may be performed entirely in hardware. 
     In certain embodiments, an apparatus may include circuitry configured to perform any of the processes or functions illustrated in  FIGS. 1-15 . For example, circuitry may be hardware-only circuit implementations, such as analog and/or digital circuitry. In another example, circuitry may be a combination of hardware circuits and software, such as a combination of analog and/or digital hardware circuit(s) with software or firmware, and/or any portions of hardware processor(s) with software (including digital signal processor(s)), software, and at least one memory that work together to cause an apparatus to perform various processes or functions. In yet another example, circuitry may be hardware circuit(s) and or processor(s), such as a microprocessor(s) or a portion of a microprocessor(s), that include software, such as firmware for operation. Software in circuitry may not be present when it is not needed for the operation of the hardware. 
       FIG. 17  illustrates an architecture according to certain embodiments.  FIG. 18  illustrates another architecture according to certain embodiments. 
     The features, structures, or characteristics of certain embodiments described throughout this specification may be combined in any suitable manner in one or more embodiments. For example, the usage of the phrases “certain embodiments,” “some embodiments,” “other embodiments,” or other similar language, throughout this specification refers to the fact that a particular feature, structure, or characteristic described in connection with the embodiment may be included in at least one embodiment of the present invention. Thus, appearance of the phrases “in certain embodiments,” “in some embodiments,” “in other embodiments,” or other similar language, throughout this specification does not necessarily 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 embodiments. 
     One having ordinary skill in the art will readily understand that the invention as discussed above may be practiced with steps in a different order, and/or with hardware elements in configurations which are different than those which are disclosed. Therefore, although the invention has been described based upon these preferred embodiments, it would be apparent to those of skill in the art that certain modifications, variations, and alternative constructions would be apparent, while remaining within the spirit and scope of the invention. 
     Partial Glossary 
     3GPP 3rd Generation Partnership Project 
     5G 5th Generation 
     BS Base Station 
     CLI Cross Link Interference 
     CLI-free CLI-free Dynamic TDD 
     CQI Channel Quality Indicator 
     CU Centralized Unit 
     DL Downlink 
     DSS Dynamic Slot Set 
     DU Distributed Unit 
     ECDF Empirical Cumulative Distribution Function 
     eMBB Enhanced Mobile Broadband 
     eNB Evolved Node B 
     EPC Evolved Packet Core 
     FDD Frequency Division Multiplexing 
     gNB New Radio Node B 
     GPS Global Positioning System 
     H-RFC Hybrid RFC Dynamic TDD 
     IRC Interference Rejection Combining 
     LTE Long-Term Evolution 
     MAC Medium Access Control 
     MCS Modulation and Coding Scheme 
     MME Mobility Management Entity 
     MTC Machine-Type Communications 
     NC Non-Coordinated Dynamic TDD 
     NG-eNB Next Generation Evolved Node-B 
     NR New Radio 
     OAM Operation, Administration, and Management 
     OFDM Orthogonal Frequency Division Multiplexing 
     PDU Protocol Data Unit 
     PRB Physical Resource Block 
     QoS Quality of Service 
     RAN Radio Access Network 
     RFC Radio Frame Configuration 
     RFCB Radio Frame Configuration Book 
     RLC Radio Link Control 
     SB Sub-Band 
     SN Sequence Number 
     SSS Static Slot Set 
     TCP Transmission Control Protocol 
     TDD Time Division Duplexing 
     TTI Transmission Time Interval 
     UE User Equipment 
     UL Uplink 
     URLLC Ultra-Reliable and Low-Latency Communication