Symbol detection in the presence of access point-to-access point interference

Abstract

According to certain embodiments, a method in a first network node comprises receiving an interfering signal from a second network node, the interfering signal received when performing reception on an uplink during at least one sample phase in a coherence block, the coherence block configured such that during the at least one sample phase each user equipment (UE) in a group of one or more UEs served by the first network node is silent or transmits only a sample value. The method comprises mitigating interference from the second network node based at least in part on information obtained by receiving the interfering signal during the sample phase.

Description

Symbol Detection in the Presence of Access Point-to-Access Point InterferenceRELATED APPLICATIONS

[0001] This application claims priority to U.S. Provisional Patent Application Nos. 63 / 536540 and 63 / 536547, both filed on September 5, 2023, the disclosure and content of each is incorporated by reference herein in its entirety.TECHNICAL FIELD

[0002] Embodiments of the present disclosure are directed to wireless communications involving an access point (AP) and more particularly to symbol detection in the presence of AP-to-AP interference.BACKGROUND

[0003] In cellular communication between a base station and user equipment (UE), simultaneous transmission and reception is typically accomplished using different resources for the uplink (UL) and the downlink (DL). As an example, simultaneous transmission and reception may be accomplished using different frequency resources, such as in a frequency division duplex (FDD) configuration where the UL frequency band and the DL frequency band are separate. As another example, simultaneous transmission and reception may be accomplished using different time resources, such as in a time division duplex (TDD) configuration where the UL and the DL use the same bandwidth but allocate different time slots for the UL and the DL.

[0004] Dynamic TDD (D-TDD) networks have the potential to easily adapt to the ratio between UL and DL traffic. However, D-TDD networks are also affected by new interference paths not seen in FDD networks or in TDD networks with a static allocation of UL and DL transmission intervals. For example, D-TDD networks experience so-called cross-link interference. Examples of cross-link interference include UE-to-UE interference (UUI) and AP-to-AP interference (AAI). In UE-to-UE interference, transmitting UEs interfere with receiving UEs operating in the same frequency band at the same time. In AP-to-AP interference, transmitting APs interfere with receiving APs operating in the same frequency band at the same time.SUMMARY

[0005] There currently exist certain challenge(s). In D-TDD systems, the switching point between UL and DL does not normally happen simultaneously at all APs. As a consequence, at a given point in time, one or more UEs may operate on the DL and another one or more UEs may operate on the UL, resulting in interference between the UEs. Similarly, at a given point in time, one or more APs may operate on the DL and another one or more APs may operate on the UL, resulting in interference between APs.

[0006] Certain aspects of the disclosure and their embodiments may provide solutions to these or other challenges. For example, a first set of embodiments may facilitate suppression of UE-to-UE interference. A second set of embodiments may facilitate symbol detection by an AP in the presence of AP-to-AP interference. Optionally, solutions from the first and second sets of embodiments may be combined to facilitate suppression of UE-to-UE interference and symbol detection by an AP in the presence of AP-to-AP interference. Certain embodiments may be well-suited to mobility conditions (e.g., to facilitate suppression of UE-to-UE interference in cases where UEs move around the environment) and / or stationary conditions (e.g., to facilitate symbol detection by an AP in cases where the positions of the APs are typically stationary).

[0007] According to certain embodiments, a method in a first network node comprises receiving an interfering signal from a second network node, the interfering signal received when performing reception on an uplink during at least one sample phase in a coherence block, the coherence block configured such that during the at least one sample phase each UE in a group of one or more UEs served by the first network node is silent or transmits only a sample value. The method comprises mitigating interference from the second network node based at least in part on information obtained by receiving the interfering signal during the sample phase.

[0008] According to certain embodiments, a network node comprises power supply circuitry and processing circuitry. The power supply circuitry is configured to supply power to the processing circuitry. The processing circuitry is configured to receive an interfering signal from a second network node, the interfering signal received when performing reception on an uplink during at least one sample phase in a coherence block, the coherence block configured such that during the at least one sample phase each UE in a group of one or more UEs served by the first network node is silent or transmits only a sample value. The processing circuitry is configured to mitigate interference from the second network node based at least in part on information obtained by receiving the interfering signal during the sample phase.

[0009] According to certain embodiments, a method in a user equipment served by a first network node comprises, during a sample phase in a coherence block, transmitting only a sample value on an uplink to the first network node or abstaining from transmitting on the uplink to the first network node.

[0010] According to certain embodiments, a user equipment comprises power supply circuitry and processing circuitry. The power supply circuitry configured to supply power to the processing circuitry. The processing circuitry configured to, during a sample phase in a coherence block, transmit only a sample value on an uplink to a first network node or abstain from transmitting on the uplink to the first network node.

[0011] Certain embodiments may provide one or more of the following technical advantage(s). Certain embodiments improve the capacity, coverage, and / or link robustness of the DL, the UL, or both in a D-TDD system. As an example, certain embodiments improve the capacity, coverage, and / or link robustness of the DL by facilitating suppression of UE-to-UE interference. As another example, certain embodiments improve the capacity, coverage, and / or link robustness of the UL by facilitating symbol detection by an AP in the presence of AP-to- AP interference. Note that the concepts of suppressing, mitigating, and / or reducing interference are referred to interchangeably throughout this disclosure.

[0012] Other advantages may be readily apparent to one having skill in the art. Certain embodiments may have none, some, or all of the recited advantages.BRIEF DESCRIPTION OF THE DRAWINGS

[0013] For a more complete understanding of the disclosed embodiments and their features and advantages, reference is now made to the drawings, in which:

[0014] Figures 1-2 each show an example of AP-to-AP interference and UE-to-UE interference in a dynamic TDD system.

[0015] Figure 3 shows an example of scheduling uplink and downlink transmissions in a dynamic TDD system in the prior art.

[0016] Figure 4 shows a flow chart illustrating an example of a method for mitigating UE- to-UE interference in a dynamic TDD system, in accordance with some embodiments.

[0017] Figures 5-10 each show an example of scheduling uplink and downlink transmissions to mitigate UE-to-UE interference in a dynamic TDD system, in accordance with some embodiments.

[0018] Figures 11-12 each show a numerical embodiment based on the scheduling shown in Figure 5, in accordance with certain embodiments.

[0019] Figure 13 shows an example of AP-to-AP interference and UE-to-UE interference in a dynamic TDD system.

[0020] Figure 14 shows an example of scheduling uplink and downlink transmissions in a dynamic TDD system in the prior art.

[0021] Figure 15 shows an example of scheduling uplink and downlink transmissions to facilitate symbol detection in the presence of AP-to-AP interference in a dynamic TDD system, in accordance with some embodiments.

[0022] Figure 16 shows a numerical embodiment based on the scheduling shown in Figure15, in accordance with certain embodiments.

[0023] Figure 17 shows an example of a user equipment (UE), in accordance with some embodiments.

[0024] Figure 18 shows an example of a network node, such as an AP, in accordance with some embodiments.

[0025] Figures 19-21 each show an example of a method performed by a wireless device (e.g., UE), in accordance with certain embodiments.

[0026] Figures 22 and 23 each show an example of a method performed by a network node (e.g., AP), in accordance with certain embodiments.DETAILED DESCRIPTION

[0027] Some of the embodiments contemplated herein will now be described more fully with reference to the accompanying drawings. Embodiments are provided by way of example to convey the scope of the subject matter to those skilled in the art.

[0028] Figure 1 illustrates an example of a dynamic TDD system comprising a first access point (AP 1), a second access point (AP 2), a first user equipment (UE 1), and a second user equipment (UE 2). Each of AP 1, AP 2, UE 1, and UE 2 may be configured to operate using the same bandwidth.

[0029] In the example illustrated in Figure 1, transmissions (as shown) are scheduled according to known methods, such as those described below with respect to Figures 2 and 3. As a result, Figure 1 illustrates uplink and downlink transmissions scheduled in a manner that may result in UE-to-UE interference and / or AP-to-AP interference. For example, at a given point in time, UE 1 transmits on the uplink to AP 1 while AP 2 transmits on the downlink to UE 2. This results in UE-to-UE interference when UE 1 transmits on the uplink while UE 2receives on the downlink. This also results in AP-to-AP interference when AP 2 transmits on the downlink while AP 1 receives on the uplink.

[0030] As further described below, embodiments of the present disclosure provide alternatives for scheduling uplink and downlink transmissions in a dynamic TDD system, such as the dynamic TDD system shown in Figure 1. For example, Figures 5-10 and 15 illustrate embodiments of the present disclosure that provide alternatives to the known scheduling shown in Figures 3 and 14. Certain embodiments of the present disclosure configure APs and UEs (such as those shown in Figure 1) based on the alternatives in order to mitigate UE-to-UE interference and / or AP-to-AP interference.

[0031] Figure 2 illustrates an example of a dynamic TDD system similar to that shown in Figure 1. Figure 2 includes more detailed notations for further explanation of the interference conditions described with respect to Figure 1. In Figure 2, the following notations are used:• Each AP has M antennas. (Anything said herein can be easily generalized to the case that the APs have different numbers of antennas.)• UE 1 has N1antennas, while UE 2 has N2antennas.• GmkG CMxWfcis the channel between AP m and UE k, where k G {1,2} and m,kG{ l,2}.• HkiG CWfcXW‘ is the UUI channel between UE k and UE t, where k, i G {1,2}.

[0032] The APs may or may not operate phase-coherently. There are two possible cases:• Case (1): The APs are connected to the same central processing unit (CPU) and serve both UEs at the same time.• Case (2): The APs are connected to different CPUs. AP 1 serves UE 1 and AP 2 serves UE 2.

[0033] Figure 3 shows an example of known scheduling of uplink and downlink transmissions in a dynamic TDD system in the prior art. The transmissions illustrated in Figure 3 normally take place in one coherence interval in a dynamic TDD system:• Phase 1 - Uplink pilot for channel estimation (UP CE): o UE 1 and UE 2 transmit their pilot signals, while the APs are silent and receive the pilot signals. o In case (1), the APs estimate the channels from both UE 1 and UE 2 to be later used for joint decoding on the uplink and joint beamforming on the downlink.o In case (2), AP 1 only estimates the channel from UE 1, while AP 2 only estimates the channel from UE 2 to be later used for separate decoding on the uplink and separate beamforming on the downlink.• Phase 2 - Uplink data transmission: o UE 1 and UE 2 transmit their data signals, while the APs use the channel estimates to construct combining matrices, apply these matrices to the received signals, and detect the data symbols. o In case (1), the APs jointly detect the data from both UE 1 and UE 2. o In case (2), AP 1 detects data from UE 1, while AP 2 detects data from UE 2.• Phase 3 - Concurrent uplink and downlink data transmission: o UE 1 transmits its uplink data signal, while UE 2 receives its downlink data signal. Consequently, there is a UE-to-UE interference from UE 1 to UE 2. o AP 1 is silent and receives uplink data from UE 1, while AP 2 transmits downlink data to UE 2. o AP 1 detects data symbols from UE 1. o AP 2 transmits data to UE 2.• Phase 4 - Downlink data transmission: o In case (1), the APs jointly transmit data to both UE 1 and UE 2. o In case (2), AP 1 transmits to UE 1 and AP 2 transmits to UE 2.

[0034] In the example, the UE-to-UE interference experienced in the UUI period (phase 3) of Figure 3 reduces the downlink channel capacity of UE 2. Certain embodiments of the present disclosure may allow for mitigating such UE-to-UE interference.User-to-User Interference (UUI) Mitigation

[0035] According to certain embodiments, a method is disclosed that can mitigate UE-to- UE interference, for example, for UEs equipped with multiple antennas. Figure 4 illustrates an example of such a method 40. In step 42, UEs estimate a UE-to-UE interference channel in a coherence interval. For example, the method 40 may dedicate some samples in each coherence interval (e.g., a resource block limited in time and frequency domains) to pilots that facilitate estimation of the UE-to-UE interference channel. Specifically, during a period of the resource block at least one UE is silent (does not transmit pilots) such that during this period the UE can estimate the channel to other UE(s). In step 44, the UEs mitigate the UE-to-UE interference using the UUI channel estimate that was determined in step 42.

[0036] In an embodiment, a dynamic TDD system comprises at least two APs (a first AP and a second AP). The system may optionally include more APs. The first AP serves a first UE, and the second AP serves a second UE. Each resource block comprises at least one pilot phase during which the first UE transmits a pilot destined to the second UE. During said pilot phase, the second UE estimates the channel to the first UE.

[0037] In a further embodiment based on the dynamic TDD system of the previous paragraph, the second UE applies receive beamforming to suppress interference from the first UE during data transmissions from the first UE.

[0038] In an alternative embodiment, the second UE applies transmit beamforming to suppress interference to the first UE during data transmissions from the second UE.

[0039] According to certain embodiments, a network node (e.g., AP) operating in a dynamic TDD system is configured to assign partly overlapping UL and DL resources to a first UE and a second UE. The network node is further configured to instruct the first UE to transmit a pilot signal and to instruct the second UE to estimate the channel to the first UE using said pilot signal for the purpose of suppressing interference from said first UE.

[0040] According to certain embodiments, a mobile device (e.g., UE) operating in a dynamic TDD system is configured to receive instructions from a network node on additional reference signals to transmit and / or receive for the purpose of enabling UE-to-UE channel estimation and interference mitigation. The mobile device is further configured to suppress UE-to-UE interference by performing transmit beamforming and / or receive beamforming based on channel state information obtained from said additional reference signal transmissions and / or receptions.

[0041] In general, certain embodiments of the proposed solution let the UEs mitigate the UUI by obtaining UUI channel estimates and then applying appropriate signal processing algorithms. Some exemplifying embodiments of the proposed method are described below in more detail, including with respect to Figures 5-10. In the examples shown in Figures 5-10, UUI occurs during a concurrent transmission and reception phase, shown in phase 4, where UE 1 (transmitting UE) transmits uplink transmission “U” that interferes with reception of downlink transmission “D” by UE 2 (receiving UE).

[0042] As an overview, Figure 5 illustrates an embodiment in which a receiving UE that is subject to interference from a transmitting UE estimates the channel over which the interference is received; the receiving UE then applies receive beamforming with null-steering that suppresses the interference from the transmitting UE. Figure 6 illustrates another embodiment in which a transmitting UE that generates interference to a receiving UE estimatesthe channel over which the interference is transmitted to the receiving UE; the transmitting UE then applies transmit beamforming with null-steering such that the interference received at the receiving UE is minimized. Figure 7-10 illustrates other embodiments. In the figures, shading is used to highlight certain modifications compared to the example of Figure 3. Scheduling described for one coherence interval may indicate what takes place in each coherence interval, for example.

[0043] Table 1 summarizes the embodiments of Figures 5-10 in terms of which UE mitigates the UUI and whether the UUI channel and the data transmission channel are estimated separately or jointly.Table 1

[0044] Figure 5 illustrates an embodiment that modifies the example of Figure 3 by including an additional phase for UE 2 to learn the UUI channel from UE 1 and then perform receive combining techniques to mitigate the UUI using the UUI channel estimate. The following paragraphs summarize scheduling for one coherence interval:

[0045] Phase 1 - Uplink pilot for channel estimation. This may be the same as phase 1 in Figure 3.

[0046] Phase 2 - Uplink pilot for UUI. UE 1 uses an additional phase (shown as UP’ CE) to transmit an uplink pilot signal. Alternatively, UE 1 may use part of UP CE of the first phase for UP’ CE to transmit an uplink pilot signal. In the phase UP’ CE, UE 2 is silent and receives the pilot signal from UE 1. Then, using this received pilot signal, UE 2 estimates the channel from UE 1.

[0047] Phase 3 - Uplink data transmission. This may be the same as phase 2 in Figure 3.

[0048] Phase 4 - Data transmission with UUI mitigation. UE 1 transmits its uplink data signal to AP 1, while UE 2 receives its downlink data signal from AP 2. AP 1 receives the uplink data signal from UE 1, while AP 2 transmits downlink data signal to UE 2. AP 1 detects the data from UE 1. When UE 2 decodes the signal from AP 2, it applies a combining matrix that suppresses UUI from UE 1. This combining matrix is constructed based on the estimated channel from UE 1 to UE 2.

[0049] Phase 5 - Downlink data transmission. This may be the same as phase 4 in Fig. 3.

[0050] Table 2 summarizes how the UUI channel estimation and subsequent receive combining at UE 2 can be implemented. Table 2

[0051] Figure 6 illustrates an embodiment that modifies the example of Figure 3 by including an additional phase in each coherence block that enables UE 1 to learn the UUI channel to UE 2, and then have UE 1 perform transmit precoding to mitigate the UUI using the UUI channel estimate. This embodiment (in contrast to the embodiment of Figure 5) requires reciprocity calibration of UE 1. The following paragraphs summarize scheduling for one coherence interval:

[0052] Phase 1 - Uplink pilot for channel estimation. This may be the same as phase 1 in Figure 3.

[0053] Phase 2 - Uplink pilot for UUI channel estimation. UE 2 uses an additional phase (shown as UP’ CE) to transmit an uplink pilot signal. Alternatively, UE 2 may use part of UP CE of the first phase of Figure 3 for UP’ CE to transmit an uplink pilot signal. In the phase UP’ CE, UE 1 is silent and receives the pilot signal from UE 2. Then, using the received pilot signal, UE 1 estimates the channel from UE 2.

[0054] Phase 3 - Uplink data transmission. This may be the same as phase 2 in Figure 3.

[0055] Phase 4 - Data transmission with UUI mitigation. UE 1 transmits its uplink data signal to AP 1, while UE 2 receives its downlink data signal from AP 2. Before UE 1 transmits signals, it applies a precoding matrix that suppresses UUI to UE 2. This precoding matrix is constructed based on the UUI channel estimate from UE 1 to UE 2 (equal to the channel from UE 2 to UE 1, by reciprocity). AP 1 receives the uplink data signal from UE 1, while AP 2 transmits downlink data to UE 2. AP 1 detects data symbols from UE 1. UE 2 detects data symbols from AP 2.

[0056] Phase 5 - Downlink data transmission. This may be the same as phase 4 in Fig. 3.

[0057] Table 3 describes how the UUI channel estimation and subsequent transmit precoding at UE 1 can be implemented.Table 3

[0058] Figure 7 illustrates an embodiment that modifies the example of Figure 3 by including additional phases for both UE 1 and UE 2 to estimate the UUI channel. Then, both UE 1 and UE 2 use the UUI channel estimate to mitigate UUI. For example, to mitigate UUI, UE 1 performs transmit precoding using the UUI channel estimate and UE 2 performs receive combining using the UUI channel estimate. The following paragraphs summarize scheduling for one coherence interval:

[0059] Phase 1 - Uplink pilot for channel estimation. This may be the same as phase 1 in Figure 3.

[0060] Phase 2 - Uplink pilot for UUI channel estimation. UE 1 uses an additional phase (shown as UP’ CE) to transmit an uplink pilot signal. Alternatively, UE 1 may use part of UP CE of the first phase of Figure 3 for UP’ CE to transmit an uplink pilot signal. In the phase UP’ CE, UE 2 is silent to receive the pilot signal from UE 1. Then, using the received pilot signal, UE 2 estimates the channel from UE 1.

[0061] Phase 3 - Uplink pilot for UUI channel estimation. UE 2 uses an additional phase (shown as UP* CE) to transmit an uplink pilot signal. Alternatively, UE 2 may use part of UP CE of the first phase of Figure 3 for UP* CE to transmit an uplink pilot signal. In the phase UP* CE, UE 1 is silent to receive the pilot signal from UE 2. Then, using the received pilot signal, UE 1 estimates the channel from UE 2.

[0062] Phase 4 - Uplink data transmission. This may be the same as phase 2 in Figure 3.

[0063] Phase 5 - Data transmission with UUI mitigation. UE 1 transmits its uplink data signal to AP 1, while UE 2 receives its downlink data signal from AP 2. UE 1 and UE 2 both use the channel estimate of UUI (i.e., the channel from UE 1 to UE 2) to mitigate UUI. For example, UE 1 uses the channel estimate of UUI to construct a transmit precoding matrix to mitigate UUI, and UE 2 uses the channel estimate of UUI to construct a receive combining matrix to mitigate UUI. AP 1 receives the uplink data signal from UE 1, while AP 2 transmits downlink data signal to UE 2. AP 1 detects data symbols from UE 1. UE 2 detect data symbols from AP 2.

[0064] Phase 6 - Downlink data transmission. This may be like phase 4 in Figure 3.

[0065] Figure 8 illustrates an embodiment that jointly performs the estimation of the data transmission channel and the estimation of the UUI channel. An advantage of this embodiment compared with the embodiment of Figure 7 is that it removes the separate phase for estimating the data transmission channel. This lengthens the data transmission phase, which can improve the overall channel capacity of the system. The following paragraphs summarize scheduling for one coherence interval:

[0066] Phase 1 - Uplink pilot for the channel estimation of both UUI and desired links. UE 1 uses a phase UP’ CE to transmit an uplink pilot signal. In the phase UP’ CE, UE 2 is silent to receive the pilot signal from UE 1. Then, using the received pilot signal, UE 2 estimates the channel from UE 1. In case (1), e.g., where the APs connect to the same CPU, both AP 1 and AP 2 estimate the channels from UE 1 for the later uplink and downlink data transmissions.In case (2), e.g., where the APs connect to different CPUs, only AP 1 estimates the channel from UE 1.

[0067] Phase 2 - Uplink pilot for the channel estimation of both UUI and desired links. UE 2 uses a phase UP* CE to transmit an uplink pilot signal. In the phase UP* CE, UE 1 is silent to receive the pilot signal from UE 2. Then, using the received pilot signal, UE 1 estimates the channel from UE 2. In case (1), both AP 1 and AP 2 estimate the channels from UE 2 for the later uplink and downlink data transmissions. In case (2), only AP 1 estimates the channel from UE 2.

[0068] Phase 3 - Uplink data transmission. This may be like phase 2 in Figure 3.

[0069] Phase 4 - Data transmission with UUI mitigation. This may be like phase 5 ofFigure 7.

[0070] Phase 5 - Downlink data transmission. This may be like phase 4 in Figure 3.

[0071] In terms of UUI mitigation, the implementation of Figure 8 may be the same as the implementation of Figure 7.

[0072] Turning to Figure 9, the general idea of the illustrated embodiment compared with the embodiment of Figure 8 is to further improve the uplink channel capacity of UE 1 by jointly performing uplink transmission, estimation of the UUI channel, and estimation of the data transmission channel. For example, UE 1 can use the second phase of estimating the UUI channel for uplink transmission instead of being silent (as in Figure 8). The following paragraphs summarize scheduling for one coherence interval:

[0073] Phase 1 - Uplink pilot for the channel estimation of both UUI and desired links. This may be the same as phase 1 in Figure 8.

[0074] Phase 2 - Joint uplink data transmission and uplink pilot for the channel estimation of both UUI and desired links. UE 2 transmits an uplink pilot signal, while UE 1 transmits its uplink data signal. Therefore, there is mutual interference between pilot and data signals in the received signal at each AP. To estimate the channel from UE 2 while detecting data symbols from UE 1 at each AP, there are two possible steps. First, using the channel estimate from UE 1 in the first phase, the APs can construct a combine matrix so that the data signal from UE 1 is mitigated in the combined signal. Second, the APs use the combined signal to estimate the channel from UE 2. The APs use the channel estimate from UE 2 and the received signal to detect the data symbols from UE 1. In case (1), both AP 1 and AP 2 detect data symbols from UE 1 and estimate the channel from UE 2. In case (2), only AP 1 detects the data symbols from UE 1, while only AP 2 estimates the channel from UE 2.

[0075] Phase 3 - Uplink data transmission. This may be the same as phase 2 in Figure 3.

[0076] Phase 4 - Data transmission with UUI mitigation. Since UE 1 does not have the channel estimate from UE 2, while UE 2 has the channel estimate from UE 1, this phase is same as phase 4 of Figure 5.

[0077] Phase 5 - Downlink data transmission. This may be like phase 4 in Figure 3.

[0078] The embodiment shown in Figure 10 uses similar principles to further improve the uplink channel capacities of UE 2 by jointly performing uplink transmission, estimation of the data transmission channel, and estimation of the UUI channel. Specifically, UE 2 can use the second phases of estimating UUI channel for uplink transmission instead of being silent. The following paragraphs summarize scheduling for one coherence interval:

[0079] Phase 1 - Uplink pilot for the channel estimation of both UUI and desired links. This may be like phase 1 in Figure 8.

[0080] Phase 2 - Joint uplink data transmission and uplink pilot for the channel estimation of both UUI and desired links. UE 1 transmits an uplink pilot signal, while UE 2 transmits its uplink data signal. Therefore, there is mutual interference between pilot and data signals in the received signal at each AP. To estimate the channel from UE 1 while detecting data symbols from UE 2 at each AP, there are two possible steps. First, using the channel estimate from UE 2 in phase 1, the APs can construct a combine matrix so that the data signal from UE 2 is mitigated in the combined signal. Second, the APs use the combined signal to estimate the channel from UE 1. The APs use the channel estimate from UE 1 and the received signal to detect the data symbols from UE 2. In case (1), both APs 1 and 2 detect data symbol from UE 2 and estimate the channel from UE 1. In case (2), only AP 2 detects the data symbols from UE 2, while only AP 1 estimates the channel from UE 1.

[0081] Phase 3 - Uplink data transmission. This may be like phase 2 in Figure 3.

[0082] Phase 4 - Data transmission with UUI mitigation. Since UE 1 has the channel estimate from UE 2, while UE 2 does not have the channel estimate from UE 1, this phase may be like phase 4 of Figure 6.

[0083] Phase 5 - Downlink data transmission. This may be like phase 4 in Figure 3.

[0084] Figures 11-12 illustrate a simple numerical example based on the scheduling shown in Figure 5. For example, Figure 11 illustrates a dynamic TDD system for comparing the bit error rate (BER) performance with and without the UUI mitigation method, and Figure 12 illustrates the result. To obtain the result, the UEs were equipped= N2= 5 antennas, and AP 2 was equipped with M = 10 antennas. The antenna arrays had angles a, 2=u,i=u,2,i=u,2,2=~ rad. The example used a line-of-sight, far-field channelmodel with uniform linear arrays at AP 2 and both UEs. The large-scale fading coefficients between UE 1 / UE 2 and AP 2 / UE 2 were set to (up to a constant) / ?12, respectively.‘J

[0085] The wavelength was A [m] . The distance d22between AP 2 and UE 2 was fixed to 10 m, while the distance d12between UE 1 and UE 2 was 10 m, 100 m, or 1000 m. The transmit power of AP 2 varied between 1 and 10 W, while both UEs had a constant transmit power of 0.2 W. The noise power was -92 dBm. As can be seen in Figure 12, the cases with UUI mitigation had lower BER compared to the cases without UUI mitigation, which indicates successful mitigation of UULSymbol Detection in the Presence of Access Point-to-Access Point Interference (AAI)

[0086] The embodiments discussed above under the heading “User-to-User Interference Mitigation” aim to improve downlink capacity in a D-TDD system by mitigating UE-to-UE interference. The following embodiments aim to improve uplink capacity in a D-TDD system by mitigating AP-to-AP interference. As an example, a method of mitigating AP-to-AP interference may comprise jointly estimating the uplink symbols and the AAI channel at an access point. This is in contrast to above-discussed methods of UE-to-UE interference that estimate the UUI channel using pilots, which are then used at the UE for interference suppression. A difference between the embodiments for mitigating AP-to-AP interference and the embodiments for mitigating UE-to-UE interference is that the embodiments for mitigating AP-to-AP interference rely on the availability of the downlink data signals at all APs, and these embodiments exploit knowledge of the signals to be cancelled. Such knowledge of signals to be cancelled is not assumed in (and is not feasible for) UUI interference cancellation.

[0087] According to certain embodiments, a method for mitigating AP-to-AP interference comprises letting a first group of UEs (e.g., UE 1 to UE K) be silent during at least one sample in each coherence interval (e.g., a resource block limited in time and frequency domains), and then having an uplink AP jointly estimate the desired symbols from the UEs, and the AP-to- AP interference channel. Other embodiments may perform a similar method, however, instead of being silent, the first group of UEs may transmit a predetermined sample during the at least one sample in each coherence interval.

[0088] According to certain embodiments, a dynamic TDD system comprises at least two APs, such as a first AP (e.g., AP 1) and a second AP (e.g., AP 2). The D-TDD system may be configured to facilitate the first AP in mitigating AP-to-AP interference that occurs when thefirst AP serves a first set of UEs on the uplink during a time when the second AP serves a second set of UEs on the downlink. For example, to facilitate the first AP in mitigating AP-to- AP interference, the D-TDD system may be configured as follows:• The first set of UEs is configured to be silent for at least one predetermined sample during a coherence block;• The first AP, during reception on the uplink, jointly estimates the symbols from the first set of UEs and the interfering channel between the second AP and the first AP;• The network routes data destined for the second set of UEs to both the first and the second APs; and• The first AP uses the estimated interfering channel and the data destined for the second set of UEs to mitigate the AP-to-AP interference signal.

[0089] Certain embodiments let the AP 1 mitigate the AAI by jointly estimating uplink symbols and the AAI channel.

[0090] On fronthaul, certain embodiments forward the data destined to AP 2 also to AP 1, where it can be used for suppression.

[0091] Figure 13 illustrates an example of a dynamic TDD system comprising a first access point (AP 1), a second access point (AP 2), and a plurality of UEs. The plurality of UEs include a number (A) of UEs served by AP 1, shown as UE 1 to UE K. The plurality of UEs include an arbitrary number of UEs served by AP 2. For simplicity, the example in Figure 13 shows that AP 2 serves a single user, UE (K+ 1 ), although the disclosure generalizes to the case of any numbers of UEs served by AP 2. Each of AP 1, AP 2, and the plurality of UEs may be configured to operate using the same bandwidth.

[0092] In the example shown in Figure 13, AP 1 has M antennas while AP 2 can have one or more antennas. For the purposes of the discussion here, we consider the suppression of a single dominant spatially rank-one signal from AP 2, in which case we can equivalently assume for the discussion that AP 2 has a single antenna.

[0093] In the example shown in Figure 13, each UE has a single antenna. Note, however, that anything said herein can be generalized to the case that the UEs have a larger number of antennas and transmit multiple streams.

[0094] With respect to G and h shown in Figure 13:G G (MxKisthe collective channel between AP 1 and the first K UEs. h G CMX1is the AAI channel between AP 2 and AP 1.

[0095] The APs may or may not operate phase -coherently.

[0096] There are two possible cases. In case (1), the APs are connected to the same CPU. In case (2), the APs are connected to different CPUs.

[0097] In the example illustrated in Figure 13, transmissions (as shown) are scheduled according to known methods, such as those described below with respect to Figure 14. As a result, Figure 13 illustrates uplink and downlink transmissions scheduled in a manner that may result in UE-to-UE interference and / or AP-to-AP interference. In particular, Figure 13 illustrates both uplink transmissions (e.g., UE 1 to UE K transmit on the UL to AP 1) and downlink transmissions (e.g., AP 2 transmits on the DL to UE (K+ 1 )) at a given point in time. This results in interference between the APs, for example, when AP 2 transmits on the DL while AP 1 receives on the UL. Similarly, this results in interference between the UEs, for example, when UE 1 to UE T transmit on the UL while UE (K+l) receives on the DL.

[0098] As further described below, embodiments of the present disclosure provide alternatives for scheduling uplink and downlink transmissions in a dynamic TDD system, such as the dynamic TDD system shown in Figure 13. For example, Figure 15 illustrates an embodiment of the present disclosure that provides an alternative to the known scheduling shown in Figures 14. Certain embodiments of the present disclosure configure APs and UEs (such as those shown in Figure 13) based on the scheduling shown in Figure 15 in order to mitigate AP-to-AP interference.

[0099] Figure 14 shows an example of known scheduling of uplink and downlink transmissions in a dynamic TDD system in the prior art. The transmissions illustrated in Figure 14 normally take place in one coherence interval in a dynamic TDD system. The following paragraphs summarize the phases shown in Figure 14:

[0100] Phase 1 - Uplink pilot for channel estimation (UP CE). All the UEs transmit their pilot signals, while the APs are silent and receive the pilot signals. In case (1), the APs estimate the channels from all the UEs to be later used for decoding on uplink and beamforming on downlink. In case (2), AP 1 only estimates the channel from the first K UEs, while AP 2 only estimates the channel from UE (A+ l ).

[0101] Phase 2 - Uplink data transmission. All the UEs transmit their data signals, while the APs use the channel estimates to construct combining matrices, apply these matrices to the received signals, and detect the data symbols. In case (1), the APs jointly detect the data from all the UEs. In case (2), AP 1 detects data from the first K UEs, while AP 2 detects data from UE (X+l).

[0102] Phase 3 - Concurrent uplink and downlink data transmission. The first K UEs transmit their uplink data signals, while UE (A+ 1 ) receives its downlink data signal. AP 1 issilent and receives uplink data from the first K UEs, while AP 2 transmits downlink data to UE (A+ 1 ). Consequently, there is AP-to-AP interference (AAI) from AP 2 to AP 1. AP 1 detects data symbols from the first K UEs. AP 2 transmits data to UE ( K+ 1 ) .

[0103] Phase 4 - Downlink data transmission. In case (1), the APs jointly transmit data to all the UEs. In case (2), AP 1 transmits to the first K UEs and AP 2 transmits to UE ( K+ 1 ) .

[0104] In phase 3, AAI is experienced, which reduces the channel capacities of the first K UEs. Certain embodiments of the present disclosure may mitigate this AAI, which may improve the channel capacities of the first K UEs.

[0105] Figure 15 shows an example of scheduling uplink and downlink transmissions to mitigate AP-to-AP interference and / or facilitate symbol detection in the presence of AP-to-AP interference in a dynamic TDD system, in accordance with some embodiments. Shading is used to highlight certain modifications compared to the example of Figure 14. In Figure 15, the first K UEs are instructed to send zeros (be silent), or a predetermined sample value, during selected parts of the coherence interval. Then AP 1 mitigates the AAI by performing joint estimation of uplink symbols and the AAI channel. (In the description here, we assume that the K UEs send zeros.) The following paragraphs summarize scheduling for one coherence interval:

[0106] Phase 1 - Uplink pilot for channel estimation. This may be the same as phase 1 in Figure 14.

[0107] Phase 2 - Uplink data transmission. This may be the same as phase 2 in Figure 14.

[0108] Phase 3 - Silent phase for the first K UEs. The first K UEs are silent. UE (A+l ) receives its signal from AP 2. AP 1 receives only the AAI signal from AP 2.

[0109] Phase 4 - Data transmission with AAI mitigation. The first K UEs transmit their uplink data signals to AP 1, while UE (A+1 ) receives its downlink data signal from AP 2. AP 1 receives the uplink data signal from the first K UEs, while AP 2 transmits downlink data signal to UE A+l . AP 1 jointly estimates the data symbols from the first K UEs and the AAI channel to mitigate AAI, relying on knowledge of the data symbols for UE +I, which have previously been forwarded over fronthaul.

[0110] Phase 5 - Downlink data transmission. This may be the same as phase 4 in Figure 14.[oni] Table 4 describes how the joint estimation of the uplink symbols of the first K UEs and the AAI channel can be implemented. Note that the AAI data are known, as they have previously been transmitted over fronthaul.Table 4

[0112] Note that for cases where the data destined for UE K+ 1 needs to be sent to both AP 2 and AP 1, some routing decision can be made by the CPU.

[0113] Figure 16 provides a numerical example based on the system setup shown in Figure 13, with one uplink AP (AP 1), one downlink AP (AP 2), one downlink UE served byAP 2, and K uplink UEs served by AP 1. The numerical example considers only the AAI period (e.g., phase 3 in Figure 14).

[0114] To illustrate the benefit of the proposed AAI mitigation method of Figure 15, the numerical example compares a BER obtained by a baseline test (without the proposed AAI mitigation) and a BER obtained by the proposed AAI mitigation method. For the baseline, AP 1 does not know about the AAI (or does nothing about it), and thus uses a least-squares estimate of the information symbols using only the knowledge of G. Specifically, the estimate X of X is the matrix obtained by removing the first column of (GHG)-1GHY , where Y is the received signal at AP 1 including the AAI.

[0115] We assume Rayleigh fading channels. Denote the large-scale fading coefficients k = 0, ... , K, where k = 0 is used for the AAI channel and k = 1, ... , K for the channels between uplink UEs and AP 1. These are computed using the outdoor 3GPP Urban Microcell model: ftk= —30.5 — 36.7 log10> where dkdenotes the distances between AP 1 and AP2 (k = 0), or between AP 1 and the uplink UEs (k = 1, ... , K). All UEs and APs are randomly distributed in a square of 0.5 x 0.5 km2, whose edges are wrapped around to avoid boundary effects.

[0116] The desired signal X and the interference signal s are both generated using binary phase-shift keying (BPSK) modulation.

[0117] We set the bandwidth B = 20 MHz and noise figure F = 9 dB. Thus, the noise power is o'2= kBT0BF, where kB= 1.381 X 10-23Joules / °K is the Boltzmann constant and To= 290°K is the temperature.1

[0118] The transmission power from UL UE k is Pu- - , where Puis the maximalUL UE transmit power. The transmit power from the DL AP is set to 1 W.

[0119] We let M = 10, K = 3, T = 50 and calculate the bit error rate (BER) for all schemes by averaging over 10000 channel realizations, see Figure 16.Additional embodiments

[0120] The method proposed here can be generalized to the case of more than one UE served by AP 2. In this case, the downlink data signal s at AP 2 is the sum of the downlink data signals to all the UEs served by AP 2. Since the downlink data signals to all the UEs served by AP 2 can be available at AP 1 by transmission over fronthaul, s is also available at AP 1. Then, a procedure similar to that discussed above can be applied.

[0121] The AAI channel h may change slowly over time (not change much from one coherence block to the next). This could be exploited:

[0122] When h changes slowly over time, e.g., one 100 ms, it might only need to be estimated once per 100 ms. In this case, there is no need for the first K UEs to be silent in every coherence interval that stays in between two times of estimating h. Alternatively, h can be estimated in every slot and a lowpass filter can be applied (e.g., moving-average or Kalman filter).

[0123] In each of these coherence intervals, AP 2 knows the estimate h of h and can subtract the AAI part hsTfrom the received signal Y. Then, the estimate X of the uplink symbol

[0124] Certain examples discussed with respect to Figures 1-16 above have been described with reference to operation of a UE. Examples of a UE include UE 200 described below. Similarly, certain examples discussed with respect to Figures 1-6 above have been described with reference to operation of an AP. The disclosure may be generalized to other types of network nodes, such as network node 300 discussed below. For example, network node 300 may be an AP or another type of network node configured to perform the operations disclosed herein as being performed by a network node or an AP.

[0125] Figure 17 shows a UE 200 in accordance with some embodiments. As used herein, a UE refers to a device capable, configured, arranged and / or operable to communicate wirelessly with network nodes (e.g., APs) and / or other UEs. Examples of a UE include, but are not limited to, a smart phone, mobile phone, cell phone, voice over IP (VoIP) phone, wireless local loop phone, desktop computer, personal digital assistant (PDA), wireless cameras, gaming console or device, music storage device, playback appliance, wearable terminal device, wireless endpoint, mobile station, tablet, laptop, laptop-embedded equipment (LEE), laptopmounted equipment (LME), smart device, wireless customer-premise equipment (CPE), vehicle, vehicle -mounted or vehicle embedded / integrated wireless device, etc. Other examples include any UE identified by the 3rd Generation Partnership Project (3GPP), including a narrow band internet of things (NB-IoT) UE, a machine type communication (MTC) UE, and / or an enhanced MTC (eMTC) UE.

[0126] A UE may support device-to-device (D2D) communication, for example by implementing a 3GPP standard for sidelink communication, Dedicated Short-Range Communication (DSRC), vehicle-to-vehicle (V2V), vehicle-to-infrastructure (V2I), orvehicle- to-everything (V2X). In other examples, a UE may not necessarily have a user in the sense ofa human user who owns and / or operates the relevant device. Instead, a UE may represent a device that is intended for sale to, or operation by, a human user but which may not, or which may not initially, be associated with a specific human user (e.g., a smart sprinkler controller). Alternatively, a UE may represent a device that is not intended for sale to, or operation by, an end user but which may be associated with or operated for the benefit of a user (e.g., a smart power meter).

[0127] The UE 200 includes processing circuitry 202 that is operatively coupled via a bus 204 to an input / output interface 206, a power source 208, a memory 210, a communication interface 212, and / or any other component, or any combination thereof. Certain UEs may utilize all or a subset of the components shown in Figure 17. The level of integration between the components may vary from one UE to another UE. Further, certain UEs may contain multiple instances of a component, such as multiple processors, memories, transceivers, transmitters, receivers, etc.

[0128] The processing circuitry 202 is configured to process instructions and data and may be configured to implement any sequential state machine operative to execute instructions stored as machine-readable computer programs in the memory 210. The processing circuitry 202 may be implemented as one or more hardware-implemented state machines (e.g., in discrete logic, field-programmable gate arrays (FPGAs), application specific integrated circuits (ASICs), etc.); programmable logic together with appropriate firmware; one or more stored computer programs, general-purpose processors, such as a microprocessor or digital signal processor (DSP), together with appropriate software; or any combination of the above. For example, the processing circuitry 202 may include multiple central processing units (CPUs).

[0129] In the example, the input / output interface 206 may be configured to provide an interface or interfaces to an input device, output device, or one or more input and / or output devices. Examples of an output device include a speaker, a sound card, a video card, a display, a monitor, a printer, an actuator, an emitter, a smartcard, another output device, or any combination thereof. An input device may allow a user to capture information into the UE 200. Examples of an input device include a touch-sensitive or presence-sensitive display, a camera (e.g., a digital camera, a digital video camera, a web camera, etc.), a microphone, a sensor, a mouse, a trackball, a directional pad, a trackpad, a scroll wheel, a smartcard, and the like. The presence-sensitive display may include a capacitive or resistive touch sensor to sense input from a user. A sensor may be, for instance, an accelerometer, a gyroscope, a tilt sensor, a force sensor, a magnetometer, an optical sensor, a proximity sensor, a biometric sensor, etc., or any combination thereof. An output device may use the same type of interface port as an inputdevice. For example, a Universal Serial Bus (USB) port may be used to provide an input device and an output device.

[0130] In some embodiments, the power source 208 is structured as a battery or battery pack. Other types of power sources, such as an external power source (e.g., an electricity outlet), photovoltaic device, or power cell, may be used. The power source 208 may further include power circuitry for delivering power from the power source 208 itself, and / or an external power source, to the various parts of the UE 200 via input circuitry or an interface such as an electrical power cable. Delivering power may be, for example, for charging of the power source 208. Power circuitry may perform any formatting, converting, or other modification to the power from the power source 208 to make the power suitable for the respective components of the UE 200 to which power is supplied.

[0131] The memory 210 may be or be configured to include memory such as random access memory (RAM), read-only memory (ROM), programmable read-only memory (PROM), erasable programmable read-only memory (EPROM), electrically erasable programmable read-only memory (EEPROM), magnetic disks, optical disks, hard disks, removable cartridges, flash drives, and so forth. In one example, the memory 210 includes one or more application programs 214, such as an operating system, web browser application, a widget, gadget engine, or other application, and corresponding data 216. The memory 210 may store, for use by the UE 200, any of a variety of various operating systems or combinations of operating systems.

[0132] The memory 210 may be configured to include a number of physical drive units, such as redundant array of independent disks (RAID), flash memory, USB flash drive, external hard disk drive, thumb drive, pen drive, key drive, high-density digital versatile disc (HD- DVD) optical disc drive, internal hard disk drive, Blu-Ray optical disc drive, holographic digital data storage (HDDS) optical disc drive, external mini-dual in-line memory module (DIMM), synchronous dynamic random access memory (SDRAM), external micro-DIMM SDRAM, smartcard memory such as tamper resistant module in the form of a universal integrated circuit card (UICC) including one or more subscriber identity modules (SIMs), such as a USIM and / or ISIM, other memory, or any combination thereof. The UICC may for example be an embedded UICC (eUICC), integrated UICC (iUICC) or a removable UICC commonly known as ‘SIM card.’ The memory 210 may allow the UE 200 to access instructions, application programs and the like, stored on transitory or non-transitory memory media, to off-load data, or to upload data. An article of manufacture, such as one utilizing acommunication system may be tangibly embodied as or in the memory 210, which may be or comprise a device-readable storage medium.

[0133] The processing circuitry 202 may be configured to communicate with an access network or other network using the communication interface 212. The communication interface 212 may comprise one or more communication subsystems and may include or be communicatively coupled to an antenna 222. The communication interface 212 may include one or more transceivers used to communicate, such as by communicating with one or more remote transceivers of another device capable of wireless communication (e.g., another UE or a network node in an access network). Each transceiver may include a transmitter 218 and / or a receiver 220 appropriate to provide network communications (e.g., optical, electrical, frequency allocations, and so forth). Moreover, the transmitter 218 and receiver 220 may be coupled to one or more antennas (e.g., antenna 222) and may share circuit components, software or firmware, or alternatively be implemented separately.

[0134] In the illustrated embodiment, communication functions of the communication interface 212 may include cellular communication, Wi-Fi communication, LPWAN communication, data communication, voice communication, multimedia communication, short-range communications such as Bluetooth, near-field communication, location-based communication such as the use of the global positioning system (GPS) to determine a location, another like communication function, or any combination thereof. Communications may be implemented in according to one or more communication protocols and / or standards, such as IEEE 802.11, Code Division Multiplexing Access (CDMA), Wideband Code Division Multiple Access (WCDMA), GSM, LTE, New Radio (NR), UMTS, WiMax, Ethernet, transmission control protocol / intemet protocol (TCP / IP), synchronous optical networking (SONET), Asynchronous Transfer Mode (ATM), QUIC, Hypertext Transfer Protocol (HTTP), and so forth.

[0135] Regardless of the type of sensor, a UE may provide an output of data captured by its sensors, through its communication interface 212, via a wireless connection to a network node. Data captured by sensors of a UE can be communicated through a wireless connection to a network node via another UE. The output may be periodic (e.g., once every 15 minutes if it reports the sensed temperature), random (e.g., to even out the load from reporting from several sensors), in response to a triggering event (e.g., when moisture is detected an alert is sent), in response to a request (e.g., a user initiated request), or a continuous stream (e.g., a live video feed of a patient).

[0136] As another example, a UE comprises an actuator, a motor, or a switch, related to a communication interface configured to receive wireless input from a network node via a wireless connection. In response to the received wireless input the states of the actuator, the motor, or the switch may change. For example, the UE may comprise a motor that adjusts the control surfaces or rotors of a drone in flight according to the received input or to a robotic arm performing a medical procedure according to the received input.

[0137] A UE, when in the form of an Internet of Things (loT) device, may be a device for use in one or more application domains, these domains comprising, but not limited to, city wearable technology, extended industrial application and healthcare. Non-limiting examples of such an loT device are a device which is or which is embedded in: a connected refrigerator or freezer, a TV, a connected lighting device, an electricity meter, a robot vacuum cleaner, a voice controlled smart speaker, a home security camera, a motion detector, a thermostat, a smoke detector, a door / window sensor, a flood / moisture sensor, an electrical door lock, a connected doorbell, an air conditioning system like a heat pump, an autonomous vehicle, a surveillance system, a weather monitoring device, a vehicle parking monitoring device, an electric vehicle charging station, a smart watch, a fitness tracker, a head-mounted display for Augmented Reality (AR) or Virtual Reality (VR), a wearable for tactile augmentation or sensory enhancement, a water sprinkler, an animal- or item-tracking device, a sensor for monitoring a plant or animal, an industrial robot, an Unmanned Aerial Vehicle (UAV), and any kind of medical device, like a heart rate monitor or a remote controlled surgical robot. A UE in the form of an loT device comprises circuitry and / or software in dependence of the intended application of the loT device in addition to other components as described in relation to the UE 200 shown in Figure 17.

[0138] As yet another specific example, in an loT scenario, a UE may represent a machine or other device that performs monitoring and / or measurements, and transmits the results of such monitoring and / or measurements to another UE and / or a network node. The UE may in this case be an M2M device, which may in a 3GPP context be referred to as an MTC device. As one particular example, the UE may implement the 3 GPP NB-IoT standard. In other scenarios, a UE may represent a vehicle, such as a car, a bus, a truck, a ship and an airplane, or other equipment that is capable of monitoring and / or reporting on its operational status or other functions associated with its operation.

[0139] In practice, any number of UEs may be used together with respect to a single use case. For example, a first UE might be or be integrated in a drone and provide the drone’s speed information (obtained through a speed sensor) to a second UE that is a remote controlleroperating the drone. When the user makes changes from the remote controller, the first UE may adjust the throttle on the drone (e.g., by controlling an actuator) to increase or decrease the drone’s speed. The first and / or the second UE can also include more than one of the functionalities described above. For example, a UE might comprise the sensor and the actuator, and handle communication of data for both the speed sensor and the actuators.

[0140] Figure 18 shows a network node 300 in accordance with some embodiments. As used herein, network node refers to equipment capable, configured, arranged and / or operable to communicate with a UE and / or with other network nodes and / or other nodes or equipment in a telecommunication network (including, e.g., core network nodes). Examples of network nodes include, but are not limited to, access points (APs) (e.g., radio access points), base stations (BSs) (e.g., radio base stations, Node Bs, evolved Node Bs (eNBs) and NR NodeBs (gNBs)), Open Radio Access Network (O-RAN) nodes or components of an O-RAN node (e.g., O-RU, O-DU, O-CU).

[0141] Base stations may be categorized based on the amount of coverage they provide (or, stated differently, their transmit power level) and so, depending on the provided amount of coverage, may be referred to as femto base stations, pico base stations, micro base stations, or macro base stations. A base station may be a relay node or a relay donor node controlling a relay. A network node may also include one or more (or all) parts of a distributed radio base station such as centralized digital units, distributed units (e.g., in an O-RAN access node) and / or remote radio units (RRUs), sometimes referred to as Remote Radio Heads (RRHs). Such remote radio units may or may not be integrated with an antenna as an antenna integrated radio. Parts of a distributed radio base station may also be referred to as nodes in a distributed antenna system (DAS).

[0142] The network node 300 includes a processing circuitry 302, a memory 304, a communication interface 306, and a power source 308. The network node 300 may be composed of multiple physically separate components (e.g., a NodeB component and a radio network controller (RNC) component, or a base transceiver station (BTS) component and a base station controller (BSC) component, etc.), which may each have their own respective components. In certain scenarios in which the network node 300 comprises multiple separate components (e.g., BTS and BSC components), one or more of the separate components may be shared among several network nodes. For example, a single RNC may control multiple NodeBs. In such a scenario, each unique NodeB and RNC pair, may in some instances be considered a single separate network node. In some embodiments, the network node 300 may be configured to support multiple radio access technologies (RATs). In such embodiments,some components may be duplicated (e.g., separate memory 304 for different RATs) and some components may be reused (e.g., a same antenna 310 may be shared by different RATs). The network node 300 may also include multiple sets of the various illustrated components for different wireless technologies integrated into network node 300, for example GSM, WCDMA, LTE, NR, WiFi, Zigbee, Z-wave, LoRaWAN, Radio Frequency Identification (RFID) or Bluetooth wireless technologies. These wireless technologies may be integrated into the same or different chip or set of chips and other components within network node 300.

[0143] The processing circuitry 302 may comprise a combination of one or more of a microprocessor, controller, microcontroller, central processing unit, digital signal processor, application-specific integrated circuit, field programmable gate array, or any other suitable computing device, resource, or combination of hardware, software and / or encoded logic operable to provide, either alone or in conjunction with other network node 300 components, such as the memory 304, to provide network node 300 functionality.

[0144] In some embodiments, the processing circuitry 302 includes a system on a chip (SOC). In some embodiments, the processing circuitry 302 includes one or more of radio frequency (RF) transceiver circuitry 312 and baseband processing circuitry 314. In some embodiments, the radio frequency (RF) transceiver circuitry 312 and the baseband processing circuitry 314 may be on separate chips (or sets of chips), boards, or units, such as radio units and digital units. In alternative embodiments, part or all of RF transceiver circuitry 312 and baseband processing circuitry 314 may be on the same chip or set of chips, boards, or units.

[0145] The memory 304 may comprise any form of volatile or non-volatile computer- readable memory including, without limitation, persistent storage, solid-state memory, remotely mounted memory, magnetic media, optical media, random access memory (RAM), read-only memory (ROM), mass storage media (for example, a hard disk), removable storage media (for example, a flash drive, a Compact Disk (CD) or a Digital Video Disk (DVD)), and / or any other volatile or non-volatile, non-transitory device-readable and / or computerexecutable memory devices that store information, data, and / or instructions that may be used by the processing circuitry 302. The memory 304 may store any suitable instructions, data, or information, including a computer program, software, an application including one or more of logic, rules, code, tables, and / or other instructions capable of being executed by the processing circuitry 302 and utilized by the network node 300. The memory 304 may be used to store any calculations made by the processing circuitry 302 and / or any data received via the communication interface 306. In some embodiments, the processing circuitry 302 and memory 304 is integrated.

[0146] The communication interface 306 is used in wired or wireless communication of signaling and / or data between a network node, access network, and / or UE. As illustrated, the communication interface 306 comprises port(s) / terminal(s) 316 to send and receive data, for example to and from a network over a wired connection. The communication interface 306 also includes radio front-end circuitry 318 that may be coupled to, or in certain embodiments a part of, the antenna 310. Radio front-end circuitry 318 comprises fdters 320 and amplifiers 322. The radio front-end circuitry 318 may be connected to an antenna 310 and processing circuitry 302. The radio front-end circuitry may be configured to condition signals communicated between antenna 310 and processing circuitry 302. The radio front-end circuitry 318 may receive digital data that is to be sent out to other network nodes or UEs via a wireless connection. The radio front-end circuitry 318 may convert the digital data into a radio signal having the appropriate channel and bandwidth parameters using a combination of filters 320 and / or amplifiers 322. The radio signal may then be transmitted via the antenna 310. Similarly, when receiving data, the antenna 310 may collect radio signals which are then converted into digital data by the radio front-end circuitry 318. The digital data may be passed to the processing circuitry 302. In other embodiments, the communication interface may comprise different components and / or different combinations of components.

[0147] In certain alternative embodiments, the network node 300 does not include separate radio front-end circuitry 318, instead, the processing circuitry 302 includes radio front-end circuitry and is connected to the antenna 310. Similarly, in some embodiments, all or some of the RF transceiver circuitry 312 is part of the communication interface 306. In still other embodiments, the communication interface 306 includes one or more ports or terminals 316, the radio front-end circuitry 318, and the RF transceiver circuitry 312, as part of a radio unit (not shown), and the communication interface 306 communicates with the baseband processing circuitry 314, which is part of a digital unit (not shown).

[0148] The antenna 310 may include one or more antennas, or antenna arrays, configured to send and / or receive wireless signals. The antenna 310 may be coupled to the radio front-end circuitry 318 and may be any type of antenna capable of transmitting and receiving data and / or signals wirelessly. In certain embodiments, the antenna 310 is separate from the network node 300 and connectable to the network node 300 through an interface or port.

[0149] The antenna 310, communication interface 306, and / or the processing circuitry 302 may be configured to perform any receiving operations and / or certain obtaining operations described herein as being performed by the network node. Any information, data and / or signals may be received from a UE, another network node and / or any other network equipment.Similarly, the antenna 310, the communication interface 306, and / or the processing circuitry 302 may be configured to perform any transmitting operations described herein as being performed by the network node. Any information, data and / or signals may be transmitted to a UE, another network node and / or any other network equipment.

[0150] The power source 308 provides power to the various components of network node 300 in a form suitable for the respective components (e.g., at a voltage and current level needed for each respective component). The power source 308 may further comprise, or be coupled to, power management circuitry to supply the components of the network node 300 with power for performing the functionality described herein. For example, the network node 300 may be connectable to an external power source (e.g., the power grid, an electricity outlet) via an input circuitry or interface such as an electrical cable, whereby the external power source supplies power to power circuitry of the power source 308. As a further example, the power source 308 may comprise a source of power in the form of a battery or battery pack which is connected to, or integrated in, power circuitry. The battery may provide backup power should the external power source fail.

[0151] Embodiments of the network node 300 may include additional components beyond those shown in Figure 18 for providing certain aspects of the network node’s functionality, including any of the functionality described herein and / or any functionality necessary to support the subject matter described herein. For example, the network node 300 may include user interface equipment to allow input of information into the network node 300 and to allow output of information from the network node 300. This may allow a user to perform diagnostic, maintenance, repair, and other administrative functions for the network node 300.

[0152] Figures 19-23 each illustrate an example of a method that may be performed to facilitate mitigation of interference. For example, Figures 19, 20, and 21 each illustrate an example of a method that may be performed by a wireless device (such as a UE), and Figures 22-23 each illustrate an example of a method that may be performed by a network node (such as an AP). The methods of Figures 19, 20, and 22 may facilitate mitigation of UE-to-UE interference, and the methods of Figures 21 and 23 may facilitate mitigation of AP-to-AP interference.

[0153] Certain embodiments of the methods described in Figures 19, 20, and / or 22 involve scheduling phases of a coherence block in a manner that facilitates a wireless device (e.g., UE) in estimating an interfering channel (UUI channel) so that the wireless device may mitigate UE-to-UE interference. Similarly, certain embodiments of the methods described in Figures 21 and / or 23 involve scheduling phases of a coherence block in a manner that facilitates a networknode (e.g., AP) in estimating an interfering channel (AAI channel) so that the network node may mitigate AP-to-AP interference.

[0154] A coherence block may refer to a resource block limited in time and frequency domains, and a phase of a coherence block may refer to a time duration, such as one or more time slot(s) or time occasion(s) of the coherence block. The position of a phase within the coherence block may be pre-defined (e.g., based on a technical standard or pre-defined by a manufacturer, a system operator, a service provider, etc.) or configured (e.g., added, removed, or modified) via signaling. The time duration of a phase within the coherence block may be pre-defined or configured via signaling. The time duration may be of any suitable length of time, e.g., with a shortest possible time duration corresponding to one time domain sample. Examples of phases (time durations) in a coherence block may include one or more of:• One or more phases to facilitate channel estimation, for example: o a UP CE phase (see, e.g., Phase 1 in each of Figures 3, 5, 6, 7, 14, and 15); o a UP’ CE phase (see, e.g., Phase 2 in each of Figures 5, 6, and 7 or Phase 1 in each of Figures 8, 9, and 10); o a UP* CE phase (see, e.g., Phase 3 in Figure 7 or Phase 2 in each of Figures 8, 9, and 10); and / or o a sample phase (see, e.g., Phase 3 in Figure 15).• A joint uplink reception phase, for example: o From the perspective of the first network node, the first network node receives uplink signals from one or more UEs served by the first network node. o From the perspective of a UE served by the first network node, the UE transmits uplink signals to the first network node. o From the perspective of the second network node, the second network node receives uplink signals from one or more UEs served by the second network node. o From the perspective of a UE served by the second network node, the UE transmits uplink signals to the second network node. o See, e.g., Figure 3 (Phase 2), Figure 5 (Phase 3), Figure 6 (Phase 3), Figure 7 (Phase 3), Figure 8 (Phase 3), Figure 9 (Phase 3), Figure 10 (Phase 3), Figure 14 (Phase 2), and Figure 15 (Phase 2).• A concurrent transmission and reception phase, for example:o From the perspective of the transmitting network node, the transmitting network node transmits downlink signals to one or more UEs served by the transmitting network node. o From the perspective of a UE served by the transmitting network node, the UE receives downlink signals from the transmitting network node. o From the perspective of the receiving network node, the receiving network node receives uplink signals from one or more UEs served by the receiving network node. o From the perspective of a UE served by the receiving network node, the UE transmits uplink signals to the receiving network node. o See, e.g., Figure 3 (Phase 3), Figure 5 (Phase 4), Figure 6 (Phase 4), Figure 7 (Phase 5), Figure 8 (Phase 4), Figure 9 (Phase 4), Figure 10 (Phase 4), Figure 14 (Phase 3), and Figure 15 (Phase 4). And / or;• A joint downlink transmission phase, for example: o From the perspective of the first network node, the first network node transmits downlink signals to one or more UEs served by the first network node. o From the perspective of a UE served by the first network node, the UE receives downlink signals from the first network node. o From the perspective of the second network node, the second network node transmits downlink signals to one or more UEs served by the second network node. o From the perspective of a UE served by the second network node, the UE receives downlink signals from the second network node. o See, e.g., Figure 3 (Phase 4), Figure 5 (Phase 5), Figure 6 (Phase 5), Figure 7 (Phase 6), Figure 8 (Phase 5), Figure 9 (Phase 5), Figure 10 (Phase 5), Figure 14 (Phase 4), and Figure 15 (Phase 5).

[0155] Note that the concept of a “phase” of a coherence block described above differs from the concept of a “phase rotation” (or “channel phase”). The phase rotation / channel phase may relate to channel estimation in the sense that channel estimation may include estimating values for the phase rotation / channel phase. As discussed above, the time duration during which the channel estimation occurs may be referred to as a phase of the coherence block. As an example, an “uplink pilot for channel estimation phase” may refer to a time duration in the coherence block during which channel estimation is performed.

[0156] Figures 19, 20, and 21 each illustrate an example of a method that may be performed by a wireless device, such as a UE described with respect to any of Figures 1-16 or UE 200 described with respect to Figure 17. As an example, in certain embodiments, the wireless device comprises at least one processor (such as processing circuitry 202) configured to perform one or more steps of the method. In certain embodiments, the wireless device comprises a computer-readable medium (such as memory 210) comprising instructions that, when executed by the at least one processor, cause the at least one processor to perform any of the steps of the method.

[0157] Figure 19 illustrates method 1900. Method 1900 begins at step 1902 with a first UE receiving a pilot from a second UE. In certain embodiments, receiving the pilot occurs during a pilot phase in a coherence block. Examples of a pilot phase where one UE may receive a pilot from another UE include those described with respect to Figures 5-10, such as UP’ CE and / or UP* CE. Method 1900 proceeds to step 1904 with estimating a channel to the second UE based on receiving the pilot from the second UE. Method 1900 continues to step 1906 with suppressing UE-to-UE interference based at least in part on the estimating of the channel to the second UE that was performed in step 1904. In certain embodiments, suppressing the interference in step 1906 may comprise determining receive beamforming based at least in part on the estimating of the channel to the second UE and applying the receive beamforming to suppress interference from the second UE during data transmission from the second UE. In certain embodiments, suppressing the interference in step 1906 may comprise determining transmit beamforming based at least in part on the estimating of the channel to the second UE and applying the transmit beamforming to suppress interference to the second UE during data transmission from the first UE. Certain embodiments may apply both receive beamforming and transmit beamforming in order to suppress interference.

[0158] In certain embodiments, a network node may facilitate method 1900. For example, the first UE may receive one or more of the following from a network node, such as an AP: an instruction to receive the pilot from the second UE, an instruction to estimate the channel to the second UE, an instruction to suppress interference from the second UE, information indicating a configuration of the pilot phase and / or a configuration of a coherence block, and / or an instruction on additional reference signals to transmit and / or receive for the purpose of enabling UE-to-UE channel estimation and / or interference mitigation.

[0159] Optionally, method 1900 may include any other suitable steps, such as any one or more steps associated with UE-to-UE interference mitigation described with respect to any of Figures 4-12 above and / or the Group C embodiments below.

[0160] Figure 20 illustrates method 2000. In certain embodiments, the method begins at step 2002 with a first UE receiving, from a network node (e.g., an AP), information to facilitate suppression of UUI. As an example, the first UE may receive one or more of: an instruction to transmit a pilot to a second UE, information indicating a configuration of the pilot phase and / or a configuration of a coherence block, and / or an instruction on additional reference signals to transmit and / or receive for the purpose of enabling UE-to-UE channel estimation and interference mitigation. The method proceeds to step 2004 with transmitting a pilot to the second UE. Transmitting the pilot facilitates the second UE in estimating a channel between the first UE and the second UE. As an example, the UE performing method 2000 of Figure 20 may transmit a pilot to the UE receiving the pilot in method 1900 of Figure 19, which may facilitate interference suppression by the UE receiving the pilot. In certain embodiments, transmitting of the pilot occurs during a pilot phase in a coherence block. Examples of a pilot phase where one UE may transmit a pilot to another UE include those described with respect to Figures 5-10, such as UP’ CE and / or UP* CE.

[0161] Optionally, method 2000 may include any other suitable steps, such as any one or more steps associated with UE-to-UE interference mitigation described with respect to any of Figures 4-12.

[0162] Figure 21 illustrates method 2100. Method 2100 may be performed by a UE served by a first network node. In certain embodiments, method 2100 begins at step 2102 with determining at least one sample phase in a coherence block. The sample phase may refer to a time duration during which the UE is to transmit only a sample value or the UE is to remain silent (e.g., abstain from transmitting non-zero values on the uplink to the first network node). The time duration of the sample phase may correspond to one time domain sample or multiple time domain samples. Determining the sample phase in step 2102 may comprise determining a presence of the sample phase within the coherence block, determining a position of the sample phase within the coherence block, and / or determining a time duration of the sample phase. As an example, determining the sample phase may be based on pre-defined information stored in memory of the UE. As another example, determining the sample phase may be based on a configuration of the sample phase obtained via signaling.

[0163] Method 2100 may proceed to step 2104 where, during the sample phase, the UE transmits only a sample value (such as a known / pre-determined bit pattern, which could be an uplink pilot or other predetermined bit pattern) on an uplink to the first network node or the UE abstains from transmitting on the uplink to the first network node. In this manner, the UE may facilitate the network node in receiving / estimating an interfering signal corresponding toa downlink transmission from a second network node in order for the first network node to obtain information for mitigating AAI interference. For an example of a sample phase, see Figure 15 at phase 3 (during which the first K UEs are silent).

[0164] In certain embodiments, method 2100 may further comprise transmitting one or more uplink transmissions to the first network node during a concurrent transmission and reception phase in the coherence block. During the concurrent transmission and reception phase, the first network node is configured to perform reception on the uplink and the second network node is configured to perform one or more downlink transmissions to at least one UE served by the second network node. Figure 15 illustrates an example of a concurrent transmission and reception phase in phase 4. In certain embodiments, the concurrent transmission and reception phase occurs after the sample phase.

[0165] In certain embodiments, method 2100 further comprises transmitting a pilot signal during an uplink pilot for channel estimation phase in the coherence block. Figure 15 illustrates an example of an uplink pilot for channel estimation phase in phase 1 (UP CE). In certain embodiments, the sample phase is located after the uplink pilot for channel estimation phase.

[0166] In certain embodiments, method 2100 may further comprise transmitting one or more uplink transmissions to the first network node during a joint uplink reception phase in the coherence block. Both the first network node and the second network node are configured to perform reception on the uplink during the joint uplink reception phase. Figure 15 illustrates an example of a joint uplink reception phase in phase 2. In certain embodiments, the sample phase is located after the joint uplink reception phase.

[0167] In certain embodiments, method 2100 may further comprise performing reception on a downlink from the first network node during a joint downlink transmission phase in the coherence block. Both the first network node and the second network node are configured to perform transmission on the downlink during the joint downlink transmission phase. Figure 15 illustrates an example of a joint downlink transmission phase in phase 5. In certain embodiments, the sample phase is located before the joint downlink transmission phase.

[0168] In certain embodiments, the first network node is configured as a first AP and / or the second network node is configured as a second AP in a D-TDD system.

[0169] In certain embodiments, a configuration of the coherence block and / or a configuration of the at least one sample phase is pre-defined. As an example, the configuration(s) may be pre-defined by a technical standard. As another example, the configuration(s) may be pre-defined by a manufacturer, a system operator, a service provider, etc. In certain embodiments, the configuration(s) may be pre-defined and stored in memory ofthe UE. In addition, or in the alternative, a configuration of the coherence block and / or a configuration of the at least one sample phase can be configured (e.g., added, removed, or modified) via signaling between the first network node and the group of one or more UEs. As an example, the first network node may determine a configuration and may indicate the configuration to the UE via signaling.

[0170] Optionally, method 2100 may include any other suitable steps, such as any one or more steps associated with AAI mitigation described with respect to any of Figures 15-16 above or the Group A embodiments below.

[0171] In certain embodiments, a wireless device (e.g., UE) may be configured to perform a combination of method 1900 of Figure 19 (e.g., to facilitate UUI mitigation by the UE), method 2000 of Figure 20 (e.g., to facilitate UUI mitigation by another UE), and / or method 2100 of Figure 21 (e.g., to facilitate AAI mitigation by a network node).

[0172] Figures 22 and 23 each illustrate an example of a method that may be performed by a network node, such as an AP described with respect to any of Figures 1-16 or network node 300 of Figure 18. As an example, in certain embodiments, the network node comprises at least one processor (such as processing circuitry 302) configured to perform one or more steps of the method. In certain embodiments, the network node comprises a computer-readable medium (such as memory 304) comprising instructions that, when executed by the at least one processor, cause the at least one processor to perform any of the steps of the method.

[0173] Figure 22 illustrates method 2200. Method 2200 may be performed by a network node that serves one or more UEs. In certain embodiments, method 2200 begins at step 2202 with determining information to facilitate mitigation of UE-to-UE interference. Method 2200 proceeds to step 2204 with communicating the information to at least a first UE of the one or more UEs.

[0174] As an example, in certain embodiments, method 2200 may be performed by a network node to facilitate a UE in performing method 1900 of Figure 19. Examples of information determined by the network node in step 2202 and communicated to the first UE in step 2204 may include one or more of: an instruction to receive a pilot from the second UE, an instruction to estimate a channel between the first UE and the second UE, an instruction to suppress interference from the second UE, information indicating a configuration of a pilot phase during which to receive the pilot from the second UE, information indicating a configuration of a coherence block, and / or an instruction on additional reference signals to transmit and / or receive for the purpose of enabling UE-to-UE channel estimation and interference mitigation.

[0175] In addition, or in the alternative, in certain embodiments, method 2200 may be performed by a network node to facilitate a UE in performing method 2000 of Figure 20. Examples of information determined by the network node in step 2202 and communicated to the first UE in step 2204 may include one or more of: an instruction to transmit a pilot to the second UE, information indicating a configuration of a pilot phase during which to transmit the pilot to the second UE, information indicating a configuration of a coherence block, and / or an instruction on additional reference signals to transmit and / or receive for the purpose of enabling UE-to-UE channel estimation and interference mitigation.

[0176] Optionally, method 2200 may include any other suitable steps, such as any one or more steps to facilitate UE-to-UE interference mitigation, such as the UUI described with respect to any of Figures 4-12 above or the Group D embodiments below.

[0177] Figure 23 illustrates method 2300. Method 2300 may be performed by a first network node. In certain embodiments, method 2300 begins at step 2302 with receiving an interfering signal from a second network node. In certain embodiments, the interfering signal corresponds to a downlink transmission from the second network node to at least one UE served by the second network node. The interfering signal is received when performing reception on an uplink during at least one sample phase in a coherence block. The sample phase may refer to a time duration during which a group of one or more UEs served by the first network node transmit only a sample value or remain silent (e.g., abstain from transmitting non-zero values on the uplink to the first network node). That is, the coherence block is configured such that during the at least one sample phase, each UE in a group of one or more UEs served by the first network node is silent or transmits only a sample value (such as a known / pre-determined bit pattern, which could be an uplink pilot or other predetermined bit pattern). The time duration of the sample phase may correspond to one time domain sample or multiple time domain samples. For an example of a sample phase, see Figure 15, phase 3, during which the first K UEs are silent, and the interfering signal corresponds to the downlink signal from the second network node to UE (K+l)).

[0178] Method 2300 continues to step 2304 with mitigating interference from the second network node based at least in part on information obtained by receiving the interfering signal during the sample phase.

[0179] In certain embodiments, the coherence block comprises at least one concurrent transmission and reception phase during which the first network node is configured to perform reception of one or more uplink transmissions from the group of one or more UEs served by the first network node while the second network node is configured to perform one or moredownlink transmissions to at least one UE served by the second network node. Mitigating interference in step 2304 may comprise, during the at least one concurrent transmission and reception phase, jointly estimating uplink symbols received from the group of one or more UEs served by the first network node and data symbols received in the interference from the second network node. Estimating the data symbols received in the interference from the second network node may be based at least in part on information obtained by receiving the interfering signal in step 2302 (during the sample phase).

[0180] In certain embodiments, mitigating interference from the second network node in step 2304 is based in part on knowledge of data included in the interference. As an example, certain embodiments obtain the knowledge of the data included in the interference via fronthaul. As another example, certain embodiments obtain the knowledge of the data included in the interference based on the first network node receiving, via a network, data to be included in the one or more downlink transmissions by the second network node. Thus, in certain embodiments, the network may send at least certain data to both the first network node (to facilitate AAI mitigation) and to the second network node (to facilitate the one or more downlink transmissions to one or more UEs served by the second network node).

[0181] In certain embodiments, the coherence block further comprises an uplink pilot for channel estimation phase. Figure 15 illustrates an example of this in phase 1 (UP CE). In certain embodiments, the sample phase is located after the uplink pilot for channel estimation phase.

[0182] In certain embodiments, the coherence block further comprises a joint uplink reception phase wherein both the first network node and the second network node are configured to perform reception on the uplink. Figure 15 illustrates an example of this in phase 2. In certain embodiments, the sample phase is located after the joint uplink reception phase.

[0183] In certain embodiments, the coherence block further comprises a joint downlink transmission phase wherein both the first network node and the second network node are configured to perform transmission on the downlink. Figure 15 illustrates an example of this in phase 5. In certain embodiments, the sample phase is located before the joint downlink transmission phase.

[0184] In certain embodiments, the first network node is configured as a first AP in a D- TDD system. In certain embodiments, the second network node is configured as a second AP in the D-TDD system. In certain embodiments, the first network node and the second network node connect to the same CPU (e.g., described as case (1) in other portions of this disclosure). In other embodiments, the first network node and the second network node connect to different CPUs (e.g., described as case (2) in other portions of this disclosure).

[0185] In certain embodiments, a configuration of the coherence block and / or a configuration of the at least one sample phase is pre-defined. As an example, the configuration(s) may be pre-defined by a technical standard. As another example, the configuration(s) may be pre-defined by a manufacturer, a system operator, a service provider, etc. In certain embodiments, the configuration(s) may be pre-defined and stored in memory of the network node. In addition, or in the alternative, a configuration of the coherence block and / or a configuration of the at least one sample phase can be configured (e.g., added, removed, or modified) via signaling between the first network node and the group of one or more UEs. As an example, the first network node may determine a configuration and may indicate the configuration to the UE via signaling.

[0186] Optionally, method 2300 may include any other suitable steps, such as any one or more steps associated with AAI mitigation described with respect to any of Figures 15-16 above or the Group B embodiments below.

[0187] In certain embodiments, a network node (e.g., AP) may be configured to perform a combination of method 2200 of Figure 22 (e.g., to facilitate UUI mitigation by one or more UEs) and method 2300 of Figure 23 (e.g., to facilitate AAI mitigation by the network node).

[0188] In certain embodiments, a wireless device (e.g., UE) and a network node (e.g., AP) may perform reciprocal operations. For example, a message sent from a wireless device to a network node may be received by the network node from the wireless device, and vice versa. Thus, portions of the disclosure describing one operation may provide context for the reciprocal operation.

[0189] Group A Embodiments

[0190] In an embodiment Al, a method in a user equipment served by a first network node comprises determining (2102) at least one sample phase in a coherence block; and during (2104) the sample phase, transmitting only a sample value on an uplink to the first network node or abstaining from transmitting on the uplink to the first network node.

[0191] In an embodiment A2, the method of embodiment Al, wherein transmitting only the sample value or abstaining from transmitting on the uplink to the first network node during the sample phase facilitates the first network node in receiving an interfering signal corresponding to a downlink transmission from a second network node in order for the first network node to obtain information for mitigating interference.

[0192] In an embodiment A3, the method of any of embodiments A1-A2, further comprises transmitting one or more uplink transmissions to the first network node during a concurrent transmission and reception phase in the coherence block, wherein during theconcurrent transmission and reception phase the first network node is configured to perform reception on the uplink and the second network node is configured to perform one or more downlink transmissions to at least one UE served by the second network node.

[0193] In an embodiment A4, the method of any of embodiments A1-A3, wherein the concurrent transmission and reception phase occurs after the sample phase.

[0194] In an embodiment A5, the method of any of embodiments A1-A4, further comprises transmitting a pilot signal during an uplink pilot for channel estimation phase in the coherence block.

[0195] In an embodiment A6, the method of embodiment A5, wherein the sample phase is located after the uplink pilot for channel estimation phase.

[0196] In an embodiment A7, the method of any of embodiments A1-A6, further comprises transmitting one or more uplink transmissions to the first network node during a joint uplink reception phase in the coherence block, wherein both the first network node and the second network node are configured to perform reception on the uplink during the joint uplink reception phase.

[0197] In an embodiment A8, the method of embodiment A7, wherein the sample phase is located after the joint uplink reception phase.

[0198] In an embodiment A9, the method of any of embodiments A1-A8, further comprises performing reception on a downlink from the first network node during a joint downlink transmission phase in the coherence block, wherein both the first network node and the second network node are configured to perform transmission on the downlink during the joint downlink transmission phase.

[0199] In an embodiment A 10, the method of embodiment A9, wherein the sample phase is located before the joint downlink transmission phase.

[0200] In an embodiment Al l, the method of any of embodiments Al -A 10, wherein the first network node is configured as a first access point and / or the second network node is configured as a second access point in a dynamic time division duplex (D-TDD) system.

[0201] In an embodiment A 12, the method of any of embodiments Al-Al l, wherein a configuration of the coherence block and / or a configuration of the at least one sample phase is pre-defined.

[0202] In an embodiment A 13, the method of any of embodiments Al -A 12, wherein a configuration of the coherence block and / or a configuration of the at least one sample phase is configured via signaling between the first network node and the group of one or more UEs.

[0203] Group B Embodiments

[0204] In an embodiment B2, a method in a first network node comprises receiving (2302) an interfering signal from a second network node, the interfering signal received when performing reception on an uplink during at least one sample phase in a coherence block, the coherence block configured such that during the at least one sample phase each user equipment (UE) in a group of one or more UEs served by the first network node is silent or transmits only a sample value; and mitigating (2304) interference from the second network node based at least in part on information obtained by receiving the interfering signal during the sample phase.

[0205] In an embodiment B2, the method of embodiment Bl, wherein the interfering signal corresponds to a downlink transmission from the second network node to at least one UE served by the second network node.

[0206] In an embodiment B3, the method of any of embodiments B1-B2, wherein the coherence block comprises at least one concurrent transmission and reception phase during which the first network node is configured to perform reception of one or more uplink transmissions from the group of one or more UEs served by the first network node while the second network node is configured to perform one or more downlink transmissions to at least one UE served by the second network node; and wherein mitigating interference from the second network node comprises, during the at least one concurrent transmission and reception phase, jointly estimating uplink symbols received from the group of one or more UEs served by the first network node and data symbols received in the interference from the second network node, wherein estimating the data symbols received in the interference from the second network node is based at least in part on information obtained by receiving the interfering signal during the sample phase.

[0207] In an embodiment B4, the method of any of embodiments B1-B3, wherein mitigating interference from the second network node is based in part on knowledge of data included in the interference.

[0208] In an embodiment B5, the method of embodiment B4, wherein the knowledge of the data included in the interference is obtained via fronthaul.

[0209] In an embodiment B6, the method of embodiment B4 or B5, wherein the knowledge of the data included in the interference is obtained based on the first network node receiving, via a network, data to be included in the one or more downlink transmissions by the second network node.

[0210] In an embodiment B7, the method of any of embodiments B1-B6, wherein the coherence block further comprises an uplink pilot for channel estimation phase.

[0211] In an embodiment B8, the method of embodiment B7, wherein the sample phase is located after the uplink pilot for channel estimation phase.

[0212] In an embodiment B9, the method of any of embodiments B1-B8, wherein the coherence block further comprises a joint uplink reception phase wherein both the first network node and the second network node are configured to perform reception on the uplink.

[0213] In an embodiment BIO, the method of embodiment B9, wherein the sample phase is located after the joint uplink reception phase.

[0214] In an embodiment Bl 1, the method of any of embodiments Bl -BIO, wherein the coherence block further comprises a joint downlink transmission phase wherein both the first network node and the second network node are configured to perform transmission on the downlink.

[0215] In an embodiment B 12, the method of embodiment B 11 , wherein the sample phase is located before the joint downlink transmission phase.

[0216] In an embodiment Bl 3, the method of any of embodiments Bl -Bl 2, wherein the first network node is configured as a first access point in a dynamic time division duplex (D- TDD) system.

[0217] In an embodiment B14, the method of embodiment Bl 3, wherein the second network node is configured as a second access point in the D-TDD system.

[0218] In an embodiment Bl 5, the method of any of embodiments Bl -Bl 4, wherein the first network node and the second network node connect to the same central processing unit (CPU).

[0219] In an embodiment Bl 6, the method of any of embodiments Bl -Bl 4, wherein the first network node and the second network node connect to different central processing units (CPUs).

[0220] In an embodiment Bl 7, the method of any of embodiments Bl -Bl 6, wherein a configuration of the coherence block and / or a configuration of the at least one sample phase is pre-defined.

[0221] In an embodiment B18, the method of any of embodiments B1-B17, wherein a configuration of the coherence block and / or a configuration of the at least one sample phase is configured via signaling between the first network node and the group of one or more UEs.

[0222] Group C Embodiments

[0223] In an embodiment C 1 , a method in a first user equipment (UE) comprises receiving (1902) a pilot from a second UE; and estimating (1904) a channel to the second UE based on receiving the pilot from the second UE.

[0224] In an embodiment C2, the method of embodiment Cl further comprises suppressing (1906) UE-to-UE interference based at least in part on the estimating of the channel to the second UE.

[0225] In an embodiment C3, the method of any of embodiments C1-C2 further comprises determining receive beamforming based at least in part on the estimating of the channel to the second UE; and applying the receive beamforming to suppress interference from the second UE during data transmission from the second UE.

[0226] In an embodiment C4, the method of any of embodiments C 1 -C3 further comprises determining transmit beamforming based at least in part on the estimating of the channel to the second UE; and applying the transmit beamforming to suppress interference to the second UE during data transmission from the first UE.

[0227] In an embodiment C5, the method of any of embodiments C1-C4, wherein the receiving the pilot occurs during a pilot phase in a coherence block.

[0228] In an embodiment C6, the method of any of embodiments C1-C5, further comprising, receiving, from a network node, one or more of: an instruction to receive the pilot from the second UE; an instruction to estimate the channel to the second UE; an instruction to suppress interference from the second UE; information indicating a configuration of the pilot phase; information indicating a configuration of a coherence block; and / or an instruction on additional reference signals to transmit and / or receive for the purpose of enabling UE-to-UE channel estimation and interference mitigation.

[0229] In an embodiment C7, a method in a first user equipment (UE) comprises transmitting (2004) a pilot to a second UE, wherein transmitting the pilot facilitates the second UE in estimating a channel between the first UE and the second UE.

[0230] In an embodiment C8, the method of embodiment C7, wherein the transmitting of the pilot occurs during a pilot phase in a coherence block.

[0231] In an embodiment C9, the method of any of embodiments C7-C8 further comprises receiving, from a network node, one or more of: an instruction to transmit the pilot to the second UE; information indicating a configuration of the pilot phase; information indicating a configuration of a coherence block; and / or an instruction on additional reference signals to transmit and / or receive for the purpose of enabling UE-to-UE channel estimation and interference mitigation.

[0232] In an embodiment CIO, the method of any of embodiments C1-C9 further comprises any one or more steps associated with UE-to-UE interference mitigation described with respect to any of Figures 4-12.

[0233] Group D Embodiments

[0234] In an embodiment DI, a method in a network node that serves one or more user equipments (UEs) comprises determining (2202) information to facilitate mitigation of UE-to- UE interference; and communicating (2204) the information to at least a first UE of the one or more UEs.

[0235] In an embodiment D2, the method of embodiment DI, wherein the information transmitted to the first UE comprises: an instruction to receive a pilot from the second UE; an instruction to estimate a channel between the first UE and the second UE; an instruction to suppress interference from the second UE; information indicating a configuration of a pilot phase during which to receive the pilot from the second UE; information indicating a configuration of a coherence block; and / or an instruction on additional reference signals to transmit and / or receive for the purpose of enabling UE-to-UE channel estimation and interference mitigation.

[0236] In an embodiment D3, the method of embodiment DI, wherein the information transmitted to the first UE comprises: an instruction to transmit a pilot to the second UE; information indicating a configuration of a pilot phase during which to transmit the pilot to the second UE; information indicating a configuration of a coherence block; and / or an instruction on additional reference signals to transmit and / or receive for the purpose of enabling UE-to- UE channel estimation and interference mitigation.

[0237] Group E Embodiments

[0238] In an embodiment El, a user equipment comprises processing circuitry configured to perform any of the steps of any of the Group A or Group C embodiments; and power supply circuitry configured to supply power to the processing circuitry.

[0239] In an embodiment E2, a network node comprises processing circuitry configured to perform any of the steps of any of the Group B or Group D embodiments; and power supply circuitry configured to supply power to the processing circuitry.

[0240] In an embodiment E3, a user equipment (UE) comprises an antenna configured to send and receive wireless signals; radio front-end circuitry connected to the antenna and to processing circuitry, and configured to condition signals communicated between the antenna and the processing circuitry; the processing circuitry being configured to perform any of the steps of any of the Group A or Group C embodiments; an input interface connected to the processing circuitry and configured to allow input of information into the UE to be processed by the processing circuitry; an output interface connected to the processing circuitry and configured to output information from the UE that has been processed by the processingcircuitry; and a battery connected to the processing circuitry and configured to supply power to the UE.

[0241] Modifications, additions, or omissions may be made to the systems and apparatuses described herein without departing from the scope of the disclosure. Although the computing devices described herein (e.g., UEs, network nodes) may include the illustrated combination of hardware components, other embodiments may comprise computing devices with different combinations of components. It is to be understood that these computing devices may comprise any suitable combination of hardware and / or software needed to perform the tasks, features, functions and methods disclosed herein. Determining, calculating, obtaining or similar operations described herein may be performed by processing circuitry, which may process information by, for example, converting the obtained information into other information, comparing the obtained information or converted information to information stored in the network node, and / or performing one or more operations based on the obtained information or converted information, and as a result of said processing making a determination. Moreover, while components are depicted as single boxes located within a larger box, or nested within multiple boxes, in practice, computing devices may comprise multiple different physical components that make up a single illustrated component, and functionality may be partitioned between separate components. For example, a communication interface may be configured to include any of the components described herein, and / or the functionality of the components may be partitioned between the processing circuitry and the communication interface. In another example, non-computationally intensive functions of any of such components may be implemented in software or firmware and computationally intensive functions may be implemented in hardware. Thus, the components of the systems and apparatuses may be integrated or separated in any suitable manner, and the operations of the systems and apparatuses may be performed by more, fewer, or other components.

[0242] In certain embodiments, some or all of the functionality described herein may be provided by processing circuitry executing instructions stored on in memory, which in certain embodiments may be a computer program product in the form of a non-transitory computer- readable storage medium. In alternative embodiments, some or all of the functionality may be provided by the processing circuitry without executing instructions stored on a separate or discrete device-readable storage medium, such as in a hard-wired manner. In any of those particular embodiments, whether executing instructions stored on a non-transitory computer- readable storage medium or not, the processing circuitry can be configured to perform thedescribed functionality. The benefits provided by such functionality are not limited to the processing circuitry alone or to other components of the computing device, but are enjoyed by the computing device as a whole, and / or by end users and a wireless network generally.

[0243] Modifications, additions, or omissions may be made to the methods described herein without departing from the scope of the disclosure. The methods may include more, fewer, or other steps. Additionally, steps may be performed in any suitable order.

[0244] Although this disclosure has been described in terms of certain embodiments, alterations and permutations of the embodiments will be apparent to those skilled in the art. Accordingly, the description of the embodiments does not constrain this disclosure. Other changes, substitutions, and alterations are possible without departing from the scope of this disclosure.

Claims

CLAIMS1. A method in a first network node, the method comprising: receiving (2302) an interfering signal from a second network node, the interfering signal received when performing reception on an uplink during at least one sample phase in a coherence block, the coherence block configured such that during the at least one sample phase each user equipment (UE) in a group of one or more UEs served by the first network node is silent or transmits only a sample value; and mitigating (2304) interference from the second network node based at least in part on information obtained by receiving the interfering signal during the sample phase.

2. The method of claim 1, wherein the interfering signal corresponds to a downlink transmission from the second network node to at least one UE served by the second network node.

3. The method of any of claims 1-2, wherein: the coherence block comprises at least one concurrent transmission and reception phase during which the first network node is configured to perform reception of one or more uplink transmissions from the group of one or more UEs served by the first network node while the second network node is configured to perform one or more downlink transmissions to at least one UE served by the second network node; and wherein mitigating interference from the second network node comprises, during the at least one concurrent transmission and reception phase, jointly estimating uplink symbols received from the group of one or more UEs served by the first network node and data symbols received in the interference from the second network node, wherein estimating the data symbols received in the interference from the second network node is based at least in part on information obtained by receiving the interfering signal during the sample phase.

4. The method of any of claims 1-3, wherein mitigating interference from the second network node is based in part on knowledge of data included in the interference.

5. The method of claim 4, wherein the knowledge of the data included in the interference is obtained via fronthaul.

6. The method of any of claims 4-5, wherein the knowledge of the data included in the interference is obtained based on the first network node receiving, via a network, data to be included in the one or more downlink transmissions by the second network node.

7. The method of any of claims 1-6, wherein the coherence block further comprises an uplink pilot for channel estimation phase.

8. The method of claim 7, wherein the sample phase is located after the uplink pilot for channel estimation phase.

9. The method of any of claims 1-8, wherein the coherence block further comprises a joint uplink reception phase wherein both the first network node and the second network node are configured to perform reception on the uplink.

10. The method of claim 9, wherein the sample phase is located after the joint uplink reception phase.

11. The method of any of claims 1-10, wherein the coherence block further comprises a joint downlink transmission phase wherein both the first network node and the second network node are configured to perform transmission on the downlink.

12. The method of claim 11, wherein the sample phase is located before the joint downlink transmission phase.

13. The method of any of claims 1-12, wherein the first network node is configured as a first access point in a dynamic time division duplex (D-TDD) system.

14. The method of claim 13, wherein the second network node is configured as a second access point in the D-TDD system.

15. The method of any of claims 1-14, wherein the first network node and the second network node connect to the same central processing unit (CPU).

16. The method of any of claims 1-14, wherein the first network node and the second network node connect to different central processing units (CPUs).

17. The method of any of claims 1-16, wherein a configuration of the coherence block and / or a configuration of the at least one sample phase is pre-defined.

18. The method of any of claims 1-17, wherein a configuration of the coherence block and / or a configuration of the at least one sample phase is configured via signaling between the first network node and the group of one or more UEs.

19. A network node (300), comprising: processing circuitry (302); and power supply circuitry (308) configured to supply power to the processing circuitry; the processing circuitry configured to: receive an interfering signal from a second network node, the interfering signal received when performing reception on an uplink during at least one sample phase in a coherence block, the coherence block configured such that during the at least one sample phase each user equipment (UE) in a group of one or more UEs served by the first network node is silent or transmits only a sample value; and mitigate interference from the second network node based at least in part on information obtained by receiving the interfering signal during the sample phase.

20. The network node of Claim 19, the processing circuitry further configured to perform the steps of any of claims 1-18.

21. A method in a user equipment served by a first network node, the method comprising: during a sample phase in a coherence block, (2104) transmitting only a sample value on an uplink to the first network node or abstaining from transmitting on the uplink to the first network node.

22. The method of claim 21, wherein transmitting only the sample value or abstaining from transmitting on the uplink to the first network node during the sample phase facilitates the first network node in receiving an interfering signal corresponding to a downlinktransmission from a second network node in order for the first network node to obtain information for mitigating interference.

23. The method of any of claims 21-22, further comprising: transmitting one or more uplink transmissions to the first network node during a concurrent transmission and reception phase in the coherence block, wherein during the concurrent transmission and reception phase the first network node is configured to perform reception on the uplink and the second network node is configured to perform one or more downlink transmissions to at least one UE served by the second network node.

24. The method of claim 23, wherein the concurrent transmission and reception phase occurs after the sample phase.

25. The method of any of claims 21-24, further comprising: transmitting a pilot signal during an uplink pilot for channel estimation phase in the coherence block.

26. The method of claim 25, wherein the sample phase is located after the uplink pilot for channel estimation phase.

27. The method of any of claims 21-26, further comprising: transmitting one or more uplink transmissions to the first network node during a joint uplink reception phase in the coherence block, wherein both the first network node and the second network node are configured to perform reception on the uplink during the joint uplink reception phase.

28. The method of claim 27, wherein the sample phase is located after the joint uplink reception phase.

29. The method of any of claims 21-28, further comprising: performing reception on a downlink from the first network node during a joint downlink transmission phase in the coherence block, wherein both the first network node and the second network node are configured to perform transmission on the downlink during the joint downlink transmission phase.

30. The method of claim 29, wherein the sample phase is located before the joint downlink transmission phase.

31. The method of any of claims 21-30, wherein the first network node is configured as a first access point and / or the second network node is configured as a second access point in a dynamic time division duplex (D-TDD) system.

32. The method of any of claims 21-31, further comprising determining (2102) the sample phase in the coherence block.

33. The method of any of claims 21-32, wherein a configuration of the coherence block and / or a configuration of the at least one sample phase is pre-defined.

34. The method of any of claims 21-32, wherein a configuration of the coherence block and / or a configuration of the at least one sample phase is configured via signaling between the first network node and the group of one or more UEs.

35. A user equipment (200), comprising: processing circuitry (202); and power supply circuitry (208) configured to supply power to the processing circuitry; the processing circuitry configured to: during a sample phase in a coherence block, transmit only a sample value on an uplink to a first network node or abstain from transmitting on the uplink to the first network node.

36. The user equipment of claim 35, the processing circuitry further configured to perform the steps of any of claims 21-34.

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