A method for channel measurement for mitigating cli

Abstract

A method for channel measurement for mitigating cross link interference (CLI) in a system comprising base stations (100) which are capable of communicating using sub-band-full- duplex (SBFD) technology, where said base stations (100) having N number of channel state information (CSI) ports and a central controller (10) for controlling said base stations (100) the method includes two step reference signal configuration using lower number of ports at first then using higher number of ports depending on the level of the measured CLI at first part. Then the method performs beam nulling based on reference signal measurements of the second part.

Description

[0001] DESCRIPTION

[0002] A METHOD FOR CHANNEL MEASUREMENT FOR MITIGATING CLI

[0003] TECHNICAL FIELD

[0004] Invention relates to a method for channel measurement for mitigating cross link interference (CLI) in a system comprising base stations which are capable of communicating using sub-band-full-duplex (SBFD) technology, where said base stations having N number of channel state information (CSI) ports and a central controller for controlling said base stations.

[0005] PRIOR ART

[0006] Sub-band non-overlapping full duplex (SBFD) is a technology introduced in 3GPP Release 19 to enhance 5G capabilities. This technology allows for simultaneous transmission and reception of signals in non-overlapping sub-bands within the same frequency band, essentially improving the efficiency of spectrum use.

[0007] In traditional duplexing methods like frequency division duplexing (FDD) and time division duplexing (TDD), the downlink (DL) and uplink (UL) either occupy different frequency bands or operate at different times, respectively. However, with SBFD, the spectrum is more efficiently utilized because it allows for simultaneous DL and UL communications in the same frequency band but in different sub-bands, thus avoiding interference. SBFD concept allows simultaneous transmission and reception in different sub-bands of the same frequency band, it enhances spectrum efficiency, which is crucial for supporting the growing demand for data in 5G networks.

[0008] In traditional duplexing methods, the allocation of UL and DL resources is often fixed, which can lead to inefficiencies, especially when there is a variable and asymmetric demand between DL and UL traffic. SBFD allows for more dynamic allocation of spectrum resources because it enables simultaneous DL and UL transmissions in separate sub-bands of the same frequency band. This flexibility means that UL resources can be increased when demand is high without compromising DL traffic, leading to more efficient use of the spectrum.

[0009] SBFD introduces new interference scenarios not typically encountered in dynamic TDD (D-TDD). These interferences arise because SBFD allows simultaneous transmission andreception within different sub-bands of the same frequency band, potentially leading to crosstalk between these sub-bands. The main types of gNB-to-gNB interference introduced by SBFD include:

[0010] One of the critical challenges in SBFD systems is self-interference. Self-interference occurs when the transmitted signal from a device leaks into its receiving sub-band, causing the receiver to pick up unwanted signals that degrade communication quality. This interference can significantly impact the performance of the system, leading to reduced data rates, increased error rates, and higher power consumption.

[0011] To effectively address interference challenges in 5G networks, especially within SBFD scenarios, the industry standards are evolving to incorporate advanced interference mitigation techniques. These methodologies are primarily focused on spatial domain strategies, coordinated scheduling across time and frequency domains, power control mechanisms, and CLI measurement and modeling techniques.

[0012] A key approach to mitigating gNB-to-gNB CLI is beam-nulling, which proves particularly effective in the Frequency Range 1 (FR-1) band. In beam-nulling, the aggressor gNB adjusts its precoding weights to create a null towards the victim gNB. The nulling process is informed by the channel between the aggressor gNB and the victim gNB, as well as the channel measurements between the aggressor gNB and its served UEs. This adjustment enables the aggressor gNB to minimize interference while still communicating effectively with its UEs. The process of beam-nulling in SBFD systems is conceptually similar to DL multi-user MIMO (DL MU-MIMO) because both involve optimizing the transmission based on channel measurements.

[0013] Channel state information reference signals (CSI-RS) can be utilized to measure the channel between the aggressor and victim gNBs. By transmitting CSI-RS, the aggressor gNB allows the victim gNB to measure the channel, which then sends the channel state feedback to the aggressor. Based on this information, the aggressor gNB can adjust its transmission to mitigate interference through beam-nulling. Utilizing a higher number of CSI-RS port configurations provides a more detailed understanding of the channel, enabling more precise beam-nulling.

[0014] In addition to the victim gNB measuring the channel, the reverse process is also possible. The victim gNB can transmit CSI-RS, allowing the aggressor gNB to measure the channel and optimize its precoding accordingly. This bidirectional exchange of channel information allowsboth gNBs to contribute to effective CLI mitigation in SBFD systems. Beam-nulling, facilitated by accurate channel measurements, thus plays a crucial role in maintaining system performance by minimizing the interference between gNBs.

[0015] The resolution and accuracy of these channel measurements are directly tied to the number of CSI-RS ports used. By using a higher number of CSI-RS ports, the system can achieve better channel resolution, enabling more precise interference mitigation, especially when performing beam-nulling. This higher channel resolution gives a clearer picture of the channel characteristics, allowing for fine-tuned adjustments that lead to improved performance in complex communication environments.

[0016] However, increasing the number of CSI-RS ports comes with a trade-off. The transmission of CSI-RS occupies valuable time-frequency resources that could otherwise be used for actual data transmission, such as the Physical Downlink Shared Channel (PDSCH) or the Physical Downlink Control Channel (PDCCH). This creates a balancing act: while more CSI-RS ports enhance the ability to measure and mitigate interference, they also reduce the resources available for user data transmission. As a result, excessive CSI-RS usage can lead to inefficient utilization of the spectrum, impacting overall system throughput.

[0017] In the prior art, channel and interference measurements are essential for enabling beamnulling techniques, particularly in scenarios where multiple next-generation NodeBs (gNBs) coexist within a network. Accurate channel estimation between aggressor and victim gNBs is necessary for effective interference management, with some solutions advocating the use of up to 128 CSI-RS ports to achieve high-quality channel estimation. In a network with multiple gNBs, these neighboring base stations must perform precise gNB-to-gNB channel measurements, but the process as it currently exists presents several challenges.

[0018] One of the main problems is the need to allocate substantial resources for CSI-RS transmissions. In these solutions, neighboring gNBs are scheduled to transmit CSI-RS signals in orthogonal time slots, requiring other gNBs to listen on those resources during their scheduled slots. This approach results in significant resource allocation dedicated solely to periodic measurements, which can become a burden for the network. With such large resource requirements for the periodic transmission and reception of CSI-RS signals, system efficiency is compromised, especially as the number of gNBs in the network increases.Furthermore, the current methods do not effectively account for dynamic interference relationships between gNBs. In scenarios where one base station may simultaneously act as both a victim and an aggressor with respect to different neighboring gNBs, the prior art lacks a flexible and dynamic mechanism for identifying and adjusting to these roles. This rigidity leads to inefficient resource usage, as there is no adequate system for dynamically identifying aggressor-victim pairs and adjusting CSI-RS resource allocation accordingly.

[0019] Additionally, the solutions in the prior art do not provide adequate support for handling scenarios with multiple aggressor-victim relationships. In such cases, the current methods result in over-provisioning of resources, as every gNB must allocate a substantial portion of its resources to channel measurement and interference management, even when it is not necessary. As a result, resource usage is not optimized, and network performance suffers.

[0020] In summary, the prior art presents inadequacies in terms of resource allocation, dynamic role identification, and scalability in multi-gNB networks, making it unsuitable for scenarios involving multiple aggressor-victim pairs. There is a need for a solution that enables efficient resource allocation and more adaptive identification of aggressor-victim pairs based on real-time interference levels, which would significantly improve network performance and resource efficiency.

[0021] WO2018223386A1 discloses a system and method for measuring and controlling cross-link interference (CLI) in wireless communication networks, particularly focusing on scenarios involving multiple base stations (gNBs) operating on both uplink (UL) and downlink (DL) channels. The system measures CLI between the gNBs using reference signals, such as CSI-RS and DMRS, and introduces several metrics for measuring the interference, including Cross-Link interference Reference Signal Received Power (CLI-RSRP) and Cross-Link interference Reference Signal Received Signal Strength Indicator (CLI-RSS I).

[0022] All the problems mentioned above have made it necessary to make an innovation in the relevant technical field as a result.

[0023] BRIEF DESCRIPTION OF THE INVENTION

[0024] The present invention relates to a method to eliminate the above-mentioned disadvantages and bring new advantages to the relevant technical field.An object of the invention is to significantly increase resource efficiency while obtaining the required level of channel resolution to perform beam nulling for CLI mitigation.

[0025] To achieve all the objects mentioned above and that will emerge from the following detailed description, the present invention relates to a method for channel measurement for mitigating cross link interference (CLI) in a system comprising base stations which are capable of communicating using sub-band-full-duplex (SBFD) technology, where said base stations having N number of channel state information (CSI) ports and a central controller for controlling said base stations. Accordingly, characterized in that comprising steps of:

[0026] - determining an initial port group having M number of ports where 0 < M <N;

[0027] - transmitting channel state information reference signal (CSI-RS) by one of a first base station or a second base station to the other using the initial port group;

[0028] - performing, by the other, CLI measurement based on received CSI-RS on the initial port group;

[0029] - accessing, by one of the first base station or the second base station, CLI measurement data; - determining a second port group having K number of ports, where M<K<N and where K is determined based on level of CLI measurement such that K increases when the CLI measurement level is higher and decreases when the CLI measurement level is lower;

[0030] - transmitting channel state information reference signal (CSI-RS) by one of the first base station or the second base station to the other using the second port group;

[0031] - performing, by the other, CSI measurement based on received CSI-RS on the second port group;

[0032] - accessing, by the aggressor base station among the first base station and the second base station, CSI measurement data;

[0033] - by the aggressor base station among the first base station and the second base station performing beam nulling based on CSI measurement data. Thus, reducing resource usage while still maintaining adequate beam-nulling performance.

[0034] A possible embodiment of the invention is characterized in that wherein the first base station is the aggressor base station (110) and the second base station is the victim base station (120); comprising the steps of:

[0035] - transmitting channel state information reference signal (CSI-RS) by the first base station to the second base station using the initial port group;

[0036] - performing, by the second base station, CLI measurement based on received CSI-RS on the initial port group;

[0037] - transmitting, by the second base station, CLI measurement data to the first base station;- accessing, by the first base station, CLI measurement data;

[0038] - determining a second port group having K number of ports, where M<K<N and where K is determined based on level of CLI measurement such that K increases when CLI measurement level is higher and decreases when CLI measurement level is lower;

[0039] - transmitting channel state information reference signal (CSI-RS) by the first base station to the second base station using the second port group;

[0040] - performing, by the second base station, CSI measurement based on received CSI-RS on the second port group;

[0041] - transmitting, by the second base station, CSI measurement data to the first base station; - accessing, by the first base station CSI measurement data;

[0042] - by the first base station performing beam nulling based on CSI measurement data.

[0043] Another possible embodiment of the invention is characterized in that wherein the first base station is the aggressor base station and the second base station is the victim base station; comprising the steps of:

[0044] - transmitting channel state information reference signal (CSI-RS) by the second base station to the first base station using the initial port group;

[0045] - performing, by the first base station, CLI measurement based on received CSI-RS on the initial port group;

[0046] - accessing, by the first base station, CLI measurement data;

[0047] - determining a second port group having K number of ports, where M<K<N and where K is determined based on level of CLI measurement such that K increases when CLI measurement level is higher and decreases when CLI measurement level is lower;

[0048] - transmitting channel state information reference signal (CSI-RS) by the second base station to the first base station using the second port group;

[0049] - performing, by the first base station, CSI measurement based on received CSI-RS on the second port group;

[0050] - accessing, by the first base station CSI measurement data;

[0051] - by the first base station performing beam nulling based on CSI measurement data.

[0052] Another possible embodiment of the invention is characterized in that when there are more than two neighboring base stations in the system, comprising the steps of;

[0053] - transmitting orthogonally CSI-RS by each base station;- each base station configures CSI-RS in its own resources, corresponding to the CSI-RS transmitted by other base stations (100) allowing each base station to measure the CLI caused by the other base stations (100) on their CSI-RS resources;

[0054] - by each base station identifying itself as a victim or an aggressor base station based on CLI measurements on CSI-RS resources or by a central controller identifying base stations as a victim or an aggressor base station based on CLI measurements on CSI-RS resources.

[0055] BRIEF DESCRIPTION OF THE DRAWINGS

[0056] Figure 1 is a drawing illustrating an embodiment of the system where an aggressor base station transmits CSI-RS to a victim base station using initial port group.

[0057] Figure 2 is a drawing illustrating an embodiment of the system where an aggressor base station transmits CSI-RS to a victim base station using second port group where measured CLI is relatively high.

[0058] Figure 3 is a drawing illustrating an embodiment of the system where an aggressor base station transmits CSI-RS to a victim base station using second port group where measured CLI is relatively low.

[0059] Figure 4-5-6 and 7 illustrating an embodiment of the system where more than two base stations are provided.

[0060] REFERENCE NUMBERS GIVEN IN THE FIGURE

[0061] 10 Central controller

[0062] 100 Base station

[0063] 110 Aggressor base station

[0064] 120 Victim base station

[0065] DETAILED DESCRIPTION OF THE INVENTION

[0066] In this detailed description, the subject matter is explained with references to examples without forming any restrictive effect only in order to make the subject more understandable.Referring to figures 1-7, the system which performs the method comprises plurality of base stations (100) and a central controller (10) for controlling base stations (100). The base stations (100) are capable of communicating using sub-band-full-duplex (SBFD) technology. Base station (100) comprises antenna arrays for beamforming, transceiver modules capable of simultaneous transmission and reception over different sub-bands, filtering and duplexing components to separate and isolate transmit and receive signals, and signal processing units for beamforming algorithms and interference cancellation.

[0067] Base stations (100) comprises ports. Ports refer to the signal paths or interfaces — such as RF chains or logical antenna ports — that connect the base station's (100) signal processing units to its antenna elements; the number of these ports determines how fine the resolution of CSI is obtained. This directly affects the beamforming efficiency and the system's ability to optimize signal quality and spatial multiplexing.

[0068] The subject matter method comprises two stages. At the first stage cross link interference (CLI) is measured using an initial number of ports then at the second stage CSI measurement is realized with an updated number of ports based on level of the interference (increasing as the interference level increases or decreasing as the interference level decreases). Then, beam nulling is performed by a base station (100) defined as the aggressor.

[0069] The method comprises the steps of:

[0070] - determining an initial port group having M number of ports where 0 < M <N;

[0071] - transmitting channel state information reference signal (CSI-RS) by one of a first base station or a second base station to the other using the initial port group (figure 1);

[0072] - performing, by the other, CLI measurement based on received CSI-RS on the initial port group;

[0073] - accessing, by one of the first base station or the second base station, CLI measurement data; - determining a second port group having K number of ports, where M<K<N and where K is determined based on level of CLI measurement such that K increases when CLI measurement level is higher and decreases when CLI measurement level is lower (figure 2 - figure 3); - transmitting channel state information reference signal (CSI-RS) by one of the first base station or the second base station to the other using the second port group;

[0074] - performing, by the other, CSI measurement based on received CSI-RS on the second port group;

[0075] - accessing, by the aggressor base station (110) among the first base station and the second base station, CSI measurement data;- by the aggressor base station (110) among the first base station and the second base station performing beam nulling based on CSI measurement data.

[0076] CLI measurement may be CLI-Received Signal Strength Indicator (CLI-RSSI) or CLI-Reference Signal Received Power (CLI-RSRP).

[0077] Referring to figure 1 , in an embodiment of the invention, the first base station is the aggressor base station (110) and the second base station is a victim base station (120). First base station transmits CSI-RS to the second base station and measurements are realized by second base station and reported back to the first base station. First base station transmits Non-Zero Power (NZP) CSI-RS in the initial step.

[0078] In another possible embodiment, first base station is the aggressor base station (110) and the second base station is a victim base station (120). Second base station transmits CSI-RS to the first base station and measurements are realized by the first base station. For instance, initial port group may have only one port. This measurement is done with minimal resource usage, ensuring efficiency at the start of the process. When a high CLI level is detected, the victim base station (120) transmits NZP CSI-RS with a higher number of ports (e.g., 32 ports) based on the CLI measurement. The aggressor base station (110) then uses this CSI-RS to measure the channel with higher resolution. This allows the aggressor gNB to perform more effective beam-nulling to mitigate interference.

[0079] The configuration of NZP and ZP CSI-RS resources can be centrally managed by the central controller (10).

[0080] Referring to figure 4, In a possible embodiment there may be more than two neighboring base stations (100). Each base station (100) transmits orthogonal NZP CSI-RS signals, allowing them to avoid interference with each other's reference signal transmissions. Alongside transmitting its own NZP CSI-RS, each base station (100) also configures ZP CSI-RS in its own resources, corresponding to the NZP CSI-RS transmitted by other base stations (100). This allows each base station (100) to measure the CLI caused by the other base stations (100) on their ZP CSI-RS resources.

[0081] The configuration of these NZP and ZP CSI-RS resources can be centrally managed by a network or master node. In this embodiment all base stations (100) simultaneously transmit their NZP CSI-RS while measuring CLI from other base stations’ (100) signals using their ZPCSI-RS. This step provides each base station (100) with an understanding of the interference caused by the transmissions of other base stations (100).

[0082] Referring to figure 5, after measuring the CLI levels from the other base stations (100), for instance a first base station may identify itself as a victim and label a second base station and a third base station as aggressors based on the measured interference. With the CLI levels from second base station and the third base station now available, first base station can request the aggressor base station (110) to adjust its CSI-RS configurations by increasing or reducing the number of CSI-RS ports. Alternatively, based on the request from first base station, second base station and third base station may specify their CSI-RS configurations by using their own CLI measurements.

[0083] The aggressor base stations (110) then configure their NZP CSI-RS ports based on this request, adjusting the number of ports to optimize beam-nulling. They transmit the updated NZP CSI-RS using the adjusted number of ports. Then, first base station, acting as the victim, measures the channel from the aggressor base stations (110) on its ZP CSI-RS. It then provides channel feedback to the aggressor base station (110) based on these measurements.

[0084] Finally, second base station and the third base station, using the channel feedback from first base station, perform beam-nulling to reduce their interference on the first base station. This entire process allows for dynamic adaptation based on real-time CLI measurements and effectively reduces interference between multiple base stations (100), improving system performance.

[0085] Referring to figure 6, once the CLI levels have been measured and the appropriate number of CSI-RS ports has been determined for each aggressor base station (110), the victim base station (120) takes the next step by transmitting NZP CSI-RS specifically targeted to each aggressor base station (110). These reference signals are transmitted with the adjusted number of ports, allowing the aggressor base stations (110) to measure the channel.

[0086] To ensure accurate measurements, the aggressor base stations (110) have ZP CSI-RS configured specifically to match the NZP CSI-RS transmitted by the victim base station (120). The aggressor base stations (110) can then use the received NZP CSI-RS to measure the channel characteristics between them and the victim base station (120). Based on this channel information, the aggressor base stations (110) can perform beam-nulling to reduce the interference they are causing to the victim base stations (120).This approach enables a dynamic response to the interference by configuring the number of CSI-RS ports according to the CLI level and allowing the aggressor base stations (110) to adapt their transmission based on accurate channel measurements provided by the victim base station (120).

[0087] In this embodiment initial step involves each base station (100) measuring CLI levels for the other base stations (100). This measurement is done using CSI-RS with a low number of ports to minimize resource usage or any other downlink reference signal (DL RS) such as demodulation reference signal (DMRS). By using these signals, each base station (100) can determine which base stations (100) are causing interference and the extent of that interference. For example,

[0088] After CLI levels have been detected and collected by all base station (100) pairs, the CSI-RS configurations can be adjusted. Referring to figure 7, this process may be centrally managed by the central controller (10). Each base station (100) can report its desired reference signal configuration for the other base stations (100), based on the measured interference. The network or master node can then make decisions about how the CSI-RS resources should be configured for each base station (100), balancing the needs of all participants.

[0089] In embodiment setup, any base station (100) can act as an aggressor or a victim, depending on the situation and the interference levels. Based on the decisions made by the central controller (10), the number of CSI-RS ports for each base station (100) is adjusted, and the CSI-RS is transmitted. Each base station (100) uses the updated CSI-RS configuration to measure the channel more precisely and can then perform interference mitigation techniques like beam-nulling.

[0090] The scope of protection of the invention is specified in the attached claims and cannot be limited to those explained for sampling purposes in this detailed description. It is evident that a person skilled in the art may exhibit similar embodiments in light of the above-mentioned facts without drifting apart from the main theme of the invention.

Claims

CLAIMS1. A method for channel measurement for mitigating cross link interference (CLI) in a system comprising base stations (100) which are capable of communicating using sub-band-full-duplex (SBFD) technology, where said base stations (100) having N number of channel state information (CSI) ports and a central controller (10) for controlling said base stations (100) characterized in that comprising steps of:- determining an initial port group having M number of ports where 0 < M <N;- transmitting channel state information reference signal (CSI-RS) by one of a first base station or a second base station to the other using the initial port group;- performing, by the other, CLI measurement based on received CSI-RS on the initial port group;- accessing, by one of the first base station or the second base station, CLI measurement data; - determining a second port group having K number of ports, where M<K<N and where K is determined based on level of CLI measurement such that K increases when CLI measurement level is higher and decreases when CLI measurement level is lower;- transmitting channel state information reference signal (CSI-RS) by one of the first base station or the second base station to the other using the second port group;- performing, by the other, CSI measurement based on received CSI-RS on the second port group;- accessing, by the aggressor base station (110) among the first base station and the second base station, CSI measurement data;- by the aggressor base station (110) among the first base station and the second base station performing beam nulling based on CSI measurement data.

2. The method according to claim 1 , characterized in that wherein the first base station is the aggressor base station (110) and the second base station is the victim base station (120); comprising the steps of:- transmitting channel state information reference signal (CSI-RS) by the first base station to the second base station using the initial port group;- performing, by the second base station, CLI measurement based on received CSI-RS on the initial port group;- transmitting, by the second base station, CLI measurement data to the first base station; - accessing, by the first base station, CLI measurement data;- determining a second port group having K number of ports, where M<K<N and where K is determined based on level of CLI measurement such that K increases when CLI measurement level is higher and decreases when CLI measurement level is lower;- transmitting channel state information reference signal (CSI-RS) by the first base station to the second base station using the second port group;- performing, by the second base station, CSI measurement based on received CSI-RS on the second port group;- transmitting, by the second base station, CSI measurement data to the first base station; - accessing, by the first base station CSI measurement data;- by the first base station performing beam nulling based on CSI measurement data.

3. The method according to claim 1 , characterized in that wherein the first base station is the aggressor base station (110) and the second base station is the victim base station (120); comprising the steps of:- transmitting channel state information reference signal (CSI-RS) by the second base station to the first base station using the initial port group;- performing, by the first base station, CLI measurement based on received CSI-RS on the initial port group;- accessing, by the first base station, CLI measurement data;- determining a second port group having K number of ports, where M<K<N and where K is determined based on level of CLI measurement such that K increases when CLI measurement level is higher and decreases when CLI measurement level is lower;- transmitting channel state information reference signal (CSI-RS) by the second base station to the first base station using the second port group;- performing, by the first base station, CSI measurement based on received CSI-RS on the second port group;- accessing, by the first base station CSI measurement data;- by the first base station performing beam nulling based on CSI measurement data.

4. The method according to claim 1, characterized in that when there are more than two neighboring base stations in the system, comprising the steps of;- transmitting orthogonally CSI-RS by each base station;- each base station (100) configures CSI-RS in its own resources, corresponding to the CSI-RS transmitted by other base stations (100) allowing each base station to measure the CLI caused by the other base stations (100) on their CSI-RS resources;- by each base station (100) identifying itself as a victim or an aggressor base station based on CLI measurements on CSI-RS resources or by a central controller (10) identifying base stations as a victim or an aggressor base station based on CLI measurements on CSI-RS resources.

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