In 6G network with extreme MIMO a potential misalignment exists between UE-centric rank selection and the internal link adaptation state of the gNB, specifically the outer loop link adaptation offset. Since this misalignment leads to inefficient resource utilization and degraded quality-of-service, it must be avoided. We present a novel adaptive rank selection algorithm that allows the gNB to dynamically influence the rank selection of the UE to bridge this gap. Our solution incorporates a gNB-configurable rank selection margin, α, which imposes a minimum required throughput gain to justify selecting a higher rank. This margin constrains the greedy rank selection by the UE, and helps aligning it with the link adaptation state of gNB. System-level results confirm that our method outperforms the conventional greedy baseline, boosting XR capacity from 14 to 15 users per cell and delivering consistent UE throughput gains across all measured percentiles for best-effort file transfer traffic.

While extended reality (XR) applications are expected to be one of the cornerstone use cases for the 6G mobile communications system, the actual performance and capacity results for XR in 6G are yet to be rigorously established. This paper bridges this gap by developing a detailed system model for a candidate 6G network and using it for evaluating the performance of XR applications through extensive system-level simulations. We investigate three enablers for the 6G networks: new spectrum utilization, extreme multiple-input multiple-output (MIMO) methods, and advanced radio resource management (RRM) techniques. Our results demonstrate a 3 times XR capacity improvement over 5G baselines at 3.5 GHz using enhanced CSI feedback framework and advanced RRM techniques. Furthermore, by utilizing the new 7 GHz upper-mid band spectrum with extreme MIMO and a larger bandwidth, XR capacity can be further improved by approximately a factor of 10, supporting more than 50 users per cell. These findings provide the first quantitative evidence of 6G’s potential for XR and offer a crucial baseline for future 6G development.

Sub-band full duplex (SBFD) is a novel duplexing scheme that enables concurrent uplink (UL) and downlink (DL) transmission on non-overlapping frequency resources within an unpaired carrier. Earlier studies indicated that to unleash the full potential gain of SBFD, the radio frame configuration must be adapted to traffic load condition and network characteristics. This paper proposes a centralized deep reinforcement learning framework, based on soft actor-critic for discrete action setting (SAC-Discrete), with a modified prioritized replay mechanism, to train a model that dynamically determines the best frame configuration based on cells' buffer statuses. This method aims to maximize the geometric mean of user throughput, ensuring fairness across all users in both link directions. Simulation results demonstrate that our proposed solution improves UL performance by maximizing the geometric mean of user throughput under varying offered loads.

The introduction of sub-band full duplex (SBFD) with simultaneous downlink and uplink transmissions has the potential to improve the uplink performance as compared to traditional static time division duplexing (TDD) with sparse uplink resources. However, SBFD benefits are limited by cross-link interferences caused by the simultaneous uplink and downlink transmissions. This paper proposes to dynamically reduce the 5G base station (gNB) transmission power during SBFD slots to mitigate the gNB self- and gNB-to-gNB-interferences, as well as corresponding link adaptation enhancements to unleash the full potential of such techniques. The SBFD system-level performance is evaluated with different levels of power reduction under varied offered load conditions for urban macro (UMa) and dense urban (DU) environments. Results indicate that for the DU, applying a 10 dB gNB transmit power reduction for SBFD slots leads to a 187% improvement of cell-edge user uplink throughput under high offered load (compared to static TDD). For UMa, at most 4 dB SBFD gNB transmit power reduction is recommended for improving the cell-edge uplink throughput while still ensuring downlink acceptable data rates.

This paper presents a performance evaluation of sub-band full duplex (SBFD) for an indoor office environment. SBFD has the potential to improve packet latency by utilizing non-overlapping uplink and downlink frequency resources simultaneously. To evaluate the SBFD performance, system- level simulations are conducted with different packet sizes and varied offered load conditions. The simulation results reveal a clear dependence of SBFD performance on the packet size of the traffic model. For small packet cases, up to 55% improvement of the average packet latency in the uplink and up to 24% in the downlink is achieved in SBFD, as compared to static TDD, when a 90 dB ratio of self-interference mitigation (RSI) is ensured. For large packet cases, including an uplink-only slot in the SBFD frame structure has the potential to improve the uplink latency, even though this adjustment leads to increased downlink latency. Furthermore, simulation results indicate that the has a noticeable impact on the SBFD performance in the downlink.

5G New Radio (NR) technology continues evolving with Release 17 bringing new features to enable Ultra-Reliable and Low-Latency Communications (URLLC) in unlicensed spectrum. New Radio-Unlicensed (NR-U) enhancements will allow further expansion of 5G application in private networks sectors in enterprise and industry. In unlicensed controlled environment conditions, a URLLC performance comparable to NR with TDD in the licensed spectrum can be achieved. However, it is still questionable whether the unlicensed spectrum can leverage URLLC in environments with uncontrolled interference from other radio access technologies, such as Wi-Fi. In this case, multi-link techniques are needed to mitigate the impact of unplanned interference on the latency and reliability performance. In this work, we study the combined use of licensed and unlicensed spectrum with the target of improving the overall system capacity. The paper shows that cross-carrier retransmission techniques are necessary to meet the strict latency and reliability targets such as 5 ms with 99.999 % reliability. The system-level simulation results exhibit that, combining licensed and unlicensed spectrum, a URLLC capacity improvement of approximately 45 % is achieved as compared to operation in licensed spectrum only, even in presence of sporadic Wi-Fi interference.

Unlicensed spectrum operation mandates the performance of channel access mechanisms to ensure the absence of transmissions by other unlicensed radio access technologies. Packets are prone to be impacted by these mechanisms as transmissions might be delayed. In this paper, we first analyse the impact of unexpected and sporadic IEEE 802.11ax interference on a New Radio-Unlicensed (NR-U) deployment in an industrial environment. Given the need for improvement in such scenarios, frequency diversity techniques are proposed to fulfil tight latency-reliability requirements and combat the impact of 802.11ax interference. A multi-channel NR-U system in which, at least, one of the channels is free of IEEE 802.11ax interference is studied. The paper shows that multi-channel techniques with a lack of flexibility in the channel selection exhibit modest benefits in scenarios with the presence of sporadic interference. A scheme with flexible channel selection is proposed and verified as the preferred option for stringent latency and reliability applications.

Communications over the unlicensed spectrum are susceptible to be delayed by mandatory channel access mechanisms. Based on the need for improving the latency-reliability performance of New Radio-Unlicensed for supporting new usecases, such as industrial applications, different types of channel access are evaluated in this paper. By using asynchronous and demand-driven channel access, it is shown that approximately 50% of the delay experienced by a downlink packet is due to listen before talk (LBT). Furthermore, UEs might be blocked by an unsuccessful uplink LBT losing the opportunity to transmit their previously scheduled data. As an alternative, synchronous channel access is evaluated. By using a coordinated LBT among the nodes, the channel access delay is reduced to a constant value. However, UEs can still be blocked when initiating their uplink transmissions due to neighbours transmissions. Motivated by this fact, an approach in which a central node is in charge of the frame selection is proposed. Therefore, all the nodes in the system are coordinated in both the channel access and the frame configuration. In this case, a latency reduction of 70% as compared to the previously mentioned alternatives is achieved at high loads and 99.9999% reliability.

In this paper, the performance impact of several high-reliable and low-latency communications technology enablers in the unlicensed spectrum for standalone operation is evaluated. Firstly, a comparison between MulteFire (MF) and New Radio-Unlicensed (NR-U) is established. It is shown that higher sub-carrier spacings and shorter processing times provide clear latency reduction benefits. Additionally, different transmission time intervals (TTI) durations are evaluated. Shortening the TTI duration decreases the latency by a factor of 5.75 at 99.99% reliability and reduces the uplink Listen Before Talk (LBT) blocking probability by 18%. The possibility of having multiple switching points during the frame is also evaluated. It is concluded that having multiple switching points provides a latency reduction mainly due to the reduction of the number of channel accesses and the reduced gaps within the frame. A time-diversity technique to cope with high uplink LBT blocking probability is also evaluated. By combining the aforementioned features, a latency reduction factor of 31 is achieved when optimized NR-U and MulteFire performances are compared.

In this paper, we study the performance of ultra- reliable low-latency communication (URLLC) for cellular standalone systems in unlicensed bands. Our focus is on the 5 GHz band, adopting a system model in coherence with the MulteFire standard, which essentially is a variant of LTE (Long Term Evolution) for unlicensed band operation. We show that especially the mandatory Listen Before Talk (LBT) procedure suppose a challenge for achieving low latency communication. Our theoretical analysis indicated that the impact of the LBT procedure prior to downlink transmissions can be significant, taking values of 3-25 ms for the considered offered load levels. Furthermore, our advanced dynamic system-level simulations show that the time spent performing LBT often accounts for 18\%-42\% of the packet latency budget, depending on the considered outage level and offered traffic. Therefore LBT represents a major challenge for achieving URLLC-alike performance in unlicensed spectrum.