H. Murat Gursu

This work provides a comprehensive examination of Layer 1/Layer 2-triggered mobility (LTM) enhancements introduced in 3rd Generation Partnership Project (3GPP) Release (Rel.) 19, extending the foundational framework established in Rel. 18. The key advancement is the extension of LTM to inter-central unit (CU) scenarios, significantly broadening its applicability across diverse network deployments. This extension necessitated comprehensive standardization work addressing security key management, dual connectivity (DC) operations, and channel state information (CSI) resource coordination mechanisms. The measurement capabilities were improved by incorporating channel state information reference signal (CSI-RS)-based layer 1 (L1)-reference signal received power (RSRP) measurements and implementing event-triggered reporting to reduce signaling overhead. Additionally, conditional LTM enhances mobility robustness through autonomous user equipment (UE)-triggered cell switching, while early CSI acquisition procedures optimize post-handover throughput performance. The paper elaborates on the technical implementation of inter-CU LTM, covering network signaling architectures, security framework adaptations, and DC integration aspects. Furthermore, we explore Rel. 20 developments focusing on LTM integration with Carrier Aggregation and adaptive measurement configuration mechanisms, alongside initial considerations for 6G mobility evolution. To emphasize the importance of reducing the handover interruption time, our system-level simulation analysis quantifies the transport layer benefits of reduced interruption times, demonstrating that reducing the interruption duration in LTM to approximately 20 ms delivers significant transmission control protocol (TCP) throughput gains over conventional handover’s 100 ms interruption, especially when TCP re-transmission timeout (RTO) timers are set at 100 ms or below.

5-th generation (5G) has brought mobility robustness and interruption time reduction enhancements to mobility procedures. Advanced beam management procedures were also introduced in 5G, including beam-based mobility. In this paper, we summarize the procedure that fuses beam-based mobility with conventional mobility procedures, namely L1/L2-triggered mobility (LTM). We first provide the Release 18 LTM procedural summary, followed by a detailed explanation of the introduced technical enhancements and an analysis of their expected benefits. Through system-level simulations, we show that having the LTM as the mobility procedure brings two major improvements, namely interruption time reduction and mobility robustness. The lower interruption time is mainly the result of configuring the network and the user equipment (UE) well in advance of the handover, early configuration decoding, early synchronization, and triggering the handover with a lightweight medium access control (MAC) command. The mobility robustness increase is the result of the triggering of the handover based on the layer 1 (L1) measurements, which are more sensitive to channel degradation. This in turn further reduces the interruption time as the radio link failure and reestablishment are avoided. On the other hand, LTM can suffer from excess unnecessary handovers, where the UE is handed over back and forth between two or three cells. Besides, the increased measurement reporting of the L1 measurements can cause additional overhead. Finally, we give a short insight on the on-going Release 19 work that addresses some the known LTM issues.

In this paper, we study binary tree-algorithms that exploit a combination of multi-packet reception (MPR) and successive interference cancellation (SIC), which so far has not been considered in the literature. Specifically, we assume that the receiver is capable of successfully decoding any collision of up to and including K concurrent packet transmissions and can perform SIC along the tree. We show a number of novel results for this type of tree algorithms. We first derive the basic performance parameters, which are the expected length of the collision resolution interval and the throughput normalized with K, conditioned on the number of contending users. We then analyze their asymptotic behaviour, identifying an oscillatory component that amplifies as K increases. In the next step, we derive the maximum stable throughput (MST) for the gated and windowed access assuming Poisson arrivals. We show that for windowed access, the bound on MST normalized with K increases with K . Finally, we discuss practical issues related to implementation of such scheme, as well as compare it to slotted ALOHA-based schemes that exploit both K -MPR and SIC.

In the above article, the authors propose $d$ -ary SICTA and derive the expected conditional length of the collision resolution interval, optimal splitting probability and the maximum stable throughput (MST) for $d \geq 2$ under stationary ergodic packet arrivals. In this correction, we show that the premise of the analysis for $d > 2$ and consequentially the results presented for $d > 2$ do not hold.

In this paper, we perform a thorough analysis of tree-algorithms with multi-packet reception (MPR) and successive interference cancellation (SIC), showing a number of novel results. We first derive the basic performance parameters, which are the expected length of the collision resolution interval and the normalized throughput, conditioned on the number of contending users. We then study their asymptotic behaviour, identifying an oscillatory component that amplifies with the increase in MPR. In the next step, we derive the throughput for the gated and windowed access, assuming Poisson arrivals. We show that for windowed access, the bound on maximum stable normalized throughput increases with the increase in MPR. his implies that investing in advanced physical capabilities, i.e., MPR and SIC pays off from the perspective of the medium access control algorithm.

5G radio access network (RAN) slicing envisions a solution to flexibly deploy heterogeneous services as slices sharing the same infrastructure. However, this level of flexibility renders slice isolation challenging, mainly due to the stochastic nature of wireless resources. In the state-of-the-art, RAN slicing algorithm’s efficiency with respect to slice isolation is related to the ability of meeting individual slice requirements. However, mostly an aggregated slice performance guarantee is considered instead of per user guarantees. Hence, state-of-the-art approaches might not always provide the satisfaction of all users within a slice. Indeed, our results demonstrate that if user requirements within a slice are not included in the RAN slicing algorithm, the per user quality-of-service (QoS) may not be fulfilled. In this paper, we investigate the definition of slice isolation as the ability to satisfy individual users’ throughput within slices, in a frequency selective, multi-cell wireless scenario with focus on maximizing slices’ throughput. Our problem is tackled with a Lyapunov optimization approach, which proves to always achieve slice isolation. Our results show that our solution does not only achieve 100% user QoS guarantees compared to 50% achieved in the state-of-the-art, but also doubles the throughput with increasing number of BSs.

In this paper, we analyze binary-tree algorithms in a setup in which the receiver can perform multi-packet reception (MPR) of up to and including K packets simultaneously. The analysis addresses both traffic-independent performance as well as performance under Poisson arrivals. For the former case, we show that the throughput, when normalized with respect to the assumed linear increase in resources required to achieve K-MPR capability, tends to the same value that holds for the single-reception setup. However, when coupled with Poisson arrivals in the windowed access scheme, the normalized throughput increases with K, and we present evidence that it asymptotically tends to 1. We also provide performance results for the modified tree algorithm with K-MPR in the clipped access scheme. To the best of our knowledge, this is the first paper that provides an analytical treatment and a number of fundamental insights in the performance of tree-algorithms with MPR.

In this letter, we propose a short-frame (SF) length approximation for the packet loss rate of Irregular Repetition Slotted Aloha (IRSA) particularly suitable for very short frames up to 50 slots, motivated by low-latency targeting IIoT applications. Our analysis is based on the Error Floor (EF) approximation ef2018. We extend the approximation through a recursive evaluation of inter-related stopping sets. Extended approximation enables user degree distribution optimization with respect to Packet Loss Rate performance for short-frames. For a scenario with 10 slots and 5 users, the degree distribution optimized by SF approximation results in a 20% lower Packet Loss Rate compared to the one optimized by EF approximation.

Age-of-information (AoI) is a metric quantifying information freshness at the receiver. It captures the delay together with packet loss and packet generation rate. However, the existing literature focuses on average or peak AoI and neglects the complete distribution. In this work, we consider a N-hop network with time-invariant packet loss probabilities on each link. We derive closed form equations for the probability mass function of AoI. We verify our findings with simulations. Our results show that the performance indicators considered in the literature such as average or peak AoI may give misleading insights into the real AoI performance.