Dmitry Bankov

Real-time applications require strict bounds on latency quantiles, which the conventional channel access method of Wi-Fi, EDCA, often fails to guarantee. The upcoming IEEE 802.11bn (Wi-Fi 8) amendment addresses this problem with Prioritized EDCA (P-EDCA). After several unsuccessful EDCA attempts, a P-EDCA station transmits a short Defer Signal frame that silences lower-priority contenders and then completes its transmission. The amendment specifies default P-EDCA parameters, but it remains unclear how to configure them for a given load and how they affect coexisting traffic. This paper considers a network in which a P-EDCA station coexists with a saturated traffic source and a station serving real-time traffic via EDCA. An analytical model estimates the throughput loss of the saturated traffic and the increase in the average latency of the EDCA real-time traffic caused by P-EDCA. Based on this model, an algorithm is proposed that selects the number of EDCA attempts before a station switches to prioritized P-EDCA access. The algorithm minimizes the 0.999-quantile of P-EDCA traffic latency while keeping both degradations within 1%. The model closely matches discrete-event simulation. Simulation results show that, in the considered scenario, neither EDCA nor P-EDCA with the default number of EDCA attempts keeps the 0.999-quantile of latency below 10 ms, whereas the tuned P-EDCA does so at low arrival rates and roughly halves this quantile relative to EDCA. The default number of EDCA attempts is optimal only at arrival rates that lie outside the intended use case of P-EDCA.

Wi-Fi is evolving to support new areas such as extended reality, Industrial Internet of Things, and environments with numerous devices. Unlike previous generations that aimed to maximize peak and user-perceived throughput, Wi-Fi 8 (also known as IEEE 802.11bn Ultra High Reliability) intends to make Wi-Fi operation more reliable, i.e., to improve performance across the full range of scenarios, particularly in worst-case conditions. Specifically, 802.11bn is striving to increase throughput at various signal to interference and noise ratio levels, diminish the 95th percentile of latency, decrease packet losses, and reduce power consumption. To attain these ambitions, Wi-Fi 8 is going to introduce a series of groundbreaking mechanisms, including distributed-tone resource units, unequal modulations, prioritized and non-primary channel access, advanced roaming features, multi-AP coordination, and so on. We present the current status of Wi-Fi 8 development with an emphasis on the targets and enabling technologies. This tutorial also discusses open research directions that require the development of new intelligent methods and algorithms.

In a number of LoRaWAN sensor network scenarios, it is required to deliver data with a given reliability and with minimal sensor energy consumption. To improve the reliability of data delivery in a LoRaWAN network, data can be transmitted in two modes: (i) with acknowledgments and retries of undelivered data, or (ii) without acknowledgments and with unconditional retries. In this paper, we develop a model of a LoRaWAN network in which some devices transmit data in the first mode and some in the second mode. The model makes it possible to find the dependence of packet loss probability, sensor energy consumption, and base station duty cycle on the traffic intensity. Based on the modeling results, we propose an algorithm for selecting the fraction of sensors transmitting data with confirmation and the number of repetitions for sensors transmitting data with unconditional repetitions that minimizes energy consumption, fulfills the limit on the duty cycle, and ensures the desired reliability of data transmission.

To ensure reliable, low-latency packet delivery required by real-time applications (RTAs), such as industrial applications, it is planned to introduce the preemptive channel access method in a new amendment to the Wi-Fi 8 standard. This access method is novel for Wi-Fi networks, so the actual task is to tune its parameters to fulfill the requirements for the quality of service of RTA traffic and increase the network throughput. In order to solve this problem, we have developed a model of a Wi-Fi 8 network, which helps to find how the RTA frame delay quantile and the efficiency of channel utilization by the network access point depend on the RTA traffic intensity and parameters of the method. We explicitly find the parameters of the method that provide the required delay and reliability of RTA traffic delivery while maximizing the channel utilization efficiency.

С каждым годом в сетях Wi-Fi увеличивается доля трафика приложений реального времени (англ.: real time application, RTA), предъявляющих строгие требования к задержкам и надежности доставки данных. Для удовлетворения данных требований часто используется резервирование канальных ресурсов с последующим их выделением для передач RTA-кадров. Однако в случае нерегулярного RTA-трафика часть зарезервированных канальных ресурсов может оказаться неиспользованной при его отсутствии, что приводит к снижению общей пропускной способности сети. Для решения этой проблемы был разработан механизм пробуждения по расписанию с ограниченным резервированием (англ.: restricted target wake time, R-TWT), запрещающий всем станциям передачу в заданный момент времени R-TWT. Механизм R-TWT одновременно позволяет RTA-трафику в момент R-TWT быстрее получить доступ к каналу и не запрещает его другим станциям после момента R-TWT. В статье представлена аналитическая модель сети Wi-Fi, при помощи которой были получены зависимости пропускной способности пользователей от параметров передачи и периода резервирования R-TWT.

We study a most recent mechanism for reserving channel resources to deliver high-priority traffic in Wi-Fi networks, Restricted Target Wake Time (R-TWT). We develop an analytical model of a Wi-Fi network using the R-TWT mechanism, which allows us to estimate the throughput of users transmitting low-priority traffic, depending on the R-TWT reservation period, restrictions on the size of transmitted frames and modulation and coding schemes used. The model shows that the dependence of the user throughput on the R-TWT period is not monotonic, and a slight increase in the R-TWT period can lead to both an increase and a significant drop in the user throughput.