基於上行鏈路 OFDMA 的隨機訪問 (UORA) 是 IEEE 802.11ax 中引入並在新定義的 IEEE 802.11be 標準中採用的一項功能，在密集環境中存在利用率低的問題。幾個建議被提出來提高 IEEE 802.11be 中 UORA 的效率。其中，一家公司將空數據包反饋報告輪詢（NFRP）觸發幀的概念與UORA相結合，提出了一種RA-NFRP來實現蜂窩網絡中常用的四步隨機訪問過程。作者提出了 RA-NFRP 的兩種選擇，並基於過度簡化的槽化 ALOHA 模型展示了它們的效率。在本論文中，我們提出了一個通用模型，可用於分析支持大規模物聯網服務的 IEEE 802.11be 系統的兩步和四步隨機訪問過程。所提出的模型考慮了 RA-NFRP 和 UORA 兩個選項的實施限制。因此，它可以用來顯示兩步（即 UORA）和四步隨機訪問過程（即 RA-NFRP 的兩個選項）在各種環境下的優缺點。進行了仿真以驗證所提出的分析模型的有效性。接著確認UORA及RA-NFRP兩種選項在不同環境下的合適操作區。

The uplink OFDMA-based random access (UORA), a feature introduced in IEEE 802.11ax and adopted in the newly defined IEEE 802.11be standard, suffers from a low utilization problem in dense environments. Several proposals were proposed to enhance the efficiency of UORA in IEEE 802.11be. Among them, one company combined the concept of the null data packet feedback report poll (NFRP) trigger frame and the UORA to propose an RA-NFRP to realize the four-step random access procedure commonly used in cellular networks.
The authors presented two options of RA-NFRP and demonstrated their efficiency based on an over-simplified slotted ALOHA model. In this thesis,
we proposed a general model that can be used to analyze the two-step and four-step random access procedures for IEEE 802.11be systems supporting massive IoT services.
The proposed model considers the implementation constraints of the two options of RA-NFRP and UORA. Thus, it can be used to show the pros and cons of the two-step (i.e., UORA) and the four-step random access procedures (i.e., two options of RA-NFRP) under various environments. Simulations were conducted to verify the effectiveness of the proposed analytical model. The suitable operation regions of UORA and the two options of RA-NFRP in different environments were then identified.

[1] E. Khorov, I. Levitsky, and I. F. Akyildiz, “Current status and directions of IEEE 802.11be, the future Wi-Fi 7,” IEEE Access, vol. 8, pp. 88 664–88 688, 2020.
[2] Wi-Fi 6E: Wi-Fi in the 6 GHz band, The Wi-Fi Alliance, 2021.
[3] “IEEE Standard for Information Technology–Telecommunications and Information Exchange between Systems Local and Metropolitan Area Networks–Specific Requirements Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications Amendment 1: Enhancements for High-Efficiency WLAN,” IEEE Std 802.11ax-2021 (Amendment to IEEE Std 802.11-2020), pp. 1–767, 2021.
[4] S. Kim, H. Park, J. Kim, K. Ryu, and H. Cho, “11ax PAR verification through OFDMA,” 2016.
[5] K. Kosek Szott and K. Domino, “An efficient backoff procedure for IEEE 802.11ax uplink OFDMAbased random access,” IEEE Access, vol. 10, pp. 8855–8863, 2022.
[6] “Draft Standard for Information Technology–Telecommunications and Information Exchange between Systems Local and Metropolitan Area Networks–Specific Requirements Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications Amendment 8: Enhancements for extremely high throughput (EHT),” IEEE P802.11be-2022/D2.1, pp. 1–767, 2022.
[7] J. Bai, H. Fang, J. Suh, O. Aboul Magd, E. Au, and X. Wang, “Adaptive uplink OFDMA random
access grouping scheme for ultra-dense networks in IEEE 802.11ax,” in 2018 IEEE/CIC International Conference on Communications in China (ICCC), 2018, pp. 34–39.
[8] D. Xie, J. Zhang, A. Tang, and X. Wang, “Multi-dimensional busy-tone arbitration for OFDMA random access in IEEE 802.11ax,” IEEE Transactions on Wireless Communications, vol. 19, no. 6, pp. 4080–4094, 2020.
[9] L. Lanante, C. Ghosh, and S. Roy, “Hybrid OFDMA random access with resource unit sensing for next-gen 802.11ax WLANs,” IEEE Transactions on Mobile Computing, vol. 20, no. 12, pp. 3338–3350, 2021.
[10] W. J. Lee, W. Shin, J. A. Ruiz de Azua, L. F. Capon, H. Park, and J. H. Kim, “NOMA-based uplink OFDMA collision reduction in 802.11ax networks,” in 2021 International Conference on Information and Communication Technology Convergence (ICTC), 2021, pp. 212–214.
[11] J. Sedin, S. Max, L. Wilhelmsson, C. Pettersson, and R. Di Taranto, “Random access using capture,”2021.
[12] S. Baron, P. Nezou, and P. Viger, “Random access for 11be,” 2021.
[13] P. Viger, S. Baron, and P. Nezou, “Random access for short feedback procedures in wireless networks,”UK GB2584885A, 2019.
[14] J. Kim, G. Lee, S. Kim, T. Taleb, S. Choi, and S. Bahk, “Two-step random access for 5G system: latest trends and challenges,” IEEE Network, vol. 35, no. 1, pp. 273–279, 2021.
[15] H. Yang, D. J. Deng, and K. C. Chen, “Performance analysis of IEEE 802.11ax UL OFDMA-based random access mechanism,” in GLOBECOM 2017 - 2017 IEEE Global Communications Conference, 2017, pp. 1–6.
[16] R. G. Cheng, C. M. Yang, B. S. Firmansyah, and R. Harwahyu, “Uplink OFDMA-based random access mechanism with bursty arrivals for IEEE 802.11ax systems,” IEEE Networking Letters, vol. 4, no. 1, pp. 34–38, 2022.
[17] S. Y. Huang, C. W. Lin, L. C. Huang, and R. G. Cheng, “Grouping-based uplink ofdma random access for ieee 802.11be system.”
[18] J. R. Huang and R. G. Cheng, “Performance of uplink ofdma-based random access (uora) with packet reservation.”
[19] C. H. Wei, R. G. Cheng, and S. L. Tsao, “Modeling and estimation of one-shot random access for finite-user multichannel slotted ALOHA systems,” IEEE Communications Letters, vol. 16, no. 8, pp. 1196–1199, 2012.
[20] C. H. Wei, G. Bianchi, and R. G. Cheng, “Modeling and analysis of random access channels with bursty arrivals in OFDMA wireless networks,” IEEE Transactions on Wireless Communications, vol. 14, no. 4, pp. 1940–1953, 2015.
[21] Z. Li, L. Tian, Y. Yin, and W. Cao, “On contention-based 2-step random access procedure,” in 2020 International Conference on Wireless Communications and Signal Processing (WCSP), 2020, pp. 771–776.