[Paper Review] MAC Protocols for IEEE 802.11ax: Avoiding Collisions on Dense Networks

Rafael Araujo da Silva, Michele Nogueira|arXiv (Cornell University)|Nov 20, 2016

Network Time Synchronization Technologies2 references3 citations

TL;DR

This paper analyzes MAC protocol enhancements for IEEE 802.11ax to mitigate collisions in dense Wi-Fi networks. It reviews CSMA/CA, OFDMA, and advanced techniques like In-Band Full-Duplex (IBFD) and frame aggregation, demonstrating up to 300% throughput gains in simulations, and outlines future trends for next-generation Wi-Fi efficiency and scalability in high-density environments.

ABSTRACT

Wireless networks have become the main form of Internet access. Statistics show that the global mobile Internet penetration should exceed 70\% until 2019. Wi-Fi is an important player in this change. Founded on IEEE 802.11, this technology has a crucial impact in how we share broadband access both in domestic and corporate networks. However, recent works have indicated performance issues in Wi-Fi networks, mainly when they have been deployed without planning and under high user density. Hence, different collision avoidance techniques and Medium Access Control protocols have been designed in order to improve Wi-Fi performance. Analyzing the collision problem, this work strengthens the claims found in the literature about the low Wi-Fi performance under dense scenarios. Then, in particular, this article overviews the MAC protocols used in the IEEE 802.11 standard and discusses solutions to mitigate collisions. Finally, it contributes presenting future trends in MAC protocols. This assists in foreseeing expected improvements for the next generation of Wi-Fi devices.

Motivation & Objective

• Address the critical performance degradation in Wi-Fi networks under high user density due to increased collisions.
• Revisit and strengthen claims about low Wi-Fi performance in dense scenarios, particularly under uncontrolled deployments.
• Provide a focused overview of MAC protocol improvements in IEEE 802.11ax, emphasizing collision avoidance mechanisms.
• Analyze emerging techniques such as OFDMA, IBFD, frame aggregation, and dynamic CCA threshold adaptation for enhanced spectrum efficiency.
• Identify future research directions and trends in MAC protocols to guide development of next-generation Wi-Fi systems.

Proposed method

• Survey and analyze existing IEEE 802.11 MAC protocols, particularly CSMA/CA, and their limitations in dense environments.
• Evaluate the integration of OFDMA in 802.11ax to allow simultaneous transmission to multiple stations, reducing contention and improving fairness.
• Examine In-Band Full-Duplex (IBFD) techniques that allow simultaneous transmission and reception on the same frequency, using Signal Interference Cancellation (SIC) to suppress self-interference.
• Assess frame aggregation methods (MSDU/MPDU) to reduce MAC header overhead and contention time, improving efficiency for bursty traffic.
• Investigate dynamic CCA threshold adaptation to adjust carrier sensing range, minimizing collision domains while preserving spatial reuse.
• Propose and evaluate signaling-based backoff mechanisms using OFDM subcarriers to reduce contention time and avoid collisions, requiring SIC support.

Experimental results

Research questions

• RQ1 How do current MAC protocols like CSMA/CA fail under high-density Wi-Fi deployments, and what are the root causes of performance degradation?
• RQ2 To what extent can OFDMA improve channel access efficiency and fairness in dense 802.11ax networks compared to legacy contention-based schemes?
• RQ3 What are the key challenges and design requirements for integrating In-Band Full-Duplex (IBFD) into 802.11ax MAC protocols?
• RQ4 How can frame aggregation and adaptive block length selection improve throughput and reduce overhead in high-density scenarios?
• RQ5 What role do dynamic CCA threshold adjustments and signaling-based backoff mechanisms play in optimizing MAC performance under varying interference conditions?

Key findings

• OFDMA in 802.11ax enables simultaneous transmission to multiple stations, significantly reducing contention and improving fairness in dense networks.
• In-Band Full-Duplex (IBFD) techniques, enabled by Signal Interference Cancellation (SIC), can yield up to 300% throughput enhancement in proposed 802.11ax scenarios.
• Frame aggregation reduces MAC header overhead and contention time, improving efficiency—especially when combined with adaptive block length selection.
• Dynamic CCA threshold adaptation can reduce collision domains by adjusting receiver sensitivity, but requires careful tuning to balance spatial reuse and interference.
• Signaling-based backoff mechanisms using OFDM subcarriers can reduce contention time and avoid collisions, though they require SIC-capable hardware.
• The integration of centralized coordination (e.g., via Access Controllers) and beacon sharing among neighboring BSS can reduce control frame overhead and improve network scalability in managed dense deployments.