Wi-Fi OBSS PD & Transmission Control Simulator for Dense Networks

Overview & Motivation

To address the challenges of severe interference and spectrum contention in ultra-dense Wi-Fi deployments, the IEEE 802.11ax (Wi-Fi 6) standard introduced Overlapping Basic Service Set Preamble Detection (OBSS PD) Spatial Reuse (SR). OBSS PD allows an Access Point (AP) or Station (STA) to initiate a concurrent transmission if the detected inter-BSS preamble power falls below a configurable threshold, provided its transmit power is proportionally reduced to protect ongoing transmissions.

However, extensive standardization evaluations and empirical studies demonstrate that standalone OBSS PD often fails to deliver the expected throughput gains, and can even severely degrade network performance. When deployed without joint cross-layer transmission control, standard OBSS PD encounters fundamental operational bottlenecks:

  • Carrier Sense Desynchronization: Asymmetric clear channel assessment (CCA-ED) energy detection thresholds cause receiving nodes to lose mid-packet preambles, triggering severe mutual packet collisions.
  • Contention Window Inflation: Packet losses induced by concurrent OBSS transmissions trigger legacy exponential backoff escalation, penalizing spatial reuse nodes for channel conditions outside their control.
  • Rate Control Blindness: Conventional rate adaptation algorithms confuse inter-BSS interference drops with channel path loss, causing inappropriate fallback to suboptimal Modulation and Coding Schemes (MCS).
  • Cell-Edge Client Starvation: Clients located near cell boundaries experience elevated interference and reduced transmit power margins, suffering catastrophic throughput collapse while centrally located clients monopolize channel resources.

To eliminate these inefficiencies, we developed a cross-layer Transmission Control Algorithm (TCA) and implemented high-fidelity simulation modules within the ns-3 discrete-event network simulator.

Key Features of the Simulation Framework

  • Carrier Sense Synchronization Fix: Dynamically coordinates energy detection to guarantee mutual detection across overlapping BSSs and eliminate premature preamble drops.
  • Robust Contention Window (CW) Adaptation: Decouples OBSS BlockAck timeouts from intra-BSS collision backoff, preventing destructive contention window growth during concurrent spatial reuse transmissions.
  • BSS-Color-Aware Thompson Sampling Rate Control: Disentangles intra-BSS channel path loss from intermittent inter-BSS interference, preserving high MCS configurations and preventing rate collapse.
  • TXOP Duration Restrictions: Enforces strict transmission opportunity duration limits during concurrent transmissions to preserve channel access fairness and prevent spatial monopolization.
  • Opportunistic Cross-Layer Multi-User Scheduling: Integrates Proportional Fair (PF), Airtime Fair, and FIFO schedulers with per-STA queue management, dynamic A-MPDU frame aggregation, and multi-user diversity.

To get more information, please read the paper below.

E. Khorov, A. Krotov, and V. Loginov, “Lessons Learned on Throughput Optimization in Dense Wi-Fi Networks with OBSS PD Spatial Reuse,” submitted to Elsevier Computer Networks, 2026.

Please cite this paper if you use the simulation tool.