## 1 Introduction  
There has been tremendous growth in the deployment of 802.11-based wireless local area networks (WLANs), especially for use in distributed emergency applications (e.g., disaster recovery) [1, 2, 3, 4]. These emergency applications require a strict quality of service (QoS) guarantee with the provision of in-channel preemption (i.e., channel access priority on arrival) for their high-priority emergency traffic.  
The original IEEE 802.11 standard [5] does not prioritise real-time traffic and uses a Stop-and-Wait ARQ mechanism, causing significant overhead from channel sensing and immediate ACK transmissions. To address these issues, IEEE 802.11e was introduced to improve QoS for real-time applications like voice and video by defining four access categories (ACs) for differentiated channel access. However, conventional EDCA only offers relative differentiation, lacking support for emergency traffic and failing to guarantee QoS under heavy loads [6, 7]. Additionally, IEEE 802.11e introduced TXOP with BlockAck schemes, which enhance throughput [8] but can lead to resequencing delays at the receiver [9].  
To overcome the limitations of EDCA (providing in-channel preemption and assuring strict QoS guarantee), we previously proposed a multi-preemptive EDCA (MP-EDCA) in WLANs [10]. The proposed scheme supports emergency traffic and provides in-channel preemption. However, MP-EDCA does not offer a QoS guarantee for life-saving emergency traffic in WLANs. To address the performance issues of MP-EDCA, in this paper, we propose a frame aggregation with a simple block acknowledgement (FASBA) mechanism [10]. The proposed FASBA provides assurance of service delivery, enhances network throughput, reduces MAC transmission overhead, and ultimately accommodates several life-saving emergency nodes in high loads. Better system performance is achieved by aggregating the frames with a simple two-bit block acknowledgement. We implemented both MP-EDCA [10] and FASBA schemes in the Riverbed Modeler simulator for performance evaluation and comparison purposes. We contributed code (written in C++) by modifying Riverbed simulation process models to create new emergency communication nodes required for system simulation.  
The main contributions of this study are summarised as follows:  
* We propose a frame aggregation with a simple block acknowledgement (FASBA) protocol to provide a strict QoS guarantee to life-saving emergency traffic in high-load WLANs. To this end, we develop an analytical model using the Markov chain considering saturated load, retry limits, and channel conditions. We derive throughput and mean packet delays mathematically to estimate the system performance.
* We develop a simulation model using Riverbed Modeler and MATLAB simulator to validate system performance.
* We implement new life-saving emergency nodes (in C++) and the corresponding process models in the Riverbed Modeler simulation environment to study the performance of FASBA and to compare it with the existing MP-EDCA.This is a significant piece of work contributing towards the implementation of emergency traffic in WLANs. The system performance is also validated by MATLAB2024a-based simulation.  
The rest of this paper is organised as follows. The related work is presented in Section 2. The proposed FASBA approach is described in Section 3. Section 4 presents an analytical model for FASBA. The system performance is evaluated in Section 5. The results are discussed in Section 6. Finally, the paper is concluded in Section 7.