## 1 Introduction  
While ensuring a stable and consistent user experience, the fifth-generation (5G) communication network provides ultra-high speed, low delay, ultra-reliability, and low-cost service quality, creating unprecedented new opportunities and convenience for society and the economy. Therefore, the large-scale commercialization of 5G networks is a current research hotspot in communication technology [1]. In the field of wireless technology, massive Multiple-Input Multiple-Output (MIMO), millimeter-Wave (mmWave) technology, carrier aggregation technology, new multi-access access, and other technologies are important means to enhance the performance of 5G [2]. In particular, massive MIMO systems can handle large network throughput and support a large number of client connections, which is expected to radically improve the capacity limitations of base stations and enable individual base stations to talk to more devices, thus driving the development of the Internet of Everything (IoE) [3]. MmWave technology, which is higher than 4G radio frequency, can provide ultra-high speed and ultra-high spectral efficiency while reducing network connectivity costs [4, 5]. These emerging 5G technologies can deliver a variety of extreme services more flexibly and reliably, supporting applications in various vertical industries to enable the IoE. Even with the rapid development of wireless network technologies, IEEE 802.11 protocol-based network technology, as a reliable and economic information network construction method, is still considered a promising technology affecting the future communication industry and is also an important component of 5G and future wireless local area networks (WLANs). The transmission of emergency information and data with ultra-high reliability and low delay is one of the challenges faced by WLANs. Therefore, when numerous real-time emergency traffic is loaded on WLANs, it is necessary to provide it with a higher quality of service, which makes us think first of reducing the delay, so analyzing this parameter is a vital step to solving the problem [6]. There have been many works on IEEE 802.11 network performance analysis and modeling [2; 3; 4; 5; 6], but few works simultaneously consider the following factors to analyze the service delay of the medium access control (MAC) layer, such as the initial-carrier-sensing (ICS) procedure, the backoff counter freezing, up-to-date standard parameters, and computational complexity, etc. In [7], [PERSON] proposed a representative 2-D Markov model to analyze the saturated throughput of the IEEE 802.11 distribution coordination function (DCF). Afterward, based on the model of [7], [PERSON] et al. In [8], the authors introduced the initial state before the node entered the backoff procedure and analyzed the throughput and delay of the 802.11 DCF. In [9], the authors compared the proposed 2-D Markov model with a model that considered continuous packet transmission without activating the backoff procedure and demonstrated that the Markov model is more accurate in predicting the performance of the 802.11 protocol, obtaining the relationship between the data rate of the transmitted packets and the packet delay, packet discard time, and throughput. In [10], the state of the channel when the buffer is idle is described, and the authors proposed a 2-D Markov model to analyze the throughput performance of the IEEE 802.11 MAC layer under non-ideal conditions. In [11], the authors proposed a system model based on the 802.11 MAC protocol applicable to multiple contentions and proved that the stochastic evolution of different station backoff states converges to deterministic evolution in the limit state. The authors in [12] analyzed an accurate MAC delay model, which considered the backoff counter decrementing time. [PERSON] et al. [13] proposed a service delay model to track the service delay behavior of 802.11 networks. The authors in [14] studied the fair issue of access to the channel by vehicles with different speeds and its impact on the network throughput.