Wi-Fi was originally designed to provide broadband wireless Internet access for devices which generate rather heavy streams. And Wi-Fi succeeded. The coming revolution of the Internet of Things with myriads of autonomous devices and machine type communications (MTC) traffic raises a question: can the Wi-Fi success story be repeated in the area of MTC? Started in 2010, IEEE 802.11 Task Group ah (TGah) has developed a draft amendment to the IEEE 802.11 standard, adapting Wi-Fi for MTC requirements. The performance of novel channel access enhancements in MTC scenarios can hardly be studied with models from Bianchi's clan, which typically assume that traffic load does not change with time. This paper contributes with a pioneer analytical approach to study Wi-Fi-based MTC, which can be used to investigate and customize many mechanisms developed by TGah.
In @cite_4 , the authors consider another protocol, IEEE 802.15.4 that uses similar to EDCA channel access. However, in .15.4 a STA senses the channel only when the backoff ends. Although both papers present performance evaluation in the scenario similar to the one described in this paper, the authors assume that collision probability is constant, while in reality, both varying contention window and the number of STAs having packets to transmit make collision probability change with time.
@cite_4
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This paper proposes analytical expressions of end-to-end throughput for IEEE 802.11e Enhanced Distributed Channel Access (EDCA) wireless string-topology multi-hop net- works. For obtaining the IEEE 802.11e EDCA performance, internal collisions between Access Categories (ACs) in a node, frame collisions with external nodes, and frame-existence probabil- ities of buffers at each AC are expressed as functions of EDCA access parameters. Therefore, it is possible to obtain the effects of the EDCA access parameters to Quality of Service (QoS) support in the EDCA. It is possible to obtain the end-to-end throughput at any offered load with respect to each AC because the buffer states can be expressed according to ACs. The obtained analytical expressions are verified by showing the quantitative agreements with sim- ulation results. Analytical modeling of the 802.11e enhanced distributed channel access (EDCA) mechanism is today a fairly mature research area, considering the very large number of papers that have appeared in the literature. However, most work in this area models the EDCA operation through per-slot statistics, namely probability of transmission and collisions referred to "slots." In so doing, they still share a methodology originally proposed for the 802.11 Distributed Coordination Function (DCF), although they do extend it by considering differentiated transmission collision probabilities over different slots.We aim to show that it is possible to devise 802.11e models that do not rely on per-slot statistics. To this purpose, we introduce and describe a novel modeling methodology that does not use per-slot transmission collision probabilities, but relies on the fixed-point computation of the whole (residual) backoff counter distribution occurring after a generic transmission attempt. The proposed approach achieves high accuracy in describing the channel access operations, not only in terms of throughput and delay performance, but also in terms of low-level performance metrics. The IEEE 802.11 standard for wireless local area networks (WLANs) employs a medium access control (MAC), called distributed coordination function (DCF), which is based on carrier sense multiple access with collision avoidance (CSMA CA). The collision avoidance mechanism utilizes the random backoff prior to each frame transmission attempt. The random nature of the backoff reduces the collision probability, but cannot completely eliminate collisions. It is known that the throughput performance of the 802.11 WLAN is significantly compromised as the number of stations increases. In this paper, we propose a novel distributed reservation-based MAC protocol, called early backoff announcement (EBA), which is backward compatible with the legacy DCF. Under EBA, a station announces its future backoff information in terms of the number of backoff slots via the MAC header of its frame being transmitted. All the stations receiving the information avoid collisions by excluding the same backoff duration when selecting their future backoff value. Through extensive simulations, EBA is found to achieve a significant increase in the throughput performance as well as a higher degree of fairness compared to the 802.11 DCF. Carrier sense multiple access with collision avoidance (CSHA CA) has been the access protocol of choice for IEEE 802.11-based WLANs. In addition to channel sensing before transmission, the probability of a collision in these WLANs is typically reduced by the application of a binary exponential backoff (BEB) algorithm that randomizes the selection of the time slot in which a given station transmits. In a system without adaptive modulation and coding (AHC), the reduction in spectral efficiency caused by BEB is outweighed by the reduction in the number of collisions. In contrast, in systems using the ubiquitous auto rate fallback (ARF) AHC algorithm, which is unable to distinguish a collision from an erroneous transmission, the remaining collisions induce a dramatic drop in system performance. This degradation is caused by the utilization of low-rate transmission modes even when the channel conditions would permit the use of much higher-rate modes. In an attempt to further reduce the number of collisions, a variant of CSHA CA, called enhanced collision avoidance (CSHA E2CA), has been recently proposed. In this paper, a model approach to the performance evaluation of both BEB-based CSHA CA and CSHA E2CA, used in conjunction with ARF, is presented and validated. Results reveal the synergistic properties of the E2CA and ARF combination, as demonstrated by the superior goodput performance when compared against other strategies.