Distributed Coordination Function Model Research Articles

Impact of LTE’s Periodic Interference on Heterogeneous Wi-Fi Transmissions

The problem of Wi-Fi and LTE coexistence has been significantly debated in the last years, with the emergence of LTE extensions enabling the utilization of unlicensed spectrum for carrier aggregation. Rather than focusing on the problem of resource sharing between the two technologies, in this paper, we study the effects of LTE's structured transmissions on the Wi-Fi random access protocol. We show how the scheduling of periodic LTE transmissions modifies the behavior of 802.11's distributed coordination function (DCF), leading to a degradation of Wi-Fi performance, both in terms of channel utilization efficiency and in terms of channel access fairness. We also discuss the applicability and limitations of a persistent DCF model in analyzing Wi-Fi performance under periodic LTE interference.

Two‐dimensional distributed coordination function model with finite buffer sizes

This study presents an unsaturated two-dimensional (2D) Markov model to analyse the packet collision probability and the throughput performances of the stations (STAs) in a distributed coordination function network. Compared with the previous 2D models, it takes the flexible buffer size of the STA into consideration. Compared with the 3D models, it has the advantage of low complexity by avoiding matrix operations. From the numerical results, the authors explain the approximations used in the analytical models proposed in the common existing literatures, and discuss their effect on the model accuracy.

Distributed Coordination Function Protocol with Unequal Frame Error Rates

This letter provides an analysis of the saturation throughputs of the individual stations (STAs) in a distributed coordination function (DCF) network. Compared with the previous DCF models, our new proposed model is suitable for more general environments where the frame error rates (FERs) are different depending on the transmitting STAs and the numbers of retransmission attempts. Numerical analyses show that FERs significantly affect the STAs' throughputs.

Performance analysis of IEEE 802.11 WLANs with rate adaptation in time-varying fading channels

The IEEE 802.11 supports multiple transmission bit rates by using different modulation and coding schemes. Due to different bit error characteristics and transmission efficiencies of the rates, stations may benefit from an adaptive use of them for a varying channel condition, called rate adaptation. The accuracy of rate adaptation is expected to be highly affected by a time varying nature of typical radio channels due to multipath fading. This paper presents an analytic model of the IEEE distributed coordination function (DCF) with the automatic rate fallback (ARF) rate adaptation algorithm, which is the most widely used one in the 802.11 market, under time-correlated Rayleigh fading. The key idea behind the approach is to exploit the first-order Markovian approximation of Rayleigh fading channels, based on which transmission failure probabilities are obtained depending on the current and previous transmission status. By using those probabilities, the ARF process of a station is modeled as a Markov chain, then, the rate distribution obtained by solving the Markov chain is fed to a DCF model. The proposed DCF model is described in a per-station manner, thus enables the analysis of heterogeneous channel conditions and medium access control (MAC) configurations among stations.

Refinements on IEEE 802.11 Distributed Coordination Function Modeling Approaches

With the popularity of the IEEE 802.11 standards, many analytical saturation throughput studies for the distributed coordination function (DCF) have been reported. In this paper, we outline a number of issues and criticalities raised by previously proposed models. In particular, a careful look at backoff counter decrement rules allows us to conclude that, under saturation conditions, the slot immediately following a successful transmission can be accessed only by the station (STA) that has successfully transmitted in the previous channel access. Moreover, due to the specific acknowledgment (ACK) timeout setting adopted in the standard, the slot immediately following a collision cannot be accessed by any STA. Thus, the hypothesis of uncorrelation between consecutive channel slots and statistical homogeneity is not generally true. We propose a new backoff decrement model that retains the simplicity of traditional DCF models while being able to take into account such a correlation, and we compare the accuracy of our model with that of previously proposed approaches.

A cross-layer approach for WLAN voice capacity planning

This paper presents an analytical approach to determining the maximum number of on/off voice flows that can be supported over a wireless local area network (WLAN), under a quality of service (QoS) constraint the authors consider multiclass distributed coordination function (DCF) based medium access control (MAC) that can provision service differentiation via contention window (CW) differentiation. Each on/off voice flow specifies a stochastic delay bound at the network layer as the QoS requirement. The downlink voice flows are multiplexed at the access point (AP) to alleviate the MAC congestion, where the AP is assigned a smaller CW compared to that of the mobile nodes to guarantee the aggregate downlink throughput. There are six-fold contributions in this paper: 1) a nonsaturated multiclass DCF model is developed; 2) a cross-layer framework is proposed, which integrates the network-layer queueing analysis with the multiclass DCF MAC modeling; 3) the channel busyness ratio control is included in the framework to guarantee the analysis accuracy; 4) the framework is exploited for statistical multiplexing gain analysis, network capacity planning, contention window optimization, and voice traffic rate design; 5) a head-of-line outage dropping (HOD) scheme is integrated with the AP traffic multiplexing to further improve the MAC channel utilization; 6) performance of the proposed cross-layer analysis and the associated applications are validated by extensive computer simulations.