Distributed Coordination Function Mode Research Articles

Velocity-Adaptive Access Scheme for MEC-Assisted Platooning Networks: Access Fairness Via Data Freshness

Platooning strategy is an important part of autonomous driving technology. Due to the limited resource of autonomous vehicles in platoons, mobile edge computing (MEC) is usually used to assist vehicles in platoons to obtain useful information, increasing its safety. Specifically, vehicles usually adopt the IEEE 802.11 distributed coordination function (DCF) mechanism to transmit large amount of data to the base station (BS) through vehicle-to-infrastructure (V2I) communications, where the useful information can be extracted by the edge server connected to the BS and then sent back to the vehicles to make correct decisions in time. However, vehicles may be moving on different lanes with different velocities, which incurs the unfair access due to the characteristics of platoons, i.e., vehicles on different lanes transmit different amount of data to the BS when they pass through the coverage of the BS, which also results in the different amount of useful information received by various vehicles. Moreover, age of information (AoI) is an important performance metric to measure the freshness of the data. Large average age of data implies not receiving the useful information in time. It is necessary to design an access scheme to jointly optimize the fairness and data freshness. In this paper, we formulate a joint optimization problem in the MEC-assisted V2I networks and present a multi-objective optimization scheme to solve the problem through adjusting the minimum contention window under the IEEE 802.11 DCF mode according to the velocities of vehicles. The effectiveness of the scheme has been demonstrated by simulation.

Performance Analysis of Heterogeneous Systems Ieee 802.11 and Ieee 802.16 Using Spectrum Sharing Mechanism

After the advent of cellular standards for mobile wireless voice telephony and data transfer, IEEE 802.11 and IEEE 802.16 standards evolved for wireless broadband data transfer. The IEEE 802.11 replaced the wired LAN and IEEE 802.16 was to wireless point-to-point provide broadband data transfer. IEEE 802.11 operates in 2.4 GHz and 5 GHz bands whereas IEEE 802.11, which was initially designed to operate on a licensed band, later switched to a 2-11 GHz band. However, both these standards used a 5 GHz unlicensed band for transmission causing the possible overlap of channels. The designed protocols fairly allow the sharing on an ad-hoc basis. IEEE 802.11 operated in distributed coordination mode using Distributed Coordination Function (DCF) and point coordinated mode using a dedicated coordinator node called Point Coordination Function (PCF). However, DCF mode allows spectrum sharing for multiple users. Both standards were not designed for coexistence and thereby they may cause interference to each other, degrading their performance. Mechanisms can be designed at various layers such as MAC or PHY to enable the coexistence with desired QoS. In this paper, a performance analysis of the impact of possible interference between IEEE 802.11 and IEEE 802.16 devices is presented. Therefore, this paper presents the approaches for allowing a reliable operation between IEEE 802.16 and IEEE 802.11 when both are sharing unlicensed spectrum 5GHz. In this paper, we propose advancements to the MAC of IEEE 802.16 Base Station (BS) where IEEE 802.11 frame transmissions are not required by an IEEE 802.16 system. Here, Co-existence between IEEE 802.11 and IEEE 802.16 is permitted without any exchange of data between both standards, and also it provides quality of service for both systems operating at unlicensed spectrum 5GHz.

AP-based CW Synchronization Scheme in IEEE 802.11 WLANs

In this paper, an optimal CW (Contention Window) synchronization scheme is proposed in IEEE 802.11 WLANs. IEEE 802.11 WLANs operates with DCF (Distributed Coordination Function) mode for the MAC (Medium Access Control). In DCF, CW becomes the minimum CW according to the success of data transmissions and increases exponentially due to the collisions. In this situation, the smaller value of the minimum CW can increase the collision probability because stations have higher opportunity to access the medium. On the other hand, the higher value of the minimum CW will delay the transmission, which can result in the network performance degradation. In IEEE 802.11, since the base minimum CW value is a fixed value depending on the hardware or standard, it is difficult to provide the optimal network performance that can be determined by the flexible CW value according to the number of active stations. In addition, the synchronization of optimal CW is required among mobile stations to adapt the network parameters. Especially for the newly joined stations such as moving or turning on stations, they need to adapt the minimum CW value to get the optimal network performance. The shorter the adaptation time is, the better the network performance can maintain. Therefore, in this paper, AP (Access Point) calculates the optimal CW and shares it with mobile stations using beacon and probe response messages for the fast CW synchronization. Extensive simulation results show that the proposed scheme outperforms the previous schemes in terms of the network throughput and adaptation time. Â

Analysis of Optimal Carrier Sensing Range in Wireless Ad Hoc Networks with Order Dependent Capture Capability

IEEE 802.11 wireless ad hoc network performance in distributed coordination function mode is limited by hidden and exposed terminals problem. Request-to-send/clear-to-send based hand shake reduces ...

Optimization of transport capacity in wireless multihop networks

Gamal et al. (IEEE Trans. Inform. Theory 52:2568–2592, 2006) showed that the end-to-end delay is n times the end-to-end throughput under centralized time division multiple access scheduling. In our other work (IEEE Trans. Mobile Computing, in press), it was proved that the relationship between the end-to-end throughput and the end-to-end delay of Gamal et al. still holds under the IEEE 802.11 distributed coordination function (DCF) when the carrier sensing range and the packet generation rate are jointly optimized. The main purpose of this study is to determine whether the result in our other work is achievable when the transmission range is adjusted instead of the carrier sensing range. To this end, we revise the transport capacity by reflecting a queue at each node and optimize the revised transport capacity by jointly controlling the transmission distance and the packet generation rate. Under our system model, it is shown that the end-to-end throughput and the end-to-end delay scale are and , respectively, where n is the number of nodes in the network. That is to say, the result that the end-to-end delay is n times the end-to-end throughput under the DCF mode is also estabilished while jointly optimizing the transmission range and packet generation rate.

Analytical modeling of bidirectional multi‐channel IEEE 802.11 MAC protocols

AbstractThis paper presents an analytical approach to model the bi‐directional multi‐channel IEEE 802.11 MAC protocols (Bi‐MCMAC) for ad hoc networks. Extensive simulation work has been done for the performance evaluation of IEEE 802.11 MAC protocols. Since simulation has several limitations, this work is primarily based on the analytical approach. The objective of this paper is to show analytically the performance advantages of Bi‐MCMAC protocol over the classical IEEE 802.11 MAC protocol. The distributed coordination function (DCF) mode of medium access control (MAC) is considered in the modeling. Two different channel scheduling strategies, namely, random channel selection and fastest channel first selection strategy are also presented in the presence of multiple channels with different transmission rates. M/G/1 queue is used to model the protocols, and stochastic reward nets (SRNs) are employed as a modeling technique as it readily captures the synchronization between events in the DCF mode of access. The average system throughput, mean delay, and server utilization of each MAC protocol are evaluated using the SRN formalism. We also validate our analytical model by comparison with simulation results. The results obtained through the analytical modeling approach illustrate the performance advantages of Bi‐MCMAC protocols with the fastest channel first scheduling strategy over the classical IEEE 802.11 protocol for TCP traffic in wireless ad hoc networks. Copyright © 2010 John Wiley & Sons, Ltd.

Channel Occupancy Time Based TCP Rate Control for Improving Fairness in IEEE 802.11 DCF

In the IEEE 802.11 distributed coordination function (DCF), the basic service set (BSS) suffers from two unfairness issues: 1) performance anomaly and 2) uplink/downlink unfairness. In this paper, to solve these issues, we propose a window control scheme in the Transmission Control Protocol (TCP) for the IEEE 802.11 DCF mode. The proposed scheme is called channel occupancy time based rate control for TCP (COTRC-TCP). COTRC-TCP controls the maximum window size based on the throughput estimated at the TCP layer so that each station can use the wireless channel for equal duration. The throughput estimation is based on the number of active stations and the channel occupancy period used by each station in the BSS, which are monitored at the Medium Access Control (MAC) layer. The proposed scheme forms a cross-layer approach that involves both MAC and transport layers. The performance of COTRC-TCP over multirate IEEE 802.11 DCF is evaluated and compared with that of previous works through extensive simulations. Simulation results show that COTRC-TCP exhibits fairness in terms of channel-occupancy time among the competing stations, which accordingly remedies the unfairness problems. The proposed scheme also improves the transmission efficiency.

Improving IEEE 802.11 power saving mechanism

This paper presents an optimization of the power saving mechanism in the Distributed Coordination Function (DCF) in an Independent Basic Service Set (IBSS) of the IEEE 802.11 standard. In the power saving mode specified for DCF, time is divided into so-called beacon intervals. At the start of each beacon interval, each node in the power saving mode periodically wakes up for a duration called the ATIM Window. Nodes are required to be synchronized to ensure that all nodes wake up at the same time. During the ATIM window, the nodes exchange control packets to determine whether they need to stay awake for the rest of the beacon interval. The size of the ATIM window has a significant impact on energy saving and throughput achieved by the nodes. This paper proposes an adaptive mechanism to dynamically choose a suitable ATIM window size. We also allow the nodes to stay awake for only a fraction of the beacon interval following the ATIM window. On the other hand, the IEEE 802.11 DCF mode requires nodes to stay awake either for the entire beacon interval following the ATIM window or not at all. Simulation results showthat the proposed approach outperforms the IEEE 802.11 power saving mechanism in terms of throughput and the amount of energy consumed.

Performance analysis of IEEE 802.11 DCF with stochastic reward nets

AbstractIn this paper, we present a performance study to evaluate the mean delay and the average system throughput of IEEE 802.11‐based wireless local area networks (WLANs). We consider the distributed co‐ordination function (DCF) mode of medium access control (MAC). Stochastic reward nets (SRNs) are used as a modelling formalism as it readily captures the synchronization between events in the DCF mode of access. We present a SRN‐based analytical model to evaluate the mean delay and the average system throughput of the IEEE 802.11 DCF by considering an on–off traffic model and taking into account the freezing of the back‐off counter due to channel capture by other stations. We also compute the mean delay suffered by a packet in the system using the SRN formulation and by modelling each station as an M/G/1 queue. We validate our analytical model by comparison with simulations. Copyright © 2006 John Wiley & Sons, Ltd.