Contention-based Channel Access Mechanism Research Articles

Throughput analysis of frequency-domain contention under realistic conditions for hyperautomation

ABSTRACT Internet of Things (IoT) has widely been deployed in various industrial fields. To achieve hyperautomation in IoT-based applications, it calls for high-efficient wireless transmission technologies to improve the response speed of IoT nodes. Frequency-domain contention (FDC) is a promising contention-based channel access mechanism to meet this requirement. However, the nature of FDC’s multiple-transmission-multiple-reception and the limit of IoT chip’s synchronization accuracy will lead to carrier frequency offset (CFO) and hence frequent transmission collisions and null transmissions. Considering integer and fractional CFO, this paper theoretically analyzes the FDC throughput and verifies the accuracy of our model via extensive simulations.

Saturated Throughput Analysis of IEEE 802.11ad EDCA For High Data Rate 5G-IoT Applications

The recently developed IEEE 802.11ad (WiGig) standard offers multi-Gbps connectivity for consumer wireless local area networks and operates in the millimeter wave frequency band (around 60 GHz). It supports two different contention-based channel access mechanisms, namely distributed coordination function, which offers fair service for every station, and the enhanced distributed channel Access (EDCA) for offering service differentiation among the stations. In this paper, we study the throughput performance of the IEEE 802.11ad EDCA mechanism under saturated traffic conditions using both analytical and simulation models. A novel five-dimensional Markov chain developed is used for analytically modeling the throughput behavior of the IEEE 802.11ad EDCA in the presence of virtual antenna sectors, high-gain directional beamforming, and presence of contention and contention-free access periods. Using this developed analytical model, the effect of the number of sectors, number of stations, arbitration inter-frame space, packet length, and minimum contention window size on the throughput of the four different access or service categories present in the EDCA under saturated traffic conditions, is investigated. When compared with the simulation outcomes, the proposed analytical model accurately analyzes the network performance by achieving less than 4% error.

Cross-layer design benchmark for throughput maximization with fairness and delay constraints in DCF systems

This paper proposes a cross-layer design for the stations (STAs) in a distributed coordination function (DCF) network. By selecting the modulation scheme, coding scheme, and packet length of each STA in the network, the design aims to maximize the total throughput of all the STAs and satisfy the minimum throughput requirement or delay requirement of each STA, thus addressing the fairness and delay issues. The proposed scheme applies to the system where each STA employs a contention based channel access mechanism, Furthermore, unlike the existing optimization schemes, it takes two important factors, changeable data rate and changeable packet error rate (PER), into consideration. Using an existing Markov chain model to predict the performance of the STAs, we propose an approach that updates the selection of each STA sequentially, thus avoiding the large complexity from the exhaustive search. Many issues are discussed based on the numerical results, including how the approximations in our design affect the processing time and result of the design, how the change of one STA affects the performance of the other STAs, how the minimum throughput constraints affect the fairness and total throughput, how to select these constraints to satisfy the delay requirements, etc.

Stochastic Geometry-Based Modeling and Analysis of Citizens Broadband Radio Service System

In this paper, we model and analyze a cellular network that operates in the licensed band of the 3.5-GHz spectrum and consists of a licensed and an unlicensed operator. Using tools from stochastic geometry, we concretely characterize the performance of this spectrum sharing system. We model the locations of the licensed base stations (BSs) as a homogeneous Poisson point process with protection zones (PZs) around each BS. Since the unlicensed BSs cannot operate within the PZs, their locations are modeled as a Poisson hole process. In addition, we consider carrier sense multiple access with collision avoidance-type contention-based channel access mechanism for the unlicensed BSs. For this setup, we first derive an approximate expression and useful lower bounds for the medium access probability of the serving unlicensed operator BS. Furthermore, by efficiently handling the correlation in the interference powers induced due to correlation in the locations of the licensed and unlicensed BSs, we provide approximate expressions for the coverage probability of a typical user of each operator. Subsequently, we study the effect of different system parameters on area spectral efficiency of the network. To the best of our knowledge, this is the first attempt toward accurate modeling and analysis of a citizens broadband radio service system using tools from stochastic geometry.

Improving Energy Efficiency in Idle Listening of IEEE 802.11 WLANs

This paper aims to improve energy efficiency of IEEE 802.11 wireless local area networks (WLANs) by effectively dealing with idle listening (IL), which is required for channel sensing and is unavoidable in a contention-based channel access mechanism. Firstly, we show that IL is a dominant source of energy drain in WLANs and it cannot be effectively alleviated by the power saving mechanism proposed in the IEEE 802.11 standard. To solve this problem, we propose an energy-efficient mechanism that combines three schemes in a systematic way: downclocking, frame aggregation, and contention window adjustment. The downclocking scheme lets a station remain in a semisleep state when overhearing frames destined to neighbor stations, whereby the station consumes the minimal energy without impairing channel access capability. As well as decreasing the channel access overhead, the frame aggregation scheme prolongs the period of semisleep time. Moreover, by controlling the size of contention window based on the number of stations, the proposed mechanism decreases unnecessary IL time due to collision and retransmission. By deriving an analysis model and performing extensive simulations, we confirm that the proposed mechanism significantly improves the energy efficiency and throughput, by up to 2.8 and 1.8 times, respectively, compared to the conventional power saving mechanisms.

Analytical model of interaction between contention-based and deterministic channel access mechanisms in Wi-Fi Mesh networks

A new analytical model was developed to estimate the degree of mutual influence of the links between the stations of Wi-Fi Mesh networks which use different channel access methods specified by the IEEE 802.11s standard, namely, contention-based channel access mechanism and the deterministic channel access mechanism based on the preliminary reservation of channel resources. The model was used to compare the efficiency of different backoff counting methods proposed in the paper for providing the interaction between two channel access methods. Additionally, the model was also used to analyze the effect of different techniques for arranging the time intervals reserved by means of the deterministic channel access mechanism on the performance of stations using contention-based channel access mechanism.

Effects of Directional Antennas in Ad Hoc Networks with Contentionbased Channel Access Mechanism

Effects of Directional Antennas in Ad Hoc Networks with Contentionbased Channel Access Mechanism

A High Throughput Medium Access Control Implementation Based on IEEE 802.11e Standard

With the growing demand for high-performance multimedia applications over wireless channels, we need to develop a Medium Access Control (MAC) system that supports high throughput and quality of service enhancements. This paper presents the standard analysis, design architecture and design issues leading to the implementation of an IEEE 802.11e based MAC system that supports MAC throughput of over 100Mbps. In order to meet the MAC layer timing constraints, a hardware/software co-design approach is adopted. The proposed MAC architecture is implemented on the Xilinx Virtex-II Pro Field-Programmable Gate Array (FPGA) (XC2VP70-5FF1704C) prototype, and connected to a host computer through an external Universal Serial Bus (USB) interface. The total FPGA resource utilization is 11, 508 out of 33, 088 (34%) available slices. The measured MAC throughput is 100.7Mbps and 109.2Mbps for voice and video access categories, transmitted at a data rate of 260Mbps based on IEEE 802.11n Physical Layer (PHY), using the contention-based hybrid coordination function channel access mechanism.

A Selective Downlink Scheduling Algorithm to Enhance Quality of VOD Services for WAVE Networks

Providing quality-of-service- (QoS-) guaranteed video on demand (VOD) services over wireless access in vehicular environments (WAVEs) is a challenge as WAVE adopts enhanced distributive channel access (EDCA), a contention-based channel access mechanism, for air interface access control. This paper proposes a selective downlink scheduling (SDS) algorithm to enhance the quality of VOD for WAVE networks. According to the importance of video decoding, video packets are categorized into high and low priorities. The categorized packets are put into different queues in roadside units (RSUs) to contend for transmission opportunities. Aiming to improve video playback quality and reduce video playback delay, the proposed SDS algorithm schedules video packets based on their importance, playback deadline, and their real-time parameters of receiving onboard units (OBUs), such as velocity and remaining dwelling time. The effectiveness of SDS algorithm is verified by simulations.

An admission control algorithm for multi-hop 802.11e-based WLANs

Recently, wireless local area network (WLAN) hotspots have been deployed in many areas. The new IEEE 802.11e standard further provides quality of service (QoS) provisioning by grouping the applications into four different access categories. The coverage area of WLANs can be extended by allowing the neighboring mobile devices to relay data to the access points. This concept is known as multi-hop WLANs or wireless mesh networks. Due to the limited network capacity and the contention-based channel access mechanism, admission control is required to regulate the number of simultaneous flows to maintain QoS. The multi-hop extension of WLANs present further challenges for admission control design due to the location-dependent contention in the network. In this paper, we propose an admission control algorithm for multi-hop 802.11e-based WLANs. In our proposed admission control algorithm, we first use a contention graph to model the contention situation in the multi-hop WLAN. It is followed by an estimation of the capacity for each maximal clique in the contention graph. A new flow is admitted if the aggregated traffic load is less than the estimated network capacity. The proposed algorithm supports both stationary and mobile nodes, as well as handoff and new connections. Simulation results show that the proposed algorithm is effective in providing QoS guarantee to the existing voice and video flows while maintaining a good performance for best effort traffic.

Improving QoS and throughput in single- and multihop WLANs through dynamic traffic prioritization

Nowadays, research efforts are being put into the design of effective mechanisms to provide service quality differentiation in IEEE 802.11-based wireless LANs. In this article we analyze the effects of augmenting the contention-based channel access mechanism of IEEE 802.11e through the assignment of dynamic traffic priorities, that adapt to either the application's quality requirements or the network congestion status. The aim is to show the effectiveness and robustness of the proposed dynamic mechanism in a wireless ad hoc network, in both single-hop and multihop scenarios, under variable traffic and network load conditions.

Evaluation of Contention-Based EDCA for IEEE 802.11e Wireless LAN

The legacy IEEE 801.11 doesn’t support QoS streams with priorities. It since causes some QoS demanding applications such as VoIP, Video streaming to be limited in its usefulness. Enhancements have been made to the MAC layer by the new 802.11e standard to support prioritized and parameterized QoS. The work of this paper is to simulate the new scheme and modify the existing OPNET WLAN MAC model to satisfy the 802.1le standard. The modification includes adding four access category queues, AP beacon with EDCA parameters, AC queue switcher and an internal collision handler to evaluate the contention-based channel access mechanism, called enhanced distributed coordination access (EDCA) in the current 802.1le. The performance of those new schemes has been compared with DCF of the 802.11 standard via simulation results. It clearly indicates the IEEE 802.11 EDCA function can effectively provide QoS differentiation.