Unsaturated Traffic Conditions Research Articles

Unsaturated Throughput Analysis of IEEE 802.11 DCF Under η − μ Fading Channel

This letter investigates the throughput performance of the IEEE 802.11 DCF protocol in unsaturated traffic conditions, taking into account the signal capture with incoherent addition of interfering signals, and channel fading following the η-μ model. A set of numerical results on the performance of the protocol is presented. The results show the adjustment flexibility of the proposed channel model and establishes the parameter μ as the one responsible for the coarse adjustment of the channel, while the parameter η defines the fine adjustment.

Improving Performance of Ieee 802.11 by a Dynamic Control Backoff Algorithm Under Unsaturated Traffic Loads

The IEEE 802.11 backoff algorithm is very important for controlling system throughput over contentionbased wireless networks. For this reason, there are many studies on wireless network performance focus on developing backoff algorithms. However, most existing models are based on saturated traffic loads, which are not a real representation of actual network conditions. In this paper, a dynamic control backoff time algorithm is proposed to enhance both delay and throughput performance of the IEEE 802.11 distributed coordination function. This algorithm considers the distinction between high and low traffic loads in order to deal with unsaturated traffic load conditions. In particular, the equilibrium point analysis model is used to represent the algorithm under various traffic load conditions. Results of extensive simulation experiments illustrate that the proposed algorithm yields better performance throughput and a better average transmission packet delay than related algorithms.

Modelling and performance analysis of dynamic contention window scheme for periodic broadcast in vehicularad hocnetworks

This study proposes an analytical model and an effective scheme for the periodic broadcast on the control channel in vehicular ad hoc networks (VANETs). An improved Markov model for analysing the performance of the periodic broadcast in VANETs is established. Compared with the traditional two-dimensional Markov chain models, the improvement of our proposed model is achieved by the considerations of the unsaturated traffic conditions with the deterministic message generation at each node, modelled by a discrete-time D/M/1 queue and the control mechanism of freezing the backoff-time counter. In adapting to the change of the vehicle densities, the authors propose to use the dynamic contention window (DCW), instead of the fixed contention window (CW), for the broadcast in the IEEE 802.11p medium access control in VANETs. For a certain vehicle density, a best CW size is chosen to achieve a more effective broadcast. Simulation results show that the proposed DCW-based broadcast performs better than the traditional fixed-CW-size broadcast in terms of the packet collision probability. The results also validate our proposed Markov model and its performance improvement than the scheme without the consideration of freezing the backoff-time counter.

Grouping-Based MAC Protocols for EV Charging Data Transmission in Smart Metering Network

The next-generation advanced metering infrastructure, with the aid of two-way smart meters, is expected to support advanced functions such as remote reading and control and demand response. In this paper, we thus focus on the design of a smart metering network (SMN) for a future scenario where data from residences/customer premises are dominated by electric vehicle charging traffic. Therefore, the well-suited multiple access control (MAC) protocol design for such event-driven data is an emerging research area. However, because the number of smart meters (communication nodes) involved in such a single SMN is much larger than those in today's local area networks, the traditional random access MAC protocol is unlikely to perform well. In order to solve this problem, we propose two grouping-based MAC protocols, namely, TDMA-DCF and group leader DCF-TDMA schemes, in this paper. These two schemes are directed at 802.11-type networks operating at frequencies below 1 GHz, which has been adopted by a new IEEE 802.11ah standardization task group. We also conduct the comprehensive throughput and delay analysis on these schemes for unsaturated traffic conditions and hidden node events. The numerical results show that these two grouping-based MAC protocols significantly outperform the traditional random access protocol DCF in a densely populated network with large coverage such as SMN.

The Optimal Spectrum Sensing Time for Maximizing Throughput of 802.11-Based MAC Protocol for Cognitive Radio Networks Under Unsaturated Traffic Conditions

Cognitive radio has attracted considerable attention as an enabling technology for addressing the problem of radio frequency shortages. In cognitive radio networks (CRNs), secondary users (SUs) are allowed to opportunistically utilize the licensed spectrum bands of primary users (PUs) when these bands are temporarily unused. Thus, SUs should monitor the licensed spectrum bands to detect any PU signal. According to the sensing outcomes, SUs should vacate the spectrum bands or may use them. Generally, the spectrum sensing accuracy depends on the sensing time which influences the overall throughput of SUs. That is, there is a fundamental tradeoff between the spectrum sensing time and the achievable throughput of SUs. To determine the optimal sensing time and improve the throughput of SUs, considerable efforts have been expended under the saturated traffic and ideal channel assumptions. However, these assumptions are hardly valid in practical CRNs. In this paper, we provide the framework of an 802.11-based medium access control for CRNs, and we analyze this framework to find the optimal spectrum sensing time under the saturated and unsaturated traffic condition. Through simulation, the proposed analytic model is verified and the fundamental problem of the sensing-throughput tradeoff for CRNs is investigated.

The Study in Diamond Interchange Traffic Organization

The diamond interchange is one of the common forms of road intersection. The design of most of the existing diamond interchanges is based on unsaturated traffic conditions, and transit operation shows its unique properties when traffic tends to reach saturation. In view of this, we analyzed the traffic organization of diamond interchange, studied the improvement of scheme and focused on the import and export of massive diamond interchange traffic organization. VISSIM software was used to simulate the adjustment effect of import and export of the massive in saturated traffic conditions with the specific parameters such as average delay time, average queue length and the times of the average parking. Import and export traffic organization before and after adjustment was also evaluated based on entropy of the congestion of intersection to make objectively assessment more effective.

Throughput and delay analysis of network coded ALOHA in wireless networks

Abstract The purpose of this article is to analyze the impact of network coding in wireless networks. We consider a network coded ALOHA that performs bi-directional network coding over the ALOHA MAC protocol in a star topology network. The transmission probabilities of each outer node and the center node, and the target signal-to-interference-plus-noise ratio (SINR) are jointly optimized to achieve the maximum throughput of coded ALOHA. We analyze and compare the optimal performance of slotted and coded ALOHA. Under the unsaturated traffic condition at the center node, we derive practical throughput and delay, considering the network coding opportunity and the maximum queue length of the center node. Under the saturated traffic condition, we obtain a throughput upper bound of coded ALOHA to judge the ideal gain of network coding. The impact of asymmetric topology is evaluated with simulations.

Performance analysis and comparison of burst transmission schemes in unsaturated 802.11e WLANs

AbstractContention free bursting (CFB) and block acknowledgement (BACK) are two innovative burst transmission schemes specified in the IEEE 802.11e standard for reducing the contention overheads and further improving the channel utilization of wireless local area networks (WLANs). Existing studies on performance analysis of the CFB and BACK schemes have been primarily focused on the system throughput and have not taken into account the realistic factors, such as unsaturated traffic loads and finite buffer capacity. To fill this gap, this paper proposes a new and comprehensive analytical model for evaluating the Quality‐of‐Service (QoS) metrics including throughput, end‐to‐end delay, and frame loss probability of both burst transmission schemes under unsaturated traffic conditions. The proposed model is validated through extensive simulation experiments and then is used to conduct performance analysis and comparison of the burst transmission schemes under various working conditions. The analytical results reveal that (1) both CFB and BACK schemes can substantially improve the QoS performance; (2) BACK scheme outperforms the CFB scheme when the transmission opportunity (TXOP) limit exceeds a threshold; (3) the analytical model can be used to identify the optimal configuration of system parameters for the burst transmission schemes subject to QoS constraints. Copyright © 2010 John Wiley & Sons, Ltd.

Analysis of the MAC protocol in low rate wireless personal area networks with bursty ON–OFF traffic

SUMMARYSupported by the IEEE 802.15.4 standard, embedded sensor networks have become popular and been widely deployed in recent years. The IEEE 802.15.4 medium access control (MAC) protocol is uniquely designed to meet the desirable requirements of the low end‐to‐end delay, low packet loss, and low power consumption in the low rate wireless personal areas networks (LR‐WPANs). This paper develops an analytical model to quantify the key performance metrics of the MAC protocol in LR‐WPANs with bursty ON–OFF traffic. This study fills the gap in the literature by removing the assumptions of saturated traffic or nonbursty unsaturated traffic conditions, which are unable to capture the characteristics of bursty multimedia traffic in sensor networks. This analytical model can be used to derive the QoS performance metrics in terms of throughput and total delay. The accuracy of the model is verified through NS‐2 (http://www.isi.edu/nsnam/ns/) simulation experiments. This model is adopted to investigate the performance of the MAC protocol in LR‐WPANs under various traffic patterns, different loads, and various numbers of stations. Numerical results show that the traffic patterns and traffic burstiness have a significant impact on the delay performance of LR‐WPANs. Copyright © 2012 John Wiley & Sons, Ltd.

Performance Analysis of IEEE 802.15.4 MAC Protocol with ACK Frame Transmission

A common way of achieving reliable data transmission in wireless sensor network applications is by using a retransmission mechanism with medium access control (MAC) level acknowledgements. The IEEE 802.15.4 standard, which is widely acknowledged as the state-of-the-art PHY/MAC standard for wireless sensor networks, supports MAC-level acknowledgements and retransmissions. In this paper, based on a three-dimensional discrete-time Markov chain, we propose a new analytical model to analyse the performance of the IEEE 802.15.4 MAC protocol with retransmission and MAC level acknowledgements under unsaturated traffic conditions. Further, we present a simplified version of the proposed analytical model with some approximations. Using the proposed analytical models, we evaluate the network performance in terms of the aggregate channel throughput, average power consumption of a node, frame discard ratio, and frame delivery ratio. The analytical results are substantiated through ns?2 simulations. The effects of the frame arrival rate, number of nodes, frame length and various MAC parameters, on the performance of the network are discussed. The results of both analytical models are compared and it is shown that the simplified model provides an acceptable accuracy with less computational complexity.

Design and Analysis of Backoff Algorithms for Random Access Channels in UMTS-LTE and IEEE 802.16 Systems

In this paper, we examine the performance of uniform backoff (UB) and binary exponential backoff (BEB) algorithms with retry limit, which can be used in the random-access channels of Universal Mobile Telecommunication System (UMTS)-Long Term Evolution (LTE) and IEEE 802.16 systems under the assumption of finite population under unsaturated traffic conditions. Additionally, we consider access prioritization schemes to provide differential performance by controlling various system parameters. We show that controlling the persistence value as specified in UMTS is effective in both backoff algorithms. The performances with and without access prioritization schemes are presented in terms of throughput, mean, and variance of packet retransmission delay, packet-dropping probability, and system stability. Finally, we consider a dynamic window assignment algorithm that is based on Bayesian broadcasting, in which the base station adaptively controls the window size of the UB algorithm under unsaturated traffic conditions. Results show that the proposed window assignment algorithm outperforms fixed window assignment in static and dynamic traffic conditions under the assumption of perfect orthogonality between random-access codes.

An analytical model of delay in multi-hop wireless ad hoc networks

Several analytical models of different wireless networking schemes such as wireless LANs and meshes have been reported in the literature. To the best of our knowledge, all these models fail to address the accurate end-to-end delay analysis of multi-hop wireless networks under unsaturated traffic condition considering the hidden and exposed terminal situation. In an effort to gain deep understanding of delay, this paper firstly proposes a new analytical model to predict accurate media access delay by obtaining its distribution function in a single wireless node. The interesting point of having the media access delay distribution is its generality that not only enables us to derive the average delay which has been reported in almost most of the previous studies as a special case but also facilitates obtaining higher moments of delay such as variance and skewness to capture the QoS parameters such as jitters in recently popular multimedia applications. Secondly, using the obtained single node media access delay distribution, we extend our modeling approach to investigate the delay in multi-hop networks. Moreover, probabilities of collisions in both hidden and exposed terminal conditions have been calculated. The validity of the model is demonstrated by comparing results predicted by the analytical model against those obtained through simulation experiments.

Exploring the feasibility of differentiating IEEE 802.15.4 networks to support health-care systems

IEEE 802.15.4 networks are a feasible platform candidate for connecting all health-care-related equipment dispersed across a hospital room to collect critical time-sensitive data about patient health state, such as the heart rate and blood pressure. To meet the quality of service requirements of health-care systems, this paper proposes a multi-priority queue system that differentiates between various types of frames. The effect of the proposed system on the average delay and throughput is explored herein. By employing different contention window parameters, as in IEEE 802.11e, this multi-queue system prioritizes frames on the basis of priority classes. Performance under both saturated and unsaturated traffic conditions was evaluated using a novel analytical model that comprehensively integrates two legacy models for 802.15.4 and 802.11e. To improve the accuracy, our model also accommodates the transmission retries and deferment algorithms that significantly affect the performance of IEEE 802.15.4. The multi-queue scheme is predicted to separate the average delay and throughput of two different classes by up to 48.4 % and 46 %, respectively, without wasting bandwidth. These outcomes imply that the multi-queue system should be employed in health-care systems for prompt allocation of synchronous channels and faster delivery of urgent information. The simulation results validate these model's predictions with a maximum deviation of 7.6%.

Sustainable Throughput of Wireless LANs with Multipacket Reception Capability under Bounded Delay-Moment Requirements

With the rapid proliferation of broadband wireless services, it is of paramount importance to understand how fast data can be sent through a wireless local area network (WLAN). Thanks to a large body of research following the seminal work of Bianchi, WLAN throughput under saturated traffic condition has been well understood. By contrast, prior investigations on throughput performance under unsaturated traffic condition was largely based on phenomenological observations, which lead to a common misconception that WLAN can support a traffic load as high as saturation throughput, if not higher, under nonsaturation condition. In this paper, we show through rigorous analysis that this misconception may result in unacceptable quality of service: mean packet delay and delay jitter may approach infinity even when the traffic load is far below the saturation throughput. Hence, saturation throughput is not a sound measure of WLAN capacity under nonsaturation condition. To bridge the gap, we define safe-bounded-mean-delay (SBMD) throughput and safe-bounded-delay-jitter (SBDJ) throughput that reflect the actual network capacity users can enjoy when they require finite mean delay and delay jitter, respectively. Our earlier work proved that in a WLAN with multi-packet reception (MPR) capability, saturation throughput scales superlinearly with the MPR capability of the network. This paper extends the investigation to the nonsaturation case and shows that superlinear scaling also holds for SBMD and SBDJ throughputs. Our results here complete the demonstration of MPR as a powerful capacity-enhancement technique for WLAN under both saturation and nonsaturation conditions.

Enhanced Markov Chain Model and Throughput Analysis of the Slotted CSMA/CA for IEEE 802.15.4 Under Unsaturated Traffic Conditions

In this paper, we propose an analytical Markov chain model of the slotted carrier-sense multiple-access/collision-avoidance (CSMA/CA) protocol for IEEE 802.15.4 under unsaturated traffic conditions. Our proposed Markov chain model reflects the characteristics of the IEEE 802.15.4 medium-access control (MAC) protocol, such as a superframe structure, acknowledgements, and retransmissions with and without limit. We evaluate the throughput performance of the slotted CSMA/CA and verify the analytical model using simulation results.

IEEE 802.11a Throughput Performance with Hidden Nodes

Analytic performance of IEEE 802.11 distributed coordination function that takes into account hidden node problem and unsaturated traffic condition is presented for symmetric networks. This enables us to estimate the performance of practical wireless local area networks more accurately. It is shown that the presence of hidden nodes barely affects the network performance in low traffic conditions, but it causes 33% performance loss in moderate traffic scenarios. Analytical results presented in the paper are backed by simulation results.

On the Linear Behaviour of the Throughput of IEEE 802.11 DCF in Non-Saturated Conditions

We propose a linear model of the throughput of the IEEE 802.11 distributed coordination function (DCF) protocol at the data link layer in non-saturated traffic conditions. We show that the throughput is a linear function of the packet arrival rate (PAR) lambda with a slope depending on both the number of contending stations and the average payload length. We also derive the interval of validity of the proposed model by showing the presence of a critical lambda, above which the station begins operating in saturated traffic conditions. The analysis is based on the multi-dimensional Markovian state transition model proposed by Liaw et al. with the aim of describing the behaviour of the MAC layer in unsaturated traffic conditions. Simulation results closely match the theoretical derivations, confirming the effectiveness of the proposed linear model.