Throughput Analysis of the IEEE 802.11 Distributed Coordination Function Considering Erroneous Channel and Capture Effects

This paper presents a performance study of the distributed coordination function （DCF） of 802.11 networks considering erroneous channel and capture effects under non-saturated traffic conditions employing a basic access method.The aggregate throughput of a practical wireless local area network （WLAN） strongly depends on the channel conditions.In a real radio environment,the received signal power at the access point from a station is subjected to deterministic path loss,shadowing,and fast multipath fading.The binary exponential backoff （BEB） mechanism of IEEE 802.11 DCF severely suffers from more channel idle time under high bit error rate （BER）.To alleviate the low performance of IEEE 802.11 DCF,a new mechanism is introduced,which greatly outperforms the existing methods under a high BER.A multidimensional Markov chain model is used to characterize the behavior of DCF in order to account both non-ideal channel conditions and capture effects.

Nonsaturation Throughput Enhancement of IEEE 802.11b Distributed Coordination Function for Heterogeneous Traffic under Noisy Environment

In this paper, we propose a mechanism named modified backoff （MB） mechanism to decrease the channel idle time in IEEE 802.11 distributed coordination function （DCF）. In the noisy channel, when signal-to-noise ratio （SNR） is low, applying this mechanism in DCF greatly improves the throughput and lowers the channel idle time. This paper presents an analytical model for the performance study of IEEE 802.11 MB-DCF for nonsaturated heterogeneous traffic in the presence of transmission errors. First, we introduce the MB-DCF and compare its performance to IEEE 802.11 DCF with binary exponential backoff （BEB）. The IEEE 802.11 DCF with BEB mechanism suffers from more channel idle time under low SNR. The MB-DCF ensures high throughput and low packet delay by reducing the channel idle time under the low traffic in the network. However, to the best of the authors＇ knowledge, there are no previous works that enhance the performance of the DCF under imperfect wireless channel. We show through analysis that the proposed mechanism greatly outperforms the original IEEE 802.11 DCF in the imperfect channel condition. The effectiveness of physical and link layer parameters on throughput performance is explored. We also present a throughput investigation of the heterogeneous traffic for different radio conditions.

Performance Improvement of Distributed Coordination Function in IEEE 802.11 Wireless LAN

This paper proposes a modification to distributed coordination function （DCF） to improve the channel utilization in IEEE 802.11 wireless local area networks （ WLANs）. In the modified DCF, when a station has contended for the channel, it may transmit multiple data frames continuously to the same destination, which is called transmission burst（TB）. When the maximum number of data packets transmitted continuously in a TB is set to be 2, the performance is expected to be the best. The theoretical analysis and simulation results show that compared with the standard DCF, the modified DCF can increase the throughput and decrease the delay of the WLAN, and the modification does not introduce any additional control overhead.

Optimal Scheduling Method in MIMO WLAN with Distributed Coordination Function

This paper addresses the optimal number of simultaneous data transmissions that maximize the system throughput in an MIMO WLAN. To facilitate simultaneous packet transmissions, both transceivers have to exchange preambles to calculate the channel state information. This exchange is combined with the RTS （request to send）/CTS （clear to send） handshake which is used to contend for the channel in WLANs. This study presents an expression for the optimal number of simultaneous data transmissions under the distributed coordinate function mechanism derived using the Markov chain model, as well as an analytical formula for the optimal system throughput given the length of the contention window and the number of nodes in the network. The analytical results show that the system throughput cannot be enhanced by simply increasing the numoer of simultaneous data transmissions.

The Effect of Resources Capabilities on Cross Functional Coordination in the Footwear Micro Industry in West Jawa

This study is aimed at analyzing resources capabilities and cross functional coordination, and recognizes the effect of resources capabilities on cross functional coordination in the footwear micro industry in West Jawa. The author conducted descriptive survey and quatitative study to determine the level of relationship of different variables on population and to measure the contribution of free variables to restricted variables. The result shows that the resources capabilities, including leather raw materials, synthetic raw materials, funding, human resources, science management, and information and technology influence cross functional coordination in footwear micro industry in West Jawa. This study also reveals that significant resources capabilities elements include leather raw materials, funding, and human resources supplies, while other elements provided insignificant impact.

Performance analysis of IEEE 802.11 DCF networks

This paper presents an analytical saturation throughput model of IEEE 802.11 DCF (distributed coordination function) with basic access in ad hoc mode. The model takes into account freezing of the backoff timer when a station senses busy channel. It is shown that taking into account this feature of DCF is important in modeling saturation throughput by yielding more accurate and realistic results than models known from literature. The proposed analytical model also takes into account the effect of transmission errors. All essential features of the proposed analytical approach are illustrated with numerical results. The presen-tation of the model is proceeded by an overview of approaches to IEEE 802.11 network performance evaluation presented in the literature.

Throughput Analysis of IEEE 802.11 Multirate WLANs with Collision Aware Rate Adaptation Algorithm

This paper presents a mathematical model that analyzes the throughput of the IEEE 802.11b distributed coordination function （DCF） with the collision aware rate adaptation （CARA） algorithm. IEEE 802.11 WLANs provide multiple transmission rates to improve system throughput by adapting the transmission rate to the current channel conditions. The system throughput is determined by some stations using low transmission rates due to bad channel conditions. CARA algorithm does not disturb the existing IEEE 802.11b formats and it can be easily incorporated into the commercial wireless local area networks （WLAN） devices. Finally, we verify our findings with simulation.

A DELAY BASED BACKOFF SCHEME FOR WLAN WITH QoS GUARANTEE AND ITS PERFORMANCE

Based on the Distributed Coordination Function (DCF) and the Enhanced DCF (EDCF) mechanisms in IEEE 802.11 and 802.11e, a novel backoff scheme for Wireless Local Area Network (WLAN) is proposed. The scheme is to solve the problem of the packet loss and the decrease of performance due to the increasing Contention Window (CW) when there are continuous collisions. In the proposed scheme, the CW of the packet will change dynamically with different delay for the different traffics. Mathematic formulas are presented to indicate the relationship between the CW and the delay character. ,The performance of the new scheme is also discussed with simulation results. The results show that it helps WLAN system handle multimedia simultaneously.

Analyzing and Enabling the Harmonious Coexistence of Heterogeneous Industrial Wireless Networks

Nowadays multiple wireless communication systems operate in industrial environments side by side.In such an environment performance of one wireless network can be degraded by the collocated hostile wireless network having higher transmission power or higher carrier sensing threshold.Unlike the previous research works which considered IEEE 802.15.4 for the Industrial Wireless communication systems(iWCS)this paper examines the coexistence of IEEE 802.11 based iWCS used for delay-stringent communication in process automation and gWLAN(general-purpose WLAN)used for non-real time communication.In this paper,we present a Markov chain-based performance model that described the transmission failure of iWCS due to geographical collision with gWLAN.The presented analytic model accurately determines throughput,packet transaction delay,and packet loss probability of iWCS when it is collocated with gWLAN.The results of the Markov model match more than 90%with our simulation results.Furthermore,we proposed an adaptive transmission power control technique for iWCS to overcome the potential interferences caused by the gWLAN transmissions.The simulation results show that the proposed technique significantly improves iWCS performance in terms of throughput,packet transaction,and cycle period reduction.Moreover,it enables the industrial network for the use of delay critical applications in the presence of gWLAN without affecting its performance.

A Media Access Control Scheme for Service Differentiation in Ad hoc Networks

IEEE 802.11 distributed coordination function(DCF)can alleviate the collision and hidden station problem,but it doesn't differentiate traffic categories(TC).Therefore,it can't provide sufficient quality of service(QoS)support for different TC.Recently,a new contention-based enhanced distributed channel access(EDCA)scheme is proposed which provides a probabilistic QoS support.In this paper,an improved EDCA scheme for service differentiation in ad hoc networks is proposed.In this scheme,signal channel resistance coefficient is used to adjust the contention window(CW).It proves that the scheme provides the traffic differentiation,high throughput and low delay through simulation.

Achieving Efficient Channel Utilization for Data Communications in IEEE 802.11 WLAN

In the IEEE g02. 11 protocol, the adoption of the exponential backoff technique leads to throughput performance strongly dependent on the initial contention window size and, most importantly, on the number of contending stations considered in the network. This paper proposes a simple but accurate method to dynamically estimate the number of contending stations in a wireless local area network （ WLAN ）. Based on estimation, all the mobile stations dynamically adjust the initial contention window in medium access control （ MAC ） layer to avoid collisions. The simulation results show that the proposed algorithm can achieve efficient channel utilization, higher system throughput, and better fairness performance.

Assessing pre/post-weaning neurobehavioral development for perinatal exposure to low doses of methylmercury

Fetuses and neonates are known to be high-risk groups for Methylmercury（MeHg）exposure.MeHg can be transferred to the fetus through the placenta and to newborn offspring through breast milk.The aim of the present study was to investigate the neurotoxic effects of low doses of MeHg（1 and 5 μg/m L in drinking water） administration,from gestational day 1 to postnatal day（PND） 21,on the neurobehavioral development of rats.The results showed that the no-observed-effect level of MeHg is somewhere in the range of 1-4 μg/mL.Neurobehavioral development analysis revealed a delayed appearance of cliff drop and negative geotaxis reflexes in the 5 μg/mL MeHg exposure group.Developmental exposure to MeHg affected locomotor activity functions for the females,but not for the males,implying that the female pups were more vulnerable than the male pups.All pups exposed to 5 μg/mL of MeHg showed a significant deficit in motor coordination in the rotarod test compared with controls,and the highest accumulated concentrations of Hg were found in the cerebellum,followed by the hippocampus and cerebral cortex,indicating that the cerebellum is a possible target for MeHg toxicity.We demonstrated adverse effects of developmental exposure to MeHg associated with tissue concentrations very close to the current human body burden of this persistent and bioaccumulative compound.

A Novel Analysis of Delay and Power Consumption for Polling Schemes in the IoT

In the Internet of Things（IoT）, various battery-powered wireless devices are connected to collect and exchange data, and typical traffic is periodic and heterogeneous. Polling with power management is a very promising technique that can be used for communication among these devices in the IoT. In this paper, we propose a novel and scalable model to study the delay and the power consumption performance for polling schemes with power management under heterogeneous settings（particularly the heterogeneous sleeping interval）. In our model,by introducing the concept of virtual polling interval, we successfully convert the considered energy-efficient polling scheme into an equivalent purely-limited vacation system. Thus, we can easily evaluate the mean and variance of the delay and the power consumption by applying existing queueing formulae, without developing a new theoretical model as required in previous works. Extensive simulations show that our analytical results are very accurate for both homogeneous and heterogeneous settings.

RSAD： A Robust Distributed Contention-Based Adaptive Mechanism for IEEE 802.11 Wireless LANs

Previous researches have shown that Distributed Coordination Function (DCF) access mode of IEEE 802.11 has lower performance in heavy contention environment. Based on the in-depth analysis of IEEE 802.11 DCF, NSAD (New Self-adapt DCF-based protocol) has been proposed to improve system saturation-throughput in heavy contention condition. The initial contention window tuning algorithm of NSAD is proved effective in error-free environment. However, problems concerning the exchanging of initial contention window occur in error-prone environment. Based on the analysis of NSAD's performance in error-prone environment, RSAD is proposed to further enhance the performance. Simulation in a more real shadowing error-prone environment is done to compare the performance of NSAD and RSAD and results have shown that RSAD can achieve further performance improvement as expected in the-error-prone environment than NSAD (i.e., better goodput and fairness index).

An adaptive cooperative MAC protocol compatible with legacy 802.11 DCF

A novel adaptive cooperative medium access control(MAC)protocol,which is completely backward compatible with the legacy IEEE 802.11 distributed coordination function(DCF),is proposed in this paper.To adapt to dynamic channel variation and network topology,the sender adaptively selects transmission scheme based on the instantaneous channel measurements.Analytical and simulation results show that the proposed protocol outperforms the existing one in terms of throughput,delay,energy and mobility.