Interframe Spaces Research Articles

Using Centrality Based Topology Control for FANET Survivability Against Jamming

Flying Ad Hoc Networks (FANETs) provide connectivity in extreme environments such as battle zones and disaster areas. Since these networks operate without infrastructure, they must calculate routes on the fly. Unfortunately, as each e2e link selfishly chooses the shortest path for its flow, they also tend to overwhelm geographically central nodes, making these nodes the bottleneck for all flows. On top of this, these networks are quite sensitive to jamming attacks, which can shut down the network’s operation entirely. In this paper, we extend our previous work CentAir with an additional operation state that enables rapid communication by reducing interframe spaces of nodes according to their eigenvector centrality measure. Following this, we propose an intelligent heuristic to enable hybrid operation among these states. This hybrid operation state improves e2e latency by modifying interframe spacing regarding the node’s eigenvector centrality. Our exhaustive simulation results show that Hybrid CentAir achieves an 18.1 percent more throughput, a 21.1 percent lower latency while being 17.8 percent more energy efficient compared to multi-channel OLSR. Additionally, our protocol shows an 11.5 percent better packet delivery ratio against randomly placed deceptive jammers that continuously transmit false packets in the area.

APPLICATION OF ORGANIC ACIDS FOR THE TREATMENT OF BEES AGAINST VARROATOSIS

The effectiveness of oxalic and lactic acids against varroatosis of honeybees was studied in laboratory and apiary conditions in the late autumn period. The studies were performed in the Tyumen Region apiaries in accordance with "Guidelines for the study of means and methods to control the varroa mite". The results of laboratory experiments showed that the maximum acaricidal activity was observed for 3.5% oxalic acid and 15% lactic acid and was 98.6±1.7% and 96.3±3.5%, respectively. In apiary conditions, the effectiveness was 87.1±2.2% (85.4–89.5%) for a single treatment of the broodless bee colonies with 3.5% oxalic acid by watering the bees in interframe spaces with 5 ml per beeway. In the control group, death of mites corresponded to 11.7±1.1%. The number of varroa mites was reduced by 90.0±2.1% (94.4–88.3%) by treating the broodless bee colonies twice in a 5 day interval with 15.0% aqueous lactic acid solution by spraying the frames with bees in a volume of 5 ml on each side of the comb. At the same time, the maximum death rate of mites was observed in the bee colonies during the first day after the treatment. The mite mortality was 10.7±1.10% in the control group during the follow-up. No death of queen-bees or bees was detected during the treatment in both experiments.

A survey on 802.11 MAC industrial standards, architecture, security & supporting emergency traffic: Future directions

The IEEE 802.11-based Wireless Local Area Network (WLAN) has become a ubiquitous networking technology deployed around the world. IEEE 802.11 WLAN are now widely used for real-time multimedia applications (e.g. voice and video streaming) and distributed emergency services such as telemedicine, healthcare, and disaster recovery. Both time-sensitive applications and emergency traffic are not only characterized by their high bandwidth requirements, but also impose severe restrictions on end-to-end packet delays (i.e. response time), jitter (i.e. delay variance) and packet losses. In other words, time-sensitive applications and emergency services require a strict Quality of Service (QoS) guarantee. Medium Access Control (MAC) protocol is one of the key factors that influence the performance of WLANs. The IEEE 802.11e working group enhanced the 802.11 MAC to provide QoS support in WLANs. However, recent studies have shown that 802.11e Enhanced Distributed Channel Access (EDCA) standard has limitations and it neither supports strict QoS guarantee nor emergency traffic. Providing a strict QoS guarantee as well as supporting emergency traffic under high traffic loads is really a challenging task in WLANs. A thorough review of literature on QoS MAC protocols reveals that most QoS schemes have focused on either network throughput enhancement or service differentiation by adjusting Contention Window (CW) or Inter-Frame Spaces (IFS). Therefore, a research on developing techniques to provide a strict QoS guarantee as well as support for emergency traffic is required in such systems. To achieve this objective, a general understanding of WLANs is required. This paper aims introduce various key concepts of WLANs that are necessary for design, model and develop such framework. Our main contribution in this paper is the QoS for IEEE 802.11 WLAN and MAC protocols for supporting industrial emergency traffic over network and future directions.

Weighted Greedy Approach for Low Latency Resource Allocation on V2X Network

In Vehicular ad-hoc networks (VANETs), resource allocation has become one of the primary tasks. Thus, a system should be well-designed so that information could be transmitted reliably and efficiently. As vehicular communication has several characteristics, efficient resource allocation scheme for D2D communications is highly required in VANET. The network topology changes rapidly as the vehicles are moving fast on the road and this makes it harder to communicate among the vehicles by predicting the best available channel. So as to overcome these issues, the proposed technique is offered in which the channel availability is predicted based on the novel mechanism like contention latency prediction using interframe spaces like Short interframe space, Distributed Coordination Function interframe space, Pointed Coordination Function and scattering based greedy weight matrix method. The implementation of this greedy mechanism in turn enhances the prediction probability of best channels that are available. Thus, the best available channel offered using greedy weight matrix scheme thereby estimates the decision probability at which the collision for available channel is computed. Thus, from this the best available channel is provided to the requested user. At last, the performance analysis is made in terms of packet delivery ratio, throughput, delay, reliability, and rate of message loss and is compared with existing techniques to prove the effectiveness of proposed strategy.

The Feasibility of Exploiting IEEE 802.11n for Addressing MAC Layer Overheads in UASNs

Underwater acoustic sensor networks (UASNs) consist of remotely deployed sensor nodes under sea or other water environments. Due to the extreme limitations faced by radio signals under water, acoustic channels are utilized for communication in such networks. However, UASNs are challenged by the characteristics of underwater acoustic channels such as lower signal propagation speed and higher signal attenuation. On top of such a challenged physical medium, MAC schemes which are designed based on their terrestrial counter parts are required to add extra overheads to the communication channel wasting the limited network resources. MAC layer overheads such as bandwidth wastage for interframe spaces and contention for occupying physical medium put limitations to the maximum reachable throughput of UASNs. IEEE 802.11n has well defined various MAC and physical layer enhancements to overcome throughput barrier in wireless LANs which includes two frame aggregation schemes, namely, A-MPDU and A-MSDU. In this paper, we study the feasibility of applying those frame aggregations well defined in IEEE 802.11n for reducing MAC layer overheads in UASNs. Based on simulation studies, we evaluate that these frame aggregation schemes are applicable in UWSNs.

IEEE 802.11e EDCA Networks: Modeling, Differentiation and Optimization

Enhanced distributed channel access (EDCA) is an extension of the distributed coordination function to support quality-of-service for IEEE 802.11 wireless local area networks. By assigning distinct backoff parameters to each access category (AC), differentiated throughput performance can be achieved when the network is saturated. Although it has been long observed that the network throughput with the current EDCA standard setting may significantly degrade as the network size grows, how to properly tune the backoff parameters to optimize the network throughput under a certain differentiation requirement remains largely unknown. In this paper, a new analytical model is proposed to address this open issue. Specifically, we focus on an M-AC IEEE 802.11e EDCA network where nodes in the same AC have identical backoff parameters, including the initial backoff window sizeW <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">(g)</sup> , the cutoff phaseK <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">(g)</sup> , and the arbitration interframe spaces (AIFS) numberA <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">(g)</sup> , g = 1, . . . , M. The network steady-state operating point in saturated conditions, i.e., pA, is characterized by using the steady-state probability of successful transmission of head-of-line (HOL) packets given that the channel is idle, based on which explicit expressions of node throughput and network throughput are further obtained. For given target ratios of node throughput of ACs, the optimal initial backoff window sizes and AIFS numbers to maximize the network throughput are derived and verified by simulation results. The analysis reveals that the maximum network throughput is solely determined by the holding time of HOL packets in successful transmission and collision states. To achieve the maximum network throughput, the initial backoff window size of each AC should be linearly increased with the network size. In the meantime, the increasing rate of the initial backoff window size, or the AIFS number, of each AC should be also carefully set according to the target ratios of node throughput. Although the maximum network throughput with pre-specified target ratios of node throughput of ACs can be achieved in both ways, the backoff window size differentiation could be a more preferable option as it requires fewer tuning parameters and provides better precision than the AIFS differentiation.

TQCR‐media access control: two‐level quality of service provisioning media access control protocol for cognitive radio network

Recently cognitive radio has been proposed to solve the problem of spectrum scarcity with the help of an opportunistic utilisation of unused spaces in the spectrum. The implementation of cognitive radio for real-time application faces with the challenge of real-time media access control (MAC) design. To this end the authors propose an energy efficient cognitive radio MAC protocol with two level of quality of service (QoS) support: two level quality of service provisioning in cognitive radio (TQCR)-MAC. The data traffic in the cognitive radio network is classified as real-time traffic and non-real-time traffic, with former having higher priority over latter. The proposed protocol utilises variable interframe spaces for implementing different priorities to data and also exploits the combination of multiple channels and time division multiple access (TDMA) scheme to further improve the QoS provisioning. The TDMA slots in different channels are used as the data carrier segment, in which a real-time data can take over the time slots reserved by non-real-time data. Thus, non-real traffic may suffer from starvation, and hence a guarantee on the non-real-time data is provided with the help of a starvation prevention algorithm. The performance analysis of the proposed MAC protocol is done against two similar MAC protocols, which shows that the performance is improved significantly, especially when the network is either biased towards real-time or non-real-time data traffic.

Throughput Analysis Model for IEEE 802.11e EDCA with Multiple Access Categories

IEEE 802.11e standard has been specified to support differentiated quality of service (QoS), one of the critical issues on the conventional IEEE 802.11 wireless local area networks (WLANs). Enhanced Distributed Channel Access (EDCA) is the fundamental and mandatory contention-based channel access method of IEEE 802.11e, and delivers traffic based on differentiated Access Categories (ACs). A general three dimensional Markov chain model of IEEE 802.11e EDCA for performance analysis is proposed in this paper. The analytical model considers multiple stations with an arbitrary number of different ACs. It also differentiates the contention window (CW) sizes and the arbitration interframe spaces (AIFSs), and considers virtual collision mechanism. Based on the model, the saturation throughput of EDCA is derived, and the accuracy of the proposed model is validated via simulations.

Group Contention-Based OFDMA MAC Protocol for Multiple Access Interference-Free in WLAN Systems

In WLAN systems, the difference in propagation delay among stations (STAs) can exceed the predefined cyclic prefix length, leading to multiple access interference (MAI). To solve this MAI problem, it is necessary to use a longer cyclic prefix length for orthogonality between different subchannels; however, this sacrifices system efficiency due to the cyclic prefix overhead. In this paper, we propose a group contention-based OFDMA to solve the MAI problem with an adequate cyclic prefix length and support a larger number of STAs. The STAs within the cyclic prefix duration that are synchronized to an access point (AP), are included in the same contending group and compete with other STAs of the group in transmitting packets. The proposed scheme allows for the adoption of an adequate cyclic prefix length without MAI, and is able to reduce the cyclic prefix overhead. In addition, since no packet errors are induced by MAI in any of the STAs, the STAs can transmit simultaneously without redundant short interframe spaces (SIFSs) and other control packets. Through analysis and simulation, we show that for a large number of STAs, the proposed scheme achieves higher throughput than 802.11 protocols and a conventional CSMA combined with OFDMA.

Fast Retransmission Scheme for Overcoming Hidden Node Problem in IEEE 802.11 Networks

To avoid collisions, IEEE 802.11 medium access control (MAC) uses predetermined inter-frame spaces and the random back-off process. However, the retransmission strategy of IEEE 802.11 MAC results in considerable time wastage. The hidden node problem is well known in wireless networks; it aggravates the consequences of time wastage for retransmission. Many collision prevention and recovery approaches have been proposed to solve the hidden node problem, but all of them have complex control overhead. In this paper, we propose a fast retransmission scheme as a recovery approach. The proposed scheme identifies collisions caused by hidden nodes and then allows retransmission without collision. Analysis and simulations show that the proposed scheme has greater throughput than request-to-send and clear-to-send (RTS/CTS) and a shorter average waiting time.

A MAC-Layer QoS Provisioning Protocol for Cognitive Radio Networks

Due to the proliferation of diverse network devices with multimedia capabilities, there is an increasing need for Quality of Service (QoS) provisioning in wireless networks. The MAC layer protocol with enhanced distributed channel access (EDCA) in the IEEE 802.11-2007 is able to provide differentiated QoS for different traffic types in wireless networks through varying the Arbitration Inter-Frame Spaces (AIFS) and contention window sizes. However, the performance of high priority traffic can be seriously degraded in the presence of strong noise over the wireless channels. Schemes utilizing adaptive modulation and coding (AMC) technique have also been proposed for the provisioning of QoS. They can provide limited protection in the presence of noise but are ineffective in a high noise scenario. Although multiple non-overlapped channels exist in the 2.4 and 5 GHz spectrum, most IEEE 802.11-based multi-hop ad hoc networks today use only a single channel at anytime. As a result, these networks cannot fully exploit the aggregate bandwidth available in the radio spectrum provisioned by the standards. By identifying vacant channels through the use of cognitive radios technique, the noise problem can be mitigated by distributing network traffic across multiple vacant channels to reduce the node density per transmission channel. In this paper, we propose the MAC-Layer QoS Provisioning Protocol (MQPP) for 802.11-based cognitive radio networks (CRNs) which combines adaptive modulation and coding with dynamic spectrum access. Simulation results demonstrate that MQPP can achieve better performance in terms of lower delay and higher throughput.

Supporting Differentiated Service in Cognitive Radio Wireless Mesh Networks

The MAC layer protocols utilizing enhanced distributed channel access (EDCA) in the recently published IEEE 802.11-2007 are able to provide differentiated QoS for different traffic types in wireless networks through varying the Arbitration Inter-Frame Spaces (AIFS) and contention window sizes. However, the performance of high priority traffic can be seriously degraded in the presence of strong noise over the wireless channels. The noise problem is further aggravated in wireless mesh networks when packets traverse multiple-hops from source to destination. The noise problem can be mitigated by distributing network traffic across multiple vacant channels to reduce the node density per transmission channel. Although multiple non-overlapped channels exist in the 2.4GHz and 5GHz spectrum, most IEEE 802.11-based multi-hop ad hoc networks today use only a single channel at anytime. As a result, these networks cannot fully exploit the aggregate bandwidth available in the radio spectrum provisioned by the standards. In this paper, we propose the Power-Controlled Rate-Adaptive MAC (CPCRA) protocol for single transceiver based Cognitive Radio Networks (CRNs) which combines adaptive modulation and coding with dynamic spectrum access. Simulation results demonstrate that CPCRA can achieve better performance in terms of lower delay and higher throughput.

A performance analysis of block ACK scheme for IEEE 802.11e networks

The demand for the IEEE 802.11 wireless local-area networks (WLANs) has been drastically increasing along with many emerging applications and services over WLAN. However, the IEEE 802.11 medium access control (MAC) is known to be limited in terms of its throughput performance due to the high MAC overhead, such as interframe spaces (IFS) or per-frame based acknowledgement (ACK) frame transmissions. The IEEE 802.11e MAC introduces the block ACK scheme for improving the system efficiency of the WLAN. Using the block ACK scheme can reduce the ACK transmission overhead by integrating multiple ACKs for a number of data frames into a bitmap that is contained in a block ACK frame, thus increasing the MAC efficiency. In this paper, we mathematically analyze the throughput and delay performance of the IEEE 802.11e block ACK scheme in an erroneous channel environment. Our extensive ns-2 simulation results validate the accuracy of our analytical model and they further demonstrate that the block ACK scheme enhances the MAC throughput performance at the cost of the resequencing delay at the receiving buffer .

Medium access control access delay analysis of IEEE 802.11e wireless LAN

The IEEE 802.11e standard is specified to support quality-of-service in wireless local area networks, and different contention parameters are designated to each type of service. This developed model is presented to analyse the scheduling and the contention between packets with different priorities, where the new features of the enhanced distributed channel access such as virtual collision, backoff, minimum contention window and different arbitration inter-frame spaces are taken into account. Based on the model, the delay performance of differentiated service traffic is analysed and a recursive method is proposed, which is capable of calculating the mean access delay. Simulations show that the model and the analysis provide an insight into the protocol and the effects of different parameters on the performance.

A token-based scheduling scheme for WLANs supporting voice/data traffic and its performance analysis

Most of the existing medium access control (MAC) protocols for wireless local area networks (WLANs) provide prioritized access by adjusting the contention window sizes or inter-frame spaces for different traffic classes. Those MAC protocols can only provide statistical priority access and limited service differentiation. In this paper, a novel token-based scheduling scheme is proposed for a fully-connected WLAN that supports both voice and data traffic. The proposed scheme can provide guaranteed priority access to voice traffic and, at the same time, provide more precise and quantitative service differentiation for data traffic, which provides great flexibility and facility to the network service provider for service class management. Simulation results demonstrate that the proposed scheme can guarantee a small delay for voice traffic. For data traffic, it can effectively achieve proportional differentiation among different classes, while achieving fair resource sharing within the same class. In addition, compared with a contention based scheme and a centralized polling scheme, the proposed scheme significantly improves the channel utilization by avoiding collisions (in the contention based scheme) and the polling overhead (in the polling scheme). The performance analysis of the proposed scheme is also presented. The accuracy of the analytical results is verified by computer simulations.

Dynamic adaptation of CSMA/CA MAC protocol for wide area wireless mesh networks

Though the popular IEEE 802.11 DCF is designed primarily for Wireless LAN (WLAN) environments, today it is being widely used for wide area wireless mesh networking. The protocol parameters of IEEE 802.11 such as timeout values, interframe spaces, and slot durations, sufficient for a general WLAN environment, need to be modified in order to efficiently operate in wide area wireless mesh networks. The current wide area wireless mesh network deployments use manual configuration of these parameters to the upper limit which essentially makes the networks operate at lower system efficiency. In this paper, we propose d802.11 (dynamic 802.11) which dynamically adapts the protocol parameters in order to operate at varying link distances. In fact, in 802.11, a transmitter can face ACK/CTS timeout even when it started receiving ACK/CTS packet before the timeout value. We present three strategies, (i) multiplicative timer backoff (MTB), (ii) additive timer backoff (ATB), and (iii) link RTT memoization (LRM), to adapt the ACK_ TIMEOUT in d802.11 in order to provide better adaptation for varying link dimensions. Through extensive simulation experiments we observed significant performance improvement for the proposed strategies. We also theoretically modeled the maximum link throughput as a function of the link dimension for the proposed system. Our results show that the LRM technique provides the best adaptation compared to all other schemes.

Saturated throughput analysis of IEEE 802.11e EDCA

IEEE 802.11e standard has been published to introduce quality of service (QoS) support to the conventional IEEE 802.11 wireless local area network (WLAN). Enhanced distributed channel access (EDCA) is used as the fundamental access mechanism for the medium access control (MAC) layer in IEEE 802.11e. In this paper, a novel Markov chain based model with a simple architecture for EDCA performance analysis under the saturated traffic load is proposed. Compared with the existing analytical models of EDCA, the proposed model incorporates more features of EDCA into the analysis. Firstly, we analyze the effect of using different arbitration interframe spaces (AIFSs) on the performance of EDCA. That is, the time interval from the end of the busy channel can be classified into different contention zones based on the different AIFSs used by different sets of stations, and these different sets of stations may have different transmission probabilities in the same contention zone. Secondly, we analyze the possibility that a station's backoff procedure may be suspended due to transmission from other stations. We consider that the contention zone specific transmission probability caused by the use of different AIFSs can affect the occurrence and the duration of the backoff suspension procedure. Based on the proposed model, saturated throughput of EDCA is analyzed. Simulation study is performed, which demonstrates that the proposed model has better accuracy than those in the literature.

Throughput and delay performance of IEEE 802.11e enhanced distributed channel access (EDCA) under saturation condition

In this paper, we analyze the saturation performance of IEEE 802.11e enhanced distributed channel access (EDCA), which provides contention-based differentiated channel access for frames of different priorities in wireless LANs. With EDCA, quality of service (QoS) support is provided with up to four access categories (ACs) in each station. Each AC behaves as an independent backoff entity. The priority among ACs is then determined by AC-specific parameters, called the EDCA parameter set. The behavior of the backoff entity of each AC is modeled as a two-state Markov chain, which is extended from Bianchi's model to capture the features of EDCA. The differences of our model from existing work for 802.11e EDCA include: (i) virtual collisions among different ACs in an EDCA station are modeled, thus more accurately capturing the behavior of EDCA; (ii) the influence of using different arbitrary inter-frame spaces (AIFS) for different ACs on saturation performance are considered; (iii) delay and delay jitter are derived, in addition to saturation throughput. The analytical model is validated via ns-2 simulations. The results show that our analytical model can accurately describe the behavior of IEEE 802.11e EDCA

Understanding 802.11e contention-based prioritization mechanisms and their coexistence with legacy 802.11 stations

The IEEE 802.11e task group has reached a stable consensus on two basic contention-based priority mechanisms to promote for standardization: usage of different arbitration interframe spaces and usage of different minimum/maximum contention windows. The goal of this article is to provide a thorough understanding of the principles behind their operation. To this purpose, rather than limit our investigation to high-level (e.g. throughput and delay) performance figures, we take a closer look at their detailed operation, also in terms of low-level performance metrics (e.g., the probability of accessing specific channel slots). Our investigation on one hand confirms that AIFS differentiation provides superior and more robust operation than contention window differentiation. On the other hand, it highlights performance issues related to the coexistence between 802.11e contention-based stations with legacy 802.11 stations, and provides guidelines for the 802.11e parameter settings when such a coexistence is the goal.

Performance modeling of IEEE 802.11 wireless LANs with stochastic Petri nets

In 1997, IEEE standardized the physical layers and the medium access for wireless local area networks. This paper presents a performance study of the distributed coordination function, the fundamental contention-based access mechanism. Most performance studies adopt unchecked simplifying assumptions or do not reveal all details of the simulation model. We develop a stochastic Petri net model, which captures all relevant system aspects in a concise way. Simulation allows to quantify the influence of many mandatory features of the standard on performance, especially the backoff procedure, extended interframe spaces, and the timing synchronization function. We identify conditions when simplifying assumptions commonly used in analytical modeling are justified. Applying these conditions, we derive a more compact and analytically tractable model from the detailed model.