DCF Protocol Research Articles

IEEE 802.11 무선 랜에서의 네크워크 코딩 성능 분석

Network coding has recently emerged as an effective solution for multicast and broadcast communications in wireless ad hoc networks. In this paper, we propose a throughput performance model for IEEE 802.11 wireless networks with network coding. Specifically, we consider IEEE 802.11 DCF protocol and linear topology in which traffic sources are located at both ends and intermediate nodes act as relays performing network coding. The proposed analytic model has the form of nonlinear equations in terms of throughput of each node. The solution of the nonliear equations thus correspond to the end-to-end throughput. Extensive simulation experiments have been performed to validate accuracy of the proposed model. Numerical results show that the results of the proposed analytic model agree fairly well with the corresponding simulation results.

Per-station throughput fairness in a WLAN hot-spot with TCP traffic

The 802.11 DCF protocol was devised to achieve per-station fairness; conversely, an harsh per-station unfairness occurs when DCF is loaded by TCP traffic. We aim at extending theoretical knowledge ...

Per-station throughput fairness in a WLAN hot-spot with TCP traffic

The 802.11 DCF protocol was devised to achieve per-station fairness; conversely, an harsh per-station unfairness occurs when DCF is loaded by TCP traffic. We aim at extending theoretical knowledge on this fairness issue and at restoring per-station fairness. The contribution of the paper is threefold. First, we introduce two findings: (i) changing the physical transmission rate of the stations does not impact the per-station fairness; (ii) packet queuing occurs in the uplink buffer of a station and has a non-negligible impact on the fairness. Second, we derive a model for evaluating fairness performance. Our model accounts for the effect of several parameters and scenarios that no other model captures in a single analytic framework. Third, and finally, we propose a technique to enforce fairness, which is easy to deploy in real systems, without having to modify existing devices. Experimental results obtained with commercial devices confirm the validity of our solution and findings. Albeit the focus of this paper is on per-station (throughput) fairness, our technique can be easily modified, e.g. to enforce time-based fairness, or per-direction or per-flow fairness.

Modeling the interactions between MAC and higher layer

We propose a new framework for worst-case performance evaluation of MAC protocols for wireless ad hoc networks. Given a protocol, its performance metrics and a network topology, our framework first generates MAC scenarios which achieve poor performance at MAC level. In order to evaluate the impact of these MAC scenarios on the end performance, we model the interactions between MAC interface and the MAC layer using a state transition graph and generate high-level scenarios using enumeration techniques. These high-level scenarios can be simulated and compared with heuristics developed by others to identify high-level scenarios that are expected to lead to the worst-case end performance. In order to demonstrate its usefulness, we use our framework to evaluate the worst-case performance of IEEE 802.11 DCF protocol by generating a library of MAC- and high-level scenarios. We simulate the high-level scenarios to demonstrate that the scenarios we generate exhibit the worst performance among all the scenarios, including those generated by using heuristics recently proposed by other researchers.

Power control of control frames in IEEE 802.11 networks

Power control design is important in IEEE 802.11 wireless networks, because the equipment sometimes is powered by the battery. There has been some research into the power control in IEEE 802.11 wireless networks. In most cases, the nodes use the same transmitted power to transmit the RTS (request to send) control frames and CTS (clear to send) control frames. We propose a protocol for power control of control frames (PCCF) in IEEE 802.11 networks. In this PCCF protocol, the RTS transmitted power is based on the carrier sense threshold, the receiving threshold and the maximum transmitted power, and then the data transmitted power is calculated based on the SINR (signal to interference and noise ratio) threshold. Based on the RTS transmitted power and the data transmitted power, the CTS transmitted power is calculated. Simulation results show that compared to the IEEE 802.11 DCF protocol, the PCCF protocol increases the system throughput, and decreases the delay and energy consumption.

Collision Classification Model-Based Collision Resolution Algorithm

Traditional backoff algorithms in IEEE 802.11 networks adopt contention window scheme for collision resolution.Collided nodes are redistributed in extended window ranges to avoid further collisions.However,as long as these distribution windows intersect with each other,collision may still occur.To solve this problem,this paper puts forward a collision classification model to classify collisions into cross collision and intra collision and proposes to solve them with different policies.It utilizes sequential discrete window distribution(SDWD) scheme to resolve cross collision by distributing the collided nodes in a series of discrete Elementary Windows and the intra collision is resolved with an appropriate elementary window size to achieve a tradeoff between intra collision probability and packet latency.Based on this proposal,two algorithms are developed featuring cross collision resolution(CCR) and collision-free CCR(CF-CCR).The extensive simulations demonstrate that compared with IEEE 802.11 DCF protocol,the CCR and CF-CCR algorithms consistently excel,in terms of collision rate,throughput,delay,fairness and delay jitter.Moreover,CCR and CF-CCR exhibit their respective advantages in different scenarios.

Markov Model of DCF Protocol Based on Fixed Slot in Multi-Hop Ad Hoc Networks

指出了现有的基于不定长时隙的DCF协议马尔可夫链模型的局限性,并在详细分析多跳ad hoc 网络环境中DCF 协议建模的难点问题基础上,提出了一种基于定长时隙的多跳ad hoc 网络DCF 协议马尔可夫链模型.通过模型的求解,得到了反映多跳ad hoc 网络饱和吞吐量性能的相关性能指标的理论值,并结合GloMoSim 网络仿真环境中的仿真实验,证明了模型的有效性.;This paper points out the limitations of the existing Markov model of DCF protocol based on un-fixed slot in ad hoc networks, and analyzes the difficulty of the modeling of DCF protocol in multi-hop ad hoc networks in detail. On the basis of this, this paper proposes a Markov model of DCF protocol based on fixed slot in multi-hop ad hoc networks. By solving this model, the theoretic value which reflects the saturated throughput performance of multi-hop ad hoc networks is obtained. The effectiveness of this model is demonstrated by the simulations in GloMoSim environment.

Comparing the results from various performance models of IEEE 802.11g DCF

IEEE 802.11 DCF is the most widely-used CSMA/CA access control mechanism . Recent analytic performance models for DCF have received acclaim for both their simplicity and reported accuracy. Most of these models share the assumptions of full single-hop connectivity among all stations, that DCF back-off may be modeled as a Markov process and that the network is saturated with traffic. In order to verify the accuracy of existing analytic models we developed a discrete-event simulator to record the performance of the DCF protocol and ensure that every detail of the standard is represented. Simultaneously we set up a hardware test bed to measure the same performance metrics in an environment that makes none of the simplifying assumptions of either the analytic models or the simulation. In the test bed, as in the simulator, we used the same physical parameter settings prescribed by the standard. As is the case for the analytic models we used, we subjected the simulator and the test bed to the same saturated workload for both basic and RTS/CTS access modes. Finally, we also implemented a non-saturating Markov Modulated Arrival Process (MMAP) workload model for our simulator to test the performance of DCF subject to more realistic internet traffic conditions. We describe both the simulator and the test bed in some detail in order to testify to the accuracy and detail of our results. The results show that the analytic models are mostly pessimistic for small numbers of nodes and optimistic for larger numbers of nodes. The performance measurements from the test bed, in turn, indicate that the simulation results are similarly optimistic when large numbers of nodes are concerned. Since the test bed uses an error-prone wireless channel, this latter result is, in principle, not surprising. The rate of deterioration in the actual performance is however something that is not widely known and is much more rapid than analytic models would suggest.

An Adaptive Learning Scheme for Medium Access with Channel Reservation in Wireless Networks

Providing effective medium access for wireless networks is a challenging task. Most of the existing protocols of IEEE 802.11 Medium Access Control (MAC) work towards the goal of achieving effective channel access by developing various backoff procedures. In this paper, we make an attempt to develop a new medium access protocol named Learning Automata (LA) based Wireless Channel Reservation (LAWCR). We use an LA approach to implement reservation for channel access for single hop wireless networks. Also, sequence procedure is used to improve the reservation mechanism. The performance of the proposed LAWCR scheme show significant improvements over the legacy DCF protocol with respect to important criteria such as the average time spent in the buffer and the throughput.

A two-level medium access framework for exploiting multi-user diversity in multi-rate IEEE 802.11 wireless LANs

Fast rate adaptation has long been recognized as an effective way to improve the PHY-layer data rate of wireless networks. However, in random access wireless networks such as IEEE 802.11 wireless LANs, MAC-layer throughput is dominated by stations with the lowest transmission rates, resulting in an underutilization of spectrum bandwidth. In this paper, we propose a novel two-level medium access framework, referred to as two-level MAC, to solve the aforementioned problem and to significantly improve system spectrum efficiency through the exploitation of multiuser diversity. The key idea of two-Level MAC is to introduce a second level of deterministic channel access on top of the traditional IEEE 802.11 DCF protocol. By doing so, higher priority is granted to high-rate stations in a fully distributed manner. Meanwhile, collisions among potential contending stations are drastically reduced. Through analysis, we show how such two-Level MAC can be optimized to achieve the maximum system throughput. The superiority of the proposed protocol is verified through analyses and extensive simulations.

Performance Analysis of Contention Based Medium Access Control Protocols

This paper studies the performance of contention based medium access control (MAC) protocols. In particular, a simple and accurate technique for estimating the throughput of the IEEE 802.11 DCF protocol is developed. The technique is based on a rigorous analysis of the Markov chain that corresponds to the time evolution of the back-off processes at the contending nodes. An extension of the technique is presented to handle the case where service differentiation is provided with the use of heterogeneous protocol parameters, as, for example, in IEEE 802.11e EDCA protocol. Our results provide new insights into the operation of such protocols. The techniques developed in the paper are applicable to a wide variety of contention based MAC protocols.

An overlapping and pipelining data transmission MAC protocol with multiple channels in ad hoc networks

In mobile ad hoc networks (MANETs), the IEEE 802.11 DCF protocol is commonly used at the medium access control (MAC) layer to reduce collision and contention. However, mobile nodes, before send out data, need to wait for other in-process data transmission in the same range to be completed. In this paper, we address this performance degradation problem in the DCF mechanism and propose an overlapping and pipelining data transmission MAC protocol to enhance throughput. The protocol regulates the actions of the neighboring nodes of both the sender and the receiver and enables the utilization of the same channel simultaneously by these neighboring nodes. A multiple sub-channel technique is proposed to avoid the interference problem caused by the control and data signals of different communication mobile node pairs. With the regulated actions and the multiple channel technique, multiple pairs of mobile nodes are provided with the desired feature of utilizing the same data sub-channel simultaneously without interfering with one another. Although the overlapping data transmission technique can increase the number of simultaneous communication pairs, an efficient bandwidth allocation of the control and data sub-channels to maximize utilization is critically important. Therefore, we further propose a bandwidth allocation strategy in which the control signals and data signals are pipelined. Performance simulation results prove the efficiency of the proposed bandwidth allocation strategy with better channel utilization. In addition, the proposed MAC protocol with the bandwidth allocation strategy, combined with the overlapping and pipelining data sub-channel technique, outperforms the IEEE 802.11 DCF in throughput (kB/s) by about 43.76%.

Distributed simulation of large-scale and detailed models

We present a new approach for the distributed simulation of large-scale and detailed models. Our approach increases the simulator speed jointly addressing two main problems of distributed simulation: the reduction of the communication overhead and the load-balancing in the execution cluster. The proposed method dynamically reconfigures the simulation, considering the performance of each part of the execution architecture. In this way, commercial-off-the-shelf hardware can be used for fast and cost-effective simulations. The performance evaluation, based on the 802.11 DCF protocol, demonstrates that this approach is feasible for the detailed simulation of very large-scale models such as wireless networks.

Intersection-Aware Channel Assignment and Routing in Multi-Channel Multi-Hop Wireless Networks with a Single Transceiver

This article proposes an intersection-aware channel assignment and routing protocol for wireless ad hoc networks with a single transceiver. This protocol increases the network capacity of an IEEE 802.11 network by exploiting frequency diversity. Using the proposed protocol, multiple communications can simultaneously take place in a region without interfering with each other. However, it must avoid a multi-channel hidden terminal problem for designing channel assignment and routing protocol. This paper considers issues regarding multiple channels at the network layer, assuming a single channel MAC protocol such as IEEE 802.11 DCF. Also, the proposed protocol assumes that each node in the network is equipped with a single transceiver. This set of assumptions is very practical, because most devices have a single wireless card implementing the IEEE 802.11 DCF protocol. Each node uses modular exponentiation congruence to represent the channel schedule, which assures that each pair of nodes has common channels for communication in every cycle. Each node switches across channels in such a manner that each pair of nodes works on the same channel when they desire to communicate; otherwise they work on a different channel, and hence do not interfere with each other. However, for the intersecting node, there is no benefit in using single radio multiple channels since the capacity around the intersection node can at most be O (W), W is the link capacity, regardless of the number of channels. The protocol lets the intersecting node always work on the same channel whereas the nonintersecting node can work on different channels. The two states for every node in the network are the state of an intersecting node and the state of non-intersecting node. Using the proposed protocol, nodes discover multiple routes to the destination node; the node selects the path with most intersecting nodes to avoid more nodes become intersecting nodes when the number of flows increases greatly. Once a node becomes an intersecting node, it will work on the same channel in a cycle. Simulation results show that the proposed protocol significantly increases the aggregate end-to-end throughput and network capacity greatly over a single-channel protocol and some other channel assignment and routing protocols in several wireless networking scenarios.

Performance Analysis of IEEE 802.11 DCF in a Multi-Rate WLAN

The IEEE 802.11 family of specifications is by far the most prominent and successful technique for accessing WLANs. Because the channel used by wireless devices is a time-varying broadcast medium, these devices need to have multi-rate and rate-adaptive capability to adapt to the changing channel so that better performance can be achieved. In this paper, we propose an analytical model, which we call Rate-Adaptive Markov Chains, to study the saturation throughput and delay performance of an 802.11 WLAN in which the mobile hosts have multi-rate support, will use the ARF protocol to adapt rates for different channel qualities, and follow the DCF protocol to contend for data transmissions in a slowly-varying channel. Simulation results are also provided to verify the correctness of the model.

A MAC-Layer Retransmission Algorithm Designed for the Physical-Layer Characteristics of Clustered Sensor Networks

We consider scenarios in which an event, such as a mobile node arriving to collect data or a data-request arriving at a node via the sensor network, initiates the collection of one packet of data from each node in the surrounding cluster of nodes. The node requesting the data broadcasts its identity and purpose to the cluster and assumes the role of clusterhead. This broadcast message is also used to synchronize all nodes in the cluster, which covers an area with a radius of several hundred meters, to within a few microseconds. We exploit this ability to synchronize the cluster to improve retransmission algorithms in CSMA/CA-based MAC protocols. The result is a retransmission algorithm that uses a synchronized, shared contention window (SSCW) that is easy to implement and results in fewer collisions than retransmission algorithms that use binary-exponential-backoff (BEB). A simple analytical approach is further proposed to optimize the size of the shared contention window. We show via analytical, numerical, and simulation results that an SSCW-based 802.11 DCF protocol performs significantly better in these scenarios we consider than both 802.15.4 (ZigBee) and BEB-based 802.11 DCF (WiFi). We also show that SSCW-based 802.11 is more fault-tolerant and fair than TDMA

Enhancing channel utilization by improving media access coordination in wireless local area networks

AbstractDistributed coordination function (DCF) is the basis protocol for IEEE 802.11 standard wireless local area networks. It is based on carrier sense multiple access with collision avoidance (CSMA/CA) mechanism. DCF uses backoff process to avoid collisions on the wireless channel. The main drawback with this process is that packets have to spend time in the backoff process which is an additional overhead in their transmission time. The channel is rendered idle when all the stations defer their transmissions due to their backoff process. Therefore, the channel utilization and the total throughput on the channel can be improved by reducing the average time spent by the packets in the backoff process. In this paper, we propose a new media access coordination function called proposed media access protocol (PMAP) that will improve the channel utilization for successful packet transmission and therefore, the total achievable throughput. In addition, we propose an analytical model for PMAP under saturated conditions. We use this model to analyze the performance of PMAP under saturated conditions. To substantiate the effectiveness of our model, we have verified the model by simulating PMAP in NS‐2. Simulation and analytical results show that under saturated conditions, PMAP shows profound improvement in the throughput performance compared to DCF. In addition, the throughput performance of PMAP under unsaturated conditions is presented. We have also presented the delay performance of PMAP and DCF through simulation in both saturated and unsaturated conditions. Simulation results show that the average delay experienced by the packets is less in PMAP compared to DCF. Further, the variance in the packet delay is same for both PMAP and DCF protocols under unsaturated conditions. From the performance results obtained for PMAP under both saturated and unsaturated conditions, it can be concluded that PMAP is superior in performance compared to DCF. Copyright © 2006 John Wiley & Sons, Ltd.

A call admission and rate control scheme for multimedia support over IEEE 802.11 wireless LANs

Quality of service (QoS) support for multimedia services in the IEEE 802.11 wireless LAN is an important issue for such WLANs to become a viable wireless access to the Internet. In this paper, we endeavor to propose a practical scheme to achieve this goal without changing the channel access mechanism. To this end, a novel call admission and rate control (CARC) scheme is proposed. The key idea of this scheme is to regulate the arriving traffic of the WLAN such that the network can work at an optimal point. We first s how that the channel busyness ratio is a good indicator of the network status in the sense that it is easy to obtain and can accurately and timely represent channel utilization. Then we propose two algorithms based on the channel busyness ratio. The call admission control algorithm is used to regulate the admission of real-time or streaming traffic and the rate control algorithm to control the transmission rate of best effort traffic. As a result, the real-time or streaming traffic is supported with statistical QoS guarantees and the best effort traffic can fully utilize the residual channel capacity left by the real-time and streaming traffic. In addition, the rate control algorithm itself provides a solution that could be used above the media access mechanism to approach the maximal theoretical channel utilization. A comprehensive simulation study in ns-2 has verified the performance of our proposed CARC scheme, showing that the original 802.11 DCF protocol can statically support strict QoS requirements, such as those required by voice over IP or streaming video, and at the same time, achieve a high channel utilization.

Study of Medium Access Delay in IEEE 802.11 Wireless Networks

With the rising popularity of delay-sensitive real-time multimedia applications (video, voice, and data) in IEEE 802.11 wireless local area networks (WLANs), it is becoming important to study the medium access control (MAC) layer delay performance of WLANs. The MAC layer delay can be classified into two categories: 1) medium access delay, and 2) delay at interface queue (IFQ). In this paper, based on a two-dimensional chain model, we analyze the medium access delay and give a method to calculate the IFQ delay. The proposed analysis is applicable to both the basic access and the RTS/CTS access mechanisms. Through extensive simulations, we evaluate our model. The simulation results show that our analysis is extremely accurate for both basic access and RTS/CTS access mechanism of the 802.11 DCF protocol.

Accurate delay distribution for IEEE 802.11 DCF

We derive the access delay generating function of the IEEE 802.11 DCF protocol. Our analysis corrects a model recently presented by O. Tickoo and B. Sikdar (see Proc. IEEE INFOCOM 2004, p.1404-13). We demonstrate that numerical transform inversion can be used to efficiently obtain values of the distribution. Simulations show that our analytical results are highly accurate.