A modified point coordination function in IEEE 802.11 wireless LAN (original) (raw)
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An Analysis of a Modified Point Coordination Function in IEEE 802.11
2003
Since the point coordination function (PCF) in the IEEE 802.11 is based on a centralized polling protocol, some bandwidth is wasted due to the polling overheads and also due to null packets that are issued in case a polled station does not have any data to transmit. In order to reduce this waste and increase the channel utilization, we have proposed a modified version of the standard PCF. The modified PCF uses a distributed polling protocol (DPP) as the access mechanism for the uplink transmission of real-time traffic. The transmission period in the modified PCF consists of a distributed polling protocol period (DPPP) which is controlled by the DPP and the real-time traffic downlink period (RTDP). Our proposal further includes a technique for dealing with the hidden station problem for use together with the proposed modification. In this paper, an analytical analysis is done to compare the performance of the modified PCF with the standard PCF in terms of number of supportable statio...
Study of Dynamic Polling in the IEEE 802.11 PCF
Point Coordination Function (PCF) of the IEEE 802.11 protocol providing a centrally-controlled polling-based multiple access to a wireless channel is very efficient in high load conditions. However, its performance degrades with increasing the number of terminals and decreasing the load, because of wastes related to unsuccessful polling attempts. To solve the problem, we propose and study analytically the generic dynamic polling policy using backoff concept. For this aim, we develop Markov models describing the network queues changes, what allows us to estimate such performance measures as the average MAC service time and the average MAC sojourn time, to show the dynamic polling efficiency and to tune optimally the backoff rule. *
1999
This paper investigates the performance of IEEE 802.11 wireless local area network (WLAN) protocol's distributed coordination function (DCF) in the presence of mobile and hidden terminals. In order to study the joint effect of hidden terminals and user mobility on the performance of IEEE 802.11 DCF, we extend Tobagi and Kleinrock's (1975) hearing graph framework to model hidden terminals in a static environment. We derive a combined mobility and hidden terminal model using a Markov chain from the hearing graph of a given physical layout. The simple model uses two parameters: α, which controls the number of hidden terminals in the steady state, and λ, which controls the rate of mobility of each terminal. By varying the values of α and λ we can systematically generate scenario with different number of hidden terminals and different mobility rates for a particular physical layout with static obstructions. We have developed a discrete event simulator which uses the parameterized model to obtain the throughput and blocking probability behavior of an IEEE 802.11 based ad hoc network in the presence of certain static obstructions. Our simulations suggest that the IEEE 802.11 DCF protocol is robust enough to handle moderate conditions of hidden terminals and mobility, but the performance may degrade under extreme conditions. Carefully selecting protocol parameters (RTS and fragmentation threshold) can help improve the performance even under extreme conditions
Performance analysis of the IEEE 802.11 MAC protocol for wireless LANs
Wireless local area networks (WLANs) are extremely popular being almost everywhere including business, office and home deployments. The IEEE 802.11 protocol is the dominating standard for WLANs. The essential medium access control (MAC) mechanism of 802.11 is called distributed co-ordination function (DCF). This paper provides a simple and accurate analysis using Markov chain modelling to compute IEEE 802.11 DCF performance, in the absence of hidden stations and transmission errors. This mathematical analysis calculates in addition to the throughput efficiency, the average packet delay, the packet drop probability and the average time to drop a packet for both basic access and RTS/CTS medium access schemes. The derived analysis, which takes into account packet retry limits, is validated by comparison with OPNET simulation results. We demonstrate that a Markov chain model presented in the literature, which also calculates throughput and packet delay by introducing an additional transition state to the Markov chain model, does not appear to model IEEE 802.11 correctly, leading to ambiguous conclusions for its performance. We also carry out an extensive and detailed study on the influence on performance of the initial contention window size (CW), maximum CW size and data rate. Performance results are presented to identify the dependence on the backoff procedure parameters and to give insights on the issues affecting IEEE 802.11 DCF performance. network connectivity, being a mouse-click away from key information and applications. Moreover, recent advances in wireless technology and mobile communications have equipped wireless capability portable devices including palmtop computers, laptops and personal digital assistants (PDAs) .
IEEE 802.11 distributed coordination function (DCF): analysis and enhancement
2002
Being a part of IEEE project 802, the 802.11 medium access control (MAC) is used to support asynchronous and time bounded delivery of radio data packets. It is proposed that a distributed coordination function (DCF), which uses carrier sense multiple access with collision avoidance (CSMA/CA) and binary slotted exponential backoff, be the basis of the IEEE 802.11 WLAN MAC protocols. This paper proposes a throughput enhancement mechanism for DCF by adjusting the contention window (CW) resetting scheme. Moreover, an analytical model based on Markov chain is introduced to compute the enhanced throughput of 802.11 DCF. The accuracy of the model and the enhancement of the proposed scheme are verified by elaborate simulations
Efficient voice communications over IEEE 802.11 WLANs using improved PCF procedures
This paper presents a new dynamically adaptable polling scheme for efficient support of voice communications over different IEEE802.11 networks. The proposed polling scheme is simple to implement and does not require any modification on the existing access protocol. The analytical approach that models the proposed polling scheme, uses a discrete-time Markov chain and proves that the specific polling scheme, when silence detection is used at the wireless terminals, improves the capability of IEEE802.11wireless LANs for handling voice traffic efficiently.
Distributed point coordination function for IEEE 802.11 wireless ad hoc networks
Ad Hoc Networks, 2012
The Distributed Point Coordination Function (DPCF) is presented in this paper as a novel Medium Access Control Protocol (MAC) for wireless ad hoc networks. DPCF extends the operation of the Point Coordination Function (PCF) defined in the IEEE 802.11 Standard to operate over wireless networks without infrastructure. In PCF, a central point coordinator polls the users to get access to the channel and data collisions are completely avoided, thus yielding high performance. In order to extend its high performance to networks without infrastructure, the DPCF is proposed in this paper as a combination of the Distributed Coordination Function (DCF) and the PCF. The general idea is to combine a dynamic, temporary, and spontaneous clustering mechanism based on DCF with the execution of PCF within each cluster. The backwards compatibility of DPCF with legacy 802.11 networks is also assessed in this paper. Comprehensive computer-based simulations demonstrate the high performance of this new protocol in both single-hop and multi-hop networks.
Enhancing performance of the IEEE 802.11 distributed coordination function via packet bursting
IEEE Global Telecommunications Conference Workshops, 2004. GlobeCom Workshops 2004., 2004
During the past few years, Wireless Local Area Networks (WLANs) have become extremely popular. The IEEE 802.11 protocol is the dominating standard for WLANs employing the Distributed Coordination Function (DCF) as its essential medium access control (MAC) mechanism. This paper presents a simple and accurate analysis using Markov chain modelling to compute IEEE 802.11 DCF performance, in the absence of hidden stations and transmission errors. This mathematical analysis calculates in addition to the throughput efficiency, the average packet delay and the packet drop probability for both basic access and RTS/CTS medium access schemes. The derived analysis, which takes into account packet retry limits, is validated by comparison with OPNET simulation results. The mathematical model is used to study the effectiveness of the RTS/CTS scheme at high data rates and the performance improvements of transmitting a burst of packets after winning the contention for medium access. Packet bursting considerably increases both throughput and packet delay performance but lowers the short-term fairness on medium access.