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Abstract
In 802.11 infrastructure BSS, the channel throughput will decrease when increasing the number of competing STAs. Also severe asymmetry exists between downlink and uplink data because AP accesses the share channel without any priority. Both problems are solved by a new MAC schema which adjusts the initial contention window of AP and STA to optimized values. A new estimation method for STA number is also proposed via dynamic MAC addresses statistic at AP side. Afterwards, optimized initial contention window values are derived from a mathematical model under downlink and uplink bandwidth control. Simulation indicates that the schema proposed can estimate the channel situation exactly and improve channel throughput with downlink/uplink bandwidth control obviously.
... The fairness issues resulting from this antagonism have been the subject of several works. [57] and [58] propose dynamic adaptations of some Medium Access Control (MAC) parameters such as the initial backoff contention window, so as to have an optimal uplink to downlink bandwidth ratio. In [59], a Automatic cell planning enhancement for IEEE 802.11 networks 80 new parameter (utilization ratio) is proposed for the MAC protocol in order to have an efficient control of the uplink and downlink traffic even under saturation condition 10 . ...
The constant evolution of wireless technologies such as Wi-Fi, mobile networks standards or IoT, has given rise to new applications and usages. The possibilities offered by this multitude of alternatives are exploited by heterogeneous wireless networks which, by combining within a single network several technologies, provide the users with a seamless access to complementary services. However, to take full advantage of these benefits, there are several technical issues to address. One of them is related to the deployment of these multi-technology networks. In practice, this task relies, most of the time, on radio network design software to achieve optimal planning. In such context, the main objective of this thesis is to establish models which can be used by radio network planning tools in order to the deployment of multi-technology wireless local area networks. This task has involved calibrating propagation models for radio coverage estimation, in residential indoor environments from 800 MHz to 60 GHz; developing a throughput model for Wi-Fi capacity estimation based on uplink and downlink traffic; and establishing a multi- objective resolution model to optimize the positioning of access points operating at 5 and 60 GHz. Moreover, this thesis also proposes practical recommendations for a better positioning of access points during deployment phases. This task has been achieved through coverage sensitivity studies to various factors, such as the transmitter surroundings or the presence of obstructing people.
... The issues generated by this antagonism have been the main subject of several studies in the literature. [2] and [3] propose dynamic adjustments in the existing Medium Access Control (MAC) parameters, such as the initial backoff contention window (CWmin), in order to get an optimal uplink to downlink bandwidth ratio. In [4], an improved MAC protocol is proposed by adding new parameters so that one may control efficiently the uplink to downlink ratio even under saturation condition. ...
With the evolution of Internet usage, the uplink traffic in Wireless Local Area Networks (WLANs) has become as important as the downlink one. This paper presents an analytical throughput model for IEEE 802.11 networks which can be used to evaluate the maximum system capacity based on the uplink to downlink throughput ratio. The proposed model can be exploited by Automatic Cell Planning (ACP) modules during optimization phases in order to determine the probability that a given configuration meets the design requirements.
... The algorithm aims at ascertaining the optimal amount of FEC redundant packets to balance the trade-off between the utilization ratio of the wireless channel and the QoS of video transmission. Our research is inspired by and developed from the work of Wu et al. (2005) and Feng et al. (2007). Based on their works, we develop an analytical model of the playable frame rate for MPEG stream with a maximum sending rate constraint. ...
In this paper, a channel adaptive FEC algorithm is proposed which balances the trade-off between the QoS of video transmission
and the bandwidth utilization ratio in wireless IP networks. Our algorithm can dynamically adjust to a suboptimal number of
FEC redundant packets to cater to the time-varying wireless channel. For the sake of obtaining the suboptimal amount of FEC
redundant packets, we derive two analytical models, one is the playable frame rate in MPEG video stream, another is the effective
utilization ratio of FEC. Based on these analytical models, a suboptimal value of redundant packets, which makes both the
quality of video stream and the effective utilization ratio of FEC approximate their maximum, is calculated by predicting
the quality of video stream and effective utilization ratio of FEC under different network conditions (characterized by packet
loss probability in this paper). The simulation results indicate that the QoS of wireless video transmission and the bandwidth
utilization ratio are improved by employing the proposed algorithm.
KeywordsAdaptive FEC-Error control-Playable frame rate-Wireless-Video
The data traffic needed to be transferred by APs is much more than the other STAs in the IEEE802.11 DCF networks. However, APs access the wireless link with the same priority as STAs, and thus the throughput between uplink and downlink is of great injustice. In this paper, an adaptive optimization scheme is proposed to achieve fairness between uplink and downlink flows. APs monitor the growing real-time data traffic, and when the network system is in heavy traffic, APs could adaptively adjust the contention window to achieve fairness. Detailed simulation results show that the scheme can effectively adapt to various networks different in data flow numbers and packet size, and consequently achieve fairness between uplink and downlink flows with the total throughput increased.
Wireless local area networks (WLANs) based on the IEEE 802.11 standard are becoming increasingly popular and widely deployed. It is likely that WLAN will become an important complementary technology for future cellular systems and will typically be used to provide hotspot coverage. In this paper, the complementary use of WLANs in conjunction with mobile cellular networks is studied. We identify the fairness problem between uplink and downlink traffic flows in the IEEE 802.11 distributed coordination function and then propose an easy solution that can be implemented at the access point (AP) in the MAC layer without modification of the standard for stations (STAs). This solution aims at providing a controllable resource-allocation method between uplink and downlink traffic flows and adapting the parameters according to the dynamic traffic load changes. The proposed solution also enhances the system utilization by reducing the probability of frame collision.
The dynamic character of complex and variable network environment, the key problem, puzzles the corresponding protocols design for wireless LANs. However, the distributed coordination function (DCF) of IEEE 802.11 MAC protocol, which is carrier sense multiple access with collision avoidance (CSMA/CA) using constant parameters, could not perform well when network environment changes. Thus many researchers try to optimize IEEE 802.11 DCF. However early dynamic optimization mechanisms for the protocol mostly depend on measuring the number of "competing" stations accurately. The problem of them is that the algorithms are too complex to apply in reality. In our research, we find that system performance approaches optimization with the same protocol parameters, when the number of competing stations changes within a certain range dynamically. Therefore, we propose a self-adaptive optimization mechanism, DOOR (dynamic optimization on range), for the IEEE 802.11 DCF. DOOR uses filter to estimate the range of competing station number and adjusts the protocol parameters to optimize system performance effectively. The detailed analytical model and performance evaluation for the new mechanism are given. Moreover, the measurement method and parameters of filter are introduced. At last, the elaborate numerical results show that our mechanism could not only achieve much higher throughput and lower delay than the standard IEEE 802.11 DCF along with the change of competing stations, but also improve the stability of system performance based on reasonably partitioned ranges.
In distributed systems like 802.11 WLANs, simple requirements like providing fair access to all users are hard to get by because of the random access protocol and the unpredictability of the wireless channel. The main contribution of this paper is the proposal of an LLC-layer algorithm that is implemented at both AP and WSs. The algorithm aims at guaranteeing fair access to the medium to every user, by awarding longer transmission opportunities to WSs that experienced short channel failures. At the same time, an adaptive contention window setting protects downlink traffic from the unbalancement typical of WLANs with AP. The proposed solution is outlined and presents a simulation study, which shows the effectiveness of the new algorithm in comparison to the standard 802.11b implementation both under a TCP and a UDP traffic scenario.
Throughput performance of the IEEE 802.11 distributed coordination function (DCF) is very sensitive to the number n of competing stations. The contribute of this paper is threefold. First, we show that n can be expressed as function of the collision probability encountered on the channel; hence, it can be estimated based on run-time measurements. Second, we show that the estimation of n, based on exponential smoothing of the measured collision probability (specifically, an ARMA filter), results to be a biased estimation, with poor performance in terms of accuracy/tracking trade-offs. Third, we propose a methodology to estimate n, based on an extended Kalman filter coupled with a change detection mechanism. This approach shows both high accuracy as well as prompt reactivity to changes in the network occupancy status. Numerical results show that, although devised in the assumption of saturated terminals, our proposed approach results effective also in non-saturated conditions, and specifically in tracking the average number of competing terminals.
The IEEE has standardized the 802.11 protocol for wireless local
area networks. The primary medium access control (MAC) technique of
802.11 is called the distributed coordination function (DCF). The DCF is
a carrier sense multiple access with collision avoidance (CSMA/CA)
scheme with binary slotted exponential backoff. This paper provides a
simple, but nevertheless extremely accurate, analytical model to compute
the 802.11 DCF throughput, in the assumption of finite number of
terminals and ideal channel conditions. The proposed analysis applies to
both the packet transmission schemes employed by DCF, namely, the basic
access and the RTS/CTS access mechanisms. In addition, it also applies
to a combination of the two schemes, in which packets longer than a
given threshold are transmitted according to the RTS/CTS mechanism. By
means of the proposed model, we provide an extensive throughput
performance evaluation of both access mechanisms of the 802.11 protocol
11 Ad-Hoc Networks, a chapter
- G Bianchi
- S Choi