Performance Of WLANs Research Articles

Mitigating starvation in dense WLANs: A multi-armed Bandit solution

With the recent 802.11ax amendment to the IEEE standard commercialized as Wi-Fi 6, WLANs have the potential to greatly improve the spatial reuse of radio channels. This resorts to the new ability for APs (Access Points) to dynamically modify their transmission power as well as the signal energy threshold beyond which they consider the radio channel to be free or busy. In general, selecting adequate values for these parameters is complex because of (i) the high dimensionality of the problem and (ii) the uncertainty of the radio environment. To overcome these difficulties, we frame this problem as a MAB (Multi-Armed Bandit) problem and propose an efficient and robust solution using Thompson sampling, an original sampling of WLAN configurations, and a tailor-made reward function. We evaluate the efficiency of our solution as well as several other ones with scenarios inspired by real-life WLANs’ deployments using the network simulator ns-3. The numerical results show the ability of our solution along with its superiority over the others at finding adequate parameterization at each AP thereby significantly improving the overall performance of WLANs.

Performance of WLAN in Downlink MU-MIMO Channel with the Least Cost in Terms of Increased Delay

To improve the performance of IEEE 802.11 wireless local area (WLAN) networks, different frame-aggregation algorithms are proposed by IEEE 802.11n/ac standards to improve the throughput performance of WLANs. However, this improvement will also have a related cost in terms of increasing delay. The traffic load generated by mixed types of applications in current modern networks demands different network performance requirements in terms of maintaining some form of an optimal trade-off between maximizing throughput and minimizing delay. However, the majority of existing researchers have only attempted to optimize either one (to maximize throughput or minimize the delay). Both the performance of throughput and delay can be affected by several factors such as a heterogeneous traffic pattern, target aggregate frame size, channel condition, competing stations, etc. However, under the effect of uncertain conditions of heterogeneous traffic patterns and channel conditions in a network, determining the optimal target aggregate frame size is a significant approach that can be controlled to manage both throughput and delay. The main contribution of this study was to propose an adaptive aggregation algorithm that allows an adaptive optimal trade-off between maximizing system throughput and minimizing system delay in the WLAN downlink MU-MIMO channel. The proposed approach adopted different aggregation policies to adaptively select the optimal aggregation policy that allowed for achieving maximum system throughput by minimizing delay. Both queue delay and transmission delay, which have a significant impact when frame-aggregation algorithms are adopted, were considered. Different test case scenarios were considered such as channel error, traffic pattern, and number of competing stations. Through system-level simulation, the performance of the proposed approach was validated over the FIFO aggregation algorithm and earlier adaptive aggregation approaches, which only focused on achieving maximum throughput at the expense of delay. The performance of the proposed approach was evaluated under the effects of heterogenous traffic patterns for VoIP and video traffic applications, channel conditions, and number of STAs for WLAN downlink MU-MIMO channels.

Enhancing Performance of Multi-Rate WLANs: Ant Colony Approach

The trade-off between users’ fairness and network throughput may be unacceptable in a multi-rate 802.11 WLAN environment. In this paper, we will design a new intuitive simplified mathematical model called simplified coefficient of variation (SCV) to closely reflect our topic. Through controlling the power of Access Points, SCV can optimize and improve the performance. Since our topic is a NP-hard problem, we use Ant Colony Algorithm to solve our model in a practical scenario. The simulation shows excellent results indicating that our model is efficient and superior to an existing method. Also we use software SAS to further reveal the relationships among the three indicators to illustrate the essence of our approach and an existing algorithm.

Detection of Selfish Manipulation of Carrier Sensing in 802.11 Networks

Recently, tuning the clear channel assessment (CCA) threshold in conjunction with power control has been considered for improving the performance of WLANs. However, we show that, CCA tuning can be exploited by selfish nodes to obtain an unfair share of the available bandwidth. Specifically, a selfish entity can manipulate the CCA threshold to ignore ongoing transmissions; this increases the probability of accessing the medium and provides the entity a higher, unfair share of the bandwidth. We experiment on our 802.11 testbed to characterize the effects of CCA tuning on both isolated links and in 802.11 WLAN configurations. We focus on AP-client(s) configurations, proposing a novel approach to detect this misbehavior. A misbehaving client is unlikely to recognize low power receptions as legitimate packets; by intelligently sending low power probe messages, an AP can efficiently detect a misbehaving node. Our key contributions are: 1) We are the first to quantify the impact of selfish CCA tuning via extensive experimentation on various 802.11 configurations. 2) We propose a lightweight scheme for detecting selfish nodes that inappropriately increase their CCAs. 3) We extensively evaluate our system on our testbed; its accuracy is 95 percent while the false positive rate is less than 5 percent.

Opportunistic Use of Client Repeaters to Improve Performance of WLANs

Currently deployed IEEE 802.11 WLANs (Wi-Fi networks) share access point (AP) bandwidth on a per-packet basis. However, various stations communicating with the AP often have different signal qualities, resulting in different transmission rates. This induces a phenomenon known as the <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">rate</i> <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">anomaly</i> <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">problem</i> , in which stations with lower signal quality transmit at lower rates and consume a significant majority of airtime, thereby dramatically reducing the throughput of stations transmitting at higher rates. We propose SoftRepeater, a practical, deployable system in which stations cooperatively address the rate anomaly problem. Specifically, higher rate Wi-Fi stations opportunistically transform themselves into repeaters for lower rate stations when transmitting data to/from the AP. The key challenge is to determine when it is beneficial to enable the repeater functionality. In view of this, we propose an initiation protocol that ensures that repeater functionality is enabled only when appropriate. Also, our system can run directly on top of today's 802.11 infrastructure networks. In addition, we describe a novel, zero-overhead network coding scheme that further alleviates undesirable symptoms of the rate anomaly problem. Using simulation and testbed implementation, we find that SoftRepeater can improve cumulative throughput by up to 200%.

WEIGHTED CHANNEL ALLOCATION AND POWER CONTROL FOR SELF-CONFIGURABLE INFRASTRUCTURE WLANS

IEEE802.11 WLANs show increasing growth in popularity. Since these networks operate in the unlicensed ISM bands where the number of non-overlapping channels is limited, the growing number of wireless nodes leads to interference. It is well known that the interference leads to degraded performance of WLANs, especially in densely populated areas where the number of overlapping nodes is very large. Channel assignment algorithms have been proposed in recent years, in order to minimize or avoid interference between neighboring access points and hence alleviating the problem. In particular, weighted assignment algorithms have been frequently occurring in the literature. However, the effects of these algorithms are currently not well understood. In this paper, we present results, which show that weighted channel assignment algorithms that do not consider traffic categories can lead to heavy interference among WLANs with delay sensitive traffic, e.g. voice traffic. In order to overcome this, we instead propose a weighted access category channel assignment algorithm (WACCA). We present results from experiments, which show that WACCA achieves a small degree of Interference (DOI) as compared with a greedy algorithm. We also show that there is a tradeoff with convergence time. Furthermore, we propose an integration of WACCA with dynamic transmission power control and show how this combined method produces even more gain.

Traffic capacity of multi-cell WLANS

Performance of WLANs has been extensively studied during the past few years. While the focus has mostly been on isolated cells, the coverage of WLANs is in practice most often realised through several cells. Cells using the same frequency channel typically interact through the exclusion region enforced by the RTS/CTS mechanism prior to the transmission of any packet. In this paper, we investigate the impact of this interaction on the overall network capacity under realistic dynamic traffic conditions. Specifically, we represent each cell as a queue and derive the stability condition of the corresponding coupled queuing system. This condition is then used to calculate the network capacity. To gain insight into the particular nature of interference in multi-cell WLANs, we apply our model to a number of simple network topologies and explicitly derive the capacity in several cases. The results notably show that the capacity gain obtained by using M frequency channels can grow significantly faster than M, the rate one might intuitively expect. In addition to stability results, we present an approximate model to derive the impact of network load on the mean transfer rate seen by the users.

A MIMO-Based Collision Mitigation Scheme in Uplink WLANs

Although there exist random backoff schemes in WLANs, a collision problem among stations (STAs) is one of the critical factors that degrade the performance of WLAN systems. To mitigate this collision problem, a MIMO-based uplink collision mitigation scheme is proposed by utilizing additional degrees of freedom through multiple antennas, and, consequently, enhances the system performance. Analysis and simulation results show that there is at least 30% throughput enhancement in a basic service set (BSS) with more than 10 STAs, compared to the performance of conventional WLANs in case of saturation traffic.

Influence of the Limited Retransmission on the Performance of WLANs Using Error-Prone Channel

In WLANs, stations sharing a common wireless channel are governed by IEEE 802.11 protocol. Many conscious studies have been conducted to utilize this precious medium efficiently. However, most of these studies have been done either under assumption of idealistic channel condition or with unlimited retransmitting number. This paper is devoted to investigate influence of limited retransmissions and error level in the utilizing channel on the network throughput, probability of packet dropping and time to drop a packet. The results show that for networks using basic access mechanism the throughput is suppressed with increasing amount of errors in the transmitting channel over all the range of the retry limit. It is also quite sensitive to the size of the network. On the other side, the networks using four-way handshaking mechanism has a good immunity against the error over the available range of retry limits. Also the throughput is unchangeable with size of the network over the range of retransmission limits. However, the throughput does not change with retry limits when it exceeds the maximum number of the backoff stage in both DCF’s mechanisms. In both mechanisms the probability of dropping a packet is a decreasing function with number of retransmissions and the time to drop a packet in the queue of a station is a strong function to the number of retry limit, size of the network, the utilizing medium access mechanism and amount of errors in the channel.

On the Impact of Security on the Performance of WLANs

This paper investigates the impact of security on the performance of WLAN. More specifically, it analyzes the impact of different implementations of encryption techniques used by two security protocols, namely Wired Equivalent Privacy (WEP) and Wi-Fi Protected Access (WPA) on the throughput over WLAN IEEE 802.11g. This paper also addresses the different issues related to the security protocols currently used in WLAN IEEE 802.11g and demonstrates how these issues affect the final results of the experiments conducted. The results show that within the same access point range the security adds moderate degradation on the throughput that may affect some applications over both infrastructure and ad hoc WLANs.

GDCF: game-theoretic distributed co-ordination function in WLANs

A game-theoretic DCF (GDCF) in IEEE 802.11 is presented, to improve the performance of WLANs by designing a simple auto-degressive backoff mechanism based on incompletely co-operative game theory. Simulation results show that GDCF can increase system throughput and decrease delay and packet-loss-rate while maintaining reasonable energy consumption

Central Manager: A Solution to Avoid Denial Of Service Attacks for Wireless LANs.

802.1x is a security protocol based on the frame structure of 802.11. It attempts to provide strong authentication, access control, and WEP key management for Wireless LANs. Unfortunately, 802.1x misses its goals in access control denial of service (DoS) attacks. Currently, there are no IEEE approved ways to solve the security hole. We propose a Central Manager (CM) not only to take the responsibility of an authentication server, but also to add functionality to prevent denial of service attacks. We analyze the performance of WLANs under DoS attacks and demonstrate the correctness of the CM solution through simulations. From the simulations, we conclude the CM solution can efficiently avoid DoS attacks and alleviate the effects from the DoS attacks.

The impact of power limitations and adjacent residence interference on the performance of WLANs for home networking applications

This paper considers the application of 5 GHz wireless LAN technology to home networking applications. An assessment of physical layer performance is presented for both the IEEE 802.11a and HIPERLAN/2 standards in the form of achievable data rate as a function of received signal to noise ratio. The transmit power limitations imposed by the relevant regulatory bodies are presented and the implications of transmit power amplifier limitations considered. Based on this information, a state of the art propagation modelling tool is used to evaluate the performance of the 802.11a and HIPERLAN/2 systems in an example residential environment. The achievable data rate and coverage is evaluated for a variety of scenarios and the implications of potential co-residence interference are evaluated. It is found that data rates greater than 20 Mbits/s can be achieved with 100% coverage if the access point is well located and the transmit power is high. Even in the case where transmit power is severely limited, data rates in excess of 10 Mbits/s can be achieved throughout much of the example environment. Adjacent residence interference is found to have a severe debilitating effect and is thus identified as topic of crucial importance.