Evaluating and Improving Wireless Local Area Networks Performance

There has been widespread deployment of IEEE 802.11 wireless local area networks (LANs) because of high demand from mobile terminals, such as iPod and Android terminals. With the increasing energy consumption of the wireless LANs, the development of power saving technologies incorporated into the wireless LANs have become important. In wireless LANs, access points (APs) continuously consume the power regardless of the communication. Therefore, we have proposed the Radio-On-Demand (ROD) wireless LAN, which provides power saving schemes on the basis of the utilization of wireless LANs. In this study, we particularly focus on the power saving scheme of the APs, and propose the decentralized association management of ROD wireless LANs. In our scheme, an AP assigns associated stations (STAs) to new APs before switching to sleep mode. Simulation results show that the proposed scheme can realize sufficient power saving.

In wireless local area networks (WLANs) packet classification is done to report matched packet to its destination node. Although several schemes are proposed, they suffer from execution corruption. In this paper initially a choleric layer is being constructed in WLANs to increase the bandwidth and performance of WLANs. We use Joint-Interface to combine all the layers. By using cross layer co-ordination among all layer is increased while comparing to the traditional layer architecture. When the packet arrives they are moved to routing table where all possible path to the nearest neighbor are found out and moved to, forwarding table which contains only the route chosen by the routing algorithm. Routing table is constructed using Ad-hoc on demand distance vector protocol. While forwarding packet, it is being double encrypted and decrypted. In order to avoid congestion occurrence near destination elliptical priority scheduling is used where time slot is given for each packet to be processed out and to send packet based on a priority algorithm are being used. Hence we can increase the classification speed and performance.

In IEEE 802.11 wireless local area networks (WLANs), TCP suffers unfairness between uplink and downlink flows due to its asymmetric reactions towards data and ACK losses at the AP (Access Point), and the AP's inability to distinguish itself from other contending stations accessing the medium. In this paper, we propose a novel dual queue management (DQM) scheme with ECN (Explicit Congestion Notification) at the AP's downlink buffer to improve TCP performance in infrastructure WLANs. Our approach maintains two queues for TCP ACK and data respectively, with their total length controlled by a PI (Proportional Integral) controller to prevent congestion. ACK/data packets are marked/dequeued dependent on uplink/downlink time usage of the wireless channel. We also propose an opportunistic scheduling mechanism of the two queues exploiting multi-rate capability and multi-user diversity for more efficient link utilization. We evaluate the proposed approach in ns-2 and our simulation results demonstrate that this design with few states can significantly improve TCP congestion control, fairness performance and link utilization in WLANs.

Collision is imminent in wireless networks (WNs) capacitated with randomized distributed channel access. In such networks, the probability of frame drop (Pdrop) is greater than zero due to successive collisions with a finite retry limit m. The IEEE 802.11 DCF is one such widely accepted protocol used in wireless local area networks (WLANs). The objective of the work reported in this paper is to provide guaranteed channel access to colliding frames for avoiding successive collisions for any loss-sensitive application, and thus, increase network throughput under finite m. We propose the semi-distributed backoff (SDB) algorithm, which operates in two modes: S-mode and R-mode. The key idea of the SDB scheme is to perform receiver-side backoff, if a mobile station encounters collision even after performing the existing sender-side backoff procedures. Using the SDB scheme, we design Semi-DCF, a MAC protocol for WLANs, which performs opportunistic migration from random to deterministic backoff. Semi-DCF functions independent of m. This protocol exploits the collision detection capability of receivers for disseminating information on optimal backoffs to the contenders using signature vectors. An analysis of Semi-DCF using the 2D Markov chain, coupled with results of network simulation establishes its superior performance in WLANs.

Rapid deployment of IEEE 802.11 wireless local area networks (WLANs) and their increasing quality of service (QoS) requirements motivate extensive performance evaluations of the upcoming 802.11e QoS-aware enhanced distributed coordination function (EDCA). Most of the analytical studies up-to-date have been based on one of the three major performance models in legacy distributed coordination function analysis, requiring a large degree of complexity in solving multidimensional Markov chains. Here, we expose the common guiding principle behind these three seemingly different models. Subsequently, by abstracting, unifying, and extending this common principle, we propose a new unified performance model and analysis method to study the saturation throughput and delay performance of EDCA, under the assumption of a finite number of stations and ideal channel conditions in a single-hop WLAN. This unified model combines the strengths of all three models, and thus, is easy to understand and apply; on the other hand, it helps increase the understanding of the existing performance analysis. Despite its appealing simplicity, our unified model and analysis are validated very well by simulation results. Ultimately, by means of the proposed model, we are able to precisely evaluate the differentiation effects of EDCA parameters on WLAN performance in very broad settings, a feature which is essential for network design.

Low proflle, light weight, easily mounted and broad bandwidth are the key charac- teristics for antennae designed for wireless applications. The microstrip antenna (MSA) suits the features mentioned except for its narrow bandwidth. The bandwidth of the microstrip antenna usually ranges from less than 1% to several percent. This paper experimentally investigates an alternative approach in enhancing the bandwidth of the microstrip antenna for the Wireless Lo- cal Area Network (WLAN) application operating at a frequency of 2.45GHz. The bandwidth enhancement technique which is studied is the Identical Dual Patch Microstrip Antenna with Air-Gap (IDMA). A bandwidth enhancement of more than 11% was achieved. Wireless applications have undergone rapid development in recent years. One particular wireless application that has experienced this trend is the Wireless Local Area Network (WLAN). The wireless application that is selected to be studied is the 2.4GHz to 2.5GHz frequency band which is based on the 802.11b WLAN standard. This frequency band is very popular due to its low cost. WLAN antenna requires being low proflle, light weight and broad bandwidth. The microstrip antenna suits the features very well except for its narrow bandwidth. The WLAN antenna should have a minimum bandwidth of 100MHz to fully utilize the WLAN band based on the 802.11b standard. The conventional microstrip antenna could not fulflll this requirement as its bandwidth usually ranges from less than 1% to several percent (1). Although the required operating frequency range is from 2.4GHz to 2.5GHz, at least double the bandwidth is required to avoid expensive tuning operations and to cause uncritical manufacturing. Therefore, there is a need to enhance the bandwidth of the microstrip antenna for WLAN applications. This paper investigates a technique which can enhance the bandwidth of the microstrip antenna without increasing the lateral size and the complexity of the microstrip antenna too much. The Identical Dual Patch Microstrip Antenna with Air-Gap (IDMA) bandwidth enhancement technique takes the advantage of using the air gap to lower the efiective permittivity and increase the total thickness of the microstrip antenna which is essential for bandwidth enhancement. This bandwidth enhanced microstrip antenna can be deployed for the WLAN application operating at a frequency of 2.45GHz. 2. SIMULATED AND MEASURED RESULTS OF THE SINGLE-LAYER MICROSTRIP ANTENNA

HIPERLAN/2 802.11a, 802.11g and HiSWANa wireless local area networks (WLAN) employ coded orthogonal frequency division multiplexing (COFDM) and provide data rates of up to 54 Mbit/s in a 20 MHz bandwidth. In this paper, space-time block coding (STBC) techniques are considered as a means of enhancing the performance of COFDM WLAN. To perform channel estimation for multiple transmit and receive antennas, it is necessary to make transmitted pilot signals orthogonal in space and time. This was achieved using a Hadamard design. A time domain least square channel estimator was used to achieve high performance. Packet error rate (PER) performance results for, the case of 2 Tx and 2 Rx antennas are presented and throughput enhancements are evaluated. It is observed that STBC doubles the link throughput for low SNR values. For the case of an 802.11a/g network, results for different packet lengths are also presented.

Examines the effect of radio capture on the performance of radio frequency wireless local area networks (LANs). In many wireless LANs, multiple remote stations may simultaneously attempt to transmit data packets. Due to the capture effect, differences in received power levels can result in the successful reception of a packet in the presence of contending transmissions. The authors compare several types of radio capture models and investigate their effects on the slotted Aloha protocol, which is a component protocol of more complex multiple access protocols that are used in wireless LANs. Specifically, they analyse a vulnerability circle capture model as well as a more detailed model that includes the cumulative effect of the interference power generated by multiple contending remote stations. The effects of Rayleigh fading, shadowing, and different spatial distributions of remote stations are also considered. >

The performance of Wireless Local Area Network (WLAN) is highly dependent on the processes that are implemented in the Medium Access Control (MAC) sublayer regulated by the IEEE 802.11 standard. In turn, various parameters affect the performance of the MAC sublayer, the most important of which is the number of stations in the network and the offered load. With the massive growth of multimedia traffic, research of the network performance depending on traffic types is relevant. In this paper, we present the impact of a high-/low-priority traffic ratio on WLAN performance with different numbers of access categories. The simulation results show different impact of high-/low-priority traffic ratio on the performance of the MAC sublayer of wireless LANs depending on different network-sizes and on network conditions. Performance of the large network with two access categories and with the prevalent high-priority traffic is significantly higher than in the case of using four categories on the MAC sublayer. This allows us to conclude that the performance improvement of the large network with the prevalent high-priority traffic can be achieved by an adaptive adjustment of the access categories number on the MAC sublayer.

Connecting vehicles to the Internet is an emerging challenge of wireless networks. There are two competing methods for achieving this. First, the wireless local area network (WLAN) approach is based on the IEEE 802.11p standard (in its European version called ETSI ITS-G5) created for Cooperative-Intelligent Transportation System applications. Second, the cellular network approach is based on LTE/5G technologies which have been exploited in recent years to support vehicular applications. Advantages such as high bandwidth, high coverage and high reliability make cellular networks a great option for the vehicular environment.This article describes two datasets that support the analysis of WLAN (ETSI ITS-G5) and Cellular (LTE/5G) technologies in a real vehicular and road environment. The two datasets summarize the results obtained in a collection of network performance tests performed in the city of Aveiro, Portugal. In these tests, a set of vehicles (8 On-Board Units) moved randomly around the city, passing near a group of stationary nodes (11 Road-Side Units) uploading data to a server. In the WLAN dataset, data was sent using the ETSI ITS-G5 technology, whereas, in the Cellular dataset, data was sent using LTE/5G technologies. While testing, location, signal quality, and network performance data (achieved throughput, jitter, etc.) were collected.This dataset can support a realistic analysis of WLAN and Cellular performance in an environment that is not only vehicular but also urban, with obstacles and interference.

More and more devices, such as Bluetooth and IEEE 802.15.4 devices forming Wireless Personal Area Networks (WPANs) and IEEE 802.11 devices constituting Wireless Local Area Networks (WLANs), share the 2.4 GHz Industrial, Scientific and Medical (ISM) band in the realm of the Internet of Things (IoT) and Smart Cities. However, the coexistence of these devices could pose a real challenge—co-channel interference that would severely compromise network performances. Although the coexistence issues has been partially discussed elsewhere in some articles, there is no single review that fully summarises and compares recent research outcomes and challenges of IEEE 802.15.4 networks, Bluetooth and WLANs together. In this work, we revisit and provide a comprehensive review on the coexistence and interference mitigation for those three types of networks. We summarize the strengths and weaknesses of the current methodologies, analysis and simulation models in terms of numerous important metrics such as the packet reception ratio, latency, scalability and energy efficiency. We discover that although Bluetooth and IEEE 802.15.4 networks are both WPANs, they show quite different performances in the presence of WLANs. IEEE 802.15.4 networks are adversely impacted by WLANs, whereas WLANs are interfered by Bluetooth. When IEEE 802.15.4 networks and Bluetooth co-locate, they are unlikely to harm each other. Finally, we also discuss the future research trends and challenges especially Deep-Learning and Reinforcement-Learning-based approaches to detecting and mitigating the co-channel interference caused by WPANs and WLANs.

In this paper, we discuss the experimental results of application-layer delay reduction methods, which can reduce the delay during TCP applications. Due to the popularization of smart phones, Wireless Local Area Network (WLAN) access such as WLAN hot spot or WLAN tethering is increasing. This increase leads to a WLAN channel being shared by multiple data flows, resulting in the degradation of the communication performance. Specifically, the delay of the real time applications that communicate over TCP can be made longer. To reduce the delay, we developed three methods: reducing the amount of data to send, triggering TCP’s fast retransmission earlier, and returning TCP’s acknowledgment immediately. In our experiments, we measured the delay during the real time TCP applications connected with each other over WLAN and commercial fixed network and analyzed the effectiveness of our methods in the case of WLAN performance being degraded by the file transfer flow. Results indicate that our methods can reduce the 95th percentile of the delay by as much as 84%.

Cognitive Radio (CR) is expected to bring about a more flexible wireless communication environment by the efficient utilization of spectrum resources. In this paper, a CR coexisting with IEEE 802.11 Wireless Local Area Networks (WLANs) is proposed. In the Distributed Coordination Function (DCF) access scheme in IEEE 802.11 WLAN, a station (STA) transmits a data frame by executing a random backoff procedure after Distributed Inter Frame Space (DIFS) period, and the destination STA of the data frame responds with Ack frame to the source STA after Short Inter Frame Space (SIFS) period. After the Ack frame is transmitted, the same procedures are repeated. The proposed CR terminal recognizes the DIFS period and the SIFS period, and then it transmits CR signals during these periods with the transmission power that does not affect the IEEE 802.11 WLAN protocol. Thus, the proposed CR terminals recognize the periods during which IEEE 802.11 STAs do not transmit any frames and they use the periods to transmit CR signals. In this paper, IEEE 802.11 WLAN STA that has the capability for the proposed CR technique in addition to the normal 802.11 WLAN capability is considered and the improved average throughputs by the CR communications are evaluated in the computer simulation, and then the effectiveness of the proposed method is clarified.

There has been a tremendous increase in the use of wire/wireless Local Area Networks (LAN) with different network configurations. Therefore, it is vital to have an accurate and a reliable generic platform to enable network developers, managers, security mangers, researchers, and students evaluating and investigating the performance of LANs of different technologies and configurations. Many network simulators have been developed throughout the years, such as: the Optimized Network Engineering Tool (OPNET), the Network Simulator (NS), the Global Mobile Simulator (GloMoSim), etc. One of the most widely-used and powerful general-purpose network simulators is OPNET, which is an object-oriented simulation environment. This chapter provides two walk through tutorials on using OPNET IT Guru (Academic Edition of OPNET) for wire/wireless LANs simulations. These tutorials demonstrate in step-by-step fashion, the procedures of initiating new simulation, setting up the simulation parameters, running the simulation, and viewing the results. The first tutorial (Tutorial #1) simulates a wired LAN of 10 computers and one server connected to a single switch, and the second tutorial (Tutorial #2) simulates a wireless ad hoc network of 10 mobile nodes and one server. This chapter demonstrates that OPNET IT Guru is a powerful tool that can be used by a range of professional users to simulate, evaluate, and investigate the performance of wire and wireless LANs. Moreover, it encourages and helps students to easily perform network simulation for better understanding of the network performance under different network conditions.

A Wireless Local Area Network otherwise as WLAN gives a flexible data communication system rather than using a wired LAN within a building. It uses radio frequency to transmit and receive data which minimizes the need for wired connections. The intention of this paper is to evaluate the performance of WLAN protocol network IEEE802.11n with the data rate of 2.4GHz which is achieved by using optimized network simulating tool, RIVERBED modeler 17.5. The performance of the protocol were measured by setting up three main functions. Media access Delay, data packet loss, Data dropped buffer overflow. Data packet received by all the workstation is larger than the other protocols. The possibility of data flow and communication will be higher. In addition, the delay that occurs can be eliminated by increasing the channel transmission rate