Bandwidth estimation and distributed traffic regulation in wireless local area networks

In this paper, we determine class specific optimal minimum contention window (CWmin) values that simultaneously maximizes aggregate saturation throughput and provides proportional throughput differentiation meeting deterministic target throughput ratios among multiple priority classes in IEEE 802.11 wireless LAN (WLAN). We show that, with the current default CWmin setting, IEEE 802.11e Enhanced Distributed Channel Access (EDCA) cannot provide satisfactory throughput differentiation among multiple priority classes. Compared to EDCA, the proportional throughput differentiation can provide consistent and adjustable differentiation among different service classes. With these optimal CWmin values, the aggregate throughput remains maximum and insensitive to the number of active nodes in the network, thus improving the scalability of the protocol.

In this paper we present and analyze a collision avoidance mechanism to increase the throughput and decrease the delay in wireless local area networks. The analysis considers the IEEE 802. I I Standard parameters employed in the Distributed Coordination Function used in the Ad Hoc mode operation. The mechanism is based on the deferral counter (DC) algorithm proposed in HomePlug Standard. The purpose of the Deferral Counter is to increase the contention window faster than the regular backoff function from IEEE 802. I I to prevent collisions. Different from IEEE 802.11, the mechanism increments the contention window of the deferring stations to minimize collisions. We implement this mechanism in ns-2 simulator in order to compare it with IEEE 802.11. We propose three different functions to use in the Deferral Counter mechanism and evaluate their performances considering network throughput, packet delay, and the percentage of overlapping transmissions. Results show that the proposed mechanism performs better when there is more than four active stations no matter the packet size. Furthermore, we also show that the DC function that achieves the best network throughput depends on the packet size and the number of active nodes.

With the rapid development of wireless local area network (WLAN) and the proliferation of intelligent terminals, the current WLAN protocol is no longer able to meet the needs of users. Therefore, the next generation WLAN: IEEE 802.11ax has emerged to meet the growing demand for user traffic. Orthogonal Frequency Division Multiple Access (OFDMA), which enables simultaneous transmission of data by different User Equipment (UEs), is considered to be one of the key technologies of IEEE 802.11ax. In order to achieve high throughput rates and low access latency to ensure quality of service (QoS), IEEE 802.11ax supports two uplink access modes: scheduling access and random access. However, how to adaptively and efficiently switch these two access mechanisms in the process of real-time operation of the system, and effectively reduce the drawbacks caused by these two mechanisms is a thorny problem. This paper proposes an evaluation mechanism of network traffic load based on OFDMA-MAC protocol, and its performance is verified by simulation. The simulation results show that the traffic load assessment mechanism effectively improves the network throughput and quality of service (QoS), and also adapts to the dynamic changes in network traffic.

In dense wireless local area networks (WLANs), the primary causes of interference and hindrance to spatial reuse are the well-known hidden node problem (HNP) and the exposed node problem (ENP). In this paper, we propose a joint solution to these problems. The proposed mechanism, referred to as Probe/PreAck (PR/PA), utilizes the concept of a two-way handshake for efficient channel reservation and spatial reuse by means of two control frames called PR and PA. The PR frame is designed for the semi-reservation of a channel initiated by a transmitting node, while the PA frame is used for the receiver-oriented permission of a channel reservation. Once a transmitting node advertises a PR frame, the channel is temporarily reserved, and the channel reservation is finally completed after the node receives the corresponding PA frame. Otherwise, the channel reservation is immediately released. Unlike the ready-to-send/clear-to-send mechanism, which is a well-known solution to HNP, the proposed mechanism does not unnecessarily prevent nodes from accessing the channel but selectively blocks transmitting and receiving nodes when they overhear the PA and PR frames transmitted by neighboring nodes, respectively. In this way, the proposed PR/PA mechanism effectively deals with both HNP and ENP in a unified framework. We further enhance the PR/PA mechanism by devising an immediate destination switching scheme, which is implemented in access points (APs) to improve the downlink throughput. If an AP fails to complete the exchange of PR and PA frames with a specific destination, it sends another PR frame to a different destination node without performing a new back-off procedure. Moreover, we adopt the transmission time control scheme to assure successful spatial reuse in multiple basic service set (BSS) WLANs. By adjusting the transmission time of the data frames simultaneously transmitted in different BSSs, severe interference between the data and acknowledgment frames can be avoided. The results of a simulation study confirmed that the proposed mechanism outperformed conventional mechanisms in dense multi-BSS WLANs; the downlink throughput was increased by more than 10 times while the overall network throughput was increased by approximately 50%.

With the rapid proliferation of broadband wireless services, it is of paramount importance to understand how fast data can be sent through a wireless local area network (WLAN). Thanks to a large body of research following the seminal work of Bianchi, WLAN throughput under saturated traffic condition has been well understood. By contrast, prior investigations on throughput performance under unsaturated traffic condition was largely based on phenomenological observations, which lead to a common misconception that WLAN can support a traffic load as high as saturation throughput, if not higher, under nonsaturation condition. In this paper, we show through rigorous analysis that this misconception may result in unacceptable quality of service: mean packet delay and delay jitter may approach infinity even when the traffic load is far below the saturation throughput. Hence, saturation throughput is not a sound measure of WLAN capacity under nonsaturation condition. To bridge the gap, we define safe-bounded-mean-delay (SBMD) throughput and safe-bounded-delay-jitter (SBDJ) throughput that reflect the actual network capacity users can enjoy when they require finite mean delay and delay jitter, respectively. Our earlier work proved that in a WLAN with multi-packet reception (MPR) capability, saturation throughput scales superlinearly with the MPR capability of the network. This paper extends the investigation to the nonsaturation case and shows that superlinear scaling also holds for SBMD and SBDJ throughputs. Our results here complete the demonstration of MPR as a powerful capacity-enhancement technique for WLAN under both saturation and nonsaturation conditions.

We uncover the reality of traffic differentiation in mobile virtual network operator (MVNO) networks and shed new light on its negative impact on the accuracy of available bandwidth (i.e., the unused capacity of an end-to-end path) estimation methods that use a probing packet train (i.e., a set of multiple probing packets). To the best of our knowledge, we report, for the first time, that multiple operational LTE MVNO networks in the Asian region are very likely to differentiate traffic according to the time of day. We find, also for the first time, that when a sender transmits a packet train to a receiver during a period of traffic differentiation, the packet loss rate of the packet train jumps up, thus degrading the accuracy of available bandwidth estimation as the packet train is corrupted by the high packet loss rate. As a countermeasure, we propose a method called PathQuick4 for accurately estimating the available bandwidth while remaining robust against traffic differentiation. The key idea is that we dynamically judge whether traffic differentiation occurs through inline measurement of packet loss characteristics by using a single packet train itself, without transmitting any extra probing packets. From this judgement, we then choose either packet-train-or packet-pair-based bandwidth estimation as appropriate. An experimental evaluation over three operational Japanese LTE MVNO networks showed that the overall estimation error of PathQuick4 across the three MVNOs during periods of traffic differentiation was close to an order of magnitude less than the error of a conventional method.

Call Admission Control (CAC) between heterogeneous networks, such as an integrated 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE) network and a Wireless Local Area Network (WLAN), plays an important role to utilize the system resources in a more efficient way. In this paper, we propose that the preference to the WLAN is determined based on the traffic load in the WLAN and the location of the cellular users. Our analysis relies on a previous study that divides the 3G cellular coverage area into zones based on the amount of resources that are required to support a connection to a mobile user. Using this model, we derive new call blocking and handoff failure probabilities as well as new call and handoff attempt failure probabilities. Through simulations, we investigate proper preference settings by changing the WLAN load in a 3 ring-based sector with a WLAN hotspot.

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.

Traffic diversion and load balancing are critical issues in Wireless Local Area Network (WLAN), such as Wi-Fi. When multi hop ad-hoc nodes are introduced between two WLANs, the performance becomes more inevitable, which brings new challenging issues, such as how to reduce the packet dropping rate, end-to-end delay, how to control traffic in more dense WLAN, how to take more advantage of multi hop relay nodes for better resource management. In this paper we proposed a traffic diversion scheme for high dense Infrastructure based WLAN. This proposed scheme consists of two parts. In the first part, we have focused on Access Point (AP) selection policy, which utilizes multi-hop adhoc nodes to divert traffic of high dense AP to less dense AP with non-overlapping coverage. In the second part, we provided a framework for routing scheme in multi hop ad-hoc nodes for exchange of information. Ongoing ns2 simulations demonstrate that the scheme that we proposed is more effective than traditional one in terms of packet drop and end to-end delay.

The new IEEE 802.lie standard is designed to provide QoS guarantees to different types of multimedia applications in WLAN. IEEE 802.lie defines two channel access mechanisms: HCCA and EDCA. Basically, HCCA is more suitable for providing strict QoS guarantees than EDCA because of its centralized TXOP allocation manner and enhanced capability of initiating a transmission at any time during the beacon interval. Nevertheless, the HCCA scheduling scheme is not yet consummate in the current standard and it only performs well under CBR real-time traffics. In this paper, we propose a scheduling algorithm and admission control policy based on Service Curve theory that can deal with bursty traffic while strict delay bounds can be provided for traffic streams. We conduct extensive simulations to evaluate our scheme and the experiment results show good improvements upon the reference scheduling algorithm of HCCA.

For wireless sensor networks, monitoring large inaccessible areas where deterministic node deployment is not possible, self-organized techniques are in demand to cover an area using optimal number of nodes. In this paper, given an initial random deployment of mobile sensor nodes, we propose a simple and novel technique for self-organized node movement to satisfy the coverage of the given region of interest using a least number of nodes, such that the maximum node displacement is minimized. We present a simple centralized algorithm and also a distributed version of it for node placement. Moreover, in case of a node failure, a distributed fault recovery algorithm is proposed to replace it locally utilizing the available free nodes. Analysis, simulation, and comparison studies show that the proposed algorithms with less neighborhood information result in significant improvement in terms of average and maximum displacement of a node, rounds of communication, and number of active nodes.

For the past ten years, heterogeneous networks wired and wireless had tended to integrate seamlessly, offering effective and reliable service for medical operations. One of the problems encountered by network practitioners is the seamless integration of network components into healthcare delivery. As a multiplexing hospital model, the implementation certainly presents some challenges. The major technical and performance issues involve are as following. The operating parameters should keep aligned to the Quality of Service (QoS) requirement throughout simulation. Bandwidth utilisation of wireless networking is a challenging issue for real-time multimedia transmission. IEEE 802.11 provides relatively lower data rate than wired networks, thus the developer tends to adopt a more compromised solution: either reduce the file size or compress the image packets. Communication performance that varies constantly with the impact of signal strength, traffic load and interference. As stated radio signal senses as a curve and attenuates greatly while metallic object and microwave exist within the active range. To ensure devices do not interfere with other electronic equipments (e.g. heart monitors), assert wireless spectrum has to be managed appropriately. This research paper aims to develop a generic hospital network scenarios using Wireless Local Area Network (WLAN) over OPNET Simulation, to evaluate the performance of the integrated network scenario for Intensive Care Units (ICU). This research makes use of computer simulation and discusses various aspects of the network design, so as to discover the performance behaviour pertaining to effect of traffic type, traffic load and network size. In the ICU scenario, the performance of video conference degrades with network size, thus, a QoS-enabled device is recommended to reduce the packet delay and data loss. IEEE 802.11a suits in hospital environment because it mitigates interference on the 2.4GHz band where most wireless devices operate. Experiment examines the effect of signal strength in WLAN. It is convinced that -88dBm is the best signal strength threshold. Although 802.11a generates slightly lower throughput than 802.11g, this issues can be addressed by placing more APs in the service area. It is convinced that 802.11a suits the hospital environments, because it mitigates interference on the popular 2.4GHz band where most wireless devices operate. It is important for medical devices which require future upgrade and Bluetooth deployment.

The recent emergence of high density wireless local area network (WLAN) deployments is a testament to both the insatiable demands for wireless broadband services and the ubiquity of WLAN technology. However, the increased capacity and extended coverage comes with a corresponding increase in contention and interference. These can cause a significant degradation in throughput unless an effective channel assignment scheme is employed. In an earlier work, we proposed a practical distributed channel assignment scheme for high density WLANs. The proposed minimum neighbour with extended Kalman filter estimator (MINEK) scheme maximizes throughput by selecting the channel with the minimum number of active neighbour nodes (nodes associated with interfering access points). The latter is estimated in-situ using an extended Kalman filter. In this paper, we present extensive performance evaluation of the MINEK scheme. Specifically, the scheme's performance is evaluated in terms of upper-bound performance, normalized density, non-saturated load, unequal load, fairness and scalability. Extensive packet-level simulations using OPNET have shown that the MINEK scheme not only provides significant throughput improvement when compared to other existing schemes but is also highly robust across various deployment scenarios.

IEEE 802.11ax uplink orthogonal frequency division multiple access (OFDMA)-based random access (UORA) is a new feature for random channel access in wireless local area networks (WLANs). Similar to the legacy random access scheme in WLANs, UORA performs the OFDMA backoff (OBO) procedure to access the channel and decides on a random OBO counter within the OFDMA contention window (OCW) value. An access point (AP) can determine the OCW range and inform each station (STA) of it. However, how to determine a reasonable OCW range is beyond the scope of the IEEE 802.11ax standard. The OCW range is crucial to the UORA performance, and it primarily depends on the number of contending STAs, but it is challenging for the AP to accurately and quickly estimate or keep track of the number of contending STAs without the aid of a specific signaling mechanism. In addition, the one for this purpose incurs an additional delay and overhead in the channel access procedure. Therefore, the performance of a UORA scheme can be degraded by an improper OCW range, especially when the number of contending STAs changes dynamically. We first observed the effect of OCW values on channel efficiency and derived its optimal value from an analytical model. Next, we proposed a simple yet effective OBO control scheme where each STA determines its own OBO counter in a distributed manner rather than adjusting the OCW value globally. In the proposed scheme, each STA determines an appropriate OBO counter depending on whether the previous transmission was successful or not so that collisions can be mitigated without leaving OFDMA resource units unnecessarily idle. The results of a simulation study confirm that the throughput of the proposed scheme is comparable to the optimal OCW-based scheme and is improved by up to 15 times compared to the standard UORA scheme.

IEEE 802.11ax introduces Uplink Orthogonal Frequency Division Multiple Access (OFDMA)-based Random Access (UORA), a novel feature for facilitating random channel access in Wireless Local Area Networks (WLANs). Similar to the conventional random access scheme in WLANs, UORA employs the OFDMA backoff (OBO) procedure to access the channel’s Resource Units (RUs) and selects a random OBO counter within the OFDMA contention window (OCW) range. The Access Point (AP) can determine and communicate this OCW range to each station (STA). Multiple STAs accessing RUs result in transmission failure due to RU collisions, which occur when specific RUs remain unassessed by any STA, leading to wastage. Efforts to optimize channel efficiency require minimizing both collisions and idle RU despite the challenges arising from UORA’s distributed and random nature. The Fisher-Yates shuffle algorithm introduces a random uniform distribution strategy for managing RU allocations among STAs. The results demonstrate that this approach enables STAs to access RUs in a distributed manner, effectively reducing idle and wasted RUs, especially in scenarios involving a limited number of STAs. Furthermore, this approach effectively mitigates collisions among STAs, even in scenarios with a more significant number of STAs.