Fast handoff scheme based on mobility prediction in public wireless LAN systems

ABSTRACTUnderstanding the potential role of Smartphones and other portable wireless devices as relay nodes in message dissemination and content delivery in Delay Tolerant and Opportunistic networks depend on the knowledge about patterns and the number of encounter events among mobile nodes. One of the main challenges for extracting encounters is overlapping in the radio coverage areas of nearby access points (APs). Data about the usage of Wi-Fi networks can be used to perform an analysis of encounters among mobile devices. A realistic estimation of the number of encounters among mobile nodes is now a big challenge. In this paper, the effects of overlapping of radio coverage area among multiple APs for extracting realistic encounters among mobile devices has been discussed, and also an analytical approach has been proposed for extracting realistic encounters from overlapping in the coverage areas of multiple nearby APs. A significant difference was observed between the number of encounters by considering and ignoring overlapping. Our study finds that Wi-Fi datasets are not reliable source to estimate the number of encounters when there are overlapping in radio coverage areas of multiple APs.

Mobile edge computing (MEC) is an innovative computing paradigm to enhance the computing capacity of mobile devices (MDs) by offloading computation‐intensive tasks to MEC servers. With the widespread deployment of wireless local area networks, each MD can offload computation task to server via multiple wireless access points (WAPs). However, computation offloading can bring a higher system cost if all users select the same access points to offload their tasks. This study proposes a computation offloading strategy and resource allocation optimisation scheme in a multiple wireless access points network with MEC, which aims to minimise the system cost by providing the optimal computation offloading strategy, transmission power allocation, bandwidth assignment, and computation resource scheduling. The proposed scheme decouples the optimisation problem into subproblems of offloading strategy and resource allocation since the problem is NP‐hard. The offloading strategy involves the optimal access point selection, which is analysed by the potential game. The resource allocation is obtained using Lagrange multiplier. The authors' analysis and simulation results verify the convergence performance of the proposed scheme, and the proposed scheme outperforms the simple resource allocation scheme and the offloading strategy optimisation scheme in terms of the system cost.

Handoff has become an essential criterion in mobile communication system, specially in urban areas, owing to the limited coverage area of Access Points (AP). Handover of calls between two BS is encountered frequently and it is essentially required to minimize the delay of the process. Many solutions attempting to improve this process have been proposed but only a few use geo-location systems in the management of the handover. Here we propose to minimize the handoff latency by minimizing the number of APs scanned by the mobile node (MN) during each handoff procedure. We consider the whole topographical area as a two dimensional plane. By GPS, we can note down the co-ordinates of the MN at any instant. The average rate of change of its latitudinal distance and longitudinal distance with a specific time period is evaluated at the end of the given time period. With the knowledge of the given parameter, it is possible to determine the latitude and longitude of the MN after a particular instant of time. Hence the direction of motion of the MN can be determined which in turns gives the AP towards which the MN is heading towards. This reduces the number of APs to be scanned. Thus, on an overall basis, the handoff latency can be reduced by almost half to one third of its value.

In wireless local area network (WLAN), mobility management becomes a sophisticated issue of research due to the limited coverage of the Access Points (AP). For the successful communication between the mobile nodes (MN), every node should be connected with an access point (AP) during their operating mode, irrespective of their mobility. When a MN travels into the coverage area of its current AP, no special technique is required to maintain the connectivity. But when a MN travels out of the coverage area of its current AP and tries to associate with another AP, a delay occurs during the handover of connection which leads to a failure of connection. Throughout the last few years plenty of researches had been done to reduce this handover delay by reducing the scanning delay as the scanning process causes 90% of the total handover delay. In this paper, we propose a new scanning technique where the most potential AP is chosen according to the direction of the MN. First, we fit a polynomial equation along the trajectory of its motion and then to predict the direction of motion, we analyze the slope of the trajectory. Our simulation results show the effectiveness and accuracy of our proposed scheme in practical field.

Aiming at the urgent demands on constructing WiFi communication networks under emergency environments such as rescue and relief work, FC-WiFi, a WiFi network based on OpenFlow was proposed. FC-WiFi employs name-based routing algorithm, and has the characteristics as follows: (i) supporting free configuration access for mobile hosts, (ii) sharing information among mobile hosts and servers, (iii) maintaining the ongoing connection during mobile hosts handover between access points. A prototype system is implemented and experiments show that, hosts can communicate with each other when they associate to FC-WiFi with free configuration. The mobile host can keep TCP connections uninterrupted while passing through multiple access points and the handover delay is under the influence of the original configuration.

Driven by the rapidly increasing popularity of Internet-connected phones, tablets and wearable devices, new wireless technologies and standards are emerging at an unprecedented pace. The evolution of wireless networking opens a myriad of possible mobile applications, which have greatly transformed the way we access information, entertain and connect with others. A critical question is how to satisfy the quality of service (QoS) requirements for various applications by delivering the data to users reliably and efficiently under different networking conditions. While many protocols have been proposed for better QoS, they usually requires modification to the networking core or heavy interaction between the layers of the networking stack. Therefore, the goal of dissertation is to develop lightweight, scalable and end-to-end transport solutions to bridge the long-standing gap between the increasing diversity of the mobile applications and the constant evolving wireless technologies. We first focus on studying how to tweak the logic and functionality of traditional TCP protocol given a new wireless networks with different link properties in the context of cognitive radio (CR) network. We start with an extensive ns-3 simulation study of three different classical end-to-end TCP flavors. We conclude that the main adverse impact to the TCP connection in a CR network is the interruption during the transmission period caused by spectrum sensing or primary user arrival events. Based on this insight, we propose TCP C^2, a method that greatly improves the flow responsiveness to abrupt variation of underlying layer spectrum availability in cellular CR architectures. We show that C^2 achieves 2x better throughput compared to TCP NewReno and TCP Westwood+, and approximately 20% improvement in throughput while also incurring 4X shorter queuing delay against Cubic (default implementation in Linux). Our second contribution is Janus, a new transport-layer framework that automatically selects among existing congestion control variants to optimize traffic in accordance with application demands. Janus solves the problem of how to select the right protocol to optimize the QoS for different applications given a large collection of existing TCP variants. We implement Janus in the Linux kernel and extensively evaluate its performance with both emulated and real Internet traffic. Our results show that Janus can significantly improve user-perceived performance according to QoE metrics, with up to 5X fewer interruptions for video streaming applications and 2X faster page loading for web-browsing applications. Finally, we seek to answer the question of how to increase the robustness of data delivery in mmWave networks with densely deployed access points (AP). We conduct real-world experiments with off- the-shelf 60GHz devices and show that naively connecting to any available AP, or even multiple APs, may not fully realize the promise of efficiently utilizing the extremely large bandwidths available in this band. To tackle this problem, we propose Multi-AP Association Protocol (MAP). MAP is a cross-layer connection management mechanism that runs only at the client-side and does not need centralized support from the APs, thus avoiding overheads of added control signaling. We show that MAP can substantially increase the QoS for videostreaming applications for mmWave networks with testbed evaluation and large-scale simulation.

Wireless multicast has been exploited to bridge the gap between the limited wireless bandwidth and the rapidly increasing mobile video traffic demand. Multicast of videos to a set of heterogeneous users over multiple wireless access points, however, is challenging because of the trade-offs between high transmission rate, load balancing, and multicast opportunities. In this paper, we present JurCast, a joint user and rate allocation scheme for video multicast over multiple APs. Our approach balances the trade-off between these factors by determining user to Access Points (APs) association, the video resolution version (quality) to be delivered for each session, and the transmission link rate for each video version. The aim of our solution is to maximize the overall received video quality over all users. We have implemented and evaluated our solution on a WiFi testbed as well as the simulation of a large scale deployment. The results indicate that our method considerably outperforms the baseline schemes and achieves up to 3dB and 55% improvements in terms of peak signal-to-noise ratio (PSNR) and goodput, respectively.

As the demand for high-throughput communications in wireless LANs increases, the need for expanding channel bandwidth also increases. However, the use of wider band channels results in the decrease of the number of channels available. Therefore, if multiple access points (APs) are in proximity and the cells overlap, it is difficult for each AP to use an orthogonal channel, and competitions thus increase between the APs using the same channel. To cope with this problem, this paper proposes coordinating APs to increase throughputs at Nash equilibria. A centralized controller coordinates the APs, which jointly select multibandwidth channels. To clarify the effect of coordinating APs, we assume a simple scenario where the cells of three APs overlap, and each AP can select multibandwidth channels. In this scenario, we consider two packet length assumptions. In the first case, the data bit amount of each packet is assumed to be the same. Thus, the packet length changes depending on a data rate. The other case assumes that the packet length is the same regardless of the data rate. Through game-theoretic analysis, it can be clarified that the coordinated APs are able to select channels more effectively than if each AP independently selects channels and that the total throughput of the coordinated APs at Nash equilibria is improved by at most 80 % in two packet length assumptions.

Many wireless LAN (WLAN) systems are densely used in conference rooms and cafes owing to the widespread use of mobile access points (APs) and smart phones with tethering functions. Under this situation, duplicate (the same) channels are often used in the 2.4-Ghz band owing to a limited bandwidth. In addition, adjacent channels interfering with other channels are also used. Then, if the WLAN uses a channel easily affected by adjacent channels, the throughput of the WLAN can decrease. As a result, it is possible that the fairness of the WLAN will decrease. Therefore, this study proposes a switching method for media access control (MAC) to improve the throughput fairness in an adjacent channel interference environment. The proposed method attempts to apply a modified MAC method to a WLAN under a dense environment in which the throughput is appropriately decreased. From the simulation results, it was found that the proposed method can improve the throughput fairness. Therefore, we confirmed the effectiveness of our method in an adjacent channel interference environment.

The IEEE 802.11n supports high data rate transmissions due its physical layer Multiple Input ‎Multiple Output (MIMO) advanced antenna system and MAC layer enhancement features (frame ‎aggregation and block acknowledgement). As a result this standard is very suitable for multimedia ‎services through its Enhanced Distributed Channel Access (EDCA). This paper focuses on ‎evaluating the Quality of Service (QoS) application on the performance of the IEEE 802.11n ‎random topology WLAN. Three different number of nodes (3, 9 and 18) random topology with one ‎access point are modeled and simulated by using the Riverbed OPNET 17.5 Modular to ‎investigate the Wireless Local Area Network (WLAN) performance for different spatial streams. ‎The result clarified the impact of QoS application and showed that its effect is best at the 18 node ‎number topology. For a 4x4 MIMO, when QoS is applied and with respect to the no QoS ‎application case, simulation results show a maximum improvement of 86.4%, 33.9%, 52.2% and ‎‎68.9% for throughput, delay, data drop and retransmission attempts, respectively. ‎

This paper presents indoor experimental results on an implemented real-time downlink multiuser multiple-input multiple-output (DL-MU-MIMO) transceiver for next generation wireless LAN systems. In the transceiver, channel state information (CSI) is estimated at each station (STA) and fed back to an access point (AP) on a real-time basis. At the AP, transmit beamforming weight for DL-MU-MIMO transmission is calculated by using the estimated CSI. This paper also proposes a fast computation scheme for computing transmit weight in real time. Indoor experiments with the DL-MU-MIMO transceiver demonstrate its feasibility. The experimental results clarify that DL-MU-MIMO transmission can achieve system throughput of greater than 500 Mbit/s with simple digital signal processing of single-antenna STAs in an indoor environment.

A hybrid wireless network is an extension to an infrastructure network, where a mobile host may connect to an access point using multi-hop wireless routes, via other mobile hosts. The access points are configured to operate on one of multiple available channels. Mobile hosts and wireless routers can select its operating channel dynamically through channel switching. In this environment, we propose a routing protocol that finds routes to balance load among channels while maintaining connectivity. The protocol works with nodes equipped with a single network interface, which distinguishes our work with other multi-channel routing protocols that require multiple interfaces per node. The protocol discovers multiple routes to multiple access points, possibly operating on different channels. Based on traffic load information, each node selects the "best" route to an access point, and synchronizes its channel with the access point. With this behavior, the channel load is balanced, removing hot spots and improving channel utilization. The protocol assures every node has at least one route to an access point, where all intermediate nodes are operating on the same channel. Our simulation results show that the proposed protocol successfully adapts to changing traffic conditions and improves performance over a single-channel protocol and a multi-channel protocol with no load balancing.

PurposeWireless local area networks (WLANs) are the predominant option for broadband wireless access network, and multiple access points (APs) will be much more available for wireless stations (WSTAs). Call admission control (CAC) on AP selection problem over 802.11 WLAN is a critical issue. In the existing architecture, strongest‐signal‐first is the default AP selection mechanism in 802.11 WLAN which uses the single criterion, received signal strength indicator, to select AP. However, this method suffers from bandwidth deficiency and unbalanced load among APs due to the uneven distribution of user load, thus degrading the system throughput. Instead, the purpose of this paper is to propose a multi‐criteria CAC on AP selection algorithms.Design/methodology/approachThe distributed multi‐criteria considered in order are RSSI, minimum required bandwidth of WSTA, estimated effective bandwidth (EEB) and AP‐WSTA distance. A semiMarkov model considering both packet retransmission limit, packet error rate and collision effect is proposed to predict the system throughput and validated through simulation results. Two multi‐criteria AP selection algorithms after EEB is evaluated are proposed and compared based on this analytical model.FindingsThe proposed algorithms outperform the traditional SSF algorithm in terms of the balance index for AP and the average system throughput.Originality/valveThe paper presents performance analysis for multi‐criteria CAC for distributed access point selection in WLANs.

The purpose of this study is to examine the impact of information placement within the confines of the online classroom architecture. Also reviewed was the impact of other variables such as course design, teaching presence and student patterns in looking for information. The sample population included students from a major online university in their first year course sequence. Students were tasked with completing a survey at the end of the course, indicating their preference for accessing information within the online classroom. The qualitative data indicated that student preference is to receive information from multiple access points and sources within the online classroom architecture. Students also expressed a desire to have information delivered through the usage of technology such as email and text messaging. In addition to receiving information from multiple sources, the qualitative data indicated students were satisfied overall, with the current ways in which they received and accessed information within the online classroom setting. Major findings suggest that instructors teaching within the online classroom should have multiple data access points within the classroom architecture. Furthermore, instructors should use a variety of communication venues to enhance the ability for students to access and receive information pertinent to the course.

In this paper, we present a framework for providing fair service and supporting quality of service (QoS) requirements in IEEE 802.11 networks with multiple access points (APs). These issues becomes critical as IEEE 802.11 wireless LAN are widely deployed in nationwide networks, linking tens of thousands of "hot-spots" for providing both real-time (voice) and non real-time (data) services to a large population of mobile users. However, both fairness and QoS guarantees cannot be supported in the current 802.11 standard. Our system, termed MiFi, relies on centralized coordination of the APs. During any given time of the "contention-free" period only a set of non-interfering APs is activated while the others are silenced. Moreover, the amount of service granted to an AP is proportional to its load and the system's performance is optimized by employing efficient scheduling algorithms. We show that such a system can be implemented without requiring any modification of the underlying MAC protocol standard or the behavior of the mobile stations. Our scheme is complementary to the emerging 802.11e standard for QoS and guarantees to overcome the hidden node and the overlapping cell problems. Our simulations establish that the system supports fairness and hence can provide QoS guarantees for real-time traffic, while maintaining a relative high throughput