Summary form only given. The layered architecture is one of the key reasons behind the explosive and continuing growth of the Internet. There are, however, special networks in which cross-layer design is appropriate and may even be necessary. Two such cases are small wireless LAN and large-scale sensor networks. We consider first the design of medium access control (MAC) for a small wireless LAN based on a multiuser physical layer. We present a complete characterization of the throughput region and present conditions under which ALOHA is optimal. Next we consider the estimation of signal field using data collected from a large scale sensor network. The impact of medium access control on estimation is examined. We show that there exists a threshold on sensor outage probability above which a distributed random access protocol (such as ALOHA) outperforms the centralized deterministic schedulers.

On cross-layer design of wireless networks

This study evaluated the status of accessibility in mobile apps by investigating the graphical user interface (GUI) structures and conformance to accessibility guidelines of 479 Android apps in 23 business categories from Google Play. An automated tool, IBM Mobile Accessibility Checker (MAC), was used to identify the accessibility issues, which were categorized as a violation (V), potential violation (PV), or warning (W). The results showed 94.8%, 97.5%, and 66.4% of apps studied contained issues related to V, PV, or W, respectively. Five widget categories (TextView, ImageView, View, Button, and ImageButton) were used to create 92% of the total number of the GUI elements and caused 89%, 78%, and 86% of V, PV, and W, respectively. These accessibility issues were mainly caused by lack of element focus, missing element description, low text color contrast, lack of sufficient spacing between elements, and less than minimum sizes of text fonts and elements. Together, these accessibility issues accounted for 97.0%, 77.8%, and 94.5% of V, PV, and W, respectively.This study proposed coverage measures to estimate the percentage of accessibility issues identified by an automated tool. The result showed that MAC, on average, identified about 67% of accessibility issues in mobile apps.Two new accessibility conformance measures were proposed in this study: inaccessible element rate (IAER) and accessibility issue rate (AIR). IAER estimates the percentage of GUI elements that are inaccessible. AIR calculates the percentage of the actual number of accessibility issues relative to the maximum number of accessibility issues. Average IAER and AIR scores were 27.3%, 19.9%, 6.3% and 20.7%, 15.0%, 5.4% for V, PV, and W, respectively, for the studied apps. The IAER score showed approximately 30% of the GUI elements had accessibility issues, and the AIR score indicated that 15% of the accessibility issues remained and need to be fixed to make the apps accessible.

The Current Status of Accessibility in Mobile Apps

Mobile apps are an integral component of our daily life. Ability to use mobile apps is important for everyone, but arguably even more so for approximately 15% of the world population with disabilities. This paper presents the results of a large-scale empirical study aimed at understanding accessibility of Android apps from three complementary perspectives. First, we analyze the prevalence of accessibility issues in over 1, 000 Android apps. We find that almost all apps are riddled with accessibility issues, hindering their use by disabled people. We then investigate the developer sentiments through a survey aimed at understanding the root causes of so many accessibility issues. We find that in large part developers are unaware of accessibility design principles and analysis tools, and the organizations in which they are employed do not place a premium on accessibility. We finally investigate user ratings and comments on app stores. We find that due to the disproportionately small number of users with disabilities, user ratings and app popularity are not indicative of the extent of accessibility issues in apps. We conclude the paper with several observations that form the foundation for future research and development.

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Accessibility issues in Android apps: state of affairs, sentiments, and ways forward

Universal design principles aim to improve accessibility by ensuring product designs consider all users, including those with certain disabilities (e.g., visual impairments). In the case of mobile apps, accessibility is mostly provided by existing features in mobile devices, like TalkBack on Android that reads information to users. However, it is not clear to what extent developers actually implement universal design principles or utilize these technologies to support accessibility of their applications. By performing a mining-based pilot study, we observed developers seldom use Accessibility APIs and there is a limited usage of assistive descriptions. Then, we focused on understanding the perspective of developers through an investigation of posts from StackOverflow. We identified the aspects of accessibility that developers implemented as well as experienced difficulty (or lack of understanding). We performed a formal open-coding of 366 discussions threads with multi-author agreement to create a taxonomy regarding the aspects discussed by developers with respect to accessibility in Android. From the qualitative analysis, we distilled lessons to guide further research and actions in aiding developers with supporting users that require assistive features.

Can Everyone use my app? An Empirical Study on Accessibility in Android Apps

Establishing stable routes over high mobility networks is a challenging field and consequently brought the attention of a lot of current researchers. In this article, a new reactive routing protocol has been proposed which is considered as a major extension of both Ad-hoc On-demand Distance Vector (AODV) and Mobility and Direction Aware AODV (MDA-AODV) prior routing protocols. It is named as Mobility Aware and Dual Phase Ad-hoc On-demand Distance Vector with Adaptive Hello Messages (MA-DP-AODV-AHM). It primarily concentrates on building routes considering vehicles’ speeds and direction of motion with respect to source vehicles, thereby establishing more stable routes and reducing the route breakages. Not only to this extent, but rather, we proposed an adaptive control packet announcement mechanism, which is directly connected to the periodic hello messages approach, with vehicles’ speeds, yielding a significant reduction in the amount of control overhead and congestion over the network. Moreover, the new protocol is proposed to alternate working among two phases, for the reason of guaranteeing the generation of efficient routes on a timely basis, which include MA-DP-AODV-AHM and AODV protocols. Our protocol has been evaluated in terms of control overhead, end-to-end delay, and energy consumption using QualNet simulator version 7.1 in which enormous simulations have been conducted under the base of vehicle density, packet rate, and constant bit rate connections. Simulation results summarize that MA-DP-AODV-AHM contributes efficiently in mitigating the network instability through generating effective stable routes and reducing link failures. Furthermore, it has proved its superiority over AODV and MDA-AODV.

Mobility aware and dual phase AODV protocol with adaptive hello messages over vehicular ad hoc networks

Inaccessible user interfaces of the applications in Android systems such as unlabeled interactive controls, lack of form element hint, lack of focus on the important interactive controls, improper directional navigation etc. are hurdles of users with all kinds of disabilities. Manual accessibility testing is tedious job for Applications developers. Also efficient semi automated Android accessibility evaluation tool which can evaluate all the accessibility developer's checklist are not available. These could be important reasons of non consideration of accessibility while developing Android applications. This paper presents enhancement of UI Automator Viewer a tool for evaluation of applications accessibility in Android environment. Limitation of UI Automator Viewer are eliminated by adding new features “Target device selection”, which allows the developer to select target device among multiple connected devices for automation testing, “Capture and play”, include Touch Event and key Event which help to send UI event to and retrieve information from connected device and “Color contrast” which shows color contrast of captured screenshot which helps the mobile application developer to represent their application for color blind and low vision persons and to make sure that all visual designs meet the minimum color-contrast ratio for normal and large text on a background. Testing accessibility of user interfaces of Android mobile applications become more efficient by the enhanced tool which can identify accessibility issues of user interfaces of Android applications and assist developers to create accessible user interfaces.

Enhanced UI Automator Viewer with improved Android accessibility evaluation features

Reactive routing protocols for MANETs have outperformed the proactive protocols as they incurred less overhead for maintaining routing information Reactive protocols working "on demand" principle rely on the flooding of route request (RREQ) packets for route discovery This flooding results in problems such as; "RREQ storm", energy consumption of nodes and bandwidth consumption of shared channel Hence, usability of reactive protocols is under scanner This paper suggests Received signal strength (RSS) based gossip flooding approach that modifies the RREQ rebroadcast mechanism of AODV Experimental results show that RSS based gossip with probability p=066 reduces the RREQ rebroadcast by 15%, without adversely affecting the network performance in terms of connectivity, throughput and PDR, or end-to-end delay

RSS-GossipAODV: Received Signal Strength based Gossip Flooding Mechanism for AODV

This On-demand route discovery mechanism of reactive protocols based on flooding of route request packets faced serious excursion of “broadcast storm”. Moreover, frequent path breakages are experienced due to link failures, as an impact of time varying characteristics of radio channel and/or node mobility. In this paper Channel Quality Adaptive Gossip Flooding mechanism for Ad hoc On-demand Distance Vector (AODV) routing protocol, named CQAG-AODV is proposed as a solution to these issues. CQAG-AODV is a cross layer approach, where in route discovery mechanism of AODV is tuned to signal quality of wireless channel. Flooding of route requests (RREQs) is controlled with probabilistic measures based on signal strength observed at the physical layer. Proposed scheme tries to discover robust paths by forwarding more RREQs along good signal quality links rather than on weaker ones. The proposed scheme is implemented using Qualnet simulator and performance is evaluated in terms of PDR, throughput, end to end delay and link breakage. Simulation results show that CQAG-AODV significantly curtails the link breakages with reduced RREQ forwarding overhead compared to conventional AODV and thus takes care of “broadcast storm” problem.

Channel quality based Adaptive Gossip Flooding mechanism for AODV

The multi-hop ad hoc networks are self organizing networks with dynamic topology. The reactive and proactive protocols are designed to handle these dynamically changing networks. Ad Hoc On-Demand Distance Vector (AODV) Routing Protocol is one such Reactive protocol that has been widely adopted in MANETs. In this protocol, routes are maintained as and when required, i.e. they operate ‘On Demand’. AODV relies on ‘Hello’ messages to maintain local link connectivity. The hello messages are sent periodically, the period of which is defined by ‘AODV hello interval. In this paper, we investigate the performance of AODV protocol by varying the hello interval. The performance is analyzed in terms of Quality of Service parameters such as throughput, End-to-end Delay and PDR. Our experimental results show that the performance of AODV is improved when hello interval is increased.

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Impact of Hello Interval on Performance of AODV Protocol

hop Ad Hoc Networks are self-organizing networks characterized by dynamically changing topology due to node mobility and time varying characteristics of the wireless channel. Routing is a crucial issue in these networks. Several routing protocols have been proposed which fall into either of these categories: proactive, reactive or hybrid routing protocols. Proactive protocols have the advantage of less route establishment latency but suffer from heavy control overhead. Since routes maintained may never be used, system resources are unnecessarily wasted making proactive approaches less efficient. The reactive protocols overcome this drawback. These incur less overhead due to their "on demand" nature; nodes maintain routing information only when it is needed. Hence reactive protocols e.g AODV, DSR etc are preferred and widely adopted. But the on-demand behavior of these approaches itself leads to another problem, e.g the "broadcast storm" problem and thus challenges their usability. In this paper we highlight limitations and operational challenges of widely adopted reactive protocols and survey different optimization approaches suggested to overcome these challenges.

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Prasanna Shete

Papers

Enhanced UI Automator Viewer with improved Android accessibility evaluation features

RSS-GossipAODV: Received Signal Strength based Gossip Flooding Mechanism for AODV

Channel quality based Adaptive Gossip Flooding mechanism for AODV

Impact of Hello Interval on Performance of AODV Protocol

Routing Protocols for Multi-hop Ad Hoc Networks: Operational Challenges and Design Optimizations