This thesis presents the research carried out to investigate and achieve highly reliable and accurate navigation system of guidance for visually impaired pedestrians. The main aim with this PhD project has been to identify the limits and insufficiencies in utilising Network Real-Time Kinematic Global Navigation Satellite Systems (NRTK GNSS) and its augmentation techniques within the frame of pedestrian applications in a variety of environments and circumstances. Moreover, the system can be used in many other applications, including unmanned vehicles, military applications, police, etc. NRTK GNSS positioning is considered to be a superior solution in comparison to the conventional standalone Global Positioning System (GPS) technique whose accuracy is highly affected by the distance dependent errors such as satellite orbital and atmospheric biases. Nevertheless, NRTK GNSS positioning is particularly constrained by wireless data link coverage, delays of correction and transmission and completeness, GPS and GLONASS signal availability, etc., which could downgrade the positioning quality of the NRTK results. This research is based on the dual frequency NRTK GNSS (GPS and GLONASS). Additionally, it is incorporated into several positioning and communication methods responsible for data correction while providing the position solutions, in which all identified contextual factors and application requirements are accounted. The positioning model operates through client-server based architecture consisted of a Navigation Service Centre (NSC) and a Mobile Navigation Unit (MNU). Hybrid functional approaches were consisting of several processing procedures allowing the positioning model to operate in position determination modes. NRTK GNSS and augmentation service is used if enough navigation information was available at the MNU using its local positioning device (GPS/GLONASS receiver).The positioning model at MNU was experimentally evaluated and centimetric accuracy was generally attained during both static and kinematic tests in various environments (urban, suburban and rural). This high accuracy was merely affected by some level of unavailability mainly caused by GPS and GLONASS signal blockage. Additionally, the influence of the number of satellites in view, dilution of precision (DOP) and age corrections (AoC) over the accuracy and stability of the NRTK GNSS solution was also investigated during this research and presented in the thesis. This positioning performance has outperformed the existing GPS service. In addition, utilising a simulation evaluation facility the positioning model at MNU performance was quantified with reference to a hybrid positioning service that will be offered by future Galileo Open Service (OS) along with GPS. However, a significant difference in terms of the service availability for the advantage of the hybrid system was experienced in all remaining scenarios and environments more especially the urban areas due to surrounding obstacles and conditions. As an outcome of this research a new and precise positioning model was proposed. The adaptive framework is understood as approaching an integration of the available positioning technology into the context of surrounding wireless communication for a maintainable performance. The positioning model has the capability of delivering indeed accurate, precise and consistent position solutions, and thus is fulfilling the requirements of visually impaired people navigation application, as identified in the adaptive framework.

According to the National Federation of the Blind, there are an estimated 10 million people in the United States who are visually impaired. Of these, 1.3 million are legally blind. Many people with extreme vision loss receive orientation and mobility training in order to help them learn skills that allow them to travel and navigate multiple types of indoor and outdoor environments. Even with this training, a fundamental problem these people face is learning new routes, especially in environments with which they are not familiar. Although the research community has developed a number of localization and navigation aids that are meant to provide navigation assistance, only a handful have reached the marketplace, and the adoption rate for these devices remains low. Most assistive navigation devices take responsibility for the navigation and localization processes, leaving the user only to respond to the devices' commands. This thesis takes a different approach and proposes that because of the high level of navigation ability achieved through years of training and everyday travel, the navigation skills of people with visual impairments should be considered an integral part of the navigation system. People with visual impairments are capable of following natural language instructions similar to those given by a visually impaired person communicating route directions over the phone to another person with visual impairments. Devices based on this premise can be built, delivering only verbal route descriptions. As a result, it is not necessary to install complex sensors in the environment. This thesis has four hypotheses that are addressed by two systems. The first hypothesis is that a navigational assistance system for the blind can leverage the skills and abilities of the visually impaired, and does not necessarily need complex sensors embedded in the environment to succeed. The second hypothesis is that verbal route descriptions are adequate for guiding a person with visual impairments when shopping in a supermarket for products located in aisles on shelves. These two hypotheses are addressed by ShopTalk, a system which helps blind users shop independently in a grocery store using verbal route descriptions. The third hypothesis is that information extraction techniques can be used to extract landmarks from natural language route descriptions. The fourth and final hypothesis is that new natural language route descriptions can be inferred from a set of landmarks and a set of natural language route descriptions whose statements have been tagged with landmarks from the landmark set. These two hypotheses are addressed by the Route Analysis Engine, an information extraction-based system for analyzing natural language route descriptions.

Screen readers for visually impaired users are poorly optimized for e-commerce websites hence the exclusion of the content. It creates a societal need for accessibility of the content in e-commerce websites for the visually impaired users. This study explores how six blindfolded participants could co-design a Voice User Interface (VUI) in an e-commerce website to convey its information that creates a good user experience for visually impaired. The result of a co-design workshop with interaction design practices showed that a VUI should be humanlike and convey relevant information. Failed speech recognition and overwhelming information had a negative impact on the user experience. To cope with the problems, the VUI should provide more control to the users by conveying explicit confirmations and retrospective information from past shopping trips. Due to the difficulties in finding visually impaired participants, the design process was not completed hence the ideation needs an additional design process.