# An Outdoor Navigation System for Blind Pedestrians Using GPS and Tactile-Foot Feedback
## 1 Introduction  
Navigation assistive technology for visually impaired and blind people has been an active subject of study for decades. Two different processes of human mobility have been identified for navigation assistive system design: sensing of the immediate environment and orientation during travel [1]. While the former refers to the gathering of spatial information for obstacle (or any other travel obstruction) detection, the latter involves the update of the traveler's location in a route and the continuous guidance to reach a destination. Systems that address one or both navigation processes can be found in the literature. Examples of obstacle detection systems can be tracked back to the 1970s when sonar technology was at its peak [2; 3]. A short while later, sonar systems evolved to ultrasonic sensors, improving the measurement accuracy of the distance to an obstacle [4; 5]. Laser telemeters have also been explored to detect obstacles ahead of a user [6; 7]. More recently, video cameras and image sensors together withcomputer vision techniques have been employed to find obstacles and clear paths in images from the nearby space [8; 9]. Examples of localization and guidance can be distinguished into two categories: outdoor and indoor navigation. Currently, there is no single technology that can offer a solution for both. Most outdoor navigation assistive systems use global positioning systems (GPS) for the traveler's localization and have made outdoor navigation much easier for blind pedestrians. The main drawback of GPS is that satellite signals become significantly weaker in indoor environments as buildings block the line of sight between the satellite and the receiver. Solutions for indoor settings have explored beacon-based approaches that use cameras [10; 11], infrared sensors [12; 13], radio frequency identification (RFID) tags [14; 15], wireless communication devices [16; 17], computer-aided design (CAD) maps [18], among others. The main challenge of the beacon approach is to install a dedicated network that efficiently covers the traveler's entire path. Despite intensive research and the variety of technological approaches, navigation assistive devices have not yet become common, and user acceptance is, in fact, quite low. Several fundamental shortcomings can be found in both obstacle detection and localization systems [19]:  
1. Obstacle detection technologies involve complex, continuous, and time-consuming operations; environment scanning requires the user to actively scan the environment. The gathered information must be analyzed before making a decision--constant activity and cognitive effort that reduces walking speed and quickly fatigues the user. 2. They provide acoustic feedback. Blind people rely on hearing environmental cues for key navigation tasks, such as awareness, orientation, mobility, and safety. A system providing continuous acoustic feedback might distract the user from the environment. While obstacle detection systems typically provide different frequency tones to indicate the distance to an object, localization systems provide spoken voice commands to guide the pedestrian along a path. 3. Long learning and training times are required to master most navigation assistive systems. Blind people invest non-negligible time to get used to the device and understand fully the system's feedback, which is certainly frustrating and discouraging. 4. They are still burdensome and conspicuous as portable or wearable devices, which are essential needs for blind pedestrians. These shortcomings limit navigation assistive devices from attaining significant and perceivable improvements in comparison with primary aids (e.g., white cane and guide dog). The white cane and the guide dog are the most popular and longstanding navigational aids for blind pedestrians. The white cane is multifunctional, reliable, cheap, compact, and lightweight. The guide dog is a very capable and reliable travel aid for leading blind people around obstacles. It also becomes a friend and companion.