2. Navigation system

Navigation is a common problem for visually impaired people since they cannot travel by themselves. They cannot visually and freely decide the direction, in which they need to go since the information surrounding them cannot be obtained. Therefore, there are some researches and innovation works conducted to support and assist the visually impaired people to achieve self-independence when traveling at an indoor environment as well as outdoor environment. Therefore, some technologies need to be included in navigation systems in order for the system to be successfully executed. The technologies, which are required, include localization, path planning, error detection and correction, etc. Meanwhile, there are some localization technologies, which are focused on by some researchers. The localization technologies such as infrared data association (IrDA), radio frequency identification (RFID), near field communication (NFC), Bluetooth, light emitting method, Wi-Fi, etc. have been developed to help the visually impaired people to move while indoors with contextual information or sound navigation [23].

However, these methods have some limitations when used in outdoor environments. Therefore, the usage of global positioning system (GPS) devices can also help to guide the visually impaired people in an outdoor environment. GPS is a satellite-based system that provides the location of the GPS device by indicating the longitude and the latitude of the location. Some researchers have proved that the GPS cannot function properly in an indoor space and they have presented the solution of GPS by using the IrDA technology, which works as a detector to guide visually impaired people in an indoor environment [24]. On the other hand, Lisa et al. combined the GPS that have developed in Drishti system and the ultrasonic sensors to be used for outdoor and indoor navigation [25]. However, one of the problems with GPS is accuracy; the accuracy of current GPS devices is about 5–10 m. The accuracy can also become worse when the measurement is done near tall buildings [26]. The measurement error is too big and very dangerous to be used by the visually impaired people since the location given by the GPS can guide them to the center of the road.

Furthermore, blind navigation system (BLI-NAV) is a navigation system, which consists of GPS receiver and path detector, designed for visually impaired people. Both devices are used to detect the user's location and determine the shortest route to the destination. Voice command is given throughout the travel. Path planning algorithm is used to determine the shortest distance from the start point to endpoint, together with the path detector. Moreover, the user is able to avoid obstacles while traveling [27]. This system gave better results in realtime performance and improved the efficiency of visually impaired travelers at an indoor environment.

On the other hand, pocket-PC–based electronic travel aid (ETA) is proposed to help visually impaired people to travel at an indoor environment. Pocket-PC will alert the user when they are near the obstacles through a warning audio [28]. An ultrasonic navigation device for visually impaired people has been designed. The microcontroller built in the device can guide the user in terms of which route should be taken through a speech output. Besides, the device helps to reduce navigation difficulties and detects obstacles using ultrasounds and vibrators. An ultrasonic range sensor is used to detect surrounding obstacles and electronic compass is used for direction navigation purpose. A stereoscopic sonar system is also used to detect the nearest obstacles and it feeds back to tell the user about the current location [29].

In addition, a visually impaired assistant navigation system that can help visually impaired people navigate independently at an indoor environment has also been developed [30]. The system provides localization by using a wireless mesh network. The server will do the path planning and then communicate using the wireless network with the portable mobile unit. The visually impaired people can give commands and receive the response from the server via audio signals using a headset with a microphone [31]. A proposed RFID technology in order to design the navigation system by providing information about their surroundings has also been developed. The system uses the RFID reader, which is mounted on one end of the stick to read the transponder tags that are installed on the tactile pavements [32]. At the same time, the research on RFID network can help to determine the shortest distance from the current location to the destination. Besides that, the system can help to find the way back if they lost their direction and recalculate a new path [33].

In addition, INSIGHT is an indoor navigation system to assist the visually impaired people to travel inside the buildings. The system uses RFID with Bluetooth technology to locate the user inside the buildings. Personal digital assistant (PDA) such as a mobile device is used to interact with the INSIGHT server and provide navigation information through voice commands. The zone that the user has walked on will be monitored by the system. The system will notify the user if the user travels in the wrong direction [34].
