# A Review of Pedestrian Indoor Positioning Systems for Mass Market Applications
## 5 Conclusions  
This work has surveyed the Indoor Positioning Systems (IPS) with a special interest in those IPS that can be applied to mass market applications. First a general classification of IPS is performed and each group is reviewed analysing the advantages and disadvantages of each system in terms of accuracy, cost and scalability. Then the hybrid systems are reviewed focusing on the current solutions available in the literature that can be applied to mass market applications. Finally, we also reviewed the state of the art of IPS based on smartphones because the popularization of the smartphones around the world is a key advantage for reducing the cost of the implementation of an IPS for mass market applications. Considering the special requirements of mass market applications, that is, accuracy, cost and scalability, we can conclude that over the large amount of IPS available in the literature, the most interesting ones for mast market applications are the RSS-IMU based hybrid systems combined with map information whenever it is available. These systems, can provide accuracies in the order of 1 meter in large indoor scenarios. Furthermore, the cost of the system is reduced if the WiFi network already deployed in lots of buildings is employed for positioning or low cost technologies are employed as RFID or BLE beacons. The scalability of the system can be guaranteed if range based or proximity methods are employed because these methods require little or no calibration effort. Note that these systems can be implemented with nowadays commercial smartphones and that in the case of employing smartphones different wireless technologies can be employed (WiFI, BLE,...) increasing the positioning accuracy without increasing the cost of the system. Although there have been great advantages in the research of IPS and the current technology is increasing the positioning accuracy continuously, the positioning problem in indoor environment is far from being solved and more research is needed in order to reach the positioning accuracy demanded by indoor location based services. From the timely and comprehensive review of the literature, this survey may further encourage new research efforts and for this reason we briefly suggest here some future research lines. In particular, we focus on the open research problems of IPS based on smartphones as we consider the smartphone as the most promising device for indoor positioning systems applied to mass market applications. _Adaptability to smartphone placement_: Smartphones are devices employed for many different applications that involve many different positions of the smartphone with respect to the body of the user. Typically a smartphone can be held in the pocket, in the hand, next to the head, in a bag or purse among many other possible positions. New IPS should take into account the position of the smartphone in order to compute the relative orientation of the inertial sensors embedded in the smartphone with respect to the navigation frame. _Heterogeneity of transceivers_: In a mass market application based on smartphones, each user will employ its own smartphone as a positioning device. With the large amount of different smartphone available in the market, we encounter devices with different sensitivities, different antenna patterns, etc. Thus, different smartphones will measure different RSS in the same conditions and this fact should be taken into account in the design of new IPS. _Battery life_: It is well known that battery lifetime in many commercial smartphones is not as good as desired. The use of fusion algorithms like the Kalman filter or the Particle filter increases the computational complexity of the IPS and reduce the battery life of the smartphones. Therefore, it is crucial to develop new energy efficient algorithms with reduced computational complexity which do not drain the battery of the smartphones. _Smartwatches_: As it happened with the smartphones years ago, the popularity of smartwatches is increasing every day.