On the Implementation of Servers for Large Scale CAR Systems based on Mobile Phones

Collaborative Augmented Reality (CAR) systems allow multiple users to share a real world environment including computer-generated images in real time. The hardware features of most current mobile phones include wireless network capabilities that offer a natural platform for CAR systems. However, the potential number of clients in CAR systems based on mobile phones is much larger than on CAR systems based on other kind of mobile devices, requiring a system design that takes into account scalability issues. This paper presents the experimental comparison of different CAR systems based on mobile phones with different server implementations. The performance evaluation results show that the best implementation is the one based on UDP messages instead of classical TCP connections, in order to improve the system throughput. The UDPbased implementation provides a significant improvement in system throughput, at the cost of loosing a very small percentage of updating messages. However, the effects of these small quantities of dropped messages cannot expand beyond some jitter (bounded within a short period of time) in a reduced number of clients of the CAR application. These results validate the proposed UDP-based implementation as the best option for large-scale CAR systems based on mobile phones.