Multicast Wi-Fi Raptor-Enabled Data Carousel Design: Simulation and Practical Implementation

Multicast is an efficient way of transmitting the same set of data to multiple interested users. Unlike the 3GPP cellular standards, for Wi-Fi there is no standardised solution for reliable multicast data transmission. Multicast packets are delivered to multiple users as a broadcast service without support for automatic repeat request. Hence, multicast transmission often results in high packet loss. In order to improve the reliability of multicast delivery, a fixed low speed (robust) transmission mode can be used. However, this results in the inefficient use of scarce and valuable radio bandwidth. This paper presentsa reliable and efficient Wi-Fi multicast delivery solution for use in challenging outdoor environments. An application layer forward error correction (AL-FEC) enabled data carousel is proposed to enhance reliability. For multicast transmission we demonstrate that limitations in the Wi-Fi clients are a majorsource of packet loss, even in ideal channel conditions. Client limitations particularly data rate limitations) were found to vary as a function of modulation & coding mode, Raptor code parameters and multicast server rate. Our initial raptor-enabled carousel designs are based on computer simulations, and lab based trials. Analysis is then extended to field trials using a practical implementation of the recommended design. These trials were performed in central Bristol with parameters such as received signal level, packet loss traces and file download times recorded at the clients. Finally we compare our site specific simulated results against real-world measurements.