An adaptive modulation method for multicast communications of hierarchical data in wireless networks

The difference in link condition of multicast users makes it difficult to use adaptive modulation in multicast communications over wireless channels. Therefore, the physical layer mode is usually adapted to the worst case link condition. We propose a new adaptive modulation method for multicast communications. The method separates data into hierarchical layers according to its importance and transmits the layers of data in the same frame adaptively. The base layer is transmitted at the lowest data rate while the higher layers are transmitted at higher rates. The number of slots for each physical layer mode is optimized and a simple closed form solution is obtained. Simulation results for 5 GHz wireless LAN show that the proposed method attains higher data rates with lower outage probability than the conventional non-uniform phase shift keying (PSK) scheme.