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We investigate opportunistic multicast scheduling schemes for sending a multicast stream in a wireless cell. We propose schemes that exploit both multiuser diversity and broadcast gains for efficient multicast, preserve the feature of synchronization of served information provided by conventional multicasting, and provide for receivers accepting sequential stream data. With knowledge of the expected sequence number (SN) of stream data and the feasible peak transmission rate for each group member, our scheme decouples the pairing of SN and rate and selects an expected SN and a peak rate that jointly maximize a utility function. Besides the amount of data accepted in one transmission, the function includes a force factor to push expected SNs to drift closely and another force factor to synchronize more expected SNs. Under i.i.d. channel conditions, we show that with the two factors to limit the diffusion of expected SNs, multicast throughput significantly increases and that without them our scheme degenerates into merely tapping multiuser diversity gain. Furthermore, we investigate optimal transmit power allocation subject to an average power constraint for multicast transmission. Results show that multicast throughput increases slightly for our scheme but substantially for traditional ones.
Date of Publication: June 2011