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In this paper, we investigate buffer-aided cooperative relaying schemes using full-duplex (FD) relay nodes with flow control. We show that incorporating various transmission options combined with proper successive interference cancellation can better exploit the opportunism of fading channels, leading to improved achievable rates. We analytically derive the optimal policy for node selection and link scheduling. To deal with the delay incurred at relay nodes, we propose flow control using a threshold-based policy on relays’ queues. For performance analysis, we develop a novel technique to derive a delay estimate of the controlled queues with general arrival and service statistics. Numerical results show that the proposed scheme achieves higher throughputs than conventional relaying schemes without FD relaying, and that the proposed estimate closely approximates the actual delay. For the delay-constrained case, our scheme is shown to achieve an improved tradeoff between throughput and delay. [ABSTRACT FROM AUTHOR]

We consider the multicast scheduling problem in the heterogeneous network using a half-duplex relay station (RS). Our goal is to minimize the delay of transmitting a block of packets to users over time-varying channels using rateless codes. Due to half-duplex operation, at each time slot, the RS can choose to either multicast a packet to the users, or fetch a packet from the macro base station. We formulate a fluid relaxation for the optimal decision problem, and reveal that the optimal policy has a threshold-based structure so as to exploit the opportunism of multicast channel: the RS should multicast only when the channel quality is sufficiently “high”. We propose an online policy based on the relaxation which does not require the knowledge of channel distribution. When the channel distribution is symmetric across users, we provide a closed-form expression of the asymptotic performance of our policy. For two-user systems, we prove that our scheme is asymptotically optimal. When the users’ channels are independent, we derive a performance bound based on water-filling rate allocation which approximates the optimal policy well. Simulation results show that our scheme performs close to theoretical bounds, under correlated as well as independent fading channels. [ABSTRACT FROM AUTHOR]

We consider the multicast scheduling problem for the block transmission of packets in a heterogeneous network using a half-duplex relay station (RS). The RS uses random linear coding to efficiently transmit packets over time-varying multicast channels. Our goal is to minimize the average decoding delay. Because of the half-duplex operation, at each time slot, the RS must decide to either: 1) fetch a new packet for encoding from the base station or 2) multicast a coded packet to wireless users. Thus, optimal scheduling hinges on exploiting multicast opportunities while persistently supplying the encoder (at the RS) with new packets. We formulate an associated fluid control problem and show that the optimal policy incorporates opportunism across multicast channels, i.e., the RS performs a multicast transmission only if the collection of channel conditions is favorable; otherwise, it performs a fetch. Based on the fluid policy, we propose an online algorithm. We prove that our algorithm asymptotically incurs no more than 4/3 and 2 times the optimal delay, for two-user and arbitrary number of user system, respectively. Simulation results show that, in fact, our algorithm’s performance is very close to theoretical bounds. [ABSTRACT FROM AUTHOR]