Delay-aware reliable broadcast scheme based on power control for VANETs

In vehicular Ad-hoc network（VANET）, many multi-hop broadcast schemes are employed to widely propagate the warning messages among vehicles and the key is to dynamically determine the optimal relay vehicle for retransmission. In order to achieve reliable and fast delivery of warning messages, this paper proposes a delay-aware and reliable broadcast protocol（DR-BP） based on transmit power control technique. First, a comprehensive model is derived to evaluate the transmission in vehicle-to-vehicle communications. This model considers the wireless channel fading, transmission delay and retransmissions characters occurring in the physical layer/medium access control（PHY/MAC） layer. Then, a local optimal relay selection mechanism based on the above model is designed. In DR-BP scheme, only the vehicle selected as the optimal relays can forward warning messages and the transmit power is time-varying. Finally, extensive simulations verify the performance of DR-BP under different traffic scenarios. Simulation results show that DR-BP outperforms the traditional slotted 1-persistence（S1P） and flooding scheme in terms of packets delivery ratio and transmission delay.

Delay-aware downlink beamforming with discrete rate adaptation for green cloud radio access network

With the popularity of variety delay-sensitive services, how to guarantee the delay requirements for mobile users （MUs） is a great challenge for downlink beamformer design in green cloud radio access networks （C-RANs）. In this paper, we consider the problem of the delay-aware downlink beamforming with discrete rate adaptation to minimize the power consumption of C-RANs. We address the problem via a mixed integer nonlinear program （MINLP）, and then reformulate the MINLP problem as a mixed integer second-order cone program （MI-SOCP）, which is a convex program when the integer variables are relaxed as continuous ones. Based on this formulation, a deflation algorithm, whose computational complexity is polynomial, is proposed to derive the suboptimal solution. The simulation results are presented to validate the effectiveness of our proposed algorithm.