SUMMARYThis paper proposes an optimized scheduling scheme in OFDMA-based WiMax networks to achieve both optimized system throughput and a complete QoS implementation for various types of traffic flows. Our scheduling scheme includes two components, one is the resource allocation for each user; the other is the QoS scheduling for various traffic sessions. Specifically an optimization problem is formulated to distribute all OFDMA channel resource among different competing users by exploiting the transmission adaption and multiuser diversity on each traffic channel. The optimized resource allocation can also be processed under different constraints to achieve different performance metrics. To ensure the WiMax QoS performance, we perform the resource allocation in a priority manner with respect to the different types of QoS requirements and get a desired transmission bandwidth for each user. Based on it we further schedule different traffic sessions at each user with respect to a proper admission control mechanism. The relevant solution and algorithms for our proposed scheduling scheme are presented in detail. Both the theoretical analysis and simulation results show that our scheme can achieve the key performance objectives such as complete QoS requirements, high channel transmission efficiency and optimal throughput over the whole OFDMA WiMax system.

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Polybenzoxazine/graphene porous nanocomposites were prepared by sol–gel and subsequent thermal curing. The porous nanocomposites showed low densities ranging from 0.154 to 0.204 g/cm3. The chemical structures and microscopic morphology of the porous nanocomposites were studied using Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM). The electromagnetic wave absorbing ability of the porous nanocomposites was investigated, and the results showed that the minimum reflection loss for the porous nanocomposite with 15 wt% of graphene (PBG‐15) can reach −35.72 dB at a thickness of 2.6 mm with a 1.5 GHz frequency bandwidth. The excellent absorption ability was due to the conductivity loss in the porous nanocomposite. Also, PBG‐15 exhibited good heat resistance with a thermal deformation temperature near 220°C and a char yield of 56%. In addition, the addition of graphene could increase the compressive strength and compressive modulus of the porous nanocomposites by up to 126% and 364%, respectively. These polybenzoxazine/graphene porous nanocomposites have good potential application in light electromagnetic wave absorbing materials.

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