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( Zhiyong Liu ),( Qinyu Zhang ),( Liwei Mu ) 한국인터넷정보학회 2016 KSII Transactions on Internet and Information Syst Vol.10 No.9
In this paper, an adjustable multiple relay selection (MRS) scheme for cooperative communication with amplify-and-forward (AF) relay under frequency selective channels is proposed. In the proposed scheme, the relays are ordered firstly by the steady-state mean square error (MSE), then the relays are sequentially selected out from N relays and the number of cooperating relays is adjusted dynamically according to the steady-state mean square joint error (MSJE). The aim of this work is to dynamically estimate the optimum number No of cooperating relays. Optimum means the minimum number of cooperating relays, No, achieving the minimum level of steady-state MSJE. Numerical results verify the analyses and show that the scheme can adaptively adjust the number of cooperating relays, and outperform conventional relay selection schemes. Hence, the proposed scheme provides better tradeoff between BER performance and spectral efficiency and to save more energy in cooperative wireless networks.
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Radio Resource Management of CoMP System in HetNet under Power and Backhaul Constraints
( Jia Yu ),( Shaohua Wu ),( Xiaodong Lin ),( Qinyu Zhang ) 한국인터넷정보학회 2014 KSII Transactions on Internet and Information Syst Vol.8 No.11
Recently, Heterogeneous Network (HetNet) with Coordinated Multi-Point (CoMP) scheme is introduced into Long Term Evolution-Advanced (LTE-A) systems to improve digital services for User Equipments (UEs), especially for cell-edge UEs. However, Radio Resource Management (RRM), including Resource Block (RB) scheduling and Power Allocation (PA), in this scenario becomes challenging, due to the intercell cooperation. In this paper, we investigate the RRM problem for downlink transmission of HetNet system with Joint Processing (JP) CoMP (both joint transmission and dynamic cell selection schemes), aiming at maximizing weighted sum data rate under the constraints of both transmission power and backhaul capacity. First, joint RB scheduling and PA problem is formulated as a constrained Mixed Integer Programming (MIP) which is NP-hard. To simplify the formulation problem, we decompose it into two problems of RB scheduling and PA. For RB scheduling, we propose an algorithm with less computational complexity to achieve a suboptimal solution. Then, according to the obtained scheduling results, we present an iterative Karush-Kuhn- Tucker (KKT) method to solve the PA problem. Extensive simulations are conducted to verify the effectiveness and efficiency of the proposed algorithms. Two kinds of JP CoMP schemes are compared with a non-CoMP greedy scheme (max capacity scheme). Simulation results prove that the CoMP schemes with the proposed RRM algorithms dramatically enhance data rate of cell-edge UEs, thereby improving UEs` fairness of data rate. Also, it is shown that the proposed PA algorithms can decrease power consumption of transmission antennas without loss of transmission performance.
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Accelerating Dissolution of Polyacrylamide in Offshore Oil Field
Qin Yu,Xiangguo Lu,Defu Zhang,Kun Xie 대한화학회 2015 Bulletin of the Korean Chemical Society Vol.36 No.10
The solubility of polyacrylamide significantly reduces the efficiency of polymer flooding in offshore oil fields, because of the low performance of polyacrylamide and the special environment. The objective of this paper is to investigate a novel approach to accelerate the dissolution of hydrolyzed polyacrylamide (HPAM) by adding a co-solvent cholamine (MEA). We investigated the effects of MEA on the microstructure and the performance of HPAM. Results showed that the addition of MEA and the temperature rise greatly shortened the dissolution time of HPAM, while improved the rheological property and seepage behavior. The enhanced solubility of polyacrylamide and the performance of polymer solution can be attributed to the enlarging of the molecular clew size, the stretching of molecular chains and the lowering of the glass transition temperature of HPAM. The new approach has high practical and the economic values for applications of the polymer flooding technology in offshore oilfields with complex reservoir conditions.
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