Research On Energy Efficient Power Allocation Technology For Distributed MIMO Systems With Beamforming

With the rapid growth of traffic,the energy consumption problem of the wireless communication becomes increasingly prominent.Thus the next generation mobile communicatin system will be committed to pursuing higher energy efficiency(EE)to realize the green communication.The distributed multiple input multiple output(MIMO)systems can reduce the transmit power effectively and enhance the coverage well.The beamforming technology can remarkably suppress the attenuation of electromagnetic wave and increase the transmit distance.Therefore,in this thesis,energy efficient adaptive power allocation(PA)schemes will be investigated in the distributed MIMO systems with the combination of the beamforming technology and the MIMO technology.These schemes are developed in order to maximize the energy efficiency of the system and reduce the complexity,which will provide a theoretical foundation for improving the EE of the distributed MIMO systems,meanwhile realizing the green communication and enhancing the practicality.The main contents of the thesis are summarized as follows:1.The energy efficient PA scheme of the distributed MISO systems is investigated.According to the definition of EE and the constraints,the objective optimization function aims at maximizing the EE of the system is formulated.Based on the Karush-Kuhn-Tucker(KKT)condition,the general form of the optimal PA solution is derived which turns the multi-dimentional solving problem into the unidimensional one and then the optimal PA solution is obtained by employing the Lambert function and the bisection method.Simulation results show that the proposed PA scheme only needs one-time Lambert function calculation or fewer bisection searches and thus it can achieve the optimal EE performance while reducing the calculation complexity.2.The energy efficient PA scheme of the distributed MIMO systems is investigated.The original objective optimization problem is first transformed into the standard form of convex optimization by means of the fractional programming theory and then the optimal PA solution is derived by employing the Cardans formula.Considering that the optimal PA scheme needs multiple iterations and has high complexity,a suboptimal PA scheme is further proposed by using the tighter lower bound of the transmission rate.Simulation results show that the developed suboptimal PA scheme can achieve the EE performance close the optimal one while reducing the calculation complexity drastically and thus it can obtain an effective tradeoff between the EE performance and the complexity.3.The adaptive energy efficient PA of the distributed MIMO systems is investigated over the channels with transmit correlation and the energy efficient PA scheme under the requirement of the minimal rate is proposed to meet the demand of quality of service.The EE optimization problem subject to the minimal rate and the maximal power constraints is given,which is a nonconvex quadratically constrainted quadratic programming(QCQP)problem and is difficult to find the globally optimal solution.Thus,the tighter lower bound of the transmission rate is proposed to simplify the optimization problem and on this basis a low-complexity suboptimal PA scheme is further developed,which can improve the EE performance while obtain an effective tradeoff between the performance and the complexity.