Chunlong He

Energy- and Spectral-Efficiency Tradeoff for Distributed Antenna Systems with Proportional Fairness

Energy efficiency(EE) has caught more and more attention in future wireless communications due to steadily rising energy costs and environmental concerns. In this paper, we propose an EE scheme with proportional fairness for the downlink multiuser distributed antenna systems (DAS). Our aim is to maximize EE, subject to constraints on overall transmit power of each remote access unit (RAU), bit-error rate (BER), and proportional data rates. We exploit multi-criteria optimization method to systematically investigate the relationship between EE and spectral efficiency (SE). Using the weighted sum method, we first convert the multi-criteria optimization problem, which is extremely complex, into a simpler single objective optimization problem. Then an optimal algorithm is developed to allocate the available power to balance the tradeoff between EE and SE. We also demonstrate the effectiveness of the proposed scheme and illustrate the fundamental tradeoff between energy- and spectral-efficient transmission through computer simulation.

Energy Efficiency and Spectral Efficiency Tradeoff in Downlink Distributed Antenna Systems

This letter investigates the tradeoff between energy efficiency (EE) and spectral efficiency (SE) in downlink multiuser distributed antenna systems (DAS). Given the SE requirement and maximum power limit, a constrained optimization problem is formulated to maximize EE. Because of the multi-dimensional and non-convex nature of the problem, we first transform the multicriteria optimization problem with high complexity into a simpler single objective optimization problem. Then a novel power allocation algorithm is proposed to achieve maximum EE. Simulation results demonstrate the effectiveness of the proposed scheme as well as illustrate the fundamental tradeoff between energy efficient and spectral efficient transmission in downlink multiuser DAS.

Energy-Efficient Resource Allocation in OFDM Systems With Distributed Antennas

In this paper, we develop an energy-efficient resource-allocation scheme with proportional fairness for downlink multiuser orthogonal frequency-division multiplexing (OFDM) systems with distributed antennas. Our aim is to maximize energy efficiency (EE) under the constraints of the overall transmit power of each remote access unit (RAU), proportional fairness data rates, and bit error rates (BERs). Because of the nonconvex nature of the optimization problem, obtaining the optimal solution is extremely computationally complex. Therefore, we develop a low-complexity suboptimal algorithm, which separates subcarrier allocation and power allocation. For the low-complexity algorithm, we first allocate subcarriers by assuming equal power distribution. Then, by exploiting the properties of fractional programming, we transform the nonconvex optimization problem in fractional form into an equivalent optimization problem in subtractive form, which includes a tractable solution. Next, an optimal energy-efficient power-allocation algorithm is developed to maximize EE while maintaining proportional fairness. Through computer simulation, we demonstrate the effectiveness of the proposed low-complexity algorithm and illustrate the fundamental tradeoff between energy- and spectral-efficient transmission designs.

Energy efficiency comparison between distributed and co‐located MIMO systems

SUMMARY Energy efficiency (EE) is becoming more and more important in future wireless communications because of limited battery power in mobile terminals. In this paper, we compare EE of the distributed MIMO (D-MIMO) and co-located MIMO (C-MIMO) in uplink systems. Taking into account both circuit and transmit power, we derive an analytical expression for EE of D-MIMO and C-MIMO systems in a composite Rayleigh-lognormal channel. What is more, an optimization algorithm is proposed to get the optimal EE values while satisfying given spectral efficiency requirement for both D-MIMO and C-MIMO systems. Simulation results show that D-MIMO systems are more energy effective than C-MIMO systems when considering the realistic systems, and the optimal EE can be obtained by the proposed algorithm while satisfying given spectral efficiency requirement. Copyright

Power Allocation Criteria for Distributed Antenna Systems

In this paper, we discuss three different design criteria for a distributed antenna system (DAS). They include maximizing throughput under the constraint of the overall transmit power, minimizing the overall transmit power while guaranteeing the minimum spectral efficiency (SE) requirements, and maximizing energy efficiency (EE) under the constraints of minimum SE requirements and overall transmit power. The optimization problems for the first two criteria are signomial programming (SP) problems when considering the interference among the mobile stations (MSs), which are nonlinear nonconvex and do not lead to the closed-form solutions directly. Exploiting the nature of geometric mean, we transform the SP problems into geometric programming (GP) problems, which can be solved by turning them into convex problems. For the third criterion, using the theorem of fractional programming, we first transform the fractional optimization problem into an equivalent optimization problem in a subtractive form, which is an SP problem. We then obtain its solution by transforming the SP to the GP problem as we have done for the previous two problems. Based on these design criteria, three power allocation algorithms are developed for the downlink multiuser DAS. Depending on the application environments, we can use the first and second criteria to achieve the highest throughput and to save energy, respectively, while balancing throughput and energy consumption using the third criterion.

Energy Efficiency Optimization for MIMO Distributed Antenna Systems

In this paper, we propose a transmit covariance optimization method to maximize the energy efficiency (EE) for the single-user distributed antenna system, where both the distributed antenna (DA) ports and the user are equipped with multiple antennas. Unlike previous related works, both the rate requirement and DA port selection are taken into consideration. Given this setup, we first propose an optimal transmit covariance optimization method to solve the EE optimization problem under fixed set of active DA ports and then the active DA port selection algorithm. For the transmit covariance optimization method, we split this problem into three subproblems, i.e., rate maximization problem, EE maximization problem without rate constraints, and power minimization problem. Then, a novel distance-based DA port selection method is proposed to determine the optimal set of active DA ports. Simulation results show that the performance of the proposed DA port selection is almost identical to the optimal exhaustive search method with significantly reduced computational complexity, and significantly outperforms the existing EE optimization methods.

Energy Efficient Comparison between Distributed MIMO and Co-Located MIMO in the Uplink Cellular Systems

In this paper, we compare EE of the distributed MIMO (D-MIMO) and co-located MIMO (C-MIMO) in the uplink cellular systems since mobile stations are battery powered. The total energy consumption includes both the circuit energy consumption and the transmission energy. We get the closed-form expression for EE of D-MIMO and C-MIMO systems. Whats more, an optimization algorithm is proposed to get the optimal EE values while satisfying given spectral efficiency (SE) requirement for both D-MIMO and C-MIMO systems. Simulation results show that the D-MIMO systems are more energy efficient than C-MIMO systems in composite fading channel, and the optimal EE value can be obtained by the proposed algorithm while satisfying given SE requirement.

Energy and spectral efficiency of distributed antenna systems

In this paper, we propose an optimal scheme for a distributed antenna system (DAS) to maximize energy efficiency (EE) under a constraint of overall transmit power of each remote access unit (RAU). We exploit the multicriteria optimization method to systematically investigate the relationship between EE and spectral efficiency (SE). Using the weighted sum method, we first convert the multicriteria optimization function, which is extremely complex, into a simpler single objective optimization function. Then an optimal algorithm is developed to allocate the available power to tradeoff EE and SE effectively. Furthermore, we also illustrate the effectiveness of the proposed method and demonstrate there is a tradeoff between energy-efficient and spectral-efficient transmission through computer simulation of a downlink multiuser DAS.

Energy efficiency of distributed MIMO systems

In this paper, we investigate energy efficiency (EE) of the co-located and the distributed multiple-input multiple output (MIMO) system. First, we obtain an approximate EE expression for different power consumption models. Then two EE properties are revealed for the distributed MIMO system. The analytical results are verified by computer simulations.

Energy and spectral efficiency trade-off for the downlink OFDM-distributed antenna systems

This paper investigates an energy efficient optimization scheme for the downlink multiuser OFDM-distributed antenna systems. We adopt a multicriteria optimization method to offer a systematic study on the relationship between spectral efficiency SE and energy efficiency EE. First, we transform the energy efficient optimization problem with high complexity into a simpler downlink multiuser OFDM problem. Then, using the weighted sum method in multicriteria optimization, an optimal energy efficient scheme is presented to allocate the available power to balance the trade-off between SE and EE efficiently. Simulation results demonstrate that the energy efficient scheme is effective, and there existed a trade-off between SE and EE in the downlink multiuser OFDM-distributed antenna systems. Copyright