Jianfeng Shi

Energy Efficient Non-Orthogonal Multiple Access for Machine-to-Machine Communications

This letter investigates an uplink energy minimization problem for machine-to-machine communications with non-orthogonal multiple access. To solve this non-convex problem, we first prove that transmitting with minimum rate and full time is optimal. Then, the original problem can be transformed into an equivalent convex problem, which can be effectively solved by the proposed optimal power control and time scheduling scheme. Numerical results show that the proposed scheme achieves the optimal energy consumption.

Energy-Efficient Resource Allocation in D2D Underlaid Cellular Uplinks

In this letter, we study the joint channel allocation and power control problem to maximize the energy efficiency (EE) of device-to-device (D2D) links in a D2D underlaid cellular network. Due to the location dispersion of D2D pairs and short-distance D2D transmission, it should be preferred that multiple D2D pairs can simultaneously share the resource with cellular users (CUs). To address the nonconvexity of the EE maximization problem, we divide the original problem into two subproblems and propose an iterative algorithm with low complexity to solve it. Simulation results show that the proposed algorithm converges rapidly and the EE of D2D links can be significantly improved compared with existing methods especially for an increasing number of CUs.

Pilot Allocation and Power Control in D2D Underlay Massive MIMO Systems

In this letter, we propose pilot reuse among device-to-device (D2D) users (DUs) in a D2D underlay massive MIMO system to shorten pilot overhead. First, we derive a lower bound on the average signal-to-interference-plus-noise ratio of DUs. Then, a revised graph coloring-based pilot allocation (RGCPA) algorithm is proposed to mitigate the pilot contamination. Finally, a power control problem to minimize D2D links’ data transmit power is formulated and an iterative scheme is adopted to solve the problem. The simulation results show that pilot overhead can be shortened greatly by pilot reuse, and the effect of pilot contamination can be almost cancelled using the proposed RGCPA algorithm. In addition, the power control scheme converges rapidly.

User Association, Resource Allocation and Power Control in Load-Coupled Heterogeneous Networks

This paper aims at network utility maximization via jointly optimizing user association, resource allocation and power control in a load-coupled heterogeneous network. We first obtain that the optimal condition for load control of each base station (BS) is to be either fully loaded or shut down. With the help this observation, the original problem is greatly simplified which allows us to propose an alternating optimization design. We transform the subproblem in the alternative optimization into a convex one and efficiently solve the other subproblem via the gradient projection method. Simulation results show that the proposed algorithm achieves better performance than the conventional network utility maximization methods.

Power control and resource allocation for multi-cell OFDM networks

In this paper, we consider the problem of minimizing the total transmit power with power control and resource allocation in OFDM networks where mutual interference exists among cells. The signal-to-interference-and-noise-ratio (SINR) relation is interpreted by the load and power coupling model, where every resource is available for each user with a probability. These probability variables can be also named as load vector. To solve this problem, we develop one low-complexity distributed power control and resource allocation algorithm. Specially, each BS updates its load vector, power vector, rate vector information and broadcasts it to all other BSs. Having collected all the information, each BS calculates its own load vector, power vector and rate vector by solving a convex program and a linear program. Compared with the existing optimization algorithm, where each resource is allocated to at most one user in a period of time, our algorithm has lower computational complexity. Numerical results verify the effectiveness and convergence of our proposed algorithm.

Power control for relay-assisted device-to-device communication underlaying cellular networks

We investigate power control problem for cooperative relaying in the device-to-device (D2D) system underlaying cellular networks. Specifically, we consider the D2D communication assisted by fixed-location relays in interference existing circumstance. Therefore, an effective power control scheme is of great importance to suppress interference between D2D and cellular communications which can improve the total system throughput and spectral efficiency. In this paper, we formulate a power control optimization problem for cellular communication and a simple on-off power control algorithm for D2D communications. We also obtain analytic expression for the coverage probability of cellular link using stochastic geometry according to proposed algorithm. Simulation results follow to show the rate of both cellular and D2D links in the various number of D2D transceivers.

Energy-Efficient Optimization with Cell Load Coupling for OFDM Networks

In this paper, we consider the problem of maximizing the sum energy efficiency (EE) for LTE networks where the interferences occur between cells. Cell load, transmit rate and transmit power, where cell load demonstrates the average resource usage in a cell, are considered in the signal-to- interference-and-noise-ratio (SINR) model. Exploiting the properties of sum EE, we prove that operating at full load is optimal and provide a distributed power control algorithm. With all other powers fixed, we transform the original nonconvex optimization problem in fractional form into an equivalent optimization problem in subtractive form. In high SINR situation, the transformed problem in subtractive form is proved a convex problem. Numerical results demonstrate the remarkable improvements in terms of EE.

Cell load coupling with power control for LTE network planning

We consider the problem of optimization of sum cell load with the constraints of cell load coupling and power control in LTE network. Our system model characterizes the coupling relation between cell load and power, considering non-uniform traffic demand and interference between cells. Solving the problem involves optimization with fixed power, and optimization with power control. We prove the the convergence of fixed-point iteration, which is used in optimization with fixed power, and provide sufficient and necessary conditions for the feasibility of cell load coupling with power control. Numerical results illustrate that our proposed solutions are superior to the conventional power allocation schemes.

Association and Load Optimization With User Priorities in Load-Coupled Heterogeneous Networks

In this paper, we consider the network utility maximization problem with various user priorities via jointly optimizing user association, load distribution, and power control in a load-coupled heterogeneous network. In order to tackle the nonconvexity of the problem, we first analyze the problem by obtaining the optimal resource allocation strategy in closed form and characterizing the optimal base station load distribution pattern. Both observations are shown essential in simplifying the original problem and making it possible to transform the nonconvex load distribution and power control problem into convex reformulation via exponential variable transformation. An iterative algorithm with low complexity is accordingly presented to obtain a suboptimal solution to the joint optimization problem. Simulation results show that the proposed algorithm achieves better performance than conventional approaches.

Robust Transmission Design for Multicell D2D Underlaid Cellular Networks

This paper investigates the robust transmission design (RTD) of a multicell device-to-device (D2D) underlaid cellular network with imperfect channel state information (CSI). The bounded model is adopted to characterize the CSI impairment and the aim is to maximize the worst-case sum rate of the system. To protect cellular communications, it is assumed that the interference from all D2D transmitters to each base station (BS) is power-limited. It is first shown that the worst-case signal-to-interference-plus-noise ratio (SINR) of each D2D link can be obtained directly, while that of cellular links cannot be similarly found since the channel estimation error vectors of cellular links are coupled in the SINR expressions. To solve the nonconvex problem, the objective function of the original problem is replaced with its lower bound, and the resulted problem is decomposed into multiple semidefinite programming (SDP) subproblems, which are convex and have computationally efficient solutions. An iterative RTD algorithm is then proposed to obtain a suboptimal solution. Simulation results show that D2D communication can significantly increase the performance of the conventional cellular systems while causing tolerable interference to cellular users. In addition, the proposed RTD algorithm outperforms the conventional nonrobust transmission design greatly in terms of network spectral efficiency.