Search

In this paper, we derive an upper bound on load-threshold of coded slotted ALOHA (CSA) for slot erasure channel (SEC) and that for packet erasure channel (PEC), respectively. In SEC, by exploiting the analogy between Gaussian elimination of solving linear equations and the iterative successive interference-cancellation (SIC) decoding procedure of CSA, we derive the upper performance bound for SEC. Subsequently, in PEC, utilizing density evolution to track the average probability of packet-decoded failure within the SIC decoding process, we obtain the upper bound for PEC. Moreover, we propose a numerical search algorithm of these bounds under a given calculating precision. The numerical results indicate that the asymptotic upper limit on load-threshold of CSA over SEC is always less than that over PEC with any given erasure probability and average transmission rate. [ABSTRACT FROM AUTHOR]

In this paper, we consider single carrier system with transmit diversity and a new multi-antenna transmission waveform is carefully designed to enable low-complexity anti-interference adaptive equalization. We propose a new space-frequency adaptive equalization method which makes use of the mutual interferences among different antennas from the desired user rather than attempts to completely remove them. We further propose two different ways to significantly reduce the computational complexity based on the idea of subband-wise processing with little sacrifice of equalization performance. Simulation results show that the proposed method exhibits a significant gain over conventional anti-interference schemes. [ABSTRACT FROM AUTHOR]

A quadratic programming based neural dynamic (QPND) controller design method is proposed for time-varying trajectory tracking of unmanned aerial vehicles (UAVs). Different from the traditional controller frameworks which only use pitch and roll angles to achieve the horizontal movement of the UAV, all the three attitude angles, i.e., roll, pitch and yaw angles, are applied for horizontal moving in this paper. There are at least three great superiorities of the proposed QPND controller. Firstly, three attitude angles can be coordinated control since the quadratic programming framework incorporates three attitudes. Secondly, the new framework enables the UAV to achieve the additional performance criteria or to perform subtasks. Third, the new controller can track time-varying trajectories due to neural dynamic approach. Specifically, the design process of the controller is divided into position controller design, attitude controller design and quadratic programming formulation. Finally, simulation experiments verify the feasibility and high efficiency of the proposed controller and its superiority compared with some state-of-the-art UAV controllers. [ABSTRACT FROM AUTHOR]

To stably control the position and attitude angles of an unmanned aerial vehicle (UAV), a varying-parameter convergent neural dynamic (VP-CND) method is proposed and applied. First, the dynamic models of multirotor UAVs are presented. Second, to meet the requirements of high accuracy and real-time control, a VP-CND method is proposed based on an error function to derive the position and attitude angle controllers. The existing fixed-parameter CND methods (e.g., the triple-Zhang dynamics or the Zhang dynamics and gradient dynamics) and the corresponding controllers are presented, and their limitations are analyzed. The proposed VP-CND control method not only can track time-varying target values but also possesses super-exponential convergence performance. Third, simulation comparisons verify the effectiveness, stability, and fast convergence of the VP-CND controllers. [ABSTRACT FROM AUTHOR]

In this paper, we consider a massive multiple-input multiple-output (MIMO) system for urban macro cellular networks. A new technique named vertical spatial filtering (VSF) is proposed to achieve low radio frequency (RF) complexity by exploiting the spatial beam redundancy in elevation domain. Specifically, VSF consists of two parts: beam mapping and beam selection. We first adopt beam mapping to transform the received signals from antenna space into beam space. Then, we use beam selection to pick out part of the RF chains so as to realize the reduction of RF complexity. A three-dimensional channel model is adopted to evaluate the system performance. Two strategies for beam selection are proposed and numerical results are presented. The results show that the reduced system with VSF has the performance comparable to the complete system, while only a small amount of RF chains is required in vertical dimension of the two-dimensional base station array. [ABSTRACT FROM PUBLISHER]