Equalization Techniques for Unmanned Aerial Vehicles Communication Based on Early Termination of Iteration

This paper investigates the doubly iterative turbo equalization of signals with high-order modulation for unmanned aerial vehicle (UAV) communication network, where the communication channel can be seen as a frequency-selective fading. In practice, the optimal detection is intractable for high-order modulations. Linear Minimum Mean Square Error (LMMSE) scheme is considered to be an efficient and low-cost alternative. Based on the turbo LMMSE equalization, expectation propagation (EP) algorithm is utilized to improve the gain by doubly iterative structure, called Block-EP (BEP). Then, considering the increasing decoding delay, an improved BEP (IBEP) algorithm in the inner loops is developed based on early termination of iteration. Moreover, hard decision aided (HDA) stopping criterion is utilized in the outer iteration. The simulation results demonstrate that the combination of IBEP and HDA stopping criterion effectively reduces the average iteration number and improve the real-time performance of double iteration, comparing conventional scheme.