Reliable long timescale decision-directed channel estimation for OFDM system

Decision-directed channel estimation (DDCE) is one kind of blind channel estimation method that tracks the channel blindly by an iterative algorithm without relying on the pilots, which can increase the utilization of wireless resource. However, one major problem of DDCE is the performance degradation caused by error accumulation during the tracking process. In this paper, we propose an reliable DDCE (RDDCE) scheme for an OFDM-based communication system in the time-varying deep fading environment. By combining the conventional DDCE and discrete Fourier transform (DFT) channel estimation method, the proposed RDDCE scheme selects the reliable estimated channels on the subcarriers which are less affected by deep fading, and then estimates the channel based on the selected subcarriers by an extended DFT channel estimation where the indices of selected subcarriers are not distributed evenly. Simulation results show that RRDCE can alleviate the performance degradation effectively, track the channel with high accuracy on a long time scale, and has good performance under time-varying and noisy channel conditions.

Joint Design of Coding and Modulation for Digital Over-the-Air Computation

Due to its high communication efficiency, over-the-air computation (AirComp) has been expected to carry out various computing tasks in the next-generation wireless networks. However, up to now, most applications of AirComp are explored in the analog domain, which limits the capability of AirComp in resisting the complex wireless environment, not to mention to integrate the AirComp technique to the existing universal communication standards, most of which are based on the digital system. In this paper, we propose a joint design of channel coding and digital modulation for digital AirComp transmission to attempt to reinforce the foundation for the application of AirComp in the digital system. Specifically, we first propose a non-binary LDPC-based channel coding scheme to enhance the error-correction capability of AirComp. Then, a digital modulation scheme is proposed to achieve the number summation from multiple transmitters via the lattice coding technique. We also provide simulation results to demonstrate the feasibility and the performance of the proposed design.