AI Enlightens Wireless Communication: Analyses and Solutions for DMRS Channel Estimation

In this paper,a systematic description of the artificial intelligence(AI)-based channel estimation track of the 2nd Wireless Communication AI Competition(WAIC)is provided,which is hosted by IMT-2020(5G)Promotion Group 5G+AIWork Group.Firstly,the system model of demodulation reference signal(DMRS)based channel estimation problem and its corresponding dataset are introduced.Then the potential approaches for enhancing the performance of AI based channel estimation are discussed from the viewpoints of data analysis,pre-processing,key components and backbone network structures.At last,the final competition results composed of different solutions are concluded.It is expected that the AI-based channel estimation track of the 2nd WAIC could provide insightful guidance for both the academia and industry.

Transmit Diversity Scheme Design for Rectangular Pulse Shaping Based OTFS

This paper investigates the transmission scheme of the orthogonal time frequency space(OTFS)system with multiple antennas.Previous works have studied the multi-antenna transmitter diversity scheme with the ideal pulse shaping in OTFS systems assuming the wireless channels of two consecutive frames duration are invariant.However,the ideal pulse shaping can not be realized in practice and the channel varies rapidly in two consecutive frames in the high-speed mobility scenarios.To this end,we redesign the multi-antenna transmitter diversity scheme to ensure its practicability in the rectangular-pulsebased OTFS systems.At first,the information symbols of each antenna are divided into two half frames along the Doppler domain.Then,the guard symbols are carefully arranged to eliminate the interference between two half frames,and to ensure the equivalent channels of two half frames being identical.By considering the positions of the guard symbols,the transmission codeword is designed and a low complexity linear detection is proposed.Finally,simulation results validate that the bit error rate performance of the proposed scheme has the superiority over the existing works.

Orthogonal Time Frequency Space Modulation in Multiple-Antenna Systems

The application of the orthogonal time frequency space(OTFS)modulation in multiple-antenna systems is investigated.The diversity and/or the multiplexing gain can be achieved by deploying various multiple-antenna techniques,and thus the reliability and/or the spectral efficiency are improved correspondingly.We provide two classes of OTFSbased multiple-antenna approaches for both the open-loop and the closed-loop systems.Spe⁃cifically,in the open-loop system,a transmitting diversity approach,which resembles the space-time coding technique,is proposed by allocating the information symbols appropriate⁃ly in the delay-Doppler domain.In the closed-loop system,we adopt the Tomlinson-Harashi⁃ma precoding in our derived delay-Doppler equivalent transmission model.Numerical evalu⁃ations demonstrate the advantages of applying the multiple-antenna techniques to the OTFS.At last,several challenges and opportunities are presented.

Differential Privacy Trajectory Protection Method Based on Spatiotemporal Correlation

Location-based services provide service and convenience,while causing the leakage of track privacy.The existing trajectory privacy protection methods lack the consideration of the correlation between the noise sequence,the user’s original trajectory sequence,and the published trajectory sequence.And they are susceptible to noise filtering attacks using filtering methods.In view of this problem,a differential privacy trajectory protection method based on spatiotemporal correlation is proposed in this paper.With this method,the concept of correlation function was introduced to establish the correlation constraint of release track sequence,and the least square method was used to fit the user’s original track and the overall direction of noise sequence to construct noise candidate set.It ensured that the added noise sequence has spatiotemporal correlation with the user’s original track sequence and release track sequence.Also,it effectively resists attackers’denoising attacks,and reduces the risk of trajectory privacy leakage.Finally,comparative experiments were carried out on the real data sets.The experimental results show that this method effectively improves the privacy protection effect and the data availability of the release track,and it also has better practicability.