8月26日下午，在新主楼第四会议室举行了本学期第一次Workshop。本次Workshop邀请到了清华大学的高飞飞博士和浙江大学的钟财军博士为我们做了报告。内容如下：

报告人：高飞飞博士
Title：Low-Cost Low-Rank Channel Estimation for TDD/FDD Massive MIMO Systems: A Unified Approach from Array Signal Processing  

Abstract：
We proposes a unified transmission strategy for multiuser time division duplex (TDD)/frequency division duplex (FDD) massive multiple-input–multiple-output (MIMO)systems, including uplink (UL)/downlink (DL) channel estimation and user scheduling for data transmission. With the aid of antenna array theory and array signal processing, we build a spatial basis expansion model (SBEM) to represent the UL/DL channels with far fewer parameter dimensions. Hence, both the UL and DL channel estimations of multiusers can be carried out with a small amount of training resource, which significantly reduces the training overhead and feedback cost. Meanwhile, the pilot contamination problem in the UL training is immediately relieved by exploiting the spatial information of users. To enhance the spectral efficiency, we also design a greedy user scheduling scheme during the data transmission period. Compared with existing low-rank models, the newly proposed SBEM offers an alternative for channel acquisition without the need for channel statistics and can be applied to both TDD and FDD systems.  

报告人：钟财军博士
Title：Multi-antenna Wireless Legitimate Surveillance Systems: Optimal Design and Performance Analysis  

Abstract：
Wireless communications provide an efficient and convenient means for establishing connections between people, which nevertheless may also facilitate the collaboration between the criminals or terrorists. Therefore, to prevent crimes or terror attacks, there is a strong need for the government agencies to legitimately monitor any suspicious communication links. In this talk, we consider a wireless legitimate surveillance system, where a full-duplex multi-antenna legitimate monitor aims to eavesdrop on a dubious communication link between a suspicious pair by jamming. To maximize the eavesdropping non-outage probability, optimal joint jamming power, transmit and receive beamforming vectors are designed. In addition, suboptimal beamforming schemes are proposed, and the achievable eavesdropping non-outage probabilities are derived in closed-form. Our results demonstrate that, by exploiting multiple antennas, the performance of the system can be substantially enhanced compared to the single antenna system.