Hua Zhou

DM-RS Based Open-Loop CoMP in LTE-A System

Coordinated multi-point transmission/reception (CoMP) has been identified as an important way of mitigating interference and improving spectral efficiency for cell edge users in LTE-A system. However, current CoMP studies mainly focus on joint transmission (JT), dynamic point selection (DPS) and coordinated scheduling/beamforming (CS/CB) which all fall into closed-loop category. When considering medium or high mobility users, closed-loop CoMP seems less effective, while open-loop CoMP is more preferred, which is similar to that observed between closed-loop and open-loop single user multiple-input multiple-output (SU-MIMO). In this paper, we propose open-loop CoMP transmission frameworks for both spatial multiplexing and transmit diversity. We design our open-loop CoMP schemes by reusing long term evolution (LTE) open-loop SU-MIMO structures as much as possible to alleviate standardization efforts, and especially consider support for demodulation reference signals (DM-RS) which will be prevalent in future LTE-Advanced systems. Simulation results verify the effectiveness of our proposed open-loop CoMP schemes.

In-Device Coexistence Interference Evaluation and Detection in LTE-A System

In this paper, the in-device coexistence (IDC) interference detection is discussed for the user equipment (UE) with collocated long-term evolution (LTE) radio and WiFi radio. First, the comprehensive analysis is carried out to derive that the LTE transmission failure caused by the IDC interference from WiFi radio is related to the number of sub-frames overlapped with the WiFi transmission (called overlapped sub-frame). After that, consider the number of the detected overlapped subframes may be larger than that used to declare the serious IDC interference, an enhanced scheme is proposed to allow the enhanced NodeB (eNB) inform UE the threshold on the number of detected overlapped sub-frames. The numerical and simulation results indicate that the proposed scheme can largely reduce the detection overhead.

Separated Horizontal and Vertical Transmission Methods in Massive MIMO Systems

Massive MIMO is a promising technology in 5G communications, it can provide large numbers of antennas and form accurate beams to the users. In conventional three dimensional (3D) MIMO studies, the antenna elements (AEs) in one column are usually virtualized as one antenna port and the transmission schemes in long term evolution system (LTE) or other systems can be reused. In this case, multi-stream transmission can only be supported by the horizontal direction. While in massive MIMO systems with more AEs, forming one antenna port in the vertical direction to support single stream transmission will be inefficient. In this paper, we propose two joint port virtualization and multi-stream transmission algorithms in the framework of separated horizontal and vertical feedback. The proposed algorithms make a better tradeoff between the beamwidth and the number of simultaneously supported data streams. A rank indication (RI) feedback scheme is also proposed to assist the multi-stream transmission.

Proactive unnecessary handover avoidance scheme in LTE-A small cells

In this paper, the unnecessary handover avoidance scheme is discussed in Long Term Evolution-Advanced (LTE-A) small cells. Specifically, a handover is considered as unnecessary one if the active time in the target cell (i.e., duration where the user equipment can perform data communication) is not larger than a pre-defined threshold, where the active time is predicted before the handover through the average increased active time due to one packet arrival and the number of packets arriving during the dwell time in the cell. After that, if the probability that the active time is not larger than the pre-defined threshold is large enough, the source eNB would not carry out such handover due to the potential unnecessary handover. The numerical and simulation results verify that the proposed scheme can avoid the unnecessary handover precisely and efficiently.