Gaofeng Cui

Base Station Density Bounded by Maximum Outage Probability in Massive MIMO System

The base station (BS) density influences the coverage performance of cellular communication system. In massive multiple input multiple output (MIMO) system, each BS is equipped with large scale antenna array. The stochastic geometric model is employed because of its analytical tractability. This paper demonstrates that BS density has to be below a certain bound in order to satisfy the coverage requirement in massive MIMO system. Closed-form expression for the BS density bounded by maximum outage probability is derived using Lambert W function. Moreover, the expression for the upper bound of successful area spectral efficiency (ASE) is also derived. Our study claims that increasing BS density will lead to the deterioration of coverage performance in massive MIMO system.

Component Carrier Selection Based on User Mobility for LTE-Advanced Systems

In component carrier (CC) selection of carrier aggregation, it is critically significant to take the effect of user mobility on system performance into consideration. In the previous CC selection schemes, in order to guarantee channel quality and avoid frequent CC handover caused by user mobility, the eNB always select the CC with the highest Reference Signal Receiving Power (RSRP) for users. However, this method would face carrier overload when the CC with high RSRP was selected for a majority of users. On the contrary, in conventional schemes considering carrier load balancing, the system would face the problem of frequent CC reselection/handover as user mobility was usually neglected, which would face unaffordable signaling overhead and time delay. In this paper, a user-mobility based CC selection (UM-CS) scheme is proposed to analyze the influence of user mobility on CC selection and achieve a compromise of carrier load balancing and handover number. In the proposed UM-CS scheme, in order to avoid frequent CC handover, the eNB-UE separation after a given time is estimated according to the users mobility and CCs that can satisfy the coverage margin are selected into the users candidate CC set. In the set, the CC with larger coverage takes higher priority in CC selection. Carrier load are balanced as the user can only select CCs from its own candidate CC set and a CC can be selected only when its carrier load balancing factor is not higher than the threshold. Simulation results validate the effectiveness of the proposed scheme in terms of carrier load balancing and handover number under different user mobility.

Self-Interference Cancellation with RF Impairments Suppression for Full-Duplex Systems

In full-duplex systems, radio circuits impairments is a significant factor that limits the cancellation of self-interference power. In this paper, we derive a closed-form expression of digital domain self- interference for a full-duplex orthogonal frequency division multiplexing (OFDM) system considering the RF impairments at the transmitter and the receiver. A digital-domain self-interference cancellation scheme (DSICS) that accounts for the power amplifier nonlinearity, IQ imbalance and phase noise effects at the transmitter and receiver is proposed. The DSICS can suppress the self-interference power effectively by compensating for the RF impairments associated with the self-interference signal.

An Enhanced Coarse Synchronization Scheme with Low Complexity for 3GPP LTE

A new coarse synchronization scheme for 3rd Generation Partnership Project Long Term Evolution (3GPP-LTE) is proposed. Existing coarse synchronization schemes based on central symmetry utilize either primary synchronization signal (PSS) and secondary synchronization signal (SSS) to fulfill initial timing synchronization. Though these two schemes perform well with relative low complexity, they can be further enhanced. Therefore a new scheme is proposed in this paper, which combines PSS with SSS and utilizes hierarchical computing to implement initial timing synchronization. Simulation results show that the new scheme can acquire higher detection accuracy rate without increasing computational complexity.

Throughput Optimization in MU-MIMO Systems via Coordinated Vertical Double-Beam Tilting

In this paper, we propose a novel framework called coordinated double-beam tilting to improve the throughput of multiple-input multiple-output (MIMO) system in a single cell via determining the tilting angles of two beams adaptively in a coordinated fashion. In this framework, two antenna beams adjust their tilting angles jointly based on the location of users to maximize the sum throughput of the scheduled users, denoted as coordinated user-specific double-beam tilting (CUSDBT) and coordinated vertical region-specific double-beam tilting (CVRSDBT). Assuming the availability of location information of scheduled users, accurate analytical expression for cell average achievable rate is provided. To determine the optimal tilting angles for BS beams to maximize sum throughput, Dividing Rectangle (DIRECT) method, an effective approach for optimization problems, is applied. Simulation results show that the proposed coordinated double-beam tilting scheme outperforms the conventional antenna tilting schemes.

An adaptive frequency allocation scheme for OFDMA femtocell networks

Due to high data rate requirement for indoor communication, femtocells have been proposed as a potential solution to increase not only indoor radio coverage but also system capacity. However, there is co-channel interference that affects the system throughput seriously due to high density of femtocells in urban environment. In this paper, an adaptive frequency allocation (AFA) for LTE network is proposed to mitigate interference. Performance evaluation is given to justify our proposed method on improving overall system throughput compared with co-channel frequency allocation (co-channel FA) and orthogonal frequency allocation (OFA).