Yu-Ngok Ruyue Li

CoMP and interference coordination in heterogeneous network for LTE-Advanced

Coordinated Multipoint Transmission and Reception (CoMP) and Enhanced Inter-cell Interference Coordination (eICIC) are two important features in 3GPP LTE-Advanced. Through CoMP and interference coordination, system performance, especially cell edge throughput is significantly improved. In 3GPP LTE-Advanced, CoMP discussion has been focusing on dynamic coordination schemes which require fast links between coordinating points. On the contrary, eICIC is considered as a semi-static co ordination scheme which is enabled through X2 backhaul interface. This paper provides an overview of CoMP and eICIC schemes discussed in the standardization process of LTE-Advanced. Performance results are provided to evaluate a novel scheme which combines dynamic CoMP and semi-static eICIC coordination under super-cell heterogeneous network deployment.

Field trial and future enhancements for TDD massive MIMO networks

Massive MIMO is one of the promising techniques to improve the spectral efficiency and network performance in future 5G networks. Compared to FDD, it is relatively easier to realize downlink massive MIMO for TDD as downlink channel information can be obtained via uplink-downlink channel reciprocity. This paper provides our field test results of massive MIMO system with a base station prototype equipped with 64 transmit antennas. Significant throughput gain is observed by performing 3D-beamforming to current LTE-Advanced handsets by using standard-transparent Multiuser(MU) MIMO techniques. With the massive MIMO base station prototype, MU-MIMO is realized by multiplexing maximum of eight handsets in spatial domain considering both azimuth and elevation directions. In addition to the field trial test results, future potential enhancements for TDD massive MIMO system are discussed. Evaluation results of evaluating some enhancements on uplink reference signal are provided.

Energy efficient small cell operation under ultra dense cloud radio access networks

Deploying dense small cells is an emerging approach to improve network throughput by providing proximate hotspot access to users. Small cell enhancement is considered as one of the hot topics in 3GPP LTE Release 12. One of the important aspects in the small cell study is how to ensure efficient small cell operation by switching on/off small cells. This paper analyzes different small cell on/off schemes. The benefits of small cell on/off and adaptive baseband unit sharing under ultra dense networks (UDN) with centralized/cloud radio access network (C-RAN) architecture are evaluated in terms of both throughput increase and energy saving.

Flexible Resource Allocation in 5G Ultra Dense Network with Self-Backhaul

Self-backhaul is flexible and cost efficient for ultra dense network (UDN) since it provides backhaul using the same wireless technology as access link. Content prediction and caching can lower the load on backhaul and improve user experience. Therefore, an algorithm named tri-stage fairness (TSF) is proposed to solve the resource allocation problem in UDN with self-backhaul and caching, in which cells without direct network connection (rTP) access core network through donor TP (dTP). In TSF, rTP determines to transmit files cached in rTP (rTP files) or the files not cached in rTP (dTP files) according to delay and link capacity, and allocate access link resource using proportional fairness algorithm. dTP allocates backhaul resource among its users and rTPs with fairness considerations, and decides the time each rTP spends on backhaul link. Fairness, efficiency, overhead and complexity are jointly considered in TSF. To facilitate system level simulation, a traffic model considering the influence of caching is also introduced. Simulation results suggest flexible resource allocation between access and backhaul link yield substantial performance gain.

Wireless backhaul of dense small cell networks with high dimension MIMO

Wireless backhaul is often the bottleneck of heterogeneous network with relay nodes especially when dense relay deployment is considered. Massive MIMO is a good candidate to improve the performance of wireless backhaul. With massive MIMO, MU-MIMO technique can be more effectively applied to multiplex transmission targeting multiple relays in the same resource. However, application of MU-MIMO is limited by available traffic and spatial separation of the relays. We investigate the application of virtual MIMO on the relay system so that multiple relays in the same cluster form a virtual MIMO system for higher dimension MIMO transmission. Evaluation is done to investigate the benefits of applying virtual MIMO on the wireless backhaul of a cluster based small cell networks.

Cell and user virtualization for ultra dense network

Ultra-dense network deployment is a clear trend considered for the next generation networks. To allow flexible deployment of small cells, self-backhauled small cell architecture is one of the important types of the future ultra-dense network architecture. In this paper, densification and virtualization are considered in both cell and user aspects. Virtualization of radio access network provides a key solution to mobility and interference issues. It enables user centric radio access. On the terminal side, more devices are expected to be connected in the network. Similarly, virtualization can be applied to the terminal side. This enables virtual resource allocation and coordination among terminals to boost up the user capability and overall network performance. This paper proposes a novel small cell architecture which considers multi-layer virtualization for dense heterogeneous network.

High-Rank MIMO Precoding for Future LTE-Advanced Pro

We study the precoding for the high-rank MIMO in the LTE-A Pro systems. Unlike the low-rank precoding, layer mapping has a relatively large impact on the performance for high-rank precoding. First, we construct a model on the relationship between layer mapping and precoding. Then we derive the system throughput with the resulting model, so that the performance of the layer mapping and precoding can be evaluated. Further, we operate a sub-space optimization for the codebook-based precoding to maximize the system throughput. Simulation results show that after optimizing layer mapping, high-rank precoding achieves much better performance.

Measurement and Evaluations of Coherent Joint Transmission for 5G Networks

Coherent joint transmission (JT), where multiple transmitters send a common message with phase constructively combined at a receiver, is a promising technique to improve the signal power and spatial diversity in 5G networks. In this paper, we reconsider the two-way and master-slave synchronization protocol for coherent JT taking into account the impact of different response of transmit/receive chains. Measurement results and system level simulations for coherent JT are provided. The results show that coherent JT provides significant throughput gains compared with other coordination schemes.

CSI feedback for massive MIMO system with dual-polarized antennas

Massive MIMO is a promising technique to provide high data rate with good energy efficiency for the future wireless cellular communication. However, its performance benefit often can be realized only when accurate channel state information (CSI) is available at the transmitter to perform accurate beamforming. With large number of antennas, full CSI consumes too much overhead to feed back without compression. To reduce CSI feedback overhead, CSI feedback scheme with dual stage precoding structure is designed to quantize the long term spatial channel correlation information and short term linear precoder information. In this paper, we discuss how to optimize this dual stage precoding scheme in the typical dual-polarized massive MIMO system. The eigenvalues of spatial correlation matrix are used to improve feedback efficiency. By relaxing the constant modulus constraint in codebook design, more flexible long term precoding can be used and adapt to the channel. A specific structure of long term precoding matrix for dual-polarized MIMO system is proposed to ensure the orthogonality of the final precoder for multi-layer transmission.