Kai Ying

Joint Optimization of Precoder and Equalizer in MIMO VLC Systems

Recently, visible light communication (VLC) has attracted much attention as a possible candidate technology to meet the ever growing demand in wireless data. However, current low-cost white LED has limited modulation bandwidth, which limits the throughput of the VLC. Optical MIMO can provide spatial diversity and thus achieve high data rate. Traditional multiple-input multiple-output (MIMO) techniques used in wireless communications cannot be directly applied to VLC. This paper studies the precoder and equalizer design of optical wireless MIMO system for VLC. First, we propose a MIMO VLC system, which can effectively support the flickering/dimming control and other VLC-specific requirements. Second, besides the transceiver design with perfect channel state information, we also take into account channel uncertainties for joint optimization in the MIMO VLC system. Numerical results show that the proposed MIMO solution for VLC is robust to combat the influence caused by the channel estimation imperfection. By taking into account the channel estimation errors, the proposed joint optimization method demonstrates the bit error rate (BER) improvements in the scenario of imperfect channel estimation.

Nonlinear distortion mitigation in visible light communications

Many physical devices used in VLC systems exhibit nonlinear effects, which can significantly degrade the overall system performance. For example, the LED is the major source of nonlinearity. The forward current is zero unless the forward voltage exceeds a turn-on value. The forward current is also limited with a maximum permissible value. In addition, the electrical-tooptical conversion is also nonlinear. In this article, we provide an overview of techniques related to modeling and distortion mitigation techniques of the nonlinearity in VLC systems. Appropriate models and robust nonlinearity mitigation techniques are crucial to support high-speed transmissions in practical VLC systems.

Cooperative data dissemination in cellular-VANET heterogeneous wireless networks

Vehicular Ad hoc Networks(VANETs) enable plenty of important applications for vehicles, such as accident prevention and traffic jam avoidance. However, VANETs can hardly provide reliable connectivity between vehicles, which makes data dissemination of the aforementioned applications extremely difficult. Compared with VANETs, 3GPP cellular networks(e.g., LTE), offer much more reliable connectivity. Furthermore, cellular networks ensures timely dissemination in large scales due to the broadcast nature. In this paper, we deploy a cellular-VANET heterogeneous network achitecture to realize efficient data dissemination. In the heterogeneous networks, a part of vehicles are selected as mobile gateways to connect the two kind of networks. Later, we apply the coalition game theory to stimulate vehicles to join coalitions which can maximize the efficient data rate. The simulation results show that, by following the protocol, maximin overall effective data rate can be achieved.

Cooperative relaying schemes for device-to-device communication underlaying cellular networks

Intra-cell interference management is one of the technical challenges for device-to-device (D2D) communication underlaying cellular networks. In this paper, we propose two superposition coding-based cooperative relaying schemes to exploit the transmission opportunities for the D2D users without deteriorating the performance of the cellular users. In the first scheme, the D2D transmitter (DT) is enabled to decode and regenerate the cellular signal, and transmit the cellular signal by superposing it with its own signal. In this way, the interference from the D2D pair to the cellular pair can be canceled by properly allocating time and power. To further exploit the transmission opportunity for the D2D pair, in the second scheme the cellular transmitter splits its signal into two parts and broadcasts these two parts in a superposition signal. DT relays only one part of the cellular signal. Analytic and numerical results confirm the efficiency of the proposed schemes.

Inter-RAT Energy Saving for Multicast Services

Green communication receives a growing number of concerns due to the consideration for energy and environment issues. On the other hand, the evolution of mobile and wireless communication also results in heterogeneous Radio Access Technologies (RATs), such as Wi-Fi, UMTS, LTE, CDMA2000 and so on. As a result, energy saving by inter-RAT cooperation has raised significant discussions in both industrial and academical worlds. In this paper, we concentrate on inter-RAT energy saving for multicast services. Moreover, we use Integer Linear Programming to model the problem and propose a distributed algorithm which can efficiently save the energy consumption.

MIMO Transceiver Design in Dynamic-Range-Limited VLC Systems

Recently, multiple-input multiple-output (MIMO) has been proposed in visible light communications (VLC) systems to boost the data rate by utilizing spatial multiplexing. Unlike RF systems in VLC, lighting requirements, such as dimming control, should be taken into consideration for the design of a VLC transceiver. Moreover, VLC systems are inherently nonlinear and dynamic-range-limited. To drive an LED transmitter, the signal is bounded by a turn-on value and a saturation value. In this letter, we show how the dynamic-range constraint and dimming control impact the design of MIMO transceiver. Three different MIMO schemes are proposed and studied by theoretical analysis and simulation.

Multicast/Broadcast Service over Heterogeneous Networks

Mobile and wireless communication has been evolved from the basic model for providing point-to-point (PtP) voice centric services into more complicated service provision technologies with point-to- multipoint (PtM) transmission mode, such as MBMS in 3GPP and BCMCS in 3GPP2. On the other hand, the evolution of mobile and wireless communication has also resulted in a large number of wireless technologies such as UMTS cellular network, WiMAX and WLAN. As a result, issues related to multicast/broadcast service over heterogeneous networks will be more complex, interesting and valuable. In this paper, we propose a solution aimed to provide seamless and ubiquitous support for multicast/broadcast service on heterogeneous accesses. Additionally, a vertical handover policy named PtM First for multicast resource management in heterogeneous networks is demonstrated.

Full-Duplex Quasi-Gapless Carrier Aggregation Using FBMC in Centralized Radio-Over-Fiber Heterogeneous Networks

Filter-bank multicarrier (FBMC) is proposed to demonstrate a full-duplex asynchronous quasi-gapless (only one subcarrier spacing) carrier aggregation for millimeter-wave (MMW) radio-over-fiber radio access technology (RAT) in next-generation 5G heterogeneous mobile-data-network (Het-Net). Fourteen broadband FBMC signals are aggregated with only one subcarrier guard band in the 60-GHz MMW downlink. In the uplink quasi-gapless asynchronous inter-RAT carrier aggregation between 60-GHz MMW and 4G long-term evolution (LTE) signals are also demonstrated. System performances assessment of FBMC and orthogonal frequency-division multiplexing (OFDM) under different operation condition are studied. Our results also show that the FBMC-based new RAT is also backward compatible with existing LTE systems in the Het-Net. Compared with OFDM-based signals with large guard bands, FBMC achieves higher spectral efficiency with better error vector magnitude performance at less received power and smaller guard bands.

Digital mobile fronthaul based on delta-sigma modulation for 32 LTE carrier aggregation and FBMC signals

We first experimentally demonstrated a digital mobile fronthaul (MFH) architecture using delta-sigma modulation as the new digitization interface to replace the conventional common public radio interface (CPRI). Both one-bit and two-bit delta-sigma modulations were demonstrated, and the digitized signals were transmitted over on-off keying (OOK) or 4-level pulse-amplitude-modulation (PAM4) optical intensity modulation-direct detection (IM-DD) links. 32 LTE component carriers (CCs) were digitized and transmitted over a 25-km single-λ 10-Gbaud OOK/PAM4 link, so that 32 LTE carrier aggregation (CA) specified by 3GPP release 13 can be supported. Compared with the conventional digitization interface based on CPRI, the fronthaul capacity is increased by four times. Error vector magnitude (EVM) less than 5% or 2.1% for all LTE CCs was obtained using one-bit and two-bit delta-sigma modulators, so that high-order modulations (256QAM/1024QAM) can be supported. As a waveform-agnostic digitization interface, delta-sigma modulation can digitize not only 4G-LTE but also 5G waveforms, and its 5G compatibility was verified by filter-bank-multicarrier (FBMC) signals. The tolerance to bit error ratio (BER) of the proposed delta-sigma modulation-based digital MFH was evaluated, and no significant EVM degradation was observed for BER up to 3 χ 10−5. A comparison with analog MFH reveals that the proposed digital MFH based on delta-sigma modulation can offer improved resilience against noise and nonlinear impairments, and it increases the fronthaul capacity by four times compared with the conventional CPRI-based digital MFH without significant EVM penalty.

Delta-sigma modulation for digital mobile fronthaul enabling carrier aggregation of 32 4G-LTE / 30 5G-FBMC signals in a single-λ 10-Gb/s IM-DD channel

A delta-sigma modulation-based digital mobile fronthaul architecture is experimentally demonstrated to support carrier aggregation of 32 4G-LTE or 30 5G-FBMC signals in a single-λ IM-DD channel with capacity enhancement of 3-4 times compared with CPRI.