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Optical Wireless Communications

Research topics:

User-Centric Visible Light Communication Networks
Prof. Lajos Hanzo, Dr. Rong Zhang, Dr. Xuan Li, Ms. Simeng Feng

[1] Visible Light Communications in Heterogeneous Networks: Pave the Way for User-Centric Design.

[2] Users First: User-Centric Cluster Formation for Interference Mitigation in Visible Light Networks.

[3] Energy Efficient Visible Light Communications Relying on Amorphous Cells.

[4] User-Centric Visible Light Communications for Energy-Efficient Scalable Video Streaming.

[5] Hybrid Positioning for the Amorphous-Cell Assisted User-Centric Visible Light Downlink.

As a beneficial counterpart of the existing network-centric cells, a user-centric (UC) cluster formation regime is proposed and studied in visible light communication (VLC) networks. The essence of the UC cluster formation is to assign the user equipments and optical access points to each other for the sake of maximising the total utility after employing vectored transmission (VT) in each of the UC-VT cluster. This procedure is entirely based on the user equipments' specific conditions and thus leads to UC clusters.

VLC can be considered as a new member in the small-cell family of the heterogeneous networks (HetNets) landscape for complementing the overloaded radio frequency band. The UC cluster formation principle designed for VLC environments constitutes a novel and competitive design paradigm for the super dense multi-tier cell combinations of HetNets, where the sophisticated user equipments can actively participate in cell planning, resource management, mobility control, service provision, signal processing, etc. As a result, the UC concept may be expected to become one of the disruptive techniques to be used in the forthcoming 5G era.

Figure 1. Amorphous cell formation with the table of user-specific access point combinations.

Video 1. User-centric visible light communications for energy-efficient scalable video streaming. The first row shows the flawless original video, the video reconstructed by using our UC cluster formation as well as the video reconstructed by using the traditional unity frequency reuse (UFR). The second row shows the differences between the original video and the videos reconstructed by using UC/UFR. The fist sub-video in the last row shows the dynamic UC cluster formation when the UC is mobile, where the access points and the users within the cluster are denoted by filled orange circles and blue asterisks, respectively. The other two sub-videos in the last row show the peak signal-to-noise ratio (PSNR) of each frame for the moving user by using the UC and UFR scheme, respectively.


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VLC-aided Heterogeneous Networks
Prof. Lajos Hanzo, Dr. Rong Zhang, Dr. Xuan Li, Dr. Fan Jin, Dr. Junyi Jiang, Dr Yongkai Huo, Dr Chuan Zhu

[1] Cooperative Load Balancing in Hybrid Visible Light Communications and WiFi

[2] Resource Allocation under Delay Guarantee Constraints for Heterogeneous Visible Light and RF Femtocells.
[3] Video Streaming in the Multiuser Indoor Visible Light Downlink.

As a complementary extension of established radio frequency (RF) wireless local area networks (WLANs), VLC using commercially available light-emitting diode (LED) transmitters offers a huge data rate potential in this license-free spectral domain, whilst simultaneously satisfying energy-efficient illumination demands. Various VLC cell formations, ranging from a regular cell-layout associated with different frequency reuse (FR) patterns to merged cells by employing advanced transmission scheme are investigated. Furthermore, a hybrid down-link offering full RF-coverage by a WLAN and additionally supported by the abundant spectral resources of a VLC network is studied. Cooperative load balancing achieving proportional fairness is implemented by using both centralized and distributed resource-allocation algorithms. The performance of this hybrid RF/VLC system is analysed both in terms of its throughput and fairness in diverse cell formation scenarios. Our simulation results demonstrate that, the VLC system advocated is capable of providing a high area spectral efficiency (ASE) and our hybrid RF/VLC system achieves the highest throughput and the highest grade of fairness in most of the scenarios considered.

Figure 2. Bandwidth efficiency surface and the mean bandwidth efficiency of different VLC cell formations. (a) A regular UFR cell formation, (b) has a FR factor of two, (c) represents merged 2-access-point cells with combined transmission, (d) shows merged 2-access-point cells with VT, (e) is a merged 16-access-point cell with VT, and (f) shows the mean bandwidth efficiency of (a)–(e), where field-of-view of the receivers is 120.


Physical-Layer Techniques for Visible Light and Free-Sapce Optical Communications
Prof. Lajos Hanzo, Prof. Sheng Chen, Dr. Rong Zhang, Dr. Junyi Jiang, Dr. Zunaira Babar, Dr. Qi Wang

[1] A Photon-Counting Spatial-Diversity-and-Multiplexing MIMO Scheme for Poisson Atmospheric Channels Relying on Q-ary PPM.

[2] Multi-Layer Modulation for Intensity-Modulated Direct-Detection Optical OFDM.

[3] Enhancing the Decoding Performance of Optical Wireless Communication Systems Using Receiver-Side Predistortion.

[4] Chip-Interleaved Optical Code Division Multiple Access Relying on A Photon-Counting Iterative Successive Interference Canceller for Free-Space Optical Channels.

[5] Performance and Capacity Analysis of Poisson Photon-Counting based Iter-PIC OCDMA Systems.

[6] An Adaptive Scaling and Biasing Scheme for OFDM-based Visible Light Communication Systems.

[7] Analysis and Design of Three-Stage Concatenated Color-Shift Keying.

[8] Reduced-Complexity Iterative Receiver for Improving the IEEE 802.15.7 Convolutional-Coded Color Shift Keying Mode.

[9] Hierarchical Colour-Shift-Keying Aided Layered Video Streaming for the Visible Light Downlink.

[10] Aperture Selection for ACO-OFDM in Free-Space Optical Turbulence Channel.

Modulation schemes constitute one of the most important physical-layer techniques in communication systems. This is especially true when jointly considering indoor illumination requirements, since the modulated signals can be used to switch on/off the LEDs, which conveys the on-off pattern-based binary information to the receiver. Since LEDs emit incoherent light, where photons have different wavelength and phase, it is an open challenge to collect appreciable signal power in a single electromagnetic mode in a practical low-cost VLC system. Hence, often the intensity modulation direct detection (IM-DD) scheme is employed, where the transmitted signal modulates the instantaneous optical power of the LEDs. Hence, IM-DD constitutes an attractive scheme and has been widely used in VLC systems.

Apart from the widely known modulation schemes, e.g. on-off keying, pulse position modulation, etc. some unique modulation techniques have also been developed for VLC systems, including colour shift keying (CSK), generalised colour modulation (GCM), optical orthogonal frequency division multiplexing (OOFDM), etc. Explicitly, the CSK scheme using multi-chip LEDs was standardised in the IEEE 802.15.7 recommendation, which may be a potential modulation scheme for future VLC systems, although it relies on sophisticated implementation. An uncoded M-CSK scheme was investigated relying on a joint maximum likelihood hard-detection based VLC system, where both simulation-based and analytical bit-error-rate results were derived. By contrast, a colour-independent GCM scheme was proposed, which had the advantages of flicker-free operation, accurate dimming control and the ability to function independently of the number of LEDs at the transmitter or the photodetectors at the receiver. Moreover, there are three popular types of OOFDM proposed for VLC systems, i.e. asymmetrically clipped OOFDM (ACO-OFDM), direct current biased OOFDM (DCO-OFDM) as well as unipolar OFDM (U-OFDM).


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