7,222 research outputs found
Data for Multiple Access Design for Ultra-Dense VLC Networks: Orthogonal v.s. Non-Orthogonal
No full textThis dataset is associated with the 2018 IEEE Transactions on Communications publication titled "Multiple Access Design for Ultra-Dense VLC Networks: Orthogonal v.s. Non-Orthogonal" by Simeng Feng et.al. The spreadsheet includes the data set for plotting each of the result-figures of the above-mentioned paper. More explicitly, this RD includes the data for plotting the x-axis and y-axis of a particular curve of the corresponding figure.</span
RDM-Hybrid Positioning Aided Amorphous-Cell Assisted User-Centric Visible Light Downlink Techniques
No full textThis RDM is associated with:
Feng, S. et al (2016). Hybrid positioning for the amorphous-cell assisted user-centric visible light downlink. IEEE Access, 4, 2705-2713.
This RDM includes the data set for plotting the result-figures of the above-mentioned paper. More explicitly, this RDM includes the data for plotting the x-axis and y-axis of a particular curve of the corresponding figure. </span
User-centric visible light networking
No full textIn this thesis, we propose a suite of schemes for indoor visible light communications (VLC), where multiple light emitting diode (LED) based access points (APs) serve multiple photo diode (PD) aided user equipment (UE). A novel user-centric (UC) VLC network is conceived, relying on user-clustering, resource allocation and sophisticated multiple access (MA) design. Our objective is to improve both the throughput and outage probability of the proposed UC-VLC network under practical indoor positioning and backhaul network design.Specifically, instead of relying on the conventional network-centric (NC) design, we conceive the novel concept of UC-VLC supported by amorphous cells exhibiting extra benefits. By beneficially clustering multiple attocells based on the location information of UEs, a centre-shifting UC-clustering strategy is proposed, leading to a multi-AP multi-UE scenario within each cluster. Upon employing the potent transmit pre-coding (TPC) concept, the multi-user interference (MUI) within each cluster can be completely eliminated, where multiple APs simultaneously serve the clustered UEs. Since the construction of the UC-clusters relies on the knowledge of the UEs' positions, the amalgamation of indoor positioning with the VLC network becomes important. Upon combining the benefits of triangulation and fingerprinting based positioning techniques, we propose a novel hybrid solution exhibiting a high accuracy, robustness and scalability.This is achieved by beneficially combining the low-complexity triangulation based positioning with high-accuracy fingerprinting, in order to efficiently support UC-clustering.Since the improvement of the UC-VLC over NC-VLC has in the past been quantified based on a number of idealized simplifying assumptions, such as operating exactly at the Shannon capacity, our motivation is to quantify the performance of the UC-VLC under more practical considerations. Therefore, adaptive modulation is invoked, which allows the individual UEs to be assigned various modulation-modes. Since the different modulation-modes require different power, the transmit power allocated to each AP is therefore dependent and dynamic. Furthermore, instead of greedily supporting all the UEs in the network, a dynamic scheduling scheme is advocated. To obtain the maximum throughput of the constructed UC-VLC under practical constraints, an efficient resource allocation strategy is required for dealing with the modulation-mode assignment, power allocation and the scheduling. To solve this complex maximization problem, a heuristic RA algorithm based on dynamic-programming is proposed. Aided by it, we will show under a range of scenarios that the achievable throughput and the outage probability of the proposed UC-VLC system are better than that of the conventional NC-VLC system.Then, we study the MA of VLC, when the APs are densely deployed, leading to an ultra-dense VLC network, where the inter-cell interference (ICI) amongst the densely-deployed APs is severe. To handle this challenge, both orthogonal MA (OMA) and non-orthogonal MA (NOMA) are considered. In order to cope with the grave ICI of our UC-VLC network, a hybrid NOMA and OMA scheme is proposed for enhancing the performance, where the frequency reuse (FR) technique and the TDMA-based scheduling may be dynamically invoked, which are further amalgamated with the spectrum-efficient NOMA scheme. We will show that the proposed MA scheme is more robust against the ICI, keeping the outage probability as low as possible, at a price of modestly degrading the achievable throughput.Finally, we consider the realistic backhaul issue of our VLC network. Since the ubiquitous mains power line constitutes a natural backbone feed for VLC, a combined power line communication (PLC) and VLC (PLC-VLC) network is conceived. More specifically, the source data arriving from the Ethernet is fed by a power line into the VLC network through the alternating current (AC) power supply, hence combining the power supply and data communication relying on PLC. In this PLC-VLC network, the power line connects the LEDs without requiring a duplicated fibre-backbone, which is implementationally convenient. To cope with the harsh impulse noise of the PLC channel, broadband OFDM PLC is used. The information gleaned from PLC is then forwarded to multiple UEs via visible light. To increase the downlink bit rate, the NOMA principle is invoked in our VLC network. For the sake of maximizing the sum-throughput of the PLC-VLC network, we conceive an optimal joint power allocation (JPA) strategy for each subcarrier in PLC and for each UE in VLC, which will be demonstrated to outperform the benchmarkers
Joint power allocation for the multi-user NOMA-downlink in a power-line-fed VLC network
No full textVisible light communications (VLC) constitutes as a promising downlink technique of supporting the ever-increasing tele-traffic. Since the ubiquitous mains power line constitutes a natural backbone feed for VLC, a combined power line and VLC network is conceived, where the source data is fed by power line communications (PLC) into the VLC network. We refer to it as a PLC-VLC network, where the power-line connects the light emitting diodes (LED) without requiring a duplicated filter-backbone. Then the information is forwarded to multiple users via visible light. Furthermore, to increase the downlink bit rate, non-orthogonal multiple access (NOMA) is invoked in VLC. For the sake of maximizing the sum-throxughput, we conceive a joint PLC-VLC power allocation (JPA) strategy, where the power allocated both to the PLC and to the VLC links is jointly determined upon analysing the power-relationship between them. Our simulations demonstrate that NOMA significantly outperforms orthogonal multiple access (OMA) with the aid of the proposed JPA.<br/
Dynamic throughput maximization for the user-centric visible light downlink in the face of practical considerations
No full textThe concept of amorphous-boundary-based user-centric cells invoked for visible light communication (VLC) was shown to offer extra throughput benefits over the conventional network-centric VLC. However, this improvement was quantified based on a number of idealized simplifying assumptions, such as operating exactly at the Shannon capacity. Also, the light emitting diode in VLC was assumed to have no non-linear distortion and no clipping distortion. Furthermore, greedily supporting all the user equipments in the system may in fact reduce the achievable throughput, when the transmit power is restricted. To provide more practical performance estimate, in this paper, the dynamic throughput maximization of user-centric VLC (UC-VLC) systems is investigated under a range of practical considerations, where the number of served UEs, the modulation-mode assignment and the power allocation strategy are all dynamically decided by our proposed heuristic dynamic-programming-based algorithm. Our simulations indicate that both the achievable throughput and the outage probability of the proposed UC-VLC system is better than that of the conventional NC-VLC system, under a range of practical constraints.</p
Interference-free hybrid optical OFDM with low-complexity receiver for wireless optical communications
No full textIn optical wireless communication (OWC), conventional superimposed optical orthogonal frequency division multiplexing (OOFDM) techniques, such as hybrid asymmetrically clipped OOFDM (HACO-OFDM), require an additional operation of interference cancellation to decode transmitted symbols, which leads to relatively high receiver complexity with processing delay. In this letter, we propose a novel superimposed OOFDM scheme with low-complexity receiver, named as interference-free hybrid OOFDM (IFHO-OFDM), for OWC. In the proposed IFHO-OFDM, two hybrid OOFDM components are combined for simultaneous transmission to achieve the appealing advantages of high spectral efficiency, and a time-selective bias is designed to guarantee the non-negativity while maintaining high power efficiency. Moreover, we propose to superimpose the two hybrid OOFDM components in an interference-free way, and thus, it can be readily demodulated by a standard low-complexity OFDM receiver. Simulation results verified the superiority of the proposed IFHO-OFDM in terms of both peak-to-average-power ratio (PAPR) and bit error rate (BER) compared to HACO-OFDM.</p
Multiple access design for ultra-dense VLC networks: Orthogonal v.s. non-orthogonal
No full textSmall cell aided ultra-dense networks (UDN) constitute an efficient solution to the ever-increasing thirst for more data. Thanks to the vast untapped high-frequency spectrum of visible light, visible light communications (VLC) is a natural candidate for UDN. In this paper, layered asymmetrically clipped optical OFDM (LACO-OFDM) aided ultra-dense VLC (UD-VLC) is investigated in terms of its user-association, multiple access (MA) and resource allocation. To handle the severe inter-cell interference (ICI) amongst the densely-deployed access points (AP), we propose a novel overlapped clustering technique relying on a hybrid non-orthogonal MA (NOMA) and orthogonal MA (OMA) scheme for enhancing the performance, with the aid of our dynamic resource allocation conceived. Our simulations show that the proposed LACO-OFDM aided UD-VLC using our hybrid MA scheme is more robust against the ICI, at a price of modestly decreasing the sum-throughput
Spectral-efficient reconstructed LACO-OFDM transmission for dimming compatible visible light communications
No full textDimming control is critical in practical visible light communication (VLC) systems to satisfy illumination demand. Upon exploiting multiple layers of asymmetrically clipped optical orthogonal frequency division multiplexing (ACO-OFDM) signals for simultaneous transmission, layered ACO-OFDM (LACO-OFDM) constitutes a promising spectral-efficient modulation technique for VLC. However, dimming by integrating the industry-preferred pulsewidth modulation (PWM) to the LACO-OFDM scheme induces severe clipping noise due to the nonlinearity of LEDs. In this paper, we conceive a reconstructed LACO-OFDM (RLACO-OFDM) scheme incorporating the PWM technique for VLC to accommodate the dimming demands for indoor illumination, while maintaining a spectral-efficient communication link. Moreover, superior to its counterparts, the transmitted symbols in the RLACO-OFDM based VLC system can be readily recovered by a standard LACO-OFDM receiver while no additional detection of the PWM signal is required, which reduces the receiver complexity. Numerical results demonstrate that the proposed RLACO-OFDM is capable of realizing high spectral efficiency over a broad dimming range.</p
Hybrid positioning for the amorphous-cell assisted user-centric visible light downlink
No full textVisible light communications (VLCs) have attracted significant attention in recent years, where the novel concept of user-centric (UC) VLC based on amorphous cells (A-Cells) exhibits extra benefits compared with conventional circular cells. The construction of A-Cells relies on the knowledge of the users' positions; hence, the intrinsic amalgamation of VLC and positioning becomes important. Therefore, we propose a novel hybrid positioning technique by beneficially combining the low-complexity of triangulation-based positioning and the high accuracy of fingerprinting, in order to support A-Cell-assisted UC VLC under practical light-emitting diode linearity constraints with clipping distortion and noise. Our simulation results demonstrate that the proposed technique is capable of achieving a much higher positioning accuracy than triangulation at a lower complexity than fingerprinting, where the resultant system throughput is similar to that of perfect positioning
A Conversation with Xianghong Feng, Author of Tourism and Prosperity in Miao Land
No full textIn this installment of Lexington Books\u27 Anthropology of Tourism: Heritage, Mobility and Society Author Conversations, series editor Michael A. Di Giovine talks to anthropologist Xianghong Feng, author of the book, Tourism and Prosperity in Miao Land: Power and Inequality in Rural China. With rich ethnographic detail, Feng focuses on the intersection of tourism development, power and inequality in the southern interior of China. Capital-intensive, elite-driven tourism has reshaped the social and cultural patterns of the ethnic Miao. Although tourism is often touted as able to empower women, lower classes, and minorities, Feng shows that often it reinforces the very power structures that it attempts to equalize
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