Visible light communication (VLC) builds upon the dual use of LED-based lighting infrastructure for data transmission. It is particularly attractive for user-dense environments and mainly positioned as a complementary wireless access technology to radio-frequency (RF) counterparts. The practical implementation of hybrid light/radio access networks requires the design of efficient vertical and horizontal handover mechanisms to exploit their complementary features. In this paper, we propose an event-triggered adaptive handover mechanism for centralized hybrid VLC/millimeter wave (MMW) systems. Unlike distributed architectures where all the functionalities are deployed in each access point (AP), the centralized systems allow better optimization of network parameters due to awareness of global network view. The proposed handover mechanism takes advantage of this architecture and uses offset-enhanced signal-to-interference plus noise ratio levels of APs as performance metrics. To ensure balanced distribution of user equipment (UE) numbers between two underlying technologies, it auto-tunes the offset variables using rule-set based algorithms based on the number of connected UEs and data rates as inputs. Our results demonstrate that the proposed handover mechanism significantly improves hybrid system performance via adaptive tuning of AP selection parameter while minimizing signaling overhead.

Visible light communication (VLC) building on the existing illumination infrastructure utilizes light emitting diode (LED) luminaries as wireless transmitters. To achieve data rates on the order of gigabits per second in VLC systems, multiple-input multiple-output (MIMO) transmission has been identified as a key technology. In this paper, we consider a centralized network architecture where the ceiling LED luminaries act as transmitter elements of a distributed massive MIMO VLC system. To obtain the full benefits of massive MIMO, channel state information must be available at the transmitter side. Downlink (DL) channel estimation in a massive MIMO system requires huge pilot overhead in DL as well as feedback overhead in uplink. This makes the implementation of massive MIMO system infeasible if not properly designed. In our study, we address the design of massive MIMO VLC systems with a limited number of DL pilot signals. We explore different DL pilot patterns (PPs) in frequency, time, and spatial domains where interpolation is performed to obtain the global channel matrix taking advantage of the indoor environment geometry and layout of luminaries. We then present data rate results for different DL PPs under the consideration of varying number of active user equipments through Monte-Carlo simulations.

Building on the existing illumination infrastructure, visible light communication (VLC) utilizes light emitting diode (LED) luminaries as wireless access points. The presence of large number of ceiling lights in conference halls, classrooms and similar public places makes possible the implementation of massive multiple-input multiple-output (MIMO) VLC systems in a distributed manner. In order to obtain the full benefits of massive MIMO communications, channel state information must be available at transmitter side. Estimation of downlink channel through pilot signals, if not judiciously designed, requires huge pilot overhead and makes the implementation of massive MIMO system infeasible. In our study, we address the design of massive MIMO VLC systems with a limited number of pilot signals. We explore different pilot arrangements in spatial, frequency, and time domains where interpolation is performed to obtain global channel matrix taking advantage of the indoor environment geometry and layout of luminaries. We consider direct current biased orthogonal frequency division multiplexing as the basis of physical layer and present simulation results to demonstrate the achievable spectral efficiencies for pilot signal arrangements under consideration.

In this paper, we propose a multiple-input multiple-output (MIMO) uplink transmission scheme for optical wireless communication applications. The transmission is based on optical single-carrier frequency domain equalization (SC-FDE) due to its low complexity where the signal is transmitted over infrared communication channels. Based on non-sequential ray tracing, we first obtained realistic infrared MIMO channel impulse responses including low-pass filter effect of infrared light-emitting-diodes. We then investigate the performance of bit-error-rate (BER) and peak to average power ratio (PAPR) with respect to different modulation orders using spatial multiplexing.

Estimation of the time-varying optical wireless channel response is crucial in order to decode received signals coherently. In this work, we investigate symbol-error-rate and mean absolute error performance of different interpolation techniques including linear, nearest, spline, and piece-wise cubic Hermite interpolating polynomial (pchip), which are used in pilot-aided channel estimation process for visible light communication. The performance of interpolators is evaluated in realistic time-varying channel model, generated on Zemax software and compared with each other under the consideration of different modulation orders, different pilot symbol periods, and different user equipment (UE) speeds through Monte Carlo simulations. The results reveal that spline and pchip techniques are more robust to low pilot symbol transmission rate and fast time-varying channel conditions as a consequence of high UE speeds. However, low complex linear interpolation technique can be chosen for highly rated pilot signal transmission cases or when optical channel varies slowly over the time.

Radio Access Network (RAN) sharing and Cloud-RAN (C-RAN) are two major candidates for next generation mobile networks. RAN sharing ensures efficient usage of network equipments among multiple mobile network operators (MNOs) and C-RAN benefits installation, evolution, management and performance improvements. Similarly, Software-Defined Networking (SDN) concept provides many features including hardware abstraction, programmable networking and centralized policy control. One of the main benefits that can be used along with these features is virtualization of RAN and core/backhaul networks to ensure network sharing among MNOs and efficient usage of the network equipments. In this work, we propose SDN-based C-RAN architecture including RAN controller integrated to virtualization controller that is crucial for core/backhaul network sharing towards next generation cellular network. In proposed architecture, eNodeB functions are shifted to the top of C-RAN controller as a consequence of separating baseband units from remote radio heads (RRHs). We further provide RRH assignment based load balancing algorithm that is executed at the top of the controller and allows sharing of RRHs among multiple MNOs. We evaluate its performance using traditional RRH distribution as benchmark and simulation results reveal that our proposed algorithm outperforms traditional distribution in terms of average number of connected user equipments to RRHs.

In this paper, we propose a novel cellular network architecture including network virtualization controller for mobile core and backhaul sharing. Software-Defined Networking (SDN) based network virtualization is applied into Evolved Packet System (EPS) architecture of Long Term Evolution (LTE) networks. After virtualization of all evolved Node-Bs (eNodeBs) associated with different Mobile Operators (MOs) as a consequence of mobile core and backhaul sharing, the performances of eNodeB assignment mechanisms with the use of quality-of-service (QoS)-aware and QoS-unaware scheduling algorithms are investigated and compared with currently deployed static eNodeB distributions through Monte-Carlo simulations. Jain's fairness index, Shannon capacity and satisfied-MO-ratio are considered as the key performance indicators (KPIs). The results reveal that our proposed architecture outperforms the currently deployed network architecture as depending on proper scheduler selection.

In order to cope with the challenges of increasing user bandwidth demands as well as create new revenues by offering innovative services and applications, Mobile Network Operators (MNOs) are willing to increase their networks' capabilities by making it more flexible, programmable and agile. MNOs are also seeking new technologies to benefit from recent advances in cloud for rapid deployments and elastically scaling services that cloud providers are mostly benefiting today. On one hand, Software-Defined Networking (SDN) concept can be helpful for enabling network infrastructure sharing/slicing and elasticity for “softwarization” of network elements. On the other hand, machine learning and game-theoretical concepts can also be utilized to address network management and orchestration needs of services and applications and improve network infrastructure's operational needs. In that regard, joint utilization of machine learning, game theoretical approaches and SDN concepts for network slicing can be beneficial to MNOs as well as infrastructure providers. In this paper, we utilize regret-matching based learning approach for efficient Radio Remote Head (RRH) assignments among MNOs in software-defined based cloud radio access network (C-RAN). Using game-theoretical approach, we demonstrate convergence of RRH allocations to mixed strategy Nash equilibrium and present significant performance improvements compared to traditional assignment approach.

Radio Access Network (RAN) sharing that ensures efficient usage of network equipments among multiple mobile network operators (MNOs) and Cloud-RAN (C-RAN) benefiting installation, evolution, management and performance improvements are two major candidates towards the next generation mobile networks. In addition to them, Software-Defined Networking (SDN) paradigm provides many features including hardware abstraction, programmable networking and centralized policy control. One of the main benefits that can be used along with these features is dynamic virtualization of RAN in order to ensure network sharing among multiple MNOs and efficient usage of the RAN equipments such as remote radio heads (RRHs). In this work, we provide a use case study of SDN-based shared RAN infrastructures for channel-aware remote radio head (RRH) assignment to multiple MNOs benefiting from global view of the network in order to provide better received signal strength levels. We propose two assignment mechanisms and compare the performance of them with traditional RRH distribution. The Monte-Carlo simulation results reveal the proposed methods' performance advantages.

Vehicular hotspots for on-board Internet access using Long Term Evolution (LTE) as the backhaul network has recently gained popularity. Currently, Wi-Fi is the most common technology to provide in-vehicle access, where data has been relayed through on board LTE receiver. Despite its wide acceptance, coexistence and contention based data rate limitations with Wi-Fi necessitates alternatives for in-vehicle data access schemes. This paper investigates the performance of hybrid LTE and visible light communication (VLC) networks using LTE as the backhaul and VLC as the on-board access network.Under the consideration of vehicle interior unique channel characteristics and light emitting diode (LED) deployment flexibility, best transmitter configuration using repetition coding (RC) and spatial multiplexing (SM) multiple input multiple output (MIMO)modes is determined. Proposed configurations based on direct current biased optical orthogonal frequency-division multiplexing(DCO-OFDM) are compared with respect to their bit-error-rate (BER) performances. Furthermore, the performance of intravehicular VLC networks for single and multi-user scenarios is investigated.

Visible light communication (VLC) has recently gained popularity as a complementary technology to radio frequency (RF) based alternatives for vehicular communications as a low-cost, secure and RF interference free technology. In this paper, we propose IEEE 802.15.7 standard-compliant physical layer (PHY) implementation and experimental evaluation, using commercial off-the-shelf (COTS) automotive light emitting diode (LED) fog light for the purpose of low-latency safety message dissemination. We first show that the standard is applicable to line of sight (LoS) vehicle-to-vehicle (V2V) VLC. We then demonstrate that the proper selection of modulation coding schemes (MCS) plays an important role in order to minimize bit-error- rate (BER) for the reliable transmission with varying inter-vehicle distances. We also addressed the angular limitations of COTS automotive LED light for viable vehicular VLC.

In this study, we investigate a relay-assisted visible light communication (VLC) system where an intermediate light source cooperates with the main light source. Specifically, we consider two light sources in an office space: one is the information source employed on the ceiling and the other one is a task light. Our system uses dc biased optical orthogonal frequency division multiplexing (DCO-OFDM) where the task light performs relaying to assist the communication and operates in half-duplex mode for both amplify-and-forward and decode-and-forward relaying. We investigate the bit error rate (BER) performance of the relay-assisted VLC system and optimize the performance through optimal ac/dc power allocation under illumination constraints. The dc power allocation is determined by sharing the number of LED chips between the terminals to satisfy a desired luminance ratio. The ac power allocation decides the fraction of the information signal power to be consumed at the terminals in order to minimize the BER. Numerical results reveal that cooperation brings significant performance gains over direct transmission. We further provide comparisons of two relaying techniques under consideration and discuss the effect of clipping noise on the error rate performance.