A hybrid Wi-Fi and light fidelity (LiFi) network combines the best of two worlds with the ubiquitous coverage of Wi-Fi and the high peak data rate of LiFi as the radio spectrum does not interfere with the light spectrum. This hybrid network might be realized by using multipath TCP (MPTCP), where Wi-Fi and LiFi paths can be simultaneously employed to potentially boost the total throughput of Wi-Fi while increasing the resilience towards network failure of LiFi due to, for example, blockage. However, naively implementing MPTCP in a hybrid Wi-Fi and LiFi network can yield an unexpected result, such as a lower throughput compared to the single-path TCP due to a Head-of-Line delay during the slow start phase of the TCP congestion control. Even though this problem can be avoided by improving the existing flow control or congestion control of TCP, these solutions still lack intelligent decision making that can improve the adaptability of MPTCP. Therefore, in this paper, we propose a model-augmented deep reinforcement learning (DRL) approach to intelligently steer MPTCP subflows (i.e., TCP connections) by using a close-to-reality scenario emulated by considering random orientation, random blockage, and random mobility of Wi-Fi-and-LiFi-enabled mobile devices. As a result, we will show later that a performance gain can be achieved compared to the state-of-the-art while maintaining ease implementation to existing MPTCP implementations.

In this paper, we present our research on modeling a synthetic light fidelity (LiFi) channel model that uses a deep learning architecture called generative adversarial networks (GAN). A research in LiFi that requires the generation of many multipath channel impulse responses (CIRs) can benefit from our proposed model. For example, future developments of autonomous (deep learning-based) network management systems that use LiFi as one of its high-speed wireless access technologies might require a dataset of many CIRs. In this paper, we use TimeGAN, which is a GAN architecture for time-series data. We will show that modifications are necessary to adopt TimeGAN in our use case. Consequently, synthetic CIRs generated by our model can track long-term dependency of LiFi multipath CIRs. The Kullback–Leibler divergence (KLD) is used in this paper to measure the small difference between samples of synthetic CIRs and real CIRs. Lastly, we also show a simple demonstration of our model that can run on a small virtual machine hosted over the Internet.

Light-fidelity (LiFi) is recognised as a promising technology for next generation wireless access networks. However, limited research efforts have been spent on the uplink (UL) transmission system in LiFi networks. In this article, a wireless infrared (IR)-based LiFi UL system is investigated. In particular, we focus on the performance of a single static user under the influence of random device orientation and link blockage. Simulations and mathematical analysis have been used to evaluate the UL system performance. The analytical expressions for the UL optical wireless channel and signal-to-noise ratio (SNR) statistics under the effects of random device orientation and link blockage are derived. The results show that the effects of random orientation and link blockage may lead to a decrease in coverage probability by 10% - 40% with various SNR thresholds.

The limited bandwidth of optical wireless communication (OWC) front-end devices motivates the use of multipleinput- multiple-output (MIMO) techniques to enhance data rates. It is known that very high multiplexing gains can be achieved by spatial multiplexing (SMX) at the cost of prohibitive detection complexity. Alternatively, in spatial modulation (SM), a single light emitting diode (LED) is activated per time instance where information is carried by both the signal and the LED index. Since only one LED is active, both the transmitter (TX) and receiver (RX) complexity reduce significantly while retaining the information transmission in the spatial domain. However, this simplified TX utilization approach leads SM to suffer from significant spectral efficiency losses compared to SMX. In this paper, we propose a technique that benefits from the advantages of both systems. Accordingly, the proposed flexible LED index modulation (FLIM) technique harnesses the inactive state of the LEDs as a transmit symbol. Therefore, the number of active LEDs changes in each transmission, unlike conventional techniques. Moreover, the system complexity is reduced by employing a linear minimum mean squared error (MMSE) equalizer and an angle perturbed receiver. Numerical results show that FLIM outperforms the reference systems by at least 6 dB in the low and medium/high spectral efficiency regions.

A task group named IEEE 802.11 Light Communications Amendment-Task Group “bb” (TGbb) was established in July 2018. By bringing light-fidelity (LiFi) technology into the WiFi ecosystem, LiFi can take advantage of the globally recognized WiFi brand, while also improving its capability due to the fact that LiFi does not interfere with WiFi. Early discussions in the task group focused on the physical (PHY) layer. There are two major proposals for the PHY layer. The first one is to use the existing IEEE 802.11 chipsets with LiFi analog front-ends. This is done by means of the frequency up and down-conversions and adding a DC bias. The second proposal is to redefine a whole PHY layer and optimize it by means of adopting adaptive bit loading in order to combat the low-pass filter characteristics of the non-line-of-sight wireless optical channels. Each approach has advantages in terms of the low-entry barrier to the mass market and better performance, respectively. The root question in determining the common mode PHY between the two approaches is how frequent LiFi encounters flat channels. That is, if the channel is flat, then the gain of the adaptive bit loading is not significant. Therefore, this paper aims to investigate the flatness of many samples from the reference channel models defined in the TGbb. We find that the majority of the channels are flat if the signal bandwidth is 20 MHz.

In July 2018, a new IEEE task group focusing on light communications was formed, namely IEEE 802.11bb (TGbb). The primary motivation of this task group is to standardize mobile, networked light communications, i.e., light fidelity (LiFi). At the time of writing, discussions in TGbb still focus on the physical (PHY) layer, and recently a common mode PHY has been agreed. The common mode PHY is defined based on the frequency upconversion of the signal outputs of existing WiFi chipsets. In addition, a DC bias is used to enable the intensity-modulation and direct-detection (IM/DD) over a light emitting diode (LED). In this paper, we compare it with another method, namely in-phase and quadrature wavelength division multiplexing (IQ-WDM). IQ-WDM refers to a method where both I and Q baseband signal from existing WiFi chipsets are transmitted independently at different wavelengths. A comprehensive comparison is done, and our error performance results indicate that IQ-WDM significantly outperforms the frequency upconversion method by 6 dB. We also show that IQ-WDM is robust againsts IQ imbalance.

A novel modulation scheme for an indoor optical wireless communication (OWC) system referred to as generalized time slot index modulation (GTIM) is proposed for single-carrier frequency domain equalization (SC-FDE) systems. This scheme is further referred to as SC-GTIM. In SC-GTIM, information bits are flexibly encoded onto both the amplitudes and positions of pulses. A set partitioning algorithm is proposed to construct a codebook for the SC-GTIM system. In this paper, SC-GTIM will be compared with the conventional pulse amplitude modulation-based SC-FDE (SC-PAM) and time slot index modulation-based SC-FDE (SC-TIM). By considering a multipath optical wireless channel and the limited dynamic range of a light emitting diode (LED), a considerable bit error ratio (BER) gain can be achieved by SC-GTIM. It is concluded that SC-GTIM is a promising technique for low to medium spectral efficiency transmission and uplink schemes.

In this paper, a cyclic-prefixed (CP) system with pulse amplitude modulation (PAM) for uplink transmission in light-fidelity (LiFi) is discussed. LiFi supports bi-directional transmission, i.e., downlink and uplink transmissions. However, there have been only a few studies on uplink LiFi despite the fact that the uplink traffic demand increases due to frequent use of, for example, video call and live streaming services. The uplink transmission is designed such that a transmitter has a low peak-to-average ratio as well as a lower computational complexity using a CP in conjunction with PAM. We investigate three different schemes, namely linear equalization (LE) where only a feedforward filter is applied, decision feedback equalization (DFE) where a feedback filter is added at the receiver and Tomlinson-Harashima precoder (THP) where a feedback filter is added at the transmitter. Both feedforward and feedback filters are jointly optimized. In addition, we consider an optical wireless channel with reflections, randomly-located and randomly-oriented user equipment, a human body acting as a reflector and a limited linear dynamic range of a light emitting diode. We conclude that a DFE system is suitable in a low spectral efficiency region, where, compared to an LE system, up to 4 dB gain is achieved. A THP system is suitable for a high spectral efficiency region, where up to 5 dB gain compared to the LE and DFE systems is achieved.

Light fidelity (LiFi), which occupies part of the optical spectrum, is a promising technology to meet the high-speed wireless data demand. For an additional throughput gain along with low energy consumption, index modulation (IM) has begun to be combined with LiFi systems. The main advantage of IM is its ability to encode information in both a conventional transmit signal as well as the index of the transmit entity such as through the transmitter, subcarrier and time-slot domain indexes. Time-slot IM (TIM) offers additional degrees of freedom to single-carrier (SC) single-input-single-output systems to encode information onto pulse activation patterns. In this paper, we propose a generalized TIM (GTIM) transmission method for SC frequency domain equalization (SC-FDE)-based systems to fully harness the benefits of TIM. In GTIM, both the number and locations of active time-slots are flexible such that they are different for each transmit symbol. Moreover, the active time-slots carry pulse amplitude modulation (PAM) symbols in the signal domain. The proposed system also benefits from SC-FDE which simplifies the transmission and detection complexity at both sides. We also propose a set partitioning algorithm that chooses the optimal transmission symbols set and labels them concurrently. The bit error ratio (BER) performance of GTIM is compared to conventional PAM and TIM under a limited dynamic range constraint and frequency-selectivity. It is shown that the proposed GTIM achieves up to a 3 dB BER performance gain.

The performance of visible light communication (VLC) systems are limited by the modulation bandwidth of light emitting diodes (LEDs), despite the availability of the wide optical spectrum. A multiple-input, multiple-output (MIMO) scheme can be employed to further improve the data rate by means of harnessing the spatial multiplexing gain. Nevertheless, it is known that the MIMO VLC channel can be rank-deficient, and consequently its performance can be degraded significantly. The rank of the MIMO VLC channel is highly affected by the geometries of light emitting diodes and photodiodes (PDs). In this paper, the effects of PD configurations on the MIMO performances are investigated. It will be shown that certain PD configurations can lead to a rank-deficient channel. We propose Irregular PD configurations (IPC) to overcome this issue. Moreover, bi-objective problems are formulized to obtain the optimal IPC. A significant gain in terms of the condition number of the channel is shown with respect to regular PD configurations, which further suggests a benefit of IPC in MIMO VLC.

Light-fidelity (LiFi) is a networked optical wireless communication (OWC) solution for high-speed indoor connectivity for fixed and mobile optical communications. Unlike conventional radio frequency wireless systems, the OWC channel is not isotropic, meaning that the device orientation affects the channel gain significantly, particularly for mobile users. However, due to the lack of a proper model for device orientation, many studies have assumed that the receiver is vertically upward and fixed. In this paper, a novel model for device orientation based on experimental measurements of 40 participants has been proposed. It is shown that the probability density function (PDF) of the polar angle can be modeled either based on a Laplace (for static users) or a Gaussian (for mobile users) distribution. In addition, a closed-form expression is obtained for the PDF of the cosine of the incidence angle based on which the line-of-sight (LOS) channel gain is described in OWC channels. An approximation of this PDF based on the truncated Laplace is proposed and the accuracy of this approximation is confirmed by the Kolmogorov-Smirnov distance. Moreover, the statistics of the LOS channel gain are calculated and the random orientation of a user equipment (UE) is modeled as a random process. The influence of the random orientation on signal-to-noise-ratio performance of OWC systems has been evaluated. Finally, an orientation-based random waypoint (ORWP) mobility model is proposed by considering the random orientation of the UE during the user's movement. The performance of ORWP is assessed on the handover rate and it is shown that it is important to take the random orientation into account.

Light-fidelity (LiFi) is a wireless communication technology that employs both infrared and visible light spectra to support multiuser access and user mobility. Considering the small wavelength of light, the optical channel is affected by the random orientation of user equipment (TIE). In this paper, a random process model for changes in the TIE orientation is proposed based on the data measurements. We show that the coherence time of the random orientation is in the order of hundreds of milliseconds. Therefore, an indoor optical wireless channel can be treated as a slowly varying channel as its delay spread is typically in the order of nanoseconds. A study of the orientation model on the performance of direct-current-biased orthogonal frequency-division multiplexing (DC-OFDM) is also presented. The performance analysis of the DC-OFDM system incorporates the effect of a diffuse link due to reflection and blockage by the user. The results show that the diffuse link and the blockage have significant effects, especially if the TIE is located relatively far away from an access point (AP). It is shown that the effect is notable if the horizontal distance between the TIE and the AP is greater than 1.5 m in a typical 5 × 3.5 × 3 m3indoor room.

This paper focuses on the handover probability as a result of the random rotation of a user equipment (UE) in hybrid light-fidelity (LiFi) and radio frequency (RF) networks. A received signal strength indicator (RSSI)-based handover algorithm is considered in this study. Using RSSI as the user association rule does not guarantee that the randomly-oriented UE is always associated with the nearest access point (AP). In some cases, depending on the orientation of the UE, the received signal powers from the LiFi APs are very weak and unreliable. Therefore, a vertical handover from the LiFi AP to the RF AP is required to maintain the user quality of service. Hence, it is essential to study the handover probability due to the change of orientation. A theoretical analysis of the handover probability based on a Markov chain model is provided. The analytical results are confirmed by the Monte Carlo simulation. The effects of some parameters, such as the threshold, hysteresis level and the trade-off between the frequency and the delay of handover are presented in this paper.

Visible light communication and its use in wireless networks, which is referred to as light fidelity (LiFi), can potentially provide ubiquitous indoor broadband connections. Most of the existing studies on LiFi consider a device that always faces upward, disregarding the importance of the orientation of the device. This paper presents experimental results on the randomly-oriented devices and a statistical model of the LiFi channel considering the random orientation. The distribution of the cosine of the incidence angle is shown to have a Laplacian form. This distribution is then applied to study the signal-to-noise ratio of the randomly-oriented and the upward-facing devices. Finally, we show that neglecting the random orientation can lead to inaccurate conclusions. Hence, it is important to take the random orientation into account in future LiFi network analyses.

Light-fidelity (LiFi) extends visible light communication into high-speed and multiuser wireless networks. As in cellular networks, co-channel interference (CCI) stemming from other access points (APs) sharing the same transmission resources is the main limiting factor in the performances of the LiFi networks; therefore, it is important to study characteristics of CCI. This paper studies the statistical characteristics of aggregate signal interference iaggin downlink LiFi networks where LiFi-enabled APs are randomly deployed following a Poisson point process (PPP). One of the advantages of considering iaggcompared to the aggregate power interference is that parameters of modulation schemes and room dimensions can both be incorporated. The paper's key finding is that the energy of iaggis not monotonically decreasing as the vertical distance of user of interest and the AP increases. In addition, we show that the distribution of iaggrapidly approaches a Gaussian distribution as PPP intensity increases.

This paper considers full data exchange for massive uncoordinated multiway relay networks (mu-mRN) applying coded random access for flexible topology changes and capable of serving massive number of users. We aim to maximize the normalized throughput of the mu-mRN using the multiuser detection (MUD) technique with MUD capability of K > 1. Specifically, our goal is multiple times improvement, i.e., ten times improvement, from the maximum normalized throughput of the mu-mRN applying slotted ALOHA (SA). First, we present a network capacity bound of the mu-mRN with general K. Then, we optimize many degree distributions for the MUD-based mu-mRN. However, as K increases, the distributions are no longer optimal to achieve the network capacity bound. We propose doubly irregular coded SA (dir-CSA) to solve the problem. Asymptotically, the mu-mRN applying dir-CSA with K = 4 can achieve the ten times throughput improvement. However, for finite number of time slots, we propose to exploit side information (SI) from neighboring users to improve the normalized throughput of the mu-mRN. The results show that the mu-mRN applying dir-CSA with SI and having optimal physical encoding can achieve ten times throughput improvement, compared with the conventional SA scheme.