Wireless backhaul communication and power provision to fifth-generation small cells (SCs) is expected to decrease their installation cost significantly. In this paper, hybrid solar/laser-based energy harvesting and storage are investigated for the self-sufficient year-round operation of outdoor SCs. The required electrical power for a SC is assumed to be 10 W according to state-of-the-art millimeter-wave phased-array transceivers. Here we show through simulations that hybrid solar/laser-based energy harvesting with storage and exclusive laser-based energy harvesting enable the SC operation not only in sunnier parts of the world but also in ‘darker’ places. Since the highest monthly power required from the laser is shown to be 10.1 W, a highly directive optical wireless link is designed using the simulation software Zemax. The operation wavelength of 1310 nm is selected because of the highest maximum permissible exposure of 1 W/cm2. The designed system is shown to be capable of harvesting 10.4 W at the distance of 100 m with transmitter-receiver dimensions of the order of cm3and meeting eye-safety regulations for Class 1M.

In this paper, a low cost optical wireless communications link with a data rate of 74 Mb/s at a bit-error ratio of 3.3×10-3is demonstrated. The components are all low cost, off-the-shelf parts, including the laser transmitter and silicon solar panel receiver. This performance is achieved by extending the usable bandwidth using analog equalization and digital techniques such as adaptive bit and power loading. Also, the performance of two spectrally efficient modulation schemes, namely direct-current biased optical orthogonal frequency division multiplexing (DCO-OFDM) and pulse amplitude modulation discrete multitone (PAM-DMT) is evaluated and compared. It is shown that DCO-OFDM outperforms PAMDMT because of efficient bandwidth usage with adaptive bit loading and pre-distortion introduced by adaptive power loading. Furthermore, it is shown that PAM-DMT can avoid complex system designs and still achieve comparable data rates to that of OFDM with higher link reliability.

The key requirement of fifth generation (5G) systems is seamless connectivity for anyone and anything. The current form of terrestrial mobile systems are mostly mature enough to provide connectivity for any terrestrial user and device. Nowadays, several projects seek to enhance the terrestrial systems to provide such connectivity to airborne users. However, providing connectivity for every airborne user needs a special design for different aircraft types. Due to the shape and structure of an aircraft, widely used system and channel models in terrestrial systems cannot be directly applied to onboard communication systems. In this paper, the realistic throughput performance of three different wireless communications technologies namely, Long Term Evolution (LTE), Wireless-Fidelity (WiFi) and Light-Fidelity (LiFi) is investigated inside a medium-sized commercial aircraft. It is shown that the average user throughput performance is 1.6 Mbps, 2.7 Mbps and 16.6 Mbps for onboard WiFi, LTE and LiFi systems, respectively.

This paper proposes a coordinated multi-point transmission (CoMP) scheduling technique in combination with inter-cell interference coordination (ICIC) techniques, almost blank subframes (ABS) and reduced-power ABS (RP-ABS). It investigates the scheduler performance in the context of an aircraft in- cabin Long Term Evolution (LTE) system deployment. The scheduling problem is solved for an ideal case and a real-world case where LTE system constraints such as common modulation and coding scheme (MCS) assignment per user, channel quality indicator (CQI) reporting and LTE resource allocation (RA) types are considered in the scheduling problem in order to provide a meaningful comparison between real-world and ideal performance. The tradeoff between fairness, which is defined as the lowest variation in user data rates across a large user population, and system throughput is considered as the performance evaluation metric of the system. It is shown that when the LTE constraints are employed, the ideal user data rate and system throughput performance is drastically degraded regardless of the used ICIC technique. In the ideal case, where the LTE constraints are not considered, RP-ABS becomes the optimum tradeoff between fairness and system throughput which achieves a variation of 4.4 Mbps between the lowest and highest user rate, an average user rate of 3 Mbps and an average system throughput of 500 Mbps. However, when the LTE system constraints are taken into account, ABS becomes the optimum technique for the considered onboard system which achieves a variation of 1.7 Mbps, an average user rate of 1.5 Mbps and an average system throughput of 265 Mbps.

An aircraft cabin can be considered as an unusual propagation environment due to the construction materials and interior furniture of the aircraft. In this paper, a measurement and modeling procedure is proposed to characterize radio propagation inside an aircraft. The proposed procedure is divided into three phases in order to characterize (1) the propagation direction; (2) the reflections from the cockpit and tail ends of the cabin; and (3) the reflections from the sidewalls of the cabin. The first phase of the proposed measurement procedure is conducted in an Airbus A321 aircraft for the 1.8 GHz frequency band. In the measurements, the receive antenna is located in 24 different passenger seats and three different transmit antenna locations are considered to investigate how the propagation characteristics change according to the propagation direction. According to the measured values, we found that the path loss exponent of the distance dependent path loss model (decay constant) differs according to the propagation direction and distance. The path loss exponent is found equal to 1.5 and 2.6 for both the propagation directions when the transmitter-receiver separation is shorter than 5 meters and longer than 14 meters, respectively. However, when the distances between 5 and 14 meters are considered, the path loss exponent is found equal to 2 for in- flight propagation direction and 2.3 for in-rear propagation direction. In light of the obtained radio propagation characteristics for the first phase of the proposed procedure, it is worthwhile to follow the remaining phases in order to improve channel propagation modeling inside an aircraft.

This paper studies complex modulation schemes, including orthogonal frequency-division multiplexing (OFDM), received by a single photon avalanche diode (SPAD) array integrated circuit (IC). A SPAD operates in the Geiger mode, and is able to detect single photons. This feature enables order of magnitude receiver sensitivity in intensity modulation (IM) / direct detection (DD) Visible Light Communication (VLC) systems. The tradeoff between received power and bit error ratio (BER) using both pulse-amplitude modulation (PAM) and OFDM is shown. A first order model of the noise in a digital SPAD receiver is derived. The noise in the experimental receiver chip approaches the predicted noise in our model, and we achieve receiver sensitivity of $-$64 dBm with a 100 kbit/s signal at a BER of 10^-5. It is concluded that future improvements in SPAD VLC receiver architecture will allow sensitivity to approach the quantum limit.

The performance of a multi-cell, multi-user Long Term Evolution (LTE) deployment in a medium-sized aircraft cabin is studied. Due to the structure and construction materials of the aircraft, channel propagation behaviour is different from conventional indoor channel models. Also, depending on the seating plan of the aircraft, user density is higher than other indoor environments. Thus, firstly, a proper channel model is adapted for an aircraft, and then the deployed LTE system is optimized using Taguchi's Method (TM). TM is a recently used optimization method for electromagnetic (EM) problems and for the optimization of communication networks. The results show that multi-cell, multi-user LTE deployment can achieve 4.33 Mbps average user data rate and 676 Mbps total system data rate with two evolved NodeBs (eNBs) deployed.

A number of inherently unipolar orthogonal frequency division multiplexing (OFDM) modulation schemes have been introduced recently in an attempt to improve the energy efficiency of OFDM-based intensity modulation and direct detection (IM/DD) systems. All such algorithms, including asymmetrically clipped optical OFDM (ACO-OFDM), pulse-amplitude-modulated discrete multitone modulation (PAM-DMT) and unipolar orthogonal frequency division multiplexing (U-OFDM), experience an inherent loss in spectral efficiency caused by the restrictions imposed on the OFDM frame structure required for the generation of a unipolar signal. The current paper presents a modified modulation approach, termed enhanced U-OFDM (eU-OFDM), which compensates the spectral efficiency loss in U-OFDM. At the same time, it still allows for the generation of an inherently unipolar modulation signal that achieves better performance in terms of both electrical power and optical power dissipation compared to the conventional state-of-the-art technique direct current (DC)-biased optical OFDM (DCO-OFDM). To the best of the authors' knowledge, the current work also presents the first experimental proof-of-concept demonstration of both U-OFDM and eU-OFDM, and clearly demonstrates the significant energy advantages that these two schemes can introduce in an optical wireless communications (OWC) system.

This paper proposes a novel design of an optical wireless communications (OWC) receiver using a solar panel as a photodetector. The proposed system is capable of simultaneous data transmission and energy harvesting. The solar panel can convert a modulated light signal into an electrical signal without any external power requirements. Furthermore, the direct current (DC) component of the modulated light can be harvested in the proposed receiver. The generated energy can potentially be used to power a user terminal or at least to prolong its operation time. The current work discusses the various parameters which need to be considered in the design of a system using a solar panel for simultaneous communication and energy harvesting. The presented theory is supported with an experimental implementation of orthogonal frequency division multiplexing (OFDM), thus, proving the validity of the analysis and demonstrating the feasibility of the proposed receiver. Using the propounded system, a communication link with a data rate of 11.84 Mbps is established for a received optical signal with a peak-to-peak amplitude of 0.7 × 10-3W/cm2.

In this paper, it is demonstrated for the first time that the problem of continuous downhole monitoring in the oil and gas industry is effectively addressed by the use of visible light communication (VLC). As a reliable, flexible and low-cost technique, VLC can fulfill a critical need of operators to maintain production efficiency and optimize gas well performance. The proposed VLC system makes use of a light emitting diode (LED) transmitter and a high sensitivity single photon detecting receiver referred to as single-photon avalanche diode (SPAD). The latter is instrumental in achieving long range communications, and the fact that ambient light is not present in a gas pipe is exploited. Specifically, the lack of ambient light enables high signal to noise ratio (SNR) at the receiver which operates in a photon counting mode. In this study, the bit error ratio (BER) performance of the system is simulated for a 4 kilometres long metal pipe. It is shown that the proposed system has superior power efficiency over conventional methods, which is important as it is assumed that the transmitter is battery operated. In addition, the theoretical BER performance is calculated and compared to the simulation results.

In this paper, we experimentally demonstrate the feasibility of optical wireless communication (OWC) systems with a solar panel as a photo-detector. The advantage of a solar panel is that it is a passive device, which does not require an additional power supply for converting the received light signal into an electrical signal. The frequency response of a solar panel shows that its 3-dB modulation bandwidth is 350 kHz. The results demonstrate that for a 1-Mbit/s on-off keying signal, a bit error rate of less than 2 × 10-3could be achieved when the average irradiance on the solar panel is 3.5 × 10-4W/cm2. In the current experimental setup, this corresponds to a transmission distance of 39 cm. A data rate of 7.01 Mbit/s is achieved by using orthogonal frequency division multiplexing. In addition, the feasibility of using the solar panel for simultaneous communication and energy harvesting is investigated. A load is connected in parallel to the receiver circuit in order to simulate the conditions of charging a battery by using the received signal's DC component. It is shown that the load does not hamper the communication capabilities. Hence, an OWC system with a solar-panel-based receiver can satisfy the requirements of simultaneous communication and energy harvesting.

In this paper, a hybrid network combining visible light communication (VLC) with a radio frequency (RF) wireless local area network (WLAN) is considered. In indoor scenarios, a light fidelity (Li-Fi) access point (AP) can provide very high throughput and satisfy any illumination demands while wireless fidelity (Wi-Fi) offers basic coverage. Such a hybrid network with both fixed and mobile users has the problem of variable user locations, and thus large fluctuations in spatially distributed traffic demand. Generally, a handover occurs in such a method when a user is allocated by the central controller unit to a different AP which is better placed to serve the user. In order to be representative of real deployments, this paper studies the problem of load balancing of a dynamic system where we consider the signalling overhead for handover. We propose a scheme for dynamic allocation of resources to users, where the utility function takes into account both throughput and fairness. The simulation results show that there is a trade off between the aggregate throughput and user fairness when handover overhead is considered. The proposed dynamic scheme always outperforms the considered benchmarks in terms of fairness and can achieve better aggregate throughput in the case of low user density.

This paper presents results of a practical implementation of a spatial shift keying (SSK) visible light communication (VLC) system. This is the first practical proof-of-concept realtime implementation of SSK for VLC to the best knowledge of the authors. The system uses four transmitter light emitting diodes (LEDs) to encode information, and four receiver photo diodes (PDs) to decode the spatial signatures and decode the incoming data signal. The achieved bit error ratio (BER) of less than 2 × 10-3allows for error-free communication if forward error correction (FEC) is to be applied. The main challenge with practical implementations of SSK in VLC is identified, namely maintaining symbol separation in the received constellation, and solutions are proposed.

This paper presents an initial study on how to model user mobility in a wireless cellular network scenario. The model provides realistic patterns of movement between a number of locations. The aforementioned mobility model is built upon to introduce a base station (BS) energy efficient power state control algorithm (EESC) that is able to provide significant energy savings for the simulated scenario. Erratic subsequent on and off BS behavior is avoided by referring to an average loading curve, generated for each BS during a learning period, when making decisions. Moreover, BSs are turned off only when the users can be handed off to nearby cells with a predefined maximum allowed predicted loss in data rate. The resulting system is able to deliver an energy consumption reduction between 36% and 11% over an always on benchmark for the simulated scenarios. There is negligible loss in terms of achieved data rate per user.

This paper presents a novel adaptation of the score-based scheduling principle along with a method for trading-off bandwidth for energy efficiency for use in Long Term Evolution (LTE) systems. The score-based principle is adapted to make use of both a relative and absolute energy efficiency metric. This results in flexible energy efficient scheduling that preserves the quality of service (QoS), as well as reduces the interference in the system. The general principle behind bandwidth expansion is to extend a user's bandwidth by a factor of α. The target throughput is maintained by switching to a lower order modulation scheme and adjusting any other link parameters as necessary. Through a theoretical derivation, it is established that the higher the user's employed modulation order is, the greater the possible gains are from employing such a transmission mode. The calculated improvement in expended energy ranges from approximately 43% to 98%. Simulations are used to empirically validate the theoretical results. When an expansion of bandwidth by a factor of 2 is simulated, the bandwidth expansion mode (BEM) is more efficient in 93% of the time, and the expended energy is reduced by 44%, while improving on the QoS delivered by the benchmark system.

This paper presents the integration of power control and the busy burst (BB) technique for a TDD OFDMA (time division duplex orthogonal frequency division multiple access) system in an urban Manhattan grid type of environment. The objective is to combine power control with the BB protocol to develop a power efficient interference-avoidance technique. Previous work has demonstrated that the time multiplexed BB can be used to achieve interference aware medium access. It has also been demonstrated in other work that the implicit feedback mechanism of BB can be exploited to achieve Pareto optimal SINR-based (signal-to-interference-plus-noise ratio) power control. However, these two applications are not compatible the former depends on fixed signal powers across users, while the latter makes use of variable signal power to achieve optimum power control. This paper proposes an amendment to the BB technique that allows the two approaches to co-exist by exploiting the frequency granularity of OFDMA to frequency multiplex two BBs one with variable and one with fixed power. The resulting control protocol exhibits an eight-fold reduction at the 50th percentile of used energy with no additional overhead as compared to the single BB protocol.

This paper analyses busy burst (BB) enabled interference avoidance for multi-user orthogonal frequency division multiple access (OFDMA) in a Manhattan grid deployment scenario. Upon successful reception of data, the receiver transmits a BB in a time-multiplexed mini-slot. Exploiting the channel reciprocity of time division duplex (TDD), an exclusion region around a victim receiver is established, where potential transmitters are denied access to reserved resources. The size of the exclusion region is determined by a threshold parameter, known to the entire network. System level simulations compare the system and user throughput of BB enabled interference avoidance with greedy resource allocation that does not attempt to avoid interference. It is shown that by adjusting the BB threshold parameter, system throughput can be traded with fairness in terms of cell-edge user throughput. By tuning the BB threshold, either up to 45% increase in system throughput or up to 7-fold increase in cell-edge user throughput are feasible compared to greedy resource allocation. Moreover, by an appropriate adjustment of the BB power further gains in system throughput without compromising fairness are achieved.