Spectral Efficiency Enhancement Research Articles

Capacity Approaching Low Density Spreading in Uplink NOMA via Asymptotic Analysis

Low-density spreading non-orthogonal multiple-access (LDS-NOMA) is considered where K single-antenna user-equipments (UEs) communicate with a base-station (BS) over F fading sub-carriers. Each UE k spreads its data symbols over d <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k</sub> <; <; F sub-carriers. The performance of LDS-NOMA system depends on the allocation of the non-zero elements in the LDS-codes. We aim to identify the LDS resource allocations, based solely on pathlosses, that maximize the ergodic mutual information (EMI). This problem can be solved only via an exhaustive search. Thus, relying on analysis in the regime where F, K, and d <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k</sub> ,∀k converge to +∞ at the same rate, we present EMI as a deterministic equivalent plus a residual term. The deterministic equivalent is a function of pathloss values and LDS-codes, and the small residual term scales as <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">O</i> (1 / min(d <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> )). First, we formulate an optimization problem to identify the resource allocations that maximize the deterministic equivalent of EMI. The Karush-Kuhn-Tucker conditions give a simple resource allocation rule that facilitates the construction of desired LDS-codes via an efficient partitioning algorithm. The finite-regime analysis shows that such sparse solutions additionally harness the small incremental gain inherent in the residual term, and thus, provides a near-optimal performance. The spectral efficiency enhancement relative to regular and random spreading is validated numerically.

Efficient user pairing algorithm for enhancement of spectral efficiency and interference cancelation in downlink NOMA system

A new subcarrier-user allocation algorithm for the downlink non-orthogonal multiple access system is presented in this paper. The proposed algorithm aims to enhance the spectral efficiency of the system and the successive interference cancelation performance by guaranteeing a high difference in channel-gain between the paired users per subcarrier. To enhance the spectral efficiency, the proposed algorithm provides a higher priority to the subcarrier that has a higher best (maximum) channel gain value rather than that has a lower best channel gain value. Also, it pairs the strong user with the second minimum channel-gain user rather than the minimum channel gain user. Besides, the proposed algorithm divides the subcarriers into two groups according to the standard deviation of the channel gain of each subcarrier. Then, it gives the priority to the group with low standard deviation values during subcarrier-user allocation to guarantee a high difference in channel-gain between the paired users per subcarrier. Later, fractional transmit power allocation is applied to distribute the subcarrier power between the paired users. Simulation results prove that the proposed algorithm improves the spectral efficiency of the system, and guarantees a significantly higher difference in channel-gain between the paired users per subcarrier compared to the conventional algorithms.

Power Adaptation for Enhancing Spectral Efficiency and Energy Efficiency in Multi-Hop Full Duplex Cognitive Wireless Relay Networks

This work investigates the energy efficiency (EE) and the spectral efficiency (SE) performance of multi-hop full duplex cognitive relay networks (MH-FDCRNs) operating in the spectrum sharing mode, under the influence of interference from the primary source. We formulate three distinct optimization problems for finding the optimal power allocation (OPA) for the secondary nodes in MH-FDCRN: (i) EE optimization with minimum SE requirement; (ii) SE optimization with minimum EE requirement; and (iii) EE-SE trade-off optimization. The impact of residual self-interference (RSI) arising due to full duplex operation at the relay nodes and the inter relay interference (IRI) arising due to frequency re-use are considered. For the EE/SE optimization problems, we transform the original non-convex optimization problems to their convex forms by expressing the numerator of the objective function as the difference of concave functions, and by using parametric transformation. For the EE-SE trade-off optimization problem, we first transform the original multi objective optimization problem into a single objective form; and then into its convex form by introducing an auxiliary variable. Computationally efficient algorithms are proposed to solve the considered problems. The convergence properties of the proposed algorithms are established through mathematical analysis as well as through computer simulation studies. We prove that the points of convergence of the proposed iterative algorithms are the Karush-Kuhn-Tucker (KKT) points of the initial non-convex problems. With the help of detailed numerical results, the best trade-off among EE and SE can be achieved by proper selection of priority factor, compared to the individual optimization approaches.

Multispectral harvesting rare-earth oxysulphide based highly efficient transparent luminescent solar concentrator

Transparent luminescent solar concentrator (LSC) is extensively regarded as the most promising sunlight tapping device for its application in buildings integrated with photovoltaics (BIPV) or as solar window glass. Conventional LSCs doped with organic dyes suffered from high reabsorption losses with no transparency; whereas, recently reported heavy metal-doped quantum dots avoided such losses but possessed the risk of high toxicity and low ambient stability. Thus, luminophores with massive spectral shifts and cordial relationships with the environment are very much desirable. In this paper, we report the fabrication of PMMA based transparent LSC embedded with nanocrystals of environmental friendiness and multispectral harvesting gadolinium oxysulphide (Gd2O2S:Er,Yb) fluorophore. The Gd2O2S:Er,Yb nanofluorophore absorbs various excitation wavelengths ranging from UV to NIR and emits in the visible region offering huge Stoke's and anti-Stoke's shift concurrently. The non-existent reabsorption losses and overlapping maxima of Gd2O2S:Er,Yb nanofluorophore generated photon flux with solar cells' responsivity enhance the efficiency characteristics of the LSC waveguide. Performance analysis of LSC as a function of varying nanofluorophore dispersion ratio and changing edge width optimizes the fabrication process and exhibits high power conversion efficiency of ∼6.93% and optical efficiency of ∼8.57%. The LSC slab demonstrates high photostability under irradiation for prolonged hours without any dip in the emission characteristics. The Gd2O2S:Er,Yb nanofluorophore diffused LSC waveguide offering spectral tunability, cost-reduction, efficiency enhancement, and high concentration factor whilst being sustainable for long term use makes it a fascinating transparent solar window.

Toeplitz concatenated matrix aided ICA algorithm for super-Nyquist multiband CAP VLC systems.

In this paper, we demonstrate a Toeplitz concatenated matrix aided independent component analysis (TCM-ICA) equalizer that can skillfully compensate for the inter-channel interference (ICI) of super-Nyquist multiband carrierless amplitude and phase modulation (m-CAP) system. In the point-to-point super-Nyquist m-CAP visible light communication (VLC) scenario, we experimentally demonstrated a system-level average spectral efficiency (SE) enhancement of 0.50 b/s/Hz in comparison to the conventional scheme. In the multiple-input single-output (MISO) super-Nyquist 5-CAP scenario, the subcarrier-level Q factor enhancements of 4.4 dB, 5.2 dB, and 6.5 dB are achieved in comparison with the least-mean-square (LMS) post-equalizer for the 2nd, 3rd and 4th subcarrier, respectively. As far as we know, the TCM-ICA equalizer is the most effective ICI compensation scheme to enhance SE in the super-Nyquist m-CAP systems.

Spectral efficiency enhancement using an antenna‐based orthogonal frequency division multiaccess technique

An approach to enhance antenna spectral efficiency is proposed based on combining spacetime electromagnetic (EM) models of Tx/Rx antennas with orthogonal frequency division multiaccess (OFDM), leading to the EM-OFDM, a technology capable of removing intersymbol interference (ISI) in high-data rate communication links caused by the EM-induced distortion antenna effects. The proposed approach differs from traditional OFDM in wireless communication in several aspects. First, the technique suggests a new decoupling approach by treating each given antenna transreceive device pair as a “stand-alone channel” with its own distortion mechanisms considered separately from the propagation channel. Moreover, the deterministic distortion caused by the nonflat pure antenna EM filtration effects is exploited to carefully design a specialized OFDM transmission techniques based on the antenna parameters, not the multipath fading channels often invoked in conventional uses of OFDM methods. (The EM-OFDM, however, can be combined with a traditional OFDM later if fading channels are present.) In this manner, a more efficient implementation of the wireless link equalization strategy may be enacted since the EM antenna origin of ISI is very different from the traditional propagation channel one. As a proof of concept, the proposed EM-OFDM method is implemented for a single-input-single-output link comprised of half-wavelength linear wire antennas. A careful use of finite difference time-domain to provide EM data allowed the construction of 64 decoupled “pure antenna OFDM subchannels.” Simulation results suggests that the antenna-based OFDM system is capable of completely neutralizing all ISI effects caused by the limited antenna matching bandwidth of the transreceive wires, therefore, supporting considerably higher data rates with low symbol error rate (SER). A concrete evaluation of the SER using quadrature phase-shift keying (QPSK) digital carrier modulation resulted in an increase of the effective antenna digital communication spectral efficiency by ratios up to 300%. Moreover, the EM-OFDM error rate was found to be close to the ideal QPSK level or the maximum possible theoretical limit. Thus, combining detailed EM knowledge with standard signal processing methods can lead to considerable improvement in system design without modifying the antenna physical layout. The proposed approach is expected to play a role in the forthcoming 5G/6G and millimetre wave technology systems currently under development where there is a trend toward integration of EM and digital signal processing at the physical layer level.

A Novel Algorithm for Improving the Spectrum Efficiency of Non-Orthogonal Multiband CAP UVLC Systems

Nowadays, how to further enhance the spectrum efficiency is one of the key technologies for band limited scenarios in underwater visible light communication (UVLC) systems. In this article, a novel subcarrier component extraction (SCE) with complex independent component analysis (ICA) algorithm is proposed in the non-orthogonal multiband CAP UVLC systems. With the proposed SCE-ICA algorithm, the non-orthogonal multiband CAP system can support a higher overlapping level in contrast to the conventional CAP scheme and therefore hold a higher spectral efficiency. In the simulation, varying degrees of performance enhancement is achieved in comparison with the conventional CAP scheme with different roll-off, compression factor (CF) and signal-noise ratio (SNR). Then, we first discover that in the simulated frequency-selective fading channels, moderate overlapping among subcarriers can achieve the best performance in system-level in contrast to the non-overlapping case. Moreover, the UVLC system experimental investigation of overlapping 2-CAP and 5-CAP scheme is carried out. The experiment demonstration shows that the utmost spectral efficiency enhancement of 40% and 18% are achieved compared with the non-compression CAP case and the conventional demodulation of the overlapping CAP case, respectively. Finally, with the low computational complexity of O(N), the proposed algorithm can be a potential candidate to handle the equalization of non-orthogonal multiband CAP schemes.

Spectral Efficient Precoding Design for Multi-cell Large MU-MIMO System

Large scale multiuser multi-input multi-output (MU-MIMO) system is an emerging wireless technology, which can impart huge spectral efficiency, enhanced link reliability, and serves several users simultaneously in the same frequency–time resource. Pilot contamination (PC) is the major bottleneck in achieving the optimum performance of a multi-cell large MU-MIMO system. We propose a new multi-cell block diagonalization-QR-minimum mean square error (M-BD-QR-MMSE) precoding scheme to diminish the effects of pilot contamination in a multi-cell MIMO system. The reduced effects of Pilot contamination result in the enhancement of spectral efficiency for the multi-cell MU-MIMO system. The design of the proposed scheme utilizes block diagonalization (BD) in combination with MMSE precoding that obtains large null space using QR decomposition operation to reduce intercell and intracell interference much efficiently than conventional precoding schemes. The gain in spectral efficiency with the proposed scheme is enhanced through non-universal pilot reuse in contrast to single-cell schemes. Furthermore, the downlink spectral efficiency expression has been derived for a large scale MIMO system, and the same is computed using Monte Carlo simulations to analyze the results. The numerical results depict that the proposed M-BD-QR-MMSE provides a significant improvement in the spectral efficiency in comparison with traditional single-cell MMSE (S-MMSE), regularized zero-forcing (R-ZF), ZF, Maximum ratio transmission (MRT) and multi-cell MMSE (M-MMSE) schemes. The proposed precoding design provides the spectral enhancements of 32.19 and 50.13 bit/s/Hz/cell in comparison to conventional multi-cell MMSE and single-cell MMSE precoding schemes respectively.

Sector Scanning Algorithm (SSA) for device discovery in D2D communication

ABSTRACT A device-to-device (D2D) communication permits wireless devices to communicate mutually without network assistance. It promises to enhancement in spectral and network efficiency in the next-generation networks. A D2D communication needs device discovery, which is considered as a primary task. It represents the geographic coordinates of the wireless devices in a cellular network. If the device discovery is not legitimated properly may present noteworthy latency, energy consumption, and inaccuracy. In this work, a novel device discovery procedure based on cell sector scanning algorithm (SSA) is proposed for in-band D2D communication and the device discovery is performed under two scenarios: haphazard walk and velocity. An experimental setup is established to receive signal strength (RSS) measurements in a specific sector. The coverage area is divided into eight sectors to discover the devices. The sectors are used to apply and verify the proposed solution and the algorithm for device discovery. It considers the existing radio resources for proximal device discovery and adjusts the discovery signal transmission appropriately. The discovery algorithm must be fast, accurate, and energy efficient at the device level and network level. This technique performs well and enhances the quality of discovery process more than 20% of the linear estimation and diminishes the energy consumption by 24% to accomplish the discovery in dense areas and makes it dynamic and adjustable for changing environments. A mathematical analysis based on the sector scanning attempts is also provided. Furthermore, the improved discovery scheme is evaluated and confirmed by the probability of isolation.

Energy-Efficiency-Based Power Allocation Scheme in Multi-user Single-DF-Relay Cognitive Networks

Due to the enhancement in both spectral efficiency and energy efficiency, cognitive radio (CR) being combined with relay cooperation technique is deemed as a promising way to realize green-broadband communication in the fifth generation (5G) networks. In this paper, for such CR-relay networks operating in underlay mode, when multiple secondary cognitive users (SUs) share a common cognitive relay in decode-and-forward manner to complete their physical transmissions, system power consumption is investigated. For the scenarios where the co-channel interference to primary users and the peak transmit power of SUs and cognitive relay are constrained, the problem of power allocation in CR-relay network is formulated to minimizing sum-system-consumption. Then, based on the principle that power-consumption minimization is equivalent to energy-efficiency maximization, a novel power allocation scheme is proposed. Further numerical simulation is used to verify the optimality of the proposed power allocation scheme.

Spectral efficiency enhancement in Massive MIMO system under pilot contamination

SummaryMassive multiple‐input, multiple‐output (MIMO) system is an effective technique to develop the spectral efficiency of the wireless communication systems. Since the number of users is much higher than the available number of orthogonal pilot sequences, the users in the neighboring cells can reuse the same pilots of the home cell. Thus, pilot contamination occurs, which restricts the system throughput. In this paper, Laplacian centralized scattering‐spatially correlated Rayleigh fading channel model with multi‐cell minimum mean square error (M‐MMSE) combining and precoding to mitigate pilot contamination and enhance cell throughput. This model gives a more accurate description, especially for cell‐edge users. It results in an accurate spatial channel correlation matrix calculation that enhances the channel estimation quality under pilot contamination. Simulation results indicate that the proposed Laplacian scattering‐spatially correlated Rayleigh fading model achieves better pilot contamination mitigation and larger spectral efficiency, as compared with both the one‐ring scattering‐spatially correlated Rayleigh fading and the uncorrelated Rayleigh fading channel models for different combining and precoding schemes at different pilot reuse factors. The cost of interference rejection and spectral efficiency enhancement is an increase in the system computational complexity.

Performance enhancement of the average spectral efficiency using an aperture averaging and spatial-coherence diversity based on the modified-PPM modulation for MISO FSO links

The performance evaluation and enhancement of the proposed model for a free-space optical (FSO) communication links using the modified pulse-position modulation (MPPM) and spatial pulse-position modulation (SPPM) is analyzed in this paper. The average spectral efficiency (ASE) is investigated for the FSO communication using MPPM, SPPM, and spatial-coherence diversity in a coherent optical wireless communication (coherent OWC) systems. We proposed the hybrid MPPM/SPPM as a new modulation to improve the ASE performance of pulse-position modulation. To reduce the atmospheric turbulence (AT) effects and scintillation, the use of an aperture averaging (AA) technique has been proposed in our work. Here, we analyze the pointing error (PE) effects on the performance of M−ary MPPM based on a multiple-input single-output (MISO) of the repetition codes (RCs) and FSO systems using SPPM. The enhancement in the ASE can be accomplished with an increase in the receiver aperture and decreasing the beam radius in the presence of PEs. The ASE performances of 53 bits/s/Hz and 37 bits/s/Hz are achieved with the average transmitted optical power of 10 dBm for an aperture diameter of 10 cm over the effect of without and with PEs for coherent OWC technique, respectively. The simulation results obtained for the bit-error-rate (BER) and ASE against various AT conditions are compared with the diversity techniques and proved that both of the hybrid SPPM and MPPM/MISO−RCs based on the AA and spatial diversity offers better performance in the average channel capacity (ACC). Numerical results show that the ASE performance can be improved using the spatial-coherence diversity in coherent OWC technique. The spatial-coherence diversity in a coherent OWC system significantly outperforms on-off keying and MPPM system even in the presence of PEs under strong turbulence. Efficient estimation of the signal-to-noise ratio also allows accurate quantification of the BER and ACC for adequate quality of service and network link resource allocation.

Multi-core fiber based coherent transceiver utilizing self-homodyne detection and ICA based channel equalization for optical intra-datacenter interconnects

We have proposed a cost-effective full-duplex datacenter inter-(or intra-) connection transmission scheme based on self-homodyne coherent detection and multi-core fiber. Independent component analysis (ICA) based channel equalization is applied to remove the requirement of training symbols (TSs) for enhancement of spectral efficiency. We validate in a proof-of-concept experiment using polarization division multiplexing (PDM-) 16QAM orthogonal frequency division multiplexing (OFDM) format over 10-km 7-core fiber in full-duplex way. The results show that the performances can below the forward error correction (FEC) threshold of 3.8 × 10−3. In addition, we investigate the effects of several parameters in the proposed scheme, including laser linewidth and distance mismatch. Finally, we experimentally compared the performance of the proposed scheme to that of employing the TSs for channel compensation to quantify the performance penalty resulting from the TSs removal.

A Low-Complexity AEPDF-assisted Precoding Scheme for Massive MIMO Systems with Transmit Antenna Correlation

Multi-user massive multiple-input multiple-output (MU M-MIMO) system employs array of hundred (or thousand) antennas and precoding/equalization capability at the base station (BS) has been adopted in recent 5G new radio (5G NR) standards. By taking advantage of the multiplexing, diversity and antenna gain inherited from this versatile system configuration, unprecedented enhancement in capacity, spectral efficiency and signal integrity can be realized. While many MU M-MIMO system related issues such as pilot contamination, channel estimation and precoding/detection algorithms have been extensively examined by research communities, the investigation of a low-complexity, effective precoding scheme aims to address performance degradation due to spatial correlation (i.e., packing vast number of antennas in a limited physical space) remained scarce. In this paper, an iterative precoding scheme based on Chebyshev acceleration is proposed for one-sided Kronecker model (i.e., Rayleigh flat fading channel with transmit (Tx) antenna correlation), often encountered in uniform linear array (ULA) configuration. From the asymptotic eigenvalue probability density function (AEPDF) constructed for the non-commutative Kronecker channel, near-optimal recurrence coefficients, initial and final estimates of the proposed Chebyshev iterative method can be obtained free from expensive eigenvalue computation. Simulation shows that the proposed algorithm achieves outstanding BER in all correlation scenarios (i.e., from low to high) while exhibiting much lower complexity compared to other state-of-the-art precoding schemes.

Enhancement of Spectral Efficiency FSO Links Using Linear Polarizer-Based MLPolSK Detection

This paper proposes the enhancement of spectral efficiency (SE) by linear polarizer based multilevel linear polarization shift keying (MLPolSK) detection in free-space optical (FSO) communication. At the transmitter end, in order to improve SE of FSO links, the various linear state of polarizations (SOPs) with an equal magnitude-spacing of x- or y-polarization are modulated for MLPolSK signal. At the receiver end, the cascaded polarization-independent semiconductor optical amplifier (SOA) and linear polarizer are introduced to detect MLPolSK signal. Polarization-independent SOA is applied to effectively mitigate the turbulence induced scintillation effect by the gain saturation without the distortion of polarization. Linear polarizer with high extinction ratio (ER) is used to transform various SOPs into the signal with an equal intensity-spacing of x- or y-polarization. Besides, the amplified spontaneous emission (ASE) noises are reduced by the polarization of ASE noises by linear polarizer. Finally, MLPolSK is detected by a single photodiode (PD) and decided by multilevel-thresholdings. In experiments, the performance of the proposed technique is evaluated under turbulence channels, which are emulated using Mach–Zehnder modulator (MZM)-based fading simulator. Experimental results show that the SE is improved up to 3 bit/s/Hz under the effective scintillation mitigation using the proposed technique.

Enhancement of Spectral Efficiency and Power Budget in WDN-PON Employing LDPC-Coded Probabilistic Shaping PAM8

A $5\times60$ Gb/s low-density parity-check (LDPC) coded WDM-PON using 8-level pulse amplitude modulation (PAM8) signals with probabilistic shaping (PS) over 20-km standard single-mode fiber (SSMF) with direct detection is proposed and experimentally demonstrated. Each optical carrier at the optical line terminal (OLT) carries a 20-Gbaud probabilistically-shaped LDPC-coded PS-PAM8 signal from a conventional uniform PAM16 signal following a designed approximate Gaussian distribution (AGD). A LDPC-based bit-interleaved coded modulation scheme with iterative decoding (BICM-ID) is utilized to recover the inherently overlapped symbols due to the proposed PS mapping. Combining decision-directed least-mean-squares (DD-LMS) and constant modulus algorithm (CMA), a blind feedback pre-equalizer is adopted to reduce the frequency loss of the signal owing to imperfect electro-optical components in experiment. As for experimental verification and application, 1.48-dB superior receiver power sensitivity and 1.7-dB launch fiber power optimization are gained respectively by using LDPC-coded PS-PAM8 signals in WDM-PON, which can bring higher spectral efficiency and power loss budget for the optical distribution networks.

Robust Energy-Efficient Design for MISO Non-Orthogonal Multiple Access Systems

Non-orthogonal multiple access (NOMA) has been envisioned as a promising multiple access technique for 5G and beyond wireless networks due to its significant enhancement of spectral efficiency. In this paper, we investigate a robust energy efficiency design for multi-user multiple-input single-output (MISO) NOMA systems, where the imperfect channel state information is available at the base station (BS). A clustering algorithm is applied to group the users into different clusters, and then, the NOMA technique is employed to share the available resources fairly among the users in each cluster. To remove the interference between clusters, two different types of zero-forcing (ZF) designs, namely, hybrid-ZF and full-ZF, are employed at the BS. The full-ZF scheme completely removes the interference leakage at the cost of more number of antennas, and the hybrid-ZF scheme partially mitigates the interference leakage. To solve the problem, Dinkelbach’s algorithm is employed to convert the non-linear fractional programming problem into a simple subtractive form. Finally, simulation results reveal that hybrid-ZF outperforms the full-ZF scheme with a few clusters, while full-ZF shows a better performance with higher number of clusters. Numerical results confirm that our proposed robust scheme outperforms the non-robust scheme in terms of the rate-satisfaction ratio at each user.

Spectral Efficiency Enhancement in Satellite Mobile Communications: A Game-Theoretical Approach

Broadband satellite services, such as satellite- based Internet of Things and cloud services, have attracted much attention recently. To achieve the goal of anytime and anywhere high-speed satellite communications, there is a big demand for satellite spectrum. The push for improving spectrum efficiency in satellite systems has been an important issue, mainly from the perspectives of spectrum reuse and dynamic spectrum access. In this article, we investigate the feasibility of improving satellite spectrum efficiency from another viewpoint, that is, introducing a game-theoretical approach, including spectrum pricing and auction, for satellite spectrum dynamic allocation. Although spectrum pricing and auction have been suggested for terrestrial networks, this work aims to establish a market-inspired model to address distinct characteristic features of satellite communications. In particular, we propose a generic satellite spectrum pricing scheme, taking into account three factors: spectrum reuse in multi-beam satellite systems (MSS), where intercell interference should be mitigated; the heterogeneous nature of satellite transmission links in different spectrum bands, in which a differential pricing scheme is desirable; and predictable and periodic satellite switching from one non-GEO satellite link to another, where traffic-oriented pricing should be used. Finally, the challenges and future works in satellite mobile communications are identified.

Performance enhancement of bulk heterojunction organic solar cells using photon upconverter

In this article, we show that significant performance enhancement can be obtained by incorporating a photo upconverter layer in bulk heterojunction organic solar cells (BHJ OSCs). We systematically optimize the photon upconversion process for P3HT:PCBM, PSBTBT:PCBM, PBDTTT-C:PCBM and PTB7-Th:PCBM based BHJ OSCs using a simple numerical model followed by optoelectronic simulations. After verifying the integrated model of upconversion with experimental reports, we analyze each type of BHJ OSC incorporating photon upconversion layer having optimized spectral characteristics and estimate efficiency enhancement of ~30.8% (4.55% → 5.95%), ~24.3% (5.02% → 6.24%), ~28.9% (6.35% → 8.19%) and ~16.9% (10.55% → 12.34%) for P3HT:PCBM, PSBTBT:PCBM, PBDTTT-C:PCBM and PTB7-Th:PCBM based OSCs, respectively. We then show that effect of photon upconversion and localized surface plasmon resonance on the best performing OSC material considered in this work i.e. PTB7-Th:PCBM, is non-linear and predict a performance boost of mere ~2.3% (12.32% → 12.62%) from additional effort (due to plasmon resonance). Finally, we discuss possibility of extending the efficiency of PTB7-Th:PCBM based BHJ OSC beyond 16% using concentrated sunlight and a practically realizable upconverter layer.

New Weight Function for Adapting Handover Margin Level over Contiguous Carrier Aggregation Deployment Scenarios in LTE-Advanced System

In this paper, an Adaptive Handover Margin algorithm based on Novel Weight Function (AHOM-NWF) is proposed through Carrier Aggregation operation in Long Term Evolution—Advanced system. The AHOM-NWF algorithm automatically adjusts the Handover Margin level based on three functions, $$f(SINR), \; f(TL)\; {\text{and}}\; f(v)$$ , which are evaluated as functions of Signal-to-Interference-plus-Noise-Ratio (SINR), Traffic Load $$(TL)$$ , and User’s velocity $$(v)$$ respectively. The weight of each function is taken into account in order to estimate an accurate margin level. Furthermore, a mathematical model for estimating the weight of each function is formulated by a simple model. However, AHOM-NWF algorithm will contribute for the perspective of SINR improvement, cell edge spectral efficiency enhancement and outage probability reduction. Simulation results have shown that the AHOM-NWF algorithm enhances system performance more than the other considered algorithms from the literature by 24.4, 14.6 and 17.9%, as average gains over all the considered algorithms in terms of SINR, cell edge spectral efficiency and outage probability reduction respectively.