Link Gain Research Articles

Energy Efficient Digital Data Link

Efficiently amplifying the high-speed and low-voltage swing outputs of single flux quantum (SFQ) logic to levels that are suitable for interfacing with room temperature electronics has been a long-standing challenge in the field of superconducting electronics. In this work, we investigate the feasibility of using a lossy passive matching network at 4 K, with a pair of differential 100 low-noise amplifiers heatsunk to 18 K and 50 K stages, respectively. The amplifiers were implemented in a 120 nm SiGe BiCMOS technology. The amplification chain is dc coupled and the small-signal link gain was measured to be approximately 48 dB. The power consumption of each of the two amplification stages was 6.3 mW. The chain was measured at 21 K using a high-speed differential nonreturn-to-zero signal having amplitude commensurate with what one would expect from a superconducting circuit, and clean eye diagrams were observed for data rates as high as 30 Gb/s. The chain was also measured when driven from an SFQ/dc interface, with the first gain stage heatsunk to 9 K. In this configuration, clean eye diagrams were observed to 5 Gb/s, with the speed limitation being related to packaging parasitics.

Modeling and simulation of RSOA with a dual‐electrode configuration

AbstractBased on the physical model of a bulk reflective semiconductor optical amplifier (RSOA) used as a modulator in radio over fiber (RoF) links, the distributions of carrier density, signal photon density, and amplified spontaneous emission photon density are demonstrated. One of limits in the use of RSOA is the lower link gain when compared with a distributed feedback laser modulator. To improve the link gain of RSOA modulator in RoF links, we investigate the characteristics of the RSOA modulator with a dual‐electrode configuration. Therefore, there are two kinds of configuration: Case I, the modulating signal is injected at the input&output facet of the ROSA modulator; Case II, the modulating signal is injected at the mirror facet. The link gain of the RSOA modulator can be improved with the dual‐electrode configuration under proper biases. The link gain improvement of about 6 dB is obtained with the Case II configuration under proper bias currents.

Emerging trends in evolving networks: Recent behaviour dominant and non-dominant model

Novel phenomenon receives similar attention as popular one. Therefore predicting novelty is as important as popularity. Emergence is the side effect of competition and ageing in evolving systems. Recent behaviour or recent link gain in networks plays an important role in emergence. We exploited this wisdom and came up with two models considering different scenarios and systems. Where recent behaviour dominates over total behaviour (total link gain) in the first one, and recent behaviour is as important as total behaviour for future link gain in the second one. It supposes that random walker walks on a network and can jump to any node, the probability of jumping or making a connection to other node is based on which node is recently more active or receiving more links. In our assumption, the random walker can also jump to the node which is already popular but recently not popular. We are able to predict emerging nodes which are generally suppressed under preferential attachment effect. To show the performance of our model we have conducted experiments on four real data sets namely, MovieLens, Netflix, Facebook and Arxiv High Energy Physics paper citation. For testing our model we used four information retrieval indices namely Precision, Novelty, Area Under Receiving Operating Characteristic (AUC) and Kendal’s rank correlation coefficient. We have used four benchmark models for validating our proposed models. Although our model does not perform better in all the cases but, it has theoretical significance in working better for recent behaviour dominated systems.

Supply Chain Cooperation by Agreed Reduction of Behavior Variability: A Simulation-based Study

Supply chain echelons normally base their operational decisions on average values of the parameters that depend on other members. However, in real-life operation the variability of said parameters decreases the link profits. Thus, a cooperative arrangement may be devised in which a link agrees to reduce the variability of its behavior to enhance the performance of other links, receiving compensation in return. This work shows the application of simulation and decision trees to assess the feasibility of this cooperation scheme, from the perspective of the central link of a three member supply chain. First, the operational parameters of the link are optimized for mean values of the variables set by adjacent members. Then, by simulating the system for different probability distributions of these variables, graphs of the expected link gain versus the variances of the distributions are plotted. The results are incorporated to decision trees to evaluate the collaboration feasibility. It was found that the increased variability of the behavior of one neighboring member decreases the benefit of lowering the variability of the behavior of the other. The manuscript closes with a discussion of the practical viability of this collaboration scheme.

Analog Photonic Link With Tunable Optical Carrier to Sideband Ratio and Balanced Detection

Optical carrier to sideband ratio (CSR) optimization and balanced detection are two effective techniques to improve the performance of an analogy photonic link (APL). Here, we proposed an APL where tunable optical CSR and balanced detection can both be implemented. A single integrated polarization division multiplexing Mach–Zehnder modulator (PDM-MZM) is used to generate a polarization multiplexed signal containing an optical carrier and two radio frequency modulated sidebands, and the optical CSR can be tuned from –15 to 15 dB by simply adjusting the direct current bias of the modulator. By optimizing the optical CSR in the proposed link, the link gain and noise figure (NF) are improved by 12 and 6.8 dB compared with conventional quadrature biased link. In addition, after balanced detection in the proposed link, the link gain, NF, third-order spurious free dynamic range (SFDR), and especially the second-order SFDR are further improved.

Improved Interference-Free Channel Allocation in Coordinated Multiuser Multiantenna Open-Access Small Cells

This paper investigates low-complexity joint interference avoidance and desired link improvement for single-channel allocation in multiuser multiantenna access points (APs) for open-access small cells. It is considered that an active user is equipped with an antenna array that can be used to suppress interference sources but not to provide spatial diversity. On the other hand, the operation of APs can be coordinated to meet design requirements, where each of which can unconditionally utilize assigned physical channels. Moreover, each AP is equipped with uncorrelated antennas that can be reused simultaneously to serve many active users. The analysis provides new approaches to exploit physical channels, transmit antennas, and APs to mitigate interference, while providing the best possible link gain to an active user through the most suitable interference-free channel. The event of concurrent service requests placed by active users on a specific interference-free channel is discussed for either interference avoidance through identifying unshared channels or desired link improvement via multiuser scheduling. The applicability of the approaches to balance downlink loads is explained, and practical scenarios due to imperfect identification of interference-free channels and/or the scheduled user are thoroughly investigated. The developed results are applicable for any statistical and geometric models of the allocated channel to an active user, as well as channel conditions of interference users. They can be used to study various performance measures. Numerical and simulation results are presented to explain some outcomes of this paper.

Highly linear dual ring resonator modulator for wide bandwidth microwave photonic links.

A highly linear dual ring resonator modulator (DRRM) design is demonstrated to provide high spur-free dynamic range (SFDR) in a wide operational bandwidth. Harmonic and intermodulation distortions are theoretically analyzed in a single ring resonator modulator (RRM) with Lorentzian-shape transfer function and a strategy is proposed to enhance modulator linearity for wide bandwidth applications by utilizing DRRM. Third order intermodulation distortion is suppressed in a frequency independent process with proper splitting ratio of optical and RF power and proper dc biasing of the ring resonators. Operational bandwidth limits of the DRRM are compared to the RRM showing the capability of the DRRM in providing higher SFDR in an unlimited operational bandwidth. DRRM bandwidth limitations are a result of the modulation index from each RRM and their resonance characteristics that limit the gain and noise figure of the microwave photonic link. The impact of the modulator on microwave photonic link figure of merits is analyzed and compared to RRM and Mach-Zehnder Interference (MZI) modulators. Considering ± 5 GHz operational bandwidth around the resonance frequency imposed by the modulation index requirement the DRRM is capable of a ~15 dB SFDR improvement (1 Hz instantaneous bandwidth) versus RRM and MZI.

Research of free motion trajectories features of continuous system defined as a consecutive chain of identical first-order aperiodic links

It is stated that the model of desired behavior has found a widespread usage in the theory and practice of control system design, with the state matrix having a binomial Newton placement of eigenvalues. A structural representation of these systems in the case of the transfer functions approach application leads to a system defined as a consecutive chain of identical first-order aperiodic links. Such model of the desired system behavior has the transient response of the system, which is characterized by the absence of overshoot, that is particularly valuable in the unique technological equipment control. Situation varies considerably when the control system with a binomial placement of eigenvalues has a nonzero initial state. Such situation may arise in the case of an unexpected power fail interrupt of the system electrical components followed by its recovery. This problem is especially important for remote online control of continuous plant in the case of the normal functioning disruption of the channel environment and its restoration in the future. The system in a form of consecutive chain of identical first-order aperiodic links mathematically has a three-parametric set as a module of the negative real eigenvalue, its multiplicity equal to the system dimension and aperiodic link gain. It was found that the three-parametric system may have trajectory emissions at any of negative eigenvalue module. The paper results are illustrated by the computer experiment.

A Phase-Modulated Microwave Photonic Link With an Extended Transmission Distance

A novel technique to transport a microwave signal over an optical fiber based on phase-modulation and coherent in-phase (I) and quadrature-phase (Q) demodulation with an extended transmission distance is proposed and experimentally demonstrated. In the transmitter, a Sagnac loop incorporating a phase modulator (PM) is used to generate two orthogonally polarized optical signals with one being phase modulated and the other with no modulation that acts as a remote optical reference signal. The orthogonally polarized optical signals are transmitted over a single-mode fiber (SMF) to a polarization and phase diversity coherent receiver, and are coherently detected with a free-running optical local oscillator at the receiver. Since the phase-modulated and the reference signals are transmitted over the same SMF, the optical phases are correlated, and the original signal can be recovered based on a digital signal processing algorithm. The proposed technique is experimentally evaluated. Compared with a phase-modulated coherent I/Q demodulated link without using an optical phase correlated reference signal, the transmission distance is extended from 50 m to 10 km, while providing a link gain and a spurious-free dynamic range (SFDR) of −9.5 dB and 115.8 dB $\cdot $ Hz $^{2/3}$ , respectively.

Elimination of cross-modulation distortion in a radio frequency–amplified intensity-modulation direct-detection analog photonic link

By cascading two standard Mach–Zehnder modulators (MZMs), we propose and demonstrate a scheme to effectively eliminate the cross-modulation distortion (XMD), which results from the out-of-band interference in multicarrier intensity-modulation direct-detection (IMDD) analog photonic links. When the bias angle of the cascaded modulator is specifically designed, the XMDs, both from the photonic link itself and from the nonlinear electrical amplifiers, are well suppressed. Our proposal is theoretically analyzed, and the performance of the cascading system is experimentally demonstrated. A suppression ratio of more than 30 dB is achieved by the cascading scheme. By using the high-performance pre- and postamplifiers, the measured link gain and noise figure are improved by 62 and 32 dB, respectively.

Sol-Gel Material-Enabled Electro-Optic Polymer Modulators.

Sol-gels are an important material class, as they provide easy modification of material properties, good processability and are easy to synthesize. In general, an electro-optic (EO) modulator transforms an electrical signal into an optical signal. The incoming electrical signal is most commonly information encoded in a voltage change. This voltage change is then transformed into either a phase change or an intensity change in the light signal. The less voltage needed to drive the modulator and the lower the optical loss, the higher the link gain and, therefore, the better the performance of the modulator. In this review, we will show how sol-gels can be used to enhance the performance of electro-optic modulators by allowing for designs with low optical loss, increased poling efficiency and manipulation of the electric field used for driving the modulator. The optical loss is influenced by the propagation loss in the device, as well as the losses occurring during fiber coupling in and out of the device. In both cases, the use of sol-gel materials can be beneficial due to the wide range of available refractive indices and low optical attenuation. The influence of material properties and synthesis conditions on the device performance will be discussed.

The Capacity of Known Interference Channel

In this paper, we investigate the capacity of a known interference channel, where a transmitter sends information to a receiver in the presence of a block-fading interference link, and the receiver knows the interference data but not the channel gain of the interference link. An upper bound and a lower bound for the capacity of this known interference channel are derived. Specifically, the capacity lower bound is achieved by a blind known interference cancellation (BKIC) scheme, which can remove the interference without the knowledge of the interference channel gain. We further show that the achievable lower bound of BKIC can approach the upper bound in high SNR regime. Our results show that the lack of the knowledge of the channel gain of the interfering link causes only a small fractional loss of degrees of freedom (capacity prelog).

Direct Link-Aware Optimal Relay Selection and a Low Feedback Variant for Underlay CR

Cooperative relaying combined with selection has been extensively studied in the literature to improve the performance of interference-constrained secondary users in underlay cognitive radio (CR). We present a novel symbol error probability (SEP)-optimal amplify-and-forward relay selection rule for an average interference-constrained underlay CR system. A fundamental principle, which is unique to average interference-constrained underlay CR, that the proposed rule brings out is that the choice of the optimal relay is affected not just by the source-to-relay, relay-to-destination, and relay-to-primary receiver links, which are local to the relay, but also by the direct source-to-destination (SD) link, even though it is not local to any relay. We also propose a simpler, practically amenable variant of the optimal rule called the 1-bit rule, which requires just one bit of feedback about the SD link gain to the relays, and incurs a marginal performance loss relative to the optimal rule. We analyze its SEP and develop an insightful asymptotic SEP analysis. The proposed rules markedly outperform several ad hoc SD link-unaware rules proposed in the literature. They also generalize the interference-unconstrained and SD link-unaware optimal rules considered in the literature.

Dynamic range improvement in analog photonic link by intermodulation-compensation receiver.

In this paper, a novel intermodulation-compensation optical receiver based on the bias-modulated photo detector (PD) is proposed and demonstrated to eliminate the third-order intermodulation (IMD3) for the intensity-modulation direct-detection (IMDD) analog photonic link. We directly extract the key nonlinear distortion from the distorted optical intensity by a low-pass optical receiver, which is used to modulate the home-made, high-speed PD with bias modulation. Inside the high speed PD, the distorted radio frequency (RF) band is mixed with the above extracted baseband signal, and the IMD3 elimination can be achieved. Our proposal is theoretically analyzed, and the performance of the bias-modulated PD is experimentally demonstrated. Spurious-free dynamic range (SFDR) of 123.4 dB within 1-Hz bandwidth is obtained with 18.1 dB improvement. A low-biased Mach-Zehnder modulator (MZM) is used, keeping a simple transmitter with an improved link gain. The proposed post linearization requires no digital processing, avoiding the high quantization noise.

Compensation of the Dispersion-Induced Power Fading in an Analog Photonic Link Based on PM–IM Conversion in a Sagnac Loop

An analog photonic link with the compensation of the dispersion-induced power fading is proposed and demonstrated based on phase modulation to intensity modulation conversion in a Sagnac loop. Due to the velocity mismatch of the modulator, only the incident light wave along the clockwise direction is effectively modulated by the radio frequency signals, while the counterclockwise light wave is not modulated. After combining the two light waves in a polarizer, an intensity modulated optical signal is generated, which can be directly detected. In addition, the phase difference between the two light waves can be adjusted through the polarization controller before the polarizer. This feature is used to shift the frequency response of a dispersive link to compensate the dispersion-induced power fading at any working frequency. Experimental results show that the power fading after transmission over both 25 and 50 km lengths of fiber in a conventional intensity modulated link can be successfully compensated in the proposed link, and thus, a high and constant link gain over a large frequency range is achieved. The spur-free dynamic ranges of the link before and after fiber transmission are also measured.

Origin of link gain fluctuations in analog radio over single-mode fiber systems

In analog Radio over Fiber systems based on single mode fibers, the possible presence of unexpected fluctuating behaviors of the received radiofrequency signal in front of monotonic environmental temperature variations, is analyzed experimentally and simulated theoretically. The possibility to understand all the aspects of this behavior allows to keep it in the right account, particularly when these systems have to be realized with stringent requirements in terms of cost and performance.

Linearization of an analog photonic link based on chirp modulation and fiber dispersion

A simple and new method to linearize an analog photonic link is proposed and demonstrated. A dual-electrode Mach–Zehnder modulator is single-electrode driven by a radio frequency (RF) signal, with the other electrode left empty, to achieve a chirp modulation. Then a dispersive single mode fiber (SMF) is followed to introduce different phase shifts on different optical sidebands. By properly selecting the working point of the modulator and the fiber length, the third-order intermodulation distortion can be suppressed. Experimental results show that an improvement of 15.7 dB in the spurious-free dynamic range and 4.5 dB in the link gain is achieved after linearization. The scheme is simple, low cost, and the low-loss SMF can also act as a transmission medium to deliver the RF signal efficiently to a remote location.

Noise performance of high-speed radio over fiber links employing vertical-cavity surface-emitting lasers

This study investigates the intensity noise in high-speed vertical-cavity surface-emitting lasers (VCSELs) and its contribution to the noise performance of radio over fiber (RoF) links. We evaluate the sinusoidal modulation of VCSELs in terms of the second-order harmonic distortion (2HD) and third-order intermodulation distortion (IMD3) in additions to the relative intensity noise (RIN). The spurious-free dynamic range of the proposed VCSEL is estimated. The noise performance of the RoF link is assessed by the noise figure. The modulation characteristics of the VCSEL and the gain and noise factor (NF) of the fiber link are compared under conventional and high-speed modulations of VCSELs. Also, we present comparison of the NF between short (300 m) and relatively long (2 km) fibers.

High-Power Photodiodes for Analog Applications

High-power, high-speed photodiodes are being used in an increasing number of applications including fiber optic antenna links, radio frequency (RF) over fiber, and photonic generation of low phase noise microwave signals. The fact that the photodiode (PD) can be operated at high photocurrent levels provides several improvements in these systems including high dynamic range, high link gain, and low noise figure. In photonic wireless systems an antenna integrated photodiode can help to increase radiated RF power without the need for electronic amplification and hence simplify the RF circuitry at the antenna unit. To achieve high RF output power, various photodiode structures have been developed [1]–[4] among which the uni-traveling carrier (UTC) photodiode [3] has demonstrated high saturation current and high bandwidth. We have developed charge-compensated modified uni-traveling carrier (MUTC) photodiodes flip-chip bonded on high-thermal conductivity substrates to address the two primary effects that limit the RF output power of photodiodes, space-charge and thermal.

Continuous-time Hopfield neural network-based optimized solution to 2-channel allocation problem

The channel allocation problem in cellular radio systems is NP-complete, and thus its general solution is not known for even the 2-channel case. It is well known that the link gain system matrix (or received-signal power system matrix) of the radio network is (and may be highly) asymmetric, and that as the Hopfield neural network is applied to optimization problems, its weight matrix should be symmetric. The main contribution of this paper is as follows: turning the channel allocation problem into a maxCut graph partitioning problem, we propose a simple and effective continuous-time Hopfield neural network-based solution by determining its symmetric weight matrix from the asymmetric received-signal-power-system matrix. Computer simulations confirm the effectiveness and superiority of the proposed solution as compared to standard algorithms for various illustrative cellular radio scenarios for the 2-channel case.