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Experiments of premixed syngas/air explosion inside parallel narrow channels were conducted. The flame propagation, explosion pressure and temperature inside the narrow channel are investigated to find out the effect of narrow channel spacing on the explosion. The experimental results show that the narrow channel spacing has an influence on the flame before and inside the parallel narrow channels. The flame inside the narrow channels accelerates and reaches a peak value at the middle or rear of the channel. The flame front velocity, the maximum explosion Pmax and the maximum explosion flame temperature Tmax decrease as the channel spacing decreases. The channel wall has an effect of heat dissipation on the flame, resulting in the explosion inside the channel weakening. The explosion pressure in rear of the narrow channel is larger than that in the front of the narrow channel. [ABSTRACT FROM AUTHOR]

Next generation optical networks require high spectral efficiency to meet the demand of high bandwidth for ultra-long haul communication. Spectrally efficient modulations using hybrid DWDM-OTDM systems can be used to achieve this. However, fiber nonlinearities such as four-wave mixing (FWM) will increase simultaneously and this will degrade the performance of WDM optical system. This paper explores the FWM reduction in 32 channels, 40 Gb/s hybrid DWDMOTDM network using RZ-OOK, 16-QAM and PDM-QPSK modulation format at 200 GHz and 100 GHz channel spacing. Optical received power, BER, Q- factor, eye diagram and FWM side band power are analyzed at -15dBm to +15dBm channel power. All these modulations have shown a significant reduction in FWM. In addition, the 16-QAM gives highest reduction in FWM along with least BER of 7.9 × 10-158 and maximum Q-value of 27.74. [ABSTRACT FROM AUTHOR]

Performance of 500 x 10 Gbps super dense Bi-directional Line Switched Ring (SD-BLSR) has been analyzed with channel spacing of 25 GHz. For the first time, best of our knowledge, acceptable rating has recorded at -25 dBm input power and data rate of 30 Gbps with the help of RAMAN-EDFA hybrid optical amplifier (HOA) without using any dispersion compensation and cost effective techniques. Final outcome has also declared to control the channel traffic for present optical communication. [ABSTRACT FROM AUTHOR]

Abstract Fiber Raman Amplifier (FRA) is a fundamental amplifier that has the capability to operate in any communication band. No exceptional doping in the optical fiber is required in order to generate amplification using Raman scattering. In present work, we have investigated the gain spectrum evolutions of a dual/triple pumped FRA for 0.8 nm, 0.4 nm and 0.2 nm channel spacings by varying number of pumps, operating pump wavelengths and their respective pump powers. It has been observed in the case of triple pumped FRA that deployment of three continuous wave (CW) lasers at 1390 nm, 1410 nm and 1440 nm wavelengths yields enhanced gain >15 dB in the region 1489.4 nm–1578.20 nm (88.8 nm) at 0.2 nm channel spacing. [ABSTRACT FROM AUTHOR]

The ever increasing heterogeneity and growing traffic volume has resulted in significant innovations and paradigm shifts within the telecom backbone networks. In order to cost-effectively respond to the diverse variety of traffic requirements having heterogeneous service demands, wavelength division multiplexed (WDM) optical networks have adopted the mixed line rate (MLR) strategy. In MLR networks, many wavelength channels with various line rates can co-exist within the same fiber which, however, raises many important design issues; one of them being the choice of the channel spacing. The quality of signal is affected by the channel spacing in terms of the bit-error rate (BER), which in turn affects the maximum optical reach of the lightpaths that depends on the line rates. In regard to the aforementioned, different methods can be adopted in order to set the width of the channel spacing, viz., (a) choice of a 50 GHz uniform fixed channel spacing specified by the ITU-T grid, (b) exploring various channel spacing values for different line rates so as to optimize the usage of the fiber spectrum, or (c) seek for an optimal value of the channel spacing which results in the minimum network cost. In the current work, we evaluate the MLR network cost for various channel spacings; hence, we find an optimal value of the channel spacing that leads to the minimum MLR network cost. The simulation results reveal that, for a MLR network, even with the assumption of uniform channel spacing, optimal values of the channel spacing for a minimum cost network can be identified. [ABSTRACT FROM AUTHOR]

The ever increasing requirements in wireless communications have led to the search for unexploited correlations that could improve channel estimation and tracking. Kalman filtering (KF) has been proposed to exploit several such correlations, e.g., the time correlation in each tap in a multipath channel. When making full use of this correlation, however, a capital disadvantage of KF is its weak performance in the face of a significant, occasional nonlinearity, such as the potential birth of a new tap in a multipath channel or an active tap's death. These nonlinearities are typical for vehicular applications. So far, solutions proposed to this birth-death nonlinearity problem have been shown to be computationally prohibitive. In this paper, a simplified detection framework is introduced and a computationally inexpensive simplified maximum a posteriori estimator is derived. Under low to medium SNR conditions, simulations show the channel tracking error can be approximately halved (versus simple KF) by this novel estimator in orthogonal frequency division multiplexing systems. [ABSTRACT FROM AUTHOR]

We consider a low earth orbit (LEO) mobile satellite system with “satellite-fixed” cells that accommodates new and handover calls of different service-classes. We provide an analytical framework for the efficient calculation of call blocking and handover failure probabilities under two channel sharing policies, namely the fixed channel reservation and the threshold call admission policies. Simulation results verify the accuracy of the proposed formulas. Furthermore, we discuss the applicability of the policies in software-defined LEO satellites. [ABSTRACT FROM AUTHOR]

A dispersion compensation scheme using the minimum number of cascaded fibre Bragg gratings (FBGs) is proposed for the transmission of 20 Gbps signal in 24 Wavelength Division Multiplexed (WDM) channels with a 0.4 nm channel spacing. The present work shows that four chirped FBGs (CFBGs) in cascade are sufficient to compensate the dispersion accumulated over 100 km of conventional fibre. The parameters of the CFBGs are optimized to obtain maximum quality factor for all the channels. The proposed setup is effective for simultaneous dispersion compensation in a WDM transmission system. [ABSTRACT FROM AUTHOR]

Motivated by communication channels in which the transmitted sequences are subjected to random permutations, as well as by certain DNA storage systems, we study the error control problem in settings where the information is stored/transmitted in the form of multisets of symbols from a given finite alphabet. A general channel model is assumed in which the transmitted multisets are potentially impaired by insertions, deletions, substitutions, and erasures of symbols. Several constructions of error-correcting codes for this channel are described, and bounds on the size of optimal codes correcting any given number of errors are derived. The construction based on the notion of Sidon sets in finite Abelian groups is shown to be optimal, in the sense of the asymptotic scaling of code redundancy, for any error radius and alphabet size. It is also shown to be optimal in the stronger sense of maximal code cardinality in various cases. [ABSTRACT FROM AUTHOR]

In this article, the channel hopping (CH) method for the rendezvous process of secondary users in multi-channel CRAHNs is overviewed. With the evolution of the Internet of Things, design criteria of CH sequences targeting these applications are discussed. While channel collision among CH sequences is inherent in realistic CRAHNs, most prior works focused on sequence designs without addressing the channel collision problem. Hence, the concept of contention resolution in CRAHNs is introduced in this article, and a "multi-round" contention resolution mechanism is studied. To quantify the performance, the RS rate of the mechanism is presented and validated with computer simulation. Finally, the rendezvous time savings, which, in turn, can enhance data throughput, of the multi-round mechanism over a single-round one are investigated. [ABSTRACT FROM AUTHOR]

In this paper, simulative analysis and performance comparison of different EDFA (Erbium-doped fiber amplifier) configurations in a 10 Gbps inter-satellite optical wireless communication (IsOWC) link have been reported for a 5,000 km long link and 1,550 nm operating wavelength. The results show that system in which both pre-amplifier and booster amplifier stages are implemented simultaneously outperforms systems with only pre-amplifier and booster amplifier stage. From the results, it can be seen that by deploying a transmission power level of 15 dBm, a link distance of 9,600 km can be achieved with a quality factor of 6.01 dB and BER (Bit error rate) of 1.07 × 10 − 9 $$1.07 \times {10^{- 9}}$$. Also, in this paper, the performance of an 8×7 Gbps WDM-IsOWC link has been reported. The results show that by using both EDFA pre-amplifier and booster amplifier stages, a link distance of 8,000 km for each channel is achievable with desired performance levels (Q≥6 and BER≤ 10 − 9 $${10^{- 9}}$$ ). Also, the effect of channel spacing on the performance of WDM-IsOWC link is investigated. The results show that the received signal has acceptable performance levels when the channel spacing is 100 GHz but when the channel spacing is reduced to 80 GHz, the quality of the received signal degrades and link distance decreases. [ABSTRACT FROM AUTHOR]

In this paper, we provide joint subcarrier assignment and power allocation schemes for quality-of-service-constrained energy-efficiency (EE) optimization in the downlink of an orthogonal frequency division multiple access based two-tier heterogeneous cellular network. Considering underlay transmission, where spectrum efficiency (SE) is fully exploited, the EE solution involves tackling a complex mixed-combinatorial and nonconvex optimization problem. With appropriate decomposition of the original problem and leveraging on the quasi-concavity of the EE function, we propose a dual-layer resource allocation approach and provide a complete solution using difference of two concave functions approximation, successive convex approximation, and gradient-search method. On the other hand, the inherent intertier interference from spectrum underlay access may degrade EE particularly under dense small-cell deployment and large bandwidth utilization. Therefore, we develop a novel resource allocation approach based on the concepts of spectrum overlay access and resource efficiency (RE) (normalized EE–SE tradeoff). Specifically, the optimization procedure is separated where the macro-cell optimal RE and the corresponding bandwidth is first determined, then the EE of small cells utilizing the remaining spectrum is maximized. Simulation results confirm the theoretical findings and demonstrate that the proposed resource allocation schemes can approach the optimal EE with each strategy being superior under certain system settings. [ABSTRACT FROM AUTHOR]

In this paper, a user selection problem for multiuser multiple-input multiple-output systems in the general wireless environment with full-rank and rank-deficient channel users is investigated. It is demonstrated that the maximum number of simultaneously supportable users is elastic, and the spatial resources occupied by each user can be squeezed in the rank-deficient environment. Therefore, a user selection algorithm is then proposed with relatively low computational overhead. The data rate requirement distinctions of different services are considered in the user selection criterion, and the resources occupied by real-time service users are primarily squeezed since they do not need extremely high data rate. Numerical results show that the effective throughput and the number of selected users achieved by the proposed user selection algorithm are larger than that of exiting researches. [ABSTRACT FROM AUTHOR]

Massive MIMO is a promising next-generation wireless access technology. By flexibly assigning different numbers of antennas among connections, the transmission rate can be adjusted according to user requirement and channel conditions. However, providing scalable-video-encoded (SVC) multimedia streams with such a technology is challenging because this cross-layer issue involves each user's allocated antennas as well as the assigned layers. In this paper, we propose a cross-layer scheme called Utility-Based Layer and Antenna Allocation (UB-LAA). Given each base station's available antennas and each user's channel conditions as well as their subscribed SVC stream, UB-LAA decides each layer's serving base station and transmitting antennas to maximize the system's total utility. Through analysis, we prove that this allocation problem is NP-complete, and our polynomial-time heuristic provides a bounded performance difference to the optimum solution. Simulation results indicated that, under various circumstances, UB-LAA flexibly allocates resources to reflect user requirements and channel conditions, and has a performance that is approximate to the optimal solution. [ABSTRACT FROM AUTHOR]

A secondary relay is used to assist bidirectional communication between two primary nodes, and thus, is allowed to use part of the licensed spectrums to transmit its own messages. All involved links are orthogonal-frequency-division-multiplexing-modulated into multiple subcarriers, and the secondary relay is full-duplex capable such that it can receive and transmit signals within the same frequency band. In the first time slot, the two primary nodes transmit to the secondary relay over the same subset of subcarriers, and meanwhile, the secondary relay transmits its own messages over the remaining subcarriers; in the second time slot, the secondary relay broadcasts the superimposed primary signals over possibly another subset of subcarriers and continues transmitting the secondary messages over the remaining subcarriers. We aim to maximize the secondary data rate while satisfying the requirements of the two primary nodes, and formulate a resource allocation problem that tackles spectrum partition, subcarrier pairing, and power allocation jointly. An asymptotically optimal solution is developed with polynomial complexity; in particular, a variant version of the classic Hungarian method is proposed to solve spectrum partition and subcarrier pairing jointly. We further show that the proposed Hungarian-variant method can solve a generalized class of “partition-and-pairing” problems efficiently. [ABSTRACT FROM AUTHOR]

Recent years have seen the development of a satellite communication system called a high-throughput satellite (HTS), which enables large-capacity communication to cope with various communication demands. Current HTSs have a fixed allocation of communication resources and cannot flexibly change this allocation during operation. Thus, effectively allocating communication resources for communication demands with a bias is not possible. Therefore, technology is being developed to add flexibility to satellite communication systems, but there is no system analysis model available to quantitatively evaluate the flexibility performance. In this study, we constructed a system analysis model to quantitatively evaluate the flexibility of a satellite communication system and used it to analyze a satellite communication system equipped with a digital channelizer. [ABSTRACT FROM AUTHOR]

High bandwidth, low cost and small size has made Inter satellite optical wireless communication a promising and advance technology with an alternative to current microwave satellite systems. In this paper, advantages of coherent-detection quadrature phase shift keying (CO-QPSK) with DSP are investigated for the mitigation of non-linear effects. The technique of carrier phase estimation has been used to prolong the transmission range to several thousand kilometers. Further, 400 Gbps WDM-QPSK system has been analyzed for different distances with 30 dB transmitting power and 11 dB LO power. At last, system has been investigated at narrow channel spacing of 50 GHz and a brief comparison has been made with system having channel spacing of 100 GHz. [ABSTRACT FROM AUTHOR]

In this paper, we consider beam-domain full-duplex (FD) transmission in massive multiple-input multiple-output (MIMO) system. By exploiting the channel spatial sparsity, massive MIMO channel is compressed in the beam-domain under certain selected basis spaces and as a result the channel dimension required to be estimated can be greatly reduced. According to the distribution of effective beams of uplink/downlink channel and self-interference (SI) channel, all the users are scheduled into several uplink and downlink groups. With the estimated effective beam-domain channel, we design the uplink and downlink beamforming matrices at the base station to suppress the SI, inter-user interference and inter-group interference. The achievable sum-rate of the proposed beam-domain FD massive MIMO transmission scheme is analyzed and the joint user and BS power allocation scheme is proposed to optimize the system achievable sum-rate. Simulation results show that the proposed beam-domain FD transmission scheme outperforms existing time division duplex (TDD) and frequency division duplex (FDD) massive MIMO and FD massive MIMO transmissions schemes on the spectral efficiency performance. [ABSTRACT FROM AUTHOR]

In this work, a multi-wavelength fiber laser with a channel spacing of 0.17 nm operating in the S-band region is proposed and demonstrated. The proposed laser exploits the stimulated Brillouin scattering (SBS) effect to generate the desired output using a 6.9 km long dispersion shifted fiber. A Thulium-Fluoride fiber (TFF) pumped at 1400 nm enables gain and operation in the S-band region. With a Brillouin pump (BP) wavelength of 1503.6 nm and power of 12 dBm, up to 3 well defined even Stokes lines are obtained at the maximum pump power of 250 mW. Furthermore, more even Stokes lines and anti-Stokes lines are also observed at the afore-mentioned setting, although they are less well defined as the first 3 even Stokes. The laser has an operating range of 1470–1515 nm, with tunability enabled by changing the BP wavelength. Furthermore, the spacing between the lasing wavelengths can be switched from 0.17 nm to 0.08 nm by adjusting the integrated air gap in the laser cavity, making the proposed laser highly suitable for applications such as communications and sensing. This is, the first time to the author's knowledge that such a system has been demonstrated. [ABSTRACT FROM AUTHOR]

We experimentally demonstrate 4 lanes of 416-Gb/s discrete multi-tone (DMT) transmission with 50-GHz channel spacing. This is the first demonstration of 4 × 100 G transmission with less than 100-GHz channel spacing and it can be compatible with dense wavelength division multiplexing (DWDM). [ABSTRACT FROM AUTHOR]

In magnetic induction communication systems, channel capacity is often a major bottleneck that limits the system performance. This paper proposes a method to increase the channel capacity in such systems by means of an antenna array. A central challenge in the design of magnetic antenna arrays is to achieve low intra-array coupling along with high gain. These two properties are essential for increasing the channel capacity in comparison to single antenna communication systems of comparable volume. The method proposed in this paper utilizes circular loop antennas to reduce the intra-array coupling using magnetic flux cancellation. The mathematic approach employed in this paper considers each coil as a system of coupled inductors, where each inductor is a single turn loop, and the total coil self and mutual inductances are computed by summing the appropriate single turn loop inductances. Volume efficient coil topologies are identified, and an optimization method is proposed to minimize the intra-array coupling, subject to a required inductance. The proposed method allows to design volume efficient, up to 3 × 3, array, or pyramidal shaped 4 × 4 arrays. The results are verified experimentally using the multiple-frequency communication mode. [ABSTRACT FROM AUTHOR]

This paper presents a novel configuration of channel drop filters based on two-dimensional photonic crystal slabs in silicon-on-insulator platforms. The structure is composed of two photonic crystal line-defect waveguides as input and output ports, along with an L3 cavity with ring-shaped border holes. The effects of structural parameters and fabrication errors on resonance frequency and drop efficiency are investigated. Band structure and propagation of electromagnetic field through device are calculated by plane wave expansion and finite-difference time-domain methods. The results show that the quality factor and line-width of output signal are ~5690 and 0.27 nm, respectively, indicating that the proposed filter can be properly used in dense wavelength division multiplexing systems with 0.8 nm channel spacing. [ABSTRACT FROM AUTHOR]

In this paper, we investigate the interference alignment (IA) for a class of partially connected multi-input multi-output heterogeneous networks, which consist of $L$ fully connected pico cells, $J$ partially connected pico cells, and one macro cell. In particular, we investigate the feasibility of IA conditions with no channel extensions, $T$ -independent channel extensions, and $T$ -dependent channel extensions, respectively, for the single beam case. We present three theorems to characterize some necessary conditions, which $L$ , $J$ , $T$ , and the channel diversity order $\overline L$ must jointly satisfy when IA conditions are feasible. These necessary conditions also implicitly impose the constraints on the upper bounds of achievable degrees of freedom with different channel extensions. [ABSTRACT FROM PUBLISHER]

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We experimentally provide an alternative solution to channel collisions through up-wavelength conversion and switching by using vertical cavity surface-emitting lasers (VCSELs). This has been achieved by utilizing purely optical wavelength conversion on VCSELs at the low attenuation, 1550 nm transmission window. The corresponding transmission and bit error-rate (BER) performance evaluation is also presented. In this paper, two 1550 nm VCSELs with 50–150 GHz channel spacing are modulated with a 10 Gb/s NRZ PRBS 2 7 -1 data and their interferences investigated. A channel interference penalty range of 0.15–1.63 dB is incurred for 150–50 GHz channel spacing without transmission. To avoid channel collisions and to minimize high interference penalties, the transmitting VCSEL with data is injected into the side-mode of a slave VCSEL to obtain a new up converted wavelength. A 16 dB extinction ratio of the incoming wavelength is achieved when a 15 dBm transmitting beam is injected into the side-mode of a −4.5 dBm slave VCSEL. At 8.5 Gb/s, a 1.1 dB conversion and a 0.5 dB transmission penalties are realized when the converted wavelength is transmitted over a 24.7 km G.655 fibre. This work offers a low-cost, effective wavelength conversion and channel switching to reduce channel collision probability by reconfiguring channels at the node of networks. [ABSTRACT FROM AUTHOR]

We derive independence tests by means of dependence measures thresholding in a semiparametric context. Precisely, the estimates of $\varphi$ -mutual informations, associated to $\varphi$ -divergences between a joint distribution and the product distribution of its marginals, are derived through the dual representation of $\varphi$ -divergences. The asymptotic properties of the proposed estimates are established, including consistency, asymptotic distributions, and large deviations principle. The obtained tests of independence are compared via their relative asymptotic Bahadur efficiency and numerical simulations. It follows that the proposed semiparametric mutual information test is the optimal one. On the other hand, the proposed approach provides a new method for estimating the mutual information in a semiparametric setting, as well as a model selection procedure in a large class of dependence models, including semiparametric copulas. [ABSTRACT FROM PUBLISHER]

We study the Ahslwede–Han problem of a point-to-point communication with partial state information available at the destination. For a class of channels, by establishing a tight converse, we show that the Wyner–Ziv compression of the channel state treating the destination’s channel output as side information is optimal. This result is more general than the modulo-sum channel studied by Aleksic et al. and the symmetric binary erasure channel with two states studied by Tandon and Ulukus. Thus, for this more general class of channels, we prove the Ahlswede–Han conjecture. [ABSTRACT FROM PUBLISHER]

In this paper, we solve the open problems raised in [8] and present some examples to illustrate the obtained results. Moreover, we work out the diophantine problem by Shi and Wang and then give the sufficient conditions for the nonexistence of two-Lee weight projective codes over \mathbb Z4 with type 4^k12^{k2} . [ABSTRACT FROM PUBLISHER]

We proposed a high performance eight channel demultiplexer using two-dimensional photonic crystal octagonal ring resonator for wavelength division multiplexing applications. The performance parameters such as transmission efficiency, Q factor, spectral width, resonant wavelength, crosstalk and channel spacing of the proposed demultiplexers are evaluated. The plane wave expansion method manipulates photonic band gap of periodic and non-periodic structure. Finite-difference time-domain method is used to evaluate the performance parameters of designed two-dimensional photonic crystal structure. The proposed demultiplexer provides overall transmission efficiency, Q factor, spectral width of about 98%, 1968 and 0.8 nm, respectively. The ultra-compact eight channel demultiplexer performs better than the reported one. Hence this work can be implemented for real time applications. [ABSTRACT FROM AUTHOR]

This paper investigated the performance of diverse optical amplifiers SOA, EDFA, Raman and hybrid amplifiers (SOA-EDFA, EDFA-EDFA, Raman-EDFA) at frequency spacing of 50 GHz in 8 × 10 Gbps WDM system. Examine the performance on the basis of output power, Q-factor, BER, and eye opening by varying distance from 20 to 200 km. It is found that SOA-EDFA provides maximum output power, acceptable Q-factor, maximum eye opening and lowest BER at a distance of 100 km. The impact of Raman fiber length on hybrid optical amplifier (Raman-EDFA) at 100 km transmission distance has been investigated and found that hybrid optical amplifier at 10 km Raman fiber length provides better output power and Q value. [ABSTRACT FROM AUTHOR]

The demand for higher speed at a lesser transmission cost per bit resulted in growth of optical networks with improved spectral efficiency even at narrower channel spacing. Incorporation of multilevel modulation formats in DWDM system led to the exploration of the 25 GHz channel grid, popularly known as Ultra Dense Wavelength Division Multiplexed (UDWDM) systems, opening new research frontiers. At such channel spacing's, nonlinear optical effects impose severe system impairments and hence robust modulation schemes are currently being investigated. This paper presents a simulative model to implement and analyze alternative polarized DQPSK modulated UDWDM system to evaluate its resilience to XPM and fiber nonlinearity. An UDWDM system supporting 32 channels, each operating at 40 Gbps and spaced at 25 GHz is studied numerically for long-haul optical communication system using OptiSystem simulator to estimate OSNR penalties to mitigate XPM effects. The major detrimental factors encountered in link design have been estimated to evaluate the system performance in terms of Q value for different number of channels and with varied input power. The analysis reports acceptable performance for DQPSK format up to a link distance of 1500 Km and also claims a better tolerance to dispersion and nonlinearities at higher input power levels. [ABSTRACT FROM AUTHOR]

The present work deals with the experimental study of effects of flow and channel spacings, Z 1 and Z 2 on the performance of a cross – flow staggered hole jet plate solar air heater. This work is carried out with mass flow rate, m ̇ 1 = 0.030–0.065 kg/s, m ̇ 2 = 0.020–0.043 kg/s, Reynolds number, Re = 2700–6900, depth ratio, Z 2 /Z 1 = 0.75–1.0, total air depth, Z = 0.14 m, jet hole diameter, D = 0.006 m, Number of jet holes, N = 1173 and tilt angle, θ = 22.6°. The experiment is performed during the month of November - December, 2013 at ISM Dhanbad, India between 9.00 AM to 3.00 PM on hourly basis in the clear sky with the help of precision instruments fitted with the setup for recording the temperature, velocity and intensity of radiation. The performance in terms of outlet temperature, collector efficiency and Nusselt no. of this solar air heater are found substantially higher at higher spacing between the jet and absorber plate (Z 2 = 0.07 m) while mass flow rate adversely affects the outlet temperature. In the present study, the non-conventional jet plate solar air heater is also compared with conventional parallel plate solar air heater and it is observed that the performance of the jet plate solar air heater is always higher than conventional solar air heater. Friction factor is not significantly changed with Z 2 . Based on the experimental data, the correlations for Nusselt number and friction factor have been developed. [ABSTRACT FROM AUTHOR]

Indoor millimeter wave propagation at the frequency of 24 GHz is studied by experimental methods. Measurements are performed to obtain temporal and spatial channel model using a channel sounder and rotating antennas in a corridor. The measured impulse responses are processed to obtain compact channel model following Saleh-Valenzuela’s model. The responses are compared with those of 5.3 GHz for the same test sites. Angular spread of 24 GHz is found to be smaller than that of 5.3 GHz, while echoes of 24 GHz are found to be longer than those of 5.3 GHz. [ABSTRACT FROM AUTHOR]

In this article, we have designed a four-channel Dense Wavelength Division Multiplexing demultiplexer through two-dimensional Photonic Crystal Square Resonant Cavity to fulfill the ITU-T G.694.1 DWDM systems. The DWDM demultiplexer consists of a Bus/Drop waveguide and Microscopic Square Resonant (MSR) cavity. The MSR cavity design has outer rods, inner rods and coupling rods. As the radius of the inner rods in MSR cavity changes, the cavity has the capability to drop different ITU-T G.6941 standard central wavelengths like 1556.5 nm, 1556.7 nm, 1556.9 nm, and 1557.1 nm with 0.2 nm / 25 GHz channel spacing. Since the simulation of various wavelengths help realization of the Q factor of 7785, uniform spectral Bandwidth of 0.2 nm, the transmission efficiency of 100%, the Crosstalk of -42 dB and the small footprint is about 395 µm². [ABSTRACT FROM AUTHOR]

Free Space Optical (FSO) communication is being realized as an effective solution for future accessing networks, offering light passed through air. The performance of FSO system can be primarily degraded by various atmospheric attenuations such as rain, fog, haze and snow. At present, hybridization of Dense Wavelength Division Multiplexing (DWDM) with Coarse Wavelength Division Multiplexing (CWDM) becomes necessary to scale the speed and high bandwidth of the services. In this paper, primarily the attenuation values for different weather conditions are calculated. Then the hybrid WDM-FSO system is proposed, designed and the network parameters such as Bit Error Rate (BER), Quality factor (Q factor) and receiver sensitivity are analyzed with respect to link distance for various weather conditions. For investigation, four CWDM (1,510 nm, 1,530 nm, 1,570 nm and 1,570 nm) channel and eight DWDM channels (1,537.4 nm, 1,538.2 nm, 1,539 nm, 1,539.8 nm, 1,540.6 nm, 1,541.4 nm, 1,542.2 nm and 1,543 nm) are considered whose corresponding channel spacing is 20 nm and 0.8 nm, respectively. In addition, the Erbium Doped Fiber Amplifier (EDFA) is inserted at the receiver end in order to enhance the link distance. The proposed hybrid WDM-FSO system is designed to handle the quality of transmission for 12 users, each at a data rate of 2.5 Gbps along an FSO link distance of about 960 km. [ABSTRACT FROM AUTHOR]

Cartilage tissue engineering is a promising approach to treat osteoarthritis. However, current techniques produce tissues too small for clinical relevance. Increasingly close-packed channels have helped overcome nutrient transport limitations in centimeter-sized chondrocyte-agarose constructs, yet optimal channel spacings to recapitulate native cartilage compositional and mechanical properties in constructs this large have not been identified. Transient active TGF-β treatment consistently reproduces native compressive Young׳s modulus ( E Y ) and glycosaminoglycan (GAG) content in constructs, but standard dosages of 10 ng/mL exacerbate matrix heterogeneity. To ultimately produce articular layer-sized constructs, we must first optimize channel spacing and investigate the role of TGF-β in the utility of channels. We cultured ∅10 mm constructs with 0, 12, 19, or 27 nutrient channels (∅1 mm) for 6–8 weeks with 0, 1, or 10 ng/mL TGF-β; subsequently we analyzed them mechanically, biochemically, and histologically. Constructs with 12 or 19 channels grew the most favorably, reaching E Y =344±113 kPa and GAG and collagen contents of 10.8±1.2% and 2.2±0.2% of construct wet weight, respectively. Constructs with 27 channels had significantly less deposited GAG than other groups. Channeled constructs given 1 or 10 ng/mL TGF-β developed similar properties. Without TGF-β, constructs with 0 or 12 channels exhibited properties that were indistinguishable, and lower than TGF-β-supplemented constructs. Taken together, these results emphasize that nutrient channels are effective only in the presence of TGF-β, and indicate that spacings equivalent to 12 channels in ∅10 mm constructs can be employed in articular-layer-sized constructs with reduced dosages of TGF-β. [ABSTRACT FROM AUTHOR]

This paper investigates the scenario in which a weak desired signal reaches a poorly selective receiver along with a high-powered pulsed radar occupying a neighboring channel. Traditionally, an automatic gain control (AGC) is used to fit the high-powered radar into the dynamic range of the receiver. However, this approach desensitizes the receiver because it also sacrifices the signal-to-noise ratio (SNR) of the desired signal. We propose the use of an auxiliary receive path to address this problem of strong neighboring channel signals. In this method, receiver gain is not lowered to avoid clipping. Instead, the strong signal is allowed to clip and distort the desired signal. This paper shows that only a subset of the symbols contained in the desired signal will be distorted; hence, redundancy within the desired signal (due to forward error correction) can be exploited to “fill the gaps” created by the distortion. The auxiliary path samples the envelope of the strong neighboring-channel signal and informs the decoder about which symbols are distorted (or “bad”) and which symbols are not distorted (or “good”). This additional information is shown to improve the estimation performance of the decoder in the presence of high-powered neighboring-channel radar. Using simulation and hardware-based experiments, it is shown that auxiliary-path-based receivers can obtain a significantly better throughput performance than AGC-based receivers. [ABSTRACT FROM AUTHOR]

To efficiently trade off system sum-rate and link fairness, this paper is dedicated to maximizing the sum of \alpha-fair utility in spectrum-sharing networks, where multiple interfering links share one channel. In the literature, three special cases, including \alpha=\mbox{0} (sum-rate maximization), \alpha=\mbox{1} (proportional fairness), and \alpha=\infty (max-min fairness), have been investigated; the complexity for cases \mbox{1} < \alpha < \infty and \mbox{0} < \alpha < \mbox{1} is still unknown. In this paper, we prove that the problem is convex when \mbox1 < \alpha < \infty and is NP-hard when \mbox0 < \alpha < \mbox1. To deal with the latter case, we transform the objective function and represent it by the difference of two concave functions (D.C.). Then, a power allocation algorithm is proposed with fast convergence to a local optimal point. Simulation results show that the proposed algorithm can obtain global optimality in two-link cases when \mbox0 < \alpha < \mbox1. In addition, we can get a flexible tradeoff between sum-rate and fairness in terms of Jain's index by adjusting $\alpha$. [ABSTRACT FROM AUTHOR]

This paper discusses over-the-air (OTA) testing for multiple-input–multiple-output (MIMO) capable terminals with emphasis on wideband MIMO channel capacity analysis in a multiprobe anechoic chamber setup. In the literature, the spatial correlation simulation accuracy at the receiver (Rx) side has been used to determine the test area size for a limited number of probes. However, it is desirable that the test area size is defined in terms of data rate deviation of the simulated channel in the laboratory from that of the target channel model. This paper reports MIMO capacity analysis results for wideband spatiotemporal channel models, with emphasis on the impact of the spatial correlation at the transmit (Tx) side, the channel model, and the spatial correlation at the Rx side on the capacity simulation accuracy. Simulation results show that the number of probes is irrelevant to capacity simulation accuracy when the spatial correlation at the Tx side is in the high region (e.g., \rho > \mbox0.7). Furthermore, when correlation at the Tx side is low, the spatial correlation accuracy is less critical with small correlation at the Rx side. The simulation results are further supported by measurements in a practical multiprobe anechoic chamber setup. The capacity simulation accuracy is shown to be a valid measure to determine the test area size. [ABSTRACT FROM AUTHOR]

In this paper, a novel maximized channel capacity based power allocation using differential evolution (DE) algorithm for multi relay Hybrid Decode-Amplify-Forward cooperative network in a Rayleigh fading environment is proposed. The closed form expression for average channel capacity with the tight approximation is derived. The proposed parametric optimization problem is defined on basis of the decoding capability of the relay. Further, the relay powers are optimized using the optimized power allocation factor. The performance of the proposed technique is validated for different channel variances and for different relay locations. From the simulation analysis, it is observed that the proposed DE based power allocation scheme performs better than the existing equal power allocation scheme. [ABSTRACT FROM AUTHOR]

We demonstrate improved performance of parametric amplifier cascaded with Raman amplifier for gain of 54.79 dB. We report amplification of L-band using 100 × 10 Gbps Dense Wavelength Division Multiplexed (DWDM) system with 25 GHz channel spacing. The gain achieved is the highest reported so far with gain flatness of 3.38 dB without using any gain flattening technique. Hybrid modulated parametric pump is used for suppressing four-wave mixing (FWM) around pump region, resulting in improvement of gain flatness by 2.42 dB. The peak to peak variation of gain is achieved less than 1.6 dB. DWDM system with 16-channel, 25 GHz spaced system has been analyzed thoroughly with hybrid modulated parametric pump amplified Raman-FOPA amplifier for gain flatness and improved performance in terms of BER and Q-factor. [ABSTRACT FROM AUTHOR]

We consider a new formulation of a class of synchronization error channels and derive analytical bounds and numerical estimates for the capacity of these channels. For the binary channel with only deletions, we obtain an expression for the symmetric information rate in terms of subsequence weights, which reduces to a tight lower bound for small deletion probabilities. We are also able to exactly characterize the Markov-1 rate for the binary channel with only replications. For a channel that introduces deletions as well as replications of input symbols, we design approximating channels that parameterize the state space and show that the information rates of these approximate channels approach that of the deletion–replication channel as the state space grows. For the case of the channel where deletions and replications occur with the same probabilities, a stronger result in the convergence of mutual information rates is shown. The numerous advantages this new formulation presents are explored. [ABSTRACT FROM AUTHOR]

The paper analyzes the four wave mixing (FWM) effect in different spectral efficient orthognal modulation formats at equal channel spacing of 100 GHz and 50 GHz to design long haul wavelength division multiplexing (WDM) optical system. Further, the comparison of reduction of FWM for existing and proposed modulation format have been analyzed by varying the laser input power from −10 dBm to 10 dBm. [ABSTRACT FROM AUTHOR]

It is urgent to solve the contradiction between limited spectrum resources and the increasing demand from the ever-growing wireless networks. Spectrum redistribution is a powerful way to mitigate the situation of spectrum scarcity.In contrast to existing mechanisms for spectrum redistribution, which aim to maximize the spectrum utilization and social welfare, we propose DIARY in this paper, which not only achieves approximate revenue maximization, but also guarantees bid privacy via differential privacy. Furthermore, we present an effective method to address the fairness issue in spectrum auctions. Results from extensive evaluations show that DIARY has substantial competitive advantages over existing mechanisms. [ABSTRACT FROM AUTHOR]

Evaluating the channel capacity is one of many key problems in information theory. In this work, we derive rather-mild sufficient conditions under which the capacity of continuous channels is finite and achievable. These conditions are derived for generic, memoryless, and possibly nonlinear additive noise channels. The results are based on a novel sufficient condition that guarantees the convergence of differential entropies under point-wise convergence of probability density functions. Perhaps surprisingly, the finiteness of channel capacity holds for the majority of setups, including those where inputs and outputs have possibly infinite second-moments. [ABSTRACT FROM AUTHOR]

Nonlinearities implanted by refractive index and scattering degrade the performance of optical networks. In this paper, FWM (Four Wave Mixing) has been analyzed for four different channels with 10 nm spacing. Due to the presence of resonant frequency, FWM interface of different channels in WDM (Wavelength Division Multiplexing) hinders the performance of the system. The system is affected by nonlinear cross talk. A system with the bandwidth of 10 Gbps has been investigated using External Modulation and an optical rectangle filter as a key parameter to improve the system performance with respect to FWM effect. [ABSTRACT FROM AUTHOR]

InP-based 4-channel AWGs for Coarse Wavelength Division Multiplexing (CWDM) with channel spacing of 20 nm and Local Area Network (LAN) WDM with channel spacing of 800 GHz are designed and fabricated. The deep-ridge waveguide is used to make the chip compact, chip size of AWG for CWDM is 0.55×3.9 mm 2 and for LAN WDM is 1.6×3 mm 2 . The measured results indicate that, the insertion losses are −5 dB and −7 dB, crosstalk levels are below −25 dB and −24 dB for AWG with 20 nm channel spacing and 800 GHz channel spacing, respectively. These AWGs can be integrated with lasers and detectors array monolithically for data center applications. [ABSTRACT FROM AUTHOR]

A broad-range tunable all optical wavelength conversion scheme that is based on a dual driven Mach-Zehnder modulator with an integrated microwave generator to tune the channel spacing along the entire C band, is proposed. Successful signal demodulation up to 8 wavelength conversions, in steps of 50-400 GHz of 100 Gbps Nyquist QPSK channels with configurable channel spacing is reported. The proposed wavelength conversion scheme enables flexible wavelength routing on gridless optical networks, as can be seen in the Superchannels with a BER lower than 10-13. [ABSTRACT FROM AUTHOR]

In cognitive radio network, the secondary users (SUs) perform cooperative spectrum sensing (CSS) to improve the sensing performance when the primary user (PU) is shadowed or in severe fading. However, the CSS may deplete some electric power including sensing power and cooperative power, thus yielding to decrease the transmission power. In this paper, a simultaneous CSS and wireless power transfer (WPT) is proposed by using a power splitter to split the received PU signal into a harvesting signal stream and a sensing signal stream. The sensing signal stream is used to perform CSS, while the radio frequency energy of the harvesting signal stream is converted into the electric power to supply the CSS simultaneously. A joint optimisation problem of sensing time, cooperative SUs and power splitting is formulated, which seeks to maximise the total spectrum access probability of the SU over all the subchannels, subject to the constraints of the detection probability, the harvested energy and the number of cooperative SUs. The simulation results have shown that the proposed simultaneous CSS and WPT can improve the transmission energy compared with the traditional CSS, and there is a trade-off between spectrum access and energy harvesting. [ABSTRACT FROM AUTHOR]

Spectrum utility efficiency is key in designing systems that can meet the heavier demands of bandwidth and data rate of future communication technologies. Shared spectrum techniques and collaborative protocols have thus been studied to better utilize already existing spectrum resources. In this paper, we present a spectrum trading approach that allows the licensed user's (LU) resources to be efficiently shared with the secondary user (SU) network in exchange for a monetary cost. The model is based on demand and supply economics, wherein the highest bidder for spectrum resource is awarded with transmission rights over licensed spectrum. The transmission opportunities for the SU consider every state of the licensed link, in the form of dynamic spectrum access (DSA), spectrum sharing, and relaying, each of which has an optimized cost that will maximize the returns for the LU. The numerical results backed by the analytical study show that this spectrum trading scheme allows for significant improvements in data rate and spectrum transmission opportunities than previous work conducted in either DSA or the spectrum sharing fields. [ABSTRACT FROM PUBLISHER]