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The fast and diversified development of Internet services leads to numerous services with differentiated delay tolerance of optical connections set-up are converging in the optical network. Consequently, the average set-up delay of optical connection is increased, which will inevitably bring pressures to optical networks. To solve this problem, a delay aware routing spectrum assignment (RSA) algorithm based on services scheduling in priority queues with dynamic virtual topology construction (QVT-RSA) is proposed. First, the QVT-RSA algorithm reasonably identifies various different services and arranges them in order according to their priority, waiting time and delay tolerance requirements. Then, software defined networks (SDN) controller with multi-threads technology is adopted to innovatively parallel serve the ordered service requests to reduce the average set-up delay of optical connections, which also offset the induced delay caused by services scheduling. The network resource is accurately shared among multi-threads using the proposed mutual exclusive resource utilization model realized by dynamic virtual topology construction. The continuously coloring and usable virtual topology linkage reconfiguration can provide topology resources for service requests and adapt the dynamic transformation among serving, waiting and new arriving service requests. The shortest-path routing and first fit spectrum assignment (SPFF-RSA) algorithm is used as the baseline algorithm. Furthermore, by combining the SPFF-RSA algorithm and partial strategy of our strategy, the QSPFF-RSA and V-RSA algorithms are proposed as baseline algorithms as described in V-B. The simulation experiment results demonstrate that the average optical connections set-up delay of QVT-RSA algorithm is reduced compared with SPFF-RSA and QSPFF-RSA algorithms, and the blocking probability of QVT-RSA algorithm is reduced compared with SPFF-RSA, QSPFF-RSA and VRSA algorithms. The optical connections set-up success probability within delay tolerance about high, medium and low priority services of QVT-RSA algorithm is higher than that of the SPFF-RSA, QSPFF-RSA and VRSA algorithms.

Physical layer authentication is an important way to ensure the security of optical communication network. We hereby propose a scheme to realize it by measuring the variation of the bit error rate (BER) on both sides of communication. In this scheme, the legitimacy of the receiver is identified by analyzing the BER variation of the optical fiber loop based on the short-term correlation of the channels. We then simulate a 16 PSK optical transmission system with intensity modulation direct detection-orthogonal frequency division multiplexing (IMDD-OFDM). The authentication effect is analyzed in the case of disturbance and beam split, as well as replacement of optical fiber channels caused by eavesdropper (Eve). The results show that this scheme is sensitive to the three kinds of attacks. A high probability of detection (PD) and a low false alarm rate (FAR) can be obtained. The experimental results show that with the increase of the frequency test, PD and FAR tend to be stable, and the authentication effect is better with the accuracy rate 100%.

This paper presents the two-channel controller with inner current loops for dual bridge, DC/DC converter, based on modular multilevel converter (MMC) technology. The DC/DC control strategy is based on two inner fast current control loops in dq rotating frame at each of the two MMC bridges. These current controls facilitate operation through dc faults at either dc bus. The active power control is shared by two MMCs, at the slower outer control level. The second outer control loop minimizes losses, which is achieved by feedback control of magnitude of both modulation indices at maximal value of 0.95 at all loading levels. The controller is symmetrical, provides bidirectional power flow and responds equally to faults on either dc bus. Under dc fault conditions, one MMC actively controls the inner ac current, while temporary blocking of MMC on faulted side is required to prevent cell capacitor discharge. The validity of the proposed control is verified on PSCAD using a 600 MW, 500-kV/640-kV test dc/dc model. The controller can be used for control/stability studies with large dc grids that contain dc/dc converters.

This paper presents a design method of broadband radar absorber (RA) combining together the features of frequency selective surfaces (FSSs), subwavelength hole array, and magnetic absorbing sheets. The absorber is constructed of a periodic array of square conducting patches embedded into a magnetic absorbing substrate perforated with circular hole arrays and backed by a metal ground. The absorption characteristics of the magnetic absorbing substrate are tuned and improved by means of perforating holes and embedding FSSs. After optimizing the dimensions of the holes and FSSs, the RA with a thickness of 2.4 mm achieves a reflection coefficient less than ${-}{\rm 10}~{\rm dB}$ from 6.3 to 17.3 GHz, which is nearly 3.6 times the bandwidth of the magnetic absorbing substrate. Meanwhile, the weight of the RA decreases by 15% due to the hole perforation, and the reflection coefficient is insensitive to incident angle from 0 $^{\circ}$ to 30 $^{\circ}$ for both TE and TM polarizations.

High impedance surface absorbers comprising of lossless dielectric substrate and resistive pattern were studied based on equivalent circuit method. Resonant conditions in terms of potential resonant frequencies and corresponding equivalent resistance were deduced. Theoretical calculation, numerical simulation and experiment showed that expected absorption was obtained by matching the capacitance, inductance and the resistance. We demonstrated that the optimal resistance of frequency-dispersive was between 0 and 377 Ω. For square, dipole and square ring pattern, a mean resistance value was required to achieve broadband absorption. It offered a way to create broadband and perfect absorbers by controlling the surface resistance of sub-wavelength structures.

A requirement of the three-level neutral-point-clamped voltage source inverter, with or without a separately supporting dc link, is to maintain the balance of the two dc-link capacitor voltages. In this paper, balancing of the capacitor voltages for these two dc-link voltage source possibilities is analyzed and an algorithm is proposed to independently balance the capacitor voltages. The algorithm considers the average energy effect of each vector on capacitor voltage and the necessary optimal vector state sequence in each modulation cycle. The algorithm minimizes the voltage rating overheads of the hardware, reduces the voltage ripple, and attenuates the negative effects associated with dc-link voltage oscillations.

In this letter, the design of an ultra-thin magnetic-type radar absorber (RA) having good absorbing performance at low frequency is demonstrated. A 2-mm-thick RA with an operating bandwidth of 1.5-2.2 GHz is obtained on the basis of polymer composites filled with carbonyl iron and Co2Z ferrite. The use of frequency selective surfaces (FSSs) results in a significant increase of operating bandwidth of the RA. By selecting the unit dimensions of FSS and its location in RA, a maximal operating bandwidth can be obtained. Experimental results are presented and compared to numerical simulations, and they demonstrated that the RA embedded with FSS has a significantly increased bandwidth of 1.19-2.89 and 1.08-3.02 GHz for the single-layer or double-layer case.