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With the rapid development of smart terminals and infrastructures, as well as diversified applications (e.g., virtual and augmented reality, remote surgery and holographic projection) with colorful requirements, current networks (e.g., 4G and upcoming 5G networks) may not be able to completely meet quickly rising traffic demands. Accordingly, efforts from both industry and academia have already been put to the research on 6G networks. Recently, artificial intelligence (AI) has been utilized as a new paradigm for the design and optimization of 6G networks with a high level of intelligence. Therefore, this article proposes an AI-enabled intelligent architecture for 6G networks to realize knowledge discovery, smart resource management, automatic network adjustment and intelligent service provisioning, where the architecture is divided into four layers: intelligent sensing layer, data mining and analytics layer, intelligent control layer and smart application layer. We then review and discuss the applications of AI techniques for 6G networks and elaborate how to employ the AI techniques to efficiently and effectively optimize the network performance, including AI-empowered mobile edge computing, intelligent mobility and handover management, and smart spectrum management. Moreover, we highlight important future research directions and potential solutions for AI-enabled intelligent 6G networks, including computation efficiency, algorithms robustness, hardware development and energy management., Comment: Published in: IEEE Network. https://doi.org/10.1109/MNET.011.2000195

Some of the work carried out within the EU Network of Excellence ISIS on radio-over-fiber systems for the support of current and emerging wireless networks is reviewed. Direct laser modulation and externally modulated links have been investigated, and demonstrations of single-mode fiber and multimode fiber systems are presented. The wireless networks studied range from personal area networks (such as ZigBee and ultrawideband) through wireless local area networks to wireless metropolitan area networks (WiMAX) and third-generation mobile communications systems. The performance of the radio-over-fiber transmission is referenced to the specifications of the relevant standard, protocol operation is verified, and complete network demonstrations are implemented.

Some of the work carried out within the EU Network of Excellence ISIS on radio-over-fiber systems for the support of current and emerging wireless networks is reviewed. Direct laser modulation and externally modulated links have been investigated, and demonstrations of single-mode fiber and multimode fiber systems are presented. The wireless networks studied range from personal area networks (such as ZigBee and ultrawideband) through wireless local area networks to wireless metropolitan area networks (WiMAX) and third-generation mobile communications systems. The performance of the radio-over-fiber transmission is referenced to the specifications of the relevant standard, protocol operation is verified, and complete network demonstrations are implemented.

An analysis of the AC characteristics of Al-GaAs/GaAs HEMT under illumination with modulated light has been carried out for small signal condition. A new model for the photovoltage calculation is outlined. The effect of the signal frequency on the photoconduc-tive current is evaluated, the results show that photo-conductive current is very small and can be neglected in calculation. The frequency dependence of photovoltage along with 2-DEG charge density, drain-source current and transconductance of the device have been studied analytically for HEMT structure.

A simulation program is developed based on Grover’s formulas and Greenhouse method to calculate the inductance value and Q-factor for particular dimension and width distribution of spiral inductors. This program changes the width distribution through a pre-determined number of quadratic distributions in an attempt to reduce energy losses and improve Q-factor. The result of this program provides a higher Q-factor together with the possibility of reducing the overall dimension of square spiral inductors as compared with conventional designs. The coordinates of dimension for the simulated inductor are also calculated enabling ease of verification and fabrication. Finally, the calculated results are verified by simulating the inductor using HPADS momentum which is MOM based electromagnetic simulator. The ease of use and rapid results of this program can find its attractiveness in wireless communications and related areas.

An analysis of the AC characteristics of Al-GaAs/GaAs HEMT under illumination with modulated light has been carried out for small signal condition. A new model for the photovoltage calculation is outlined. The effect of the signal frequency on the photoconduc-tive current is evaluated, the results show that photo-conductive current is very small and can be neglected in calculation. The frequency dependence of photovoltage along with 2-DEG charge density, drain-source current and transconductance of the device have been studied analytically for HEMT structure.

A simulation program is developed based on Grover’s formulas and Greenhouse method to calculate the inductance value and Q-factor for particular dimension and width distribution of spiral inductors. This program changes the width distribution through a pre-determined number of quadratic distributions in an attempt to reduce energy losses and improve Q-factor. The result of this program provides a higher Q-factor together with the possibility of reducing the overall dimension of square spiral inductors as compared with conventional designs. The coordinates of dimension for the simulated inductor are also calculated enabling ease of verification and fabrication. Finally, the calculated results are verified by simulating the inductor using HPADS momentum which is MOM based electromagnetic simulator. The ease of use and rapid results of this program can find its attractiveness in wireless communications and related areas.

GaAs and Al0.3Ga0.7As layers grown by MBE at low temperatures (LT) and subsequently annealed at normal growth temperature (600°C) were used as insulators in the gate structure of GaAs MISFETs. We observed improvement in the transconductance (gm) frequency dispersion characteristics of MISFET devices when compared to that of MESFETs. The high resistivity of in-situ annealed LT-grown insulator layers are due to arsenic precipitates and deep centres. Under long-term operation these defects might migrate towards the interface and deteriorate the gn, frequency dispersion characteristics. To validate these MISFET devices for long-term operation, gm frequency dispersion studies were carried out before and after thermal stressing.

GaAs and Al0.3Ga0.7As layers grown by MBE at low temperatures (LT) and subsequently annealed at normal growth temperature (600°C) were used as insulators in the gate structure of GaAs MISFETs. We observed improvement in the transconductance (gm) frequency dispersion characteristics of MISFET devices when compared to that of MESFETs. The high resistivity of in-situ annealed LT-grown insulator layers are due to arsenic precipitates and deep centres. Under long-term operation these defects might migrate towards the interface and deteriorate the gn, frequency dispersion characteristics. To validate these MISFET devices for long-term operation, gm frequency dispersion studies were carried out before and after thermal stressing.