KEYWORDS: Extremely high frequency, Radio over Fiber, Analog electronics, Receivers, Modulation, Radio optics, Orthogonal frequency division multiplexing, Network architectures, Signal detection, Signal generators
Fifth-generation (5G) wireless access network promises to support higher access data rate with more than 1,000 times capacity with respect to current long-term evolution (LTE) systems. New radio-access-technologies (RATs) based on higher carrier frequencies to millimeter-wave (MMW) radio-over-fiber, and carrier-aggregation (CA) using multi-band resources are intensively studied to support the high data rate access and effectively use of frequency resources in heterogeneous mobile network (Het-Net). In this paper, we investigate several enabling technologies for MMW RoF systems in 5G Het-Net. Efficient mobile fronthaul (MFH) solutions for 5G centralized radio access network (C-RAN) and beyond are proposed, analyzed and experimentally demonstrated based on the analog scheme. Digital predistortion based on memory polynomial for analog MFH linearization are presented with improved EVM performances and receiver sensitivity. We also propose and experimentally demonstrate a novel inter-/intra- RAT CA scheme for 5G Het- Net. The real-time standard 4G-LTE signal is carrier-aggregated with three broadband 60GHz MMW signals based on proposed optical-domain band-mapping method. RATs based on new waveforms have also been studied here to achieve higher spectral-efficiency (SE) in asynchronous environments. Full-duplex asynchronous quasi-gapless carrier aggregation scheme for MMW ROF inter-/intra-RAT based on the FBMC is also presented with 4G-LTE signals. Compared with OFDM-based signals with large guard-bands, FBMC achieves higher spectral-efficiency with better EVM performance at less received power and smaller guard-bands.
KEYWORDS: Antennas, Transceivers, Analog electronics, Multiplexing, Receivers, Digital signal processing, Extremely high frequency, Signal to noise ratio, Chemical mechanical planarization, Copper
Millimeter-wave wireless interconnects is an emerging technology for ultra-short-reach off-chip transmission, providing
spatial flexibility and power-efficient high-speed data transportation. Integrated with carrier-over-fiber technology, we
propose a low-phase-noise multi-wireless-transceiver architecture to improve the bit-error-rate performance of
conventional wireless interconnects. Multiplexing schemes, including frequency division multiplexing, spatial
multiplexing, and beam isolation, can be facilitated by carrier-over-fiber techniques. We introduce a potential application
of the multi-input-multi-output high-speed analog multiplexing with open-loop analog circuits and digital feedback.
We proposed a novel optical coupling technology for short-reach interconnection (<10m) on flexible polymer
waveguides. In order to decrease time and cost of fabrication and assembly, edge-emitting lasers and edge-viewing
photodetectors are embedded directly into flexible polymer waveguide in a parallel lithography process. This avoids
lenses or angle-reflected components, such as 45° mirrors or volume gratings, which are widely used for VCSEL
coupling. Multi-channel optical interconnection can be implemented by passive alignment in a one-time optical
lithography process, and no additional expensive components are needed to achieve high coupling efficiency.
Multimode interference (MMI) devices operating at high data rates are important for integrated optics and optical networks. Their 1×N splitting provides a basic functionality in these applications. Ultra-high speed data transmission at 40Gb/s per channel with a total bandwidth of 320Gb/s for all 8 output ports is demonstrated for the first time on a 1 × 8 photo-definable polymer-based MMI power splitter. The transmission integrity is confirmed by the bit-error-rate (BER) testing. To further determine the speed limitations of MMI devices, ultra-short pulse response of these devices is quantified. For example, for 20fs Gaussian input pulses into a 1×8 polymer-based MMI splitter, the output pulses are severely degraded in coupling efficiency (47%) and completely broken up in time and in space primarily due to inter-modal and intra-modal (waveguide) dispersions.
Recent progress toward implementing high-density, optical-digital building blocks necessary to accomplish efficient, end-to-end optical interconnect architecture on low cost FR-4 boards has been demonstrated. The optical interconnect system consists of fabricating an optical buffer layer separating board metallurgy from the optical lightwave circuit layer, and implementing optical links between embedded lasers and detectors. We will show an example of 1310 nm light from an edge emitting distributed-feedback or Fabry-Perot laser operating at 10 Gb/s being guided to the photo-detector by a polymer waveguide. Both lasers and detector are embedded in the waveguide and all construction is built on a low-cost FR-4 board with 3 levels of metallurgy.
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