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A new concept for ultra-high capacity wireless networks

Periodic Reporting for period 2 - ATTO (A new concept for ultra-high capacity wireless networks)

Reporting period: 2018-07-01 to 2019-12-31

The ATTO project investigates how to provide each individual entity in a dense group of moving objects with a dedicated, ultra-high-speed mobile connection of 100 Gbps - in combination with extremely low mobile signal delays (less than 10 μs). As such, we aim to lay the foundation for a completely new range of mobile applications that require high-performance and instantaneous computing resources. An example includes the creation of intelligent swarms of robots. This new concept for ultra-high capacity wireless networks will open up many more opportunities in reconfigurable robot factories, intelligent hospitals, flexible offices, dense public spaces, smart schools, having a large impact on society.
No wireless technology exists today that can realize these very demanding requirements simultaneously. Therefore, the ATTO projects introduced a completely new approach: the use of very small antenna cells (ATTO-cells) integrated in floors (see Figure 1). These will establish a close proximity high-frequency wireless connection with moving antennas mounted at floor-facing surfaces of the mobile objects.
To interconnect all these floor antennas, a high bandwidth backbone is required, which will be implemented by a fiber network. This network can establish an interconnection between two moving objects, provide access to local computing power or can connect to the internet. A gateway will be responsible to select and activate the right ATTO-cells to keep continuous wireless connectivity with the moving objects through very fast handovers.
In the first period of the project, we have worked on three separate tracks. The conception of novel antennas suited for integration in the floor. Technology to interconnect the antennas by transporting radio signals over optical fiber. And last,we also studied the amount of electromagnetic radiation that is expected from an ATTO floor and how it compares with 5G mobile communication networks.

(1) Antennas
We have focused on the conception of novel low-cost planar antenna systems that enable pervasive and straightforward integration of active electronic and optic components on the antenna platform and that are compatible for mass production processes and with mass deployment scenarios. A dedicated research strategy was adopted in which we proceeded along two parallel research tracks. In both tracks, the operation frequency of the antenna system will be gradually increased. After the conception of novel dedicated antenna topologies for the envisaged ATTO deployment scenarios and for seamless integration of active components on the antenna platform, first passive antenna prototypes were designed, manufactured and characterized. The most promising antennas were then turned into active antenna systems by the co-design and co-optimization of the antenna geometry and its on-board active components. The first research track applies conventional high-frequency laminates as building blocks for novel cheap, compact, low-profile antenna systems, operating at increasing frequencies. The second track implements antennas in unconventional materials, which typically do not serve as antenna building blocks, but that are cheap and readily available in the envisaged applications.

(2) Radio-over-fiber interconnects
To deliver very high-bandwidth and high-frequency signals to a huge number of antennas, it is important to realize a low-power and low-cost interconnection technology. We have investigated different ways to transport radio signals over fiber. In the end, it was concluded that the most efficient solution is to directly modulate radio signals on an optical carrier. This allows to realize very compact ATTO-cells that consume little power. Dedicated optical receivers (resonant transimpedance amplifiers) that were tuned to the radio signal frequency were designed to ensure low power but high-quality transfer between the optical signal and the antenna. We have demonstrated these receivers around 28 GHz and are currently evaluating the same approach at 60 GHz.

(3) Exposure
The ATTO approach is disruptive in the sense that a huge number of antennas will be deployed a given area. One might assume that the level of the electromagnetic radiation would increase significantly. However, this is not the case. Because, the communication only happens over a very short reach, the transmit power can be drastically reduced. To compare the ATTO approach with upcoming 5G solutions, we have designed dedicated simulation tools. Using these, we were able to conclude that in a typical ATTO scenario the exposure levels will be comparable with what is expected in a Massive MIMO 5G scenario (e.g. at 10m, for 5W, industrial environment).
Different project results have already been disseminated on scientific conferences and in peer-reviewed journals. In different areas we have significantly outperformed the state of the art.

(1) Broadband antenna design
Given the recent developments for the 5G wireless communication system and its envisaged frequency bands, first an extremely compact, low-profile 28/38 GHz coupled quarter-mode SIW dual band antenna was developed on a 508-µm-thick single layer of a Rogers Duroid 5880 high-frequency laminate. Next, an extremely compact, low-profile, low-cost 60 GHz SIW antenna was designed on a single layer, 500μm-thick Rogers RO4350B high-frequency laminate. In addition, a hybrid on-chip/PCB 60 GHz air-filled SIW antenna was designed consisting of an air-filled SIW antenna cavity in intrinsic silicon, which is flip-chipped on a standard PCB.

(2) Opto-antenna design
After the design, construction and validation of novel passive antenna prototypes, we have integrated opto-electronic components on the antenna platform that directly convert the optical signal into an electrical signal ready for transmission by the antenna. First, a passive opto-antenna was realized, serving as a downlink remote antenna unit in the 3.30-3.70 GHz CBRS frequency band. Next, a more compact implementation was achieved by omitting the matching network and instead realizing optimal power transfer from photodetector to antenna through conjugate matching. This new compact wideband transmit opto-antenna covers the complete 5.15–5.85 GHz (U-NII) frequency band. We intend to further gradually increase the antenna’s operating frequency and bandwidth. Currently, 28GHz-band (27.5-29.5 GHz) transmit and receive opto-antennas are being designed for the 5G wireless communication system.

(3) Sigma-delta modulated radio over fiber transmission
In search of very low cost means to transport radio signals over an optical fiber, we have devices a solution that disguises an analog radio signal as a digital communication signal. By pre-processing the continuous radio signal, we can quantize it two levels without any significant degradation in signal quality by using a sigma-delta modulator. This pre-processed signal can be transported with standard data com equipment which is a mass consumer product. At the receiver side near the antenna, the signal can be easily recovered using a passive filter. No digital signal processing is required. Simultaneously, we have developed optical receivers that only operate around a specific radio frequency. This makes the receiver much more efficient and because the receiver only operates around the radio signal, it automatically performs the filtering operation required to recover the original radio signal from the sigma-delta modulated stream.
ATTO cell architecture