Periodic Reporting for period 4 - ATTO (A new concept for ultra-high capacity wireless networks)
Berichtszeitraum: 2021-07-01 bis 2023-06-30
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.
The action has developed the basic building blocks of the ATTO concept: novel antennas suited for integration in the floor and the technology to interconnect the antennas by transporting radio signals over optical fiber. We in addition studied the amount of electromagnetic radiation that is expected from an ATTO floor and how it compares with 5G mobile communication networks.
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.
The action has developed the basic building blocks of the ATTO concept: novel antennas suited for integration in the floor and the technology to interconnect the antennas by transporting radio signals over optical fiber. We in addition studied the amount of electromagnetic radiation that is expected from an ATTO floor and how it compares with 5G mobile communication networks.
Antennas
We have focused on the conception of novel low-cost planar antenna systems that enable pervasive and straightforward integration of active electronic and opto-electronic components on the antenna platform, that feature best-in-class performance in terms of bandwidth, radiation efficiency, and compact footprint, that maintain their excellent performance when deployed in harsh indoor environments, and that are compatible with mass production processes. First we applied conventional high-frequency laminates extending this to unconventional materials, which typically do not serve as antenna building blocks, but that are cheap and readily available in the envisaged applications.It was found that the air-filled Substrate-integrated-waveguide technology is the perfect candidate to address the very strict ATTO requirements.
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. Similarly, also transmitter circuits have been realized. At 28 GHz an intensity modulated approach was adapted. At 60 GHz, single side band transmission was realized using a combination of electrical and optical Q-hybrids. We have demonstrated these receivers chipsets around 28 GHz and evaluatied the same approach at 60 GHz.
Exposure
The ATTO approach is disruptive in the sense that a huge number of antennas will be deployed within 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. 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). Moreover, mm-wave 6G distributed massive multiple-input multiple-output (DMaMIMO) base stations at 28 GHz were investigated and with equal power, distributed base stations contribute 2 to 3 times less to exposure than collocated base stations.
We have focused on the conception of novel low-cost planar antenna systems that enable pervasive and straightforward integration of active electronic and opto-electronic components on the antenna platform, that feature best-in-class performance in terms of bandwidth, radiation efficiency, and compact footprint, that maintain their excellent performance when deployed in harsh indoor environments, and that are compatible with mass production processes. First we applied conventional high-frequency laminates extending this to unconventional materials, which typically do not serve as antenna building blocks, but that are cheap and readily available in the envisaged applications.It was found that the air-filled Substrate-integrated-waveguide technology is the perfect candidate to address the very strict ATTO requirements.
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. Similarly, also transmitter circuits have been realized. At 28 GHz an intensity modulated approach was adapted. At 60 GHz, single side band transmission was realized using a combination of electrical and optical Q-hybrids. We have demonstrated these receivers chipsets around 28 GHz and evaluatied the same approach at 60 GHz.
Exposure
The ATTO approach is disruptive in the sense that a huge number of antennas will be deployed within 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. 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). Moreover, mm-wave 6G distributed massive multiple-input multiple-output (DMaMIMO) base stations at 28 GHz were investigated and with equal power, distributed base stations contribute 2 to 3 times less to exposure than collocated base stations.
Broadband antenna design
Given the recent developments for the 5G wireless communication system and its envisaged frequency bands, low-profile 28/38 GHz coupled quarter-mode SIW dual band antenna and low-cost 60 GHz SIW antenna were developed. Since the dielectric losses substantially reduce the radiation efficiency, air-filled SIW technology was proposed and combined with novel fractional-mode miniaturisation techniques to achieve unprecedented performance in terms of bandwidth, efficiency, and footprint.
Opto-antenna design
We integrated opto-electronic components on the antenna platform to directly convert the optical signals into electrical signals for fiber-wireless downlink communication, and vice versa for uplink communication. A new compact wideband transmit opto-antenna covers the complete 5.15–5.85 GHz (U-NII) frequency band.This was scaled towards higher antenna operating frequencies and bandwidths. Several suitable array beamforming strategies were identified, including optical beamforming, leaky-wave-antenna-based beamforming, and Butler-matrix-based solutions. Based on these RAUs, we demonstrated a mmWave-over-fiber DAS with data rates up to 48 Gb/s.
Sigma-delta modulated radio over fiber transmission
In search of very low cost means to transport radio signals over an optical fiber, we have developed a solution that disguises an analog radio signal as a digital communication signal. By pre-processing the continuous radio signal, we can quantise it in two levels without any significant degradation in signal quality by using a sigma-delta modulator. This pre-processed signal can be transported with standard datacom 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. Further, because no signal processing is involved, the fiber becomes transparent and can be seen as part of the wireless channel forming a seamless fiber-wireless connection. This has huge benefits: it allows to distribute antennas over an array while from a signal processing perspective they all seem to originate from the same central point. This enables us to deliver signals to multiple users at the same time (as can be done with Massive MIMO), however, with distributed antennas. This approach is called Cell-Free MIMO and is heavily investigated as an evolution of the current 5G networking.
Given the recent developments for the 5G wireless communication system and its envisaged frequency bands, low-profile 28/38 GHz coupled quarter-mode SIW dual band antenna and low-cost 60 GHz SIW antenna were developed. Since the dielectric losses substantially reduce the radiation efficiency, air-filled SIW technology was proposed and combined with novel fractional-mode miniaturisation techniques to achieve unprecedented performance in terms of bandwidth, efficiency, and footprint.
Opto-antenna design
We integrated opto-electronic components on the antenna platform to directly convert the optical signals into electrical signals for fiber-wireless downlink communication, and vice versa for uplink communication. A new compact wideband transmit opto-antenna covers the complete 5.15–5.85 GHz (U-NII) frequency band.This was scaled towards higher antenna operating frequencies and bandwidths. Several suitable array beamforming strategies were identified, including optical beamforming, leaky-wave-antenna-based beamforming, and Butler-matrix-based solutions. Based on these RAUs, we demonstrated a mmWave-over-fiber DAS with data rates up to 48 Gb/s.
Sigma-delta modulated radio over fiber transmission
In search of very low cost means to transport radio signals over an optical fiber, we have developed a solution that disguises an analog radio signal as a digital communication signal. By pre-processing the continuous radio signal, we can quantise it in two levels without any significant degradation in signal quality by using a sigma-delta modulator. This pre-processed signal can be transported with standard datacom 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. Further, because no signal processing is involved, the fiber becomes transparent and can be seen as part of the wireless channel forming a seamless fiber-wireless connection. This has huge benefits: it allows to distribute antennas over an array while from a signal processing perspective they all seem to originate from the same central point. This enables us to deliver signals to multiple users at the same time (as can be done with Massive MIMO), however, with distributed antennas. This approach is called Cell-Free MIMO and is heavily investigated as an evolution of the current 5G networking.