Wireless data traffic is experiencing an unprecedented growth in recent years. There is an expectation that everyone will be permanently connected to the Internet, no matter where they are. The internet protocol traffic is expected to grow beyond 130 exabytes per month by 2018. At the same time, the massive use of mobile connection is pushing the need for wide bandwidth delivered up to the end users in a wireless regime. People are expecting that more information of a higher quality is delivered immediately. The newer services are requiring higher and higher data volumes and transfer rates.
Among various data traffic, the video traffic is expected to be dominant. Some video traffic has already posed severe challenges to mobile networks, including the forthcoming 5G mobile networks. For instance, it is expected that at least 10 Gbps traffic is needed for one virtual reality (VR) device. Moreover, full High Definition video is becoming increasingly important for mobile devices, and devices using Ultra High Definition (UHD) (4K and 8K) and 3-D rendering are also expected to become widely available in not so distant future.An uncompressed UHD video may reach 24 Gbps rate, and an uncompressed 3-D video with UHD can reach 100 Gbps. Ultimately, It is predicted that data rates will reach Terabit-per-second (Tbps) within the next five to ten years.
However, existing wireless technology is hard to support Tbps links. The state-of-the-art communication systems in ultra-wideband (UWB) or millimeter wave (mmWave) can only achieve Gigabit-per-second (Gbps) rates. On the other hand, communications over the infrared (IR) or visible light (VLC), are restricted by several technical and safety limitations.
One way to achieve this is to move to higher frequencies for wireless links. Amongst others, the Terahertz (THz) band, 0.1–10 THz, stands out as one of the promising alternatives. Terahertz can provide hundredfold, increase in the frequency compared to the mmWave addressing spectrum scarcity and capacity limitation in current wireless systems. Terahertz wi-fi could in theory support data rates up to 100Gb/s within ranges of about 10m.
In February 2017, researchers from the Panasonic Corporation and National Institute of Information and Communications Technology (Hiroshima University), developed a THz transmitter data at a staggering rate of 100 Gbps over a single channel of 300 GHz. At this data rate, you can transfer a 0.1 terabit file before you can say the word ‘it!’
The terahertz spectrum possibly can be the basis for the next “5G” network for cellphones. If cellphones on a current “4G” network can download data at 10 to 15 megabits per second, terahertz technology can potentially send data back and forth at terabits per second (or millions of megabits per second). Terabits per second shall enable super high-speed link to communication satellites, faster content download from servers to the mobile terminal, improved use in applications requiring real-time quality communication (like in orbit), and quick exchange of 3D videos in high definition.
In the past, the frequency spectrum ranging from 0.3 to 3THz (or 300 to 3000GHz) was spoken as infamous “Terahertz Gap” as it lies between traditional microwave and infrared domains but remained “untouchable” via either electronic or photonic means. The conventional “transit-time-limited” electronic devices can hardly operate even at its lowest frequency; the “band-gap-limited” photonic devices on the other hand can only operate beyond its highest frequency. However continuous progress is being made for Terahertz components and devices to overcome electronic/photonic barriers for realizing highly integrated Terahertz systems.
“Imaging, radar, spectroscopy, and communications systems that operate in the millimeter-wave (MMW) and sub-MMW bands of the electromagnetic spectrum have been difficult to develop because of technical challenges associated with generating, detecting, processing and radiating the high-frequency signals associated with these wavelengths. To control and manipulate radiation in this especially challenging portion of the RF spectrum, new electronic devices must be developed that can operate at frequencies above one Terahertz (THz), or one trillion cycles per second,” says DARPA.
The Researchers from the Tokyo Institute of Technology have already demonstrated 3Gb/s transmission at 542 GHz. At the heart of the team’s 1mm-square device is what is known as a resonant tunnelling diode, or RTD. During the 2008 Olympic Games in Beijing, scientists from Osaka University and NTT Corp. already demonstrated a 120 GHz data link across a distance of 1 km.
Information showers: The inherently small communication range of THz cells (few meters radius maximum) and extremely high-rate (up to Tbps) cells can be used for deployment of THz access points (APs) in the areas with high human flow (e.g. gates to the metro station, public building entrances, shopping mall halls, etc.). With such a deployment strategy, each of the passing user is able to receive bulk data (up to several GBs), just while passing this AP. Such information showers can be used do seamlessly deliver software updates as well as other types of heavy traffic, such as high-quality video (e.g. a movie to watch in a train)
Mobile access: The applicability of THz communications to typical usage scenarios (e.g. indoor WLAN access) is limited due to considerable propagation losses. This could be addressed by trading the capacity of THz access points for coverage, primarily by reducing the utilized bandwidth
and moving the entire communications from above 1 THz to the so-called “lower terahertz” carriers around 300GHz. As a result, it is possible to create reliable wireless links over tens of meters while retaining the capacity of tens of gigabits per second, which makes Wi-Fi-like THz access points (or even femto-cells for cellular access) become feasible.
Fiber-equivalent wireless links: The strategy for next generation wireless networks (5G and Beyond) envision the appearance of numerous high-rate small cells, operating in the mm Waves spectrum. The feasibility of multi-gigabit-per second wireless links in the lower THz band for the distances
up to 1 km long have been recently experimentally validated.
Connectivity with miniature devices: The possibility to create micro-scale transceivers operating in the THz band allow networking of several micro- and nano-scale robots, capable to assist the society in many different areas, from environmental sensing to medicine .
Terahertz for Future Military and Space Communications
Terahertz wireless sensor networks shall also enable gigabit secure battlefield wireless sensor network and provide multi sensor fusion of wide range of imaging and non-imaging sensors. An ability to create highly directional beams with miniature size antenna arrays in conjunction with the high theoretical capacity of THz links results in a number of benefits for the security-sensitive usage, especially in military applications. THz ad hoc network can be formed in the battlefield to connect soldiers, armoured personnel carriers, tanks, etc. The limited transmission range and highly directional antennas makes eavesdropping extremely difficult.
In outer space, the transmission of THz is lossless, so we can achieve long-range secure Gigabit Aircraft to satellite Communication with very little power space. A single THz satellite communication link will support broadband data transfer rates far beyond (>20X) the limits of current microwave technology.
The easier pointing due to their wider beam width, it is suitable for the application in the GEO-GEO or LEO-GEO inter-satellite links, which can support the high-throughput (Gigabit) communication with high security as well as the ability to defeat the interference.
The increased bandwidth of terahertz shall also enable UWB Code Division Multiple Access (CDMA) communications schemes which provide high immunity to fading, large processing gain for combating jamming and low probability of detection and interception.
ISSCC: Panasonic develop ‘A 105Gb/s 300GHz CMOS Transmitter’.
Hiroshima University, National Institute of Information and Communications Technology, and Panasonic Corporation announced the development of a terahertz (THz) transmitter capable of transmitting digital data at a rate exceeding 100 gigabits (= 0.1 terabit) per second over a single channel using the 300-GHz band. The research group has developed a transmitter that achieves a communication speed of 105 gigabits per second using the frequency range from 290 GHz to 315 GHz. At this data rate, the contents of an entire DVD can be transferred in a fraction of a second
“This year, we developed a transmitter with 10 times higher transmission power than the previous version’s,” said Hiroshima Professor Minoru Fujishima. “This made the per-channel data rate above 100Gbit/s at 300GHz possible. Terahertz could offer ultrahigh-speed links to satellites, and that could, in turn, significantly boost in-flight network connection speeds, for example.” Other possible applications include fast download from contents servers to mobile devices and ultrafast wireless links between base stations, he added.
“This year, they showed six times higher per-channel data rate, exceeding 100Gbit/s for the first time as an integrated-circuit-based transmitter,” said Panasonic, which worked with Hiroshima University and the Japanese National Institute of Information and Communications Technology to develop the transmitter. He pointed out that such links could beat optical fibres because that are made from glass where the speed of light is slower than in air or space, increasing data latency and barring them from systems that require ultra-fast responses. “Today, you must make a choice between high data rate fibre optics and minimum-latency microwave links. You can’t have them both,” said Fujishima. “But with terahertz wireless, we could have light-speed minimum-latency links supporting fibre-optic data rates.”
Panasonic points out that the range of frequencies used are currently unallocated, falling within the 275-450 GHz whose usage is to be discussed at the World Radiocommunication Conference (WRC) 2019 under the International Telecommunication Union Radiocommunication Section (ITU-R).
FUJITSU and NTT develop compact terahertz band receivers
FUJITSU has developed the world’s first compact 300GHz receiver (which is part of the terahertz waveband in which attenuation during propagation of signals through the atmosphere is low) capable of wireless communications at tens of gigabits per second. They have developed an integrated module that combines receiver-amplifier chip and terahertz-band antenna with a low-loss connection within the cubic capacity at 0.75 of a centimeter, and that can be installed in mobile devices.
The use of this Fujitsu-developed technology will enable small devices to receive 4K or 8K HD video instantly, such as from a download kiosk with a multi-gigabit connection. It will also be possible to expand into such applications as split-second data transfers between mobile devices and split-second backup between mobile devices and servers.
They commonly used printed-circuit substrate to connect the antenna and the receiver-amplifier chip is ceramic, quartz, or Teflon. They replace the material with a low-loss polyimide, which can be micro-fabricated into printed circuit boards.
While polyimide as a material has a 10 percent higher loss than quartz, but since its processing accuracy is more than four times higher, the through-hole vias can be placed within several tens of microns of each other, halving the loss as compared to a connecting circuit on a quartz printed circuit. This allows the receiver to be highly sensitive which compensates the strong attenuation of terahertz waves when propagating through atmosphere.
NTT has also developed 300-GHz, a wireless-use IC for ultrahigh-speed short-distance wireless communication system.
In the IC, a modulator and a power amplifier (which are required components of a transmission unit for wireless transmission) are monolithically integrated. High output power and low-loss wiring were achieved by multi-parallelization of the amplifier, and high data rate was achieved by a travelling-wave modulator. Moreover, by using low-loss and wideband waveguide-to-IC transition we designed, the deterioration of the characteristics due to packaging was negligible. By applying this module high-speed operation (i.e., 20 Gbit/s) was confirmed
References and Resources also include:
http://Terahertz Band Communications: Applications, Research Challenges, and Standardization Activities: V. Petrov, A. Pyattaev, D. Moltchanov, Y. Koucheryavy Department of Electronics and Communications Engineering, Tampere University of Technology, Tampere, Finland