Pioneering 60 GHz communication (1992 – 1999)
TNO pioneered 60 GHz millimetre wave communication starting in 1992. The bandwidth around 60 GHz was hardly exploited at the time for communication purposes, while the bandwidth now is of hot interest to many parties developing 5G. In the early 1990s, it was already known that electromagnetic fields with radio frequencies around 60 GHz had specific, interesting characteristics.
What is so special about 60 GHz?
Radio frequencies around 60 GHz have a unique characteristic: the energy of radio waves with this frequency is partially absorbed by oxygen atoms. As a result, the range for practical transceivers is at most 1 kilometre. For the use of wireless communications this small range offers interesting possibilities that cannot be realised with other radio frequencies. For example, soldiers can broadcast short-distance messages at 60 GHz. No opponent outside the communication range can detect that a broadcast is being made. This not only prevents the message contents from falling into enemy hands, but the presence of the unit itself goes unnoticed as well. Inspired by the ‘stealth fighter’, TNO named this secret form of communication ‘stealth communication‘. The high 60 GHz frequency also has the great advantage that a large amount of information can be transmitted in a short period.
These characteristics asked for further exploration of military applications such as wireless communication between tanks during ‘radio silence’ and broadband wireless LANs within command posts. In early 1992, TNO at Waalsdorp decided to start a feasibility study on 60 GHz applications and implementations using internal research funds. As part of this project, a 60 GHz set had to be purchased and possibly modified. Silicon communication ICs for 60 GHz user equipment are now available for a few euros each. In the early 1990s, there were only a few manufacturers who could supply (expensive) solid-state 60 GHz transceiver sets using discrete technology because a 60 GHz IC was very special at that time.
It was challenging to acquire the set given the available budget. Extensive negotiations were needed. The vendor mentioned ‘nice Russian stuff’ that appeared on the market after the ‘glasnost’. We had, however, the necessary doubts about delivery and quality. We wanted two American Millitech transceivers. In the end, we agreed on the price and the practical side of the project could also go ahead. For example, a directional connection for transmitting analogue video images was set up with a maximum reach of a few hundred meters.
In retrospect, we discovered recently that the PTT Neherlab, which was later incorporated by TNO, conducted research in the degree of eavesdropping of 60 GHz quasi-conducting transmissions in the period 1989 – 1992.
For TNO it was important to collaborate with the 60 GHz research at TU Eindhoven, where Mr Peter FM Smulders was working on his PhD regarding the feasibility of 60 GHz broadband wireless LANs, especially for indoor environments such as open office spaces. At this time, that application seems to be obsoleted by Visible Light Communication (VLC).
He was able to benefit from the transceivers present at TNO, which were modified for digital transmissions based on Frequency Shift Keying (FSK, a digital version of FM). He also provided a student who could carry out measurements under TNO supervision. On the part of TU Eindhoven, these measurements were supplemented with computer simulations.
Several special antennas were developed. These so-called bi-conic antennas had a virtually constant transmit and receive sensitivity all around in the horizontal plane. Five of these antennas were manufactured by Waalsdorp (see photo below). Such a biconical antenna would replace the standard target antenna of the commercial 60 GHz transceiver when required for a specific application to be experimented with.
As mentioned above, the use of 60 GHz as a radio frequency for broadband wireless local area networks (LANs) was obvious, both for civil and military applications. 60 GHz was also thought of as a radio frequency for mobile systems. The required network was designed according to a rigid cellular concept whereby fixed frequencies were assigned for fixed contiguous areas. Here, the limited range of 60 GHz radio waves could offer a solution because the same frequency could be reused at short distances, i.e. after only a few cells at the most (this is also a promise of 5G). That saved valuable spectrum space while many users could communicate per cell at the same time. It should be noted that this design was developed by TNO in the period that GSM had just been introduced in the Netherlands!
In addition, talks were held with the Royal Netherlands Navy about an ‘electronic signal lamp’ at 60 GHz (see also the previous attempt in the ’50s/’60s for improving non-eavesdroppable ship-to-ship communications). Later, various applications of 60 GHz communication were devised for the Royal Netherlands Air Force.
The joint TNO-TU Eindhoven research results were published in a paper for the IEEE International Symposium on Personal, Indoor and Mobile Radio Communications (PIMRC) ’94, a symposium that was held in the Congresgebouw in The Hague. During the presentation at the symposium, a rather grumpy Australian symposium participant was very sceptical about the technical realisation perspectives of 60 GHz communication systems, especially for the consumer market. He was not receptive to a visionary talk… Fortunately, reactions from the audience showed that a majority of those present could appreciate the essence of the presented joint work.
In the meantime, contacts were made with NCR and Ericsson, the PTT Research organisation, the branch Association of Office, Information and Communication Technology Companies (VIFKA), the Navy and the Army to gain insight into the need for wireless systems in this frequency spectrum and the possible role of TNO in the development and deployment of these systems. Therefore, the TNO system was demonstrated during various thematic events. On one of these occasions, a journalist from Jane’s Defence Weekly was also present. He reported on our activities. This aroused the interest of the Royal British Navy, which approached us through the newly established DERA (Defence Evaluation and Research Agency). After a good face-to-face meeting, TNO was awarded a contract to investigate the maritime applicability of 60 GHz and its practical feasibility at the end of 1994. The emphasis was on communication between a flight deck and a helicopter. In the project, the expertise and competence of the TNO group that works intensively on MMICs (Monolithic Microwave Integrated Circuits) were used to make a statement about the feasibility of 60 GHz systems in an integrated form. At that time, Gallium Arsenide technology with some variants was the only technical feasibility for such systems. This technology was, however, too expensive at that time and not suitable for generating the required level of transmission power. The reproducibility of such MMICs for 60 GHz was also still poor.
At the end of 1994, an improved 60 GHz system could be developed as part of a second internal project. This time we made our design to integrate components. Many of the components were sourced from Farran Technologies in Ireland. Three transceivers were developed to realise a wireless LAN. Because the existing communication protocols were not completely compatible with the characteristics of our transceivers, this project did not lead to a stable system. However, the transceivers were successfully deployed during the Army communication exercise ‘Show It’ in 1996, as well as in a subsequent measurement campaign in which the possibilities of 60 GHz communication for Army applications in various operational settings were researched. But no matter how great those applications were, the bottom line conclusion was that it was too early to use affordable handy equipment with such a high radio frequency.
In 1999, the possibilities of millimetre-wave communication equipment at 44 and 60 GHz were explored for the Royal Netherlands Air Force. This included communication possibilities for the combat and transport helicopters and the then-unknown successor of the F-16. Because of the line-of-sight nature of the transmission, the feasibility of all considered applications was established based on internationally recognised radio propagation models and previous insights gained in experiments with TNO’s 60 GHz system.
Meanwhile, a European Advanced Communications Technologies and Services Program (ACTS) project called MEDIAN was established in 1995. Median researched Wireless Broadband CPN (Customer Premises Network) and LAN for Professional and Residential Multimedia Applications. TNO was able to participate in the international Median consortium of eleven partners, including Dassault Electronique, the Eindhoven University of Technology (led by the aforementioned Peter Smulders), IMST, Motorola and the Finnish VTT Electronics. The consortium worked for several years on the realisation of a wireless LAN to demonstrate the feasibility of broadband data services at 60 GHz.
The joint efforts of this MEDIAN consortium were far beyond what TNO could deliver on its own. TNO contributed substantially to this consortium in the development of the wireless communication protocol and digital signal processing. How the transmission signal was created was a basic form of communication technology that is now used in 4G and which will also be used in 5G in an even more advanced form. In 1999, at the end of the project, successful demonstrations were given for the EC project officer at the TNO location Waalsdorp and the ACTS Mobile Summit in Sorrento, with video as a demonstration application. The technology was not yet miniaturised, but the project already indicated that this would be a matter of time. That ultimately took about 20 years. For example, the IEEE 802.11ad Wireless LAN standard for the 60 GHz band was agreed upon in December 2012.
Overduin, R., & Smulders, P. F. M. (1994). Feasibility of broadband in-room radio communications at 60 GHz. In Proc. 5th IEEE International Symposium on Personal, Indoor and Mobile Radio Communications, PIMRC 1994 (pp. 119-126)
This contribution was written by Ir. R. Overduin and his colleagues