Case study: Full reception for mobile communications thanks to laser technology

With modern architecture and contemporary building materials, a future-orientated rescue station with plenty of light and transparent surfaces was built in the district of Teltow-Fläming in 2021. In daily use, however, this energy-efficient construction and glazing proved to be a modern challenge: inside the building, the signal strength for GPS and mobile communications was very low. In a pilot project, the glass panes were subsequently textured by laser, the change was documented, and reception was demonstrably improved.

Initial situation: No position determination of ambulances

Due to the materials used, such as thermally insulating glass panes with low-E coating, the building envelope had a strong attenuating effect on radio waves. The resulting poor reception of the GPS signal was a recurring limitation for the tasks carried out at the rescue station. The ambulances were unable to receive sufficient signal strength in the vehicle hall to determine their position. As a result, the control centre was unable to reliably determine the position of the available vehicles. In addition, this regularly led to delays in navigation. Only after leaving the hall could the ambulance be detected and a correct route planned to the scene.

The Teltow-Fläming central rescue services approached HEGLA boraident and the technical specialists of SPIE with this requirement. The aim was to improve the GPS reception inside the building. "We are seeing more and more often that there is no more reception after new glazing is installed, or in new buildings such as hotels, companies or public buildings," explains Dr Thomas Rainer, Head of Organisation and Development at HEGLA boraident in Halle. "Highly efficient construction materials and metallic coated glass panes lead to attenuated signal strengths."

Measurement of existing reception

At the beginning of the case study, the situation in terms of reception for GPS and mobile communications was determined at various measuring points. The measurements were carried out both with the gates closed and open in order to map the change in reception levels. The background to this method is to initially record the GPS and mobile communications coverage under the various conditions and to estimate the attenuation of the metallic coated windows.

The measurements showed that only one satellite with an SNR level (signal-to-noise ratio) of 12 to 14 was available when the gates were closed. Due to this reception situation, the satellite receiver was not able to determine the position at any measuring point.

Technical solution to limited indoor reception

In order to realise the RF transparency of the windows and glass panes, functional patterns were applied to the attenuating thermal insulation coating using a laser. This significantly increases the penetration of radio signals without compromising the desired insulating function or the aesthetics of the glass. The functional pattern consists of a dodecagon texture. The line thickness is thinner than a human hair and therefore barely visible.

The laser treatment was carried out on site at the rescue station using a mobile laser robot from HEGLA boraident, without removing the glass panes. The laser system used is designed to subsequently texturise building glazing and thus enable penetration by radio waves again. A metal plate was attached to the outside of the glass panes to be treated to prevent uncontrolled spreading of laser radiation.

Result: Full reception for GPS and mobile communications

After laser treatment of the glass panes, the reception was measured again in order to demonstrate an improvement in the reception level indoors and with the entry gates closed. The laser treatment had already led to a considerable improvement in the GPS and mobile communications signal after texturising of two glass panes per gate. Depending on the measuring point, six to eight satellite signals with an SNR level of 13–33 could be reached. Position determination was also possible at all points with an accuracy of one to four metres. These results were confirmed to the same extent on the receivers in the ambulances.

The main task was to improve the GPS reception. As laser texturising works in the frequency range from 0.5 GHz to 7 GHz, mobile communications coverage in the vehicle hall before and after laser treatment was also determined besides the GPS signal. Overall, it was determined that the reception levels indoors have improved for both satellite coverage and mobile communications. A comparison of the signals in the indoor and outdoor areas of the rescue station showed a significant reduction in attenuation after laser treatment. Reception was fully restored without any loss. 

Position determination for ambulances without delay

The case study at the rescue station has shown that laser texturising of the thermal insulation glazing leads to a significant improvement in reception in the frequency ranges of satellite and mobile communications. This enables the rescue station to determine the position of vehicles and provide navigation in the vehicle hall without delay. "Providing technical support to the rescue station for more reception was an important and exciting project for us. Modern buildings place high demands on thermal insulation and technical design. Thanks to laser texturising, we were able to restore full reception and perhaps even save a second or two, which is important for rescue operations," says Dr Thomas Rainer, Head of Organisation and Development at HEGLA boraident.

Figure 1: Case study: Full reception of the GPS signal in the vehicle hall thanks to laser texturising of the metallic low-E coating of the glass panes.

Figure 2: Laser treatment of the thermal insulation coating on the glass results in full reception in the frequency range from 0.5 to 7 GHz for GPS or mobile communications.

Figure 3: The mobile laser robot from HEGLA boraident can be used for subsequent treatment of glass panes and windows to establish RF transparency or fit a bird protection pattern.

Figure 4:  Laser treatment is carried out on site – here with a prototype as part of the case study

Figures 5+6:     To prevent uncontrolled spreading of laser radiation, the glass panes to be treated were each shielded from the outside with a metal plate.

Figure 7:  Dr Thomas Rainer has played a key role in various laser applications for glass since 1995 and has implemented a range of different products like bird protection glass.