Atsushi Tomiki

Measurements and characterization of ultra wideband propagation within spacecrafts

Ultra wideband (UWB) propagation was measured and characterized within spacecrafts, with a view to partly replacing onboard data buses with wireless connections. Spatial distributions of UWB and narrowband propagation in frequency (from 3.1 to 10.6 GHz) and time domains were measured with a microwave vector network analyzer. While narrowband resulted in a number of dead spots (deep fading points) within the conductive enclosures, UWB yielded none. This implies the UWB systems have an advantage over narrowband ones from the viewpoint of reducing fading margins. It was also found that delay spreads can be suppressed by partially panelling a radio absorber on the inner surfaces to facilitate high data rate transmission.

Measurements and Characterization of Ultra Wideband Propagation within Spacecrafts--Proposal of Wireless Transmission for Replacing Wired Interface Buses

Ultra wideband (UWB) propagation was measured and characterized within spacecrafts, with a view to partly replacing onboard data buses with wireless connections. Spatial distributions of UWB and narrowband propagation in frequency (from 3.1 to 10.6 GHz) and time domains were measured with a microwave vector network analyzer. While narrowband resulted in a number of dead spots (deep fading points) within the conductive enclosures, UWB yielded none. This implies the UWB systems have an advantage over narrowband ones from the viewpoint of reducing fading margins. It was also found that delay spreads can be suppressed by partially panelling a radio absorber on the inner surfaces to facilitate high data rate transmission.

Wireless connections within spacecrafts to replace wired interface buses

This paper describes measurement and characterization of radio propagation and transmission - particularly of ultra wideband (UWB) signals - within spacecrafts with a view to partly replacing on-board data buses with wireless connections. Adaption of wireless technologies within spacecraft could contribute to reduction of cable weight and resulting launching costs, and more reliable connections at rotary, moving, and sliding joints. This paper presents measurements and characteristics of radio propagation and transmission and addresses the effects of apertures perforated on the outer surface of satellites on the UWB propagation and transmission for low- and high-band UWB within a shield box. Channel responses, spatial distributions of UWB and narrowband propagation gains, delay spreads, and throughputs were derived from measurements. On the effects of apertures, the larger total area of apertures resulted in lower UWB propagation gains, shorter delay spreads, and (slightly) higher link throughput. The propagation study was followed up with experimental evaluation of UWB link throughput within a simulated spacecraft. Commercially off-the-shelf UWB devices were used in the experiments of ultra wideband technology to facilitate a high data rate (e.g. maximum of 400 Mb/s per node attained with SpaceWire, equaling the standards of a wired onboard data bus) and to reduce the fading margin.

Experimental evaluation of ultra wideband wireless transmission within a simulated spacecraft for replacing wired interface buses

Ultra wideband (UWB) communication was evaluated within a closed space, with a view to partly replacing onboard data buses with wireless connections. Spatial distributions of UWB propagation in frequency (from 3.1 to 10.6 GHz), time domains and throughput with use of a radio absorber were derived from measured. It was also found that delay spreads can be suppressed by partially panelling a radio absorber on the inner surfaces to facilitate high data rate transmission. Even within the empty shield box, the delay spreads were adequately suppressed to accommodate a data rate exceeding 100 Mb/s, when the absorber panel covered typically 8% of the total inner surface area.

Effects of Inner Volume on UWB Propagation Channels within Closed Spaces

Experimental evaluation of ultra wideband (UWB) wireless transmission was carried out with a view to replacing wired interface buses in spacecrafts. Application of wireless technologies within the spacecrafts could contribute to reduction in cable weight; reduction in the cost of design, manufacture, and test; more flexibility in layout of spacecraft subsystems; and reliable connections at rotary, moving, and sliding joints. However, multipath propagation in semi-closed conductive enclosures, such as spacecrafts, restricts the link performance. Spatial distributions of UWB and narrowband propagation gains, delay spreads, and throughputs were measured with use of four different-sized shield boxes (simulated miniature satellites). Then UWB link throughput was experimentally evaluated in the boxes with use of connecting off-the-shelf MB-OFDM UWB devices. Increase in the inner volume of boxes resulted in higher UWB propagation gains, but wider delay spreads and hence lower link throughput.

High speed downlink system for small satellite and high-efficiency x-band GaN SSPA

A high-speed downlink communication system is required to meet various applications for nano/small satellites. The purpose of this research is to develop a high-data-rate X band downlink system with low power consumption. A high efficient RF circuits using GaN-HEMT SSPA and low power consumption digital circuits were important. We developed over 300Mbps with occupied BW150MHz, RF power 2W, power consumption 20W, mass 1.4kg.

Experimental evaluation of ultra wideband propagation and transmission within a spacecraft for replacing wired interface buses

Ultra wideband (UWB) technology has been expected to communicate in very high data rates by wireless within closed environments, such as spacecrafts. With a view to replacing onboard wired interface buses by wireless connection, UWB and narrowband propagation were measured in a UWB frequency band (from 3.1 to 10.6 GHz) within a small spacecraft. While narrowband propagation resulted in considerable spatial variations in path gain due to interferences caused by multipaths, UWB yielded nearly no fading. This suggests that the UWB systems have an advantage over narrowband from a viewpoint of reducing fading margins. Propagation gains were measured with full-, low-, and high-band UWBs, and narrowband (20 MHz bandwidth) for various antenna settings and polarization configurations for transmission and reception. Polarization configurations were found to produce almost no effect on average power delay profiles. Throughputs were also measured with a WiMedia UWB device. More than 85-Mb/s throughputs were observed for all antenna settings and propagation configurations.

Experimental evaluation of ultra wideband wireless transmission within a spacecraft for replacing wired interface buses

Ultra wideband (UWB) transmission was evaluated within a small scientific spacecraft, with a view to partly replacing onboard data buses with wireless connections. Spatial distributions of UWB link throughput were derived from measurements. The results revealed that commercially-available UWB devices were capable of accommodating up to around 90-Mb/s data buses within spacecrafts.

Local Time Dependence of the Thermal Structure in the Venusian Equatorial Upper Atmosphere: Comparison of Akatsuki Radio Occultation Measurements and GCM Results

Plain Language Summary Temperature profiles of the Venus atmosphere obtained by the Akatsuki radio occultation measurements showed a prominent local time dependence above 65-km altitude at low latitudes equatorward of 35 degrees. A zonal wavenumber 2 component is predominant in the temperature field, and its phase (i.e., isothermal) surfaces descend with local time, suggesting its downward phase propagation. A general circulation model (GCM) for the Venus atmosphere, AFES-Venus, reproduced the local time-dependent thermal structure qualitatively consistent with the radio occultation measurements. Based on a comparison between the radio occultation measurements and the GCM results, the observed zonal wavenumber 2 structure is attributed to the semidiurnal tide. Applying the dispersion relationship for internal gravity waves to the observed wave structure, the zonally averaged zonal wind speed at 75- to 85-km altitudes was found to be significantly smaller than that at the cloud top. The decrease of the zonal wind speed with altitude is attributed to the momentum deposition by the upwardly propagating semidiurnal tide excited in the cloud layer. Akatsuki radio occultation measurements showed the local time dependence of the Venus atmosphere in the equatorial region. By comparing the measurements with a general circulation model, it is attributed to the upward propagating semidiurnal tide generated in the cloud layer. And then, we proposed a new method to estimate the zonal wind speed above the cloud layer, where any optical instruments cannot be measured, for the first time.

Low-cost and ultimately-downsized X-band deep-space telecommunication system for PROCYON mission

PROCYON is a first full-scale, 50-kg-class probe featuring most of the key technologies for deep-space exploration. It was developed by the University of Tokyo and ISAS/JAXA and launched with Hayabusa 2 on 3 Dec 2014. PROCYON has a newly developed X-band telecommunication system fully compatible with the frequency range, up- and down-link turn-around ratio, modulation scheme, and DDOR tones following CCSDS-recommended standards, and it can establish X-band coherent two-way communication and ranging links with deep-space stations as larger deep-space probes have done. The total mass of the onboard telecommunication system is 7.3 kg excluding its RF coaxial harness, and total power consumption during two-way communication, 15 W of RF output power at SSPA, is 54.3 W. After launch, PROCYONs telecommunication system has been successfully working according to the system design. These achievements will provide core technologies for next-generation deep-space exploration by ultra-small probes.