TOMIKI ATSUSHI

A high-speed downlink communication system is required to meet different applications for nano/small satellites. Therefore, it is essential to implement a power- and weight-limited transmitter in such satellites. Our recent research has focused on an efficient system adopting CCSDS 131.0-R signaling formats with the limited transmitter incorporating a powerful ground station receiver. To overcome signal distortion at the cost of some limitations of the transmitter, an SCCC turbo equalization system equipped with nonlinear distortion compensation techniques in the receiver has been developed. We simulate the system using practical distortion models to determine the performances of BER and synchronization.

High reliability S-band communication and X-band communication for fast mission data transmission are both required for many satellite users. But for small satellite users, it is difficult to use both the S-band and the X-band transponder in order to limitation of on-borad power, area, mass and so on. By these current conditions, we start concept study of the multi-band transponder for category-A region.

The replacement of wired data buses among space-borne subsystems with wireless connections enhances onboard component layouts, reduces a connecting cable mass, and enables higher-speed data bus connections. We have proposed to apply Ultra Wideband (UWB) technologies to a spacecraft inner closed space filled with bus and science instruments. While narrowband resulted in a number of dead spots (deep fading points) within the conductive enclosures like inside of spacecraft, UWB yielded none. This implies the UWB systems have an advantage over narrowband ones from a viewpoint of reducing fading margins. We measured spatial distributions of UWB and narrowband propagation in frequency (from 3.1 to 10.6 GHz) and time domains with a mockup of REIMEI satellite, UWB monopole antennas, and a microwave vector network analyzer. We also investigated spatial distributions of data throughputs inside REIMEI using commercially available UWB devices. The influences of polarization of UWB antennas on the above propagation and throughputs characteristics have also been evaluated for this report. They are so small and limited that the polarization is not a factor needing careful wireless link designs and layout considerations.

A deep space communication testbed for Ka-band and X-band has developed at Japan Aerospace Exploration Agency (JAXA). High-quality communication technologies are required to combat severe conditions including a deep space radio channel, a low SNR, a power limitation, and a long time synchronization. For this requirements, a phase noise significantly affect a specific quality-of-service. We therefore measured the phase noise using the testbed to understand the behavior in terms of a temperature variation, and then found two types of phase difference, a slow variation during the constant temperature and a fast variation during the temperature variation more than one degree. The two types of phase noise are modeled using a stochastic method. The characteristics of jitter and BER performance affected by the phase noise were obtained by several QPSK system simulations.

Spectrum analyzers (SAs) are usually used to measure average and peak power spectra of ultra wideband (UWB) signals. Whereas the average power is measured in a 1-MHz resolution bandwidth (RBW), the UWB peak power is defined in a 50-MHz RBW. Most of the SAs, however, are not equipped with the 50-MHz RBW. Hence the power spectrum measured in a narrower RBW must be converted into the peak power spectrum in the 50-MHz RBW, but the conversion formula has not been well established. The RBW is defined with an impulse bandwidth (IBW) for peak power measurement in CISPR Publication 16-1-1, but most SAs do not strictly follow the CISPR definition. In this report, the IBWs of seven different SAs were measured by using an impulse signal. Then the three different UWB signals were measured in a 1-MHz RBW with the seven SAs, and the power spectra were converted into 50-MHz peak power spectra using conventional and new formulas. These UWB signals were also measured with a digital storage oscilloscope and then Fourier-transformed into 50-MHz-RBW spectra. The new formula using IBW instead of RBW yielded the consistent peak power spectra, which were found to be independent of SAs and to agree with the oscilloscope measurements.

A Ka-band coherent transmission function has been prototyped to be added to an existing X-band deep space digital transponder. An onboard ultra stable oscillator (USO) has been also developed to enhance the performance in communication and ranging. The coherence is guaranteed at direct digital synthesizers by multiplying a reference frequency by the numbers corresponding to the frequency ratios: 3328/749, 3344/749, and 3360/749, respectively. This paper describes experimental evaluation of high speed modulation and phase noise characteristics of the Ka-band transmission function. Distortion was found low enough to attain the high-rate transmission up to 500M symbols/s.

This paper presents the simulated interference effects from multiband orthogonal frequency division multiplexing (MB-OFDM) and direct sequence ultra wideband (DS-UWB) systems to a quadrature phase shift keying (QPSK) narrowband digital wireless transmission system in flat Rayleigh and Nakagami-Rice fading channels. The simulation utilized modified equivalent baseband system, embracing the fading channel models. Average bit error rate (BER) and error vector magnitude (EVM) performances were estimated. The interference effects of MB-OFDM and DS-UWB signals were almost the same as the that of additive white gassing noise. When the interference of UWB signal had lower power than receiver noise, the effect of fading channel dominated the BER and the EVM performances.

Scale COupling in the Plasma universE (SCOPE) is a formation flight mission ongoing in Japan Aerospace Exploration Agency (JAXA). This has been studied for realizing its upcoming magnetospheric exploration with advanced instruments. In this mission, a ranging function between the spacecraft is crucial along with data communications. The distances the between spacecrafts will vary from 1 to 100km; and the required accuracy is its 1/100. To meet these requirements, a time division multiplex and time division multiple access (TDM/TDMA) inter-spacecraft link system has been proposed. A breadboard model (BBM) comprising a mother and two daughter spacecrafts was constructed. The experimental result of ranging performances met the requirements for various transmission rates of data links.

Ultra wideband (UWB) signal propagation was measured and characterized in comparison with narrowband inside a typical some satellite, considering the potential to realize ultra-high-speed wireless bus connection with in mass and layout restrictions. Spatial distributions of UWB and narrowband path gain, delay profiles, and delay spreads within the mockup were derived from frequency-domain responses (from 3.1 to 10.6GHz) measured with a vector network analyzer and UWB monopole antennas. While narrowband resulted in a number of dead spots (deep fading points), UWB yielded none. This means the UWB systems have an advantage over narrowband ones from this propagation a viewpoint for reducing the fading margins.

NASA and ESA have taken advantage to use Ka-band (32GHz) for the purpose of higher-rate data transmission, more precise orbit determination, and radio science tools for planetary explorations. JAXA has developed a next generation X-band deep space digital transponder for our deep space programs such as Planet-C and MMO. As a next step, we will soon give a Ka-band coherent transmitter function to extend this X-band transponder capability. We will discuss primary design on this Ka-band transmitter attachment. We are also interested in a highly stable onboard oscillator which limits availability of Ka-band telecommunications in deep space. We will introduce our approach to JAXA's USO (ultra stable oscillator) and its in-house validation method for future development.

The paper experimentally validates the simulated interference effects from multiband orthogonal frequency division multiplexing (MB-OFDM) systems and direct sequence ultra wideband (DS-UWB) systems to a quadrature phase shift keying (QPSK)-modulated narrowband digital wireless transmission systems. Average bit error rate (BER) degradation of victim systems was evaluated under the in-band interference from the UWB sources. The experimental results of the BER degradation were nearly identical to the simulated ones. The BER degradation caused by the UWB sources was similar to AWGN. The proposed modified equivalent baseband system reduced the simulation cost. The simulation time using the proposed modified equivalent baseband system is significantly shorter than that using real frequency system.

This paper reports on a study of the interference effects from 2 types of ultra wideband (UWB) sources on a QPSK transmission system by simulation. The culprit UWB sources were: multi-band orthogonal frequency-division multiple-access (MB-OFDM) and direct-sequence UWB (DS-UWB), which were modeled on the proposal specifications in the IEEE802.15.3a to standardize high-speed wireless personal area networks. Average bit error rate (BER) degradation of the victim system was evaluated under in-band interference from the UWB signals. The proposed modified equivalent baseband system was employed in the simulation in order to reduce the simulation costs. Interference effects from the UWB sources were also examined under a Rayleigh fading channel.

The paper experimentally evaluates the interference from multiband orthogonal frequency division multiplexing (MB-OFDM) systems and direct sequence ultra wideband (DS-UWB) systems to a quadrature phase shift keying (QPSK)-modulated narrowband digital wireless transmission systems. Statistical properties of the UWB sources and the average bit error rate degradation of the QPSK system are presented. The UWB sources and additive white gaussian noise (AWGN) nearly identical statistical properties. The amplitude probability distributions (APDs) of the DS-UWB signal greater than small probability is different the AWGN when the center frequency of the victim reciever coincides a multiple of the pulse repetition frequency of the impulse.

The interference was studied between direct sequence ultra wideband (DS-UWB) systems and quadrature phase shift keying (QPSK)-modulated narrowband digital wireless transmission systems. Experimental (from UWB to narrowband) and numerical (from narrowband to UWB) evaluation of average bit error rates was carried out. Electromagnetic compatibility of the two systems was discussed in an additive white gaussian noise channel without fading.

This report studies the interference between multiband orthogonal frequency division multiplexing (MB-OFDM) systems and quadrature phase shift keying (QPSK)-modulated narrowband digital wireless transmission systems. Experimental (from UWB to narrowband) and numerical (from narrowband to UWB) evaluation of average bit error rates or packet error rates were carried out. Electromagnetic compatibility of the two systems was discussed in an additive white gaussian noise channel without fading.

This paper studies the interference effects from 4 types of ultra wideband (UWB) sources on a narrowband π/4-shift differential quadrature phase keying (DQPSK) transmission system by simulation. The culprit UWB sources were : multi-band orthogonal frequency-division multiple-access (MB-OFDM), direct-sequence code-division multiple-access (DS-CDMA), DS spread spectrum UWB (DS-SS UWB), and additive white Gaussian noise (AWGN). The MB-OFDM and DS-CDMA were modeled based on the proposal specifications in the IEEE.802.15.3a to standardize high-speed wireless personal area networks. Average bit error rates (BER) degradation of the victim system was evaluated in the presence of the UWB signals as a source of interference. We propose a modified equivalent baseband system to accelerate the simulation speed. In the proposed system, the victim system was generated in the p assband domain, while the UWB signals were generated at the equivalent baseband domain to lower the sampling rate of the simulation. It was found that the interference effects of the UWB signals vary according to their statistical characteristics entering the victim receiver. The MB-OFDM marks spectral peaks at every 3.2 MHz in the frequency spectrum, thus, would severely degraded the BER performance in the victim system. The amplitude probability distributions of the UWB signals entering the victim receiver were also investigated.

Ultra wideband (UWB) wireless technologies have attracted extensive attention, due to their potential to realize ultra-high-speed communications and high precision telelocation, and to economize devices though COMS technologies. Whereas most of the research activities on UWB technologies have been carried out by simulations, the authors have been focused on experimental studies on UWB propagation and interference to the incumbent narrowband systems. This paper introduces an omnidirectional, low-VSWR UWB antenna, UWB signal sources and receivers, a UWB over fiber transmission system, and UWB electromagnetic phantom materials. Some of their applications to experimental studies are also presented.