Welcome to Masayoshi Tanaka  Website  

Research activities of wireless & satellite communications in the following laboratories.
-  College of Industrial Technology, Nihon University, 
     Department of Electrical and Electronic
     Engineering.​
-  NTT Electrical Communications Laboratories.
  

We developed spatially superposed highly efficient 32 APSK and 64QAM modulation broadband communication systems.

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Recent advances in information technology have led to a growing demand for high-speed access to the Internet anytime, anywhere, and at a reasonable cost to the consumer. A broadband multimedia satellite communications system is a promising network access system because it would allow us to easily and rapidly construct a broadband system over a wide area as compared to other wired systems.

 

However, we have to resolve some issues for satellite communications systems to play a leading role in a broadband network. One such issue is to establish an economical system design. The other is to boost capacity and to find a way to transmit over a band-limited channel at very high data rates.

 

To address the issue of the transmission, using M-ary signals would be effective for broadband transmission in a frequency-band-limited system. However, an M-ary modulation scheme is generally much more vulnerable to thermal noise and nonlinear distortion from power devices than a widely used QPSK scheme. This means we have to increase the carrier-to-noise power ratio (CNR) and reduce the distortion to achieve a specific transmission quality.

 

Some back-off is effective in attaining an acceptable level of distortion in a practical power amplifier. However, power efficiency decreases when back-off occurs. Increasing the output power and the power consumption of high-power transmitters is undesirable for constructing an economical satellite system. This is the main reason an M-ary system has not been widely used for power-limited systems and is the major barrier to achieving an inexpensive satellite communications system.

 

We developed highly efficient 16QAM, 32 APSK, and 64-quadrature amplitude modulation (64QAM) transmission systems for satellite broadband communication that improve the usage efficiency of frequency resources and energy.

 

They feature multi-beam spatial superposition. The systems incorporate quaternary phase-shift keying (QPSK) modulators and/or an 8PSK modulator and multiple high-power amplifiers (HPAs) that operate in their nonlinear region at a high level of efficiency.

 

The lower amplitude change for the QPSK and 8PSK signals enables the HPAs in the proposed system to operate in the nonlinear high-efficiency region in which conventional systems cannot operate. After being power-amplified, their output signals are spatially superposed using a specially tailored antenna to produce  16QAM, 32APSK, and 64QAM signals.

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1. 8x4 =32 APSK:

We developed a highly efficient 8x4 amplitude-phase shift keying (8x4 APSK) modulation broadband communication system that features a compact two-beam spatial superposition that improves the usage efficiency of the frequency resources and energy.

 

The system incorporates an eight phase-shift keying (8PSK) modulator, a quadrature phase-shift keying (QPSK) modulator, and multiple high power amplifiers (HPAs) that operate in their nonlinear region at a high level of efficiency. Their output signals are spatially combined using a specially tailored antenna array to produce a new 8x4 APSK signal.

 

The system had a better bit error rate (BER) performance than a conventional 32APSK system when operated in the HPA nonlinear high-efficiency region. Theoretical transmission analysis showed acceptable spatial superposition errors.

 

We also proposed an antenna array system suitable for combining the two beams. An antenna array study demonstrated that the acceptable errors were attained with the proposed circular array system over a +/- 5-degree angle and this range is wide enough to cover satellite communication service areas. The HPA power consumption was reduced by about 50% compared with that of the conventional system. Thus, the proposed compact system is feasible and will enable broadband transmission while using the available amount of energy and bandwidth more efficiently.