Fumihiro Yamashita

Broadband multiple satellite MIMO system

This paper proposes a multiple satellite MIMO system for broadband mobile services. It also proposes a MIMO receiver that can handle the large spatial correlation and the different propagation delay of paths created by the use of multiple satellites. The receiver is characterized by multi-stage interference cancellation and maximal ratio combining. Several simulations are conducted assuming two satellites on the same GEO stationary orbit that are separated by about one degree. The simulation results show that the proposed receiver can typically obtain the diversity gain of about 1.0 dB at BER=10 -5 from the theoretical SISO BER curve due to its use of Even in the worst propagation case, the BER degradation is suppressed to about 1.5 dB.

Variable Polarization/Frequency Division Multiplexing (VPFDM) for Satellite Communications

To realize advanced broadband mobile satellite communications, this paper proposes a new wireless access approach named variable polarization frequency division multiplexing (VPFDM); it assigns the resources created by dual polarization states as well as frequency bandwidth to customers. The most significant problem in using dual polarization is cross-polarization interference. For satellite communications, when existing terminals and/or satellites employs asynchronous frequency conversion of V/H polarizations, received signals undergo a mixture of frequency offsets. Aiming to overcome this satellite-specific problem, we propose a novel VPFDM modem that can handle multi-carrier multi-rate dual polarization signals. The results of simulations and experiments show that the proposed modem is applicable to satellite communications.

Feasibility evaluation of VPFDM modem for polarization tracking-free Ku broadband mobile satellite communications

This paper introduces the results of experiments on a Variable Polarization Frequency Division Multiplexing (VPFDM) system for Ku broadband mobile communications systems. The VPFDM system eliminates the need for earth stations to provide polarization-tracking and enables dual polarization to be used efficiently. The results allow us to conclude that Ku band polarization-tracking-free systems can be realized with the additional link budget margin of just 0.8 dB.

Variable Polarization Frequency Division Multiplexing (VPFDM) Demodulator Tolerant of Tx and Rx Frequency Asynchronicity Between Polarizations

This paper proposes a new Variable Polarization Frequency Division Multiplexing (VPFDM) demodulator for Ku broadband mobile satellite communications system. VPFDM allows each user to utilize multi-carrier frequency slots of the Vertical and Horizontal polarizations simultaneously. Since the VPFDM demodulator cancels cross-polarization interference by using signal processing, a polarization tracking satellite antenna is not needed, which makes the user earth station simple and economical. Furthermore, VPFDM is based on multi-carrier system that flexibly utilizes unused and scattered frequency slots on the satellite transponder. Therefore, frequency utilization efficiency is improved. In this paper, to increase system flexibility, we introduce a novel VPFDM demodulator that does not depend upon the configuration of the RF module. The new VPFDM demodulator cancels cross-polarization interference even though V/H frequencies are asynchronous among the base station / satellite / user earth station. This paper focuses on the key technologies of the demodulator; details are given, and its performance is evaluated via computer simulations.

Multi-Carrier Multi-Rate Modem for Universal FDMA/TDMA systems

*† ‡ § This paper introduces a new multi-carrier multi-rate modem (MCMRM) module designed to support the Universal FDMA/TDMA system. Universal FDMA/TDMA is a new system that flexibly supports MF-TDMA and TDMA, as well as multi-rate FDMA. We believe that the Universal FDMA/TDMA system will allow both system operators and customers to utilize frequency and/or time resources more efficiently than is possible with conventional systems. To implement this system, we have developed a new MCMRM module. This module has several advanced functions such as a novel frequency multiplexer/demultiplexer, multi-carrier frequency decomposition/regeneration, and multi-carrier burst demodulation. This paper provides a detailed outline of those functions and evaluates their performance by computer simulations and experiments.

Broadband Multi-Satellite/Multi-Beam System with Single Frequency Reuse

This paper studies a multi-satellite multi-beam system with single frequency reuse which applies the MIMO (Multi Input Multi Output) technique. To improve the spectral efficiency of satellite systems in support of broadband communications, MIMO is the one of the most important approaches. Since it was difficult to achieve high spectral efficiency by simply combining a multi-beam system with single frequency reuse and a multiple satellite system, this paper newly proposes a pre- coding technique that takes account of the frequency offsets caused by the multiple satellites. We then evaluate our proposal by a cumulative distribution function (CDF) related to channel capacity and show the improvement of the spectral efficiency compared to the conventional satellite systems.

A Novel Digitally Polarization Tracking Antenna for Ku-band Mobile Satellite Communication Systems

This paper presents a novel electrical polarization tracking method for mobile satellite communication systems that use linear polarization. It consists of two main technologies; the first estimates the mobile station antenna’s relative polarization angle against that of the satellite’s onboard antenna, the second forms counter polarization against the estimated value. We use a Ku-band communication satellite to evaluate the polarization tracking characteristics and BER performances. These results show that the proposed antenna offers the desired performances.

Adaptive Multi-Carrier Demodulator for Variable Polarization Frequency Division Multiplexing

This paper proposes a new Variable Polarization Frequency Division Multiplexing (VPFDM) demodulator for Ku broadband mobile satellite communications. VPFDM allows each user to utilize multi-carrier frequency slots of the Vertical and Horizontal polarizations simultaneously. Since the VPFDM demodulator cancels cross-polarization interference by using signal processing, the user station can use a simple antenna that does not track polarization. In this paper, we introduce a new VPFDM demodulator with adaptive multi-carrier modulation (AMCM); it can vary the modulation level carrier by carrier to enhance frequency and power efficiency. We then propose a noise and frequency offset tolerant AFC that is the key to the success of AMCM. Finally, simulation results show its excellent performance. Keywords-component; Satellite communication, Adaptive signal processing, Polarization multiplexing, VPFDM

Seamless Symbol Rate Switching Scheme for Multi-Rate FDMA Modem

A new seamless symbol rate switchable modem for multi-rate FDMA systems is proposed in this paper. In the new modem, a novel clock phase compensation algorithm makes it possible to switch the symbol rate synchronously between the transmitter and the receiver, with no degradation in BER when the symbol rate is changed. In addition, by matching the interpolation filter to the symbol rate, this modem is capable of operating at lower clock speeds, which greatly reduces the consumption power. Computer simulations confirm its fundamental performance. Simulation results show that the proposed power-efficient symbol rate switchable modem can change the symbol rate without degrading BER performance.

AFC CONFIGURATION APPLICABLE TO A WIDE RANGE OF FREQUENCY OFFSET

This paper presents a new automatic-frequency control (AFC) configuration capable of removing a large amount of frequency offset (up to about +/- 0.625 fs, where fs means symbol rate of signals). The new AFC consists of the AFC that removes frequency offsets between +/- 0.125 fs and another AFC that detects the frequency offset range coarsely between +/- 0.625 fs. First, the principle of the new AFC configuration is described. Then, the performance of the new AFC is confirmed via computer simulation. It is shown that the proposed AFC configuration can accommodate wide range frequency offsets as well as reduce the acquisition time.