Katsuyuki Motoyoshi

Likelihood Estimation for Reduced-Complexity ML Detectors in a MIMO Spatial-Multiplexing System

This paper proposes a likelihood estimation method for reduced-complexity maximum-likelihood (ML) detectors in a multiple-input multiple-output (MIMO) spatial-multiplexing (SM) system. Reduced-complexity ML detectors, e. g., Sphere Decoder (SD) and QR decomposition (QRD)-M algorithm, are very promising as MIMO detectors because they can estimate the ML or a quasi-ML symbol with very low computational complexity. However, they may lose likelihood information about signal vectors having the opposite bit to the hard decision and bit error rate performance of the reduced-complexity ML detectors are inferior to that of the ML detector when soft-decision decoding is employed. This paper proposes a simple estimation method of the lost likelihood information suitable for the reduced-complexity ML detectors. The proposed likelihood estimation method is applicable to any reduced-complexity ML detectors and produces accurate soft-decision bits. Computer simulation confirms that the proposed method provides excellent decoding performance, keeping the advantage of low computational cost of the reduced-complexity ML detectors.

An Adaptive Beam Control Technique for Q Band Satellite to Maximize Diversity Gain and Mitigate Interference to Terrestrial Networks

The earth observation missions have been improved its sensor performance which results in a huge amount of data to be stored in remote sensing satellite and transmitted to a ground station. Although, satellite to ground transmitter had been usually used X band, several mitigation techniques for rain attenuation have been studied in recent years to migrate to Ka band for broadband transmission. Furthermore, Q band is expected to achieve higher data rate because of its broader bandwidth. However, Q band is shared with terrestrial networks, remote sensing satellite has to take into account potential constrains to them. Therefore, this paper addresses remote sensing satellite network and proposes novel beam control technique to coexist with the terrestrial networks in Q band. The proposed method controls satellites transmitting antenna boresight adaptively to maximize signal to noise power ratio of satellite ground station and minimize interference to terrestrial networks. The effectiveness of our proposal is verified through simulation results.

An adaptive beam control technique for diversity gain maximization in LEO satellite to ground transmissions

The earth observation missions have improved its sensor performance, it results in a huge amount of data to be stored and transmitted to a ground station. Although, satellite to ground transmitter had been usually used X band, migration to Ka band has been studied in recent years for broadband transmission. Relative to X band, higher frequency has severe atmospheric effects, site diversity is one of the popular technique to mitigate rain attenuation. However, if Signal to Noise power Ratio (SNR) is different between receivers because of receiving antenna gain and rain attenuation, diversity gain decreases. This paper proposes novel beam controlling method to improve SNR performance for satellite to ground transmission. The proposed method estimates SNR in each of candidate transmitting antenna boresight, and update boresight in order to be equal SNR between receivers. Simulation results show that, proposed method improves SNR especially at a low elevation angle.

Flexibility-Enhanced HTS System for Disaster Management: Responding to Communication Demand Explosion in a Disaster

Natural disaster interrupts essential services due to the facility damage and lack of power supply. Especially, significant communication outages occurs in a wide area for hierarchical network such as cellular communication system in case core nodes are damaged or congested. In order to provide alternative communication ability, high throughput satellite (HTS) is one of the ideal candidates for disaster management because it provides operative communication for a wide area regardless of the availability of regular terrestrial infrastructures. However, conventional HTS relays data with predetermined beam bandwidth and connection, it is inefficient when the communication demand explodes in a disaster area. Therefore, this paper proposes novel frequency allocation technique with flexibility-enhanced HTS system for disaster management to respond to communication demand explosion. While related research works consider user-link resource allocation, this paper focuses on how to control feeder-link and user-link bandwidths in case that the both links can be assigned at continuous frequency such as Ka-band. Furthermore, our proposal addresses resilient satellite network by selecting optimum gateway based on the traffic demand at neighboring user-link beams. The effectiveness of our proposal is verified through simulation results.

Frequency-Domain Equalization Incorporated with Frequency-Domain Redundancy for OFDM Systems

This paper proposes a frequency-domain equalizer (FEQ) which utilizes not only guard interval but also redundancy in the frequency domain to eliminate inter-symbol and inter-carrier interferences. The proposed FEQ employs the hybrid criterion, i.e., the zero-forcing (ZF) criterion for compensating desired subcarriers and the minimum mean square error (MMSE) criterion for suppressing interference. The proposed Hybrid-FEQ achieves a good equalization performance, because it can suppress the noise enhancement caused by the ZF criterion with relatively small computational complexity exploiting soft-decision forward error correction (FEC). In this paper, we show its equalization performance and complexity compared with the conventional FEQs.

A Co-channel Interference Cancellation Method Using Low Dimensional Sphere Decoding for MIMO Communication Systems

This paper proposes a co-channel interference cancellation method for multiple-input multiple-output (MIMO) wireless communication systems. Maximum-likelihood multi-user detection (ML-MUD), which is one of the co-channel interference cancellation methods at a receiver side, has excellent bit error rate (BER) performance. However, computational complexity of the ML-MUD is prohibitive, because the ML-MUD must search for the most probable symbol vector from all candidates of the transmitted signals. We apply sphere decoding (SD) to the ML-MUD in order to reduce the computational complexity of the ML-MUD, and moreover we propose a modified version of the SD suitable for the ML-MUD. The proposed method extracts desired signal components from a received signal vector and a channel matrix decomposed the upper triangular form, and then performs the SD to the low dimensional model in order to detect the transmitted signals of the desired user. Computer simulation confirms that the proposed method can suppress the undesired signals and detect the desired signals, offering significant reduction of the computational complexity of the conventional method.