Possibility Of Performance Enhancement Research Articles

On Pilot Spoofing Attack in Massive MIMO Systems: Detection and Countermeasure

Massive MIMO systems are vulnerable to pilot spoofing attacks (PSAs) since the estimated channel state information can be contaminated by the eavesdropping link, thus incurring severe information leakage in downlink transmission. To safeguard legitimate communications, this paper proposes a PSA detection method which relies on pilot manipulation. Specifically, users randomly partition pilot sequences into two parts, where the first part remains unchanged and the second one is multiplied with a diagonal matrix. Although a malicious node may follow the same way to send pilots, this makes it more likely to be detected. According to the principle of the likelihood-ratio test, the proposed detector is designed based on a decision metric that does not include the legitimate channel. This feature differentiates our scheme from existing ones and remarkably improves the detection accuracy. Besides, the possibility of performance enhancement by joint detection is discussed. Furthermore, based on pilot manipulation, a jamming-resistant receiver is designed. The key of this receiver is a new channel estimator that is robust to the PSA. Finally, extensive simulations are carried out to validate our proposed algorithms.

Long-distance distributed acoustic sensing utilizing negative frequency band.

Wider bandwidth always means better overall performance for an information system. Naturally, this criterion can also be applied to phase-sensitive optical time domain reflectometry (Φ-OTDR), which is a typical distributed optical fiber sensing (DOFS) system. Thus, an indispensable way to enhance the performance of Φ-OTDR is to increase the available system bandwidth, which is usually limited by the electrical components. As a kind of frequency resources, the negative frequency band (NFB) has been used in communication systems based on coherent receivers and high-order modulation, but is still rarely used in DOFS. In this paper, we make a comprehensive study on how to utilize NFB in Φ-OTDR and thus double the available system bandwidth. Moreover, the related improvement of sensing performance is experimentally demonstrated. The positive and negative frequency multiplexing is utilized together with frequency division multiplexing to break the inherent trade-off between sensing distance and scan-rate. As a result, 21.6 kHz scan-rate is experimentally achieved on a 103 km fiber, with 97 pε/Hz strain resolution and 9.3 m spatial resolution. To the best of our knowledge, this is the best sensing performance in long distance Φ-OTDR > 100 km. The proposed scheme can also be applied to other DOFS systems with heterodyne-detection, opening up new possibilities for performance enhancement in DOFS systems.

Conceptual design and exergy analysis of combined cryogenic energy storage and LNG regasification processes: Cold and power integration

This study aims to develop an efficient cryogenic energy storage (CES) process using the exergy from liquefied natural gas (LNG) regasification. While LNG has low internal energy, it has high exergy because of its cryogenic characteristics, and much of this exergy is wasted in the process of regasification. Thus, this work focuses on the recovery of LNG cold exergy to store cryogenic energy using air as a working fluid. The cold exergy of LNG is transferred in two forms: cold transfer by heat exchange to liquefy air, and shaft work transfer by direct expansion of LNG to compress the air. Thermodynamic analysis of the proposed process is carried out in three exergy flow steps: the LNG regasification step, the air liquefaction step, and the air expansion step. In addition, the proposed system has an advantage which system can store and release the energy simultaneously. Therefore, daily produced energy by CES system is more than double compare to the most recent contributions that have divided operation modes for energy storage and release. This study not only proposes an efficient energy storage process that can generate power flexibly but also highlights further possibilities for performance enhancement by thermodynamic analysis.

ガーメントの力学特性が走動作へ及ぼす影響

The purpose of this study is to develop a methodology that enables to directly evaluate the wearing effect of sport apparel on athletic performance. The torque due to garment is estimated by using the musculo-skeletal model SIMM, The mechanical properties of garment are obtained from a mechanical test. The relationship between exerted garment torque and movement are induced by using motion equations with the components of the body and a garment on it. With the methodology, the possibility of performance enhancement in sprinting was investigated with a world-wide top athlete by calculating the contribution of exerted garment torque to the sprint speed. The results indicate that the exerted garment torque would help to increase the sprint speed and the contribution of the garment to the performance increased gradually toward the end of contact phase. It is suggested that the garment structure that supports plantar flexion movements in sprinting can provide plantar flexion torque even at take off phase.

Energy Relay Systems for Efficient Organic Light-Emitting Devices: Influence of Formation of Exciplex as Revealed by Photoexcitation

We investigated potential of performance enhancement for organic light-emitting diodes (OLEDs) by an energy relay system through exciplex formed between a hole transport material (HTM) and an electron transport material (ETM) as revealed by photoexcitation. An enhancement of a dopant (Coumarin 6) emission occurred depending on combination of HTM and ETM, and the dependency can be explained by an overlap integral between an exciplex emission and an absorption of Coumarin 6 as a dopant. Possibility of performance enhancement by the energy relay system was suggested experimentally.