Ken-ya Hashimoto

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In recent, orthogonal frequency division multiple access (OFDMA) has been used for a multiuser wireless communication. In a wireless network, the transmitted signal of each user has independent channel fluctuation characteristic. By using this characteristic, OFDMA can achieve the multiuser diversity (MUDiv). Until this time, to achieve a low complexity and(More)
A direct-conversion receiver (DCR) reduces the power consumption and cost. However, DCR in Orthogonal frequency division multiplex (OFDM) systems suffer from IQ imbalance. Until this time, many algorithms are proposed to compensate IQ imbalance in OFDM. However, the complexity is still considerable work. On the other hand, time-frequency interferometry-OFDM(More)
Massive MIMO has been recognized as promising ways to provide high speed data transmission. However, since the number of pilot symbol is proportionally depending on the number of transmit antenna, the total transmission rate of massive MIMO would be degraded. To solve this problem, channel estimation by virtual pilot signal (VPS) with a few pilot signals(More)
At present, the theory and algorithm of wireless indoor positioning systems have been widely researched. Some applications of these systems have been successfully used such as inventory management. Nevertheless, positioning using radio signals indoor is subject to multipath propagation and other causes. Therefore, how to determine the location accurately(More)
Wireless visible light communication system uses LED illumination for data transmission. It is important for a performance index to evaluate a variation of communication quality with the number of users. Although CDMA (Code Division Multiple Access) is a representative of a conventional multiple access in a wireless communication, the maximum number of(More)
Recently, visible light communication(VLC) is widely researched due to the spreading of LED usage. It satisfies demands of ubiquity and high speed communication. However, it is impossible to transmit the phase information and frequency information due to limitation of LED. From this reason, the achievable transmission rate is worse than that of wireless(More)