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Satoshi Taroda,Ken Tezuka,Shoichi Higuchi,안창준,Kazuki Maruta 한국통신학회 2019 ICT Express Vol.5 No.4
Due to large peak-to-average power ratio (PAPR) at the time domain OFDM signal, various peak signal reduction methods for OFDM systems have been proposed. However, in a transmit OFDM beamforming, multiplication of the transmit signal using the weights causes transmit power imbalance between antennas and increases peak signal. We propose two approaches to mitigate these problems. Adding the pseudo-noise to covariance matrix at the process of weight calculation can alleviate the transmit power imbalance. Furthermore, the companding transform of time domain signal can reduce the peak signals. We show details of proposed methods and evaluate PAPR and BER performance.
Variable-channel Threshold-based Hybrid AF-DF Cooperative Communications with Packet Splitting
Ken Tezuka,Satoshi Taroda,Shoichi Higuchi,Kazuki Maruta,Chang-Jun Ahn 대한전자공학회 2018 IEIE Transactions on Smart Processing & Computing Vol.7 No.5
Cooperative communications has been widely researched as an attractive way to improve wireless communications systems with a small number of antennas and low power consumption. However, forward processing in the relay terminals means consuming the power of relays in other terminals. Therefore, the waste of electricity from forwarding is to be reduced as much as possible. In this paper, we propose and analyze a new relay system for three-node, hybrid, cooperative communications systems, where the relay terminal may choose to transmit messages using amplifyand-forward (AF) with expansion of the channel matrix or using decode-and-forward (DF) with packet-splitting transmission. This is based on the qualities of the channels in the source–relay and source–destination links. Then, in the proposed system, the decision on the forwarding scheme is made in order to calculate a threshold based on the equation of the channel capacity. From the simulation results, the proposed system can improve the bit error rate and reduce the load from forward processing latency at the relay.