Yasuyuki Hatakawa

Experimental evaluation of open-loop precoding MIMO using the testbed targeted at IMT-Advanced system

This paper presents an experimental evaluation of open-loop precoding MIMO (multiple input multiple output) using a testbed targeted at IMT-Advanced systems. Open-loop MIMO is realized by applying rotational OFDM (R-OFDM), that is previously proposed by authors, to MIMO transmission. MIMO R-OFDM is more robust with respect to correlated channels than conventional open-loop MIMO-OFDM, because it optimizes the distances between the constellation points using simple phase rotation. The angle of phase rotation depends on the modulation orders and coding rate, hence the receiver does not need to feed the CSI (channel state information) back to the transmitter. In this paper, MIMO R-OFDM is implemented in a testbed targeted at IMT-Advanced systems, it is then evaluated experimentally and by computer simulations. The results of the evaluation reveal that MIMO R-OFDM is effective in correlated channels, and the gain in terms of the CIR (carrier to interference ratio) with respect to conventional MIMO OFDM to achieve PER (packet error rate) = 0.01 is about 1.5 dB when MIMO R-OFDM is used in correlated channels.

A Study on Rotational OFDM Transmission with Multi-Dimensional Demodulator and Twin Turbo Decoder

This paper proposes rotational orthogonal frequency division multiplexing (R-OFDM) transmission with multi-dimensional demodulator (MDD) and twin turbo decoder (T2D). R-OFDM uses rotational multi-carrier modulation (R-MCM), which provides suitable frequency diversity gain in any coding rates although coded OFDM cannot obtain it in high coding rates. In addition, by applying MDD to its receiver, R-OFDM does not cause inter symbol interference degrading multi-carrier code division multiplexing (MC-CDM) with Walsh code multiplexing (WCM). Then, aiming at high spectrum efficiency, T2D is also proposed. T2D is based on a turbo decoder and has the proposed likelihood estimation taking into account the mutual information between multiplexed bits in the identical received symbol. Computer simulations verify that the proposed scheme improves the packet error rate (PER) performance of not only MC-CDM with WCM, but also OFDM, and the required Es/N0 of the OFDM obtaining a PER of 1% is improved by about 1.5 dB at the maximum.

A Study on Likelihood Estimation Method Taking Account of Mutual Information in Multi-Level Symbol ~ A Proposal of Twin Turbo Decoder ~

Aiming at high spectrum efficiency, this paper proposes the twin turbo decoder. The received symbol carried by multi-level modulation or MIMO (multi-input multi-output) transmission consists of two or more bits, and these bits share mutual information. However, the conventional likelihood estimation neglects this mutual information and deteriorates the estimation accuracy. This paper presents an alternative estimation method taking into account the above mutual information and applies our proposal to an iterative MAP (maximum a posteriori probability) decoder in order to improve its error correction capability. Computer simulations verify that the proposed scheme improves the PER (packet error rate) performance with the conventional method, and the required E SN0 obtaining a PER of 1 % is improved by about 1.0 dB at maximum. Note that our proposed method is called the twin iterative decoder (twin turbo decoder) because it has double feedback loops

Implementation and Experimental Results of Rotational OFDM Transmission: Rotational OFDM Performance with Turbo Decoder

This paper presents the experimental results of rotational orthogonal frequency division multiplexing (R-OFDM) performance with a turbo decoder implemented in an IMT-Advanced testbed. Taking into account recent advances in research and development toward realization of the IMT-Advanced system era, the authors are developing the testbed. The R-OFDM is multi-carrier transmission scheme and previously proposed by the authors. Its feature is to use rotational code division multiplexing that enables OFDM to obtain suitable frequency diversity gain. However, the previous work is only predicated on computer simulation. In this paper, the R-OFDM is implemented on the testbed and experimentally evaluated by distorting the R-OFDM signal on radio wave with a fading simulator. When packet error rate is measured, it is verified that measurement results are in good agreement with simulation results. The measured deterioration of required carrier-to-interference power ratio (CIR) is suppressed by about 0.5 dB compared with the simulation. The experimental results also demonstrate that the R-OFDM can reduce the required CIR of OFDM even without T2 decoder by about 1.1 dB.