Masayuki Orihashi

Varying interleave patterns with iterative decoding for improved performance in MIMO systems

This paper examines an iterative decoder for reproducing transmitted data correctly and executing cancellation of interference channel signals accurately in convolutionally encoded MIMO (multi-input multi-output) systems. We propose the iterative decoder equipped with VIP (varying interleave patterns) for each transmission channel, and demonstrate the decoder can obtain a gain value close to full diversity gain in the MIMO systems. The results in a computer simulation indicate clearly that, due to mutual random interleave effect; a gain value near full diversity gain can be obtained under Rayleigh fading channels.

Performance Analysis Based on Channel Matrix Eigenvalue for MIMO Systems in LOS Environments

This paper makes an examination of BER (bit error rate) performance in 2 × 2 MIMO (Multi-Input Multi-Output) systems using spatial multiplexing in a LOS (line-of-sight) environment by analysis using the eigenvalue and eigenvector of the channel matrix and simulation. It is shown that BER performance in a LOS environment is dependent on the phase relation of direct paths and the minimum squared absolute value of the eigenvalue, which are determined by the propagated distance. A technique for improving BER performance in a LOS environment is then considered based on these findings. A receive antenna selection (RAS) technique is presented which uses the minimum squared absolute value of the channel matrix eigenvalue. Proof is then given that BER performance is improved using this RAS technique, thus making clear the validity of this approach for obtaining optimum BER performance in a LOS environment.

Adaptive predistortion linearizer with digital quadrature modem

Linearization of power amplifiers using baseband signal processing is an important technique applied in digital mobile communication equipment. However, the linearizer performance has been severely influenced by IQ gain/phase imbalance and DC offset in quadrature modems, significant elements of linearizers. In order to eliminate these detrimental influences, a linearizer using a digital quadrature modem has been developed. This paper describes an adaptive predistortion linearizer using a simplified digital quadrature modem with which experimental results of less than -63 dBc of ACI (adjacent channel interference) have been obtained. This excellent performance may be applied in base stations relating to mobile communication systems.

Channel synthesized modulation employing singular vector for secured access on physical layer

This paper proposes the channel synthesized modulation (CSM) employing singular vector. The channel synthesized modulation is designed to decompose the modulation waveform to n transmitting signals according to the channel parameter between transmitter and receiver. Since the singular value decomposition (SVD) produces singular vectors as characteristics of matrix, these are suitable parameters for the channel synthesized modulation to decompose. And these parameters also enable establishment of secured access easily. This paper describes the principle of the channel synthesized modulation and SVD analysis, and introduces secured access employing the singular vectors with the channel synthesized modulation, and then shows its performance.

Analysis of BER performances using channel matrix eigenvalue in MIMO systems under Rayleigh and Rician fading channels

In this paper BER (bit error rate) performances in MIMO (multi-input multi-output) systems under Rayleigh and Rician fading channels are examined using the channel matrix eigenvalue. We show that BER performances employing inverse channel detection can approximate those by analysis using the channel matrix eigenvalue under Rayleigh fading channels. We then examine BER performances under Rician fading channels by simulation, adding the phase of the direct path as a parameter. The results clearly indicate that the phase of the direct path has a great influence on BER performances under Rician fading channels.

Soft-decision decoder employing eigenvalue of channel matrix in MIMO systems

This paper proposes a new soft-decision decoder employing the eigenvalue of the channel matrix as a weighting factor for conventional codes in MIMO (multi-input multi-output) systems. As is generally known, sufficient coding gain in a soft-decision decoder can only be obtained by employing the square Euclidean distance as a branch metric under AWGN (additive white Gaussian noise) channels. On the other hand, this gain cannot be obtained by simply doing the same under Rayleigh fading channels. This paper studies a suitable weighting factor for obtaining the coding gain in soft-decision decoders under Rayleigh fading channels in MIMO systems. First, we propose that the minimum eigenvalue power of the channel matrix indicates an effective carrier power in MIMO systems. Next, we propose the effective carrier power as a weighting factor for soft-decision decoders. We then calculate BER performance. According to the results, the proposed decoder gives a margin of about 5 dB at BER=10/sup -4/ compared to a conventional decoder employing received power as a weighting factor. The results also demonstrate that the proposed weighting factor can enhance the ability of soft-decision decoders under frequency non-selective Rayleigh fading channels in MIMO systems.

Performance Evaluation of Transmission Technique Utilizing Linear Combination Diversity in MIMO Spatial Multiplexing Systems

In this paper, we evaluate BER (bit error rate) performance and diversity gain when employing a transmission technique utilizing LC (Linear Combination) diversity using 2 time slots with QPSK channels in 2×2 MIMO (Multiple-Input Multiple-Output) spatial multiplexing systems by comparing it with the upper and lower bound on BER. This evaluation shows that this transmission technique realizes high diversity gain and high transmission rate in LOS (line-of-sight) and NLOS (non line-of-sight) environments.

A new design of pilot symbol in 16 QAM channels

Pilot symbols are generally inserted as a compensation technique in wireless communication systems employing 16-quadrature amplitude modulation (16 QAM). This paper describes newly developed pilot symbol techniques in 16 QAM channels. There are two methodologies; one is where the pilot symbol is put on the in-phase (I) or quadrature-phase (Q) axis, and the other is where a signal state of a individual symbol before and after the pilot symbol is set on the line passing through the origin and the signal point of the pilot symbol. According to our investigation of peak-to-average power ratio (PAPR) for transmitted signal and bit error rate (BER) performances in a receiver, the first technique gives a margin of about 1.0 dB at a BER of 1.0/spl times/10/sup -6/ without affecting the PAPR compared with conventional techniques. Furthermore, BER performance becomes error free when the roll-off factor is /spl alpha/=0.2 where in the second technique the symbol synchronization offset exists and Eb/No=/spl infin/. This suggests that our proposed technique improves both transmitter and receiver performance in narrow band wireless communication employing 16 QAM.

Multiplex and division techniques of non-spread and spread spectrum signals

This paper proposes a technique where non-spread and spread spectrum (SS) signals are combined in the same frequency band. It shows that the multiplex technique proposed is an effective method for making good use of a limited frequency band. Furthermore a system using this multiplex technique can transmit data of different speeds and quality at the same time. The multiplex signal presented here is where non-spread quadrature phase shift keying (QPSK) and direct sequence spread spectrum DS-SS signals are combined, with reference symbols being inserted without multiplexing for easy estimation of the channel condition. A technique is then proposed to divide the multiplex signal in the receiver. Using this technique, bit error rate (BER) performances of non-spread QPSK and DS-SS are calculated under additive white Gaussian noise (AWGN) and Rayleigh fading channels. According to the results of the BER performance for non-spread QPSK and DS-SS, it is clear that the multiplex signal can be divided and data can be retrieved in the receiver.

Likelihood Detection Utilizing Ordering and Decision of Partial Bits in MIMO Systems

We propose a likelihood detection scheme that utilizes ordering and decision of partial bits in MIMO spatial multiplexing systems. We compute BER performance of the proposed detection scheme under Rayleigh fading channels in a 3 x 3 MIMO spatial multiplexing system and compare it with BER performance using MLD only and detection utilizing ZF or MMSE only. In addition, the computational complexity of the proposed detection scheme is compared with that of MLD and detection utilizing ZF or MMSE. The results of our investigation show that the proposed detection is a scheme achieves both good BER performance and low computational complexity.