Kazuhiko Fukawa

10 Gbps millimeter-wave OFDM experimental system with iterative phase noise compensation

This paper presents a 10 Gbps millimeter wave OFDM experimental system using a highly efficient modulation and coding scheme where iterative phase noise compensation can drastically alleviate performance degradation due to phase noise. 60 GHz frequency synthesizer in a silicon RF-CMOS IC suffers from relatively large phase noise, which severely degrades the performance of the 10 Gbps OFDM using 64QAM and LDPC code with coding rate of 14/15. In order to alleviate this impairment, the experimental system applies combination of decision-directed phase noise compensation (DD-PNC), decision-directed channel estimation (DDCE) and packet interleaving (P-IL) to OFDM reception processing. The sophisticated combination of iterative processing provides a synergistic effect on coping with the influence of the phase noise by exploiting outputs of the LDPC decoder. Experimental results of the 10 Gbps OFDM with 60 GHz cable connection demonstrate that the combination can achieve 10 Gbps throughput at SNR of 25.8 dB when the phase noise level is -89 dBc/Hz at 1 MHz offset.

Iterative receiver employing phase noise compensation and channel estimation for millimeter-wave OFDM systems

This paper proposes an iterative OFDM millimeterwave receiver employing low-complexity decision-directed phase noise compensation (DD-PNC) to alleviate degradation due to the phase noise. High bit-rate OFDM transceivers based on the single-chip Si RF-CMOS IC technology in the 60-GHz millimeter-wave band have been extensively studied for wireless personal area network (WPAN) systems, and the relatively large phase noise in the phase locked loop (PLL) synthesizer severely degrades transmission performance. The proposed OFDM receiver iterates DD-PNC and decision-directed channel estimation (DDCE) by exploiting the output of the channel decoder. DDPNC estimates the phase noise each sampling time by using the decoder output, and then it removes the estimate from a time-domain received signal. In addition, DDCE estimates a channel impulse response by using the compensated received signal. Computer simulations demonstrate that in the 64QAM modulation with the coding rate of 3/4, the proposed receiver with DD-PNC and DDCE can perfectly remove the phase noise of -85 dBc/Hz at 1 MHz offset, and that it can alleviate the degradation of the channel estimation due to the phase noise.

Performance of Iterative Multiuser Detection with Channel Estimation for MC-IDMA and Comparison with Chip-Interleaved MC-CDMA

This paper applies iterative multiuser detection employing new channel estimation to multicarrier interleave- division multiple access (MC-IDMA), known as OFDM-IDMA, which is expected to improve spectral efficiency in mobile communications. The MC-IDMA transmitter uses both a low-rate channel code and an individual chip interleaver for each user. The MC-IDMA receiver, which this paper investigates, repeats the iterative multiuser detection and soft decision-directed channel estimation (SDCE) by exploiting log-likelihood ratios (LLRs) of the coded bits which the MAP-based channel decoders for all users provide. SDCE estimates channel impulse responses of all users by the LMS algorithm, which aims to minimize the mean squared error between the received signal and its replica. This paper investigates the performance of MC-IDMA employing SDCE and compares it with those of three MC-CDMA techniques. Computer simulations demonstrate that MC-IDMA employing SDCE outperforms time-spread MC-CDMA and frequency-spread MC-CDMA, and that it can achieve almost the same bit error rate performance as chip-interleaved MC-CDMA while requiring lower complexity.

PAPR Reduction Methods for Eigenmode MIMO-OFDM Transmission

This paper proposes methods that can reduce peak- to-average power ratio (PAPR) while maintaining performance improvement by linear precoding for the eigenmode MIMO- OFDM transmission. In the eigenmode MIMO-OFDM system, a transmitter performs linear precoding using channel state information (CSI), and thus excellent transmission performance can be achieved. However, the transmitted signal still has high PAPR because of OFDM characteristics. To reduce such PAPR, this paper enhances selected mapping (SLM) and partial transmit sequence (PTS) which are known as PAPR reduction methods for OFDM. The enhanced methods, which are referred to as eigenmode transmission SLM (EM-SLM) and eigenmode transmission PTS (EM-PTS), can be applied to the eigenmode MIMO- OFDM without any performance degradation. Computer simulations demonstrate that in 4times4 MIMO-OFDM, the proposed methods can drastically reduce PAPR, and thus they can alleviate performance degradation due to nonlinear amplification.

Suboptimal Algorithm of MLD Using Gradient Signal Search in Direction of Noise Enhancement for MIMO Channels

This paper proposes a suboptimal algorithm for the maximum likelihood detection (MLD) in multiple-input multiple-output (MIMO) communications. The proposed algorithm regards transmitted signals as continuous variables in the same way as a common method for the discrete optimization problem, and then searches for candidates of the transmitted signals in the direction of a modified gradient vector of the metric. The vector is almost proportional to the direction of the noise enhancement, from which zero-forcing (ZF) or minimum mean square error (MMSE) algorithms suffer. This method sets the initial guess to the solution by ZF or MMSE algorithms, which can be recursively calculated. Also, the proposed algorithm has the same complexity order as that of conventional suboptimal algorithms. Computer simulations demonstrate that it is much superior in BER performance to the conventional ones.

MIMO-OFDM MAP Receiver with Spatial-Temporal Filters Employing Decision-Directed Recursive Eigenvalue Decomposition Parameter Estimation

This paper proposes a new parameter estimation method for the MIMO-OFDM MAP receiver with spatial-temporal filters. The proposed method employs eigenvalue decomposition (EVD) so as to attain precise estimates especially under interference-limited conditions in MIMO-OFDM mobile communications. Recursive EVD is introduced to reduce the computational complexity compared to the nonrecursive EVD. The spatial-temporal prewhitening is placed prior to FFT because this arrangement is superior to that of conventional prewhitening posterior to FFT in accuracy of the parameter estimation. In order to improve tracking capability to fast fading, the proposed scheme applies a decision-directed algorithm to the parameter estimation by using log-likelihood ratios of coded bits. Computer simulations demonstrate that the proposed scheme can track fast fading and reduce the complexity to 18 percents of the conventional one, and that the spatial-temporal filtering prior to FFT outperforms the conventional one posterior to FFT.

Coded Single-Sideband QPSK and Its Turbo Detection for Mobile Communication Systems

This paper proposes a novel single-sideband quadrature phase shift keying (SSB QPSK) modulation scheme that utilizes a single-reference carrier frequency and transforms both baseband I and Q components into the same radio frequency band, whose width is exactly half that of QPSK. The modulation method is first derived and followed by the analysis of the matched filter demodulation. The analysis shows that there are performance degradations due to intersymbol interference (ISI) in the received signal and correlation in the received noise. To suppress the degradations, this paper employs a turbo equalizer for demodulation, in which the effects of ISI and noise correlation can be suppressed by a soft canceler and a noise whitening filter in the minimum mean square error (MMSE) linear equalizer, respectively. The computer simulations are then used to verify the proposed modulation scheme. At the transmitter, the root-raised cosine rolloff filter is employed for pulse shaping and Hilbert-transformed pulse generation. The truncation of the signal pulse is performed by the window function. The results show that the proposed modulation scheme outperforms 16-quadratic-amplitude modulation (16-QAM) with the turbo code in the Rayleigh-fading environment.

MIMO-OFDM Precoding Technique for Minimizing BER Upper Bound of MLD

This paper proposes a new MIMO-OFDM precoding technique that aims to minimize a bit error rate (BER) upper bound of the maximum likelihood detection (MLD) in mobile radio communications. Using a steepest descent algorithm, the proposed method estimates linear precoding matrices that can minimize the upper bound of BER under power constraints. Since the upper bound is derived from all the pairwise error probabilities, this method can effectively optimize overall Euclidean distances between signals received by multiple antennas and their replicas. Computer simulations evaluate the BER performance and channel capacity of the proposed scheme for 2×2 and 4×4 MIMO-OFDM systems with BPSK, QPSK, and 16QAM. It is demonstrated that the proposed precoding technique is superior in terms of average BER to conventional precoding methods including a precoder which maximizes only the minimum Euclidean distance as the worst case.

PAPR Reduction Method for Block Diagonalization in Multiuser MIMO-OFDM Systems

This paper proposes a peak-to-average power ratio (PAPR) reduction method that maintains an effect of linear precoding by block diagonalization (BD) for multiuser (MU) MIMO-OFDM systems. In the downlink MU-MIMO-OFDM, BD orthogonalizes multiple signals of all users by the linear precoding using channel state information, but the transmitted signal still has high PAPR due to OFDM characteristics. Therefore, BD suffers from waveform distortion caused by a nonlinear transmit power amplifier, especially when the number of transmit antennas is set large enough for the orthogonalization. This paper proposes BD transmission selected mapping (BD-SLM) that can reduce PAPR while maintaining the BD effect. BD-SLM performs the phase shift to modulation signals of all users before the linear precoding. From several phase sequences, it selects a phase sequence that minimizes the peak of the time-domain signals at all transmit antennas. Computer simulations demonstrate that BD-SLM can drastically reduce PAPR in 16-by-4 MIMO-OFDM with four users, and that it can alleviate the performance degradation even when the power amplifier causes nonlinear distortion.

Channel Estimation using Differential Model of Fading Fluctuation for EM Algorithm Applied to OFDM MAP Detection

This paper proposes a new channel estimation method for the expectation-maximization (EM) algorithm applied to an OFDM receiver. Conventional schemes using the EM algorithm assume the random walk model as a process equation of a channel impulse response, and thus have insufficient tracking ability to fading fluctuation over fast fading channels. To improve the tracking ability, the proposed channel estimation method employs the differential model having the first and higher order differentials of the channel impulse response with respect to time. Computer simulations under the fast fading condition demonstrate that the proposed method is much superior in packet error rate to the conventional schemes employing the random walk model.