Fumiaki Maehara

Series expression of BER performance for DQPSK/OFDM signals employing selection combining diversity reception over nonlinear fading channels

This paper presents an analytical expression of the bit error rate (BER) performance for DQPSK/OFDM signals using selection combining diversity reception under nonlinear fading channels. In the proposed approach, the soft envelope limiter is assumed to be a peak limited devices and the effects of nonlinear distortion are treated as the additive Gaussian noise with zero mean and suitable variance. This approach has an advantage of reducing the computational cost dramatically compared with the computer simulation because the proposed formula for predicting the BER performance consists of a simple series form. The theoretical results show perfect agreement with those obtained by the computer simulation.

Channel estimation and interference cancellation for MIMO-OFDM systems

This paper proposes a new channel estimation method and a new interference cancellation scheme for multiple-input multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) systems in the presence of intersymbol interference (IS1). The proposed channel estimation method uses special training sequences (TSs) to have a desirable crest-factor of the transmitted training signal, and to prevent the influence of ISI on the channel estimation performance. By using the recommended training sequences, the ill-conditioned problem of the least square (LS) filter integrated in the proposed channel estimator can be avoided. The proposed interference cancellation scheme uses the estimated channel coefficients and the channel state information (CSI) to reproduce the interference components, which are then iteratively cancelled from the received signals. To reduced the error-floor of the demodulated symbols using for the calculations of the interference components, the so-called remodulation technique is also included in the proposed interference cancellation scheme. Simulation results show that the proposed channel estimation method outperforms conventional channel estimation methods, especially in the presence of ISI and if the signal-to-noise ratio (SNR) is larger than 15 dB. The combination of the proposed method with a space-time block code (STBC) to combat the interference influences results in an excellent system performance in terms of symbol error ratio (SER). In comparison with a STBC MIMO-OFDM system with sufficient guard interval (GI), this combination gains 1.52 dB of SNR at the same SER of 1.1 10 -6 even after performing only one iteration of interference cancellation.

Performance of space diversity reception for coded carrier interferometry OFDM

Carrier interferometry orthogonal frequency division multiplexing (CI/OFDM) creates a full frequency diversity benefit without bandwidth expansion. We present the bit error rate (BER) performance of carrier interferometry coded OFDM (CI/COFDM) employing multiple receive antennas over frequency and time selective fading channels. The main feature of this architecture is to combine the time diversity benefit achieved by channel coding with the space and frequency diversity benefits exploited by CI/OFDM using space diversity reception. We also compare the BER performance of this architecture with that of typical coded OFDM (COFDM) employing subchannel space combining diversity reception. Numerical results obtained by computer simulation show that CI/OFDM outperforms OFDM when applying both space diversity reception and channel coding.

A novel clipping and filtering method employing transmit power control for OFDM systems

This paper proposes a novel clipping and filtering method employing transmit power control to improve the bit error rate (BER) performance in MIMO-OFDM transmission. The feature of the proposed approach is to perform the transmit power control before clipping and filtering to alleviate the BER degradation caused by clipping and filtering. Since the transmit power control to satisfy maximum signal-to-noise-plus-distortion ratio (SNDR) tends to lower the transmit power level especially in a relatively large CNR, the combination of its transmit power control with clipping and filtering surely improves the BER performance while suppressing the out-of-band radiation. Considering that MIMO systems suffer from the nonlinear distortion much more than SISO systems, the performance evaluation is to be conducted on MIMO systems, and the effectiveness of the proposed approach is demonstrated in comparison with the traditional clipping and filtering method with the constant transmit power level.

Coverage area prediction of in-car wireless communications employing MB-OFDM UWB systems

This paper investigates the coverage area of MB-OFDM UWB system under in-car propagation environments. The coverage area of each transmission speed to satisfy a certain quality of service (QoS) is predicted by combining the transmission performance of MB-OFDM UWB system with actual in-car propagation characteristics. Since the transmission performance of MB-OFDM strongly depends on the delay spread, the coverage area prediction takes into account the delay spread based on the distance between the transmitter and the receiver, as well as the propagation loss. The coverage area in the occupied scenario with four passengers is compared with that in the empty scenario. Computer simulation results show that the coverage area in the occupied scenario turns out to be much smaller than that in the empty scenario due to the large propagation loss and the decrease in the delay spread.

Vector perturbation using signal space conversion assisted vector ranking algorithm

Nonlinear precoding multi-user multiple-input multiple-output using vector perturbation (VP MU-MIMO) can provide good frequency efficiency at the cost of computational complexity, which exponentially increases as the number of spatial multiplexed users increases. This is because the original VP precoding requires to exhaustively search the optimum transmit signal vector among all the combinations of each users transmit signal candidates. To reduce the computational complexity, in this paper, we propose signal space conversion assisted vector ranking algorithm, which exploits the equivalency between the search of optimum transmit signal vector in the VP precoding and the signal detection from received signal in the general signal transmission. And, its transmission performance and computational complexity are evaluated by computer simulation.

Approximate equation of average bit-error rate in DS-CDMA systems over fading channels

The transmission quality in mobile wireless communications is affected not only by additive white Gaussian noise, but also by multipath fading, which drastically changes the amplitudes and phases of wireless signals. It is one of the key themes in direct-sequence code-division multiple-access systems to evaluate average bit error rate (BER) performances as parameters of the Doppler frequency, the delay profile, the number of simultaneous access users, and so on. This paper proposes the approximate equation for easily calculating the average BER over fading channels (multiray fading models). The performance evaluations are carried out in the two-ray model, the IMT2000 model, and the COST207 model. It is confirmed from the coincidence of approximate results with computer simulation results that the proposed approach is applicable to a variety of parameters.

An enhanced MMSE subchannel decision feedback equalizer with ICI suppression for FBMC/OQAM systems

This paper proposes an enhanced decision feedback equalizer (DFE) for filter bank multicarrier (FBMC) systems over offset quadrature amplitude modulation (OQAM) based on a minimal mean square error (MMSE) criterion. For each subcarrier, besides one feedforward (FF) filter and one feedback (FB) filter, we add two intercarrier interference (ICI)-suppressing filters, which feed back detected precursors extracted from neighboring subchannels to enhance ICI suppression in the presence of multipath channels. Our simulation results indicate our proposal makes a considerable improvement comparing with MMSE-DFE under a severe ICI and ISI scenario despite few extra costs in computational complexity.

Efficient combination of multi-user MIMO THP and user selection based on spatial orthogonality

This paper proposes an efficient method for combing multi-user MIMO (MU-MIMO) employing Tomlinson Harashima precoding (THP) with semiorthogonal user selection (SUS). Although the ordering of MU-MIMO THP and SUS create space diversity benefit and multi-user diversity benefit, respectively, a significant computational effort is required, which is expected to be relaxed while retaining the system level performance. The proposed method is inspired by the fact that the ordering calculations of MU-MIMO THP and SUS are commonly based on the spatial orthogonality. If that is the case, the result of the ordering of SUS is fully reused for the ordering of MU-MIMO THP, which can eliminate the calculation process of the ordering of MU-MIMO THP. The effectiveness of the proposed method is demonstrated in comparison with the traditional method with the ordering of MU-MIMO THP by means of computer simulations.

Coverage performance of UWB in-car wireless communication in the presence of multiple terminals

Recent years, the increase in complicated wire harness increases the weight and consequently harms the environment friendliness especially in a luxury car. Therefore, it is expected that in-car network is effectively built by using wireless connection as well as wired connection. In this paper, we investigate the coverage area performance of MB-OFDM UWB in-car communication in the presence of plural mobile terminals. In our approach, simultaneous multi-user wireless transmission is realized by multi-user MIMO (MU-MIMO) employing linear precoding with restriction of the total transmit power which satisfies the UWB power density limitation. Numerical results show the influence of the number of terminals on the coverage area under in-car propagation and verify the applicability of MU-MIMO to MB-OFDM UWB in-car wireless communication.