The high power consumption of analog-to-digital converters (ADCs) with high resolution is a bottleneck in the high data rate communication systems. 1-bit ADC system is considered a key communication system resolving the issue. Recently, 1-bit ADC system with time-oversampling has been studied because the additional information leads to increase in the achievable rate. A variety of studies have been carried out to enhance the data rate of the system with 1-bit ADC and time-oversampling assuming the channel is known. On one side, the channel estimation in a such system is a challenging issue. We design the pilot sequence and maximum likelihood (ML) estimator to evaluate the channel phase which is a critical parameter in 1-bit ADC system. By taking account of the distribution of channel power gain in flat Rayleigh fading channel indirectly, the estimator operates in the absence of channel power gain information, which is hard to obtain due to the nonlinearity of 1-bit ADC. The simulation results demonstrate the effectiveness of the proposed scheme in terms of mean squared error (MSE) with reasonably short pilot sequence. Specifically, the MSE performance does not show error floor regardless of the prior knowledge of the channel power gain at the receiver.

Wireless communication in millimeter wave frequency provides a high data rate using a wide bandwidth. However, the large array antenna is necessary to overcome the high path loss, which may result in the high feedback overhead and hardware complexity. Moreover, the characteristics of frequency selective channel should be considered due to the wide bandwidth. To deal with these problems, we propose the orthogonal frequency division modulation (OFDM)-based hybrid beamforming (HBF) scheme with limited feedback. While the conventional OFDM-based HBF schemes are based on minimizing the sum of the Frobenius norm of the differences between digital BF (DBF) and HBF as simple extension of the narrowband systems, our approach is based on the achievable sum rate maximization of all the subcarriers. In particualr, we derive a design criterion to jointly optimize the HBF matrices of the transmitter and receiver. Specifically, we propose a HBF method which designs subchannel gain product based orthogonal matching pursuit. Through this, an analog BF algorithm considering both the transitter and receiver is proposed, while the baseband BF is based on the conventional digital precoding scheme. Simulation results show that the proposed HBF scheme outperforms the conventional ones. Notably, the results show that the proposed HBF scheme is robust to channel estimation error.

Millimeter wave (mmWave) wireless communication systems suffer from high path loss compared to conventional cellular communication systems. Angle of arrival (AoA) of received signal is prerequisite for beamforming technique to overcome high path loss in mmWave communications. Considering mobile environments, conventional beam estimation methods with large overhead are unacceptable for rapidly varying AoA. Therefore, beam tracking algorithm with low complexity corresponding to rapidly varying AoA is required. This paper studies on beam tracking algorithm for mmWave MIMO systems in mobile environments. We define the AoA model, and propose beam tracking algorithm using auxiliary beam pair (ABP) and extended Kalman filter (EKF). The simulation results show that proposed algorithm has better beam tracking performance than the existing methods in low signal to noise ratio (SNR) region.

With demand for high speed wireless communication system in 5G, using 1-bit analog-to-digital converter (ADC) at the receiver is considered to be a promising architecture. Several studies have been proposed to maximize the achievable data rate employing time-oversampling with 1-bit ADC. However, there remains problems on the minimally required oversampling factor in general case and how to design the communication system practically. This paper provides the minimum oversampling factor for pulse amplitude modulation (PAM) in additive white Gaussian noise channel and proposes the mapper- demapper architecture. The mapper converts symbols into predefined classes, and constructs the unique symbol sequence based on state machine. For demapper algorithm, the Bahl-Cocke-Jelinek-Raviv (BCJR) algorithm is implemented. Simulation results demonstrate that the proposed algorithms work well in terms of symbol-error-rate and detecting failure probability at high signal-to-noise ratio region.

In this paper, we introduce a simple bit-interleaved binary space-time code (B-STC) for a coded multi-input multi-output (MIMO) system to obtain an increase in information rate, where two transmit and two receive antennas are used. We derive a probability density function (pdf) of log-likelihood ratio (LLR) for the B-STC decoder output and approximate it with the pdf of MIMO detector output having the degraded SNR. The average bit error probability at the i-th iteration is represented in terms of moment generating function with differently distributed SNRs. Although the iterative decoder in the B-STC structure increases the computational complexity, the number of iterations i is not large (i≤3). Because the proposed B-STC scheme is a binary code for MIMO systems, different types of channel codes and various space-time codes can be concatenated. To achieve near-capacity performance on MIMO channels, an iterative receiver structure with a soft interference cancellation scheme can be also adopted as an outer iteration. And the proposed scheme can be extended to arbitrary number of transmit and receive antennas.

We investigate the secrecy capacity of an ergodic fading wiretap channel when the main and eavesdropper channels are correlated. Assuming that the transmitter knows the full channel state information (CSI) (i.e., the channel gains from the transmitter to the legitimate receiver and eavesdropper), we quantify the loss of the secrecy capacity due to the correlation and investigate the asymptotic behavior of the secrecy capacity in the high signal-to-noise ratio (SNR) regime. While the ergodic capacity of fading channels grows logarithmically with SNR in general, we have found that the secrecy capacity converges to an upper-bound (a closed-form expression is derived) that will be shown to be a function of two channel parameters; the correlation coefficient and the ratio of the main to eavesdropper channel gains. From this, we are able to see how the two channel parameters affect the secrecy capacity and conclude that the excessively large signal power does not help to improve the secrecy capacity and the loss due to the correlation could be significant especially when the ratio of the main to eavesdropper channel gains is low.

While multiple-input multiple-output (MIMO) system gives many advantages to wireless communication, the complexity of multiple RF chains gives a burden to the system. Antenna selection is introduced as a technique to reduce the burden. On the transmit antenna selection scheme, the exhaustive search for optimal antenna set quickly becomes impractical as adopting more antennas. To reduce complexity for searching, we propose an efficient transmit antenna selection method. We first make a threshold for optimal antenna set by using Poincare separation theorem. Instead of exhaustive search, we select a transmit antenna subset that exceeds the threshold. On the exponentially correlated channel of array antennas, we give an order to search for reducing complexity further. We search from the most remotely located antenna subset which in generally less correlated to the closely located antennas which is more correlated. Finally, we show the BER performance and tradeoff relation between performance and complexity by Monte-Carlo simulations.

In this letter, we introduce an analytical expression to the coded bit error rate (BER) of a MIMO system with a linear minimum mean square error (MMSE) receiver. We derive the moment generating function (MGF) of the SINR for arbitrary antenna configurations from the cumulative density function of SINR.We show that the moment generating function of the SINR at the MMSE detector output can be used to estimate the BER performance of a coded MIMO system. The analysis is simple and gives an accurate BER estimation at a high SNR. Based on the analytical and simulated results, the diversity order is dependent on the antenna configuration and the free distance of the convolutional code. Finally, we compare the analytical expression with simulated results for validation.

In 1974, BCJR algorithm[l] was invented for maximum a posteriori (MAP) decoding of error correcting codes defined on trellises. In this paper, we apply BCJR algorithm to the detector for coded multiple-input multiple-output (MIMO) system to achieve high detection performance. With known channel information, coded MIMO detector can compute log- likelihood ratio (LLR) on the channel trellis by BCJR algorithm. We also propose a simple BCJR algorithm with computational cost reduction. Simulation results show that BCJR algorithm achieves higher performance than maximum likelihood (ML), and there is negligible performance difference between proposed simple method and conventional BCJR algorithm.

This paper considers the uncoded multiple-input multiple-output (MIMO) system with linear minimum mean square error (MMSE) detection under ideal fast fading. The distribution of SINR at the output of the MMSE detection is derived for a small number of transmit and receive antennas. We present new approximation for the Gaussian Q-function driven by numerical simulation. Based on the SINR distribution and new approximation for Q-function, we analyze the performance of linear MMSE detection under ideal fast fading environment. By comparing the analytical results and Monte Carlo simulated results, we validate the analytical results.

In the multiple-antenna broadcast channel, each user is not allowed to cooperate with other users, so the efficient and well-designed preceding scheme to reduce other users' interferences is required. Recently, the use of lattice basis reduction(LR) has been shown to be a very effective method for preceding in multiuser multiple antenna systems. Lattice basis reduction helps to reduce the average transmitted energy by modifying the region which includes the constellation points. Even though the LR precoding method achieves a full diversity order, the performance loss caused by quantization error still remains. In this paper, we propose a simple precoding technique to reduce the quantization error. The proposed scheme establishes a lattice list to provide more candidates for transmission power reduction based on the analysis of the patterns of the error. Simulation results show that the proposed scheme achieves the BER performance as good as that of more complex precedents (such as the vector perturbation using sphere-encoding) with significant saving in complexity.remains.

Open-loop full-diversity full-rate (FDFR) code can achieve both high data rate and good reliability at the expense of significantly increased decoding complexity. To mitigate the decoding complexity, low-complexity FDFR code was designed for closed-loop system, combining the preceding and constellation rotation with channel state information (CSI) at the transmitter. Since conventional closed loop FDFR encoding procedure is similar to that of open loop FDFR code, however, it suffers from latency problem due to multiple-symbol-periods encoding and decoding process. Also, the rotation matrix is fixed irrespective of temporal channel response. In this paper, we propose simple FDFR scheme which performs single-symbol- period encoding and decoding procedure. Moreover, we improve error performance of closed-loop FDFR code by exploiting a adaptive rotation matrix corresponding to temporal channel state, especially the singular values of channel. The adaptive rotation matrix construction aims at maximizing the minimum Euclidean distance among received signals. Simulation results support the validity of the proposed FDFR scheme.

We introduce and analyze an enhanced cooperative diversity system where the source, relay, and destination are equipped with single antenna, respectively. A time-division multiple-access (TDMA) based cooperative protocol is considered. This protocol has full data rate because the source transmits two symbols during two time slots. However, the protocol does not obtain full diversity gain, because each column of effective channel matrix has a different distribution. We propose the constellation rotation scheme to solve the problem. Also, we analyze the diversity gain of the proposed system with the maximum-likelihood (ML) receiver by deriving the pairwise error probability (PEP). The analysis proves that the system applying the constellation rotation scheme achieves a full diversity. Also, we verify the superiority of the proposed scheme from the simulations.

Lattice reduction (LR) has been recently used in signal detection for multiple-input multiple-output (MIMO) systems. The conventional LR aided detection schemes are combinations of LR and signal detection methods such as zero-forcing (ZF) and minimum mean square error (MMSE) detection schemes. In this paper, we propose the LR aided scheme based on the augmented channel matrix and develop the method that corrects the errors occurred in the quantization step. Numerical simulations show that the proposed LR scheme exhibits improved performance and a slight increase in complexity. Moreover, if we combine the conventional LR aided scheme with the quantization error correction, then bit error ratio (BER) performance is improved with trivial complexity increase at high SNR.

In this correspondence, we construct theta series that are Jacobi forms, from the complete enumerator of Type II codes over Z/sub 2m/. Moreover, we construct a map from a certain invariant space to the space of Jacobi forms on the full modular group.