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The intelligent reflecting surface (IRS) is a novel and innovative communication technology that aims at the control of the wireless environment. The IRS is considered as a promising technology for sixth-generation wireless communication. In the last few years, machine learning has emerged as a powerful tool for solving complex problems in diverse application areas. In this paper, we propose a convolutional neural network (CNN)-based demodulation technique called Demod-CNN in IRS-based wireless communication for multiple users. A multiple-input multiple-output based orthogonal multiple frequency division multiplexing system is considered for channel modeling. The received signal data are used for training and testing the model. The simulation results show that the proposed model performs better than the conventional demodulation technique. [ABSTRACT FROM AUTHOR]

Synchronization is a challenging problem of device-to-device (D2D) communications, particularly when D2D devices are out-of-network coverage. This article proposes an efficient initial synchronization method for D2D communication in a long term evolution system. The proposed synchronization approach is based on the correlation between both received primary sidelink synchronization signal and secondary sidelink synchronization signal to remove the effects of channel fading and symbol timing offset (STO). This design facilitates reduced-complexity joint detection of carrier frequency offset, sidelink synchronization signal, and cyclic prefix (CP) mode during the initial synchronization procedure. Simulation results show that the proposed synchronization scheme achieves robust and low-complexity detection of carrier frequency offset, sidelink synchronization signal, and CP mode when there is a nonnegligible STO or frequency-selective fading distortion. [ABSTRACT FROM AUTHOR]

The main features for future machine-type communication (MTC) cellular networks are to support low-power consumption, low-bandwidth, and long-range communication. One of the most challenging issues to meet these goals in the MTC cellular network is a low-complexity and reliable initial synchronization. To address this issue, in this article an efficient joint detection of integer carrier frequency offset (IFO) and cell identity (CID) is proposed for MTC in a long-term evolution (LTE) system. Unlike the conventional approach, the primary synchronization signal (PSS) and secondary synchronization signal (SSS) transmitted in the LTE-MTC system are used together to remove the effect of channel fading and symbol timing offset (STO). This design facilitates robust detection of the IFO and CID in the presence of residual STO without priori information on the SSS. The grouping of PSS subcarriers is integrated for joint detection, which plays an important role on reducing computational load. Both analytical and simulation results are provided to corroborate the feasibility of the proposed method. It has been demonstrated that the unique characteristics of the PSS and SSS sequences are effectively used for robust cell search in the presence of residual STO, compared to existing methods. [ABSTRACT FROM AUTHOR]

In wireless communication systems, reliability, low latency and power are essential in large scale multi-hop environment. Multi-hop based cooperative communication is an efficient way to achieve goals of wireless networks. This paper proposes a relay selection scheme for reliable transmission by selecting an optimal relay. The proposed scheme uses a signal-to-noise ratio (SNR) based Q-learning relay selection scheme to select an optimal relay in multi-hop transmission. Q-learning consists of an agent, environment, state, action and reward. When the learning is converged, the agent learns the optimal policy which is a rule of the actions that maximize the reward. In other words, the base station (BS) knows the optimal relay to select and transmit the signal. At this time, the cooperative communication scheme used in this paper is a decode-and-forward (DF) scheme in orthogonal frequency division multiplexing (OFDM) system. The Q-learning in the proposed scheme defines an environment to maximize a reward which is defined as SNR. After the learning process, the proposed scheme finds an optimal policy. Furthermore, this paper defines a reward which is based on the SNR. The simulation results show that the proposed scheme has the same bit error rate (BER) performance as the conventional relay selection scheme. However, this paper proposes an advantage of selecting fewer relays than conventional scheme when the target BER is satisfied. This can reduce the latency and the waste of resources. Therefore, the performance of the multi-hop transmission in wireless networks is enhanced. [ABSTRACT FROM AUTHOR]

Recently, wireless communication systems use a multi-hop transmission scheme using a relay to expand the cell coverage of the system. The multi-hop transmission scheme can expand the cell coverage of wireless communication systems. However, if an appropriate relay is not selected, errors generated during signal processing in the relay are transmitted to the receiver. Therefore, a relay selection scheme is essential for reliable multi-hop transmission. This paper proposes a relay selection scheme for reliable multi-hop transmission in a multi user-multiple input multiple output (MU-MIMO) system. The proposed relay selection scheme uses a MIMO channel matrix between the transmitter and relays to select an appropriate relay. The proposed relay selection scheme obtains the singular values of the MIMO channel matrix using the singular value decomposition (SVD). Then, the sum of the singular values is calculated, and the relay having the largest value is selected. Therefore, in the proposed relay selection scheme, although the transmitter only knows the channel information between the transmitter and relays, the transmitter can select an appropriate relay for reliable multi-hop transmission. [ABSTRACT FROM AUTHOR]

This paper proposes an adaptive coordinated multi point (CoMP) scheme using pre-coding in order to improve the reliability of wireless communication systems based on orthogonal frequency division multiplexing (OFDM). In the conventional scheme, the received signal to noise ratio (SNR) of the mobile is degraded due to the interference signal. Therefore, the bit error rate (BER) performance is degraded, as is, the reliability of the system, due to inter-cell interference (ICI). Therefore, the BER performance of the system is reduced and the transmitter must perform unnecessary re-transmission. The proposed scheme uses the CoMP scheme to improve reliability in a heterogeneous network (HetNet) system. Additionally, the proposed scheme uses the constructive spatial phase coding (SPC) scheme to mitigate the received SNR reduction due to the interference signal. Therefore, the proposed scheme can prevent performance degradation caused by the interference signal. When a mobile is located in the cell edge, the transmission signal is distorted by the transmitted signal from the adjacent cell. The proposed scheme can reduce the SNR of the interference signal by using the destructive SPC scheme. Therefore, this scheme can improve the reliability of the system. The simulation results show that the BER performance of the proposed scheme is better than that of the conventional scheme. As a result, the proposed scheme improves the reliability of systems by adaptively applying the CoMP and SPC schemes. [ABSTRACT FROM AUTHOR]

In this paper, we propose a low-complexity joint detection of sector cell index and integer carrier frequency offset for a long-term evolution downlink system. In order to implement a low-cost detection scheme, a primary synchronization signal used for joint parameter estimation is grouped into a number of subsets so that the pilots in each subset are strongly correlated. The estimation performance and the computational load of the proposed scheme are compared with those of the commonly used conventional detection scheme using a differential correlation to remove common channel effects. It is found that the proposed scheme can jointly detect the cell index and integer carrier frequency offset with higher accuracy and much lower complexity, compared with the conventional scheme. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

This paper proposes the phase adjustment signaling based on packet structure for the Wi-Fi backscatter system. The Wi-Fi backscatter system has very low data rate due to the transmission method by unit of packet. In addition, because the Wi-Fi backscatter system uses simple energy detection method for identification of request information from the reader, the system has very low reliability. In order to solve these problems, the signaling that adjusts transmission power in according to transmitting information is proposed. For improvement of data rate of the system, the proposed signaling uses the transmission method by unit of OFDM symbol in Wi-Fi packet. Also, for improvement of reliability of the system, the proposed signaling uses the iterative transmission method in Wi-Fi packet. The simulations show that the proposed signaling improves performance of the Wi-Fi backscatter system. Also, because the proposed signaling can easily achieve diverse data rate or reliability in according to the parameters, it is useful to meet the demands of IoT application for specific data rate or reliability. [ABSTRACT FROM PUBLISHER]

Cyclic delay diversity (CDD) is a simple transmit diversity technique for coded OFDM systems with multiple transmit antennas. However, high frequency selectivity caused by CDD degrades the performance of post- FFT estimation, i.e., integer frequency offset (IFO). This paper suggests a simple way of improving the performance of the IFO estimator based on the pilot subset partitioning which is designed to reduce the effect of frequency selective fading by adopting the CDD. By partitioning uncorrelated pilot subcarriers into subsets to satisfy high correlation, and performing frequency estimation for each pilot subset, a robust IFO estimation scheme is derived. The simulation results show that the proposed method can provide benefit to the overall system performance . [ABSTRACT FROM AUTHOR]

High peak-to-average power ratio (PAPR) of the transmit signal is a major drawback of multicarrier transmission such as orthogonal frequency division multiplexing (OFDM). Most of recent works have focused on minimizing the PAPR of OFDM signal to enhance performance. However, after relating this issue with the specific characteristics of high power amplifier (HPA), we propose a new scheme based on iterative partial transmit sequence (1-PTS) scheme that uses the amount of OFDM signal's nonlinear distortion to be caused by high power amplifier (HPA) as a new measure. The proposed scheme can have simple subblock combining method by applying iterative PTS and then, a new measure which is called adaptive nonlinear estimator (ANE), is achieved by estimating the mean square error (MSE) between the OFDM signals before and after the nonlinear HPA. The one with the minimum MSE among OFDM candidate signals is selected for transmission. From the results, it can be seen that a proposed scheme based-iterative PTS can be easily implemented with low combining complexity, still maintaining a better BER performance, compared to the conventional PTS approach. [ABSTRACT FROM AUTHOR]

A combining of MIMO signal processing with OFDM is regarded as a promising solution of enhancing the performance of next generation wireless system. Therefore, in the paper, an OFDM-based wireless system employing layered space-time architecture is considered for a high-rate transmission. With an emphasis on a preamble design for multi-channel separation, we address a channel estimation based on the time-domain windowing and its imperfectness in MIMO-OFDM system. By properly designing each preamble for multiple antennas to be orthogonal in the time domain, the channel estimation can be executed based on semi-blind processing in the case of more than two transmitting antennas. And also we evaluate PAR performance in the MIMO-OFDM system using the SLM and PTS approaches. The investigated SLM and PTS schemes for MIMO-OFDM signals select the transmitted sequence with lowest average PAR over all transmitting antennas and retrieve the side information very accurately at the expense of a slight degradation of the PAR performance. The low probability of false side information can improve the overall detection performance of the MIMO-OFDM system with erroneous side information compared to the ordinary SLM and PTS approaches, respectively. Also, we provide closed form of the average BER performance in MIMO-OFDM system using analytic approach. [ABSTRACT FROM AUTHOR]

This paper presents a frame synchronization and two frequency synchronization techniques for high-rate wireless LANs (Local Area Networks). Also, to improve the reliable communication under the multipath fading channel, we propose the wireless LAN system employing the space-time code. The proposed frame synchronization technique using the threshold checking scheme is directly based on the correlation method. We then describe a coarse frequency synchronization technique combining two conventional synchronization techniques to estimate an integral frequency-offset and a frequency synchronization technique employing interpolation method to estimate the integral and fractional frequency- offsets at the same time, respectively. Finally, by simulation, the performance of the proposed techniques is evaluated. [ABSTRACT FROM AUTHOR]

For a low complexity signal detector to reduce the power consumption for multiple input and multiple output orthogonal frequency division multiplexing (MIMO-OFDM) systems, the depth-first sphere decoding (DFSD) detection scheme was proposed. However, the DFSD detection scheme still has high complexity in the hardware implementation. The complexity is especially high when the signal-to-noise ratio (SNR) is low. Therefore, this paper proposes an adaptive DFSD detection scheme. The proposed detection scheme arrays nodes, sorting by ascending order of squared Euclidean distance (ED) at the top layer of tree structure. Then, the proposed detection scheme uses the different number of nodes according to thresholds based on channel condition. In the simulation results, the proposed detection scheme has similar error performance and low complexity compared with the conventional DFSD detection scheme. Therefore, the proposed detection scheme reduces the power consumption in the signal detector. [ABSTRACT FROM AUTHOR]

DVB standards are currently being implemented in various countries, not only in Europe, but also around the world. In order to meet various consumers' demands, the DVB standards support interactive services. Among the interactive broadcasting services, DVB-RCT based on OFDM can be used for interactive broadcasting service in terrestrial broadcasting network. To improve the DVB-RCT system performance, a combining of MIMO signal processing with OFDM is very efficient solution. To detect the received MIMO signal with low complexity, an efficient detection technique with K-best scheme is proposed in this paper. The proposed technique can overcome the limitations of K-best scheme which are performance limitation and high complexity. [ABSTRACT FROM PUBLISHER]