Xiaohu Liang

Symbol-by-symbol detection for faster-than-Nyquist signaling aided with frequency-domain precoding

Faster-than-Nyquist signaling is a promising waveform scheme in the fifth generation mobile communications for achieving higher spectrum efficiency. However, the FTN-caused intentional intersymbol interference will make the dectection process more complex. In this paper, a new precoding scheme is proposed for faster-than-Nyquist (FTN) signaling system aiming at reducing the burden of the receiver. Aided with the proposed frequency-domain precoding at the transmitter, the receiver can estimate the transmitted symbols by performing the symbol-by-symbol detection, which reduces the detection complexity dramatically. Moreover, the proposed precoding method can be applied into the high-order modulation directly, such as M-PSK or M-QAM. Further, the performance of proposed precoding scheme for FTN is verified and tested. Numerical results demonstrate that the proposed precoding scheme can not only realize symbol-by-symbol detection without bit-error-rate (BER) loss but also not broaden the spectrum of FTN signal at the transmitter.

MMSE Turbo Equalization and Detection for Multicarrier Faster-Than-Nyquist Signaling

In this paper, two minimum mean-squared error (MMSE) turbo equalization and detection schemes for spectral efficient multicarrier faster-than-Nyquist (MFTN) signaling system are presented. First, the two-dimensional (2-D) soft input and soft output (SISO) MMSE equalization intended for magnetic recording channels, i.e., 2-D intersymbol interference (ISI), is extended to the detection of MFTN signals. Although the 2-D MMSE turbo equalization exhibits an attractive bit-error-rate (BER) performance under certain time-frequency spacing packing between adjacent symbols/subcarriers, the BER performance will be degraded when introducing serious intercarrier interference. Second, a 1-D SISO MMSE equalization combined with soft successive interference cancellation (SIC) is further proposed for the detection of MFTN signals, and it shows that the MMSE equalization combined with SIC could asymptotically approach the maximum a posterior equalization combined with SIC with negligible BER performance loss. Our computational complexity analysis and numerous simulation results demonstrate that the proposed MMSE turbo equalization schemes may be more preferred choice in the practical detection of MFTN signals.

Secrecy analysis of UL transmission for SWIPT in WSNs with densely clustered eavesdroppers

This paper studies the physical layer security of uplink (UL) transmission in simultaneous wireless information and power transfer (SWIPT) deployed in wireless sensor networks (WSNs). Firstly, we model the random network as Poisson cluster process (PCP) to focus on the case where eavesdroppers hide around certain targets to intercept the confidential information successfully. Then, the communication model of time division multiple access (TDMA) is established to avoid inter-node interferences and extend the time for energy harvesting (EH). After that, aiming at the sensor nodes that work in “harvesting-transmitting” (H-T) mode with time switching (TS) receiver, we derive the energy outage probabilities (EOP), connection outage probabilities (COP) and secrecy outage probabilities (SOP) through comprehensive analysis on downlink (DL) and UL transmissions, based on which the uplink secrecy throughput (STP) is obtained to characterize the overall performance. Finally, our theoretical derivations are verified and the influences of various parameters on uplink STP are revealed by the simulation results, which indicate the existence of an optimal energy threshold and a partition coefficient of DL and UL period that can achieve the best secrecy performance.

On the practical benefit of hexagonal multicarrier faster-than-Nyquist signaling

In this paper, we investigate the hexagonal multicarrier faster-than-Nyquist (MFTN) signaling, which is considered to be a more promising technique than conventional rectangular MFTN in future communication systems. Specifically, different from previous works that mainly focused on the minimal Euclidean distance (or Mazo limit), we study the intersymbol interference (ISI) and/or intercarrier interference (ICI) introduced by time-frequency packing in MFTN signaling systems. We theoretically prove the asymptotical equivalence of the hexagonal MFTN and conventional rectangular MFTN when the time packing factor is small enough. Moreover, we also demonstrate the potential benefit of hexagonal MFTN than conventional rectangular MFTN signaling system for moderate time-frequency packing. Numerical results validate the theoretical analyses.

On the Detection Algorithm for Faster-than-Nyquist Signaling

FTN has been proposed for several decades, and it is attractive for the reason that it can boost the symbol rate without changing the power spectral density. Actually, FTN has been used in some 5G standards. FTN signaling detection is an important element in FTN signaling scheme. In this paper, we shall introduce some FTN signaling detection algorithms that were proposed in literatures.

PAPR Reduction of Multicarrier Faster-Than-Nyquist Signals With Partial Transmit Sequence

Multicarrier faster-than-Nyquist (MFTN) signaling is a spectral efficient transmission scheme for future communication systems. Similar as general multicarrier signals, the high peak-to-average power ratio (PAPR) is also one of the main drawbacks of MFTN signals. Unfortunately, the PAPR problem in MFTN signaling system has rarely been considered in the literatures. In this paper, we investigate the PAPR reduction for MFTN signals. First, we derive an inverse fast Fourier transform (IFFT)-based implementation of the MFTN transmitter. Based on which, a novel partial transmit sequence (PTS) scheme is proposed for the PAPR reduction of MFTN signals. The proposed PTS scheme relies on a two-stage optimization of the phase weighting factors for the parallel IFFT blocks as well as the phase weighting factors for the information symbols before the summation operation. It is shown that the proposed scheme substantially outperforms the direct employment of conventional Nyquist multicarrier transmission systems-based PTS scheme and also robust to the overlap-add operation introduced by pulse shaping.

Turbo equalization and detection for faster-than-nyqusit signaling: A comparative study

Due to the inherent intersymbol interference (ISI), the detection for faster-than-Nyquisy (FTN) signaling is long considered to be a challenging problem. In this paper, we study three equalization and detection schemes in terms of their performance and computational complexity for FTN signaling system. The first one is the widely employed optimal maximum a posterior (MAP) equalization implemented by the Bahl-Cocke-Jelinek-Raviv (BCJR) algorithm. Although with optimal bit-error-rate (BER) performance, however, it is at the price of greatly increased computational complexity. The following two schemes are mainly based on the linear turbo equalization with much lower complexity. The first one is the frequency domain equalization (FDE) and the second one is the minimum mean-squared error (MMSE) equalization. Computational complexity analysis and numerous simulation results show that even with lower complexity, the linear turbo equalization could asymptotically approach the MAP equalization with negligible BER performance loss, and the MMSE turbo equalization may be a much more suitable detection scheme for future FTN signaling system.

A new detection method for faster-than-Nyquist signaling based on sphere algorithm

This paper focuses on the low complexity detection for the Faster-than-Nyquist (FTN) signaling, which is an important problem in the practical application. Considering intersymbol interference (ISI) and colored noise caused by FTN, a new whiten matched filter (WMF) is proposed to decorrelate the colored noise with matrix decomposition. Exploring the structure of upper-triangle matrix, the detection problem for FTN is transformed to a similar type problem of tree-searching. A novel receiver for FTN is proposed based on sphere detection algorithm. Furthermore, for reducing the random detection complexity, a new way is proposed to choose an initial sphere radius size. Numerical results suggest that the proposed method for choosing the initial sphere radius size performs well even in the low signal-to-noise ratio (SNR) region. Moreover, the bit error rate (BER) performance of the proposed method reaches the maximum-likelihood (ML) bound closely.

Symbol-by-symbol detection for turbo-coded FTN aided with precoding

Faster-than-Nyquist (FTN) signaling has been considered a promising technique for higher frequency bandwidth efficiency. However, symbol detection at the receiver suffers rather high computation complexity due to the intentionally introduced infinite inter-symbol interference (ISI) caused by the way of FTN signaling. For solving this problem, a new method is proposed based on precoding at the transmitter. In this schema, precoding technique is used to eliminate the ISI and lower complexity of the detection of the receiver and Turbo-code is used to reduce the system’s bit error rate (BER). Moreover, the precoding method can be extended to the MQAM. Numerical examination of the proposed method shows performance improvement of the proposed approach over FTN signaling.

A new reduced-complexity LMMSE receiver of adaptive transmission system based on FTN signaling in satellite communications

Adaptive Transmission Systems, such as the adaptive coding and modulation (ACM) system, improve the spectral efficiency in satellite channels. At the same time, the FTN signaling, as an unique modulation of high spectral efficiency, can transmit more data without increasing bandwidth. The scheme that adopts the FTN signaling in the adaptive transmission system for satellite communications can improve the spectral efficiency further by adjusting the code rates and packing ratios. However, the variable symbol rate and colored noise induced by the FTN signaling bring extra complexity to the receiver of adaptive transmission system. In this paper, we propose a new LMMSE receiver which can detect FTN signal at constant sampling rate. The receiver adopts an orthogonal match-filter to reduce the demodulation complexity brought by colored noise. Through simulations, the new receivers bit error rate (BER) performance reaches the ISI-free system with low complexity, and the receiver can be flexibly used in the adaptive transmission system based on FTN signaling.