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For deep learning detection networks in the multiple-input-multiple-output (MIMO) channel, deepening the network does not significantly improve performance beyond a certain number of layers. In this letter, we propose a parallel detection network (PDN) that consists of several deep learning detection networks in parallel without connection. By designing a specific loss function and reducing similarity between detection networks, the PDN obtains a considerable diversity effect. The performance of the PDN improves significantly as the number of parallel detection networks increases in time-varying MIMO channels. This is superior to the existing deep learning detection networks, in both performance and complexity. [ABSTRACT FROM AUTHOR]

In this correspondence paper, a decode-forward relay system with a source, a relay, and a destination is considered. A new switching superposition-coded (NSSC) relay scheme is proposed to improve error performance by increasing the equivalent squared minimum distance. On the receiver side, a low-complexity linear-combining successive-interference-cancellation decoder is proposed for the NSSC scheme. The theoretical and simulation results show that the NSSC scheme achieves better performance compared to the existing superposition-coded relay schemes. [ABSTRACT FROM AUTHOR]

Twin-interleaver bit-interleaved LDPC coded modulation (BICM) has been widely adopted and studied in the context of digital terrestrial transmission (DTT) systems. Extrinsic-information transfer (EXIT) charts have been used as an analysis tool to evaluate the iterative decoding performance and to design a twin-interleaver BICM system. Since BICM using iterative decoding (BICM-ID) exhibits capacity-approaching decoding performance, developing the conventional twin-interleaver BICM DTT system to a BICM-ID system has also been attempted. When considering the twin-interleaver BICM-ID systems, there are a couple of aspects that should be taken into account. We will demonstrate that anti-Gray mapping should be adopted for improving the iterative decoding performance instead of the classic Gray symbol mapping. However, the previous literature related to designing the associated row-permutation interleaver (RPI) was mainly focused on BICM systems relying on Gray mapping. Hence, we will design the RPI of the twin-interleaver BICM-ID DTT systems using an anti-Gray mapping. Explicitly, we use: 1) the EXIT-chart analysis that accurately visualizes the overall iterative decoding and demapping performance of the twin-interleaver BICM-ID DTT systems using anti-Gray mapping and 2) a preprocessing stage for eliminating duplicate RPI candidates by using a parameter that roughly predicts the EXIT-chart analysis result before the EXIT-chart analysis is involved. By the elimination of the duplicates, over 99% of the initial candidates of the RPIs can be removed from the original M ! candidates, where M stands for the number of modulated bits in a symbol. Given this drastically reduced number of candidates, the proposed design method finds novel RPIs, having superior bit-error ratio performances over the conventional RPIs in the context of the DVB-T2 standard. [ABSTRACT FROM PUBLISHER]

The cross ambiguity function (CAF) has been commonly used to find time difference of arrival (TDOA) and frequency difference of arrival (FDOA). In most cases, direct computation of the CAF by using a conventional method such as fast Fourier transform is too computationally intensive. Thus, a two-stage approach consisting of a coarse mode to find rough TDOA/FDOA estimates and a fine mode for precise estimation was introduced. However, there has been no methodology for selecting an interpolation factor determined by the sampling frequency and target precision which significantly affects the computational complexity. In addition, even if the computational complexity can be reduced by using the optimal interpolation factor, the huge transmission data through the datalink between sensors and the central station still remains to be an obstacle for an electronic warfare (EW) system. In this respect, we derive an optimal interpolation factor and then propose a new two-stage TDOA/FDOA estimation algorithm using a resampling block to reduce the computational complexity and the data size simultaneously in EW systems. In the proposed method, the optimal interpolation factor can be used irrespective of the sampling frequency and the target precision. Simulation results show that the optimal interpolation factor efficiently reduces the computational burden without the loss of estimation performance. [ABSTRACT FROM AUTHOR]

Linear frequency modulation (LFM) signals have been widely used for target detection in active sonar systems due to their robustness to reverberation. However, LFM active sonar requires a large number of reference signals for detecting targets moving with unknown speeds. To obtain more accurate detection results, more reference signals are required, resulting in an increased computational burden and memory size. To cope up with this problem, we propose a new fast target detection method that is robust to the variation of unknown target speed. A large number of reference signals come into a single reference signal by aligning them with precalculated time-shifts, which is followed by a summation process. Both narrowband and wideband cases are considered. The proposed method secures a signal-to-noise ratio (SNR), approaching that of the optimal matched filter output, that is also robust to the variation of target speed and thus it is very useful for the practical use in antitorpedo torpedoes or supercavitating underwater missiles that need to equip low-complexity and robust signal processing systems. Moreover, a rough Doppler estimation is presented using the proposed replica design method. Performance analyses show that the proposed method provides output SNR close to the optimal performance and that the computational load is extremely reduced as compared to the conventional LFM target detection method. [ABSTRACT FROM AUTHOR]

Electronic warfare support (ES) plays an important role in gathering and analyzing signals from enemy emitters to provide friendly electronic attack (EA) systems or electronic protection (EP) systems with crucial information. However, ES systems may have difficulty in gathering meaningful signals because there is no prior information about the signal in most cases, and the signal is sometimes too weak or distorted. In this paper, we propose a novel weak-signal detection method to solve these problems based on a modified sinc wavelet transform. This method exploits the frequency shifting property to change the center frequency of a band-pass filter and then applies the scaling property of the continuous-time wavelet transform to vary its bandwidth. This approach is distinguished from previous works in terms of the detection capability of weak signals with high-frequency or multifrequency components. Computer simulation results show that the proposed method can be used in practical implementation to deal with signals that have a low signal-to-noise ratio (SNR). [ABSTRACT FROM PUBLISHER]

Higher-order modulation schemes are employed to improve the spectral efficiency in modern communication systems. However, the conventional Max-Log-MAP symbol-to-bit demapper suffers from a large computational burden. To cope with this problem, this letter proposes a novel log-likelihood ratio computation algorithm for Gray-coded higher-order pulse-amplitude modulation (PAM). The proposed method reduces the order of complexity from $O(2^M) $ to $O(M)$ without any difference of the LLR values compared with the Max-Log-MAP demapper, where $M$ is the number of bits in one PAM symbol. Moreover, it is also shown that the proposed algorithm achieves superior complexity reduction compared with a recently proposed low-complexity demapper. [ABSTRACT FROM PUBLISHER]

In this paper, we consider a decode-forward relay system with a source, a relay, and a destination, where two-layer superposition codes are used at the source and the relay. An equivalent squared minimum distance (ESMD) that determines the error performance is derived by using an upper bound on the pair-wise error probability. Without deriving error probabilities, the error performance level for each of superimposed symbols can be shown in a straightforward manner by the ESMD. An optimal superposition-coded relay scheme and a suboptimal switched-power superposition coding scheme are proposed by improving the ESMD. Closed-form power allocation that maximizes the ESMD for the switched scheme is derived for 2-ary pulse amplitude modulation (PAM). An $M$-ary PAM generalization for the switched-power superposition-coded relay scheme is also presented. Simulation results show that significant signal-to-noise ratio gains are achieved in the optimal and switched-power superposition coding strategies for 2-ary and 4-ary PAM over the Rayleigh fading channel. [ABSTRACT FROM PUBLISHER]

Future generations of brain-machine interface (BMI) will require more dexterous motion control such as hand and finger movements. Since a population of neurons in the primary motor cortex (M1) area is correlated with finger movements, neural activities recorded in M1 area are used to reconstruct an intended finger movement. In a BMI system, decoding discrete finger movements from a large number of input neurons does not guarantee a higher decoding accuracy in spite of the increase in computational burden. Hence, we hypothesize that selecting neurons important for coding dexterous flexion/extension of finger movements would improve the BMI performance. In this paper, two metrics are presented to quantitatively measure the importance of each neuron based on Bayes risk minimization and deflection coefficient maximization in a statistical decision problem. Since motor cortical neurons are active with movements of several different fingers, the proposed method is more suitable for a discrete decoding of flexion-extension finger movements than the previous methods for decoding reaching movements. In particular, the proposed metrics yielded high decoding accuracies across all subjects and also in the case of including six combined two-finger movements. While our data acquisition and analysis was done off-line and post processing, our results point to the significance of highly coding neurons in improving BMI performance. [ABSTRACT FROM AUTHOR]

Spatial aliasing is an undesirable phenomenon that prevents the unique determination of the direction of arrival (DOA) of impinging signals in array signal processing. However, the characteristics of spatial aliasing that generates ambiguous DOAs can be also used to reduce the computational complexity in maximum-likelihood (ML) DOA estimation. This paper proposes a structural method to dramatically reduce the computational complexity of the ML DOA estimation using the spatial aliasing generated by a nested array structure with a doubly scaled aperture. An ML full grid search is computationally simplified by the highly compressed searching range and the small number of candidate values to be searched which are derived based on spatial aliasing. Performance analyses based on the theoretical bounds and computational complexity with computer simulations show that the proposed method requires an extremely reduced computational load compared to the conventional ML DOA estimation with a uniform linear array (ULA) while achieving the performance enhancement in the estimation accuracy due to the enlarged array aperture. [ABSTRACT FROM PUBLISHER]

This paper presents a novel feedback canceller for a terrestrial digital multimedia broadcasting (T-DMB) on-channel repeater (OCR). There is a crucial requirement for an OCR that the isolation between the transmitter and the receiver antennas should be sufficiently secured to prevent unwanted oscillation. The required isolation, however, may not be satisfied by some physical or technical limitations. In order to overcome these obstacles, undesired feedback signals have been usually reduced by feedback cancellation techniques based on pilot-aided frequency-domain channel estimation (FDCE). In case of the T-DMB system, however, there are no pilot symbols except for the phase reference symbols (PRSs), which are transmitted only once every 76 OFDM symbols. Consequently, the convergence speed and the tracking capability of the FDCE-type feedback cancellers may not meet the required robustness in coping with dynamic feedback channels. To improve the immunity to time-varying channels, we increase the usable number of updates in our feedback canceller, where the PRS is divided into several sub-PRSs during the PRS period and pseudo pilots are generated by decision-directed estimation in the data-symbol duration. Simulation results show that the proposed methods do improve the convergence speed and the tracking capability of the conventional method in both static and dynamic feedback channels. [ABSTRACT FROM PUBLISHER]

Presents a reply to comments on adaptive filtering with monic normalization equation error (MNEE) algorithm. Convergence issues in MNEE.

In the advanced T-DMB (AT-DMB) system, the performance of the base layer is affected by both modulation noise and a demodulation method. The amount of modulation noise is determined by the hierarchy parameter of the transmitter, and thus it is not controllable at the receiver. On the other hand, a demodulation method for the base layer can be freely selected by the designer and it dominates the performance of the base layer. This paper focuses on the performance analysis of the base layer in the AT-DMB system according to the choice of a demodulation method and provides useful information for designing receivers for the AT-DMB system. [ABSTRACT FROM PUBLISHER]