Decision-feedback Differential Detection Research Articles

Reordered Amplitude Phase Shift Keying Aided Differential Spatial Modulation: DFDD-Based Low-Complexity Detector and Performance Analysis Over Fading Channels

Differential spatial modulation (DSM) is a multiple input multiple output (MIMO) wireless transmission technique that achieves additional data bit transmission by utilizing antenna activation indexes. Combined with amplitude phase shift keying (APSK) constellations, the spectrum efficiency of DSM system can be further improved. However, the theoretically optimal maximum likelihood (ML) detection suffers from a high complexity that grows exponentially with the number of transmit antennas (TAs). Besides, the imperfect channel state information in fast fading channels leads to a severe deterioration of the detection performance. To address these problems, we propose a novel transmission scheme named reordered amplitude phase shift keying aided differential spatial modulation (RAPSK-DSM) and its low-complexity decision-feedback differential detection (DFDD) based detection algorithm. The proposed RAPSK-DSM scheme provides a better solution for addressing the error propagation problem and its detector utilizes the preceding channel gain vectors from previous detection results to mitigate the performance loss caused by time-selective channel fading. Furthermore, by decomposing and pre-computing the detection process, the complexity of proposed detector is effectively reduced due to the avoidance of redundant computations. Numerical analyses and simulation results show that the proposed RAPSK-DSM system is able to achieve substantial bit error rate (BER) performance improvement under fast fading channel conditions at the expense of low complexity.

A DFDD Based Detector for Space-Time Block Coded Differential Spatial Modulation Under Time-Selective Channels

Space-time block coded differential spatial modulation (STBC-DSM) is a recently proposed spectral efficient multiple-input-multiple-output (MIMO) transmission technique. Existing detection algorithms for STBC-DSM are designed for quasi-static channels, which limits the application of STBC-DSM in fast fading channels. In this letter, we propose a novel decision-feedback differential detection (DFDD) based detector for STBC-DSM system under fast-fading channels. The proposed detector mitigates the impact of channel vector changes by using the DFDD metric which contains multiple previous detection results. Simulation results show that the proposed detector is more tolerable in time-selective channels than other existing STBC-DSM detectors.

On Multi-User Deep-Learning-Based Non-Coherent DPSK Multiple-Symbol Differential Detection in Massive MIMO Systems

In view of reducing the complexity of signal detection in massive multiple-input multiple-output (MIMO) receivers, the use of non-coherent detection is favored over usual coherent techniques that require complex channel estimation. In this paper, a deep-learning approach to implement non-coherent multiple-symbol detection for differential phase-shift keying (DPSK) multi-user massive MIMO systems is proposed. The proposed deep-learning implementation reduces the high computational complexity required in conventional DPSK detection techniques. Two deep-learning-based multiple-symbol differential detection receiver designs are proposed and compared with decision-feedback differential detection (DFDD), and conventional multiple-symbol differential detection (MSDD) for the same system parameters. Multiple-symbol differential sphere detection (MSDSD) is used to implement conventional MSDD. The results show that the proposed deep-learning-based multiple-symbol differential detection implementation outperforms decision-feedback differential detection and achieves an optimal performance compared to conventional multiple-symbol differential detection implemented by multiple-symbol differential sphere detection for single-user and multi-user scenarios.

Adaptive Coherent/Non-Coherent Single/Multiple-Antenna Aided Channel Coded Ground-to-Air Aeronautical Communication

In this treatise, first of all, we conceive a generic multiple-symbol differential sphere detection (MSDSD) solution for both single- and multiple-antenna-based noncoherent schemes in both uncoded and coded scenarios, where the high-mobility aeronautical Ricean fading features are taken into account. The bespoke design is the first MSDSD solution in the open literature that is applicable to the generic differential space-time modulation (DSTM) for transmission over Ricean fading. In the light of this development, the recently developed differential spatial modulation and its diversity counterpart of differential space-time block coding using index shift keying are specifically recommended for aeronautical applications owing to their low-complexity single-RF and finite-cardinality features. Moreover, we further devise a noncoherent decision-feedback differential detection and a channel-state information estimation aided coherent detection, which also take into account the same Ricean features. Finally, the advantages of the proposed techniques in different scenarios lead us to propose for the aeronautical systems to adaptively: 1) switch between coherent and non-coherent schemes; 2) switch between single- and multiple-antenna-based schemes as well as; and 3) switch between high-diversity and high-throughput DSTM schemes.

Differential Downlink Transmission in Massive MU-MIMO Systems

In this paper, a differential downlink transmission scheme is proposed for a massive multiple-input multiple-output (MIMO) system without explicit channel estimation. In particular, we use a downlink precoding technique combined with a different encoding scheme to simplify the overall system complexity. A novel precoder is proposed, which, with a large number of transmit antennas, can effectively precancel the multiple access interference (MAI) for each user, thus enhancing the system performance. Maximizing the worst case signal-to-interference-plus-noise ratio (SINR) is used to optimize the precoder for the users in which full power space profile (PSP) knowledge is available to the base station (BS). In addition, we provide two suboptimal solutions based on the matched and the orthogonality approach of the PSP to separate the data streams of multiple users. The decision feedback differential detection (DFDD) technique is employed to further improve the performance. The proposed schemes eliminate the MAI, enhance system performance, and achieve a simple low complexity transmission scheme. Moreover, transmission overheads are significantly reduced using the proposed scheme, since it avoids explicit channel estimation at both ends. The Monte Carlo simulation results demonstrate the effectiveness of the proposed schemes.

Multiple-Symbol Differential Sphere Detection and Decision-Feedback Differential Detection Conceived for Differential QAM

Multiple-symbol differential sphere detection (MSDSD) relies on the knowledge of channel correlation. More explicitly, for differential phase-shift keying (DPSK), the transmitted symbols' phases form a unitary matrix, which can be separated from the channel's correlation matrix by the classic multiple-symbol differential detection (MSDD), so that a lower triangular matrix extracted from the inverted channel correlation matrix is utilized for the MSDSD's sphere decoding. However, for differential quadrature amplitude modulation (DQAM), the transmitted symbols' amplitudes cannot form a unitary matrix, which implies that the MSDD's channel correlation matrix becomes amplitude dependent and remains unknown unless all the data-carrying symbol amplitudes are detected. To tackle this open problem, in this paper, we propose to determine the MSDD's nonconstant amplitude-dependent channel correlation matrix with the aid of a sphere decoder (SD) so that the classic MSDSD algorithms that were originally conceived for DPSK may also be invoked for DQAM detection. As a result, our simulation results demonstrate that the MSDSD-aided DQAM schemes substantially outperform their DPSK counterparts. However, the price paid is that the detection complexity of MSDSD is also significantly increased. To mitigate this, we then propose a reduced-complexity MSDSD search strategy specifically conceived for DQAM constellations, which separately map bits to their ring-amplitude index and phase index. Furthermore, the classic decision-feedback differential detection (DFDD) conceived for DQAM relies on a constant channel correlation matrix, which implies that these DFDD solutions are suboptimal and that they are not equivalent to the optimum MSDD operating in decision-feedback mode. With the advent for solving the open problem of MSDSD-aided DQAM, we further propose to improve the conventional DFDD-aided DQAM solutions in this paper.

Soft-Decision Multiple-Symbol Differential Sphere Detection and Decision-Feedback Differential Detection for Differential QAM Dispensing with Channel Estimation in the Face of Rapidly Fading Channels

Turbo detection performed by exchanging extrinsic information between the soft-decision QAM detector and the channel decoder is beneficial for the sake of exploring the bit dependency imposed both by modulation and by channel coding. However, when the soft-decision coherent QAM detectors are provided with imperfect channel estimates in rapidly fading channels, they tend to produce potentially unreliable LLRs that deviate from the true probabilities, which degrades the turbo detection performance. Against this background, in this paper, we propose a range of new soft-decision multiple-symbol differential sphere detection (MSDSD) and decision-feedback differential detection (DFDD) solutions for differential QAM (DQAM), which dispense with channel estimation in the face of rapidly fading channels. Our proposed design aims for solving the two inherent problems in soft-decision DQAM detection design, which have also been the most substantial obstacle in the way of offering a solution for turbo detected MSDSD aided differential MIMO schemes using QAM: 1) how to facilitate the soft-decision detection of the DQAM’s amplitudes, which—in contrast to the DPSK phases—do not form a unitary matrix, and 2) how to separate and streamline the DQAM’s soft-decision amplitude and phase detectors. Our simulation results demonstrate that our proposed MSDSD aided DQAM solution is capable of substantially outperforming its MSDSD aided DPSK counterpart in coded systems without imposing a higher complexity . Moreover, our proposed DFDD aided DQAM solution is shown to outperform the conventional solutions in literature. Our discussions on the important subject of coherent versus noncoherent schemes suggest that compared to coherent square QAM relying on realistic imperfect channel estimation, MSDSD aided DQAM may be deemed as a better candidate for turbo detection assisted coded systems operating at high Doppler frequencies.

簡易な1次伝送路予測による判定帰還多重遅延検波とその音響通信への応用

簡易な1次伝送路予測による判定帰還多重遅延検波とその音響通信への応用

Decision-Feedback Differential Detection in Impulse-Radio Ultra-Wideband Systems

In this paper we present decision-feedback differential detection (DF-DD) schemes for autocorrelation-based detection in impulse-radio ultra-wideband (IR-UWB) systems, a signaling scheme regarded as a promising candidate in particular for low-complexity wireless sensor networks. To this end, we first discuss ideal noncoherent sequence estimation and approximations thereof based on block-wise multiple-symbol differential detection (MSDD) and the Viterbi algorithm (VA) from the perspective of tree-search/trellis decoding. Exploiting relations well-known from tree-search decoding, we are able to derive the novel decision-feedback differential detection (DF-DD) schemes. A comprehensive comparison with respect to performance and complexity of the presented schemes in a typical IR-UWB scenario reveals-along with novel insights in techniques for complexity reduction of the sphere decoder applied for MSDD- that sorted DF-DD achieves close-to-optimum performance at very low, and in particular constant receiver complexity.

On Noncoherent Receivers for DSTM in Spatially Correlated Fading

In this letter, we derive a multiple-symbol differential detection (MSDD) and a novel MSDD-based decision-feedback differential detection (MS-DFDD) receiver for differential space-time modulation transmitted over spatially correlated multiple-input multiple-output fading channels. We show that MS-DFDD outperforms previously proposed DFDD schemes that are based on scalar and vector prediction (SP-DFDD and VP-DFDD). In addition, we prove that at high signal-to-noise ratio (SNR) VP-DFDD is equivalent to SP-DFDD and thus fails to properly exploit the spatial fading correlations.

Adaptive MDPSK DS/CDMA receivers with performance analysis

AbstractFor direct‐sequence code‐division multiple‐access (DS/CDMA) systems, the multiuser and multipath interferences are always present. When the demodulation is coherent, a coherent carrier reference must be generated prior to demodulation. The generation of coherent reference at low signal‐to‐interference‐and‐noise ratio (SINR) is difficult. In the downlink CDMA communications, numbers of active users transmit information simultaneously by different signature waveform. However, the multipath channel and multiple‐access interference (MAI) limit the system capacity. Adaptive single‐user receivers do not require knowledge of MAI parameters and need fewer computations. In this paper, we propose adaptive receivers with decision‐feedback differential detection (DF‐DD) and compare variations of the receiver structure proposed in Schrober's paper for noncoherent channels. In the absence of knowledge of the carrier phase, we derive the minimum mean square error (MMSE) of the proposed receivers to show that the performances of the proposed receivers with M‐ary differential phase‐shift keying (MDPSK) signals approach that of the coherent receiver with MPSK signal. Some simulation examples are given to demonstrate the effectiveness and compare the performances of the proposed adaptive receivers. Copyright © 2008 John Wiley & Sons, Ltd.

Decision-Feedback Subset Multiple-Symbol Differential Detection for Unitary Space-Time Modulation

In this paper, a novel noncoherent detection algorithm for differential space-time modulation (DSTM) over flat-fading multiple-input-multiple-output channels is presented. This algorithm, which is referred to as decision-feedback subset multiple-symbol differential detection (DF-S-MSDD), combines ideas from decision-feedback differential detection (DFDD) and subset multiple-symbol differential detection (S-MSDD). More specifically, the DF-S-MSDD decision metric includes a number of previous decisions (i.e., decision feedback), and the optimization over the remaining hypothetical symbols returns decisions only on a subset of these symbols (i.e., S-MSDD). Furthermore, an implementation of DF-S-MSDD based on tree-search (TS) methods is devised. Due to the concept of subset detection, DF-S-MSDD outperforms MSDD in terms of error-rate performance. At the same time, due to the use of decision feedback, it also requires lower computational complexity than the TS-based MSDD schemes for the DSTM recently proposed in the literature.

A unified performance analysis framework for differential detection in MIMO Rayleigh fading channels

In this paper, a unified framework for the analysis of differential detection (DD) schemes in time-variant multiple- input multiple-output Rayleigh fading channels is provided. The present results are very general in that they apply to transmission with differential phase-shift keying, unitary differential space- time modulation (DSTM), and block DSTM and reception with conventional DD (CDD), multiple-symbol DD (MSDD), decision- feedback DD (DFDD), and (differentially) coherent detection (CD). New result for general quadratic forms of Gaussian random variables are derived which allows us to obtain elegant closed-form expressions for the pairwise error probabilities (PEPs) of the dominant error events of the considered detectors. Furthermore, it is shown that a unified treatment of all considered detectors is possible with a properly defined effective signal- to-noise ratio (ESNR) and a useful connection between MSDD and minimum-mean-squared-error (MMSE) interpolation is established. Interesting novel results obtained from this analysis include: (i) DSTM constellations designed for CDD and CD are also optimum for MSDD and DFDD; (ii) the error floor entailed by MSDD and DFDD in time-variant fading decreases exponentially with the observation window size N; and (iii) in time-variant fading with effective normalized fading bandwidth Bh,effT MSDD with N rarr infin suffers only from an SNR loss of (1-2Bh,effT) compared to CD, whereas DFDD suffers from a diversity loss of (1-2Bh,effT).

Adaptive DS-CDMA Receiver with Code Tracking in Phase Unknown Environments

In this paper, we propose and analyze a new noncoherent receiver with PN code tracking for direct sequence code division multiple access (DS-CDMA) communication systems in multipath channels. We employ the decision-feedback differential detection method to detect MDPSK signals. An ;error signal; is used to update the tap weights and the estimated code delay. Increasing the number of feedback symbols can improve the performance of the proposed noncoherent receiver. For an infinite number of feedback symbols, the optimum weight can be derived analytically, and the performance of the proposed noncoherent receiver approaches to that of the conventional coherent receiver. Simulations show good agreement with the theoretical derivation.

Multiple-Bit Differential Detection of Shaped-Offset QPSK

We consider multiple-bit differential detection (MBDD) of differentially encoded shaped-offset quadrature phase-shift keying (SOQPSK), a highly bandwidth-efficient and popular constant-envelope modulation. We propose two MBDD schemes that are based on a recent continuous phase modulation interpretation of SOQPSK. We show that the performance of these MBDD schemes approaches that of coherent detection (CD) as the multiple-bit observation N window increases. The first scheme uses a detection window that spans the full-bit observation window (F-MBDD), and is shown to require very large values of N to approach the performance of CD. This presents a practical problem since the complexity of MBDD grows exponentially with N. The second scheme is an improved version (I-MBDD) with a detection window that is shortened to N-2 bit intervals. Although the complexity of I-MBDD also increases exponentially with N, it represents a significant improvement since only modest values of N are needed for high performance. These performance characteristics are identified via a detailed performance analysis, which provides asymptotic formulas for the bit error probability that are confirmed with computer simulations. The analysis is also used to find the symmetric frequency pulse shapes with the best and worst error performance. Finally, we develop a simplified and practical decision feedback differential detection algorithm that achieves near-optimal performance with complexity that grows only linearly with N.

Multi-Chip Differential Space-Time Block Coding for DS-CDMA

In this letter, we propose a novel space-time coding scheme for fast time-variant direct-sequence code-division multiple access (DS-CDMA) channels. The proposed scheme employs multi-chip differential space-time block coding (MC-DSTBC) and robustness against fast fading is further improved by low-complexity decision-feedback differential detection (DF-DD). Both analytical and simulation results show in good agreement the excellent performance of the novel design in fast time-variant channels.

Differential spatial multiplexing

In this paper, we present a novel differential space-time (DST) architecture which is well suited for high data-rate applications but requires only a linear decoding complexity. Multiple transmit antennas are divided into groups and DST encoding is applied individually to each group. Instead of using the optimum joint-group decoding approach, the proposed receiver combines group interference suppression (GIS) and decision-feedback differential detection (DF-DD) to reduce the decoding complexity. By taking advantage of the differential encoding at the transmitter, the GIS filters can be calculated without explicit knowledge of channel state information. Since the optimization of the GIS filters requires a generalized eigendecomposition of two correlation matrices, we also devise efficient adaptive algorithms for recursive filter optimization. It is shown that both the GIS filter computation and the detection scheme are robust against carrier phase variations

Decision-feedback detection for block differential space-time modulation

Time variation on fading channels hinders accurate channel estimation in differential space-time modulation and deteriorates the performance. Decision-feedback differential detection is studied for block differential space-time modulation, and compared with conventional differential space-time modulation. It is observed that the proposed scheme does not suffer effective fading bandwidth expansion, as does the conventional scheme. An improved effective signal-to-noise ratio approach is proposed for analyzing the performance of the proposed scheme in time-varying flat Rayleigh fading. Theoretical analysis and simulations show the improved performance of the proposed scheme over the conventional scheme.

Bound-Intersection Detection for Multiple-Symbol Differential Unitary Space–Time Modulation

This paper considers multiple-symbol differential detection (MSD) of differential unitary space-time modulation (DUSTM) over multiple-antenna systems. We derive a novel exact maximum-likelihood (ML) detector, called the bound-intersection detector (BID), using the extended Euclidean algorithm for single-symbol detection of diagonal constellations. While the ML search complexity is exponential in the number of transmit antennas and the data rate, our algorithm, particularly in high signal-to-noise ratio, achieves significant computational savings over the naive ML algorithm and the previous detector based on lattice reduction. We also develop four BID variants for MSD. The first two are ML and use branch-and-bound, the third one is suboptimal, which first uses BID to generate a candidate subset and then exhaustively searches over the reduced space, and the last one generalizes decision-feedback differential detection. Simulation results show that the BID and its MSD variants perform nearly ML, but do so with significantly reduced complexity.

Differentially coherent parallel interference cancellation for DS-CDMA

In this paper, we propose a novel differentially coherent (DC) parallel interference cancellation (PIC) scheme for direct-sequence code-division multiple access (DS-CDMA) employing differential phase-shift keying (DPSK). The proposed scheme combines decision-feedback differential detection (DF-DD) and PIC. For optimization of the DF-DD and interference cancellation (IC) filters three different criteria are adopted. The first (DC-PIC I) and the second (DC-PIC II) criteria assume a constant channel and a channel with a small constant frequency offset, respectively, whereas the third criterion (DC-PIC III) optimizes the filters in the minimum mean-squared error (MMSE) sense taking into account the statistical properties of the underlying channel. Simulations show the high achievable performance and the robustness of the novel DC-PIC receiver. A comparison with linear DC receivers and a previously proposed DC-PIC scheme show the superiority of the proposed approach.