Based on pruning techniques that interpret polar codes as low-density parity-check-like (LDPC-like) codes, this paper develops novel belief propagation (BP)-based decoders utilizing the concept of schedule diversity. By analyzing the impact of hidden variable nodes (VNHs), scheduling algorithms that guarantee fast convergence speeds and superior error performance are devised for the LDPC-like sparse factor graph (SPF), incorporating both standard sequential scheduling (SSS) and informed dynamic scheduling (IDS) algorithms. To further enhance error performance, cyclic redundancy check (CRC) bits are integrated into the LDPC-like SPF, and random update sequences are introduced to reduce computational complexity while implementing schedule diversity. Inspired by belief propagation list decoding, the proposed approaches eventually update messages in the LDPC-like SPF according to various schedules, thereby producing diverse decoding outcomes. Compared to the CRC-aided successive cancellation list (CA-SCL) decoder and benchmark soft-output decoders in the literature, the proposed schemes achieve comparable or improved error performance while reducing computational complexity in the high SNR region. These results serve as preliminary findings on the BP algorithm over LDPC-like SFGs and provide useful insights for the design and practical improvement of polar decoders.

This paper explores a robust and computationally efficient soft-output fixed-complexity sphere decoder (FSD) designed for large-scale multiple-input multiple-output (MIMO) detection. A partial expansion strategy is designed for the first two layers of the proposed FSD, utilizing enumeration orders for both the real and imaginary components of the signal space. Additionally, a section-wise list candidate selection method, incorporating an innovative grouping strategy, is specifically designed for the leaf layer. These techniques complement each other to significantly reduce computational complexity and minimize processing delays. Furthermore, log-likelihood ratio (LLR) refinement is implemented to counteract overestimation caused by the bit-flipping algorithm, leading to notable improvements in error performance. Simulation results demonstrate that the proposed soft-output FSD achieves superior error performance compared to benchmark schemes and approaches the list sphere decoder, while maintaining significantly lower complexity.

Premature convergence is a critical issue of Particle Swarm Optimization (PSO). The weak global search capability causes particles trapped in local minima at early stage of learning process. There is several research dedicate to solve this problem over the decade. This paper proposes a new algorithm combined Isolation Forest and Particle Swarm Optimization called Isolation Forest Backward Particle Swarm Optimization (IFB-PSO). The proposed new learning scheme helps particles escaping from local minima. The particle will jump backward to the targeted position when the particle trapped over specific iterations. The destination is precisely selected by Isolation Forest to endow the backward particle hopeful future. IFB-PSO is evaluated by a classic benchmark suite, cart-pole problem, and mountain car problem. Experimental results show that IFB-PSO gets competitive results on the benchmark suite with different dimensions and two control problems in comparison with 11 well-known optimization algorithms. The behavior of backward particles is also analyzed to inspect the utility and efficiency of the backward process.

In this letter, an error-correction-based iris recognition (EC-IR) scheme, which utilizes multi-scale dominating feature points (msDFPs), is constructed to enhance the security level against a stricter concern of error-correction-based attack, where the intruder is assumed to be fully aware of the architecture of the adopted error-correcting code. The extraction method of the msDFPs is proposed to alter the essence of raw iris data. Accordingly, it is shown that the proposed msDFPs-based EC-IR scheme provides a balanced design which guarantees both a large value of security bits and an enhanced recognition performance, and is particularly suited for real-world applications where a high-level security is paramount.

In this paper, an error-correction-based iris recognition (EC-IR) scheme that guarantees both secure template storage and high-level recognition accuracy is first constructed for personal authentication. From the analysis of both the soft reliability values for the iris bits and the recovery capability values for the low-density parity-check (LDPC) code bits, a method called template mapping is devised in order to freely adjust the error-correction capability of the EC-IR scheme. The design process for suitable LDPC codes is then investigated so as to provide a stable and high-rate EC-IR scheme. In order to further enhance the security level of the EC-IR scheme, we propose locating the dominating feature points (DFPs), and then using them for iris recognition rather than using the original binary templates acquired from the iris database. The DFP-based EC-IR scheme not only enhances the security level, but also provides a better equal error rate (EER) performance and a faster processing speed during the verification stage. As a result, an iris cryptosystem based on the fuzzy commitment strategy is eventually constructed founded on a comprehensive consideration of both a satisfactory recognition performance combined with a high security level.

In this work, we investigate rate-splitting multiple access (RSMA) for a multiuser downlink wireless network consisting of an unmanned aerial vehicle (UAV)-assisted base station (BS) that serves multiple ground users (GUs) simultaneously. Considering two different transmission regimes, namely infinite blocklength (IBL), and finite blocklength (FBL), we analyze the performance of the considered network under the effect of imperfections in channel state information (CSI) estimation and successive interference cancellation (SIC) with the probabilistic line of sight fading channels. For IBL transmission, we derive the closed-form expressions of the outage probability, throughput, and achievable ergodic rate at each GU. Furthermore, for short packet communication, the closed-form expressions of block error rate (BLER), goodput, and achievable ergodic rate are determined with FBL transmission. Moreover, for the FBL regime we also formulate an optimization problem that jointly optimizes the 3D-position of the UAV, power allocated to each user, and common rate distribution at each user to maximize the ergodic sum rate subject to the practical constraints such as maximum tolerable BLER, minimum private and total rate at each user. We then propose an alternating optimization-based iterative algorithm to solve the problem. Monte-Carlo simulations are used to verify the accuracy of derived analytical results and demonstrate the trade-off between transmit power and achievable BLER. In addition to this, the effectiveness of RSMA in UAV-assisted communication under IBL and FBL transmission regimes is also observed compared to non-orthogonal multiple access.

Sparse code multiple access (SCMA) is a promising code-domain non-orthogonal multiple access (NOMA) technique that supports high-level connectivity. Through the combination of SCMA and multiple-input multiple-output (MIMO) techniques, MIMO-SCMA schemes are capable of enhancing the overall spectral efficiency. This paper proposes novel MIMO-SCMA designs for both uplink and downlink Rayleigh fading channels. Rather than directly combining the SCMA and spatial multiplexing techniques presented in the previous literature, the proposed designs consider not only the frequency or time diversity, but also simultaneously include space diversity. Codebook design criteria for different transmission scenarios are respectively investigated, and a low-complexity codebook design algorithm is proposed based on the cross-entropy method. In addition, since the new designs suggest a dense factor graph, conventional message-passing algorithm (MPA)-based detectors are less suitable. Consequently, low-complexity MIMO-SCMA codeword detectors based on depth-first and breadth-first tree-search algorithms are respectively investigated. It is shown that the overall designs are able to simultaneously achieve a higher diversity order, enhanced BER results, and lower levels of detection complexity for both uplink and downlink scenarios, when compared to conventional MIMO-SCMA schemes.

Spatial multiplexing aided spatial modulation (SMx-SM) is a communication technology which essentially combines the concepts of Vertical Bell Labs Layered SpaceTime (V-BLAST) and spatial modulation (SM). In this paper, we construct a high-rate spatial multiplexing aided generalized spatial modulation (SMx-GSM) scheme which guarantees a very low detection complexity. Benefiting from the codebook structure, a tree-search based MIMO detector for the SMx-GSM scheme can be devised. Simulation results show that the detection complexity can be significantly reduced, which makes a highrate system feasible, and an error performance which is very close to that of the maximum-likelihood (ML) detector can be achieved, especially for the case of a high-rate large-scale SMx- GSM system with a large number of activated transmit antennas.

Sparse code multiple access (SCMA) is one of the competitive non-orthogonal multiple access (NOMA) techniques for the next generation of communication systems. In this paper, a systematic construction procedure for the design of SCMA codebooks under various channel environments is proposed in order to achieve near-optimal designs, especially for cases which consider small-scale SCMA parameters. The procedure includes the rotation angle design, the construction of multi-dimensional codebooks, and the design of labelling rules. The detailed design criteria and the related properties are derived and investigated. A low-complexity construction algorithm is further proposed for the cases of fading channels. Numerical results show that the designed SCMA codebooks provide improvements in error performance for all of the considered channel conditions, when compared to the codebooks presented in the prior literature.

In this paper, we focus on near-optimal designs for variable-length error-correcting (VLEC) codes, while considering the performance in terms of both the average codeword length (ACL) and the symbol-error rate (SER). The criteria for narrowing the search space and enhancing the SER performance are investigated. An efficient code construction algorithm is then devised based on a random search process. Taking advantage of the significantly reduced search complexity, we are able to construct near-optimal VLEC codes for large source alphabets. Numerical results obtained for various free distance values and alphabet sizes show that constructed VLEC codes have both reduced ACL values and enhanced SER performances. Performance improvement is more notable for large source alphabets.

A sequence is said to be perfect if it has an ideal periodic autocorrelation function. In addition, the degree of a sequence is defined as the number of distinct nonzero elements within each period of the sequence. This study presents a systematic method for constructing perfect sequences (PSs) of odd prime periods, where the general constraint equations for the sequence coefficients are derived, providing a solid theoretical foundation to the construction of PSs. The proposed scheme commences by partitioning a cyclic group ZP= {1, 2,⋯, P - 1} into K cosets of cardinality M, where P = K · M + 1 is an odd prime. Based on this partition, the degree-(K + 1) PSs are then constructed. Finally, case studies are presented to illustrate the proposed construction.

In this paper, a cooperative single-carrier transmission scheme considering a distributed quasi-orthogonal space-frequency block code (QOSFBC) that provides improved peak-to-average power ratio (PAPR) performance is constructed for uplink communications. Focused on reducing the size and computational complexity, the source node, i.e., the mobile devices, is equipped with two transmit antennas, while only one antenna is required at the relay node in order to collaboratively generate a distributed QOSFBC signal using four transmit antennas. To achieve full diversity, a phase rotation strategy is proposed at the relay node. In addition, since single-carrier schemes considering SFBCs re-permute the spectral components of the transmitted signal and induce high PAPR value, a modified SFBC coding technique is proposed that allows the high-PAPR problem to be mitigated. Consequently, the designed distributed single-carrier frequency-division multiple access (SC-FDMA) QOSFBC scheme is able to provide full transmit diversity over frequency-selective fading channels, with a lower PAPR value on mobile devices when compared with a conventional SC-FDMA QOSFBC scheme.

In this paper, a coded modulation scheme using extremely sparse low-density parity-check (LDPC) codes is proposed for the stored signal of triple-level-cell (TLC) NAND flash, where both the encoding and the decoding complexity can be significantly reduced with the advantage of the extremely sparse code graph. In order to enhance the performance of decoder, iterative detection decoding (IDD) is introduced to extract the extrinsic information from the symbol detector, and the cooperative non-Gray mapping is also designed. In addition, for error floor lowering, an interleaver is inserted to ensure the cascaded degree-2 variable nodes are separated to individual symbols. The simulation results show that the proposed coded modulation scheme can provide a practical error floor performance with a low decoding complexity.

In this paper, we investigate a Raptor-coded distributed noncoherent scheme based on a non-orthogonal spacetime modulation (NOSTM) signal and a dynamic decode-and-forward (DF) relaying scenario. The distributed NOSTM signal is firstly proposed based on unitary space-time modulation (USTM) and spatial multiplexing (SM). The dynamic DF relaying protocol is investigated to process the non-orthogonal feature of the NOSTM signal. A Raptor-coded distributed scheme is then constructed for the relay network, and the corresponding transmission and reception procedures are also investigated. It is shown that the throughput performance can be effectively improved, especially for cases when the location of the chosen relay nodes is distant from the source node.

It is known that by extracting log-likelihood ratio (LLR) values from the received MIMO signals, a MIMO detector is able to exchange a posteriori soft information with a channel decoder to improve the error performance. A minimum mean-square error with parallel interference cancellation (MMSE-PIC) detector is considered to be a practical MIMO detector, but the computational complexity for the LLR computation is still at a high level for higher-order modulations. This paper presents a low-complexity LLR computation algorithm together with the hardware implementation for MMSE-PIC detectors. The complexity is evaluated using logic synthesis based on a 90-nm CMOS technology. For 256-QAM modulation, a 50% reduction in area is achieved. In addition, a 44% reduction in area can be achieved for a multi-mode MMSE-PIC detector that supports multiple modulations for signals up to 256-QAM.

In this paper, we investigate Raptor-coded distributed unitary space-time modulation (USTM) schemes, where both the amplify-and-forward (AF) and decode-and-forward (DF) relaying scenarios are considered, under a wireless relay network with arbitrary path gains for the channel fading coefficients. First, the AF and DF relaying procedures are investigated based on the use of an inner USTM signal and an outer Raptor code, and the related noncoherent detectors are also derived. The constellation search for the USTM signal, as well as the optimization for the Raptor code, is then investigated in order to enhance the system performance. It is shown that the designed systems effectively approach the predicted limit in throughput performances and outperform the noncoherent distributed MIMO scheme reported in the previous literature.

In this paper, we investigate differential amplitude/ phase modulation (APM) schemes for correlated Rayleigh fading channels. Considering the noncoherent maximum-likelihood receiver, a theoretical pairwise error probability (PEP) formula for differential signal vectors with arbitrary power values is derived. The design criterion for the signal set of differential vectors is then proposed based on the asymptotic analysis of the PEP. For both uncoded and coded APM schemes, the design criteria and optimization procedures for bit labeling rules are investigated. The designed differential APM schemes are shown to provide significant improvement in bit-error-rate performance, particularly in the error-floor regions.

In this paper, we focus on the design of differential amplitude/phase modulation schemes by a look-up table for Rayleigh fading channels. In the first part of this paper, we first propose the noncoherent distance measure for each two signal vectors based on the maximum-likelihood (ML) signal detection under Rayleigh fading channels. The design criterion/procedure of the look-up table is then investigated. In the second part of this paper, linear dispersion codes are used to construct a multi-dimensional differential amplitude/phase modulation scheme, with the aid of the genetic algorithm. Both schemes are shown to provide improvements in error performance, when comparing to the conventional scheme provided in the literature.

In this paper, a full-duplex compress-and-forward (CF) protocol for cooperative communication systems using Raptor codes is first investigated. It is verified that the throughput of the full-duplex CF protocol is superior to that of the full-duplex decode-and-forward (DF) protocol when the relay-to- destination channel has a much higher quality compared to the source-to-relay channel, while the full-duplex DF protocol works more effectively than the full-duplex CF protocol in the reverse situation. A full-duplex adaptive relaying protocol that is devised based on both CF and DF protocols is then proposed. In the proposed protocol, the CF and DF protocols are adaptively switched, depending on the channel conditions of the wireless links. In addition, the throughput of the overall system is enhanced using an outer Raptor code. Simulation results show that the proposed scheme smoothly switches between the two conventional protocols to cope with different channel conditions.

Cognitive radio (CR) technology can be been applied in hierarchical cellular systems to allow concurrent transmissions for licensed (primary) and unlicensed (secondary) users to improve spectrum utilization. The major challenge of hierarchical CR systems is to manage the inter-cell interference between the primary and secondary systems. In the paper, we first present an optimal multiple-input multiple- output (MIMO) orthogonal frequency division multiplexing (OFDM) uplink transmission scheme for hierarchical CR systems that can maximize the sum rate of the underlay secondary CR users, and prevent the primary systems from the severe interference of the secondary systems. The main contribution of this work is to propose a methodology to transform the signal to interference plus noise ratio (SINR) maximization problem of the secondary system into a quasi-convex form, thereby obtaining the optimal beamforming solution using a simple bisection method. Furthermore, we proposed a sub-optimal user scheduling algorithm in the secondary system to effectively mitigate the interference to the primary system.

In the encoding of Luby transform (LT) codes, information bits (variable nodes) are randomly connected to the check nodes. Although the check-node degrees have been optimized for error-rate performance, the arbitrary connections in the code graph cannot guarantee efficient propagation of the channel information (intrinsic messages), and may slow down the convergence speed of the iterative decoding. This paper presents a design for a generator matrix such that the intrinsic messages can be efficiently propagated through the arranged connections. In addition, the convergence speed of rateless codes can also be accelerated using the proposed degree-oriented scheduling (DOS), where the intrinsic messages are propagated based on the order of check node degrees. An improvement in the convergence speed can be achieved without sacrificing the error-rate performance. In the case of Raptor codes, the BER performance can be significantly improved.

In this paper, we investigate noncoherent transmission schemes using amplitude/phase modulation. For uncoded transmission schemes, we derive the pairwise error probability (PEP) and its high-SNR approximation for signal vectors with unequal power values using a noncoherent maximum-likelihood detector under Rayleigh block fading channels. For coded transmission schemes, we consider differential amplitude/phase modulated signals and introduce a codeword-interleaving strategy to improve the error performance. The design criteria for the signal labelling and bit interleaving are also derived via the high-SNR approximation of the PEP. At the receiver, we devise an iterative channel amplitude estimator to enhance the detection reliability. With the help of a specially-designed iterative receiving algorithm, the designed noncoherent coded scheme can provide a significant improvement, either in the error-floor or the waterfall region.

As part of the tradeoff between error performance, decoding complexity and the overhead of rateless codes, the combination of incremental decoding (ID) and informed dynamic scheduling (IDS), known as IDIDS (incremental decoding with informed dynamic scheduling), is an attractive solution in binary symmetric channels (BSC). However, applying IDIDS in the AWGN (additive white Gaussian noise) channel may cause a degradation in BER performance, since the incrementally received symbols from the AWGN channel may not be immediately utilized in the decoding process directed by IDS. In addition, a stopping criterion combined with IDS may cause the current decoding attempt to terminate too early, and the channel information contained in the originally received codeword will not be used efficiently. In this paper, a dynamic decoding schedule strategy is proposed. In the proposed decoder, the new received symbols can be immediately utilized in the decoding process. For Luby transform (LT) codes and Raptor codes over the AWGN channel, the proposed algorithm provides a more balanced tradeoff. In the case of Raptor codes, the BER performance is obviously improved.

As technology continues to shrink, reducing leakage is critical to achieving energy efficiency. Previous studies on low-power GPUs (Graphics Processing Units) focused on techniques for dynamic power reduction, such as DVFS (Dynamic Voltage and Frequency Scaling) and clock gating. In this paper, we explore the potential of adopting architecture-level power gating techniques for leakage reduction on GPUs. We propose three strategies for applying power gating on different modules in GPUs. The Predictive Shader Shutdown technique exploits workload variation across frames to eliminate leakage in shader clusters. Deferred Geometry Pipeline seeks to minimize leakage in fixed-function geometry units by utilizing an imbalance between geometry and fragment computation across batches. Finally, the simple time-out power gating method is applied to nonshader execution units to exploit a finer granularity of the idle time. Our results indicate that Predictive Shader Shutdown eliminates up to 60% of the leakage in shader clusters, Deferred Geometry Pipeline removes up to 57% of the leakage in the fixed-function geometry units, and the simple time-out power gating mechanism eliminates 83.3% of the leakage in nonshader execution units on average. All three schemes incur negligible performance degradation, less than 1%.

In this paper, we present a turbo coded space-time modulation scheme for noncoherent block fading channels, where neither the transmitter nor the receiver knows the channel state information. The turbo coded bits are divided into two parts which are respectively transmitted through information-bearing pilots and spatial multiplexing (SM). Since this approach effectively increases the cardinality of the set of possible transmit (space-time) signal matrices, a large rate gain can be obtained without increasing the modulation order, as shown through achievable-rate analysis. At the receiver, an iterative detection-decoding algorithm is performed cooperatively among the turbo decoder, the coherent demapper for the SM, and the noncoherent demapper for the information-bearing pilots through the help of the proposed signal matrix detector, which enables these two demappers to utilize the channel information inherent in all the received symbols within the same fading block. Compared to the previous work in the literature, the proposed scheme can provide advantages in both error performance and complexity.

In this paper, we propose to approach the capacity limit for channels with fast phase variation by using a serial concatenation scheme with an outer turbo encoder and an inner block modulator. A distinct feature of the proposed transmission scheme is that coded symbols from adjacent codewords are interleaved into the same input vectors of the block modulator. At the receiver, we not only perform the iterative noncoherent demodulation and decoding algorithm, but also exchange extrinsic information between adjacent codewords due to the codeword interleaved structure. It is shown through the extrinsic information transfer (EXIT) chart that the resultant block demodulator and channel decoder can match well with each other, and can achieve a near-capacity performance.

In this paper, we propose a turbo coded MIMO (multiple-input multiple-output) scheme for noncoherent fast fading channels, where neither the transmitter nor the receiver knows the channel state information. The turbo coded bits are alternatively transmitted by using the unitary space-time modulation (USTM) or spatial multiplexing (SM). At the receiver, a novel iterative detection-decoding algorithm is performed among the turbo decoder, the coherent demapper used for SM, and the noncoherent demapper for USTM. As compared to the scheme in the literature, the proposed scheme, in some cases, can provide better error performance with lower complexity.

A novel noncoherent block coding scheme, called noncoherent block-coded MPSK (NBC-MPSK), was proposed recently. In this paper, we present further research results on NBC-MPSK. We first focus on the rotational invariance (RI) of NBC-MPSK. Based on the RI property of NBC-MPSK with multistage decoding, a noncoherent near-optimal linear complexity multistage decoder for NBC-MPSK is proposed. Then we investigate a tree-search ML decoding algorithm for NBCMPSK. The derived algorithm is shown to have low complexity and excellent error performance. In this paper, we also utilize the idea of the NBC-MPSK to design noncoherent space-time block codes, called noncoherent space-time block-coded MPSK (NSTBC-MPSK). For two transmit antennas, we propose a signal set with set partitioning and derive the minimum noncohent distance of NSTBC-MPSK with this signal set. For the decoding of NSTBC-MPSK, we modify the ML decoding algorithm of NBC-MPSK and propose an iterative hard-decision decoding algorithm. Compared with training codes and unitary space-time modulation, NBC-MPSK and NSTBC-MPSK have larger minimum noncoherent distance and thus better error performance for the noncoherent ML decoder.

A novel noncoherent block coding scheme, called noncoherent block-coded MPSK (NBC-MPSK), was proposed in [1] recently. This NBC-MPSK scheme was generalized to multiple-antenna systems in [2] as well. In this paper, we present further research results on NBC-MPSK and its generalization. We first focus on the rotational invariance (RI) of NBC-MPSK. Based on the RI property of NBC-MPSK with multistage decoding, a noncoherent near-optimal linear-complexity multistage decoder for NBC-MPSK is proposed. Then we propose a tree-search ML decoding algorithm for NBC-MPSK. The proposed algorithm is shown to have low complexity and excellent error performance. This ML decoding algorithm can also be applied to the generalized NBC-MPSK for multiple antennas. In addition, we propose a new signal set with partitioning for the generalized NBC-MPSK. Error performance and complexity of decoding algorithms is verified by simulations.

A multi-microprocessor-based structure for controlling the manipulator motion in Cartesian space is presented. The objective is to investigate the feasibility of implementing hand-based control laws using present day microprocessors. computational complexity analysis indicates that the control schemes involving full inverse-kinematics and inverse-dynamics computations can be realised using the proposed control structure.