This paper presents a polar-coded orthogonal frequency-division multiplexing (OFDM) system that utilizes adaptive code rate selection based on channel impulse response. In conventional OFDM systems, power levels vary across subcarriers because of channel frequency selectivity. To ensure reliable communication in polar-coded OFDM systems, it is essential to predict communication quality using estimated channel state information (CSI) and to adaptively allocate the code rate. This approach aims to meet specified reliability constraints while optimizing system performance. The estimated block error rate (BLER) serves as an indicator of communication quality and can be accurately predicted using the estimated CSI. We develop a scheme that adaptively selects the code rate according to the CSI by identifying the maximum number of information bits while ensuring that the estimated BLER stays below a specified target BLER. To assess the effectiveness of the proposed method, we perform computer simulations and analyze its performance in terms of both BLER and achievable throughput in a general retransmission framework with hybrid automatic repeat request (HARQ).

Furudoi T., Takahashi T., Ochiai H.. Discrete-Valued Signal Estimation via GAMP under Finite-Sized Highly Correlated GLMs. Proceedings of the IEEE International Conference on Communications (ICC 2026); https://doi.org/10.1109/ICC59461.2026.11587545.

We address a design of high-capacity and low-peak-to-average power ratio (PAPR) orthogonal frequency-division multiplexing (OFDM) systems based on bit-interleaved coded modulation (BICM) utilizing non-equiprobable and non-uniform (NENU) constellations as well as clipping and filtering (CAF). The proposed constellations are generated using a truncated Gaussian distribution and the merging of constellation points, where the former creates a non-uniform constellation (NUC), and the latter adjusts the number of signal points for further improving the total bitwise mutual information (BMI). Unlike other exhaustive search-based approaches, the proposed constellations are uniquely determined by only two parameters associated with NUC and cardinality. Due to this property of limited degrees of freedom, the complexity required for the numerical optimization process can be significantly low. We focus on the constellation design based on one dimension, i.e., pulse amplitude modulation (PAM), which facilitates the reduction of demapping complexity for the BICM receiver. The use of CAF at the transmitter can efficiently reduce the PAPR of OFDM signals; however, it introduces clipping noise that may degrade error rate performance, making the application of clipping noise cancellation (CNC) at the receiver essential. Therefore, we optimize the NENU constellations in the presence of CAF and CNC. Simulation results demonstrate that the combination of constellation shaping with CAF and CNC enables BICM-OFDM systems to simultaneously achieve low PAPR and high spectral efficiency over additive white Gaussian noise (AWGN) as well as frequency-selective fading channels. Furthermore, comparative studies confirm that the proposed system significantly outperforms the single-carrier counterpart (i.e., DFT-precoded BICM-OFDM) in terms of PAPR and bit error rate (BER) performance over fading channels.

For channels that are doubly selective, delay-Doppler (DD) modulation, commonly called orthogonal time frequency space (OTFS) modulation, allows for the correction of both delay and Doppler shifts at the same time. However, the signal using OTFS has a high peak-to-average power ratio (PAPR) due to the precoding in the delay-Doppler domain. To overcome this problem, we propose a single-carrier transmission for delay Doppler shifts (SC-DD) in the framework of OFDM with DFT precoding, where a single time-domain pilot symbol is transmitted in each block with a sufficient separation from the modulated data symbols. At the receiver, the channel delay-Doppler response is estimated on a slot-by-slot basis consisting of multiple blocks. By utilizing the band matrix structure induced by the insertion of the pilot symbol, the low-complexity minimum mean square error (MMSE) equalization can be employed in the time domain. Through computer simulations, the PAPR distribution and bit error rate (BER) performance of the proposed system are compared with those of conventional OTFS, OFDM, and single-carrier transmission with frequency-domain equalization (SC-FDE). It is shown that the proposed SC-DD achieves much lower PAPR than OTFS, while it exhibits slightly higher PAPR compared to SC-FDE due to the pilot symbol insertion. As a result, our proposed SC-DD demonstrates superior BER performance compared to OTFS, taking into account the nonlinear distortion caused by the power amplifier.

This paper proposes a novel Bayesian reciprocity calibration method that consistently ensures uplink and downlink channel reciprocity in repeater-assisted multiple-input multiple-output (MIMO) systems. The proposed algorithm is formulated under the minimum mean-square error (MMSE) criterion. Its Bayesian framework incorporates complete statistical knowledge of the signal model, noise, and prior distributions, enabling a coherent design that achieves both low computational complexity and high calibration accuracy. To further enhance phase alignment accuracy, which is critical for calibration tasks, we develop a von Mises denoiser that exploits the fact that the target parameters lie on the circle in the complex plane. Simulation results demonstrate that the proposed MMSE algorithm achieves substantially improved estimation accuracy compared with conventional deterministic non-linear least-squares (NLS) methods, while maintaining comparable computational complexity. Furthermore, the proposed method exhibits remarkably fast convergence, making it well suited for practical implementation.

In this work, we propose a systematic shaping design based on nonuniform quadrature amplitude modulation (NU-QAM) constellations for rate-adaptive bit-interleaved coded modulation (BICM) systems. Since our main interest lies in low-complexity signal design and high bandwidth efficiency, we focus on one-dimensional nonuniform constellations (1-D NUCs). In the proposed approach, the constellation points are first generated according to a truncated Gaussian distribution specified by a single parameter, and then a novel Gray labeling strategy with many-to-one mapping is applied. This scheme enables a systematic and flexible constellation design in terms of the number of constellation points and its geometrical distribution. Simulation results using turbo codes show that the proposed constellation achieves noticeable shaping gains over the conventional uniformly-spaced QAM across a wide range of SNRs and is almost comparable to the 1-D NUCs adopted by the ATSC 3.0 standard. The major practical advantage of the proposed shaping scheme is its lower demapping complexity due to the reduced number of constellation points. Our numerical analysis indicates that, compared to the equivalent NUC of ATSC 3.0, the proposed constellation with 1024 bit labels successfully reduces the complexity associated with the demapping process by 69% and 41% for code rates of 2/5 and 3/5, respectively, at the cost of a slight loss in shaping gain.

This paper proposes a novel sparse Bayesian learning (SBL) algorithm for channel estimation (CE) in multiple-input multiple-output orthogonal time frequency space (MIMO-OTFS) systems, aiming to exploit both the row and group (RG) sparsity and pseudo-sparsity inherent in practical delay– Doppler (DD)-domain channels. Conventional CE approaches model the DD-domain OTFS channel as strictly sparse; however, due to fractional delay and Doppler shifts, the DD-domain channel observed in practical bases does not exhibit strict sparsity, even if the original impulse response is sparse. Instead, it exhibits a structure characterized by numerous small but nonzero elements, with significant variations in signal strength across entries. Capturing this pseudo-sparse structure is crucial for further performance improvement. To address this, we design a new prior distribution that integrates a heavy-tailed complex t-distribution, which effectively captures pseudo-sparsity, with RG sparsity to model the clustered sparse patterns inherent in MIMO-OTFS channels. Simulation results demonstrate that the proposed method significantly outperforms state-of-the-art (SotA) sparse signal recovery (SSR)-based alternatives in terms of both CE accuracy and data detection performance.

Generalized approximate message passing (GAMP) achieves near-optimal performance in detecting spatially multiplexed massive multiple-input multiple-output (MIMO) signals with significantly reduced computational complexity under independent and identically distributed (i.i.d.) measurements. However, in spatially correlated MIMO channels where the ideal assumption of large-scale uncorrelated observation does not hold, the detection capability severely deteriorates. This performance degradation can be compensated for by optimizing GAMP with embedded learnable parameters via deep unfolding (DU) techniques, i.e., data-driven tuning; however, the learning process becomes quite unstable. To address this issue, we propose a novel method that achieves stable learning by incorporating a monotonic increase constraint on the reliability of propagated messages by learning the differential (incremental) values of the learnable parameters between two consecutive iterations. The efficacy of the proposed method is confirmed through numerical results in terms of loss trajectory in the learning process and bit error rate (BER) of massive MIMO detection.

This paper proposes a novel vector similarity search (VSS)-based modulation and coding scheme (MCS) selection for massive multi-user multiple-input multiple-output orthogonal frequency division multiplexing (MU-MIMO-OFDM) systems that employ uplink multi-user detection (MUD) based on iterative signal estimation. To maximize the uplink throughput of MU-MIMO-OFDM systems, it is necessary to assign a carefully selected MCS to each user according to an accurate prediction of the mutual information (MI) that can be achieved with MUD based on the knowledge of the estimated channel state information (CSI). However, since the detection accuracy of iterative MUDs, such as expectation propagation (EP), varies depending on the convergence characteristics, it is challenging to analytically predict the achievable MI in the presence of MUD. To address this difficulty, we propose a novel method for predicting the achievable MI by creating a vector database (VDB) offline that stores feature vectors (keys) computed from CSI and the actual MI (values) achieved with iterative MUD, and then searching this VDB online using approximate nearest neighbors (ANN) search, which enables VSS at ultra-high speed. Simulation results show that the MCS selection based on the proposed MI prediction achieves higher uplink throughput than the conventional schemes in MU-MIMO-OFDM systems using the EP-based MUD.

The majority of modern communication systems adopt quadrature amplitude modulation (QAM) constellations. However, they suffer from a high peak-to-average power ratio (PAPR) as the modulation order grows, which severely reduces the efficiency of the power amplifier. This issue becomes even more critical when the signal points are non-uniformly spaced to improve the achievable information rate (AIR) along with bit-interleaved coded modulation (BICM). On the other hand, amplitude phase shift keying (APSK) constellations provide important benefits compared to QAM due to their circular shape, helping to increase the AIR and reduce the PAPR. In this work, we propose a systematic design approach for a class of APSK constellations composed of multiple concentric rings, each containing the same number of points. In the proposed method, all the radii of the rings are determined by a single parameter, making it easier to identify the best constellation that increases the AIR while keeping the PAPR within limits. Simulation results indicate that in a single-carrier system with pulse shaping, the proposed 1024-APSK constellation increases the AIR by 0.25 bits per symbol compared to the regular 1024QAM with the same signal PAPR, or it can reduce the PAPR by 1.0 dB while maintaining the same spectral efficiency.

We investigate the rate-distortion-leakage region of the Chief Executive Officer (CEO) problem, considering the presence of a passive eavesdropper and privacy constraints. We start by examining the region where a general distortion measure quantifies the distortion. While the inner bound of the region is derived from previous work, this paper newly develops an outer bound. To derive the outer bound, we introduce a new lemma tailored for analyzing privacy constraints. Next, as a specific instance of the general distortion measure, we demonstrate that the tight bound for discrete and Gaussian sources is obtained when the eavesdropper has no side information, and the distortion is quantified by the log-loss distortion measure. We further investigate the rate-distortion-leakage region for a scenario where the eavesdropper has side information, and the distortion is quantified by the log-loss distortion measure and provide an outer bound for this case. The derived outer bound differs from the inner bound by only a minor quantity that appears in the constraints associated with the privacy-leakage rates, and these bounds match when the distortion is large.

We compare the performance of orthogonal frequency division multiplexing (OFDM) system with high-order quadrature amplitude modulation (QAM) and single-carrier (SC) system with amplitude-phase shift keying (APSK) in conjunction with practical bit-interleaved coded modulation (BICM) considering their peak to average power ratio (PAPR) property. BICM-OFDM with high-order QAM is commonly adopted in several recent high-speed wireless communications standards, whereas APSK in conjunction with single-carrier signaling is adopted in satellite communications due to its low PAPR property compared to OFDM systems. In order to make a fair comparison, SC system is implemented as a discrete Fourier transform (DFT) precoding of OFDM such that the spectral efficiency of the two schemes is identical. Furthermore, clipping and filtering (CAF) is applied to the two systems so as to compare them under the same PAPR constraint. Simulation results over a frequency-selective Rician fading channel indicate that if the fading is moderate, SC with APSK can achieve significant gain over OFDM with QAM at the cost of increasing transmitter/receiver complexity.

This paper proposes a novel precoder design for time-varying millimeter-wave (mmWave) multiple-input multiple-output (MIMO) signal detection based on expectation propagation (EP). In mmWave wireless communications, millisecond-scale fluctuations in the surrounding environment cause significant changes in the wireless channel, and the channel aging over time causes a mismatch between the beam and actual channel. The proposed precoder attempts to maximize detection performance by adjusting information propagated across iterations when employing the EP-based iterative algorithm to suppress interference components due to channel aging at the receiver. Simulation results show that the precoders that impose heterogeneity in quality among streams of MIMO spatial multiplexing minimize the bit error rate (BER). We conjecture that this phenomenon is due to the improved detection accuracy in the early iterations caused by the heterogeneity among streams, and discuss appropriate precoder design criteria by quantitatively evaluating the performance improvement.

This paper proposes a novel beam-domain channel estimation (CE) algorithm based on sparse Bayesian learning (SBL) using complex t-prior for massive multi-user multiple-input multiple-output (MU-MIMO) systems. Due to the sidelobe leakage and insufficient observation resolution, the equivalent channel after digital beamforming at the receiver does not have a sparse structure strictly consisting of zero/non-zero elements, but has a structure characterized by differences in signal intensity consisting of a large number of small non-zero elements and a few large elements. To fully capture this pseudo-sparse structure, a complex t-distribution with appropriate degrees of freedom (DoF) is incorporated into the SBL algorithm as a hierarchical Bayesian model. This heavy-tailed prior allows for efficient beam-domain CE accounting for small but non-negligible elements, which is verified by the analysis of regularization based on an equivalent optimization problem. Simulation results show that the proposed method significantly outperforms the state-of-the-art (SotA) sparse signal recovery (SSR)-based alternatives in sub-6 GHz wireless communication scenarios.

We investigate the application of geometric constellation shaping for standard bit-interleaved coded modulation (BICM) systems employing Gray labeling and high-order quadrature amplitude modulation (QAM). We focus on the non-uniform Gaussian-like distributions, and analyze their performance in terms of the mutual information as well as more practical bit-wise mutual information (BMI). We also propose a new systematic constellation design approach based on truncated Gaussian distribution, where a single parameter balances the two extreme constellations represented by uniform and Gaussian distributions. We also evaluate the peak-to-average power ratio (PAPR) of the resulting constellations, where a good trade-off between the BMI and PAPR can be achieved by optimizing the associated parameter. Simulation results based on the conventional Gray-labeled BICM with binary turbo codes show that a noticeable shaping gain can be achieved by the proposed constellation design.

In this work, we introduce a covert communication system based on the superposition of polar-coded OFDM and artificial noise (AN) where the OFDM signal is used for information transmission. We show that the use of OFDM signaling makes the warden difficult to detect the signal from the received samples in the time domain due to the Gaussian nature of OFDM signals. On the other hand, when the warden is able to detect the samples in the frequency domain, we should rely on AN to increase the detection error probability of the warden. The price is its reduced effective SNR for the legitimate receiver. Therefore, we propose a use of polar codes with their code rate adjusted such that the desirable block error rate is achievable. The importance of frozen bit randomization is also discussed by analyzing the time-domain property of the resulting OFDM signals.

We propose a practical covert communication technique for IoT networks based on serially concatenated systematic coded (SCSC) wireless steganography, where the secret information is transmitted by orthogonal frequency division multiplexing (OFDM) signal. Instead of sending the Gaussian artificial noise (AN) so as to prevent the detection by the warden, the secret OFDM signal is hidden into the cover DFT-spread OFDM (DFT-s-OFDM) signal as a public signal since it is suitable for low-cost IoT devices due to its low peak-to-average power ratio (PAPR) property. In our proposed system, the public signal is generated from the parity bits of the secret information by utilizing systematic encoding. As a result, the legitimate receiver improves the error rate performance by concatenating the likelihood corresponding to both secret and public signals. On the other hand, since the parity bits are broadcast as the public signal, there is a risk of the secret information being decoded by the unintended receiver, warden. Therefore, we derive the conditions for systematic codes so as to achieve secure covert communications. Through computer simulation, we demonstrate that the coded bit error rate (BER) performance of our proposed scheme significantly outperforms that of the conventional system, and this enhancement can be achieved without the expense of the secrecy evaluated in terms of the probability of event detection error at the warden.

Today, we rely on contactless smart cards to perform several critical operations (e.g., payments and accessing buildings). Attacking smart cards can have severe consequences, such as losing money or leaking sensitive information. Although the security protections embedded in smart cards have evolved over the years, those with weak security properties are still commonly used. Among the different solutions, blocking cards are affordable devices to protect smart cards. These devices are placed close to the smart cards, generating a noisy jamming signal or shielding them. Whereas vendors claim the reliability of their blocking cards, no previous study has ever focused on evaluating their effectiveness.

In this work, the performance of indoor visible light communication (VLC) networks with mobile devices in the presence of a passive eavesdropper is investigated in terms of the achievable throughput and secrecy. We consider a body blockage model of the users as well as the eavesdropper in order to capture the effect when the communication links from light-emitting diodes (LEDs) to the devices are blocked by their bodies. We introduce a novel LED arrangement as well as LED linking strategy under the framework of non-orthogonal multiple access (NOMA) so as to improve the secrecy performance and throughput without any knowledge of the channel state information of the eavesdropper. The effectiveness of the proposed system is demonstrated by simulation results.

Clipping and filtering (CAF) is known as the simplest but effective approach for peak-to-average power ratio (PAPR) reduction of OFDM signals. As a means to compensate for nonlinear distortion caused by CAF at the receiver, clipping noise cancellation (CNC) has been proposed. Since the use of high-order modulation and coding is essential for achieving higher data rate, the joint design of coded modulation and CAF/CNC should play an important role. In this work, we focus on the use of multi-level coded modulation with multi-stage decoding (MLC/MSD) for OFDM with CAF/CNC and address its design based on the capacity rule as well as its low-complexity implementation. We attempt to reduce the average computational complexity associated with iterative decoding by early termination of iteration using cyclic redundancy check (CRC) code. To further improve the performance of CNC, we also introduce a receiver structure that reapplies CNC after channel decoding. The effectiveness of our approach is demonstrated by simulations using turbo codes concatenated with CRC code.

We investigate the spectral efficiency of non-orthogonal frequency division multiplexing (NOFDM). NOFDM is regarded as a frequency-domain faster-than-Nyquist (FTN) signaling with block transmission, where each subcarrier is compressed in the frequency domain by utilizing the discrete fractional Fourier transform (DFRFT). Since pulse shaping filters are not employed, the effective bandwidth of the NOFDM signal should take into account the resulting out-of-band (OOB) radiation. Therefore, we derive a closed-form expression for the power spectral density (PSD) of the NOFDM signal with windowing for OOB reduction. Through numerical comparison, it is shown that NOFDM outperforms OFDM in view of the effective signal bandwidth if they are compared under the same number of subcarriers. On the other hand, by the capacity analysis based on the asymptotic spectral efficiency with a large number of subcarriers, we elucidate that NOFDM may not outperform OFDM from an information-theoretic perspective.

This paper revisits polar code design for a binary-input additive white Gaussian noise (BI-AWGN) channel when successive cancellation (SC) decoding is applied at the receiver. We focus on the so-called reciprocal channel approximation (RCA), which is often adopted in the design of low-density parity-check (LDPC) codes. Implementation of RCA requires the computation of the mutual information of BPSK signaling as well as a corresponding function known as the reciprocal channel mapping, and thus we develop rigorous closed-form approximations of these that are easy to calculate numerically and also valid over a wide range of SNR. Through numerical evaluation we find that, compared to approaches based on the popular Gaussian approximation (GA) as well as the so-called improved GA (IGA), the proposed RCA approach offers better estimates of the bit error rate of polarized channels with no additional computational cost. As a result, polar codes designed by the proposed RCA can achieve further improvement in terms of block error rate (BLER) performance. The gain achieved by the new approach becomes significant as the codeword length increases.

Secret-key agreement using physical identifiers is a promising security protocol for the authentication of users and devices with small chips, owing to its lightweight security. In the previous studies, the fundamental limits of such a protocol were analyzed, and the results showed that two auxiliary random variables were involved in the capacity region expressions. However, with two auxiliary random variables, it is difficult to directly apply the expressions to derive the computable forms of the capacity regions for certain information sources such as binary and Gaussian sources, which hold importance in practical applications. In this paper, we explore the structure of authentication channels and reveal that for the classes of degraded and less noisy authentication channels, a single auxiliary random variable is sufficient to express the capacity regions. As specific examples, we use the expressions with one auxiliary random variable to derive the computable forms for binary and Gaussian sources. Numerical calculations for the Gaussian case show the trade-off between secret-key and privacy-leakage rates under a given storage rate, which illustrates how the noise in the enrollment phase affects the capacity region.

We propose a power efficient non-orthogonal multiple access (NOMA) scheme suitable for Internet of Things (IoT) and device-to-device (D2D) communications. OFDM-based power-domain NOMA (PD-NOMA) is one of the promising approaches to achieve simultaneous connections of massive devices. Nevertheless, the problem of high peak-to-average power ratio (PAPR) is a major challenge, since power amplifier (PA) efficiency is a critical factor for IoT and D2D devices consisting of low-cost hardware components. This paper overcomes this problem by introducing time-frequency domain NOMA (TF-NOMA), where OFDM and DFT-spread OFDM (DFT-s-OFDM) are superposed over the time-frequency domain. By utilizing the low PAPR property achieved by DFT-precoding, TF-NOMA can efficiently reduce the PAPR of the downlink signal transmitted by the base station (BS) as well as the uplink signals of the devices located far from BS. As a result, the proposed TF-NOMA can operate with higher PA efficiency than the conventional OFDM-based PD-NOMA. Furthermore, the insertion of DFT-precoding with the aim of PAPR reduction also enhances the error propagation resistance due to the resulting Gaussian mixture signal property. Throughout the mathematical analysis and computer simulations, we demonstrate that TF-NOMA achieves better error rate performance than the conventional PD-NOMA with significant improvement of PA efficiency.

Secret-key agreement based on biometric or physical identifiers is a promising security protocol for authenticating users or devices with small chips and has been extensively studied recently. Kittichokechai and Caire (2015) investigated the optimal trade-off in a secret-key agreement model with physical identifiers, where the structure of the authentication channels is similar to the wiretap channels, from information theoretic approaches. Later, the model was extended by Günlü et al. (2018) introducing noise in the enrollment phase and cost-constrained actions at the decoder. The results of these studies show that two auxiliary random variables are involved in the expressions of the optimal rate regions of secret-key, storage, and privacy-leakage rates. However, with these two auxiliary random variables, the complexity of computing the rate region may be prohibitively high. Due to this problem, we are interested in exploring classes of authentication channels that need only one auxiliary random variable in the capacity region expression for discrete source settings. The result shows for the class of degraded and less noisy authentication channels, a single auxiliary random variable is sufficient to express the capacity region of the model. As an example, we also derive the capacity region of secret-key, storage, and privacy-leakage rates for binary sources. Furthermore, the capacity region for scalar Gaussian sources is derived under Gaussian authentication channels.

We consider the downlink of a multi-cell massive MIMO system suffering from asymptotic rate saturation due to pilot contamination. As opposed to treating pilot contamination interference as noise (TIN), we study the performance of decoding the pilot contamination interference. We model pilot-sharing users as an interference channel (IC) and study the performance of schemes that decode this interferencepartiallybased on rate-splitting (RS), and compare the performance to schemes that decode the interference in itsentiretybased on simultaneous unique decoding (SD) or non-unique decoding (SND). For RS, we non-uniquely decode each layer of the pilot contamination interference and use one common power splitting coefficient per IC. Additionally, we establish an achievable region for this RS scheme. Solving a maximum symmetric rate allocation problem based on linear programming (LP), we show that for zero-forcing (ZF) with spatially correlated/uncorrelated channels and with a practical number of BS antennas, RS achieves significantly higher spectral efficiencies than TIN, SD and SND. Furthermore, we numerically examine the impact of increasing the correlation of the channel across antennas, the number of users as well as the degree of shadow fading. In all cases, we show that RS maintains significant gain over TIN, SD and SND.

We propose a new interference cancellation (IC) approach designed for coded uplink multiple-input multiple-output (MIMO) systems that support a massive number of Internet-of-Things (IoT) devices. The performance of MIMO spatial multiplexing depends on the symbol detection schemes, which in general offer a trade-off between the error rate performance and computational complexity. Previous studies have shown that a simple matched-filter (MF)-based detector with powerful channel coding can achieve near-optimal performance as the number of base station (BS) antennas increases even without IC. However, if the number of BS antennas is the same order as that of the IoT devices supported by the BS, its achievable rate will be significantly degraded. Furthermore, channel estimation errors due to the lack of orthogonal pilot sequences should also become a dominant factor. This paper overcomes this problem by introducing a MF detector with quadrature interference cancellation (MF-QIC), which can improve error performance and spectral efficiency. Taking polar codes as our channel coding example, we propose a code design based on mutual information tailored for MF-QIC. Our simulation results demonstrate that the proposed low-complexity polar-coded MF-QIC outperforms other conventional approaches even in the presence of imperfect channel state information.

We propose a new probabilistic amplitude shaping (PAS) scheme based on short linear block codes. In the proposed system, the capacity-approaching signal distribution is generated in the process of decoding linear block codes for a given information bit sequence. We associate the design problem of shaping codes with the classical covering problem, suggesting the use of good covering codes for shaping. From simulation results, it is demonstrated that by selectingperfectbinary codes as our shaping codes, the proposed scheme offers a shaping gain of around 0.3–1.0 dB. By comparing with the enumerative sphere shaping (ESS) of the same block length, we verify that the proposed scheme achieves significantly lower storage complexity and computational complexity at the receiver even with comparable block error rate performance.

This paper focuses on an improved Gaussian approximation (GA) based construction of polar codes with successive cancellation (SC) decoding over an additive white Gaussian noise (AWGN) channel. Arıkan proved that polar codes with low-complexity SC decoding can approach the channel capacity of an arbitrary symmetric binary-input discrete memoryless channel, provided that the code length is chosen large enough. Nevertheless, how to construct such codes over an AWGN channel with low computational effort has been an open problem. Compared to density evolution, the GA is known as a low complexity yet powerful technique that traces the evolution of the mean log likelihood ratio (LLR) value by iterating a nonlinear function. Therefore, its high-precision numerical evaluation is critical as the code length increases. In this work, by analyzing the asymptotic behavior of this nonlinear function, we propose an improved GA approach that makes an accurate trace of mean LLR evolution feasible. With this improved GA, through numerical analysis and simulations with code lengths up to N = 218, we explicitly demonstrate that various code-rate polar codes with long codeword and capacity approaching behavior can be easily designed.

A well-known drawback of orthogonal frequency-division multiplexing (OFDM) is its signal with high peak-to-average power ratio (PAPR). Among a number of PAPR reduction techniques, clipping and filtering (CAF) is the simplest approach, which effectively reduces the PAPR of band-limited OFDM signals at the cost of increasing in-band distortion. In order to mitigate the performance degradation caused by the in-band distortion, several iterative distortion recovery techniques have been proposed in the literature, and they are largely classified into time-domain (TD) and frequency-domain (FD) compensation approaches: The former and latter are represented by the decision-aided reconstruction (DAR) and clipping noise cancellation (CNC), respectively. To date, however, their theoretical performance limits have not been studied. In this work, we revisit the performance limits of CAF and derive a closed-form signal-to-distortion power ratio (SDR) expression. Furthermore, we introduce a time-domain distortion model for characterizing the OFDM signal with CAF, based on which we make performance comparison between the two compensation approaches. Theoretical analysis and simulations in terms of their achievable symbol error rate (SER) reveal that, unlike the FD counterpart, the TD compensation may suffer from unrecoverable distortion when filtering after clipping is applied at the transmitter.

Polar codes are shown to achieve channel capacity as the code length becomes infinity, and recent studies have shown that the concatenation of polar codes and cyclic redundancy check (CRC) codes with successive cancellation list decoding can outperform the other capacity approaching codes even with moderate code length. In order to achieve higher bandwidth efficiency by polar codes, it should be combined with coded modulation. In this work, we study the use of multilevel coded modulation (MLC) and multistage decoding (MSD) with the CRC-concatenated polar codes as its binary component codes focusing on the code rate design based on the channel capacity rule. Furthermore, in order to mitigate the decoder complexity and latency associated with MLC/MSD, we propose to replace the codes in the higher levels by simple punctured convolutional codes with Viterbi decoding, demonstrating negligible performance loss provided that the code length is of moderate size.

Spatial modulation (SM) exploits multiple transmit antennas for index modulation and thus alleviates the complexity issues inherent in the conventional MIMO schemes. Even though a significant amount of studies have been devoted to SM, its coded performance combined with low-complexity linear detectors has not been well investigated. In this work, we propose a practical low-complexity SM approach based on the combination of the scaling matched-filter (MF) detector and capacity-approaching channel codes. The scaling MF detector is sub-optimal but can be implemented with significantly less complexity than the maximum likelihood (ML) detector. The major challenge in the design of detectors for coded SM is how to calculate the soft output corresponding to the coded bits associated with index modulation that will be processed by the subsequent binary channel decoder, and we develop suitable soft output metrics based on the theoretical analysis of the associated scaling MF detector output. Through computer simulations, the effectiveness of our proposed coded SM system is demonstrated.

We propose a physical-layer security approach based on the concept of steganography for IoT networks. Similar to the covert communications, the transmitter (Alice) attempts to send her secret signal to the legitimate receiver (Bob) avoiding being detected by the warden (Willie). Instead of sending the weak signal that is barely detectable by Willie, we hide secret signal in the cover signal that is transmitted over the same channel such that its existence may not be easily detected without any knowledge of prior information. Considering the practical applications to IoT networks, the DFT-precoded OFDM is adopted for the cover signal and conventional OFDM for the secret signal. Through theoretical analysis and corresponding simulations, the detection error probability of Willie is evaluated over an AWGN channel, revealing that judicious selection of cover signal power may increase the detection error probability of Willie and thus improve the covertness.

In this paper, we consider a data collection from sensor networks by a single unmanned aerial vehicle (UAV), where each sensor is also powered by the data-collecting UAV for its signal transmission. In the first phase, the UAV powers all the sensor nodes distributed in a given area through wireless energy transfer (WET), and it collects their data in the second phase. Under the assumption of Rician fading channels, we analyze the outage probability of the network and identify the time ratio of the two phases that minimizes the resulting outage probability. Through the theoretical analysis, we demonstrate that for a given set of target information rate, acceptable outage probability, and UAV location, the achievable service range can be uniquely determined.

Among various MIMO detectors, the matched filter (MF) detector is known as the least complex receiver. It has been shown that with powerful channel coding, MF detector works well under the low SNR regime with diversity-rich environment, such as ergodic fading channels with a large number of antennas. On the other hand, if the diversity order is not sufficient, the performance of MF detector becomes poor. In this paper, we first review the fact that the per-antenna mutual information of MF detector will decrease as the number of both transmit and receive antennas increases over an ergodic Rayleigh fading channel. Since the use of powerful channel codes is essential for the MIMO system with MF detector, we apply polar codes with CRC-assisted successive cancellation list decoder and demonstrate its superiority over the conventional turbo codes. Focusing on such a practical scenario, we further investigate the use of interference cancellation (IC) with MF detector as a low- complexity alternative. After performance comparison of several IC schemes, we also propose an adaptive IC switching approach that can achieve the best performance over a wide range of SNR.

We consider the unmanned aerial vehicle (UAV) enabled relaying networks where the ground station transmits its information to the destination through the cooperation of M UAV-aided relaying nodes in the presence of a single UAV- aided eavesdropper. Among M relays, the one with the best channel state information (CSI) is selected as an actual relay node, whereas the remaining M â'1 relays operate as jammers such that the outage probability of successful decoding by the eavesdropper is increased. In order to reflect the imperfection of detection by the eavesdropper, its backhaul reliability is also considered. The asymptotic expressions for the outage probabilities of destination as well as eavesdropper over Rician fading channels in the case of high SNR are developed in closed form. Numerical results verify the accuracy of the derived analytical expressions.

The matched-filter (MF) detector is the lowest complexity linear detector in practical MIMO spatial multiplexing systems. Its performance is significantly affected by the number of available antennas and an operating channel SNR. In this paper, we analyze the exact performance of the MF detector without any restrictions on the numbers of the transmit and receive antennas. To this end, we first develop the exact, closed-form expression of the MF detector output over uncorrelated Rayleigh fading channels with an arbitrary number of antennas. Based on this result, we derive the exact closed-form bit error rate expressions for uncoded BPSK, QPSK, and M-ary QAM signaling, which can be seen as the generalized forms of the conventional receiver diversity based on maximum ratio combining. We also elucidate the conditions on the numbers of antennas and channel SNR, where the use of MF detector should become effective. Furthermore, in the case of coded MIMO systems, we develop the optimal metric derived from the exact MF output. The corresponding mutual information justifies the simulated performance of LDPC-encoded MIMO spatial multiplexing with the MF detector over ideally interleaved Rayleigh fading channels. Finally, we extend our analysis to more practical systems with imperfect channel estimation.

The decoding of Construction D lattices is described. While similar to the multistage decoding of Code Formula codes, modification is required so that lattice components are subtracted in a process called reencoding. A generator matrix for Construction D lattices is given. Construction D lattices obtained from BCH codes were described by Barnes and Sloane. In this paper, we consider some practical issues of encoding and decoding these lattices. Using ordered statistics decoding, dimension 128 BCH code lattices outperform turbo lattices and low-density lattice codes of similar dimension. These results show relatively good performance of lattices based on algebraic constructions, compared to lattices typically designed for high dimensions. The performance over power-constrained channel is also evaluated, where the near-optimal performance is demonstrated.

In this paper, we develop capacity-approaching non- binary turbo codes defined over high-order finite fields. Since the performance of turbo codes is characterized by the convergence behavior of iterative decoding and error floor in the high SNR region, we attempt to design the non-binary turbo codes based on the following two-stage optimization processes: In the first stage, we employ a Gaussian approximation method for non-binary turbo codes and analyze the convergence property of iterative decoding. After reducing the search space by the first stage, the best component convolutional codes are identified by examining the truncated union bound under the assumption of the uniform interleaver. Simulation results demonstrate that our non-binary turbo codes as designed above can outperform the conventional non-binary LDPC codes.

This paper describes a real-time implementation of the orthogonal frequency-division multiplexing (OFDM)-based system concatenated with super-orthogonal convolutional code (SOCC) and Golay complementary sequence using a software defined radio platform. The SOCC is a powerful low-rate channel code that guarantees low decoding latency and high reliability, and the use of Golay sequence ensures that the resulting signal peak-to-average power ratio (PAPR) is within 3 dB, which significantly improves the power amplifier efficiency. Comparison of bit error rate (BER) performance results demonstrates that the implemented system can approach the ideal performance suggested by computer simulation. We also report its performance after nonlinear power amplification through a testbed employing a real power amplifier device.

In order to mitigate the high peak-to-average power ratio (PAPR) problem of orthogonal frequency-division multiplexing (OFDM) signals, various PAPR reduction techniques have been studied. In this work, we focus on the trellis shaping (TS) which controls a signal by utilizing the structure of convolutional code at the transmitter. TS has flexibility of design and shows high PAPR reduction capability without causing any nonlinear distortion. However, the major drawback of the conventional TS is its computational complexity required for metric calculation in the codeword search associated with PAPR reduction. In this paper, we propose an alternative approach that makes use of signal clipping to generate a replica of the reference symbols in the Viterbi algorithm so as to reduce the complexity of the metric calculation. Through extensive simulations in the framework of BICM-OFDM, we demonstrate the effectiveness of the proposed approach as well as its cost in return for significant reduction of the transmitter complexity.

This paper proposes a new physical layer architecture based on orthogonal frequency-division multiplexing (OFDM) for uplink multiple access. It aims at high reliability with fixed decoder latency targeting emergent low-latency wireless applications, such as transmission of control information in machine-to-machine (M2M) and device-to-device (D2D) communications. Our proposed system is based on the judicious combination of subcarrier hopping and super-orthogonal convolutional codes for achieving high coding gain and frequency diversity, together with Golay complementary sequences for low peak-to-average power ratio (PAPR) signaling. The low PAPR nature improves the power efficiency at a power amplifier (PA) and thus contributes to the transmission range enhancement. Furthermore, by introducing non-orthogonality among users through the assignment of the same set of subcarriers to multiple users, the overall spectral efficiency can be improved. In order to suppress multiple access interference caused by the non-orthogonal overlap of users, multiuser detection (MUD) is employed. Theoretical expressions of approximate bit error rate for the proposed system with MUD are also developed. Numerical results reveal that our proposed system achieves higher reliability and higher spectral efficiency than the conventional orthogonal frequency-division multiple access (OFDMA)-based system.

Successive cancellation list (SCL) decoding of polar codes is an effective approach that can significantly outperform the original successive cancellation (SC) decoding, provided that proper cyclic redundancy‐check (CRC) codes are employed at the stage of candidate selection. Previous studies on CRC‐assisted polar codes mostly focus on improvement of the decoding algorithms as well as their implementation, and little attention has been paid to the CRC code structure itself. For the CRC‐concatenated polar codes with CRC code as their outer code, the use of longer CRC code leads to reduction of information rate, whereas the use of shorter CRC code may reduce the error detection probability, thus degrading the frame error rate (FER) performance. Therefore, CRC codes of proper length should be employed in order to optimize the FER performance for a given signal‐to‐noise ratio (SNR) per information bit. In this paper, we investigate the effect of CRC codes on the FER performance of polar codes with list decoding in terms of the CRC code length as well as its generator polynomials. Both the original nonsystematic and systematic polar codes are considered, and we also demonstrate that different behaviors of CRC codes should be observed depending on whether the inner polar code is systematic or not.

Real-time wireless communications such as motion controls of vehicles and machines have been attractive in recent years, in which latency and reliability are of significant importance. A new orthogonal frequency-division multiplexing (OFDM)-based uplink multiple access system called subcarrier hopping multiple access (SHMA) can achieve high reliability due to both coding gain and frequency diversity gain without increasing decoding delay by combining super-orthogonal convolutional codes (SOCC) with subcarrier hopping. In order to improve the spectral efficiency, multiple users should share the same set of subcarriers together with multiuser detection and decoding (MUD) at the receiver to mitigate multiple access interference. In this work, we focus on two representative MUD schemes, i.e., super-trellis decoding (STD) and successive interference cancellation (SIC), and develop approximate bit error rate expressions when each MUD scheme is employed. Through the comparison with simulation results, we demonstrate that our analysis is useful for predicting the behavior of MUD. Also shown is the effectiveness of our proposed hopping design in fully achieving frequency diversity gain over static fading channels.

We theoretically analyze the performance of the matched filter (MF) detector for multiple-input multiple- output (MIMO) systems with an arbitrary number of transmit and receive antennas over uncorrelated Rayleigh fading channels. As is the case with the MIMO systems with a large number of antennas, the MF detector is known as the simplest practical linear detector and thus is of significant practical interest when the complexity of the receiver is severely limited. Despite its poor uncoded performance in high signal to noise ratio (SNR) region, with the help of powerful channel codes, it has been shown that near optimal performance can be approached in low SNR with substantially low computational complexity. Nevertheless, its exact analysis in terms of bit error rate (BER) even in the case of uncoded scenarios has not been well established. In this work, we analyze the distribution of the output of MF detector, and develop the exact BER expressions for the uncoded MIMO systems with an arbitrary number of transmit and receive antennas. Furthermore, we develop an optimal soft-output of MF detector for the coded scenario. The accuracy of our derived expressions is verified by the corresponding simulation results.

Concatenation of polar codes with cyclic redundancy check (CRC) codes, together with successive cancellation list (SCL) decoding, is known to be an effective approach that can significantly enhance the performance of the original polar codes. Most of the studies on the concatenation of CRC and polar codes, however, pay little attention to the structure of CRC codes themselves, even though the longer CRC may lead to loss in terms of information rate. In this work, we investigate the effect of CRC length on the CRC-concatenated polar code performance by developing an analytical bound for the frame error rate (FER) after the CRC-assisted list decoding. As a result, we reveal that there is a trade-off between the CRC length and FER performance, and for a given target FER, there is the minimum length of CRC that satisfies the FER constraint in high signal-to-noise ratio (SNR). The validity of our analytical framework is confirmed by extensive simulation over an additive white Gaussian noise (AWGN) channel. The results thus offer a useful guideline when designing CRC codes for polar codes with SCL decoding.

In this paper, we present a new bandwidth-efficient coded modulation scheme based on parallel concatenation of the three component trellis coded modulation (TCM) encoders. The resulting triple parallel concatenated TCM (TPCTCM) is investigated for the spectral efficiency of 2 to 7 bits/sec/Hz based on two-dimensional (2-D) TCM employing PSK and QAM signal sets. The component code is designed based on the symbol-based three-dimensional (3-D) extrinsic information transfer (EXIT) charts. The simulation results in terms of frame error rate (FER) performance demonstrate that the proposed TPCTCM can significantly reduce the error floor of the conventional parallel concatenated TCM.

This paper discusses a statistical property of single- carrier and OFDM signals pulse-shaped by the square- root raised-cosine (RRC) filter. In general, strictly band- limited signals exhibit high peak power, and the baseband signal with large signal dynamic range severely suffers from nonlinearity of power amplifiers. Therefore, in practical systems operated with a pulse-shaping filter, its roll-off factor (or excess bandwidth) should be carefully chosen considering the trade-off between the bandwidth and dynamic range of resulting signals. In this work, we investigate this trade-off relationship for the RRC-filtered single-carrier signals composed of statistically independent input symbols through the analysis of their fourth-order moments. The expression for the complementary cumulative distribution function (CCDF) of the instantaneous power in the case of RRC-filtered Gaussian signals is also developed, which serves as an accurate reference for the RRC-filtered OFDM signals with a large number of subcarriers. Based on these observations, we show that the RRC filtered OFDM signals tend to exhibit larger dynamic range than the conventional OFDM signaling filtered by a periodic sinc function.

This paper investigates the aerial networks where the two unmanned aerial vehicles (UAVs) with different altitudes communicate with each other using the same spectral resources as the ground communication links. We propose a spectral sharing approach based on power control for aerial communication link such that the interference observed by the ground communication links is maintained below a predetermined threshold. Through theoretical analysis based on Nakagami-Rice fading channel model, the trade- off relationship between the acceptable interference observed by the ground terminals and the information rate achieved by the aerial communication link is elucidated.

A new time switching protocol referred to as TS- APS is proposed for the energy harvesting (EH) relay networks based on the combination of conventional time switching (TS) protocol and adaptive power splitting (APS). In the framework of the decode and forward (DF) relaying with multiple relays, we derive the closed-form expression for the outage probability of the proposed scheme and discuss its effective transmission rate considering the random relay selection (RRS) and opportunistic relay selection (ORS) scenarios. Through numerical analysis, we show that the proposed scheme can achieve better outage performance and the effective transmission rate as compared to the conventional TS and power splitting (PS) schemes proposed in the literature, irrespective of relay selection scenarios. By properly selecting time switching (TS) ratio, we demonstrate that the effective transmission rate of the proposed protocol can be optimized only with partial knowledge of channel gains in the network, which makes the proposed approach suitable for the distributed relay selection scenarios.

We consider a new uplink multiple access system based on orthogonal frequency-division multiplexing (OFDM), subcarrier hopping, and super-orthogonal convolutional codes (SOCC) that can achieve high coding gain and frequency diversity without sacrificing latency. Such a system is of significant importance for future wireless communications targeting motion controls of machines and vehicles. In order to improve the spectral usage, multiple users should share the same subcarriers with multiuser detection and decoding (MUD) at the receiver. In this work, we focus on super-trellis decoding (STD) and successive interference cancellation (SIC) in the framework of our proposed multiple access system. Through the extensive analysis based on simulations, we reveal that 1) properly designed SIC can achieve almost the same performance as the optimum STD with much lower complexity than the STD, and 2) our proposed system with SIC can outperform the conventional orthogonal frequency-division multiple access (OFDMA) with twice as much spectrum efficiency as OFDMA. The major drawback of SIC is its increased latency as the number of the users increases. Therefore, we also propose an alternative multiple access approach based on STD that can achieve optimum performance and low latency.

In this paper, a novel hardware scheme of trellis shaping (TS) for PAPR reduction of OFDM signals is presented. A practical implementation of TS is challenging, and thus we demonstrate a possibility of its hardware implementation using FPGA. In particular, we focus on its hardware resource consumption and develop an approach to efficiently implement its functionality. The experimental results show that TS can be realized with a reasonable size of hardware resources based on the proposed approach on a Virtex-7 FPGA. Moreover, a trellis window truncation of TS that allows us to significantly reduce its computational complexity is also implemented in this paper, which enables an efficient PAPR reduction of 256-subcarrier OFDM signals with limited hardware resources.

We consider a new orthogonal frequency-division multiplexing (OFDM)-based uplink multiple access system called subcarrier hopping multiple access (SHMA) targeting real-time wireless communications such as motion controls of vehicles and machines. By applying the super-orthogonal convolutional codes (SOCC) as a channel code with subcarrier hopping, it can achieve reliable communications due to the frequency diversity and coding gain without increasing decoding latency. In this work, we attempt to evaluate its system level performance according to the specifications and channel models of the IEEE 802.11n standard, aiming at its use for WiFi compatible environment. In particular, the frame error rate (FER) performance comparison reveals that the proposed SHMA can achieve higher reliability than the IEEE 802.11n standard at the cost of reduced data rate, which is still suitable for the purpose of motion control applications. The proposed SHMA system exploits Golay sequences as the outputs of SOCC in order to suppress the peak power of OFDM signals. We also evaluate the gain provided by this low peak power property taking into account the power amplifier (PA) efficiency. Finally, we address how these gains contribute to the enhancement of the transmission range over the conventional WiFi standard for a given amount of average power at the transmitter.

With a large number of antennas at the transmitter and receiver, massive multiple-input multiple-output (MIMO) systems can achieve substantially high spectral efficiency as well as high stability and reliability. Nevertheless, one of the major challenges for its practical use is its computational complexity for symbol detection that grows exponentially with the number of antennas. In this work, we focus on a low complexity implementation of massive MIMO detector based on matched filter (MF) detection with parallel interference cancellation (PIC). In general, MF-based detector performs poorly in the high SNR region. Nevertheless, with the help of powerful channel coding such as low-density parity-check (LDPC) codes and the well-designed PIC, the resulting error performance of the proposed MF-PIC can approach or even outperform the conventional minimum mean square error (MMSE)-based detector with much less complexity. Furthermore, due to its parallel structure, low latency implementation based on parallel architecture is possible and thus is suitable for practical massive MIMO systems.

Peak cancellation (PC) is known as one of the simplest peak-to-average power ratio (PAPR) reduction techniques that are applicable to various communications standards. The salient advantage of PC is its ease of hardware implementation, but it induces in-band distortion and out-of-band radiation. In order to restrict the amount of distortion within an acceptable level, it is critical to carefully design the cancelling pulses as well as the envelope threshold over which PC is applied. In most studies, however, they are determined empirically through computer simulations. This paper thus focuses on a rigorous theoretical analysis of PC applied to band-limited orthogonal frequency division multiplexing (OFDM) signals, and discusses its validity and limitation for practical applications. Based on the level-crossing rate approximation of the peak distribution, we derive a closed-form expression for the achievable signal-to-distortion power ratio (SDR). We also analyze the adjacent channel leakage ratio (ACLR) as well as error vector magnitude (EVM), with which the symbol error rate (SER) over an additive white Gaussian noise (AWGN) channel is obtained. All the theoretical results developed in this work are compared with those based on the corresponding computer simulations to justify our analytical approach. It thus serves as a useful and accurate tool for designing cancelling pulses as well as the threshold level, for given specific system requirements such as SDR (or EVM) and ACLR.

Bit-interleaved coded modulation (BICM), together with orthogonal frequency-division multiplexing (OFDM) signaling, has found its application in many recent wireless standards. BICM-OFDM systems are able to simplify the design of coding and modulation with various information rates for link adaptation. Furthermore, they provide robustness against frequency-selective fading channels. The combination of BICM-OFDM and convolutional code turns out to be attractive as it allows for low complexity and low latency decoding architecture at the receiver. It has been known that the performance of convolutionally coded BICM-OFDM systems depends on the bit interleaver structure, but little attention has been paid for its theoretical performance analysis. In this paper, we develop a novel theoretical expression for approximate BER of convolutionally coded BICM-OFDM that can be used for evaluating the performance of a given bit interleaver structure, and propose a design guideline for its optimization. Numerical comparisons between the optimized interleaver that satisfies our guideline and other random and structured interleavers demonstrate the validity of our design criterion.

In this paper, we develop a wireless relay network model for an unmanned aircraft (UA) system, where an UA serves as a resilient moving relay among the ground stations with disconnected communication links in the event of disasters. A fixed-wing type is considered as our UA model, since it can operate longer than a rotary-wing UA without recharging battery, but the former can fly only in a circular manner and thus is difficult to stay at a fixed position. When the UA relays the received information to the destination with a conventional fixed-rate decode-and-forward protocol, the circular flight operation of a fixed-wing UA imposes a severe limitation on the achievable performance in terms of outage probability and information rate as they considerably depend on the location of the UA. Therefore, we propose a variable-rate relaying approach that enables us to optimize the achievable performance. Based on the theoretical derivation of the outage probability and formulation of its optimization process, we demonstrate that significant improvement over a conventional fixed-rate relaying can be achieved by the proposed rate optimization.

This paper proposes a new physical layer architecture for uplink multiple access based on orthogonal frequency division multiplexing (OFDM). It achieves low peak-to-average power ratio (PAPR) and high reliability with low computational complexity at both the transmitter and receiver, targeting low-latency communications such as transmission of control information in machine-to-machine (M2M) and device-to-device (D2D) communications. Our approach is based on the judicious combination of subcarrier hopping and super-orthogonal convolutional codes (SOCC) for achieving high coding gain and frequency diversity, together with Golay complementary sequences for low PAPR signaling. By introducing non-orthogonal multiple access where the subcarriers of different users are partially overlapped, the overall bandwidth efficiency can be improved. Furthermore, the low PAPR nature improves the power efficiency and thus enhances the transmission range. Employing the successive interference cancellation at the receiver further mitigates the resulting multiple access interference.

In most practical communication systems where the source encoder is followed by the channel encoder, there is some mismatch between the length of the bits from the source encoder and that fed into the channel encoder. Therefore, dummy bits are usually padded to the source coded bits so as to fill the gap, and these padded bits are usually discarded after channel decoding at the receiver. In this paper, considering the padding event at the transmitter side as a probabilistic event, a novel integrated decoder that detects the zero padding (ZP) sequence together with the trellis pruning technique is proposed assuming that the turbo code is used as a channel code. The performance depends on how these padded bits are allocated in the information sequences, and two representative approaches, referred to as consecutive zero padding (CZP) and sparse zero insertion (SZI), are introduced. Through the EXIT chart analysis, it is shown that the latter approach results in considerably better performance than the former due to the effect of trellis pruning. Furthermore, simulation results show that the proposed decoder can improve the throughput of the system in comparison with the conventional system where the padding bits simply reduce the effective throughput.

Active constellation extension (ACE) has been proposed for a peak-to-average power (PAPR) reduction of orthogonal frequency- division multiplexing (OFDM) signals, which projects the clipping noise generated by iterative clipping and filtering (CAF) onto the outside region of the constellation such that its minimum Euclidean distance (MED) is not reduced. Due to this arrangement, some amount of average power increase is introduced, but ACE can achieve better trade-off between uncoded bit-error rate (BER) and power amplifier (PA) efficiency compared to simple CAF. However, the coded BER of ACE has not been analyzed so far, where the degradation of signal-to-noise power ratio (SNR) due to the average power increase may have dominant effect on the performance. Moreover, in order to perform effective error correction, the statistical property of the clipping noise imposed by ACE should be developed. This paper empirically models the clipping noise distribution after ACE such that soft decoding can be employed at its receiver, and investigates its performance in terms of mutual information and coded BER employing near optimal channel coding. It is revealed that the simple CAF may outperform the ACE in terms of both PA efficiency and BER performance when both are protected by practical channel coding.

Bit-interleaved coded modulation (BICM) has found its application in various wireless communication systems due to its simplicity in the design of coding and modulation. In particular, the BICM combined with convolutional coding has been adopted by several recent standards due to its low complexity and low latency at the decoder side. The performance of the convolutionally coded BICM depends not only on the constraint length of the code but also significantly on the structure of the bit interleavers introduced mainly for the purpose of dispersing the correlated bits. To date, however, theoretical analysis of the performance that well captures its dependence on the interleaver structures has not been presented in conjunction with the convolutionally coded BICM due to its complexity in precise analysis. In this paper, we derive a tight approximate BER expression over AWGN channels to evaluate its performance for a given bit interleaver structure, and present a design guideline for an optimal interleaver structure with its performance over fading channels in mind.

Recently, orthogonal frequency-division multiplexing (OFDM) is adopted by various wireless communications standards, but its high peak-to-average power ratio (PAPR) nature significantly degrades the power amplifier (PA) efficiency. To address this problem, various PAPR reduction schemes have been proposed in the literature, and clipping and filtering (CAF) has been considered as the simplest method while it imposes severe nonlinear in-band distortion. In contrast, selected mapping (SLM) and trellis shaping (TS) have been recognized as well- studied distortionless PAPR reduction methods. In this paper, we investigate the application of such distortionless PAPR reduction techniques prior to the OFDM systems with CAF in order to alleviate the resulting in-band distortion. Our simulation results demonstrate that the additional PAPR reduction based on SLM or TS will help improving the performance in terms of PAPR reduction capability, PA efficiency, and the resulting system level performance for a given amount of out-of-band power radiation.

Trellis shaping (TS) is a promising technique for controlling signal transition and capable of making the shape of the signal into a desired form by exploiting the trellis structure of convolutional codes. TS was originally proposed by Forney for the average power reduction of quadrature amplitude modulation (QAM) signals, and subsequently, it has found its application in the field of the peak-to-average power ratio (PAPR) reduction of the single-carrier as well as orthogonal frequency-division multiplexing (OFDM) signals. So far, due to its rather complicated signal generation structure, the performance of TS has been studied mostly based on computer simulations and, to the best of the authors' knowledge, its precise theoretical analysis has been left undeveloped even for uncoded cases. In this paper, we thus analyze the theoretical symbol error rate (SER) and bit error rate (BER) of TS over AWGN and frequency-selective Rayleigh fading channels and develop their closed form expressions that asymptotically match the exact results obtained by the simulations.

Convolutional lattice codes, also known as signal codes, have been proposed as a technique to generate structured codes that have good performance. While in principle optimal decoding can be achieved using the Viterbi Algorithm, in practice due to Tomlinson-Harashima precoding, the size of the state space is too large, and one must resort to suboptimal techniques such as sequential decoding. In this paper, we take an alternate approach. By employing a judicious selection of tap coefficients and in combination with precoding, we show that the state space can be constrained to a relatively small set such that Viterbi decoding is practical. The performance of such codes still exhibits a large gap to capacity, and we further propose a parallel concatenation similar to that of turbo codes, resulting in a “turbo signal code.” Due to the relatively small state space, iterative decoding based on the BCJR algorithm is now possible. The gaps between the SNR for a frame error rate of 1% and the optimal performance theoretically achievable for a code of the same rate over an AWGN channel are found by simulation to be within 0.75-0.85 dB with a block length of 8192.

This paper analyzes the high-order moments of linearly modulated single-carrier as well as orthogonal frequency-division multiplexing (OFDM) signals assuming that the modulated symbols that form resulting continuous signal waveform are statistically independent. For a single-carrier case with the ideal low-pass filter used for pulse shaping, closed-form expressions of the moments with up to the eighth-order are derived. The proposed approach is then extended to Gaussianity assessment of OFDM signals; we show how the moments of OFDM signals can approach to those of Gaussian distribution as the number of subcarriers increases for a given modulation constraint on each subcarrier. Also reported is the peculiar nonstationary behavior of the fourth-order moments in the case of BPSK modulated OFDM signals.

One of the major drawbacks of orthogonal frequency-division multiplexing (OFDM) systems is their high peak-to-average power ratio (PAPR) signals, and trellis shaping (TS) is a promising approach for reducing both peak power and average power of OFDM signals. In practice, OFDM should be employed with coded modulation for improving reliability, and bit-interleaved coded modulation (BICM) has been often combined with OFDM to gain robustness against severe fading channels. In this work, we propose a new BICM-OFDM system concatenated with TS for achieving good error performance. To this end, a novel soft-in-soft-out decoder for TS is developed. Optimization of the shaping convolutional code in terms of transmitter performance is also discussed. The effectiveness of our system is demonstrated through the analysis in terms of average mutual information as well as frame error rate (FER) over an additive white Gaussian noise channel. Furthermore, the FER is evaluated over a frequency-selective Rayleigh fading channel and compared with the theoretical outage probability. The simulation results reveal that our system can achieve good frequency diversity effect over such a fading channel while enjoying much lower PAPR.

In this paper, we propose a novel unequal error protection (UEP) design based on multilevel coded modulation (MLC) for a broadcasting system which attempts to maximize average user satisfaction within the coverage area of the transmitter. To this end, a new quantitative measure is introduced that takes into account both quality of the received data and the distance of the user location from the transmitter. Based on the proposed measure, an optimal rate allocation algorithm utilizing the capacity rule is developed for MLC. As a specific example, by employing JPEG images for source coding and modern capacity-approaching codes for component codes of MLC, our numerical results reveal that well-designed MLC systems can provide better average user satisfaction than a conventional coded modulation (CM) system.

In order to improve the bandwidth efficiency of communication systems under strict power limitation, the use of multilevel modulation together with near capacity channel coding is essential. However, such an approach is sensitive to nonlinear distortion associated with high peak-to-average power ratio (PAPR) of the resulting signals. We consider the application of the multilevel coded modulation with multi-stage decoding (MLC/MSD) over nonlinear communication channels and propose a robust unconventional set partitioning approach in conjunction with the metric adjusted to the statistical characteristics of nonlinear distortion. Numerical results show that the proposed method outperforms the system with the conventional labeling in terms of achievable average mutual information (AMI) and frame error rate (FER).

We propose a new peak-to-average power ratio (PAPR) reduction technique for orthogonal frequency-division multiplexing (OFDM) signals based on the trellis structure. The major drawback of the previously proposed trellis shaping (TS) is that since the constellation controlling and information bit sequences are mixed in a single codeword, its soft-in soft-out (SISO) decoder requires an additional complex process for extracting the soft-outputs from the mixed codeword. On the other hand, our new technique is able to select a controlling sequence separately from information sequences, resulting in a simpler decoder with even a better soft decoding performance. Moreover, we develop an appropriate constellation labeling for our proposed method to enhance its PAPR reduction capability. It is shown that the proposed technique can achieve better bit-error ratio (BER) performance than the conventional TS in the scenario of the soft decoding with a slight loss of PAPR reduction capability.

This paper proposes a virtual MIMO system model for the unmanned aircraft system (UAS) that consists of a small unmanned aircraft (UA) and multiple ground stations (GSs). Since it is difficult to equip a small UA with multiple antennas due to the limitation of its payload, the proposed system exploits a mobility of the single-antenna UA to realize virtual MIMO channels. The channel is assumed to be either Rayleigh or Rician fading, and in the case of Rician, we also investigate the case where the UA fails to receive the line-of-sight (LOS) path due to some turbulence as a probabilistic event. The comparison of the bit error rate (BER) performance through computer simulations shows that when the channel fading is severe or the LOS path is lost with non-negligible probability, a significant improvement of BER performance can be achieved by the diversity gain through the proposed virtual MIMO approach.

Bit-interleaved coded modulation (BICM) system combined with orthogonal frequency-division multiplexing (OFDM) has been adopted in many recent wireless standards, where the random interleaver is commonly assumed due to its simplicity of analysis for BICM. On the other hand, the recent results have shown that BICM using convolutional code without any interleaving shows better performance than that with bit interleaving over an AWGN channel without fading. Nevertheless, the interleaver design suitable for BICM with convolutional code over general fading channels has not been well studied. In this paper, we propose an approach for optimizing conventional block interleavers in the framework of BICM-OFDM and demonstrate its effectiveness over frequency-selective Rayleigh and Ricean fading channels.

Due to the growing concerns toward green communications, future wireless communications systems should aim at higher data rate with even lower power consumption. Since the power amplifier (PA) is a major power consuming analog component, its efficient use is of primary concern in such green communications framework. Orthogonal frequency division multiplexing (OFDM) is a standard approach for achieving high data rate communications with high reliability, but one of its well-known drawbacks is low PA efficiency caused by its signal with high peak-to-average power ratio (PAPR). The use of iterative clipping and filter (ICF) has been widely studied to reduce peak-to-average ratio (PAPR) so that sufficient usage of PA is achieved, but at a cost of in-band distortion and increasing complexity at the transmitter. In many communication standards, however, there is a constraint in acceptable in-band distortion level and thus the question is how much improvement can one achieve in terms of PA efficiency for a given in-band distortion constraint. In this paper, we investigate the trade-off between amplifier efficiency and distortion for an OFDM system operated with ICF in the long term evolution (LTE) framework, and reveal its limitation when considering the effect of PA that comes after the ICF in a practical circuit.

We propose a new approach that achieves near maxlog optimal performance by improving soft information of the eliminated bits in reduced and fixed complexity coded multiple-input multiple-output (MIMO) systems. As a fixed-complexity MIMO detection, we consider both the QR decomposition with M-algorithm (QRM) and the fixed-complexity sphere decoding (FSD). In general, for the MIMO system with channel coding, the detector needs to calculate soft information for each coded bit. However, the reduced complexity detection often eliminates the candidate symbols that are required for accurate soft information calculation. We propose a novel symbol recovery approach that can retrieve the coded bits and thus recalculate the soft information with improved error performance. Simulation results demonstrate the effectiveness of the proposed soft information calculation approach under the example system with 4 × 4 MIMO-OFDM employing 16-QAM and 64-QAM.

The amplitude and phase shift keying (APSK) signal has been adopted in the recent satellite communication standards such as DVB-S2 due to its peak-to-average power ratio (PAPR) property lower than the quadrature amplitude modulation (QAM). Unlike square QAM constellations that allow separate detection of in-phase and quadrature components (i.e., I-Q decomposition), the detection process for APSK is generally complex. This paper investigates the use of multilevel coding (MLC) together with multistage decoding (MSD) for APSK with particular emphasis on an introduction of a novel labeling that allows I-Q decomposition at the highest level, thereby significantly reducing the decoding complexity at the cost of slight performance degradation.

This paper proposes a relaying protocol which combines a network coding with a mobility of small unmanned aircraft (UA) for wireless relay networks. We consider the scenario where the UA circles above around the networks automatically and bridges the signals between ground access points (GAPs) of the distant networks. Such wireless relay networks using UA can be considered particularly useful for emergencies e.g., when the communication networks are partially or completely interrupted after the disaster or power failure. The proposed protocol using network coding and UA can provide a significant diversity gain in contrast to conventional relay protocol. In this paper, simulation results are presented to demonstrate the reliability of the proposed protocol. The bit error rate of the proposed protocol can be lower than that of the conventional relay protocol. This paper also reveals that the diversity gain can be achieved by the proposed protocol.

Signal shaping is an important factor to achieve Shannon capacity in wireless communications, and trellis shaping (TS) is an effective shaping method to reduce average power by exploiting the trellis structure at the transmitter. TS uses a convolutional code for shaping, but no analysis has so far been presented in the literature that reveals the dependence of the average power reduction capability on the trellis code structure. In this paper, we propose a soft-in soft-output (SISO) decoding for TS in the framework of bit- interleaved coded modulation (BICM) and analyze the relationships between its performance and the structure of the shaping convolutional codes in terms of average power reduction capability and achievable average mutual information (AMI). It is also shown that the minimum free distance of shaping code has a dominant effect on the resulting bit-error rate (BER) performance of TS.

Considering growing concerns toward green communications, not only their bandwidth efficiency but also their power consumption is expected to gain increasing importance for future communication systems. A power amplifier (PA) is one of the most power consuming analog devices at the transmitter in communication systems and a precise estimation of the power consumption at the transmitter circuit requires the knowledge of its efficiency that depends on the distribution of input signal envelope and the amount of input back-off. In this paper, we develop a simple analytical model that can be used for estimating achievable efficiency of a linear PA as well as the amount of resulting nonlinear distortion for a given modulated signal exclusively from its envelope distribution. Based on this model, the trade-off relationships between the efficiency and signal-to-distortion power ratio for several spectrally efficient linear modulations are examined. It is also shown that in some special cases of Gaussian input and memoryless nonlinearity PA models, the results can be represented in simple closed-form expressions.

In communication theory, the conventional role of precoding is to reshape a spectrally flat sequence of data symbols in favor of a particular inter-symbol interference (ISI) channel such that signal-to-noise power ratio (SNR) is maximized. In contrast, in this paper a novel precoding technique is devised to exploit a particular property of the information source rather than the channel. Specifically, we focus on the scenario where the source sequence has an inherent correlation that is known a priori, and design a precoding filter that attempts to reduce the average power of the resulting transmit symbol sequences. The proposed precoding technique is thus termed power-reductive precoding (PRP). This reduction of average transmit power accrues without changing the amplitude of the original sequence and thus can be treated as a system gain. An apparent drawback of this approach is the intentional ISI introduced by the precoding filter, which may lessen the minimum distance among legitimate sequences. Nevertheless, we show that even if the loss associated with the minimum distance penalty is properly taken into account, the achievable error rate versus SNR can be made superior to the case without precoding.

In this paper, we propose a new simple relaying strategy based on bit-interleaved convolutionally coded star-quadrature amplitude modulation (QAM) along with coherent/noncoherent detection. Star-QAM is composed of multiple concentric circles of phase-shift keying (PSK). Exploiting this property, a hard limiter is used to enhance power amplifier (PA) efficiency at the relay. Moreover, we show that the proposed approach retains differential detectability, which results in a significant reduction of receiver complexity with robustness against phase ambiguity. By analyzing our proposed cooperation with coherent/noncoherent detection in terms of asymptotic pairwise error probability (PEP), we show that the full diversity order can be achieved on the condition that the minimum free distance of the convolutional codes is larger than the predetermined value specified by the number of available relays. Furthermore, the effectiveness of the proposed scheme in terms of PA efficiency is confirmed by comparing the statistical distributions of the corresponding instantaneous signal powers. All the theoretical results agree with those obtained by computer simulations.

Single-carrier modulation technique has been adopted by the fourth generation mobile wireless communication system as a special form known as single-carrier frequency division multiple access (SC-FDMA) for uplink transmission, mainly due to its signal lower peak-to-average power ratio (PAPR) than that of orthogonal frequency division multiplexing (OFDM). Since a user terminal is mostly operated by battery, power consumption is of primary importance. Considering the fact that the most of the supplied power is consumed by the power amplifier and it increases if the signal has higher PAPR, the use of PAPR reduction even for SC-FDMA system may further improve battery life of user terminal. In this paper, by a novel modification the peak power reduction technique based on the trellis shaping developed for conventional single-carrier modulation, we demonstrate that significant PAPR reduction can be achieved for SC-FDMA signals.

In multiple-input multiple-output (MIMO) wireless communication systems, their error rate performance is mostly determined by detection algorithms. Recently, a novel low-complexity MIMO detection algorithm based on symbol distribution approximation has been proposed. In this paper, provided that the symbol constellation is restricted to M-ary phase shift keying (PSK) or amplitude-modulated PSK (APSK), we propose an approach that can further reduce detection complexity without noticeable performance degradation.

Orthogonal frequency-division multiplexing (OFDM) can achieve remarkable performance in terms of spectral efficiency. However, its well-known drawback is that the OFDM signals have high peak-to-average power ratio (PAPR), and this causes performance degradation in terms of power amplifier (PA) efficiency. Trellis shaping (TS) is an effective method to reduce PAPR without signal distortion by exploiting the trellis structure at the transmitter. In practice, OFDM should be combined with channel coding in order to achieve frequency diversity. In this paper, we propose a serial concatenation of channel coding and trellis shaping such that the frequency diversity effect and peak power reduction can be simultaneously achieved. A novel BCJR-based LLR metric calculation for trellis shaping bits is introduced for this purpose. The effectiveness of the proposed approach is confirmed by simulation over AWGN and frequency-selective fading channels.

In this paper, we propose a new cooperative wireless transmission in a scenario where the source salvages the energy during the relay's transmission considering the fact that the source does not need to retrieve the transmitted message. We also evaluate a direct wireless transmission with wireless energy transfer as a reference. We analyze the performance of these transmission techniques in terms of outage probability. Our analytical results reveal the advantage of energy salvage in combination with spatial diversity over the direct transmission even if the energy transfer efficiency is considerably low.

Physical-layer network coding is a protocol capable of increasing throughput over conventional relaying in the two- way relay channel, but is sensitive to phase and frequency offsets among transmitted signals. Modulation techniques which require no phase synchronization such as noncoherent FSK can compensate for phase offset, however, the relay receiver must still compensate for frequency offset. In this work, a soft- output noncoherent detector for the relay is derived, under the assumption that the source oscillators generating FSK tones lack frequency synchronization. The derived detector is shown through simulation to improve error rate performance over a conventional detector which does not model offset, for offset values on the order of a few hundredths of a fraction of FSK tone spacing.

Trellis shaping (TS) is known as a flexible technique that controls a transmit symbol sequence such that the resulting transmitted signals meet a certain desired property. Our recent work has shown that TS can generate a near constant envelope signal for PSK signaling even with strict bandwidth limitation through the use of a near rectangular pulse-shaping filter. In this work, we combine this TS approach with several coded modulation schemes and compare their performances in terms of achievable peak power reduction capability and bit error rate over an AWGN channel.

In this paper, we analyze the instantaneous power distributions of the transmitting signals at the relay in the non-regenerative and regenerative cooperation scenarios with linear modulation. We study the following four relay function scenarios: fixed gain amplify and forward (AF) relay, variable gain AF relay, estimate and forward (EF) relay, and decode and forward (DF) relay. The analytical results show that the transmitting signals from non-regenerative relaying tend to suffer from high peak power, which is even prohibitive when the power amplifier (PA) efficiency at the relay is of primary concern.

We study the energy consumption of wireless sensor network links applying three widely used digital modulation schemes, i.e. MQAM, MPSK, and noncoherent MFSK. For MQAM and MPSK, pulse shaping is considered. Both transmitted signal power and circuit power are taken into account where the former is modeled using the relationship between cutoff rate and signal-to-noise ratio (SNR) and the latter is modeled considering the power consumption of typical hardware used in wireless sensor nodes. For each modulation type, the optimum parameters for minimizing the energy per information bit are derived. Moreover, a comparison among the three modulation types is presented.

In this paper, we study the instantaneous power distributions of the transmitting signals at the relay in the non-regenerative and regenerative cooperation scenarios with linear modulation under the band-limited scenario. We study the following three relay function scenarios: fixed gain amplify and forward (AF) relay, variable gain AF relay, and decode and forward (DF) relay. Based on the analytical results, we reveal practical limitations of non-regenerative relays when the power amplifier (PA) efficiency is of primary concern.

Trellis shaping (TS) is known as one of flexible methods to reduce peak-to-average power ratio (PAPR) of OFDM signals. However, the complexity of the conventional TS based on the Viterbi algorithm (VA) increases substantially as one increases the number of trellis states for improved PAPR reduction performance. In this paper, we consider the application of M-algorithm to the TS for possible computational reduction. It is observed that the use of M-algorithm results in effective reduction of computation compared to the VA with comparable peak power reduction performance. The two contrastive metrics in time and frequency domain proposed in the literature are also investigated for comparison.

This paper proposes a novel cooperative diversity protocol using multilevel coded (MLC) modulation, which aims at wireless networks composed of more than two cooperative nodes. If the time-division (TD) based cooperative diversity is applied to the case of multiple sources, its transmission efficiency decreases in proportion to the number of sources which results in the degradation of performance. Although several cooperative diversity protocols based on symbol superposition have been proposed to overcome this inherent degradation, most of them are designed for a two-node cooperation and their complexity increases exponentially with the number of cooperating nodes. To the contrary, the proposed MLC cooperation takes advantage of the simplicity of MLC structure and allows a flexible design, without exponential increase of overall complexity. We introduce two rate allocation design criteria, i.e., minimum outage probability and maximum transmission rate, and demonstrate the advantages of the MLC cooperation in terms of outage probability and frame error rate (FER) performance.

We develop two approaches to calculating statistical distributions of instantaneous power of pulse-shaped single-carrier signals. Our first approach is to derive a formula that can calculate exact distributions of pulse-shaped signals with arbitrary constellations. The exact approach is versatile but turns out to be computationally demanding except for some cases where the constellation has circular symmetry. Our second approach is thus based on approximation, which is valid only for M-ary phase shift keying (MPSK) or phase-shifted MPSK constellations, but requires substantially less computation. The validity of the proposed approaches is confirmed by numerical analysis.

We study the energy consumption of individual links in wireless sensor networks (WSN). Three widely used digital modulation schemes, i.e. MQAM, MPSK, and MFSK, are analyzed and compared. Both transmitted signal power and circuit power consumptions are considered. For modeling the signal power, we use the relation between channel capacity or cutoff rate and signal to noise ratio (SNR). By numerical calculation, we find the optimized parameters for minimizing the energy consumption per information bit in a point-to-point wireless link.

We develop a method of calculating approximate statistical distribution of band-limited PSK signals in the single-carrier framework. The analytical form is valid for MPSK as well as π/M-shifted MPSK. The numerical results based on the proposed approximation show good agreement with those obtained by conventional Monte-Carlo simulations when the roll-off factor of the pulse-shaping filter is moderately large.

In this paper, we propose a dynamic coded cooperation using multiple turbo codes. Our proposed cooperation is able to provide the diversity gain efficiently without loss of bandwidth efficiency. Moreover, in our proposed scheme, the relay can dynamically determine if it should cooperate or not. Thus, we investigate a design of a simple power detection to estimate a precise duration of cooperation phase upon decoding information at the destination. Computer simulations show that our proposed approach is able to achieve a full diversity and superior frame error rate compared with the conventional coded cooperation based on turbo codes especially in low signal to noise ratio (SNR) regime.

Orthogonal frequency division multiplexing (OFDM) has an advantage of high bandwidth efficiency, but it suffers from high peak-to-average power ratio (PAPR) which causes severe nonlinear distortion in actual devices such as power amplifiers. Several techniques have been proposed in order to reduce PAPR. Among them, clipping and filtering (CAF) is considered attractive due to its simple structure. The CAF can reduce nonlinear distortion in analog devices and as a result out-of-band radiation is reduced. However, it causes the so-called in-band distortion and thus increases signal distortion or error vector magnitude (EVM). In this paper, we analyze the effects of the CAF on the OFDM system through experiment using a real power amplifier. By adjusting the input back-off (IBO) of the power amplifier, we evaluate the increase of the received power for a given EVM and sidelobe level of power spectra that may contribute to adjacent channel interference (ACI). It is shown that by appropriately adjusting the IBO and clipping ratio, the received power can be improved by several dB while maintaining the amount of ACI for a given EVM.

Trellis shaping (TS) is known as a flexible technique to generate transmit symbols constrained (or controlled) for a particular desired property of communication systems. In our recent results, an application of TS for peak-to-average power ratio (PAPR) reduction of single-carrier (SC) signals has been extensively studied, to show that even a highly fluctuating envelope can be reduced to a nearly constant level. In this paper, we first demonstrate that the performance of the proposed TS in terms of the bit error rate (BER) and PAPR reduction capability strongly depends on the bit labeling. We then propose a new bit labeling for high-order PSK constellation that can efficiently reduce PAPR while achieving BER performance comparable to that of the Gray labeling (GL).

Much work has been done aiming at minimization of energy consumption for transmission of information in energy constrained wireless networks. However, most of them assume uncoded system, not considering the effect of channel coding. In this paper, using the relation between channel capacity or cutoff rate of MQAM modulation in AWGN channel and signal to noise ratio (SNR), we formulate the problem of energy consumption and numerically analyze the optimized parameters for minimizing the energy consumption in a point-to-point communication link.

Trellis shaping (TS) has found its application in the peak power control of band-limited single-carrier signals. Our recent work has demonstrated that a well-designed TS can control the symbol transitions such that the output signal has almost constant envelope, which significantly alleviates the linearity requirement of power amplifiers. Compared to transmission without constellation shaping, however, the TS involves signal constellation expansion exclusively for peak power control. Therefore, unlike trellis coded modulation (TCM) that increases the minimum Euclidean distances (MED), the TS decreases the MED, thus incurring the increase in signal-to-noise power ratio (SNR) required for achieving a certain error rate. In this letter, in order to overcome this drawback, we propose a serial concatenation of coding and shaping together with an effective decoding algorithm that utilizes the memory effect (i.e., error correcting capability) of the shaped symbols. The achievable performance of the proposed system is analyzed in terms of the average mutual information. The simulation results demonstrate that the iterative decoding of the proposed concatenated system with outer convolutional codes and inner trellis shaping offers a significant performance gain.

In this paper, we present a new modulation code, named symbol insertion (SI), that simultaneously achieves both peak-to-average power ratio (PAPR) reduction and forward error correction for pulse-shaped single-carrier systems in a low-complexity manner. Based on the fact that PAPR highly depends on the successive phase patterns of discrete complex symbols, the proposed code controls phase shifts by inserting a redundant symbol between consecutive information-bearing symbols. At the receiver, by viewing the inserted symbols as parities, we exploit them for error correction. We show that, when the SI is used as an inner code of serially concatenated codes, its error rate performance is close to those of conventional capacity-approaching codes. The proposed system thus becomes favorable if the amount of PAPR reduction is taken into account. Furthermore, the SI with a rotationally invariant insertion scheme can accommodate itself to noncoherent detection.

This paper studies a statistical distribution of instantaneous power in pulse-shaped single-carrier (SC) modulation. Such knowledge is of significant importance to estimate several concerns associated with the non-linearity of power amplifiers, e.g., required back-off level or clipping distortion in amplified signals. However, existing works often rely on Monte-Carlo simulations, since analytical derivation of the statistical distribution of SC signals is a complex problem involving combined dependency of a constellation format and a pulse shape. In this paper, we tackle this problem and propose two new analytical methods based on the uniform distribution approximation of discrete signal points. The derived expressions can be easily evaluated and serve as tight upper bounds for high-order pulse amplitude modulation (PAM) and quadrature amplitude modulation (QAM).

This paper analyzes statistical distribution of instantaneous power in pulse-shaped single-carrier (SC) modulation. Such knowledge is of significant importance to estimate several concerns associated with the non-linearity of power amplifiers, e.g., required back-off level or clipping distortion in amplified signals. However, existing works often rely on Monte-Carlo simulations, since analytical derivation of the statistical distribution of SC signals is a complex problem involving combined dependency of a constellation format and a pulse shape. In this paper, we tackle this problem and propose a new efficient analytical method by using the approximation of infinite number constellation points. Tight upper bounds for high-order pulse amplitude modulation (PAM) and quadrature amplitude modulation (QAM) can be calculated from the proposed method.

We propose a novel cooperative diversity using multilevel coded modulation which can perform with arbitrary number of cooperative nodes. The proposed multilevel coded cooperation makes use of a signal superposition, which is one form of analog network coding techniques. Due to the ability and flexibility of a multilevel coded modulation, the proposed multilevel coded cooperation can outperform not only a time-division cooperative diversity but also a signal superposition cooperative diversity in the case where the number of cooperating nodes is more than two. Moreover, achievable outage probability and channel capacity are analyzed and two design criteria based on the analysis are proposed.

Single-carrier (SC) transmission is considered as a promising candidate for the uplink of the next generation cellular systems due to its relatively low peak-to-average power ratio (PAR) compared to multi-carrier systems such as orthogonal frequency division multiplexing (OFDM). In SC systems, bandwidth efficiency can be effectively enhanced by the use of waveform shaping filter with low roll-off factor. However, as a price, non- negligible increase of PAR is incurred in pulse-shaped signals even for phase shift keying (PSK) modulation. To balance both low PAR and high bandwidth efficiency, the authors have recently proposed a novel PAR reduction technique for SC-PSK based on trellis shaping (TS). In this paper, we evaluate its effectiveness and feasibility through implementation with field programmable gate array (FPGA) and testbed experiments with a sample RF power amplifier (PA).

We analyze pulse-shaped transmit signals with correlated input sequences in the framework of band-limited liner modulations. These signals are formed by superposition (convolution) of the shaping pulses and may have different amplitude statistics depending on the correlation properties of the input sequences. Hence, even if the sequences have a unit average power in discrete-time domain, the resulting transmit signals exhibit smaller (or larger) average power if there are many destructive (or constructive) superpositions produced by the correlated source. Since such a reduction of average transmit power does not change the amplitude of the underlying discrete-time sequence, one may expect the so-called shaping gain. We comprehensively analyze the shaping gain achieved by the correlation of the input sequences, and show that the use of a pulse shape, which convolves the sequence destructively, is capable of increasing the achievable information rate of the system.

The authors have recently proposed a novel trellis shaping (TS) approach for peak power reduction of single-carrier signals. In this paper, we propose the use of M algorithm as well as sequential decoding with stack algorithm for the purpose of complexity reduction. Our comparative studies with the Viterbi algorithm (VA) show that the TS with these low-complexity algorithms can still offer substantial peak power reduction capabilities that are comparable to the VA.

In this paper, we propose a bandwidth efficient coded cooperation using rate compatible turbo codes. The design of rate compatible turbo codes for the proposed collaboration is investigated based on the analysis of pairwise error probability (PEP). Some numerical results show that the diversity gain can be achieved by using our proposed approach.

In band-limited communications, the use of root-Nyquist pulse-shaping filters, such as root raised cosine (RRC), is a common premise to guarantee no inter-symbol interference (ISI) in the output from matched filtering. We have recently shown that, for correlated source symbols, some non-root-Nyquist filter is capable of increasing the mutual information of the resulting channel. In this paper, we show that performance improvement can also be achieved in terms of bit error rate.

Orthogonal frequency division multiplexing (OFDM) based multiple access systems have found their applications in many wireless communication systems. However, similar to conventional OFDM systems, they have a major drawback that their signal waveforms have a large peak-to-average power ratio (PAR). The resulting systems have low power amplifier efficiency, which is prohibitive for battery driven terminals. In this paper, we propose a simple OFDM-based multiple access system that combines low-rate super-orthogonal convolutional codes (SOCC) and Golay complementary sequences with applications to the uplink of low-cost wireless communication systems such as sensor networks. The proposed system has a PAR as low as 3 dB and can also achieve a frequency diversity gain due to the spreading of sequences in the frequency domain similar to a conventional coded OFDM architecture. The use of differential encoding with differential detection at the receiver further simplifies the overall system.

In this paper, we propose a powerful trellis shaping for peak-to-average power ratio (PAR) reduction of pulse-shaped phase shift keying (PSK) systems. The proposed approach consists of 1) memory extension of trellis shaping encoder for capturing the full effect of pulse shaping filter impulse response, and 2) simple branch metrics that quantify envelope fluctuation of the filter output. Simulation results demonstrate that achieving near constant envelope is possible even if a pulse shaping filter with a roll-off factor as low as 0.1 is employed. Furthermore, due to the circular nature of the resulting signal trajectory, the proposed system also exhibits a robustness against sampling timing jitter at the receiver.

In this paper, the bit-interleaved convolutionally coded differential phase shift keying (DPSK) in combination with cyclic delay diversity (CDD) is theoretically analyzed in terms of pairwise error probability (PEP). We show that bit-interleaved coded DPSK with CDD can achieve full spatial and frequency diversity offered by the frequency selectivity of wireless channel conditioned that the minimum free distance dfreeof the convolutional code is larger than the target diversity order. The design criterion of the considered system is presented based on the analysis of diversity and coding gains. Finally, the theoretical results obtained in this paper are confirmed by computer simulations.

We propose a new coded modulation called hexagonal shell modulation (HSM). The HSM has a signal constellation composed of shell-like tiling of hexagons and thus has a lower peak-to-average power ratio (PAR) than a standard square quadrature amplitude modulation (QAM) with comparable bandwidth efficiency and minimum Euclidean distance. The main challenge is that HSM has a non-power-of-two number of constellation points, and thus assignment of binary information to HSM is not straightforward. We resolve this by applying a multilevel coded modulation (MLC) scheme where a ternary set partitioning combined with binary-input ternary-output (BITO) turbo codes is employed to fully exploit the property of the nonpower- of-two constellation points. Throughout this letter, we focus on an 18-ary HSM with the information rate of 3 bit/symbol as a specific example. It is shown that this system outperforms the standard square 16-QAM with the same rate when PAR is constrained.

Cyclic delay diversity (CDD) exploits the principle of the orthogonal frequency division multiplexing (OFDM) that transforms the delay spread into the frequency selectivity. In order to investigate the performance of the CDD, OFDM in combination with bit-interleaved coded differential phase shift keying (DPSK) is theoretically analyzed in terms of pairwise error probability (PEP). We show that bit-interleaved coded DPSK with OFDM can achieve the full frequency diversity caused by the frequency selectivity of the wireless channel and that maximum diversity can be obtained with any kind of power delay profile (PDP), conditioned on the minimum free distance dfreeof the convolutional codes. Based on the above discussions, the bit- interleaved coded DPSK with CDD is studied. Finally, theoretical results are confirmed via computer simulations.

In order to guarantee highly reliable communications over noisy channels, the use of retransmission techniques is necessary, and the hybrid auto repeat request (HARQ) technique has been widely adopted in packet-based data communication systems. A common approach is to retransmit the entire packet that contains uncorrectable errors. However, this approach is inefficient if the number of errors in those packets is small. In this paper, we propose a new HARQ system based on multilevel coded modulation and multi-stage decoding at the receiver. In this system, retransmission is performed based on each level of multilevel signaling with reduced constellation size. The major advantage of this approach is that not only retransmission is efficient, but also the receiver complexity for code combining is low. Moreover, this approach offers a flexibility in the retransmission patterns. We derive an optimal algorithm of retransmission based on the channel capacity rule in this framework. The simulation results demonstrate that the proposed HARQ can significantly outperform the HARQ system based on the bit-interleaved coded modulation (BICM).

We extend our trellis shaping approach of reducing peak-to-average power ratio (PAR) of single-carrier PSK systems to high-order quadrature amplitude modulations (QAMs). Simulation results show that, with only one-bit redundancy per transmitted symbol, significant PAR reduction can be achieved. For example, band-limited transmission with PAR below 3 dB can be achieved with a square 64-QAM after pulse shaping with a roll off factor of as low as 0.1. Furthermore, the newly developed shaping metric offers a capability of simultaneously reducing the average power. The reduction of the PAR and average power can be flexibly controlled by adjusting a parameter associated with the shaping metric.

In this paper, a simple modulation code called symbol insertion for band-limited single-carrier systems is proposed. This code can reduce the peak-to-average power ratio (PAR) with an inherent forward error correction (FEC) capability. The idea of the proposed code is as follows; since the PAR is largely proportional to the phase shifts of consecutive discrete symbols, we eliminate large phase shifts by inserting redundant symbols every after information symbols. Furthermore, exploiting the fact that the insertion process has a trellis structure, we employ the symbol insertion as a component code of concatenated codes. An 8-PSK example demonstrates not only that the PAR reduction performance is superior to conventional PAR reduction schemes, but also that the coding gain is as large as those of conventional capacity-approaching turbo and LDPC codes. Another advantage of the proposed system is simplicity of both coding and decoding processes.

In order to alleviate development cost, many application-oriented wireless networks make use of the off-the- shelf wireless standards such as the Bluetooth, IEEE802.15.4 (Zigbee), and IEEE802.11, which are originally developed for personal area networks (PAN) and local area networks (LAN). Examples of such applications are medical monitoring and control. These applications do not require data rates as high as these standards, but instead they require higher reliability with lower latency. As a means to meet such requirements based on these standards, we propose an efficient error control technique named embedded forward error control technique (EFECT). This technique enables an additional forward error correction to the existing standards without any additional costs. Some design guidelines based on Reed-Solomon (RS) codes are proposed and, as a specific example, achievable gains by applying the EFECT are studied for the Bluetooth standard.

In order to alleviate development cost, many application-oriented wireless networks make use of the off-the- shelf wireless standards such as the Bluetooth, IEEE802.15.4 (Zigbee), and IEEE802.11, which are originally developed for personal area networks (PAN) and local area networks (LAN). Examples of such applications are medical monitoring and control. These applications do not require data rates as high as these standards, but instead they require higher reliability with lower latency. As a means to meet such requirements based on these standards, we propose an efficient error control technique named Embedded Forward Error Control Technique (EFECT). This technique enables an additional forward error correction to the existing standards without any additional costs. Some design guidelines based on Reed-Solomon (RS) codes and sphere packing bound are proposed and, as a specific example, achievable gains by applying the EFECT are studied for the Bluetooth standard.

The trellis shaping (TS) is an effective technique not only for average power reduction of high-order QAM signals, but also for peak power reduction of band-limited single-carrier PSK signals. Our recent work has demonstrated that signals with almost constant envelope can be generated. Compared to the unshaped PSK system, however, this shaping process introduces signal constellation expansion exclusively for peak power reduction and thus reduces the minimum Euclidean distance of the PSK signal constellation, rendering the overall system sensitive to channel noise. To overcome this drawback, this paper proposes a new decoding algorithm of the TS that exploits the Markov process property of the shaped symbols. This decoding algorithm can work alone, but becomes more effective when the shaping encoder is serially concatenated with a channel coding. The simulation results demonstrate that this serial concatenation together with an iterative decoding between shaping and coding can achieve a significant amount of coding gain.

In this paper, a novel peak power reduction scheme based on trellis shaping is proposed for single-carrier pulse- shaped phase shift keying (PSK) systems. The use of PSK generally results in relatively low signal dynamic range, but its peak-to-average power ratio tends to increase as the bandwidth of pulse shaping filter becomes narrower. The simulation results demonstrate that the proposed approach can generate signals with almost constant envelope, even with the existence of pulse- shaping filters operated with roll-off factors as low as 0.1.

In this paper, we propose a low complexity bit-interleaved coded DAPSK in combination with cyclic delay diversity, which transmits delayed replicas of an orthogonal frequency division multiplexing (OFDM) signal in cyclic manner and thereby enjoys full diversity without loss of bandwidth efficiency. Here, the frequency diversity induced by delayed replicas can be exploited by a subsequent channel decoder. The performance of the proposed system is evaluated over frequency selective block Rayleigh fading channels. We also show that our proposed system is robust against the blockage effect caused by some obstacles.

Orthogonal frequency division multiplexing (OFDM) has become a popular technique because of its robustness against multipath fading and high bandwidth efficiency. However, OFDM signals have a critical drawback; their peak-to-average power ratio (PAR) is very high compared to that of single-carrier signals. The clipping and filtering method is an effective method to cope with such a problem. However, as the required transmission rate increases with high signal-to-noise ratio (SNR), clipping distortion becomes dominant and causes burst errors. In this paper, we study a use of Reed-Solomon (RS) code for mitigating the clipping distortion. It is shown that judicious selection of the code parameters can improve the overall system performance. The decoding error rate as well as achievable throughput of the proposed system is calculated based on the combination of theoretical analysis and computer simulations.

In this paper, the performance of low-density parity-check (LDPC) codes with differential detection is studied over additive white Gaussian noise (AWGN) and Rayleigh fading channels with particular emphasis on the sensitivity of signal-to-noise ratio (SNR) parameters required for metric calculation. Two simple metrics are derived and compared. Computer simulation results demonstrate that an SNR mismatch has a considerable effect on the performance of LDPC codes, and optimal SNR mismatches are explored in terms of bit error rate performances. It is shown that in some cases a pessimistic SNR estimation can improve the overall performance.

The performance of two-phase collaborative communication protocols is studied for wireless networks. All the communication nodes in the cluster are assumed to share the same channel and transmit or receive collaboratively in a quasi-static Rayleigh flat-fading environment. In addition to small-scale fading, the effect of large-scale path loss is also considered. Based on a decode-and-forward approach, we consider various variable-rate two-phase protocols that can achieve full diversity order and analyze the effect of node geometry on their performance in terms of the outage probability of mutual information. For the single-relay node case, it is shown that if the collaborator node is close to the source node, a protocol based on space-time coding (STC) can achieve good diversity gain. Otherwise, a protocol based on receiver diversity performs better. These protocols are also compared with one based on fixed-rate repetition coding and their performance tradeoffs with node geometry are studied. The second part deals with multiple relays. It is known that with N relays an asymptotic diversity order of N+1 is achievable with STC-based protocols in the two-phase framework. However, in the framework of collaborative STC, those relay nodes which fail to decode remain silent (this event is referred to as a node erasure). We show that this node erasure has the potential to considerably reduce the diversity order and point out the importance of designing the STC to be robust against such node erasure

The performance of collaborative beamforming is studied using the theory of random arrays within the framework of wireless sensor networks. With the application to ad hoc networks in mind, two scenarios, one denoted closed-loop and the other open-loop, are considered. Associated with these scenarios, the effects of phase jitter and location estimation errors on the average beam pattern are analyzed.

The use of the spatial dimension is known to greatly increase the reliability of quasi-static (non-ergodic) wireless channels. In this paper we demonstrate that most of this gain can also he achieved through collaborative communications with single-antenna/multiple-antenna nodes when there is one receiving agent. In particular, for the single antenna case, we consider communication to take place between clusters of nearby nodes. We show the existence of collaborative codes for communications for which the intra-cluster negotiation penalty is in principle small and almost all the diversity gain of traditional space-time codes may be realized. For example, for single transmitter/receiver nodes with two collaborators that have as little as 10 dB path loss advantage over the receiver, the penalty for collaboration over traditional space-time systems is negligible.

We analyze the achievable performance of bit-interleaved coded differential amplitude and phase-shift keying (DAPSK) systems over frequency nonselective Rayleigh-fading channels with suboptimal differential detection assuming an ideal bit interleaving. The suboptimal differential detection in this work refers to the bit metric calculation based only on the difference between two consecutive symbols, in contrast to more complex maximum-likelihood (ML)-based differential detection, which makes use of all the observed consecutive symbols for its metric calculation in channel decoding. As benchmarks of coded system performance, we analyze the average mutual information (AMI) and cutoff rate of this system. Exact probability density functions of the suboptimal differential detector outputs are derived for this purpose. Comparative studies suggest that the performance loss of the suboptimal approach is in fact noticeable. Therefore, we also develop a low-complexity receiver structure in the framework of suboptimal differential detection that can approach the performance of ML-based system by suitably incorporating the amplitude statistics of received symbols. The theoretical framework developed in this paper is also confirmed by simulations using convolutional and turbo codes.

The use of the spatial dimension is known to greatly increase the reliability of quasi-static (i.e., nonergodic) wireless channels. In this paper, it is demonstrated that most of this gain can also be achieved through collaborative communications with single-antenna/multiple-antenna nodes when there is one receiving agent. In particular, for the single-antenna case, communication is considered to take place between clusters of nearby nodes. The existence of collaborative codes for which the intra-cluster negotiation penalty is, in principle, small (and almost all the diversity gain of traditional space-time codes may be realized) is shown. For example, for a single transmitter node with two collaborators and one receiver node, if the collaborators have as little as a 10-dB path loss advantage over the receiver, the penalty for collaboration over traditional space-time systems is negligible.

We analyze the achievable performance of the coded differential amplitude and phase shift keying (DAPSK) over a frequency non-selective Rayleigh fading channel with ideal bit interleaving. The bit metrics based on the exact probability density of detector output and the average mutual information of the system with conventional differential detection are derived and compared with that of multiple-symbol differential detection (MSDD). It is shown that by suitably incorporating the amplitude statistics of transmitted signals into bit metrics, the performance of conventional DAPSK can be significantly improved without increasing complexity. Theoretical framework developed above is also justified by the comparative simulation results using convolutional and turbo codes.

The performance of collaborative beamforming is analyzed using the theory of random arrays. The statistical average and distribution of the beam patterns of randomly generated phased arrays are derived in the framework of wireless ad hoc sensor networks. Each sensor node is assumed to have a single isotropic antenna and nodes in the cluster collaboratively transmit the signal such that the signal in the target direction is coherently added in the far-field region. The distribution of the maximum beam pattern sidelobe is also analyzed and a closed-form bound is derived based on the Gaussian approximation method.

The effect of the phase noise on the performance of bandwidth-efficient coded modulation is studied. To this end, the average mutual information (AMI) for specific constellations such as 8-phase-shift keying and 16-quadrature amplitude modulation is calculated in the presence of carrier phase error caused by imperfect carrier tracking over an additive white Gaussian noise channel. The AMI not only quantifies the effect of the phase noise from an information-theoretic viewpoint, but also serves as an estimate for a permissible amount of the phase noise for a given signal-to-noise ratio. The bit-error rate (BER) performance of a near-optimal turbo trellis-coded modulation scheme is then investigated over such a channel. For this purpose, an optimal branch metric which best fits the channel characteristics is derived. Furthermore, simple branch metrics (referred to as suboptimal, simplified, and Gaussian metrics) are derived, which may offer the tradeoff between BER performance and computational complexity. Numerical analysis shows that a near-optimal coded-modulation scheme renders a transmission system more robust against phase noise than is the case with a conventional trellis-coded modulation scheme.

A new trellis shaping design is proposed for reducing the peak-to-average power ratio of the bandlimited orthogonal frequency-division multiplexing (OFDM) signals. The approach is based on recursive minimization of the autocorrelation sidelobes of an OFDM data sequence. A novel metric in conjunction with the Viterbi algorithm is devised. The performance of the trellis shaping depends on signal mapping strategy, and the two types of mapping, referred to as Type-I and Type-II, are proposed. The Type-I mapping has no capability of reducing the average power, but it can achieve a significant reduction of the peak-to-average power ratio. On the other hand, the Type-II mapping is designed to achieve both peak and average power reduction. The bit error probability of the system over an AWGN channel is evaluated based on the simulations, which confirms the effectiveness of the proposed scheme.

The performance of optimal detection based on maximum-likelihood criterion is analyzed for the uncoded OFDM system with the deliberate clipping and filtering. Since the maximum-likelihood detector is difficult to implement, a low-complexity suboptimal detection method is also developed for the system. The analysis based on the truncated union bound and simulation results show that one can achieve clipping gain if the system is appropriately designed. Furthermore, the performance improvement due to the frequency diversity effect is also achieved with moderate clipping and suboptimal detection over frequency-selective Rayleigh fading channels, even without any channel coding.

The performance of the orthogonal frequency-division-multiplexing (OFDM) system over the strictly peak power and band-limited channel is analyzed in terms of the required input back-off, bit-error rate (BER), and channel capacity on the assumption that the power amplifier is perfectly linearized. The peak-power limitation is implemented by linearly scaling the band-limited OFDM signal such that the maximum peak power of each OFDM symbol is always below the saturation level of the amplifier. The theoretical performance analysis requires the knowledge of the distribution of the peak power normalized by the symbol-wise (local) average power, referred to as symbol-wise peak-to-average power ratio (PAR) in the paper, and we also develop a method to numerically calculate its statistical distribution. The analysis of BER performance suggests that the linear scaling causes practically negligible degradation. Furthermore, the benefit of additional application of simple PAR reduction schemes, such as symbol selection and deliberate clipping and filtering, is also examined.

We analyze the performance of the clipped orthogonal frequency division multiplexing (OFDM) system in terms of peak power reduction capability and degradation of channel capacity. The clipping is performed on the baseband OFDM signals with and without oversampling, followed by the ideal low-pass filter. First, the effect of the envelope clipping on the peak-to-average power ratio (PAPR) and the instantaneous power of the band-limited OFDM signal is studied. We then discuss the channel capacity of the oversampled and clipped OFDM signals over the additive white Gaussian noise and ideally interleaved Rayleigh fading channels. The capacity is calculated based on the assumption that the distortion terms caused by the clipping are Gaussian. It is shown that the SNR penalty due to the clipping can be considerably alleviated by using optimal coding and reducing the information data rate. The results are justified by the simulation results using near optimal turbo codes.

The distribution of the peak-to-average power ratio (PAPR) in strictly band-limited orthogonal frequency-division multiplexing (OFDM) signals is studied. Assuming that the base-band OFDM signal is characterized as a band-limited complex Gaussian process, we first attempt to derive the exact distribution of the PAPR in the band-limited OFDM signals. Since this distribution cannot be expressed in a closed form, we further develop a simple closed-form approximation, based on the level-crossing rate analysis. Comparisons of the proposed distributions with those obtained by computer simulations show good agreement and convergence with an increase in the number of subcarriers.

The effect of digital envelope clipping on the peak power of the bandlimited OFDM signal is studied. The system consists of the concatenation of digital clipping of the OFDM signal with and without oversampling and bandpass filtering, followed by the ideal low-pass filter. It is shown that without oversampling, the clipped OFDM signal may suffer considerable peak power regrowth compared to those with oversampling. To justify this empirical result, the distribution of the instantaneous power in the digitally clipped OFDM signals without oversampling is theoretically analyzed by its lower bound.

The performance of the strictly band-limited OFDM systems with deliberate clipping is examined in terms of the peak-to-average power ratio (PAPR) and the resultant bit error performance. The clipping is performed on the OFDM signals sampled at the Nyquist rate, followed by the ideal low-pass filter, Since the low-pass filter considerably enlarges the PAPR, there is a severe limitation in PAPR reduction capability. Thus, in order to achieve further reduction of the PAPR, the application of the adaptive symbol selection scheme is also considered. It is shown that the significant PAPR reduction with moderate complexity can be achieved by the combination of the clipping and the adaptive symbol selection. The price to be paid for PAPR reduction by this scheme is its performance degradation. The paper theoretically analyzes the bit error rate performance of the OFDM system with the Nyquist-rate clipping combined with the adaptive symbol selection, and considers the use of the forward error correction for compensation of the degradation. It is shown that even though the clipping scheme causes severe loss in required signal-to-noise ratio, the use of a powerful channel coding scheme such as turbo codes significantly alleviates the bit error rate performance degradation.

We discuss the construction method of orthogonal sequences for downlink OFDM-CDMA, in terms of the peak to average power ratio (PAPR) of the transmitted signals. The PAPR property is studied based on two orthogonal sets of sequences: Walsh-Hadamard and complementary sequences. It is shown that for relatively few active users, Walsh-Hadamard sequences tend to have very large PAPR, while the PAPR of complementary sequences remains stable near its theoretical value. A simple but effective peak reduction scheme is also proposed for OFDM-CDMA.