Low Peak-to-average Power Ratio Research Articles

DFT-Precoded MIMO OFDM Underwater Acoustic Communications

The discrete Fourier transform (DFT) precoded orthogonal frequency-division multiplexing (OFDM) has been adopted as the uplink transmission technique in the long-term evolution terrestrial communication standard, for its lower peak-to-average power ratio (PAPR) and similar receiver complexity, compared with the standard OFDM. However, its application in the underwater acoustic (UWA) communications remains doubtful, mainly for the lack of systematic studies as well as sufficient experimental verifications. This paper provides a comprehensive investigation on the DFT-precoded OFDM UWA communication with a multiple-input–multiple-output (MIMO) configuration, and corroborates its superiority for implementing a practical UWA communication modem. The DFT precoding is applied on the data symbols to achieve a lower PAPR than that of the standard OFDM, and it is optional for the pilot symbols. The frequency-domain turbo equalization (FDTE) technique, especially suitable for interference-intensive scenarios, is employed on the receiver side to combat the intersymbol interference (ISI) and the multiplexing interference. Experimental results are provided to demonstrate the performance of the proposed transceiver scheme. It is shown reliable communication is achieved for the two-transducer transmission with a QPSK modulation and the one-transducer transmission with a 16QAM modulation, even without running any iteration for the FDTE. With the help of turbo iterations, a two-transducer transmission with a 16QAM modulation also achieves a satisfactory performance.

An erasure-based scheme for reduction of PAPR in spatial multiplexing MIMO-OFDM using Reed-Solomon codes over GF(216 + 1)

ABSTRACTIn this paper, a novel erasure-based scheme which uses long Reed-Solomon (RS) codes over GF(65537) is proposed for the reduction of the peak-to-average power ratio (PAPR) in coded orthogonal frequency division multiplexing (OFDM). The motivation for using the field GF(65537) is to generate long code words (up to 65536 symbols in just one code word). Using long codes results in greater flexibility to search for low PAPR OFDM frames within the subsets of symbols of a code word because RS codes are maximum distance separable and any subset of a high enough number of symbols is sufficient for the recovery of data. Over this field, the lengths of code words are exponents of 2. Hence, low-complexity radix-2 fast Fourier transform can be exploited. RS codes are deployed for both PAPR reduction and error correction. Simulation results show that in similar PAPR reduction performances, the proposed scheme outperforms the previously reported work with RS codes in both error correction and computation complexity. The proposed scheme can be applied to both single-input single-output and multi-input multi-output systems.

A novel PAPR reduction scheme for VLC DCO-OFDM systems

In this study, we aim to reduce the peak-to-average power ratio (PAPR) for indoor visible light communication (VLC) orthogonal frequency division multiplexing (OFDM) systems and improve the system performance. By utilizing the spatial multiplexing (SMP) technique, we propose a subcarrier spatial grouping (SSG) scheme to address the high PAPR and LED restricted linear range problems. In this scheme, the high-PAPR wideband OFDM signals are partitioned into several low-PAPR narrowband independent signals that are simultaneously transmitted from multiple LED light sources. At the receiver, zero forcing (ZF) is used to reverse the impairments of the channel transform. The computer simulation results demonstrate that the proposed approach achieves lower PAPR and more robustness to LED nonlinearities leading to better bit error rate performance for the same spectral efficiency than that of the conventional DCO-OFDM scheme does in the whole signal-to-noise ratios range.

A low PAPR multicarrier and multiple access schemes for VLC

The omnipresence of solid-state illuminating devices like Light Emitting Diodes (LEDs) has driven Visible Light Communication (VLC) to acquire mammoth eminence. However, the limited dynamic range of LEDs leads to deleterious non-linear distortion when employing the high data rate multicarrier modulation technique like optical orthogonal frequency division multiplexing (OOFDM) resulting in high Peak to Average Power Ratio (PAPR). Furthermore, since VLC has profound applicability in a cellular network, there is an urge to investigate different PAPR mitigation techniques. In this paper, Discrete Cosine Transform-Spread-Fast-Optical OFDM (DCT-S-FOOFDM) is proposed and compared with other PAPR reduction schemes like Partial Transmit Sequence (PTS), clipping and filtering techniques. This work focuses on imparting Discrete Fourier Transform (DFT)-spreading for Optical Orthogonal Frequency Division Multiple Access (OOFDMA) and DCT-spreading for Fast Optical Orthogonal Frequency Division Multiple Access (FOOFDMA) system to reduce PAPR. Here, an elaborate mathematical analysis of the time-domain signal is accomplished for Asymmetrically clipped DC biased-Optical-Interleaved FDMA (ADO-IFDMA), Asymmetrically clipped-Optical-Localized FDMA (ACO-LFDMA), Fast-Optical-IFDMA (F-O-IFDMA) and Fast-Optical-LFDMA (F-O-LFDMA). The simulated result analysis emphasizes that PAPR is reduced significantly by employing DCT-Spreading in FOOFDM. Among the multiple access schemes, PAPR reduction in F-O-IFDMA is superior than F-O-LFDMA and outperforms FOOFDMA.

A New Uplink Multiple Access Based on OFDM With Low PAPR, Low Latency, and High Reliability

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.

Generalised precoding method for PAPR reduction with low complexity in OFDM systems

High peak-to-average power ratio (PAPR) is one of the major drawbacks of orthogonal frequency-division multiplexing (OFDM) systems. The precoding method is famous for providing a flexible way to reduce PAPR efficiently via adjustable precoding matrix (PM) but it also leads to high computational complexity. This study proposes a generalised precoding method that uses a generalised PM to provide a flexible scheme to generate precoded data with low PAPR and complexity. As compared to the OFDM system, the proposed generalised precoding OFDM systems achieve close bit-error ratio (BER) performance with lower PAPR reduction. Moreover, the BER performance of generalised precoding-based OFDM system is superior to that of OFDM system at low signal-to-noise ratio. The well known single-carrier frequency-division multiple access is a special case of discrete Fourier transform (DFT)-based generalised precoding method; therefore, the proposed method is promising in OFDM systems for achieving low PAPR and complexity with better BER performance.

Achieving Full Diversity on a Single-Carrier Distributed QOSFBC Transmission Scheme Utilizing PAPR Reduction

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

PTS based on DisABC algorithm for PAPR reduction in OFDM systems

A novel discrete artificial bee colony algorithm-based partial transmit sequences (DisABC-PTS) scheme is proposed to reduce peak-to-average power ratio (PAPR) of orthogonal frequency division multiplexing signals. Compared to ABC algorithm-based PTS scheme (ABC-PTS) proposed previously, the DisABC-PTS scheme works directly in discrete space, which has a high computational efficiency. Simulation results indicate that DisABC-PTS scheme can obtain lower PAPR than existing PTS schemes and has a low computational complexity.

An efficient joint algorithm for reducing PAPR of SC-FDMA system in cognitive radio networks

Cognitive radio (CR) has been proposed as a solution for the spectrum scarcity problem. This paper investigates single-carrier frequency division multiple access (SC-FDMA) for cognitive radios. Recently, SC-FDMA has been suggested as a candidate for multicarrier based CR systems. In this paper, we propose enhanced techniques to reduce the peak to average power ratio (PAPR) in SC-FDMA for Cognitive Radio Network (CRN). We start by showing the effect of two standard PAPR reduction techniques (interleaver based and selective mapping) to reduce the PAPR in SC-FDMA based CR. Then, a proposed joint algorithm interleaver with selective mapping in a way that is suitable for SC-FDMA based CR will be proposed that results in a lower PAPR than using them individually. Simulation results show that the SC-FDMA with proposed techniques has a lower PAPR when compared with the conventional SC-FDMA system for CRN, while the complexity of the system slightly increases. Results also reveal that the no. of interleavers and SLM sequences must be chosen carefully in order to limit the PAPR with slightly increases in the complexity of the system.

Waveform evaluations subject to hardware impairments for mm-wave mobile communications

Millimeter-wave bands are receiving great attention for mobile radio communications due to potential availability of enormous channel bandwidths. Larger channel bandwidths are very important to meet ever increasing data rate and capacity demands of future wireless networks. At high carrier frequencies, transmitted and received signals can suffer from severe hardware impairments. We evaluate the performance of several state-of-the-art waveforms, e.g., Cyclic-Prefix (CP)-OFDM, Windowed (W)-OFDM, Pulse-shaped (P)-OFDM, Universal-Filtered (UF)-OFDM, Filter-Bank Multi-Carrier with Offset Quadrature Amplitude Modulation, and DFT-spread (DFT-s)-OFDM, in the presence of hardware impairments. In particular, waveform comparisons have been evaluated in terms of bit error rate, error vector magnitude, and spectral confinement subject to oscillator phase noise and nonlinear power amplifier. It is observed that all waveforms perform similarly subject to hardware impairments—making CP-OFDM with low complexity filtering/windowing operations an attractive option to improve the spectral confinement. One major drawback of multi-carrier waveforms is the high peak-to-average power ratio (PAPR). Various low complexity PAPR reduction techniques for OFDM have been evaluated subject to hardware impairments. It is observed that in case of nonlinear PA and high power transmission, these simple PAPR reduction schemes can achieve similar performance as compared to DFT-s-OFDM, making OFDM also suitable for coverage limited scenarios where power efficiency is important.

Preamble Design With Interference Cancellation for Channel Estimation in MIMO-FBMC/OQAM Systems

Multiple-input multiple-output filter bank multicarrier with offset quadrature amplitude modulation (MIMO-FBMC/OQAM) system utilizes the multiple antennas technology, and it can provide more advantages than conventional FBMC/OQAM system. However, due to the inherent imaginary interference, the convention preamble-based channel estimation (CE) methods in MIMO-FBMC/OQAM systems cannot achieve high CE performance and mostly suffer from high peak to average power ratio (PAPR). Motivated by these problems, in this paper, we focus on the efficient preamble design for CE in MIMO-FBMC/OQAM systems. We propose an extended preamble structure which exploits the symmetry pattern to cancel interference and the interference weights in the symmetric structure is taken into account. Since the preamble length is extended, the additional interference effect from the middle of the preamble structure is also considered. The simulation results demonstrate that the proposed preamble method has low PAPR, better bit error ratio (BER), and better mean square error (MSE) performance compared to the conventional preamble methods.

Low PAPR FBMC

Unlike single carrier-frequency division multiple access (SC-FDMA), just combining discrete Fourier transform (DFT) spreading and filter bank multicarrier with offset quadrature amplitude modulation (FBMC-OQAM) results in only marginal peak to average power ratio (PAPR) reduction. To utilize the single carrier effect of DFT spreading, a special condition of the coefficients at each subcarrier’s in-phase and quadrature-phase (IQ) channels should be satisfied. As a starting point, we first derive this condition, which we call the identically-time-shifted-multicarrier (ITSM) condition. Then, based on this condition, we propose a new type of FBMC for low PAPR. The main features of the proposed scheme are summarized as follows. First, in order to further enhance the amount of PAPR reduction, we generate the four candidate versions of the DFT-spread and ITSM-conditioned FBMC waveform and select the one with minimum peak power. Even with multiple candidate generation, the major computation parts, such as DFT and IDFT are shared and need to be performed only once, unlike the conventional side information (SI)-based PAPR reduction schemes. Consequently, with a fractional complexity overhead compared with the previous DFT-spread FBMC, the proposed scheme achieves a PAPR reduction comparable to that of SC-FDMA. Second, the proposed scheme transmits only two bit SI per data block consisting of multiple FBMC-OQAM symbols. Hence, the SI overhead is significantly low compared with the usual SI-based schemes, such as selective mapping or partial transmit sequence.

Channel Estimation and Peak‐to‐Average Power Ratio Analysis of Narrowband Internet of Things Uplink Systems

Narrowband Internet of Things (NB‐IoT) is a cellular based promising low‐power wide‐area network (LPWN) technology standardized by the 3rd Generation Partnership Project (3GPP) in release‐13 as a part of the future 5th Generation (5G) wireless communication systems. The main design target of NB‐IoT was to enhance radio coverage by repeating signal over an additional period of time for the ultralow‐end IoT devices that would be operated in extreme coverage environments. But the power efficiency of the low‐cost NB‐IoT user equipment (NB‐IoT UE) in the uplink is the major concern. Coverage improvement from signal repetitions depends on the channel estimation quality at extremely bad radio conditions. The typical operating signal‐to‐noise ratio (SNR) for NB‐IoT is expected to be much lower than the zero. In this paper, we have proposed two efficient narrowband demodulation reference signal (NDMRS)‐assisted channel estimation algorithms based on the conventional least squares (LS) and minimum mean square error (MMSE) estimation methods. The theoretical analysis and the link‐level performance of our proposed estimation methods are presented. Simulation results exhibit that the proposed methods provide better estimation precision compared to the traditional LS and MMSE methods at the low SNR situations. Furthermore, we have analyzed the raised‐cosine (RC) and square‐root‐raised cosine (RRC) pulse shaping to reduce peak‐to‐average power ratio (PAPR) as an uplink transmit filter. The PAPR values are evaluated through extensive computer simulations for both single‐tone and multi‐tone transmissions. Our evaluation results vindicate that the RRC pulse shaping with lower PAPR values is feasible to design of practical NB‐IoT uplink transmitter and increases power efficiency.

Two-radii 8APSK and Two-radii 16APSK Modulations as Alternatives to 8PSK and 16QAM

In regard to the M-ary phase-shift keying (MPSK) modulation and the quadrature amplitude modulation (MQAM), MPSK is preferred up to M = 8, with MQAM being the most common choice for M > 8. In this letter, the modulations two-radii 8-ary and 16-ary amplitude-phase shift keying (APSK), respectively named 2r8APSK and 2r16APSK, are proposed as alternatives to 8PSK and square 16QAM, in this order. The 2r8APSK achieves higher power efficiency than the 8PSK, at the cost of a higher peak-to-average power ratio (PAPR) and a slightly more complex receiver. The 2r16APSK yields lower PAPR than the 16QAM, with roughly the same receiver complexity, but at the cost of a slightly lower power efficiency. Comparisons with other APSK-based modulations are made as well.

A CCM‐Based OFDM System with Low PAPR for Sparse Source

Orthogonal frequency division multiplexing (OFDM) usually suffers high peak‐to‐average power ratio (PAPR). As shown in this paper, PAPR becomes even severe for sparse source due to many identical nonzero frequency OFDM symbols. Thus, this paper introduces compressive coded modulation (CCM) in order to restrain PAPR by reducing identical nonzero frequency symbols for sparse source. As a result, the proposed CCM‐based OFDM system, together with iterative clipping and filtering, can efficiently restrain the high PAPR for sparse source. Simulation results show that it outperforms about 4 dB over the traditional OFDM system when source sparsity is 0.1.

Fireflies Algorithm Based Optimal Scrambling to Reduce PAPR in SFBC Based MIMO-OFDM

Space Frequency Block Codes (SFBC) diversity technique with OFDM multicarrier system is efficient to overcome the effect of uncorrelated fading in frequency-selective fading wireless environment. But the critical problem existing in OFDM space frequency system is the data transmission with high peak to average power ratio (PAPR). This paper proposes the Firefly Algorithm (FA) based scrambling technique which reduces the PAPR. Subsequently, the analysis of PAPR and bit error rate (BER) of the proposed FA method is carried out and it is compared with other existing methods such as the traditional selective mapping scrambling, the optimization of scrambling like particle swarm and bee colony. The analytical and simulation outcomes show that the proposed FA based scrambling finds optimized phase set for the transmission of low PAPR signal as compared to other existing methods and it also achieve a low bit error rate.

PAPR reduction for Flip-OFDM in IM/DD systems via PTS technique

ABSTRACTOptical wireless communication (OWC) has recently gained much attention for addressing the increasing demand in the global broadband access market. Flip-orthogonal frequency division multiplexing (Flip-OFDM) is a type of OFDM that can be implemented in indoor OWC. Due to the ability of Flip-OFDM to keep the same bit error rate performance in asymmetrically clipped optical OFDM (ACO-OFDM) while saving 50% of the receiver hardware complexity, it can be used as an alternative to ACO-OFDM. However, the main drawback that can reduce the performance of the Flip-OFDM is the high peak-to-average power ratio (PAPR). So, in this article, partial transmit sequence (PTS) is applied to reduce the PAPR of Flip-OFDM over ceiling bounce model. Simulation results show that the proposed PTS-based Flip-OFDM achieves significantly lower PAPR values compared to Flip-OFDM.

PAPR analysis of superimposed training based SISO/MIMO-OFDM systems with orthogonal affine precoder

Superimposed training (ST) is used to estimate channel in orthogonal frequency division multiplexing (OFDM) systems which results in higher throughput than the time/frequency multiplexed training schemes. Orthogonal affine precoders (OAP) are used in ST-based SISO/MIMO-OFDM system to cancel the interference caused due to simultaneous data transmission. We analyze the peak to average power ratio (PAPR) of SISO/MIMO-OFDM systems which use OAP-based ST scheme. We show that the OAP-based ST scheme has higher PAPR than the conventional OFDM (without OAP-based ST) systems. We design an OAP using Zadoff–Chu (ZC) sequence, which has lower PAPR than the conventional OAPs. We further reduce the PAPR of the ST systems using selective mapping (SLM), but by increasing the system complexity. We show that the PAPR of the ST-based SISO/MIMO-OFDM systems with ZC-based OAP and SLM is identical to that of the conventional OFDM using SLM.

A Low Complexity PAPR Reduction Method Based on FWFT and PEC for OFDM Systems

Orthogonal frequency division multiplexing (OFDM) is a multi-carrier modulation technique for transmitting large volumes of digital data but suffers high peak-to-average power ratio (PAPR) at the transmitter. In this paper, we propose a PAPR reduction technique based on the combination of a low complexity transform-Fast Walsh–Hadamard and Fourier transform (FWFT) and the parameter-adjustable piecewise exponential companding (PEC). To reduce algorithm complexity, FWFT uses a fast orthonormal unitary transform to calculate both the Walsh–Hadamard transform (WHT) and the discrete Fourier transform (DFT). In FWFT, WHT realizes precoding to OFDM signals and as a result the PAPR is reduced first. Moreover, the parameter-adjustable PEC transform is adopted to further reduce PAPR by transforming the statistics of the companded signal into exponential distribution with adjustable parameters. Simulation results show that the hybrid method achieves significant PAPR reduction and improves the BER performance of OFDM systems when used in multipath fading channels.

Interleaved single-carrier frequency-division multiplexing for optical interconnects.

In this paper, we propose a real-valued interleaved single-carrier frequency-division multiplexing (I-SC-FDM) scheme for intensity-modulation and direct-detection optical interconnects. By simplifying the encoding structure, the computational complexity can be reduced from Nlog2N complex multiplications to N complex multiplications. At the complementary cumulative distribution function of 10-2, a reduction of 10 dB and 7.5 dB for the peak-to-average power ratio (PAPR) of the I-SC-FDM is achieved than that of orthogonal frequency-division multiplexing modulated with QPSK and 16QAM, respectively, when the subcarrier number is set to 4096. We experimentally demonstrate the I-SC-FDM scheme for optical interconnects with data rates of 12 Gbit/s, 24 Gbit/s and 128 Gbit/s transmitted over 22.5-km, 22.5-km and 2.4-km standard single mode fiber, respectively. The I-SC-FDM scheme shows great potential for cost-sensitive and power-sensitive optical interconnects owing to its low computational complexity and low PAPR.