A DHT precoded OFDM system with full diversity and low PAPR

Selected Mapping (SLM) is a popular technique used for Peak-to Average Power (PAPR) reduction in OFDM systems. Normally SLM techniques require explicit side information to be transmitted to allow decoding at the receiver. Alternative SLM techniques use shift register scramblers to embed the side information into the transmitted OFDM symbols. In this paper the concept of an SLM Simplified Scrambler is introduced. The advantages of this technique are (a) no explicit side information is transmitted, and (b) the simplified scrambler helps to avoid the problem of shift register error propagation in the receiver descrambler. The Simplified Scrambler SLM-OFDM approach is investigated in terms of PAPR reduction, Power Spectral Density (PSD) and Bit-Error Rate (BER) performance. It is shown that the Simplified Scrambler SLM-OFDM technique exhibits the same PSD and BER as general OFDM as well as improving the BER performance over SLM shift-register scrambler techniques.

Orthogonal frequency division multiplexing (OFDM) is advantageous in terms of the spectral efficiency it offers. However, in OFDM, the bandwidth-efficient multicarrier modulation (MM) is limited by the peak-to-average power (PAPR) problem. Iterative clipping and filtering (ICF) method has been used in this work to address such issue. The ICF is regarded as a practical scheme that has become widely accepted and used due to the fact that it is characterized by low computational complexity. This method is also easily implemented, characterized by non-expansion of bandwidth, and it does not require the support to the receiver side during implementation. Nevertheless, the significant of this work is on further improvement where the method involves the iterative clipping of the same signals with a fixed clipping threshold (CT) in every clipping operation. Particle swarm optimization based ICF-OFDM, which is proposed in this research work, literally finds the most suitable clipping ratio, that eventually solves the problem of output power instability. Subsequently, the proposed method is implemented with asymmetrical clipped optical OFDM (ACO-OFDM) to validate the proposed method through the use of Matlab simulation. The PAPR reduction of the proposed method is then compared with the PAPR of the Hartley transform (DHT)-based ACO-OFDM and the traditional ACO-OFDM and DCO-OFDM. The best BER performance has been investigated via two modulation index. Results indicate that our method outperforms the counterparts in term of PAPR reduction and BER performance.

Discrete Hartley transform (DHT) based orthogonal frequency division multiplexing (OFDM) outperforms the OFDM based on discrete Fourier transform (DFT) for its intrinsic frequency diversity. However, the space-frequency block coding (SFBC) cannot be applied since the symbols in Hartley domain are coupled. In this paper, by using the properties of DHT and DFT, we propose a DHT based SFBC-OFDM system design with better performance than and similar complexity to the DFT counterpart. Moreover, a low complexity algorithm is derived based on the properties of DHT to get the time domain signals of the DHT based SFBC code words with about halved complexity. Finally, analysis and simulations are provided to validate its feasibility and ability to exploit both the frequency and spatial diversity, as a promising alternative to the DFT counterpart.

High PAPR (Peak-to-Average Power) is one of the major drawbacks of OFDM systems. To improve the HPA efficiency and reduce nonlinear distortion, PAPR reduction techniques are used. Various PAPR reduction techniques have been proposed, and clipping based methods are attractive for its simplicity and easy implementation. Clipping based methods generally are iterative. Different clipping method leads to different performance. In this paper, two clipping methods, clipping and enlipping, are analyzed and compared in terms of PAPR, convergent rate and increase of average power. The simulation results show that enlipping can achieve faster convergent rate, but the average power is increased significantly which will incur degradation of overall system performance.

Conventional computer networks are being replaced with more pervasive networks such as the Internet of Things (IoT) and fog computing networks. Pervasive networks lay a constraint on the amount of processing power and memory for the diverse type of connected devices. This leads to investigating security measures which can be applied to the pervasive network structure so that it secures the network at multiple levels of the OSI model. This paper presents a proactive approach which combines leveraging the channel state information (CSI) as well as minimizing the PAPR of the system so as to enhance the security in both aspects of security aware channel assignment as well as introducing imperceptibility in data transmission over the security aware channel assignment protocol. The effectiveness of leveraging security aware channel assignment is evaluated in terms of the BER and sum secrecy rate of the system while the imperceptibility is evaluated in terms of the PAPR or crest factor value. The paper also combines MIMO-equalization so as to enhance the spectral efficiency of the system. A comparison with existing work in the domain clearly demonstrates the improvement of the proposed approach in terms of the performance metrics.

Peak to average power (PAPR) reduction of OFDM signals is critical in order to improve power amplifier (PA) efficiency in base stations. For massive MIMO, the complexity of these methods can become a real bottleneck in implementing low power digital signal processing chains. In this work, we consider an antenna reservation technique, which uses a low complexity clipping method to reduce signal peaks and leverages the benefit of massive antennas, by reserving a subset of antennas in order to compensate for the clipping distortion. Reserving antennas on the other hand reduces the potential array gain in the massive MIMO system, complicating the application of antenna reservation. This work explores various design space parameters in antenna reservation such as number of reserved antennas, amount of peak reduction and clipping methods. We investigate the impact of these parameters on the error vector magnitude at the user and on the adjacent channel power ratio at both transmitter and user positions. Our results enable a deeper understanding of antenna reservation as a low complexity PAPR reduction method in massive MIMO systems.

The discrete Hartley transform (DHT) is a real-valued transform closely related to the discrete Fourier transform (DFT) of a real-valued sequence. Several fast algorithms for the computation of the DHT (FHTs) have been proposed. A new cascade circuit for computing the DHT is presented in two versions, which implement, respectively, the radix-2 decimation-in-time and decimation-in-frequency FHT algorithms. The circuit makes use of CORDIC processors and allows an easy computation of the DFT, the amplitude and phase spectra, and the cyclic convolution and correlation of two sequences. Some architectures to perform such operations are also presented.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

This paper investigates optical orthogonal frequency division multiplexing (O-OFDM) systems with index modulation (IM) based on discrete Hartley transform (DHT) for visible light communications (VLC). An interesting trade-off between spectral efficiency (SE), energy efficiency, peak-to-average power ratio (PAPR) and bit error rate (BER) performance can be made by using the IM technique. And the DHT-based O-OFDM-IM systems can achieve higher SE compared with the DFT (discrete Fourier transform)-based counterparts. Employing DHT instead of DFT enables the removal of the Hermitian symmetry requirement, which contributes to transmitting more index bits and results in SE improvement. To acquire the same SE, the proposed systems can significantly lower the constellation order leading to better BER performance by contrast with the DFT-based counterparts. We employ DC (direct current) biasing and AC (Asymmetrically clipped) techniques to investigate the O-OFDM-IM systems in this paper. Simulation results indicate that SNR gains can be obtained by the DHT-based DCO/ACO-IM in comparison to the DFT-based counterparts. We also propose a novel reduced-complexity ML (maximum likelihood) detector specifically applicable to VLC. The new detector exhibits the same BER performance as the ML detector and performs better than the LLR (log-likelihood ratio) detector with reduced computational complexity.

Recently, R.N. Bracewell (1983) introduced the discrete Hartley transform (DHT) as an alternative to the discrete Fourier transform (DFT). Two linear systolic array models for the (DHT) are derived. One model requires O(2N-1) in the computational phase and O(N) in the preloading phase. The other model requires O(2N-1) in the computational phase and O(N) in the output phase. A square systolic array for two-dimensional DHT is also constructed by combining the individual advantages of each model. The CORDIC algorithm is proposed as an alternative to conventional multipliers. To speed up the systolic array, two-level pipelining with CORDIC is also possible. >

The Fast Hartley Transform (FHT) is similar to the Cooley-Tukey Fast Fourier Transform (FFT) but performs much faster because it requires only real arithmetic computations compared to the complex arithmetic computations required by the FFT. Through use of the FHT, Discrete Cosine Transforms (DOT) and Discrete Fourier Transforms (DFT) can be obtained. The recursive nature of the FHT algorithm derived in this paper enables us to generate the next higher-order FHT from two identical lower-order FHTs. In practice, this recursive relationship offers flexibility in programming different sizes of transforms, while the orderly structure of its signal flow graphs indicates an ease of implementation in VSLI.

In this paper we present the Peak-to-Average Power Ratio decrease method targeted at energy efficiency improvement of the Radio-over-fiber telecommunication systems based on the Orthogonal Frequency Division Multiplexing. The scheme for the proposed method that consists in the signal precoding with discrete function is discussed in details. The simulation results obtained for five different precoding functions: Discrete Hartley Transform, Discrete Cosine Transform, Discrete Sine Transform, Fast Walsh-Hadamard Transform, and Discrete Fourier Transform, show the peak-to-average power ratio decrease of the transmitted signal up to 7 dB without degradation in noise immunity. Such a gain in transmitted power reduction corresponds to energy efficiency improvement by 5.15 dB in the case of 16-position quadrature amplitude modulation. The experimental study confirms the simulation results, providing the 6.5 dB peak-to-average power ratio decrease for Discrete Fourier Transform function.

An efficient radix-3/9 fast Hartley transform (FHT) algorithm is proposed. It shows a great improvement over the previous radix-3 FHT algorithm such that nearly 50% of the number of multiplications is saved. For the computation of real-valued DFTs (discrete Fourier transforms) with sequence lengths which are powers of 3, the proposed radix-3/9 algorithm gives an average of 16.2% reduction in the number of multiplications over the fastest radix-3/9 FFT (fast Fourier transform) algorithm. The improvement is mainly the result of the simplicity of the computing structure of the proposed algorithm and the use of fast length-3 and fast length-9 DHT modules.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

As a promising solution for short-to-medium transmission systems, direct detection optical orthogonal frequency division multiplexing (DDO-OFDM) or discrete multi-tone (DMT) has been intensively investigated in last decade. Benefitting from the advantages of peak-to-average power (PAPR) reduction and signal-to-noise ratio (SNR) equalization, precoding techniques are widely applied to enhance the performance of DDO-OFDM systems. However, the conventional method of partitioning precoding sets limits the ability of precoding schemes to optimize the SNR variation and the allocation of modulation formats. Thus, the precoding transmission systems are hard to reach the capacity that traditional bit-power loading (BPL) techniques, like the Levin-Campello (LC) algorithm, can achieve. In this paper, we investigate the principle of SNR variation for precoded DDO-OFDM systems and theoretically demonstrate that the SNR equalization effect of precoding techniques is actually determined by the noise equalization process. Based on this fact, we propose an adaptively partitioned precoding (APP) algorithm to unlock the ability to control the SNR of each subcarrier. As demonstrated by the simulation and experimental results, the proposed APP algorithm achieves the transmission capacity as high as the LC algorithm and has nearly 1 dB PAPR reduction. Besides, the look-up table (LUT) operation ensures low complexity of the proposed APP algorithm compared with LC algorithm. To avoid severe chromatic dispersion (CD) induced spectral fading, single sideband (SSB) modulation is also implemented. We find that SSB modulation can reach the capacity of double sideband (DSB) modulation in optical back-to-back (OB2B) configuration by optimizing the modulation index. Therefore, the APP based SSB-DDO-OFDM scheme can sufficiently enhance the performance of cost-sensitive short-to-medium reach optical fiber communication systems.

Conventional orthogonal frequency division multiplexing (OFDM) systems use discrete Fourier transform (DFT) as the basis function. Recently, it was shown that it is possible to use other sinusoidal transforms, e.g. discrete cosine transform (DCT), as OFDM basis functions. However, relative little is known regarding the performance of these alternative basis functions and how they compare with traditional DFT. This paper investigates the performance of OFDM modems employing alternative basis functions under different fading channel models in both double sideband and single sideband operation modes. A semi-analytical approach is also developed to predict and compare the error performance between different basis functions. The predicted results are close to the simulations thus verifying the simulation model. It was found that in general DFT has a better error performance, but interspersed basis is capable of offering a higher net throughout under certain channel conditions.

Selected Mapping (SLM) is the assuring peak to average power reduction (PAPR) technique for OFDM system. But this technique undergoes a very complex process for finding optimum phase sequence for the reduction of PAPR. Hence, in this paper highly optimized phases are derived and analyzed from proposed algorithm for selected mapping using several modulation schemes such as binary phase shift keying (BPSK), quadrature phase shift keying (QPSK), 8-PSK, 64-PSK, and 64-quadrature amplitude modulation (QAM). The simulation results are performed in MATLAB using complementary cumulative distribution function (CCDF) which clearly depicts that the performance of proposed schemes HIGHLY-OPTIMIZED-SLM2 (HOS-2) and HIGHLY-OPTIMIZED-SLM1 (HOS-1) is remarkable under 64-QAM because gain achieved are 2.95 dB, 1.35 dB respectively as compared with original OFDM system.