A low complexity PAPR reduction scheme based on radix-II IFFT

Due to no feedback process and simplicity in searching algorithm, conventional selected mapping (CSLM) is an efficient crest factor reduction (CFR) technique in orthogonal frequency division multiplexing (OFDM) systems. However high number of inverse fast Fourier transform (IFFT) block is required to achieve the desired PAPR reduction performance. In this paper a PAPR reduction method based on N point radix-2 IFFT is proposed in which the number of IFFTs is reduced to one. The gist of the proposed method is based on storing a part of calculations and using them for the next searching operation results in elimination of the redundant calculations. Simulation results show at least 46.8% complexity reduction compared to CSLM by comparable PAPR performance

On the Reduced Complexity Interleaving Method for OFDM PAPR Reduction

Many methods for OFDM Peak to Average Power Ratio reduction have been proposed during approximately last ten years. There are nowadays many research efforts on PAPR reduction methods with reduced computational complexity. The method presented in this paper is based on adaptive symbol selection principle, with several replicas of signal created using set of interleavers incorporated inside an IFFT block at OFDM transmitter. This paper also discusses some practical aspects of this method - influence of zero padding and pilot positions

Image multiplexing using residue number system coding over MIMO-OFDM communication system

Image transmission over Orthogonal Frequency-Division Multiplexing (OFDM) communication system is prone to distortion and noise due to the encountered High-Peak-to-Average-Power-Ratio (PAPR) generated from the OFDM block. This paper studies the utilization of Residue Number System (RNS) as a coding scheme for digital image transmission over Multiple-Input-Multiple-Output (MIMO) – OFDM transceiver communication system. The use of the independent parallel feature of RNS, as well as the reduced signal amplitude to convert the input signal to parallel smaller residue signals, enable to reduce the signal PAPR, decreasing the signal distortion and the Bit Error Rate (BER). Consequently, improving the received Signal-to-Noise Ratio (SNR) and enhancing the received image quality. The performance analyzed though BER, and PAPR. Moreover, image quality measurement is achieved through evaluating the Mean Squared Error (MSE), Peak Signal to Noise Ratio (PSNR), and the correlation values between the initial and retrieved images. Simulation results had shown the performance of transmission/reception model with and without RNS coding implementation.

Frequency-Selective PAPR Reduction for OFDM

We study the peak-to-average power ratio (PAPR) problem in orthogonal frequency-division multiplexing (OFDM) systems. In conventional clipping and filtering based PAPR reduction techniques, clipping noise is allowed to spread over the whole active passband, thus degrading the transmit signal quality similarly at all active subcarriers. However, since modern radio networks support frequency-multiplexing of users and services with highly different quality-of-service expectations, clipping noise from PAPR reduction should be distributed unequally over the corresponding physical resource blocks (PRBs). To facilitate this, we present an efficient PAPR reduction technique, where clipping noise can be flexibly controlled and filtered inside the transmitter passband, allowing to control the transmitted signal quality per PRB. Numerical results are provided in 5G New Radio (NR) mobile network context, demonstrating the flexibility and efficiency of the proposed method.Comment: Accepted for publication as a Correspondence in the IEEE Transactions on Vehicular Technology in March 2019. This is the revised version of original manuscript, and it is in press at the momen

Adjacent Partitioning Based MIMO-OFDM System with Partial Transmit Sequence for PAPR Reduction

The multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) transmission approach has been chosen to be a standard of fourth-generation (4G) wireless communication systems, but it has to cope with the main disadvantages and challenges of OFDM-based techniques, including the high peak-to-average power ratio (PAPR). Peak to average power ratio (PAPR) being a predictable random variable in multicarrier system and it can be minimized by different techniques. Complementary cumulative distribution function (CCDF) is used to describe the PAPR appropriately. Partial transmit sequence (PTS) is an attractive distortion less peak-to-average power ratio (PAPR) reduction technique for orthogonal frequency division multiplexing (OFDM) system. In this paper the performance of one of scrambling technique called partial transmit sequence (PTS) in MIMO-OFDM system and adjacent partitioning(one of the partitioning technique) in MIMO-OFDM system with PTS are analyzed based on the characteristics of CCDF DOI: 10.17762/ijritcc2321-8169.150514

Automatic transmit power control for power efficient communications in UAS

Nowadays, unmanned aerial vehicles (UAV) have become one of the most popular tools that can be used in commercial, scientific, agricultural and military applications. As drones become faster, smaller and cheaper, with the ability to add payloads, the usage of the drone can be versatile. In most of the cases, unmanned aerials systems (UAS) are equipped with a wireless communication system to establish a link with the ground control station to transfer the control commands, video stream, and payload data. However, with the limited onboard calculation resources in the UAS, and the growing size and volume of the payload data, computational complex signal processing such as deep learning cannot be easily done on the drone. Hence, in many drone applications, the UAS is just a tool for capturing and storing data, and then the data is post-processed off-line in a more powerful computing device. The other solution is to stream payload data to the ground control station (GCS) and let the powerful computer on the ground station to handle these data in real-time. With the development of communication techniques such as orthogonal frequency-division multiplexing (OFDM) and multiple-input multiple-output (MIMO) transmissions, it is possible to increase the spectral efficiency over large bandwidths and consequently achieve high transmission rates. However, the drone and the communication system are usually being designed separately, which means that regardless of the situation of the drone, the communication system is working independently to provide the data link. Consequently, by taking into account the position of the drone, the communication system has some room to optimize the link budget efficiency. In this master thesis, a power-efficient wireless communication downlink for UAS has been designed. It is achieved by developing an automatic transmit power control system and a custom OFDM communication system. The work has been divided into three parts: research of the drone communication system, an optimized communication system design and finally, FPGA implementation. In the first part, an overview on commercial drone communication schemes is presented and discussed. The advantages and disadvantages shown are the source of inspiration for improvement. With these ideas, an optimized scheme is presented. In the second part, an automatic transmit power control system for UAV wireless communication and a power-efficient OFDM downlink scheme are proposed. The automatic transmit power control system can estimate the required power level by the relative position between the drone and the GCS and then inform the system to adjust the power amplifier (PA) gain and power supply settings. To obtain high power efficiency for different output power levels, a searching strategy has been applied to the PA testbed to find out the best voltage supply and gain configurations. Besides, the OFDM signal generation developed in Python can encode data bytes to the baseband signal for testing purpose. Digital predistortion (DPD) linearization has been included in the transmitter’s design to guarantee the signal linearity. In the third part, two core algorithms: IFFT and LUT-based DPD, have been implemented in the FPGA platform to meet the real-time and high-speed I/O requirements. By using the high-level synthesis design process provided by Xilinx Corp, the algorithms are implemented as reusable IP blocks. The conclusion of the project is given in the end, including the summary of the proposed drone communication system and envisioning possible future lines of research

Multicarrier modulation with variable peak‐to‐average power ratio using partial fast Fourier transform

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/166180/1/cmu2bf01398.pd

FPGA-Based Realisation of SDR with OFDM Tranceiver

Software-defined radio architecture is the key point of next generation communication systems in which some of the functional units are designed as software on a reconfigurable processor. This paper proposes the physical layer architecture of SDR with modified orthogonal frequency division multiplexing (OFDM). One of the main drawbacks of OFDM is that its high peak-to-average reduction (PAPR) ratio. The PAPR can be reduced using filtering and adaptive peak windowing method with Kaiser window. The adaptive window method finds the positions of maximum peak values using a peak detector in the signal and applies the window function with variable parameter. The radix 2 scalable N point FFT algorithm is used in the system. The mapping of the information signal is done with BPSK, PSK, and 16 QAM modulation. According to the signal-to- noise ratio (SNR) value, the type of modulation can be selected. Decoding of the OFDM signal in the receiver is done with Viterbi decoding algorithm. The communication system simulation is done in MATLAB and the baseband operations are implemented on Xilinx FPGA.Defence Science Journal, Vol. 65, No. 3, May 2015, pp.233-239, DOI: http://dx.doi.org/10.14429/dsj.65.601

OFDM 시스템을 위한 새로운 저 복잡도 SLM 방식 및 클리핑 잡음 제거 기법 연구

학위논문 (박사)-- 서울대학교 대학원 : 전기·컴퓨터공학부, 2015. 2. 노종선.In this dissertation, several research results for the peak-to-average power ratio (PAPR) reduction schemes for orthogonal frequency division multiplexing (OFDM) systems are discussed. First, the basic principle and implementation of the OFDM systems are introduced, where high PAPR of OFDM signal is one of main drawbacks of OFDM systems. Thus, many PAPR reduction schemes to solve this problem have been studied such as clipping, selected mapping (SLM), partial transmit sequence (PTS), and tone reservation. In the first part of this dissertation, a low-complexity SLM scheme is proposed, where the proposed SLM scheme generates alternative OFDM signal sequences by cyclically shifting the connections in each subblock at an intermediate stage of inverse fast Fourier transform (IFFT). Compared with the conventional SLM scheme, the proposed SLM scheme achieves similar PAPR reduction performance with much lower computational complexity and no bit error rate (BER) degradation. The performance of the proposed SLM scheme is analyzed mathematically and verified through numerical analysis. Also, it is shown that the proposed SLM scheme has the lowest computational complexity among the existing low-complexity SLM schemes exploiting the signals at an intermediate stage of IFFT. In the second part of this dissertation, an efficient selection (ES) method of the OFDM signal sequence with the minimum PAPR among many alternative OFDM signal sequences is proposed, which can be used for various SLM schemes. The proposed ES method efficiently generates each component of alternative OFDM signal by utilizing the structure of IFFT and calculates its power, and such generation procedure is interrupted if the calculated power is larger than the given threshold. By using the proposed ES method, the average computational complexity of considered SLM schemes is substantially reduced without degradation of PAPR reduction performance, which is confirmed by analytical and numerical results. In the third part of this dissertation, a clipping noise cancellation scheme using compressed sensing (CS) technique is proposed for OFDM systems. The proposed scheme does not need reserved tones or pilot tones, which is different from the previous works using CS technique. Instead, observations of the clipping noise in data tones are exploited, which leads to no loss of data rate. Also, in contrast with the previous works, the proposed scheme selectively exploits the reliable observations of the clipping noise instead of using whole observations, which results in minimizing the bad influence of channel noise. From the selected reliable observations, the clipping noise in time domain is reconstructed and cancelled by using CS technique. Simulation results show that the proposed scheme performs well compared to other conventional clipping noise cancellation schemes and shows the best performance in the severely clipped cases.1. Introduction 1 1.1. Background 1 1.2. Overview of Dissertation 4 2. OFDM Systems 6 2.1. OFDM System Model 7 2.2. Peak-to-Average Power Ratio 8 2.2.1. Definition of PAPR 9 2.2.2. Distribution of PAPR 9 3. PAPR Reduction Schemes 11 3.1. Clipping 11 3.1.1. Clipping at Transmitter 11 3.1.2. A Statistical Model of Clipped Signals 13 3.1.3. Conventional Receiver without Clipping Noise Cancellation Scheme 15 3.2. Selected Mapping 16 3.3. Low-Complexity SLM Schemes 18 3.3.1. Lims SLM Scheme [25] 18 3.3.2. Wangs SLM Scheme [22] 19 3.3.3. Baxleys SLM Scheme [27] 19 3.4. Tone Reservation 20 4. A New Low-Complexity SLM Scheme for OFDM Systems 22 4.1. A New SLM Scheme with Low-Complexity 23 4.1.1. A New SLM Scheme 23 4.1.2. Relation Between the Proposed SLM Scheme and the Conventional SLM Scheme 26 4.1.3. Good Shift Values for the Proposed SLM Scheme 28 4.1.4. Methods to Generate Good Shift Values 31 4.1.5. Computational Complexity 33 4.2. Simulation Results 36 4.3. Conclusions 37 5. An Efficient Selection Method of a Transmitted OFDM Signal Sequence for Various SLM Schemes 42 5.1. ES Method and Its Application to the Conventional SLM Scheme 43 5.1.1. Sequential Generation of OFDM Signal Components in the Conventional SLM Scheme 43 5.1.2. Application of the ES Method to the Conventional SLM Scheme 45 5.1.3. Complexity Analysis for Nyquist Sampling Case 47 5.1.3.1. Characteristics of a Nyquist-Sampled OFDM Signal Sequence 48 5.1.3.2. Derivation of KN(b) 49 5.1.3.3. Distribution of pBu(bu) 51 5.1.4. Complexity Analysis for Oversampling Case 52 5.1.4.1. Characteristics of a Four-Times Oversampled OFDM Signal Sequence 52 5.1.4.2. Derivation of K4N(b) 53 5.1.4.3. Distribution of pBu(bu) 54 5.1.5. Comparison between Analytical and Simulation Results 55 5.2. Application of the ES Method to Various Low-Complexity SLM Schemes 57 5.2.1. Lims SLM Scheme Aided by the ES Method 57 5.2.2. Wangs SLM Scheme Aided by the ES Method 58 5.2.3. Baxelys SLM Scheme Aided by the ES Method 58 5.3. Simulation Results 59 5.3.1. Simulation Results for the Conventional SLM Scheme Aided by the ES Method 59 5.3.2. Simulation Results for Low-Complexity SLM Schemes Aided by the ES Method 60 5.4. Conclusions 62 6. Clipping Noise Cancellation for OFDM Systems Using Reliable Observations Based on Compressed Sensing 68 6.1. Preliminaries 71 6.1.1. Notation 71 6.1.2. Compressed Sensing 71 6.2. Clipping Noise Cancellation for OFDM Systems Based on CS 73 6.2.1. Sparsity of c 73 6.2.1.1. Sparsity of c for Clipping at the Nyquist Sampling Rate 73 6.2.1.2. Sparsity of c for Clipping and Filtering at an Oversampling Rate 74 6.2.2. Reconstruction of the Clipping Noise c by CS 75 6.2.3. Construction of the Compressed Observation Vector Y 77 6.2.3.1. Which Observations Should Be Selected 78 6.2.3.2. Estimation of θ(k) Based on H1(k)Y (k) 78 6.2.3.3. Selection Criterion of Observations 81 6.2.4. Computational Complexity 81 6.3. Simulation Results 82 6.3.1. AWGN Channel 82 6.3.2. Rayleigh Fading Channel 83 6.4. Conclusion 86 7. Conclusions 93 Bibliography 96 초록 104Docto