Distributions of Upper PAPR and Lower PAPR of OFDM Signals in Visible Light Communications

Orthogonal frequency-division multiplexing (OFDM) in visible light communications (VLC) inherits the disadvantage of high peak-to-average power ratio (PAPR) from OFDM in radio frequency (RF) communications. The upper peak power and lower peak power of real-valued VLC-OFDM signals are both limited by the dynamic constraints of light emitting diodes (LEDs). The efficiency and transmitted electrical power are directly related with the upper PAPR (UPAPR) and lower PAPR (LPAPR) of VLC-OFDM. In this paper, we will derive the complementary cumulative distribution function (CCDF) of UPAPR and LPAPR, and investigate the joint distribution of UPAPR and LPAPR.Comment: acceptted by IEEE ICASSP 2014. arXiv admin note: text overlap with arXiv:1304.019

Peak-to-average power ratio analysis for OFDM-based mixed-numerology transmissions

In this paper, the probability distribution of the peak to average power ratio (PAPR) is analyzed for the mixed numerologies transmission based on orthogonal frequency division multiplexing (OFDM). State of the art theoretical analysis implicitly assumes continuous and symmetric frequency spectrum of OFDM signals. Thus, it is difficult to be applied to the mixed-numerology system due to its complication. By comprehensively considering system parameters, including numerology, bandwidth and power level of each subband, we propose a generic analytical distribution function of PAPR for continuous-time signals based on level-crossing theory. The proposed approach can be applied to both conventional single numerology and mixed-numerology systems. In addition, it also ensures the validity for the noncontinuous-OFDM (NC-OFDM). Given the derived distribution expression, we further investigate the effect of power allocation between different numerologies on PAPR. Simulations are presented and show the good match of the proposed theoretical results

Joint Frequency Offset and Channel Estimation for OFDM Systems Using Pilot Symbols and Virtual Carriers

We consider joint estimation of carrier frequency offset and channel impulse response (CIR) for orthogonal frequency division multiplexing (OFDM) systems with pilot symbols and virtual subcarriers (VCs). We derive the receive-signal correlation structure due to the pilots and VCs, give the evidence of joint multivariate Gaussian distribution of the received samples, and derive an approximate maximum likelihood (ML) frequency offset estimator. We also derive the asymptotic mean-square error (MSE) and an approximate Cramer-Rao bound (CRB) and establish the asymptotic unbiasedness. Without pilots, in high signal-to-noise ratio, our estimator is equivalent to Liu and Tureli's estimator with Nv virtual carriers. When the pilot number (Np) is greater than the channel length L, our estimator acts as a subspace-based estimator with Nv + Np - L virtual carriers. A decision-directed joint ML estimator is derived to iteratively update the estimates of frequency offset, data symbols and CIR. The optimal pilot and virtual carrier placement strategies are also discussed. The resulting decision-directed joint estimator performs within 0.8 dB of the ideal case even when the frequency offset is as large as 20%

A modern extreme value theory approach to calculating the distribution of the peak-to-average power ratio in OFDM systems

Orthogonal frequency division multiplexing (OFDM) is a promising framework for future wireless communication systems. One of the main impediments that has limited the applicability of OFDM systems in low-power wireless communication systems is the highly variable amplitude of the baseband transmitted signal; thus, a number of recent analyses have characterized this variation. These analyses have generally employed the following two components: (1) the assumption that the complex envelope of the OFDM signal converges to a Gaussian random process in some sense as the number of subcarriers becomes large, and (2) Rice\u27s classical results on level-crossing rates for the envelope of Gaussian random processes. In this work, we improve on both of these components to arrive at a simple, accurate, and rigorously-established expression for the peak distribution of the OFDM envelope. In particular, using a rigorous (and non-trivial) proof establishing the convergence in (1) above as justification, the modern extreme value theory for chi-squared processes is applied to the problem. Numerical results for both uncoded and coded systems establish that the simple expression obtained for the distribution of the peaks of the envelope process is extremely accurate, even for a modest number of subcarriers

저복잡도 후보 OFDM 신호 생성을 이용한 새로운 PTS 방법

학위논문 (박사)-- 서울대학교 대학원 : 전기·컴퓨터공학부, 2014. 2. 노종선.This dissertation proposes several research results on the peak-to-average power ratio (PAPR) reduction schemes for the orthogonal frequency division multiplexing (OFDM) systems. The PAPR is the one of major drawback of OFDM system which causes signal distortion when OFDM signal passes through nonlinear high power amplifier (HPA). Various schemes have been proposed to reduce the PAPR of OFDM signals such as clipping, selected mapping (SLM), partial transmit sequence (PTS), active constellation extension (ACE), companding, and tone reservation (TR). Among them, PTS scheme can transmit an OFDM signal vector by generating many alternative OFDM signal vectors using the partitioned subblock signals and selecting the optimal OFDM signal vector with the minimum PAPR. However, the PTS scheme requires large computational complexity, because it needs many inverse fast Fourier transforms (IFFTs) of subblock signals and lots of alternative OFDM signal vectors are generated. In this dissertation, we concentrate on reducing the computational complexity of the PTS scheme. In the first part of this dissertation, we propose a new PTS scheme with low computational complexity using two search steps to find a subset of phase rotating vectors showing good PAPR reduction performance. In the first step, sequences with low correlation are used as phase rotating vectors for PTS scheme, which are called the initial phase vectors. Kasami sequence and quaternary sequence are used in this step as the initial phase vectors. In the second step, local search is performed based on the initial phase vectors to find additional phase rotating vectors which show good PAPR reduction performance. Numerical analysis shows that the proposed PTS scheme can achieve almost the same PAPR reduction performance as the conventional PTS scheme with much lower computational complexity than other low-complexity PTS schemes. In the second part of the dissertation, we propose another low-complexity PTS schemes using the dominant time-domain OFDM signal samples, which are only used to calculate PAPR of each alternative OFDM signal vector. In this PTS scheme, we propose efficient metrics to select the dominant time-domain samples. For further lowering the computational complexity, dominant time-domain samples are sorted in decreasing order by the proposed metric values and then the power of each sample is compared with the minimum PAPR of the previously examined alternative OFDM signal vectors. Numerical results confirm that the proposed PTS schemes using new metrics show large computational complexity reduction compared to other existing low-complexity PTS schemes without PAPR degradation. In the last part of the dissertation, for the reduced-complexity PTS scheme, a new selection method of the dominant time-domain samples is proposed by rotating the IFFTed signal samples to the area on which the IFFTed signal sample of the first subblock is located in the signal space. Moreover, the method of pre-exclusion of the phase rotating vectors using the time-domain sample rotation is proposed to reduce the number of alternative OFDM signal vectors. Further, three proposed PTS schemes are introduced to reduce the computational complexity by using simple OFDM signal rotation and pre-exclusion of the phase rotating vectors. Numerical analysis shows that the proposed PTS schemes achieve the same PAPR reduction performance as that of the conventional PTS scheme with the large computational complexity reduction.Docto