Flexible Multi-Group Single-Carrier Modulation: Optimal Subcarrier Grouping and Rate Maximization

Orthogonal frequency division multiplexing (OFDM) and single-carrier frequency domain equalization (SC-FDE) are two commonly adopted modulation schemes for frequency-selective channels. Compared to SC-FDE, OFDM generally achieves higher data rate, but at the cost of higher transmit signal peak-to-average power ratio (PAPR) that leads to lower power amplifier efficiency. This paper proposes a new modulation scheme, called flexible multi-group single-carrier (FMG-SC), which encapsulates both OFDM and SC-FDE as special cases, thus achieving more flexible rate-PAPR trade-offs between them. Specifically, a set of frequency subcarriers are flexibly divided into orthogonal groups based on their channel gains, and SC-FDE is applied over each of the groups to send different data streams in parallel. We aim to maximize the achievable sum-rate of all groups by optimizing the subcarrier-group mapping. We propose two low-complexity subcarrier grouping methods and show via simulation that they perform very close to the optimal grouping by exhaustive search. Simulation results also show the effectiveness of the proposed FMG-SC modulation scheme with optimized subcarrier grouping in improving the rate-PAPR trade-off over conventional OFDM and SC-FDE.Comment: Submitted for possible conference publicatio

A Survey on Peak to Average Power Ratio Reduction Methods for LTE-OFDM

OFDM (Orthogonal Frequency Division Multiplexing) is generally preferred for high data rate transmission in digital communication. The Long-Term Evolution (LTE) standards for the fourth generation (4G) wireless communication systems. Orthogonal Frequency Division Multiple Access (OFDMA) and Single Carrier Frequency Division Multiple Access (SC-FDMA) are the two multiple access techniques which are generally used in LTE.OFDM system has a major shortcoming of high peak to average power ratio (PAPR) value. This paper explains different PAPR reduction techniques and presents a comparison of the various techniques based on theoretical results. It also presents a survey of the various PAPR reduction techniques and the state of the art in this area

Performance Comparison Analysis of Piecewise Linear companding for OFDM And WHT Precoded OFDM

Orthogonal Frequency Division Multiplexing (OFDM) is amalgamation of modulation and multiplexing, it helps to allow huge data rates for wireless applications with great spectrum efficiency. Besides of advantages, the uncomfortable issue for OFDM is peak to average power ratio (PAPR). Number of methods was proposed to minimize PAPR, but those are minimizing PAPR at the cost of either increasing the BER, or performance degradation of PSD. In this paper “a composite companding transform by using WHT precoding with piecewise linear companding” is proposed to minimize the PAPR without sacrificing the BER and PSD performances. Simulation results display that this proposed method gives the better trade off between the PAPR minimization and BER performance without sacrificing the PSD

Boosted PTS Method with Mu-Law Companding Techniques for PAPR Reduction in OFDM Systems

This paper proposes an enhanced PAPR reduction technique which combines an enhanced PTS method with Mu-Law companding. The enhanced PTS method improves performances in both the partitioning and phase rotation steps. Enhancement in partitioning is achieved through a judicious incorporation of AP-PTS scheme into the IP-PTS. As for phase rotation, an optimal set of rotation vectors is derived based on the correlation properties of candidate signals. The PAPR reduction of this enhanced PTS method is further improved by annexing Mu-Law companding at the end of the enhanced PTS. This application of Mu-Law characteristic in the time domain of OFDM signal significantly improves the PAPR reduction capability of the approach. Simulation results show that the PAPR performance of the enhanced PTS method with Mu-Law companding technique on various scenarios with different modulation schemes is better than that of the PRP-PTS. This approach can be considered as a very attractive candidate for achieving a significant reduction of PAPR, while maintaining a low computational complexity

A HYBRID TECHNIQUE FOR PAPR REDUCTION OF OFDM USING DHT PRECODING WITH PIECEWISE LINEAR COMPANDING

Orthogonal Frequency Division Multiplexing (OFDM) is a fascinating approach for wireless communication applications which require huge amount of data rates. However, OFDM signal suffers from its large Peak-to-Average Power Ratio (PAPR), which results in significant distortion while passing through a nonlinear device, such as a transmitter high power amplifier (HPA). Due to this high PAPR, the complexity of HPA as well as DAC also increases. For the reduction of PAPR in OFDM many techniques are available. Among them companding is an attractive low complexity technique for the OFDM signal’s PAPR reduction. Recently, a piecewise linear companding technique is recommended aiming at minimizing companding distortion. In this paper, a collective piecewise linear companding approach with Discrete Hartley Transform (DHT) method is expected to reduce peak-to-average of OFDM to a great extent. Simulation results shows that this new proposed method obtains significant PAPR reduction while maintaining improved performance in the Bit Error Rate (BER) and Power Spectral Density (PSD) compared to piecewise linear companding method

Constrained Clipping For Peak-to-average Power Ratio (Crest Factor) Reduction In Multicarrier Transmission Systems

Disclosed is a constrained clipping technique for reducing the peak-to-average power ratio (PAR) or crest factor of a multicarrier communications signal. This is a transmitter-side processing technique that does not impose any modification at the receiver. Constrained clipping achieves PAR reduction while simultaneously satisfying spectral mask and error vector magnitude (EVM) constraints that are specified by most modern communications standards. The constrained clipping technique includes two independent processing units, one to satisfy an in-band EVM constraint and the other to satisfy an out-of-band spectral constraint. Achievable PAR reduction results vary depending on a particular standard's requirements, but by using constrained clipping on a QPSK WiMax signal with 256 subcarriers, for example, a 4.5 dB PAR reduction at the 10^-2 complementary cumulative distribution function (CCDF) level can be obtained.Georgia Tech Research Corporatio

PAPR REDUCTION IN ACO-OFDM FOR VISIBLE LIGHT COMMUNICATION SYSTEM

Visible Light Communication (VLC) is gaining popularity in optical wireless. In conventional OFDM, bi-polar signals having both positive and negative values are considered. However, in optical OFDM uni-polar signals, which have only positive values, are used. Therefore, suitable changes have to be done in conventional OFDM to make it compatible with O-OFDM. These modifications lead to the generation of asymmetrically clipped optical Orthogonal Frequency Division Multiplexing (ACO-OFDM) technology. In ACO-OFDM systems Peak to Average Power Ratio (PAPR) is a detrimental effect and should be suppressed. In ACO-OFDM, the estimation of probability density function (pdf) is not straightforward; therefore, a very limited literature is available. In this paper, an attempt is made to estimate pdf and Complimentary Cumulative Distribution Function (CCDF) expression for an ACO-OFDM with intensity modulation and direct detection (IM/DD), and its validity is checked by using simulation results. For ACO-OFDM scheme PAPR reduction methodology is used by applying various clipping strategies along with non-linear µ-law companding scheme. The results presented in the paper are obtained through computer simulation using MATLAB software. As clipping increases Bit Error Rate (BER), therefore, at various clipping mechanism BER are also obtained. It has been found, that by choosing suitable clipping along with non-linear companding scheme, PAPR can be reduced significantly while maintaining reasonable good BER performance. It is found, that with the proposed technique, PAPR is reduced by 76.10% as compared to raw ACO-OFDM