Companding Scheme Research Articles

Efficient PAPR Reduction in OFDM Systems Based on a Companding Technique With Trapezium Distribution

Orthogonal Frequency Division Multiplexing (OFDM) has become the most widely adopted technology in wireless communication systems. OFDM is limited mainly by its high Peak-to-Average Power Ratio (PAPR). A uniformly distributed nonlinear companding scheme efficiently reduces PAPR with a low Bit Error Rate (BER). However, the uniformly distributed companding scheme cannot perform variably to satisfy the different performance requirements for the systems. Therefore, this work proposes a novel scheme that transforms the OFDM signals into a trapezium distribution. The uniformly distributed companding scheme is a special case of the proposed scheme. The general formulas of the proposed scheme are derived and the trade-off between PAPR reduction and BER performance is achieved by setting the value of a parameter. Then, the simulation results show the PAPR reduction and the BER over the AWGN and multipath channels, indicating that the proposed scheme provides a favorable trade-off between the PAPR reduction and the BER.

Implementation of low-complexity companding technique for efficient peak-to-average power ratio reduction in orthogonal frequency division multiplexing systems

Orthogonal frequency division multiplexing (OFDM) system has become an extremely popular wireless communication system in recent years. However, since the OFDM system is limited by a high peak-to-average power ratio (PAPR), companding techniques are often used to reduce PAPR. A uniformly distributed non-linear companding scheme offers efficient PAPR reduction with a low bit error rate (BER). However, such a scheme is difficult to implement. This work presents the referred companding scheme, expanded as a Taylor polynomial. Further, a novel low-complexity companding technique is developed to simplify the Taylor polynomial scheme by using the Pade approximation. Simulation results indicate that the performance of the proposed scheme is nearly the same as that of the referred scheme and the Taylor polynomial scheme over the additive white Gaussian noise (AWGN) channel or the multipath fading channel. Furthermore, the results of the hardware implementation demonstrate that the proposed scheme has lower complexity and computational time than the referred and Taylor polynomial schemes.

Correlation Power Analysis with Companding Methods

Companding methods have been profoundly applied in signal processing for quantization. And various companding schemes have been proposed to improve the PAPR (Peak to Average Power Ratio) of OFDM systems. In this paper, based on the exploration of the features of μ-law functions, we propose Correlation Power Analysis (CPA) with μ-law companding methods. μ-law expanding function is used to preprocess the power traces collected during AES encryption on ASIC and FPGA respectively. Experiments show that it reduces the number of power traces to recover all the key bytes as much as 25.8% than the conventional CPA.

Companding schemes based on transforming signal statistics into trigonal distributions for PAPR reduction in OFDM systems

AbstractThis paper proposes four companding transforms to reduce the peak‐to‐average power ratio in orthogonal frequency division multiplexing systems. The four companding transforms are obtained by transforming signal statistics into four trigonal distributions. Computer simulations show that the proposed schemes can effectively improve the PAPR performance and bit error rate performance of OFDM systems. Copyright © 2010 John Wiley & Sons, Ltd.

Peak-to-Average Power Ratio Reduction of OFDM Signals With Nonlinear Companding Scheme

Companding transform is a simple and efficient method in reducing the Peak-to-Average Power Ratio (PAPR) of Orthogonal Frequency Division Multiplexing (OFDM) systems. In this paper, a novel nonlinear companding scheme is proposed to reduce the PAPR and improve Bit Error Rate (BER) for OFDM systems. This proposed scheme mainly focuses on compressing the large signals, while maintaining the average power constant by properly choosing transform parameters. Moreover, analysis shows that the proposed scheme without de-companding at the receiver can also offer a good BER performance. Finally, simulation results show that the proposed scheme outperforms other companding scheme in terms of spectrum side-lobes, PAPR reduction and BER performance.

A Novel Multi-Exponential Function-based Companding Technique for Uniform Signal Compression over Channels with Limited Dynamic Range

A Novel Multi-Exponential Function-based Companding Technique for Uniform Signal Compression over Channels with Limited Dynamic Range Companding, as a variant of audio level compression, can help reduce the dynamic range of an audio signal. In analog (digital) systems, this can increase the signal-to-noise ratio (signal to quantization noise ratio) achieved during transmission. The μ-law algorithm that is primarily used in the digital telecommunication systems of North America and Japan, adapts a companding scheme that can expand small signals and compress large signals especially at the presence of high peak signals. In this paper, we present a novel multi-exponential companding function that can achieve more uniform compression on both large and small signals so that the relative signal strength over the time is preserved. That is, although larger signals may get considerably compressed, unlike μ-law algorithm, it is guaranteed that these signals after companding will definitely not be smaller than expanded signals that were originally small. Performance of the proposed algorithm is compared with μ-law using real audio signal, and results show that the proposed companding algorithm can achieve much smaller quantization errors with a modest increase in computation time.

Transforming the distribution of OFDM signals for peak‐to‐average power ratio reduction

AbstractLarge peak‐to‐average power ratio (PAPR) is the main drawback of orthogonal frequency division multiplexing (OFDM) systems. In this paper, a novel nonlinear scheme is proposed to reduce the PAPR. This scheme transforms the amplitude of original OFDM signals from Rayleigh distribution into beta distribution. Moreover, given different parameters, this scheme has different transformation expressions. It is demonstrated that the well‐known companding schemes based on exponential function and error function are actually the special cases of the proposed scheme. Further, we derive another simpler expression of the proposed scheme. Simulation results show that the new transformation can achieve a better tradeoff between PAPR reduction and bit‐error rate (BER) performance than the exponential function and error function companding schemes. Copyright © 2010 John Wiley & Sons, Ltd.

Trapezoidal companding scheme for peak-to-average power ratio reduction of OFDM signals

A novel nonlinear companding scheme is proposed to reduce the peak-to-average power ratio (PAPR) of orthogonal frequency division multiplexing (OFDM) signals. This scheme can transform the original Gaussian-distributed OFDM signals into trapezoidal-distributed. Moreover, by properly choosing variable parameters of the proposed scheme, it can achieve an effective trade-off between PAPR reduction and bit error rate performance, which gives the OFDM system more design flexibility.

Two Novel Nonlinear Companding Schemes With Iterative Receiver to Reduce PAPR in Multi-Carrier Modulation Systems

Companding transform is an efficient and simple method to reduce the Peak-to-Average Power Ratio (PAPR) for Multi-Carrier Modulation (MCM) systems. But if the MCM signal is only simply operated by inverse companding transform at the receiver, the resultant spectrum may exhibit severe in-band and out-of-band radiation of the distortion components, and considerable peak regrowth by excessive channel noises etc. In order to prevent these problems from occurring, in this paper, two novel nonlinear companding schemes with a iterative receiver are proposed to reduce the PAPR. By transforming the amplitude or power of the original MCM signals into uniform distributed signals, the novel schemes can effectively reduce PAPR for different modulation formats and sub-carrier sizes. Despite moderate complexity increasing at the receiver, but it is especially suitable to be combined with iterative channel estimation. Computer simulation results show that the proposed schemes can offer good system performances without any bandwidth expansion.

Reducing the Peak-to-Average Power Ratio of OFDM system with low complexity

This paper proposes a companding scheme, where small signals are enlarged and large signals are reduced, to reduce the Peak-to-Average Power Ratio(PAPR). Computer simulation results show that the proposed technique has two advantages at least when compared with the conventional methods such as partial transmit sequence, selective mapping and the previous companding. First, it gets better PAPR performances with a lower complexity. Second, the scheme achieves greater performances gain with hardly any damnification of OFDM signals in some degree.

Exponential Companding Technique for PAPR Reduction in OFDM Systems

In this paper, a new nonlinear companding technique, called "exponential companding", is proposed to reduce the high Peak-to-Average Power Ratio (PAPR) of Orthogonal Frequency Division Multiplexing (OFDM) signals. Unlike the /spl mu/-law companding scheme, which enlarges only small signals so that increases the average power, the schemes based on exponential companding technique adjust both large and small signals and can keep the average power at the same level. By transforming the original OFDM signals into uniformly distributed signals (with a specific degree), the exponential companding schemes can effectively reduce PAPR for different modulation formats and sub-carrier sizes. Moreover, many PAPR reduction schemes, such as /spl mu/-law companding scheme, cause spectrum side-lobes generation, but the exponential companding schemes cause less spectrum side-lobes. Computer simulations, which consider a baseband OFDM system with Additive White Gaussian Noise (AWGN) channels and a Solid State Power Amplifier (SSPA), show that the proposed exponential companding schemes can offer better PAPR reduction, Bit Error Rate (BER), and phase error performance than the /spl mu/-law companding scheme.

Nonlinear Companding Transform for Reducing Peak-to-Average Power Ratio of OFDM Signals

A new nonlinear companding transform scheme is proposed to reduce the peak-to-average ratio (PAPR) in orthogonal frequency division multiplexing (OFDM) signals. By exploiting statistical distribution of transmitted OFDM signals, the proposed scheme effectively reduces the PAPR by compressing the peak signals and expanding the small signals, while maintaining the average power unchanged by properly choosing transform parameters. The fact that the proposed companding scheme is described by a single-valued function allows to be transformed before amplification and to be restored the signals at the receiver. The proposed scheme can be applicable with any modulation format and subcarriers. Our simulations results confirm that the suggested scheme exhibits a good ability to reduce PAPR and a good BER performance with a solid state power amplifier (SSPA) in an additive white Gaussian noise (AWGN) channel.

High-resolution source coding for non-difference distortion measures: multidimensional companding

Entropy-coded vector quantization is studied using high-resolution multidimensional companding over a class of nondifference distortion measures. For distortion measures which are locally quadratic a rigorous derivation of the asymptotic distortion and entropy-coded rate of multidimensional companders is given along with conditions for the optimal choice of the compressor function. This optimum compressor, when it exists, depends on the distortion measure but not on the source distribution. The rate-distortion performance of the companding scheme is studied using an asymptotic expression for the rate-distortion function which parallels the Shannon lower bound for difference distortion measures. It is proved that the high-resolution performance of the scheme is arbitrarily close to the rate-distortion limit for large quantizer dimensions if the compressor function and the lattice quantizer used in the companding scheme are optimal, extending an analogous statement for entropy-coded lattice quantization and MSE distortion. The companding approach is applied to obtain a high-resolution quantizing scheme for noisy sources.

Hybrid Companding Delta Modulation

We present a reasonably complete account of an improved adaptive delta modulation (ADM) system called hybrid companding delta modulation (HCDM). The HCDM system that is far superior to continuously variable slope DM (CVSD) or constant factor DM (CFDM) is advantageous, particularly for speech coding. It employs both syllabic and instantaneous companding schemes. Performance analysis of the system has been done and verified by computer simulation. In getting the mathematical formula for HCDM granular noise, a new method based on amplitude distribution is proposed. Optimization of the system parameter values by simulation is also discussed. In addition, an efficient method of hardware implementation is considered.

Companding and random quantization in several dimensions

The problem of implementing multidimensional quantizers is discussed. A general equation is derived that can be used to evaluate the performance of multidimensional compandors. It is demonstrated that the optimal compandor must be conformal almost everywhere. An example is given to show that asymptotically optimal performance could be obtained through nonconformal companding schemes. Random quantizers are discussed and two techniques are evaluated for reducing memory and computation time in the implementation of such devices.