Désiré Guel

Analysis and comparison of clipping techniques for OFDM Peak-to-Average Power Ratio reduction

One of the main disadvantages of Orthogonal Frequency Division Multiplexing (OFDM) is its high Peak-to-Average Power Ratio (PAPR), which significantly reduces the efficiency of the High Power Amplifier (HPA). Due to the simplest way for PAPR reduction, clipping techniques are frequently used in practice for OFDM PAPR reduction. In this paper, Classical-Clipping (CC), Heavyside-Clipping (HC), Deep-Clipping (DC) and Smooth-Clipping (SC) are implemented for reducing the PAPR of an OFDM system. The effectiveness of these techniques in terms of PAPR-reduction, average power variation and total system degradation are evaluated. From the analysis and simulation results, it is very difficult to say which of these four is the best. But, because of its flexibility in PAPR reduction, in total system degradation and in average power variation, DC technique appears to be the best of the four.

Tone reservation technique based on geometric method for orthogonal frequency division multiplexing peak-to-average power ratio reduction

Orthogonal frequency division multiplexing (OFDM), has recently attracted considerable attention because of its features to combat delay spread or frequency selective fading of wireless or wireline channels. One of the major drawbacks of OFDM is the peak-to-average power ratio (PAPR) which leads to an inefficient use of high power amplifiers (HPA) in communications systems. The authors first briefly review the principle of geometric method (GM) that they previously proposed. This method has a couple of well identified drawbacks as the necessity of adding a radio frequency (RF) filter, the increasing of power amplifier band and the bit error rate degradation if PAPR is largely mitigated. Consequently we propose in this paper a new method to improve GM performance. This method mixes tone reservation (TR) technique and GM called ‘TR-GM’ in order to efficiency reduce the high PAPR of OFDM signals. In addition, the proposed TR-GM technique is compared with TR based on second order cone programming (‘TR-SOCP’) and TR based on the gradient-project (‘TR-GP’) techniques in terms of PAPR reduction, average power variation and complexity. The comparative study has shown that, the proposed TR technique seems to be a good compromise between PAPR reduction, complexity, and average power variation.

OFDM PAPR Reduction Based on Nonlinear Functions without BER Degradation and Out-of-Band Emission

Peak-to-Average Power Ratio (PAPR) reduction techniques based on nonlinear functions (clipping, companding techniques, etc) are the most straightforward PAPR reduction methods. These techniques reduce the PAPR at the cost of generating distortions. In this paper, we prove basing on Bussgang theorem [1] that in context of PAPR reduction techniques using nonlinear functions, the uncorrelated component resulting in nonlinear process of the input signal amplitude is the component for PAPR reduction. Based on this result, we propose to reduce PAPR of multicarrier systems by exploiting the unused subcarriers embedded in their spectrums to carry the component for PAPR reduction without BER degradation and without Out-Of-Band (OOB) emission.Later in the paper, the classical clipping function is used to reduce the PAPR of the Wireless Local Area Networks (WLAN) system based on IEEE 802.11a/g standard whitout BER degradation and OOB emission.

A Geometric Method for Papr Reduction in a Signal Adding Context for OFDM Signals

This paper presents a new technique for OFDM signal PAPR reduction by adding an artificial signal in order to restrict the envelope of the resulting signal. The algorithm is presented, some simulation results and a complexity study are given. According to these results, the new method outperforms the conclusions presented in [1]. The PAPR is reduced of about 2 dB for a CCDF value of 10-3. In term of complexity, the presented method is similar to [1] which realizes 7 * additions and 9 * multiplications while geometric technique realizes 5 * additions and 10 *N multiplications (represents the number of samples per OFDM symbol).

Performance comparison of PRC based PAPR reduction schemes for WiLAN Systems

High peak to average power ratio (PAPR) is a main area of concern in multi-carrier communications as in orthogonal frequency division multiplexing (OFDM) modulated transmission. Several techniques have been devised to reduce the PAPR of the OFDM signal. One of these PAPR reduction techniques is based on peak reducing carriers (PRC) concept where a set of sub-carriers is not used to transmit information but to reduce the temporal signals peak. There exist different methods to generate the peak reducing carriers like geometric method, gradient method and second order cone programming (SOCP) based optimization method. This paper compares the performance of these three PRC methods for a wireless local area network (WiLAN) system in terms of PAPR reduction capabilities and computational complexities while justifying that neither in-band nor out-of-band interference is generated upon the application of these methods. For an IEEE 802.11g standard, it is found that, on average, SOCP reduces ¿ 2.5 dB more PAPR than geometric method but its complexity is 18 times the complexity of geometric method. While gradient method lies in between these two methods regarding performance and complexity criteria, this paper presents a trade-off between PAPR reduction performance and complexity for three different PRC implementation schemes.

Frequency based asymptotic distribution of the PAPR for geometric adding signal approach in OFDM signals context

The distribution of the peak-to-average power ratio (PAPR) for geometric method of PAPR reduction in orthogonal frequency-division multiplexing (OFDM) signals is evaluated in order to analyse the influence of the carrier frequency of adding signal on the PAPR reduction. Assuming that the baseband OFDM signal is characterized as a band-limited complex Gaussian process, we first recall the principle of the geometric approach for PAPR reduction, and we further develop an asymptotic distribution of the PAPR for the method of PAPR reduction.

Artificial signals addition for reducing PAPR of OFDM systems

One of the major drawbacks of OFDM modulation is the large envelope fluctuations which either result in an inefficient use of high power amplifiers (HPA) or decreased transmission system performance. Peak-to-Average Power Ratio (PAPR) is a very well known measure of the envelope fluctuations and has become the cost function used to evaluate and design OFDM systems. In this paper, we propose a PAPR reduction scheme known as adding signal method for which the principle is to reduce the PAPR of the OFDM signals by adding several artificial signals. It is an extension of the method that we have proposed in. The major advantages of this technique include downward compatibility, no performance degradation and no transmission of side information. A method is said to be downward compatibility if its implementation in a transmitter does not imply modifications in the associated receiver. According to simulation results, the method outperforms the PAPR-reduction performance presented. For example, at 10-2 of the Complementary Cumulative Distribution Function (CCDF), the PAPR is reduced about 3.5 dB for 5 artificial signals addition, whereas this reduction is about 1.5 dB for method which is the case of one artificial signal addition.