Convolutional Code Based PAPR Reduction Scheme for Multicarrier Transmission with Higher Number of Subcarriers

Multicarrier transmission technique has become a prominent transmission technique in high-speed wireless communication systems. It is due to its frequency diversity,small inter-symbol interference in the multipath fading channel, simple equalizer structure, and high bandwidth efficiency. Nevertheless, in thetime domain, multicarrier transmission signal has high PAPR (Peak-to-Average Power Ratio) thatinterprets to low power amplifier efficiencies. To decrease the PAPR, a CCSLM (Convolutional Code Selective Mapping) scheme for multicarrier transmission with a high number of subcarriers is proposed in this paper. Proposed scheme is based on SLM method and employs interleaver and convolutional coding. Related works on the PAPR reduction have considered either 128 or 256 number of subcarriers. However, PAPR of multicarrier transmission signal will increase as a number of subcarriers increases. The proposed method achieves significant PAPR reduction for ahigher number of subcarriers as well as better power amplifier efficiency. Simulation outcomes validate the usefulness of projected scheme.


INTRODUCTION
M ulticarrier transmission technique has several advantages over the single-carrier scheme, including high ratetransmission,frequency diversity, and small inter-symbol interference in the multipath fading channel. Therefore, it is widely used in several telecommunication standards e.g. ADSL (Asymmetric Digital Subscriber Line), DAB, and WLAN (Wireless Local Area Network) [1]. However, a major drawback of multicarrier transmission schemes is elevated PAPR, which consequences inin-band distortion that impairs BER (Bit Error Rate), and out-of-band radiation that impedes with adjacent frequency bands [2]. To counter this high PAPR of the multicarrier transmission signal, the HPA (High Power Amplifier) needs to be operated in or near its linear region, however, this leads to small power efficiency and costly transmitter [3]. Therefore, it is obligatory to address high PAPR problem of multicarrier transmission technique in order to make multicarrier transmission cost effective in low-cost applications.
In this paper, CCSLM scheme for MC-CDMA systems is suggested to decrease the PAPR with 256,512,…,4096 a number of subcarriers. The proposed method is based on SLM method and employs interleaver and convolutional coding. The 2 u different candidate data sequences of theoriginal data sequence, all corresponding to thesame information as the original data sequence, are first generated by adding u-tuple index bits to it, then processed by the interleaver and convolutional coding.
Utilization of the interleaver and the convolutional codingcauses every sequence further random and decreases the probability of in-phase summation of subcarriers, which consecutively, enhances the probability of PAPR diminution. Proposed method can achieve noteworthy PAPR diminutionwith better power efficiency, and also shunrequirement for the sideinformation transmission.
The remaining of this paper is prepared as pursues. In Section 2, system model for multicarrier transmission is discussed. Section 3 presents efficiency of the HPA in detail. In Section 4, conventional SLM method, CCSLM method and computational complexityare debated. The simulations and their outcomes are debated in Section 5. Section 6 presents power efficiency analysis of CCSLM method and to end with,some conclusions aremade in Section 7.

SYSTEM MODEL
where MC-CDMA symbol period anda total number of users are represented by Tand E, respectively. The PAPR of a baseband multicarrier transmission signal in Equation (1) can be described as the ratio of largest instantaneous peak power to average power of multicarrier transmission signal [1][2][3][4][5][6][7] and it can be expressed as: where average power is represented by P av that can be given as: Where E(|b(n)| 2 ) represents mathematical expectation operator.
It is indispensable to estimate statistical characteristics of PAPR because user data are non-deterministicin nature.

CCDF (Complementary Cumulative Distribution Function)
is the most traditional way foranalyses of PAPR and it is explained as the probability of PAPR above a definite level w [17].

HIGH POWER AMPLIFIER EFFICIENCY
Consider the most linear HPA, that is Class A amplifier, which devours a steady quantityof power, P DC , in spite ofinput power. Efficiency of HPA, η, is describedas ratio of the average output power P out,avg to P DC ; that is: For a known multicarrier transmission signal, average input power must be fine-tuned so thatpeaks of thesignalare barely clipped. That is, an input IBO must have to be applied to signal before amplification.

CONVOLUTIONAL CODE SLM METHOD
The CCSLM method is based on convolutional code and SLM method; therefore it is convenient to first briefly explain the convolutional code and conventional SLM method prior to explaining the CCSLM method, respectively.

Convolutional Code
The convolutional codes integrateerror detection and correctionability, which make it the enviable option to diminish the PAPR for multicarrier transmission systems [16]. A multicarrier transmission signal is the addition of several data symbols modulated ontosub-carriers. In Elias created binary convolutional codes [18]. They belong to a particular class of error control codes in which encoding can seem as filtering or convolution operation.
Unlikeblock encoder, a convolutional encoder is a memory device [19]. Table 1 listed the parameters that are needed to explain a convolutional encoder. Fig. 2 illustrates nonsystematic feedforward convolutional encoder, which is used in this paper due to their great free distance and enhanced presentation with Viterbi decoding contrasted to systematic convolutional encoders [20]. After that, a data block having the least PAPR value in the modified set of data blocks κ (n) is picked for transmission [15][16][17]21].

CCSLM Method
A CCSLM method uses u-tuple of u index bits trailed by an interleaver and convolutional code is proposed in this paper. This methodhas anidenticalconcept for PAPR diminution as that of SLM scheme [8]; however, it also has the error-correction capability, as it employs

Computational Complexity
One of the most important parameters to exhibit performance of PAPR diminution method is computational complexity. In general, PAPR diminution potential of more complicated schemes with fewer unwanted effects is superior tosimple ones. The computational complexity of CCSLM scheme is definitely higher than SLM as it uses interleaver and convolutional code to diminish PAPR.
However, the PAPR of a multicarrier transmission signal will increase as the number of subcarriers increases.
Therefore, the projected CCSLM scheme is contrasted with conventional SLM for M=256,512,…,4096 number of subcarriers. The PAPR performance of the CCSLM method for multicarrier transmission systems has been compared with conventional SLM method in Fig. 4

POWER EFFICIENCY OF NESLM METHOD
As stated in Section 3 that Class A HPAs have maximum power efficiency and that is 50%. Therefore, an ideal model for Class A HPA to analyze the power efficiency of CCSLM method is considered. The PAPR performance comparison of CCSLM method with RPA method [12] and conventional SLM method has been plotted for the multicarrier transmission systems in Fig. 3 also be observed among number of u index bits and PAPR diminution in the simulation results. That is larger the number of index bits higher will be the PAPR reduction but system will be more complex than the system with alower number of index bits. Therefore, a moderate number of index bit should be chosen that can give better PAPR reduction performance with theless complex system.

ACKNOWLEDGEMENT
The authors thank the anonymous reviewers and the editors for their many helpful suggestions.