Why papr is high in ofdm

The demand for data transmission in mobile communication has increased consistently. OFDM system has gained interest in the fourth-generation mobile communication due to its ability to provide high bandwidth efficiency and high data rate in both digital audio and video broadcasting wireless communication.

The basic principle of OFDM is to split a high-data rate stream into a number of lower data rate streams in parallel using several orthogonal subcarriers. When the subcarriers have appropriate spacing and satisfy the orthogonality, their spectra will overlap [ 1 , 2 , 3 ]. If the product of two deterministic signals is equal to zero, these signals are said to be orthogonal to each other [ 1 ].

OFDM offers many advantages over carrier modulation; however, the major difficulty with the scheme is the high peak-to-average power ratio PAPR that distorts the signal if the transmitter contains nonlinear components such as power amplifier, affects the signal and results in the attenuation of the received signal [ 4 ]. The high PAPR of OFDM means that if the signal is not to be distorted, many of the components in the transmitter and receiver must have a wide dynamic range. The output amplifier of the transmitter must be very linear over a wide range of signal levels.

In wireless system, the expense and power consumption of these amplifiers are often the important design constraints [ 5 , 6 ]. Moreover, the presence of a large number of subcarriers with varying amplitude results in high peak-to-average power ratio of the system OFDM and has implication in the efficiency of the radio frequency amplifier. This degrades the bit error rate and increases the cost of the system. To respond to the abovementioned problems, different methods and techniques were proposed by researchers such as coding techniques, tone injection, filtering, oversampling and multiple signal representation.

The main purpose of this study is to propose techniques for the reduction of peak-to-average power ratio in OFDM system with emphasis on 4G network.

In this paper, two techniques are proposed to solve the problem observed when using the OFDM system: the peak windowing and the clipping techniques. The behavior of the peak-to-average power ratio and bit error rate using reduction techniques were emphasized in this paper: first, this study considered the clipping technique by analyzing the performance of the system by allocating different clipping levels in the system, and analyzing the bit error rate and signal-to-noise ratio for clipped and conventional OFDM; second, designed and analyzed the reduction on PAPR using peak windowing technique.

To come out with a good reduction in PAPR, researchers proposed the recursive Golay complementary sequence [ 7 ] and the results showed that the PAPR of the sequence is bounded up to 3. The author of [ 8 ] proposed a PAPR reduction method with low computation complexity based on a combination of cuckoo search optimization algorithm with peak windowing scheme in OFDM system.

In [ 9 ], the author proposed that new segmentation schemes to enhance the PAPR mitigation performance of the peak windowing algorithm rely upon the number of partitioned sub-blocks, the number of the phase rotation vectors, and the kind of the segmentation scheme utilized.

The research proposed simple techniques for the reduction of high peak-to-average power ratio based on clipping and differential scaling, in orthogonal frequency division multiplexing OFDM. The proposed up- and downscaling techniques were to achieve PAPR reduction of the order of 8. A reduction of 3. The performance comparison of two clipping-based filtering methods for PAPR reduction in OFDM signal [ 11 ] was proposed to solve the major generic problem of OFDM techniques which is high peak-to-average power ratio defined as the ratio of the peak power to the average power of the OFDM signal [ 12 ].

To solve the main problem in OFDM, the high peak-to-average power ratio, using windowing technique and to improve the BER, the technique proposed is Kaiser and Hamming which uses cumulative distribution function.

The power spectral frequency is same for different normalized frequency but they are equal for maximum value. X N represents the transmitted information in the n th subcarriers and N the number of subcarriers.

Normally, the instantaneous output of the OFDM system has a large fluctuation compared to single carrier system. Windowing consists of multiplying the signal by finite length window with amptitude that varies smoothly toward zero at the edges [ 15 ]. In this study, we considered three windows:. Considering the envelop of the OFDM signal to be Se t and the window function Wf, the function is expressed as [ 16 , 17 ]. The clipping techniques used reduce PAPR by clipping the high peak of the OFDM signals by limiting the peak amplitude value to the threshold value [ 18 ].

Mathematically, clipping techniques can be defined as. The modified PAPR resulting from clipping can be expressed as. Amplitude above the threshold value is clipped and information is lost. Due to the nonlinear operation, clipping causes the in-band distortion and out-band radiation. Due to the in-band distortion, BER performance is reduced [ 19 , 20 ]. The clipping method was used to eliminate the peak values of the power and consider the BER performance.

Table 1 shows the simulation parameters used. The results highlighted in Fig. The tool used for the evaluation of the PAPR is the complementary cumulative distribution function CCDF to estimate the bound for the minimum number of redundancy bits.

From the results above, one can observe the contribution of the clipping technique when comparing with the conventional OFDM. As mentioned previously, one of the parameters that can influence the PAPR is the number of subcarriers; from Fig. In a similar comparison considering the number of subcarrier to be equal to see Fig. Therefore, when increasing the number of subcarriers, the OFDM signal degraded and then distortion and noises were observed.

International Conference on Computing and Communication Systems. Authors Authors and affiliations M. Sumithra M. Conference paper. This is a preview of subscription content, log in to check access. Bauml, R. Foomooljareon, P. Schulze, H. Yin, H. Bonaccorso, M. Prasad, R. Rana, M. Paiement, R. Define the cost function from Equation Initialize parameters and of the SCF scheme.

Calculate frequency-domain clipping noise. Get the label data from Equation Update coefficients according to Adam algorithm. Algorithm 1. Table 1. Figure 2. Figure 3. Figure 4. Comparison of BER performance between the proposed scheme and other schemes.

Figure 5. BER performance of the proposed scheme under different weight. Figure 6. References X. Liu, X. Zhai, W. Lu, and C. Liu and X. Vappangi and V. Iraqi and A. Xu and I. Hu, K.

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