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the transmitter architecture for N-x-OFDMA system with two stages of Noise shaping process is shown in fig.2.

Let us consider = 0, 1…N-1 be the input block of frequency domain modulated symbols. At here N is the

number of Symbols in each Component Carrier (CC). If clipping is performed with the Nyquist sampling rate in

the discrete time domain it may affect the high frequency components in the in-band and the clipping noise

directly sits in the desired in-band which may degrade the BER performance. An oversampling rate factor of L ≥4 will be used so that the PAR before D/A conversion accurately describes the one after D/A. To examine the

out-band distortions introduced by the noise shaping algorithm, Oversampling is also necessary.

--- represents the oversampled discrete-time domain OFDM symbols . it can be calculated as follows

Fig. 3 shows the Block diagram of the First stage Noise shaping process . either Cartesian or polar clipping can be used To clip the peak of teh signal, the In-phase and qudrrature components are clipped independently with

the Cartesian clipping.the phase of signal will be preserved and the magnitude will be clipped by using polar

clipping.with polar clipping. At here we using the polar clipping to limit the PAPR of the signal. the polar

clipping provides better results in terms of overall signal distortion (i.e. lower EVM and ACLR performance).

the PAPR of the signal can be maintained at a desired level By selecting an appropriate threshold Amax. Polar

clipping of the time domain discrete data ------- with clipping threshold Amax results in the following equation.

To generate the clipping noise , polar clipped signal is subtracted from the delayed version of the incoming

OFDM symbols

the noise shaping low pass filter has the characteristics similar to that of a single carrier before it has been

unconverted. Raised-cosine function adopted the Spectrum shaping Low pass filter structure with roll-factor β

= 0.22.

At here h(n) represents impulse response of the Raised cosine filter.It is given by

At last a signal with lower PAPR is created by substracting spectrally shaped clipping noise from the delayed

version of the incoming OFDM signal.

The above technique doesn’t involves any hard clipping on the OFDM signal. So there will be minimal impact

on the in-band and out-band performance .After that individual component carriers are frequency shifted to

the band of interest in the given spectrum. Time domain data of each Component Carrier can be described as y

(i, j), here i is the ith Component carrier and j is the sub-frame.

Then the PAPR of aggregated k component carriers can be represented as

since few subcarriers of CC’s may add up constructively in time domain after Carrier aggregation ,So PAPR of

the aggregated carriers may increase even after clipping individual component carriers using Noise shaping

technique. We amy face this effect if the component carriers are Contiguous. To achieve the desired PAPR

further iterations of Noise shaping technique are required.



The clipping is performed on sufficiently oversampled (R≥ 4) pass band carrier aggregated OFDM signals By

the second iteration of noise shaping process .then Oversampling results in lower in-band distortion upon

clipping the pass band signal because the clipping noise will transit into out-band which could be further

filtered out.

The Clipping noise is generated by subtracting the polar clipped signal from the delayed version of theComposite pass band signal. It is further spectrally shaped by using noise shaping filter. filtering has

to be done for multiple frequency components in the spectrum to support multiple CC’s .The

spectrum of the complex composite signal might be asymmetrical . Then the number of taps required

to implement such filter is often quite high. Fig. 4.illustrates the process , the pass band clipping noise

will be down converted to baseband and perform low pass filtering ,then up convert the filtered

noise back to its carrier frequency. This approach provides more flexible multi-band filtering capability

that supports dynamically changing carrier configurations.

........ represents the inputs to the noise shaping filter. the down converted output noise with k component

carriers is given by

by raising cosine function The down converted clipping noise will be spectrally shaped . In next

step we do frequency shift of each filtered noise

component from baseband to corresponding center frequency. ........ represents the inputs to the noise shaping

filter. then the up converted noise output with k component carriers is given by

By frequency translation the individual k component carriers are summed to form composite pass band

clipping noise.

By noise shaping, the spectrally confined clipping noise is subtracted from an appropriately delayed version of

the CFR input signal which results in desired PAPR.We simulates different scenarios using contiguous & non-contiguous frequency bands for carrier aggregation.

PAPR performance with and without Noise shaping technique is evaluated using the below equation.

PAPR performance can be compared by using Complementary cumulative distribution function (CCDF),It

shows the probability of the signal PAPR > PAPR0.



simulation of different scenarios are described inThis section. At here we considered 5 component carries, of

each component carrier has bandwidth of 5 MHz ,2560 subcarriers and each component carrier input 512, 16

QAM symbols.. So the total aggregated system bandwidth of 25 MHz Raised cosine filter with

β =0.22 is used for Noise Shaping.

Fig. 5 illustartes the comparison in PAPR performance between original signal, with only a single stage

Noise shaping process and the two stage Noise shaping process using QAM modulation of contiguous 5

CC’s aggregated

Fig. 6 illustartes the comparison in PAPR performance between original, single stage and two stages Noise

shaping process using QAM modulation of non-contiguous 2 CC’s aggregated (1st and 4th component carriers are

considered in simulation).

The approach will be similar to determine the PAPR performance of inter band non-contiguous carrier

aggregated OFDM signals.

Fig. 7 illustartes the power spectral density of original signal and the clipped signal of 5 CC’s aggregated. It

could be seen that the out of band spectral emissions are lower using the proposed two stages of Noise shaping process.

Fig. 8 illustartes the power spectral density of original signal and the clipped signal of 2 Noncontiguous CC’s

aggregated. It could be seen that the Out of band spectral emissions are lower using the proposed two stages of

Noise shaping process.

1st and 4th component carriers of 5MHz bandwidth each are considered in simulation.

At here we have proposed a two stage Noise shaping process to reduce the PAPR while satisfying EVM andACLR /spectral mask constraints. For contiguous bands scenario the first stage of Noise shaping process

reduces the PAPR of the individual component carriers to some optimized threshold but the effect will be

minimal since after carrier aggregation some of the subcarriers of different CC’s may add up constructivelyresulting in little improvement in PAPR. Then the second Noise shaping process is utilized to further reduce

the PAPR to desired level.For non-contiguous bands scenario, since the Component carriers are far apart, the

first noise shaping process itself results in higher PAPR improvement even after carrier aggregation since the

impact of component carriers adding up constructively in time domain will be minimal. The improvement in

PAPR with the use of two stages of Noise shaping process will be better in case of Non-contiguous scenario

compared to the contiguous.

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