a hybrid technique for papr reduction & capacity improvement in ofdm … · 2018-11-16 · a...

A Hybrid Technique for PAPR Reduction & Capacity Improvement

in OFDM System

1 Rajinder Kumar, 2 Dr.Kapil Gupta 1,2 Electronics & Communication Engineering. Deptt., M.M. Deemed to be University, Mullana

Abstract— Orthogonal Frequency Division Multiplexing (OFDM) is the technique based on parallel

transmission and it converts frequency selective fading channel into N flat fading channels, where N is the

number of sub-carriers. The main problem in OFDM is high PAPR. The PAPR reduction can be done by

improvement in capacity of system. The objective of this work is to implement a hybrid technique for reducing

high PAPR value in OFDM system. The value of PAPR improves under different modulation formats by using

a hybrid technique. The capacity is improved by optimization algorithm that helps to improve system

performance. The paper presents the performance comparison of proposed hybrid technique for reducing high

PAPR value with amplitude clipping and selective mapping techniques. The system works on QPSK, 16 QAM

and 64 QAM modulation formats. All simulations are done in MATLAB.

Keywords- OFDM System, PAPR in OFDM, BER under ISI etc.

I. INTRODUCTION

With the expansion of mobile devices, the demand of high data rate & Quality of Service (QOS)

increases rapidly. So, 3GPP has specified new standards for mobile communication on GSM (Global System for

mobile communication)/EDGE and Universal Mobile Telecommunications System (UMTS). In the

communication system, high data rate networks are the necessity of human being, therefore it is important for

research. The massive number of applications concerning high data rate made it necessary to attain the finest

achievable performance with the least probable cost. These high data rate network occurrence from the survival

of multipath channels. This causes the reality that receiver is being not able to separate unlike symbols because

of delay occurred in each copy of symbol which is transmitted & arrived at receiver. Thus it requires equalizers

at receivers end [1]. The solution for this problem is provided by use of OFDM system.

The OFDM signal transmission is isolated into minor sub-groups; each sub-band is having a low split

information rate. The primary issue is Inter-symbol Interference (ISI) which is stayed away from by expansion

of a watch period between succeeding signals [2]. This is the cost to be paid for this sort of collector structures.

Though OFDM takes care of this issue yet it presents new issues itself.

The problem of high PAPR value in the system decreases energy efficiency of system [3]. The problem

of high traffic requires high energy usage in the network which decreases the channel capacity of system.

PAPR is defined as the ratio between the maximum powers of a sample in a given OFDM transmit

symbol to the average power of that OFDM symbol. It is expressed in the units of dB. In a multicarrier system,

when the different sub-carriers are out of phase with each other PAPR occurs. When all the points achieve the

maximum value simultaneously; this will cause the output envelope to abruptly rise which causes a ‘peak’ in the

output envelope. The peak value of the system can be very high as compared to the average of the whole system

because large number of independently modulated subcarriers in an OFDM system is present; this ratio of the

peak to average power value is termed as Peak-to-Average Power Ratio. Many different techniques had been

proposed to deal with the high PAPR problem for OFDM, they are Selective Mapping (SLM) [4,5], Partial

Transmit Sequences (PTS) [6], clipping [7,8].

JASC: Journal of Applied Science and Computations

Volume 5, Issue 11, November/2018

ISSN NO: 1076-5131

Page No:619

The paper is organized as follows. Section II, contains the introduction of OFDM system. Section III

explains various PAPR reduction techniques. Section IV, provides the description of proposed system and

explain the concept of hybrid technique for PAPR reduction with capacity improvement by optimization

algorithm. The results are presented in section V. Finally, conclusion is made in section VI.

II. INTRODUCTION TO OFDM SYSTEM

The block diagram of OFDM system model is shown in figure 1.

Figure 1: OFDM System Model [2]

The discrete time baseband OFDM system with subcarriers consists of transmitter, channel and receiver blocks.

1. Transmitter

In this model, a block of input bits (symbols) are modulated by M-ary data modulators and these

symbols are transferred to the serial to parallel converter. Different types of data modulator can be used such as

M-PSK & M-QAM depending upon system requirement. The complex parallel data symbols obtained by using

modulation techniques are then passed to N-point IFFT block.

2. Addition of Guard Band

To remove Inter Symbol interference (ISI) which is established between consecutive OFDM symbols, a

guard interval is used in OFDM system. ISI is caused by the delay spread of multipath channel in OFDM

symbols. To remove ISI exclusively a guard band interval with no signal transmission can be used but it

can generate ICI because of higher spectral components, results due to quickly change of waveform. The guard

interval can be used in two ways- zero padding (ZP) and cyclic prefix (CP) [9]. In cyclic prefix, small part or

portion of transmitted symbols are utilized and repeat that small portion as the prefix of transmitted symbol.

The length of the CP should take in such a way so that it should be greater than delay spread of a multipath

channel. If the CP is less than delay spread of multipath channel then the beginning part of the next OFDM

symbol will be altered by the ending part of preceding OFDM symbol, causes ISI. The cyclic prefix larger than

the delay spread of the multipath channel maintains the orthogonality among the subcarriers.

In zero padding top and bottom portion of the transmitted symbols are filled with zeros. The actual

length of an OFDM symbol containing CP is larger than that of an OFDM symbol containing ZP. In

comparison with an OFDM symbol containing CP, an OFDM symbol containing ZP has the larger out-of-band

power and Power Spectral Density (PSD) with the smaller in to band ripple that allowing more power to be

used for transmission with the fixed peak transmission power.



ISSN NO: 1076-5131

Page No:620

3. Channel Model

The observable fact of noise and multipath environment can be calculated by using channel

model. Noise can be generated by adding a small number of random data to the OFDM symbol and

multipath environment can be generated by adding attenuated and delayed copies of the OFDM signal. The

tap coefficients h(t) are modelled as zero mean complex Gaussian random variables having unit variance.

Rayleigh fading model provide a suitable background of wireless signal.

4. Receiver

Inverse operation of the transmitter is performed at the receiver end. The very first step is to remove

guard interval of OFDM symbol. Then, these unguarded OFDM symbol passed through FFT block. The FFT

converts these parallel OFDM data streams into frequency domain. The OFDM signal �(�) can be expressed as:

�(�) = � ��exp (�2�(�� + �∆�)�)

��

��

= exp (�2��) ∑ ��exp (�2��∆��)��

= exp(�2��) �(�), (1)

where ��, 0 ≤ � ≤ � − 1 representing data in complex-valued constellation points and �� = �� +

�∆�, 0 ≤ � ≤ � − 1, is the �� subcarrier, with �� being the lowest subcarrier frequency. The frequency

spacing between adjacent subcarriers is representing by ∆�, chosen to be 1/�� to make sure that the subcarriers

are orthogonal. If �(�) is sampled at rate � samples per second, where � is replaced by ��

�, � = 0, … � − 1,

then �(�) is represented by the sampled function �[�] expressed as:

�[�] = � �� exp ��2��

�� (2)

��

��

The fundamental principle of an OFDM system is to send the complex information symbols by set of

sinusoids. Each sinusoid conveys the information corresponding to data symbol. The superposition of these

signals forms the received signal.

III. PAPR REDUCTION TECHNIQUES

PAPR known as Peak to Average Power ratio defined as the ratio of peak power to average power.

Higher the PAPR in the system less will be stability. So, reduction of PAPR in the system is required. For this,

various techniques are presented below:

1. Clipping and Filtering

This method make use of a clipper circuit that restrictions the signal envelope to a predetermined

clipping level for the condition that the signal exceeds that level. If condition is not satisfied then the clipper

passes the signal without change. Clipping is a non-linear process that leads to both in-band and out-of-

band distortions.



ISSN NO: 1076-5131

Page No:621

The out-of-band distortion causes spectral spreading and can be eliminated by filtering the signal after

clipping but the in-band distortion can degrade the BER performance and cannot be reduced by

filtering method.

Figure 2: Clipping & Filtering Method

Figure 2 shows the block diagram of clipping & filtering approach for PAPR reduction in system. A

challenge to reduce the PAPR value is made without increasing roll-off factor by introducing clipping after pre-

coding. The pre-coding makes the envelope almost constant and then clipping reduces the peak value to any

needed level. This dual operation of pre-coding and clipping provides better PAPR than both conventional pre-

coding and clipping method. For the clipping purpose, a clipping method is presented which is based on

averaging of high amplitude samples. This clipping algorithm can be called as soft clipping or iterative clipping.

This algorithm can be applied both with normal OFDM system (without pre-coding) and with pre-coded

OFDM system.

2. Selective Mapping (SLM)

The central idea in this technique is to generate a set of sufficiently different data blocks by the

transmitter where all the data blocks represents the same information as the original data block and select the

favorable having the least PAPR for transmission. In SLM, the input data sequences are multiplied by

each of the phase sequences to generate another input symbol sequences. Each of these substitute

input data sequences are then applied to IFFT operation, and then the one with the lowest PAPR is chosen

for transmission.

Only one with the lowest PAPR is selected for transmission. The corresponding selected phase

factor also transmitted at receiver end as side information. For implementation of SLM OFDM systems, the

SLM technique needs U-IFFT operation and the number of required bits as side information is for each data

block. Therefore, the ability of PAPR reduction in SLM depends on the number of phase factors and the design

of the phase factors.

Figure 3: Selective Mapping Method

DATA SOURCE

PARTITION INTO BLOCKS AND S/P CONVERSION

SELECT ONE WITH MIN PAPR

IFFT

IFFT

IFFT

B1

B2

Bu



ISSN NO: 1076-5131

Page No:622

IV. DESCRIPTION OF PROPOSED SYSTEM

The problem of high PAPR value in the system ultimately decreases energy efficiency of system and high

traffic demands high energy usage in the network which decreases the channel capacity of system. As

amplification is non-linear orthogonality property of OFDM is lost. A hybrid PAPR reduction technique can be

used for improving the performance of system that helps to improve capacity of system.

The proposed work presents the reduction in PAPR for OFDM system in wireless frameworks by using a

hybrid technique. A Root Cosine filtering technique is used to decrease the PAPR value in system and also for

reducing noise value of signal. The improvement in selective mapping method helps to reduce PAPR of system.

An equivalent capacity is calculated & helps to improve system performance.

The PAPR for the continuous-time signal x(t) is the ratio of the maximum instantaneous power to the

average power. For the discrete-time version x[n], PAPR is expressed as:

��(�[�]) = ��|�[�]|��

�{|�[�]|�}�, (3)

Where E[.] is the expectation operator. It is worth mentioning here that PAPR is evaluated per OFDM symbol.

�(�) represents the amplitude of the complex pass band signal. Such high peaks will produce signal excursions

into nonlinear region of operation of the power amplifier (PA) at the transmitter, thereby leading to nonlinear

distortions and spectral spreading.

The proposed algorithm breaks complete data symbols into four parts and then operates it separately.

That’s make it easy to handle and operate rather than complete signal at a time. The proposed block diagram is

shown in figure 4.

Figure 4: Proposed Method

In Proposed scheme, an input data block of length N is partitioned into a number of disjoint sub-

blocks. Then each of these sub-blocks are padded with zeros and weighted by a phase factor. In first step,

sequences with low correlation or quaternary sequences of family are used as initial phase rotating vectors for

PTS scheme. In the second step, to find additional phase rotating vectors, a local search is performed

based on the initial phase vectors with good PAPR reduction performance.

It is a hybrid technique that contains combination of selective mapping and partial transmit sequence

method. Each OFDM frame is mapped to a number of U independent candidate sequences. From this one of

the lowest PAPR is selected. These independent candidate sequences can be generated by multiplying carrier

wise the initial OFDM frame X by U phase vectors.



ISSN NO: 1076-5131

Page No:623

The minimum PAPR value OFDM frame x(u) is selected as best OFDM frame and it is

transmitted. To recover the original frames at the receiver, the ‘side information’ frames are required to indicate

the vector P(u) which have to be communicated to the receiver. At that point every one of these sub-squares are

cushioned with zeros and weighted by a stage factor. ISI effect can be reduced by introducing a guard interval

(cyclic prefix). The cyclic prefix or guard interval is a periodic extension of the final section of an OFDM

symbol that is appended to the forepart of the symbol in the transmitter, and is removed at the receiver before

demodulation.

After PAPR reduction by proposed method, its power is used to calculate equivalent capacity of system.

If system has large PAPR value then its equivalent capacity is lower as compared to other. The system uses

carrier components for carrier aggregation to optimize the equivalent capacity. System uses the cognitive

bandwidth allocation because it has stronger adaptability in capturing the time-varying traffic demands of

different users, thus having higher bandwidth utilization. For capacity improvement, optimization algorithm

named water filling is used. In water-Filling calculation, which is ideal power assignment calculation in regular

OFDM framework, we utilize the aggregate power allotment by uniform stacking as the power imperative. The

allotted power in the ith subcarrier on account of the �th subcarrier due to the �th impedance requirement is

composed as (3):

�� =�

�� (3)

where � can be calculated by assuming strict equality in the �th interference constraint. The technique contains

codes for PAPR reduction as well as for capacity improvement. The complexity is decreased in this scheme

due to the cross functional use of IFFT operations. The need for transfer of side information to the receiver

without any margin for transmission errors is very crucial under the fading channels.

V. RESULTS & DISCUSSION

The figure 5, 6 & 7, shows the PAPR value for OFDM with QPSK, 16 QAM & 64 QAM modulation

respectively. It consists of total subcarrier 6817 and data block size is 16. High PAPR in OFDM is observed

due to large dynamic range of its symbol waveforms. These plot depicts the performance analysis of

system with change in modulation. The 64 QAM shows the better improvement in PAPR value as compared to

other formats as depicts in figure 8.

An OFDM signal consists of a number of independently modulated subcarriers. When these subcarriers

added up coherently results in large PAPR value. When N signals are added with the same phase, they produce a

peak power that is N times the average power. The figures 5, 6, and 7 shows the CCDF of the PAPR of OFDM

signal with N=128 subcarriers w.r.t PAPRo at the x-axis. As standard PAPR gets increased, the CCDF of signal

gets reduced. It has good PAPR reduction capability with very less bandwidth expansion and low computational

complexity. The other advantage is that the signal can be recovered at the receiver through inverse companding

transform.

Presence of large number of independently modulated sub-carriers in an OFDM system makes the peak

value of the system can be very high as compared to the average of the whole system. This ratio of the peak

to average power value is termed as Peak-to-Average Power Ratio. Coherent addition of N signals of same

phase produces a peak which is N times the average signal. The major disadvantages of a high PAPR is the

increased complexity in the analog to digital and digital to analog converter and second is the reduction is

efficiency of RF amplifiers. The PAPR value of QPSK, 16 QAM and 64 QAM is shown in form of graph curves.

The results show the performance of 64 QAM is better than QPSK and 16 QAM mode.



ISSN NO: 1076-5131

Page No:624

The figure 9 to 20, shows the CCDF of the PAPR of OFDM signal with different reduction methods

with N=128 subcarriers w.r.t PAPRo at the x-axis. It shows the performance comparison of proposed technique

with amplitude clipping and selective mapping method. In amplitude clipping method, the signal gets slightly

clipped. Due to this, it increase the PAPR value as compared to the original signal. In SLM, the input data

sequences are multiplied by each of the phase sequences to generate alternative input symbol sequences.

Each of these alternative input data sequences are then applied to IFFT operation, and then the one with

the lowest PAPR is selected for transmission. Due to this, it shows better performance as compared to

amplitude clipping.

The comparison between the CCDF of the PAPR of OFDM signal with normal OFDM

system with amplitude clipping, selective mapping coding and proposed hybrid method is shown in Table 1.

Following are the observations:

(a) All techniques performed better than clipping method.

(b) As the clipping level increases, the PAPR reduces.

(c) The proposed hybrid shows better results in terms of PAPR due to modification in pre-coded matrix.

The PAPR response is shown under different modulation formats like QPSK, 16 QAM and 64 QAM and their

comparison is shown in fig 8.

Figure 5: PAPR Value for QPSK Mode

Figure 6: PAPR Value for 16QAM Mode



ISSN NO: 1076-5131

Page No:625

Figure 7: PAPR Value for 64QAM Mode

Figure 8: PAPR Value of OFDM System under Different Formats

Figure 9: Original Signal PAPR Response for QPSK Mode

6.16

6.086.06

Modulation FormatsPA

PR

Val

ue

(d

B)

PAPR Value of OFDM Under Different Formats (dB)

QPSK 16QAM 64 QAM



ISSN NO: 1076-5131

Page No:626

Figure 10: PAPR Response using Amplitude Clipping for QPSK Mode

Figure 11: PAPR Response using Selective Mapping for QPSK Mode

Figure 12: PAPR Response using Proposed Method for QPSK Mode

Figure 13: Original Signal PAPR Response for 16 QAM Mode



ISSN NO: 1076-5131

Page No:627

Figure 14: PAPR Response using Amplitude Clipping for 16 QAM Mode

Figure 15: PAPR Response using Selective Mapping for 16 QAM Mode

Figure 16: PAPR Response using Proposed Method for 16 QAM Mode

Figure 17: Original Signal PAPR Response for 64 QAM Mode



ISSN NO: 1076-5131

Page No:628

Figure 18: PAPR Response using Amplitude Clipping for 64 QAM Mode

Figure 19: PAPR Response using Selective Mapping for 64 QAM Mode

Figure 20: PAPR Response using Proposed Method for 64 QAM Mode

The results shows the performance of 64 QAM is better in terms of PAPR reduction value. After this, various

PAPR reduction techniques are applied on OFDM signal to reduce the PAPR value of signal. The proposed

technique uses hybrid concept. Due to this, it provides better PAPR reduction value as compared to other

PAPR reduction techniques as shown in Table 1.



ISSN NO: 1076-5131

Page No:629

Table 1: Performance Comparison of PAPR Response

S.N. METHOD PAPR

VALUE

QPSK

(dB)

PAPR

VALUE

16

QAM

(dB)

PAPR

VALUE

64

QAM

(dB)

1 AMPLITUDE

CLIPPING

10.28 9.87 9.25

2 SELECTIVE

MAPPING

6.81 6.91 6.80

3 PROPOSED

TECHNIQUE

3.33 3.45 3.31

Figure 21: Capacity Response for Proposed System in QPSK Mode

Figure 22: Proposed Capacity of System in 16 QAM Mode



ISSN NO: 1076-5131

Page No:630

Figure 23: Proposed Capacity of System in 64 QAM Mode

Figure 21 to 23, shows the capacity response for proposed system in QPSK, 16 QAM and 64 QAM

modes. As the number of CCs increases, the equivalent capacity gets also increased. Capacity gets improved

when PAPR gets reduced in the system. PAPR reduction is done by use of hybrid technique.

ISI effect can be reduced by interesting a guard interval (cyclic prefix). The cyclic prefix or guard interval

is a periodic extension of the final section of an OFDM symbol that is appended to the forepart of the symbol

in the transmitter, and is removed at the receiver before demodulation.

The BER curve response of system is shown in figure 24, 25 and 26 for QPSK, 16 QAM and 64 QAM

respectively. BER is an important parameter for finding the error reducing ability of system. As value of SNR

increases, the value of BER gets decreased. The BER performance is evaluated over Rayleigh frequency

selective fading channel. It is clearly visible from graph that the pre-coded based OFDM system performs

better than the original OFDM system. This is because of diversity gain obtained via pre-coding matrix.

Figure 24: BER Response of System for QPSK Mode



ISSN NO: 1076-5131

Page No:631

Figure 25: BER Response of System using 16 QAM

Figure 26: BER Response of System using 64 QAM

VI. CONCLUSION

The concept of PAPR reduction by a hybrid method used in OFDM system is discussed. This paper is

focused on the performance analysis of OFDM systems in terms of PAPR & equivalent capacity. Different

types of modulation techniques such as QPSK, 16QAM, and 64QAM are used with different subcarriers and

different block sizes. PAPR increases in both types of FDM sub-carrier mapped with respect to the type of

modulation used. It also provides a solution for finding optimal result for high data rate downlink receiver. For

high data rate, high modulation format will be used. The main objective is to reduce high PAPR value by a

hybrid approach with improvement in capacity of system. We used all of three modulations and compared the

results of all graphs and concluded that the value of PAPR is lower in case of 64 QAM modulations with

proposed technique and capacity is higher in case of 64 QAM modulation. Both PAPR and capacity are inter-

related. If PAPR is low for system, then its capacity is better as compared to other. The BER of system is also

analyzed.

BER



ISSN NO: 1076-5131

Page No:632

REFFERENCES

[1] Yasir Rahmatallah and Seshadri Mohan, "Peak-To-Average Power Ratio Reduction in OFDM Systems: A Survey And

Taxonomy," IEEE Commun. Surveys and Tutorials, vol. 15, issue 4,pp. 1567-1592,March 2013.

[2] LaSorte, N, Barnes, W. J, Refai, H. H. , "The History of Orthogonal Frequency Division Multiplexing," in Global

Telecommunications Conference, 2008. IEEE GLOBECOM 2008. IEEE, pp.I-5, December, 2008.

[3] R. V. Nee, G. Awater, M. Morikura, H. Takanashi, M. Webster, and K. W. Halford, "New high-rate wireless LAN

standards," IEEE Commun. Mag., vol. 37, no. 12, pp. 82-88, December1966.

[4] M. Sghaier, F. Abdelkefi, and M. Siala, "Efficient embedded signaling through rotated modulation constellations for SLM-based

OFDM systems," in Communications (ICC), 2013 IEEE International Conference on, 2013, pp. 5252-5256.

[5] Kavita Singh , Kapil Gupta , “Novel Papr Reduction Techniques By Combining SLM With Clipping And Filtering Techniques

For MIMO-OFDM International Conference on Electromagnetic Interference and Compatibility System” , International Journal

of Advances in Engineering Research ,vol 13, issue 5, pp. 1-10, June 2017.

[6] G. Tan, Z. Li, J. Su, and H. Zhang, "Superimposed training for PTS-PAPR reduction in OFDM: A side information free data

recovery scheme," in Communications and Networking in China (CHINACOM), 2013 8th International ICST Conference on,

2013, pp. 694-698.

[7] L. Yao, J. He, and X. Xu, "Analysis and comparison of two clipping methods in PAPR reduction for OFDM system," in

Biomedical Engineering and Informatics (BMEI), 2012 5th International Conference on, 2012, pp. 1435-1438.

[8] Kavita Singh and Kapil Gupta , “ Paper Reduction With Amplitude Clipping & Filtering SLM & PTS Techniques for

MIMO-OFDM System : A Brief Review”, International Journal on Recent and Innovation Trends in Computing and

Communication, vol 5, issue 5, pp.1266-1270 May 2017.

[9] H. Schulze and C. luders, Theory and Applications of OFDM and CDMA. John Wiley & Sons Ltd., 2005.



ISSN NO: 1076-5131

Page No:633

A Comprehensive Survey on Software Defined Wireless Sensor

Network and its Possible Security Measures

1 S. Nagavalli, 2 Dr. G. Ramachandran 1 Research Scholar, Department of Computer and Information Sciences, Annamalai University, Annamalainagar

– 608 002, Tamil Nadu, India. 2 Assistant Professor, Department of Computer Science & Engineering, Annamalai University

Annamalainagar – 608 002, Tamil Nadu, India.

Email : [email protected] Email: [email protected]

ABSTRACT

In this paper, the comprehensive survey on the state of the art techniques used in software defined WSN in

particular to routing, data transmission, node architecture, scheduling etc. are discussed. Initially, this paper

presents a complete introduction about sensor, node architecture, and data transmission. Then, the applications

are explored by the sensing application tasks and the sensor network. Further, a comprehensive survey to

analyze the state of the art techniques was also discussed. The scheduling part used in present day sensor

network is also outlined. Finally, the paper explores three major open issues.

Keywords: WSN, Scheduling, Energy Efficiency

1.1 INTRODUCTION The Wireless Sensor Network (WSN) with numerous functions finds in widespread applications. It is also

one of an emerging technology. WSN belongs to the class of techniques which enhances human life in various

ways. WSN contains a large number of sensor nodes distributed over a large geographical area and the position

of sensor nodes need not be pre-determined. By capturing and revealing real-world phenomena, the sensors

plays a major role of providing a link between physical world and digital world, which is the primary function of

sensors. Sensors convert the physical parameters into a form that can be stored, processed, and acted upon by

digital systems. Sensor nodes in WSN are cooperative and self-organize into appropriate network infrastructure

for data communication. WSN is capable of autonomous sensing, collecting, storing, processing, communicating

and event actuation. These sensor nodes are cheap, tiny and when deployed over a larger area can self-organize

into an appropriate network infrastructure. To reveal some of the characteristics about the phenomena, sensor

nodes transform the sensed data into electric signals which are then processed and studied.

The sensor node normally transfer data to the external Base Station (BS) or sink directly or in a hop by hop

manner from one node to another until it reaches the base station or sink nodes. The sink nodes may be either

static or mobile and acts as a border between the network and the stationary base stations.

The architecture of a typical wireless sensor node in WSN is shown in Fig. 1. Sensing units are the central

element in WSN. Other important constituents of the sensor node consist of communication unit, processing

unit, power unit and other application dependents units such as a location finding system, power generator and

mobilize [6]. Sensing units are usually composed of two subunits: sensors and Analog-to-Digital Converters

(ADCs).



ISSN NO: 1076-5131

Page No:634

a hybrid technique for papr reduction & capacity improvement in ofdm … · 2018-11-16 · a...

Documents