Implementation of Digital Modulation Scheme using ...

Implementation of Digital Modulation Scheme using LabVIEW An Easy and Interactive Approach Dr. D S SURESH1 VIDYARANI K R2 SEKAR R3 and SHALINI D V4

This paper contributes a detail implementation of digital modulation and detection of original data in LabVIEW. The objective of this work is to give an outline of the digital modulation techniques used in wireless communication systems. The move to digital modulation provides more information capacity, compatibility with digital data services, advanced data security, improved quality communications, and faster system availability. This article offering different modulation techniques such as On-off keying/Amplitude shift keying, Frequency shift Keying, Binary phase shift keying, Differential phase shift keying and Quadrature Phase Shift Keying. Abstract—

Keywords— LabVIEW, On-Off Keying, Frequency Shift Keying and Phase Shift Keying.

popularity. It can be used to communicate with hardware such as DAQ, Vision, and motion control devices [2]. The basic forms of digital modulation techniques are Amplitude Shift Keying (ASK), Frequency Shift Keying (FSK) and Phase Shift Keying (PSK). In this work basic digital modulations are carried out using LabVIEW[3]. The paper [2] had demonstrated through some experimental outcome of the concepts, in the course on digital communication using the ability of the LabVIEW programming environment. The graphical programming environment is easy to learn and simple to transform an equation or concept to a working program. This work failed to demonstrate digital detection technique using the LabVIEW software. The proposed work deals with the identification of demodulation output and error is also calculated. II.

I. INTRODUCTION Fundamental to entire communication process is modulation; it is defined as the process of varying one or more properties of a periodic waveform, with a baseband signal that typically contains information to be transmitted. The main goal of modulation is to compress as much data into the least amount of spectrum possible. This is known as spectral efficiency, measures how quickly data can be transmitted in an assigned bandwidth. The unit is bit per second per Hz ((bit/s)/Hz). Multiple techniques have developed to achieve and improve spectral efficiency [1]. Nowadays most of wireless transmissions are digital, and with the limited spectrum available. In a digital communication system, the source to be transmitted is discrete both in time and amplitude. In this system, the modulating signal may be represented as a time sequence of symbols or pulses, where each symbol has ‘m’ finite states. Each symbol represents ‘n’ bits of information where n = log2m bits/symbol. The major advantage of using digital modulation technique is that the use of digital signals minimize hardware, provides greater noise exemption, easier multiplexing of various forms of information like voice, data and video. LabVIEW (Laboratory Virtual Instrumentation Engineering Workbench) developed by National Instruments (NI), is a data acquisition, instrumentation and control programming tool widely used in industry. It is a graphical programming environment with many software features and hardware options is the main reason for its increasing

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SOFTWARE DESCRIPTION

LabVIEW provides a single graphical design tool for algorithm development, embedded system design, prototyping and interfacing with real-world hardware. Additional modules have been designed to expand the real time operating system, DSP and FPGA programming. National Instruments is increasingly focusing on the capability of deploying LabVIEW code onto an increasing number of targets including devices like Phar Lap or Vx Works OS based LabVIEW Real-Time Controllers, FPGAs Pocket PCs and PDAs. The LabVIEW graphical programming environment with the included examples and documentation, makes it simple to create small applications. The practical benefit of the graphical approach is that it puts more focus on data and the operations being performed on that data, and abstracts much of the administrative complexity of computer programming such as memory allocation and language syntax. G Programming language is a Intuitive and flowchart-like dataflow programming model.  Shorter learning curve than traditional text-based programming.  Naturally represents data-driven applications with timing and parallelism. LabVIEW contains a powerful optimizing compiler that examines the block diagram and directly generates efficient machine code, avoiding the performance penalty associated

with interpreted or cross-compiled languages. From a technical standpoint, G(Graphical) is a graphical dataflow language in which nodes (operations or functions) operate on data as soon as it becomes available, rather than in the sequential line-by-line manner that most programming languages employ. Fig. 1 shows the LabVIEW front panel with associated block diagram.

function returns the value wired to ‘t’. If ‘s’ is FALSE, this function returns the value wired to ‘f’. The connector pane displays the default data types for this polymorphic function (shown in Fig.3). Implementation of OOK in LabVIEW is explained in Fig.4. To recover original binary data in LABVIEW is explained in Fig.5.

Fig.3: Select SubVI Fig.1: LabVIEW front panel with associated block diagram

III.

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METHODOLOGY

This paper describes methodology to generate ASK, FSK and PSK modulation using LabVIEW. The developed algorithm will perform modulation and detection of original digital signal. The periodic signal is varied in accordance with digital input (Binary 1010111) to achieve desired modulation. The modulated signal is send through detector circuit to recover original signal. Fig.2. shows the block diagram of system architecture.

Fig.4: Flow Diagram of ASK implementation in LabVIEW

Fig.2: Block diagram of system architecture

IV.

SYSTEM IMPLEMENTATION

This section describes method of implementation in LabVIEW. There are many types of digital modulation techniques and also their combinations depending upon the need. This work involves discussion about the prominent ones such as OOK, FSK and PSK. In PSK different deviations are implemented such as BPSK, DPSK and QPSK. The basic modulations taken for explanation is On-Off keying, Frequency shift keying and Binary shift keying. OnOff keying is a simplest form of ASK, where the carrier is selected based on the digital signal input. Here the amplitude of carrier is varied according to digital input. If binary input is ‘1’ then the carrier signal of 2V is selected. If the binary data is ‘0’ then output will be 0V [as explained in equation (1)]. OOK is most frequently used to send Morse code over RF channel. It as high spectral efficiency than FSK but more susceptible to noise. Fig.4 shows the flow diagram implementation in LabVIEW software. Identifying the data as ‘1’ or ‘0’ and selecting the required carrier is achieved with ‘select’ function from block diagram pallet. It is available in ‘Express’ sub-palette. It returns the value wired to the ‘t’ input or ‘f’ input, depending on the value of ‘s’. If ‘s’ is TRUE, this

Fig.5: Flow Diagram of ASK Detection implementation in LabVIEW

FSK is a type of frequency modulation scheme in digital modulation. Now the frequency of carrier is varied according to the binary input. If binary input is ‘1’ then the carrier signal of frequency (f1 Hz) is selected. If the binary data is ‘0’ then carrier signal of frequency (f2 Hz) is selected [as explained in equation (2)]. FSK is less sensitive to errors than ASK with minimal noise effect. FSK is used in high-frequency radio transmission. Fig.6 shows the flow diagram implementation of FSK in LabVIEW. .…..(2)

Fig.6: Flow Diagram of FSK implementation in LabVIEW

Phase Shift Keying (PSK) is a digital modulation scheme. Carrier signal changes its phase according to the binary input is called as Binary PSK (BPSK). In BPSK, the transmitted signal is a sinusoid of fixed amplitude. It has one fixed phase when the data is at one level and at the other level, phase difference by 180 degree[4]. Consider if the input is ‘1’ then the carrier is 0o phase shift and if the input is ‘0’ then the carrier with 180o phase shift is selected which is shown in constellation diagram (Fig.7 and equation (3)). Due to PSK’s simplicity, compared to Quadrature amplitude modulation, it is broadly used in wireless LANs, RFIDs and Bluetooth communication [5]. This modulation is the most robust of all the PSKs since it is less resistant to noise so the demodulator reaches an incorrect decision. This scheme able to modulate the data at the rate of 1 Mbit/symbol and so is not appropriate for high data rate application. Fig.8 explains the flow diagram implementation of BPSK in LabVIEW.

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Fig. 9: Flow diagram of DPSK demodulation using LabVIEW

Quadrature Phase-Shift Keying (QPSK) is a very important and special digital modulation because it actually transmits two bits per symbol. In other prospective, QPSK symbols represents 00, 01, 10 or 11. Henceforth in QPSK, the carrier wave diverges in four possible phase shifts [4]. Those are mapped to 450, 1350, 2250 and 3150 states respectively (shown in Fig.10). Fig.11 shows the constellation diagram for QPSK modulation. With four phases, QPSK can encode two bits per symbol to minimize the BER (bit error rate).

Fig.7: Constellation Diagram of BPSK

Fig.10: QPSK sample data represented with corresponding degree

Fig.8: Flow Diagram of BPSK implementation in LabVIEW

Differential PSK can afford the extended data rate of 2 Mbit/symbol. Modulation scheme is realized for encoded data not for direct input data so it improves the security. DPSK is simple to implement than ordinary PSK, since there is no need for the demodulator to have a copy of the reference signal to determine the exact phase of the received signal (it is a noncoherent scheme).

Fig.11: QPSK Constalletion diagram

V.

RESULTS AND DISCUSSION

This section discusses results of the above stated modulation techniques. Fig.12 shows the ON-OFF keying modulation and demodulation program as GUI program in block diagram panel. Here Carrier signal-1 is a 2V, 10Hz signal whereas carrier signal-2 is a 0V. The corresponding carrier will be selected based on the input data. Here the input data/message signal is a square wave input and taken as reference to measure the error or delay between input data and demodulated output. Fig.8: Flow Diagram of DPSK implementation in LabVIEW

Fig.14 Shows the Front panel and Block diagram of FSK modulation and demodulation using LabVIEW. The main logic of obtaining ASK from FSK because it helps to retain the same demodulation technique. The obtained ASK should be of high frequency carrier signal. To obtain the desired ASK=FSK-ASK (of Low frequency Carrier signal). Fig.13 shows the front panel and block diagram BPSK modulation and demodulation techniques. Same methods of FSK demodulation is followed to obtain BPSK demodulated signal.

Fig.12: Block diagram and Square wave ON-Off Keying/ASK, Filter, and Error measurement output waveform in LabVIEW

Fig.13 illustrates the binary input/symbol for demonstrating same ON-OFF Keying modulation and demodulation. Waveform charts and binary array are shown in front panel of LabVIEW.

Fig.13: Block diagram and Binary input ON-OFF Keying/ASK, Filter, demodulated output waveform in LabVIEW

Fig.14: Block Diagram and Binary input FSK, Filter, Demodulated output waveform in LabVIEW

Fig.15 shows the program in block diagram for BPSK implementation in LabVIEW. Only two phase shifts are observed and clearly shown in front panel waveform window.

Fig.15: Block Diagram and Binary input BPSK, Filter, Demodulated output waveform in LabVIEW

Fig.16 shows the detailed implementation of DPSK modulation. The binary data is encoded using Exclusive-OR gate. For the encoded data modulation is performed. The demodulation is implemented in simple possible steps.

VI.

CONCLUSION

This paper demonstrated the user friendly environment realization of digital modulation techniques which are useful in wireless communication system is verified in LabVIEW. The simulation and the output waveform of the different digital modulation techniques have been conversed in this paper. The choice of digital modulation technique is purely dependent on the type of precise application. Many applications may need higher accuracy in reception of data, while the other constraint may be existing bandwidth or power. The facility provided by wireless communication system can be significantly improved with the help of proper selection of modulation scheme. The importance of this paper is implementation of demodulation scheme of digital modulation techniques is explained and discussed using LabVIEW in detail and concluded that in WLAN QPSK is best suited.

References [1]

[2] [3]

Fig.16: Block diagram and Binary input DPSK, Filter, Demodulated output waveform in LabVIEW

Fig.17 shows the QPSK modulation technique implementation in LabVIEW. The groupings of two bits are performed for the given bits and phase shifts are selected based on Fig.11 as shown.

[4]

[5]

D.K.Sharma, A. Mishra and Rajiv “Saxena Analog & Digital Modulation Techniques: An Overview” TECHNIA International Journal of Computing Science and Communication Technologies, VOL. 3, NO. 1, July 2010. (ISSN 0974-3375). B Kanmani “Digital Communication Using LabVIEW” 978-1-47991626-9/13/$31.00_c 2013 IEEE. Vidyarani K R, Tejaswini S, Ankitha B M and Shalini D V, “Implementation of Analog Modulation Techniques using TMS320C6748 and LabVIEW”, IOSR Journal of Research & Method in Education (IOSR-JRME) e-ISSN: 2320–7388,p-ISSN: 2320–737X Volume 7, Issue 4 Ver. I (Jul - Aug 2017), PP 46-50 www.iosrjournals.org. Hemant Dhabhai, Prof. Ravindra Prakash Gupta “A Performance Analysis of Digital Modulation Techniques under Simulation Environment” JETIR1405013 (ISSN-2349-5162). Virendrakumar V. Raut “Implementation of digital modulation techniques using in MATLAB” International Journal of Advanced Technology in Engineering and Science www.ijates.com Volume No.02, Issue No. 07, July 2014.

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Dr. Suresh D S corresponding author is member of IEEE and currently working as Principal and Director of Channabasaveshwara Institute of Technology, NH 206, Gubbi, Tumkur, Karnataka, India-572216. Vidyarani K. R is Assitant Professor, Department of ECE, Channabasaveshwara Institute of Technology, NH 206, Gubbi, Tumkur, Karnataka, India-572216.

Sekar R is Associate Professor, Department of ECE, Channabasaveshwara Institute of Technology, NH 206, Gubbi, Tumkur, Karnataka, India-572216.

Shalini D V is Assitant Professor, Department of ECE, Channabasaveshwara Institute of Technology, NH 206, Gubbi, Tumkur, Karnataka, India-572216. Fig.17: Block diagram and Binary input QPSK waveform in LabVIEW