Bit Error Rate Analysis Using QAM Modulation for Satellite ... · waves, using the digital...

Procedia Technology 25 ( 2016 ) 456 – 463

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2212-0173 © 2016 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).Peer-review under responsibility of the organizing committee of RAEREST 2016doi: 10.1016/j.protcy.2016.08.132

Global Colloquium in Recent Advancement and Effectual Researches in Engineering, Science and Technology (RAEREST 2016)

Bit Error Rate Analysis Using QAM Modulation for Satellite Communication Link

*Usha S.Ma, Dr. K.R. Natarajb

*a Department of Electronics and Communication Engineering, JSS Academy of Technical Education, Bangaluru-560 060, Research scholar - VTU Belgaum, India.

b Department of Electronics and Communication Engineering, SJB Institute of Technology, Bangaluru-560 060, India.

Abstract

The two main advances in the twentieth century are automobiles and telecommunication. These two fields changed the way people lived. The telecommunication systems have now made it likely to communicate effectively anyone at any time. Artificial earth satellites have been used in communication system become an essential part of the world’s telecommunication structure. Satellite allow people to talk by telephone and exchange electronic mail from anywhere in the world and receive hundreds of TV channels in their homes. The modulation is the technique used for multiline communication. The modulation is nothing but altering the characteristics of the carrier wave with the characteristics of another wave called as modulating signal. In this paper satellite communication link is established using Simulink tool. The Bit Error Rate (BER) analysis is performed using different configuration of QAM (Quadrature Amplitude Modulation) such as 16 QAM, 64 QAM, 128 QAM and 256 QAM with the same satellite link. In the downlink channel the free space path loss of 196 dB and phase and frequency offset are introduced. The transmitter signal and received signal after and before filtering are represented. This paper is implemented by using MATLAB and Simulink. The results are analyzed and compared. © 2015 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the organizing committee of RAEREST 2016.

Keywords:MATLAB; Simulink; QAM; BER;Satellite link;

1. Introduction

Analog wireless communication is used in earlier days and the drawback is multiple conversations lead to a lot of signal loss. The digital communication has started with the goal of increasing speed and exactness including selecting the suitable carrier, checking path loss, proficiently modulating the carrier, avoiding channel interference and noise.

© 2016 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).Peer-review under responsibility of the organizing committee of RAEREST 2016

457 S.M. Usha and K.R. Nataraj / Procedia Technology 25 ( 2016 ) 456 – 463

A method by which such multiple transmission is called multiplexing. The different types of modulation techniques are available today. The basic modulation techniques are Amplitude Modulation (AM), Frequency Modulation (FM) and Phase Modulation (PM). The analog versions of QAM are used to allow multiple analog signals to be carried on a single carrier. It is used in PAL and NTSC television systems, where the different channels provided by QAM enable it to carry the components of color information. The digital formats of QAM are used for data communications. The various forms of QAM are used in wireless communication systems such as Wi-Fi and WIMAX. It is the combination of amplitude and phase modulation. BPSK modulation is 2-QAM modulation.16 QAM provides 4:1 efficiency of transmission over BPSK. It enhances the ability to correct data without retransmission [1].

The first part of the paper explains the basics of satellite communication system and QAM modulation technique.

The second part explains the proposed satellite communication link in Simulink. The third part of this paper explains the results, analysis and comparison.

1.1. Introduction to satellite Communication System

The satellite communication systems exist because the earth is a sphere. Electromagnetic waves travel in straight lines at the microwave frequencies used for wideband communications. A repeater is needed to convey signals over long distances. A repeater is simply a receiver linked to a transmitter, always using different radio frequencies that can receive a signal from one earth station, amplify it, and retransmit it to another earth station. A communication satellite is an artificial satellite that amplifies radio signals via a transponder; it creates a channel between a source transmitter and a receiver at different locations on Earth. The communication satellites are used for television, telephone, radio, internet, and military applications [2, 3, 4, and 5]. Fig. 1. Shows the block diagram of basic satellite communication system.

Fig.1. Satellite communication block diagram.


1.2. Quadrature Amplitude Modulation (QAM)

It conveys two analog message signals, or two digital bit streams, by modulating the amplitudes of two carrier waves, using the digital modulation scheme such as amplitude-shift keying (ASK) or the analog modulation scheme such as amplitude modulation (AM). The two carrier waves are sinusoids, out of phase with each other by 90° and are thus called quadrature components. The modulated waves are summed and the final waveform is a combination of both phase-shift keying (PSK) and amplitude-shift keying (ASK) or the combination of phase modulation (PM) and amplitude modulation in the case of analog signal. In the digital QAM case, a finite number of at least two phases, two amplitudes are used. QAM is used extensively as a modulation scheme for digital telecommunication system. Subjectively high spectral efficiencies can be achieved with QAM by setting a suitable constellation size, limited only by the noise level and linearity of the communication channel. The QAM signal S (t) is given in equation (1). The Fig. 2. Shows the generated QAM signal [6, 7 and 8].

(1)

Fig.2. QAM signal generation.

The advantage of using QAM is that more bits of information per symbol can be carried. The data rate of a link can be increased by selecting a higher order QAM configuration.

2. Proposed System in Simulink

The higher order modulation rates are able to offer much faster data rates and higher levels of spectral efficiency for the radio communication system but the higher order modulation schemes are considerably less resilient to noise and interference. Hence the higher order versions of QAM are only used with an adequate high signal to noise ratio.

The Fig.3. Shows the implementation of satellite link in Simulink. The blocks of this system is explained below.

The input is the random integer data source. The data is modulated by using different QAM configurations such as 16, 64, 128, 256 QAM at a time respectively.

The modulated signal is filtered using raised cosine transmitter filter. The filtered signal is amplified by high power amplifier. The signal is transmitted using antenna. The free space path loss and frequency offset is added to the modulated

signal

S (t) = P I(t) cos2 + PQ(t) sin 2


The receiving antenna captures the signal. The phase and frequency compensation blocks are added, DC offset compensation is provided.

Finally the signal is filtered and demodulated. The QAM appears to increase the efficiency of transmission for radio communication system by utilizing both

amplitude and phase variations. It has a number of drawbacks. The first is that it is more susceptible to noise. Secondly, Since QAM contains an amplitude component, linearity must be maintained, but the linear amplifiers are less efficient and consume more power. The table 1. Shows the summary of the bit rates of different forms of QAM and PSK [9, 8, 10 and 11].

Fig.3. Satellite communication link in Simulink.


3. Results and Analysis

The results are analyzed in this section. The design is simulated and implemented on MATLAB Simulink R2014a. The bit error rates are analyzed. The Fig. 4 and 5 initializes the function block parameters for transmitter dish antenna gain, Doppler and phase errors respectively.

The transmitter antenna gain is represented as 12.426, sample time -1 is mentioned in fig 4.

Fig. 4 and 5.Defines the functional block parameters of transmitter dish antenna gain, Doppler and phase error.

The distance and the frequency can be marked by using the functional block below as shown in fig 6. The parameters for QAM modulator are listed in the pop window as shown below in fig 7.

Fig. 6 and 7. Defines the functional block parameters for downlink path and QAM modulator.

Table 1. A summary of the bit rates for different forms of QAM and PSK Modulation Bits/ Symbol Symbol rate BPSK 1 1 X bit rate QPSK 2 ½ bit rate 8PSK 3 1/3 bit rate 16 QAM 4 ¼ bit rate 32 QAM 5 1/5 bit rate

64 QAM 6 1/6 bit rate


Fig. 8 and 9 presents the functional block parameters defined for phase noise and I/Q imbalance

Fig. 8 and 9.Shows the functional block parameters - I /Q imbalance and Phase Noise.

The phase noise level -100 dBc/Hz, frequency offset of 100 Hz, sample rate of 1024 Hz with initial seed 2137 is marked in fig 8. The transmit RRC filtered signal and received constellation is marked in fig10, 11and 12 as shown below.

Fig. 10, 11 and 12 shows the transmit RRC filter signal, and received constellation.

The figure 13, 14 and 15 interprets transmit and receive spectrum. transmitted signal and blue color represents the received spectrum. As the result indicates the transmitted

spectrum is more erroneous and noisy than the received signal.

Fig. 13, 14 and 15 represents transmit and received constellation.


The Fig. 16, 17 and 18 shows the BER analysis for different forms of QAM configuration. This shows that as the order of modulation increases the error rate also increases.

Fig. 16 and 17 shows the BER, symbols and errors for different QAM configuration.

Fig. 16, 17 and 18 shows the BER, symbols and errors for different QAM configuration.




.

Fig. 18 shows the BER, symbols and errors for different QAM configuration.

For the modulation type of 16 QAM considering 100 symbols the BER is 0.28, for 32 QAM it is 0.34, for 64 QAM it is 0.53 and for other higher order modulation the bit error rate prevailed is 1 and for the same symbol rate, as the order of modulation increased the error rate is also raised as shown in Table 2.


Table 2. The table below gives a summary of the bit rates of different forms of QAM

Modulation Symbols BER

16 QAM 100 0.28

32 QAM 100 0.34

64QAM 100 0.53

128 QAM 100 1

256 QAM 100 1

4. Conclusion

The satellite communication system is effective and low cost communication technique compared to other communication systems. It covers the entire earth region including remote places. The QAM modulation is used in many radio communications and data delivery applications. In this paper the satellite link is established for various QAM configurations. By using higher order modulation more data can be transmitted in trade off with the error rate. This shows that as the order of modulation increases the error rate also heightened. The work is concluded with comparing the error rate for all QAM modulation formats.

Acknowledgements

I sincerely thank our research guide Dr. K. R. Nataraj for his consistent support. I would like to express my gratitude to my working organization JSS ATE and the Research Centre SJBIT for proving the lab facility to complete this work. Sincerely I thank to the University VTU Belgaum for proving the opportunity for registration.

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