Reliability Analysis of Digital Communication for Various Data Types Transmission Using GNU Radio and USRP

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1 Reliability Analysis of Digital Communication for Various Data Types Transmission Using GNU Radio and USRP Ahmad Zainudin, Amang Sudarsono, I Gede Puja Astawa Postgraduate Applied Engineering of Technology Division of Electrical Engineering, Dept. of Electrical Engineering Electronic Engineering Polytechnic Institute of Surabaya (EEPIS) EEPIS Campus, Jalan Raya ITS, Sukolilo 60111, Indonesia (Telp:+62(31) ; Fax:+62(31) {zai,amang,puja}@eepis-its.edu) Abstract This paper discusses about transmission of various data types with DBPSK, DQPSK, and GMSK modulation techniques, respectively. We used USRP board as the RF front-end. We confirm that text, image, audio, and video data types can be successfully passed through all the above techniques. The reliability of digital communication is observed based on file integrity and Packet Error Rate (PER) of transmitted data. In addition, data rate and the corresponding PER of transmitter amplitude also have been investigated. The experimental results show that the average of data rate using DBPSK modulation technique is kbps. Meanwhile, DQPSK and GMSK techniques offer kbps and kbps, respectively. The average of PER using DBPSK and GMSK techniques achieves %, and it is more resistant to noise environment than DQPSK technique which reaches %. We set the number of transmitter amplitude between 0.25 volt and volt to obtain a good performance. Keywords: digital communication, sdr, gnu radio, usrp. 1. Introduction Recently, demand of transmission with complexity data type over wireless channel is incresing. Text, image audio and video are transmitted on the same wireless channel [1]. Reliability of delivery various data types would be strongly desirable. Software Defined Radio (SDR) in digital communication is one of the interesting research topics. SDR is a radio communication development system which changes hardware device components (e.g., mixers, filters, amplifiers, modulators/demodulators, detectors, etc) into software applications on a personal computer or other embedded system [2]. Hence, the change of service, standards and technologies is not required for new hardware changes. Here, only the SDR software configuration should be changed. This property has an advantage for service providers for their investment of communication equipments. SDR comprises baseband processing, ADC/DAC and RF front-end functions. Whereas, the RF front-end is used for down converting signal into lower frequency (Intermediate Frequency), due to the limitation of the speed of current Commercial of The Shelf (COST) ADC. USRP (Universal Software Radio Peripheral) is one of the front-end parts in the SDR system architecture. USRP is able to work in a fairly wide frequency margin from 0 to 5 GHz. In this case, frequency margin depends on the use of USRP s doughterboard [3]. A good performance in wireless communication can be achieved by combining USRP and GNU Radio. GNU radio is an open source software that supports radio functionalities. Currently, digital communications using GNU radio and USRP have been widely implemented by many researchers. For example, analog and digital modulation techniques were built up using graphical user interface called GNU radio companion (GRC), which is reported by Gandhiraj, et. al. [4]. This system supports a basic signal operation functions such as the basic of addition, subtraction and multiplication operations. In addition, it also demonstrates sampling, interpolation, decimation, analog modulation functions (i.e., AM and FM modulations), and digital modulation functions (i.e., ASK, FSK and PAM modulations). However, the experimentals only involved a single USRP, such that no data transmission over wireless can be demonstrated. The goal of experiments in [4] was just to observe spectrum signal and modulated/demodulated signal using GRC open source software tool, where the output signal was connected to the scope sink and FFT sink. Marpanji, et. al [5-7] implemented and observed DBPSK, DQPSK and GMSK modulation techniques on SDR platform. The observation includes DBPSK, DQPSK and GMSK modulation performance evaluation in term of Packet Error Rate (PER), Eb/No or S/N ratio, carrier frequency, bit rate, gain, roll-off factor of root Nyquist filter or root raised cosine filter, and payload size from delivered data. In this measurement, sent data is data packets generated by GNU Radio which transmitted along with coaxial cable connection. 91

2 Wireless transmission of JPEG file using GNU Radio and USRP has been implemented by Sachin Hirve, et. al [8]. This project was divided into two parts. The first part is transfering the JPEG file from one USRP to another through a loop-back cable connection. Second part is transfering the JPEG file over wireless network using DBPSK modulation. Environmental effects of received JPEG file such as packet transmission, distortion, duplicate packets and posible packet loss affect image quality are also measured. However, in the current wireless communication, reliable transmitting various data types should be strongly considered. In this paper, we employ DBPSK, DQPSK and GMSK modulation techniques for transferring various data types such as text, image, audio and video file over wireless medium. To convince the reliability of the system, we analize the performance of DBPSK, DQPSK and GMSK modulation techniques by combining GNU radio and USRP based on Packet Error Rate (PER) and the integrity of transferred data. To accomplish our analysis, we show the spectrum signals of digital modulation techniques through visualizations. In addition, the relationship PER with transmitter amplitude is also observed. Our experimentals use frequencies for data transmission 2.4 GHz under Ubuntu Linux operating system. Our experimental results show that data transmission with various file size from 703 KB to 2MB are successfully delivered using DBPSK, DQPSK and GMSK modulation techniques over data rate about 13 kbps with PER less than 0.2%. The rest of the paper is organized as follows. Firstly, we introduce software defined radio, USRP, differential PSK and Gaussian Minimum Shift Keying (GMSK) modulations. Section 2 describes the implementation of digital modulation for wireless transmission of various data types. The result and experimentals analysis are explained in Section 3. Finally, the conclusion of our experimentals is explained in Section Software Defined Radio (SDR) SDR is software of radio communication development system, where the block communication system is originally implemented as hardware form such as mixers, filters, amplifiers, modulator/demodulator and the detector are transformed as software in the PC or embedded systems. Hardware changing is not required in SDR if there are standard modification, due to SDR is flexible. All radio parameters are set in software and they are configurable through the software. This contributes for development and research to be easier, faster and cheaper. We can use SDR to construct a communication system prototype and measure many parameter variations and configurations. SDR enables variety of communication modes or waveforms and allows the same hardware to be operated with any type of waveform. Most researchers use SDR GNU Radio on their researches. GNU Radio is an open source software for digital signal processing (DSP) function that was developed using C++ (low-level code) and python (high-level code) programming. SDR blocks which are written in C++ including demodulation of an incoming radio signal, restructuring the information into packets or performing frequency domain signal filtering. Python code is used for connecting various signal processing blocks together with a directed graph [9]. Figure 1 illustrates SDR transmitter and receiver architecture. Tx computer host generates complex baseband (BB) signal and converts up to intermediate frequency (IF) signal that processed on DSP block. Through digital to analog (DAC) block, IF is converted to radio frequency which transmitted over antenna. On SDR receiver, received RF signal through analog to digital (ADC) block is down converted into intermediate frequency (IF). And then, IF is down converted into complex baseband (BB) signal by DSP block and processed by Rx computer host. Figure 1. SDR Architecture for Transmitter and Receiver 3. Universal Software Radio Peripheral (USRP) USRP is a hardware device that acts as a front-end in the architecture of a SDR. USRP is created by Matt Ettus Research [9]. Communication between USRP and PC is connected via USB 2.0 connection and supplied by a 6 Volts DC adapter. The USRP has four high-speed analogto-digital converters (ADCs) and four high-speed digitalto-analog converters (DACs). These four input and output channels are connected to an Altera Cyclone EP1C12 FPGA [2]. Figure 2 shows a block diagram of basic USRP system. USRP can serve as a transmitter and a receiver with difference frequency. Simple USRP consists of motherboard, daughterboard and antenna. Motherboard allows to insert four daughterboards: two for transmitters and two for receivers. The RF daughterboards determine the set of working frequency. In this experiment, we use 92

3 RFX2400 daughterboard and VERT2450 antenna. This daughterboard allows two antenna with SMA connector. The RFX2400 is a high-performance RF doughterboard with full duplex transceiver designed specifically for operation in the 2.4 GHz band. The RFX2400 provides a typical power output of 50 mw. Figure 3. Diagram block of DBPSK demodulator [10]. Table 1. The Rule Phase Shift DQPSK System Pair bit input Phase shift (radians) π/2 11 3π/2 10 -π/2 Figure 2. Block diagram of basic USRP system 4. Differential PSK BPSK uses Double Side Band Suppressed Carrier (DSBSC), whereas receiver uses a carrier recovery for synchronization. The effect of carrier recovery in BPSK system is phase ambiguity between 0 and π radiant. The problem is solved by differential detection or encoding technique. Differential encoding in transmitter occurs when bit 1 information is transmitted by shifting the phase of modulated signal relative to the previous phase of the modulated signal. On the other hand, when bit 0 information is transmitted without shifting the phase of modulated signal relative to the previous phase of the modulated signal. DBPSK does not require a coherent reference signal, but it uses the phase difference previous symbol as the reference for demodulating of the current symbol. Block diagram DBPSK demodulator is depicted in Figure 3. On differential QPSK, initial phase of modulated signal is effected by the initial phase of the previous modulated signal. Transmitted signal is the addition result between the phase shift and the initial phase of previous modulated signal. First step on DQPSK system is determining the rule of phase shift as a pair bit input. Table 1 shows the rule of phase shifting in DQPSK system. The second step is the addition result between the phase shift and the initial phase of previous modulated signal as phase output modulated signal of transmitter. On demodulator DQPSK, output LPF through differential decoded and phase received signal is compared with the phase of previous signal. If there is a phase difference, this indicates the flow of bits information. DQPSK demodulator shown in Figure 4. Figure 4. Diagram block of DQPSK demodulator [10]. 5. Gaussian Minimum Shift Keying (GMSK) GMSK is a modulation scheme which input bits rectangular shaping (+1,-1) are convered into gaussian pulse by gaussian low pass filter before modulation process. Gaussian filter response generates a signal which has a lower lobes and narrower main lobe than rectangular signal. It is high bandwidth effiency, and it may reduce the required power. The GSM mobile radio system uses GMSK. The Gaussian filters have a bandwidth khz (0.3 BT) and it is used for GSM standards. GMSK is the modulation format for most widely used in Europe. GMSK modulator and demodulator are shown in Figure 5 and Figure 6, respectively. 93

4 change data type (text, image, audio and video) with default USRP distance. Figure 5. Diagram block of GMSK modulator [11]. Figure 6. Diagram block of GMSK demodulator [11]. 6. Implementation In this section, we describe our implementation of digital modulation for sending various types of data between USRP boards. We use two PC/laptop hosts (transmitter and receiver) which connected with USRP respectively. Distance between the USRP is set such that there is no interference, and it is typically minimum three meters. Daughterboard used in this experiment is RFX2400 with frequency center 2.4 GHz. For the experiments, we use Ubuntu version as the development platform and GNU radio Experimental set up is shown in Figure Experiment Results The observations include transmission of text, image, audio and video data file using DBPSK, DQPSK and GMSK modulation techniques, measurements of Packet Error Rate (PER) and data rate transmission. Observation relationship is performed between transmitter amplitude and PER. File size used in these experiments are grouped into two groups. They are small file size dan large file size. Small file size consists of 771 KB for text file, 770 KB for image file, 789 KB for audio file and 703 KB for video file. Big file size includes KB for text file, KB for image file, KB for audio file and KB for video file. 7.1 Data transmission with DBPSK, DQPSK and GMSK modulation The experimental of sending data packet from text, image, audio and video file is done from one usrp to another. Data transmission uses bit rate 100 kbps and tx amplitude 0.25 volts. Spectrum signals of DBPSK, DQPSK and GMSK modulaions, respectively are shown in Figure 6, 7 and 8. Each modulation has different spectrum signal. DBPSK modulation technique has fequency band 60kHz ( GHz GHz). Frequency band in DQPSK modulation technique is narrower than DBPSK and GMSK modulation techniques. That is 40 khz ( GHz GHz). Whereas frequency band in GMSK modulation technique is 50 khz ( GHz GHz). DQPSK has the most narrow frequency band, this benefit can be used by user to operate other channels. Figure 7. Experimentals set up For sending various types of data, we reconfigure benchmark_tx.py and benchmark_rx.py codes in /gnuradio/gnuradio-example/python/digital using phyton programming. The program has default value packet size 1500 bytes, bit rate 100 kbps and transmitter amplitude 0.25 volt. Experiments are performed indoor by changing the modulation (DBPSK, DQPSK and GMSK) and we Figure 6. Spectrum signal DBPSK 94

5 Packet Error Rate (PER)(%) Industrial Electronic Seminar 2013 ISBN Figure 7. Spectrum signal DQPSK Figure 8. Spectrum signal GMSK Table 2. Data rate and PER for DBPSK, DQPSK and GMSK modulation for small file size Data file Modulation Data rate PER Text DBPSK Kbps 0 % Image DBPSK Kbps % Audio DBPSK Kbps % Video DBPSK Kbps 0 % Text DQPSK Kbps % Image DQPSK Kbps % Audio DQPSK Kbps % Video DQPSK Kbps % Text GMSK Kbps % Image GMSK 13.1 Kbps 0 % Audio GMSK Kbps 0 % Video GMSK Kbps 0 % Data transmission time is measured for getting data rate from file size which successfully sent. In addition, packet error rate is obtainable from transmission of DBPSK, DQPSK and GMSK modulations for all data types. Data rate and PER for each modulation for small and large file size are shown in Table 2 and 3, respectively. DBPSK, DQPSK and GMSK modulations have data rate values which almost the same around kbps. The average data rate in DBPSK modulation is kbps for small file size and kbps for large file size. Whereas, data rate in DQPSK modultion technique are kbps for small size and kbps for large file size. Moreover, kbps for small file size and kbps are pointed out in GMSK modulation. DBPSK and GMSK are more resistant to noise enviroment with average PER value % for current measurement of small file size. On the other hand, DQPSK is less resistant to noise, its PER is % for small file size. Table 3. Data rate and PER for DBPSK, DQPSK and GMSK modulation for large file size Data file Modulation Data rate PER Text DBPSK Kbps 0 % Image DBPSK Kbps 0 % Audio DBPSK Kbps 0.012% Video DBPSK 12.53Kbps 0 % Text DQPSK Kbps % Image DQPSK Kbps % Audio DQPSK Kbps % Video DQPSK Kbps % Text GMSK Kbps % Image GMSK Kbps 0 % Audio GMSK 12.94Kbps % Video GMSK Kbps 0 % 7.2 Relationship PER with transmitter amplitude Default value of tx amplitude in GNU radio is This experiment will get PER with change of tx amplitude value between 0 until 1 with grading 0,0625. PER value is obtained when image transmission process. When using tx amplitude less than 0.25, data transmission has PER sizeable. Tx amplitude values are set between 0.25 and PER will be worst when using tx amplitude greater than to achieve PER 100% Relationship PER with Tx Amplitude Tx Amplitude (Volt) Figure 9. PER with tx amplitude change 8. Conclusion and Future Work We have presented a digital communication for transmission various data types using DBPSK, DQPSK and GMSK modulations. Three modulations have data rate around kbps for small and large file size. DBPSK and GMSK are more resistant to noise enviroment. PER value for DBPSK and GMSK modulations achieves around % for current measurement of small file size. Transmitter digital amplitude values is suggested between 0.25 Volt and Volt. Our future works include a development of OFDM communication system with Zero Forcing (ZF) and 95

6 MMSE equalizer using gnuradio and USRP. Equalization methods will be adopted to combat the problem of intersymbol interference (ISI). Communication Engineering, pp 6-11,Vol. 2, No. 2, June References [1] S. Aramvith and R. D. Cajote, Handbook of Research on Secure Multimedia Distribution, ISBN-13: ,Pp , Information Science Reference,2009 [2] A.M. Wyglinski, M. Nekovee, T. Hou, Cognitive Radio Communications and Networks Principles and Practice. ELSEVIER Inc., [3] Z. Tong, M.S. Arifianto, C.F. Liau, Wireless Transmission using Universal Software Radio Peripheral.Procending of the 2009 International Conference on Space Science and Communication, Port Dickson, Negeri Sembilan, Malaysia, October [4] R. Gandhiraj, R. Ram, K.P. Soman, Analog and Digital Modulation Toolkit for Software Defined Radio.International Conference on Communication Technology and System Design, Publised by Elsevier Ltd, [5] E. Marpanaji, B. Riyanto, A.Z.R. Langi, A. Kurniawan, Studi Eksperimen Unjuk Kerja Modulasi DBPSK Pada Platform Software-Defined Radi (SDR). Jurnal Technoscientia, ISTA Yogyakarta, Vol. No. 1. Agustus pp 14-22, ISSN: [6] E. Marpanji, B.R. Trilaksono, A.Z.R. Langi, A. Kurniawan, A. Mahendra, T. Liung, Experimental Study of DQPSK Modulation on SDR Platform. ITB J. ICT Vol. 1, No. 2, 2007, 84-98, [7] E. Marpanaji, B. Riyanto, A.Z.R. Langi, A. Mahendra, T. Liung, Simulation and Experimental Study of GMSK Modulation on SDR Platform.International Joint Conference TSSA & WSSA, [8] S. Hirve, S. Gumudavally, Wireless Transmission of JPEG file using GNU Radio and USRP.Department of Electrical and Computer Engineering, Clevelan State University, [9] D.C. Tucker, G.A. Tagliarini, Prototyping with GNU radio and the USRP - Where to Begin.Southeastcon, ISBN: , pp [10] T.B. Santoso, Final Report of Telecommunication Engineering Training Chapter 4 and Chapter 6.Suzuki Laboratory, Mobile Communicatio Group by Cambridge Tokyo Institute of Technology, Japan. [11] P.K. Govindaiah, Design and Development of Gaussian Minimum Shift Keying (GMSK) Demodulator for Satellite Communication, Bonfring International Journal of Research in 96

Experimental Study of DQPSK Modulation on SDR Platform

ITB Journal of Information and Communication Technology, Vol. 1, No. 2, November 2008. pp. 84-98. ISSN: 1978-3086 1 Experimental Study of DQPSK Modulation on SDR Platform 1,2 Eko Marpanaji, 2 Bambang Riyanto