An Implementation of Error Minimization Data Transmission in OFDM using Modified Convolutional Code

EMITTER International Journal of Engineering Technology Vol.3, No.2, December 2015 ISSN: 2443-1168 An Implementation of Error Minimization Data Transmission in OFDM using Modified Convolutional Code Hendy Briantoro, I Gede Puja Astawa, Amang Sudarsono Politeknik Elektronika Negeri Surabaya Jl. Raya ITS - Kampus ITS Sukolilo, Surabaya 60111, INDONESIA Telp : 62 31 594 7280, Fax : 62 31 594 6114 E-mail: , , Abstract This paper presents about error minimization in OFDM system. In conventional system, usually using channel coding such as BCH Code or Convolutional Code. But, performance BCH Code or Convolutional Code is not good in implementation of OFDM System. Error bits of OFDM system without channel coding is 5.77%. Then, we used convolutional code with code rate 1/2, it can reduce error bitsonly up to 3.85%. So, we proposed OFDM system with Modified Convolutional Code. In this implementation, we used Software Define Radio (SDR), namely Universal Software Radio Peripheral (USRP) NI 2920 as the transmitter and receiver. The result of OFDM system using Modified Convolutional Code with code rate is able recover all character received so can decrease until 0% error bit. Increasing performance of Modified Convolutional Code is about 1 dB in BER of 10-4 from BCH Code and Convolutional Code. So, performance of Modified Convolutional better than BCH Code or Convolutional Code. Keywords: OFDM, BCH Code, Convolutional Code, Modified Convolutional Code, SDR, USRP 1. INTRODUCTION Orthogonal Frequency Division Multiplexing (OFDM) is multicarrier efficiency bandwidth scheme for digital communication where the frequency of its subcarrier overlaps the other [1]. There has been some researches related to OFDM, whether simulation using MATLAB software or implementation using Field Programmable Gate Array (FPGA) hardware. One of them was conducted in Universidade de Aveiro Portugal [2], the research was about OFDM which implemented in FPGA. This FPGA used Virtex-6 processor. The receiver used was Maximum Likelihood (ML) and Carrier Frequency Offset (CFO) Estimator to reduce the excessive information in Cyclic Prefix (CP). The channel equalization used Zero Forcing and channel estimation used Least Square [2]. However, the implementation of this Copyright © 2015 EMITTER International Journal of Engineering Technology - Published by EEPIS 43 44 Volume 3, No. 2, December 2015 research only used Xilinx System Generator in MATLAB with one FPGA. The data transmission was not done in the real condition from one device to another device but only in one device. OFDMsystem has data rate faster than single carrier systems because the OFDM signal is split into multiple subcarriers. In addition, there was a researchby Ahmad Zainudin et al [3]. The reasearch was about data transmision use DPSK, DQPSK and GMSK modulation which is implemented usingUniversal Software Radio Peripheral (USRP).Unfortunately, the implementation presented and measured whether data is received succesfully or not, and was not able to recover received data [3]. In order data can be received well, it needsone or more additional techniques to increase data robustness. One of the techniques used is channel coding. There are some types of channel coding such as block code, LDPC code, BCH code and Convolutional code. A research related to channel coding has been already done by Henry Hendrix [4]. His research implemented Convolutional code and Viterbi Decode using DSK TMS320C55x Board. The drawback of the implementation is that data transmission was not done from one device to another device but only in one device. Only in one DSK TMS320C55x Board. Due to the lack of the previous researches, this research proposes an implementation of OFDM system using channel coding Modified Convolutional Code in USRP for error minimalization for data transmision. Error bits of OFDM system without channel coding is 5.77%. Then, we used convolutional code with code rate 1/2, it can reduce error bits up to 3.85%. The result of OFDM system using Modified Convolutional Code with same code rate is able recover all character received so can decrease error bits until 5.77%. Meanwhile in NLoS condition, Modified Convolutional Code can decode all data when using 8 characters. In 12 characters, only there is a error bit or 1.04% of transmitted data. In 14 characters, there are 2 error bits or 1.79% of transmitted data. Then, in 16 characters there are 9 error bits or 7.03% of transmitted data. From the result of the experiment above, it can be analyzed that performance Modified Convolutional Code is enough good in NLoS condition. This research uses NI USRP 2920. This device is supported by FPGA chip. FPGA is programmable device. The programming languages used are VHDL, C, Phyton, and LabView. This device has been completed with RF front-end module to transmit or receive signal, so user is able to interface radio signal to transmit or receive easily. This is the reason why we use NI USRP 2920. By using this device we can easily implement complex algorithm in our research and able to finish it faster with satisfactory result. We can develop many algorithms but only use one device. It has bandwidth streaming at 25 MS/s for host-based processing with NI LabVIEW [5]. This paper is organized as follows, firstly we describe the introduction about this research. In second section, we present related work of this research. Then, we explain our proposed system in Section 3. In Section 4, we explain about OFDM system, Convolutional code, and proposed Modified Convolutional Code. Furthermore, we present system implementation in Section 5.Section EMITTER International Journal of Engineering Technology, ISSN: 2443-1168 Volume 3, No. 2, December 2015 45 6, we discuss about experimental result. Finally, our conclusion is created in Section 7. 2. RELATED WORKS In Universidade de Aveiro Portugal, there was a research by Tiago Pereiraet al [2]. It was about OFDM which implemented in FPGA. FPGA used was Virtex-6 processor. The receiver used was Maximum Likelihood (ML) and Carrier Frequency Offset (CFO) Estimator to reduce the excessive information in Cyclic Prefix (CP). The channel equalization used Zero Forcing and channel estimation used Least Square. However, the implementation of this research only used Xilinx System Generator in MATLAB with one FPGA. The data transmission was not done in the real condition from one device to another device but only in one device[2]. In addition, there was aresearch by Abirami et al[6] on analyzing the performance of OFDM using Software Define Radio (SDR) and Universal Software Radio Peripheral (USRP) in real time. Here, they use two methods, OFDM simulation in GNU Radio and OFDM in real time.The implementation of OFDM systems uses SISO(Single Input Single Output) [6]. Next, there was a researchby Ahmad Zainudin et al [3]. The reasearch was about data transmision use DPSK, DQPSK and GMSK modulation which is implemented using US (...truncated)