FPGA Based Implementation Of Baseband OFDM Transceiver Using VHDL A. S. Chavan , P. S. Kurhe , K. V. Karad , Department of Electronics and Telecommunication, SRES’ College of Engineering, Kopargaon. University of Pune, (M.S.) India. Abstract— Orthogonal Frequency Division Multiplexing (OFDM) is a multicarrier communication system. It is widely used because of its immunity to frequency selective fading channels. In this paper, the design and an implementation of OFDM transceiver on FPGA is presented. The system is designed using VHDL, synthesized using high level synthesis tool and targeted on Xilinx Spartan 3e device. Presented design is simulated on ISE simulator and the results are presented. Resources utilization for transmitter and receiver is given in this paper. The design utilizes the Intellectual Property (IP) cores provided by Xilinx for floating point multiplication, addition subtraction and division. DIT radix-2 butterfly approach is used to calculate IFFT and FFT. Keywords-FPGA, FFT, IFFT, DIT, ISE, VHDL. I. INTRODUCTION The modern digital mobile communication systems are increasingly using baseband OFDM for multi-carrier transceiver. Idea behind the high spectral efficiency of OFDM is elimination of guard bands and use of the overlapping but orthogonal subcarriers. High rate data stream is divided into a number of low rate data streams that are transmitted over a number of multiplexed orthogonal subcarriers [1]. The low rate data streams allow adding sufficient guard time between two symbols which was very small in high rate data stream. This helps in enabling the system to perform well in dispersive channel which causes the symbols to spread in time and interfere with each other called as inter symbol interference (ISI). Fig 1 Block diagram of basic baseband OFDM system OFDM can be viewed as either a modulation or multiplexing technique, and its hierarchy lies in the physical and medium access layer. A basic OFDM transceiver consists of a QAM or PSK modulator/demodulator, a serial to parallel/parallel to serial converter, and an IFFT/FFT module [1]. The block diagram of basic OFDM system is shown in Fig 1. The transmitter consists of a input bit stream, serial to parallel converter, constellation mapping, IFFT, DAC. The receiver consists of ADC, FFT, parallel to serial converter, demodulation, and output bit stream. This paper is organized as follows. Section II presents the design flow to implement an OFDM transceiver from system design to circuitry realization on FPGA. The implementation aspects of the transmitter and receiver are demonstrated in section 3 and 4. The results are discussed in section 5 and finally the conclusion is given in section 6. II. DESIGN FLOW Initially transmitter and receiver is implemented independently and tested on kit, and then both the subsystems were merged to form one system. The system is designed for two sets of subcarriers one is using 4 subcarriers and the other using 8 subcarriers. Design flow for both the system is same. It is explained as follows. The design of system starts with the understanding of the block diagram. It gives the idea about operations needed to be performed with help of FPGA. Then the algorithm is developed for the sequential and concurrent operations. To make the design more parallel the operations are broken in to processes and independently written in VHDL. Some blocks contain floating point complex operations, for that Intellectual Property (IP) cores provided by Xilinx are used. IP cores are used for all types of floating operations. The system is designed completely on Xilinx Project Navigator using VHDL coding as design entry method. Then the system is simulated on ISE simulator for timing analysis. Finally the design is synthesized on FPGA Spartan 3e device using high level synthesis tool. Serial To Parallel QPSK Modulator IFFT Processor Digital To Analog Parallel To Serial QPSK Demodul ator FFT Processor Analog To Digital A. S. Chavan et al, / (IJCSIT) International Journal of Computer Science and Information Technologies, Vol. 5 (3) , 2014, 4446-4449 www.ijcsit.com 4446