Implementation and performance evaluation of orthogonal frequency division multiplexing (OFDM) using WARP

Abstract

The main problem in high data rate transmision is frequency selective fading due to multipath propagation. This fading causes deep fade on signal spectrum at one particular frequency. To overcome this problem, many researchers proposed a multi-carrier technique, which divides wideband signal bandwidth into multiple narrowband signal before transmitted using certain number of subcarriers. By using this technique, the depth fade can be localized, hence only one subcarrier will be affected such that the number of error bit can be minimize. Orthogonal Frequency Division Multiplexing (OFDM) is a form of multi-carrier technique which uses bandwidth effectively. This OFDM system can be implemented on Wireless Open-Access Research Platform (WARP) that is one of the Software Defined Radio (SDR). By implementing OFDM on WARP module, the bit error rate (BER) system performance can be analysis in the real channel. The implementation of OFDM technique on WARP modul is based on IEEE 802.11 standard. If the range between transmitter (Tx) and receiver (Rx) short enough (less than 10 m), the distance variation didn't affect the BER performance significantly. Whereas, if there is an obstacle between transmitter and receiver, the BER will increase significantly compared no obstacle (dear condition) for short range Tx-Rx distance. For example, BER is 0 in clear condition when the transmit power is -26.125 dBm, meanwhile the BER value is 9.3 × 10-6 in obstacle condition and for short range distance, the objects near propagation path provide reflected signal power with significant contribution.