OFDM technique has wide usage in modern communication systems, it can offer efficient use of frequency spectrum and high service quality for users. In literature, there are some software defined radio implementations of OFDM technique. OFDMA technique that can deliver advantages of OFDM technique to multi-user and dynamic based systems is more important for modern communications systems. In this study, for the first time in literature, multi-transmitter OFDMA, which is seen a generalized case of OFDM, is implemented using software defined radio technology. Handicaps of multi-user systems are tackled and solved with our implementation. This implementation is also an important step for understanding the basics and structure of modern and future communication technologies.