In numerous communication systems different users need to share the same bandwidth known as Multiple Access. In the past, multiuser systems used to be dominated by some multiple access schemes such as CDMA and Hybrid FDMA-TDMA. Whereas, after successfully implementation of Orthogonal Frequency Division Multiplexing (OFDM) in many digital systems, many effective steps have been taken to exploit OFDM in multiuser systems leading to dawn of some new brilliant techniques. In this work we are going to implement and compare two of these OFDM based multiuser systems including Orthogonal Frequency Division Multiple Access (OFDMA) and Multi-Carrier Code Division Multiple Access (MC-CDMA) over a frequency selective channel. Furthermore, to increase the error correction capability of the system powerful Low-Density Parity Check (LDPC) codes will be deployed. Regarding to the performance results, LDPC coded MC-CDMA performs slightly better than LDPC coded OFDMA. Moreover, usual Sum-Product Algorithm (SPA) LDPC decoding encounters does not work properly while transmitting over multipath fading channels, should be replaced by another decoding method known as Min-sum Algorithm decoding which is designed based upon the SPA.