In this paper we present a novel joint network-channel coding scheme for the time-division Multiple Access Relay Channel (MARC), which combines Bit-Interleaved Coded Modulation with iterative decoding (BICM-ID) based on nonbinary Low-Density Parity Check (LDPC) codes, along with the linear combination of blocks of data at the relay. The common receiver iteratively exchanges soft information between a joint soft demapper and the LDPC decoder associated to the transmitting nodes. The performance of the proposed system is compared, in terms of Frame Error Rate (FER) and through intensive Monte Carlo simulations, with the corresponding theoretical outage rate for different values of the spectral efficiency of the overall setup. Two main conclusions are drawn: 1) small FER degradation is obtained as the spectral efficiency increases; and 2) no diversity is lost with respect to the theoretical outage rate.