OFDM multi-antenna designs with concatenated codes

This paper considers practical link designs that include different transmit, receive, and coding schemes for an OFDM system with two transmit and two receive antennas. In conjunction with studies on theoretical outage capacity, we compare link designs in terms of simulated frame error rate (FER) performance in different propagation environments. For channel coding, serial and parallel concatenated turbo-like codes are used and compared. For receive schemes, we compare maximum likelihood (ML) and linear MIMO receive algorithms and propose modifications to improve turbo decoding. For transmit schemes, we compare the Alamouti (1998) diversity scheme, a single-stream MIMO, and a multi-stream MIMO design. Interestingly, a 2×2 MIMO-OFDM design with ML receivers is found to under-perform the 2×2 Alamouti-OFDM design at low spectral efficiencies (e.g., 2, 4 b/subcarrier), even though MIMO has a slightly higher theoretical capacity. Also, the gap between the SNR required by the theoretical 1% outage capacity and that required by the single-stream MIMO-ML design at 10^-2 FER is only 1-2 dB at spectral efficiencies of 2, 4 and 6 b/subcarrier, in an environment with rich spatial and frequency diversity.