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On rising demand for high quality, mobility and data rate, a considerable effort has been given to develop robust coding techniques for wideband channels. Significant achievements are obtained with multiantenna communications and Orthogonal Frequency Division Multiplexing (OFDM). After the work of Agrawal et al. (1998), the application of Space-Time Block Codes (STBC) to OFDM was suggested by Lee and Williams (2000). Afterwards, the efforts to increase the performance of Multiple-Input Multiple- Output (MIMO) OFDM systems are ongoing. The MIMO OFDM system performance is primarily affected by achieved diversity, and there is a tradeoff between rate, diversity and constellation size. Hence, the only way to increase the diversity in a wideband channel, with unlimited number of channel taps, fixed number of transmit and receive antennas, fixed bandwidth, and bandwidth efficiency, is to extend the constellation of the signals modulating OFDM subcarriers and to encode through these subcarriers. Such systems achieving multipath diversity in wideband channels are the Linear Constellation Precoded (LCP) OFDM and the concatenated LCP and STBC (LCP-STBC) OFDM proposed by Liu et al. (2003; 2002). It is further possible to achieve multipath diversity by trellis encoding through OFDM subcarriers. Such system is the serial concatenated outer convolutional code and LCP-STBC (SC-LCP-STBC) proposed by Wang et al. (2003). The high computational complexity of Maximum Likelihood (ML) sphere decoder (Damen et al., 2000) used with LCP-STBC and turbo decoder used with SC-LCP-STBC leads to a search for techniques with lower decoding complexities. The concatenation of an outer trellis code and STBC (TC-STBC) for OFDM proposed by Gong and Letaief (2003) is an effective coding technique with simple Viterbi decoding. In this system the 8-PSK trellis codes (Jamali and Le-Ngoc, 1991; Schlegel and Costello, 1989) designed for fast fading channels are involved. Gong and Letaief (2003) showed that TC-STBC has superior performance compared to the other trellis coded MIMO OFDM systems (Agrawal et al., 1998; Lu and Wang, 2000). On the other hand, coordinate interleaving (Boulle and Belfiore, 1992; Jelicic and Roy, 1994), applied to MIMO OFDM by Rao et al. (2004), is a powerful technique providing diversity by extending the considered signal constellation. Additionally, the single symbol decodability of Coordinate Interleaved Orthogonal Designs (CIOD) is an important feature ensuring low decoding complexity. In this paper, we propose a concatenated outer trellis code and CIOD (TC-CIOD) OFDM system for high-speed wireless transmission. Our system combines a coordinate interleaver and trellis code to boost the MIMO OFDM performance. The coordinate interleaver provides signal space diversity and improves the Codeword Error Rate (CER) performance of the system in wideband channels. The pairwise error probability analysis of the new system for two transmit antennas shows that the system provides full spatial and multipath diversity, and the TC-CIOD achieves diversity as high as SC-LCPSTBC (Wang et al., 2003) and nearly four times greater than TC-STBC system (Gong and Letaief, 2003), while still preserving the advantage of simple ML Viterbi decoding.… [ABSTRACT FROM AUTHOR]