MIMO-OFDM: Basic Relations between Coding, Spreading, Multicarrier and Singlecarrier Transmission

This contribution considers the basic relations between coding, spreading, multicarrier and singlecarrier transmission against the background of MIMO-OFDM. MIMO-OFDM is taken, because it can be regarded as a scheme which contains many others as special cases, and also because of its increasing relevance for future wireless communication. It is shown that spreading plays a central role: Spreading in space, time and frequency can be considered as the most general form of linear space-time-frequency-coding. Additionally it is demonstrated that spreading can be used to transform multicarrier transmissions into singlecarrier transmissions. Moreover, fading channels can be transformed in nonfading ones. This will be demonstrated for the case of Rayleigh fading channels with additive gaussian noise, which become simple gaussian channels. After an introduction and a short description of MIMO-OFDM, the concept of spreading and despreading is explained. It is shown, how spreading produces diversity which can be exploited at the receiving side. If no knowledge about the MIMO channel is available at the transmit side, i.e. if no backward channel can be used, this is an excellent means to cope with frequency- and/or time-selective channels. It is also shown what conventional channel coding can do in this context and what this means at the receiving side. Coding at the transmit side is concatenated with spreading and the MIMO channel. This results in a potential, that can be exploited by iterative detection schemes (turbo equalization/decoding). Simulation results are presented to underline the relevance of theoretical derivations.