Design and analysis of post-coded OFDM systems

This paper discusses the design and analysis of post coded OFDM (PC-OFDM) systems. Coded or precoded OFDM systems are generally employed to overcome the symbol recovery problem in uncoded OFDM systems. We show that PCOFDM systems are a special case of precoded OFDM systems that offer advantageous complexity-performance trade-offs. In particular, PC-OFDM systems introduce frequency diversity by manipulating the OFDM symbols in the time domain so that the computational complexity of the system can be significantly reduced. We discuss the design principles of PC-OFDM transmitter that uses upsampling operation and the spreading codes to introduce frequency diversity. We obtain the spreading code construction criterion for minimum error performance and give examples of spreading codes for PC-OFDM systems. We also describe the design of low-complexity receiver for PC-OFDM systems. In particular, our proposed partial spreading scheme results in a low complexity decoupled detector. The probability of error analysis of the receiver leads us to postulate different design criteria. We investigate different choices for detection algorithms suitable for PC-OFDM receiver and compare their performance through simulations over Rayleigh and IEEE UWB channels.