Non-Redundant and Redundant Post Coding in OFDM Systems
Orthogonal frequency division multiplexing (OFDM) provides a viable solution to communicate over frequency selective fading channels by converting them to an equivalent collection of flat fading channels. In doing so, OFDM systems fail to reap the benefits of diversity available in multipath fading channels. To ameliorate this shortcoming of OFDM, explicit diversity in the form of redundant or non-redundant coding is needed. Our main goal in this paper is to explore different options for low complexity encoder design and compare their performance and complexity. Specifically, in the class of non-redundant codes we discuss the use of signal space diversity codes in OFDM systems. For redundant codes, we introduce a novel low complexity postcoded-OFDM system where coding is employed after performing the IFFT (inverse fast Fourier transform) in the transmitter to reduce system complexity. Simulation results show that postcoded-OFDM with redundant coding outperforms other choices of encoder design considered in this paper