OFDM and its application to 4G

Summary form only given. Orthogonal frequency-division multiplexing (OFDM) is a bandwidth-efficient signaling scheme for wideband digital communications. The main difference between frequency division multiplexing (FDM) and OFDM is that in OFDM, the spectrum of the individual carriers mutually overlap. Nevertheless, the OFDM carriers exhibit orthogonality on a symbol interval if they are spaced in frequency exactly at the reciprocal of the symbol interval, which can be accomplished by utilizing the discrete Fourier transform (DFT). With the development of modern digital signal processing technology, OFDM has become practical to implement and has been proposed as an efficient modulation scheme for applications ranging from modems, digital audio broadcast, to next-generation high-speed wireless data communications. For example, the high-speed wireless LAN standard IEEE 802.11a is based on OFDM. We discuss receiver design for OFDM systems signaling through unknown frequency-selective fading channels. In particular, we focus on the design of turbo receivers in a number of OFDM systems, including an OFDM system with frequency offset, a space-time block coded OFDM system, and a space-time coded OFDM system based on low-density parity-check (LDPC) codes.