2
OFDM and OFDMA
2.1 Introduction
The wireless communications industry is evolving from circuit switched systems to all IP packet centric platforms. A common theme for this evolution is the use of OFDM (Orthogonal Frequency Division Multiplexing) and associated multiple access technique called OFDMA (Orthogonal Frequency Division Multiple Access). A major difference between 3G and NGMN (Next Generation Mobile Networks) is that all 3G networks are based on CDMA while NGMN (like 3G-LTE and WiMAX) are based on OFDMA. Thus, it becomes important that we learn about OFDM first before we dive into NGMN.1
Multi carrier modulation systems, of which OFDM is a key example, were first developed in the 1950s for military applications. However, the low cost implementation of OFDM only became possible with the advances in Digital Fourier Transform (DFT) in the 1980s. Further along in history, it was not until the 1990s that we witnessed the first wireless OFDM based standard – the Digital Audio Broadcasting (DAB). Next we highlight some historical perspectives [1] in the development of OFDM:
- 1958: Kineplex, a military multi-carrier high frequency communication system (R.R. Mosier and R.G. Clabaugh).
- 1966: R. W. Chang at Bell Labs published the OFDM paper “Synthesis of band-limited orthogonal signals for multi-channel data transmission.”
- 1970: First patent (US3488445 “Orthogonal Frequency Multiplex Data Transmission System”) issued to R. W. Chang on OFDM.
- 1971: Weinstein and Ebert proposed the ...
