Modern Digital and Analog Communication Systems
Modern Digital and Analog Communication Systems
Bandwidth-efficient wireless OFDM
IEEE Journal on Selected Areas in Communications
| Hi-index | 0.00 |
Orthogonal frequency division multiplexing (OFDM) is a block transmission technique with bandwidth efficient signalling scheme for wideband digital communications. In OFDM the spectrum of the individual carriers mutually overlaps. 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 time Fourier transform (DFT). In the baseband, complex-valued data symbols modulate a large number of tightly grouped carrier waveforms. The transmitted OFDM signal multiplexes several low-rate data streams each data stream is associated with a given subcarrier. The main advantage of this concept in a radio environment is that each of the data streams experiences an almost flat fading channel. In slowly fading channels, the inter-symbol interference (ISI) and inter-carrier interference (ICI) within an OFDM symbol can be avoided with a small loss of transmission energy using the concept of a cyclic prefix. With the development of modern 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. The high speed wireless LAN standard IEEE 802.11a is based on OFDM. Also OFDM is been used for WIMAX and a candidate for 4G technology. This paper is an attempt to understand multiple effects of varying length of cyclic prefix for Additive White Gaussian Noise (AWGN) channel and with Rayleigh fading channel.