Alternative interleaving schemes for interleaved orthogonal frequency division multiplexing

Abstract

Interleaved OFDM was proposed as an effective solution for improving code rate over slowly varying channels, without affecting the Peak-Average Power Ratio. The system was proposed with a particular interleaving scheme. In this work, a matrix model for Interleaved OFDM (lOFDM) is presented, and it is shown that the interleaving scheme originally proposed for lOFDM is not unique, and that any invertible transform can be used in the place of the interleaving scheme to obtain the same efficient receiver structure. A class of interleaving schemes that preserve the complexity of the original lOFDM system is also presented. An analytical expression for the BER of lOFDM is obtained, and it is shown that the BER performance of lOFDM is independent of the interleaving scheme used, under certain conditions. This also explains why the BER performance of lOFDM is close to that of conventional OFDM systems. The Space-Time Block Coding scheme that was proposed for lOFDM is also analysed using the matrix model. It is shown that the Space-Time Block Coding scheme is independent of the interleaving used at the transmitter. A modification to this scheme is proposed, which yields a little saving in computation at the receiver, without sacrificing performance.