Effects of code rate and channel estimation on OFDM and OFDM-CDMA waveforms

Orthogonal Frequency Division Multiplexing (OFDM) is a widely used technique for data transmission on multipath fading channels. The multipath component of these types of channels causes a phenomenon known as frequency selective fading. This type of fading can severely degrade or completely eliminate the signal energy of many of the OFDM tones producing an irreducible error rate, even when no noise is present. In the early 1990's, researchers combined some of the characteristics of Code Division Multiple Access (CDMA) and Spread Spectrum (SS) with OFDM in order to create a more robust modulation scheme capable of surviving frequency selective fading without the need for forward error correction (FEC) techniques and thus OFDM-CDMA was born. This paper will investigate how the code rate and channel estimation affect the performance of coded OFDM and OFDM-CDMA waveforms on various HF multipath/fading channels.

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