The impact of coupling/filtering on orthogonal M-FSK

Abstract

This study exposes the impact of the transmitter coupling circuitry's varying filter characteristic, as a result of the fluctuation in power-line impedance, on the performance of individual orthogonal M-FSK (M-ary frequency shift keying) symbol carriers in the presence of AWGN. Traditionally, performance characteristics for orthogonal M-FSK in the presence of AWGN assume that the individual symbol carriers are exposed to the same channel signal-to-noise ratio (SNR). This is true in the case where only the flat part of the magnitude response of the coupling circuit is considered adequate for symbol carrier positioning. However, with bit loading techniques and error correction even the non-flat parts with steep roll-off can be used to position additional symbol carriers, thus creating possibilities for increased robustness against frequency-related disturbances as a result of using more symbol carriers. When this option is used, the individual symbol carriers are not always exposed to the same channel SNR. This study assumes only the presence of AWGN, due to its emphasis on the impact of the transmitter coupling circuitry's varying filter characteristic.