On the error floor of MSK signal transmission over a multipath channel with small time dispersion
The error floor of minimum shift keying (MSK) signal transmission over a mobile radio channel with small time dispersion is analyzed. In contrast to previous investigations, no restrictive assumptions about the impulse response of the channel and/or sampling time are made, and closed-form analytical expressions for the error floor and optimum sampling time are derived. It is found that, generally, the error probability depends on the variance of relative delay (which conforms to the conventional RMS delay spread) as well as on the product of mean relative delays of echoes advancing and succeeding the chosen sampling time, weighted by corresponding mean powers. This implies that (elsewhere widely accepted) simple determination of the error floor by RMS delay spread only can now be seen as a special case when sampling is at mean delay and distribution of the delay profile's power around it is balanced. Furthermore, it is shown that the novel formula reflects the impact of delay profile shape on the error performance (that has been usually neglected, although not always justifiably), and that in general case, the optimum sampling instant is not at the mean delay. The theoretical results are verified by comparison with Monte Carlo (MC) simulations' results; achieved agreement lies within the accuracy of the simulations.