Wideband Time Frequency Coding

We present a wideband time frequency coding scheme which combines the impulsive frequency shift keying scheme, shown to achieve the additive white Gaussian noise channel capacity in the wideband regime, with pulse position modulation. This coding scheme allows for information to be encoded in the position of the signal, which impulsive frequency shift keying does not take advantage of. We show that this scheme achieves rates which are comparable with the additive white Gaussian noise channel capacity upper bound, and performs well under a wide range of fading statistics and bandwidths. We show that our proposed scheme outperforms the impulsive frequency shift keying in lower bandwidths, even without optimization of the duty cycle. The scheme is also shown to perform similarly to impulsive frequency shift keying with smaller duty cycles in the wideband regime, indicating that continually decreasing duty cycles are not necessary to achieve rates on the order of additive white Gaussian noise channel capacity. We also discuss comparisons with other spread-spectrum signaling methods under noncoherent fading.