  In the wideband regime, the performance of many of the popular modulation
schemes such as code division multiple access and orthogonal frequency division
multiplexing falls quickly without channel state information. Obtaining the
amount of channel information required for these techniques to work is costly
and difficult, which suggests the need for schemes which can perform well
without channel state information. In this work, we present one such scheme,
called wideband time frequency coding, which achieves rates on the order of the
additive white Gaussian noise capacity without requiring any channel state
information. Wideband time frequency coding combines impulsive frequency shift
keying with pulse position modulation, which allows for information to be
encoded in both the transmitted frequency and the transmission time period. On
the detection side, we propose a non-coherent decoder based on a square-law
detector, akin to the optimal decoder for frequency shift keying based signals.
The impacts of various parameters on the symbol error probability and capacity
of wideband time frequency coding are investigated, and the results show that
it is robust to shadowing and highly fading channels. When compared to other
modulation schemes such as code division multiple access, orthogonal frequency
division multiplexing, pulse position modulation, and impulsive frequency shift
keying without channel state information, wideband time frequency coding
achieves higher rates in the wideband regime, and performs comparably in
smaller bandwidths.
