In the transmission of a signal between two points, a set of primary parameters is the ratio 2B of transmission bandwidth to signal bandwidth, the required signal-to-noise ratio P 0 , the ratio P c of transmitted power-to-noise density, and some measure of system complexity. The constraint here imposed on system complexity is not to allow coding in the time domain beyond that which is incidental to expanding the base signal bandwidth. Typically, the original signal is first quantized into M levels where M = \sqrt{2P_{0} + 1} . The M -ary digits are then transformed, into M ' ary digits, where M'/log M' = 4B/log M . This is done to have the transmitted signal just fill the available transmission bandwidth. Transmission space is divided into M ' biorthogonal components, such as two quadrature channels in each of M'/4 noninterfering frequency channels. The M ' integer then transmitted is a pulse in the appropriate one of the M ' phase-frequency channels, and is detected by a maximum likelihood device. The resulting coding scheme reduces to conventional modulation methods such as AM, FM, PM, and PCM for certain combinations of P 0 and B , but for all other cases requires lower P c .