CESSB (controlled-envelope single-sideband) is a

narrowband Narrowband signals are signals that occupy a narrow range of frequencies or that have a small fractional bandwidth. In the audio spectrum, narrowband sounds are sounds that occupy a narrow range of frequencies. In telephony, narrowband is usua ...

modulation In electronics and telecommunications, modulation is the process of varying one or more properties of a periodic waveform, called the ''carrier signal'', with a separate signal called the ''modulation signal'' that typically contains informatio ...

method using a

single sideband In radio communications, single-sideband modulation (SSB) or single-sideband suppressed-carrier modulation (SSB-SC) is a type of modulation used to transmit information, such as an audio signal, by radio waves. A refinement of amplitude modul ...

, whose peak envelope level is controlled so that the peak-to-average power ratio of CESSB is much reduced compared to standard SSB modulation and offers improved effective range over standard SSB modulation while simultaneously retaining backwards compatibility with standard SSB radios. A drawback of standard SSB modulation is the generation of large envelope overshoots well above the average envelope level for a sinusoidal tone (even when the audio signal is peak-limited). In combination with RF amplifiers with non-linear properties this causes severe distortions of the transmitted audio signal. Therefore, the average RF power level must be reduced in order to accommodate the overshoots. The standard SSB envelope peaks are due to truncation of the spectrum and nonlinear phase distortion from the approximation errors of the practical implementation of the required

Hilbert transform In mathematics and in signal processing, the Hilbert transform is a specific linear operator that takes a function, of a real variable and produces another function of a real variable . This linear operator is given by convolution with the functi ...

. It was recently shown that suitable overshoot compensation (so-called controlled-envelope SSB, or CESSB) achieves about 3.8 dB of peak reduction for speech transmission. This results in an effective average power increase of about 140%. Although the generation of the CESSB signal can be integrated into the SSB modulator, it is feasible to separate the generation of the CESSB signal (e.g. in form of an external speech preprocessor) from a conventional SSB radio. This requires that the SSB radio's modulator be linear-phase and have a sufficient bandwidth to pass the CESSB signal. If an otherwise conventional SSB modulator meets these requirements, then the envelope control by the CESSB process is preserved. CESSB is being used experimentally by

amateur radio Amateur radio, also known as ham radio, is the use of the radio frequency spectrum for purposes of non-commercial exchange of messages, wireless experimentation, self-training, private recreation, radiosport, contesting, and emergency communic ...

operators and is implemented by some radios in the amateur marketplace. SmartSDR software by Flex Radio Systems implements CESSB, as does the Elecraft K4 transceiver.

References

Radio modulation modes {{telecomm-stub

See also

References