A new class of SETI beacons that contain information (22-aug-2010)

TL;DR

This paper proposes a new class of interstellar SETI beacons using wideband signals with delayed copies, enabling both easy detection and high information capacity, and outlines an efficient autocorrelation-based discovery method.

Contribution

It introduces a novel wideband beacon design with delayed copies that cancel dispersion effects and provides an efficient autocorrelation detection scheme.

Findings

Wideband signals with delayed copies are effective beacons.

Detection can be achieved with roughly twice the processing of traditional sine wave searches.

The proposed method allows high information rates limited by atmospheric transparency.

Abstract

In the cm-wavelength range, an extraterrestrial electromagnetic narrow band (sine wave) beacon is an excellent choice to get alien attention across interstellar distances because 1) it is not strongly affected by interstellar / interplanetary dispersion or scattering, and 2) searching for narrowband signals is computationally efficient (scales as Ns log(Ns) where Ns = number of voltage samples). Here we consider a special case wideband signal where two or more delayed copies of the same signal are transmitted over the same frequency and bandwidth, with the result that ISM dispersion and scattering cancel out during the detection stage. Such a signal is both a good beacon (easy to find) and carries arbitrarily large information rate (limited only by the atmospheric transparency to about 10 GHz). The discovery process uses an autocorrelation algorithm, and we outline a compute scheme where the beacon discovery search can be accomplished with only 2x the processing of a conventional sine wave search, and discuss signal to background response for sighting the beacon. Once the beacon is discovered, the focus turns to information extraction. Information extraction requires similar processing as for generic wideband signal searches, but since we have already identified the beacon, the efficiency of information extraction is negligible.