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Abstract

A SAMA QAM demodulator and packet detector receives SAMA transmissions from multiple transmitters. The received data packets have bits divided into chips in a first spreading sequence in the in phase branches of the transmitters, and a second spreading sequence in the quadrature branches of the transmitters. A demodulator at the hub station has a received signal splitter and an oscillator and phase shifter and multipliers for mixing the incoming signals with the oscillator output and with the phase shifted oscillator output on different branches. Low pass filters are connected to the mixers to remove the carrier signals and to leave chip signals with cosine and sine of phase offsets. The signal from each low pass filter is fed to an in phase matched filter and a quadrature matched filter, four matched filters in total, to produce despread signals from all of the active transmitters with phase relation and start offsets. The signals from the individual matched filters are passed to packet synchronization sequence detectors, which detect the start times of each of the data packets. The start times of the data packets and estimates of the phase angles are used in bit decisions in which substantially concurrent data packets received from remote transmitters are separated.

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