A Digital Spectral Limiter for a Synchronous Multiple-Access Satellite Communication.
MASSACHUSETTS INST OF TECH LEXINGTON LINCOLN LAB
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A satellite processing concept for automatically power-balancing the simultaneous accesses of non-cooperative users was investigated. Basically, the scheme consists of a forward and backward fast Fourier transformation with an intermediate clipping operation on spectral magnitudes exceeding an adaptive threshold. The clipper is suitable for applications involving many low-cost mobile terminals where the transmitting terminals need not or cannot pre-correct Doppler shifts or fine timing. As a satellite component preceding a bandpass hard-limiting transponder, the spectral clipper presents an easier alternative to complete in-satellite demodulation of the user signals. Computer simulations of ten pseudorandomly specified users indicate a significant improvement in the performance of the weaker users compared to a hard-limiting transponder. Both an orthogonal block code and a convolutional code with maximum-likelihood decoding were simulated. The spectral-clipping scheme would also be effective with PSK modems and in strong narrowband interference. Implementations composed of 100 integrated circuit packages consuming 10 watts of power are feasible. Author
- Radio Communications