The concept of a processing satellite with multiple slotted ALOHA uplinks to efficiently fill a TDM downlink is extended to include multiple downlinks. Throughput is derived for a general configuration withnALOHA uplinks andmTDM downlinks. An optimization procedure is described to select thenandmwhich maximize throughput for a given bandwidth constraint. The ALOHA/TDM system with multiple downlink capacity is found to be up to 32% more spectrum-efficient than the conventional slotted ALOHA system. The ALOHA/TDM system also has the potential for payload power and weight savings and decreased passive intermodulation problems.

For FDM users with arbitrary quadrature-carrier modulation, signal smoothness at bit transitions is shown to completely determine mean-square crosstalk between users at large frequency spacings. To find modulation forms which reduce interference between users at closer spacings, where crosstalk is not dependent solely on bit transition smoothness, optimum windows are generated by numerical minimization of mean-square crosstalk. First a one-parameter class of modulation which includes MSK and SFSK is optimized. Then optimization is extended to the general class of constant-envelope quadrature modulation. The resulting modulation forms experience lower crosstalk than MSK or SFSK and permit closer spacing of users.

Expressions for probability of block error,P_{f}(M,N), the probability of more thanMerrors in a block ofNdigits, are derived for binary signaling over a channel with very slow nonselective Reyleigh fading and additive Gaussian noise. The analysis is applicable to noncoherent FSK, coherent FSK, and coherent PSK signaling. An asymptotic expression for the block error probability, suitable for high signal-to-noise ratio, is also derived. Computations ofP_{f}(0,N)are presented for a broad range of error probabilities and block sizes, and the characteristics of block error probabilities for the fading and nonfading cases are compared.