A two-level packet satellite network architecture is proposed to provide efficient communications for a large number of low duty factor terminals. At the first level, disjoint subnets of prioritized users employ a minislotted alternating priorities (MSAP) protocol. At the second level, a time division multiple access (TDMA) or frequency division multiple access (FDMA) uplink, and a time division multiplexed (TDM) or frequency division multiplexed (FDM) downlink is assumed, with the satellite regenerating and reformatting the data appropriately. Examples with a large number of terminals show that the two-level schemes provide superior delay performance over single-level methods for wide ranges of throughput.

Modulation waveforms with continuous derivatives in conjunction with a receiver whose impulse response has continuous derivatives is shown to generate crosstalk interference in a correlation demodulator that decreases at least as the cube of the carrier spacing between waveforms. Constant envelope, continuous-frequency modulations called Continuous (Frequency) Shift Keying (CSK) are proposed which not only achieve this asymptotic crosstalk behavior but are better then Phase Shift Keying (PSK) and Minimum Shift Keying (MSK) for carrier spacings of at least 1.1 times and 2.0 times the data rate, respectively. CSK can be demodulated in Gaussian noise with no loss with respect to optimum hard-decision receivers of antipodal signals, i.e., with the same performance as PSK and MSK.

A suboptimal receiver of constant envelope, continuousfrequency MSK-type modulations called Continuous Shift Keying (CSK) is proposed that halves demodulator complexity with no more than a 1.6 dB loss in detectability in AWGN. The technique is especially applicable to a frequency division multiple access system composed of many unsynchronized user terminals.

The effects of worst-case crosstalk (from a time-domain point of view) on unsynchronized frequency division multiplexed (FDM) constant envelope modulations are considered assuming coherent hard-decision receivers and no filtering for bandwidth constraint. Continuous-phase frequency shift keying (FSK) is found to be superior to various forms of phase shift keying (PSK).

The degradation in correlation receiver performance due to signal distortion at the transmitting antenna is computed as a function of processing delay for simple but representative models of the Sanguine antenna and input waveforms. The optimum delay and minimum distortion loss are given parametrically in terms of the ratio of the 3 dB bandwidth of the signal process to that of the antenna. For the more realistic model considered the degradation can be reduced significantly to just a fraction of a dB by optimizing the receiver delay.

Given the alphabetA = \{ \pm a_0, \cdots, \pm a_i, \cdots, \pm a_{N-1} \}the problem investigated is the construction of the largest set of mutually orthogonal sequences of lengthnunder the following constraint on the form of the sequences. Each sequence is a concatenation ofnelements fromAbut not all concatenations are allowed. Rather, the sign of thejth element is negative if and only if the(j - 1)st element is negative with an odd subscript, or the(j - 1)st element is positive with an even subscript. Such sequences have application in continuous-phase frequency-shift-keyed communication. The principal result is the construction of optimal sets of\nu (N,n)mutually orthogonal sequences under the phase constraint. Ifnis the order of a Hadamard matrix, then\nu = nN/2, forNeven, andn(N - 1)/2 + 1, forNodd.