A family of new non-orthogonal multiple access techniques named Scrambled Coded Multiple Access (SCMA) is described. It allows different users of a communications system to efficiently share the same bandwidth by using specific scramblers to separate user bursts. SCMA technology is designed for satellite communications with extremely small antenna terminals for potential applications such as asset tracking, sensor networking, and smart grid; and also for latency reduction. The latest variation, Asynchronous Scrambled Coded Multiple Access (A-SCMA) on the other hand, not only removes the need for timeslot synchronization and precise power control, but also offers an unprecedented system throughput of more than 4 bits/symbol at a modest per user signal to noise ratio (SNR).

Asynchronous Scrambled Coded Multiple Access (A- SCMA) has been shown to offer high spectral efficiencies on Random Access (RA) channels. This paper describes a new multiple access scheme, SA- SCMA, that adds spreading. Even modest spreading provides significant gains in spectral efficiency, while the use of large RRC rolloff combined with adjacent channel interference cancellation (ACIC) further enhances performance. Spectral efficiencies achieved are high enough to offer data transfer over RA, eliminating the usual 2-way propagation delay needed to assign resources, lowering latency, an important consideration for geostationary satellite inroutes. Additionally, spreading reduces flux density, enabling smaller antenna apertures needed for lower cost applications. The use of SA- SCMA on a saturated radio to further reduce user terminal cost is also discussed.

Fixed, portable and mobile terminals use Random Access (RA) to transfer data or request more spectrally efficient dedicated resources. This paper describes a new multiple access scheme, A- SCMA, that operates with unsynchronized transmission and low power, making it particularly suitable to small machine-to-machine communications in satellite or terrestrial applications. A multicarrier version operates with large and variable packet sizes without reduced throughput or large delays.

The problem of efficient utilization of the frequency spectrum for satellite systems is investigated; one which results as a consequence of highly crowding adjacent channels. An analytical characterization of the resulting interference channel is introduced and then exploited for interference cancellation. Two classes of cancelers are investigated. The first approach does not benefit from the forward error control (FEC) coding information which limits the performance gain. This motivates the second approach where a joint implementation of interference cancellation and decoding is developed using soft-input-soft-output (SISO) modules along with the iterative structure. It is shown that iterative interference cancellation techniques can achieve significant gains compared with the single-user matched filter receiver.

The problem of efficient utilization of the frequency spectrum for coded satellite systems is investigated; one which results as a consequence of highly crowding adjacent channels. An analytical characterization of the resulting interference channel is introduced based on concepts in statistical decision theory and is then exploited for interference cancellation. A joint implementation of MMSE interference cancellation and forward error control (FEC) decoding is considered where soft-input soft-output (SISO) modules are used along with the iterative structure. It is shown that, for example, one can operate a satellite system with convolutionally encoded QPSK modulation that uses practical pulse shaping at the channel spacing valve of 0.75 of the symbol rate, or bandwidth efficiency level of 2.67 bits-per-second/Hz, with minimum additional energy requirement. (This corresponds to a spectral efficiency improvement of 55% compared with a conservative baseline system.).