Iterative Estimation and Demodulation for Improved Joint Random Access Satellite Communications
Dickson, Ernest Paul
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This thesis investigates high throughput random access communications in the satellite up-link environment. In this environment it is typical for a large number of un-coordinated, mobile transmitters scattered over a large geographic area to connect intermittently to a single receiver over the satellite channel. This configuration fundamentally results in a random access scenario, where a large number of potential users contend for access to limited channel resources. Complexity is increased due to the geographic spread and localized weather effects which make it possible for each user have its own independent channel that must be estimated to ensure a high level of system performance. To this point research efforts have been focused on the development of access protocols capable of approaching the single user capacity, and have succeeded in asymptotically approaching it, however previous efforts have shown that the application of joint detection and multiple packet reception (MPR) techniques make it is possible to surpass the capacity of the current single-user random access channel. The majority of this previous work is focused on improving ALOHA protocols which show a common behavior of collapsing when the number of users is the system exceeds the number of signaling dimensions. While previous results have excelled at reducing the packet loss ratio and achievable throughputs at low SNR with low normalized system loads, little has been done to address the high-SNR case where the expected number of transmissions per signaling dimension is greater than one. In this thesis it is proven that it is possible to operate in an uncoordinated multi-user environment with system loads up to 1.96 in the high-SNR region under realistic conditions.