Overview
NeTS: Small: Low Latency Uplink Communications in Low Earth Orbit (LEO) Satellite Networks with Chirp Permutation Multiple Access (CPMA)
Low Earth Orbit (LEO) satellite networks have emerged as an attractive option that complements the existing wireless infrastructure, especially for providing broadband wireless data services to areas that are traditionally difficult to reach, such as rural areas and ocean. One of the main challenges in LEO networks is to support applications that require low latency, such as automatic driving, because the signal propagation time is much longer than those in 5G and Wi-Fi networks due to the physical distance from the user terminal to the satellite, which can be 550 km (340 mi) or more. In this project, a novel wireless technology, referred to as Chirp Permutation Multiple Access (CPMA), is proposed. With CPMA, the latency is minimized because the communication is grant-free, i.e., the user terminal can simply transmit the data when the data arrives. This simple ALOHA-style operation is enabled by the novel physical layer of CPMA, which allows the satellite to decode overlapped packets from multiple user terminals. Therefore, CPMA will likely broaden the spectrum of applications that can be supported by LEO networks.
CPMA modulates data by transforming the chirp, which is a complex vector with constant magnitude and linearly increasing frequency. The key novelty of CPMA is to permute the chirp, which can very effectively reduce the impact of interference from one user terminal to others. In this project, both the physical layer and the link layer of CPMA will be designed, implemented, and tested. The physical layer will be optimized with permutations that have proven guarantees and a novel multi-layer modulation that employs multiple type of transformations of the chirp. The link layer will fully harness the capabilities of the physical layer and solve problems such as efficient packet retransmission and power control. Theoretical analysis will be conducted to reveal the network capacity and prove the optimality of the design. CPMA will be implemented on USRPs and demonstrated in open platforms such as POWDER, as well as evaluated with simulations driven by widely accepted channel models and channel traces.
