Multi-User Analog Network Coding with Spread Spectrum

In this paper, we propose a physical layer network coding technique combined with asynchronous code division multiple access (CDMA). We consider a scenario where there are multiple pair of nodes with a single relay, and each pair of nodes exchange information asynchronously. With the assumption of asynchronous transmission, there is a trade-off between the number of nodes and the inter-user interference because the spreading codes are not orthogonal to each other. The BER and the throughput of the system are analyzed, and simulations are performed to verify the results. It is shown that physical layer (analog) network coding improves throughput compared to the conventional routing protocol with large E_b/N₀, low number of users, and large spreading factor.