Performance analysis of multi-user mixed RF and hybrid RF/FSO cooperative systems with buffers based on GC-LDPC codes

This article analyzes the impact of the use of error correcting codes, in particular globally coupled LDPC codes (GC-LDPC) in a double-hop relay system composed a multiuser mixed radio frequency (RF) and hybrid RF/FSO (free-space optical). For this configuration, communication between mobile users and a destination is via a buffer assisted decoding and retransmission relay node. Users transmit their data to the relay node over RF links using a virtual multiple input multiple output (MIMO) system. The relay node after decoding the data of all users using two-phase local-global decoding, this data will be transmitted to the destination via an FSO link supported by an RF MIMO backup system to the destination. A multi-antenna listener listens to information by decoding data received from users. The relay temporally stores user data in its buffer memory until the best channel conditions on the relay-destination link are met. For this communication setup, we first suggest using GC-LDPC codes for data encoding and decoding. The numerical results validate that buffering in the physical layer and the use of GC-LDPC codes significantly improve system performance. It is also found that the use of the relay buffer memory, the back-up RF link (in the second hop) and the use of GC-LDPC codes help protect user data against atmospheric turbulence.