Abstract
Free space optical (FSO) communication systems provide wireless line of sight connectivity in the unlicensed spectrum, and wireless optical communication achieves higher data rates compared to their radio frequency (RF) counterparts. FSO systems are particularly attractive for last mile access problem by bridging fiber optic backbone connectivity to RF access networks. To cope with this practical deployment scenario, there has been increasing attention to the so-called dual-hop (RF/FSO) systems where RF transmission is used at a hop followed by FSO transmission to another. In this article, we study the performance of cooperative transmission systems using a mixed RF-FSO DF (decode and forward) relay using error-correcting codes including QC-LDPC codes at the relay level. The FSO link is modeled by the gamma-gamma distribution, and the RF link is modeled by the Additive White Gaussian Noise (AWGN) model. Another innovation in this article is the use of cooperative systems using a mixed FSO/RF DF relay using quasicyclic low-density parity check (QC-LDPC) codes at the relay level. We also use the space-coupled low-density parity check (SC-LDPC) codes on the same scheme to show its importance in cooperative optical transmission but also in hybrid RF/FSO transmission. The latter will be compared with QC-LDPC codes. The use of mixed RF/FSO cooperative transmission systems can improve the reliability and transmission of information in networks. The results demonstrate an improvement in the performance of the cooperative RF/FSO DF system based on QC-LDPC and SC-LDPC codes compared to RF/FSO systems without the use of codes, but also to the DF systems proposed in the existing literature.
Highlights
Radiofrequency (RF) communication systems have advantages such as low power with a good operating range and alongside these, here the line of sight (LOS) is not mandatory for communication
By considering a gamma-gamma model free space optical (FSO) optical channel, an Additive White Gaussian Noise (AWGN) model RF channel, PPM modulation, and using quasicyclic low-density parity check (QC-low-density parity check (LDPC)) codes (Figure 3), Figure 7 presents the BER performances obtained as a function of SNR in decibel to compare the performances of the RF/FSO cooperative system using a QC-LDPC decoding before retransmission (DF) relay (Figure 3), a cooperative system using an RF/FSO relay without the QC-LDPC codes and a FSO cooperative system
It is shown that hybrid RF/FSO systems give better performance in atmospheric conditions of low turbulence compared to atmospheric conditions of high turbulence
Summary
Radiofrequency (RF) communication systems have advantages such as low power with a good operating range and alongside these, here the line of sight (LOS) is not mandatory for communication. This is an advantage which improves information security (interception of data impossible from the outside), but which obviously limits the coverage and makes this technology very sensitive to blocking phenomena It is in this launch that we are proposing an RF/FSO architecture in which we use RF links over long distances, that is to say between the aggregation node to the BST antennas, from a BTS antenna to the other BST antenna and FSO transmission over short distances of less than 1 km is from the BTS antenna towards the places of destination (inside cities).
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