The soon to be deployed 5G systems are expected to cater an agglomerate of services at profuse data rates wirelessly. Radio over fiber (RoF) networks are the most suitable to implement such systems. In situations where the practical implementation of RoF systems are non-viable, radio over free space optical (RoFSO) links can be employed. The traditional wavelength division multiplexing (WDM) technology can be incorporated to multiply the data rates. However, the link performance may be degraded due to various atmospheric factors. This can be compensated using multiple input multiple output (MIMO) techniques. In this paper, the performance analysis of such a WDM RoFSO link for 5G frequencies is carried out. The work also presents quantitative performance comparison between single input single output (SISO) and MIMO RoFSO links for 5G systems which will be useful for researchers in this area. It is observed that, while WDM provides additional data capacity, it degrades the link performance under adverse weather conditions which can be counterbalanced using MIMO techniques.

The ubiquitous deployment of 5G systems is expected shortly. The 5th generation systems are envisioned to deliver a comprehensive selection of services with revolutionary data rates through a single network. Optical fiber networks are going to be the backbone of such 5G systems endowing huge data transfers. Radio over Fiber (RoF) is a promising network architecture that can provide all the provisions envisaged in the development of 5G systems. However, in certain scenarios, these fiber optic networks may encounter empirical problems in deployment. Radio over Free Space Optical (RoFSO) links can be used as an alternate in such environments. To increase the data carrying capacity of the link, Wavelength Division Multiplexing (WDM) communication equipping multiple wavelengths can be used. The free space link may suffer from atmospheric disturbances like rain, fog, and haze. In such adverse conditions, Multiple Input Multiple Output (MIMO) transceivers can be used to increase the link performance. In this work, the performance analysis of such WDM MIMO RoFSO links carrying 5G frequencies is carried out. The work also presents a comparison of single path and MIMO RoFSO links, single channel and WDM RoFSO links, and a combination of these. It is found that, transporting data over WDM channels can increase the capacity of the RoFSO system tremendously while the MIMO link setup can maintain the transmission range and link performance even when high data rates are used. HIGHLIGHTS A quantitative performance comparison of Radio over Free Space Optical links WDM increases the capacity while the MIMO links help to maintain the transmission range A combination of WDM and MIMO RoFSO links is identified to be the best

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