Basically 5G networks operate just like previous generations of mobile communications networks (2G, 3G or 4G) – the base station transmits a radio frequency signal and communicates with a mobile device. The 5G network will be developed gradually, through upgrading of existing networks at existing locations.

The frequency bands to be used primarily for 5G technology in Croatia are 700 MHz and 3.6 GHz, and at a later stage 26 GHz. In the future, a part of the bands currently used for 2G, 3G and 4G will also be used for 5G, as well as additional new frequency bands.

Given the expected data transmission speed and the large capacity of 5G networks, the number of base stations will increase, especially the newly installed small cells, which will cover areas that are not sufficiently covered by macro base stations. Also, for the same reason base stations will have to connect each other using high capacity and low latency aggregation networks, which will in most cases be realized with a fibre-optic network.
Radio frequency bands to be primarily used for 5G compared to 2G/3G/4G:

2G/3G/4G 5G
800 MHz 700 MHz
900 MHz 3,6 GHz
1800 MHz 26 GHz
2,1 GHz  
2,6 GHz  

The 700 MHz frequency band (694-790 MHz) will primarily be used for the widest possible geographical coverage of areas in rural and remote environments. Harmonised technical conditions are laid down in Decision (EU) 2016/687 i.e.ECC/DEC/(15)01.

The 3.6 GHz band (3.4-3.8 GHz) will be mainly used to achieve as high capacity as possible in urban areas. Harmonised technical conditions are prescribed by Decision (EU) 2019/235 i.e.ECC/DEC/(11)06 for base stations with inactive antenna systems (non-AAS) and with active antenna systems (AAS).

The 26 GHz band (24.25-27.5 GHz) will initially be used for high capacity Fixed Wireless Access (FWA). Harmonised technical conditions are prescribed by Decision (EU) 2019/784, odnosno ECC/DEC/(18)06.

Coverage of large geographic areas in mobile communication networks is achieved by macro base stations placed on masts and roof tops. In case the additional capacity in the network is needed or in case of indoor installations, small cells shall be installed. Possible types of such installations include installations on side walls of existing buildings, traffic infrastructure, advertising boards, street lights and street furniture in general. Since the implementation of 5G networks is expected to increase the number of such stations, at the EU level it is planned to prescribe the technical characteristics of such base stations for which a simplified legal installation procedure is predicted. These are small area access points (up to 30 l volume) operating with small radiated power (EIRP up to 10 W), which will be deployed closer to small and micro-target coverage areas. The technical characteristics of these small cells and their installation shall comply with the European standard EN 62232:2017.

More information on the opinion of the European Commission on the simplified procedure for the deployment of 5G stations and EMP issues can be found in the following document.
The 5G base station must support gigabit transmission speeds, for which it is necessary to ensure and build an aggregation network of high capacity and low latency. It is predicted that in most cases the optical network shall be deployed.
Detailed technical specifications can be found on the following link of 3GPP initiative.