GSM repeaters are designed specially to use with GSM mobile phones. These repeaters use to amplify the GSM signals so that better services of GSM can be availed. There are many reasons because of which low signals are not accepted by the cell phones.
Most of the time in the blind zones network coverage use to be low and with that same is experienced in the building with thick walls or in locations which are below the ground. In all these situations it is difficult that radio waves can reach to the device. So to here we get help from these GSM repeaters to boost the network services.