Cellular coverage inside concrete buildings is usually less than optimal. The thick, dense walls block the cellular signal. Several options can boost your reception inside this type of structure. External antennas are the least expensive option, but they only work for one phone at a time, and require a physical connection between the phone and antenna. Femtocells are wireless and work for multiple phones, but many carriers charge a subscription fee for using one, on top of the charge for the unit itself. Cellular repeaters don't require a subscription, but are more expensive than the cost of a femtocell unit and require a permanent installation.
1. Add an external antenna to your phone. These antennas use two parts. The adapter cable plugs into the external antenna jack on the phone and connects to the antenna unit. This allows manufacturers to use a single antenna with different phones. Some phones have an external antenna jack. On phones without an antenna jack, you can use a stick-on adapter. Sit the antenna in a window for the best reception.
2. Purchase a femtocell, which is a wireless device that connects to a broadband Internet connection. It works much like a regular Wi-Fi hotspot, and some actually have a Wi-Fi hotspot built-in. They broadcast a cellular signal and connect to the carrier's network over the Internet. You can get a femtocell from your cellular carrier.
3. Consider adding a cellular repeater. Cellular repeaters amplify and rebroadcast the carrier's signal. You mount the repeater antenna on the exterior of the building and install the transmitter inside. To prevent interference between the antenna and the transmitter, you must place them a minimum distance apart. In general, the more powerful the repeater, the further the minimum distance. Check the documentation on the repeater for the correct distances before you buy.