Sets of frequency ranges allocated among mobile networks for mobile phone use. Cell phone repeaters are created to improve different frequencies.
Communication signal exchange goes the following way:
Cell Tower>>Donor antenna>>Repeater Outdoor downlink (amplifies signals)>>Sever antenna>> Mobile phone (receives signal after amplification). After it communication goes in reverse order: the phone (transmits signal)>>Sever antenna>>Repeater indoor uplink>>Donor antenna>>Cell Tower.
To put it shortly, the signal goes in two directions: to phone and from it.