Systems, methods, and circuitries are provided for performing sidelink communication. An example method indicates a frequency resource reservation in sidelink control information (SCI). The method includes identifying a transport block (TB) for transmission to a UE; determining a total number of sub-channels (NSL) in a resource pool for sidelink communication, a number of sub-channels (Lsub) of the TB, a first starting sub-channel index x1 of a first retransmission of the TB, and a second starting sub-channel index x2 of a second retransmission of the TB. The method includes determining a frequency resource indication value (FRIV) based on NSL, LSUB, x1, and x2, wherein the FRIV represents a result of a predetermined function of Lsub, x1, and x2 that generates a unique value for possible combinations of Lsub, x1, and x2. The FRIV is encoded in SCI and the SCI is transmitted to the UE.