1. A method for transmitting Channel State Information (CSI) in a communication system, the CSI having a reporting mode and being transmitted from a User Equipment (UE) over a Physical Uplink (UL) Shared CHannel (PUSCH) transmission in an UL cell, the UL cell being associated with a Downlink (DL) cell, the PUSCH transmission being in response to a receiving, by the UE, of a Downlink Control Information (DCI) format that includes a CSI request field indicating CSI transmission, the CSI corresponding to one of CSI process sets respectively associated with measurements of respective reference signals, the method comprising: obtaining, from the CSI request field, an indication of a CSI process set for a CSI transmission; and transmitting the CSI for the CSI process set indicated by the CSI request field, wherein the CSI request field includes 2 bits of a first CSI process set having a first set of interpretations, wherein, for the 2 bits of the first CSI process set, the first set of interpretations are a 2 bit value of ‘00’ indicates no CSI transmission, a 2 bit value of ‘01’ indicates CSI transmission for a CSI process set corresponding to the DL cell, a 2 bit value of ‘10’ indicates CSI transmission for a first CSI process set, and a 2 bit value of ‘11’ indicates CSI transmission for a second CSI process set.