RSCP: The “Received Signal Code Power” (RSCP) is the collected RF energy after the correlation / descrambling process, usually given in dBm. Only this code power is of interest for the following receiver stages when judging on the quality of the reception.
Ec/Io: This is the ratio of the received energy per chip (= code bit) and the interference level, usually given in dB. In case no true interference is present, the interference level is equal to the noise level.
Because of the system gain (see 1), the interference level can be higher than the wanted signal level. Therefore, at the coverage border, the value of Ec/I0 is usually negative.
RSSI: The Received Signal Strength Indicator (RSSI) is a value that takes into account both RSCP and Ec/I0. It is usually given in dBm and can be calculated as follows: RSSI [dBm] = RSCP [dBm] – Ec/I0 [dB]