A mobile communication system and method for adaptive modulation and coding, combining pilot-aided and ACK/NACK based decision on the employed modulation and coding scheme level

摘要

A mobile communication system and method for adaptive modulation and coding (64) (AMC) which employs a predefined set of possible modulation and coding scheme (MCS) levels is disclosed. The transmitter determines the MCS level to be used based both on periodic specific feedback messages from the receiver and on the ACK and NACKs. The transmitter periodically sends a pilot signal ("CPICH"), which is employed by the receiver for obtaining an estimate of the channel (84). This value is compared to a threshold in order to select a MCS level group (86) (neighbouring MCS levels have been grouped together, thus reducing the operations required in the receiver as well as the overhead needed to inform the transmitter) and the decision is sent through a feedback channel (72) to the transmitter. The transmitter then employs the lowest (most robust) level of the MCS level group selected and adapts subsequently the level in function of the ACKs and NACKs (66). In particular, after a predetermined number of consecutive ACKs have been received, the MCS level is increased to the next more efficient one, whereas every NACK produces a decrease in the MCS level.