The residual energy in multi-code CDMA systems
is not used to transmit any useful information and may increase
up to the incremental energy multiplied with the number of
multi-code channels. A two-group resource allocation scheme is
developed to reduce this upper bound on the residual energy
down to as low as a single-channel incremental energy, resulting
higher energy utilization to improve the sum capacity. Since the
incremental energy is the additional energy required to increase
a data rate to a higher data rate by an additional amount called
bit granularity, a new design of modulation and coding scheme
based on the rate multiplication of outer and inner codes can
be developed to produce different data rates such that the bit
granularity is reduced, hence decreasing the incremental energy
to further maximize the sum capacity. The two-group resource
allocation scheme implemented with the proposed modulation
and coding scheme is observed to have a 4dB gain over the
current HSDPA systems.