A SCHEME FOR THROUGHPUT MAXIMIZATION IN A DUAL-CLASS CDMA SYSTEM

This work focuses on the problem of efficient exploitation of the avai lable band\width in order to provide high bit rates on the wireless Li nk, as will be required in future wireless systems interfacing to brao dband fixed networks, In particular, the uplink of a CDMA system with two user classes is considered. One of the classes consists of delay-i ntolerant users requiring support for a constant information bit rate, while the other consists of delay-tolerant users needing support for an information bit rate larger than a given value. It is assumed that when not transmitting information, synchronization contact is maintain ed with the base station at a given rate, The objective is to maximize the throughput of the delay tolerant users, while ensuring that the i nterference to other cells is as low as possible by minimizing the sum of all of the transmit powers used by the mobiles. Two transmission m odes for the delay-tolerant users are considered, In the first mode, a ll of the users are allowed to transmit information when they wish. In the second mode, the transmissions of the delay-tolerant users are sc heduled, so that only a limited number of them are transmitting inform ation at any given time instant. It is shown that the second transmiss ion mode, which is a time-scheduled scheme for the delay-tolerant user s (with hybrid CDMA/TDMA as a special case), affords a better throughp ut while imposing the same average power requirements as conventional transmission, The results in this paper can be interpreted using resul ts from previous work based on information theory.