Approximation algorithms for bin packing: a survey
Approximation algorithms for NP-hard problems
IEEE Transactions on Information Theory
Optimal sequences and sum capacity of synchronous CDMA systems
IEEE Transactions on Information Theory
Evolution of wireless data services: IS-95 to cdma2000
IEEE Communications Magazine
Spreading code assignment strategies for MIMO-CDMA systems operating in frequency-selective channels
EURASIP Journal on Wireless Communications and Networking
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Next generation wireless CDMA systems will provide high and variable data rates by using multicode structures, controllable code spreading gains, and transmit power adaptation. We address the emerging resource allocation problem in that context and consider maximizing the total achievable user rate while satisfying minimum rate requirements of users. We devise symbol-synchronous and asynchronous models that capture different communication scenarios. The synchronous model holds for down-link transmission in one cell. The asynchronous model captures up-link single-cell communication and down-link or up-link scenarios in multicell systems. It can also account for multipath with each path corresponding to a virtual user. We propose a class of two-stage resource allocation algorithms. First, an admissible set of codes is constructed with criteria that capture code cross-correlation, induced interference to the system, and code rates. Next, the codes are allocated to users so as to satisfy their rate requirements. In the synchronous case, the problem structure allows the distinction of the two stages. In the asynchronous case, this distinction is not feasible due to different user delay profiles perceived at the receiver. Our models and numerical results indicate interesting trends and lead to useful conclusions and design guidelines for resource allocation algorithms under the aforementioned regimes.