This paper presents variable power and rate allocation (PRA) for a multiuser orthogonal frequency division multiple access code division multiplexing (OFDMA-CDM) system which exploits both orthogonality among users and symbol-level diversity. To predict the link performance, we analyze the postprocessing SNR as the transmit power (TP) varies when the minimum mean square error combiner (MMSEC) is employed. It is shown from analysis that the MMSEC SNR is nonlinear in TP, but is bounded by the harmonic and the arithmetic means of the subcarrier SNRs. From the observation, we propose two variable PRA methods using a simple channel quality indication and a required TP estimation method. Simulation results show that the proposed methods not only guarantee the target performance but also increase the throughput at the same or slightly increased feedback overhead compared with the fixed TP allocation case.
Bibliographical noteFunding Information:
Manuscript received March 26, 2008; revised July 26, 2008, October 11, 2008, and January 9, 2009; accepted February 21, 2009. The associate editor coordinating the review of this letter and approving it for publication was H. Chen. K. S. Kim is with the Dept. of Electrical and Electronic Engineering, Yonsei University, Seoul 120-749, Korea (e-mail: firstname.lastname@example.org). Y. H. Kim is with the Dept. of Electronics and Radio Engineering, Kyung Hee University, Yongin, Gyeonggi 446-701, Korea (e-mail: email@example.com). This work was supported by the MKE, Korea, under the ITRC support program supervised by the IITA (IITA-2009-C1090-0902-0010). Digital Object Identifier 10.1109/TWC.2009.080413
All Science Journal Classification (ASJC) codes
- Computer Science Applications
- Electrical and Electronic Engineering
- Applied Mathematics