1. Transmit Power Adaptation for Multiuser OFDM Systems Jiho Jang, Student Member, IEEE, and Kwang Bok Lee, Member, IEEE IEEE JOURNAL ON SELECTED AREAS IN COMMUNICATIONS, VOL. 21, NO. 2, FEBRUARY 2003 學生：黃亮穎 學號： 96325510

2. Outline Introduction System Model Transmit Power Adaptation Number Results Conclusion Reference

3. Introduction In order to reduce the computational complexity in calculating water-filling level in the proposed transmit power adaptation method Transmit power is equally

4. System Model

5. Signal-to-interference-plus noise ratio (SINR)

6. Assuming that QAM modulation and ideal phase detection are used as in [11] we replace the average signal-to-noise ratio (SNR) in the [11,eq. (17)] with the SINR (2)

7. The total data rate of the multiuser OFDM system may be represented by is appropriately adjusted by the transmit power adaptation method

8. Transmit Power Adaptation Considering a downlink transmission ， the constraint of total transmit power is written as we divide the problem into two steps – subcarrier assignment for users – power allocation for subcarriers

9. For the first step – we assign a subcarrier to a set of users to maximize the feasible data rate for that subcarrier Theorem 1: – subcarrier should be assigned to only one user who has the best channel gain for that subcarrier. proof ： See the Appendix

10. For the second step – Theorem 1, FDMA system with dynamic subcarrier allocation The total data rate (5) and the total transmit power constraint (6) may be rewritten as

11. we define the Lagrangian as where is a Lagrange multiplier

12. transmit power should be allocated as The proposed equal power allocation strategy may be represented by

13. Simulation Rayleigh fading Average SNR define Fixed bandwidth B BER = 10 -3 AWGN capacity Obtain average data rate

14. Number Results

17. Conclusion The two proposed transmit power adaptation schemes significantly increases with the number of users and is much greater than that for the conventional FDMA-like transmit power adaptation methods.

18. Reference [8] C. Y. Wong, R. S. Cheng, K. B. Letaief, and R. D. Murch, “Multiuser OFDM with adaptive subcarrier, bit and power allocation,” IEEE J. Select. Areas Commun., vol. 17, pp. 1747–1758, Oct. 1999. [9] W. Rhee and J. M. Cioffi, “Increase in capacity of multiuser OFDM system using dynamic subchannel allocation,” in Proc. IEEE Vehicular Technology Conf. (VTC 2000), Tokyo, Japan, May 2000, pp. 1085–1089. [11] A. J. Goldsmith and S.-G. Chua, “Variable-rate variable-power MQAM for fading channels,” IEEE Trans. Commun., vol. 45, pp. 1218–1230,Oct. 1997.