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Transmit Power Adaptation for Multiuser OFDM Systems

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. Outline. Introduction System Model Transmit Power Adaptation

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Transmit Power Adaptation for Multiuser OFDM Systems

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

  2. Outline • Introduction • SystemModel • TransmitPowerAdaptation • NumberResults • Conclusion • Reference

  3. Introduction • In order to reduce the computationalcomplexity in calculating water-filling level inthe proposedtransmit power adaptation method • Transmit power is equally

  4. SystemModel

  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. TransmitPowerAdaptation • 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 tomaximize the feasible data rate for that subcarrier • Theorem 1: • subcarrier shouldbe assigned to only one user who has the best channel gain forthat subcarrier. proof：See the Appendix

  10. For the second step • Theorem 1, FDMA system with dynamic subcarrier allocation • The totaldata rate (5) and the total transmit power constraint (6) may berewritten 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. NumberResults

  15. Conclusion • The two proposed transmitpower adaptation schemes significantly increases with the numberof users and is much greater than that for the conventionalFDMA-like transmit power adaptation methods.

  16. 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.

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