Transmit Power Adaptation for Multiuser OFDM Systems

1
Transmit Power Adaptation for Multiuser OFDM
Systems

• Jiho Jang, Student Member, IEEE, and Kwang Bok
  Lee, Member, IEEEIEEE JOURNAL ON SELECTED AREAS
  IN COMMUNICATIONS, VOL. 21, NO. 2, FEBRUARY 2003
• ?????
• ??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.
• proofSee 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

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Number Results
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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. 17471758,
  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. 10851089.
• 11 A. J. Goldsmith and S.-G. Chua,
  Variable-rate variable-power MQAM for fading
  channels, IEEE Trans. Commun., vol. 45, pp.
  12181230,Oct. 1997.