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Multiuser OFDM with Adaptive Subcarrier, Bit and Power Allocation

Multiuser OFDM with Adaptive Subcarrier, Bit and Power Allocation. (IEEE JOURNAL ON SELECTED AREAS IN COMMUNICATIONS, VOL. 17, NO. 10, OCTOBER 1999). Outline. Motivation for Multiuser OFDM Bit Allocation Algorithm for Single User Multiuser Subcarrier and Bit Allocation Algorithm

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Multiuser OFDM with Adaptive Subcarrier, Bit and Power Allocation

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  1. Multiuser OFDM with Adaptive Subcarrier, Bit and Power Allocation (IEEE JOURNAL ON SELECTED AREAS IN COMMUNICATIONS, VOL. 17, NO. 10, OCTOBER 1999)

  2. Outline • Motivation for Multiuser OFDM • Bit Allocation Algorithm for Single User • Multiuser Subcarrier and Bit Allocation Algorithm • Simulation Results • Conclusions • References

  3. Motivation • Orthogonal Frequency Division Multiplexing (OFDM) provides a transmission scheme to avoid frequency selective fading in a wide band wireless communications. • How to allocate different user to use different subcarriers with adaptive optimal bit (modulation) and power becomes an interesting problem in a wireless multiuser environment.

  4. Motivation

  5. Multiple Access Schemes

  6. System Model

  7. Problem Formulation • -magnitude of the channel gain • Assume =1 for all users • required received power • Then the transmitted power:

  8. Problem Formulation

  9. Bit Allocation Algorithm for Single User • Greedy Algorithm back

  10. Multiuser Subcarrier and Bit Allocation Algorithm • As users can not share the same subcarrier, this dependency makes the greedy algorithm a non-optimal solution. • Some relaxations on previous problem have to be made. to

  11. Relaxzation of the Constraints • Let be a real number and introduce another variable

  12. Lagrangian Optimization • Using the Lagrangian Multipliers to solve the problem

  13. Lagrangian Optimization

  14. Lagrangian Optimization

  15. Optimal Solution

  16. Optimal Solution (Cont) • The nth subcarrier are selected by the kth user if • To satisfy the bit rate requirement, increase • =>H decrease => will increase the pr to become 1 to transmit data • However, optimal may be not an interger

  17. Multiuser Adaptive OFDM (MAO) • Satisfy the constraint: • Using the optimal method to decide the proper carrier for a specific user. • Then use the single user bits allocation algorithm to satisfy its data rate requiremet. • Note that to

  18. Simulation Results • The required power for supporting c bits/symbol at a given BER Pe:

  19. Simulation Results

  20. Simulation Results

  21. Simulation Results

  22. Simulation Results

  23. Simulation Results

  24. Conclusions • The proposed MAO outperforms than the conventional MA techniques in an OFDM system. • Quantify the performance improvement in terms of SNR, BER and Outage Pr.

  25. References • Multiuser OFDM with Adaptive Subcarrier, Bit, and Power Allocation (IEEE JOURNAL ON SELECTED AREAS IN COMMUNICATIONS, VOL. 17, NO. 10, OCTOBER 1999) • Digital Communication, Prokis, 4th edition • Wireless Communications, Rappaport,2nd edition

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