1. OFDMA Based Two-hop Cooperative Relay Network Resources Allocation Mohamad Khattar Awad, Xuemin (Sherman) Shen Student Member, IEEE Senior Member, IEEE Department of Electrical & Computer Engineering, University of Waterloo, Waterloo, Ontario, N2L 3G1, Canada ICC 2008 Speaker: Chan-Ying Lien (HuHu)

2. 2 Outline Introduction System Model Problem Formulation Proposed Algorithm and Complexity Analysis Performance Evaluation Conclusions

3. 3 Introduction The channel suffers from –Frequency selective fading OFDMA –Distance dependent fading (i.e., large-scale fading) Amplify-and-Forward scheme (AF)

4. 4 Introduction To further exploit the wireless channel capacity –A RS can cooperate with a SS in the Time Division Duplex (TDD) scheme. The problem of resource allocation in this network is NP-Complete

5. 5 Introduction A low complexity resource allocation protocol –Each SS communicates with the BS in non-cooperative mode in cooperative mode with only one of the available RSs –Users are allocated a sufficient number of subcarriers to guarantee their minimum rate requirements –Each subcarrier is exclusively allocated to one SS and RS pair

6. 6 System Model Consider a single cell scenario –One BS –Multiple fixed RSs –Multiple SSs RSRSRSRS RSRS RSRSRSRS RSRS

7. 7 System Model Full channel state information (CSI) SSs and RSs report their CSI to the BS –SS: minimum rate requirements The central resource allocation unit at the BS performs the resource allocation –The subcarriers assignments and RSs assignments to each SS and RS

8. 8 System Model TDD Half-duplex The SS transmits while the RS and BS receive in the first half of the time slot In the second half of the slot, the RS transmits to the BS

9. 9 Problem Formulation A SSs –A = {s 1, …, s a, …, s A } B RSs –B = {r 1, …, r b, …, r B } A subscriber stations share a total of N sc subcarriers available to the cell –N = {1, …, n, …,N sc }

10. 10 Problem Formulation The maximum achievable rate in (bits/sec/Hz) by s a on subcarrier n with the cooperation of r b is given by a: MS b: RS d: BS β b : r b ’s amplifying gain

11. 11 Problem Formulation The direct transmission maximum achievable rate in (bits/sec/Hz) over both time slots is given by

12. 12 Problem Formulation Binary Integer Programming (BIP) –Satisfying SSs’ minimum rate requirements c a –y ab ∈ {0, 1} y ab = 1 means that s a is cooperating with r b –x n ab ∈ {0, 1} x n ab = 1 means that the subcarrier n is allocated to the pair s a − r b

13. 13 Problem Formulation Because both SS and RS transmit on the same frequency, but in different time slots, and the resource allocation is time independent, the BS d can be represented by a virtual relay r B+1 Adding a virtual relay station enlarges the set B to B + To use a uniform cost function in the optimization problem where δ( ・ ) is the Dirac delta function β n (B+1) = 0 d = B+1

14. 14 Problem Formulation

15. 15 Proposed Algorithm and Complexity Analysis

16. 16 Performance Evaluation 300m 150m RSRSRSRSRSRS RSRSRSRS RSRS A(MS) = 50 B(RS) = 6

17. 17 Performance Evaluation The large-scale fading is distance dependant and follows the inverse-power law: D is the distance between the transmitter and receiver in meters κ is the path loss exponent |α n | 2 is the nth subcarrier channel gain at the transmitter

18. 18 Performance Evaluation

19. 19 Performance Evaluation

20. 20 Performance Evaluation

21. 21 Performance Evaluation 25 SSs (A = 25), 4 RSs (B = 4) 64 subcarriers (N sc = 64)

22. 22 Conclusions In this paper, the resource allocation for the two-hop OFDMA cooperative relay networks has been addressed. Numerical and complexity analysis demonstrate that the proposed algorithm achieves near optimal allocation in relatively short running time. In particular, the algorithm achieves about 70% to 90% of the optimum in only 2% to 12% of the optimization tool running time.

23. 23 T hank You