OFDMA_Part30

# OFDMA_Part30 - (3 removes all the subcarriers at once Thus...

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30 The BABS algorithm first calculates how many subcarriers are needed for each user. This step is described in Box (1) of Figure 12. is the minimum require rate for user k and R max is the average maximum rate available on each subcarrier. Next, the BABS algorithm finds the total number of allocated subcarriers. If this number is larger than N subcarriers [Box (2)], the algorithm finds and de-allocates all the subcarriers belonging to the user that has the least number of subcarriers [Box (3)]. Finally, in Box (4), the BABS algorithm wants to make sure that all the subcarriers are allocated to the users. There might be some empty subcarriers because the users may not need all the subcarriers to satisfy their minimum rate requirement in Box (1). Another reason is that the algorithm in Box
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Unformatted text preview: (3) removes all the subcarriers at once. Thus the total number of allocated subcarriers may drop much below N and leave some empty subcarriers. The algorithm uses a greedy approach in Box (5). It finds the user who has the most power drop G k when he or she is allocated one more subcarrier. This ensures the achievement of the minimum power goal of the MA approach. The function f in the G k formula is the power-rate function. This power-rate function is convex and uniformly increasing. This function is approximated as f(r) = 0.6 * r 3 and is shown in Figure 13. Figure 13. SNR vs. Transmission Rate for P e = 10-6 [32]...
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