31
So the first stage of [32]’s algorithm determines the number of subcarriers for each user. The
BABS algorithm is unfair to the lowest rate user because the step in Box (3) may cause the
allocation scheme to completely ignore the lowest rate user in an attempt to make the total
number of allocated subcarriers less than
N
. Nevertheless, BABS is optimal for flatfading
channels and has a computational complexity of
O
(
KN
).
After knowing the number of subcarriers for each user, the second stage of [32]’s algorithm
allocates specific subcarriers to each user. In this stage, the author introduces two main
algorithms. The first algorithm is RateCraving Greedy (RCG) and is shown in Figure 14. This
algorithm aims to maximize the total transmission rate.
The first step of this algorithm is finding the transmission rate for user
k
on subcarrier
n
[
r
k
(
n
)]
whose formula is shown in Box (1) of Figure 14. In the next step,
N
subcarriers are distributed
into
K
sets {C
1
… C
k
}, where #C
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 Spring '09
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