Resource Allocation in OFDM Based Wireless Relay Networks ...

2.5 Simulation Results
2.4.2 Suboptimal Algorithm
To reduce the computational complexity, we extend the suboptimal algorithm in
Section 2.3.3 to the multi-relay case. The idea is to allocate sub-carriers among RSs
over the second hop in a similar fashion as for the MUs over the first hop.
We only illustrate the difference from the Section 2.3.3 here:
1) Select K best sub-carriers at hop-1, such that each sub-carrier is allocated to
a unique MU that has the best channel gain for this particular sub-carrier.
2) Select K best sub-carriers at hop-2, where each sub-carrier is allocated to a
unique RS that has the best channel gain for this sub-carrier.
3) Sort the K selected sub-carriers from step 1 and the K selected sub-carriers
from step 2, respectively. Then pair them according to their magnitude.
4) For the sub-carrier allocation and pairing found in previous three step, find
the power allocation following the same way in (2.46) and (2.47).
The algorithm requires a total complexity of O(K(I ′′′ + M + N + 2)), where I ′′′
denote the number of iterations required for sub gradient updates.
2.5 Simulation Results
In this section, we provide numerical examples to evaluate the performance of our
proposed algorithms. The frequency domain channels are generated using i.i.d
Rayleigh distributed time domain taps. A flat fading channel condition is assumed
for each sub-carrier. We choose K = 32 and assign the same total power to all
MUs and RSs. The figure of the merit is taken as the per tone rate, i.e., sum
rate divided by K and is obtained from the average of 10000 different channel
realizations.. Moreover, the rates are obtained from the actual rate expression (2.7)
while the solutions are computed from the high SNR approximation. The following
algorithms are compared
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