Resource Allocation in OFDM Based Wireless Relay Networks ...

4.5 Simulations
algorithm converges in 20 iterations, which are four times more than that of FP.
Orthogonal transmission
Under orthogonal transmission, we compare four different algorithms.
The proposed joint power allocation and sub-carrier pairing solution.
1) JPSC:
2) Pow:
An algorithm where optimum power allocation is obtained without considering
sub-carrier pairing. 3) EPSC: A solution where the sub-carriers are paired according
to the proposed algorithm under uniform power distribution such that the available
power at each node is equally divided among all the sub-carriers. 4) EP: In this case,
without considering sub-carrier pairing, each node equally distribute the available
power to the K sub-carriers. The throughput performance of four different methods
versus SNR where the relays transmit in preassigned time slots is shown in Fig.
4.4. We have set P = Q n = 10, ∀n. We observe that JPSC yields the best
performance over all other algorithms.
Further, the optimized power allocation
solution (Pow) out performs the uniform power allocation solutions. Optimizing only
the sub-carrier pairing also provides performance gain in EPSC over the EP solution
which validate the idea of performance achievement from sub-carrier matching over
two hops. Finally, as expected, we observe that the system throughput decreases
while increasing the number of relay nodes which is due to the lower TDMA factor
( 1 ) for higher N.
N+1
Next we examine the performance of the end-to-end rate versus the SNR under
the relay selection scenario.
The results for different algorithms are shown in
Fig. 4.5, where the parameters are same as that of in Fig. 1. Similar to the
previous example, JPSC yields the best performance among different methods and
the proposed suboptimal methods (Pow, EPSC) also outperform the trivial solution
(EP). Comparing the results with Fig.
4.4, all the schemes exhibit performance
gain. Further, unlike the previous example, increasing the number of relay nodes
improves the performance. This is consistent with the results in [56].
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