Resource Allocation in OFDM Based Wireless Relay Networks ...

7. Conclusions
were considered for the maximization of end-to-end data rate. We developed an
iterative joint resource optimization algorithm and validated the convergence and
the performance though numerical examples. To reduce computational burden,
a low complexity suboptimal scheme was also presented which demonstrated its
comparable performance. Then, we looked into the problem under orthogonal
transmission where each relay node transmits in an independent time slot. Further, a
relay selection scheme was also developed which performs better than the orthogonal
scheme. Numerical results corroborated the proposed schemes.
Next we presented the lifetime maximization problem in multi-hop energy
limited sensor relay networks. The power allocation over different sub-carriers
was optimized to maximize the end-to-end lifetime of the network. We formulated
problem considering both the initial energy and the power constraint at each node in
the network. Through numerical results, we observed that at lower rate requirement,
increasing the initial energy is more advantageous for lifetime maximization.
Finally, we considered the resource allocation in OFDM based cognitive radio
relay networks. We maximized the secondary user’s throughput while interference
introduced to the primary user remain below a give limit. We explored the impact
of sub-carrier pairing and the power allocation at the secondary user’s performance
subject the power and interference constraints. Numerical results showed that the
power allocation and the sub-carrier pairing algorithms developed for conventional
OFDM relay networks perform worst when applied to the CR relay networks and
the proposed algorithms outperform the trivial schemes.
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