Resource Allocation in OFDM Based Wireless Relay Networks ...

5.5 Simulation Results
350
300
250
E=50
E=60
E=70
E=80
E=90
Lifetime (S)
200
150
100
50
55 60 65 70 75
R−Req
Figure 5.5: Lifetime vs R-Req
after 275 iterations and is equal to 138.6 seconds. Fig. 5.4 (b) shows the convergence
of rates at first and the fifth hop. We see that, with convergence of variable t, the
rate at each hop converges to the R-Req, which satisfies our statement in Section
5.4. For the clarity in figure, we showed the rate convergence only at two hops. The
rates at other hops also converge in a similar way.
In Fig. 5.5, we look into the relationship of lifetime with rate constraint
and initial energy. We observe that, there is always a trade off between network
lifetime and R-Req. Increasing the minimum rate requirement decreases the lifetime.
We observe that the slope of lines increases with the increasing of initial energy.
Therefore the rate constraint is more crucial to the lifetime at high initial energy.
Similarly we can see that at lower R-Req, increasing the initial energy is more
beneficial to the network lifetime.
Fig. 5.6 (a) shows the network lifetimes at different SNR values. It can be
seen that at low SNR the OPT-SOL does not perform well. The lifetime is much
less than the EP-SOL. However before concluding, we look into Fig. 5.6 (b) which
shows the minimum hop rate (R-min), i.e., the end-to-end network rate, provided
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