Simulation Results and Performance Evaluation
Chapter 6 Future Work
The following issues can be further studied in the future.
Performance of other cooperative networking schemes
Other cooperative networking schemes mentioned in chapter 2 are quite similar to either CoopMAC or CMAC. But their performances are still worth studying.
When is appropriate to use cooperative networking schemes?
The simulations conducted in this thesis are generally simple. For CoopMAC, if there are many helper stations around the source station but they are often busy, the throughput improvement then becomes limited. For CMAC, if there are too many helper stations around, they may compete to retransmit packets and result in more collisions. The two schemes can both be further improved to handle such scenarios.
Combine the capabilities of CoopMAC and CMAC
CMAC does not exploit the multi-rate capability. Though this makes it simple, CMAC has little performance improvement. If CMAC retransmits packets using higher data rate as CoopMAC does, the performance may become better. Also in this thesis we do not examine the performance of CMAC under higher data rates. In our study CMAC has only 1.89% improvement in throughput, as mentioned in chapter 4.2.
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By conducting simple simulation with 3 stations, we can find out that such throughput improvement can reach 8~12% if higher data rates are used. Such improvement can be further studied.
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Chapter 7 Conclusion
In the paradigm of cooperative communication /networking, except for the source station and the destination station, other helper station(s) are also involved in the communication. Thus in general researchers also see wireless ad hoc routing protocols such as AODV, DSR as schemes of cooperative communication, like in [2]. In this thesis we concentrate on MAC layer designs.
Unlike ad hoc routing protocols, which may have lower throughput due to multi-hop transmission, these MAC layer schemes only exploit two-hop transmission and manage to achieve higher throughput.
We choose two such schemes and evaluate their performances. CoopMAC exploits multi data rate feature of the 802.11 network, while CMAC only help fast-retransmit packets. By conducting simulations using NCTUns, we can see that CoopMAC can achieve higher throughputs. But the higher throughput relies on idle helper stations. On the other hand the throughput improvement of CMAC is very little, but even if the helper station has its packets to transmit, it can occasionally help the retransmission of others without disturbing its own packet transmission.
It is possible to combine the advantages of these two schemes to achieve better performance when the helper stations also have their own packets to transmit.
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