**5. Summaries and future works**

The issues of improving fast retransmission schemes under CD environments can be essential to many delay-sensitive applications. This chapter has widely covered the conceptual description of many representative retransmission schemes under various environments and presented a novel fast packet retransmission scheme intended for effectively transporting delay-sensitive flows in a general CD environment. The presented retransmission scheme and other related works should have provided a sufficient collection of schemes and analysis methodologies for designing further wireless communication systems with similar requirements.

Furthermore, due to the fact that in most practical scenarios the terminals are batterypowered, the design of the energy-efficiency transmission satisfying the respectively specific QoS requirements of these users in the network is very crucial to prolonging the battery life of these terminals. Consequently, the issue concerning the energy consumption has been increasingly paid much attention. We suggest incorporating such a concern with the present work to design an efficiently power-saving fast packet retransmission scheme in a general CD environment for delay-sensitive flows in the future. Additionally, the well design of an efficient retransmission scheme to be employed in such a CD environment simultaneously considering the issue of effective throughput, QoS, fairness, complexity, and power saving is still an open issue for research.
