  Ad hoc network is a collection of different types of nodes, which are
connected in heterogeneous or homogeneous manner. It is also known as
self-organizing-wireless network. The dynamic nature of ad hoc networks make
them more attractive, which is used in many different applications. Every coin
has two sides: one is the advantage part and other is disadvantages, in the
same manner nature of ad hoc network make it more attractive from one side in
other hand there are some issues too. Energy efficiency is a core factor which
effects on ad hoc network in terms of battery life, throughput, overhead of
messages, transmission error. For solving issues of energy constraints,
different mechanisms are proposed by various researchers. In this paper, we
survey various existing schemes which attempt to improve energy efficiency of
different types of ad hoc routing protocol to increase network lifetime.
Furthermore we outline future scope of these existing schemes which may help
researches to carry out further research in this direction.
