Wireless
Sensor Networks (WSNs) are utilized to screen certain parameters in numerous
applications like environment monitoring, agriculture field monitoring,
habitant monitoring and smart homes. These wireless sensors are scattered in
sensing area to monitor field. WBAN is new rising sub-field of WSN. WBAN are
getting developing interest because of their suitability for medical, non-medical
and psychological applications. The health monitoring is key application of
WBAN. Wireless sensors are set on the human body or embedded in the body to
screen vital sign such as body temperature, glucose level, blood pressure, EMG
and position. The patients are monitored at home for longer period with the
help of WBAN. Sensors persistently sense information and forward to medical server
via internet. Utilization of WBAN technology to monitor health parameters
essentially reduces the expenditures of patient in hospital 1.

The
sensor nodes are operated with limited energy source in WBAN. The limited
energy is needed to utilize least power for transmitting information from
sensor node to sink node. To overcome the limited energy issue an energy
efficient routing protocol is required. In WBAN one of the major difficulties
is to recharge the batteries. Hence an energy efficient routing protocol is
required to conquer this problem of recharging batteries. In WSN technology
numerous energy efficient routing protocols are proposed. WBANs and WSNs have
different architectures, programs and work in various circumstances. Routing
protocol developed for WSN but may not implement for WBAN. Therefore energy
efficient routing protocol for WBAN is particularly needed to keep track of
sufferers for a longer time. 2 . Nodes are placed in or on the human body as shown
in the figure 1, which are accountable to deliver the gathered data at the
specified location (doctor specialist) through internet. In next section
challenges to design routing protocols are discussed

.

                               Fig. 1:
Deployment of nodes

Routing
protocols are used in WBAN for better network performance in term of delay,
throughput, energy efficiency etc.  Here,
this paper discussed few factors which make it difficult to choose a routing
protocol for WBAN.

A.    Heterogeneous
Environment: Different types of sensor nodes are implanted in body to sense and
monitor the different health parameters of human beings. Every node is
heterogeneous in nature because energy consumption and storage capabilities are
different from one to another 19.

B.     Security
and privacy: Routing protocol should be offering secure information and
handling the data.

C.     Quality
of Services: Different types of data require different quality of services in
WBANs. Patient data classified into reliable sensitive data, critical data, delay
sensitive data and ordinary data.  The
suggested method should be aware of these types of information 6.

D.    Energy
consumption: The sensor nodes consume more energy as compared to sensing and
processing data. The greater distance between are main factor of energy
consumption. Battery power cannot be frequently recharged or replaced when
nodes are placed on body.

E.     Mobility
support: The network topology is changed and routes among are altered with
movement of body. The data loss is very high so, WBAN require flexible routing
protocol that adjusts the mobility 1.

Limited resource:
WBANs have limited energy resource, limited storage capacity, poor computation
capabilities and radio frequency transmission. Designing protocols should be
aware of limited resource foe WBANs.