1) 3G Power States: Different from Wi-Fi which is more
similar to the LANed Internet access, 3G cellular services suffer
from the limited radio resources, and therefore each user equipment
(UE) needs to be regulated by a Radio Resource Control
(RRC) state machine [25]. Different 3G carriers may customize
and deploy complex states in their respective cellular
networks. Different states indicate different levels of allocated radio resources, and hence different levels of energy consumptions.
For ease of implementation, we consider three basic states
in our design, which are commonly employed by many carriers,
namely CELL_DCH (a dedicated physical channel is allocated
to the UE in both the uplink and the downlink), CELL_FACH
(no dedicated channel is allocated but the UE is assigned a default
common transport channel in the uplink), and IDLE, in
decreasing order of power levels [25]. Contrary to intuition,
the energy consumption for data transmission depends largely
on the state a UE is working in, but has little to do with the
volume of data transmitted, i.e., a UE may stay at a high-power
state (CELL_DCH) for data transmission even the data rate is
very low [25] (this has also been verified in our experiments in
Section V).