Background: Vehicular ad hoc networks (VANET) is a talented system which allows
different applications such as road traffic safety, Internet access, advertising and multimedia streaming,
as described in the various patents as well. VANETs can work according to two modes of communications,
Vehicle to Vehicle (V2V) and Vehicle to Infrastructure (V2I). In the second case, a permanent
communication infrastructure, i.e. Road Side Units (RSUs) can be used to undertake the various
safety messages or to act as a gateway to the Internet. From the roadside infrastructure viewpoint,
the majority of the previous works suppose metropolitan situation where the conventional wired
power is offered at a rational rate. However, this assumption is not always true in practical. Our goal
here is to propose a self powered VANET infrastructure and the major player in such an infrastructure
is the road side unit. We propose that the RSUs can gather the energy required for their work from the
surrounding environment, particularly solar energy. Such a proposal allows to set up the RSUs in any
location without taking into consideration the power supply availability and hence, a wider area is
covered by the VANET infrastructure.
Methods: UBICOM IP2022 network processer platform is adopted to implement the proposed Road
Side Unit (RSU). Comprehensive design steps were described and the values of the system components
(i.e., the number of the solar panels, the capacity of the battery cells, etc.) were given in details.
In order to reduce the power utilization of the recommended RSUs and to lengthen the duration of
their batteries, a new power management scheme called Event Driven Duty Cycling (EDDC) is suggested
and implemented. This technique makes use of an important feature in the Ubicom board
"Clock Stop Mode"; in which the system clock may be disabled which disables the CPU core clock
and hence, the Ubicom board. When the system clock is disabled, the interrupt logic continues to
function, and a Sleep timer is enabled to keep running. The recovery from the clock stop mode
(SLEEP Mode) to the normal execution is possible using Sleep timer interrupts or in response to an
external interrupt form the WLAN NIC.
Results: The results presented in the paper declare that a RSU (when working in SLEEP mode) needs
less number of paralleled solar panels and smaller batteries to run multiple VANET applications.
These results prove the effectiveness of the suggested power management scheme to extend the life of
the solar energy harvested-battery based road side units and their serviceability which will be reflected
positively on building a reliable and an available VANET infrastructure. Compared to the other duty
cycling methods, the suggested EDDC method has the best performance in terms of data loss and
extra power consumption. The main reasons behind this enhanced performance are firstly the precise
choice of the sleep periods (according to the timing requirements of the scheduled tasks) and secondly
the fast wake up manner (in response to an external WLAN NIC interrupt) which guarantees the reception
of all incoming packets without loss.
Conclusion: This paper presents a novel design of self powered Road Side Units (RSUs) using the
network processor technology. We suggest a new power management method, we called Event Driven
Duty Cycling (EDDC), to manage the solar energy stored in the RSUs’ battery cells. RSUs are essential
devices which undertake significant responsibilities in the VANET's communication infrastructure.
The permanent functionality of these devices assures the accomplishment of the VANET's establishment
purposes. On the other hand, the capability to gather the power from the surroundings symbolizes
an imperative technology district which eliminates wires and battery preservation for VANET's
purposes and allows deploying self powered RSUs. The combination between these technologies
and the intelligent administration of the energy resources forms a firm establishment to institute a
dependable and green VANET communication infrastructure.