2 research outputs found
What you lose when you snooze: how duty cycling impacts on the contact process in opportunistic networks
In opportunistic networks, putting devices in energy saving mode is crucial
to preserve their battery, and hence to increase the lifetime of the network
and foster user participation. A popular strategy for energy saving is duty
cycling. However, when in energy saving mode, users cannot communicate with
each other. The side effects of duty cycling are twofold. On the one hand, duty
cycling may reduce the number of usable contacts for delivering messages,
increasing intercontact times and delays. On the other hand, duty cycling may
break long contacts into smaller contacts, thus also reducing the capacity of
the opportunistic network. Despite the potential serious effects, the role
played by duty cycling in opportunistic networks has been often neglected in
the literature. In order to fill this gap, in this paper we propose a general
model for deriving the pairwise contact and intercontact times measured when a
duty cycling policy is superimposed on the original encounter process
determined only by node mobility. The model we propose is general, i.e., not
bound to a specific distribution of contact and intercontact times, and very
accurate, as we show exploiting two traces of real human mobility for
validation. Using this model, we derive several interesting results about the
properties of measured contact and intercontact times with duty cycling: their
distribution, how their coefficient of variation changes depending on the duty
cycle value, how the duty cycling affects the capacity and delay of an
opportunistic network. The applicability of these results is broad, ranging
from performance models for opportunistic networks that factor in the duty
cycling effect, to the optimisation of the duty cycle to meet a certain target
performance.Comment: Accepted for publication on ACM Transactions on Modeling and
Performance Evaluation of Computing Systems (ToMPECS
Contact-Aware Opportunistic Data Forwarding in Disconnected LoRaWAN Mobile Networks
LoRaWAN is one of the leading Low Power Wide Area Network (LPWAN)
architectures. It was originally designed for systems consisting of static
sensor or Internet of Things (IoT) devices and static gateways. It was recently
updated to introduce new features such as nano-second timestamps which open up
applications to enable LoRaWAN to be adopted for mobile device tracking and
localisation. In such mobile scenarios, devices could temporarily lose
communication with the gateways because of interference from obstacles or deep
fading, causing throughput reduction and delays in data transmission. To
overcome this problem, we propose a new data forwarding scheme. Instead of
holding the data until the next contact with gateways, devices can forward
their data to nearby devices that have a higher probability of being in contact
with gateways. We propose a new network metric called Real-Time Contact-Aware
Expected Transmission Count (RCA-ETX) to model this contact probability in
real-time. Without making any assumption on mobility models, this metric
exploits data transmission delays to model complex device mobility. We also
extend RCA-ETX with a throughput-optimal stochastic backpressure routing scheme
and propose Real-Time Opportunistic Backpressure Collection (ROBC), a protocol
to counter the stochastic behaviours resulting from the dynamics associated
with mobility. To apply our approaches seamlessly to LoRaWAN-enabled devices,
we further propose two new LaRaWAN classes, namely Modified Class-C and
Queue-based Class-A. Both of them are compatible with LoRaWAN Class-A devices.
Our data-driven experiments, based on the London bus network, show that our
approaches can reduce data transmission delays up to and provide a
throughput improvement in data transfer performance.Comment: Accepted for publication at ICDCS 202