Laissez-Faire : Fully Asymmetric Backscatter
Communication
Pan Hu, Pengyu Zhang, Deepak Ganesan
College of Information and Computer Sciences
University of Massachusetts, Amherst, MA 01003
{panhu, pyzhang, dganesan}@cs.umass.edu
ABSTRACT
Backscatter provides dual-benefits of energy harvesting
and low-power communication, making it attractive to
a broad class of wireless sensors. But the design of a
protocol that enables extremely power-efficient radios
for harvesting-based sensors as well as high-rate data
transfer for data-rich sensors presents a conundrum. In
this paper, we present a new fully asymmetric backscat-
ter communication protocol where nodes blindly trans-
mit data as and when they sense. This model enables
fully flexible node designs, from extraordinarily power-
efficient backscatter radios th at consume barely a few
micro-watts to high-throughput radios t hat can stream
at hundreds of Kbps while consuming a pal try tens of
micro-watts. The challenge, however, lies in decoding
concurrent streams at the reader, which we achieve us-
ing a novel combination of time-domain separation of
interleaved signal edges, and phase-domain separation
of colliding transmissions. We pr ovide an implemen-
tation of our protocol, LF-Backscatter, and show that
it can achieve an order of magnitude or mor e improve-
ment in throughput, latency and power over state-of-art
alternatives.
CCS Concepts
•Networks → Network architectures; W i reless
access networks;
Keywords
Backscatter; Wireless; Architecture
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DOI: http://dx.doi.org/10.1145/2785956.2787477
1. INTRODUCTION
As we enter a world where sensors are embed ded in
walls, wearables, and within bodies, a question that
demands attention is what wireless technology is best
suited for these devices. Backscatter has emerged as a
strong contender for this regime because of its ability to
deliver p ower while simultaneously offering an u ltra-low
power wireless backhaul.
One of the extraordinary benefits of backscatter is
that it c an help design wireless sensors that operate at
end-to-end power budgets of under a few micro-watts,
thereby enabling battery-less operation. For example,
a backscatter-based temperature sensor that samples at
1Hz, and operates in a sense-transmit loop with no oth-
er overheads (i.e. no receive circuit, no protocol over-
head, etc) would barely consume 10 µW of power, which
makes it possible for such devices to operate continuous-
ly using a small amount of harvested power.
Backscatter is also attractive as a replacement to ac-
tive radios on battery-powered sensors since it can sup-
port hundreds of Kbps while consuming only tens of
micro-watts of power [26]. Backscatter achieves this
power efficiency by shif ting carrier generation to the
reader, and only uses power for clocking its RF tran-
sistor. High-speed ultra low power radios can enable
a paradigm shift in wireless sensing — continuous da-
ta offload from a variety of data-rich sensors such as
cameras and microphones becomes extremely efficient,
thereby enabling sophisticated distributed sensing ap-
plications.
While backscatter offers many advantages for wireless
sensors, our ability to realize these benefits depends on
the design choices made by the protocol. Seemingly in-
nocuous protocol choices have important ramification-
s. For ex ample, a proto c ol designed with the ex pec ta-
tion that the radio can support bitrates of hundreds of
Kbps significantly impacts power efficiency for simple
low-rate sensors such as the backscatter-based temper-
ature sensor described above. Despite its low sampling
rate and limited communication needs, such a sensor
would need to accumulate samples in a buffer, and use
a high-speed clock to toggle its RF transistor, which in-
creases power consumption by several tens of µWs over
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