126 research outputs found
Time-Spread Pilot-Based Channel Estimation for Backscatter Networks
Current backscatter channel estimators employ an inefficient silent pilot
transmission protocol, where tags alternate between silent and active states.
To enhance performance, we propose a novel approach where tags remain active
simultaneously throughout the entire training phase. This enables a one-shot
estimation of both the direct and cascaded channels and accommodates various
backscatter network configurations. We derive the conditions for optimal pilot
sequences and also establish that the minimum variance unbiased (MVU) estimator
attains the Cramer-Rao lower bound. Next, we propose new pilot designs to avoid
pilot contamination. We then present several linear estimation methods,
including least square (LS), scaled LS, and linear minimum mean square error
(MMSE), to evaluate the performance of our proposed scheme. We also derive the
analytical MMSE estimator using our proposed pilot designs. Furthermore, we
adapt our method for cellular-based passive Internet-of-Things (IoT) networks
with multiple tags and cellular users. Extensive numerical results and
simulations are provided to validate the effectiveness of our approach.
Notably, at least 10 dBm and 12 dBm power savings compared to the prior art are
achieved when estimating the direct and cascaded channels. These findings
underscore the practical benefits and superiority of our proposed technique
Wirelessly Powered Backscatter Communication Networks: Modeling, Coverage and Capacity
Future Internet-of-Things (IoT) will connect billions of small computing
devices embedded in the environment and support their device-to-device (D2D)
communication. Powering this massive number of embedded devices is a key
challenge of designing IoT since batteries increase the devices' form factors
and battery recharging/replacement is difficult. To tackle this challenge, we
propose a novel network architecture that enables D2D communication between
passive nodes by integrating wireless power transfer and backscatter
communication, which is called a wirelessly powered backscatter communication
(WP-BackCom) network. In the network, standalone power beacons (PBs) are
deployed for wirelessly powering nodes by beaming unmodulated carrier signals
to targeted nodes. Provisioned with a backscatter antenna, a node transmits
data to an intended receiver by modulating and reflecting a fraction of a
carrier signal. Such transmission by backscatter consumes orders-of-magnitude
less power than a traditional radio. Thereby, the dense deployment of
low-complexity PBs with high transmission power can power a large-scale IoT. In
this paper, a WP-BackCom network is modeled as a random Poisson cluster process
in the horizontal plane where PBs are Poisson distributed and active ad-hoc
pairs of backscatter communication nodes with fixed separation distances form
random clusters centered at PBs. The backscatter nodes can harvest energy from
and backscatter carrier signals transmitted by PBs. Furthermore, the
transmission power of each node depends on the distance from the associated PB.
Applying stochastic geometry, the network coverage probability and transmission
capacity are derived and optimized as functions of backscatter parameters,
including backscatter duty cycle and reflection coefficient, as well as the PB
density. The effects of the parameters on network performance are
characterized.Comment: 28 pages, 11 figures, has been submitted to IEEE Trans. on Wireless
Communicatio
Time-Hopping Multiple-Access for Backscatter Interference Networks
Future Internet-of-Things (IoT) is expected to
wirelessly connect tens of billions of low-complexity devices.
Extending the finite battery life of massive number of IoT
devices is a crucial challenge. The ultra-low-power backscatter
communications (BackCom) with the inherent feature of RF
energy harvesting is a promising technology for tackling this
challenge. Moreover, many future IoT applications will require
the deployment of dense IoT devices, which induces strong
interference for wireless information transfer (IT). To tackle these
challenges, in this paper, we propose the design of a novel
multiple-access scheme based on time-hopping spread-spectrum
(TH-SS) to simultaneously suppress interference and enable both
two-way wireless IT and one-way wireless energy transfer (ET) in
coexisting backscatter reader-tag links. The performance analysis
of the BackCom network is presented, including the bit-error
rates for forward and backward IT and the expected energytransfer
rate for forward ET, which account for non-coherent and
coherent detection at tags and readers, and energy harvesting at
tags, respectively. Our analysis demonstrates a tradeoff between
energy harvesting and interference performance. Thus, system
parameters need to be chosen carefully to satisfy given BackCom
system performance requirement.ARC Discovery Projects Grant DP14010113
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