1,138 research outputs found
Ambient Backscatter Communications: A Contemporary Survey
Recently, ambient backscatter communications has been introduced as a
cutting-edge technology which enables smart devices to communicate by utilizing
ambient radio frequency (RF) signals without requiring active RF transmission.
This technology is especially effective in addressing communication and energy
efficiency problems for low-power communications systems such as sensor
networks. It is expected to realize numerous Internet-of-Things (IoT)
applications. Therefore, this paper aims to provide a contemporary and
comprehensive literature review on fundamentals, applications, challenges, and
research efforts/progress of ambient backscatter communications. In particular,
we first present fundamentals of backscatter communications and briefly review
bistatic backscatter communications systems. Then, the general architecture,
advantages, and solutions to address existing issues and limitations of ambient
backscatter communications systems are discussed. Additionally, emerging
applications of ambient backscatter communications are highlighted. Finally, we
outline some open issues and future research directions.Comment: 32 pages, 18 figures, journa
Spectrum Sharing for Internet of Things: A Survey
The Internet of Things (IoT) is a promising paradigm to accommodate massive
device connections in 5G and beyond. To pave the way for future IoT, the
spectrum should be planed in advance. Spectrum sharing is a preferable solution
for IoT due to the scarcity of available spectrum resource. In particular,
mobile operators are inclined to exploit the existing standards and
infrastructures of current cellular networks and deploy IoT within licensed
cellular spectrum. Yet, proprietary companies prefer to deploy IoT within
unlicensed spectrum to avoid any licence fee. In this paper, we provide a
survey on prevalent IoT technologies deployed within licensed cellular spectrum
and unlicensed spectrum. Notably, emphasis will be on the spectrum sharing
solutions including the shared spectrum, interference model, and interference
management. To this end, we discuss both advantages and disadvantages of
different IoT technologies. Finally, we identify challenges for future IoT and
suggest potential research directions
Ambient Backscatter Networking: A Novel Paradigm to Assist Wireless Powered Communications
Ambient backscatter communication technology has been introduced recently,
and is then quickly becoming a promising choice for self-sustainable
communication systems as an external power supply or a dedicated carrier
emitter is not required. By leveraging existing RF signal resources, ambient
backscatter technology can support sustainable and independent communications
and consequently open up a whole new set of applications that facilitate
Internet-of-Things (IoT). In this article, we study an integration of ambient
backscatter with wireless powered communication networks (WPCNs). We first
present an overview of backscatter communication systems with an emphasis on
the emerging ambient backscatter technology. Then we propose a novel hybrid
transmitter design by combining the advantages of both ambient backscatter and
wireless powered communications. Furthermore, in the cognitive radio
environment, we introduce a multiple access scheme to coordinate the hybrid
data transmissions. The performance evaluation shows that the hybrid
transmitter outperforms traditional designs. In addition, we discuss some open
issues related to the ambient backscatter networking.Comment: A shortened version of this article is to appear in IEEE Wireless
Communication
Modulation in the Air: Backscatter Communication over Ambient OFDM Carrier
Ambient backscatter communication (AmBC) enables radio-frequency (RF) powered
backscatter devices (BDs) (e.g., sensors, tags) to modulate their information
bits over ambient RF carriers in an over-the-air manner. This technology also
called "modulation in the air", thus has emerged as a promising solution to
achieve green communications for future Internet-of-Things. This paper studies
an AmBC system by leveraging the ambient orthogonal frequency division
multiplexing (OFDM) modulated signals in the air. We first model such AmBC
system from a spread-spectrum communication perspective, upon which a novel
joint design for BD waveform and receiver detector is proposed. The BD symbol
period is designed to be in general an integer multiplication of the OFDM
symbol period, and the waveform for BD bit `0' maintains the same state within
a BD symbol period, while the waveform for BD bit `1' has a state transition in
the middle of each OFDM symbol period within a BD symbol period. In the
receiver detector design, we construct the test statistic that cancels out the
direct-link interference by exploiting the repeating structure of the ambient
OFDM signals due to the use of cyclic prefix. For the system with a
single-antenna receiver, the maximum-likelihood detector is proposed to recover
the BD bits, for which the optimal threshold is obtained in closed-form
expression. For the system with a multi-antenna receiver, we propose a new test
statistic, and derive the optimal detector. Moreover, practical timing
synchronization algorithms are proposed, and we also analyze the effect of
various system parameters on the system performance. Finally, extensive
numerical results are provided to verify that the proposed transceiver design
can improve the system bit-error-rate (BER) performance and the operating range
significantly, and achieve much higher data rate, as compared to the
conventional design.Comment: 32 pages, 10 figures, journal pape
Optimal Resource Allocation in Full-Duplex Ambient Backscatter Communication Networks for Wireless-Powered IoT
This paper considers an ambient backscatter communication (AmBC) network in
which a full-duplex access point (FAP) simultaneously transmits downlink
orthogonal frequency division multiplexing (OFDM) signals to its legacy user
(LU) and receives uplink signals backscattered from multiple BDs in a
time-division-multiple-access manner. To maximize the system throughput and
ensure fairness, we aim to maximize the minimum throughput among all BDs by
jointly optimizing the backscatter time and reflection coefficients of the BDs,
and the FAP's subcarrier power allocation, subject to the LU's throughput
constraint, the BDs' harvested-energy constraints, and other practical
constraints. For the case with a single BD, we obtain closed-form solutions and
propose an efficient algorithm by using the Lagrange duality method. For the
general case with multiple BDs, we propose an iterative algorithm by leveraging
the block coordinated decent and successive convex optimization techniques. We
further show the convergence performances of the proposed algorithms and
analyze their complexities. In addition, we study the throughput region which
characterizes the Pareto-optimal throughput trade-offs among all BDs. Finally,
extensive simulation results show that the proposed joint design achieves
significant throughput gain as compared to the benchmark schemes.Comment: 13 pages. This is the third work focusing on ambient backscatter
communication (AmBC) systems for cognitive (energy- and spectrum- efficient)
IoT. The other two published works are "Modulation in the air: Backscatter
communication over ambient OFDM carrier" (IEEE Trans. Commun., 2018) and
"Cooperative ambient backscatter communications for green
Internet-of-Things"(IEEE IoT Journal, 2018
Achievable information rates of ambient backscatter communications
Ambient backscatter is an intriguing wireless communication paradigm that
allows small devices to compute and communicate by using only the power they
harvest from radio-frequency (RF) signals in the air. Ambient backscattering
devices reflect existing RF signals emitted by legacy communications systems,
such as digital TV broadcasting, cellular or Wi-Fi ones, which would be
otherwise treated as harmful sources of interference. This paper deals with the
ultimate performance limits of ambient backscatter systems in broadband fading
environments, by considering different amounts of network state information at
the receivers. After introducing a detailed signal model of the relevant
communication links, we study the influence of physical parameters on the
capacity of both legacy and backscatter systems. We find that, under reasonable
operative conditions, a legacy system employing multicarrier modulation can
turn the RF interference arising from the backscatter process into a form of
multipath diversity that can be suitably exploited to noticeably increase its
performance. Moreover, we show that, even when employing simple single-carrier
modulation techniques, the backscatter system can achieve significant data
rates over relatively short distances, especially when the intended recipient
of the backscatter signal is co-located with the legacy transmitter, i.e., they
are on the same machine.Comment: 29 pages, 11 figure
Transceiver Design for Ambient Backscatter Communication over Frequency-Selective Channels
Existing studies about ambient backscatter communication mostly assume
flat-fading channels. However, frequency-selective channels widely exist in
many practical scenarios. Therefore, this paper investigates ambient
backscatter communication systems over frequency-selective channels. In
particular, we propose an interference-free transceiver design to facilitate
signal detection at the reader. Our design utilizes the cyclic prefix (CP) of
orthogonal frequency-division multiplexing (OFDM) source symbols, which can
cancel the signal interference and thus enhance the detection accuracy at the
reader. Meanwhile, our design leads to no interference on the existing OFDM
communication systems. Next we suggest a chi-square based detector for the
reader and derive the optimal detection threshold. Simulations are then
provided to corroborate our proposed studies.Comment: 5 pages, 5 figures. arXiv admin note: substantial text overlap with
arXiv:1812.1127
Hybrid Beamformer Design for High Dynamic Range Ambient Backscatter Receivers
In bi-static Ambient Backscatter Communications (AmBC) systems, the direct
path from the ambient source to the receiver can be several orders of magnitude
stronger than the scattered path modulated by the AmBC device. Because of the
large power difference between these two signals, the receiver needs to operate
at a large dynamic range. In this paper, we propose a novel analog-digital
hybrid null-steering beamformer which allows the backscatter receiver to detect
and decode the weak AmBC-modulated signal buried in the strong direct path
signals and the noise without requiring the instantaneous channel state
information. The analog cancellation of the strong signal components allow the
receiver automatic gain control to adjust to the level of the weak AmBC
signals. This hence allows common analog-to-digital converters to be used for
sampling the signal. After cancelling the strong components, the ambient source
signal appears as zero mean fast fading from the AmBC system point of view. We
use the direct path signal component to track the phase of the unknown ambient
signal. In order to avoid channel estimation, we propose AmBC to use orthogonal
channelization codes.Comment: 6 page
Novel Sparse-Coded Ambient Backscatter Communication for Massive IoT Connectivity
Low-power ambient backscatter communication (AmBC) relying on radio-frequency
(RF) energy harvesting is an energy-efficient solution for batteryless Internet
of things (IoT). However, ambient backscatter signals are severely faded by
dyadic backscatter channel (DBC), limiting connectivity in conventional
orthogonal time-division-based AmBC (TD-AmBC). In order to support massive
connectivity in AmBC, we propose sparse-coded AmBC (SC-AmBC) based on
non-orthogonal signaling. Sparse code utilizes inherent sparsity of AmBC where
power supplies of RF tags rely on ambient RF energy harvesting. Consequently,
sparse-coded backscatter modulation algorithm (SC-BMA) can enable
non-orthogonal multiple access (NOMA) as well as M-ary modulation for
concurrent backscatter transmissions, providing additional diversity gain.
These sparse codewords from multiple tags can be efficiently detected at access
point (AP) using iterative message passing algorithm (MPA). To overcome DBC
along with intersymbol interference (ISI), we propose dyadic channel estimation
algorithm (D-CEA) and dyadic MPA (D-MPA) exploiting weighted-sum of the ISI for
information exchange in factor graph. Simulation results validate the potential
of the SC-AmBC in terms of connectivity, detection performance and sum
throughput.Comment: 15 pages, 10 figure
Riding on the Primary: A New Spectrum Sharing Paradigm for Wireless-Powered IoT Devices
In this paper, a new spectrum sharing model referred to as riding on the
primary (ROP) is proposed for wireless-powered IoT devices with ambient
backscatter communication capabilities. The key idea of ROP is that the
secondary transmitter harvests energy from the primary signal, then modulates
its information bits to the primary signal, and reflects the modulated signal
to the secondary receiver without violating the primary system's interference
requirement. Compared with the conventional spectrum sharing model, the
secondary system in the proposed ROP not only utilizes the spectrum of the
primary system but also takes advantage of the primary signal to harvest energy
and to carry its information. In this paper, we investigate the performance of
such a spectrum sharing system under fading channels. To be specific, we
maximize the ergodic capacity of the secondary system by jointly optimizing the
transmit power of the primary signal and the reflection coefficient of the
secondary ambient backscatter. Different (ideal/practical) energy consumption
models, different (peak/average) transmit power constraints, different types
(fixed/dynamically adjustable) reflection coefficient, different primary
system's interference requirements (rate/outage) are considered. Optimal power
allocation and reflection coefficient are obtained for each scenario.Comment: Submitted to IEEE Trans. Wireless Communication
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