Ambient backscatter for 6G MTC

Prof. Riku JänttiDepartment of Communications and Networking

Ambient backscatterfor 6G MTC

Outline

1. Motivation2. Basic principle3. State-of-the art4. Modulation methods5. Propagation6. Mitigating the direct path interference at the receiver7. Co-existence with incumbent8. Fundamental limits9. Backscatter communications for 6G MTC10. Backscatter communications for beyond 7G MTC11. Conclusions

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1. Motivation

Motivation

• The state-of-art IoT connectivity solutions can be two powerhungry for ultra-low power / passive sensor devices.

• Transceiver is typically the most power hungry part of the IoTdevice.

• Can we communicate without having a transceiver in the IoTdevice?

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There is a lot of ambient signalsaround us!

Why we still need to generate newsignals?

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Power can be harvested from AmbientRF Sources…

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…but it is quite low for powering activetransceivers

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2. Basic principle

Backscatter communications

• Backscatter of radio waves from an object has been a subject ofactive study since the development of radar back in the 1930’s,and the use of backscattered radio for communications sinceHarry Stockman's work in 1948.

• Backscatter Communications (BC) is widely used in RFID wherea reader device generates an unmodulated carrier signal, apassive tag absorbs the energy of this signal and then sendsback the modulated signal to the reader.

• BC devices do not need a power-hungry transceiver and canachieve up to 1000 times lower power consumption and 10 to100 times lower device cost than contemporary active-transceiver-based solutions.

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Ambient backscatter communications• Passive radar systems encompass a class of radar systems that detect and

track objects by processing reflections from non-cooperative sources ofillumination in the environment, such as commercial broadcast andcommunications signals. It is a specific case of bistatic radar, the latter alsoincluding the exploitation of cooperative and non-cooperative radartransmitters.

• Passive radar is almost as old as radar with first experiments in UK in 1935.• Ambient backscatter communications can be interpreted as a

communication technology using the passive radar principle. Ambientbackscatter was invented by researchers at University of Washingtonaround 2013.

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Ambient Backscatter Communications

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Sigcomm 2013

Backscatter communications

• Modulated backscatter systems (MBS)

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Tx

Rxs equivalent base band carrierx1 complex reflection coefficient

reader

MBS

Ambient backscatter communications

• Modulate ambient RF is modulated and reflected

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tx

rxs equivalent base band carrierx0 symbol carried by the ambient RFx1 complex reflection coefficient

MBS

Ambient backscatter communications

• Simple non-coherent transmit and receive strategies can beused for ultra-low power devices

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RF Energy Detector & Hard decoder

RectifierLogarithmic

Amplifier

Comparator

Channel Filter

OOK

Bi-static modulated re-scatter system

• Can we decode both symbols x0 and x1? (Yes, we can)

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tx

rxs equivalent base band carrierx0 symbol carried by the ambient RFx1 complex reflection coefficient

mod

ulat

ed c

arrie

r x 0

s

MBS

Ambient Backscatter Deploymentoptions

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2. State-of-art andapplications

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Audio and video communications

Battery free cell phone Battery free HD video streaming

http://batteryfreevideo.cs.washington.edu/https://www.washington.edu/news/2017/07/05/first-battery-free-cell-phone-makes-calls-by-harvesting-ambient-power/

Healthcare sensors

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Backscatter basedImplantable alcohol-monitoringchip

https://ucsdnews.ucsd.edu/pressrelease/tiny_injectable_sensor_could_provide_unobtrusive_long_term_alcohol_monitori

Wireless cardiac pacing

source: Ho, J. S.; Yeh, A. J.; Neofytou, E.; Kim, S.; Tanabe, Y.; Patlolla, B.;Beygui, R. E. & Poon, A. S. Y., ”Wireless power transfer to deep-tissuemicroimplants,” Proceedings of the National Academy of Sciences (PNAS),2014, 111, 7974-7979.

Wireless analytics for 3D printedobjects

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Iyer, V., Chan, J. and Gollakota, S., 2017. 3D printing wireless connectedobjects. ACM Transactions on Graphics (TOG), 36(6), p.242.

Mechanical movement is convertedto backscatter modulation

Enviromental sensors

• Agricultural monitoring.• Indoor sensing applications.• Wireless humidity sensing.

(backscatter device is the sensor)• …

Challenges: Backscatter devices aredistributed in a large area=> long distance between the ambient

source and the backscatter device.

Possible solutions: ambient FMbroadcasting and LoRa signals.

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Daskalakis, S.N., Kimionis, J., Collado, A.,Tentzeris, M.M. and Georgiadis, A., 2017, June.Ambient FM backscattering for smart agriculturalmonitoring. In 2017 IEEE MTT-S InternationalMicrowave Symposium (IMS) (pp. 1339-1341).IEEE.

Manzari, S., Occhiuzzi, C., Nawale, S., Catini, A., DiNatale, C. and Marrocco, G., 2012. Humidity sensingby polymer-loaded UHF RFID antennas. IEEESensors Journal, 12(9), pp.2851-2858.

Improving IoT security withBackscatter Assistance

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Fig: Illustration of active attack

• Intentionally createmulti-pathpropagationsignatures with thecareful deployment ofbackscatters.

• These signatures canbe used to construct asensitive profile toidentify the locationof the signals’ arrival,and thus detect thethreat.Z. Luo, W. Wang, J. Qu, T. Jiang, and Q. Zhang, “ShieldScatter: Improving IoT Security with

Backscatter Assistance,” in Proc. ACM SenSys., Shenzhen, China, 2018, pp. 185–198.

3. Modulation

Load modulation

• The backscattering device varies the complex antenna loadreflection coefficient by switching the antenna load betweenstates.

• Modulated backscatter can generate, for instance,- Amplitude Shift Keying (ASK): resistive modulator impedance [Ishizaki et al. 2011];

OOK: Load modulator.- Frequency shift keying (FSK): digital [Vougioukas et al. 2016]; Frequency shifting:

low-power ring oscillator-based clock generator [Zhang et al. 2016].- Phase shift keying (PSK), reactive modulator impedance in the Gen2 standard;

transmission line for RFID .- Quadrature amplitude modulation (QAM).

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*

*L a

L a

Z ZZ Z

-G =

+*

: reflection coefficient,: the antenna load impetence,: the antenna impedance.

L

a

ZZ

G

Simple backscatter modulators• On-off keying

(OOK)• Very wideband

(limited byantenna)

• 30 dB between onand off-state

• Binary phase shiftkeying (BPSK)

• Wideband, butphase shift dependon the utilizedfrequency.

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OOK modulator

RL

RL

Transmission line

S1

S1 S2

BPSK modulator

Backscatter modulation methods

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Frequency shifting

Single sideband mixer

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cos(2pDf×t) sin(2pDf×t)

Transmission linecausing 90° phaseshift

bias voltage

Frequency shifting

Transmission line provides 90 degrees phase shift for the carrierfrequency fc. For other frequencies there is a small error.Input: = cos 2p + f , f = arg{ }Output:

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Phase deviation

Frequency shifting

In practical modulationschemes the bandwidth istypically less than 10% ofthe carrier frequency =>more than 40 dB adjacentchannel protection.

Bandpass filter could beimplemented to reduce theadjacent channelinterference.

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Modulation methods: Chirp Pulses

• Chirp spectrum spread (CSS) modulationtechnique uses chirp pulses to conveyinformation.

• Principles: A time delay in the chirp signaltranslates to a frequency shift.

• Advantage: improving the spectral efficiencyby canceling the sideband harmonics.

• Synchronization of the slots across differentbackscatter devices: using a unique ON-OFFkeying sync pattern at the beginning of theTDMA round robin. This allows devices todetermine the slot boundaries for a wholeround-robin duration.

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[Talla2017 Peng et al. 2018, Hessar et al. 2019]

Chirp Pulses

Chirp spread spectrum (CSS):• LoRA: bits are encoded by cyclic

shifts of the chirps• NetScatter: Users are separated

by cyclic shifts. Bits are encodedusing on-off keying.

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(b) Netscatter CSS CodingHessar, M., Najafi, A. and Gollakota, S., 2018. Netscatter: Enabling large-scale backscatter networks. arXiv preprint arXiv:1808.05195.

Talla, V., Hessar, M., Kellogg, B., Najafi, A., Smith, J.R. and Gollakota, S.,2017. Lora backscatter: Enabling the vision of ubiquitousconnectivity. Proceedings of the ACM on Interactive, Mobile, Wearable andUbiquitous Technologies, 1(3), p.105.

Analog Pulse Width Modulation (PWM)

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Naderiparizi, S., Hessar, M., Talla, V., Gollakota, S. and Smith, J.R.,2018. Towards battery-free {HD} video streaming. In 15th {USENIX}Symposium on Networked Systems Design and Implementation({NSDI} 18) (pp. 233-247).

A simple method to generate the PWM pulse traincorresponding to a given signal is the intersectivePWM: the signal (here the red sine wave) iscompared with a sawtooth waveform (blue). Whenthe latter is less than the former, the PWM signal(magenta) is in high state (1). Otherwise it is in thelow state (0).

https://en.wikipedia.org/wiki/Pulse-width_modulation

Analog modulation

• Several backscatter sensor designs have been proposed thatdirectly modulate the analog sensor output signal without digitalprocessing.

• Positives• Help to save energy as analog-to-digital converters and

microcontrollers are not needed.• Minimizes latency.

• Negatives• Requires high Signal-to-noise+interferenc ratio• No encryption, no error correction

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Analog AM modulation

The battery free cell phone used analog AM modulation totransmit voice

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Talla, V., Kellogg, B., Gollakota, S. and Smith, J.R.,2017. Battery-free cellphone. Proceedings of the ACMon Interactive, Mobile, Wearable and UbiquitousTechnologies, 1(2), p.25.

Analog FM modulation I

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Islam, M.M., Rasilainen, K. and Viikari, V., 2015.Implementation of sensor RFID: Carrying sensorinformation in the modulation frequency. IEEETransactions on Microwave Theory andTechniques, 63(8), pp.2672-2681.

Analog FM modulation II

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Viikari, V. and Seppa, H., 2009. RFID MEMS sensorconcept based on intermodulation distortion. IEEESensors Journal, 9(12), pp.1918-1923.

MEMSSwitchin vacuum

Sensorantenna

Prototype:Frequency: 870 MHz RFID-bandReceiver sensitivity: -104 dBmSensor reading distance: 17 m

Reflection amplifiers

Intelligent ReflectiveSurfaces

Backscatter modulation withreflection amplificationA backscatter device with reflection amplifier is similar toamplify and forward relay except in addition to amplifying thesignal it also modulates the amplified signal.

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Backscatter modulation withreflection amplification

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F. Amato, C. W. Peterson, B. P. Degnan and G. D. Durgin,"Tunneling RFID Tags for Long-Range and Low-PowerMicrowave Applications," in IEEE Journal of Radio FrequencyIdentification, vol. 2, no. 2, pp. 93-103, June 2018.

Packet level modulation

WiFi backscatter [Kellogg et al. 2014]: encodes a bit ‘1’ when theWiFi packets are present, otherwise it encodes a bit ‘0’ (silenceperiod); the tag receiver detects the different periods of the WiFipackets using an energy detector. To avoid other readers to transmitduring the silence period, the reader needs to send a CTS_to_SELFpacket before transmitting encoded information.

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Kellogg, B., Parks, A., Gollakota, S., Smith, J.R. and Wetherall, D., 2014, August. Wi-Fi backscatter: Internet connectivity for RF-powereddevices. In ACM SIGCOMM Computer Communication Review (Vol. 44, No. 4, pp. 607-618). ACM.

From scattering to reflection

• Reflector size is proportional to the wavelength.• Hence, reflection based communication becomes more attractive

when moving to higher frequencies.

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http://www.valmontstructures.com/products-solutions/communications-structures/passive-repeaters

UHF band reflector


Controllable reflectors have been developed for radarapplications

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Onoe, M., Hasebe, N. and Zamas, T., 1980. Radar reflectorswith controllable reflection. Electronics and Communications inJapan (Part I: Communications), 63(3), pp.51-58.

Lewis, B.L. and Le Roy, P., Radiation Inc,1968. Modulated retrodirective corner reflector. U.S.Patent 3,417,398.https://patents.google.com/patent/US3308464A/en


Recently the use of large intelligent reflecting surfaces (LIS) hasbeen proposed to enhance wireless communications

LIS could also modulate the signal as proposed inE. Basar “Transmission Through Large Intelligent Surfaces: A New Frontier in Wireless Communications” https://arxiv.org/abs/1902.08463

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X. Tan, Z. Sun, J. M. Jornet, and D. Pados,“Increasing indoor spectrumsharing capacity using smart reflect-array,” inProc. 2016 IEEE Int. Conf.Commun. (ICC), Kuala Lumpur, Malaysia, May2016, pp. 1–6.

5. Propagation

Propagation

Backscatter communications link budget in bi-static case:

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PR Received powerPT Transmit powerGT Transmitter antenna gainGR Receiver antenna gainGBC BC antenna gainL wavelengthXf Forwardlink polarization mismatchXBC BC link polarization mismatchrf Forward link distancerBC BC link distanceBf Forward link blockage (shadow fading)BBC BC link blockage

M BC modulation loss Q On-object penaltyFBDBCS Fade margin

Forward link BC link

Propagation

Measurement setup:f = 590 MHz Digital TV bandPT = 10 dBm Tx powerGT=GR =GBC 0 dBi Isotropic antennasM = -6.63 dB Modulator factor at the tag

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Badihi B, Liljemark A., Sheik. M. U., Lietzen J., Jäntti R. “LinkBudget Validation for Backscatter-Radio System in Sub-1GHz”submitted to IEEE WCNC 2019

Propagation

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Propagation

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Propagation

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PropagationScattering link gain Reflection link gain

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=l

4l

4=

l4 +

> 1

< 1

> 100

Fading

• Backscatter radio systems operate in the dyadic backscatterchannel: product of the forward and backscattered channel.

• Both links can experience fading.• Depending on the environment, this fading can be either

correlated or uncorrelated.

• Also the amplitude variation of the ambient signal appear asfading fort the AmBC receiver.

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Fading

Fading marginal for Nagagami – Nagagami and Rayleigh-Nagagami-Nagagami channels

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Constant amplitudeambient signal

Gaussianambient signal

Product of gamma random variables

Let Xj , j=1,2,…m be gamma distributed random variables with unit mean. Its pdfis given by

Let Y=∏ . Its pdf and cdf can be expressed using Meijer G-function

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=1

G( )

=∏

∏ G( ) ,, ∏

−− 1, … , − 1

=1

∏ G( ) ,, ∏ 1

, … , , 0

=G( − 1 + )

G( )

Mellin transform

6. Mitigating directpath interferenceat the receiver

Dynamic range problem (1/2)

l WavelengthGm MBS antenna gainM MBS modulation lossSNR0 Direct path SNRSNR1 Scattered path SNR

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tx MBS

rx

D0

D1

D2

=l

Dynamic range problem (2/2)

l = 3 m (FM band)Gm = 0 dBM = 0 dBSNR0 = 50 dB

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=l

SNR

1-SN

R0

D2

D1+D2=D0

Required dynamic range is a limiting factor

Direct path interference

• Received signal

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tx

rx

h direct path (complex channel gain)gt signal path from tx to AmBCgr signal path from AmBC to rxx0 symbol carried by the ambient RFx1 complex reflection coefficient

AmBChgt

gr

y=(h+grgtx1)x0 + z=(grgtx0)x1 + (hx0+z)

Fading Interference+ noise

Impact of direct path interference

x0~CN(0,1) Complex Gaussian ambient signalx1Î{0,1} AmBC uses on-off-keying

y|x1~CN(0,|h0|2+|g0g1|2x1+sz2)

Hypotehesis testingH0: y~CN(0,|h0|2+sz

2)H1: y~CN(0,|h0|2+|g0g1|2+sz

2)

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Direct path interference

Bit error probability forOn-off-keying

AWGN channel withComplex Gaussianambient signal

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Gaussian ambientSinusoidal ambient

In order to improverange, the impactof direct path should bemitigated.

Direct path interference mitigation

1. Time domain approach2. Frequency domain approach3. Spatial domain approach4. Signal processing approach

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Time domain approach

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Moving Window Average

MBS uses on – off keying (OOK) with long symbols

0 1 0 1 0 1 0 1 0 1 0 0 0 0 0 0 0 0 0 0

Frequency domain approach 1

Shift the spectrum of the scattered path in frequency domainY(f)=H(f)X0(f) + Gr(f) {X1(f)*[Gt(f)X0(f)]} + Z(f)

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f

Spectral density

SNR1>>SNR0

Frequency modulationX1(f)=1/2(d(f-f0)+d(f+f0)

Mohamed A. ElMossallamy, Zhu Han, Miao Pan, Riku Jäntti, KarimG. Seddik and Geoffrey Ye Li, ” Backscatter Communicationsover Ambient OFDM Signals using Null Subcarriers ” 2018


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FPGA generating sinusoidal wavefrormusing pulse width modulation

AmBC modulator

Direct path (FM signal)

Backscatteredsignal

Frequency domain approach 2Frequency shift keying

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f

f

Cycle throughPhase shifters

El Mossallamy, M.A., Pan, M., Jäntti, R., Seddik, K.G., Li,G.Y. and Han, Z., 2019. Noncoherent BackscatterCommunications over Ambient OFDM Signals. IEEETransactions on Communications


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Number of inband null sub-carriers

Nf FFT block sizeNcp Cyclic prefix length

Ambient

Backscatter


• AmBC spreads part of the legacy signal• Receiver performs dispreading which spreads the direct path

signal

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R. Duan, R. Jantti, M. ElMossallamy, Z. Han and M.Pan, "Multi-Antenna Receiver for Ambient BackscatterCommunication Systems," 2018 IEEE 19thInternational Workshop on Signal Processing Advancesin Wireless Communications (SPAWC), Kalamata, 2018,pp. 1-5.

Legacy signal

AmBC input filter

Filtered legacy signal

Spread filtered legacy signaland spread legacy signal

Spatial domain approach 1: Twoantenna amplitude ratiommo two antenna receiver for on-off key modulated signal

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Amplitude ratio

Antenna outputs

hrf direct path linkhb backscatter linls(t) ambient signalb(t) backscatter signal

Parks, A.N., Liu, A., Gollakota, S. and Smith, J.R., 2015. Turbochargingambient backscatter communication. ACM SIGCOMM ComputerCommunication Review, 44(4), pp.619-630.

Spatial domain approach 2

Null steerign

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Null steering with 8 antenna receiverR. Duan, E. Menta, H. Yigitler, R. Jäntti and Z. Han,“Hybrid Beamformer Design for High Dynamic Range AmbientBackscatter Receivers” Sumbitter 2019https://arxiv.org/abs/1901.05323v2

h0h1

sx


Two antenna testbed

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Theoretically -¥ dBIn practice »-30 dB


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Two stage beam-former

Beam-former outputs Cross-correlation

unknown phase of theambient signal is removed

Direct pathinterference is nulled


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Carrier frequency: 500 MHz; receive antenna array has 8 elements; AoA estimation iscarried out using the Bartlett method; denotes a length-M Hadamard codeword.

Polarization domain approach

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B. W. Pike, “Power transfer between two antennas with specialreferenceto polarization,” AIR FORCE WESTERN TEST RANGEVANDEN-BERG AFB CA, Tech. Rep., 1965.

By AmBC antenna designseparate the direct path andScattered path polarizations

Polarization domain approach

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Theoretically -¥ dBIn practice »-30 dB

J. Lietzen, R. Duan, R. Jäntti, and V. Viikari,“Polarimetry-based Ambient Backscatter System”In preparation 2019

Signal processing approach

Sequential interference cancellation

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y=(h+grgtx1)x0 + z => x0

x0*(y-hx0)= (grgt|x0|2) x1 + z’ => x1

AWGN channel looks like Rayleigh fadingfor Gaussian Ambient

If ambient has constant amplitude, it doesnot impact the receiver performance at all

Data assistedchannel estimation

7. Co-existencewith Incumbent

Ambient backscatter communicationsfrom incumbent point of viewlooks like

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a) Passive repeater b) Moving objector

Digital TV receiver

• Digital TV (DVB-T/DVB-T2) uses OFDM• The pilot structure of the waveform and the equalizer used at

the TV receiver defines the equalization window.• If multi-path components are within the window they can be

coherently combined• If multi-path components are outside the window they cause inter

symbols interference.

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DVB-T2 scattered pilot pattern

Digital TV receiver

Useful signal power from multipath components

Interference due to channel estimation error

ITU-R BT.1368.13: wanted-to-unanted signal D/U ratio for co-channel interference should be at least 39 dB:

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t Path delayTu Useful symbol timeTg Guard time

Impact of backscatter on digital TVreceiver• The fraction of the AmBC signal

path power that generateinterference depend on the AmBCsystem symbol duration

• If AmBC uses on-off-keying (OOK)and the symbol duration is muchlonger than the OFDM symbolduration w»1 and the OFDMreceiver is able to track the AmBCinduced channel variations.

• If the symbol duration is shorterthan the OFDM symbol duration,w»0 and the channel estimator isnot able to track the changes.

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Worst case D/U

Notable interferenceonly if the AmBCantenna is very closeto receiver

K. Ruttik, R. Duan, R. Jäntti, and Z. Han, ”Does AmbientBackscatter Communication Need AdditionalRegulations?” IEEE DySPAN 2018

Example: HitchHike: Co-existence withWiFi• Frequency-shifting (FS) technique Without need of infrastructure

support.• HitchHike uses codeword translation and frequency shift techniques.ü The backscatter translates one 802.11b codeword to another one by

encoding its own information on the standard 802.11b packages.ü The backscatter performs single band FS in order to ensure efficient

spectrum use and not to cause interference.

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P. Zhang, D. Bharadia, K. Joshi, and S. Katti, “HitchHike: Practical Backscatter UsingCommodity WiFi,” in Proc. the 14th ACM SenSys, Stanford, CA, 2016, pp. 259–271.

Example: HitchHike: Co-existence withWiFiTo deal with the direct path self-interference HitchHike shiftthe frequency of the modulated packet to neighboring band

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OriginalWiFi signal

HitchHikeWiFi signal

8. Fundamentallimits

Co-existence – fundamental limits

• No Channel stateinformation at hetransmitter

• Legacy MIMO systemuse complex Gaussianchannel input: x0~CN(0,pI).

• AWGN channel: Noiseis complex Gaussian z~CN(0,I).

• AmBC has K antennasand uses phasemodulation |xk|=1

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K AmBC antennas

= b / ∑ 0 +

a,b scaling factors

Massive MIMO limit

When the number of receive antennas grow the cross termsvanish from the channel covariance matrix

and the matric becomes independent of xk

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∑ ∑ ∗ ®∑

has strictly larger eigenvalues than 0 0

Hence, the system with AmBC devices always has largerachievable rate than the one without.

0 0 0

0 0 0

: 0,

: 0,t

r

H Hr t rk r n

Hr t tk t n

n n n

n n n

³ ® ®

< ® ®

G g G G I

G g G G I

( )2

11rn K

ba

=+

Uncorrelted scattering

Normalized receiver SNR

Massive MIMO limit

• Large number of receive antennas

• Large number of transmit antennas

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( ) ( )22

,0 1 2 22 2

1log 1 log 1

1 1

Kt k

tkt t

r r nn K n K

g ag

a a=

æ ö æ öç ÷ ç ÷+ ® + + +ç ÷ ç ÷ç ÷ ç ÷+ +è ø è ø

åg

rn ® ¥

MIMO channel capacityin rich scattering

K keyhole MIMO channelcapacity

( ) ( ) ( )22

,0 1 2 22 2

1log 1 log 1

1 1

Kt k

rkr r

r r n Kn K n K

g ag

a a=

æ ö æ öç ÷ ç ÷+ ® - + + +ç ÷ ç ÷ç ÷ ç ÷+ +è ø è ø

åg

tn ® ¥

0 0 0

0 0 0

: 0,

: 0,t

r

H Hr t rk r n

Hr t tk t n

n n n

n n n

³ ® ®

< ® ®

G g G G I

G g G G I

( )2

11rn K

ba

=+

Uncorrelted scattering

Normalized receiver SNR

Achievable rate for AmBC device

• Single antenna AmBC decice (K=1)• AmBC device without reflection amplifier:

• Strict peak power limit |x|2£1=> Wyner polyphaser coding

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Am

BC

Achievable rate region

AmBC can share co-exist withthe Legacy system withoutcausing harmful interference.

AmBC can also help thelegacy system by acting as apassive relay.

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R. Duan, R. Jäntti, H. Yiğitler, and K. Ruttik. “On the AchievableRate of Bi-Static Modulated Re-Scatter Systems,” IEEE Transactionson Vehicular Technology, 2017.

9. Backscattercommunicationsfor 6G MTC

Backscatter communications forcellular IoT

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a) b)

c)

Backscatter D2D

Backscatter communications forcellular IoT – Is it feasible?Macrocellular setup downtown Helsinki.

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Area under consideration with site locationsand cell azimuths

Backscatter device distribution.

M. U. Sheikh, F. Jameel, H. Yiğitler, W. Xiyu, and R. Jäntti,“Monostatic Backscatter Communication in Urban MicrocellularEnvironment Using Cellular Networks” IEEE WCNC 2020, 6-9 April,Seoul, South Korea, 2020.

Simulation parameters (Ray tracing)

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Parameters Unit ValueTX Power dBm 43TX Ant Horz HPBW degree 65TX Ant Vert HPBW degree 7TX max antenna gain dB 17.7Tag antenna gain dB 0Fast fading margin dB 16Slow fading margin dB 13Poarization miss match loss dB 3Modulation loss at tag dB 6Blockage loss dB 0

• 3GPP antenna model parameters are• General simulation parameters

Frequency BPL-Low [dB] BPL-High [dB]200 MHz 4.985 10.84500 MHz 5.816 12700 MHz 6.332 12.75900 MHz 6.817 13.5

• Building penetration loss values • Received sensitivity=-174+10*log10(BW)+NF+SNR-149 dBm

LoRA receiver sensitivity for SF12 and BW=7.5 kHz

Received power at the base station

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CDF of tag received power atthe reader (=Base station)

OK outdoor coverageOK coverage on the 5th and 7th floorPoor coverage on the ground floor

Outage

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Low BPL loss model High BPL loss model

700 MHz

Performance

• Backscatter system could use the existing cell sites toobtain good or full outdoor coverage in urban setting for< 700 MHz and reasonable outdoor coverage for <900 MHz.

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Frequency BPL

Meantag power

dBm

Meanreceived power

dBm

Mean Outdoorreceived power

dBm

Mean Indoorreceived power

dBm

Overall outageProbability

%

Outdoor Outageprobability

%

Indoor OutageProbability

%200 Low -33.8768 -109.4358 -94.1442 -109.6399 0 0 0200 High -38.8496 -119.3815 -94.1442 -121.3499 1.7333 0 2.0408500 Low -43.4924 -128.5645 -110.9884 -128.1055 8.6667 0 10.2041500 High -48.7447 -139.069 -110.9884 -140.4735 30.8 0 36.2637700 Low -47.1847 -135.8992 -117.1131 -135.1799 21.7333 2.6549 25.1177700 High -52.6357 -146.8012 -117.1131 -148.0159 48.9333 2.6549 57.1429900 Low -49.9827 -141.4932 -121.6627 -140.7639 35.0667 10.6195 39.4035900 High -55.6588 -152.8454 -121.6627 -154.1299 64 10.6195 73.4694

10. Backscattercommunicationsfor beyond 7GMTC

Microwave Quantum BackscatterCommunicationsQuantum radar is anemerging remote-sensingtechnology that utilizes non-classical quantumcorrelations to enhance thedetector sensitivity.Microwave quantumbackscatter communicationsapplies the quantum radartechniques for wirelesscommunications.

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Microwave Quantum BackscatterCommunications

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SI

Entangledphoton pairgeneration

Txantenna

Rxantenna

Receiver

Secure transactions• Quantum key

exchange• Low probability of

detection

Biomedical & laboratoryapplications• Low electromagnetic

exposure• Low interference to

precision instruments

Very low temperature High temperature

Bit

erro

r pro

babi

lity

• R. Jäntti, R. Di Candia, R. Duan, and K. Ruttik, “Multiantenna Quantum BackscatterCommunications,” Quantum Communications and Information Technology 2017(QCIT'17) Workshop at Globecom 2017.

• R. Di Candia, R. Jäntti, R. Duan, J. Lietzen, K. Hany and K. Ruttik, “Quantum BackscatterCommunications: A New Paradigm,” In Proc. ISWCS 2018, 28-31 August, Lisbon,Portugal, 2018.

• K. Hany and R. Jäntti, “Quantum backscatter communication with photon number states,”Workshop on Quantum Communications and Information Technology (QCIT'18) at IEEEGlobecom 2018, December 9-13, Abu Dhabi, 2018.

• H. Khalifa and R. Jäntti, “Retrieving quantum backscattered signals in the presence ofnoise” IEEE GLOBECOM 2019 Workshop on Quantum Communications and InformationTechnology, 9-13 December, Waikola, HI, USA, 2019.

• R. Jäntti, R. Duan, J. Lietzen, H. Khalifa, and L. Hanzo, ”Quantum Enhanced MicrowaveBackscattering Communications,” IEEE Communications Magazine, 2020.

Ns Average number of generated photonsNz Average number of thermal photonsh Round trip transmissivity (RTT)M=WT number of independent mode pairsW Phase matching bandwidthT Pulse duration

11. Conclusions

Conclusions

• Ambient backscatter communications is a promising low-powercommunication scheme.

• It can share spectrum with incumbent system without causingharmful interference to the incumbent.

• It has very low power consumption and device cost• Efficient ambient backscatter communication receiver design must

mitigate the impact of the strong direct path interference.

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Department of Communicationsand Networking (Comnet)

Ambient backscatter for 6G MTC

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