Exploiting Multi-Path for SafeguardingmmWave Communications Against

RandomlyLocated Eavesdroppers

Rohith TalwarNancy Amala

George MedinaAkshadeep Singh Jida

Mohammed E. Eltayeb

1

2

Why MIMO at mmWave?

300 MHz 3 GHz

30 GHz 300 GHz

cellular WiFi

note: log scale so even smaller over here

Abundance of bandwidth to support

Gpbs data rates

Small wavelength enables small-sized

arrays

Large arrays provide high directivity to combat path loss

[1] Shu Sun, T. Rappapport, R. W. Heath, Jr., A. Nix, and S. Rangan, `` MIMO for Millimeter Wave Wireless Communications: Beamforming, Spatial Multiplexing, or Both?,'' IEEE Communications Magazine, December 2014. [2] S. Zihir, O. Gurbuz, A. Karroy, S. Raman, and G. Rebeiz, "A 60 GHz 64-element wafer-scale phased-array with full-reticle design," in Microwave Symposium (IMS), 2015 IEEE MTT-S International , vol., no., pp.1-3, 17-22 May 2015.

64 element phase array [2]

Eavesdropping attack Information extraction

Message replayattacks

Message falsificationattack

Important to secure communication links

3

Examples of security threats

Base Station

Traditional PHY encryption not suitable for mmWave

systems(hardware limitations)

Tx uses multiple antennas to degrade

eavesdropper’s channel

Does not rely on upper-layer data encryption or

secret keys

PHY LAYER SECURITY

LIMITATIONS

Recent mmWave PHY techniques are not suitable

for mainlobe security

Physical layer encryption

4

Address the problem of overlapped communication channel paths between the receiver and eavesdropper

Two transmission techniques that enhance the security of mmWavesystems with NLoS channels are proposed

Contributions

4

Proposed techniques enhances secrecy by employing path and antenna selection to jam eavesdroppers.

System model• We consider a mmWave system where the transmitter communicates with a

single antenna receiver via NLoS communications paths.• The transmitter has one RF chain and N antennas. • To transmit 𝑘𝑘𝑡𝑡𝑡 information symbols s 𝑘𝑘 to the receiver the transmitter

multiplies s 𝑘𝑘 by unit norm transmitting vector f(k).• The received signal at the receiver in the presence of additive noise z(k) is given

by

• The channel h is given by

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Number of channel paths

lth AoD

Transmitter array response

lth path complex gain

• In this technique the transmitter transmits each data symbol along random path. The transmitters inner antenna phase shifts are set as:

• The beam forming vector is given by• At the receivers end we get

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𝑓𝑓𝑛𝑛 𝑘𝑘 =1𝑁𝑁

e𝑗𝑗𝑟𝑟𝑛𝑛 𝑘𝑘

𝛾𝛾𝑛𝑛 𝑘𝑘 =𝑁𝑁 − 1𝑁𝑁

− 𝑛𝑛 𝜋𝜋2𝑑𝑑𝜆𝜆

cos 𝜃𝜃𝑙𝑙

Enhancing Secrecy with random path selection

• At the eavesdropper we get

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Enhancing Secrecy with random path selection

• The drawback here is that we require large number of paths L, to

induce randomness.

• We propose to randomize both antennas and angle of departure to

maximize artificial noise when L is small.

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Enhancing Secrecy with random path selection

• A random set IM of antennas is used to transmit along the strongest path and the remaining set IL of antennas are used to transmit along a random path.

• The transmit antenna phase shifts are set as

• The receiver receives

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Enhancing secrecy with joint path and antenna selection

• The eavesdropper receives

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Enhancing secrecy with joint path and antenna selection

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Performance evaluation

SNR at target receiver

SNR at eavesdropper

zero secrecy rate achieved by directional beamforming

techniques

non-zero secrecy rate irrespective of eavesdropper location (AoD)

Secrecy rate versus the eavesdropper’s angle of departure for different number of transmission paths

Setup• A transmitter (Tx) with a single RF chain is

communicating to a single antenna receiver (Rx)via NLoS links.

• Tx is equipped with ULA with half wavelengthseparation and N= 32 antennas.

• Eavesdropper and strongest receiver AoDoverlap at AoD 40 degrees.

Assumptions• Tx and Rx have perfect knowledge of their

channels and path/antenna selection sequence.• Tx and Rx are not aware of eavesdropper

presence.

Secrecy Rate

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Performance evaluationSetup• A transmitter (Tx) with a single RF chain is

communicating to a single antenna receiver (Rx)via NLoS links.

• Tx is equipped with ULA with half wavelengthseparation and N= 32 antennas.

• Eavesdropper and strongest receiver AoDoverlap at AoD 40 degrees.

Assumptions• Tx and Rx have perfect knowledge of their

channels and path/antenna selection sequence.• Tx and Rx are not aware of eavesdropper

presence.

Secrecy Rate

SNR at target receiver

SNR at eavesdropper

Secrecy rate versus the eavesdropper’s Evesdropper average channel gain to receiver noise ratio; L = 12, eavesdropper located along the

strongest path AoD 40 deg.

Secrecy rate of directional techniques plummets to

zero

All techniques achieve high secrecy rate for low SNRE

Secrecy rate of proposed techniques deteriorate at a

slower rate

• Problem of PLS in the presence of an eavesdropper with overlapped channelpaths with the target receiver is addressed.

• Two transmission techniques suitable for mmWave systems with analogantenna architectures are proposed.

• Random path selection and joint path and antenna selection induces noise-like signals at an arbitrary eavesdropper and improves the secrecy of thecommunication system.

• Proposed techniques require the number of paths L>1. For single path, LoSlink, the proposed techniques can not safeguard against eavesdropping.

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Conclusions

Questions

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Please forward all questions/comments to the authors

Exploiting Multi-Path for Safeguarding�mmWave Communications Against Randomly�Located EavesdroppersWhy MIMO at mmWave? Slide Number 3Slide Number 4Slide Number 5System modelSlide Number 7Slide Number 8Slide Number 9Slide Number 10Slide Number 11Slide Number 12Slide Number 13Slide Number 14Questions