Secure Two-way Communication Via a Wireless Powered Untrusted Relay and Friendly Jammer

Milad Tatar Mamaghani, Abbas Mohammadi, Phee Lep Yeoh, and Ali Kuhestani

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Electrical Engineering Department, Amirkabir University of Technology (Tehran Polytechnic), Tehran, Iran

School of Electrical and Information Engineering, The University of Sydney, NSW, Australia

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Presentation Outline

• Introduction
• Proposed System model
• Performance analysis
• Numerical results
• Summary and conclusions

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Introduction

• Communication Security
• Physical Layer Security (PLS)
• Wireless Energy Harvesting (WEH)
• Untrusted Relaying

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Introduction

• Why?
• The open nature of wireless transmissions makes it more vulnerable than wired communications to information security threats such as
• Passive eavesdropping for data interception
• Active jamming for disrupting legitimate transmissions
• Traffic analysis
• Masquerade attack
• Massage modification
• How?
• Conventional methods: Encryption & cryptography techniques which seriously depends on
• Computational capability
• Key generation and management
• Spectral inefficiency

which leads to challenging issues especially in infrastructure-less networks, i.e. Ad-hoc.

• Emerging technique: Physical-layer security approach

Communication Security

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Introduction

• The basis of PLS was presented by Wyner, who introduced the wiretap channel.

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• Secure transmission is possible if the eavesdropper’s channel is worse than the legitimate channel, i.e., to guarantee perfect secure transmission, the received SNR at the eavesdropper must be degraded compared to that at the legitimate receiver

Physical Layer Security (PLS)

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Introduction

• Physical-layer security (PLS) is a prominent paradigm for improving the information transmission security of future generation communications networks
• PLS can guarantee information security at the physical layer of the protocol stack
• PLS exploits the dynamics of the physical medium and difference between the main channel and the wiretap channel(s), without using encryption key leading to the advantageous of lower computational complexity and resource saving
• PLS techniques include
• Information-theoretic security
• Artificial noise or Cooperative Jamming
• Beamforming
• Diversity, e.g., adopting multiple antennas
• Physical layer key generation
• …

Physical Layer Security (PLS)

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Introduction

• WEH is a key promising technology to realize 5G wireless networks.
• Wireless power transfer can prolong the lifetime of an energy-constrained network
• Simultaneous wireless information and power transfer (SWIPT) extends the function of traditional wireless communications, especially in cooperative networks where the helper nodes can be fed by the main nodes.
• Energy harvesting circuitry is less sensitive than the information decoding one, Therefore, Thus, if a power receiver is malicious, it may successfully decode the information, resulting in information leakage.
• Recent research have considered the use of wireless energy harvesting in PLS scenarios.

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Wireless Energy Harvesting (WEH)

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Introduction

• Introducing a friendly jammer (FJ) could result in a positive secrecy rate for a

One-way untrusted and Two-way untrusted relaying

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Untrusted Relaying

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Introduction

• However, secrecy performances of a PLS-based Tow-way untrusted relaying with WEH capability has not been proposed so far, and hence, absorbed our attention to consider such scenario in this research work!

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Untrusted Relaying

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Proposed System Model

• System Diagram
• Channel Properties
• Time Switching Based Relaying Protocol
• Signal Representation

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Proposed System Model

System model of two-way secure wireless powered network via an untrusted relay and a friendly jammer

System Diagram

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Practical applications:

• Heterogeneous networks
• D2D communications
• Physiological information for e-health
• Commercial networks:
• Account information
• Credit card detail

i.e., mobile payment

• Military applications

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Proposed System Model

• S1, S2 communicate via an untrusted AF relay (R)
• The energy-starved helper nodes, R and FJ
• All the nodes are equipped with a single antenna
• The absence of direct link between S1 and S2 is assumed, since:
• Two communicating sources are located far away from
• Within heavily shadowed areas
• Reciprocal channels following a quasi-static block-fading Rayleigh model
• Perfect CSI is available

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Channel Properties

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Proposed System Model

• Data exchange between S1 and S2 lasts a period of T in three phases:
• T1: both R and FJ harvest the energy of the RF signals transmitted by.
• T2: S1 and S2 send their information signals to R, while FJ transmits its jamming signal
• T3: R broadcasts the signal so each sources extracts their corresponding information

Time Switching Based Relaying Protocol

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Proposed System Model

Signal Representation

• Let denote transmitted signals by the nodes with the powers of , respectively.
• The scaling factor of is

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• The broadcast signal from the relay to the sources is
• The received signal at the source

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• where

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Proposed System Model

• After self-interference and jamming cancellation, the corresponding received signals and end-to-end signal to noise ratio (SNR) at the relay (By adopting multi-user decoding(MUD)) and the sources are given by:

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• where

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Signal Representation (Continue…)

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@Relay

Signal

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SNR

@Source S2

Signal

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SNR

Performance Analysis

• Power Outage Probability
• Ergodic Secrecy Sum Rate
• Lower Bound Ergodic Secrecy Sum Rate

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Performance analysis

• Activating the energy harvesting circuitry at both the relay and FJ is essential.
• The received power at the relay (PR) and the FJ (PJ) should be greater than minimum power threshold ΘR unless they remain inactive.
• The Power outage probability at the relay is defined as

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• Ppoj is similar to Ppor, but considering the FJ’s channel properties

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Power Outage Probability

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Incomplete Gamma function

Performance analysis

• The ESSR characterizes the rate below which the average secure transmission is not achievable.
• Assuming the Relay performs multiuser decoding, ESSR is calculated analytically as

Ergodic Secrecy Sum Rate

• Numerical calculation of the above multiple integration can be readily obtained, while we further proceed to achieve a tight lower bound closed-form expression.

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Performance analysis

Lower Bound Ergodic Secrecy Sum Rate

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Numerical Results �

• Effect of TS Ratio on the ESSR
• Effect of Nodes Distance on the ESSR
• Effect of Transmit SNR on the ESSR

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Numerical results

• ESSR is a quasi-concave function of TS ratio
• The security of the network is highly dependent on the both jamming strategies and TS ratio
• is a key parameter in the system design
• TS ratio↓ Energy harvesting↓ Power outage ↑
• TS ratio ↑ broadcast time ↓ SNR ↓
• Trade-off between security and reliability

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Effect of TS Ratio on the ESSR

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Fig. 1. Impact of time switching ratio on the ESSR

Numerical results

• The two-way WFJ scenario significantly outperforms the one-way and two-way WoFJ communications when the network nodes are close together.
• The maximum ESSR can be achieved if more time is dedicated to RF energy harvesting.
• To achieve the maximum ESSR of the proposed WFJ scenario, the more time is required to harvest RF energy in the first phase as the network topology extends.

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Effect of Nodes Distance on the ESSR

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Fig. 5. ESSR versus the energy harvesting time ratio

Numerical results

• The exact numerical expression is well-approximated in the high SNR regime by our derived closed-form lower bound expression
• The ESSR is significantly enhanced as the transmit SNR increases
• In the high SNR regime the proposed two-way WFJ communication significantly outperforms the one-way and two-way WoFJ scenarios
• At SNR = 50 dB, the ESSR of the two-way WFJ scenario is 1 bit/s/Hz more than that the one-way transmission scenario provides; approximately two times as much as it does
• Evidently, the high SNR-slope of the proposed two-way WFJ communication is twice the one-way scenario and the two-way WoFJ scenario

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Effect of Transmit SNR on the ESSR

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Fig. 5. ESSR versus the transmit SNR

• Summary and conclusions

• Security threats makes wireless communications vulnerable to various attacks.
• Physical layer security is a promising technology which guarantees information security.
• SWPIT can extend the lifetime of energy-constrained and cooperative networks.
• Inspiring the technologies mentioned above, we proposed a wirelessly powered two-way cooperative untrusted relaying network which exploits a friendly jammer (FJ).
• We adapted the time switching (TS) protocol at the relay as enabling SWIPT technology.
• Then, we investigated the ergodic secrecy sum rate with friendly jamming, and derived an accurate and well-tight lower bound expression for the ESSR.
• Numerical results confirmed the accuracy of the obtained lower bound expression, and more importantly, revealed the priority of the proposed two-way WFJ policy, thanks to its significant performance in terms of the ESSR.

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Thank you �for �your attention!�

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