Special Topics In Wireless Communication 1

Study Of Physical Layer Security In Relay Networks Including Performance

Evaluation Of Friendly Jamming And Noise Forwarding.

Presented By: Advisor:Yugank Purohit Dr. Hua Mu

4/29/2015

Special Topics In Wireless Communications 2

Introduction• We are in a significant transition decade of wireless communication technologies

and services. In the consumer market, people are increasingly spending a large amount of time on wireless devices for the commerce and social needs. A lot of actions performed on wireless networks have high secrecy requirements, e.g., sensitive emails, private user profile and wireless transactions.• Ensuring secrecy is the other critical issue that a wireless system is facing. An

untrusted, or unfriendly node can wiretap the transmitted signals, thus compromising the secrecy of the communications links. Considering the information secrecy, the design goal is to deliver information to the legitimate destination with a data rate as high as possible while preventing untrusted nodes from hearing the useful information. The secrecy requirement has been primarily handled with cryptographic approaches that involve public and private keys

4/29/2015

• However, the key-based cryptographic methods are challenged by possible key leakage and/or surprise attacks. • Recently, physical layer secrecy approach approaches have become popular

because they provide a more fundamental way to achieve the secrecy goal regardless of the decoding ability and key availability at the untrusted node. Therefore, physical layer secrecy approaches can provide absolute secrecy.

Open Systems Interconnection (OSI)

• It is the root to the fundamental elements of computer networking since long back i.e 1984.• The main goal of the OSI model is to supply a set of design standards for

equipment manufacturers so that they can be in touch with each other. This model provides a definition to a hierarchical architecture that logically divides the functions required to provide a base for system-to-system communication.

Seven Layers of OSI

The seven OSI layers are defined as follows• 7. Application: Provides a set of services to the application• 6. Presentation: Converts the information• 5. Session: Handles issues which are not pertaining to communication.• 4. Transport: Provides end to end control in communication• 3. Network: Provides a specific path to the information• 2. Data Link: Minimizes error• 1. Physical: Connects the system to the transmission media

Physical Layer Secrecy Communication

• The basic meaning of physical layer security is to let the exchange of confidential messages be possible over a wireless medium in the presence of eavesdropper and without relying on a more higher level of encryption. This can be done in two different ways.

1. Without the use for a secret key by intelligently designing transmit coding methods2. By exploiting the wireless communication medium to develop secret keys over public channels.

• The basic principle behind physical layer security is to exploit the randomness of noise and communication channels to stop the amount of information that can be extracted at the ‘bit’ level by an unwanted receiver.• With properly designed coding and transmit precoding schemes along with the

exploitation of any present channel state information, physical layer security schemes enable encrypted communication over a wireless medium without the help of a secret key.

Friendly jamming• The role of friendly jamming is a method to increase the security and encryption

of wireless communication. Specifically to characterize the effect of cooperative/friendly jamming on the secrecy outage probability of a quasi-static wiretap fading channel. • It was introduced that the jamming coverage and jamming efficiency as a security

metrics, and to evaluate the performance of three different jamming strategies that rely on different levels of channel state information (CSI).• The analysis provides insight for the design of optimal jamming configurations

and indicates that one jammer is not enough to maximize both metrics simultaneously.

The Idea Of Friendly Jamming In Communication System

• Jamming can be used to improve the noise level of the eavesdropper and to make sure that a higher secrecy capacity is achieved.

• According to the discussions in IEEE conference held in 2010 it was observed that the role of jamming is a method to increase the security and encryption of wireless communication. Specifically to characterize the effect of cooperative/friendly jamming on the secrecy outage probability of a quasi-static wiretap fading channel.

There are two solutions to increase the secrecy rate: • (a) To improving the SNR of the legitimate receiver (e.g. by minimizing the distance to the

source) • (b) Reducing the SNR of the eavesdropper (e.g. by adding controlled interference). Interference

then emerges as a valuable resource for wireless security. From the point of view of the attacker, correlated jamming techniques are known to cause a major disruption of the communications flow by exploiting the information present on the transmitted signals.

Physical Layer Security In Relay Network

• A relay network is a broad class of network topology commonly used in wireless networks, where the source and destination are connected by the way of some nodes. • In such a network the source and destination cannot communicate to each other

directly as the distance between the source and destination is greater than the transmission range of both of them and so the need of intermediate node(s) is needed to transmit the information securely to the destination.

Security issues in relay networks can be divided into two broad categories:

• Relays are untrusted nodes from where the transmitted messages must be kept

encrypted and confidential even while using them to transfer those messages from source to the destination.

 • Relays are trusted nodes from where the transmitted messages are to be kept

secret.

The Wireless Physical Layer Security Using Multiple Relays

• We consider a distributed wireless network configuration as depicted in Fig. A, with one source, one destination, one eavesdropper and K friendly relays shown as R . hSD, hSRi, hSE, hRiE, hRiD, hDE are the respective channel gains between the source and the destination, the source and the ith relay, the source and the eavesdropper, the ith relay and the eavesdropper, the ith relay and the destination, and the destination and the eavesdropper.

Source

RelaysDestination

Eavesdropper

• The relays operate in half duplex decode and forward protocol, i.e., each relay must hear the signal correctly in the first slot and and decode it before transmitting it in the second slot. Therefore, the system secrecy rate is limited by the minimal secrecy between the source and all the relays, i.e.,

• Where is the source transmission power for the data signal.

As the number of relays get increased, the constraint becomes tighter and it decreases the overall secrecy rate.

Relay selection

Optimal Relay SelectionThe source can measure the secrecy rate for any relay i, i = 1,...,K by using the power allocation technique. So, the source can select the optimal relay that increases the secrecy, via completely exhaustive search as follows,

iopt = arg max

Where is the secrecy rate obtained with the ith relay being selected and using the proposed optimal power allocation

Algorithm 1- Relay selection based on the S-R and R-D CSI.• Sort the channel gains of source-relay channels of all relays into sequential

manner in decreasing order.• Sort the channel gains of relay-destination channels of all relays into SeqRD in

decreasing order.• Let be the places of the ith relay in SeqSR and SeqRD.• The “optimal” relay i ∗ is selected according to i ∗= argmin• If there are more than one relays satisfying the above selection criterion, the one

with the minimal |Xih − Xi

g| is chosen.

Distributed relay selection with limited feedback channels

• In this section we consider a distributed relay selection technique, in which, instead of letting the source to maintain information on all relays’ CSI, all the relays participate in determining the optimal power allocation by informing the source on their secrecy rate. For a more realistic option, we consider the case in which this communication occurs through a limited feedback channel. The scheme proceeds as in Algorithm 2.• Along with the Algorithm 2, the computation load for relay selection can be

distributed evenly to all relays. This is particularly important in a system without a powerful fusion center.

Algorithm 2 – Distributed Relay selection• The source and destination send training signals to the relays. Based on the training symbols,

each relay recovers the source-relay and destination-relay CSI and the source measures hSD. It is taken as assumption that the recovery is perfectly and that the destination-relay and rely-destination channels are most probably same.

• The source sends a quantized version of hSD to the relays.• The ith relay (i = 1,...,K) measures (11) based on its local CSI, hS−Ri, and hRi−D, the CSI of the

source-destination link that was sent by the source in step 2. • The relays feed the quantized secrecy rate to the source one by one.• The source measures and select the relay i ∗with the largest secrecy rate and distributes the index.• The relay i ∗measures wSD−E and wSR−E and sends the quantized weight vector to the source and

destination.• The transmission initiates with the assigned weights and equal power allocation.

Relay selection under incomplete eavesdropper CSI• Assuming perfect eavesdropper CSI knowledge might not be possible in a

practical situation, we consider the case in which only analytical information on eavesdropper CSI is present to us. • As the beamforming step does not require any eavesdropper CSI, only the effects

on relay selection and power allocation need to be taken into consideration. The channels hSD−R and hSR−D are available fully.

Source

RelaysDestination

Eavesdropper

• Now let us take an assumption that hSE, hDE and hRE are i.i.d. Gaussian distributed with zero mean and variance of one unit. In this case, a closed form expression, or the limit of min{C1s,C2s}, are very difficult to measure. Therefore, we use a technique to use a modified secrecy rate expression by substituting |[hSE,hDE] |wSD−E|2, |[hSE,hDE] |wSD−E|2 and |[hSE,hRE] |wSR−E|2 by their assumed value, i.e., 1, to approximately know their the secrecy rate. The modified secrecy rate becomes

• The expression of the secrecy rate has the same form as the secrecy rate in case of perfect eavesdropper CSI, thus the proposed optimal power allocation method should still be applicable.• Now since the eavesdropper CSI is not known, the relay selection is rooted only

on the source-relay and relay-destination channels, i.e.,

iopt = arg max

Noise Forwarding

• Noise Forwarding is nothing but the transmission of a dummy codeword from the sender to the receiver which is derived from the codebook and are known to the legitimate senders and receivers. • The main aim if noise forwarding is to increase the secrecy rate when using

multiple relay strategies so that the information cannot be decoded by the eavesdropper and the security increases.

Noise Forwarding StrategiesThe idea of noise forwarding

• The notion of introducing artificial noise in a GWT channel by a helpful interferer to confuse the eavesdropper and improve over the secrecy capacity of the original wiretap channel was introduced. This notion was called cooperative jamming (CJ). • The idea of helping interferer was applied to the GWT channel in a scheme

tantamount to the CJ scheme of the two-user multiple access wiretap channel where one of the users performs cooperative jamming. The destination carried out jamming over the feedback channel to confuse the eavesdropper.

• The role of a relay node to provide and improve secrecy in a wiretap. In particular, the passive (deaf) mode of cooperation, called noise forwarding (NF), in which the relay node sends a dummy (context-free) codeword drawn at random from a codebook that is known to both the legitimate receiver and the eavesdropper to introduce helpful interference that would hurt the eavesdropper more than the legitimate receiver.• The idea of such strategy is to create a virtual multiple access wiretap channel where

only one user (the source) is active, i.e., sending relevant information, while the other user (the relay) is acting as an interferer that sends a signal drawn from a given codebook. In this way, the destination can perform successive decoding and cancel out the relay signal and achieve higher secrecy rate for the intended message.

Simulation ResultsPerformance evaluation of friendly jamming under perfect CSI• Figure A: Secrecy rate versus transmit power for a system with 10 relays.

Performance Evaluation Under Limited FeedbackSecrecy rate versus power for the distributed relay selection scheme with

limited feedback.

Secrecy rate versus multiple relays of (10 1000 relays) ∼for the distributed relay selection scheme with limited

feedback.

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• www.sans.org/reading-room/.../osi-model-overview-543• The OSI Model: An Overview Rachelle L. Miller GSEC Practical Assignment Version 1.2e• http://www.linfo.org/physical_layer.html• Deaf Cooperation for secrecy in multiple relay networks by Raef Bassily And Sennur

Ulukus.University of Maryland, College Park, MD.

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