A review on distributed beam forming techniques an approach in wireless relay networks

IJRET: International Journal of Research in Engineering and Technology eISSN: 2319-1163 | pISSN: 2321-7308
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Volume: 03 Issue: 11 | Nov-2014, Available @ http://www.ijret.org 421
A REVIEW ON DISTRIBUTED BEAM FORMING TECHNIQUES -AN
APPROACH IN WIRELESS RELAY NETWORKS
Megha G. Paserkar1
, Shrikant D. Zade2
1
Research Scholar, Department of Computer Science and Engineering, Priyadarshini Institute of Engineering and
Technology, Nagpur, Maharashtra, India
2
Assistant Professor, Department of Computer Science and Engineering, Priyadarshini Institute of Engineering and
Technology, Nagpur, Maharashtra, India
Abstract
Physical layer security can be considered to solve the security problem from the point of view of information theory in wireless
networks. The combination of cryptographic schemes with channel coding techniques is called for in the basic principle of
information-theoretic security. Due to the presence of one or more eavesdropper in wireless relay networks, secrecy of
communication is in jeopardy. For such a scenario secrecy rate of the network provide a good measure of performance of the
system. In this paper our focus is on secrecy capacity and its optimization with appropriate weight designs of relays taking into
consideration the channels through which the eavesdroppers are connected to the relays. We propose the AF and DF based
optimal beam forming scheme to improve the wireless security against eavesdropping attack by detecting and removing the
eavesdroppers from the wireless relay networks and thus finding measures to maximize the efficiency, response time and the
throughput of the system It includes an auto-regression technique as first approach and the use of RC6 algorithm for encrypting
the confidential messages. The scheme is a two way approach that will not only provides security to the confidential messages, to
be communicated within a wireless relay network in presence of multiple relays and eavesdroppers, but also it will deal with the
saving the consumed power by detecting and removing the nodes which are malicious or defected which in turn will consume
more power in order to perform malicious activity on the messages or may try to create interferences in the network. The
eavesdropper nodes in the proposed system are considered to be working as relays so it may either be connected to source or
destination directly or in between the relays.
Keywords: Beamforming, Channel State Information, Eavesdropper Attack, Power Consumption, Secrecy Capacity.
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1. INTRODUCTION
Recently a significant amount of research is going on to
ensure secure communication in wireless networks. The
implementation of security schemes at physical layer
becomes a hotspot, as the high-layer secure protocols have
attracted growing attacks in recent years. Due to broadcast
nature of wireless transmission, the transmitted messages
are susceptible to be intercepted by eavesdroppers.
However, due to the fading effect and the broadcast property
of radio transmission, wireless communication are always
vulnerable to eavesdropping which consequently makes
security schemes of great importance in it as a promising
approach to communicate confidential messages and so the
secrecy capacity is severely limited in wireless
communications. If the eavesdropper node is not detected
within appropriate time then the messages transmitted in the
network could be read and used for malicious activities. To
that end, user cooperation as an emerging spatial diversity
technique can effectively combat wireless fading and thus
improves the secrecy capacity of wireless transmissions in
the presence of eavesdropping attack. In particular, node
cooperation via relays can increase the achievable secrecy
rate by exploiting/mitigating the channel effects. There are
mainly two relaying protocols for the cooperative secure
transmission: decode and-forward (DF) and amplify-and-
forward (AF). The secrecy rate based on single-antenna
systems is hampered by channel conditions.
Cooperative communications uses multiple nodes which
help each other to transmit messages and has been widely
acknowledged as an effective way to improve system
performance. Beamforming is an attempt to achieve spatial
diversity through the use of the partner‟s antenna. Apart
from the cellular scenario, user cooperation diversity has the
potential to be successfully used in wireless ad hoc networks
also. Typically, the main channel capacity with multiple
relays can be significantly increased by using cooperative
beam forming. More specifically, multiple relays can form a
virtual antenna array and cooperate with each other to
perform transmit beam forming such that the signals
received at the intended destination experience constructive
interference while the others (received at eavesdropper)
experience destructive interference. With the cooperative
beam forming, the received signal strength of destination
will be much higher than that of eavesdropper. In DF
relaying protocol the relay first decodes its received signal
from source and then re-encodes and transmits its decoded
outcome to the destination. In an AF protocol, the source
broadcasts message in the form of signal in the first hop
where the information symbol is selected from a codebook
and is normalized. The received signal at relay is the actual

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message with additive noise. In the second hop, each relay
forwards a weighted version of the noisy signal it just
received. Amplify and forward relay networking scheme is
simplest among them where each node transmits the
message it has received after amplification (scaling).
Though simplest in nature but the significance of this
scheme lies in its low cost implementation and effectiveness
against fading.
In this paper, we propose an auto regression technique and
RC6 algorithm for maximizing the secrecy capacity of
message being transmitted within a wireless relay network.
For this, assuming that the global channel state information
(CSI) is available, we consider a multi-hop network
consisting of a single source and a single destination along
with multiple relay nodes in between. However, due to the
presence of one or more eavesdropper, secrecy of
communication is in jeopardy. For such a scenario secrecy
rate of the network provide a good measure of performance
of the system. Unlike some previous works where only total
relay power constraints are assumed, we consider the
individual relay power constraint also. Generally, in
practice, the relay nodes are powered by their individual
power source without any means to share their power
sources (e.g. battery). Therefore, individual relay constraint
is more relevant in practical situations and general.
Auto regression technique here takes power consumption
constraint into consideration. The proposed system is
considered to be an ergodic system which is based only on
past or present values of each node within a wireless relay
network that participates in data transmission. In order to
gain high efficiency this strategy of auto regression can be
very helpful since it deals with power consumption in this
paper. At each moment while transmitting message or signal
the sensor‟s power consumption output will be compared to
an already set threshold value. If the threshold value
exceeds, it can be easily possible to detect an eavesdropper
node since it may consume more power in order to process
or observe the data for its malicious use.
The RC6 algorithm on the other hand provides a way to
secure the transmission by encoding the message in such a
way that if any other node except the trusted ones tries to
decode the message by applying a random incorrect key,
then the message will be destroyed and will not be available
again to that suspicious eavesdropper node. Now since the
feedback is included in the network due to cooperative
relays. The missing packet can be recognized and resent
from a different route. In this way, the proposed paper
provides a 2- way secure approach for achieving secrecy in
confidential message transmission in wireless relay
networks using beamforming.
2. OVERVIEW OF EXISTING METHODS
In this paper we provide a comprehensive review of the
published research on beamforming techniques using
multiple relays, focusing to maintain secrecy capacity of the
message. This section describes the existing techniques and
algorithms related to confidential message transmission in
wireless relay networks using relays and beamforming
techniques for providing security and efficiency
improvement in the relay nodes considering various
parameters.
For improving security in physical layer, a design of
beamforming in wireless relay networks is given by author
in [1]. Beamforming solutions for amplify-and-forward (AF)
and decode-and-forward (DF) relay networks have been
proposed for secrecy capacity in presence of multiple
eavesdroppers. It shows that the secrecy capacity does not
always grow as the eavesdropper moves away from the
relays or as total relay transmit power increases in an AF
network. Also, if the destination is nearer to the relays than
the eavesdropper, a suboptimal power is derived in closed
form through monotonicity analysis of secrecy capacity.
Whereas, in DF network, secrecy capacity is shown to be a
single Rayleigh quotient problem that can be solved easily
and if the relay-eavesdropper distances are nearly same, then
in this case it is unnecessary to consider the eavesdropper in
a DF network.
Author in [2] has worked on theoretical aspect of the system
for obtaining new forms of transmit diversities so that the
limitations in mobile user‟s data rate and quality of service
can be overcome. The technique of user cooperation is
implemented in a conventional low-rate code-division
multiple-access (CDMA) system. In this, active mobile
users are observed in CDMA implementation under
consideration of information theoretic channel capacity ,
signal outage and cellular coverage and the gains obtained
from user cooperation technique was found to be two
pronged i.e. the higher data rate and decrement in sensitivity
to channel variations. User cooperation strategy for mobile
users in this case necessitates the need of ability to detect the
uplink signals. The implementation of system in this
involved increased complexity in the mobile receiver. The
cooperative strategy in some sense, involves resending, of
information using a cooperative signal. Another possibility
for the two users involved in communication is to always
transmit new information, even during the cooperative
periods, thus necessitating the use of sequence detection due
to the inter-symbol interference that would result from such
a strategy.
The practical implementation aspect of diversity in user
cooperation and analysis of its performance dealing with in-
cell user cooperation is made in [3]. In particular, the
optimal and suboptimal receiver design, the benefits of user
cooperation technique of [2] and practical issues within the
CDMA framework is extended and investigated. In this, the
user cooperation in absence of the channel state information
for high rate CDMA whereas the suboptimal reception and
performance related issues for conventional CDMA is
investigated. The reduced susceptibility to Rayleigh fading
due to cooperation is attested to by a “smoother” data rate as
a function of time, which can be measured by calculating the
variance of the effective data rate.

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To combat signal outage for cooperative diversity in
wireless networks, low-complexity cooperative diversity
protocol, selection and incremental relaying protocols has
been introduced in [4]. Incremental relaying protocol
exploits limited feedback to overcome bandwidth
inefficiency by rare repetition of message to be transmitted
thereby improving spectral efficiency of both fixed as well
as selection relaying. For fixed relaying, the relays are
allowed to either amplify their received signals subject to
their power constraints, or to decode, re-encode and
retransmit the messages. Analytically it has been shown
that, except for fixed decode-and-forward, cooperative
protocols achieves full diversity, i.e., outage probability
decays with inverse proportion to square of signal to noise
ratio (SNR), whereas without cooperation it decays with
inverse proportion to SNR.
Gaussian wire-tap channel with feedback in [5] is an
extension to the Wyner‟s results of achievable region for
discrete memoryless wire-tap channels in [14]. Using
converse theorem and time sharing curve the results
obtained in [5] therefore, shows the secrecy capacity as the
difference between the capacities of the main and wiretap
channel, considering the uncertainties of the signal to noise
ratios of the corresponding channels.
In [6], the authors have considered a collaborative use of AF
relays in order to form beamforming system and to provide
security at physical layer for a wireless machine to machine
system taking power constraint into consideration. For
several optimization problems various beamforming
schemes have been proposed viz., secrecy rate maximization
(SRM), semi-definite relaxation (SDR), virtual
eavesdropper-based SRM (VE-SRM), relay power
minimization (RPM) and virtual eavesdropper-based RPM
(VE-RPM) beamforming scheme. Each of these schemes
combats the complexities of its predecessor. SRM has been
developed to maximize the secrecy rate at relays under total
power constraint but it is difficult to implement SRM due to
the existence of multiple semi-definite programs (SDPs). A
two-level optimization problem can be formed by the
problem of secrecy rate maximization in SRM and to solve
it SDR technique was introduced. The VE-SRM
beamforming scheme relaxes the constraint of selecting the
eavesdropper with the highest eavesdropping rate. The
power constraints consideration of the RPM beamforming
scheme is relaxed by introducing the virtual eavesdropper-
based RPM (VERPM). All these beamforming schemes do
not rely on the null space conditions.
In order to increase secrecy of message in cooperative
wireless communication via relays, it is important to have a
method that helps selecting an optimal relay. One such
method of AF and DF based optimal relay selection schemes
are explored in [7]. And also the multiple relay combining
MRC framework has been investigated in which signals
from multiple relays are combined at destination node in
presence of single eavesdropper. Unlike traditional approach
in which only the CSI of two-hop relay links are considered,
additional CSI is also considered along with. In order to
evaluate the diversity order performance of optimal relay
selection schemes in comparison with traditional schemes,
an asymptotic intercept probability analysis has been carried
out. And it has been found that intercept probability of
proposed scheme is always smaller than traditional scheme.
Author in [8] provides three cooperative schemes for
improving physical layer security while using cooperative
relays. These schemes are: a) decode-and-forward (DF), b)
amplify-and-forward (AF) and c) cooperative jamming (CJ).
System design in this is determined in such a way that the
achievable secrecy rate maximizes subject to a transmit
power constraint, or, the transmit power minimizes with
respect to a secrecy rate constraint. Each node is assumed to
carry a single omni-directional antenna, i.e. beamforming
scheme and that global CSI is available. For AF and DF, the
message broadcasting stages are as explained in [1], whereas
in CJ the relays transmit a weighted jamming signal with the
purpose of prohibiting the eavesdroppers while the source
broadcasts its message in the network. For designing relay
weights and allocating the transmit power separate methods
are carried out for DF and CJ. In CJ, complete nullification
of the total jamming signal sent from relays is done at
destination whereas in DF a closed form optimal solution for
the relay weights, in presence of an eavesdropper, is
derived.
3. CONCLUSION
Data security has always been a very important issue while
transmitting data in a wireless relay networks. So to deal
with this, various beamforming techniques as well as
cryptographic methods has been used but it worked for two
hop message transmission process and also it did not
provide the efficient security in case when the number of
relays increased, thereby increasing the number of hops and
demanding measures for increased secrecy of confidential
message. Beamforming enables the pair of wireless
terminals, each with a single antenna, to fully exploit spatial
diversity in the channel by focussing its complete signal
array in the direction of the receiver node directly. Relay
nodes uses amplify and forward and decode-and-forward
relaying to convey the source message to the destination via
the relays. The alternate solution is the use of auto-
regression technique and RC6 algorithm which therefore
provides two way security and so is power saving. The
different parameters used are time consumption, power
consumption and cryptography to produce result. Since,
managing the limited resources along with increased
security is an important issue to be dealt in the wireless
networks, appropriate techniques and system design
modifications providing higher system throughput and
efficiency can be made in the system as future scope.
REFERENCES
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beamforming designs to improve physical layer
security in wireless relay networks”, EURASIP
Journal on advances in signal processing 2014,
2014:56.

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