Performance Improvement in Infrastructureless Networks by Using Smart Antenna Technology

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					   International Journal of Emerging Trends & Technology in Computer Science (IJETTCS)
       Web Site: Email:,
Volume 1, Issue 2, July – August 2012                                          ISSN 2278-6856

    Performance Improvement in Infrastructureless
    Networks by Using Smart Antenna Technology
                                       Nalin Gahlaut1, Sandip Vijay2, S. C. Gupta3
                                       Doctoral Candidate, Uttarakhand Technical University
                                                     Dehradun (U.K.)-India
                               Wireless Computing Research Lab, Department of Electronics & Computer
                                                    I.I.T. Roorkee (U.K.)-India.
                                    Professor Emeritus, Department of Electronics & Computer
                                                   I.I.T. Roorkee (U.K.)-India

                                                                 in particular direction and to produce nulls in the
Abstract: Infrastructureless network is a collection of          directions of interferers. Generally, wireless nodes in
wireless nodes, which are connected in decentralized             infrastructureless networks can’t know the actual
structure. Nodes in infrastructureless networks can              directions of incoming signals. In past decades, some of
communicate with each other and can move from one place          the researchers proposed beamforming algorithms which
to another. By using omnidirectional antennas, the channel       can estimate DOA of the incoming signals before
in infrastructureless networks cannot be utilized 100%, so for   generating antenna beam pattern. Some popular adaptive
improving channel utilization we proposed an adaptive MAC
                                                                 beamforming algorithms are LMS (Least Mean Square),
protocol which makes use of smart antenna technology. The
proposed protocol use Global Positioning System to direct
                                                                 RLS (Recursive Least Square), CMA (Constant Modulus
their main beam to desired direction and nulls in the            Algorithm) and SMI (Sampling Matrix Inversion) etc.
direction of interferers. Our proposed protocol shows            In this work, we proposed a MAC protocol using adaptive
tremendous improvement in throughput, when used with             array antenna. The scalability problem can be solved by
smart antennas.                                                  GPS device that is equipped at each node. By the use of
                                                                 location information gathered by GPS, nodes can steer
Keywords: Infrastructureless network, smart antenna,
                                                                 their beam patterns to the desired directions. Nodes can
array element, GPS.
                                                                 utilize the location information gathered by GPS to steer
                                                                 their beam patterns to the desired directions instead of
1. INTRODUCTION                                                  using adaptive beamforming algorithms. Our proposed
                                                                 protocol gives tremendous improvement in channel
An infrastructureless network is a collection of wireless        utilization over IEEE 802.11 MAC using omnidirectional
nodes which can communicate with each other in                   antenna system.
decentralized manner. Because of the use of
omnidirectional antennas in infrastructureless network,
the channel is underutilized. To avoid interference, nodes
                                                                 2. RELATED WORKS
within the communicating node’s coverage are prohibited          In past, researchers [2][8][9] presented that use of smart
to establish communication with other nodes. Many of the         antenna(directional) efficiently increases channel
researchers suggested use of smart antennas to improve           utilization. But the use of smart antenna also increases
the channel utilization. By the use of smart antenna             complexity, some of the researchers proposed solution of
technology, many of the nodes can simultaneously                 this problem. Many researchers [9][10] proposed their
communicate with each other, and the network                     designed protocol that are based upon RTS/CTS exchange
throughput can be improved tremendously, but there must          procedure of IEEE 802.11 MAC standard protocol. Some
be a redesigned adaptive MAC protocol that can take              of the researchers uses GPS system to solve scalability
advantage of smart antenna technology.                           problem and to know the direction of incoming signals.
There are two categories of smart antenna systems:               In [7], author describes about the smart antennas and how
switched beam antenna and adaptive array antenna.                the smart antenna technology can be beneficial for
Switched beam antenna generates a set of predefined              wireless systems. In [11], two of the important topics
beams and which have very high sensitivity in their              discussed in this paper are the topics concerning medium
directions. By using one of the predefined beams, we can         access control on the physical layer and the
select any desired signal and the signals from other             implementation of neighbor discovery between nodes. In
directions can be rejected significantly. Adaptive array         regards to the medium access control methods, they
antenna use beamforming algorithms to direct their beam          propose a type of packet sending that is similar the

Volume 1, Issue 2 July-August 2012                                                                               Page 80
   International Journal of Emerging Trends & Technology in Computer Science (IJETTCS)
       Web Site: Email:,
Volume 1, Issue 2, July – August 2012                                          ISSN 2278-6856

currently implemented CSMA/CA approach that is a bit          procedure is adopted by destination node, which
more aggressive. The state of a node is either in an idle     encapsulates its location information in CTS packets and
state (whether it be a forced idle of a natural idle) or a    after receiving this CTS packet by source node,
transmitting state. In addition to the MAC level protocol     encapsulated information used for directing its main
changes, the types of neighbor discovery will also be         beam in the direction of the destination node. Both of the
different.                                                    source & destination node produces null in other
In [12], author focuses on the different types of smart       directions, so the interference from other nodes
antennas and how they can be basically implemented in         minimized. When CTS/RTS packets are received by
ad hoc networks to maximize performance. These are            source/destination nodes, then they utilize power control
multibeam antennas or adaptive array antennas. A              mechanism proposed in [3] to adjust the transmit power
directional antenna is an antenna with a variety of           for sending the data frames.
antennas and on the incoming reception of a signal            We know, the relationship between transmit power and
focuses on the antenna with the best reception. It then       distance is
forms a direct beacon for transmission and reception. An                    PRX = PTX (λ/4πl)n GT GR      (i)
adaptive array receives the signals across an array of        Where:
antennas and then calculates the best combination of          λ : carrier wavelength
antennas to receive the incoming transmissions. Then, it      l : distance between source & destination node
uses that information to create a collective direct beam in   n : path loss coefficient
the direction of the incoming signal.                         GT/GR : Transmitter and receiver antenna gain
                                                              Since PTX is the power by which source/destination node
                                                              transmits RTS/CTS packet and PRX is the power by which
3. IEEE 802.11 MAC & OUR PROPOSED                             destination/source node receives RTS/CTS packet.
PROTOCOL                                                      Assuming PMN is the smallest possible power level which
In IEEE 802.11MAC, When a source node X wants to              nodes can receive and P is adjusted transmit power, so
send a packet, it transmits (broadcasts) a RTS (Request to                   PMN = P (λ/4πl)n GT GR     (ii)
Send) packet in omnidirectional mode and wait for a           From (i) & (ii), we have
particular time to receive acknowledgement from                                P = PTX . PMN / PRX   (iii)
destination node Y. When destination node Y receives
this packet, it replies back by sending a CTS (Clear to
Send) packet to node X in omnidirectional mode. After
exchange of RTS/CTS packets, the source node X starts
sending data frames to the destination node Y. If the
sending node X does not receive the CTS packet within
selected time period then it resends the RTS packet and
follows retransmission procedure. When the destination
node Y successfully receives a data frame, then it will
send an ACK to the source. Then the next data frame            Figure 2: Scenario shows node Y locates in coverage of
transmitted.                                                  node X & node Z locates in coverage of node W and node

         Figure 1: IEE 802.11 Basic Operations
In our proposed MAC protocol, we have modified the
format of RTS/CTS packets to carry location information.      Figure 3: Scenario of W and X communicates with each
Nodes performs power control mechanism to adjust their                    other with smallest angle 120o.
transmit power, during RTS/CTS transmission-reception.        In our work, the transmitted power is adjusted by using
When a source node wants to send data then it                 equation (iii). The RTS/CTS packets received by
encapsulates location information within RTS packet and       neighbouring nodes have the information related to
broadcasts this packet, in omnidirectional mode with          directions in which sending and receiving nodes are
transmit power PTX. The location information                  situated. Considering a scenario in which node W and
encapsulated in RTS packet is used by destination node to     node X are communicating node. Node Y located in the
direct its main beam in source node direction. The same       common coverage of node X and node Y will receive RTS
Volume 1, Issue 2 July-August 2012                                                                            Page 81
   International Journal of Emerging Trends & Technology in Computer Science (IJETTCS)
       Web Site: Email:,
Volume 1, Issue 2, July – August 2012                                          ISSN 2278-6856

& CTS packets. Node Z will receives either RTS or CTS         4. SIMULATION ENVIRONMENT
packet. The signal sent by node Y directly interfere
                                                              For simulation purpose, we have designed an
communication between node W and node X but the
                                                              infrastructureless network having 25 nodes that are
signal sent by node Z may not disturb current
                                                              placed in 5x5 grid. The horizontally & vertically distance
communication between W and Y, under condition that
                                                              between nodes is 150 meters. Here the comparison of our
main lobe width Φ that is formed by W and X must be
                                                              proposed protocol with IEEE 802.11 MAC using
smaller than threshold. From fig. 3, we see that angle
                                                              omnidirectional antennas is presented. The packets are
MXM' will be 120o and this angle will be smallest for all
                                                              generated by Poisson distribution and the destination
scenarios in which W and X can communicate with each
                                                              node is selected randomly.
other. So, if W and X can form main beam width smaller
than 120o, than the signal sent by node Y will not                         Table 1: Simulation Parameters
interfere the communication between node W and node                      Parameter                      Value
So from above description, we can define a node as an         Data Packet Generation Rate        500 packets/second
interfering node if, “Either this node receives both RTS      Each   Node’s Transmission         325 meters
and CTS packets or this node receives any one of the          Range
RTS/CTS packet and also which can’t form main lobe
                                                              Antenna System Used                smart antenna system
beam width smaller than 120o”. In proposed scheme, if
                                                                                                 (in circular array)
the signal from interfering node directly propagates to
communicating nodes then its antenna beam pattern             Data Packet Size                   1.1Kbytes
changed adequately.                                           Network Bandwidth                  11Mbps
For adjusting antenna beam pattern of interfering node,
the location information extracted from RTS/CTS packets       Main lobe width                    64o
is used and the distance from current communicating           (If 8 element circular array)
node is calculated. After this, the antenna beam pattern is   Main lobe width                    124o
decreased in direction from which RTS/CTS received.           (If 4 element circular array)
The antenna beam pattern can be adjusted by,
             ψb' = ψb (PMN/PTX)(4πl/λ)n (iv)
where,                                                        5. SIMULATION RESULTS
ψb: Original antenna beam pattern                             Our proposed scheme performs better than IEEE 802.11
ψb': Adjusted antenna beam pattern                            MAC using omnidirectional antenna, with four elements
l: is the distance between the RTS/CTS sender and the         circular array. Fig.7 shows amount of data packets
node that received the RTS/CTS.                               transmitted by all nodes. When circular array of four
For this requirement, adaptive array antenna adjusts their    elements is used then nodes can’t generates main lobe
weights to change antenna beam pattern and the adjusted       smaller than 120o, so by circular array of four elements
beam pattern shall be used during network allocation          we can’t improve channel utilization in large amount.
vector period that is recorded in RTS/CTS.

                                                                  Figure 5: Circular array with 8 antenna elements.

Figure 4: Pattern of MVDR beamformer obtained with
ULA of 16 antenna elements. The desired source is at 0o
           & interferers are at 35o & –45o.

Volume 1, Issue 2 July-August 2012                                                                             Page 82
   International Journal of Emerging Trends & Technology in Computer Science (IJETTCS)
       Web Site: Email:,
Volume 1, Issue 2, July – August 2012                                          ISSN 2278-6856

    Figure 6: Circular array with 4 antenna elements.
                                                               Figure 8: Data Packets Transmitted by Node Positioned
Besides this, circular array of eight elements can transmit
                                                                                 at (150m, 150m).
large number of data packets. Fig.8 & fig.9 shows the
data packets transmitted by a node that is positioned at
coordinate (150m, 150m) and a node that is positioned at
coordinate (300m, 300m) respectively. The node
positioned at coordinate (300m, 300m) transmits smallest
amount of data because it is considered as interfering
node. From these two figures, we observed that if smart
antenna system form smaller main lobe then the channel
utilization improves tremendously.
So from all simulation results, we can say that the
channel utilization can be improved tremendously if our
antenna system form narrower main lobe beam and to
meet this requirement, we required more antenna
elements. But use of more number of antenna elements
will be costly, but if we use more antenna elements in
dense distributed networks and lesser antenna elements in      Figure 8: Data Packets Transmitted by Node Positioned
sparse distributed networks then cost problem could be                           at (300m, 300m).
                                                              6. CONCLUSIONS
                                                              In this work, we proposed an adaptive MAC protocol for
                                                              infrastructureless networks. The smart antenna
                                                              technology is also used in this research work. To solve the
                                                              scalability problem, we used a GPS technology by which
                                                              each of the nodes can find the directions of any signal.
                                                              After completion of RTS/CTS packets exchange,
                                                              communicating nodes perform power control to improve
                                                              performance of network. If the RTS/CTS packets are
                                                              received by interfering neighbour nodes then they use
                                                              beamforming algorithms to steer their antenna beam
                                                              pattern, for interference-free communication between
                                                              sending & receiving nodes. The simulation result shows
                                                              that if we use our proposed protocol with smart antenna
        Figure 7: Total Data Packets Transmitted              technology      then   channel      utilization  improves
                                                              tremendously and we found better results than IEEE
                                                              802.11 MAC using omnidirectional antennas.

                                                              [1] Rajesh Radhakrishnan, Dhananjay Lal, James
                                                                  Caffery Jr., and Dharma P. Agrawal, "Performance
                                                                  Comparison of Smart Antenna Techniques for

Volume 1, Issue 2 July-August 2012                                                                             Page 83
   International Journal of Emerging Trends & Technology in Computer Science (IJETTCS)
       Web Site: Email:,
Volume 1, Issue 2, July – August 2012                                          ISSN 2278-6856

     Spatial Multiplexing in Wireless Ad Hoc Networks,"      AUTHORS:
     in Proc. of the Fifth International Symposium on                     Nalin Gahlaut received the B.Tech in the
     Wireless Personal Multimedia communications, Oct.                    field of Electronics & Communication
                                                                          Engineering from Uttar Pradesh Technical
                                                                          University, Lucknow (U.P.)-India and
[2] Nader Fahmy, Terence D. Todd, and Vytas                               M.Tech.(with Hons.) in the field of Digital
     Kezys,”Ad Hoc Networks with Smart Antenna Using         Communication from Uttarakhand Technical University,
     IEEE 802.11-Based Protocols,” in Proc. of IEEE          Dehradun (Uttarakhand)-India in year 2007 & 2009,
     International Conference on Communications 2002,        respectively. Presently, he is Ph.D candidate at
     April 2002.                                             Uttarakhand             Technical            University,
                                                             Dehradun (Uttarakhand)-India. He has about four years of
[3] S. -L. Wu, Y. -C. Tseng, and J. -P. Sheu, "Intelligent
                                                             teaching experience. He has published more than fifteen
     Medium Access for Mobile Ad Hoc Networks with           papers in the area of Wireless Communication &
     Busy Tones and Power Control", IEEE Journal on          Computing at National/International Level. He is life
     Selected Areas in Communications, Sep. 2000.            member of International Association of Engineers
[4] Harry L. Van Trees, Optimum Array Processing             (IAENG), Hong Kong and member International
     Part IV: Detection, Estimation, and Modulation          Association of Computer Science and Information
     Theory, Wiley, 2002.                                    Technology (IACSIT), Singapore and member of
                                                             National Academy of Engineering. His area of interest
[5] IEEE       Standards    Department,      “ANSI//IEEE
                                                             includes Wireless Communication, Computer Networks,
     Standard 802.11,” IEEE Press, 1999.                     and Communication Technologies.
[6] T.S      Pappaport,     Wireless    Communications,
     Principles and Practice, Prentice Hall, 1996.
[7] Jack H. Winters, “Smart Antenna for Wireless                          Dr. Sandip Vijay received B.Sc. (Engg.)
     Systems,” IEEE Personal Communications, 5(1),                        from NIT Patna (erstwhile Patna University),
                                                                          M.Tech. (Elect. & Comm. Engg.), Ph.D
     Feb. 1998.
                                                                          from I.I.T. Roorkee (erstwhile UOR), the
[8] S. Bandyopadhyay, K. Hasuike, S. Horisawa, S.            member of IEEE(USA), NSBE(USA), IANEG(USA),
     Tawara, "An Adaptive MAC Protocol for Wireless          ISOC(USA), Life Member of ISTE (INDIA) has
     Ad Hoc Community Network (WACNet) Using                 published over Eighty research papers in national and
     Electronically Steerable Passive Array Radiator         international journals/conferences and IEEE proceeding
     Antenna", in Proc. of the IEEE GLOBECOM 2001,           publication in field of Wireless &               Digital
                                                             Communication Network and supervised more than 30
                                                             projects/dissertation of M.Tech. & B.Tech. Students. He
[9] Young-Bae Ko, Vinaychandra Shankarkumar and              started his career as R&D Engineer in various Dell
     Nitin H. Vaidya, “Medium Access Control Protocols       Computers in the field of Quality Assurance Engineer
     using Direction antennas in Ad Hoc Networks,” in        then joined teaching profession as a Lecturer and later
     Proc. of IEEE INFOCOM 2000, Mar 2000.                   on promoted as Asst. Professor in GEIT, Uttaranchal
[10] A. Nasipuri, S. Ye, J. You and R.E. Hiromoto, “A        Technical University (Now Graphic Era University). He
                                                             has successfully completed major research projects
     MAC Protocol for Mobile Ad Hoc Networks using
                                                             independently by VSI & DA-IICT, Gandhi Nagar, in the
     Directional Antennas,” in Proc. of IEEE WCNC            field of VLSI Design. His many research papers have
     2002, 2002.                                             been awarded by National/International conferences.
[11] Ramanathan, R.; Redi, J.; Santivanez, C.; Wiggins,      Presently, he is working as Professor & Head of deptt. of
     D.; Polit, S., “Ad hoc networking with directional      ECE & AIE in D.I.T. Dehradun.
     antennas: a complete system solution,” Selected
     Areas in Communications, IEEE Journal on , vol.23,                  Dr. S.C. Gupta is Professor emeritus,
                                                                         Electronics & computer Discipline at I.I.T.
     no.3, pp. 496-506, March 2005.
                                                                         Roorkee. He received B.Sc., B.Tech.,
[12] Jack H. Winters, “Smart Antenna Techniques and                      M.TECH., Ph.D and published many
     Their Application to Wireless Ad Hoc Networks,”         research papers at national and international levels.
     IEEE Wireless Communications, August 2006.

Volume 1, Issue 2 July-August 2012                                                                           Page 84

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