Directionality Based Preventive Protocol for Mobile Ad Hoc Networks
VI. PERFORMANCE EVALUATION A. Simulation Environment
Now, we illustrate simulation scenario that uses the developed antenna models along with OPNET [1] to characterize network performance. The wireless communication channel is modeled by 13 pipeline stages including antenna gains, propagation delay, signal-to-noise ratio, calculation of background noise and interference noise, transmission delay, etc. This powerful simulation environment enables designers to create realistic wireless scenarios. In this work, we have modified the MANET node model to make it to work with four individual antennas. We have used predefined and fixed beams and created an antenna pointer model. The antenna gain pattern specified in the Antenna Pattern Editor is used to provide the gain values. Model includes four different antennas to cover four different directions. The antenna patterns have directional gain of 10 dBm with 900 beamwidth.
Orientation threshold of 3 dBm was chosen.
We use the network of 50 nodes placed randomly over area of 2500 x 2500 sq. meter. We have 5 random JASANI ET AL.
168
sources of CBR (constant bit rate) each of which generates 1024 bytes data packets to a randomly chosen destination at a rate of 2 to 50 packets per second with starting time lag of 10s. All five sources start data transmission with different times. All connections/communications end when simulation ends. We use random waypoint mobility model to simulate different patterns of mobility (speed of nodes and pause time). The DPMAC is used as MAC layer protocol for simulation. Simulations are run for 600 seconds and all results are averaged over 5 different seeds.
We compare our results with original DSR.
B. Simulation Results and Discussions
In this subsection, we analyze the simulation results in terms of aggregate throughput, end-to-end delay (latency), and routing overhead. Aggregate Throughput is the total number of bits transmitted from one node to other nodes in the network per unit of time. It is the total traffic sent and received in bits per second for entire network. We collected this statistic in our simulation scenario and compared with original DSR (with omnidirectional antenna nodes). Our PLM scheme performs better in different scenarios since preventive link maintenance scheme allows link to live longer than omnidirectional case. An establishment of directional link postpones the route rediscovery process and also reduces frequent disconnection. Figure 1 shows that aggregate throughput is higher in our scheme using directional antenna. Aggregate throughput (performance) of entire network for our scheme is about 75% higher than original DSR for higher packet/data rate.
End-to-end delay (latency) of packets for the entire network is the time elapsed between the creation of the packet at its source and its destruction at its destination.
It is almost half in case of our scheme when we have five flows communicating simultaneously in compare to smaller number of simultaneous flows. In other words, the average end-to-end delay per packet increases much more sharply for original DSR algorithm than our scheme as shown in Figure 2. It can be concluded that routing performance improves when we have many simultaneous connections. It is also because of the number of directional antennas (four) we use in our simulation.
Aggregate Throughput (mbps)
0 1 2 3 4 5 6 7
1 2 3 4 5 6 7 8 9 1 11
Packets/Second Aggregate Throughput (mbps)
Orig PLM
Figure 1. Aggregate Throughput Average End-to-End Delay
0 2 4 6 8
1 2 3 4 5
Number of simultaneous communications Average End-to- End Delay (s)
Orig PLM
Figure 2. Average end-to-end delay (latency)
Routing overhead per received packet is the ratio of the total number of routing control packets (including RREQ, RREP and RERR) generated/forwarded to the data packets received correctly at the destination. Figure 3 shows that routing overhead is about 40% to 60% less than original DSR. For high mobility scenario, original DSR produce larger routing overhead where as our scheme has lower routing overhead. Routing overhead increases as speed of mobile node increases, but the increment is slight.
In summary, our results are encouraging to use PLM scheme for MANET.
Routing Overhead
0 0.5 1 1.5 2 2.5 3
2.5 5 7.5 10 12.5 15 17.5 20
Mobility (meters/sec) Routing Overhead per Packet
Orig PLM
Figure 3. Routing Overhead per Packet
VII. CONCLUSIONS
Directionality based preventive link maintenance scheme is proposed to improve the performance of mobile ad hoc networks. The MAC is modified accordingly to incorporate the proposed scheme using directional antenna.
A directional antenna module is implemented in OPNET simulator with two separate modes of operations:
omnidirectional and directional. The antenna module has been incorporated in wireless node model and simulations are performed to characterize the performance improvement of DSR Ad Hoc routing protocol. Link breakage happens due to the node movement and subsequent reducing signal strength of receiving packets.
PROTOCOL FOR MOBILE AD HOC NETWORKS 169
Performance improvement is achieved by orienting neighboring nodes antennas towards each other by using the position/location information of nodes or Angle of Arrival information. It helps ad hoc network to avoid or postpone costly operation of route rediscovery while using on-demand routing protocols. We compare the simulation results of PLM scheme with omnidirectional scheme (original DSR algorithm) by collecting the statistics of aggregate throughput, end-to-end delay, and routing overhead. Use of directional antennas has been found encouraging for on demand routing protocols of MANET using our proposed preventive link maintenance scheme.
REFERENCES
[1] Online Documentation, “OPNET Modeler”, http://www.opnet.com/, Date visited: February 2006
[2] D.B. Johnson, D.A. Maltz, Y.-C. Hu and J.G. Jetcheva,
“The dynamic source routing protocol for mobile ad hoc networks,” IETF Internet draft (November 2001) draft-ietf-manet-dsr-06.txt
[3] H. Dajing, J. Shengming and R. Jianqiang, “A link availability prediction model for wireless ad hoc networks,” Proc. of the International Workshop on Wireless Networks and Mobile Computing, Taipei, Taiwan, April 2000.
[4] A. Nasipuri, S. Ye, J. You and R. Hiromoto, “A MAC protocol for mobile ad hoc networks using directional antennas,” Proc. of the IEEE Wireless Communications and Networking Conference, Chicago, Illinois, Vol. 3, September 23-28, 2000, pp. 1214-1219.
[5] Z. Huang and C. Shen, “A comparison study of omnidirectional and directional MAC protocols for ad hoc networks,” In Proc. of IEEE Globecom’02, 2002.
[6] L. Bao, and J.J. Garcia-Luna-Aceves, “Transmission scheduling in ad hoc networks with directional antennas,” In ACM/SIGMOBILE MobiCom 2002, 23-28 Sept. 2002.
[7] M. Takai, J. Martin, R. Bagrodia and A. Ren,
“Directional virtual carrier sensing for directional antennas in mobile ad hoc networks,” Proc. of the ACM MobiHoc’02, Lausanne, Switzerland, June 9-11, 2002, pp. 183-193.
[8] R. Choudhury, X. Yang, R. Ramanathan and N. H.
Vaidya, “Using directional antennas for medium access control in ad hoc networks,” Proc. of the MOBICOM, Atlanta, Georgia, September 23-28, 2002, pp. 59-70.
[9] Abhilash P., Srinath Perur and Sridhar Iyer, “Router Handoff: An Approach for Preemptive Route Repair in Mobile Ad Hoc Networks,” Proc. of High Performance Computing, 2002.
[10] IEEE, ”Wireless LAN Medium Access Control(MAC) and Physical Layer(PHY) Specifications”, IEEE Standard 802.11, June 1999.
[11] R. Ramanathan, “On the performance of ad hoc networks with beamforming antennas,” Proc. of the ACM
MobiHoc, Long Beach, California, October 4-5, 2001, pp. 95-105.
[12] S. Roy, D. Saha, S. Bandyopadhyay, T. Ueda, and S.
Tanaka, “A network aware MAC and routing protocol for effective load balancing in ad hoc wireless networks with directional antenna,” In ACM Mobihoc’03, June 2003.
[13] S. Horisawa S. Bandyopadhyay, K. Hausike and S.
Tawara, “An adaptive MAC and directional routing protocol for ad hoc wireless networks using ESPAR antenna,” In ACM/SIGMOBILE MobiHoc’01, Oct 2001.
[14] M. Sanchez, T. Giles and J. Zander, “CSMA/CA with beam forming antennas in multi-hop packet ratio,” Proc.
of the Swedish Workshop on Wireless Ad Hoc Networks, March 5-6, 2001.
[15] T. Goff, N.B. Abu Ghazaleh, D. Phatak and R.
Kahvecioglu, “Preemptive Routing in Ad Hoc Networks,” In Proc. of ACM SIGMOBILE, Rome, pp.43-52, 2001
[16] D. Johnson, D. Maltz, “Dynamic source routing in ad hoc wireless networks,” edited by T. Imielinski and H. Korth, Kluwer Academic Publisher, pp. 153-181, 1996.
[17] R. Choudhury, N. H. Vaidya, “Performance of Ad Hoc Routing using Directional Antennas,” Journal of Ad Hoc Networks - Elsevier Publishers, November, 2004.
JASANI ET AL.
170