Results Analysis

A). Frame size vs. Reserving rate:

First, the aim of this experiment is to study the reserving rate relate to the frame size. As shown in Figure 22, the number of nodes is inversely proportional to the percentage of reserved nodes on RR-ALOHA. On the other word, PC-ALOHA needs a fewer slots to achieve 100% reserving rate than RR-ALOHA in a dense network. A larger frame size may incur a larger delay since each node has to wait for a longer period of time before the next frame coming. Otherwise, the smaller frame size can update the message more quickly.

collision

0 50 75 100 125 150

Figure 23. Frame size vs. Reserving rate

B) Single-hop performance:

As shown in Figure 23, RR-ALOHA requires 33 slots to achieve 100% of reserving rate, but PC-ALOHA requires only 28 slots to achieve 100% of reserving rate. PC-ALOHA can save about 15% frame size (28/33 =84.5%). PC-ALOHA frame size is smaller than RR-ALOHA, PC-ALOHA has a lower message update delay. It shows clearly, the slot reserving rate of RR-ALOHA is related to the frames size.

PC-ALOHA always keeps the nodes reserving rate upon 98%. However, it is a dangerous when the channel is congestion in RR-ALOHA network. Because of many nodes have neither the right to transmit nor the guarantee of receiving packet from all its neighbors. In other words, the congestion nodes do not join to the network.

As shown in Figure 24, in order to enhance the slot reserving rate, PC–ALOHA need to reduce the transmissions range for slot time re-using. If the frame size is smaller, nodes will transmit at a smaller transmission range.

0 22 24 26 28 30 32 34 36 38 40

Figure 25. average transmission range C) Convergence :

Although schedule-based MAC protocol can provide each node a contention-free opportunity for data transmission without collision, the node still need to contend for slot reservation by using RR-ALOHA or PC-ALOHA. Especially when it comes to

result, it may take several frames until all the reservation processes complete.

As shown in Figure 25 and Figure 26, the RR-ALOHA protocol slot reserving rate almost can upon 100%. It means that the channel is not congestion. So the power control mechanism did not need to be triggered often. As a result, the PC-ALOHA will not increase the system convergence overhead compared to RR-ALOHA protocol.

Convergence (50 Nodes . Frame size :15 Slots)

Percentage of reserved nodes

RR-50 nodes PC-50 nodes

Figure 26. Convergence (50 Nodes)

Figure 27. Convergence (100 nodes) D) Performance under 100% reserving ratio:

As shown in Table 4, the relationship between slot reserving ratio of nodes and

0 5 10 15 20 25 30 35

Convergence (100 Nodes . Frame size :30 Slots)

RR-100 nodes PC-100 nodes

the number of frame sizes, average flooding hop counts and number of frame sizes, and average relaying delay and number of frame sizes in the different network density.

There are two values in each field. Above number in the field presents the average value and below number in the field presents the maximum one. (e.g., the RR-ALOHA requires 32 slots upon 100% reserving ratio and the maximum number of slot is 33. PC-ALOHA only requires 26.2 slots upon 100% reserving ratio and the maximum number of slot is 28). As a result of the simulation: in the deployment region, the frame sizes under 100% slot reserving ratio is based on the nodes density.

The results show that the PC/RR ratio of required slots decreases as the number of nodes increases, since the higher density, the larger frame size is required, which implies that our approach has more chance to find a free slot by reducing the node’s power. On the other hand, PC–ALOHA will save a larger percentage of frame sizes in the high dense networking.

node

Required slots Hop counts Relaying delay (ms) (Hop count*Frame size)

Table 4. Performance under 100% reserving ratio

E) Flooding Delay

We analyzed transmissions delay problem with the maximum frame size above

simulation case (e.g., 100 nodes frame size is 33 in RR-ALOHA, 28 slots in PC-ALOHA). As shown in Figure 27, (1) in dense networking, RR-ALOHA average delay is higher than PC-ALOHA. (2) The maximum delay in 150 nodes simulation case, RR-ALOHA is higher than PC-ALOHA about 28% and the average delay is about 11%. Therefore, it is a serious issue for safety-critical application message exchange.

0 50 100 150 200

0 20 40 60 80 100 120

Number of nodes

Delay time (ms)

Flooding Delay

PC-AVG. Delay RR-AVG. Delay PC-MAX. Delay RR-MAX. Delay

Figure 28. Flooding Delay

Chapter 6 Conclusion

In this paper, we have proposed a low-delay distributed TDMA Protocol with congestion control for wireless Ad Hoc networks base on previous RR-ALOHA MAC protocol. The most important features of PC-ALOHA MAC protocol are resolving the congestion problem and at the same time achieving a lower end-to-end delivery delay for the Ad Hoc networks. At same time, our PC-ALOHA MAC protocol guarantees the network connectivity even if transmission range of some nodes were reduced. As the result, in dense networking, our protocol decreases at most 28% in delay than RR-ALOHA. It proof our MAC protocol is suitable for the current delay-sensitive safety application, such as Cooperative Collision Avoidance (CCA) in vehicular networks. In future, we will further consider how to assign slots to nodes most quickly and a fewer convergence time in a dense network.

Reference

[1] X. Yang, J. Liu, and F. Zhao, “A Vehicle-to-vehicle Communication Protocol for Cooperative Collision Warning”, In Proceeding of the 1st Annual International Conference on Mobile and Ubiquitous Systems Networking and Services, IEEE Computer Society, Massachusetts, USA, pp. 114 - 123, 2004.

[2] V.S. Raghavan S. Kumar and J. Deng. “Medium access control protocols for ad-hoc wireless networks: A survey.” Elsevier Ad-Hoc Networks Journal, 4(3):

pp. 326 - 358, May 2006.

[3] L. Armstrong, “Dedicated Short Range Communications (DSRC),” [Online].

Available: http://www.leearmstrong.com/dsrc/DSRCHome.htm

[4] M. Torrent-Moreno, P. Santi, and H. Hartenstein, “Fair Sharing of Bandwidth in VANET”, in Proceedings of the 2nd ACM International Workshop on Vehicular Ad Hoc Networks (VANET), Cologne, Germany, pp. 49 - 58, 2005.

[5] Xu Guan, Raja Sengupta, Hariharan Krishnan, Fan Bai “A Feedback-Based Power Control Algorithm Design Based Power Control Algorithm Design for VANET”, Mobile Networking for Vehicular Environments, pp. 67 – 72, 2007.

[6] J. Zang, L. Stibor, et al. “Congestion Control in Wireless Networks for Vehicular Safety Applications”, In Proceeding The 8th European Wireless Conference, Paris, France. pp. 7, 2007.

[7] Fan Yu and Subir Biswas, “Self-configuring TDMA protocol for enhancing vehicle safety with DSRC based vehicle-to-vehicle communication”, IEEE Journal Selected Areas in Communications, vol. 25, no. 8, pp. 1526 – 1537, 2007.

[8] Hassan-Aboubakr Omar, Weihua Zhuang, and Li Li, “VeMAC: A novel multichannel MAC protocol for vehicular ad hoc networks”, in Proc. of IEEE

Conf. on Computer Communication Workshop, pp. 413 – 418, 2011.

[9] F. Borgonove, A. Capone, M. Cesana, and L. Fratta, “ADHOC MAC: New MAC architecture for ad hoc networks providing efficient and reliable point-to-point and broadcast services”, Wireless Networks, vol. 10, pp. 359 – 366, 2004.

[10] Ning Lu, Xinhong Wang, Ping Wang, Peiyuan Lai, Fuqiang Liu “A distributed reliable multi-channel MAC protocol for vehicular ad hoc networks”, in Proc. of IEEE Intelligent Vehicles Symposium, pp. 1078 – 1082, 2009.

[11] Ning Lu, Yusheng Ji, Fuqiang Liu, and Xinhong Wang “A dedicated multi-channel MAC protocol design for vanet with adaptive broadcasting”, WCNC, pp. 1 -6 ,2010.

[12] Jia Liu, Fengyuan Ren, Limin Miao, Chuang Lin “A-ADHOC: an adaptive real-time distributed mac protocol for vehicular ad hoc network”, ChinaCOM, pp.

1 – 6, 2009.

[13] F. Borgonovo, A. Capone, M. Cesana, L. Fratta, "RR-ALOHA, a Reliable R-ALOHA Broadcast Channel for Ad Hoc Inter-Vehicle Communication Networks", Med-Hoc-Net, Baia Chia, Italy, 2002.

[14] B. Hull, K. Jamieson, and H. Balakrishnan, “Mitigating Congestion in Wireless Sensor Networks”, In Proc. of 2nd ACM Conference on Embedded Networked Sensor Systems, pp. 134-147, November 2004.

[15] W. Crowther, R. Rettberg, D. Waldem, S. Ornstein, and F. Heart, “A System for Broadcast Communication: Reservation-ALOHA,” in Proceedings of the Sixth Hawaii International Conference on System Sciences, January 1973.

[16] F. Borgonovo, L. Campelli, M. Cesana, and L. Fratta, “Impact of user mobility on the broadcast service efficiency of the ADHOC MAC protocol”, Proc. IEEE VTC, vol. 4, pp. 2310-2314, 2005.

[17] Marc Torrent-Moreno, Jens Mittag, Student Member “Vehicle-to-Vehicle

Communication: Fair Transmit Power Control for Safety-Critical Information”, IEEE TRANSACTIONS ON VEHICULAR TECHNOLOGY, VOL. 58, NO. 7, pp.

3684 – 3703, 2009.

[18] M. Torrent-Moreno, P. Santi, and H. Hartenstein, “Distributed fair transmit power adjustment for vehicular ad hoc networks.” In SECON ’06 3rd Annual IEEE Communications Society, pp. 479-488, 2006.

[19] J. Mittag, F. Schmidt-Eise nlohr, M. Killat, J. Harri and H. Hartenstein,”Analysis and Design of Effective and Low-overhead transmission power control for VANETs.” in Proc. 5th ACM Int. Workshop VANET, pp. 39-48 , 2008.

[20] Ghassan Samara, Sureswaran Ramadas, Wafaa A.H. Al-Salihy “Safety Message Power Transmission Control for Vehicular Ad hoc Networks”, J. Computer Sci., 6 (10): 1027-1032, 2010.

[21] Chunxiao Chigan and Jialiang Li “A Delay-Bounded Dynamic Interactive Power Control Algorithm for VANETs”, IEEE ICC, pp. 5849 – 5855, 2007.

[22] K.R. Gabriel and R.R. Sokal. “A New Statistical Approach to Geographic Variation Analysis.” Systematic Zoology, vol. 18, pp. 259 - 278, 1969.

[23] “The network simulator (NS2) ”, http://www.isi.edu/nsnamlns/

[24] T. Liu, J. A. Sylvester, and A. Polydoros, “Performance evaluation of R-ALOHA in distributed packet radio networks with hard real-time communication,” in Proc. IEEE Veh. Technol. Conf., pp. 554 - 558 vol.2 1995.

[25] R. Verdone, “Multihop R-ALOHA for intervehicle communications at millimeter waves”, IEEE Trans. Veh. Technol., no. 4, pp. 992 – 1005, 1997.

[26] Y. Wang and B. Bensaou, “Achieving fairness in IEEE 802.11 DFWMAC with variable packet size,” in Proc. IEEE Global Telecommun. Conf., pp. 3588 - 3593 vol.6, 2001.

[27] W. Crowther, R. Rettberg, D. Waldem, S. Ornstein and F. Heart, A system for

broadcast communications: Reservation ALOHA, in: Proceedings of 6th Hawaii Internat. Conf. Sist. Sci., pp. 596–603, 1973.

[28] Flaminio Borgonovo, Luca Campelli, Matteo Cesana “Topology Control In Ad Hoc Networks: A MAC Layer Solution”, International Journal on Wireless {&}

Optical Communications, VOL. 3, NO. 1, pp. 101 – 117, 2006.