Presenter : Cao Trong Hieu , Ph.D Faculty of Information Technology, Hanoi University (HANU)

1. Routing on Multi-rate Multi-hop Wireless Network: Problem Statements and an Effective Solution using Information Entropy Approach Presenter: Cao Trong Hieu, Ph.D Faculty of Information Technology, Hanoi University (HANU) hieuct@mails.hanu.edu.vn 12 March, 2011

2. Outline • Routing Issues in Wireless Ad-hoc Networks • Motivations and Contributions • Related Work • Proposed Routing Protocol • Routing Metric • Route Discovery Strategy • Protocol Operation • Performance Analysis • Conclusions • Appendix

3. Routing Issues in Wireless Ad-hoc Networks • Wireless Ad hoc Networks contain many kind of networks which have the same key features: distributed (self-organizing) topology, power and computational constrains. • Example: Wireless Sensor Network (WSN), Wireless Mobile Ad hoc Network (MANET), Wireless Mesh Network (WMN), Wireless Vehicular Network (VANET), etc. • For routing, all of them have to deal with: • Wireless propagation issues • Distributed topology • Multi-hop communication • Mobility problem (in case of moving nodes) • Power constraint (no fixed power supply) • Computation constraint (small, lightweight devices) • …

4. Expected Properties of a Routing Protocol • Distributed: A routing protocol for Wireless networks should be distributed in manner in order to increase its reliability. • Unidirectional links: Wireless medium may cause a wireless link to be opened in uni-direction only due to physical factors. It may not be possible to communicate bi-directionally. • Power-efficient: It should be power efficient • Computational complexity: should be simple! • Accuracy and efficiency: found optimal route • Security: The routing protocol should consider its security (based on the application at hand) • Hybrid nature: Hybrid protocols, which combine the benefits of different routing protocols can be preferred in many cases • QoS: A routing protocol should be aware of Quality of Service (QoS), so that a real time application might rely on it.

5. Routing Issues in Wireless Ad-hoc Networks • For Multi-hop network: • In-range node has the ability to communicate directly (1-hop neighbors), • Out-of-range nodes use intermediary hops to communicate with each other. • For supported Multi-rate communication: • Traditional hop-count metric is no longer effective • Many routing metrics have been proposed, and should be used based on desired achievement target: throughput?, or delay?, or network lifetime?, etc.  Need a routing protocol efficiently works will this most common used network.

6. Currently, physical layer enhancements support multiple data rates. Example: the IEEE 802.11g standard with OFDM technology support 8 data rates according to the selected Modulation and Coding Scheme (MCS) as showed in the Table 1.

7. Motivations • Recently, using lower layer information (packet delivery ratio, and RSSI), routing more efficiently! • For wireless communication: distance and path loss effect the data rate • For multi-rate ad hoc networks, direct relationship : a low speed link can cover the distance to the destination in few hops, while a high speed link requires more hops to reach the destination. • The received signal strength: • Let Pr = Rx sensitivity, the transmission range corresponding to rate rk using the log-distance path loss model [2], • The received sensitivity Prprovided by RSSI is used to compare with the referenced sensitivity to determine the highest possible rate for data transmission.

8. 1 2 3 • Show the advantages of proposed protocol by proofs and simulations. Propose a Route Assessment Index (RAI) metric, and Route Discovery Strategy Apply RAI metric for AODV protocol with some modifications. Motivations and Contributions • Motivations: • How to relate the distance between two communicating nodes into the corresponding highest possible data rate. • How define a routing metric that can determine a reliable, high throughput, and no link bottleneck route. • Contributions:

9. Related Work • A lot of routing protocols have been proposed for the (mobile) wireless ad hoc networks, with two major strategies: proactive ( DSDV [3] and OLSR [4]) and reactive (on-demand) ( AODV [5] and DSR [6]). • For multi-rate adhoc networks, The Automatic Rate Fallback (ARF) is widely adopted by the industries to determine the initial transmission rate. • Medium Time Metric (MTM) [7] is a remarkable proposal which assigns weight for each link rate, and choose route with minimum time delay. • None of them: • relate the distance with the highest possible data rate. • has a routing metric which ensures all expected properties that a route needs as mentioned in the motivations.

10. Route Assesment Index (RAI) metric • Based on the properties of Entropy function: with • Maximality: among observing sets which contain the same number of elements in each set, the set with more resemble elements will have the higher entropy outcome. Especially, a set of homogeneous elements will have the maximum entropy outcome. • Uniform distribution: for sets with the different number of homogeneous elements, the higher number of elements a set has, the lower entropy outcome per element that set gets.

11. RAI metric (cont.) • Consider multi-hop, multi-rate wireless network • The link reliability when node x and y communicates at rate rk: where, df and dr are the delivery ratios of in the forward and reverse direction, respectively. • For a route, the weight associated with the i-th position is : the effective link capacity at rate rk rmax : the maximum supported rate.

12. RAI metric (cont.) • If the value of rkis much different with rl (ex: rk « rl), the route will have link bottleneck between (i-1)-th and i-th positions. Hence, define cost of node i-th: • For Ni is the number of intermediate nodes in the route, define the coefficient: • The Route Assessment Index (RAI):

13. RAI metric (cont.) • RAI satisfies the condition:  Selecting the best route?  choose the route with minimum RAI value! • Theorem 1: The route with minimum RAI value is the route with the small number of hops between source and destination. • Theorem 2: The route with the minimum RAI value (consequently, has maximum cost Ci)can avoid link’s bottleneck. • Theorem 3: The route with the minimum RAI value has the highest throughput among route candidates • Proof: straightforward, using the properties of entropy function!

14. Route Discovery Strategy • Propose to use 2-hop information. • A node should include a list of its 1-hop neighbors in the Hello messages  Has a complete view of the 1-hop neighbor topology, also of its 2-hop neighbors and their connectivity with the 1-hop neighborhoods. • The advantage of using 2-hop information is shown in the example: • AODV will choose {S; I2; I6; D} because it is the minimum hop count. • But contains a link bottleneck (I2; I6)  not a high throughput route. • With 2-hop knowledge, I6 knows that the best route from source to it must go through node I4 (no need to receive RREQ from its neighbors anymore).  The best route is {S; I2; I4; I6; D} (verified by RAI value!)

15. Protocol Operations • Based on AODV with RREQ, RREP, RERR messages. • Adaptive modifications: • Use RAIas the routing metric • Exchange information between MAC and routing layer • Node maintains additional entries: {destination, {Ci}, Ni}; • Allow duplicated RREQ • Update and forward RREQ only when new Ciis higher. • The first received request is replied with an unicast RREP packet that contains the RAI value of the route. • Only latter RREQ with lower RAI value will be updated and sending a new RREP back to source.  each node calculates RAI loccaly and in distributed fashion, hence, the protocol is implementable without the consideration of computation complexity.

16. Performance Analysis • The number of nodes, varying from 50 to 250, are randomly distributed over a 500m x 500m area using NS-2. • Based on the IEEE 802.11g, which supported data rates (i.e., 6, 9, 12, 18, 24, 36, 48 or 54 Mbps). • Pick up some source-destination pairs randomly. • UDP flows with the packet size is set to 1024 bytes are applied in the source nodes. • The log-distance path loss radio propagation model is used with the path loss exponent =3. • Compare with Hop Count of AODV, and MTM.

17. Results • Route Discovery Time, Loss Rate, Delay, and Throughput comparisons

18. Conclusions • Propose a new routing protocol using the RSSI and link reliability from lower layer, which reflects actual network conditions, to choose the high throughput route. • The metric has the form of entropy function, which is used to prove the advanced properties of a communication route. • The chosen route is also free of link bottleneck and small relay hops by minimizing the value of Route Assessment Index (RAI). • For the future, consider multi-path routing for multi-rate network. More analysis and comparisons with other routing metrics need to be done.

19. Properties of Information Entropy (Shannon Entropy) and its application for route assessment in Multi-hop Communication Networks. Appendix

20. In information theory, Shannon's entropy [6] was introduce as the measure of uncertainty. Definition: Let  be a discrete random variable, takes finite number of possible values (x1, x2, …, xn), with probabilities (p1, p2, …, pn), respectively. For and , we have The function (or ) is a nonnegative, continuous, and symmetric function.

21. Entropy PropertiesSupporting Route Assessment Property 1: Maximality: The entropy is maximum when all the probabilities are equal. with equality if and only if Proof: We have the Relative Entropy Also, Then, applying the Eq. (3) for H(P) and we have: Hence,

22. Property 2: Uniform Distribution (Reduced entropy per degree of freedom): Suppose we have , then Proof: The proof is straightforward using the result of property 1. We have and . Also, .  the entropy function will reduce when the number of elements in the set increases (n large), and theorem is proven. Entropy PropertiesSupporting Route Assessment

23. Apply to Multi-hop Communications Consider a route with Ni intermediate nodes,  exist (Ni+1) links in that route. Model the nodes with their cost (ex. bandwidth, remaining energy, etc.). Transform those costs into variables for applying Entropy function. How? Define the coefficient i for the cost Ci of position i-th in the route as Hence, , satisfies the condition of a standard (independent and complete) set.

24. Define an assessment indicator, which has the following form, for a route The following theorems show the advantages of a route using IR as preference indicator. Theorem I: Among route candidates, the route with the maximum IR value should be chosen to avoid link bottlenecks. Proof: Using the maximality properties, IR has higher value when there are more similar links in the route, and the maximum value when every link in the route is equal. If there exists one link with a data rate much lower than those of the other links in the route, then IR will be reduced. Apply to Multi-hop Communications

25. Theorem II: The route with maximum IR value will have small number of intermediate nodes. Proof: Using the property 2, if the number of intermediate nodes of route 1 and 2 are N(1) and N(2), respectively. Also, if , then Hence, the route with small number of hops is prefered. Theorem III: The route with the maximum IR value has the highest throughput among route candidates. Proof: Obviously, if we can find a communication route with high throughput in each link, no link bottleneck, and small number of intermediate nodes (shown above), then that route is a high throughput route. The results are shown in [2] and [3]. Apply to Multi-hop Communications

26. References T. M. Cover and J. A. Thomas, “Elements of Information Theory”, Wiley-Interscience; 2nd edition, 2006. Cao Trong Hieu, and Choong Seon Hong, “A New Routing Protocol with High Throughput Route Metric for Multi-Rate Mobile Ad-hoc Networks”, the 17th IEEE Workshop on Local and Metropolitan Area Networks (LANMAN 2010), Long Branch, New Jersey, USA, May 05-07, 2010. Cao Trong Hieu, and Choong Seon Hong, “A Reliable and High Throughput Multi-Rate Ad Hoc Routing Protocol: Cross Layer Approach”, The International Conference on ICT Convergence (ICTC 2010), Jeju Island, Korea, November 17-19, 2010. Cao Trong Hieu, “Effective Routing Strategies for Wireless Networks using Cross-layer Approach”, Ph.D Dissertation in Computer Enginerring, December 2010.

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