1. Location-Aware Routing Protocols in a Mobile Ad Hoc Network
Professor Yu-Chee Tseng
Dept. of Computer Science and Information Engineering
National Chiao-Tung University
(交通大學 資訊工程系 曾煜棋) 1

2. Notebook + GPS

3. Location-Aided Routing
LAR: in MobiCom 1998.
Main Idea
Using location information to reduce the number of nodes to whom route request is propagated.
Location-aided route discovery based on “limited” flooding

4. Location Information
Consider a node S that needs to find a route to node D.
Assumption:
each host in the ad hoc network knows its current location precisely (location error considered in one of their simulations)
node S knows that node D was at location L at time t0, and that the current time is t1
Location services in ad hoc networks, refer to
A survey on position-based routing in mobile ad hoc networks, M. Mauve, J. Widmer, and H. Hartenstein, IEEE Network, Vol. 15 No. 6,  2001.

5. Expected Zone
expected zone of D ---- the region that node S expects to contain node D at time t1, only an estimate made by node S

6. Request Zone LAR’s limited flooding
A node forwards a route request only if it belongs to the request zone
The request zone should include
expected zone
other regions around the expected zone
No guarantee that a path can be found consisting only of the hosts in a chosen request zone.
timeout
expanded request zone
Trade-off between
latency of route determination
the message overhead

7. Membership of Request Zone
How a node determines if it is in the request zone for a particular route request
LAR scheme 1: inside or outside the request zone
LAR scheme 2: based on whether there is any progress

8. Two cases: whether the source node is inside or outside
LAR Scheme 1
Two cases: whether the source node is inside or outside
the expected zone?

9. LAR Scheme 2 S knows the location (Xd, Yd) of node D at time t0
Node S calculates its distance from location (Xd, Yd): DISTs
Node I receives the route request, calculates its distance from location (Xd, Yd): DISTi
For some parameter δ,
If DISTs + δ ≥ DISTi, node I replaces DISKs by DISKi and forwards the request to its neighbors; otherwise discards the route request

10. Telecommunication Systems, 2001.
“GRID: A Fully Location-Aware Routing Protocol for Mobile Ad Hoc Networks”
Telecommunication Systems, 2001.

11. Basic Idea Adopt Positioning Systems
such as GPS receivers
President Clinton ordered to discontinue SA (selective availability) in May 2000
will increase the accuracy by an order
Fully utilize location information:
route discovery
data forwarding
route maintenance
We propose a new protocol called GRID.

12. How to Utilize Location Information: Observation 1
Determine route quality based on location information:
passing B is better than passing A

13. How to Utilize Location Information: Observation 2 (“Route Handover”)
Improving the vulnerability and quality of a route based on location information:
When B moves away, E can work on behalf of B.
When F roams in, using F is more reliable.

14. Comparison of Using Location Information
Scheme
Route Discovery
Packet Relay
Route Maintenance
DSR 
AODV
ZRP
LAR 
GRID

15. The GRID Routing Protocol
Partition the physical area into d x d squares called grid.

16. Protocol Overview
In each grid, a leader will be elected, called gateway.
Routing is performed in a grid-by-grid manner.
Responsibility of gateway:
forward route discovery packets
propagate data packets to neighbor grids
maintain routes which passes the grid

17. Route Search We can adopt any existing route discovery protocol.
Major features/differences:
limit the search range by the locations of source and destination
only gateway will help with the discovery process
The more crowded the area is, the more saving.
routing table is indicated by grid ID (instead of host address)

18. Route Search Example
route search route reply

19. Route Search Range Options

20. Routing Table Format Next-hop routing:
the next hop is identified by grid ID (not host ID)
Node S B E F D
Destination
Next hop
(2, 2)
(3, 2)
(4, 2)
(5, 3)
null

21. Route Maintenance Two issues: Special Feature:
how to maintain a gateway in each grid
how to maintain a grid-by-grid route
Special Feature:
longer route lifetime:
as long as there is a host in each gateway, a route will be alive
more robust
In existing protocols, once a node in the route roams away, the route will be broken.

22. Gateway Election in a Grid
Any “leader election” protocol in distributed computing can be used.
Weaker than leader election:
It is acceptable that there are multiple leaders in a grid.
But “without leader” is less acceptable.
Preference in electing a gateway:
near the physical center of the grid
likely to remain in the grid for longer time
once elected, a gateway will remain so until leaving the grid
to avoid ping-pong effect X

23. Gateway Election Details
BID(g, loc)
GATE(g, loc)
RETIRE(g, T)

24. How to Maintain a Grid-by-Grid Route
Strength: more robust route
mobility-resistant
Problems:
Gateway moves away:
The gateway election will find the new gateway.
So the route will remain alive.
Source moves away: (see next page)
getting closer
getting farther away
Destination move away: (similar)

25. (a) getting closer
(b) same length
(c) getting farther,
remaining connected
(d) getting farther,
but disconnected

26. Relationship of Grid Size and Transmission Distance
r = radio transmission distance
d = grid size

27. Simulation Model Physical area of size 1000m1000m
n = number of hosts: 100~300
r=300m
d = grid size
GRID-1:
GRID-2:
GRID-3:
Roaming speed: 30 km/hr, 60 km/hr

28. Route Lifetime
With better route maintenance, our route lifetime is longer.
30 km/hr km/hr

29. Routing Cost (s=30 km/hr)
(number of hosts)
GRID is better in
more crowded area.

30. Delivery Rate
With less routing cost (and thus less traffic load), our packets can be delivered with higher success rate.
30 km/hr km/hr

31. Route Length
Limited by gateway positions, the route length could be longer for GRID approach.
30 km/hr km/hr

32. Implementation Experience
Platform:
Red Hat Linus
building our routing protocol in the kernel
5 ~ 10 notebooks
WaveLAN cards
Application:
ad hoc classroom (隨意教室)
打破傳統教室界線
anytime, anywhere classroom

33. Conclusions A FULLY location-aware routing protocol:
route discovery: by gateways only
data forwarding: by gateway ID, instead of host ID
route maintenance: like handoff in GSM systems
Taking advantage of geometric property of network.
instead of graph property in other approaches
Less routing cost
longer route lifetime, more resilient route
less traffic load

34. Geographical Routing Using Partial Information for Wireless Ad Hoc Networks
Pahul Jain, Anuj Puri, Raja Sengupta
University of California, Berkeley
IEEE Personal Communication, 2001

35. Basic Idea
to use the geographical position of the destination in making routing decisions
acyclic routes

36. Rule 1: Packet Forwarding
When a node S receives a packet for destination D, it finds the neighboring host X which is closest to D than any other neighbors.
then forward the packet to X X D S

37. Rule 2: Route Discovery
If S itself is closest to D than any other hosts. We say that the packet is stuck.
Node S initiates a route discovery to destination D, following the DSR protocol. D S
Stuck, initiating route discovery

38. Example physical location ** Initially, everyone only knows its
neighbors.

39. Case 1: node A needs a route to destination C at (3, 1).
Forward the packet to node B (closest to (3, 1)).
B forwards the packet to C.
Case 2: node A needs a route to destination D at (2.5, 0)
It gets stuck (no one is closer to (2.5) than itself).
A initiates Route Discovery.
finding a new path <A,B,C,D >
A updates its routing table.
then forward the packet.
See Table 5 (next page).

40. newly learned
learned
from snooping

41. Case 3: node A needs a route to destination E
D is the nearest to E in A’s routing table.
forward the packet to Next(D) = B
Node B forwards the packet to node C.
Node C forward the packet to node E.
note: C will behave based on its own routing table.

42. Conclusion Advantage: Disadvantage: Routing table is small in size.
Routing tables are cycle-free.
Low communication overhead.
Disadvantage:
Destination position is known by the source before routing.
A location discovery service is required.

43. Geocasting Geocasting: Geocast region Geocast group
sending a message to everyone WITHIN a specific geographical region
Application:
emergency messages to a building, or an assembly ground
geographic advertisement
Geocast region
Geocast group