1. Ad Hoc/Sensor Networking and Multihop WLANs
May 2005
doc.: IEEE /0461r2
May 2005
Ad Hoc/Sensor Networking and Multihop WLANs
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CH Yeh, Queen's University
CH Yeh, Queen's University

2. May 2005
doc.: IEEE /0461r2
May 2005
Abstract
This talk presents problems that will be introduced when current MAC protocols are applied to multihop networking, including mobile ad hoc networks, sensor networks, and multihop WLANs. We point out the issues to be addressed, current status for research and development, and incentives for deploying multihop networking.
CH Yeh, Queen's University
CH Yeh, Queen's University

3. Examples for Multihop Networks
May 2005
Examples for Multihop Networks
Ad hoc networks (MANET)
Sensor networks
Home networks with repeaters
Mesh networks
Multihop WLANs
Others: Multihop cellular networks
CH Yeh, Queen's University

4. Mobile Ad Hoc Networks (MANET)
May 2005
Mobile Ad Hoc Networks (MANET)
Mobile stations communicate with each other directly
Absence of any predefined infrastructure
High mobility possible
Every node acts as a router
Wireless Link
Node
CH Yeh, Queen's University

5. Wireless Sensor Networks
May 2005
Wireless Sensor Networks
Large number of small devices
Static stations communicate with each other directly
Sinks for gathering data
Every relay node acts as a router
Sink
Sink
CH Yeh, Queen's University

6. May 2005
Home Networks
Intelligent appliances (IAs) communicate with access point (AP) directly or through a repeater
IEEE or ultrawideband (UWB) may be used
CH Yeh, Queen's University

7. May 2005
Mesh Networking AP MP
Mesh points (MPs) communicate with each other wirelessly
Only some of the access points have wired connections to the Internet
Every node also acts as a router
CH Yeh, Queen's University

8. Multihop WLANs May 2005 Combining ad hoc networks and wireless LANs
Mobile stations communicate with each other directly
Packets are routed to APs to access the Internet
Each participating node also acts as a router
CH Yeh, Queen's University

9. Ad Hoc Cellular Networks
May 2005
Ad Hoc Cellular Networks
Combining ad hoc networks and cellular networks
Mobile stations communicate with each other directly
Packets are routed to APs to access the Internet
Each participating node also acts as a router
CH Yeh, Queen's University

10. Advantages for Multihop Networking
May 2005
Advantages for Multihop Networking
Ad hoc networks
Infrastructureless
Sensor networks
Great commercial values
WLAN Mesh
Range extension with lower infrastructure cost
Multihop WLAN/cellular networks
Range extension without additional infrastructure
Dead zone elimination/mitigation
Lower power consumption
Higher speed (due to shorter distance)
Lower interference and better spatial reuse
Higher throughput (potentially)
CH Yeh, Queen's University

11. Why Commercial Ad Hoc Networking Has Not Happened
May 2005
Why Commercial Ad Hoc Networking Has Not Happened
Routing protocols were not standardized till 2004
The number of laptop computers did not reach a critical mass
Lack of killer applications
E.g., ad hoc networking in conference venues is replaced by WLAN coverage
Poor performance (in ad hoc networking environments) based on current products
Low throughput due to relaying
Some problems remain unsolved
Difficult configuration
CH Yeh, Queen's University

12. New Driving Forces for Multihop Networking
May 2005
New Driving Forces for Multihop Networking
VOIP over WLAN
becoming available on smart phones
Reaching critical mass
Extended range is beneficial for WLAN access
Energy efficiency is critical
Proliferation of hot spots
Range extension = making more money
Feasible with higher speeds and advanced technology
National/muni WiFi to be deployed
Range extension = infrastructure cost reduction
Extending to sensor networking
Huge market
CH Yeh, Queen's University

13. Problems with Current WLAN MAC in Multihop Networking Environments
May 2005
Problems with Current WLAN MAC in Multihop Networking Environments
High collision rate
TCP and in multihop networking environments
Interference problems
Interference-range hidden/exposed terminal problem
Additive interference problem
Problems associated with power control
Heterogeneous hidden/exposed terminal problem
Single-channel MAC difficult
QoS and fairness problems
Alternate blocking problems
Fairness problems
Exposed terminal problem
CH Yeh, Queen's University

14. Interference-range Hidden/Exposed Terminal Problem
May 2005
doc.: IEEE /0461r2
May 2005
Interference-range Hidden/Exposed Terminal Problem
The interference range is typically larger than that of transmission range
A potential transmitter D that cannot be reached by the CTS message of B may send a packet and collide with B’s reception A B D E
(a)
(b)
(c)
RTS
CTS
Data
RLT also solves various other problems. Will be presented in Globecom’03
CH Yeh, Queen's University
CH Yeh, Queen's University

15. Additive Interference Problem
May 2005
doc.: IEEE /0461r2
May 2005
Additive Interference Problem
A receiver is outside the interference radius of any other transmitters (except for its own transmitter), but the sum of nearby interference collide the reception anyway
Relatively difficult to solve
RLT also solves various other problems. Will be presented in Globecom’03
CH Yeh, Queen's University
CH Yeh, Queen's University

16. Heterogeneous Terminal Problem
May 2005
Heterogeneous Terminal Problem E D F C H
CTS G B A
CH Yeh, Queen's University

17. Alternate Blocking Problem
May 2005
Alternate Blocking Problem
CTS
CTS A B C D E
CH Yeh, Queen's University

18. Exposed Terminal Problem
May 2005
Exposed Terminal Problem
Data
CTS
Data
CTS A B C D A B C D
(b)
(a)
CH Yeh, Queen's University

19. Issues Needed to Be Addressed
May 2005
Issues Needed to Be Addressed
Resolving/mitigating aforementioned problems
Routing
Mobility
Energy efficiency
Security, privacy, and reliability
Incorporating emerging technologies
Applicability to sensor networks
Cooperation from users
Billing and Business model
CH Yeh, Queen's University

20. Distinction from TGs May 2005 TGs focus on the following context:
Residential networks
Office networks
Campus/public networks
Safety/military networks
Mesh points are different from laptops/smart phones/PDAs
Infrastructure
Power supply available
Stationary in nature
Single-hop networking from mobile stations (users) to mesh points
Likely outcome
Aiming at relatively smaller number of mesh points
Likely based on infrastructure mode between mesh points
Minimum/moderate changes to current MAC (esp. for mobile stations)
Question:
Evolve from TGs solutions or start a new effort?
CH Yeh, Queen's University

21. Distinction from TG5 Current TG5 proposals
May 2005
Distinction from TG5
Current TG5 proposals
Synchronized MAC
Hierarchical/clustered architecture
Lower mobility than MANET
Relatively smaller range
Relatively lower speed
Not applicable to PHY
CH Yeh, Queen's University

22. Current Status in Research and Development
May 2005
doc.: IEEE /0461r2
May 2005
Current Status in Research and Development
Four experimental routing protocol RFCs standardized by IETF
Numerous ad hoc network testbeds in universities
Some commercial products based on AODV, , and/or proprietary solutions
Intensively researched in academia and industry
Military applications for about 3-4 decades
Renewed interests for about 1 decade
Mainly focused on routing
Problems well known
Interesting techniques and solutions
but some may be complex or even infeasible
CH Yeh, Queen's University
CH Yeh, Queen's University

23. Concluding Remarks Everything will be ad hoc in the future
May 2005
Concluding Remarks
Everything will be ad hoc in the future
Multihop networking will be a norm, rather than an exception
Time to look into multihop networking issues
Emerging technologies should be incorporated
CH Yeh, Queen's University

24. May 2005
References
Sadeghi, B., “On hidden and exposed terminal problems,” IEEE /0065r0.
Yeh, C.-H., “The advance access mechanism for differentiated service, power control, and radio efficiency in ad hoc MAC protocols,” Proc. IEEE VTC’03F, 2003.
CH Yeh, Queen's University