1. Multi hop connections using 802.11
May 2004
doc.: IEEE /xxxr0
July 2004
Multi hop connections using
Guido R. Hiertz, Yunpeng Zang
ComNets
Chair of Communication Networks
Aachen University (RWTH)
Germany
Jörg Habetha
Philips Research
Aachen
Guido R. Hiertz, ComNets, Aachen University (RWTH)
Guido R. Hiertz, ComNets, Aachen University

2. Multi frequency Mesh Advantages of multi frequency mesh networks
July 2004
Multi frequency Mesh
Advantages of multi frequency mesh networks
Less interference
Exclusive channels
Reuse patterns …
Disadvantages of multi frequency mesh networks
Frequency planning
Frequency coordination
Multiple transceivers …
COST (!)
Guido R. Hiertz, ComNets, Aachen University (RWTH)

3. Solutions for single frequency mesh needed, too
July 2004
Single frequency Mesh
E.g. Consumer Electronics
Mass production
Limited power
Limited computing power
Ease of use …
Cost sensitive (!)
Even 50¢ extra might be too much
Single transceiver solutions
Easy to implement
Available
Well known …
Solutions for single frequency mesh needed, too
Guido R. Hiertz, ComNets, Aachen University (RWTH)

4. Spatial frequency reuse (1)
July 2004
Spatial frequency reuse (1)
Assumption
TDMA channel
Equal transmission duration
Equal transmission power
Equal distance between stations
No errors on wireless medium
Simplex connection
Interference range limited to neighboring station
Reception limited to neighboring station
Best case
Guido R. Hiertz, ComNets, Aachen University (RWTH)

5. Spatial frequency reuse (2)
July 2004
Spatial frequency reuse (2)
Reuse limited by neighbor
Reuse distance min. 4 hops
Guido R. Hiertz, ComNets, Aachen University (RWTH)

6. Packet forwarding in 802.11 July 2004
Guido R. Hiertz, ComNets, Aachen University (RWTH)

7. Packet forwarding in 802.11 (2)
July 2004
Packet forwarding in (2)
Guido R. Hiertz, ComNets, Aachen University (RWTH)

8. 802.11 forwarding in detail July 2004
Guido R. Hiertz, ComNets, Aachen University (RWTH)

9. 802.11 = Single hop MAC Distributed Coordination Function
July 2004
= Single hop MAC
Distributed Coordination Function
Coordinates single hop
Local BSS only
No Coordination for Multi Hop
Independent process in each STA
Network Allocation Vector (NAV) reserves single only
No priority to forwarding
Guido R. Hiertz, ComNets, Aachen University (RWTH)

10. No Multi Hop concept in 802.11 Infrastructure based BSS
May 2004
doc.: IEEE /xxxr0
July 2004
No Multi Hop concept in
Infrastructure based BSS
Multi hop connection via AP
Hops to/from AP wireless
Wired backbone
Four address format
Independent BSS
All stations in reception range
No forwarding procedure defined
Guido R. Hiertz, ComNets, Aachen University (RWTH)
Guido R. Hiertz, ComNets, Aachen University

11. 802.11 duplex route in detail July 2004
Guido R. Hiertz, ComNets, Aachen University (RWTH)

12. Duplex multi hop Much worse than simplex connection
July 2004
Duplex multi hop
Much worse than simplex connection
Forwarding stations = Bottleneck
“Neighborhood capture” (11-01/596r1)
For system level, intra BSS
Here: For multi hop between stations
No equal channel access probability
Un-proportional reduced for forwarding nodes
Steady collisions with neighbors
No priority to forwarding
Uncoordinated access
Guido R. Hiertz, ComNets, Aachen University (RWTH)

13. Without useful protocol for multi hop in core network, mesh will fail
July 2004
Conclusion
MAC is not sufficient for multi hop
leaves information unused for multi hop
Multi hop is key element to mesh networks
Without useful protocol for multi hop in core network, mesh will fail
Guido R. Hiertz, ComNets, Aachen University (RWTH)

14. Thank you for you attention
July 2004
Thank you for you attention
Guido R. Hiertz, ComNets, Aachen University (RWTH)