A comparison of distributed STDMA and CSMA
for mobile ad hoc networks
Jimmi Grönkvist, Ulf Sterner,
Per Zeijlon, Anders Hansson
Anders Hansson
[email protected]
1
STDMA is good for QoS
guarantees!
- But is this true for distributed
STDMA in mobile scenarios?
Anders Hansson
[email protected]
2
1
STDMA
Spatial reuse Time Division Multiple Access
Conflict-free time-slotted
scheduling
1
2
Interference-based
4
3
5
6
Anders Hansson
[email protected]
3
STDMA – Node assignment
5
8
4
6
3
2
7
1
1
3
5
6
2
4
7
8
Time slot
Anders Hansson
[email protected]
4
2
STDMA – Link assignment
5
8
3
4
2
6
7
1
1,4 8,2 3,2 2,3 1,6 6,1 6,5 5,6
6,5 5,6 4,8 8,4 4,5 5,4 8,4 4,8
2,8 4,1 1,6 6,1 3,7 7,3 2,7 7,2
Time slot
Anders Hansson
[email protected]
5
Distributed STDMA setup
Maximal amount of overhead traffic: 25 %
Frame length: 100 time-slots
Interference margin for used links
Anders Hansson
[email protected]
6
3
CSMA
Carrier Sense Multiple Access
802.11 standard
Dynamic allocation
Carrier sensing
RTS/CTS for data packets down to 256 Bytes
Anders Hansson
[email protected]
7
Data traffic sessions with delay
requirements
Voice:
256 bit packets
Max 5% of the packets delayed 150 ms
File transfers
12 kb packets
No packets delayed 2000 ms
Mixed traffic
Anders Hansson
[email protected]
8
4
Network Model
Links
Calculated from terrain variations
1 Mbps
Mobility
Random directions within 4x4 km
2 m/s or 10 m/s
Generated networks
32 nodes
Optimal routing, on average 2 hops/route
Anders Hansson
[email protected]
9
Simulation results: low mobility (2 m/s)
Average
success
rate (%)
Average number of running sessions
Anders Hansson
[email protected]
10
5
Conclusions from simulations
STDMA
☺ Good performance compared to CSMA for low
mobility (up to 10 m/s).
CSMA
☺ Unaffected by mobility
Voice traffic (small packets)
Anders Hansson
[email protected]
11
6