1. User Cooperation for Improving Spatial Spectral Utilization in Multhop Wireless Networks
March 1, 2006
Chansu Yu
3/1/2006
NEONet 2006

2. Overview Wireless multihop networks What’s wrong?
Solutions for broadcast
Solutions for packet relaying
Solutions for spatial reuse
Conclusions & future work
3/1/2006
NEONet 2006

3. Multihop Ad Hoc Networks
Introduction
Multihop Ad Hoc Networks
3/1/2006
NEONet 2006

4. HQ Mobile nodes, Wireless links Infrastructure-less Multi-hop routing
Minimal administration HQ
3/1/2006
NEONet 2006

5. Introduction New serious applications Reconsiderations
Wireless sensor networks
Wireless mesh networks
Reconsiderations
PHY/MAC
Ad hoc routing algorithms
Akyildiz, I.F., Wang, X. and Wang, W., “Wireless Mesh Networks: A Survey,” Computer Networks Journal (Elsevier), March 2005.
3/1/2006
NEONet 2006

6. What’s Wrong? 802.11 PHY/MAC is optimized for single-hop communication
“Relay” not considered  the most frequent operation in multihop scenarios
CS, RTS/CTS and NAV is to provide an exclusive access to the medium because every communication involves the AP  Spatial reusability is important
Broadcasting is meant to be one-hop  Broadcast storm problem in multihop scenarios
Shortest-path routing algorithms are not practical  Expected transmission time (ETT), …
3/1/2006
NEONet 2006

7. Solutions for Broadcast
Gossip (INFOCOM ‘02)
Manycast (MobiHoc ’03)
Epidemic routing (Computer, May ‘04)
RandomCast (ICDCS ’05)
Unconditional broadcast S D A B C
RandomCast
Who to relay?
3/1/2006
NEONet 2006

8. Solutions for Packet Relaying
Packet salvaging at network layer
“Packet salvaging” in DSR
“Local repair” in AODV
Packet salvaging at MAC layer
Extremely Opportunistic Routing (HotNet-II’03)
Implicit Geographic Forwarding (TR, UVA, ‘03)
Geographic Random Forwarding (TMC, April’03)
Multiple Access with Salvation Army (MobiHoc’05)
3/1/2006
NEONet 2006

9. MASA Algorithm No collision Collision at receiver s Salvation army i j
(1) DATA
(1) DATA
(1) DATA
(3) SDATA
(2) ACK
(2) SACK
(4) ACK
Salvation army
3/1/2006
NEONet 2006

10. MASA: Selection of Relay Node
Based on “relaying backoff”
A candidate gives up its relaying activity when the packet is relayed by another candidate
Otherwise, it becomes the relay node and sends SACK
Sender (i)
Receiver (j)
Relay (s)
DATA D
ACKTimeout
DIFS
SIFS D
ACK
tr. time
ACK
(not delivered) t
SACK
Relaying
backoff ( t S )
Relaying
interval (T SI )
Who to relay?
3/1/2006
NEONet 2006

11. Simulation Environment
System parameters
Simulation time: 900s
100 nodes in 3001500 m2
Mobility parameters
Random waypoint mobility model
Maximum speed: 5m/s
Simulator
ns with modification for cumulative interference and signal capture
Traffic parameters
40 CBR connections
Packet rate: 3 packets/s Packet size: 256 bytes
40 — 100 TCP connections
Other parameters
AODV routing
Two-ray ground propagation model
250m TR range; 350m and 550m CS
range for MASA and DCF, respectively
3/1/2006
NEONet 2006

12. Simulation with A Single Interferer
Simulation scenario
Simulation parameters
Simulation time: 180s
Transmission range: 250m
Propagation model: two-ray ground propagation channel
Packets: 512 bytes CBR or TCP packets
Data rate: 2Mbps
(a) Direct scenario
Major interest
Interfering communication
(b) Relaying scenario
Relay node
3/1/2006
NEONet 2006

13. Simulation Results with CBR Traffic
(a) Direct scenario
(b) Relaying scenario
Instantaneous throughput (kbps)
Instantaneous throughput ( kbps)
Packet relaying is helpful to alleviate the unfairness problem and to improve the performance.
Unfairness for i-j communication
Fair and Higher aggregate throughput
3/1/2006
NEONet 2006

14. Simulation with Multiple Interferers
DCF2
DCF with two-way handshake (without RTS/CTS)
DCF4
DCF with four-way handshake (with RTS/CTS)
MASA
With two-way handshake (without RTS/CTS)
3/1/2006
NEONet 2006

15. Solutions for Spatial Reuse
Proactively look for an opportunity to transmit my packet when I’m not relaying
Let us consider the radio propagation model
3/1/2006
NEONet 2006

16. Radio Propagation Model
Two-ray ground propagation model
Reception Model
CPj
CSj i j
TRj
(z0: capture ratio) i j
3/1/2006
NEONet 2006

17. Radio Propagation Model
Two-ray ground propagation model
Reception Model
CPj
CSj i j
TRj
(z0: capture ratio) i j
Nodes in this area
do not cause collisions
3/1/2006
NEONet 2006

18. DCF of IEEE 802.11 Carrier sense mechanism Hidden terminal problem
Vulnerable Space (VS)
Nodes within VS can not sense ongoing communication but can cause collision to receiver.
Exposed terminal problem
Wasted Space (WS)
Nodes within WS can sense ongoing communication but will not cause collision to receiver.
3/1/2006
NEONet 2006

19. DCF of IEEE 802.11 Carrier sense mechanism Hidden terminal problem
Vulnerable Space (VS)
Nodes within VS can not sense ongoing communication but can cause collision to receiver.
Exposed terminal problem
Wasted Space (WS)
Nodes within WS can sense ongoing communication but will not cause collision to receiver.
3/1/2006
NEONet 2006

20. An Example of VS and WS 915 MHz WaveLAN radio hardware
Transmission range
250m
Carrier sense range
550m
Communication distance
200m
Capture zone
356m (when z0=10dB)
VS ≈ 
WS = large
3/1/2006
NEONet 2006

21. Solutions for Spatial Reuse
Carrier sense mechanism in this case not only reduces interference but also solves the hidden terminal problem (VS becomes very small).
But it introduces another serious problem, the exposed terminal problem (large WS), which greatly reduces the spatial reusability.
CS, RTS/CTS, EIFS in fail to efficiently reuse the spatial spectral resource.
3/1/2006
NEONet 2006

22. Solutions for Spatial Reuse
Adaptive Selection of Carrier Sense Thresholds (TR, UIUC, ‘04): product of transmit power and CS threshold should be kept to be a fixed constant
Adaptive Physical Carrier Sensing (ICC’04)
Optimal Physical Carrier Sensing (INFOCOM ’05)
Physical Carrier Sensing and Spatial Reuse (INFOCOM ‘06)
Aggressive Virtual Carrier Sensing (Globecom’03)
Enhanced Carrier Sensing (IFIP Networking, ’04): Adaptive EIFS scheme
Is it safe to transmit
if not relaying?
3/1/2006
NEONet 2006

23. Future Work Who to Relay & When to Tx?
R. Ramanathan, “A Radically New Architecture for Next Generation Mobile Ad
Hoc Networks,” ACM Mobicom, 2005.
3/1/2006
NEONet 2006

24. Another Dimension: Cooperative Communication?
Destination
When a packet is not received
at the Destination (or received
with error), a relay node that
successfully overheard the
packet may relay this to the
destination.
Source
Relay
3/1/2006
NEONet 2006
Klaus Fosmark, University of
Texas at Dallas, 3/11/05

25. A. Nosratinia, T. Hunter, A. Hedayat, Cooperative communication in
wireless networks, IEEE Comm.,
2004
3/1/2006
NEONet 2006

26. Approaches
Move “Routing” and “Forwarding” functions to the physical layer
Extract certain information (destination, signal strength,..) from the front of the packet
Define new PHY format
Neighborhood information is critical
3/1/2006
NEONet 2006

27. THANK YOU !
3/1/2006
NEONet 2006