(Phy-Link) Layers in the Brave New World

1
(Phy-Link) Layers in the Brave New World

• Nitin Vaidya
• University of Illinois at Urbana-Champaign
• August 2, 2005
• NSF WMPG Workshop at Rutgers
• www.crhc.uiuc.edu/wireless/

2
Wireless Networks

• Look Ma, no links !

C
D
E
B
F
A
3
Wireless Networks

• For the most part, the protocol stackshave
  pretended that wireless links areequivalent to
  wired links (with errors)

4
New Reality

• With denser deployment, per-user capacity
  degrading
• Greater incentive for deploying more complex
  mechanisms

Simplicity (purer layers)
Performance (with cross-layer optimization)
5

• However, if raw capacity improves,the balance
  may tilt the other way
• Congnitive radios, Ultra-wide band ?

Performance (with cross-layer optimization)
Simplicity (purer layers)
6
New Reality

• With denser deployment, greater incentive for
• deploying more complex mechanisms

Other stuff
Transport
Network
Most to lose
Link
Phy
7
New Reality

• With denser deployment, greater incentive for
• deploying more complex mechanisms at lower layers

• Rise of cooperativewireless networks
• Adaptations aplenty

Other stuff
Transport
Network
Most to lose
Link
Phy
8
Cooperative Wireless Networks
9
Ad Hoc, Mesh, Sensor Networks

• Hosts cooperating to routedata or information
  onmulti-hop wireless routes

C
D
E
B
F
A
10
(Without) Cooperative Diversity
Higher layer
F(PB)
C
B
PB
A
P
11
(With) Cooperative Diversity
C
B
A
12
Adaptations Aplenty

• Power/Rate Control
• Antenna beamforms
• Channel
• Retransmissions/Coding
• ??

13
Cross-Layer Adaptations

• Physical layer can perform many of these
  adaptations
• But need cross-layer interactions to maximize
  benefits

14
Impact on Protocol Layers
15
The Vanishing Link

• What is a link anyway ?
• Does a link span multiple hops ?

Higher layer
F(PB,PD)
f(PC)
C
PD
PC
B
PB
P
A
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The Vanishing Link

• What is a link anyway ?
• Diversity muddles the notion of a link

R0
D
C
R1
Rate R0 lt R1 lt R2
B
R2
A
17
The Vanishing Link

• Diversity muddles the notion of a link

Channel C0 C1 C2
C
D
C1
B
C0
C2
A
18
The Vanishing Link

• Diversity muddles the notion of a link

Beamform B0 B1 B2
C
D
B1
B
B2
B0
A
19
The Vanishing Link

• Physical layer plays an important role
• Often need network-phy interaction formaximal
  performance

Other stuff
Transport
Network
Link
Phy
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The Vanishing Boundary

• Wired autonomous systems, even if in the same
  physical space, can be treated as separable

AS 2
AS 2
AS 1
AS 1
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The Vanishing Boundary

• Wireless autonomous systems are not so autonomous
• Internal decisions in an AS can affectinternal
  performance of other ASs

AS 2
AS 1
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Issues

• Notions of link and boundary imprecise in
  wireless
• Can (Should) we maintain meaningful separation
  between lower layers ?

23
On a related note

• Will you know an ad hoc network when yousee one?

C
D
E
B
F
A
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On a related note

• Will you know an ad hoc network when yousee one?

AP
C
AP
D
E
B
F
A
AP
25
Thanks!