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(Phy-Link) Layers in the Brave New World

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Wireless Networks For the most part ... Physical layer plays an important role Often need network-phy interaction for maximal performance ... Mobile and Wireless ... – PowerPoint PPT presentation

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Title: (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 stacks have
    pretended that wireless links are equivalent 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 cooperative wireless 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 route data or information
    on multi-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
16
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 for maximal
    performance

Other stuff
Transport
Network
Link
Phy
20
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
21
The Vanishing Boundary
  • Wireless autonomous systems are not so autonomous
  • Internal decisions in an AS can affect internal
    performance of other ASs

AS 2
AS 1
22
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 you see one?

C
D
E
B
F
A
24
On a related note
  • Will you know an ad hoc network when you see one?

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