Upload
bethanie-summers
View
221
Download
3
Tags:
Embed Size (px)
Citation preview
1
Heterogeneity inMulti-Hop Wireless Networks
Nitin H. Vaidya
University of Illinois at Urbana-Champaign
www.crhc.uiuc.edu/~nhv
© 2003 Vaidya
2
Summary
Heterogeneity is essential Heterogeneity is beneficial
Research Agenda Develop protocols that exploit the heterogeneity Develop mechanisms to better evaluate wireless systems
Proof by example …
3
Heterogeneity
Many dimensions of heterogeneity:
Architecture
Physical capability of hosts
Higher layers
5
Pure Ad Hoc Networks
No “infrastructure” All communication over (one or more) wireless hops
EA
B CD
X
Z
Ad hoc connectivity
Y
6
Hybrid Networks
Infrastructure + Ad hoc connectivity
EA
B CD
AP1 AP2
X
Z
infrastructure
Ad hoc connectivity
Y
7
Hybrid Networks
Infrastructure may include wireless relays
EA
CD
AP1 AP2
X
Z
infrastructure
Ad hoc connectivity
Y
B
RP
8
Hybrid Networks
Heterogeneity Some hosts connected to a backbone, most are not Access points may have more processing capacity, energy
EA
B CD
AP1 AP2
X
Z
infrastructure
Ad hoc connectivity
Y
9
Hybrid Networks
Heterogeneous wireless technologies
EA
B CD
AP1 AP2
X
Z
infrastructure
Y
Type 1(3G)
Type 2(802.11)
10
Hybrid Networks
Heterogeneity is essential
Pure ad hoc or pure infrastructure networks inadequate for many environments
Heterogeneity is beneficial …
11
Benefit over Pure Ad Hoc Networks
Infrastructure provides a frame of reference Can assign approximate locations to the mobiles
– Provide location-aware services
– Reduce route discovery overhead
AP0 AP1 AP2 AP3
A
B DR2R1 R3
A
12
Benefit over Pure Ad Hoc Networks
Infrastructure can reduce diameter of the network Lower delay Potentially greater per-flow throughput
EA
CD
AP1 AP2
X
Z
infrastructure
Ad hoc connectivity
Y
B
RP
13
Infrastructure Facilitates New Trade-Offs (hypothetical curves)
User density distributionaffects the trade-offAd hoc-ness = K
co
nn
ec
tiv
ity
ov
erh
ea
d
Poor Man’s Ad Hoc Network
14
Infrastructure Helps in Resource AllocationAddress Assignment
Unique IP addresses need to be assigned to hosts in a network
DHCP used in traditional networks
Difficult to use DHCP in pure ad hoc networks
But Can also be deployed on the infrastructure in a hybrid network
15
Infrastructure Helps in Resource AllocationAddress Assignment
Impossible to detect address duplication in networks that can get partitioned
• Unbounded delays cause difficulty
Clusters of hosts may partition from the infrastructure, rejoin, over time
Need a mechanism to assign unique addresses despite partitions
• Impossible with unbounded message delays
17
Weak Duplicate Address Detection
Packets from a given host to a given address
should be routed to the same destination,
despite duplication of the address
Achievable despite unbounded delay, but incurs overhead
Infrastructure to the rescue: Use weak DAD only for nodes partitioned from the infrastructure
Can this extend to other resource allocation problems?
18
Benefit over Pure Infrastructure Networks
Ad hoc routing increases the “reach” of the infrastructure
Connectivity can be traded with overhead
Example: Limit “ad hoc-ness” to K hops
19
Hybrid Networks: Research Issues
How to implement infrastructure?
How to deploy relays/access points?
• Density, distribution
What functionality should be given to relays and access points?
• Should they cooperate? With each other? With mobiles?
Are relays an optimization or necessary components?
Should the spectrum be divided between the infrastructure and ad hoc components?
20
Hybrid Networks: Research IssuesHow to design protocols?
How to trade “complexity” with “performance” ?
• Parameterize ad hoc-ness ?
How to design protocols that maximize “performance” for a given complexity?
• Power control: How should the heterogeneity affect power control?
• MAC: Should the infrastructure do more work?
• Routing: Reduce overhead using infrastructure
• Transport: How to approach theoretical capacity bounds?
• How to deal with potentially unbounded delays?
The answers to the above questions are inter-dependent
• Power control, MAC, routing, transport protocols affect each other’s behavior
• Cross-layer design needed
21
Heterogeneity
Many dimensions of heterogeneity:
Architecture
Physical capability of hosts– Antennas
– Topology control mechanisms
– Processing capability
– Energy availability
Higher layers
22
Antenna Capabilities
“Fixed beam” antennas prevalent on mobile devices Omnidirectional antennas
“Movable beam” antennas likely to become more prevalent over time Switched, steered, adaptive, smart …
– Can form narrow beamforms, which may be changed over time
Re-configurable antennas– Beamforms can be changed over time by reconfiguring the
antenna
Different devices may incorporate different antennas
23
Antenna Heterogeneity
All antennas are not made equal
Beamforms: Only directional, or omni too?
Timescale: Can beams be “moved” at packet timescales?
Single beam or multiple beams?
Variations with time?
24
Antenna Capabilities
Protocols designed for omnidirectional (fixed beam) antennas inadequate with movable beam antennas
State of the art: MAC Protocols designed for specific antenna capabilities
Need “antenna-adaptive” MAC and routing protocols that allow for antenna heterogeneity
25
Antenna Heterogeneity
Heterogeneity is essential
Enforcing homogeneity will limit benefits from antenna improvements
Heterogeneity is beneficial
Devices can employ best antennas that they can “afford”– Device constraints: energy, processing, size, weight, $$– Access points may use more capable antenna than mobiles
Antenna-adaptive protocols allow separation of the antenna as a “layer” in the protocol stack
26
Antenna Heterogeneity: Research Challenge
How to design “antenna-adaptive” protocols ?
Need to develop suitable antenna abstractions that span a range of antenna designs
Forces us to think about essential characteristics of antennas
– Example: Variability of beam patterns a more fundamental property than directionality
28
Capacity
Capacity analysis:
• Capacity results useful to determine the gap between actual performance and the best case scenario
• Significant progress in recent years
• Need further work to model heterogeneous environments
29
Evaluation of Wireless Protocols
Benchmarks: Need benchmarks for comparison of different protocols
• State of the art: Toy benchmarks, almost no real data (for evaluating multi-hop wireless networks)
Simulations
• Commonly used simulation models are poor
• Need better physical layer models accessible to protocol community
30
Evaluation of Wireless Protocols
Experimentation:
“Full scale” experiments not always practical
Need mechanisms to build and experimentally evaluate “scaled models” of the network
– Physical dimensions
– Mobility
– Number of hosts
– Traffic density
How to “scale down” the network, and still maintain essential behaviors?
32
Conclusions
Heterogeneity essential, and beneficial
Heterogeneity Complexity ? Not necessarily Thinking about heterogeneity useful in arriving at better abstractions
Need protocols that can exploit heterogeneity
Need approaches for realistic comparative evaluation of protocols