Interference Avoidance and Control

1
Interference Avoidance and Control
Ramki Gummadi (MIT)? Joint work with Rabin Patra
(UCB)? Hari Balakrishnan (MIT)? Eric Brewer (UCB)?
2
Interference-limited networks

• Interference Fundamental consequence of resource
  sharing
• Wireless LANs
• 3G, WiMax
• Mesh networks
• Increasingly interference-limited, not
  noise-limited

3
Interference Friend or foe?

• Challenges Interference is time-varying
• Bursty data traffic, not predictable voice
  traffic
• Radio propagation hard to model or predict
• Opportunity Unlike noise, interference isnt
  random
• If strong enough, understand and cancel it
• Avoid or control internal interference
• So, treating interference as noise is inefficient

4
Goal Improve aggregate throughput

• Concurrent transmissions improve throughput
• More total received power
• But they also increase interference
• Eliminate interference, maintaining concurrency?

5
VWID Variable WIDth channels

• Interferers in orthogonal channels
• Variable widths for heterogeneous SINRs and
  bursty demands

6
Key questions (and talk outline)?

• How does VWID compare analytically to
• TDMA?
• CSMA?
• How much improvement in practice?

7
Capacity of variable-width channels

• Multiple transmitters, one receiver
• Radios have a power limit
• Single antenna at a node
• Channel doesnt vary in frequency or time
• Restriction removed in implementation
• Additive White Gaussian Noise (AWGN)?

8
(No Transcript)
9
(No Transcript)
10
(No Transcript)
11
(No Transcript)
12
(No Transcript)
13
Key questions (and talk outline)?

• How does VWID compare analytically to
• TDMA?
• CSMA?
• How much improvement in practice?

14
VWID design

• Channel assignment algorithm
• 5,10 or 20 MHz variable-width sub-channels
• Maximize measured aggregate throughput
• Fairness Dont degrade link throughput
• Exhaustive search for sub-channels
• Accounts for frequency-selective fading
• Worst-case exponential in interferers

15
(No Transcript)
16
Point-point throughput improvement
Median link throughput improves by 50
VWID Point-Point
VWID Point-Point
No VWID, Point-Point
17
Point-Multipoint throughput improvement
VWID Point-Point
No VWID, Point-Point
Worst link throughput improves by 2x
18
Related Work

• Interference cancellation
• Decode colliding transmissions jointly
• Signals typically differ by large SINR or coding
  rates
• ZigZag decoding
• No coordination, but no net concurrency increase

1st timeslot
2nd timeslot
19
Conclusions

• Increase concurrency, total received power
• Throughput improvements 50-100 over TDMA and
  CSMA
• Weakness Inter-AP coordination (tomorrow)?
• Future work Practical implementation