DIRC: Increasing Indoor Wireless Capacity Using Directional Antennas

1
DIRC Increasing Indoor Wireless CapacityUsing
Directional Antennas

• Xi Liu1, Anmol Sheth2, Konstantina Papagiannaki3,
  Michael Kaminsky3, Srinivasan Seshan1, Peter
  Steenkiste1

1Carnegie Mellon University 2Intel Labs
Seattle 3Intel Labs Pittsburgh
2
Driving Demand for Wireless Capacity

• Wide adoption of wireless technologies causes
  dense deployment of wireless devices
• Examples include conference rooms, enterprise
  networks, and home

future home will have 1000 radios
3
Driving Demand for Wireless Capacity

• Interference at this scale becomes a big issue
• 3 orthogonal domains to avoid interference

4
What Are Directional Antennas?

• Less power to undesired directions
• More power to desired directions
• Primarily used to form long distance
  point-to-point links
• Can also provide spatial reuse

Directional antennas
5
Phased Array Antennas

• Multiple antenna radio system provides ability to
  electronically steer signal
• Fast reconfiguration 100µs steering delay
• Assumption only APs use them
• Still too bulky for clients
• Incremental deployment

6
Limitations of Directional Antennas in Indoors
Environment
Outdoor Use LOS direction
Indoor LOS Blocked
Indoor unintended interf.
intended rx

• Indoor space is rich-scattered
• LOS may be blocked
• May cause unintended interference
• Conventional wisdom directional antennas are not
  effective in indoors environment

unintended rx
7
Spatial Reuse Through Antenna Coordination
Max SNR No Spatial Reuse
Use Alternative Path Spatial Reuse

• Straightforward way to orient antennas maximize
  signal strength at receiver (Max SNR)

8
Challenge I How to Find Antenna Orientations?

• Naive solution Max Cap
• Too slow in practice, e.g., 8 minutes for this
  setup
• Challenge I finding optimal antenna
  orientations quickly
• Goal is to find a solution cost the same as Max
  SNR, i.e., each AP scans once
• Use SINR model

9
Challenge II Coordination

• Among dirc. senders to identify non-interfering
  transmissions and choose orientations
• Centralized controller
• TDMA scheduling MAC
• Among dirc. and omni. senders
• Two phased TDMA to separate dirc. and omni.
  senders

10
Is It Worth the Effort?
Campus 80m10m
Lab 50m50m

• Two indoor testbeds office and lab
• 3 directional APs, 6 omni-directional clients
• Phocus phased array directional antenna 45º
  beamwidth, 16 dirc. patterns, 1 omni pattern,
  100µs steering delay

11
Upper-bound Performance

• Directional antennas can provide 70-80
  improvement over omni-directional antennas
• Max SNR does not maximize network capacity

12
System Overview

• Directional APs
• Omni-directional users
• Centralized controller

13
DIRC Operation
environment changes
timer expires
14
SINR Model

• SINR Model whether a frame can be successfully
  received depends on whether the SINR is larger
  than a threshold
• S(i,j,k) denote signal strength from AP i to
  client j with direction k
• For example, to determine whether transmissions
  (i1,j1,k1) and (i2,j2,k2) can happen
  simultaneously

15
DIRC Operation I - Measurement
S(S1,R1,?)
S(S1,R1, ?)
S(S1,R1, ?)
S(S1,R1, ?)
S(S1,R1, ?)
S(S1,R1, ?)
S(S1,R1, ?)
S(S1,R1, ?)
S(S1,R2,?)
S(S1,R2, ?)
S(S1,R2, ?)
S(S1,R2, ?)
S(S1,R2, ?)
S(S1,R2, ?)
S(S1,R2, ?)
S(S1,R2, ?)

• The scheduler instructs each AP to scan once,
  e.g., 240ms overhead for 3 APs.

16
DIRC Operation I - Measurement
S(S1,R1,?)
S(S1,R1, ?)
S(S2,R1,?)
S(S2,R1, ?)
S(S1,R1, ?)
S(S1,R1, ?)
S(S2,R1, ?)
S(S2,R1, ?)
S(S1,R1, ?)
S(S1,R1, ?)
S(S2,R1, ?)
S(S2,R1, ?)
S(S1,R1, ?)
S(S1,R1, ?)
S(S2,R1, ?)
S(S2,R1, ?)
S(S1,R2,?)
S(S1,R2, ?)
S(S2,R2,?)
S(S2,R2, ?)
S(S1,R2, ?)
S(S1,R2, ?)
S(S2,R2, ?)
S(S2,R2, ?)
S(S1,R2, ?)
S(S1,R2, ?)
S(S2,R2, ?)
S(S2,R2, ?)
S(S1,R2, ?)
S(S1,R2, ?)
S(S2,R2, ?)
S(S2,R2, ?)

• The scheduler instructs each AP to scan once,
  e.g., 240ms overhead for 3 APs.

17
DIRC Operation II Compute Schedules
S1,R1,? S1,R1,?
S(S1,R1,?)
S(S1,R1, ?)
S(S2,R1,?)
S(S2,R1, ?)
S(S1,R1, ?)
S(S1,R1, ?)
S(S2,R1, ?)
S(S2,R1, ?)
S(S1,R1, ?)
S(S1,R1, ?)
S2,R2, ?
S2,R2, ?
S(S2,R1, ?)
S(S2,R1, ?)
NO
?
S(S1,R1, ?)
S(S1,R1, ?)
S(S2,R1, ?)
S(S2,R1, ?)
S(S1,R2,?)
S(S1,R2, ?)
S(S2,R2,?)
S(S2,R2, ?)
S(S1,R2, ?)
S(S1,R2, ?)
S(S2,R2, ?)
S(S2,R2, ?)
S(S1,R2, ?)
S(S1,R2, ?)
S(S2,R2, ?)
S(S2,R2, ?)
S(S1,R2, ?)
S(S1,R2, ?)
S(S2,R2, ?)
S(S2,R2, ?)
X

• SINR1 S(S1,R1,?) / S(S2,R1,?)
• SINR2 S(S2,R2,?) / S(S1,R2,?)

S(S1,R1,?)
S(S2,R1,?)
lt SINRthresh
X
S(S2,R2,?)
S(S1,R2,?)
lt SINRthresh
18
DIRC Operation II Compute Schedules
S1,R1,? S1,R1,?
S(S1,R1,?)
S(S1,R1, ?)
S(S2,R1,?)
S(S2,R1, ?)
S(S1,R1, ?)
S(S1,R1, ?)
S(S2,R1, ?)
S(S2,R1, ?)
S(S1,R1, ?)
S(S1,R1, ?)
S2,R2, ?
S2,R2, ?
S2,R2, ?
S2,R2, ?
S(S2,R1, ?)
S(S2,R1, ?)
NO
NO
NO
?
S(S1,R1, ?)
S(S1,R1, ?)
S(S2,R1, ?)
S(S2,R1, ?)
S(S1,R2,?)
S(S1,R2, ?)
S(S2,R2,?)
S(S2,R2, ?)
S(S1,R2, ?)
S(S1,R2, ?)
S(S2,R2, ?)
S(S2,R2, ?)
S(S1,R2, ?)
S(S1,R2, ?)
S(S2,R2, ?)
S(S2,R2, ?)
S(S1,R2, ?)
S(S1,R2, ?)
S(S2,R2, ?)
S(S2,R2, ?)
X
SINR1 S(S1,R1,?) / S(S2,R1,?) SINR2
S(S2,R2,?) / S(S1,R2,?)
S(S1,R1,?)
S(S2,R1,?)
lt SINRthresh
S(S2,R2,?)
S(S1,R2,?)
gt SINRthresh
19
DIRC Operation II Compute Schedules
S1,R1,? S1,R1,?
S(S1,R1,?)
S(S1,R1, ?)
S(S2,R1,?)
S(S2,R1, ?)
S(S1,R1, ?)
S(S1,R1, ?)
S(S2,R1, ?)
S(S2,R1, ?)
S(S1,R1, ?)
S(S1,R1, ?)
S2,R2, ?
S2,R2, ?
S2,R2, ?
S2,R2, ?
S2,R2, ?
S2,R2, ?
S(S2,R1, ?)
S(S2,R1, ?)
NO
NO
NO
NO
NO
?
S(S1,R1, ?)
S(S1,R1, ?)
S(S2,R1, ?)
S(S2,R1, ?)
S(S1,R2,?)
S(S1,R2, ?)
S(S2,R2,?)
S(S2,R2, ?)
S(S1,R2, ?)
S(S1,R2, ?)
S(S2,R2, ?)
S(S2,R2, ?)
NO
S(S1,R2, ?)
S(S1,R2, ?)
S(S2,R2, ?)
S(S2,R2, ?)
S(S1,R2, ?)
S(S1,R2, ?)
S(S2,R2, ?)
S(S2,R2, ?)
SINR1 S(S1,R1,?) / S(S2,R1,?) SINR2
S(S2,R2,?) / S(S1,R2,?)
S(S1,R1,?)
S(S2,R1,?)
gt SINRthresh
X
S(S2,R2,?)
S(S1,R2,?)
lt SINRthresh
20
DIRC Operation II Compute Schedules
S1,R1,? S1,R1,?
S(S1,R1,?)
S(S1,R1, ?)
S(S2,R1,?)
S(S2,R1, ?)
S(S1,R1, ?)
S(S1,R1, ?)
S(S2,R1, ?)
S(S2,R1, ?)
S(S1,R1, ?)
S(S1,R1, ?)
S(S2,R1, ?)
S(S2,R1, ?)
S2,R2, ?
S2,R2, ?
NO
NO
NO
NO
NO
NO
NO
NO
NO
NO
NO
NO
?
S(S1,R1, ?)
S(S1,R1, ?)
S(S2,R1, ?)
S(S2,R1, ?)
S(S1,R2,?)
S(S1,R2, ?)
S(S2,R2,?)
S(S2,R2, ?)
S(S1,R2, ?)
S(S1,R2, ?)
S(S2,R2, ?)
S(S2,R2, ?)
NO
YES
NO
NO
S(S1,R2, ?)
S(S1,R2, ?)
S(S2,R2, ?)
S(S2,R2, ?)
S(S1,R2, ?)
S(S1,R2, ?)
S(S2,R2, ?)
S(S2,R2, ?)
SINR1 S(S1,R1,?) / S(S2,R1,?) SINR2
S(S2,R2,?) / S(S1,R2,?)
S(S1,R1,?)
S(S2,R1,?)
gt SINRthresh
S(S2,R2,?)
S(S1,R2,?)
gt SINRthresh
21
DIRC Operation III - Transmit

• dirc-tx and omni-tx phases for data transfer
• APs inform controller that they have frames to
  send
• Scheduler compute schedules

22
DIRC Performance
1.6X
2X
UDP Performance

• Office scenario, iperf UDP (including protocol
  overhead)
• DIRC significantly improves network capacity in
  this office environment

23
Node Movement

• Question Can DIRC handle node movement?

24
Conclusion

• Coordination is required to use directional
  antennas effectively in indoors environment
• DIRC is a practical and light-weight solution
  that address the challenges
• DIRC is flexible enough to handle the inherent
  dynamics of the environment