CSI-SF: Estimating Wireless Channel State

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CSI-SF Estimating Wireless Channel State Using
CSI Sampling Fusion
Riccardo Crepaldi, Jeongkeun Lee, Raul Etkin,
Sung-Ju Lee, Robin Kravets University of
Illinois at Urbana-Champaign Hewlett-Packard
Laboratories
Improving Performance in High Speed Wireless
Channel Quality Metrics

• How do systems describe the channel quality?
• Pros
• Finer granularity compared to SNR
• Fading and phase shift information for each
  subcarrier
• Tighter bound with channel performance
  Halperin10
• Cons

• PHY Layer enhancements
• MIMO technology
• OFDM
• Channel Bonding
• Adaptive protocols for
• Rate adaptation
• Channel selection
• Optimal antenna scheme selection
• Best AP selection
• Choices based on
• Channel quality

N Input streams
M spatial streams
Signal-to-Noise Ratio (SNR) One scalar value per
packet Accurate only for narrow-band channel
Channel State Information (CSI) M x N x W
complex matrix W Number of OFDM
subcarriers Current 802.11n devices M3, N3
W56 (20MHz) or W114 (40MHz)
Why CSI?
CSI Matrix Combining

• CSI-SF enables estimation of uninvestigated
  channel configurations

• A real networking problem Rate Adaptation
• Metrics SNR, effective SNR, estimated effective
  SNR
• Whats a good metric?
• Small or no gaps
• Monotonic behavior

CSI

• Ex Estimate of a 2x3 configuration using two 1x3
  received packets

2x3 20MHz
Large gaps
Non-monotonic beavior
2x3 40MHz
3x3 20MHz
eSNR (effective SNR based on real samples)
e2SNR (effective SNR based on CSI-SF estimates)

• SNR is not a good metric, eSNR and e2SNR are
  better
• Compared to standard eSNR, e2SNR uses estimates
  instead of real samples thus limiting the overhead

• Example of CSI-SF combining two 1x3 packets in a
  2x3 packets

Packet 1 1x3 Ant B
CSI-SF Reduces Overhead

• Hypoyetical channel variation
• Overhead required to rate control to converge
  using different metrics

Packet 3 2x3 Ant AB
Real CSI
Estimated CSI
Hewlett Packard LaboratoriesUniversity of
Illinois _at_ Urbana-Champaign, Department of
Computer Science Mobicom 2011