IEEE 802.15.4 Multipath

1
Project IEEE P802.15 Working Group for Wireless
Personal Area Networks (WPANs) Submission Title
802.15.4 Multipath Date Submitted July
2004 Source Paul Gorday Company
Motorola Address 8000 W. Sunrise Blvd.,
Plantation, FL, 33322, USA Voice1 561 723
4047, E-Mailpaul.gorday_at_motorola.com Re
IEEE 802.15.4 Abstract This contribution
presents simulated performance of a simple
802.15.4 (2.4 GHz PHY) receiver in multipath
channel conditions. Purpose To encourage
discussion. Notice This document has been
prepared to assist the IEEE P802.15. It is
offered as a basis for discussion and is not
binding on the contributing individual(s) or
organization(s). The material in this document is
subject to change in form and content after
further study. The contributor(s) reserve(s) the
right to add, amend or withdraw material
contained herein. Release The contributor
acknowledges and accepts that this contribution
becomes the property of IEEE and may be made
publicly available by P802.15.
2
Motivation

• Proposed modifications to 868/915 MHz PHY
  consider additional multipath tolerance for
  long-range applications.
• Provide benchmark simulation results for the 2.4
  GHz PHY, which would also apply to the proposed
  down-banded version.

3
2.4 GHz PHY Simulation

• Floating point simulation of optimum non-coherent
  demodulator.
• Detection based on largest correlation peak
  (largest path) No RAKE or equalizer.
• Assume channel is constant throughout packet
  (quasi-static) and uncorrelated from packet to
  packet.
• Record average packet error rate (PER) vs. Eb/No.

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2.4 GHz Channel Model

• No channel model was specified by 802.15.4
• Commonly used diffuse exponential model
• 802.11 Handbook 1
• 802.15.3a Narrowband Model 2
• ETSI BRAN, HIPERLAN/2 3
• Many textbooks e.g., 4
• Detailed channel models are being developed by
  802.15.4a for a variety of environments, but are
  not finished.

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Diffuse Exponential Model

• Diffuse each delay bin
• contains multipath energy
• Exponential average power
• decays exponentially
• Fading - each delay bin has
• independent Rayleigh fading
• Single Parameter
• RMS delay spread ?
• Mean excess delay ? ?
• Max excess delay (10 dB) ? 2.5?
• Max excess delay (20 dB) ? 5?

C Normalization Constant Ts Simulation Sample
Period
Normalized Average Power
Depicted ? 4Ts
k (Bin )
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Results for 2.4 GHz PHY

• Acceptable performance
• for ? ? 400 ns
• RMS delay spread 400 ns
• Mean excess delay ? 400 ns
• Max excess delay (10 dB) ? 1 ?s
• Max excess delay (20 dB) ? 2 ?s
• Results scale with chip rate
• ? half-rate at 915 MHz would
• tolerate RMS delay spreads
• up to 800 ns

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802.11a/HIPERLAN/2 Models 3
Channel Environment RMS Delay Spread (ns)
A Typical office (NLOS) 50
B Typical large open space (NLOS) 100
C Large open space indoor (NLOS) 150
D Large open space indoor/outdoor (LOS) 140
E Large open space outdoor (NLOS) 250
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IEEE 802.11 Handbook 1
Environment RMS Delay Spread (ns)
Typical Home lt 50
Typical Office 100
Typical Manufacturing 200-300
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Factory/Office Measurements 4
Location Type Mean RMS Delay Spread (ns) Max RMS Delay Spread (ns)
A Factory 16 40
B Factory 29 60
C Factory 52 152
D Factory 73 150
E Factory 33 146
F Office 16 48
G Office 39 55
H Office 55 146

• Tx-Rx separation lt 30 m

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Conclusions

• 802.15.4 (2.4 GHz PHY) with simple non-coherent
  demodulator can tolerate RMS delay spreads up to
  400 ns ? sufficient for most WLAN applications,
  more than enough for WPAN applications.
• Down-banded, half-rate 2.4 GHz PHY would tolerate
  RMS delay spreads up to 800 ns.
• Additional delay spread tolerance may be
  achievable with some increase in demodulator
  complexity.

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References

• 1 B. OHara and A. Petrick, IEEE 802.11
  Handbook A Designers Companion, IEEE Press,
  1999.
• 2 J. Foester, Channel Modeling Sub-committee
  Report (Final), IEEE P802.15-02/490r1-SG3a, Feb.
  2003.
• 3 J. Medbo and P. Schramm, Channel Models for
  HIPERLAN/2, ETSI/BRAN doc. No. 3ERI085B, 1998.
• 4 K. Pahlavan and A. Levesque, Wireless
  Information Networks, John Wiley Sons, 1995.