Packet Detection of OFDM and WLAN

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Packet Detection of OFDM and WLAN

• Wei-Hsuan Chang

Sept. 20, 2005
Wei-Hsuan Chang
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Outline

• Synchronization of OFDM System
• Packet Detection
• Conclutions

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Synchronization of OFDM System

• Synchronization
• Packet detection
• Timing estimation
• Frequency synchronization
• Channel estimation
• IEEE 802.11a standard preamble

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Packet Detection(1/3)

• The way to estimate the start of the preamble of
  a data packet
• A binary hypothesis test
• H0mnltTh gt Packet not present
• H1mn?Th gt Packet present
• Algorithms
• Sliding window
• Double sliding window
• Delay and correlate

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Packet Detection(2/3)

• The performance of the packet detection algorithm
• Probability of detection PD
• Probability of false alarm PFA
• PDPr( detecting a packet the packet is real)
• Higher PD will be better
• PFAPr( error detecting a presentation of a
  packet theres no packet)
• Lower will be better, but not necessary

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Packet Detection(3/3)

• PD
• PFA

q
The packet is sent
Detect a packet
p
1-q
The packet is not sent
Rx
r
The packet is sent
1-p
Detect no packet
1-r
The packet is not sent
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Sliding Window Packet Detection

• Received signal energy detection

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Double Sliding Window Packet Detection(1/3)

• Difficulty of sliding window packet detection
• How to find the threshold (TH)
• Using two windows

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Double Sliding Window Packet Detection(2/3)

• Variable mn and SNR

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Double Sliding Window Packet Detection(3/3)

• Simulation

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Delay and Correlate Algorithm(1/3)

• Using the structure of the preamble for packet
  detection
• Block diagram

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Delay and Correlate Algorithm(2/3)

• Variable mn

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Delay and Correlate Algorithm(3/3)

• Simulation

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Conclusions

• Synchronization is important for every
  communication system, and packet detection will
  be the first part of synchronization
• There are several methods for packet detection,
  but the performances of double sliding window
  algorithm and delay and correlate algorithm are
  better