Synchronization in WLAN

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Symbol Timing • Symbol Timing is the task of finding the precise moment of when individual OFDM symbols start and end • Packet Detection provides an estimate of the packet edge • Symbol timing refines the estimate to the symbol level • Symbol timing is essential in OFDM • The symbol timing results defines the DFT window, i.e., the set of samples used to calculate DFT of each received OFDM symbol • The DFT result is then used to demodulate the subcarriers of the symbol WLAN Synchronization 16.3.2004 © Hafeth Hourani 20
Symbol Timing Algorithm • Symbol timing can be performed by calculating the crosscorrelation of the received signal r n and a known reference t k |m n | Correct symbol timing point L−1 tˆ s = arg max ∑ r t n k = 0 * n+ k k In the equation, the value of n that corresponds to maximum absolute value of the crosscorrelation is the symbol timing estimate 2 Sample index The output of the crosscorrelator that uses the first 64 samples of the long training symbols of IEEE 802.11 preamble SNR = 10 dB WLAN Synchronization 16.3.2004 © Hafeth Hourani 21
Page 1 and 2: S-72.333 Postgraduate Course in Rad
Page 3 and 4: Next . . . •Overview • Timing E
Page 5 and 6: Synchronization in Packet-Switched
Page 7 and 8: Timing Estimation Overview Timing E
Page 9 and 10: • Packet detection test H H 0 1 :
Page 11 and 12: Packet Detection Methods Timing Est
Page 13 and 14: Received Signal Energy Detection (c
Page 15 and 16: • The result of the DSW does not
Page 17 and 18: Preamble Aided Detection (cont’d)
Page 19: Packet Detection Methods Timing Est
Page 23 and 24: Sample Clock Synchronization • Th
Page 25 and 26: Estimating the Sampling Frequency E
Page 27 and 28: Next . . . • Overview • Timing
Page 29 and 30: Frequency Synchronization Approache
Page 31 and 32: Channel Estimation • Channel Esti
Page 33 and 34: Frequency Domain Channel Estimation
Page 35 and 36: Next . . . • Overview • Timing
Page 37 and 38: References • OFDM Wireless LANs:
Page 39: Homework • Q1. In that equation i

Synchronization in WLAN

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