22-09-2014, 12:20 PM
Robust Frequency and Timing
Synchronization for OFDM
[attachment=68288]
Abstract
— A rapid synchronization method is presented for
an orthogonal frequency-division multiplexing (OFDM) system
using either a continuous transmission or a burst operation over
a frequency-selective channel. The presence of a signal can be
detected upon the receipt of just one training sequence of two
symbols. The start of the frame and the beginning of the symbol
can be found, and carrier frequency offsets of many subchannels
spacings can be corrected. The algorithms operate near the
Cramer–Rao lower bound for the variance of the frequency ´
offset estimate, and the inherent averaging over many subcarriers
allows acquisition at very low signal-to-noise ratios (SNR’s).
INTRODUCTION
N AN orthogonal frequency-division multiplexing (OFDM)
system, synchronization at the receiver is one important
step that must be performed. This paper describes a method
to acquire synchronization for either a continuous stream of
data as in a broadcast application or for bursty data as in
a wireless local area network (WLAN). In both cases the
receiver must continuously scan for incoming data, and rapid
acquisition is needed. The ratio of the number of overhead bits
for synchronization to the number of message bits must be kept
to a minimum, and low-complexity algorithms are needed.
Performance of Symbol Timing Estimator
There are two issues to consider when evaluating the
performance of the symbol timing estimator. First, since the
timing metric is also used to determine whether the training
sequence has been received, there is a probability of either
missing a training sequence and not detecting the signal or
falsely detecting a training sequence when none is there. In
this paper the distribution of the timing metric at the correct
start of the frame is calculated. Using this distribution, the
number of samples that need to be processed during the
detection phase can be determined and a threshold can be
CONCLUSION
A method has been presented for the rapid and robust
synchronization of OFDM signals, and acquisition is obtained
upon the receipt of just one training sequence. By averaging
over all the subchannels, it works well in frequency selective
channels. This method also gives very accurate estimates of
symbol timing and carrier frequency offset and provides a
very wide acquisition range for the carrier frequency offset.
It also provides an estimate of the SNR, and the probability of
false locks or missing the training symbols is very low. For a
wireless LAN, such a fast and low-overhead synchronization
process is necessary because there will be only one training
sequence transmitted in each burst for synchronization
Synchronization for OFDM
[attachment=68288]
Abstract
— A rapid synchronization method is presented for
an orthogonal frequency-division multiplexing (OFDM) system
using either a continuous transmission or a burst operation over
a frequency-selective channel. The presence of a signal can be
detected upon the receipt of just one training sequence of two
symbols. The start of the frame and the beginning of the symbol
can be found, and carrier frequency offsets of many subchannels
spacings can be corrected. The algorithms operate near the
Cramer–Rao lower bound for the variance of the frequency ´
offset estimate, and the inherent averaging over many subcarriers
allows acquisition at very low signal-to-noise ratios (SNR’s).
INTRODUCTION
N AN orthogonal frequency-division multiplexing (OFDM)
system, synchronization at the receiver is one important
step that must be performed. This paper describes a method
to acquire synchronization for either a continuous stream of
data as in a broadcast application or for bursty data as in
a wireless local area network (WLAN). In both cases the
receiver must continuously scan for incoming data, and rapid
acquisition is needed. The ratio of the number of overhead bits
for synchronization to the number of message bits must be kept
to a minimum, and low-complexity algorithms are needed.
Performance of Symbol Timing Estimator
There are two issues to consider when evaluating the
performance of the symbol timing estimator. First, since the
timing metric is also used to determine whether the training
sequence has been received, there is a probability of either
missing a training sequence and not detecting the signal or
falsely detecting a training sequence when none is there. In
this paper the distribution of the timing metric at the correct
start of the frame is calculated. Using this distribution, the
number of samples that need to be processed during the
detection phase can be determined and a threshold can be
CONCLUSION
A method has been presented for the rapid and robust
synchronization of OFDM signals, and acquisition is obtained
upon the receipt of just one training sequence. By averaging
over all the subchannels, it works well in frequency selective
channels. This method also gives very accurate estimates of
symbol timing and carrier frequency offset and provides a
very wide acquisition range for the carrier frequency offset.
It also provides an estimate of the SNR, and the probability of
false locks or missing the training symbols is very low. For a
wireless LAN, such a fast and low-overhead synchronization
process is necessary because there will be only one training
sequence transmitted in each burst for synchronization