Loopback signal, receiver and transmitter for synchronization
A loopback receiver to synchronize timing and frequency with a loopback signal relayed to the loopback receiver, the loopback receiver including: an Rx signal representing the loopback signal received at the loopback receiver; and a common Fast Fourier Transform (FFT) to estimate, during an acquisition mode and a tracking mode, an estimated timing offset and an estimated frequency offset of the Rx signal compared to the loopback signal, wherein the loopback signal includes a burst including a GOLD Pseudo Noise (PN) sequence having a good circular correlation and the GOLD PN sequence has cross-correlations within a set. Some embodiments may eliminate a bias of the estimated timing offset and the estimated frequency offset with double linearization.
1 . A loopback receiver to synchronize timing and frequency with a loopback signal relayed to the loopback receiver, the loopback receiver comprising:
an Rx signal representing the loopback signal received at the loopback receiver; and
a common Fast Fourier Transform (FFT) to estimate, during an acquisition mode and a tracking mode, an estimated timing offset and an estimated frequency offset of the Rx signal compared to the loopback signal,
wherein the loopback signal comprises a burst comprising a GOLD Pseudo Noise (PN) sequence having a good circular correlation and the GOLD PN sequence has cross-correlations within a set.
2 . The loopback receiver of claim 1 , further comprising a square time estimator, in the tracking mode of the Rx signal, to calculate the estimated timing offset.
3 . The loopback receiver of claim 1 , further comprising a generalized complex interpolator, in the acquisition mode and the tracking mode of the Rx signal, to calculate the estimated timing offset and the estimated frequency offset.
4 . The loopback receiver of claim 3 , further comprising a filter to linearize, in the acquisition mode of the Rx signal, a bias of the estimated timing offset and the estimated frequency offset.
5 . The loopback receiver of claim 3 , further comprising a recursive filter tuned by a configurable forgetting factor (Y) to follow frequency variations of the Rx signal, wherein the configurable forgetting factor is based on one more of a target SNR, a timing drift rate and a frequency drift rate.
6 . The loopback receiver of claim 3 , further comprising a first order filter having a forgetting factor (γ) of 0.1 to follow frequency and timing variations of the Rx signal.
7 . The loopback receiver of claim 3 , further comprising a double linearizer, in the tracking mode, to correct a bias of the estimated timing offset and the estimated frequency offset.
8 . The loopback receiver of claim 1 , wherein the common FFT transitions from the acquisition mode to the tracking mode after N trans acquisitions of the Rx signal.
9 . The loopback receiver of claim 1 , wherein a Signal to Noise Ratio (SNR) of the Rx signal is less than 5 dB.
10 . The loopback receiver of claim 1 , wherein a Signal to Noise Ratio (SNR) of the Rx signal is less than 0 dB.
11 . The loopback receiver of claim 1 , wherein the FFT provides an outage flag metric to indicate that the loopback receiver has detected an outage of the Rx signal and is operating in an outage state.
12 . The loopback receiver of claim 11 , wherein, the common FFT in the tracking mode, saves a filter state when not in outage and sets the filter state to the saved filter state when exiting from the outage state.
13 . A method for synchronizing timing and frequency with a loopback signal relayed to a loopback receiver, the method comprising:
receiving, at the loopback receiver, an Rx signal representing the loopback signal; and
estimating with a common Fast Fourier Transform (FFT), during an acquisition mode and a tracking mode, an estimated timing offset and an estimated frequency offset of the Rx signal compared to the loopback signal,
wherein the loopback signal comprises a burst comprising a GOLD Pseudo Noise (PN) sequence having a good circular correlation and the GOLD PN sequence has cross-correlations within a set.
14 . The method of claim 13 , further comprising generalized complex interpolating, in the acquisition mode and the tracking mode, the estimated timing offset and the estimated frequency offset of the Rx signal.
15 . The method of claim 14 , further comprising linearizing, in the acquisition mode, a bias of the estimated timing offset and the estimated frequency offset of the Rx signal.
16 . The method of claim 14 , further comprising using a recursive filter tuned by a configurable forgetting factor (γ) to follow frequency variations of the Rx signal, wherein the configurable forgetting factor is based on one more of a target SNR, a timing drift rate and a frequency drift rate.
17 . A receiver to synchronize timing and frequency with a signal relayed to the receiver, the receiver comprising:
an Rx signal representing the signal received at the receiver;
a common Fast Fourier Transform (FFT) to estimate, during an acquisition mode and a tracking mode, an estimated timing offset and an estimated frequency offset of the Rx signal compared to the signal;
a generalized complex interpolator, in the acquisition mode and the tracking mode of the Rx signal, to calculate the estimated timing offset and the estimated frequency offset; and
a double linearizer, in the tracking mode, to correct a bias of the estimated timing offset and the estimated frequency offset.
18 . The receiver of claim 17 , further comprising a square time estimator, in the tracking mode of the Rx signal; and setting a linearized timing offset equal to the estimated timing offset.
19 . The receiver of claim 17 , wherein the double linearizer comprises a look up table and a linearized frequency offset is based on using a multiplier BF determined as a value associated with the estimated timing offset in the look up table.
20 . The receiver of claim 17 , further comprising a filter to linearize, in the acquisition mode of the Rx signal, a bias of the estimated timing offset and the estimated frequency offset.