Fixed wireless node with frequency synthesizer
A high frequency data network access system includes an aggregation node and endpoint nodes that employ an approach to achieve frequency stability without the need for a separate auxiliary radio frequency (RF) signal, such as a GPS signal, which would require its own receiver and antenna. The endpoint and/or subscriber nodes derive the timing and frequency stability, and specifically disciplines a local reference oscillator and local reference time base.
1 . A method for frequency synchronization of a node in a millimeter wave fixed wireless access network, the method comprising: downconverting frequency of an input signal to an intermediate frequency (IF); amplifying the downconverted IF signal to an amplified signal using a variable gain amplifier; converting the amplified signal into a digital signal, using an analog to digital converter (ADC); correlating the digital signal with a delayed input signal to form a correlated output signal; and feeding the correlated output signal to a frequency synthesizer, for the frequency synchronization of the terminal devices in the millimeter wave fixed wireless access network.
2 . The method of claim 1 , wherein the magnitude of the output signal of the ADC or a memory is squared and fed to an automatic gain control (AGC) for setting a variable gain.
3 . The method of claim 1 , further comprising forming an immediate estimation of the frequency using an angle of the correlated output signal.
4 . The method of claim 3 , wherein the frequency estimate is windowed to select valid window samples and exclude invalid samples when buffer has not been filled up.
5 . The method of claim 4 , wherein timing for the windowed frequency estimate is set by a valid packet timing detector.
6 . The method of claim 4 , further comprising averaging the valid window samples using a low pass filter (LPF).
7 . The method of claim 6 , wherein the valid window samples are scaled such that a scaled error is driven to a pre-determined tolerance by adjusting the frequency in the frequency synthesizer using digital means, such as a fractional-N or Direct Digital Synthesizer.
8 . The method of claim 1 , wherein the node is a subscriber node.
9 . A node in a millimeter wave fixed wireless access network, comprising:
mixer for up converting intermediate frequency signals from a modem to high frequency signals for transmission to an aggregation node and for down converting high frequency signals received from an aggregation node to intermediate frequency signals for the modem;
a variable gain amplifier is configured to amplify intermediate frequency signals to an amplified signal;
an analog-to-digital converter (ADC) configured to convert the amplified signal to a digital signal;
a correlator for processing the digital signal with a delayed input signal to form a correlated output signal; and
a frequency synthesizer for generating a local oscillator signal for the mixer based on the correlated output signal.
10 . The node of claim 9 , wherein magnitude of the ADC or a memory is squared and fed to an automatic gain control (AGC) for setting a variable gain.
11 . The node of claim 9 , further comprising an estimator for forming an immediate estimation of the frequency using an angle of the correlated output signal.
12 . The node of claim 11 , wherein the frequency estimate is windowed to select valid window samples and exclude invalid samples when buffer has not been filled up.
13 . The node of claim 12 , wherein timing for the windowed frequency estimate is set by a valid packet timing detector.
14 . The method of claim 4 , further comprising a low pass filter for averaging the valid window samples.
15 . The node of claim 14 , wherein the valid window samples are scaled such that a scaled error is driven to a pre-determined tolerance by adjusting the frequency in the frequency synthesizer using digital means, such as a fractional-N or Direct Digital Synthesizer.
16 . The node of claim 9 , wherein the node is a subscriber node.