Methods and devices for communications in device-to-device networks
A wireless device includes a radio transceiver, and a digital transmitter configured to transmit, via the radio transceiver, a first data symbol, and to transmit, via the radio transceiver, a repetition of the first data symbol immediately after the first data symbol, where the first data symbol forms a cyclic prefix for the repetition of the first data symbol.
1. A wireless device comprising:
a digital receiver configured to estimate a frequency offset between a local frequency and a reference frequency of a received synchronization signal;
a frequency controller configured to determine, based on the frequency offset, a correction to the local frequency that compensates temperature-based frequency drift in the local frequency; and
a frequency tuner configured to adjust the local frequency based on the correction to obtain a corrected local frequency;
wherein the frequency controller is configured to determine the correction based on a control loop including a delay element that delays an output of the control loop to obtain a delayed output, a first proportional factor before the delay element that weights the frequency offset, and a second proportional factor after the delay element that weights the delayed output.
2. The wireless device of claim 1 , wherein the digital receiver is configured to estimate the frequency offset between the local frequency and the reference frequency of the received synchronization signal by:
generating a local reference signal based on the local frequency;
determining a cross-correlation between the local reference signal and the received synchronization signal;
determining a phase offset between the local reference signal and the received synchronization signal based on the cross-correlation; and
estimating the frequency offset based on the phase offset.
3. The wireless device of claim 1 , wherein the correction is a frequency correction instruction and the frequency controller is configured to send the frequency correction instruction to the frequency tuner, and wherein the frequency tuner is configured to adjust the local frequency based on the correction to obtain a corrected local frequency by sampling a native clock signal of the wireless device based on the frequency correction instruction to obtain the corrected local frequency.
4. The wireless device of claim 1 , wherein the first proportional factor and the second proportional factor produce a combined factor that tunes a gain of the control loop to 1.
5. The wireless device of claim 1 , wherein the digital receiver is a baseband physical layer receiver.
6. The wireless device of claim 1 , wherein the frequency controller is configured to determine the correction by applying a second-order low-pass control loop to the frequent offset to obtain the correction.
7. The wireless device of claim 1 , wherein the frequency controller is configured to determine the correction based on a control loop including a delay element that delays an output of the control loop to obtain a delayed output, a first proportional factor before the delay element that weights the frequency offset, and a second proportional factor after the delay element that weights the delayed output.
8. The wireless device of claim 1 , wherein the first proportional factor and the second proportional factor produce a combined factor that tunes a gain of the control loop to 1.
9. The wireless device of claim 1 , wherein an output of the control loop based on a sum of the weighted delayed output and the weighed frequency offset.
10. The wireless device of claim 1 , wherein the frequency controller is configured to repeatedly determined updated corrections over time based on varying frequency offsets and the frequency tuner is configured to repeatedly adjust the local frequency over time based on the updated corrections, wherein the updated corrections compensate for temperature-based frequency drift in the local frequency.
11. The wireless device of claim 1 , wherein the updated corrections average out a measurement noise over time that is present in the estimating of the frequency offset.
12. The wireless device of claim 1 , wherein the frequency controller is configured to repeatedly determine the updated corrections based on a control loop that weights a current sample of the frequency offset to obtain a weighted sample and adds the weighted sample to a past sample of the correction.