Symbol tracking for AM in-band on-channel radio receivers
View Patent ↗A method for symbol tracking in AM in-band on-channel radio receivers comprises the steps of: receiving a stream of time domain samples; assembling a set of the time domain samples equal to a symbol time plus a half symbol delay in response to a symbol timing adjustment value for each symbol period; interpolating the time domain samples; partitioning the interpolated time domain samples into a first group of samples representing half-off symbols and a second group of samples representing on-time symbols; processing the first and second groups of samples to produce the symbol timing adjustment value; and outputting the second group of samples representing on-time symbols at a symbol rate. An apparatus that performs the method is also included.
1. A method for symbol tracking in AM in-band on-channel radio receivers, the method comprising the steps of:
receiving a stream of time domain samples;
assembling a set of the time domain samples equal to a symbol time plus a half symbol delay in response to a symbol timing adjustment value for each symbol period;
interpolating the time domain samples;
partitioning the interpolated time domain samples into a first group of samples representing half-off symbols and a second group of samples representing on-time symbols;
processing the first and second groups of samples to produce the symbol timing adjustment value; and
outputting the second group of samples representing on-time symbols at a symbol rate.
2. The method of claim 1 , wherein the first and second groups of samples overlap.
3. The method of claim 1 , wherein the timing adjustment value includes a fractional interpolation control value.
4. The method of claim 1 , further comprising the step of:
applying a window/fold function to both the on-time symbol samples and the half-off symbol samples.
5. The method of claim 1 , wherein the stream of time domain samples are received on a main carrier and a pair of BPSK subcarriers and the method further comprises the step of:
demodulating symbol values for the main carrier and the BPSK subcarriers.
6. The method of claim 5 , further comprising the step of:
deriving a symbol timing error from the demodulated BPSK symbols.
7. The method of claim 6 , further comprising the step of:
resolving half-off symbol timing error ambiguity.
8. The method of claim 6 , further comprising the step of:
normalizing the symbol timing error using a symbol peak value.
9. The method of claim 1 , further comprising the step of:
adaptively controlling loop gain in the processing step.
10. The method of claim 1 , further comprising the step of:
computing a slope variable in the processing step.
11. An apparatus for symbol tracking in AM in-band on-channel radio receivers, the apparatus comprising:
an input for receiving a stream of time domain samples;
a processor for assembling a set of the time domain samples equal to a symbol time plus a half symbol delay in response to a symbol timing adjustment value for each symbol period, interpolating the time domain samples, partitioning the interpolated time domain samples into a first group of samples representing half-off symbols and a second group of samples representing on-time symbols, and processing the first and second groups of samples to produce the symbol timing adjustment value; and
an output for outputting the second group of samples representing on-time symbols at a symbol rate.
12. The apparatus of claim 11 , wherein the first and second groups of samples overlap.
13. The apparatus of claim 11 , wherein the timing adjustment value includes a fractional interpolation control value.
14. The apparatus of claim 11 , wherein the processor applies a window/fold function to both the on-time symbol samples and the half-off symbol samples.
15. The apparatus of claim 11 , wherein the stream of time domain samples are received on a main carrier and a pair of BPSK subcarriers and wherein the processor demodulates symbol values for the main carrier and the BPSK subcarriers.
16. The apparatus of claim 15 , wherein the processor derives a symbol timing error from the demodulated BPSK symbols.
17. The apparatus of claim 16 , wherein the processor resolves half-off symbol timing error ambiguity.
18. The apparatus of claim 16 , wherein the processor normalizes the symbol timing error using a symbol peak value.
19. The apparatus of claim 11 , wherein the processor adaptively controls loop gain in the processing step.
20. The apparatus of claim 11 , wherein the processor computes a slope variable in the processing step.