Method and apparatus for timing and/or frequency synchronization in an RF receiver
The present invention provides methods and systems for allowing a receiver in a (wireless) communication system to synchronize its timing and frequency subsystems in accordance with a received signal. In accordance with one aspect, a method is provided in which a relative time of arrival of sync values provided in a received signal are determined and used to align the receiver's reference signal(s) accordingly. Other aspects of the invention will become apparent from the detailed description of exemplary embodiments that follows.
1. A method for timing acquisition in a receiver, the method comprising:
receiving data modulated according to a first modulation scheme;
receiving a first and a second synch value modulated according to a second modulation scheme;
wherein the first synch value is included in a first frame and the second synch value is included in a second frame that is different than the first frame;
generating, based on a reference signal, a receive RF local oscillator signal that is used to down-convert a received RF signal;
based on the down-converted RF signal, determining a relative time of arrival between the first and second synch values, and
tuning the reference signal based on a relative time of arrival between the first and the second synch values;
wherein tuning the reference signal comprises synchronizing a timing of the reference signal to a timing associated with the received RF signal;
wherein the reference signal is used to process the data modulated according to the first modulation scheme.
2. The method of claim 1 , wherein the first and second synch values represent synch words transmitted at a predetermined interval.
3. The method of claim 2 , wherein the second modulation scheme is at least one of DBPSK, BPSK, FSK encoding.
4. The method of claim 3 , wherein the first modulation scheme involves QAM encoding.
5. The method of claim 1 , wherein the second modulation scheme for the first and second synch words is selected to be frequency-insensitive.
6. The method of claim 1 , wherein tuning the reference signal comprises tuning a frequency of a local oscillator of a receiver.
7. The method of claim 1 , wherein tuning the reference signal comprises tuning a reference clock signal for acquiring the data.
8. The method of claim 3 , further comprising differentially decoding the first and second synch values.
9. The method of claim 8 , further comprising detecting the first and second synch values using a differential decoder taking into account relative phases changes on a synch value-to-synch-value basis.
10. The method of claim 1 , wherein synchronizing a timing of the reference signal to a timing associated with the received RF signal comprises synchronizing a frequency of the reference signal with a frequency associated with the received RF signal.
11. The method of claim 1 , wherein synchronizing a timing of the reference signal to a timing associated with the received RF signal comprises synchronizing a phase of the reference signal with a phase associated with the received RF signal.
12. A receiver comprising:
a reference timing signal generator to generate an internal timing signal:
a sync detector to detect relative times of arrival of a set of received sync values, the received sync values contained in signals received by the receiver;
a reference sync generator, coupled to the reference timing signal generator, to generate an internal sync value based on the internal timing signal;
a comparator, coupled to the sync detector and to the reference sync generator, to compare timing of the internal sync value to the relative times of arrival of the set of received sync values;
a loop filter, coupled to the comparator and to the reference timing signal generator, to adjust the reference timing signal generator based on the set of received sync values, such that the timing of the internal sync value is in alignment to the relative times of arrival of the set of received sync values; and
an RF synthesizer that uses the internal timing signal to generate a receive RF local oscillator signal that is used to down-convert a received RF signal received by the receiver, wherein the received RF signal comprises the set of received sync values.
13. The receiver of claim 12 , further comprising a symbol clock synchronized as a function of the internal timing signal.
14. A transmitter comprising:
a reference clock that generates a reference clock signal;
a sync symbol generator that uses the reference clock signal to generate and modulate a plurality of sync values;
a RF synthesizer that uses the reference clock signal to generate a transmit RF local oscillator signal;
an up converter that up-converts the plurality of sync values to RF frequencies;
wherein the transmit RF local oscillator signal allows the up converter to transmit the up-converted sync values at an RF frequency that is to be received by a receiving communication device;
wherein the relative time of transmission between the up-converted sync values indicates a timing associated with the reference clock signal.
15. The transmitter of claim 14 , wherein the sync symbol generator is configured to modulate the plurality of sync values using differential Bi-Phase Shift Keying (DBPSK).