Frequency correction in a multi-carrier communication system
View Patent ↗Methods and systems for correction of frequency errors in multi-carrier communication systems. The composite frequency error associated with the downlink signals are used to infer or derive the composite frequency error associated with the uplink signals, which are used to pre-compensate the uplink signals. Special signal components are transmitted by multiple base stations to facilitate frequency-error estimation and other system control functionalities at a mobile device. The mobile device carries out temporal, spatial, or spatial-temporal processing of the composite frequency errors associated with one or more base stations to determine the clock frequency error and the Doppler shift with respect to its serving base station.
1. A signal conditioning method for a mobile device configured to receive signals, the method comprising:
receiving a first error detection signal from a first transmitter over a first control subchannel;
receiving a second error detection signal from a second transmitter over a second control subchannel;
deriving a composite frequency error based on at least the received first error detection and second error detection signals; and
conditioning signals subsequently received at the mobile device from the first transmitter based on the derived composite frequency error, wherein the signals are conditioned in order to correct for frequency errors;
wherein:
each of the first and the second control subchannels occupies a center portion of a channel bandwidth;
each of the first and the second control subchannels is periodically contained in one orthogonal frequency division multiplexing (OFDM) symbol in a time slot comprising multiple OFDM symbols, the periodicity based on multiples of a time slot; and
the first and the second control subchannels are orthogonal to each other in frequency.
2. The method of claim 1 , wherein each of the first control subchannel and the second control subchannel comprises a plurality of subcarriers.
3. The method of claim 1 , wherein conditioning signals further comprises adjusting a reference frequency source of the mobile device.
4. The method of claim 1 , wherein conditioning signals further comprises digitally rotating a phase of the received signals in the time domain.
5. The method of claim 1 , wherein deriving the composite frequency error uses attributes of the first and second error detection signals.
6. The method of claim 5 , wherein the attributes include a signal strength or a signal-to-noise ratio (SNR).
7. The method of claim 1 , wherein deriving the composite frequency error uses temporal averaging or filtering.
8. A mobile device configured to receive signals comprising:
a receiver configured to receive a first error detection signal from a first transmitter over a first control subchannel;
a receiver configured to receive a second error detection signal from a second transmitter over a second control subchannel;
a processor configured to derive a composite frequency error based on at least the received first error detection and second error detection signals; and
a signal conditioner configured to condition signals received from the first transmitter based on the derived composite frequency error, wherein the signals are conditioned in order to correct for frequency errors;
wherein:
each of the first and the second control subchannels occupies a center portion of a channel bandwidth;
each of the first and the second control subchannels is periodically contained in one orthogonal frequency division multiplexing (OFDM) symbol in a time slot comprising OFDM symbols, the periodicity based on multiples of a time slot; and the first and the second control subchannels are orthogonal to each other in frequency.
9. The mobile device of claim 8 , wherein each of the first control subchannel and the second control subchannel comprises a plurality of subcarriers.
10. The mobile device of claim 8 , wherein the signal conditioner is further configured to adjust a reference frequency source of the mobile device.
11. The mobile device of claim 8 , wherein the signal conditioner is further configured to digitally rotate a phase of the received signals in the time domain.
12. The mobile device of claim 8 , wherein the processor is further configured to use attributes of the first and second error detection signals to derive the composite frequency error.
13. The mobile device of claim 12 , wherein the attributes include a signal strength or a signal-to-noise ratio (SNR).
14. The mobile device of claim 8 , wherein the processor is further configured to perform temporal averaging or filtering to derive the composite frequency error.