Doppler compensation scheme
AssigneeQUALCOMM Incorporated
InventorsPei Chen, Ivan Fernandez-Corbaton
Life of this patent
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Abstract
At least one embodiment of the invention provides an automated frequency offset compensation method, system, and apparatus that improves throughput between one or more wireless communication devices by compensating for frequency offsets caused by a Doppler effect. In particular, one implementation estimates the frequency offset and uses this to compensate the carrier signal power to interference power ratio (C/I) when the transmitting and receiving devices are moving relative to each other such that a Doppler effect creates a frequency offset in the perceived frequency of the received carrier signal.
Claims20
A wireless communication device comprising:
- an input interface coupled to an antenna to receive a wireless signal;
- and
- a signal processor configured to
- receive the wireless signal from the input interface,
- estimate a frequency offset for the received wireless signal, and
- determine a received carrier signal power to interference signal power ratio (C/I) by using the frequency offset to compensate for Doppler shift.
The wireless communication device of 1 further comprising:
- a memory device coupled to the signal processor to store a lookup table of predetermined frequency offset correction values to determine C/I.
The wireless communication device of 1 wherein the offset frequency is estimated by a ratio of the cross product discriminator and dot product discriminator of a pilot burst in the wireless signal.
The wireless communication device of 3 wherein the offset frequency is a factor of the maximum frequency offset δfmax, estimated by δfmax≈(fc×v )/c, where fc is the carrier frequency, v is the maximum speed difference between a receiver of the carrier signal and a transmitter of the carrier signal, and c is the speed of light.
The wireless communication device of 1 wherein the wireless signal originates with a candidate base station.
The wireless communication device of 1 wherein the signal processor is further configured to
- select the candidate base station from a plurality of candidate base stations based on their corresponding C/I.
The wireless communication device of 1 wherein the signal processor is further configured to
- establish a communication link with the selected candidate base station.
A wireless communication device comprising:
- means for receiving a wireless carrier signal;
- means for estimating a frequency offset for the carrier signal;
- and
- means for estimating a received carrier signal power to interference signal power ratio (C/I) by using the frequency offset to compensate for Doppler shift between a receiver of the wireless carrier signal and a transmitter of the wireless carrier signal.
A frequency compensation method comprising:
- receiving a wireless carrier signal;
- estimating a frequency offset for the carrier signal;
- and
- estimating a received carrier signal power to interference signal power ratio (C/I) by using the frequency offset to compensate for Doppler shift between a receiver of the wireless carrier signal and a transmitter of the wireless carrier signal.
The method of 9 wherein the wireless carrier signal is a pilot signal from a candidate base station.
The method of 9 wherein estimating the frequency offset includes
- determining a cross product discriminator of the wireless carrier signal, and
- determining a dot product discriminator of the wireless carrier signal.
The method of 9 wherein the frequency offset estimate is determined by a ratio of the cross product discriminator and dot product discriminator of a pilot burst in the wireless signal
The method of 9 wherein the offset frequency is a factor of the maximum frequency offset δfmax, estimated by δfmax≈(fc×v)/c, where fc is the carrier frequency, v is the maximum speed difference between a receiver of the carrier signal and a transmitter of the carrier signal, and c is the speed of light.
A processor comprising:
- an input interface to couple an antenna and receive a carrier signal;
- a circuit coupled to the input interface to receive the carrier signal and configured to
- estimate a frequency offset for the carrier signal, and
- determine a carrier signal power to interference signal power ratio (C/I) by using the frequency offset to compensate for Doppler shift.
The processor of 14 wherein the carrier signal is a pilot signal from a candidate base station and there is a relative motion between a receiver of the pilot signal and the candidate base station.
The processor of 14 wherein the circuit is further configured to estimate the frequency offset by a ratio of the cross product discriminator and dot product discriminator of a pilot burst in the wireless signal a factor of the maximum frequency offset δfmax, estimated by δfmax≈(fc×v)/c, where fc is the carrier frequency, v is the maximum speed difference between a receiver of the carrier signal and a transmitter of the carrier signal, and c is the speed of light.
The processor of 14 wherein the circuit is farther configured to retrieve a pre-calculated offset value from a look-up table to determine C/I.
The processor of 14 wherein the circuit is further configured
- search for candidate base stations;
- and
- switch from a current base station to a candidate base station, if a better communication link can be established with the candidate base station than is available with the current base station.
A machine-readable medium having one or more instructions for compensating for a frequency offset when a receiver selects between candidate base stations, which when executed by a processor causes the processor to:
- receive one or more pilot signals from one or more candidate base stations;
- estimate a frequency offset for the one or more pilot signals;
- and
- estimate a received carrier signal power to interference signal power ratio (C/I) by using the frequency offset to compensate for Doppler shift between the receiver and the one or more candidate base stations.
The machine-readable medium of 19 further having one or more instructions which when executed by a processor causes the processor to:
- select the candidate base station from the one or more candidate base stations based on their corresponding C/I;
- and
- switch from a current base station to a candidate base station, if a better communication link can be established with the candidate base station than is available with the current base station.
Dependencies are inferred from the claim text.