Cellular communication system computation of RSRP in the presence of large frequency errors

1. A method of producing a Reference Signal Received Power (RSRP) value from a received Orthogonal Frequency Division Multiplexed (OFDM) signal that comprises a plurality of reference symbols located at known sub-carrier frequencies and times within the received OFDM signal, the method comprising:

for each hypothesized error state selected from a plurality of different hypothesized error states, ascertaining a corresponding hypothesized RSRP value, wherein:

each of the hypothesized error states is a hypothesized frequency error paired with a hypothesized timing error; and

the corresponding hypothesized RSRP value is produced by adjusting one or more measured channel estimates as a function of the hypothesized error state; and

using the hypothesized RSRP values as a basis for determining a value for use as the produced RSRP value.

2. The method of claim 1 , wherein using the hypothesized RSRP values as a basis for determining the value for use as the produced RSRP value comprises selecting a maximum one of the hypothesized RSRP values for use as the produced RSRP value.

3. The method of claim 1 , wherein using the hypothesized RSRP values as a basis for determining the value for use as the produced RSRP value comprises averaging a known number of highest hypothesized RSRP values to produce an average value, and using the average value as the produced RSRP value.

4. The method of claim 1 , wherein adjusting the one or more measured channel estimates as a function of the hypothesized error state comprises multiplying a frequency domain representation of the one or more measured channel estimates by an adjustment factor that satisfies:

e 2πi·Δt·l e 2πi·Δf·k ,

where:

i represents the square root of −1;

k is a frequency index of a reference symbol within the received OFDM signal for which the channel estimate was measured;

l is an OFDM symbol index of the reference symbol for which the channel estimate was measured;

Δf is a hypothesized frequency error; and

Δt is a hypothesized timing error.

5. The method of claim 1 , wherein adjusting the one or more measured channel estimates as a function of the hypothesized error state comprises multiplying a frequency domain representation of the one or more measured channel estimates by an adjustment factor that satisfies:

e 2πi·Δt·φ t (l) e 2πi·Δf·φ f (k) ,

where:

i represents the square root of −1;

k is a frequency index of a reference symbol within the received OFDM signal for which the channel estimate was measured;

l is an OFDM symbol index of the reference symbol for which the channel estimate was measured;

Δf is a hypothesized frequency error;

Δt is a hypothesized timing error;

φ t ( ) is a function that models an irregularity of a frequency/time symbol grid in the time domain; and

φ f ( ) is a function that models an irregularity of the frequency/time symbol grid in the frequency domain.

6. The method of claim 1 , wherein adjusting the one or more measured channel estimates as a function of the hypothesized error state comprises:

measuring a channel estimate for each of a plurality of reference symbols having mutually different frequency and symbol indices within the received OFDM symbol; and

producing a plurality of adjusted channel estimates by adjusting each of the measured channel estimates as a function of the hypothesized error state.

7. The method of claim 6 , wherein ascertaining a corresponding hypothesized RSRP value for the hypothesized error state comprises:

averaging the plurality of adjusted channel estimates.

8. The method of claim 1 , comprising:

receiving the OFDM signal from a non-serving cell in a cellular communication system to produce the received OFDM signal.

9. An apparatus for producing a Reference Signal Received Power (RSRP) value from a received Orthogonal Frequency Division Multiplexed (OFDM) signal that comprises a plurality of reference symbols located at known sub-carrier frequencies and times within the received OFDM signal, the apparatus comprising:

circuitry configured to ascertain, for each hypothesized error state selected from a plurality of different hypothesized error states, a corresponding hypothesized RSRP value, wherein:

each of the hypothesized error states is a hypothesized frequency error paired with a hypothesized timing error; and

the corresponding hypothesized RSRP value is produced by adjusting one or more measured channel estimates as a function of the hypothesized error state; and

circuitry configured to use the hypothesized RSRP values as a basis for determining a value for use as the produced RSRP value.

10. The apparatus of claim 9 , wherein the circuitry configured to use the hypothesized RSRP values as a basis for determining the value for use as the produced RSRP value comprises circuitry configured to select a maximum one of the hypothesized RSRP values for use as the produced RSRP value.

11. The apparatus of claim 9 , wherein the circuitry configured to use the hypothesized RSRP values as a basis for determining the value for use as the produced RSRP value comprises circuitry configured to average a known number of highest hypothesized RSRP values to produce an average value, and to use the average value as the produced RSRP value.

12. The apparatus of claim 9 , wherein adjusting the one or more measured channel estimates as a function of the hypothesized error state comprises multiplying a frequency domain representation of the one or more measured channel estimates by an adjustment factor that satisfies:

e 2πi·Δt·l e 2πi·Δf·k ,

where:

i represents the square root of −1;

k is a frequency index of a reference symbol within the received OFDM signal for which the channel estimate was measured;

l is an OFDM symbol index of the reference symbol for which the channel estimate was measured;

Δf is a hypothesized frequency error; and

Δt is a hypothesized timing error.

13. The apparatus of claim 9 , wherein adjusting the one or more measured channel estimates as a function of the hypothesized error state comprises multiplying a frequency domain representation of the one or more measured channel estimates by an adjustment factor that satisfies:

e 2πi·Δt·φ t (l) e 2πi·Δf·φ f (k) ,

where

i represents the square root of −1;

k is a frequency index of a reference symbol within the received OFDM signal for which the channel estimate was measured;

l is an OFDM symbol index of the reference symbol for which the channel estimate was measured;

Δf is a hypothesized frequency error;

Δt is a hypothesized timing error;

φ t ( ) is a function that models an irregularity of a frequency/time symbol grid in the time domain; and

φ f ( ) is a function that models an irregularity of the frequency/time symbol grid in the frequency domain.

14. The apparatus of claim 9 , wherein adjusting the one or more measured channel estimates as a function of the hypothesized error state comprises:

measuring a channel estimate for each of a plurality of reference symbols having mutually different frequency and symbol indices within the received OFDM symbol; and

producing a plurality of adjusted channel estimates by adjusting each of the measured channel estimates as a function of the hypothesized error state.

15. The apparatus of claim 14 , wherein the circuitry configured to ascertain a corresponding hypothesized RSRP value for the hypothesized error state comprises:

circuitry configured to average the plurality of adjusted channel estimates.

16. The apparatus of claim 9 , comprising:

circuitry configured to receive the OFDM signal from a non-serving cell in a cellular communication system to produce the received OFDM signal.