ERROR VECTOR MAGNITUDE-BASED SUPPRESSION OF DISCRETE INTERFERERS
Systems and methods for error vector magnitude (EVM) based suppression of discrete interferers are described herein. In certain embodiments, a system includes a control unit that receives a signal having a plurality of subcarriers, wherein the signal has a wanted portion affected by one or more discrete interferers. Further, the control unit calculates EVM measurements for multiple subcarriers in the plurality of subcarriers. Also, the control unit identifies one or more sets of proximate subcarriers affected by EVM impairments. Moreover, the control unit calculates a frequency and a magnitude for a discrete interferer for each of the sets of proximate subcarriers based on one or more EVM measurements for each of the sets of proximate subcarriers. Additionally, for each calculated frequency and magnitude, the control unit generates a control signal that can be used to reduce effects of the discrete interferer associated with the calculated frequency and magnitude.
1 . A system comprising:
a control unit configured to receive a signal having a plurality of subcarriers, wherein the signal has a wanted portion affected by one or more discrete interferers, wherein the control unit is further configured to:
calculate error vector magnitude (EVM) measurements for multiple subcarriers in the plurality of subcarriers;
identify one or more sets of proximate subcarriers affected by EVM impairments;
calculate a frequency and a magnitude for a discrete interferer for each of the one or more sets of proximate subcarriers based on one or more EVM measurements for each of the one or more sets of proximate subcarriers; and
for each calculated frequency and each magnitude, generate a control signal that can be used to reduce effects of the discrete interferer associated with the calculated frequency and the calculated magnitude.
2 . The system of claim 1 , further comprising a continuous wave signal generator configured to receive the control signal, wherein the continuous wave signal generator generates a continuous wave signal having the calculated frequency and the calculated magnitude.
3 . The system of claim 2 , wherein the continuous wave signal generator generates the continuous wave signal in at least one of the analog domain and the digital domain.
4 . The system of claim 1 , wherein the control unit receives the signal in the digital domain.
5 . The system of claim 1 , further comprising an analog-to-digital converter configured to receive the signal in the analog domain and convert the signal into the digital domain before reception by the control unit.
6 . The system of claim 1 , wherein the control unit is further configured to receive a feedback signal representing the signal with a reduced discrete interferer, wherein the control unit adjusts a phase associated with the discrete interferer in the control signal.
7 . The system of claim 1 , wherein the control unit is configured to determine the calculated frequency for the discrete interferer by determining whether a set in the one or more sets of proximate subcarriers comprises more than one subcarrier affected by the EVM impairments;
wherein when the set comprises one subcarrier affected by an EVM impairment, the control unit determines the calculated frequency for the discrete interferer to be the frequency of the one subcarrier and the magnitude of the discrete interferer to be proportional to the EVM measurement;
wherein when the set comprises more than one subcarrier affected by the EVM impairment, the control unit is configured to:
identify two proximate subcarriers in the set associated with the EVM measurements with a greatest magnitude;
calculate a ratio of the EVM measurements for a lower subcarrier frequency in the two proximate subcarriers and an upper subcarrier frequency in the two proximate subcarriers; and
determine an offset frequency from the lower subcarrier frequency based on the ratio.
8 . The system of claim 7 , wherein the control unit is configured to determine the offset frequency by identifying the offset frequency associated with the ratio in a look-up table.
9 . The system of claim 1 , wherein the control unit is configured to calculate the magnitude for the discrete interferer using quadratic addition with subsequent root formation with the EVM measurements for the set of proximate subcarriers.
10 . A method comprising:
receiving a signal having at least one subcarrier, wherein the signal has a wanted portion affected by one or more discrete interferers;
calculating error vector magnitude (EVM) measurements for the at least one subcarrier;
identifying one or more sets of proximate subcarriers affected by EVM impairments;
calculating a frequency and a magnitude for a discrete interferer for each of the one or more sets of proximate subcarriers based on one or more EVM measurements for each of the one or more sets of proximate subcarriers;
generating a control signal that directs a signal generator to generate a continuous wave signal having the calculated frequency and the calculated magnitude; and
subtracting the continuous wave signal from the received signal.
11 . The method of claim 10 , wherein the signal generator generates the continuous wave signal in at least one of the analog domain and the digital domain.
12 . The method of claim 10 , wherein receiving the signal further comprises receiving an analog signal and converting the analog signal into a digital signal before calculating the EVM measurements.
13 . The method of claim 10 , further comprising:
receiving a feedback signal representing the signal after subtracting the continuous wave signal from the received signal; and
adjusting a phase associated with the continuous wave signal.
14 . The method of claim 10 , wherein calculating the frequency further comprises:
determining whether a set in the one or more sets of proximate subcarriers comprise more than one subcarrier affected by the EVM impairments;
when the set comprises one subcarrier affected by an EVM impairment, determining the calculated frequency for the discrete interferer to be the frequency of the one subcarrier and the magnitude of the amplitude of the discrete interferer to be proportional to the EVM measurement; and
when the set comprises more than one subcarrier affected by the EVM impairments:
identifying two proximate subcarriers in the set associated with the EVM measurements with a greatest magnitude;
calculating a ratio of the EVM measurements for a lower subcarrier frequency in the two proximate subcarriers and an upper subcarrier frequency in the two proximate subcarriers; and
determining an offset frequency from the lower subcarrier frequency based on the ratio.
15 . The method of claim 14 , wherein determining the offset frequency further comprises identifying the offset frequency associated with the ratio in a look-up table.
16 . The method of claim 10 , wherein calculating the magnitude for the discrete interferer comprises using quadratic addition with subsequent root formation with the EVM measurements for the set of proximate subcarriers.
17 . A system comprising:
a control unit configured to receive a signal having a plurality of subcarriers, wherein the signal has a wanted portion affected by one or more discrete interferers, wherein the control unit is further configured to:
calculate error vector magnitude (EVM) measurements for multiple subcarriers in the plurality of subcarriers;
identify one or more sets of proximate subcarriers affected by EVM impairments;
calculate a frequency and a magnitude for a discrete interferer for each of the one or more sets of proximate subcarriers based on one or more EVM measurements for each of the one or more sets of proximate subcarriers; and
for each calculated frequency and each calculated magnitude, generate a control signal that can be used to reduce the effects of the discrete interferer associated with the calculated frequency and the calculated magnitude;
a continuous wave signal generator configured to receive the control signal, wherein the continuous wave signal generator generates a continuous wave signal having the calculated frequency and the calculated magnitude; and
a summer configured to subtract the continuous wave signal from the received signal to create a modified signal;
wherein the control unit is further configured to receive the modified signal and adjust a phase associated with the discrete interferer in the control signal.
18 . The system of claim 17 , wherein the control unit is configured to determine the calculated frequency for the discrete interferer by determining whether a set in the one or more sets of proximate subcarriers comprises more than one subcarrier affected by the EVM impairments;
wherein when the set comprises one subcarrier affected by an EVM impairment, the control unit determines the calculated frequency for the discrete interferer to be the frequency of the one subcarrier and the magnitude of the discrete interferer to be proportional to the EVM measurement;
wherein when the set comprises more than one subcarrier affected by the EVM impairments, the control unit is configured to:
identify two proximate subcarriers in the set associated with the EVM measurements with a greatest magnitude;
calculate a ratio of the EVM measurements for a lower subcarrier frequency in the two proximate subcarriers and an upper subcarrier frequency in the two proximate subcarriers; and
determine an offset frequency from the lower subcarrier frequency based on the ratio.
19 . The system of claim 18 , wherein the control unit is configured to determine the offset frequency by identifying the offset frequency associated with the ratio in a look-up table.
20 . The system of claim 17 , wherein the control unit is configured to calculate the magnitude for the discrete interferer using quadratic addition with subsequent root formation with the EVM measurements for the set of proximate subcarriers.