Equalizer for AM in-band on-channel radio receivers that does not require analog signal bandwidth information
View Patent ↗A method is provided for equalizing OFDM symbol vectors received on AM in-band on-channel radio signal including a main carrier and first and second BPSK modulated subcarriers. The method comprises: computing a BPSK magnitude signal; filtering the BPSK magnitude signal; filtering complex samples received on the main carrier; using the filtered BPSK magnitude signal and the filtered complex samples received on the main carrier to compute a plurality of flat fade equalization coefficients; and multiplying the OFDM symbol vectors by the flat fade equalization coefficients. A receiver that includes an equalizer, which operates in accordance with the method is also provided.
1. A method of equalizing OFDM symbol vectors received on an AM in-band on-channel radio signal including a main carrier and first and second BPSK modulated subcarriers, the method comprising:
using a processor to compute a BPSK magnitude signal;
filtering the BPSK magnitude signal;
filtering complex samples received on the main carrier;
using the filtered BPSK magnitude signal and the filtered complex samples received on the main carrier to compute a plurality of flat fade equalization coefficients; and
multiplying the OFDM symbol vectors by the flat fade equalization coefficients.
2. The method of claim 1 , wherein the step of filtering the BPSK magnitude signal comprises:
passing the BPSK magnitude signal through a median filter and a finite impulse response filter.
3. The method of claim 1 , wherein the step of filtering complex samples received on the main carrier comprises:
passing the complex samples received on the main carrier through a finite impulse response filter.
4. The method of claim 1 , wherein the step of computing a BPSK magnitude signal comprises:
extracting an absolute value of an imaginary component of a BPSK symbol.
5. The method of claim 1 , wherein the first and second BPSK modulated subcarriers are modulated in quadrature to the main carrier.
6. The method of claim 1 , wherein the first and second BPSK modulated subcarriers are modulated as a complementary pair of subcarriers.
7. The method of claim 1 , wherein the step of multiplying the OFDM symbol vectors by the flat fade equalization coefficients produces flat fade equalized OFDM symbol vectors, and the method further comprises:
computing a plurality of partition equalization coefficients; and
multiplying the flat fade equalized OFDM symbol vectors by the partition equalization coefficients to produce output OFDM symbol vectors.
8. A receiver for receiving an AM in-band on-channel radio signal including a main carrier and first and second BPSK modulated subcarriers, the receiver comprising:
an input for receiving the AM in-band on-channel radio signal;
an equalizer for computing a BPSK magnitude signal, for filtering the BPSK magnitude signal, for filtering complex samples received on the main carrier, for using the filtered BPSK magnitude signal and the filtered complex samples received on the main carrier to compute a plurality of flat fade equalization coefficients, and for multiplying the OFDM symbol vectors by the flat fade equalization coefficients; and
an output device for producing an output in response to the AM in-band on-channel radio signal.
9. The receiver of claim 8 , wherein the equalizer comprises:
a median filter and a finite impulse response filter for filtering the BPSK magnitude signal.
10. The receiver of claim 8 , wherein the equalizer comprises:
a finite impulse response filter for filtering the complex samples received on the main carrier.
11. The receiver of claim 8 , wherein the equalizer computes the BPSK magnitude signal by extracting an absolute value of an imaginary component of a BPSK symbol.
12. The receiver of claim 8 , further comprising;
a partition equalizer for computing a plurality of partition equalization coefficients, and multiplying the flat fade equalized OFDM symbol vectors by the partition equalization coefficients to produce output OFDM symbol vectors.