Decision feedback equalizer for code division multiplexed signals
A decision feedback equalizer (DFE) processes a signal having multiple code channels by filtering an error signal based on a difference between a received signal and an estimated received signal. The received signal is processed to recover data on each of the code channels and to generate an estimate of a transmitted signal corresponding to the received signal. A channel estimate is applied to the resulting estimated transmitted signal to generate the estimated received signal. After the filter filters the error signal, a combiner combines the filtered error signal and the estimated transmitted signal.
1. A decision feedback equalizer (DFE) comprising:
a signal estimator configured to process a received signal to recover data on each of a plurality of code channels and to generate an estimated transmitted signal of a transmitted signal corresponding to the received signal;
a virtual channel processor configured to apply a channel estimate to the estimated transmitted signal to generate an estimated received signal;
a filter configured to filter an error signal based on a difference between the received signal and the estimated received signal, wherein the filter comprises a filter response based on a relationship between the received signal and the error signal; and
a combiner configured to combine a filtered error signal generated by the filter and the estimated transmitted signal.
2. The DFE in accordance with claim 1 , wherein the signal estimator comprises:
a data estimator configured to despread and demodulate each of the plurality of code channels to recover the data; and
a signal reconstructor configured to modulate and spread the data to generate the estimated transmitted signal.
3. The DFE in accordance with claim 2 wherein the data estimator is further configured to descramble each of the plurality of code channels.
4. The DFE in accordance with claim 1 , wherein the filter response is further based on the channel estimate.
5. The DFE in accordance with claim 4 , wherein the filter response is further based on an estimated noise of the received signal.
6. The DFE in accordance with claim 4 , wherein the filter response is further based on a pulse shape.
7. The DFE in accordance with claim 1 , further comprising:
a linear equalizer configured to equalize the received signal before the signal estimator generates the estimated transmitted signal.
8. The DFE in accordance with claim 7 , wherein the filter is a linear equalizer.
9. The DFE in accordance with claim 1 , wherein the relationship between the received signal and the error signal is a power ratio.
10. The DFE in accordance with claim 9 , wherein the power ratio is defined as:
E
{
p
2
2
-
n
2
}
E
{
p
1
2
-
n
2
}
,
where p 1 2 is a power contained in the received signal averaged across a signal bandwidth, p 2 2 is a power contained in the error signal averaged across the signal bandwidth, and n 2 is an estimated power of the noise across the signal bandwidth.
11. A decision feedback equalizer (DFE) comprising:
a linear equalizer configured to apply an equalization to a received signal to reduce wireless channel effects and to generate an equalized received signal;
a despreader configured to despread the equalized signal to generate a despread signal;
a demodulator configured to demodulate the despread signal to generate estimated data;
a modulator configured to modulate the estimated data to generate an estimated modulated signal;
a spreader configured to spread the estimated data to generate an estimated transmitted signal of a transmitted signal corresponding to the received signal;
a virtual channel processor configured to apply a channel estimate to the estimated transmitted signal to generate an estimated received signal;
a filter configured to filter an error signal based on a difference between the received signal and the estimated received signal, the filter having a response based, at least partially, on the channel estimate and a relationship between the received signal and the error signal, the despreader configured to despread a filtered error signal generated by the filter; and
a combiner configured to combine the estimated modulated signal and the despread filtered error signal.
12. The DFE in accordance with claim 11 , further comprising:
a descrambler configured to descramble a despreader output of the despreader; and
a scrambler configured to scramble a spreader output of the spreader.
13. The DFE in accordance with claim 11 , further comprising:
a first Fast Fourier Transform (FFT) processor configured to transform the received signal from a time domain to a frequency domain;
an inverse FFT processor configured to transform the filtered error signal from the frequency domain to the time domain; and
a second FFT processor configured to transform a scrambler output from the time domain to the frequency domain.
14. The DFE in accordance with claim 11 , wherein the relationship between the received signal and the error signal is a power ratio.
15. The DFE in accordance with claim 14 , wherein the power ratio is defined as:
E
{
p
2
2
-
n
2
}
E
{
p
1
2
-
n
2
}
,
where p 1 2 is a power contained in the received signal averaged across a signal bandwidth, p 2 2 is a power contained in the error signal averaged across the signal bandwidth, and n 2 is an estimated power of the noise across the signal bandwidth.
16. A method for receiving a code division multiplexed (CDM) signal, the method comprising:
generating an estimated transmitted signal corresponding to a transmitted signal by recovering data on each of a plurality of code channels of a received signal corresponding to the transmitted signal;
generating an estimated received signal by applying a channel estimate to the estimated transmitted signal;
filtering an error signal based on a difference between the received signal and the estimated received signal and based on a relationship between the received signal and the error signal; and
combining the filtered error signal generated by the filter and the estimated transmitted signal.
17. The method in accordance with claim 16 , wherein the generating the estimated transmitted signal comprises:
despreading and demodulating each of the plurality of code channels to estimate transmitted data; and
modulating and spreading the estimated transmitted data to generate the estimated transmitted signal.
18. The method in accordance with claim 17 , further comprising:
descrambling each of the plurality of code channels before demodulating; and
scrambling the estimated transmitted data after modulating the estimated transmitted data.
19. The method in accordance with claim 16 , wherein the filtering comprises filtering based on the channel estimate.
20. The method in accordance with claim 19 , wherein the filtering comprises filtering based on an estimated noise of the received signal.
21. The method in accordance with claim 19 , wherein the filtering comprises filtering based on a pulse shape.
22. The method in accordance with claim 16 , further comprising:
applying linear equalization to the received signal before the generating the estimated transmitted signal.
23. The method in accordance with claim 16 , wherein the relationship between the received signal and the error signal is a power ratio.
24. The method in accordance with claim 23 , wherein the power ratio is defined as:
E
{
p
2
2
-
n
2
}
E
{
p
1
2
-
n
2
}
,
where p 1 2 is a power contained in the received signal averaged across a signal bandwidth, p 2 2 is a power contained in the error signal averaged across the signal bandwidth, and n 2 is an estimated power of the noise across the signal bandwidth.
25. A program product for applying decision feedback filtering to code division multiplexed signals, the program product comprising:
a non-transitory computer-readable medium containing computer-executable logic and configured for causing the following computer-executed step to occur:
generating an estimated transmitted signal corresponding to a transmitted signal by recovering data on each of a plurality of code channels of a received signal corresponding to the transmitted signal;
generating an estimated received signal by applying a channel estimate to the estimated transmitted signal;
filtering an error signal based on a difference between the received signal and the estimated received signal and based on a relationship between the received signal and the error signal; and
combining the filtered error signal generated by the filter and the estimated transmitted signal.
26. The program product in accordance with claim 25 , the computer-executable logic further configured for causing the following computer-executed step to occur:
despreading and demodulating each of the plurality of code channels to estimate transmitted data; and
modulating and spreading the estimated transmitted data to generate the estimated transmitted signal.
27. The program product in accordance with claim 25 , wherein the relationship between the received signal and the error signal is a power ratio.
28. The program product in accordance with claim 27 , wherein the power ratio is defined as:
E
{
p
2
2
-
n
2
}
E
{
p
1
2
-
n
2
}
,
where p 1 2 is a power contained in the received signal averaged across a signal bandwidth, p 2 2 is a power contained in the error signal averaged across the signal bandwidth, and n 2 is an estimated power of the noise across the signal bandwidth.
29. An apparatus for wireless communication, comprising:
means for generating an estimated transmitted signal corresponding to a transmitted signal by recovering data on each of a plurality of code channels of a received signal corresponding to the transmitted signal;
means for generating an estimated received signal by applying a channel estimate to the estimated transmitted signal;
means for filtering an error signal based on a difference between the received signal and the estimated received signal and based on a relationship between the received signal and the error signal; and
means for combining the filtered error signal generated by the filter and the estimated transmitted signal.
30. The apparatus in accordance with claim 29 , wherein the means for generating the estimated transmitted signal comprises:
means for despreading and demodulating each of the plurality of code channels to estimate transmitted data; and
means for modulating and spreading the estimated transmitted data to generate the estimated transmitted signal.
31. The apparatus in accordance with claim 30 , further comprising:
means for descrambling each of the plurality of code channels before demodulating; and
means for scrambling the estimated transmitted data after modulating the estimated transmitted data.
32. The apparatus in accordance with claim 29 , wherein the means for filtering comprises means for filtering based on the channel estimate.
33. The apparatus in accordance with claim 32 , wherein the means for filtering comprises means for filtering based on an estimated noise of the received signal.
34. The apparatus in accordance with claim 32 , wherein the means for filtering comprises means for filtering based on a pulse shape.
35. The apparatus in accordance with claim 29 , further comprising means for applying linear equalization to the received signal before the generating the estimated transmitted signal.
36. The apparatus in accordance with claim 29 , wherein the relationship between the received signal and the error signal is a power ratio.
37. The apparatus in accordance with claim 36 , wherein the power ratio is defined as:
E
{
p
2
2
-
n
2
}
E
{
p
1
2
-
n
2
}
,
where p 1 2 is a power contained in the received signal averaged across a signal bandwidth, p 2 2 is a power contained in the error signal averaged across the signal bandwidth, and n 2 is an estimated power of the noise across the signal bandwidth.