Windowed-based decision feedback equalizer and decision feedback sequence estimator
View Patent ↗A method and system are provided for performing Decision Feedback Equalization (DFE) and Decision Feedback Sequence Estimation (DFSE) in high-throughput applications that are not latency critical. In an embodiment, overlapping blocks of samples are used to allow for the parallelization of the computation and the breaking of the critical path. In addition, the overlap of the windows addresses issues associated with performance loss due to what is termed “ramp-up” and “ramp-down” BER loss.
1. A method for feedback equalization comprising:
receiving an input signal including first, second, third and fourth sequential symbols;
generating first and second overlapping blocks each having a data portion and a padding portion, the data portion of the first overlapping block comprising the first and second symbols, the data portion of the second overlapping block comprising the third and fourth symbols, the padding portion of the second overlapping block comprising the second symbol;
applying the first and second overlapping blocks one clock cycle apart to inputs of first and second parallel feedback equalizers, respectively;
generating, at the first and second parallel feedback equalizers, first and second intermediate blocks having a size corresponding to the first and second overlapping blocks; producing first and second non-overlapping output signal blocks based on the intermediate signal blocks, the first and second non-overlapping output signal blocks each having a size corresponding to the data portion; and
combining the output signal blocks into an output signal.
2. The method of claim 1 further comprising estimating the first overlapping block padding portion contents and the second overlapping block padding portion contents based upon the input signal.
3. The method of claim 1 wherein the padding portion of the second overlapping block comprises the first symbol.
4. The method of claim 1 further comprising:
receiving a degraded signal from a communication channel;
applying the degraded signal to a feed forward equalizer;
generating the input signal by the feed forward equalizer, the feedforward equalizer having a transfer function inversely proportional to the attenuation of the communication channel.
5. A method for feedback equalization comprising:
receiving an input signal including first, second, third and fourth sequential symbols;
generating first and second overlapping blocks each having a data portion and a padding portion, the data portion of the first overlapping block comprising the first and second symbols, the data portion of the second overlapping block comprising the third and fourth symbols, the padding portion of the second overlapping block comprising the second symbol;
applying the first and second overlapping block to inputs of first and second parallel feedback equalizers, respectively;
generating, at the first and second parallel feedback equalizers, first and second intermediate blocks having a size corresponding to the first and second overlapping blocks; producing first and second non-overlapping output signal blocks based on the intermediate signal blocks, the first and second non-overlapping output signal blocks each having a size corresponding to the data portion;
combining the output signal blocks into an output signal;
applying the received input signal to a ramp up improvement circuit;
generating, at the ramp up improvement circuit, an estimate of the first overlapping block padding portion contents and the second overlapping block padding portion contents; and
applying the estimate of the first overlapping block padding portion contents and the second overlapping block padding portion contents to the first and second parallel feedback equalizers respectively to reduce the ramp up length.
6. A feedback equalizer comprising:
a capture circuit configured to receive an input signal and separate from the input signal first and a second overlapping blocks, the first and second overlapping blocks each having a padding portion and a data portion;
a first load circuit configured to apply the first overlapping block to a first parallel feedback equalizer;
a second load circuit configured to apply the second overlapping block to a second parallel feedback equalizer;
a timing circuit configured to apply the first and second overlapping blocks to the first and second parallel feedback equalizers one clock cycle apart;
the first parallel feedback equalizer generating a first intermediate block having a size corresponding to the first overlapping block;
the second parallel feedback equalizer generating a second intermediate block having a size corresponding to the second overlapping block;
a first collect circuit configured to produce a first non-overlapping output signal block from the first intermediate block, the first non-overlapping output signal block having a size corresponding to the data portion of the first non-overlapping block;
a second collect circuit configured to produce a second non-overlapping output signal block from the second intermediate block, the second non-overlapping output signal block having a size corresponding to the data portion of the second non-overlapping block; and
a merge circuit configured to combine the first and second non-overlapping blocks into an output signal.
7. The feedback equalizer of claim 6 wherein the parallel feedback equalizers are decision feedback equalizers.
8. The feedback equalizer of claim 6 wherein the parallel feedback equalizers are decision feedback sequence estimators.
9. The feedback equalizer of claim 6 wherein the size of the second overlapping block is equal to the size of the first overlapping block.
10. The feedback equalizer of claim 6 wherein the size of the second data portion is equal to the size of the first data portion.
11. The feedback equalizer of claim 6 further comprising a copper based communication network interface for coupling to a copper based communication network.
12. The feedback equalizer of claim 6 further comprising an optical based communication network interface for coupling to an optical based communication network.
13. The feedback equalizer of claim 6 further comprising a backplane system interface for coupling to a backplane system.
14. A feedback equalizer comprising:
a capture circuit configured to receive an input signal and separate from the input signal first and a second overlapping blocks, the first and second overlapping blocks each having a padding portion and a data portion;
a first load circuit configured to apply the first overlapping block to a first parallel feedback equalizer;
a second load circuit configured to apply the second overlapping block to a second parallel feedback equalizer;
the first parallel feedback equalizer generating a first intermediate block having a size corresponding to the first overlapping block;
the second parallel feedback equalizer generating a second intermediate block having a size corresponding to the second overlapping block;
a first collect circuit configured to produce a first non-overlapping output signal block from the first intermediate block, the first non-overlapping output signal block having a size corresponding to the data portion of the first non-overlapping block;
a second collect circuit configured to produce a second non-overlapping output signal block from the second intermediate block, the second non-overlapping output signal block having a size corresponding to the data portion of the second non-overlapping block;
a merge circuit configured to combine the first and second non-overlapping blocks into an output signal; and
a ramp up improvement circuit configured to receive the input signal, generate an improvement signal and apply the improvement signal to the parallel feedback equalizers.
15. The feedback equalizer of claim 14 wherein the ramp up improvement circuit comprises an infinite impulse response filter.
16. The feedback equalizer of claim 15 wherein the first and second parallel equalizers and the ramp up improvement circuit all have the same transfer function.