High-speed receiver architecture
View Patent ↗A receiver (e.g., for a 10G fiber communications link) includes an interleaved ADC coupled to a multi-channel equalizer that can provide different equalization for different ADC channels within the interleaved ADC. That is, the multi-channel equalizer can compensate for channel-dependent impairments. In one approach, the multi-channel equalizer is a feedforward equalizer (FFE) coupled to a Viterbi decoder, for example a sliding block Viterbi decoder (SBVD); and the FFE and/or the channel estimator for the Viterbi decoder are adapted using the LMS algorithm.
1. A receiver comprising:
an analog-to-digital converter that generates signal samples from a received signal having combined non-Gaussian noise and Gaussian noise;
a feedforward equalizer coupled to receive the signal samples from the analog-to-digital converter, and to apply equalization to generate equalized samples;
a decoder coupled to an output of the feedforward equalizer, the decoder determining detected symbols from the equalized samples and a channel model by minimizing a cumulative metric that compensates the combined Gaussian and non-Gaussian noise in the received signal; and
a channel estimator to receive the output of the feedforward equalizer and an output of the decoder and to generate the channel model and an error feedback signal to adaptively update coefficients of the feedforward equalizer based on the error feedback signal,
wherein the cumulative metric approximated by M≈Σ n [(ŷ n ) v −(ŝ n ) v ] 2 where M is the cumulative metric, ŷ n represents a sample at the output of the feedforward equalizer, ŝ n is a noise-free signal component of ŷ n , where 0<v≦1.
2. The receiver of claim 1 , where v is given by
v
≈
1
+
0.5
log
(
M
2
,
1
/
M
2
,
0
)
log
(
S
0
/
S
1
)
,
where M 2,0 and M 2,1 are conditional second-order central moments of noise and where S 0 =f(0, 0, . . . , 0), S 1 =f(1, 1, . . . , 1).
3. The receiver of claim 1 , further comprising:
a transformation block to provide an approximate solution to (ŷ n ) v , wherein the transformation block implements a function LUT(ŷ n )=(ŷ n +y min ) v when the sample ŷ n is in an interval between −y min and +y min .
4. The receiver of claim 1 , further comprising:
a transformation block to provide an approximate solution to (ŷ n ) v , wherein the transformation block implements a function y v ≈y v ref └1+(v−v ref )log(y)+0.5(v−v ref ) 2 (log(y)) 2 ┘ where v ref is a tabulated reference.
5. The receiver of claim 1 , further comprising:
a transformation block to provide an approximate solution to (ŷ n ) v , wherein the transformation block implements a function K −1 ŷ 0.5 +(v−0.5)ŷ where K is a constant.
6. The receiver of claim 1 , where v is given by v=0.5 if M 2,1 /M 2,0 >K 0.5 and by v=1, where K 0.5 is a programmable threshold level.
7. The receiver of claim 1 , wherein the non-Gaussian noise comprises amplified spontaneous emission (ASE) noise.
8. A method for equalizing a received signal, the method comprising:
generating, by an analog-to-digital converter, signal samples from the received signal having combined non-Gaussian noise and Gaussian noise;
applying, by a feedforward equalizer an equalization to the signal samples from the analog-to-digital converter to generate equalized samples;
determining, by a decoder coupled to an output of the feedforward equalizer, detected symbols from the equalized samples and a channel model by minimizing a cumulative metric that compensates the combined Gaussian and non-Gaussian noise in the received signal; and
generating, by a channel estimator, the channel model and an error feedback signal to adaptively update coefficients of the feedforward equalizer based on the error feedback signal,
wherein the cumulative metric is approximated by M≈Σ n [(ŷ n ) v −(ŝ n ) v ] 2 where M is the cumulative metric, ŷ n represents a sample at the output of the feedforward equalizer, ŝ n is a noise-free signal component of ŷ n , where 0<v≦1.
9. The method of claim 8 , where v is given by
v
≈
1
+
0.5
log
(
M
2
,
1
/
M
2
,
0
)
log
(
S
0
/
S
1
)
,
where M 2,0 and M 2,1 are conditional second-order central moments of noise and where S 0 =f(0, 0, . . . , 0), S 1 =f(1, 1, . . . , 1).
10. The method of claim 8 , further comprising:
providing an approximate solution to (ŷ n ) v by implementing a function LUT(ŷ n )=(ŷ n +y min ) v when the sample ŷ n is in an interval between −y min and +y min .
11. The method of claim 8 , further comprising:
providing an approximate solution to (ŷ n ) v a function y v ≈y v ref └1+(v−v ref )log(y)+0.5(v−v ref ) 2 (log(y)) 2 ┘ where v ref is a tabulated reference.
12. The method of claim 8 , further comprising:
providing an approximate solution to (ŷ n ) v , by implementing a function K −1 ŷ 0.5 +(v−0.5)ŷ where K is a constant.
13. The method of claim 8 , where v is given by v=0.5 if M 2,1 /M 2,0 >K 0.5 and by v=1, where K 0.5 is a programmable threshold level.
14. The method of claim 8 , wherein the non-Gaussian noise comprises amplified spontaneous emission (ASE) noise.
15. A transceiver chip for communication over an optical fiber, the transceiver chip comprising:
a host interface for providing encoded data in a host format for transmitting over the optical fiber and for receiving decoded data in the host format originating from the optical fiber;
transmit path circuitry to receive the encoded data from the host interface and generate an electrical signal suitable for driving a laser coupled to the optical fiber;
an input port for receiving a received signal originating from the optical fiber having combined non-Gaussian noise and Gaussian noise; and
receive path circuitry coupled between the input port and the host interface, the receive path circuitry comprising:
an analog-to-digital converter that generates signal samples from the received signal having the combined non-Gaussian noise and Gaussian noise;
a feedforward equalizer coupled to receive the signal samples from the analog-to-digital converter, and to apply equalization to generate equalized samples;
a decoder coupled to an output of the feedforward equalizer, the decoder determining detected symbols from the equalized samples and a channel model by minimizing a cumulative metric that compensates the combined Gaussian and non-Gaussian noise in the received signal, the decoder to generate the decoded data; and
a channel estimator to receive the output of the feedforward equalizer and an output of the decoder and to generate the channel model and an error feedback signal to adaptively update coefficients of the feedforward equalizer based on the error feedback signal,
wherein the cumulative metric is approximated by M≈Σ n [(ŷ n ) v −(ŝ n ) v ] 2 where M is the cumulative metric, ŷ n represents a sample at the output of the feedforward equalizer, ŝ n is a noise-free signal component of ŷ n , where 0<v≦1.
16. The transceiver chip of claim 15 , where v is given by
v
≈
1
+
0.5
log
(
M
2
,
1
/
M
2
,
0
)
log
(
S
0
/
S
1
)
,
where M 2,0 and M 2,1 are conditional second-order central moments of noise and where S 0 =f(0, 0, . . . , 0), S 1 βf(1, 1, . . . , 1).
17. The transceiver chip of claim 15 , further comprising:
a transformation block to provide an approximate solution to (ŷ n ) v , wherein the transformation block implements a function LUT (ŷ n )=(ŷ n +y min ) v when the sample ŷ n is in an interval between −y min and +y min .