Generalized transmit pre-coding for optical and backplane channels
View Patent ↗Systems that allow for DFE functionality to be eliminated from the receiver side of a communication system and for a DFE-like functionality to be implemented instead at the transmitter side of the communication system are provided. By removing the DFE functionality from the receiver side, error propagation can be eliminated at the receiver and receiver complexity can be reduced drastically. At the transmitter side, the DFE-like functionality provides the same DFE benefits, and with the transmitter environment being noise-free, no errors can occur due noise boosting, for example. The DFE-like functionality at the transmitter side can be implemented using non-linear (recursive or feed-forward) pre-coders or a combination of non-linear pre-coders and linear filters, which can be configured to invert a net communication channel between the transmitter and the receiver. Embodiments particularly suitable for fiber optic channels and server backplane channels are also provided.
1. A transmitter, comprising:
a non-linear pre-coder comprising a non-linear Finite Impulse Response (FIR) pre-coder configured to receive a sequence of data symbols and to generate a sequence of pre-coded data symbols, wherein the non-linear FIR pre-coder comprises:
an adder configured to sum the sequence of data symbols with a feedback signal based on an output of a modulo-M circuit to generate an input signal;
a FIR filter configured to filter the input signal to generate a sequence of filtered data symbols; and
the modulo-M circuit, coupled to the FIR filter, configured to perform a modulo-M operation on the sequence of filtered data symbols to generate the sequence of pre-coded data symbols; and
analog transmit circuitry, coupled to the non-linear pre-coder, configured to transmit the sequence of pre-coded data symbols over a communication channel to a receiver,
wherein the non-linear pre-coder is further configured to match substantially an inverse transfer function of a net communication channel, the net communication channel including the analog transmit circuitry, the communication channel, and an analog receive circuitry of the receiver.
2. The transmitter of claim 1 , wherein the sequence of data symbols includes Pulse Amplitude Modulated (PAM)-M modulated symbols.
3. The transmitter of claim 1 , wherein the net communication channel is an Infinite Impulse Response (IIR) channel.
4. The transmitter of claim 1 , wherein the communication channel is a fiber optic channel.
5. The transmitter of claim 1 , wherein the FIR filter of the non-linear FIR pre-coder is represented by a polynomial having coefficients from a number set that can be described mathematically as {integer/q}, where q is an integer greater than 1.
6. The transmitter of claim 1 , wherein the communication channel is a server backplane channel.
7. The transmitter of claim 1 , wherein the net communication channel is a hybrid FIR/Infinite Impulse Response (IIR) channel.
8. The transmitter of claim 7 , wherein the non-linear pre-coder further comprises a non-linear IIR pre-coder, which forms together with the non-linear FIR pre-coder a non-linear hybrid IIR/FIR pre-coder.
9. A communication system, comprising:
a transmitter, comprising:
a non-linear pre-coder comprising a non-linear Finite Impulse Response (FIR) pre-coder configured to receive a sequence of Pulse Amplitude Modulation (PAM)-M modulated data symbols and to generate a sequence of pre-coded data symbols, wherein the non-linear FIR pre-coder comprises:
an adder configured to sum the sequence of PAM-M modulated data symbols with a feedback signal based on an output of a modulo-M circuit to generate an input signal;
a FIR filter configured to filter the input signal to generate a sequence of filtered data symbols; and
the modulo-M circuit, coupled to the FIR filter, configured to perform a modulo-M operation on the sequence of filtered data symbols to generate the sequence of pre-coded data symbols; and
analog transmit circuitry, coupled to the non-linear pre-coder, configured to transmit the sequence of pre-coded data symbols over a communication channel; and
a receiver, coupled via the communication channel to the transmitter, comprising:
analog receive circuitry configured to receive the sequence of pre-coded data symbols over the communication channel; and
a data detector configured to map each of the pre-coded data symbols to a respective amplitude level from a set of M amplitude levels,
wherein the non-linear pre-coder is further configured to match substantially an inverse transfer function of a net communication channel, the net communication channel including the analog transmit circuitry, the communication channel, and the analog receive circuitry of the receiver.
10. The communication system of claim 9 , wherein the data detector comprises:
a slicer configured to slice each of the pre-coded data symbols to a respective slicer level from a multiple of M amplitude levels; and
a modulo-M circuit configured to perform a modulo-M operation on the respective slicer level to generate the respective amplitude level for each of the pre-coded data symbols.
11. The communication system of claim 9 , wherein the FIR filter of the non-linear FIR pre-coder is represented by a polynomial having coefficients from a number set that can be described mathematically as {integer/q}, where q is an integer greater than 1.
12. The communication system of claim 9 , wherein the communication channel is a fiber optic channel.
13. The communication system of claim 9 , wherein the net communication channel is a hybrid FIR/Infinite Impulse Response (IIR) channel.
14. The communication system of claim 13 , wherein the non-linear pre-coder further comprises a non-linear IIR pre-coder, which forms together with the non-linear FIR pre-coder a non-linear hybrid IIR/FIR pre-coder.
15. The communication system of claim 9 , wherein the data detector is Decision Feedback Equalizer (DFE)-less.
16. The communication system of claim 9 , wherein the receiver is configured to send receiver feedback via a back-channel to the transmitter, and wherein the transmitter is configured to adapt the non-linear pre-coder responsive to the receiver feedback.
17. A transmitter for Pulse Amplitude Modulation (PAM)-M transmission over a fiber optic channel, comprising:
an adder configured to sum a sequence of PAM-M modulated data symbols with a feedback signal based on an output of a modulo-M circuit to generate an input signal;
a Finite Impulse Response (FIR) filter configured to filter the input signal to generate a sequence of filtered data symbols;
the modulo-M circuit, coupled to the FIR filter, configured to perform a modulo-M operation on the sequence of filtered data symbols to generate a sequence of pre-coded data symbols; and
analog transmit circuitry configured to transmit the sequence of pre-coded data symbols over the fiber optic channel to a receiver.
18. The transmitter of claim 17 , wherein the FIR filter is configured to have a transfer function substantially equal to the inverse of a transfer function of a net communication channel, the net communication channel including the analog transmit circuitry of the transmitter, the fiber optic channel, and analog receive circuitry of the receiver.